Ferromagnetism and superconductivity in CeFeAs1-xPxO (0⩽x⩽40)

NASA Astrophysics Data System (ADS)

Jesche, A.; Förster, T.; Spehling, J.; Nicklas, M.; de Souza, M.; Gumeniuk, R.; Luetkens, H.; Goltz, T.; Krellner, C.; Lang, M.; Sichelschmidt, J.; Klauss, H.-H.; Geibel, C.

2012-07-01

We report on superconductivity in CeFeAs1-xPxO and the possible coexistence with Ce ferromagnetism (FM) in a small homogeneity range around x=30% with ordering temperatures of TSC≅TC≅4 K. The antiferromagnetic (AFM) ordering temperature of Fe at this critical concentration is suppressed to TNFe≈40 K and does not shift to lower temperatures with a further increase of the P concentration. Therefore, a quantum-critical-point scenario with TNFe→0 K which is widely discussed for the iron based superconductors can be excluded for this alloy series. Surprisingly, thermal expansion and x-ray powder diffraction indicate the absence of an orthorhombic distortion despite clear evidence for short-range AFM Fe ordering from muon-spin-rotation measurements. Furthermore, we discovered the formation of a sharp electron spin resonance signal unambiguously connected with the emergence of FM ordering.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jesche, A.; Förster, T.; Spehling, J.

We report on superconductivity in CeFeAs 1-xP xO and the possible coexistence with Ce ferromagnetism (FM) in a small homogeneity range around x=30% with ordering temperatures of T SC≅T C≅4 K. The antiferromagnetic (AFM) ordering temperature of Fe at this critical concentration is suppressed to Tmore » $$Fe\\atop{N}$$≈40 K and does not shift to lower temperatures with a further increase of the P concentration. Therefore, a quantum-critical-point scenario with T$$Fe\\atop{N}$$→0 K which is widely discussed for the iron based superconductors can be excluded for this alloy series. Surprisingly, thermal expansion and x-ray powder diffraction indicate the absence of an orthorhombic distortion despite clear evidence for short-range AFM Fe ordering from muon-spin-rotation measurements. Furthermore, we discovered the formation of a sharp electron spin resonance signal unambiguously connected with the emergence of FM ordering.« less

Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca ( Fe 1 – x Co x ) 2 As 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sapkota, A.; Das, P.; Bohmer, A. E.

Results of inelastic neutron scattering measurements are reported for two annealed compositions of Ca(Fe 1–xCo x) 2As 2, x = 0.026 and 0.030, which possess stripe-type antiferromagnetically ordered and superconducting ground states, respectively. In the AFM ground state, well-defined and gapped spin waves are observed for x = 0.026, similar to the parent CaFe 2As 2 compound. We conclude that the well-defined spin waves are likely to be present for all x corresponding to the AFM state. This behavior is in contrast to the smooth evolution to overdamped spin dynamics observed in Ba(Fe 1–xCo x) 2As 2, wherein the crossovermore » corresponds to microscopically coexisting AFM order and SC at low temperature. The smooth evolution is likely absent in Ca(Fe 1–xCo x) 2As 2 due to the mutual exclusion of AFM ordered and SC states. Overdamped spin dynamics characterize paramagnetism of the x = 0.030 sample and high-temperature x = 0.026 sample. A sizable loss of magnetic intensity is observed over a wide energy range upon cooling the x = 0.030 sample, at temperatures just above and within the superconducting phase. This phenomenon is unique amongst the iron-based superconductors and is consistent with a temperature-dependent reduction in the fluctuating moment. In conclusion, one possible scenario ascribes this loss of moment to a sensitivity to the c-axis lattice parameter in proximity to the nonmagnetic collapsed tetragonal phase and another scenario ascribes the loss to a formation of a pseudogap.« less

Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca ( Fe 1 – x Co x ) 2 As 2

DOE PAGES

Sapkota, A.; Das, P.; Bohmer, A. E.; ...

2018-05-29

Results of inelastic neutron scattering measurements are reported for two annealed compositions of Ca(Fe 1–xCo x) 2As 2, x = 0.026 and 0.030, which possess stripe-type antiferromagnetically ordered and superconducting ground states, respectively. In the AFM ground state, well-defined and gapped spin waves are observed for x = 0.026, similar to the parent CaFe 2As 2 compound. We conclude that the well-defined spin waves are likely to be present for all x corresponding to the AFM state. This behavior is in contrast to the smooth evolution to overdamped spin dynamics observed in Ba(Fe 1–xCo x) 2As 2, wherein the crossovermore » corresponds to microscopically coexisting AFM order and SC at low temperature. The smooth evolution is likely absent in Ca(Fe 1–xCo x) 2As 2 due to the mutual exclusion of AFM ordered and SC states. Overdamped spin dynamics characterize paramagnetism of the x = 0.030 sample and high-temperature x = 0.026 sample. A sizable loss of magnetic intensity is observed over a wide energy range upon cooling the x = 0.030 sample, at temperatures just above and within the superconducting phase. This phenomenon is unique amongst the iron-based superconductors and is consistent with a temperature-dependent reduction in the fluctuating moment. In conclusion, one possible scenario ascribes this loss of moment to a sensitivity to the c-axis lattice parameter in proximity to the nonmagnetic collapsed tetragonal phase and another scenario ascribes the loss to a formation of a pseudogap.« less

The effect of pressure and temperature on the magnetic and magnetocaloric properties of an MnNi0.9Ge1.1 alloy

NASA Astrophysics Data System (ADS)

Das, S. C.; Mandal, K.; Dutta, P.; Pramanick, S.; Chatterjee, S.

2018-02-01

The magnetic and magnetocaloric properties of a self-doped MnNiGe alloy of nominal composition MnNi0.9Ge1.1 have been investigated in ambient as well as in high pressure conditions. It orders ferromagnetically below around 225 K and undergoes first order martensitic phase transition (MPT) to an antiferromagnetic (AFM) martensite phase below 147 K. This self-doping results in a significant decrease in the lattice volume and hence the Mn-Mn intra-layer distance which induces ferromagnetism (FM) in otherwise AFM alloys. MPT affects this FM ordering and the alloy becomes predominantly AFM in nature below the structural transition temperature. The observed values of the magnetocaloric effects (MCE) are reasonably large at the magnetic (-5.5 J kg-1 K-1 for magnetic field changing from 0 to 50 kOe around 210 K) and structural (8.3 J kg-1 K-1 for magnetic field changing from 0 to 50 kOe around 136 K) transition temperatures in ambient condition. MCE is found to decrease with increasing external hydrostatic pressure (P) at MPT region, whilst this external P has vanishingly small effect on MCE around the magnetic transition temperature.

Influence of classical anisotropy fields on the properties of Heisenberg antiferromagnets within unified molecular field theory

DOE PAGES

Johnston, David C.

2017-12-26

Here, a comprehensive study of the influence of classical anisotropy fields on the magnetic properties of Heisenberg antiferromagnets within unified molecular field theory versus temperature T, magnetic field H, and anisotropy field parameter h A1 is presented for systems comprised of identical crystallographically-equivalent local moments. The anisotropy field for collinear z-axis antiferromagnetic (AFM) ordering is constructed so that it is aligned in the direction of each ordered and/or field-induced thermal-average moment with a magnitude proportional to the moment, whereas that for XY anisotropy is defined to be in the direction of the projection of the moment onto the xy plane,more » again with a magnitude proportional to the moment. Properties studied include the zero-field Néel temperature T N, ordered moment, heat capacity, and anisotropic magnetic susceptibility of the AFM phase versus T with moments aligned either along the z axis or in the xy plane. Also determined are the high-field magnetization perpendicular to the axis or plane of collinear or planar noncollinear AFM ordering, the high-field magnetization along the z axis of a collinear z-axis AFM, spin-flop (SF), and paramagnetic (PM) phases, and the free energies of these phases versus T, H, and h A1. Phase diagrams at T=0 in the H z– h A1 plane and at T > 0 in the H z– T plane are constructed for spins S=1/2. For h A1=0, the SF phase is stable at low field and the PM phase at high field with no AFM phase present. As h A1 increases, the phase diagram contains the AFM, SF, and PM phases. Further increases in h A1 lead to the disappearance of the SF phase and the appearance of a tricritical point on the AFM-PM transition curve. Furthermore, applications of the theory to extract h A1 from experimental low-field magnetic susceptibility data and high-field magnetization versus field isotherms for single crystals of AFMs are discussed.« less

Influence of classical anisotropy fields on the properties of Heisenberg antiferromagnets within unified molecular field theory

NASA Astrophysics Data System (ADS)

Johnston, David C.

2017-12-01

A comprehensive study of the influence of classical anisotropy fields on the magnetic properties of Heisenberg antiferromagnets within unified molecular field theory versus temperature T , magnetic field H , and anisotropy field parameter hA 1 is presented for systems comprised of identical crystallographically-equivalent local moments. The anisotropy field for collinear z -axis antiferromagnetic (AFM) ordering is constructed so that it is aligned in the direction of each ordered and/or field-induced thermal-average moment with a magnitude proportional to the moment, whereas that for XY anisotropy is defined to be in the direction of the projection of the moment onto the x y plane, again with a magnitude proportional to the moment. Properties studied include the zero-field Néel temperature TN, ordered moment, heat capacity, and anisotropic magnetic susceptibility of the AFM phase versus T with moments aligned either along the z axis or in the x y plane. Also determined are the high-field magnetization perpendicular to the axis or plane of collinear or planar noncollinear AFM ordering, the high-field magnetization along the z axis of a collinear z -axis AFM, spin-flop (SF), and paramagnetic (PM) phases, and the free energies of these phases versus T ,H , and hA 1. Phase diagrams at T =0 in the Hz-hA 1 plane and at T >0 in the Hz-T plane are constructed for spins S =1 /2 . For hA 1=0 , the SF phase is stable at low field and the PM phase at high field with no AFM phase present. As hA 1 increases, the phase diagram contains the AFM, SF, and PM phases. Further increases in hA 1 lead to the disappearance of the SF phase and the appearance of a tricritical point on the AFM-PM transition curve. Applications of the theory to extract hA 1 from experimental low-field magnetic susceptibility data and high-field magnetization versus field isotherms for single crystals of AFMs are discussed.

Influence of classical anisotropy fields on the properties of Heisenberg antiferromagnets within unified molecular field theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnston, David C.

Here, a comprehensive study of the influence of classical anisotropy fields on the magnetic properties of Heisenberg antiferromagnets within unified molecular field theory versus temperature T, magnetic field H, and anisotropy field parameter h A1 is presented for systems comprised of identical crystallographically-equivalent local moments. The anisotropy field for collinear z-axis antiferromagnetic (AFM) ordering is constructed so that it is aligned in the direction of each ordered and/or field-induced thermal-average moment with a magnitude proportional to the moment, whereas that for XY anisotropy is defined to be in the direction of the projection of the moment onto the xy plane,more » again with a magnitude proportional to the moment. Properties studied include the zero-field Néel temperature T N, ordered moment, heat capacity, and anisotropic magnetic susceptibility of the AFM phase versus T with moments aligned either along the z axis or in the xy plane. Also determined are the high-field magnetization perpendicular to the axis or plane of collinear or planar noncollinear AFM ordering, the high-field magnetization along the z axis of a collinear z-axis AFM, spin-flop (SF), and paramagnetic (PM) phases, and the free energies of these phases versus T, H, and h A1. Phase diagrams at T=0 in the H z– h A1 plane and at T > 0 in the H z– T plane are constructed for spins S=1/2. For h A1=0, the SF phase is stable at low field and the PM phase at high field with no AFM phase present. As h A1 increases, the phase diagram contains the AFM, SF, and PM phases. Further increases in h A1 lead to the disappearance of the SF phase and the appearance of a tricritical point on the AFM-PM transition curve. Furthermore, applications of the theory to extract h A1 from experimental low-field magnetic susceptibility data and high-field magnetization versus field isotherms for single crystals of AFMs are discussed.« less

NMR studies of the incommensurate helical antiferromagnet EuCo 2 P 2 : Determination of antiferromagnetic propagation vector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Higa, Nonoka; Ding, Qing -Ping; Yogi, Mamoru

Recently, Q.-P. Ding et al. reported that their nuclear magnetic resonance (NMR) study on EuCo 2As 2 successfully characterized the antiferromagnetic (AFM) propagation vector of the incommensurate helix AFM state, showing that NMR is a unique tool for determination of the spin structures in incommensurate helical AFMs. Motivated by this work, we have carried out 153Eu, 31P, and 59Co NMR measurements on the helical antiferromagnet EuCo 2P 2 with an AFM ordering temperature T N = 66.5 K. An incommensurate helical AFM structure was clearly confirmed by 153Eu and 31P NMR spectra on single-crystalline EuCo 2P 2 in zero magneticmore » field at 1.6 K and its external magnetic field dependence. Furthermore, based on 59Co NMR data in both the paramagnetic and incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector k = (0,0,0.73±0.09)2π/c, where c is the c-axis lattice parameter. As a result, the temperature dependence of k is also discussed.« less

NMR studies of the incommensurate helical antiferromagnet EuCo 2 P 2 : Determination of antiferromagnetic propagation vector

DOE PAGES

Higa, Nonoka; Ding, Qing -Ping; Yogi, Mamoru; ...

2017-07-06

Recently, Q.-P. Ding et al. reported that their nuclear magnetic resonance (NMR) study on EuCo 2As 2 successfully characterized the antiferromagnetic (AFM) propagation vector of the incommensurate helix AFM state, showing that NMR is a unique tool for determination of the spin structures in incommensurate helical AFMs. Motivated by this work, we have carried out 153Eu, 31P, and 59Co NMR measurements on the helical antiferromagnet EuCo 2P 2 with an AFM ordering temperature T N = 66.5 K. An incommensurate helical AFM structure was clearly confirmed by 153Eu and 31P NMR spectra on single-crystalline EuCo 2P 2 in zero magneticmore » field at 1.6 K and its external magnetic field dependence. Furthermore, based on 59Co NMR data in both the paramagnetic and incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector k = (0,0,0.73±0.09)2π/c, where c is the c-axis lattice parameter. As a result, the temperature dependence of k is also discussed.« less

Magnetic dipole interactions in crystals

DOE PAGES

Johnston, David

2016-01-13

The influence of magnetic dipole interactions (MDIs) on the magnetic properties of local-moment Heisenberg spin systems is investigated. A general formulation is presented for calculating the eigenvalues λ and eigenvectors μ ˆ of the MDI tensor of the magnetic dipoles in a line (one dimension, 1D), within a circle (2D) or a sphere (3D) of radius r surrounding a given moment μ → i for given magnetic propagation vectors k for collinear and coplanar noncollinear magnetic structures on both Bravais and non-Bravais spin lattices. Results are calculated for collinear ordering on 1D chains, 2D square and simple-hexagonal (triangular) Bravaismore » lattices, 2D honeycomb and kagomé non-Bravais lattices, and 3D cubic Bravais lattices. The λ and μ ˆ values are compared with previously reported results. Calculations for collinear ordering on 3D simple tetragonal, body-centered tetragonal, and stacked triangular and honeycomb lattices are presented for c/a ratios from 0.5 to 3 in both graphical and tabular form to facilitate comparison of experimentally determined easy axes of ordering on these Bravais lattices with the predictions for MDIs. Comparisons with the easy axes measured for several illustrative collinear antiferromagnets (AFMs) are given. The calculations are extended to the cycloidal noncollinear 120 ° AFM ordering on the triangular lattice where λ is found to be the same as for collinear AFM ordering with the same k. The angular orientation of the ordered moments in the noncollinear coplanar AFM structure of GdB 4 with a distorted stacked 3D Shastry-Sutherland spin-lattice geometry is calculated and found to be in disagreement with experimental observations, indicating the presence of another source of anisotropy. Similar calculations for the undistorted 2D and stacked 3D Shastry-Sutherland lattices are reported. The thermodynamics of dipolar magnets are calculated using the Weiss molecular field theory for quantum spins, including the magnetic transition temperature T m and the ordered moment, magnetic heat capacity, and anisotropic magnetic susceptibility χ versus temperature T . The anisotropic Weiss temperature θ p in the Curie-Weiss law for T>T m is calculated. A quantitative study of the competition between FM and AFM ordering on cubic Bravais lattices versus the demagnetization factor in the absence of FM domain effects is presented. The contributions of Heisenberg exchange interactions and of the MDIs to T m and to θ p are found to be additive, which simplifies analysis of experimental data. Some properties in the magnetically-ordered state versus T are presented, including the ordered moment and magnetic heat capacity and, for AFMs, the dipolar anisotropy of the free energy and the perpendicular critical field. The anisotropic χ for dipolar AFMs is calculated both above and below the Néel temperature T N and the results are illustrated for a simple tetragonal lattice with c/a>1, c/a=1 (cubic), and c/a<1 , where a change in sign of the χ anisotropy is found at c/a=1 . Finally, following the early work of Keffer [Phys. Rev. 87, 608 (1952)], the dipolar anisotropy of χ above T N =69 K of the prototype collinear Heisenberg-exchange-coupled tetragonal compound MnF 2 is calculated and found to be in excellent agreement with experimental single-crystal literature data above 130 K, where the smoothly increasing deviation of the experimental data from the theory on cooling from 130 K to T N is deduced to arise from dynamic short-range collinear c -axis AFM ordering in this temperature range driven by the exchange interactions.« less

Interplay between superconductivity and magnetism in Fe1−xPdxTe

PubMed Central

Karki, Amar B.; Garlea, V. Ovidiu; Custelcean, Radu; Stadler, Shane; Plummer, E. W.; Jin, Rongying

2013-01-01

The attractive/repulsive relationship between superconductivity and magnetic ordering has fascinated the condensed matter physics community for a century. In the early days, magnetic impurities doped into a superconductor were found to quickly suppress superconductivity. Later, a variety of systems, such as cuprates, heavy fermions, and Fe pnictides, showed superconductivity in a narrow region near the border to antiferromagnetism (AFM) as a function of pressure or doping. However, the coexistence of superconductivity and ferromagnetic (FM) or AFM ordering is found in a few compounds [RRh4B4 (R = Nd, Sm, Tm, Er), R′Mo6X8 (R′ = Tb, Dy, Er, Ho, and X = S, Se), UMGe (M = Ge, Rh, Co), CeCoIn5, EuFe2(As1−xPx)2, etc.], providing evidence for their compatibility. Here, we present a third situation, where superconductivity coexists with FM and near the border of AFM in Fe1−xPdxTe. The doping of Pd for Fe gradually suppresses the first-order AFM ordering at temperature TN/S, and turns into short-range AFM correlation with a characteristic peak in magnetic susceptibility at T′N. Superconductivity sets in when T′N reaches zero. However, there is a gigantic ferromagnetic dome imposed in the superconducting-AFM (short-range) cross-over regime. Such a system is ideal for studying the interplay between superconductivity and two types of magnetic (FM and AFM) interactions. PMID:23690601

Interplay between Superconductivity and Magnetism in Fe1-xPdxTe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karki, A B; Garlea, Vasile O; Custelcean, Radu

The love/hate relationship between superconductivity and magnetic ordering has fascinated the condensed matter physics community for a century. In the early days, magnetic impurities doped into a superconductor were found to quickly suppress superconductivity. Later, a variety of systems, such as cuprates, heavy fermions and Fe pnictides, show superconductivity in a narrow region near the border to antiferromagnetism (AFM) as a function of pressure or doping. On the other hand, the coexistence of superconductivity and ferromagnetic (FM) or AFM ordering is found in a few compounds (RRh4B4 (R = Nd, Sm, Tm, Er), R'Mo6X8 (R' = Tb, Dy, Er, Ho,more » and X = S, Se), UMGe (M = Ge, Rh, Co), CeCoIn5, EuFe2(As1-xPx)2 etc.), providing evidence for their compatibility. Here, we present a third situation, where superconductivity coexists with FM and near the border of AFM in Fe1-xPdxTe. The doping of Pd for Fe gradually suppresses the first-order AFM ordering at temperature TN/S, and turns into short-range (SR) AFM correlation with a characteristic peak in magnetic susceptibility at T'N. Superconductivity sets in when T'N reaches zero. However, there is a gigantic ferromagnetic dome imposed in the superconducting-AFM (SR) crossover regime. Such a system is ideal for studying the interplay between superconductivity and two types of magnetic interactions (FM and AFM).« less

Magnetically driven negative thermal expansion in antiperovskite Ga1-xMnxN0.8Mn3 (0.1 ≤ x ≤ 0.3)

NASA Astrophysics Data System (ADS)

Guo, X. G.; Lin, J. C.; Tong, P.; Wang, M.; Wu, Y.; Yang, C.; Song, B.; Lin, S.; Song, W. H.; Sun, Y. P.

2015-11-01

Negative thermal expansion (NTE) was investigated for Ga1-xMnxN0.8Mn3 (0.1 ≤ x ≤ 0.3). As x increases, the temperature range where lattice contracts upon heating becomes broad and shifts to lower temperatures. The coefficient of linear thermal expansion beyond -40 ppm/K with a temperature interval of ˜50 K was obtained around room temperature in x = 0.2 and 0.25. Local lattice distortion which was thought to be intimately related to NTE is invisible in the X-ray pair distribution function of x = 0.3. Furthermore, a zero-field-cooling exchange bias was observed as a result of competing ferromagnetic (FM) and antiferromagnetic (AFM) orders. The concomitant FM order serves as an impediment to the growth of the AFM order, and thus broadens the temperature range of NTE. Our result suggests that NTE can be achieved in antiperovskite manganese nitrides by manipulating the magnetic orders without distorting the local structure.

Antiferromagnetism in EuCu 2As 2 and EuCu 1.82Sb 2 single crystals

DOE PAGES

Anand, V. K.; Johnston, D. C.

2015-05-07

Single crystals of EuCu 2As 2 and EuCu 2Sb 2 were grown from CuAs and CuSb self-flux, respectively. The crystallographic, magnetic, thermal, and electronic transport properties of the single crystals were investigated by room-temperature x-ray diffraction (XRD), magnetic susceptibility χ versus temperature T, isothermal magnetization M versus magnetic field H, specific heat C p(T), and electrical resistivity ρ(T) measurements. EuCu 2As 2 crystallizes in the body-centered tetragonal ThCr 2Si 2-type structure (space group I4/mmm), whereas EuCu 2Sb 2 crystallizes in the related primitive tetragonal CaBe 2Ge 2-type structure (space group P4/nmm). The energy-dispersive x-ray spectroscopy and XRD data for themore » EuCu 2Sb 2 crystals showed the presence of vacancies on the Cu sites, yielding the actual composition EuCu 1.82Sb 2. The ρ(T) and C p(T) data reveal metallic character for both EuCu 2As 2 and EuCu 1.82Sb 2. Antiferromagnetic (AFM) ordering is indicated from the χ(T),C p(T), and ρ(T) data for both EuCu 2As 2 (T N = 17.5 K) and EuCu 1.82Sb 2 (T N = 5.1 K). In EuCu 1.82Sb 2, the ordered-state χ(T) and M(H) data suggest either a collinear A-type AFM ordering of Eu +2 spins S = 7/2 or a planar noncollinear AFM structure, with the ordered moments oriented in the tetragonal ab plane in either case. This ordered-moment orientation for the A-type AFM is consistent with calculations with magnetic dipole interactions. As a result, the anisotropic χ(T) and isothermal M(H) data for EuCu 2As 2, also containing Eu +2 spins S = 7/2, strongly deviate from the predictions of molecular field theory for collinear AFM ordering and the AFM structure appears to be both noncollinear and noncoplanar.« less

Magnetization, resistivity, specific heat and ab initio calculations of Gd₅Sb₃.

PubMed

Samatham, S Shanmukharao; Patel, Akhilesh Kumar; Lukoyanov, Alexey V; Suresh, K G

2018-06-07

We report on the combined results of structural, magnetic, transport and calorimetric properties of Mn₅Si₃-type hexagonal Gd₅Sb₃, together with <i>ab-initio</i> calculations. It exhibits a ferromagnetic (FM)-like transition at 265 K, antiferromagnetic (AFM) Néel transition at 95.5 K followed by a spin-orientation transition at 62 K. The system is found to be in AFM state down to 2 K in a field of 70 kOe. The FM-AFM phase coexistence is not noticeable despite large positive Curie-Weiss temperature (θ_CW = 223.5 ± 0.2 K). Instead, low-temperature AFM and high-temperature FM-like phases are separated in large temperatures. Temperature-magnetic field (<i>H</i>-<i>T</i>) phase diagram reveals field-driven complex magnetic phases. Within the AFM phase, the system is observed to undergo field-driven spin-orientation transitions. Field-induced tricritical and quantum critical points appear to be absent due to strong AFM nature and by the intervention of FM-like state between paramagnetic and AFM states, respectively. The metallic behavior of the compound is inferred from resistivity along with large Sommerfeld parameter. However, no sign of strong electron-correlations is reasoned from the Kadowaki-Wood's ratio <i>A</i>/γ² ∼ 1.9×10^-6 μΩ.cm.(mol.K)²(mJ)^-2, despite heavy γ. Essentially, <i>ab initio</i> calculations accounting for electronic correlations confirm AFM nature of low-temperature magnetic state in Gd₅Sb₃ and attainable FM ordering in agreement with experimental data. © 2018 IOP Publishing Ltd.

Distribution of blocking temperatures in nano-oxide layers of specular spin valves

NASA Astrophysics Data System (ADS)

Ventura, J.; Araujo, J. P.; Sousa, J. B.; Veloso, A.; Freitas, P. P.

2007-06-01

Specular spin valves show enhanced giant magnetoresistive (GMR) ratio when compared to other, simpler, spin valve structures. The enhancement of GMR results from specular reflection in nano-oxide layers (NOLs) formed by the partial oxidation of the pinned and free layer. These oxides forming the NOL order antiferromagnetically (AFM) below a temperature T ˜175 K. Here, we study the effects of the pinned layer magnetization and its domain structure on the AFM ordering of the NOL by performing field cooling measurements with different cooling fields (H0). We observe enhanced (reduced) exchange field and magnetoresistive ratio for H0>0(<0), i.e., parallel (antiparallel) to the pinned magnetization. These measurements allowed us to confirm the existence of a wide distribution of blocking temperatures (TB) in the NOL of specular spin valves, having a maximum at T ≈175 K, and extending to NOL regions with TB as low as 15 K.

In-field X-ray and neutron diffraction studies of re-entrant charge-ordering and field induced metastability in La0.175Pr0.45Ca0.375MnO3-δ

NASA Astrophysics Data System (ADS)

Sharma, Shivani; Shahee, Aga; Yadav, Poonam; da Silva, Ivan; Lalla, N. P.

2017-11-01

Low-temperature high-magnetic field (2 K, 8 T) (LTHM) powder X-ray diffraction (XRD) and time of flight powder neutron diffraction (NPD), low-temperature transmission electron microscopic (TEM), and resistivity and magnetization measurements have been carried out to investigate the re-entrant charge ordering (CO), field induced structural phase transitions, and metastability in phase-separated La0.175Pr0.45Ca0.375MnO3-δ (LPCMO). Low-temperature TEM and XRD studies reveal that on cooling under zero-field, paramagnetic Pnma phase transforms to P21/m CO antiferromagnetic (AFM) insulating phase below ˜233 K. Unlike reported literature, no structural signature of CO AFM P21/m to ferromagnetic (FM) Pnma phase-transition during cooling down to 2 K under zero-field was observed. However, the CO phase was found to undergo a re-entrant transition at ˜40 K. Neutron diffraction studies revealed a pseudo CE type spin arrangement of the observed CO phase. The low-temperature resistance, while cooled under zero-field, shows insulator to metal like transition below ˜105 K with minima at ˜25 K. On application of field, the CO P21/m phase was found to undergo field-induced transition to FM Pnma phase, which shows irreversibility on field removal below ˜40 K. Zero-field warming XRD and NPD studies reveal that field-induced FM Pnma phase is a metastable phase, which arise due to the arrest of kinetics of the first-order phase transition of FM Pnma to CO-AFM P21/m phase, below 40 K. Thus, a strong magneto-structural coupling is observed for this system. A field-temperature (H-T) phase-diagram has been constructed based on the LTHM-XRD, which matches very nicely with the reported H-T phase-diagram constructed based on magnetic measurements. Due to the occurrence of gradual growth of the re-entrant CO phase and the absence of a clear structural signature of phase-separation of CO-AFM P21/m and FM Pnma phases, the H-T minima in the phase-diagram of the present LPCMO sample has been attributed to the strengthening of AFM interaction during re-entrant CO transition and not to glass like "dynamic to frozen" transition.

NMR determination of an incommensurate helical antiferromagnetic structure in EuCo 2 As 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ding, Q. -P.; Higa, N.; Sangeetha, N. S.

In this paper, we report 153Eu, 75As, and 59Co nuclear magnetic resonance (NMR) results on EuCo 2As 2 single crystal. Observations of 153Eu and 75As NMR spectra in zero magnetic field at 4.3 K below an antiferromagnetic (AFM) ordering temperature T N = 45 K and its external magnetic field dependence clearly evidence an incommensurate helical AFM structure in EuCo 2As 2. Furthermore, based on 59Co NMR data in both the paramagnetic and the incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector k = (0,0,0.73 ± 0.07)2π/c, where c is the c lattice parameter.more » Finally, the incommensurate helical AFM state was characterized by only NMR data with model-independent analyses, showing NMR to be a unique tool for determination of the spin structure in incommensurate helical AFMs.« less

NMR determination of an incommensurate helical antiferromagnetic structure in EuCo 2 As 2

DOE PAGES

Ding, Q. -P.; Higa, N.; Sangeetha, N. S.; ...

2017-05-05

In this paper, we report 153Eu, 75As, and 59Co nuclear magnetic resonance (NMR) results on EuCo 2As 2 single crystal. Observations of 153Eu and 75As NMR spectra in zero magnetic field at 4.3 K below an antiferromagnetic (AFM) ordering temperature T N = 45 K and its external magnetic field dependence clearly evidence an incommensurate helical AFM structure in EuCo 2As 2. Furthermore, based on 59Co NMR data in both the paramagnetic and the incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector k = (0,0,0.73 ± 0.07)2π/c, where c is the c lattice parameter.more » Finally, the incommensurate helical AFM state was characterized by only NMR data with model-independent analyses, showing NMR to be a unique tool for determination of the spin structure in incommensurate helical AFMs.« less

Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron Antiferromagnet Ca 1 - x Sr x Co 2 - y As 2

DOE PAGES

Sangeetha, N. S.; Smetana, V.; Mudring, A. -V.; ...

2017-12-20

We report the inference of Ying et al. [Europhys. Lett. 104, 67005 (2013)] of a composition-induced change from c-axis ordered-moment alignment in a collinear A-type antiferromagnetic (AFM) structure at small x to ab-plane alignment in an unknown AFM structure at larger x in Ca 1-xSr xCo 2-yAs 2 with the body-centered tetragonal ThCr 2Si 2 structure is confirmed. Our major finding is an anomalous magnetic behavior in the crossover region 0.2 ≲ x ≲ 0.3 between these two phases. Also, in this region the magnetic susceptibility vs temperature χ ab(T) measured with magnetic fields H applied in the ab planemore » exhibit typical AFM behaviors with cusps at the Néel temperatures of ~ 65 K, whereas χ c(T) and the low-temperature isothermal magnetization M c(H) with H aligned along the c axis exhibit extremely soft ferromagneticlike behaviors.« less

Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron Antiferromagnet Ca 1 - x Sr x Co 2 - y As 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sangeetha, N. S.; Smetana, V.; Mudring, A. -V.

We report the inference of Ying et al. [Europhys. Lett. 104, 67005 (2013)] of a composition-induced change from c-axis ordered-moment alignment in a collinear A-type antiferromagnetic (AFM) structure at small x to ab-plane alignment in an unknown AFM structure at larger x in Ca 1-xSr xCo 2-yAs 2 with the body-centered tetragonal ThCr 2Si 2 structure is confirmed. Our major finding is an anomalous magnetic behavior in the crossover region 0.2 ≲ x ≲ 0.3 between these two phases. Also, in this region the magnetic susceptibility vs temperature χ ab(T) measured with magnetic fields H applied in the ab planemore » exhibit typical AFM behaviors with cusps at the Néel temperatures of ~ 65 K, whereas χ c(T) and the low-temperature isothermal magnetization M c(H) with H aligned along the c axis exhibit extremely soft ferromagneticlike behaviors.« less

Unexpected Competition between Antiferromagnetic and Ferromagnetic States in Hf2MnRu5B2: Predicted and Realized.

PubMed

Shankhari, Pritam; Zhang, Yuemei; Stekovic, Dejan; Itkis, Mikhail E; Fokwa, Boniface P T

2017-11-06

Materials "design" is increasingly gaining importance in the solid-state materials community in general and in the field of magnetic materials in particular. Density functional theory (DFT) predicted the competition between ferromagnetic (FM) and antiferromagnetic (AFM) ground states in a ruthenium-rich Ti 3 Co 5 B 2 -type boride (Hf 2 MnRu 5 B 2 ) for the first time. Vienna ab initio simulation package (VASP) total energy calculations indicated that the FM model was marginally more stable than one of the AFM models (AFM1), indicating very weak interactions between magnetic 1D Mn chains that can be easily perturbated by external means (magnetic field or composition). The predicted phase was then synthesized by arc-melting and characterized as Hf 2 Mn 1-x Ru 5+x B 2 (x = 0.27). Vibrating-scanning magnetometry shows an AFM ground state with T N ≈ 20 K under low magnetic field (0.005 T). At moderate-to-higher fields, AFM ordering vanishes while FM ordering emerges with a Curie temperature of 115 K. These experimental outcomes confirm the weak nature of the interchain interactions, as predicted by DFT calculations.

Interfacial superconductivity in a bi-collinear antiferromagnetically ordered FeTe monolayer on a topological insulator

NASA Astrophysics Data System (ADS)

Manna, S.; Kamlapure, A.; Cornils, L.; Hänke, T.; Hedegaard, E. M. J.; Bremholm, M.; Iversen, B. B.; Hofmann, Ph.; Wiebe, J.; Wiesendanger, R.

2017-01-01

The discovery of high-temperature superconductivity in Fe-based compounds triggered numerous investigations on the interplay between superconductivity and magnetism, and on the enhancement of transition temperatures through interface effects. It is widely believed that the emergence of optimal superconductivity is intimately linked to the suppression of long-range antiferromagnetic (AFM) order, although the exact microscopic picture remains elusive because of the lack of atomically resolved data. Here we present spin-polarized scanning tunnelling spectroscopy of ultrathin FeTe1-xSex (x=0, 0.5) films on bulk topological insulators. Surprisingly, we find an energy gap at the Fermi level, indicating superconducting correlations up to Tc~6 K for one unit cell FeTe grown on Bi2Te3, in contrast to the non-superconducting bulk FeTe. The gap spatially coexists with bi-collinear AFM order. This finding opens perspectives for theoretical studies of competing orders in Fe-based superconductors and for experimental investigations of exotic phases in superconducting layers on topological insulators.

Molecular Dynamic Simulations of Interaction of an AFM Probe with the Surface of an SCN Sample

NASA Technical Reports Server (NTRS)

Bune, Adris; Kaukler, William; Rose, M. Franklin (Technical Monitor)

2001-01-01

Molecular dynamic (MD) simulations is conducted in order to estimate forces of probe-substrate interaction in the Atomic Force Microscope (AFM). First a review of available molecular dynamic techniques is given. Implementation of MD simulation is based on an object-oriented code developed at the University of Delft. Modeling of the sample material - succinonitrile (SCN) - is based on the Lennard-Jones potentials. For the polystyrene probe an atomic interaction potential is used. Due to object-oriented structure of the code modification of an atomic interaction potential is straight forward. Calculation of melting temperature is used for validation of the code and of the interaction potentials. Various fitting parameters of the probe-substrate interaction potentials are considered, as potentials fitted to certain properties and temperature ranges may not be reliable for the others. This research provides theoretical foundation for an interpretation of actual measurements of an interaction forces using AFM.

Influence of interstitial Fe to the phase diagram of Fe1+yTe1-xSex single crystals

NASA Astrophysics Data System (ADS)

Sun, Yue; Yamada, Tatsuhiro; Pyon, Sunseng; Tamegai, Tsuyoshi

2016-08-01

Superconductivity (SC) with the suppression of long-range antiferromagnetic (AFM) order is observed in the parent compounds of both iron-based and cuprate superconductors. The AFM wave vectors are bicollinear (π, 0) in the parent compound FeTe different from the collinear AFM order (π, π) in most iron pnictides. Study of the phase diagram of Fe1+yTe1-xSex is the most direct way to investigate the competition between bicollinear AFM and SC. However, presence of interstitial Fe affects both magnetism and SC of Fe1+yTe1-xSex, which hinders the establishment of the real phase diagram. Here, we report the comparison of doping-temperature (x-T) phase diagrams for Fe1+yTe1-xSex (0 ≤ x ≤ 0.43) single crystals before and after removing interstitial Fe. Without interstitial Fe, the AFM state survives only for x < 0.05, and bulk SC emerges from x = 0.05, and does not coexist with the AFM state. The previously reported spin glass state, and the coexistence of AFM and SC may be originated from the effect of the interstitial Fe. The phase diagram of Fe1+yTe1-xSex is found to be similar to the case of the “1111” system such as LaFeAsO1-xFx, and is different from that of the “122” system.

Correlating melting and collapse of charge ordering with magnetic transitions in La{sub 0.5-x}Pr{sub x}Ca{sub 0.5}MnO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nadeem, M., E-mail: mnadeemsb@gmail.com; Iqbal, M. Javid; Farhan, M. Arshad

2016-08-15

Highlights: • Concept of normalized magnetization is introduced to explain relative magnetic transitions. • Coexistence of two magnetic modes is correlated with the magnetic transitions and MIT. • Field induced melting and collapse of charge ordered antiferromagnetic (CO-AFM) state into ferromagnetic (FM) state is conferred. - Abstract: The magnetic properties of polycrystalline La{sub 0.5-x}Pr{sub x}Ca{sub 0.5}MnO{sub 3} material are investigated at different temperatures. The existence of magnetically diverse phases associated with various relaxation modes and their modulation with temperature and doping is analyzed. La{sub 0.5}Ca{sub 0.5}MnO{sub 3} exhibited field induced melting and collapse of charge ordered antiferromagnetic (CO-AFM) phase intomore » ferromagnetic (FM) state. This phenomenon results in lowering of Neel’s temperature (T{sub N}) along with changes in the slope of magnetic moment with temperature. Using normalized M(T) curves, the variation and interplay of charge ordered temperature (T{sub CO}), Curie temperature (T{sub C}) and T{sub N} is conferred. The coexistence of two magnetic modes is explained as major ingredient for the magnetic transitions as well as metal to insulator transition (MIT); where melting and collapse of charge ordering is conversed as basic feature in these Praseodymium (Pr) doped La{sub 0.5}Ca{sub 0.5}MnO{sub 3} materials.« less

Ferri-magnetic order in Mn induced spinel Co3-xMnxO4 (0.1≤x≤1.0) ceramic compositions

NASA Astrophysics Data System (ADS)

Meena, P. L.; Sreenivas, K.; Singh, M. R.; Kumar, Ashok; Singh, S. P.; Kumar, Ravi

2016-04-01

We report structural and magnetic properties of spinel Co3-xMnxO4 (x=0.1-1.0) synthesized by solid state reaction technique. Rietveld refinement analysis of X-ray diffraction (XRD) data, revealed the formation of polycrystalline single phase Co3-xMnxO4 without any significant structural change in cubic crystal symmetry with Mn substitution, except change in lattice parameter. Temperature dependent magnetization data show changes in magnetic ordering temperature, indicating formation of antiferromagnetic (AFM) and ferrimagnetic (FM) phase at low Mn concentration (x≤0.3) and well-defined FM phase at high Mn concentration (x≥0.5). The isothermal magnetization records established an AFM/FM mixed phase for composition ranging 0.10.5.

Nanoscale Trapping and Squeeze-Out of Confined Alkane Monolayers.

PubMed

Gosvami, N N; O'Shea, S J

2015-12-01

We present combined force curve and conduction atomic force microscopy (AFM) data for the linear alkanes CnH2n+2 (n = 10, 12, 14, 16) confined between a gold-coated AFM tip and a graphite surface. Solvation layering is observed in the force curves for all liquids, and conduction AFM is used to study in detail the removal of the confined (mono)layer closest to the graphite surface. The squeeze-out behavior of the monolayer can be very different depending upon the temperature. Below the monolayer melting transition temperatures the molecules are in an ordered state on the graphite surface, and fast and complete removal of the confined molecules is observed. However, above the melting transition temperature the molecules are in a disordered state, and even at large applied pressure a few liquid molecules are trapped within the tip-sample contact zone. These findings are similar to a previous study for branched alkanes [ Gosvami Phys. Rev. Lett. 2008, 100, 076101 ], but the observation for the linear alkane homologue series demonstrates clearly the dependence of the squeeze-out and trapping on the state of the confined material.

Observation of giant exchange bias in bulk Mn50Ni42Sn8 Heusler alloy

NASA Astrophysics Data System (ADS)

Sharma, Jyoti; Suresh, K. G.

2015-02-01

We report a giant exchange bias (EB) field of 3520 Oe in bulk Mn50Ni42Sn8 Heusler alloy. The low temperature magnetic state of the martensite phase has been studied by DC magnetization and AC susceptibility measurements. Frequency dependence of spin freezing temperature (Tf) on critical slowing down relation and observation of memory effect in zero field cooling mode confirms the super spin glass (SSG) phase at low temperatures. Large EB is attributed to the strong exchange coupling between the SSG clusters formed by small regions of ferromagnetic order embedded in an antiferromagnetic (AFM) matrix. The temperature and cooling field dependence of EB have been studied and related to the change in unidirectional anisotropy at SSG/AFM interface. The training effect also corroborates with the presence of frozen (SSG) moments at the interface and their role in EB.

Carrier induced magnetic coupling transitions in phthalocyanine-based organometallic sheet.

PubMed

Zhou, Jian; Sun, Qiang

2014-01-07

A two-dimensional sheet with long range ferromagnetic (FM) order has been hotly pursued currently. The recent success in synthesizing polymerized Fe-phthalocyanine (poly-FePc) porous sheets paves a possible way to achieve this goal. However, the poly-FePc and its analog poly-CrPc structure are intrinsically antiferromagnetic (AFM). Using first principles combined with Monte-Carlo simulations, we study systematically the carrier-induced magnetic coupling transitions in poly-CrPc and poly-FePc sheets. We show that electron doping can induce stable FM states with Curie temperatures of 130-140 K, while hole doping will enhance the stability of the AFM states. Such changes in magnetic couplings depend on the balance of AFM superexchange and FM p-d exchange.

Evolution from 4f-electron antiferromagnetic to ferromagnetic order in the CeCu(Ge1-xSnx ) alloy series (0 ≤x ≤1 )

NASA Astrophysics Data System (ADS)

Altayeb, A.; Sondezi, B. M.; Tchoula Tchokonté, M. B.; Strydom, A. M.; Doyle, T. B.; Kaczorowski, D.

2017-05-01

We report the evolution from ferromagnetic (FM) to antiferromagnetic (AFM) state in CeCu(Ge1-xSnx ) investigated by means of magnetic and heat capacity measurements. X-ray diffraction studies for all compositions indicate the ZrBeSi - type hexagonal crystal structure with space group P63/mmc (No. 194). The magnetic susceptibility, χ (T ) at high temperature follows the Curie - Weiss relation with an effective magnetic moment close to the value of 2.54 μB expected for free Ce3+ - ion. At low temperatures, χ (T ) data indicate AFM transition for alloys in the concentration range 0.7 ≤x ≤1 and FM for x ≤0.6 . The magnetization, M (μ0H ) of samples exhibiting AFM behaviour shows metamagnetic transition at low magnetic fields with some irreversibility in the process of increasing and decreasing magnetic field. In turn, M (μ0H ) of samples exhibiting FM behaviour shows saturation in high magnetic fields. Heat capacity, Cp(T) data confirm the AFM and FM transitions observed in magnetic measurements. An additional anomaly below TC and TN is observed in Cp(T)/T, which likely arises from spin reorientation or rearrangement in FM or AFM structure. Below in FM region, Cp(T) can be well described assuming spin-waves excitations with an energy gap ΔC.

The impact of chemical doping on the magnetic state of the Sr{sub 2}YRuO{sub 6} double perovskite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kayser, Paula; Ranjbar, Ben; Kennedy, Brendan J.

The impact of chemical doping of the type Sr{sub 2−x}A{sub x}YRuO{sub 6} (A=Ca, Ba) on the low temperature magnetic properties of Sr{sub 2}YRuO{sub 6}, probed using variable temperature magnetic susceptibility, neutron diffraction and heat capacity measurements, are described. Specific-heat measurements of un-doped Sr{sub 2}YRuO{sub 6} reveal two features at ∼26 and ∼30 K. Neutron scattering measurements at these temperatures are consistent with a change from a 2D ordered state to the 3D type 1 AFM state. Magnetic and structural studies of a number of doped oxides are described that highlight the unique low temperature behavior of Sr{sub 2}YRuO{sub 6} andmore » demonstrate that doping destabilizes the intermediate 2D ordered state. - Graphical abstract: Neutron diffraction measurements of the ordered double perovskite Sr{sub 2}YRuO{sub 6}reveal a with a change from a 2D ordered state to the 3D type 1 AFM state upon cooling. The impact of chemical doping Sr{sub 2−x}A{sub x}YRuO{sub 6} (A=Ca, Ba) on the low temperature magnetic properties have also been investigated and these highlight the unique low temperature behavior of Sr{sub 2}YRuO{sub 6} with doping destabilizing the intermediate 2D ordered state. - Highlights: • Crystal and Magnetic Structure of Sr{sub 2}YRuO{sub 3} was studied using Neutron Diffraction. • Effect of doping on the magnetic ground state established. • Origin of two low temperature transitions discussed.« less

Spin density wave instability in a ferromagnet.

PubMed

Wu, Yan; Ning, Zhenhua; Cao, Huibo; Cao, Guixin; Benavides, Katherine A; Karna, S; McCandless, Gregory T; Jin, R; Chan, Julia Y; Shelton, W A; DiTusa, J F

2018-03-27

Due to its cooperative nature, magnetic ordering involves a complex interplay between spin, charge, and lattice degrees of freedom, which can lead to strong competition between magnetic states. Binary Fe 3 Ga 4 is one such material that exhibits competing orders having a ferromagnetic (FM) ground state, an antiferromagnetic (AFM) behavior at intermediate temperatures, and a conspicuous re-entrance of the FM state at high temperature. Through a combination of neutron diffraction experiments and simulations, we have discovered that the AFM state is an incommensurate spin-density wave (ISDW) ordering generated by nesting in the spin polarized Fermi surface. These two magnetic states, FM and ISDW, are seldom observed in the same material without application of a polarizing magnetic field. To date, this unusual mechanism has never been observed and its elemental origins could have far reaching implications in many other magnetic systems that contain strong competition between these types of magnetic order. Furthermore, the competition between magnetic states results in a susceptibility to external perturbations allowing the magnetic transitions in Fe 3 Ga 4 to be controlled via temperature, magnetic field, disorder, and pressure. Thus, Fe 3 Ga 4 has potential for application in novel magnetic memory devices, such as the magnetic components of tunneling magnetoresistance spintronics devices.

Optimizing pentacene thin-film transistor performance: Temperature and surface condition induced layer growth modification.

PubMed

Lassnig, R; Hollerer, M; Striedinger, B; Fian, A; Stadlober, B; Winkler, A

2015-11-01

In this work we present in situ electrical and surface analytical, as well as ex situ atomic force microscopy (AFM) studies on temperature and surface condition induced pentacene layer growth modifications, leading to the selection of optimized deposition conditions and entailing performance improvements. We prepared p ++ -silicon/silicon dioxide bottom-gate, gold bottom-contact transistor samples and evaluated the pentacene layer growth for three different surface conditions (sputtered, sputtered + carbon and unsputtered + carbon) at sample temperatures during deposition of 200 K, 300 K and 350 K. The AFM investigations focused on the gold contacts, the silicon dioxide channel region and the highly critical transition area. Evaluations of coverage dependent saturation mobilities, threshold voltages and corresponding AFM analysis were able to confirm that the first 3-4 full monolayers contribute to the majority of charge transport within the channel region. At high temperatures and on sputtered surfaces uniform layer formation in the contact-channel transition area is limited by dewetting, leading to the formation of trenches and the partial development of double layer islands within the channel region instead of full wetting layers. By combining the advantages of an initial high temperature deposition (well-ordered islands in the channel) and a subsequent low temperature deposition (continuous film formation for low contact resistance) we were able to prepare very thin (8 ML) pentacene transistors of comparably high mobility.

Optimizing pentacene thin-film transistor performance: Temperature and surface condition induced layer growth modification

PubMed Central

Lassnig, R.; Hollerer, M.; Striedinger, B.; Fian, A.; Stadlober, B.; Winkler, A.

2015-01-01

In this work we present in situ electrical and surface analytical, as well as ex situ atomic force microscopy (AFM) studies on temperature and surface condition induced pentacene layer growth modifications, leading to the selection of optimized deposition conditions and entailing performance improvements. We prepared p++-silicon/silicon dioxide bottom-gate, gold bottom-contact transistor samples and evaluated the pentacene layer growth for three different surface conditions (sputtered, sputtered + carbon and unsputtered + carbon) at sample temperatures during deposition of 200 K, 300 K and 350 K. The AFM investigations focused on the gold contacts, the silicon dioxide channel region and the highly critical transition area. Evaluations of coverage dependent saturation mobilities, threshold voltages and corresponding AFM analysis were able to confirm that the first 3–4 full monolayers contribute to the majority of charge transport within the channel region. At high temperatures and on sputtered surfaces uniform layer formation in the contact–channel transition area is limited by dewetting, leading to the formation of trenches and the partial development of double layer islands within the channel region instead of full wetting layers. By combining the advantages of an initial high temperature deposition (well-ordered islands in the channel) and a subsequent low temperature deposition (continuous film formation for low contact resistance) we were able to prepare very thin (8 ML) pentacene transistors of comparably high mobility. PMID:26543442

NMR studies of the helical antiferromagnetic compound EuCo2P2

NASA Astrophysics Data System (ADS)

Higa, N.; Ding, Q.-P.; Kubota, F.; Uehara, H.; Yogi, M.; Furukawa, Y.; Sangeetha, N. S.; Johnston, D. C.; Nakamura, A.; Hedo, M.; Nakama, T.; Ōnuki, Y.

2018-05-01

In EuCo2P2, 4f electron spins of Eu2+ ions order antiferromagnetically below a Néel temperature TN = 66.5 K . The magnetic structure below TN was reported to be helical with the helix axis along the c-axis from the neutron diffraction study. We report the results of 153Eu, 59Co and 31P nuclear magnetic resonance (NMR) measurements on EuCo2P2 using a single crystal and a powdered sample. In the antiferromagnetic (AFM) state, we succeeded in observing 153Eu, 59Co and 31P NMR spectra in zero magnetic field. The sharp 153Eu zero field NMR (ZF NMR) lines indicate homogeneous Eu ordered moment. The 59Co and 31P ZF NMR spectra showed an asymmetric spectral shape, indicating a distribution of the internal magnetic induction at each nuclear position. The AFM propagation vector k characterizing the helical AFM state can be determined from the internal magnetic induction at Co site. We have determined the model-independent value of the AFM propagation vector k distributed from (0, 0, 0.86)2π/c to (0, 0, 0.73)2π/c, where c is the lattice parameter.

Elastic modulus measurements at variable temperature: Validation of atomic force microscopy techniques

NASA Astrophysics Data System (ADS)

Natali, Marco; Reggente, Melania; Passeri, Daniele; Rossi, Marco

2016-06-01

The development of polymer-based nanocomposites to be used in critical thermal environments requires the characterization of their mechanical properties, which are related to their chemical composition, size, morphology and operating temperature. Atomic force microscopy (AFM) has been proven to be a useful tool to develop techniques for the mechanical characterization of these materials, thanks to its nanometer lateral resolution and to the capability of exerting ultra-low loads, down to the piconewton range. In this work, we demonstrate two techniques, one quasi-static, i.e., AFM-based indentation (I-AFM), and one dynamic, i.e., contact resonance AFM (CR-AFM), for the mechanical characterization of compliant materials at variable temperature. A cross-validation of I-AFM and CR-AFM has been performed by comparing the results obtained on two reference materials, i.e., low-density polyethylene (LDPE) and polycarbonate (PC), which demonstrated the accuracy of the techniques.

Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helm, T.; Bachmann, M.; Moll, P.J.W.

2017-03-23

Electronic nematicity appears in proximity to unconventional high-temperature superconductivity in the cuprates and iron-arsenides, yet whether they cooperate or compete is widely discussed. While many parallels are drawn between high-T c and heavy fermion superconductors, electronic nematicity was not believed to be an important aspect in their superconductivity. We have found evidence for a field-induced strong electronic in-plane symmetry breaking in the tetragonal heavy fermion superconductor CeRhIn 5. At ambient pressure and zero field, it hosts an anti-ferromagnetic order (AFM) of nominally localized 4f electrons at TN=3.8K(1). Moderate pressure of 17kBar suppresses the AFM order and a dome of superconductivitymore » appears around the quantum critical point. Similarly, a density-wave-like correlated phase appears centered around the field-induced AFM quantum critical point. In this phase, we have now observed electronic nematic behavior.« less

Room temperature exchange bias in multiferroic BiFeO3 nano- and microcrystals with antiferromagnetic core and two-dimensional diluted antiferromagnetic shell

NASA Astrophysics Data System (ADS)

Zhang, Chuang; Wang, Shou Yu; Liu, Wei Fang; Xu, Xun Ling; Li, Xiu; Zhang, Hong; Gao, Ju; Li, De Jun

2017-05-01

Exchange bias (EB) of multiferroics presents many potential opportunities for magnetic devices. However, instead of using low-temperature field cooling in the hysteresis loop measurement, which usually shows an effective approach to obtain obvious EB phenomenon, there are few room temperature EB. In this article, extensive studies on room temperature EB without field cooling were observed in BiFeO3 nano- and microcrystals. Moreover, with increasing size the hysteresis loops shift from horizontal negative exchange bias (NEB) to positive exchange bias (PEB). In order to explain the tunable EB behaviors with size dependence, a phenomenological qualitative model based on the framework of antiferromagnetic (AFM) core-two-dimensional diluted antiferromagnet in a field (2D-DAFF) shell structure was proposed. The training effect (TE) ascertained the validity of model and the presence of unstable magnetic structure using Binek's model. Experimental results show that the tunable EB effect can be explained by the competition of ferromagnetic (FM) exchange coupling and AFM exchange coupling interaction between AFM core and 2D-DAFF shell. Additionally, the local distortion of lattice fringes was observed in hexagonal-shaped BiFeO3 nanocrystals with well-dispersed behavior. The electrical conduction properties agreed well with the space charge-limited conduction mechanism.

Revival of ferromagnetic behavior in charge-ordered Pr0.75Na0.25MnO3 manganite by ruthenium doping at Mn site and its MR effect

NASA Astrophysics Data System (ADS)

Elyana, E.; Mohamed, Z.; Kamil, S. A.; Supardan, S. N.; Chen, S. K.; Yahya, A. K.

2018-02-01

Ru doping in charge-ordered Pr0.75Na0.25Mn1-xRuxO3 (x = 0-0.1) manganites was studied to investigate its effect on structure, electrical transport, magnetic properties, and magnetotransport properties. DC electrical resistivity (ρ), magnetic susceptibility, and χ' measurements showed that sample x = 0 exhibits insulating behavior within the entire temperature range and antiferromagnetic (AFM) behavior below the charge-ordering (CO) transition temperature TCO of 221 K. Ru4+ substitution (x>0.01) suppressed the CO state, which resulted in the revival of paramagnetic to ferromagnetic (FM) transition at the Curie temperature Tc, increasing from 120 K (x = 0.01) to 193 K (x = 0.1). Deviation from the Curie-Weiss law above Tc in the 1/χ' versus T plot for x = 0.01 doped samples indicated the existence of Griffiths phase with Griffith temperature at 169 K. Electrical resistivity measurements showed that Ru4+ substitution increased the metallic-to-insulating transition temperature TMI from 144 K (x = 0.01) to 192 K (x = 0.05) due to enhanced double-exchange mechanism, but TMI decreased to 176 K (x = 0.1) probably due to the existence of AFM clusters within the FM domain. The present work also discussed the possible theoretical models at the resistivity curve of Pr0.75Na0.25Mn1-xRuxO3 (x = 0-0.1) for the entire temperature range.

Magnetocaloric effect and negative thermal expansion in hexagonal Fe doped MnNiGe compounds with a magnetoelastic AFM-FM-like transition

PubMed Central

Xu, Kun; Li, Zhe; Liu, Enke; Zhou, Haichun; Zhang, Yuanlei; Jing, Chao

2017-01-01

We report a detailed study of two successive first-order transitions, including a martensitic transition (MT) and an antiferromagnetic (AFM)-ferromagnetic (FM)-like transition, in Mn1-xFexNiGe (x = 0, 0.06, 0.11) alloys by X-ray diffraction, differential scanning calorimetry, magnetization and linear thermal expansion measurements. Such an AFM-FM-like transition occurring in the martensitic state has seldom been observed in the M(T) curves. The results of Arrott plot and linear relationship of the critical temperature with M2 provide explicit evidence of its first-order magnetoelastic nature. On the other hand, their performances as magnetocaloric and negative thermal expansion materials were characterized. The isothermal entropy change for a field change of 30 kOe reaches an impressive value of −25.8 J/kg K at 203 K for x = 0.11 compared to the other two samples. It demonstrates that the magneto-responsive ability has been significantly promoted since an appropriate amount of Fe doping can break the local Ni-6Mn AFM configuration. Moreover, the Fe-doped samples reveal both the giant negative thermal expansion and near-zero thermal expansion for different temperature ranges. For instance, the average thermal expansion coefficient ā of x = 0.06 reaches −60.7 × 10−6/K over T = 231–338 K and 0.6 × 10−6/K over T = 175–231 K during cooling. PMID:28134355

Magnetic properties of Mn{sub 1.9}Cu{sub 0.1}Sb under high pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsumoto, Yoshihiro; Hiroi, Masahiko; Mitsui, Yoshifuru

2016-08-26

Magnetization measurements were carried out for polycrystalline Mn{sub 1.9}Cu{sub 0.1}Sb in magnetic fields up to 5 T in the 10-300 K temperature range under high pressures up to 1 GPa in order to investigate the magnetic properties and the thermal transformation arrest (TTA) phenomenon under high pressures. The spin-reorientation temperature increased from 202 K for 0.1 MPa to 244 K for 1 GPa, whereas the transition temperature from the ferrimagnetic (FRI) to antiferromagnetic (AFM) state did not drastically change at ∼116 K. The magnetic relaxation behavior from the FRI to AFM state was observed in 10 < T ≤ 70more » K, which was analyzed using the Kohlrausch-Williams-Watts model. Obtained results indicated that the TTA phenomenon of Mn{sub 1.9}Cu{sub 0.1}Sb was suppressed by the application of high pressures.« less

Influence of Pt substitution on magnetic properties of multipolar ordering compounds Ce(Pd,Pt)3S4

NASA Astrophysics Data System (ADS)

Michimura, S.; Nishikawa, Ushio; Shimizu, Akihide; Kosaka, Masashi; Numakura, Ryosuke; Iizuka, Ryosuke; Katano, Susumu

2018-05-01

We have studied the magnetic properties of the multipolar ordering compounds Ce(Pd1-xPtx) 3S4 with 0.00 ≤ x ≤ 0.53 by means of magnetic susceptibility and magnetization measurements. In CePd3S4 , a simultaneous phase transition of the antiferro quadrupolar (AFQ) ordering and ferro magnetic (FM) ordering has been observed at 6.3 K. It has been suggested that the primary order parameter of CePd3S4 is the quadrupole moments, and it has not been understood why the FM ordering occurs at very high temperature which is almost the same magnetic transition temperature of GdPd3S4 . GdPd3S4 shows an antiferromagnetic (AFM) transition at 5.8 K. With increasing Pt substitution in CePd3S4 , the FM transition temperature TC (x) is rapidly suppressed to 2.4 K for x ≃ 0.3 and approaches asymptotically to 1.9 K (x = 0.53) . The results of magnetization curve suggest that the ordered state below TC (x) remains FM and AFQ ordered state for the whole range of x. For x ≥ 0.29 , TC (x) reaches at around 2 K, a new AFM transition was observed at TN (x) ≃ 7 K . We determined the T - x phase diagram, and discuss the phase transitions at TC (x) and TN (x) . The results suggest the possibility of the presence of the correlation between the magnetic interaction and the quadrupole interaction, and the correlation is not understood based on the previous multipolar model.

Spin-flop quasi-first order phase transition and putative tricritical point in Gd3Co

NASA Astrophysics Data System (ADS)

Samatham, S. Shanmukharao; Barua, Soumendu; Suresh, K. G.

2017-12-01

Magnetic nature of Gd3Co is investigated using detailed measurements of temperature and field dependent magnetization. The antiferromagnetic phase is field-instable due to prevailing ferromagnetic exchange correlations above Néel temperature TN ∼ 130K . Below TN , with gradually increasing magnetic fields, the compound undergoes a quasi-first order phase transition from AFM to spin-flop over region and eventually acquires ferromagnetic phase in higher fields. Further the point at which the quasi-first order transition ends and second order transition sets in is the tricritical point, TTCP ∼ 125.6K , HTCP ∼ 4.4kOe .

Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids.

PubMed

Gumí-Audenis, Berta; Costa, Luca; Carlá, Francesco; Comin, Fabio; Sanz, Fausto; Giannotti, Marina I

2016-12-19

Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information.

Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids

PubMed Central

Gumí-Audenis, Berta; Costa, Luca; Carlá, Francesco; Comin, Fabio; Sanz, Fausto; Giannotti, Marina I.

2016-01-01

Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information. PMID:27999368

NMR studies of the helical antiferromagnetic compound EuCo 2P 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Higa, N.; Ding, Q. -P.; Johnston, D. C.

In EuCo 2P 2, 4 f electron spins of Eu 2+ ions order antiferromagnetically below a Neel temperature T N = 66.5K. The magnetic structure below T N was reported to be helical with the helix axis along the c-axis from the neutron diffraction study. We report the results of 153Eu, 59Co and 31P nuclear magnetic resonance (NMR) measurements on EuCo 2P 2 using a single crystal and a powdered sample. In the antiferromagnetic (AFM) state, we succeeded in observing 153Eu, 59Co and 31P NMR spectra in zero magnetic field. The sharp 153Eu zero field NMR (ZF NMR) lines indicatemore » homogeneous Eu ordered moment. The 59Co and 31P ZF NMR spectra showed an asymmetric spectral shape, indicating a distribution of the internal magnetic induction at each nuclear position. The AFM propagation vector k characterizing the helical AFM state can be determined from the internal magnetic induction at Co site. In conclusion, we have determined the model-independent value of the AFM propagation vector k distributed from (0, 0, 0.86)2π/c to (0, 0, 0.73)2π/c, where c is the lattice parameter.« less

NMR studies of the helical antiferromagnetic compound EuCo 2P 2

DOE PAGES

Higa, N.; Ding, Q. -P.; Johnston, D. C.; ...

2017-09-18

In EuCo 2P 2, 4 f electron spins of Eu 2+ ions order antiferromagnetically below a Neel temperature T N = 66.5K. The magnetic structure below T N was reported to be helical with the helix axis along the c-axis from the neutron diffraction study. We report the results of 153Eu, 59Co and 31P nuclear magnetic resonance (NMR) measurements on EuCo 2P 2 using a single crystal and a powdered sample. In the antiferromagnetic (AFM) state, we succeeded in observing 153Eu, 59Co and 31P NMR spectra in zero magnetic field. The sharp 153Eu zero field NMR (ZF NMR) lines indicatemore » homogeneous Eu ordered moment. The 59Co and 31P ZF NMR spectra showed an asymmetric spectral shape, indicating a distribution of the internal magnetic induction at each nuclear position. The AFM propagation vector k characterizing the helical AFM state can be determined from the internal magnetic induction at Co site. In conclusion, we have determined the model-independent value of the AFM propagation vector k distributed from (0, 0, 0.86)2π/c to (0, 0, 0.73)2π/c, where c is the lattice parameter.« less

Observation of giant exchange bias in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Jyoti; Suresh, K. G., E-mail: suresh@iitb.ac.in

2015-02-16

We report a giant exchange bias (EB) field of 3520 Oe in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy. The low temperature magnetic state of the martensite phase has been studied by DC magnetization and AC susceptibility measurements. Frequency dependence of spin freezing temperature (T{sub f}) on critical slowing down relation and observation of memory effect in zero field cooling mode confirms the super spin glass (SSG) phase at low temperatures. Large EB is attributed to the strong exchange coupling between the SSG clusters formed by small regions of ferromagnetic order embedded in an antiferromagnetic (AFM) matrix. The temperature and coolingmore » field dependence of EB have been studied and related to the change in unidirectional anisotropy at SSG/AFM interface. The training effect also corroborates with the presence of frozen (SSG) moments at the interface and their role in EB.« less

Magnetic and thermoelectric properties of electron doped Ca0.85Pr0.15MnO3

NASA Astrophysics Data System (ADS)

Hossain Khan, Momin; Pal, Sudipta; Bose, Esa

2015-10-01

We have investigated temperature-dependent magnetization (M), magnetic susceptibility (χ) and thermoelectric (S) properties of the electron-doped Ca0.85Pr0.15MnO3. With decrease of temperature, paramagnetic (PM) to antiferromagnetic (AFM) phase transition occurs with a well-defined Néel temperature (TN=122 K). Magnetic susceptibility measurements reveal that the paramagnetic state involves modified Curie-Weiss paramagnetism. Field cooled and zero field cooled magnetization measurements indicate a signature of magnetic frustration. Ferromagnetic (FM) double-exchange interactions associated with doped eg electrons are favored over competing AFM interactions below Tirr=112 K. Magnetization data also shows a second-order phase transition. The sign reversal in S(T) has been interpreted in terms of the change in the electronic structure relating to the orbital degrees of freedom of the doped eg electron. Low temperature (5-140 K) thermoelectric power, S (T) signifies the importance of electron-magnon scattering process.

Interplay between crystal and magnetic structures in YFe{sub 2}(H{sub α}D{sub 1−α}){sub 4.2} compounds studied by neutron diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paul-Boncour, V., E-mail: paulbon@icmpe.cnrs.fr; Guillot, M.; Isnard, O.

We report a detailed magnetic structure investigation of YFe{sub 2}(H{sub α}D{sub 1−α}){sub 4.2} (α=0, 0.64, 1) compounds presenting a strong (H,D) isotope effect by neutron diffraction and Mössbauer spectroscopy analysis. They crystallize in the same monoclinic structure (Pc space group) with 8 inequivalent Fe sites having different H(D) environment. At low temperature, the compounds are ferromagnetic (FM) and show an easy magnetization axis perpendicular to the b axis and only slightly tilted away from the c axis. Upon heating, they display a first order transition from a ferromagnetic towards an antiferromagnetic (AFM) structure at T{sub M0} which is sensitive tomore » the H/D isotope nature. The AFM cell is described by doubling the crystal cell along the monoclinic b axis. It presents an unusual coexistence of non magnetic Fe layer sandwiched by two thicker ferromagnetic Fe layers which are antiparallel to each other. This FM-AFM transition is driven by the loss of ordered moment on one Fe site (Fe7) through an itinerant electron metamagnetic (IEM) behaviour. The key role of the Fe7 position is assigned to both its hydrogen rich atomic environment and its geometric position. Above T{sub M0} a field induced metamagnetic transition is observed from the AFM towards the FM structure accompanied by a cell volume increase. Both thermal and magnetic field dependence of the magnetic structure are found strongly related to the anisotropic cell distortion induced by (H,D) order in interstitial sites. - Graphical abstract: Representation of the FM-AFM magnetic structures of YFe{sub 2}D{sub 4.2} deuteride. - Highlights: • YFe{sub 2}(H,D){sub 4.2} compounds undergoes a isotope sensitive FM-AFM transition at T{sub M0}. • The FM structure is formed of Fe moments perpendicular to the monoclinic b axis. • AFM structure is formed by antiparallel Fe layers separated by non-magnetic Fe layer. • One Fe site among eight loses its moment at T{sub M0} due to larger Fe–H bonding. • Magnetic properties are driven by the monoclinic distortion induced by D order.« less

Training effect in specular spin valves

NASA Astrophysics Data System (ADS)

Ventura, J.; Araujo, J. P.; Sousa, J. B.; Veloso, A.; Freitas, P. P.

2008-05-01

Specular spin valves show an enhanced giant magnetoresistive (GMR) ratio due to specular reflection in nano-oxide layers (NOLs) formed by the partial oxidation of CoFe pinned and free layers. The oxides that form the (pinned layer) NOL were recently shown to antiferromagnetically order at Ttilde 175K . Here, we study the training effect (TE) in MnIr/CoFe/NOL/CoFe/Cu/CoFe/NOL/Ta specular spin valves in the 300-15 K temperature range. The exchange bias direction between the MnIr and CoFe layers impressed during annealing is taken as the positive direction. The training effect is observed in antiferromagnetic (AFM)/ferromagnetic (FM) exchange systems and related to the rearrangement of interfacial AFM spin structure with the number of hysteretic cycles performed (n) , resulting in the decrease of the exchange field (Hexch) . Here, in the studied specular spin valve, TE was only observed for T<175K and is thus related to the pinned layer NOL-AFM ordering and to the evolution of the corresponding spin structure with n . We show that FM spins that are strongly coupled to AFM domains do not align with the applied positive magnetic field (H) , giving rise to a residual MR at H≫0 . Such nonsaturating MR will be related with a spin-glass-like behavior of the interfacial magnetism induced by the nano-oxide layer. The observed dependence of the training effect on the field cooling procedure is also likely associated with the existence of different spin configurations available in the magnetically disordered oxide. Furthermore, anomalous magnetoresistance cycles measured after cooling runs under -500Oe are here related to induced NOL exchange bias/applied magnetic field misalignment. The temperature dependence of the training effect was obtained and fitted by using a recent theoretical model.

Neutron diffraction studies of magnetic ordering in Ni-doped LaCoO3

NASA Astrophysics Data System (ADS)

Rajeevan, N. E.; Kumar, Vinod; Kumar, Rajesh; Kumar, Ravi; Kaushik, S. D.

2015-11-01

Research in rare earth cobaltite has recently been intensified due to its fascinating magnetic properties. LaCoO3, an important cobaltite, exhibits two prominent susceptibility features at 90 K and 500 K in low field measurement. The magnetic behavior below 100 K is predominantly antiferromagnetic (AFM), but absence of pure AFM ordering and emergence of ferromagnetic coupling on further decreasing temperature made situation more intricate. The present work of studying the effect of Ni substitution at Co site in polycrystalline LaCo1-xNixO3 (0≤x≤0.3) is motivated by the interesting changes in magnetic and electronic properties. For lucid understanding, temperature dependent neutron diffraction (ND) study was carried out. ND patterns fitted with rhombohedral structure in perovskite form with R-3c space group, elucidated information on phase purity. Further temperature dependent cell parameter, Co-O bond-length and Co-O-Co bond angle were calculated for the series of Ni doped LaCoO3. The results are explained in terms of decrease in the crystal field energy which led to the transition of cobalt from low Spin (LS) state to intermediate spin state (IS).

Phase transition behaviors of the supported DPPC bilayer investigated by sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM).

PubMed

Wu, Heng-Liang; Tong, Yujin; Peng, Qiling; Li, Na; Ye, Shen

2016-01-21

The phase transition behaviors of a supported bilayer of dipalmitoylphosphatidyl-choline (DPPC) have been systematically evaluated by in situ sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM). By using an asymmetric bilayer composed of per-deuterated and per-protonated monolayers, i.e., DPPC-d75/DPPC and a symmetric bilayer of DPPC/DPPC, we were able to probe the molecular structural changes during the phase transition process of the lipid bilayer by SFG spectroscopy. It was found that the DPPC bilayer is sequentially melted from the top (adjacent to the solution) to bottom leaflet (adjacent to the substrate) over a wide temperature range. The conformational ordering of the supported bilayer does not decrease (even slightly increases) during the phase transition process. The conformational defects in the bilayer can be removed after the complete melting process. The phase transition enthalpy for the bottom leaflet was found to be approximately three times greater than that for the top leaflet, indicating a strong interaction of the lipids with the substrate. The present SFG and AFM observations revealed similar temperature dependent profiles. Based on these results, the temperature-induced structural changes in the supported lipid bilayer during its phase transition process are discussed in comparison with previous studies.

Temperature dependence of the enhanced inverse spin Hall voltage in Pt/Antiferromagnetic/ Y3Fe5O12

NASA Astrophysics Data System (ADS)

Brangham, J. T.; Lee, A. J.; Cheng, Y.; Yu, S. S.; Dunsiger, S. R.; Page, M. R.; Hammel, P. C.; Yang, F. Y.

The generation, propagation, and detection of spin currents are of intense interest in the field of spintronics. Spin current generation by FMR spin pumping using Y3Fe5O12 (YIG) and spin current detection by the inverse spin Hall effect (ISHE) in metals such as Pt have been well studied. This is due to YIG's exceptionally low damping and insulating behavior and the large spin Hall angle of Pt. Previously, our group showed that the ISHE voltages are significantly enhanced by adding a thin intermediate layer of an antiferromagnet (AFM) between Pt and YIG at room temperature. Recent theoretical work predicts a mechanism for this enhancement as well as the temperature dependence of the ISHE voltages of metal/AFM/YIG trilayers. The predictions show a maximum in the ISHE voltages for these systems near the magnetic phase transition temperature of the AFM. Here we present experimental results showing the temperature dependence for Pt/AFM/YIG structures with various AFMs. DOE Grant No. DE-SC0001304.

Magnetic properties and large reversible magnetocaloric effect in Er3Pd2

NASA Astrophysics Data System (ADS)

Maji, Bibekananda; Ray, Mayukh K.; Modak, M.; Mondal, S.; Suresh, K. G.; Banerjee, S.

2018-06-01

The magnetic properties and magnetocaloric effect (MCE) of binary intermetallic compound Er3Pd2 were studied. It exhibits a paramagnetic (PM) to antiferromagnetic (AFM) transition at Néel temperature (TN) = 10 K. A large reversible MCE was observed which is related to a second order magnetic transition from PM to AFM state. The values of maximum magnetic entropy change (- Δ SMmax) and adiabatic temperature change (Δ Tadmax) reach 8.9 J/kg-K and 2.9 K respectively for the field change of 50 kOe with no obvious hysteresis loss. The effective magnetic moment was determined to be 10.16 μB/Er3+, which is notably higher than that of free ion value of Er3+ (9.59 μB), suggests that Pd ions also have considerable amount of magnetic moments in this compound.

Spin dynamics near a putative antiferromagnetic quantum critical point in Cu-substituted BaFe 2 As 2 and its relation to high-temperature superconductivity

DOE PAGES

Kim, M. G.; Wang, M.; Tucker, G. S.; ...

2015-12-02

We present the results of elastic and inelastic neutron scattering measurements on nonsuperconducting Ba(Fe 0.957Cu 0.043) 2As 2, a composition close to a quantum critical point between antiferromagnetic (AFM) ordered and paramagnetic phases. By comparing these results with the spin fluctuations in the low-Cu composition as well as the parent compound BaFe 2As 2 and superconducting Ba(Fe 1–xNi x) 2As 2 compounds, we demonstrate that paramagnon-like spin fluctuations are evident in the antiferromagnetically ordered state of Ba(Fe 0.957Cu 0.043) 2As 2, which is distinct from the AFM-like spin fluctuations in the superconducting compounds. Our observations suggest that Cu substitution decouplesmore » the interaction between quasiparticles and the spin fluctuations. In addition, we show that the spin-spin correlation length ξ(T) increases rapidly as the temperature is lowered and find ω/T scaling behavior, the hallmark of quantum criticality, at an antiferromagnetic quantum critical point.« less

Switching adhesion forces by crossing the metal–insulator transition in Magnéli-type vanadium oxide crystals

PubMed Central

Klemm, Matthias; Horn, Siegfried; Woydt, Mathias

2011-01-01

Summary Magnéli-type vanadium oxides form the homologous series VnO2 n -1 and exhibit a temperature-induced, reversible metal–insulator first order phase transition (MIT). We studied the change of the adhesion force across the transition temperature between the cleavage planes of various vanadium oxide Magnéli phases (n = 3 … 7) and spherical titanium atomic force microscope (AFM) tips by systematic force–distance measurements with a variable-temperature AFM under ultrahigh vacuum conditions (UHV). The results show, for all investigated samples, that crossing the transition temperatures leads to a distinct change of the adhesion force. Low adhesion corresponds consistently to the metallic state. Accordingly, the ability to modify the electronic structure of the vanadium Magnéli phases while maintaining composition, stoichiometry and crystallographic integrity, allows for relating frictional and electronic material properties at the nano scale. This behavior makes the vanadium Magnéli phases interesting candidates for technology, e.g., as intelligent devices or coatings where switching of adhesion or friction is desired. PMID:21977416

Determination of outer layer and bulk dehydration kinetics of trehalose dihydrate using atomic force microscopy, gravimetric vapour sorption and near infrared spectroscopy.

PubMed

Jones, Matthew D; Beezer, Anthony E; Buckton, Graham

2008-10-01

Knowledge of the kinetics of solid state reactions is important when considering the stability of many medicines. Potentially, such reactions could follow different kinetics on the surface of particles when compared with their interior, yet solid state processes are routinely followed using only bulk characterisation techniques. Atomic force microscopy (AFM) has previously been shown to be a suitable technique for the investigation of surface processes, but has not been combined with bulk techniques in order to analyse surface and bulk kinetics separately. This report therefore describes the investigation of the outer layer and bulk kinetics of the dehydration of trehalose dihydrate at ambient temperature and low humidity, using AFM, dynamic vapour sorption (DVS) and near infrared spectroscopy (NIR). The use of AFM enabled the dehydration kinetics of the outer layers to be determined both directly and from bulk data. There were no significant differences between the outer layer dehydration kinetics determined using these methods. AFM also enabled the bulk-only kinetics to be analysed from the DVS and NIR data. These results suggest that the combination of AFM and bulk characterisation techniques should enable a more complete understanding of the kinetics of certain solid state reactions to be achieved. (c) 2008 Wiley-Liss, Inc. and the American Pharmacists Association

Phase diagram of (Li(1-x)Fe(x))OHFeSe: a bridge between iron selenide and arsenide superconductors.

PubMed

Dong, Xiaoli; Zhou, Huaxue; Yang, Huaixin; Yuan, Jie; Jin, Kui; Zhou, Fang; Yuan, Dongna; Wei, Linlin; Li, Jianqi; Wang, Xinqiang; Zhang, Guangming; Zhao, Zhongxian

2015-01-14

Previous experimental results have shown important differences between iron selenide and arsenide superconductors which seem to suggest that the high-temperature superconductivity in these two subgroups of iron-based families may arise from different electronic ground states. Here we report the complete phase diagram of a newly synthesized superconducting (SC) system, (Li1-xFex)OHFeSe, with a structure similar to that of FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at ∼127 K. This is the first example to demonstrate such an SDW phase in an FeSe-based superconductor system. Transmission electron microscopy shows that a well-known √5×√5 iron vacancy ordered state, resulting in an AFM order at ∼500 K in AyFe2-xSe2 (A = metal ions) superconductor systems, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q = (1)/2(1,1,0), identical to that seen in the SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature Tc = 40 K). Hence, we conclude that the high-Tc superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors.

Metallic behavior induced by potassium doping of the trigonal antiferromagnetic insulator EuMn 2 As 2

DOE PAGES

Anand, V. K.; Johnston, D. C.

2016-07-22

Here, we report magnetic susceptibility χ, isothermal magnetization M, heat capacity C p, and electrical resistivity ρ measurements on undoped EuMn 2As 2 and K-doped Eu 0.96K 0.04Mn 2As 2 and Eu 0.93K 0.07Mn 2As 2 single crystals with the trigonal CaAl 2Si 2-type structure as a function of temperature T and magnetic field H. EuMn 2As 2 has an insulating ground state with an activation energy of 52 meV and exhibits antiferromagnetic (AFM) ordering of the Eu +2 spins S=7/2 at T N1=15 K from C p(T) and χ(T) data with a likely spin-reorientation transition at T N2=5.0 K.more » The Mn +2 3d 5 spins-5/2 exhibit AFM ordering at T N=142 K from all three types of measurements. The M(H) isotherm and χ(T) data indicate that the Eu AFM structure is both noncollinear and noncoplanar. The AFM structure of the Mn spins is also unclear. A 4% substitution of K for Eu in Eu 0.96K 0.04Mn 2As 2 is sufficient to induce a metallic ground state. We found evidence for a difference in the AFM structure of the Eu moments in the metallic crystals from that of undoped EuMn 2As 2 versus both T and H. For metallic Eu 0.96K 0.04Mn 2As 2 and Eu 0.93K 0.07Mn 2As 2, an anomalous S-shape T dependence of ρ related to the Mn magnetism is found. Upon cooling from 200 K, ρ exhibits a strong negative curvature, reaches maximum positive slope at the Mn T N≈150 K, and then continues to decrease but more slowly below T N. Finally, this suggests that dynamic short-range AFM order of the Mn spins above the Mn T N strongly suppresses the resistivity, contrary to the conventional decrease of ρ that is only observed upon cooling below T N of an antiferromagnet.« less

High-field magnetoconductance in La-Sr manganites of FM and AFM ground states

NASA Astrophysics Data System (ADS)

Jirák, Zdeněk; Kaman, Ondřej; Knížek, Karel; Levinský, Petr; Míšek, Martin; Veverka, Pavel; Hejtmánek, Jiří

2018-06-01

Large-grain La1-xSrxMnO3 ceramic samples of compositions x = 0.45 and 0.55, representing the ferromagnetic (FM) and A-type antiferromagnetic (AFM) ground states, were produced via classical sintering at 1500 °C of cold-pressed sol-gel prepared single-phase nanoparticles. Using the same precursors, nanogranular forms of both manganite ceramics were prepared by fast spark plasma sintering at low temperature of 900 °C, which limits the growth of crystal grains. The magnetotransport of both the bulk and nanogranular forms was investigated in a broad range of magnetic fields up to 130 kOe and analyzed on the basis of detailed magnetic measurements. Both the large-grain and nanogranular systems with x = 0.45, possessing a pure FM state with similar Curie tempereature TC ≈ 345 K), show nearly the same conductivity enhancement in external fields when expressed relatively to the zero-field values. This positive magnetoconductance (MC) can be separated into two terms: (i) the hysteretic low-field MC that reflects the field-induced orientation of magnetic moments of individual grains, and (ii) the high-field MC that depends linearly on external field. In the case of large-grain ceramics with x = 0.55, a partially ordered FM state formed below TC = 264 K is replaced by pure A-type AFM ground state below 204 K. This A-type AFM state is characterized by positive magnetoconductance that is essentially of quadratic dependence on external field in the investigated range up to 130 kOe. On contrary, the nanogranular product with x = 0.55 exhibits a mixed FM/AFM state at low temperatures, and, as a consequence, its magnetotransport combines the features of FM and A-type AFM systems, in which the quadratic term is much enhanced and clearly dominates at high fields. For interpretation of observed behaviors, the theory of grain-boundary tunneling is revisited.

Large-moment antiferromagnetic order in overdoped high-Tc superconductor 154SmFeAsO1-xDx

NASA Astrophysics Data System (ADS)

Iimura, Soshi; Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Honda, Takashi; Ikeda, Kazutaka; Hansen, Thomas C.; Otomo, Toshiya; Hosono, Hideo

2017-05-01

In iron-based superconductors, high critical temperature (Tc) superconductivity over 50 K has only been accomplished in electron-doped hREFeAsO (hRE is heavy rare earth (RE) element). Although hREFeAsO has the highest bulk Tc (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of 154SmFeAsO1-xDx, and the discovery of a long-range antiferromagnetic ordering with x ≥ 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 μB/Fe, which is the largest in all nondoped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3dxy orbital, in which the nearest-neighbor hopping parameter becomes zero. The unique phase diagram, i.e., highest-Tc superconducting phase adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity.

Low-Temperature Reduction of Graphene Oxide: Electrical Conductance and Scanning Kelvin Probe Force Microscopy

NASA Astrophysics Data System (ADS)

Slobodian, Oleksandr M.; Lytvyn, Peter M.; Nikolenko, Andrii S.; Naseka, Victor M.; Khyzhun, Oleg Yu.; Vasin, Andrey V.; Sevostianov, Stanislav V.; Nazarov, Alexei N.

2018-05-01

Graphene oxide (GO) films were formed by drop-casting method and were studied by FTIR spectroscopy, micro-Raman spectroscopy (mRS), X-ray photoelectron spectroscopy (XPS), four-points probe method, atomic force microscopy (AFM), and scanning Kelvin probe force (SKPFM) microscopy after low-temperature annealing at ambient conditions. It was shown that in temperature range from 50 to 250 °C the electrical resistivity of the GO films decreases by seven orders of magnitude and is governed by two processes with activation energies of 6.22 and 1.65 eV, respectively. It was shown that the first process is mainly associated with water and OH groups desorption reducing the thickness of the film by 35% and causing the resistivity decrease by five orders of magnitude. The corresponding activation energy is the effective value determined by desorption and electrical connection of GO flakes from different layers. The second process is mainly associated with desorption of oxygen epoxy and alkoxy groups connected with carbon located in the basal plane of GO. AFM and SKPFM methods showed that during the second process, first, the surface of GO plane is destroyed forming nanostructured surface with low work function and then at higher temperature a flat carbon plane is formed that results in an increase of the work function of reduced GO.

Directly probing spin dynamics in insulating antiferromagnets using ultrashort terahertz pulses

DOE PAGES

Bowlan, Pamela Renee; Trugman, Stuart Alan; Wang, X.; ...

2016-11-22

We investigate spin dynamics in the antiferromagnetic (AFM) multiferroic TbMnO3 using opticalpump, terahertz (THz)-probe spectroscopy. Photoexcitation results in a broadband THz transmission change, with an onset time of 25 ps at 6 K that becomes faster at higher temperatures. We attribute this time constant to spin-lattice thermalization. The excellent agreement between our measurements and previous ultrafast resonant x-ray diffraction measurements on the same material confirms that our THz pulse directly probes spin order. We suggest that this could be the case in general for insulating AFM materials, if the origin of the static absorption in the THz spectral range ismore » magnetic.« less

Modification of crystal anisotropy and enhancement of magnetic moment of Co-doped SnO2 thin films annealed under magnetic field

PubMed Central

2014-01-01

Co-doped SnO2 thin films were grown by sputtering technique on SiO2/Si(001) substrates at room temperature, and then, thermal treatments with and without an applied magnetic field (HTT) were performed in vacuum at 600°C for 20 min. HTT was applied parallel and perpendicular to the substrate surface. Magnetic M(H) measurements reveal the coexistence of a strong antiferromagnetic (AFM) signal and a ferromagnetic (FM) component. The AFM component has a Néel temperature higher than room temperature, the spin axis lies parallel to the substrate surface, and the highest magnetic moment m =7 μB/Co at. is obtained when HTT is applied parallel to the substrate surface. Our results show an enhancement of FM moment per Co+2 from 0.06 to 0.42 μB/Co at. for the sample on which HTT was applied perpendicular to the surface. The FM order is attributed to the coupling of Co+2 ions through electrons trapped at the site of oxygen vacancies, as described by the bound magnetic polaron model. Our results suggest that FM order is aligned along [101] direction of Co-doped SnO2 nanocrystals, which is proposed to be the easy magnetization axis. PMID:25489286

Simultaneous noncontact AFM and STM of Ag:Si(111)-(3×3)R30∘

NASA Astrophysics Data System (ADS)

Sweetman, Adam; Stannard, Andrew; Sugimoto, Yoshiaki; Abe, Masayuki; Morita, Seizo; Moriarty, Philip

2013-02-01

The Ag:Si(111)-(3×3)R30∘ surface structure has attracted considerable debate concerning interpretation of scanning tunneling microscope (STM) and noncontact atomic force microscope (NC-AFM) images. In particular, the accepted interpretation of atomic resolution images in NC-AFM has been questioned by theoretical and STM studies. In this paper, we use combined NC-AFM and STM to conclusively show that the inequivalent trimer (IET) configuration best describes the surface ground state. Thermal-averaging effects result in a honeycomb-chained-trimer (HCT) appearance at room temperature, in contrast to studies suggesting that the IET configuration remains stable at higher temperatures [Zhang, Gustafsson, and Johansson, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.74.201304 74, 201304(R) (2006) and J. Phys.: Conf. Ser.1742-658810.1088/1742-6596/61/1/264 61, 1336 (2007)]. We also comment on results obtained at an intermediate temperature that suggest an intriguing difference between the imaging mechanisms of NC-AFM and STM on structurally fluctuating samples.

Reentrant cluster glass and stability of ferromagnetism in the Ga2MnCo Heusler alloy

NASA Astrophysics Data System (ADS)

Samanta, Tamalika; Bhobe, P. A.; Das, A.; Kumar, A.; Nigam, A. K.

2018-05-01

We present here a detailed investigation into the magnetic ordering of a full Heusler alloy Ga2MnCo using dc and ac magnetization measurements, neutron diffraction, and neutron depolarization experiments. The crystal structure at room temperature was first confirmed to be L 21 using the highly intense synchrotron x-ray diffraction technique. Temperature-dependent magnetization reveals that Ga2MnCo enters a ferromagnetic (FM) state at TC=154 K, characterized by a sharp increase in magnetization and a plateaulike region hereafter. As the temperature is decreased further, a sharp drop in magnetization is observed at Tf=50 K, hinting toward an antiferromagnetic (AFM) phase change. Neutron diffraction (ND) recorded over the range of temperature from 6 to 300 K provides combined information regarding crystal as well as magnetic structure. Accordingly, an increase in the intensity of the ND pattern is seen at 150 K, signaling the onset of long-range FM order. However, there is no sign of the appearance of superlattice reflections corresponding to the AFM phase in the patterns recorded below 50 K. An unusual discontinuity in the unit-cell volume is seen around Tf, indicating a coupling of this second transition with the contraction of the lattice. Attempts to unravel this interesting magnetic behavior using ac susceptibility measurements led to the existence of glassy magnetism below Tf. Systematic analysis of the susceptibility results along with neutron depolarization measurement identifies the low-temperature phase as a reentrant cluster glass.

Electric double-layer transistor using layered iron selenide Mott insulator TlFe1.6Se2

PubMed Central

Katase, Takayoshi; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

2014-01-01

A1–xFe2–ySe2 (A = K, Cs, Rb, Tl) are recently discovered iron-based superconductors with critical temperatures (Tc) ranging up to 32 K. Their parent phases have unique properties compared with other iron-based superconductors; e.g., their crystal structures include ordered Fe vacancies, their normal states are antiferromagnetic (AFM) insulating phases, and they have extremely high Néel transition temperatures. However, control of carrier doping into the parent AFM insulators has been difficult due to their intrinsic phase separation. Here, we fabricated an Fe-vacancy-ordered TlFe1.6Se2 insulating epitaxial film with an atomically flat surface and examined its electrostatic carrier doping using an electric double-layer transistor (EDLT) structure with an ionic liquid gate. The positive gate voltage gave a conductance modulation of three orders of magnitude at 25 K, and further induced and manipulated a phase transition; i.e., delocalized carrier generation by electrostatic doping is the origin of the phase transition. This is the first demonstration, to the authors' knowledge, of an EDLT using a Mott insulator iron selenide channel and opens a way to explore high Tc superconductivity in iron-based layered materials, where carrier doping by conventional chemical means is difficult. PMID:24591598

Manganese-induced magnetic symmetry breaking and its correlation with the metal-insulator transition in bilayered S r3(Ru1-xM nx) 2O7

NASA Astrophysics Data System (ADS)

Zhang, Qiang; Ye, Feng; Tian, Wei; Cao, Huibo; Chi, Songxue; Hu, Biao; Diao, Zhenyu; Tennant, David A.; Jin, Rongying; Zhang, Jiandi; Plummer, Ward

2017-06-01

Bilayered S r3R u2O7 is an unusual metamagnetic metal with inherently antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial substitution of Ru by Mn results in the establishment of a metal-insulator transition (MIT) at TMIT and AFM ordering at TM in S r3(Ru1-xM nx) 2O7 . Using elastic neutron scattering, we investigated the effect of Mn doping on the magnetic structure, in-plane magnetic correlation lengths and their correlation to the MIT in S r3(Ru1-xM nx) 2O7 (x =0.06 and 0.12). With the increase of Mn doping (x ) from 0.06 to 0.12 or the decrease of temperatures for x =0.12 , an evolution from an in-plane short-range to long-range antiferromagnetic (AFM) ground state occurs. For both compounds, the magnetic ordering has a double-stripe configuration, and the onset of magnetic correlation with an anisotropic behavior coincides with the sharp rise in electrical resistivity and specific heat. Since it does not induce a measurable lattice distortion, the double-stripe antiferromagnetic order with anisotropic spin texture breaks symmetry from a C4 v crystal lattice to a C2 v magnetic sublattice. These observations shed light on an age-old question regarding the Slater versus Mott-type MIT.

Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current.

PubMed

Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A; Slavin, Andrei

2017-03-06

The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1-2.0 THz with the driving current in the Pt layer from 10 8  A/cm 2 to 10 9  A/cm 2 . The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.

Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current

NASA Astrophysics Data System (ADS)

Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei

2017-03-01

The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1-2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.

FeRh ground state and martensitic transformation

DOE PAGES

Zarkevich, Nikolai A.; Johnson, Duane D.

2018-01-09

Cubic B2 FeRh exhibits a metamagnetic transition [(111) antiferromagnet (AFM) to ferromagnet (FM)] around 353 K and remains structurally stable at higher temperatures. However, the calculated zero-Kelvin phonons of AFM FeRh exhibit imaginary modes at M points in the Brillouin zone, indicating a premartensitic instability, which is a precursor to a martensitic transformation at low temperatures. Combining electronic-structure calculations with ab initio molecular dynamics, conjugate gradient relaxation, and the solid-state nudged-elastic band methods, we predict that AFM B2 FeRh becomes unstable at ambient pressure and transforms without a barrier to an AFM(111) orthorhombic (martensitic) ground state below 90±10K. In conclusion,more » we also consider competing structures, in particular, a tetragonal AFM(100) phase that is not the global ground state, as proposed, but a constrained solution.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zarkevich, Nikolai A.; Johnson, Duane D.

Cubic B2 FeRh exhibits a metamagnetic transition [(111) antiferromagnet (AFM) to ferromagnet (FM)] around 353 K and remains structurally stable at higher temperatures. However, the calculated zero-Kelvin phonons of AFM FeRh exhibit imaginary modes at M points in the Brillouin zone, indicating a premartensitic instability, which is a precursor to a martensitic transformation at low temperatures. Combining electronic-structure calculations with ab initio molecular dynamics, conjugate gradient relaxation, and the solid-state nudged-elastic band methods, we predict that AFM B2 FeRh becomes unstable at ambient pressure and transforms without a barrier to an AFM(111) orthorhombic (martensitic) ground state below 90±10K. In conclusion,more » we also consider competing structures, in particular, a tetragonal AFM(100) phase that is not the global ground state, as proposed, but a constrained solution.« less

Structure and Dynamics of Confined Alcohol-Water Mixtures.

PubMed

Bampoulis, Pantelis; Witteveen, Jorn P; Kooij, E Stefan; Lohse, Detlef; Poelsema, Bene; Zandvliet, Harold J W

2016-07-26

The effect of confinement between mica and graphene on the structure and dynamics of alcohol-water mixtures has been studied in situ and in real time at the molecular level by atomic force microscopy (AFM) at room temperature. AFM images reveal that the adsorbed molecules are segregated into faceted alcohol-rich islands on top of an ice layer on mica, surrounded by a pre-existing multilayer water-rich film. These faceted islands are in direct contact with the graphene surface, revealing a preferred adsorption site. Moreover, alcohol adsorption at low relative humidity (RH) reveals a strong preference of the alcohol molecules for the ordered ice interface. The growth dynamics of the alcohol islands is governed by supersaturation, temperature, the free energy of attachment of molecules to the island edge and two-dimensional (2D) diffusion. The measured diffusion coefficients display a size dependence on the molecular size of the alcohols, and are about 6 orders of magnitude smaller than the bulk diffusion coefficients, demonstrating the effect of confinement on the behavior of the alcohols. These experimental results provide new insights into the behavior of multicomponent fluids in confined geometries, which is of paramount importance in nanofluidics and biology.

Distinct magnetic spectra in the hidden order and antiferromagnetic phases in URu 2 - x Fe x Si 2

DOE PAGES

Butch, Nicholas P.; Ran, Sheng; Jeon, Inho; ...

2016-11-07

We use neutron scattering to compare the magnetic excitations in the hidden order (HO) and antiferromagnetic (AFM) phases in URu 2-xFe xSi 2 as a function of Fe concentration. The magnetic excitation spectra change significantly between x = 0.05 and x = 0.10, following the enhancement of the AFM ordered moment, in good analogy to the behavior of the parent compound under applied pressure. Prominent lattice-commensurate low-energy excitations characteristic of the HO phase vanish in the AFM phase. The magnetic scattering is dominated by strong excitations along the Brillouin zone edges, underscoring the important role of electron hybridization to bothmore » HO and AFM phases, and the similarity of the underlying electronic structure. The stability of the AFM phase is correlated with enhanced local-itinerant electron hybridization.« less

Exchange field and Hc dependence on the ferromagnetic material in exchange couples with CoO (abstract)

NASA Astrophysics Data System (ADS)

Takano, Kentaro; Berkowitz, A. E.

1997-04-01

As recording density increases, magnetoresistive (MR) sensors are becoming increasingly important in read heads. NixCo(1-x)O is receiving technological attention for biasing magnetoresistive sensors as a robust alternative to FeMn. The interfacial exchange coupling between a ferromagnetic (FM) layer and an antiferromagnetic (AFM) is observed as an exchange field and an enhanced coercive field of the FM layer. The AFM/FM coupling is sensitive to the interfacial structure and the AFM and FM magnetic parameters. In this work, we deposited various FM layers on similar 300 Å CoO base layers to study the dependence of the FM exchange integral parameter J on the exchange HE and coercive HC fields. CoO was selected as the AFM material because (i) its simple spin and crystal structures facilitate the structural characterization and modeling of its magnetic properties, and (ii) it's modest Néel temperature of 300 K facilitates the use of a superconducting quantum interference device for the magnetic measurements at temperatures ranging from 5 to 400 K. The 300 Å CoO films were reactively sputtered on silicon substrates and capped with various 300 Å FM films, Ni, Co, Fe, and permalloy (Ni81Fe19). The 300 Å CoO base layer films were polycrystalline with columnar grains. The CoO deposition conditions were reproduced to ensure similar structural and magnetic interfacial AF environments. The observed HE temperature dependence cannot be explained by current theoretical models. The temperature dependence of the exchange fields have the common features (i) a blocking temperature Tb=300 K, which corresponds to the bulk Néel temperature of CoO, (ii) a rise in the exchange field with decreasing temperature, (iii) an intermediate temperature region of constant HE (plateau value), and (iv) a second region of linearly increasing HE with decreasing temperatures down to 0 K. The plateau value of the HE decreased inversely with increasing FM magnetization as predicted by theory. The low-temperature increase of HE is more significant in the FM with higher exchange integral J values. The crossover temperature from the plateau to the low-temperature rise in HE appears to be dependent on FM's J value. The increase in the interfacial coupling strength could suggest the magnetic ordering of a secondary phase localized at the interfacial atoms. The temperature dependence of HC enhancement does not share the nonlinear temperature behavior of HE. For T<300 K, HC increases linearly with decreasing temperatures down to 10 K. Although the HC enhancement may have magnetoelastic contributions, the disappearance of the linear enhancement at 300 K, the Néel temperature of CoO, indicates that the dominant mechanism is the interfacial magnetic coupling.

Low temperature corneal laser welding investigated by atomic force microscopy

NASA Astrophysics Data System (ADS)

Matteini, Paolo; Sbrana, Francesca; Tiribilli, Bruno; Pini, Roberto

2009-02-01

The structural modifications in the stromal matrix induced by low-temperature corneal laser welding were investigated by atomic force microscopy (AFM). This procedure consists of staining the wound with Indocyanine Green (ICG), followed by irradiation with a near-infrared laser operated at low-power densities. This induces a local heating in the 55-65 °C range. In welded tissue, extracellular components undergo heat-induced structural modifications, resulting in a joining effect between the cut edges. However, the exact mechanism generating the welding, to date, is not completely understood. Full-thickness cuts, 3.5 mm in length, were made in fresh porcine cornea samples, and these were then subjected to laser welding operated at 16.7 W/cm2 power density. AFM imaging was performed on resin-embedded semi-thin slices once they had been cleared by chemical etching, in order to expose the stromal bulk of the tissue within the section. We then carried out a morphological analysis of characteristic fibrillar features in the laser-treated and control samples. AFM images of control stromal regions highlighted well-organized collagen fibrils (36.2 +/- 8.7 nm in size) running parallel to each other as in a typical lamellar domain. The fibrils exhibited a beaded pattern with a 22-39 nm axial periodicity. Laser-treated corneal regions were characterized by a significant disorganization of the intralamellar architecture. At the weld site, groups of interwoven fibrils joined the cut edges, showing structural properties that were fully comparable with those of control regions. This suggested that fibrillar collagen is not denatured by low-temperature laser welding, confirming previous transmission electron microscopy (TEM) observations, and thus it is probably not involved in the closure mechanism of corneal cuts. The loss of fibrillar organization may be related to some structural modifications in some interfibrillar substance as proteoglycans or collagen VI. Furthermore, AFM imaging was demonstrated to be a suitable tool for attaining three-dimensional information on the fibrillar assembly of corneal stroma. The results suggested that AFM analyses of resin-embedded histological sections subjected to chemical etching provide a rapid and cost-effective response, with an imaging resolution that is quite similar to that of TEM.

Temperature-Controlled High-Speed AFM: Real-Time Observation of Ripple Phase Transitions.

PubMed

Takahashi, Hirohide; Miyagi, Atsushi; Redondo-Morata, Lorena; Scheuring, Simon

2016-11-01

With nanometer lateral and Angstrom vertical resolution, atomic force microscopy (AFM) has contributed unique data improving the understanding of lipid bilayers. Lipid bilayers are found in several different temperature-dependent states, termed phases; the main phases are solid and fluid phases. The transition temperature between solid and fluid phases is lipid composition specific. Under certain conditions some lipid bilayers adopt a so-called ripple phase, a structure where solid and fluid phase domains alternate with constant periodicity. Because of its narrow regime of existence and heterogeneity ripple phase and its transition dynamics remain poorly understood. Here, a temperature control device to high-speed atomic force microscopy (HS-AFM) to observe dynamics of phase transition from ripple phase to fluid phase reversibly in real time is developed and integrated. Based on HS-AFM imaging, the phase transition processes from ripple phase to fluid phase and from ripple phase to metastable ripple phase to fluid phase could be reversibly, phenomenologically, and quantitatively studied. The results here show phase transition hysteresis in fast cooling and heating processes, while both melting and condensation occur at 24.15 °C in quasi-steady state situation. A second metastable ripple phase with larger periodicity is formed at the ripple phase to fluid phase transition when the buffer contains Ca 2+ . The presented temperature-controlled HS-AFM is a new unique experimental system to observe dynamics of temperature-sensitive processes at the nanoscopic level. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetic characterization of mixed phases in FeVO4sbnd Co3V2O8 system

NASA Astrophysics Data System (ADS)

Guskos, N.; Zolnierkiewicz, G.; Pilarska, M.; Typek, J.; Berczynski, P.; Blonska-Tabero, A.; Aidinis, K.

2018-04-01

Dynamic and static magnetic properties of four nFeVO4/(1-n)Co3V2O8 composites obtained in reactions between nFeVO4 and (1-n)Co3V2O8 (n = 0.82, 0.80, 0.78 and 0.76) have been investigated by dc magnetometry and electron paramagnetic resonance (EPR). All samples were diphase containing both the howardevansite-type and the lyonsite-type phases in different proportions. Dc magnetic susceptibility study showed the Curie-Weiss paramagnetic behavior with strong antiferromagnetic (AFM) interaction in the high-temperature range and the phase transition to the AFM state at low temperatures. The calculated effective magnetic moment could be justified by the presence of high spin Fe3+ and Co2+ ions. The appearance of hysteresis loop in isothermal magnetisation at low temperature indicates the existence of the ferromagnetic component in all four samples, but only 0.5% of all magnetic ions are involved in this phase. EPR spectra recorded in high-temperature range (T > 90 K) consisted of a single broad line centred at ∼3.2 kG. The fitting of observed spectra with two Gaussian lineshape functions allowed to study the temperature dependence of EPR parameters (resonance field, linewidth, integrated intensity). This analysis suggests that EPR signal arises from two spin subsystems: paramagnetic Fe3+ ions subjected to AFM interaction and AFM spin pairs/clusters of iron/cobalt visible only at high temperatures. At low temperatures two transitions to AFM states, due to the mixture of two structural phases, are registered in magnetic susceptibility measurements.

Large-moment antiferromagnetic order in overdoped high-Tc superconductor 154SmFeAsO1-x D x .

PubMed

Iimura, Soshi; Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Honda, Takashi; Ikeda, Kazutaka; Hansen, Thomas C; Otomo, Toshiya; Hosono, Hideo

2017-05-30

In iron-based superconductors, high critical temperature ( T c ) superconductivity over 50 K has only been accomplished in electron-doped hRE FeAsO ( hRE is heavy rare earth ( RE ) element). Although hRE FeAsO has the highest bulk T c (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of 154 SmFeAsO 1- x D x , and the discovery of a long-range antiferromagnetic ordering with x ≥ 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 μ B /Fe, which is the largest in all nondoped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3 d xy orbital, in which the nearest-neighbor hopping parameter becomes zero. The unique phase diagram, i.e., highest- T c superconducting phase adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity.

FeRh ground state and martensitic transformation

NASA Astrophysics Data System (ADS)

Zarkevich, Nikolai A.; Johnson, Duane D.

2018-01-01

Cubic B 2 FeRh exhibits a metamagnetic transition [(111) antiferromagnet (AFM) to ferromagnet (FM)] around 353 K and remains structurally stable at higher temperatures. However, the calculated zero-Kelvin phonons of AFM FeRh exhibit imaginary modes at M points in the Brillouin zone, indicating a premartensitic instability, which is a precursor to a martensitic transformation at low temperatures. Combining electronic-structure calculations with ab initio molecular dynamics, conjugate gradient relaxation, and the solid-state nudged-elastic band methods, we predict that AFM B 2 FeRh becomes unstable at ambient pressure and transforms without a barrier to an AFM(111) orthorhombic (martensitic) ground state below 90 ±10 K . We also consider competing structures, in particular, a tetragonal AFM(100) phase that is not the global ground state, as proposed [Phys. Rev. B 94, 180407(R) (2016), 10.1103/PhysRevB.94.180407], but a constrained solution.

Reversible Dissolution of Microdomains in Detergent-Resistant Membranes at Physiological Temperature

PubMed Central

Cremona, Andrea; Orsini, Francesco; Corsetto, Paola A.; Hoogenboom, Bart W.; Rizzo, Angela M.

2015-01-01

The formation of lipid microdomains (“rafts”) is presumed to play an important role in various cellular functions, but their nature remains controversial. Here we report on microdomain formation in isolated, detergent-resistant membranes from MDA-MB-231 human breast cancer cells, studied by atomic force microscopy (AFM). Whereas microdomains were readily observed at room temperature, they shrunk in size and mostly disappeared at higher temperatures. This shrinking in microdomain size was accompanied by a gradual reduction of the height difference between the microdomains and the surrounding membrane, consistent with the behaviour expected for lipids that are laterally segregated in liquid ordered and liquid disordered domains. Immunolabeling experiments demonstrated that the microdomains contained flotillin-1, a protein associated with lipid rafts. The microdomains reversibly dissolved and reappeared, respectively, on heating to and cooling below temperatures around 37°C, which is indicative of radical changes in local membrane order close to physiological temperature. PMID:26147107

Contact resonance atomic force microscopy for viscoelastic characterization of polymer-based nanocomposites at variable temperature

NASA Astrophysics Data System (ADS)

Natali, Marco; Passeri, Daniele; Reggente, Melania; Tamburri, Emanuela; Terranova, Maria Letizia; Rossi, Marco

2016-06-01

Characterization of mechanical properties at the nanometer scale at variable temperature is one of the main challenges in the development of polymer-based nanocomposites for application in high temperature environments. Contact resonance atomic force microscopy (CR-AFM) is a powerful technique to characterize viscoelastic properties of materials at the nanoscale. In this work, we demonstrate the capability of CR-AFM of characterizing viscoelastic properties (i.e., storage and loss moduli, as well as loss tangent) of polymer-based nanocomposites at variable temperature. CR-AFM is first illustrated on two polymeric reference samples, i.e., low-density polyethylene (LDPE) and polycarbonate (PC). Then, temperature-dependent viscoelastic properties (in terms of loss tangent) of a nanocomposite sample constituted by a epoxy resin reinforced with single-wall carbon nanotubes (SWCNTs) are investigated.

Formation of gapless Z 2 spin liquid phase manganites in the (Sm1- y Gd y )0.55Sr0.45MnO3 system in zero magnetic field: Topological phase transitions to states with low and high density of 2D-vortex pairs induced by the magnetic field

NASA Astrophysics Data System (ADS)

Bukhan'ko, F. N.; Bukhan'ko, A. F.

2017-12-01

The evolution of the ground state of the manganese spin ensemble in the (Sm1- y Gd y )0.55Sr0.45MnO3 in the case of isovalent substitution of rare-earth samarium ions with large radii with gadolinium ions with significantly smaller radii is studied. The measured temperature dependences of the ac magnetic susceptibility and the field dependences of the dc magnetizations are analyzed using the Heisenberg-Kitaev model describing the transition from the ordered spin state with classical isotropic AFM exchange to the frustrated spin state with quantum highly anisotropic FM exchange. A continuous transition from the 3D ferromagnetic state of manganese spins in the initial sample with y = 0 to zigzag AFM ordering of CE-type spins in ab planes for y = 0.5, coexisting in samples with y = 0.5, 0.6, and 0.7 at temperatures below T N ≅ 48.5 K with a disordered phase such as a quantum Griffiths phase is identified. As the gadolinium concentration further increases, the CE-type zigzag AFM structure is molten, which leads to the appearance of an unusual phase in Gd0.55Sr0.45MnO3 in the temperature range close to the absolute zero. This phase has characteristic features of a gapless Z 2 quantum spin liquid in zero external magnetic field. The step changes in the magnetization isotherms measured at 4.2 K in the field range of ±75 kOe are explained by quantum phase transitions of the Z 2 spin liquid to a phase with topological order in weak magnetic fields and a polarized phase in strong fields. The significant difference between critical fields and magnetization jumps in isotherms indicates the existence of hysteretic phenomena in quantum spin liquid magnetization-demagnetization processes caused by the difference between localization-delocalization of 2D vortex pairs induced by a magnetic field in a quantum spin liquid with disorder.

Giant Controllable Magnetization Changes Induced by Structural Phase Transitions in a Metamagnetic Artificial Multiferroic

PubMed Central

Bennett, S. P.; Wong, A. T.; Glavic, A.; Herklotz, A.; Urban, C.; Valmianski, I.; Biegalski, M. D.; Christen, H. M.; Ward, T. Z.; Lauter, V.

2016-01-01

The realization of a controllable metamagnetic transition from AFM to FM ordering would open the door to a plethora of new spintronics based devices that, rather than reorienting spins in a ferromagnet, harness direct control of a materials intrinsic magnetic ordering. In this study FeRh films with drastically reduced transition temperatures and a large magneto-thermal hysteresis were produced for magnetocaloric and spintronics applications. Remarkably, giant controllable magnetization changes (measured to be as high has ~25%) are realized by manipulating the strain transfer from the external lattice when subjected to two structural phase transitions of BaTiO3 (001) single crystal substrate. These magnetization changes are the largest seen to date to be controllably induced in the FeRh system. Using polarized neutron reflectometry we reveal how just a slight in plane surface strain change at ~290C results in a massive magnetic transformation in the bottom half of the film clearly demonstrating a strong lattice-spin coupling in FeRh. By means of these substrate induced strain changes we show a way to reproducibly explore the effects of temperature and strain on the relative stabilities of the FM and AFM phases in multi-domain metamagnetic systems. This study also demonstrates for the first time the depth dependent nature of a controllable magnetic order using strain in an artificial multiferroic heterostructure. PMID:26940159

Giant Controllable Magnetization Changes Induced by Structural Phase Transitions in a Metamagnetic Artificial Multiferroic

DOE PAGES

Bennett, S. P.; Wong, A. T.; Glavic, A.; ...

2016-03-04

We realize that a controllable metamagnetic transition from AFM to FM ordering would open the door to a plethora of new spintronics based devices that, rather than reorienting spins in a ferromagnet, harness direct control of a materials intrinsic magnetic ordering. In this study FeRh films with drastically reduced transition temperatures and a large magneto-thermal hysteresis were produced for magnetocaloric and spintronics applications. Remarkably, giant controllable magnetization changes (measured to be as high has ~25%) are realized and by manipulating the strain transfer from the external lattice when subjected to two structural phase transitions of BaTiO3 (001) single crystal substrate.more » These magnetization changes are the largest seen to date to be controllably induced in the FeRh system. Using polarized neutron reflectometry we reveal how just a slight in plane surface strain change at ~290C results in a massive magnetic transformation in the bottom half of the film clearly demonstrating a strong lattice-spin coupling in FeRh. By means of these substrate induced strain changes we show a way to reproducibly explore the effects of temperature and strain on the relative stabilities of the FM and AFM phases in multi-domain metamagnetic systems. In our study also demonstrates for the first time the depth dependent nature of a controllable magnetic order using strain in an artificial multiferroic heterostructure.« less

Enhanced moments of Eu in single crystals of the metallic helical antiferromagnet EuCo2 -yAs2

NASA Astrophysics Data System (ADS)

Sangeetha, N. S.; Anand, V. K.; Cuervo-Reyes, Eduardo; Smetana, V.; Mudring, A.-V.; Johnston, D. C.

2018-04-01

The compound EuCo2 -yAs2 with the tetragonal ThCr2Si2 structure is known to contain Eu+2 ions with spin S =7/2 that order below a temperature TN≈47 K into an antiferromagnetic (AFM) proper helical structure with the ordered moments aligned in the tetragonal a b plane, perpendicular to the helix axis along the c axis, with no contribution from the Co atoms. Here we carry out a detailed investigation of the properties of single crystals. We consistently find about 5% vacancies on the Co site from energy-dispersive x-ray analysis and x-ray diffraction refinements. Enhanced ordered and effective moments of the Eu spins are found in most of our crystals. Electronic structure calculations indicate that the enhanced moments arise from polarization of the d bands, as occurs in ferromagnetic Gd metal. Electrical resistivity measurements indicate metallic behavior. The low-field in-plane magnetic susceptibilities χa b(T

Manganese-induced magnetic symmetry breaking and its correlation with the metal-insulator transition in bilayered S r 3 ( R u 1 - x M n x ) 2 O 7

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Qiang; Ye, Feng; Tian, Wei

Bilayered Sr 3Ru 2O 7 is an unusual metamagnetic metal with inherently antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial substitution of Ru by Mn results in the establishment of a metal-insulator transition (MIT) at TMIT and AFM ordering at TM in Sr 3(Ru 1-xMn x) 2O 7. Using elastic neutron scattering, we investigated the effect of Mn doping on the magnetic structure, in-plane magnetic correlation lengths and their correlation to the MIT in Sr 3(Ru 1-xMn x) 2O 7 (x=0.06 and 0.12). With the increase of Mn doping (x) from 0.06 to 0.12 or the decrease of temperatures for x=0.12,more » an evolution from an in-plane short-range to long-range antiferromagnetic (AFM) ground state occurs. For both compounds, the magnetic ordering has a double-stripe configuration, and the onset of magnetic correlation with an anisotropic behavior coincides with the sharp rise in electrical resistivity and specific heat. Since it does not induce a measurable lattice distortion, the double-stripe antiferromagnetic order with anisotropic spin texture breaks symmetry from a C 4v crystal lattice to a C 2v magnetic sublattice. These observations shed light on an age-old question regarding the Slater versus Mott-type MIT.« less

Manganese-induced magnetic symmetry breaking and its correlation with the metal-insulator transition in bilayered S r 3 ( R u 1 - x M n x ) 2 O 7

DOE PAGES

Zhang, Qiang; Ye, Feng; Tian, Wei; ...

2017-06-12

Bilayered Sr 3Ru 2O 7 is an unusual metamagnetic metal with inherently antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial substitution of Ru by Mn results in the establishment of a metal-insulator transition (MIT) at TMIT and AFM ordering at TM in Sr 3(Ru 1-xMn x) 2O 7. Using elastic neutron scattering, we investigated the effect of Mn doping on the magnetic structure, in-plane magnetic correlation lengths and their correlation to the MIT in Sr 3(Ru 1-xMn x) 2O 7 (x=0.06 and 0.12). With the increase of Mn doping (x) from 0.06 to 0.12 or the decrease of temperatures for x=0.12,more » an evolution from an in-plane short-range to long-range antiferromagnetic (AFM) ground state occurs. For both compounds, the magnetic ordering has a double-stripe configuration, and the onset of magnetic correlation with an anisotropic behavior coincides with the sharp rise in electrical resistivity and specific heat. Since it does not induce a measurable lattice distortion, the double-stripe antiferromagnetic order with anisotropic spin texture breaks symmetry from a C 4v crystal lattice to a C 2v magnetic sublattice. These observations shed light on an age-old question regarding the Slater versus Mott-type MIT.« less

Decoupling of the antiferromagnetic and insulating states in Tb-doped Sr 2IrO 4

DOE PAGES

Wang, J. C.; Aswartham, S.; Ye, Feng; ...

2015-12-08

Sr 2IrO 4 is a spin-orbit coupled insulator with an antiferromagnetic (AFM) transition at T N = 240 K. We report results of a comprehensive study of single-crystal Sr 2Ir 1-xTb xO 4 (0≤x≤0.03). This study found that mere 3% (x=0.03) tetravalent Tb 4+(4f 7) substituting for Ir 4+ (rather than Sr 2+) completely suppresses the long-range collinear AFM transition but retains the insulating state, leading to a phase diagram featuring a decoupling of magnetic interactions and charge gap. The insulating state at x = 0.03 is characterized by an unusually large specific heat at low temperatures and an incommensuratemore » magnetic state having magnetic peaks at (0.95, 0, 0) and (0, 0.95, 0) in the neutron diffraction, suggesting a spiral or spin density wave order. It is apparent that Tb doping effectively changes the relative strength of the SOI and the tetragonal CEF and enhances the Hund’s rule coupling that competes with the SOI, and destabilizes the AFM state. However, the disappearance of the AFM accompanies no metallic state chiefly because an energy level mismatch for the Ir and Tb sites weakens charge carrier hopping and renders a persistent insulating state. Furthermore, this work highlights an unconventional correlation between the AFM and insulating states in which the magnetic transition plays no critical role in the formation of the charge gap in the iridate.« less

Strain driven anisotropic magnetoresistance in antiferromagnetic La0.4Sr0.6MnO3 thin films

NASA Astrophysics Data System (ADS)

Ward, T. Zac; Wong, A. T.; Takamura, Yayoi; Herklotz, Andreas

2015-03-01

Antiferromagnets (AFM) are a promising alternative to ferromagnets (FM) in spintronic applications. The reason stems from the fact that at high data storage densities stray fields could destroy FM set states while AFMs would be relatively insensitive to this data corruption. This work presents the first ever example of antiferromagnetic La0.4Sr0.6MnO3 thin films stabilized in different strain states. Strain is found to drive different types of AFM ordering, and these variations in ordering type are shown to have a profound impact on both the magnitude and character of the materials' resistive response to magnetic field direction, or anisotropic magnetoresistance (AMR) behavior (one standard of spintronic suitability). The compressively strained film shows the highest recorded AMR response in an ohmic AFM device of 63%, while the tensile strained film shows a typical AFM AMR of 0.6%. These findings demonstrate the necessity of understanding electron ordering in AFM spintronic applications and provide a new benchmark for AMR response. This work was supported by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division.

A hydrothermal atomic force microscope for imaging in aqueous solution up to 150 °C

NASA Astrophysics Data System (ADS)

Higgins, Steven R.; Eggleston, Carrick M.; Knauss, Kevin G.; Boro, Carl O.

1998-08-01

We present the design of a contact atomic force microscope (AFM) that can be used to image solid surfaces in aqueous solution up to 150 °C and 6 atm. The main features of this unique AFM are: (1) an inert gas pressurized microscope base containing stepper motor for coarse advance and the piezoelectric tube scanner; (2) a chemically inert membrane separating these parts from the fluid cell; (3) a titanium fluid cell with fluid inlet-outlet ports, a thermocouple port, and a sapphire optical window; (4) a resistively heated ceramic booster heater for the fluid cell to maintain the temperature of solutions sourced from a hydrothermal bomb; and (5) mass flow control. The design overcomes current limitations on the temperature and pressure range accessible to AFM imaging in aqueous solutions. Images taken at temperature and pressure are presented, demonstrating the unit-cell scale (<1 nm) vertical resolution of the AFM under hydrothermal conditions.

Magnetic ordering induced giant optical property change in tetragonal BiFeO3

NASA Astrophysics Data System (ADS)

Tong, Wen-Yi; Ding, Hang-Chen; Gong, Shi Jing; Wan, Xiangang; Duan, Chun-Gang

2015-12-01

Magnetic ordering could have significant influence on band structures, spin-dependent transport, and other important properties of materials. Its measurement, especially for the case of antiferromagnetic (AFM) ordering, however, is generally difficult to be achieved. Here we demonstrate the feasibility of magnetic ordering detection using a noncontact and nondestructive optical method. Taking the tetragonal BiFeO3 (BFO) as an example and combining density functional theory calculations with tight-binding models, we find that when BFO changes from C1-type to G-type AFM phase, the top of valance band shifts from the Z point to Γ point, which makes the original direct band gap become indirect. This can be explained by Slater-Koster parameters using the Harrison approach. The impact of magnetic ordering on band dispersion dramatically changes the optical properties. For the linear ones, the energy shift of the optical band gap could be as large as 0.4 eV. As for the nonlinear ones, the change is even larger. The second-harmonic generation coefficient d33 of G-AFM becomes more than 13 times smaller than that of C1-AFM case. Finally, we propose a practical way to distinguish the two AFM phases of BFO using the optical method, which is of great importance in next-generation information storage technologies.

Quasi-Particle Relaxation and Quantum Femtosecond Magnetism in Non-Equilibrium Phases of Insulating Manganites

NASA Astrophysics Data System (ADS)

Perakis, Ilias; Kapetanakis, Myron; Lingos, Panagiotis; Barmparis, George; Patz, A.; Li, T.; Wang, Jigang

We study the role of spin quantum fluctuations driven by photoelectrons during 100fs photo-excitation of colossal magneto-resistive manganites in anti-ferromagnetic (AFM) charge-ordered insulating states with Jahn-Teller distortions. Our mean-field calculation of composite fermion excitations demonstrates that spin fluctuations reduce the energy gap by quasi-instantaneously deforming the AFM background, thus opening a conductive electronic pathway via FM correlation. We obtain two quasi-particle bands with distinct spin-charge dynamics and dependence on lattice distortions. To connect with fs-resolved spectroscopy experiments, we note the emergence of fs magnetization in the low-temperature magneto-optical signal, with threshold dependence on laser intensity characteristic of a photo-induced phase transition. Simultaneously, the differential reflectivity shows bi-exponential relaxation, with fs component, small at low intensity, exceeding ps component above threshold for fs AFM-to-FM switching. This suggests the emergence of a non-equilibrium metallic FM phase prior to establishment of a new lattice structure, linked with quantum magnetism via spin/charge/lattice couplings for weak magnetic fields.

A comprehensive study of magnetic exchanges in the layered oxychalcogenides Sr 3 Fe 2 O 5 Cu 2 Q 2 ( Q = S, Se)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lü, Minfeng; Mentré, Olivier; Gordon, Elijah E.

2017-12-01

The layered oxysulfide Sr3Fe2O5Cu2S2 was prepared, and its crystal structure and magnetic properties were characterized by synchrotron X-ray diffraction (XRD), powder neutron diffraction (PND), Mössbauer spectroscopy measurements and by density functional theory (DFT) calculations. In addition, the spin exchange interactions leading to the ordered magnetic structure of Sr3Fe2O5Cu2S2 were compared with those of its selenium analogue Sr3Fe2O5Cu2Se2. The oxysulfide Sr3Fe2O5Cu2S2 adopts a G-type antiferromagnetic (AFM) structure at a temperature in the range 485–512 K, which is comparable with the three-dimensional (3D) AFM ordering temperature, TN ≈ 490 K, found for Sr3Fe2O5Cu2Se2. Consistent with this observation, the spin exchange interactions ofmore » the magnetic (Sr3Fe2O5)2+ layers are slightly greater (but comparable) for oxysulfide than for the oxyselenide. Attempts to reduce or oxidize Sr3Fe2O5Cu2S2 using topochemical routes yield metallic Fe.« less

Theory of the interplay between the superconductivity and the blocked antiferromagnetic order in A(y)Fe(2-x)Se2.

PubMed

Jiang, Hong-Min

2012-09-26

Based on an effective two-orbital tight-binding model, we examine the possible superconducting states in iron-vacancy-ordered A(y)Fe(2-x)Se(2). In the presence of ordered vacancies and blocked antiferromagnetic order, it is shown that the emergent SC pairing is the nodeless next-nearest-neighbor (NNN)-pairing due to the dominant antiferromagnetic (AFM) interaction between the inter-block NNN sites. In particular, we show that due to the ordered vacancies and the associated blocked AFM order, the interplay between the superconducting and AFM states results in three distinct states in the phase diagram as doping is varied. The divergent experimental observations can be accounted for by considering the different charge carrier concentrations in their respective compounds.

Electrical characterization of HgTe nanowires using conductive atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gundersen, P.; Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim; Kongshaug, K. O.

Self-organized HgTe nanowires grown by molecular beam epitaxy (MBE) have been characterized using conductive atomic force microscopy. As HgTe will degrade or evaporate at normal baking temperatures for electron beam lithography (EBL) resists, an alternative method was developed. Using low temperature optical lithography processes, large Au contacts were deposited on a sample covered with randomly oriented, lateral HgTe nanowires. Nanowires partly covered by the large electrodes were identified with a scanning electron microscope and then localized in the atomic force microscope (AFM). The conductive tip of the AFM was then used as a movable electrode to measure current-voltage curves atmore » several locations on HgTe nanowires. The measurements revealed that polycrystalline nanowires had diffusive electron transport, with resistivities two orders of magnitude larger than that of an MBE-grown HgTe film. The difference can be explained by scattering at the rough surface walls and at the grain boundaries in the wires. The method can be a solution when EBL is not available or requires too high temperature, or when measurements at several positions along a wire are required.« less

Using ultrashort terahertz pulses to directly probe spin dynamics in insulating antiferromagnets

NASA Astrophysics Data System (ADS)

Bowlan, P.; Trugman, S. A.; Yarotski, D. A.; Taylor, A. J.; Prasankumar, R. P.

2018-05-01

Terahertz pulses are a direct and general probe of ultrafast spin dynamics in insulating antiferromagnets (AFM). This is shown by using optical-pump, THz-probe spectroscopy to directly track AFM spin dynamics in the hexagonal multiferroic HoMnO3 and the orthorhombic multiferroic TbMnO3. Our studies show that despite the different structural and spin orders in these materials, THz pulses can unambiguously resolve spin dynamics after optical photoexcitation. We believe that this approach is quite general and can be applied to a broad range of materials with different AFM spin alignments, providing a novel non-contact approach for probing AFM order with femtosecond temporal resolution.

Local suppression of the hidden-order phase by impurities in URu2Si2

NASA Astrophysics Data System (ADS)

Pezzoli, Maria E.; Graf, Matthias J.; Haule, Kristjan; Kotliar, Gabriel; Balatsky, Alexander V.

2011-06-01

We consider the effects of impurities on the enigmatic hidden order (HO) state of the heavy-fermion material URu2Si2. In particular, we focus on local effects of Rh impurities as a tool to probe the suppression of the HO state. To study local properties, we introduce a lattice free energy, where the time invariant HO order parameter Ψ and local antiferromagnetic (AFM) order parameter M are competing orders. Near each Rh atom, the HO order parameter is suppressed, creating a hole in which local AFM order emerges as a result of competition. These local holes are created in the fabric of the HO state like in a Swiss cheese and “filled” with droplets of AFM order. We compare our analysis with recent NMR results on U(RhxRu1-x)2Si2 and find good agreement with the data.

Athermalization in atomic force microscope based force spectroscopy using matched microstructure coupling.

PubMed

Torun, H; Finkler, O; Degertekin, F L

2009-07-01

The authors describe a method for athermalization in atomic force microscope (AFM) based force spectroscopy applications using microstructures that thermomechanically match the AFM probes. The method uses a setup where the AFM probe is coupled with the matched structure and the displacements of both structures are read out simultaneously. The matched structure displaces with the AFM probe as temperature changes, thus the force applied to the sample can be kept constant without the need for a separate feedback loop for thermal drift compensation, and the differential signal can be used to cancel the shift in zero-force level of the AFM.

Tuning antiferromagnetic exchange interaction for spontaneous exchange bias in MnNiSnSi system

NASA Astrophysics Data System (ADS)

Jia, Liyun; Shen, Jianlei; Li, Mengmeng; Wang, Xi; Ma, Li; Zhen, Congmian; Hou, Denglu; Liu, Enke; Wang, Wenhong; Wu, Guangheng

2017-12-01

Based on almost all the data from the literature on spontaneous exchange bias (SEB), it is expected that the system will show SEB if it meets two conditions simultaneously: (i) there are the coexistence and competition of antiferromagnetic (AFM) and ferromagnetic (FM) interactions and (ii) AFM interaction should dominate but not be too strong in this competition. In order to verify this view, a systematic study on SEB has been performed in this work. Mn50Ni40Sn10 with strong FM interaction and without SEB is chosen as the mother composition, and the negative chemical pressure is introduced by the substitution of Sn by Si to enhance AFM interaction. It is found that a long-range FM ordering window is closed, and a long-range AFM ordering window is opened. As a result, SEB is triggered and a continuous tuning of the spontaneous exchange bias field (HSEB) from 0 Oe to 1300 Oe has been realized in a Mn50Ni40Sn10-xSix system by the enhanced AFM interaction.

Oxygen plasma ashing effects on aluminum and titanium space protective coatings

NASA Technical Reports Server (NTRS)

Synowicki, R.; Kubik, R. D.; Hale, J. S.; Peterkin, Jane; Nafis, S.; Woollam, John A.; Zaat, S.

1991-01-01

Using variable angle spectroscopic ellipsometry and atomic force microscopy (AFM), the surface roughness and oxidation of aluminum and titanium thin films have been studied as a function of substrate deposition temperature and oxygen plasma exposure. Increasing substrate deposition temperatures affect film microstructure by greatly increasing grain size. Short exposures to an oxygen plasma environment produce sharp spikes rising rapidly above the surface as seen by AFM. Ellipsometric measurements were made over a wide range of plasma exposure times, and results at longer exposure times suggest that the surface is greater than 30% void. This is qualitatively verified by the AFM images.

[AFM fishing of proteins under impulse electric field].

PubMed

Ivanov, Yu D; Pleshakova, T O; Malsagova, K A; Kaysheva, A L; Kopylov, A T; Izotov, A A; Tatur, V Yu; Vesnin, S G; Ivanova, N D; Ziborov, V S; Archakov, A I

2016-05-01

A combination of (atomic force microscopy)-based fishing (AFM-fishing) and mass spectrometry allows to capture protein molecules from solutions, concentrate and visualize them on an atomically flat surface of the AFM chip and identify by subsequent mass spectrometric analysis. In order to increase the AFM-fishing efficiency we have applied pulsed voltage with the rise time of the front of about 1 ns to the AFM chip. The AFM-chip was made using a conductive material, highly oriented pyrolytic graphite (HOPG). The increased efficiency of AFM-fishing has been demonstrated using detection of cytochrome b5 protein. Selection of the stimulating pulse with a rise time of 1 ns, corresponding to the GHz frequency range, by the effect of intrinsic emission from water observed in this frequency range during water injection into the cell.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cui, J.; Roy, B.; Tanatar, M. A.

We report 75As nuclear magnetic resonance (NMR) measurements of single-crystalline Ca(Fe 1–xCo x) 2As 2 (x=0.023, 0.028, 0.033, and 0.059) annealed at 350°C for 7 days. From the observation of a characteristic shape of 75As NMR spectra in the stripe-type antiferromagnetic (AFM) state, as in the case of x=0 (T N=170 K), clear evidence for the commensurate AFM phase transition with the concomitant structural phase transition is observed in x=0.023 (T N=106 K) and x=0.028 (T N=53 K). Through the temperature dependence of the Knight shifts and the nuclear spin lattice relaxation rates (1/T 1), although stripe-type AFM spin fluctuationsmore » are realized in the paramagnetic state as in the case of other iron pnictide superconductors, we found a gradual decrease of the AFM spin fluctuations below a crossover temperature T* that was nearly independent of Co-substitution concentration, and it is attributed to a pseudogaplike behavior in the spin excitation spectra of these systems. The T* feature finds correlation with features in the temperature-dependent interplane resistivity, ρc(T), but not with the in-plane resistivity ρa(T). The temperature evolution of anisotropic stripe-type AFM spin fluctuations is tracked in the paramagnetic and pseudogap phases by the 1/T 1 data measured under magnetic fields parallel and perpendicular to the c axis. As a result, based on our NMR data, we have added a pseudogaplike phase to the magnetic and electronic phase diagram of Ca(Fe 1–xCo x) 2As 2.« less

Pb 2MnTeO 6 Double Perovskite: An Antipolar Anti-ferromagnet

DOE PAGES

Retuerto, Maria; Skiadopoulou, Stella; Li, Man-Rong; ...

2016-04-08

Pb 2MnTeO 6, a new double perovskite, has been synthesized. Its crystal structure was determined by synchrotron X-ray and powder neutron diffraction.Pb 2MnTeO 6 is monoclinic (I2/m) at room temperature with a regular arrangement of all the cations in their polyhedra. However, when the temperature is lowered to ~120 K it undergoes a phase transition from I2/m to C2/c structure. This transition is accompanied by a displacement of the Pb atoms from the center of their polyhedra due to the 6s 2 lone-pair electrons, together with a surprising off-centering of Mn 2+ (d 5) magnetic cations. This strong first-order phasemore » transition is also evidenced by specific heat, dielectric, Raman, and infrared spectroscopy measurements. The magnetic characterizations indicate an anti-ferromagnetic (AFM) order below T N ≈ 20 K; analysis of powder neutron diffraction data confirms the magnetic structure with propagation vector k = (0 1 0) and collinear AFM spins. The observed jump in dielectric permittivity near ~150 K implies possible anti-ferroelectric behavior; however, the absence of switching suggests that Pb 2MnTeO 6 can only be antipolar. First-principle calculations confirmed that the crystal and magnetic structures determined are locally stable and that anti-ferroelectric switching is unlikely to be observed in Pb 2MnTeO 6.« less

Temperature-dependent bifurcation of cooperative interactions in pure and enriched in β-carotene DPPC liposomes.

PubMed

Augustyńska, D; Burda, K; Jemioła-Rzemińska, M; Strzałka, K

2016-08-25

We examined the influence of temperature on lipid intermolecular interactions and the organization of bilayers within multilamellar dipalmitoylphosphatidylcholine (DPPC) liposomes. We also investigated the effect of 0.5 mol% β-carotene, a non-polar carotenoid, on the adhesive properties of these liposomes. Atomic force microscopy (AFM) and differential scanning calorimetry (DSC) were used to correlate the changes in the physical properties of the liposomal systems with their thermotropic behaviour. Using DSC we detected two transitions in pure DPPC vesicles and in those containing 0.5 mol% β-carotene. In both systems the pretransition occurred at 34.5(1)°C and the main phase transition at 41.4 °C during heating. Upon cooling, the temperatures of the pretransition and the main transition decreased by about 6 °C and 1 °C, respectively. Changes in enthalpy and entropy were also similar in the two investigated systems. Data obtained in parallel AFM force experiments show that the adhesive forces between the liposomal systems and AFM probe strongly depend on the loading rate. Moreover, their characteristic monotonic changes and discontinuities are sensitive to temperature. In the range of temperatures from 27 °C to 31 °C, i.e. below the temperature of phase transition from gel to ripple phase, the adhesive forces measured in a water environment are about an order of magnitude higher in the presence of β-carotene than in pure DPPC liposomes. The observed variable dependence of adhesion on the loading rate suggests that there are changes in the long- and short-range interactions between lipids, and that these may be related to the occurrence of some clustering effects. In addition, the simultaneous existence of different subphases was found in the gel phase of DPPC liposomes. The presence of β-carotene at a level of 0.5 mol% stimulates the structural reorganization of DPPC multilamellar vesicles and enhances the bifurcation phenomenon detected in these systems. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Predicting the melting temperature of ice-Ih with only electronic structure information as input.

PubMed

Pinnick, Eric R; Erramilli, Shyamsunder; Wang, Feng

2012-07-07

The melting temperature of ice-Ih was calculated with only electronic structure information as input by creating a problem-specific force field. The force field, Water model by AFM for Ice and Liquid (WAIL), was developed with the adaptive force matching (AFM) method by fitting to post-Hartree-Fock quality forces obtained in quantum mechanics∕molecular mechanics calculations. WAIL predicts the ice-Ih melting temperature to be 270 K. The model also predicts the densities of ice and water, the temperature of maximum density of water, the heat of vaporizations, and the radial distribution functions for both ice and water in good agreement with experimental measurements. The non-dissociative WAIL model is very similar to a flexible version of the popular TIP4P potential and has comparable computational cost. By customizing to problem-specific configurations with the AFM approach, the resulting model is remarkably more accurate than any variants of TIP4P for simulating ice-Ih and water in the temperature range from 253 K and 293 K under ambient pressure.

Exchange bias in multiferroic Ca3Mn2O7 effected by Dzyaloshinskii-Moriya interaction

NASA Astrophysics Data System (ADS)

Sahlot, Pooja; Jana, Anupam; Awasthi, A. M.

2018-04-01

Ruddlesden-Popper manganite Ca3Mn2O7 has been synthesized in single phase orthorhombic structure with Cmcm space group. Temperature dependent magnetization M(T) shows that Ca3Mn2O7 undergoes long range antiferromagnetic (AFM) transition below 123 K, with weak ferromagnetism (WFM) at lower temperatures. Field dependent magnetization M(H) confirms WFM character below ˜110 K in the AFM-base magnetic structure. Detailed analysis of the zero field cooled magnetic hysteresis loops reveals a measurable exchange bias (EB) effect in the sample. EB is attributed to the high anisotropy in the sample and the presence of Dzyaloshinskii-Moriya (D-M) interaction, responsible for the canted interfacial-spins that couple "FM-clusters" with the "AFM-matrix". Temperature dependence of horizontal shifts of the M(H) loops in terms of the coercive fields (Hc±) and vertical shifts in terms of the remnant magnetizations (Mr±) is presented.

Radiation pressure excitation of a low temperature atomic force/magnetic force microscope for imaging in 4-300 K temperature range

NASA Astrophysics Data System (ADS)

Ćelik, Ümit; Karcı, Özgür; Uysallı, Yiǧit; Özer, H. Özgür; Oral, Ahmet

2017-01-01

We describe a novel radiation pressure based cantilever excitation method for imaging in dynamic mode atomic force microscopy (AFM) for the first time. Piezo-excitation is the most common method for cantilever excitation, however it may cause spurious resonance peaks. Therefore, the direct excitation of the cantilever plays a crucial role in AFM imaging. A fiber optic interferometer with a 1310 nm laser was used both for the excitation of the cantilever at the resonance and the deflection measurement of the cantilever in a commercial low temperature atomic force microscope/magnetic force microscope (AFM/MFM) from NanoMagnetics Instruments. The laser power was modulated at the cantilever's resonance frequency by a digital Phase Locked Loop (PLL). The laser beam is typically modulated by ˜500 μW, and ˜141.8 nmpp oscillation amplitude is obtained in moderate vacuum levels between 4 and 300 K. We have demonstrated the performance of the radiation pressure excitation in AFM/MFM by imaging atomic steps in graphite, magnetic domains in CoPt multilayers between 4 and 300 K and Abrikosov vortex lattice in BSCCO(2212) single crystal at 4 K for the first time.

Radiation pressure excitation of a low temperature atomic force/magnetic force microscope for imaging in 4-300 K temperature range.

PubMed

Çelik, Ümit; Karcı, Özgür; Uysallı, Yiğit; Özer, H Özgür; Oral, Ahmet

2017-01-01

We describe a novel radiation pressure based cantilever excitation method for imaging in dynamic mode atomic force microscopy (AFM) for the first time. Piezo-excitation is the most common method for cantilever excitation, however it may cause spurious resonance peaks. Therefore, the direct excitation of the cantilever plays a crucial role in AFM imaging. A fiber optic interferometer with a 1310 nm laser was used both for the excitation of the cantilever at the resonance and the deflection measurement of the cantilever in a commercial low temperature atomic force microscope/magnetic force microscope (AFM/MFM) from NanoMagnetics Instruments. The laser power was modulated at the cantilever's resonance frequency by a digital Phase Locked Loop (PLL). The laser beam is typically modulated by ∼500 μW, and ∼141.8 nm pp oscillation amplitude is obtained in moderate vacuum levels between 4 and 300 K. We have demonstrated the performance of the radiation pressure excitation in AFM/MFM by imaging atomic steps in graphite, magnetic domains in CoPt multilayers between 4 and 300 K and Abrikosov vortex lattice in BSCCO(2212) single crystal at 4 K for the first time.

Effects of temperature and cellular interactions on the mechanics and morphology of human cancer cells investigated by atomic force microscopy.

PubMed

Li, Mi; Liu, LianQing; Xi, Ning; Wang, YueChao; Xiao, XiuBin; Zhang, WeiJing

2015-09-01

Cell mechanics plays an important role in cellular physiological activities. Recent studies have shown that cellular mechanical properties are novel biomarkers for indicating the cell states. In this article, temperature-controllable atomic force microscopy (AFM) was applied to quantitatively investigate the effects of temperature and cellular interactions on the mechanics and morphology of human cancer cells. First, AFM indenting experiments were performed on six types of human cells to investigate the changes of cellular Young's modulus at different temperatures and the results showed that the mechanical responses to the changes of temperature were variable for different types of cancer cells. Second, AFM imaging experiments were performed to observe the morphological changes in living cells at different temperatures and the results showed the significant changes of cell morphology caused by the alterations of temperature. Finally, by co-culturing human cancer cells with human immune cells, the mechanical and morphological changes in cancer cells were investigated. The results showed that the co-culture of cancer cells and immune cells could cause the distinct mechanical changes in cancer cells, but no significant morphological differences were observed. The experimental results improved our understanding of the effects of temperature and cellular interactions on the mechanics and morphology of cancer cells.

Overview of NASA GRCs Green Propellant Infusion Mission Thruster Testing and Plume Diagnostics

NASA Technical Reports Server (NTRS)

Deans, Matthew C.; Reed, Brian D.; Yim, John T.; Arrington, Lynn A.; Williams, George J.; Kojima, Jun J.; McLean, Christopher H.

2014-01-01

The Green Propellant Infusion Mission (GPIM) is sponsored by NASA's Space Technology Mission Directorate (STMD) Technology Demonstration Mission (TDM) office. The goal of GPIM is to advance the technology readiness level of a green propulsion system, specifically, one using the monopropellant, AF-M315E, by demonstrating ground handling, spacecraft processing, and on-orbit operations. One of the risks identified for GPIM is potential contamination of sensitive spacecraft surfaces from the effluents in the plumes of AF-M315E thrusters. NASA Glenn Research Center (GRC) is conducting activities to characterize the effects of AF-M315E plume impingement and deposition. GRC has established individual plume models of the 22-N and 1-N thrusters that will be used on the GPIM spacecraft. The models describe the pressure, temperature, density, Mach number, and species concentration of the AF-M315E thruster exhaust plumes. The models are being used to assess the impingement effects of the AF-M315E thrusters on the GPIM spacecraft. The model simulations will be correlated with plume measurement data from Laboratory and Engineering Model 22-N, AF-M315E thrusters. The thrusters will be tested in a small rocket, altitude facility at NASA GRC. The GRC thruster testing will be conducted at duty cycles representatives of the planned GPIM maneuvers. A suite of laser-based diagnostics, including Raman spectroscopy, Rayleigh spectroscopy, Schlieren imaging, and physical probes will be used to acquire plume measurements of AFM315E thrusters. Plume data will include temperature, velocity, relative density, and species concentration. The plume measurement data will be compared to the corresponding simulations of the plume model. The GRC effort will establish a data set of AF-M315E plume measurements and a plume model that can be used for future AF-M315E applications.

Antiferromagnetic spin correlations and pseudogaplike behavior in Ca(Fe 1-xCo x) 2As 2 studied by 75As nuclear magnetic resonance and anisotropic resistivity

DOE PAGES

Cui, J.; Roy, B.; Tanatar, M. A.; ...

2015-11-06

We report 75As nuclear magnetic resonance (NMR) measurements of single-crystalline Ca(Fe 1–xCo x) 2As 2 (x=0.023, 0.028, 0.033, and 0.059) annealed at 350°C for 7 days. From the observation of a characteristic shape of 75As NMR spectra in the stripe-type antiferromagnetic (AFM) state, as in the case of x=0 (T N=170 K), clear evidence for the commensurate AFM phase transition with the concomitant structural phase transition is observed in x=0.023 (T N=106 K) and x=0.028 (T N=53 K). Through the temperature dependence of the Knight shifts and the nuclear spin lattice relaxation rates (1/T 1), although stripe-type AFM spin fluctuationsmore » are realized in the paramagnetic state as in the case of other iron pnictide superconductors, we found a gradual decrease of the AFM spin fluctuations below a crossover temperature T* that was nearly independent of Co-substitution concentration, and it is attributed to a pseudogaplike behavior in the spin excitation spectra of these systems. The T* feature finds correlation with features in the temperature-dependent interplane resistivity, ρc(T), but not with the in-plane resistivity ρa(T). The temperature evolution of anisotropic stripe-type AFM spin fluctuations is tracked in the paramagnetic and pseudogap phases by the 1/T 1 data measured under magnetic fields parallel and perpendicular to the c axis. As a result, based on our NMR data, we have added a pseudogaplike phase to the magnetic and electronic phase diagram of Ca(Fe 1–xCo x) 2As 2.« less

Magnetism and phase transitions in LaCoO3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belanger, David P; Durand, Alice M; Booth, C

2013-01-01

Neutron scattering and magnetometry measurements have been used to study phase transitions in LaCoO3 (LCO). For H 100 Oe, evidence for a ferromagnetic (FM) transition is observed at Tc 87 K. For 1 kOe H 60 kOe, no transition is apparent. For all H, Curie Weiss analysis shows predominantly antiferromagnetic (AFM) interactions for T > Tc, but the lack of long-range AFM order indicates magnetic frustration. We argue that the weak ferromagnetism in bulk LCO is induced by lattice strain, as is the case with thin films and nanoparticles. The lattice strain is present at the bulk surfaces and atmore » the interfaces between the LCO and a trace cobalt oxide phase. The ferromagnetic ordering in the LCO bulk is strongly affected by the Co O Co angle ( ), in agreement with recent band calculations which predict that ferromagnetic long-range order can only take place above a critical value, C. Consistent with recent thin film estimations, we find C D 162:8. For > C, we observe power-law behavior in the structural parameters. decreases with T until the critical temperature, To 37 K; below To the rate of change becomes very small. For T < To, FM order appears to be confined to regions close to the surfaces, likely due to the lattice strain keeping the local Co O Co angle above C.« less

Low temperature thermopower and magnetoresistance of Sc-rich CeSc1-xTixGe

NASA Astrophysics Data System (ADS)

Encina, S.; Pedrazzini, P.; Sereni, J. G.; Geibel, C.

2018-05-01

In CeSc1-xTixGe, Ti-alloying reduces the record-high antiferromagnetic (AFM) ordering temperature found in CeScGe at TN = 46 K and induces ferromagnetism for x ≥ 0.5 . In this work we focus on the AFM side, i.e. Sc-rich samples, and study their thermopower S (T) and magnetoresistance ρ (H , T) . The measured S (T) is small in comparison with the thermopower of other Ce-systems and shows some features that are compatible with a weak hybridization between the 4 f and band states. This is a further hint pointing to the local character of magnetism in this alloy. Magnetic fields up to 16 T have a minor effect on the electrical resistivity of stoichiometric CeScGe. On the other hand, for x = 0.65 , we find that fields above 4 T suppress the hump in ρ (T) . Furthermore, the 4.2 K magnetoresistance displays a strong decrease in the same field range, also in coincidence with magnetization results from the literature. Our results indicate that ρ (T , H) is a proper tool to assess the H - T phase diagram of this system.

Investigation of polymer derived ceramics cantilevers for application of high speed atomic force microscopy

NASA Astrophysics Data System (ADS)

Wu, Chia-Yun

High speed Atomic Force Microscopy (AFM) has a wide variety of applications ranging from nanomanufacturing to biophysics. In order to have higher scanning speed of certain AFM modes, high resonant frequency cantilevers are needed; therefore, the goal of this research is to investigate using polymer derived ceramics for possible applications in making high resonant frequency AFM cantilevers using complex cross sections. The polymer derived ceramic that will be studied, is silicon carbide. Polymer derived ceramics offer a potentially more economic fabrication approach for MEMS due to their relatively low processing temperatures and ease of complex shape design. Photolithography was used to make the desired cantilever shapes with micron scale size followed by a wet etching process to release the cantilevers from the substrates. The whole manufacturing process we use borrow well-developed techniques from the semiconducting industry, and as such this project also could offer the opportunity to reduce the fabrication cost of AFM cantilevers and MEMS in general. The characteristics of silicon carbide made from the precursor polymer, SMP-10 (Starfire Systems), were studied. In order to produce high qualities of silicon carbide cantilevers, where the major concern is defects, proper process parameters needed to be determined. Films of polymer derived ceramics often have defects due to shrinkage during the conversion process. Thus control of defects was a central issue in this study. A second, related concern was preventing oxidation; the polymer derived ceramics we chose is easily oxidized during processing. Establishing an environment without oxygen in the whole process was a significant challenge in the project. The optimization of the parameters for using photolithography and wet etching process was the final and central goal of the project; well established techniques used in microfabrication were modified for use in making the cantilever in the project. The techniques developed here open a path to the fabrication of cantilevers with unconventional cross sections.

Zigzag antiferromagnetic ground state with anisotropic correlation lengths in the quasi-two-dimensional honeycomb lattice compound N a2C o2Te O6

NASA Astrophysics Data System (ADS)

Bera, A. K.; Yusuf, S. M.; Kumar, Amit; Ritter, C.

2017-03-01

The crystal structure, magnetic ground state, and the temperature-dependent microscopic spin-spin correlations of the frustrated honeycomb lattice antiferromagnet N a2C o2Te O6 have been investigated by powder neutron diffraction. A long-range antiferromagnetic (AFM) ordering has been found below TN˜24.8 K . The magnetic ground state, determined to be zigzag antiferromagnetic and characterized by a propagation vector k =(1 /2 0 0 ) , occurs due to the competing exchange interactions up to third-nearest neighbors within the honeycomb lattice. The exceptional existence of a limited magnetic correlation length along the c axis (perpendicular to the honeycomb layers in the a b planes) has been found even at 1.8 K, well below the TN˜24.8 K . The observed limited correlation along the c axis is explained by the disorder distribution of the Na ions within the intermediate layers between honeycomb planes. The reduced ordered moments mCo (1 )=2.77 (3 ) μB/C o2 + and mCo (2 )=2.45 (2 ) μB/C o2 + at 1.8 K reflect the persistence of spin fluctuations in the ordered state. Above TN˜24.8 K , the presence of short-range magnetic correlations, manifested by broad diffuse magnetic peaks in the diffraction patterns, has been found. Reverse Monte Carlo analysis of the experimental diffuse magnetic scattering data reveals that the spin correlations are mainly confined within the two-dimensional honeycomb layers (a b plane) with a correlation length of ˜12 Å at 25 K. The nature of the spin arrangements is found to be similar in both the short-range and long-range ordered magnetic states. This implies that the short-range correlation grows with decreasing temperature and leads to the zigzag AFM ordering at T ≤TN . The present study provides a comprehensive picture of the magnetic correlations over the temperature range above and below the TN and their relation to the crystal structure. The role of intermediate soft Na layers on the magnetic coupling between honeycomb planes is discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Naritsuka, M.; Rosa, P. F. S.; Luo, Yongkang

Unconventional superconductivity and magnetism are intertwined on a microscopic level in a wide class of materials. A new approach to this most fundamental and hotly debated issue focuses on the role of interactions between superconducting electrons and bosonic fluctuations at the interface between adjacent layers in heterostructures. In this paper, we fabricate hybrid superlattices consisting of alternating atomic layers of the heavy-fermion superconductormore » $${\\mathrm{CeCoIn}}_{5}$$ and antiferromagnetic (AFM) metal $${\\mathrm{CeRhIn}}_{5}$$, in which the AFM order can be suppressed by applying pressure. We find that the superconducting and AFM states coexist in spatially separated layers, but their mutual coupling via the interface significantly modifies the superconducting properties. An analysis of upper critical fields reveals that, upon suppressing the AFM order by applied pressure, the force binding superconducting electron pairs acquires an extreme strong-coupling nature. Finally, this demonstrates that superconducting pairing can be tuned nontrivially by magnetic fluctuations (paramagnons) injected through the interface.« less

Transformation twinning of Ni-Mn-Ga characterized with temperature-controlled atomic force microscopy.

PubMed

Reinhold, Matthew; Watson, Chad; Knowlton, William B; Müllner, Peter

2010-06-01

The magnetomechanical properties of ferromagnetic shape memory alloy Ni-Mn-Ga single crystals depend strongly on the twin microstructure, which can be modified through thermomagnetomechanical training. Atomic force microscopy (AFM) and magnetic force microscopy (MFM) were used to characterize the evolution of twin microstructures during thermomechanical training of a Ni-Mn-Ga single crystal. Experiments were performed in the martensite phase at 25 degrees C and in the austenite phase at 55 degrees C. Two distinct twinning surface reliefs were observed at room temperature. At elevated temperature (55 degrees C), the surface relief of one twinning mode disappeared while the other relief remained unchanged. When cooled back to 25 degrees C, the twin surface relief recovered. The relief persisting at elevated temperature specifies the positions of twin boundaries that were present when the sample was polished prior to surface characterization. AFM and MFM following thermomechanical treatment provide a nondestructive method to identify the crystallographic orientation of each twin and of each twin boundary plane. Temperature dependent AFM and MFM experiments reveal the twinning history thereby establishing the technique as a unique predictive tool for revealing the path of the martensitic and reverse transformations of magnetic shape memory alloys.

Transformation twinning of Ni–Mn–Ga characterized with temperature-controlled atomic force microscopy

PubMed Central

Reinhold, Matthew; Watson, Chad; Knowlton, William B.; Müllner, Peter

2010-01-01

The magnetomechanical properties of ferromagnetic shape memory alloy Ni–Mn–Ga single crystals depend strongly on the twin microstructure, which can be modified through thermomagnetomechanical training. Atomic force microscopy (AFM) and magnetic force microscopy (MFM) were used to characterize the evolution of twin microstructures during thermomechanical training of a Ni–Mn–Ga single crystal. Experiments were performed in the martensite phase at 25 °C and in the austenite phase at 55 °C. Two distinct twinning surface reliefs were observed at room temperature. At elevated temperature (55 °C), the surface relief of one twinning mode disappeared while the other relief remained unchanged. When cooled back to 25 °C, the twin surface relief recovered. The relief persisting at elevated temperature specifies the positions of twin boundaries that were present when the sample was polished prior to surface characterization. AFM and MFM following thermomechanical treatment provide a nondestructive method to identify the crystallographic orientation of each twin and of each twin boundary plane. Temperature dependent AFM and MFM experiments reveal the twinning history thereby establishing the technique as a unique predictive tool for revealing the path of the martensitic and reverse transformations of magnetic shape memory alloys. PMID:20589105

Probing ternary solvent effect in high V oc polymer solar cells using advanced AFM techniques

DOE PAGES

Li, Chao; Soleman, Mikhael; Lorenzo, Josie; ...

2016-01-25

This work describes a simple method to develop a high V oc low band gap PSCs. In addition, two new atomic force microscopy (AFM)-based nanoscale characterization techniques to study the surface morphology and physical properties of the structured active layer are introduced. With the help of ternary solvent processing of the active layer and C 60 buffer layer, a bulk heterojunction PSC with V oc more than 0.9 V and conversion efficiency 7.5% is developed. In order to understand the fundamental properties of the materials ruling the performance of the PSCs tested, AFM-based nanoscale characterization techniques including Pulsed-Force-Mode AFM (PFM-AFM)more » and Mode-Synthesizing AFM (MSAFM) are introduced. Interestingly, MSAFM exhibits high sensitivity for direct visualization of the donor–acceptor phases in the active layer of the PSCs. Lastly, conductive-AFM (cAFM) studies reveal local variations in conductivity in the donor and acceptor phases as well as a significant increase in photocurrent in the PTB7:ICBA sample obtained with the ternary solvent processing.« less

Emergence of superconductivity and magnetic ordering tuned by Fe-vacancy in alkali-metal Fe chalcogenides RbxFe2-ySe2

NASA Astrophysics Data System (ADS)

Kobayashi, Yoshiaki; Kototani, Shouhei; Itoh, Masayuki; Sato, Masatoshi

2014-12-01

Samples of RbxFe2-ySe2 exhibiting superconductivity [superconducting (SC) samples] undergo a phase-separation into two phases, a Fe-vacancy ordered phase with antiferromagnetic (AFM) transition at TN1~500 K (AFM1 phase) and a phase with little Fe- vacancy and SC transition at Tc~30 K (SC phase). The samples of RbxFe2-ySe2 exhibiting no SC behaviour (non-SC samples) are phase-separated into three phases, the AFM1 phase, another AFM phase with TN2 ~150 K (AFM2 phase), and a paramagnetic phase with no SC transitions (paramagnetic non-SC phase). In this paper, we present the experimental results of magnetic susceptibility, electrical resistivity, and NMR measurements on single crystals of RbxFe2-ySe2 to reveal physical properties of these co-existing phases in the SC and non-SC samples. The 87Rb and 77Se NMR spectra show that the Fe vacancy concentration is very small in the Fe planes of the SC phase, whereas the AFM2 and paramagnetic non-SC phases in non-SC samples have larger amount of Fe vacancies. The randomness induced by the Fe vacancy in the non-SC samples makes the AFM2 and paramagnetic non-SC phases insulating/semiconducting and magnetically active, resulting in the absence of the superconductivity in RbxFe2-ySe2.

NMR Study of the New Magnetic Superconductor CaK(Fe 0:951Ni0:049) 4As 4: Microscopic Coexistence of Hedgehog Spin-vortex Crystal and Superconductivity

DOE PAGES

Ding, Q. P.; Meier, W. R.; Bohmer, A. E.; ...

2017-12-29

Coexistence of a new-type antiferromagnetic (AFM) state, the so-called hedgehog spin-vortex crystal (SVC), and superconductivity (SC) is evidenced by 75As nuclear magnetic resonance study on single-crystalline CaK(Fe 0:951Ni0:049) 4As 4. The hedgehog SVC order is clearly demonstrated by the direct observation of the internal magnetic induction along the c axis at the As1 site (close to K) and a zero net internal magnetic induction at the As2 site (close to Ca) below an AFM ordering temperature T N ~ 52 K. The nuclear spin-lattice relaxation rate 1/T 1 shows a distinct decrease below T c ~ 10 K, providing alsomore » unambiguous evidence for the microscopic coexistence. Furthermore, based on the analysis of the 1/T 1 data, the hedgehog SVC-type spin correlations are found to be enhanced below T ~ 150 K in the paramagnetic state. Furthermore, these results indicate the hedgehog SVC-type spin correlations play an important role for the appearance of SC in the new magnetic superconductor.« less

NMR Study of the New Magnetic Superconductor CaK(Fe 0:951Ni0:049) 4As 4: Microscopic Coexistence of Hedgehog Spin-vortex Crystal and Superconductivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ding, Q. P.; Meier, W. R.; Bohmer, A. E.

Coexistence of a new-type antiferromagnetic (AFM) state, the so-called hedgehog spin-vortex crystal (SVC), and superconductivity (SC) is evidenced by 75As nuclear magnetic resonance study on single-crystalline CaK(Fe 0:951Ni0:049) 4As 4. The hedgehog SVC order is clearly demonstrated by the direct observation of the internal magnetic induction along the c axis at the As1 site (close to K) and a zero net internal magnetic induction at the As2 site (close to Ca) below an AFM ordering temperature T N ~ 52 K. The nuclear spin-lattice relaxation rate 1/T 1 shows a distinct decrease below T c ~ 10 K, providing alsomore » unambiguous evidence for the microscopic coexistence. Furthermore, based on the analysis of the 1/T 1 data, the hedgehog SVC-type spin correlations are found to be enhanced below T ~ 150 K in the paramagnetic state. Furthermore, these results indicate the hedgehog SVC-type spin correlations play an important role for the appearance of SC in the new magnetic superconductor.« less

Magnetic and magnetocaloric properties of HoCr0.75Fe0.25O3 compound

NASA Astrophysics Data System (ADS)

Kotnana, Ganesh; Babu, P. D.; Jammalamadaka, S. Narayana

2018-05-01

We report on the magnetic and magnetocaloric properties of HoCr0.75Fe0.25O3 compound around the Néel temperature (TN), which is due to Cr3+ ordering. Susceptibility (χ) vs. temperature (T) graph of HoCr0.75Fe0.25O3 compound infer two transitions due to the ordering of Cr3+ moments (TN ˜ 155 K) and Ho3+ moments (TNHo ˜ 8 K). Magnetic entropy (-ΔSM) value of 1.14 J kg-1 K-1 around 157.5 K with a magnetic field (H) of 90 kOe is attributed to antiferromagnetic (AFM) ordering of Cr3+ moments. A maximum value of adiabatic temperature (ΔTad) ˜ 0.41 K around TN is obtained and is found to increases with applied magnetic field. Negative slope for H/M vs. M2 graph is evident for HoCr0.75Fe0.25O3 compound below TN, which indicates the first order phase transition. Quantified values of -ΔSM and ΔTad open the way to explore rare earth orthochromites for the MCE properties and refrigeration applications.

Magnetoelectric effect in antiferromagnetic multiferroic Pb (F e1 /2N b1 /2)O3 and its solid solutions with PbTi O3

NASA Astrophysics Data System (ADS)

Laguta, V. V.; Stephanovich, V. A.; Raevski, I. P.; Raevskaya, S. I.; Titov, V. V.; Smotrakov, V. G.; Eremkin, V. V.

2017-01-01

Antiferromagnets (AFMs) are presently considered as promising materials for applications in spintronics and random access memories due to the robustness of information stored in the AFM state against perturbing magnetic fields. In this respect, AFM multiferroics may be attractive alternatives for conventional AFMs as the coupling of magnetism with ferroelectricity (magnetoelectric effect) offers an elegant possibility of electric-field control and switching of AFM domains. Here we report the results of comprehensive experimental and theoretical investigations of the quadratic magnetoelectric (ME) effect in single crystals and highly resistive ceramics of Pb (F e1 /2N b1 /2)O3 (PFN) and (1 -x ) Pb (F e1 /2N b1 /2) O3-x PbTi O3(PFN -x PT ) . We are interested primarily in the temperature range of the multiferroic phase, T <150 K , where the ME coupling coefficient is extremely large (as compared to the well-known multiferroic BiFe O3 ) and shows sign reversal at the paramagnetic-to-antiferromagnetic phase transition. Moreover, we observe strong ME response nonlinearity in the AFM phase in the magnetic fields of only a few kOe. To describe the temperature and magnetic field dependencies of the above unusual features of the ME effect in PFN and PFN-x PT , we use a simple phenomenological Landau approach which explains experimental data surprisingly well. Our ME measurements demonstrate that the electric field of only 20-25 kV/cm is able to switch the AFM domains and align them with ferroelectric ones even in PFN ceramic samples.

Tunable Noncollinear Antiferromagnetic Resistive Memory through Oxide Superlattice Design

NASA Astrophysics Data System (ADS)

Hoffman, Jason D.; Wu, Stephen M.; Kirby, Brian J.; Bhattacharya, Anand

2018-04-01

Antiferromagnets (AFMs) have recently gathered a large amount of attention as a potential replacement for ferromagnets (FMs) in spintronic devices due to their lack of stray magnetic fields, invisibility to external magnetic probes, and faster magnetization dynamics. Their development into a practical technology, however, has been hampered by the small number of materials where the antiferromagnetic state can be both controlled and read out. We show that by relaxing the strict criterion on pure antiferromagnetism, we can engineer an alternative class of magnetic materials that overcome these limitations. This is accomplished by stabilizing a noncollinear magnetic phase in LaNiO3 /La2 /3Sr1 /3MnO3 superlattices. This state can be continuously tuned between AFM and FM coupling through varying the superlattice spacing, strain, applied magnetic field, or temperature. By using this alternative "knob" to tune magnetic ordering, we take a nanoscale materials-by-design approach to engineering ferromagneticlike controllability into antiferromagnetic synthetic magnetic structures. This approach can be used to trade-off between the favorable and unfavorable properties of FMs and AFMs when designing realistic resistive antiferromagnetic memories. We demonstrate a memory device in one such superlattice, where the magnetic state of the noncollinear antiferromagnet is reversibly switched between different orientations using a small magnetic field and read out in real time with anisotropic magnetoresistance measurements.

Magnetic study of the low temperature anomalies in the underdoped PrBCO compound

NASA Astrophysics Data System (ADS)

Lahoubi, Mahieddine

2018-05-01

The low temperature anomalous magnetic properties of a non-superconducting PrBCO6+x compound in an underdoped oxygen state of concentration (x = 0.44) are characterized by paraprocess magnetic susceptibility χH(T) measurements carried out as a function of temperature T under different values of a DC magnetic field H up to 110 kOe. The derivatives dχH(T)/dT curves reveal a significant reduction with increasing H in the Néel temperature TN = 9 K of the Pr antiferromagnetic (AFM) ordering for which the transition subsists at 100 kOe. The small anomaly at T2 = 6-7 K is confirmed at 20 kOe and the previous spin reorientation attributed to this transition temperature seems to be suppressed above 60 kOe. The well defined anomaly in the vicinity of the low-critical point Tcr = 4-5 K which occurs simultaneously, is still present when the strength of H is increased up to 100 kOe. Weak field induced phase transitions are observed between T2 and TN at a low transition-field (Ht<11 kOe) in the differential magnetic susceptibility dMT(H)/dH as a function of H deduced from the isothermal magnetizations MT(H) with H up to 21 kOe, whereas a weak ferromagnetic behavior of the Pr sublattice appears below Tcr. The magnetic field effects give rise to more evidence for the Pr-Cu(2) coupling with 'exchange-frustrated AFM' interactions and ascertain the main role of the Pr sublattice whereas the Cu(2) sublattice seems to be less efficient.

A versatile atomic force microscope integrated with a scanning electron microscope.

PubMed

Kreith, J; Strunz, T; Fantner, E J; Fantner, G E; Cordill, M J

2017-05-01

A versatile atomic force microscope (AFM), which can be installed in a scanning electron microscope (SEM), is introduced. The flexible design of the instrument enables correlated analysis for different experimental configurations, such as AFM imaging directly after nanoindentation in vacuum. In order to demonstrate the capabilities of the specially designed AFM installed inside a SEM, slip steps emanating around nanoindents in single crystalline brass were examined. This example showcases how the combination of AFM and SEM imaging can be utilized for quantitative dislocation analysis through the measurement of the slip step heights without the hindrance of oxide formation. Finally, an in situ nanoindentation technique is introduced, illustrating the use of AFM imaging during indentation experiments to examine plastic deformation occurring under the indenter tip. The mechanical indentation data are correlated to the SEM and AFM images to estimate the number of dislocations emitted to the surface.

Structure and magnetic properties of L n MnSbO ( L n = La and Ce)

DOE PAGES

Zhang, Qiang; Kumar, C. M. N.; Tian, Wei; ...

2016-03-11

Here, a neutron powder diffraction (NPD) study of LnMnSbO (Ln = La or Ce) reveals differences between the magnetic ground state of the two compounds due to the strong Ce-Mn coupling compared to La-Mn. The two compounds adopt the P4/nmm space group down to 2 K, and whereas magnetization measurements do not show obvious anomaly at high temperatures, NPD reveals a C-type antiferromagnetic (AFM) order below T N = 255K for LaMnSbO and 240 K for CeMnSbO. While the magnetic structure of LaMnSbO is preserved to base temperature, a sharp transition at T SR = 4.5K is observed in CeMnSbOmore » due to a spin-reorientation (SR) transition of the Mn 2+ magnetic moments from pointing along the c axis to the ab plane. The SR transition in CeMnSbO is accompanied by a simultaneous long-range AFM ordering of the Ce moments, which indicates that the Mn SR transition is driven by the Ce-Mn coupling. The ordered moments are found to be somewhat smaller than those expected for Mn 2+ (S = 5/2) in insulators, but large enough to suggest that these compounds belong to the class of local-moment antiferromagnets. The lower T N found in these two compounds compared to the As-based counterparts (T N = 317 for LaMnAsO, T N = 347K for CeMnAsO) indicates that the Mn-Pn (Pn=As or Sb) hybridization that mediates the superexchange Mn-Pn-Mn coupling is weaker for the Sb-based compounds.« less

Atomic force microscope-assisted scanning tunneling spectroscopy under ambient conditions.

PubMed

Vakhshouri, Amin; Hashimoto, Katsushi; Hirayama, Yoshiro

2014-12-01

We have developed a method of atomic force microscopy (AFM)-assisted scanning tunneling spectroscopy (STS) under ambient conditions. An AFM function is used for rapid access to a selected position prior to performing STS. The AFM feedback is further used to suppress vertical thermal drift of the tip-sample distance during spectroscopy, enabling flexible and stable spectroscopy measurements at room temperature. © The Author 2014. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Stability enhancement of an atomic force microscope for long-term force measurement including cantilever modification for whole cell deformation

NASA Astrophysics Data System (ADS)

Weafer, P. P.; McGarry, J. P.; van Es, M. H.; Kilpatrick, J. I.; Ronan, W.; Nolan, D. R.; Jarvis, S. P.

2012-09-01

Atomic force microscopy (AFM) is widely used in the study of both morphology and mechanical properties of living cells under physiologically relevant conditions. However, quantitative experiments on timescales of minutes to hours are generally limited by thermal drift in the instrument, particularly in the vertical (z) direction. In addition, we demonstrate the necessity to remove all air-liquid interfaces within the system for measurements in liquid environments, which may otherwise result in perturbations in the measured deflection. These effects severely limit the use of AFM as a practical tool for the study of long-term cell behavior, where precise knowledge of the tip-sample distance is a crucial requirement. Here we present a readily implementable, cost effective method of minimizing z-drift and liquid instabilities by utilizing active temperature control combined with a customized fluid cell system. Long-term whole cell mechanical measurements were performed using this stabilized AFM by attaching a large sphere to a cantilever in order to approximate a parallel plate system. An extensive examination of the effects of sphere attachment on AFM data is presented. Profiling of cantilever bending during substrate indentation revealed that the optical lever assumption of free ended cantilevering is inappropriate when sphere constraining occurs, which applies an additional torque to the cantilevers "free" end. Here we present the steps required to accurately determine force-indentation measurements for such a scenario. Combining these readily implementable modifications, we demonstrate the ability to investigate long-term whole cell mechanics by performing strain controlled cyclic deformation of single osteoblasts.

Recent advances in micromechanical characterization of polymer, biomaterial, and cell surfaces with atomic force microscopy

NASA Astrophysics Data System (ADS)

Chyasnavichyus, Marius; Young, Seth L.; Tsukruk, Vladimir V.

2015-08-01

Probing of micro- and nanoscale mechanical properties of soft materials with atomic force microscopy (AFM) gives essential information about the performance of the nanostructured polymer systems, natural nanocomposites, ultrathin coatings, and cell functioning. AFM provides efficient and is some cases the exclusive way to study these properties nondestructively in controlled environment. Precise force control in AFM methods allows its application to variety of soft materials and can be used to go beyond elastic properties and examine temperature and rate dependent materials response. In this review, we discuss experimental AFM methods currently used in the field of soft nanostructured composites and biomaterials. We discuss advantages and disadvantages of common AFM probing techniques, which allow for both qualitative and quantitative mappings of the elastic modulus of soft materials with nanosacle resolution. We also discuss several advanced techniques for more elaborate measurements of viscoelastic properties of soft materials and experiments on single cells.

Characterization of titanyl phthalocyanine (TiOPc) thin films by microscopic and spectroscopic method

NASA Astrophysics Data System (ADS)

Skonieczny, R.; Makowiecki, J.; Bursa, B.; Krzykowski, A.; Szybowicz, M.

2018-02-01

The titanyl phthalocyanine (TiOPc) thin film deposited on glass, silicon and gold substrate have been studied using Raman spectroscopy, atomic force microscopy (AFM), absorption and profilometry measurements. The TiOPc thin layers have been deposited at room temperature by the quasi-molecular beam evaporation technique. The Raman spectra have been recorded using micro Raman system equipped with a confocal microscope. Using surface Raman mapping techni que with polarized Raman spectra the polymorphic forms of the TiOPc thin films distribution have been obtained. The AFM height and phase image were examined in order to find surface features and morphology of the thin films. Additionally to compare experimental results, structure optimization and vibrational spectra calculation of single TiOPc molecule were performed using DFT calculations. The received results showed that the parameters like polymorphic form, grain size, roughness of the surface in TiOPc thin films can well characterize the obtained organic thin films structures in terms of their use in optoelectronics and photovoltaics devices.

Ionic Gel Modulation of RKKY Interactions in Synthetic Anti-Ferromagnetic Nanostructures for Low Power Wearable Spintronic Devices.

PubMed

Yang, Qu; Zhou, Ziyao; Wang, Liqian; Zhang, Hongjia; Cheng, Yuxin; Hu, Zhongqiang; Peng, Bin; Liu, Ming

2018-05-01

To meet the demand of developing compatible and energy-efficient flexible spintronics, voltage manipulation of magnetism on soft substrates is in demand. Here, a voltage tunable flexible field-effect transistor structure by ionic gel (IG) gating in perpendicular synthetic anti-ferromagnetic nanostructure is demonstrated. As a result, the interlayer Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction can be tuned electrically at room temperature. With a circuit gating voltage, anti-ferromagnetic (AFM) ordering is enhanced or converted into an AFM-ferromagnetic (FM) intermediate state, accompanying with the dynamic domain switching. This IG gating process can be repeated stably at different curvatures, confirming an excellent mechanical property. The IG-induced modification of interlayer exchange coupling is related to the change of Fermi level aroused by the disturbance of itinerant electrons. The voltage modulation of RKKY interaction with excellent flexibility proposes an application potential for wearable spintronic devices with energy efficiency and ultralow operation voltage. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Long range magnetic ordering of ultracold fermions in an optical lattice

NASA Astrophysics Data System (ADS)

Duarte, P. M.; Hart, R. A.; Yang, T.-L.; Hulet, R. G.

2013-05-01

We present progress towards the observation of long range antiferromagnetic (AFM) ordering of fermionic 6Li atoms in an optical lattice. We prepare a two spin state mixture of 106 atoms at T /TF = 0 . 1 by evaporatively cooling in an optical dipole trap. The sample is then transferred to a dimple trap formed by three retroreflected laser beams at 1064 nm that propagate in orthogonal directions. The polarization of the retroreflected light is controlled using liquid crystal retarders, which allow us to adiabatically transform the dimple trap into a 3D lattice. Overlapped with each of the three dimple/lattice beams is a beam at 532 nm, which can cancel the harmonic confinement and flatten the band structure in the lattice. This setup offers the possibility of implementing proposed schemes which enlarge the size of the AFM phase in the trap. As a probe for AFM we use Bragg scattering of light. We have observed Bragg scattering off of the (100) lattice planes, and using an off-angle probe we can see the diffuse scattering from the sample which serves as background for the small signals expected before the onset of AFM ordering. Supported by NSF, ONR, DARPA, and the Welch Foundation.

Tuning the Pairing Interaction in a d -Wave Superconductor by Paramagnons Injected through Interfaces

DOE PAGES

Naritsuka, M.; Rosa, P. F. S.; Luo, Yongkang; ...

2018-05-04

Unconventional superconductivity and magnetism are intertwined on a microscopic level in a wide class of materials. A new approach to this most fundamental and hotly debated issue focuses on the role of interactions between superconducting electrons and bosonic fluctuations at the interface between adjacent layers in heterostructures. In this paper, we fabricate hybrid superlattices consisting of alternating atomic layers of the heavy-fermion superconductormore » $${\\mathrm{CeCoIn}}_{5}$$ and antiferromagnetic (AFM) metal $${\\mathrm{CeRhIn}}_{5}$$, in which the AFM order can be suppressed by applying pressure. We find that the superconducting and AFM states coexist in spatially separated layers, but their mutual coupling via the interface significantly modifies the superconducting properties. An analysis of upper critical fields reveals that, upon suppressing the AFM order by applied pressure, the force binding superconducting electron pairs acquires an extreme strong-coupling nature. Finally, this demonstrates that superconducting pairing can be tuned nontrivially by magnetic fluctuations (paramagnons) injected through the interface.« less

Tuning the Pairing Interaction in a d -Wave Superconductor by Paramagnons Injected through Interfaces

NASA Astrophysics Data System (ADS)

Naritsuka, M.; Rosa, P. F. S.; Luo, Yongkang; Kasahara, Y.; Tokiwa, Y.; Ishii, T.; Miyake, S.; Terashima, T.; Shibauchi, T.; Ronning, F.; Thompson, J. D.; Matsuda, Y.

2018-05-01

Unconventional superconductivity and magnetism are intertwined on a microscopic level in a wide class of materials. A new approach to this most fundamental and hotly debated issue focuses on the role of interactions between superconducting electrons and bosonic fluctuations at the interface between adjacent layers in heterostructures. Here we fabricate hybrid superlattices consisting of alternating atomic layers of the heavy-fermion superconductor CeCoIn5 and antiferromagnetic (AFM) metal CeRhIn5 , in which the AFM order can be suppressed by applying pressure. We find that the superconducting and AFM states coexist in spatially separated layers, but their mutual coupling via the interface significantly modifies the superconducting properties. An analysis of upper critical fields reveals that, upon suppressing the AFM order by applied pressure, the force binding superconducting electron pairs acquires an extreme strong-coupling nature. This demonstrates that superconducting pairing can be tuned nontrivially by magnetic fluctuations (paramagnons) injected through the interface.

Magnetism in nanoparticle LaCoO3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Durand, A. M.; Belanger, D. P.; Booth, C. H.

2014-06-24

Neutron scattering and magnetometry measurements have been used to study phase transitions in LaCoO3 (LCO). For H <= 100 Oe, evidence for a ferromagnetic (FM) transition is observed at T-c approximate to 87 K. For 1 kOe <= H <= 60 kOe, no transition is apparent. For all H, Curie-Weiss analysis shows predominantly antiferromagnetic (AFM) interactions for T > T-c, but the lack of long-range AFM order indicates magnetic frustration. We argue that the weak ferromagnetism in bulk LCO is induced by lattice strain, as is the case with thin films and nanoparticles. The lattice strain is present at themore » bulk surfaces and at the interfaces between the LCO and a trace cobalt oxide phase. The ferromagnetic ordering in the LCO bulk is strongly affected by the Co-O-Co angle (gamma), in agreement with recent band calculations which predict that ferromagnetic long-range order can only take place above a critical value, gamma C. Consistent with recent thin film estimations, we find gamma C = 162.8 degrees. For gamma > gamma C, we observe power-law behavior in the structural parameters. gamma decreases with T until the critical temperature, T-o approximate to 37 K; below T-o the rate of change becomes very small. For T < T-o, FM order appears to be confined to regions close to the surfaces, likely due to the lattice strain keeping the local Co-O-Co angle above gamma C.« less

Characterization of prepared In2O3 thin films: The FT-IR, FT-Raman, UV-Visible investigation and optical analysis.

PubMed

Panneerdoss, I Joseph; Jeyakumar, S Johnson; Ramalingam, S; Jothibas, M

2015-08-05

In this original work, the Indium oxide (In2O3) thin film is deposited cleanly on microscope glass substrate at different temperatures by spray pyrolysis technique. The physical properties of the films are characterized by XRD, SEM, AFM and AFM measurements. The spectroscopic investigation has been carried out on the results of FT-IR, FT-Raman and UV-Visible. XRD analysis exposed that the structural transformation of films from stoichiometric to non-stoichiometric orientation of the plane vice versa and also found that, the film is polycrystalline in nature having cubic crystal structure with a preferred grain orientation along (222) plane. SEM and AFM studies revealed that, the film with 0.1M at 500°C has spherical grains with uniform dimension. The complete vibrational analysis has been carried out and the optimized parameters are calculated using HF and DFT (CAM-B3LYP, B3LYP and B3PW91) methods with 3-21G(d,p) basis set. Furthermore, NMR chemical shifts are calculated by using the gauge independent atomic orbital (GIAO) technique. The molecular electronic properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, molecular electrostatic potential energy (MEP) analysis and Polarizability first order hyperpolarizability calculations are performed by time dependent DFT (TD-DFT) approach. The energy excitation on electronic structure is investigated and the assignment of the absorption bands in the electronic spectra of steady compound is discussed. The calculated HOMO and LUMO energies showed the enhancement of energy gap by the addition of substitutions with the base molecule. The thermodynamic properties (heat capacity, entropy, and enthalpy) at different temperatures are calculated and interpreted in gas phase. Crown Copyright © 2015. Published by Elsevier B.V. All rights reserved.

Membrane-based actuation for high-speed single molecule force spectroscopy studies using AFM.

PubMed

Sarangapani, Krishna; Torun, Hamdi; Finkler, Ofer; Zhu, Cheng; Degertekin, Levent

2010-07-01

Atomic force microscopy (AFM)-based dynamic force spectroscopy of single molecular interactions involves characterizing unbinding/unfolding force distributions over a range of pulling speeds. Owing to their size and stiffness, AFM cantilevers are adversely affected by hydrodynamic forces, especially at pulling speeds >10 microm/s, when the viscous drag becomes comparable to the unbinding/unfolding forces. To circumvent these adverse effects, we have fabricated polymer-based membranes capable of actuating commercial AFM cantilevers at speeds >or=100 microm/s with minimal viscous drag effects. We have used FLUENT, a computational fluid dynamics (CFD) software, to simulate high-speed pulling and fast actuation of AFM cantilevers and membranes in different experimental configurations. The simulation results support the experimental findings on a variety of commercial AFM cantilevers and predict significant reduction in drag forces when membrane actuators are used. Unbinding force experiments involving human antibodies using these membranes demonstrate that it is possible to achieve bond loading rates >or=10(6) pN/s, an order of magnitude greater than that reported with commercial AFM cantilevers and systems.

Fractal analysis as a potential tool for surface morphology of thin films

NASA Astrophysics Data System (ADS)

Soumya, S.; Swapna, M. S.; Raj, Vimal; Mahadevan Pillai, V. P.; Sankararaman, S.

2017-12-01

Fractal geometry developed by Mandelbrot has emerged as a potential tool for analyzing complex systems in the diversified fields of science, social science, and technology. Self-similar objects having the same details in different scales are referred to as fractals and are analyzed using the mathematics of non-Euclidean geometry. The present work is an attempt to correlate fractal dimension for surface characterization by Atomic Force Microscopy (AFM). Taking the AFM images of zinc sulphide (ZnS) thin films prepared by pulsed laser deposition (PLD) technique, under different annealing temperatures, the effect of annealing temperature and surface roughness on fractal dimension is studied. The annealing temperature and surface roughness show a strong correlation with fractal dimension. From the regression equation set, the surface roughness at a given annealing temperature can be calculated from the fractal dimension. The AFM images are processed using Photoshop and fractal dimension is calculated by box-counting method. The fractal dimension decreases from 1.986 to 1.633 while the surface roughness increases from 1.110 to 3.427, for a change of annealing temperature 30 ° C to 600 ° C. The images are also analyzed by power spectrum method to find the fractal dimension. The study reveals that the box-counting method gives better results compared to the power spectrum method.

Nano-defect management in directed self-assembly of block copolymers (Conference Presentation)

NASA Astrophysics Data System (ADS)

Azuma, Tsukasa; Seino, Yuriko; Sato, Hironobu; Kasahara, Yusuke; Kodera, Katsuyoshi; Jiravanichsakul, Phubes; Hayakawa, Teruaki; Yoshimoto, Kenji; Takenaka, Mikihito

2017-03-01

Directed self-assembly (DSA) of block copolymers (BCPs) has been expected to become one of the most promising next generation lithography candidates for sub-15 nm line patterning and sub-20 nm contact hole patterning. In order to provide the DSA lithography to practical use in advanced semiconductor device manufacturing, defect mitigation in the DSA materials and processes is the primary challenge. We need to clarify the defect generation mechanism using in-situ measurement of self-assembling processes of BCPs in cooperation with modeling approaches to attain the DSA defect mitigation. In this work, we thus employed in-situ atomic force microscope (AFM) and grazing-incidence small angle X-ray scattering (GI-SAXS) and investigated development of surface morphology as well as internal structure during annealing processes. Figure 1 shows series of the AFM images of PMAPOSS-b-PTFEMA films during annealing processes. The images clearly show that vitrified sponge-like structure without long-range order in as-spun film transforms into lamellar structure and that the long range order of the lamellar structure increases with annealing temperature. It is well-known that ordering processes of BCPs from disordered state in bulk progress via nucleation and growth. In contrary to the case of bulk, the observed processes seem to be spinodal decomposition. This is because the structure in as-spun film is not the concentration fluctuation of disordered state but the vitrified sponge-like structure. The annealing processes induce order-order transition from non-equilibrium ordered-state to the lamellar structure. The surface tension assists the transition and directs the orientation. Figure 2 shows scattering patterns of (a) vicinity of film top and (b) whole sample of the GI-SAXS. We can find vertically oriented lamellar structure in the vicinity of film top while horizontally oriented lamellar structures in the vicinity of film bottom, indicating that the GI-SAXS measurement can clarify the variation of the morphologies in depth direction and that the surface tension affects the orientation of the lamellar structure. Finally a combination of the time development data in the in-situ AFM and the GI-SAXS is used to develop a kinetic modeling for prediction of dynamical change in three-dimensional nano-structures. A part of this work was funded by the New Energy and Industrial Technology Development Organization (NEDO) in Japan under the EIDEC project.

Detection of atomic force microscopy cantilever displacement with a transmitted electron beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wagner, R.; Woehl, T. J.; Keller, R. R.

2016-07-25

The response time of an atomic force microscopy (AFM) cantilever can be decreased by reducing cantilever size; however, the fastest AFM cantilevers are currently nearing the smallest size that can be detected with the conventional optical lever approach. Here, we demonstrate an electron beam detection scheme for measuring AFM cantilever oscillations. The oscillating AFM tip is positioned perpendicular to and in the path of a stationary focused nanometer sized electron beam. As the tip oscillates, the thickness of the material under the electron beam changes, causing a fluctuation in the number of scattered transmitted electrons that are detected. We demonstratemore » detection of sub-nanometer vibration amplitudes with an electron beam, providing a pathway for dynamic AFM with cantilevers that are orders of magnitude smaller and faster than the current state of the art.« less

AFM investigation and optical band gap study of chemically deposited PbS thin films

NASA Astrophysics Data System (ADS)

Zaman, S.; Mansoor, M.; Abubakar; Asim, M. M.

2016-08-01

The interest into deposition of nanocrystalline PbS thin films, the potential of designing and tailoring both the topographical features and the band gap energy (Eg) by controlling growth parameters, has significant technological importance. Nanocrystalline thin films of lead sulfide were grown onto glass substrates by chemical bath deposition (CBD) method. The experiments were carried out by varying deposition temperature. We report on the modification of structural and optical properties as a function of deposition temperature. The morphological changes of the films were analyzed by using SEM and AFM. AFM was also used to calculate average roughness of the films. XRD spectra indicated preferred growth of cubic phase of PbS films in (200) direction with increasing deposition time. Optical properties have been studied by UV-Spectrophotometer. From the diffused reflectance spectra we have calculated the optical Eg shift from 0.649-0.636 eV with increasing deposition time.

Exchange Bias in Layered GdBaCo2O5.5 Cobaltite

NASA Astrophysics Data System (ADS)

Solin, N. I.; Naumov, S. V.; Telegin, S. V.; Korolev, A. V.

2017-12-01

It is established that excess oxygen content δ influences the exchange bias (EB) in layered GdBa-Co2O5 + δ cobaltite. The EB effect arises in p-type (δ > 0.5) cobaltite and disappears in n-type (δ < 0.5) cobaltite. The main parameters of EB in GdBaCo2O5.52(2) polycrystals are determined, including the field and temperature dependences of EB field H EB , blocking temperature T B , exchange coupling energy J i of antiferromagnet-ferromagnet (AFM-FM) interface, and dimensions of FM clusters. The training effect inherent in systems with EB has been studied. The results are explained in terms of exchange interaction between the FM and AFM phases. It is assumed that the EB originates from the coexistence of Co3+ and Co4+ ions that leads to the formation of monodomain FM clusters in the AFM matrix of cobaltite.

Competing magnetic ground states and their coupling to the crystal lattice in CuFe2Ge2

NASA Astrophysics Data System (ADS)

May, Andrew; Calder, Stuart; Parker, David; Sales, Brian; McGuire, Michael

CuFe2Ge2 has been identified as a system with competing magnetic ground states that are strongly coupled to the crystal lattice and easily manipulated by temperature or applied magnetic field. Powder neutron diffraction data reveal the emergence of antiferromagnetic (AFM) order near TN = 175 K, as well as a transition into an incommensurate AFM spin structure below approximately 125 K. Together with refined moments of approximately 1 Bohr magneton per iron, the incommensurate structure supports an itinerant picture of magnetism in CuFe2Ge2, which is consistent with theoretical calculations. Bulk magnetization measurements suggest that the spin structures are easily manipulated with an applied field, which further demonstrates the near-degeneracy of different magnetic configurations. Interestingly, the thermal expansion is found to be very anisotropic, and the c lattice parameter has anomalous temperature dependence near TN. These results show that the ground state of CuFe2Ge2 is easily manipulated by external forces, making it a potential parent compound for a rich phase diagram of emergent phenomena. Research supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division and Scientific User Facilities Division.

Pressure-induced metal-insulator transitions in chalcogenide NiS2-xSex

NASA Astrophysics Data System (ADS)

Hussain, Tayyaba; Oh, Myeong-jun; Nauman, Muhammad; Jo, Younjung; Han, Garam; Kim, Changyoung; Kang, Woun

2018-05-01

We report the temperature-dependent resistivity ρ(T) of chalcogenide NiS2-xSex (x = 0.1) using hydrostatic pressure as a control parameter in the temperature range of 4-300 K. The insulating behavior of ρ(T) survives at low temperatures in the pressure regime below 7.5 kbar, whereas a clear insulator-to-metallic transition is observed above 7.5 kbar. Two types of magnetic transitions, from the paramagnetic (PM) to the antiferromagnetic (AFM) state and from the AFM state to the weak ferromagnetic (WF) state, were evaluated and confirmed by magnetization measurement. According to the temperature-pressure phase diagram, the WF phase survives up to 7.5 kbar, and the transition temperature of the WF transition decreases as the pressure increases, whereas the metal-insulator transition temperature increases up to 9.4 kbar. We analyzed the metallic behavior and proposed Fermi-liquid behavior of NiS1.9Se0.1.

Surfactant Mediated Growth of Co on MgO(111)

NASA Astrophysics Data System (ADS)

Johnson-Steigelman, H. Trevor; Parihar, Somendra S.; Lyman, Paul F.

2010-03-01

Monolayer films of Co were deposited using an electrostatic electron-beam evaporator on single-crystal MgO(111)- √3 x√3 R 30^o substrates held at room temperature, with subsequent annealing of temperatures 400 C to 800 C. These films were characterized using low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and x-ray diffraction (XRD). After short anneals of 400 C, AFM, LEED, and XPS suggest that islanding has occurred at the surface. XPS and XRD indicate the presence of elemental Co. 1-2 ML films of Ag were examined as a potential surfactant to aid in the growth of smooth Co films. Despite the fact that Ag itself formed islands, it was found that the presence of Ag did have a surfactant effect upon the thin-film growth of Co on Ag/MgO(111)- √3 x√3 R 30^o. Co islands were still present, but much more smooth than islands formed without Ag. XPS and AFM suggest strongly that Ag floated to the top of these samples at temperatures above 400 ^oC.

Nanostructure of aluminium (Al) - Doped zinc oxide (AZO) thin films

NASA Astrophysics Data System (ADS)

Hussin, Rosniza; Husin, M. Asri

2017-12-01

Aluminium (Al)-doped Zinc Oxide (ZnO) was deposited on glass substrates by using the sol-gel dip coating technique. Next, AZO sol-gel solution was produced via sol-gel method. Al was used as doped element with molar ratios of 1%, 2%, and 3%, while the calcination temperatures were set at 400°C, 500°C, and 600°C for 2 hours. In fact, characterization was carried out in order to determine the effect of calcination temperature and molar ratio of doping by using several techniques, such as X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FESEM), and Ultraviolet-Visible spectroscopy (UV-Vis). XRD was performed to investigate the crystal structure in which the ZnO was in wurtzite hexagonal form. Next, Energy Dispersive Spectroscopy (EDS) was used to determine the composition of thin films where the result revealed the existence of zinc, oxygen, and aluminium. The roughness of the deposited film was later measured by using the AFM approach where the findings indicated increment in RMS from 8.496 nm to 35.883 nm as the temperature was increased. Additionally, FESEM was carried out to look into the microstructure surfaces of the deposited AZO thin film for increased temperature caused the particle to grow bigger for all molar ratio of dopant. Lastly, UV-Vis was conducted to study the optical properties of AZO, in which the result demonstrated that AZO thin film possessed the highest transmittance percentage among all samples above 90% with band gap value that ranged from 3.25 eV to 3.32 eV.

BOREAS AFM-06 Mean Temperature Profile Data

NASA Technical Reports Server (NTRS)

Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

2000-01-01

The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from the National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) tower from 21 May 1994 to 20 Sep 1994. The data set provides temperature profiles at 15 heights, containing the variables of virtual temperature, vertical velocity, the speed of sound, and w-bar. The data are stored in tabular ASCII files. The mean temperature profile data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

Preliminary Results on Thermal Shock Behavior of CuZnAl Shape Memory Alloy Using a Solar Concentrator as Heating Source

NASA Astrophysics Data System (ADS)

Tudora, C.; Abrudeanu, M.; Stanciu, S.; Anghel, D.; Plaiaşu, G. A.; Rizea, V.; Ştirbu, I.; Cimpoeşu, N.

2018-06-01

It is highly accepted that martensitic transformation can be induced by temperature variation and by stress solicitation. Using a solar concentrator, we manage to increase the material surface temperature (till 573 respectively 873 K) in very short periods of time in order to analyze the material behavior under thermal shocks. The heating/cooling process was registered and analyzed during the experiments. Material surface was analyzed before and after thermal shocks by microstructure point of view using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The experiments follow the material behavior during fast heating and propose the possibility of activating smart materials using the sun heat for aerospace applications.

Tribochemical wear of single crystal aluminum in NaCl solution studied by atomic force microscopy

NASA Astrophysics Data System (ADS)

Cai, M.; Langford, S. C.; Dickinson, J. T.

2011-09-01

We report a systematic study of chemically enhanced wear of single crystal aluminum surfaces in aqueous solutions using an environmentally equipped atomic force microscope (AFM). The experiments were conducted by using a standard Si3N4 AFM tip to apply a localized force on a polished, single crystal aluminum (110) surface. Most measurements were performed in 0.5 M NaCl solution. We show the effect of applied force, number of scans, chemical solution, and temperature on the chemical-mechanical wear of aluminum on the nanometer scale. Aggressive chemical environments significantly enhance the wear of aluminum relative to scanning in dry air. Quantitative measurements show that the wear volume increases in proportion to the square root of force and the number of scans (or time). Arrhenius plots of wear volume versus temperature are consistent with an activation energy of 31 kJ/mol for scanning in 0.5 M NaCl. The wear of the AFM tip and the aluminum substrate is explained in terms of the synergistic surface chemical reactions and mechanical action of the tip. We compare these results to previous studies of AFM wear of silicate glass.

NC-AFM observation of atomic scale structure of rutile-type TiO2(110) surface prepared by wet chemical process.

PubMed

Namai, Yoshimichi; Matsuoka, Osamu

2006-04-06

We succeeded in observing the atomic scale structure of a rutile-type TiO2(110) single-crystal surface prepared by the wet chemical method of chemical etching in an acid solution and surface annealing in air. Ultrahigh vacuum noncontact atomic force microscopy (UHV-NC-AFM) was used for observing the atomic scale structures of the surface. The UHV-NC-AFM measurements at 450 K, which is above a desorption temperature of molecularly adsorbed water on the TiO2(110) surface, enabled us to observe the atomic scale structure of the TiO2(110) surface prepared by the wet chemical method. In the UHV-NC-AFM measurements at room temperature (RT), however, the atomic scale structure of the TiO2(110) surface was not observed. The TiO2(110) surface may be covered with molecularly adsorbed water after the surface was prepared by the wet chemical method. The structure of the TiO2(110) surface that was prepared by the wet chemical method was consistent with the (1 x 1) bulk-terminated model of the TiO2(110) surface.

Tuning the Curie temperature of L 1 0 ordered FePt thin films through site-specific substitution of Rh

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Dongbin; Sun, Cheng-Jun; Chen, Jing-Sheng

2014-10-14

In structurally ordered magnetic thin films, the Curie temperature (TC) of ferromagnetic films depends on the exchange integral of the short range ordered neighboring atoms. The exchange integral may be adjusted by controlling elemental substitutional concentration at the lattice site of interest. We show how to control the TC in high anisotropy L10 Fe50Pt50 magnetic thin films by substituting Rh into the Pt site. Rh substitution in L10 FePt modified the local atomic environment and corresponding electronic properties while retaining the ordered L10 phase. The analysis of extended x-ray Absorption Fine Structure (EXAFS) spectra shows that Rh uniformly substitutes formore » Pt in L10 FePt. With 15 at. % of Rh substitution, temperature-dependent magnetic measurements show that the saturation magnetization (Ms) decreases from 1152 emu/cc to 670 emu/cc, the magnetocrystalline anisotropy (Ku) drops from 5×107 erg/cc to 2×107 erg/cc, and TC decreased from 750 to 500 K. A model of antiferromagnetic (AFM) defects caused by controlled Rh substitution of the Pt site, reducing the TC, is proposed to interpret this phenomenon and the validity is further examined by ab initio density functional calculations.« less

Crystal Growth of Undoped and Doped ZnSe

NASA Technical Reports Server (NTRS)

Davis, Swanson L.; Chen, K.-T.; George, M. A.; Shi, D. T.; Collins, W. E.; Burger, Arnold

1997-01-01

The surface morphology of freshly cleaved ZnSe single crystal grown by the physical vapor transport (PVT) method was investigated by Atomic Force Microscopy (AFM) and the results were correlated with Differential Scanning Calorimetry (DSC) data. Selenium precipitates have been revealed in undoped doped ZnSe crystals having a size of about 50 nm. A transition temperature around 221 C in the DSC measurements is interpreted as the eutectic temperature of Se-saturated ZnSe. The AFM images of doped ZnSe also show that possible Cr clusters are uniformly distributed and they have an estimated size of about 6 nm.

Scanning hall probe microscopy (SHPM) using quartz crystal AFM feedback.

PubMed

Dede, M; Urkmen, K; Girişen, O; Atabak, M; Oral, A; Farrer, I; Ritchie, D

2008-02-01

Scanning Hall Probe Microscopy (SHPM) is a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations such as ferromagnetic domains with high spatial and magnetic field resolution of approximately 50 nm and 7 mG/Hz(1/2) at room temperature. In the SHPM technique, scanning tunneling microscope (STM) or atomic force microscope (AFM) feedback is used to keep the Hall sensor in close proximity of the sample surface. However, STM tracking SHPM requires conductive samples; therefore the insulating substrates have to be coated with a thin layer of gold. This constraint can be eliminated with the AFM feedback using sophisticated Hall probes that are integrated with AFM cantilevers. However it is very difficult to micro fabricate these sensors. In this work, we have eliminated the difficulty in the cantilever-Hall probe integration process, just by gluing a Hall Probe chip to a quartz crystal tuning fork force sensor. The Hall sensor chip is simply glued at the end of a 32.768 kHz or 100 kHz Quartz crystal, which is used as force sensor. An LT-SHPM system is used to scan the samples. The sensor assembly is dithered at the resonance frequency using a digital Phase Locked Loop circuit and frequency shifts are used for AFM tracking. SHPM electronics is modified to detect AFM topography and the frequency shift, along with the magnetic field image. Magnetic domains and topography of an Iron Garnet thin film crystal, NdFeB demagnetised magnet and hard disk samples are presented at room temperature. The performance is found to be comparable with the SHPM using STM feedback.

Probing Cytoskeletal Structures by Coupling Optical Superresolution and AFM Techniques for a Correlative Approach

PubMed Central

Chacko, Jenu Varghese; Zanacchi, Francesca Cella; Diaspro, Alberto

2013-01-01

In this article, we describe and show the application of some of the most advanced fluorescence superresolution techniques, STED AFM and STORM AFM microscopy towards imaging of cytoskeletal structures, such as microtubule filaments. Mechanical and structural properties can play a relevant role in the investigation of cytoskeletal structures of interest, such as microtubules, that provide support to the cell structure. In fact, the mechanical properties, such as the local stiffness and the elasticity, can be investigated by AFM force spectroscopy with tens of nanometers resolution. Force curves can be analyzed in order to obtain the local elasticity (and the Young's modulus calculation by fitting the force curves from every pixel of interest), and the combination with STED/STORM microscopy integrates the measurement with high specificity and yields superresolution structural information. This hybrid modality of superresolution-AFM working is a clear example of correlative multimodal microscopy. PMID:24027190

Covalent modification and exfoliation of graphene oxide using ferrocene

NASA Astrophysics Data System (ADS)

Avinash, M. B.; Subrahmanyam, K. S.; Sundarayya, Y.; Govindaraju, T.

2010-09-01

Large scale preparation of single-layer graphene and graphene oxide is of great importance due to their potential applications. We report a simple room temperature method for the exfoliation of graphene oxide using covalent modification of graphene oxide with ferrocene to obtain single-layer graphene oxide sheets. The samples were characterized by FESEM, HRTEM, AFM, EDAX, FT-IR, Raman and Mössbauer spectroscopic studies. HRTEM micrograph of the covalently modified graphene oxide showed increased interlayer spacing of ~2.4 nm due to ferrocene intercalation. The presence of single-layer graphene oxide sheets were confirmed by AFM studies. The covalently modified ferrocene-graphene oxide composite showed interesting magnetic behavior.Large scale preparation of single-layer graphene and graphene oxide is of great importance due to their potential applications. We report a simple room temperature method for the exfoliation of graphene oxide using covalent modification of graphene oxide with ferrocene to obtain single-layer graphene oxide sheets. The samples were characterized by FESEM, HRTEM, AFM, EDAX, FT-IR, Raman and Mössbauer spectroscopic studies. HRTEM micrograph of the covalently modified graphene oxide showed increased interlayer spacing of ~2.4 nm due to ferrocene intercalation. The presence of single-layer graphene oxide sheets were confirmed by AFM studies. The covalently modified ferrocene-graphene oxide composite showed interesting magnetic behavior. Electronic supplementary information (ESI) available: Magnetic data; AFM images; TEM micrographs; and Mössbauer spectroscopic data. See DOI: 10.1039/c0nr00024h

Growth and characterization of high quality ZnS thin films by RF sputtering

NASA Astrophysics Data System (ADS)

Mukherjee, C.; Rajiv, K.; Gupta, P.; Sinha, A. K.; Abhinandan, L.

2012-06-01

High optical quality ZnS films are deposited on glass and Si wafer by RF sputtering from pure ZnS target. Optical transmittance, reflectance, ellipsometry, FTIR and AFM measurements are carried out. Effect of substrate temperature and chamber baking for long duration on film properties have been studied. Roughness of the films as measured by AFM are low (1-2Å).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aadila, A., E-mail: aadilaazizali@gmail.com; Afaah, A. N.; Asib, N. A. M.

Poly(methyl methacrylate) (PMMA) films were deposited on glass substrate by sol-gel spin-coating method. The films were annealed for 10 minutes in furnace at different annealing temperature of room temperature, 50, 100, 150 and 200 °C. The effect of annealing temperatures to the surface and optical properties of PMMA films spin-coated on the substrate were investigated by Atomic Force Microscope (AFM) and Ultraviolet-Visible (UV-Vis) Spectroscopy. It was observed in AFM analysis all the annealed films show excellent smooth surface with zero roughness. All the samples demonstrate a high transmittance of 80% in UV region as shown in UV-Vis measurement. Highly transparentmore » films indicate the films are good optical properties and could be applied in various optical applications and also in non-linear optics.« less

Dimensionality tuning of the electronic structure in Fe3Ga4 magnetic materials

NASA Astrophysics Data System (ADS)

Moura, K. O.; de Oliveira, L. A. S.; Rosa, P. F. S.; Jesus, C. B. R.; Saleta, M. E.; Granado, E.; Béron, F.; Pagliuso, P. G.; Pirota, K. R.

2016-06-01

This work reports on the dimensionality effects on the magnetic behavior of Fe3Ga4 compounds by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. Our results show that reducing the Fe3Ga4 dimensionality, via nanowire shape, intriguingly modifies its electronic structure. In particular, the bulk system exhibits two transitions, a ferromagnetic (FM) transition temperature at T1 = 50 K and an antiferromagnetic (AFM) one at T2 = 390 K. On the other hand, nanowires shift these transition temperatures, towards higher and lower temperature for T1 and T2, respectively. Moreover, the dimensionality reduction seems to also modify the microscopic nature of the T1 transition. Instead of a FM to AFM transition, as observed in the 3D system, a transition from FM to ferrimagnetic (FERRI) or to coexistence of FM and AFM phases is found for the nanowires. Our results allowed us to propose the magnetic field-temperature phase diagram for Fe3Ga4 in both bulk and nanostructured forms. The interesting microscopic tuning of the magnetic interactions induced by dimensionality in Fe3Ga4 opens a new route to optimize the use of such materials in nanostructured devices.

Dimensionality tuning of the electronic structure in Fe3Ga4 magnetic materials

PubMed Central

Moura, K. O.; de Oliveira, L. A. S.; Rosa, P. F. S.; Jesus, C. B. R.; Saleta, M. E.; Granado, E.; Béron, F.; Pagliuso, P. G.; Pirota, K. R.

2016-01-01

This work reports on the dimensionality effects on the magnetic behavior of Fe3Ga4 compounds by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. Our results show that reducing the Fe3Ga4 dimensionality, via nanowire shape, intriguingly modifies its electronic structure. In particular, the bulk system exhibits two transitions, a ferromagnetic (FM) transition temperature at T1 = 50 K and an antiferromagnetic (AFM) one at T2 = 390 K. On the other hand, nanowires shift these transition temperatures, towards higher and lower temperature for T1 and T2, respectively. Moreover, the dimensionality reduction seems to also modify the microscopic nature of the T1 transition. Instead of a FM to AFM transition, as observed in the 3D system, a transition from FM to ferrimagnetic (FERRI) or to coexistence of FM and AFM phases is found for the nanowires. Our results allowed us to propose the magnetic field-temperature phase diagram for Fe3Ga4 in both bulk and nanostructured forms. The interesting microscopic tuning of the magnetic interactions induced by dimensionality in Fe3Ga4 opens a new route to optimize the use of such materials in nanostructured devices. PMID:27329581

Neutron Diffraction Study of Parasitic Nd-Moment Order in the Checkerboard-Type Phase Nd 1.3Sr 0.7NiO 4

DOE PAGES

Kobayashi, Riki; Yoshizawa, Hideki; Matsuda, Masaaki; ...

2015-05-25

In this paper, the Nd-moment order in the layered nickelate Nd 2-xSr xNiO 4 (x = 0.7) has been investigated by performing a neutron diffraction experiment using a single crystal sample. First, the checkerboard (CB)-type charge order was confirmed by observing the temperature dependence of the nuclear superlattice peak at Q=(5,0,0) between 1.9 and 300 K, which indicates that the transition temperature of the CB-type charge order is above 300 K. Magnetic superlattice peaks with the propagation vector k=(1-ε,0,1) appear below 67 K, and the value of ε was determined to be 0.455 in good agreement with previous studies. Themore » intensity of the magnetic superlattice peaks appearing below 67 K shows a sharp increase below ≈20 K. This behavior indicates that the Nd moments freeze under the influence of the Ni ordering. The CB-type antiferromagnetic (AFM) Ni order in the NiO 2 layers is stacked antiferromagnetically in the c-axis direction, while the Nd moments in the Nd/SrO 2 layers are coupled antiferromagnetically with the Ni moments. Finally, the Nd moments are parallel to the c-axis, while the Ni moments are canted towards the c-axis direction from the basal ab-plane at low temperatures where the Nd moments are well ordered.« less

Tip Characterization Method using Multi-feature Characterizer for CD-AFM

PubMed Central

Orji, Ndubuisi G.; Itoh, Hiroshi; Wang, Chumei; Dixson, Ronald G.; Walecki, Peter S.; Schmidt, Sebastian W.; Irmer, Bernd

2016-01-01

In atomic force microscopy (AFM) metrology, the tip is a key source of uncertainty. Images taken with an AFM show a change in feature width and shape that depends on tip geometry. This geometric dilation is more pronounced when measuring features with high aspect ratios, and makes it difficult to obtain absolute dimensions. In order to accurately measure nanoscale features using an AFM, the tip dimensions should be known with a high degree of precision. We evaluate a new AFM tip characterizer, and apply it to critical dimension AFM (CD-AFM) tips used for high aspect ratio features. The characterizer is made up of comb-shaped lines and spaces, and includes a series of gratings that could be used as an integrated nanoscale length reference. We also demonstrate a simulation method that could be used to specify what range of tip sizes and shapes the characterizer can measure. Our experiments show that for non re-entrant features, the results obtained with this characterizer are consistent to 1 nm with the results obtained by using widely accepted but slower methods that are common practice in CD-AFM metrology. A validation of the integrated length standard using displacement interferometry indicates a uniformity of better than 0.75%, suggesting that the sample could be used as highly accurate and SI traceable lateral scale for the whole evaluation process. PMID:26720439

Studies of the micromorphology of sputtered TiN thin films by autocorrelation techniques

NASA Astrophysics Data System (ADS)

Smagoń, Kamil; Stach, Sebastian; Ţălu, Ştefan; Arman, Ali; Achour, Amine; Luna, Carlos; Ghobadi, Nader; Mardani, Mohsen; Hafezi, Fatemeh; Ahmadpourian, Azin; Ganji, Mohsen; Grayeli Korpi, Alireza

2017-12-01

Autocorrelation techniques are crucial tools for the study of the micromorphology of surfaces: They provide the description of anisotropic properties and the identification of repeated patterns on the surface, facilitating the comparison of samples. In the present investigation, some fundamental concepts of these techniques including the autocorrelation function and autocorrelation length have been reviewed and applied in the study of titanium nitride thin films by atomic force microscopy (AFM). The studied samples were grown on glass substrates by reactive magnetron sputtering at different substrate temperatures (from 25 {}°C to 400 {}°C , and their micromorphology was studied by AFM. The obtained AFM data were analyzed using MountainsMap Premium software obtaining the correlation function, the structure of isotropy and the spatial parameters according to ISO 25178 and EUR 15178N. These studies indicated that the substrate temperature during the deposition process is an important parameter to modify the micromorphology of sputtered TiN thin films and to find optimized surface properties. For instance, the autocorrelation length exhibited a maximum value for the sample prepared at a substrate temperature of 300 {}°C , and the sample obtained at 400 {}°C presented a maximum angle of the direction of the surface structure.

78 FR 24343 - Airworthiness Directives; Cessna Aircraft Company Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2013-04-25

... learned that the temperature limitations were inadvertently removed from later revisions to the AFM. In... Removal of Statement About Operating Temperature Limitations Cessna requested removal of the statement in... operators must remain aware of operating temperature limitations as detailed in the specific airplane flight...

Low Energy Spectrum of Proximate Kitaev Spin Liquid α -RuCl3 by Terahertz Spectroscopy

NASA Astrophysics Data System (ADS)

Little, Arielle; Wu, Liang; Kelley, Paige; Banerjee, Arnab; Bridges, Craig; Yan, Jiaqiang; Nagler, Stephen; Mandrus, David; Orenstein, Joseph

A Quantum Spin Liquid (QSL) is an ultra-quantum state of matter with no ordered ground state. Recently, a route to a QSL identified by Kitaev has received a great deal of attention. The compound α -RuCl3, in which Ru atoms form a honeycomb lattice, has been shown to possess Kitaev exchange interactions, although a smaller Heisenberg interaction exists and leads to a zig-zag antiferromagnetic state below 7 K. Because of proximity to the exactly-solvable Kitaev spin-liquid model, this material is considered a potential host for Majorana-like modes. In this work, we use time-domain terahertz (THz) Spectroscopy to probe the low-energy excitations of α -RuCl3. We observe the emergence of a sharp magnetic spin-wave absorption peak below the AFM ordering temperature at 7 K on top of a broad continuum that persists up to room temperature. Additionally we report the polarization dependence of the THz absorption, which reveals optical birefringence, indicating the presence of large monoclinic domains.

Temperature-assisted morphological transition in CuPc thin films

NASA Astrophysics Data System (ADS)

Bae, Yu Jeong; Pham, Thi Kim Hang; Kim, Tae Hee

2016-05-01

Ex-situ and in-situ morphological analyses were performed for Cu-phthalocyanine (CuPc) organic semiconductor films by using atomic force microscopy (AFM) and reflection high-energy electron diffraction (RHEED). The focus was the effects of post-annealing on the structural characteristics of CuPc films grown on MgO(001) layers by using an ultra-high-vacuum thermal evaporator. Sphere-to-nanofibril and 2-D to 3-D morphological transitions were observed with increasing CuPc thickness beyond 3 nm. The surface morphology and the crystallinity were drastically improved after an additional cooling of the post-annealed CuPc films thinner than 3 nm. Our results highlight that molecular orientation and structural ordering can be effectively controlled by using different temperature treatments and a proper combination of material, film thickness, and substrate.

AFM feature definition for neural cells on nanofibrillar tissue scaffolds.

PubMed

Tiryaki, Volkan M; Khan, Adeel A; Ayres, Virginia M

2012-01-01

A diagnostic approach is developed and implemented that provides clear feature definition in atomic force microscopy (AFM) images of neural cells on nanofibrillar tissue scaffolds. Because the cellular edges and processes are on the same order as the background nanofibers, this imaging situation presents a feature definition problem. The diagnostic approach is based on analysis of discrete Fourier transforms of standard AFM section measurements. The diagnostic conclusion that the combination of dynamic range enhancement with low-frequency component suppression enhances feature definition is shown to be correct and to lead to clear-featured images that could change previously held assumptions about the cell-cell interactions present. Clear feature definition of cells on scaffolds extends the usefulness of AFM imaging for use in regenerative medicine. © Wiley Periodicals, Inc.

Spin Order and Phase Transitions in Chains of Polariton Condensates.

PubMed

Ohadi, H; Ramsay, A J; Sigurdsson, H; Del Valle-Inclan Redondo, Y; Tsintzos, S I; Hatzopoulos, Z; Liew, T C H; Shelykh, I A; Rubo, Y G; Savvidis, P G; Baumberg, J J

2017-08-11

We demonstrate that multiply coupled spinor polariton condensates can be optically tuned through a sequence of spin-ordered phases by changing the coupling strength between nearest neighbors. For closed four-condensate chains these phases span from ferromagnetic (FM) to antiferromagnetic (AFM), separated by an unexpected crossover phase. This crossover phase is composed of alternating FM-AFM bonds. For larger eight-condensate chains, we show the critical role of spatial inhomogeneities and demonstrate a scheme to overcome them and prepare any desired spin state. Our observations thus demonstrate a fully controllable nonequilibrium spin lattice.

Surfactant-mediated growth of cobalt on magnesium oxide(111)

NASA Astrophysics Data System (ADS)

Johnson-Steigelman, Harry Trevor

Monolayer films of Co have been deposited using an electrostatic electron-beam evaporator on single-crystal MgO(111)-( 3x3 ) R 30° and MgO(111)-(1x1) substrates held at room temperature (RT), with subsequent annealing of temperatures 400°C to 800°C. These films have been characterized using low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Upon RT deposition of Co, the LEED pattern of the substrate disappears and the XPS signal of MgO features reduce in intensity. After short anneals of 400°C, the LEED pattern returns and the MgO features increase in intensity. AFM images suggest that islanding has occurred at the surface. This conclusion is supported by the behavior of thicker films of Co on MgO(111), which showed pronounced changes in the MgO related XPS features. The behavior of the Mg 2p and O 1s features were analyzed and compared to previously reported reconstructions of the MgO(111)-(1x1) and MgO(111)-( 3x3 ) R 30° surfaces. Ag was examined as a potential surfactant to aid in the growth of smooth Co films. Ag was deposited onto MgO(111)-( 3x3 ) R 30° substrates and investigated using XPS, LEED, and AFM. It was found that Ag formed islands upon annealing. Despite the fact that Ag formed islands, it was found that the presence of Ag did have a surfactant effect upon the thin-film growth of Co on Ag/MgO(111)-( 3x3 ) R 30° substrates with 1-2 ML of Ag. Co islands were still present, but much more smooth than islands formed without the Ag surfactant. XPS peak intensity changes and AFM suggest strongly that Ag floated to the top of these samples at temperatures above 400°C. The Co growth mode appears to be Volmer-Weber island growth, as seen in AFM.

BOREAS AFM-04 Twin Otter Aircraft Sounding Data

NASA Technical Reports Server (NTRS)

MacPherson, J. Ian; Desjardins, Raymond L.; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Smith, David E. (Technical Monitor)

2000-01-01

The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-4 team used the National Research Council, Canada (NRC) Twin Otter aircraft to make sounding measurements through the boundary layer. These measurements included concentrations of carbon dioxide and ozone, atmospheric pressure, dry bulb temperature, potential temperature, dewpoint temperature, calculated mixing ratio, and wind speed and direction. Aircraft position, heading, and altitude were also recorded. Data were collected at both the Northern Study Area (NSA) and the Southern Study Area (SSA) in 1994 and 1996. These data are stored in tabular ASCII files. The Twin Otter aircraft sounding data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files also are available on a CD-ROM (see document number 20010000884).

Magnetic behaviors in melt spun Fe{sub 52−x}Mn{sub 23+x}Ga{sub 25} (x = 0–3) ribbons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shih, C. W.; Lee, Y. I.; Chang, W. C., E-mail: phywcc@ccu.edu.tw

2014-05-07

The effect of volume fraction of B2-type ferromagnetic (FM) phase on magnetic behavior of melt-spun Fe{sub 52−x}Mn{sub 23+x}Ga{sub 25} (x = 0, 1, 2, and 3) ribbons has been investigated. X-ray diffraction (XRD) results show that the volume fraction of the B2 phase is decreased, accompanied by the increased antiferromagnetic (AFM) fcc phase, with increasing x. The magnetization isotherms of these ribbons at different temperatures demonstrate that there exists a critical field H{sub CR} from AFM to FM state, and the H{sub CR} decreases and vanishes finally with increasing temperature. High exchange bias field (H{sub EB}) at 10 K through a cooling fieldmore » at H{sub CR} from 300 K could be found and correlated to the volume fraction of B2-type FM phase. Both H{sub CR} and H{sub EB} are increased with decreasing the amount of B2-type FM phase. The H{sub CR} is increased from 20 kOe for x = 0 to 50 kOe for x = 3, and H{sub EB} is increased from 0.9 kOe for x = 0 to 2.5 kOe for x = 2. The latter phenomenon might be attributed to the change of exchange interactions at FM/AFM interfaces due to the change of proportion of FM and AFM phase at low temperature.« less

Study of thermal and acoustic noise interferences in low stiffness atomic force microscope cantilevers and characterization of their dynamic properties.

PubMed

Boudaoud, Mokrane; Haddab, Yassine; Le Gorrec, Yann; Lutz, Philippe

2012-01-01

The atomic force microscope (AFM) is a powerful tool for the measurement of forces at the micro/nano scale when calibrated cantilevers are used. Besides many existing calibration techniques, the thermal calibration is one of the simplest and fastest methods for the dynamic characterization of an AFM cantilever. This method is efficient provided that the Brownian motion (thermal noise) is the most important source of excitation during the calibration process. Otherwise, the value of spring constant is underestimated. This paper investigates noise interference ranges in low stiffness AFM cantilevers taking into account thermal fluctuations and acoustic pressures as two main sources of noise. As a result, a preliminary knowledge about the conditions in which thermal fluctuations and acoustic pressures have closely the same effect on the AFM cantilever (noise interference) is provided with both theoretical and experimental arguments. Consequently, beyond the noise interference range, commercial low stiffness AFM cantilevers are calibrated in two ways: using the thermal noise (in a wide temperature range) and acoustic pressures generated by a loudspeaker. We then demonstrate that acoustic noises can also be used for an efficient characterization and calibration of low stiffness AFM cantilevers. The accuracy of the acoustic characterization is evaluated by comparison with results from the thermal calibration.

Competing exchange bias and field-induced ferromagnetism in La-doped BaFe O3

NASA Astrophysics Data System (ADS)

Fita, I.; Wisniewski, A.; Puzniak, R.; Iwanowski, P.; Markovich, V.; Kolesnik, S.; Dabrowski, B.

2017-04-01

An exchange bias (EB) effect was observed in mixed valent L axB a1 -xFe O3 (x =0.125 , 0.25, 0.33) perovskites exhibiting the antiferromagnetic (AFM) helical order among F e4 + ions coexisting with the ferromagnetic (FM) cluster phase in the ground state. The L a3 + ions for B a2 + site substitution, associated with increase in number of the AFM coupled F e3 + - F e4 + pairs as well as some F e3 + - F e3 + pairs, leads to strengthening of the AFM phase and consequently to the alteration of the EB characteristics, which depend on level of the La doping x . At low doping x ≤0.25 , an abnormal dependence of the EB field, HEB, on the cooling field, Hcool, was found. The HEB increases rapidly with increasing cooling field at low Hcool, but it falls suddenly at cooling fields higher than 20 kOe, reducing by an order of magnitude at 90 kOe. The suppression of EB is caused by the field-induced increased volume of the FM phase, due to the transformation of the AFM helical spin structure into the FM one. Thus, low-doped L axB a1 -xFe O3 demonstrates a competition of two alternate cooling-field-induced effects, one of which leads to the EB anisotropy and another one to the enhanced ferromagnetism. In contrast, the x =0.33 sample, having a strong AFM constituent, shows no field-induced FM and no drop in the EB field. Accordingly, the HEB vs Hcool dependence was found to be well explained in the framework of a model describing phase-separated AFM-FM systems, namely, the model assuming isolated FM clusters of size ˜4 nm embedded in the AFM matrix.

Atomic force microscopy nanomanipulation of silicon nanocrystals for nanodevice fabrication

NASA Astrophysics Data System (ADS)

Decossas, Sébastien; Mazen, Frédéric; Baron, Thierry; Brémond, Georges; Souifi, Abdelkader

2003-12-01

An atomic force microscopy (AFM) tip has been used to manipulate silicon nanocrystals deposited by low-pressure chemical vapour deposition on thermally oxidized p-type Si wafer. Three nanomanipulation methods are presented. The first one catches a nanocrystal with the AFM tip and deposits it elsewhere: the tip is used as an electrostatic 'nano-crane'. The second one simultaneously manipulates a set of nanocrystals in order to draw well-defined unidimensional lines: the tip is used as a 'nano-broom'. The third one manipulates individual nanocrystals with a precision of about 10 nm using both oscillating and contact AFM modes. Switching from strong interaction forces (chemical) to weak ones (van der Waals, electrostatic or capillarity) is the basis of these manipulation methods. We have applied the second method to connect two electrodes drawn by e-beam and lift-off with a 70 nm long silicon nanocrystal chain. Current versus voltage characterization of the nanofabricated device shows that the increase in nanocrystal density gives rise to conduction between the connected electrodes. Resonant tunnelling effects resulting from Si nanocrystal (nc-Si) multiple tunnel junctions have been observed at 300 K. We also show that offset charges directly influence the position of the resonant tunnelling peaks. Finally, the possibility of manipulating nc-Si with a diameter of around 5 nm is shown to be a promising way to fabricate single electron devices operating at room temperature and fully compatible with silicon technology.

Tuning the magnetism of the top-layer FeAs on BaFe2As2 (001): First-principles study

NASA Astrophysics Data System (ADS)

Zhang, Bing-Jing; Liu, Kai; Lu, Zhong-Yi

2018-04-01

Magnetism may play an important role in inducing the superconductivity in iron-based superconductors. As a prototypical system, the surface of BaFe2As2 provides a good platform for studying related magnetic properties. We have designed systematic first-principles calculations to clarify the surface magnetism of BaFe2As2 (001), which previously has received little attention in comparison with surface structures and electronic states. We find that the surface environment has an important influence on the magnetic properties of the top-layer FeAs. For As-terminated surfaces, the magnetic ground state of the top-layer FeAs is in the staggered dimer antiferromagnetic (AFM) order, distinct from that of the bulk, while for Ba-terminated surfaces the collinear (single-stripe) AFM order is the most stable, the same as that in the bulk. When a certain coverage of Ba or K atoms is deposited onto the As-terminated surface, the calculated energy differences among different AFM orders for the top-layer FeAs on BaFe2As2 (001) can be much reduced, indicating enhanced spin fluctuations. To compare our results with available scanning tunneling microscopy (STM) measurements, we have simulated the STM images of several structural/magnetic terminations. Astonishingly, when the top-layer FeAs is in the staggered dimer AFM order, a stripe pattern appears in the simulated STM image even when the surface Ba atoms adopt a √{2 }×√{2 } structure, while a √{2 }×√{2 } square pattern comes out for the 1 ×1 full As termination. Our results suggest: (i) the magnetic state at the BaFe2As2 (001) surface can be quite different from that in the bulk; (ii) the magnetic properties of the top-layer FeAs can be tuned effectively by surface doping, which may likely induce superconductivity at the surface layer; (iii) both the surface termination and the AFM order in the top-layer FeAs can affect the STM image of BaFe2As2 (001), which needs to be taken into account when identifying the surface termination.

Electronic structure and magnetic ordering in manganese hydride

NASA Astrophysics Data System (ADS)

Magnitskaya, M. V.; Kulikov, N. I.

1991-03-01

The self-consistent electron energy bands of antiferromagnetic (AFM) and non-magnetic manganese hydride are calculated using the linear muffintin orbital method (LMTO). The calculated values of equilibrium volume and of magnetic moment on the manganese site are in good agreement with experiment. The Fermi surface of paramagnetic MnH contains two nesting parts, and their superposition gives rise to AFM gap.

Contact resonances of U-shaped atomic force microscope probes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rezaei, E.; Turner, J. A., E-mail: jaturner@unl.edu

Recent approaches used to characterize the elastic or viscoelastic properties of materials with nanoscale resolution have focused on the contact resonances of atomic force microscope (CR-AFM) probes. The experiments for these CR-AFM methods involve measurement of several contact resonances from which the resonant frequency and peak width are found. The contact resonance values are then compared with the noncontact values in order for the sample properties to be evaluated. The data analysis requires vibration models associated with the probe during contact in order for the beam response to be deconvolved from the measured spectra. To date, the majority of CR-AFMmore » research has used rectangular probes that have a relatively simple vibration response. Recently, U-shaped AFM probes have created much interest because they allow local sample heating. However, the vibration response of these probes is much more complex such that CR-AFM is still in its infancy. In this article, a simplified analytical model of U-shaped probes is evaluated for contact resonance applications relative to a more complex finite element (FE) computational model. The tip-sample contact is modeled using three orthogonal Kelvin-Voigt elements such that the resonant frequency and peak width of each mode are functions of the contact conditions. For the purely elastic case, the frequency results of the simple model are within 8% of the FE model for the lowest six modes over a wide range of contact stiffness values. Results for the viscoelastic contact problem for which the quality factor of the lowest six modes is compared show agreement to within 13%. These results suggest that this simple model can be used effectively to evaluate CR-AFM experimental results during AFM scanning such that quantitative mapping of viscoelastic properties may be possible using U-shaped probes.« less

Magnetic and thermal property studies of RCrTeO6 (R=trivalent lanthanides) with layered honeycomb sublattices

NASA Astrophysics Data System (ADS)

Narsinga Rao, G.; Sankar, R.; Panneer Muthuselvam, I.; Chou, F. C.

2014-12-01

We have investigated the magnetic ordering of the RCrTeO6 (R=Y, La, Tb and Er) samples comprising Cr3+ (S=3/2). The X-ray diffraction structure analysis revealed that all samples are a hexagonal structure with the space group P 3bar. The magnetic susceptibility χ(T) and heat capacity CP(T) measurement results reveal that both short range and long range antiferromagnetic (AFM) orderings exist in non-magnetic rare earth R=Y and La compounds. For isostructural compounds of R=Tb and Er, CP(T) curves show long range ordering at the same temperature as non-magnetic R=Y, which indicates that the super-super exchange of Cr spins dominates. For R elements of Tb and Er with large spins sitting between honeycomb sublattices composed of CrO6-TeO6 octahedra, the two sublattices of R and Cr appear to be independently magnetic.

Improved AFM Mapping of ICF Target Surfaces

NASA Astrophysics Data System (ADS)

Olson, D. K.; Drake, T.; Frey, D.; Huang, H.; Stephens, R. B.

2003-10-01

Targets for Inertial Confinement Fusion (ICF) research are made from spherical shells with very strict requirements on surface smoothness. Hydrodynamic instabilities are amplified by the presence of surface defects, greatly reducing the gain of ICF targets. Sub-micron variations in the surface can be examined using an Atomic Force Microscope. The current sphere mapping assembly at General Atomics is designed to trace near the equator of a rotating sphere under the AFM head. Spheres are traced on three mutually orthogonal planes. The ˜10 mm piezo-electric actuator range limits how far off the equator we can scan spheres of millimeter diameter. Because only a small fraction of the target's surface can be covered, localized high-mode defects are difficult to detect. In order to meet the needs of ICF research, we need to scan more surface area of the sphere with the AFM. By integrating an additional stepping motor to the sphere mapping assembly, we will be able to recenter the piezo driver of the AFM while mapping. This additional ability allows us to increase the amount of the sphere's surface we are able to scan with the AFM by extending the range of the AFM from the sphere's equator.

Structure evolution of zinc oxide thin films deposited by unbalance DC magnetron sputtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aryanto, Didik, E-mail: didi027@lipi.go.id; Materials Research Group, Physics Department, Universitas Negeri Semarang, Gunungpati, Semarang 50229 Jawa Tengah; Marwoto, Putut

Zinc oxide (ZnO) thin films are deposited on corning glass substrates using unbalanced DC magnetron sputtering. The effect of growth temperature on surface morphology and crystallographic orientation of ZnO thin film is studied using atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. The surface morphology and crystallographic orientation of ZnO thin film are transformed against the increasing of growth temperature. The mean grain size of film and the surface roughness are inversely and directly proportional towards the growth temperature from room temperature to 300 °C, respectively. The smaller grain size and finer roughness of ZnO thin film are obtainedmore » at growth temperature of 400 °C. The result of AFM analysis is in good agreement with the result of XRD analysis. ZnO thin films deposited in a series of growth temperatures have hexagonal wurtzite polycrystalline structures and they exhibit transformations in the crystallographic orientation. The results in this study reveal that the growth temperature strongly influences the surface morphology and crystallographic orientation of ZnO thin film.« less

Temperature-Dependent Magnetic Response of Antiferromagnetic Doping in Cobalt Ferrite Nanostructures.

PubMed

Nairan, Adeela; Khan, Maaz; Khan, Usman; Iqbal, Munawar; Riaz, Saira; Naseem, Shahzad

2016-04-18

In this work Mn x Co 1- x Fe₂O₄ nanoparticles (NPs) were synthesized using a chemical co-precipitation method. Phase purity and structural analyses of synthesized NPs were performed by X-ray diffractometer (XRD). Transmission electron microscopy (TEM) reveals the presence of highly crystalline and narrowly-dispersed NPs with average diameter of 14 nm. The Fourier transform infrared (FTIR) spectrum was measured in the range of 400-4000 cm -1 which confirmed the formation of vibrational frequency bands associated with the entire spinel structure. Temperature-dependent magnetic properties in anti-ferromagnet (AFM) and ferromagnet (FM) structure were investigated with the aid of a physical property measurement system (PPMS). It was observed that magnetic interactions between the AFM (Mn) and FM (CoFe₂O₄) material arise below the Neel temperature of the dopant. Furthermore, hysteresis response was clearly pronounced for the enhancement in magnetic parameters by varying temperature towards absolute zero. It is shown that magnetic properties have been tuned as a function of temperature and an externally-applied field.

Suppression of electron correlations in the collapsed tetragonal phase of CaFe2As2 under ambient pressure demonstrated by As75 NMR/NQR measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Furukawa, Yuji; Roy, Beas; Ran, Sheng

2014-03-20

The static and the dynamic spin correlations in the low-temperature collapsed tetragonal and the high-temperature tetragonal phase in CaFe2As2 have been investigated by As75 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements. Through the temperature (T) dependence of the nuclear spin lattice relaxation rates (1/T1) and the Knight shifts, although stripe-type antiferromagnetic (AFM) spin correlations are realized in the high-temperature tetragonal phase, no trace of the AFM spin correlations can be found in the nonsuperconducting, low-temperature, collapsed tetragonal (cT) phase. Given that there is no magnetic broadening in As75 NMR spectra, together with the T-independent behavior of magneticmore » susceptibility χ and the T dependence of 1/T1Tχ, we conclude that Fe spin correlations are completely quenched statically and dynamically in the nonsuperconducting cT phase in CaFe2As2.« less

Topological transitions induced by antiferromagnetism in a thin-film topological insulator

NASA Astrophysics Data System (ADS)

Yin, Gen; He, Qinglin; Yu, Luyan; Pan, Lei; Wang, Kang

Ferromagnetism introduced in topological insulators (TIs) opens a non-trivial exchange band gap, providing an exciting platform to control the topological order through an external magnetic field. The magnetization induces a topological transition that breaks time-reversal symmetry, resulting in anomalous Hall effects. Recently, it was experimentally shown that the surface of an antiferromagnetic (AFM) thin film can magnetize the surface Dirac fermions in a TI thin film similar to the case induced by ferromagnetism. Here, we show that when a TI thin film is sandwiched between two antiferromagnetic layers, an unsynchronized magnetic reversal introduces two intermediate spin configurations during the scan of the external field, resulting in a new topological phase with second Chern numbers. This topological phase introduces two counter-propagating chiral edge modes inside the exchange gap, changing the total number of transport channels drastically when the fermi level is close to the Dirac point. Induced by this change, the magnetoresistance of the channel presents an antisymmetric feature during the field scan. With the the help of the high ordering temperature of AFM layers, this transport signature of the phase transition persists up to 90K experimentally. This work is supported by (i) SHINES, an EFRC by US-DOE, Office of Science, BES, #SC0012670. (ii) US-NSF (DMR-1411085), (iii) ARO program W911NF-15-1-10561, and (iv) FAME Center in STARnet, an SRC program by MARCO and DARPA.

The Green Propellant Infusion Mission Thruster Performance Testing for Plume Diagnostics

NASA Technical Reports Server (NTRS)

Deans, Matthew C.; Reed, Brian D.; Arrington, Lynn A.; Williams, George J.; Kojima, Jun J.; Kinzbach, McKenzie I.; McLean, Christopher H.

2014-01-01

The Green Propellant Infusion Mission (GPIM) is sponsored by NASA's Space Technology Mission Directorate (STMD) Technology Demonstration Mission (TDM) office. The goal of GPIM is to advance the technology readiness level of a green propulsion system, specifically, one using the monopropellant, AF-M315E, by demonstrating ground handling, spacecraft processing, and on-orbit operations. One of the risks identified for GPIM is potential contamination of sensitive spacecraft surfaces from the effluents in the plumes of AF-M315E thrusters. NASA Glenn Research Center (GRC) is conducting activities to characterize the effects of AF-M315E plume impingement and deposition. GRC has established individual plume models of the 22-N and 1-N thrusters that will be used on the GPIM spacecraft. The model simulations will be correlated with plume measurement data from Laboratory and Engineering Model 22-N, AF-M315E thrusters. The thrusters are currently being tested in a small rocket, altitude facility at NASA GRC. A suite of diagnostics, including Raman spectroscopy, Rayleigh spectroscopy, and Schlieren imaging are being used to acquire plume measurements of AF-M315E thrusters. Plume data will include temperature, velocity, relative density, and species concentration. The plume measurement data will be compared to the corresponding simulations of the plume model. The GRC effort will establish a data set of AF-M315E plume measurements and a plume model that can be used for future AF-M315E applications.

Quantitative force measurements in liquid using frequency modulation atomic force microscopy

NASA Astrophysics Data System (ADS)

Uchihashi, Takayuki; Higgins, Michael J.; Yasuda, Satoshi; Jarvis, Suzanne P.; Akita, Seiji; Nakayama, Yoshikazu; Sader, John E.

2004-10-01

The measurement of short-range forces with the atomic force microscope (AFM) typically requires implementation of dynamic techniques to maintain sensitivity and stability. While frequency modulation atomic force microscopy (FM-AFM) is used widely for high-resolution imaging and quantitative force measurements in vacuum, quantitative force measurements using FM-AFM in liquids have proven elusive. Here we demonstrate that the formalism derived for operation in vacuum can also be used in liquids, provided certain modifications are implemented. To facilitate comparison with previous measurements taken using surface forces apparatus, we choose a model system (octamethylcyclotetrasiloxane) that is known to exhibit short-ranged structural ordering when confined between two surfaces. Force measurements obtained are found to be in excellent agreement with previously reported results. This study therefore establishes FM-AFM as a powerful tool for the quantitative measurement of forces in liquid.

Manufacturing and advanced characterization of sub-25nm diameter CD-AFM probes with sub-10nm tip edges radius

NASA Astrophysics Data System (ADS)

Foucher, Johann; Filippov, Pavel; Penzkofer, Christian; Irmer, Bernd; Schmidt, Sebastian W.

2013-04-01

Atomic force microscopy (AFM) is increasingly used in the semiconductor industry as a versatile monitoring tool for highly critical lithography and etching process steps. Applications range from the inspection of the surface roughness of new materials, over accurate depth measurements to the determination of critical dimension structures. The aim to address the rapidly growing demands on measurement uncertainty and throughput more and more shifts the focus of attention to the AFM tip, which represents the crucial link between AFM tool and the sample to be monitored. Consequently, in order to reach the AFM tool's full potential, the performance of the AFM tip has to be considered as a determining parameter. Currently available AFM tips made from silicon are generally limited by their diameter, radius, and sharpness, considerably restricting the AFM measurement capabilities on sub-30nm spaces. In addition to that, there's lack of adequate characterization structures to accurately characterize sub-25nm tip diameters. Here, we present and discuss a recently introduced AFM tip design (T-shape like design) with precise tip diameters down to 15nm and tip radii down to 5nm fabricated from amorphous, high density diamond-like carbon (HDC/DLC) using electron beam induced processing (EBIP). In addition to that advanced design, we propose a new characterizer structure, which allows for accurate characterization and design control of sub-25nm tip diameters and sub-10nm tip edges radii. We demonstrate the potential advantages of combining a small tip shape design, i.e. tip diameter and tip edge radius, and an advanced tip characterizer for the semiconductor industry by the measurement of advanced lithography patterns.

Adiabatic Compression Sensitivity of AF-M315E

DTIC Science & Technology

2015-07-01

the current work is to expand the knowledge base from previous experiments completed at AFRL for AF-M315E in stainless steel U-tubes at room...addressed, to some degree, with the use of clamps and a large stainless steel plate to dissipate any major vibrations. A large preheated bath of 50:50 v/v...autocatalytic chain decomposition in the propellant. This exothermic decomposition decreases the fume -off initiation temperature of the propellant and its

Thermomagnetic, dielectric and EPR studies on four new multiferroics

NASA Astrophysics Data System (ADS)

Ramachandran, Vasanth

Multiferroics are materials which exhibit at least two or all three of the ferroic (ferroelectric, ferromagnetic and ferroelastic) orders co-existing in them, and are of high current interest in both the fundamental research and in the discovery of new multifunctional materials. This dissertation presents thermomagnetic, dielectric and electron paramagnetic resonance (EPR) studies on some new multiferroics. The primary focus of this work is on these four compounds: [(CH3)2NH2]Mn(HCOO)3, K3Fe5F15, Pb(Fe1/2Nb1/2)O 3, and MnV2O4. Chapter 3 discusses our discovery of multiferroic behavior of the metal-organic framework (MOF) compound dimethylammonium manganese formate, [(CH3)2NH2]Mn(HCOO) 3, with the aid of single crystal heat capacity and EPR measurements on the compound. Simultaneous occurrence of ferroelectric and antiferromagnetic long-range orders in this compound established its multiferroic nature. Chapter 4 describes the multiferroic nature of the 'tetragonal tungsten bronze'-type ferroelectric potassium iron fluoride, K3Fe5 F15, studied by magnetic susceptibility, magnetization, dielectric and EPR characterization of single crystal and polycrystalline samples. A weak ferromagnetic (FM) ordering due to spin canting caused by the antisymmetric exchange interaction between the Fe ions, and its influence on the dielectric constant evident by the observation of an anomaly around the FM ordering temperature, together indicate an intrinsic magnetoelectric coupling present in this compound. Chapter 5 describes multiferroic behavior of the complex oxide perovskite lead iron niobate, Pb(Fe1/2Nb1/2)O3 abbreviated as PFN. Systematic (9.4, 34, 381, 683 GHz) EPR and magnetic susceptibility measurements on polycrystalline PFN samples show an antiferromagnetic (AFM) ordering, the presence of a small finite internal field well above the AFM ordering temperature, and the first observation of an anomaly in the susceptibility near the ferroelectric Curie point, together implying the presence of magnetoelectric effect. Chapter 6 presents ac and dc magnetic susceptibility experiments on the magnetoelastic spinel compound manganese vanadate, MnV2O4. The compound is shown to exhibit a re-entrant spin glass behavior. The results and perspectives presented here should contribute to the advancement and fundamental understanding of multiferroic materials.

Combined low-temperature scanning tunneling/atomic force microscope for atomic resolution imaging and site-specific force spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwarz, Udo; Albers, Boris J.; Liebmann, Marcus

2008-02-27

The authors present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based sensor provides flexibility in selecting probe tip materials, which can be either metallic or nonmetallic. When choosing a conducting tip and sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems providing simultaneous STM/NC-AFM capabilities are its combination of relative compactness (on-top bath cryostat needs no pit), in situ exchange of tip and sample at low temperatures, short turnaroundmore » times, modest helium consumption, and unrestricted access from dedicated flanges. The latter permits not only the optical surveillance of the tip during approach but also the direct deposition of molecules or atoms on either tip or sample while they remain cold. Atomic corrugations as low as 1 pm could successfully be resolved. In addition, lateral drifts rates of below 15 pm/h allow long-term data acquisition series and the recording of site-specific spectroscopy maps. Results obtained on Cu(111) and graphite illustrate the microscope's performance.« less

Crystallization behaviour of nanostructured hybrid SiO2-TiO2 gel glasses to nanocomposites.

PubMed

Tsvetelina, Gerganova; Yordanka, Ivanova; Yuliya, Vueva; Miranda, Salvado Isabel M; Helena, Fernandes Maria

2010-04-01

The crystallization behaviour of hybrid SiO2-TiO2 nanocomposites derived from titanosiloxanes by sol-gel method has been investigated depending on the type of siloxane precursor and the pirolysis temperature. The resulting hybrid titanosiloxanes, crosslinked with trimethylsilil isocyanate (nitrogen-modified) or methyltrietoxisilane (carbon-modified), were pirolyzed in an inert atmosphere in the temperature range between 600 to 1100 degrees C in order to form C-(N)-Si-O-TiO2 nanocomposites. By means of XRD, FTIR, 29Si NMR, SEM, TEM and AFM investigations have been established that the transformation of the nanostructured SiO2-TiO2 hybrid materials into nanocomposites as well as the crystalline size depend on the titanium content and the type of cross-linking agents used in the synthesizes.

Electronic Phase Separation in Iron Selenide (Li,Fe)OHFeSe Superconductor System

NASA Astrophysics Data System (ADS)

Mao, Yiyuan; Li, Jun; Huan, Yulong; Yuan, Jie; Li, Zi-an; Chai, Ke; Ma, Mingwei; Ni, Shunli; Tian, Jinpeng; Liu, Shaobo; Zhou, Huaxue; Zhou, Fang; Li, Jianqi; Zhang, Guangming; Jin, Kui; Dong, Xiaoli; Zhao, Zhongxian

2018-05-01

The phenomenon of phase separation into antiferromagnetic (AFM) and superconducting (SC) or normal-state regions has great implication for the origin of high-temperature (high-Tc) superconductivity. However, the occurrence of an intrinsic antiferromagnetism above the Tc of (Li, Fe)OHFeSe superconductor is questioned. Here we report a systematic study on a series of (Li, Fe)OHFeSe single crystal samples with Tc up to ~41 K. We observe an evident drop in the static magnetization at Tafm ~125 K, in some of the SC (Tc < ~38 K, cell parameter c < ~9.27 {\\AA}) and non-SC samples. We verify that this AFM signal is intrinsic to (Li, Fe)OHFeSe. Thus, our observations indicate mesoscopic-to-macroscopic coexistence of an AFM state with the normal (below Tafm) or SC (below Tc) state in (Li, Fe)OHFeSe. We explain such coexistence by electronic phase separation, similar to that in high-Tc cuprates and iron arsenides. However, such an AFM signal can be absent in some other samples of (Li, Fe)OHFeSe, particularly it is never observed in the SC samples of Tc > ~38 K, owing to a spatial scale of the phase separation too small for the macroscopic magnetic probe. For this case, we propose a microscopic electronic phase separation. It is suggested that the microscopic static phase separation reaches vanishing point in high-Tc (Li, Fe)OHFeSe, by the occurrence of two-dimensional AFM spin fluctuations below nearly the same temperature as Tafm reported previously for a (Li, Fe)OHFeSe (Tc ~42 K) single crystal. A complete phase diagram is thus established. Our study provides key information of the underlying physics for high-Tc superconductivity.

Radiation pressure excitation of Low Temperature Atomic Force & Magnetic Force Microscope (LT-AFM/MFM) for Imaging

NASA Astrophysics Data System (ADS)

Karci, Ozgur; Celik, Umit; Oral, Ahmet; NanoMagnetics Instruments Ltd. Team; Middle East Tech Univ Team

2015-03-01

We describe a novel method for excitation of Atomic Force Microscope (AFM) cantilevers by means of radiation pressure for imaging in an AFM for the first time. Piezo excitation is the most common method for cantilever excitation, but it may cause spurious resonance peaks. A fiber optic interferometer with 1310 nm laser was used both to measure the deflection of cantilever and apply a force to the cantilever in a LT-AFM/MFM from NanoMagnetics Instruments. The laser power was modulated at the cantilever`s resonance frequency by a digital Phase Lock Loop (PLL). The force exerted by the radiation pressure on a perfectly reflecting surface by a laser beam of power P is F = 2P/c. We typically modulate the laser beam by ~ 800 μW and obtain 10nm oscillation amplitude with Q ~ 8,000 at 2.5x10-4 mbar. The cantilever's stiffness can be accurately calibrated by using the radiation pressure. We have demonstrated performance of the radiation pressure excitation in AFM/MFM by imaging a hard disk sample between 4-300K and Abrikosov vortex lattice in BSCCO single crystal at 4K to for the first time.

A high-pressure atomic force microscope for imaging in supercritical carbon dioxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lea, Alan S.; Higgins, Steven R.; Knauss, Kevin G.

2011-04-26

A high-pressure atomic force microscope (AFM) that enables in-situ, atomic scale measurements of topography of solid surfaces in contact with supercritical CO2 (scCO2) fluids has been developed. This apparatus overcomes the pressure limitations of the hydrothermal AFM and is designed to handle pressures up to 100 atm at temperatures up to ~ 350 K. A standard optically-based cantilever deflection detection system was chosen. When imaging in compressible supercritical fluids such as scCO2, precise control of pressure and temperature in the fluid cell is the primary technical challenge. Noise levels and imaging resolution depend on minimization of fluid density fluctuations thatmore » change the fluid refractive index and hence the laser path. We demonstrate with our apparatus in-situ atomic scale imaging of a calcite (CaCO3) mineral surface in scCO2; both single, monatomic steps and dynamic processes occurring on the (10¯14) surface are presented. This new AFM provides unprecedented in-situ access to interfacial phenomena at solid-fluid interfaces under pressure.« less

Spin dynamics and exchange interactions in CuO measured by neutron scattering

NASA Astrophysics Data System (ADS)

Jacobsen, H.; Gaw, S. M.; Princep, A. J.; Hamilton, E.; Tóth, S.; Ewings, R. A.; Enderle, M.; Wheeler, E. M. Hétroy; Prabhakaran, D.; Boothroyd, A. T.

2018-04-01

The magnetic properties of CuO encompass several contemporary themes in condensed-matter physics, including quantum magnetism, magnetic frustration, magnetically-induced ferroelectricity, and orbital currents. Here we report polarized and unpolarized neutron inelastic scattering measurements which provide a comprehensive map of the cooperative spin dynamics in the low-temperature antiferromagnetic (AFM) phase of CuO throughout much of the Brillouin zone. At high energies (E ≳100 meV ), the spectrum displays continuum features consistent with the des Cloizeax-Pearson dispersion for an ideal S =1/2 Heisenberg AFM chain. At lower energies, the spectrum becomes more three dimensional, and we find that a linear spin-wave model for a Heisenberg AFM provides a very good description of the data, allowing for an accurate determination of the relevant exchange constants in an effective spin Hamiltonian for CuO. In the high-temperature helicoidal phase, there are features in the measured low-energy spectrum that we could not reproduce with a spin-only model. We discuss how these might be associated with the magnetically-induced multiferroic behavior observed in this phase.

Features of the electronic structure of FeTe compounds

NASA Astrophysics Data System (ADS)

Grechnev, G. E.; Lyogenkaya, A. A.; Panfilov, A. S.; Logosha, A. V.; Kotlyar, O. V.; Gnezdilov, V. P.; Makarova, I. P.; Chareev, D. A.; Mitrofanova, E. S.

2015-12-01

A theoretical and experimental study of the electronic structure and nature of the chemical bonds in FeTe compounds in antiferromagnetic (AFM) and paramagnetic phases was carried out. It is established that the nature of the chemical bonds is mainly metallic, and the presence of covalent bonds Fe-Te and Te-Te helps to stabilize the structural distortions of the tetragonal phase of FeTe in the low-temperature region. It is found that the bicollinear AFM structure corresponds to the ground state of the FeTe compound and the calculated value of the magnetic moment MFe = -2.4μB is in good agreement with the data from neutron diffraction measurements. At the same time, the Fermi surface (FS) of the low-temperature AFM phase is radically different from the FS of the paramagnetic FeTe. Reconstructing the FS can lead to a sign change of the Hall coefficient observed in FeTe. The calculation results serve as evidence of the fact that the electronic structures and magnetic properties of FeTe are well-described by the model of itinerant d-electrons and the density functional theory (DFT-GGA).

Revealing the hidden structural phases of FeRh

NASA Astrophysics Data System (ADS)

Kim, Jinwoong; Ramesh, R.; Kioussis, Nicholas

2016-11-01

Ab initio electronic structure calculations reveal that tetragonal distortion has a dramatic effect on the relative stability of the various magnetic structures (C-, A-, G-, A'-AFM, and FM) of FeRh giving rise to a wide range of novel stable/metastable structures and magnetic phase transitions between these states. We predict that the cubic G-AFM structure, which was believed thus far to be the ground state, is metastable and that the tetragonally expanded G-AFM is the stable structure. The low energy barrier separating these states suggests phase coexistence at room temperature. We propose an A'-AFM phase to be the global ground state among all magnetic phases which arises from the strain-induced tuning of the exchange interactions. The results elucidate the underlying mechanism for the recent experimental findings of electric-field control of magnetic phase transition driven via tetragonal strain. The magnetic phase transitions open interesting prospects for exploiting strain engineering for the next-generation memory devices.

Direct observation of the actin filament by tip-scan atomic force microscopy

PubMed Central

Narita, Akihiro; Usukura, Eiji; Yagi, Akira; Tateyama, Kiyohiko; Akizuki, Shogo; Kikumoto, Mahito; Matsumoto, Tomoharu; Maéda, Yuichiro; Ito, Shuichi; Usukura, Jiro

2016-01-01

Actin filaments, the actin–myosin complex and the actin–tropomyosin complex were observed by a tip-scan atomic force microscope (AFM), which was recently developed by Olympus as the AFM part of a correlative microscope. This newly developed AFM uses cantilevers of similar size as stage-scan AFMs to improve substantially the spatial and temporal resolution. Such an approach has previously never been possible by a tip-scan system, in which a cantilever moves in the x, y and z directions. We evaluated the performance of this developed tip-scan AFM by observing the molecular structure of actin filaments and the actin–tropomyosin complex. In the image of the actin filament, the molecular interval of the actin subunits (∼5.5 nm) was clearly observed as stripes. From the shape of the stripes, the polarity of the actin filament was directly determined and the results were consistent with the polarity determined by myosin binding. In the image of the actin–tropomyosin complex, each tropomyosin molecule (∼2 nm in diameter) on the actin filament was directly observed without averaging images of different molecules. Each tropomyosin molecule on the actin filament has never been directly observed by AFM or electron microscopy. Thus, our developed tip-scan AFM offers significant potential in observing purified proteins and cellular structures at nanometer resolution. Current results represent an important step in the development of a new correlative microscope to observe nm-order structures at an acceptable frame rate (∼10 s/frame) by AFM at the position indicated by the fluorescent dye observed under a light microscope. PMID:27242058

A phase 1 study of the bispecific anti-CD30/CD16A antibody construct AFM13 in patients with relapsed or refractory Hodgkin lymphoma.

PubMed

Rothe, Achim; Sasse, Stephanie; Topp, Max S; Eichenauer, Dennis A; Hummel, Horst; Reiners, Katrin S; Dietlein, Markus; Kuhnert, Georg; Kessler, Joerg; Buerkle, Carolin; Ravic, Miroslav; Knackmuss, Stefan; Marschner, Jens-Peter; Pogge von Strandmann, Elke; Borchmann, Peter; Engert, Andreas

2015-06-25

AFM13 is a bispecific, tetravalent chimeric antibody construct (TandAb) designed for the treatment of CD30-expressing malignancies. AFM13 recruits natural killer (NK) cells via binding to CD16A as immune effector cells. In this phase 1 dose-escalation study, 28 patients with heavily pretreated relapsed or refractory Hodgkin lymphoma received AFM13 at doses of 0.01 to 7 mg/kg body weight. Primary objectives were safety and tolerability. Secondary objectives included pharmacokinetics, antitumor activity, and pharmacodynamics. Adverse events were generally mild to moderate. The maximum tolerated dose was not reached. Pharmacokinetics assessment revealed a half-life of up to 19 hours. Three of 26 evaluable patients achieved partial remission (11.5%) and 13 patients achieved stable disease (50%), with an overall disease control rate of 61.5%. AFM13 was also active in brentuximab vedotin-refractory patients. In 13 patients who received doses of ≥1.5 mg/kg AFM13, the overall response rate was 23% and the disease control rate was 77%. AFM13 treatment resulted in a significant NK-cell activation and a decrease of soluble CD30 in peripheral blood. In conclusion, AFM13 represents a well-tolerated, safe, and active targeted immunotherapy of Hodgkin lymphoma. A phase 2 study is currently planned to optimize the dosing schedule in order to further improve the therapeutic efficacy. This phase 1 study was registered at www.clinicaltrials.gov as #NCT01221571. © 2015 by The American Society of Hematology.

A phase 1 study of the bispecific anti-CD30/CD16A antibody construct AFM13 in patients with relapsed or refractory Hodgkin lymphoma

PubMed Central

Rothe, Achim; Sasse, Stephanie; Topp, Max S.; Eichenauer, Dennis A.; Hummel, Horst; Reiners, Katrin S.; Dietlein, Markus; Kuhnert, Georg; Kessler, Joerg; Buerkle, Carolin; Ravic, Miroslav; Knackmuss, Stefan; Marschner, Jens-Peter; Pogge von Strandmann, Elke; Borchmann, Peter

2015-01-01

AFM13 is a bispecific, tetravalent chimeric antibody construct (TandAb) designed for the treatment of CD30-expressing malignancies. AFM13 recruits natural killer (NK) cells via binding to CD16A as immune effector cells. In this phase 1 dose-escalation study, 28 patients with heavily pretreated relapsed or refractory Hodgkin lymphoma received AFM13 at doses of 0.01 to 7 mg/kg body weight. Primary objectives were safety and tolerability. Secondary objectives included pharmacokinetics, antitumor activity, and pharmacodynamics. Adverse events were generally mild to moderate. The maximum tolerated dose was not reached. Pharmacokinetics assessment revealed a half-life of up to 19 hours. Three of 26 evaluable patients achieved partial remission (11.5%) and 13 patients achieved stable disease (50%), with an overall disease control rate of 61.5%. AFM13 was also active in brentuximab vedotin–refractory patients. In 13 patients who received doses of ≥1.5 mg/kg AFM13, the overall response rate was 23% and the disease control rate was 77%. AFM13 treatment resulted in a significant NK-cell activation and a decrease of soluble CD30 in peripheral blood. In conclusion, AFM13 represents a well-tolerated, safe, and active targeted immunotherapy of Hodgkin lymphoma. A phase 2 study is currently planned to optimize the dosing schedule in order to further improve the therapeutic efficacy. This phase 1 study was registered at www.clinicaltrials.gov as #NCT01221571. PMID:25887777

Space charge limited current measurements on conjugated polymer films using conductive atomic force microscopy.

PubMed

Reid, Obadiah G; Munechika, Keiko; Ginger, David S

2008-06-01

We describe local (~150 nm resolution), quantitative measurements of charge carrier mobility in conjugated polymer films that are commonly used in thin-film transistors and nanostructured solar cells. We measure space charge limited currents (SCLC) through these films using conductive atomic force microscopy (c-AFM) and in macroscopic diodes. The current densities we measure with c-AFM are substantially higher than those observed in planar devices at the same bias. This leads to an overestimation of carrier mobility by up to 3 orders of magnitude when using the standard Mott-Gurney law to fit the c-AFM data. We reconcile this apparent discrepancy between c-AFM and planar device measurements by accounting for the proper tip-sample geometry using finite element simulations of tip-sample currents. We show that a semiempirical scaling factor based on the ratio of the tip contact area diameter to the sample thickness can be used to correct c-AFM current-voltage curves and thus extract mobilities that are in good agreement with values measured in the conventional planar device geometry.

Estimation of polymer-surface interfacial interaction strength by a contact AFM technique.

PubMed

Dvir, H; Jopp, J; Gottlieb, M

2006-12-01

Atomic force microscopy (AFM) measurements were employed to assess polymer-surface interfacial interaction strength. The main feature of the measurement is the use of contact-mode AFM as a tool to scratch off the polymer monolayer adsorbed on the solid surface. Tapping-mode AFM was used to determine the depth of the scraped recess. Independent determination of the layer thickness obtained from optical phase interference microscopy (OPIM) confirmed the depth of the AFM scratch. The force required for the complete removal of the polymer layer with no apparent damage to the substrate surface was determined. Polypropylene (PP), low-density polyethylene (PE), and PP-grafted-maleic anhydride (PP-g-ma) were scraped off silane-treated glass slabs, and the strength of surface interaction of the polymer layer was determined. In all cases it was determined that the magnitude of surface interaction force is of the order of van der Waals (VDW) interactions. The interaction strength is influenced either by polymer ability to wet the surface (hydrophobic or hydrophilic interactions) or by hydrogen bonding between the polymer and the surface treatment.

A Novel Method to Reconstruct the Force Curve by Higher Harmonics of the First Two Flexural Modes in Frequency Modulation Atomic Force Microscope (FM-AFM).

PubMed

Zhang, Suoxin; Qian, Jianqiang; Li, Yingzi; Zhang, Yingxu; Wang, Zhenyu

2018-06-04

Atomic force microscope (AFM) is an idealized tool to measure the physical and chemical properties of the sample surfaces by reconstructing the force curve, which is of great significance to materials science, biology, and medicine science. Frequency modulation atomic force microscope (FM-AFM) collects the frequency shift as feedback thus having high force sensitivity and it accomplishes a true noncontact mode, which means great potential in biological sample detection field. However, it is a challenge to establish the relationship between the cantilever properties observed in practice and the tip-sample interaction theoretically. Moreover, there is no existing method to reconstruct the force curve in FM-AFM combining the higher harmonics and the higher flexural modes. This paper proposes a novel method that a full force curve can be reconstructed by any order higher harmonics of the first two flexural modes under any vibration amplitude in FM-AFM. Moreover, in the small amplitude regime, short range forces are reconstructed more accurately by higher harmonics analysis compared with fundamental harmonics using the Sader-Jarvis formula.

Aflatoxin B1 and M1: Biological Properties and Their Involvement in Cancer Development.

PubMed

Marchese, Silvia; Polo, Andrea; Ariano, Andrea; Velotto, Salvatore; Costantini, Susan; Severino, Lorella

2018-05-24

Aflatoxins are fungal metabolites found in feeds and foods. When the ruminants eat feedstuffs containing Aflatoxin B1 (AFB1), this toxin is metabolized and Aflatoxin M1 (AFM1) is excreted in milk. International Agency for Research on Cancer (IARC) classified AFB1 and AFM1 as human carcinogens belonging to Group 1 and Group 2B, respectively, with the formation of DNA adducts. In the last years, some epidemiological studies were conducted on cancer patients aimed to evaluate the effects of AFB1 and AFM1 exposure on cancer cells in order to verify the correlation between toxin exposure and cancer cell proliferation and invasion. In this review, we summarize the activation pathways of AFB1 and AFM1 and the data already reported in literature about their correlation with cancer development and progression. Moreover, considering that few data are still reported about what genes/proteins/miRNAs can be used as damage markers due to AFB1 and AFM1 exposure, we performed a bioinformatic analysis based on interaction network and miRNA predictions to identify a panel of genes/proteins/miRNAs that can be used as targets in further studies for evaluating the effects of the damages induced by AFB1 and AFM1 and their capacity to induce cancer initiation.

H-T magnetic phase diagrams of electron-doped Sm1-xCaxMnO3: Evidence for phase separation and metamagnetic transitions

NASA Astrophysics Data System (ADS)

Respaud, M.; Broto, J. M.; Rakoto, H.; Vanacken, J.; Wagner, P.; Martin, C.; Maignan, A.; Raveau, B.

2001-04-01

The magnetic properties of the polycrystalline manganites Sm1-xCaxMnO3 have been studied for (1>=x>=2/3) under high magnetic fields up to 50 T. The phase diagrams in the H-T plane have been determined. The more representative systems have also been studied by means of neutron diffraction experiments. Increasing the electron concentration in CaMnO3 leads to an increasing minor ferromagnetic (FM) component superimposed on the antiferromagnetic (AFM) background. A cluster-glass regime is observed for x=0.9, where FM clusters are embedded in the G-type AFM matrix of the parent compound. For 0.8>=x, field-induced transitions from the AFM ground state to a FM one have been observed. They correspond to the melting of the C-type AFM orbital-ordered phase for x=0.8, and to the collapse of the charge-ordered phase for x=3/4. In between these two characteristic domains of concentration, x~0.85, the magnetization curves show a superposition of the two above behaviors, suggesting phase separation. This scenario is consistent with the neutron diffraction results showing that the crystalline and magnetic structures of each phase coexist.

Intrinsic crystal phase separation in the antiferromagnetic superconductor Rb(y)Fe(2-x)Se2: a diffraction study.

PubMed

Yu Pomjakushin, V; Krzton-Maziopa, A; Pomjakushina, E V; Conder, K; Chernyshov, D; Svitlyk, V; Bosak, A

2012-10-31

The crystal and magnetic structures of the superconducting iron-based chalcogenides Rb(y)Fe(2-x)Se(2) have been studied by means of single-crystal synchrotron x-ray and high-resolution neutron powder diffraction in the temperature range 2-570 K. The ground state of the crystal is an intrinsically phase-separated state with two distinct-by-symmetry phases. The main phase has the iron vacancy ordered √5 × √5 superstructure (I4/m space group) with AFM ordered Fe spins. The minority phase does not have √5 × √5-type of ordering and has a smaller in-plane lattice constant a and larger tetragonal c-axis and can be well described by assuming the parent average vacancy disordered structure (I4/mmm space group) with the refined stoichiometry Rb(0.60(5))(Fe(1.10(5))Se)(2). The minority phase amounts to 8-10% mass fraction. The unit cell volume of the minority phase is 3.2% smaller than the one of the main phase at T = 2 K and has quite different temperature dependence. The minority phase merges with the main vacancy ordered phase on heating above the phase separation temperature T(P) = 475 K. The spatial dimensions of the phase domains strongly increase above T(P) from 1000 to >2500 Å due to the integration of the regions of the main phase that were separated by the second phase at low temperatures. Additional annealing of the crystals at a temperature T = 488 K, close to T(P), for a long time drastically reduces the amount of the minority phase.

Self-assembled PCBM bilayers on graphene and HOPG examined by AFM and STM

NASA Astrophysics Data System (ADS)

Li, Yanlong; Chen, Chuanhui; Burton, John; Park, Kyungwha; Heflin, James R.; Tao, Chenggang

2018-05-01

In this work we report fabrication and characterization of phenyl-C61-butyric acid methyl ester (PCBM) bilayer structures on graphene and highly oriented pyrolytic graphite (HOPG). Through careful control of the PCBM solution concentration (from 0.1 to 2 mg ml-1) and the deposition conditions, we demonstrate that PCBM molecules self-assemble into bilayer structures on graphene and HOPG substrates. Interestingly, the PCBM bilayers are formed with two distinct heights on HOPG, but only one unique representative height on graphene. At elevated annealing temperatures, edge diffusion allows neighboring vacancies to merge into a more ordered structure. This is, to the best of our knowledge, the first experimental realization of PCBM bilayer structures on graphene. This work could provide valuable insight into fabrication of new hybrid, ordered structures for applications to organic solar cells.

Self-assembled PCBM bilayers on graphene and HOPG examined by AFM and STM.

PubMed

Li, Yanlong; Chen, Chuanhui; Burton, John; Park, Kyungwha; Heflin, James R; Tao, Chenggang

2018-05-04

In this work we report fabrication and characterization of phenyl-C61-butyric acid methyl ester (PCBM) bilayer structures on graphene and highly oriented pyrolytic graphite (HOPG). Through careful control of the PCBM solution concentration (from 0.1 to 2 mg ml -1 ) and the deposition conditions, we demonstrate that PCBM molecules self-assemble into bilayer structures on graphene and HOPG substrates. Interestingly, the PCBM bilayers are formed with two distinct heights on HOPG, but only one unique representative height on graphene. At elevated annealing temperatures, edge diffusion allows neighboring vacancies to merge into a more ordered structure. This is, to the best of our knowledge, the first experimental realization of PCBM bilayer structures on graphene. This work could provide valuable insight into fabrication of new hybrid, ordered structures for applications to organic solar cells.

Electrostatic nanolithography in polymer materials: an alternative technique for nanostructures formation

NASA Astrophysics Data System (ADS)

Lyuksyutov, Sergei F.; Paramonov, Pavel B.; Sigalov, Grigori; Vaia, Richard A.; Juhl, Shane; Sancaktar, Erol

2003-10-01

The combination of localized softening attolitres (10^2 -10^4) of polymer film by Jule heating, extremely non-uniform electric field gradients to polarize and manipulate the soften polymer, and single step technique using conventional atomic force microscopy (AFM), establishes a new paradigm for nanolithography in a broad class of polymer materials allowing rapid (order of milliseconds) creation of raised and depressed nanostructures without external heating of a polymer film of AFM tip-film contact [1]. In this work we present recent studies of AFM-assisted electrostatic nanolithography (AFMEN) such as amplitude-modulated AFMEN, and the humidity influence on nanostructures formation during contact mode AFMEN. It has been shown that the aspect ratio of nanostructures grows on the order of magnitude (0.2), while the lateral dimensions of nanodots decreases down to 10-15 nm. [1] S.F. Lyuksyutov, R.A. Vaia, P.B. Paramonov, S. Juhl, L. Waterhouse, R.M. Ralich, G. Sigalov, and E. Sancaktar, "Electrostatic nanolithography in polymers using atomic force microscopy," Nature Materials 2, 468-472 (2003)

Mechanical properties of monolayer graphene oxide.

PubMed

Suk, Ji Won; Piner, Richard D; An, Jinho; Ruoff, Rodney S

2010-11-23

Mechanical properties of ultrathin membranes consisting of one layer, two overlapped layers, and three overlapped layers of graphene oxide platelets were investigated by atomic force microscopy (AFM) imaging in contact mode. In order to evaluate both the elastic modulus and prestress of thin membranes, the AFM measurement was combined with the finite element method (FEM) in a new approach for evaluating the mechanics of ultrathin membranes. Monolayer graphene oxide was found to have a lower effective Young's modulus (207.6 ± 23.4 GPa when a thickness of 0.7 nm is used) as compared to the value reported for "pristine" graphene. The prestress (39.7-76.8 MPa) of the graphene oxide membranes obtained by solution-based deposition was found to be 1 order of magnitude lower than that obtained by others for mechanically cleaved graphene. The novel AFM imaging and FEM-based mapping methods presented here are of general utility for obtaining the elastic modulus and prestress of thin membranes.

A diamond-based scanning probe spin sensor operating at low temperature in ultra-high vacuum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schaefer-Nolte, E.; Wrachtrup, J.; 3rd Institute of Physics and Research Center SCoPE, University Stuttgart, 70569 Stuttgart

2014-01-15

We present the design and performance of an ultra-high vacuum (UHV) low temperature scanning probe microscope employing the nitrogen-vacancy color center in diamond as an ultrasensitive magnetic field sensor. Using this center as an atomic-size scanning probe has enabled imaging of nanoscale magnetic fields and single spins under ambient conditions. In this article we describe an experimental setup to operate this sensor in a cryogenic UHV environment. This will extend the applicability to a variety of molecular systems due to the enhanced target spin lifetimes at low temperature and the controlled sample preparation under UHV conditions. The instrument combines amore » tuning-fork based atomic force microscope (AFM) with a high numeric aperture confocal microscope and the facilities for application of radio-frequency (RF) fields for spin manipulation. We verify a sample temperature of <50 K even for strong laser and RF excitation and demonstrate magnetic resonance imaging with a magnetic AFM tip.« less

Versatile variable temperature and magnetic field scanning probe microscope for advanced material research

NASA Astrophysics Data System (ADS)

Jung, Jin-Oh; Choi, Seokhwan; Lee, Yeonghoon; Kim, Jinwoo; Son, Donghyeon; Lee, Jhinhwan

2017-10-01

We have built a variable temperature scanning probe microscope (SPM) that covers 4.6 K-180 K and up to 7 T whose SPM head fits in a 52 mm bore magnet. It features a temperature-controlled sample stage thermally well isolated from the SPM body in good thermal contact with the liquid helium bath. It has a 7-sample-holder storage carousel at liquid helium temperature for systematic studies using multiple samples and field emission targets intended for spin-polarized spectroscopic-imaging scanning tunneling microscopy (STM) study on samples with various compositions and doping conditions. The system is equipped with a UHV sample preparation chamber and mounted on a two-stage vibration isolation system made of a heavy concrete block and a granite table on pneumatic vibration isolators. A quartz resonator (qPlus)-based non-contact atomic force microscope (AFM) sensor is used for simultaneous STM/AFM operation for research on samples with highly insulating properties such as strongly underdoped cuprates and strongly correlated electron systems.

Terahertz Nanofocusing with Cantilevered Terahertz-Resonant Antenna Tips.

PubMed

Mastel, Stefan; Lundeberg, Mark B; Alonso-González, Pablo; Gao, Yuanda; Watanabe, Kenji; Taniguchi, Takashi; Hone, James; Koppens, Frank H L; Nikitin, Alexey Y; Hillenbrand, Rainer

2017-11-08

We developed THz-resonant scanning probe tips, yielding strongly enhanced and nanoscale confined THz near fields at their tip apex. The tips with length in the order of the THz wavelength (λ = 96.5 μm) were fabricated by focused ion beam (FIB) machining and attached to standard atomic force microscopy (AFM) cantilevers. Measurements of the near-field intensity at the very tip apex (25 nm radius) as a function of tip length, via graphene-based (thermoelectric) near-field detection, indicate their first and second order geometrical antenna resonances for tip length of 33 and 78 μm, respectively. On resonance, we find that the near-field intensity is enhanced by one order of magnitude compared to tips of 17 μm length (standard AFM tip length), which is corroborated by numerical simulations that further predict remarkable intensity enhancements of about 10 7 relative to the incident field. Because of the strong field enhancement and standard AFM operation of our tips, we envision manifold and straightforward future application in scattering-type THz near-field nanoscopy and THz photocurrent nanoimaging, nanoscale nonlinear THz imaging, or nanoscale control and manipulation of matter employing ultrastrong and ultrashort THz pulses.

Room temperature magnetism and metal to semiconducting transition in dilute Fe doped Sb1-xSex semiconducting alloy thin films

NASA Astrophysics Data System (ADS)

Agrawal, Naveen; Sarkar, Mitesh; Chawda, Mukesh; Ganesan, V.; Bodas, Dhananjay

2015-02-01

The magnetism was observed in very dilute Fe doped alloy thin film Fe0.008Sb1-xSex, for x = 0.01 to 0.10. These thin films were grown on silicon substrate using thermal evaporation technique. Structural, electrical, optical, charge carrier concentration measurement, surface morphology and magnetic properties were observed using glancing incidence x-ray diffraction (GIXRD), four probe resistivity, photoluminescence, Hall measurement, atomic force microscopy (AFM) and magnetic force microscopy (MFM) techniques, respectively. No peaks of iron were seen in GIXRD. The resistivity results show that activation energy increases with increase in selenium (Se) concentration. The Arrhenius plot reveals metallic behavior below room temperature. The low temperature conduction is explained by variable range-hopping mechanism, which fits very well in the temperature range 150-300 K. The decrease in density of states has been observed with increasing selenium concentration (x = 0.01 to 0.10). There is a metal-to-semiconductor phase transition observed above room temperature. This transition temperature is Se concentration dependent. The particle size distribution ˜47-61 nm is evaluated using AFM images. These thin films exhibit ferromagnetic interactions at room temperature.

Influence of grain orientation on the incipient oxidation behavior of Haynes 230 at 900 °C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xu, E-mail: xuw388@mail.usask.ca; Fan, Fan; Szpunar, Jerzy A.

Ni-based superalloy Haynes 230 is used in many applications such as very high temperature reactor (VHTR) or solid oxide fuel cells (SOFCs) where it is exposed to high temperature service environment. In order to improve the resistance for high temperature oxidation, the effect of crystallographic orientation on the early stage oxidation was investigated. It was demonstrated that different oxide thicknesses are formed on grains having different orientations. Comparison of electron backscatter diffraction (EBSD) orientation maps before and after oxidation at 900 °C indicates that grains near (111) orientation, especially with the deviation angle from <111> that is smaller than 20°,more » are more oxidation resistant than grains of other orientations. Correlation between the results of electron backscatter diffraction (EBSD) and atomic force microscopy (AFM) was used to compare the oxidation rate of grains having different crystallographic orientation. The oxidation rate was found to change with the crystallographic orientation as follows (111) < (110) < (100), also it was demonstrated that the oxidation rate changes are a nearly linear function of the angle of deviation from <111> direction. The morphology of surface oxide also depends on the orientation of grains. - Highlights: • Comparison of EBSD maps before and after oxidation allows to investigate the effect of orientation on oxidation in a more direct way; • Effect of crystallographic orientation on oxidation behavior of alloy 230 is studied by combination of EBSD and AFM; • Different thickness of oxide is formed on grain with different orientation and dependence of anisotropic oxidation behavior is discussed; • The morphology of grains is also orientation dependence.« less

Exchange-coupling of hard and soft magnetic sublattices and magnetic anomalies in mixed spinel NiFe0.75Cr1.25O4 nanoparticles

NASA Astrophysics Data System (ADS)

Lyubutin, I. S.; Starchikov, S. S.; Baskakov, A. O.; Gervits, N. E.; Lin, Chun-Rong; Tseng, Yaw-Teng; Lee, Wen-Jen; Shih, Kun-Yauh

2018-04-01

A set of single-crystalline nanoparticles (NPs) of nickel-chromium ferrite NiFe0.75Cr1.25O4 with a cubic spinel structure were synthesized and investigated. The NPs size can be varied from about 5 to 50 nm by the final annealing of the precursor at different temperatures. The distribution of cations over the tetrahedral (A) and the octahedral [B] sites (Fe0.75 Ni0.25) [Ni0.75 Cr1.25] O4 was established from the magnetic and Mössbauer measurements. In large NPs, the magnetic structure at low temperatures is close to the collinear antiferromagnetic (AFM) structure of the Neel type; and the total magnetic moment Mtot of the ferrite coincides with the direction of the B-sublattice moment. Several size-dependent magnetic anomalies were revealed. Three types of magnetic ions present in the A- and B- sublattices cause the competition of AFM and FM exchange interactions resulting in the highly frustrated magnetic ordering and the occurrence of canted magnetic structure in the octahedral B-sublattice. The frustrated structure is very flexible and significantly subjected to temperature and applied field. It results in several magnetic anomalies observed, including the occurrence of magnetic compensation, abnormal behavior of ZFC and FC magnetization curves and hysteresis loops. It was shown that magnetic anomalies can be explained in terms of exchange coupling of "soft" and "hard" magnetic B- and A-sublattices. This effect in the (Fe0.75 Ni0.25) [Ni0.75Cr1.25] O4 NPs can be considered as an atomic-scale analog of a similar effect observed in two-phase exchange-coupled alloys developed for permanent magnets and for the perpendicular recoding media.

Silane coupling agent for attaching fusion-bonded epoxy to steel.

PubMed

Tchoquessi Diodjo, Madeleine R; Belec, Lénaïk; Aragon, Emmanuel; Joliff, Yoann; Lanarde, Lise; Perrin, François-Xavier

2013-07-24

We describe the possibility of using γ-aminopropyltriethoxysilane (γ-APS) to increase the durability of epoxy powder coating/steel joints. The curing temperature of epoxy powder coatings is frequently above 200 °C, which is seen so far as a major limitation for the use of the heat-sensitive aminosilane coupling agent. Despite this limitation, we demonstrate that aminosilane is a competitive alternative to traditional chromate conversion to enhance the durability of epoxy powder coatings/steel joints. Fourier-transform reflection-absorption infrared spectroscopy (FT-RAIRS), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) were used to identify the silane deposition conditions that influence the adhesion of epoxy powder coatings on steel. We show that AFM analysis provides highly sensitive measurements of mechanical property development and, as such, the degree of condensation of the silane. The joint durability in water at 60 °C was lower when the pH of the γ-APS solution was controlled at 4.6 using formic acid, rather than that at natural pH (10.6). At the curing temperature of 220 °C, oxidation of the carbon adjacent to the amine headgroup of γ-APS gives amide species by a pseudofirst-order kinetics. However, a few amino functionalities remain to react with oxirane groups of epoxy resin and, thus, strengthen the epoxy/silane interphase. The formation of ammonium formate in the acidic silane inhibits the reaction between silane and epoxy, which consequently decreases the epoxy/silane interphase cohesion. We find that the nanoroughness of silane deposits increases with the cure temperature which is beneficial to the wet stability of the epoxy/steel joints, due to increased mechanical interlocking.

Development and characterization of a layer by layer ultrasound assisted spray deposition process for thin polymer films

NASA Astrophysics Data System (ADS)

Balakrishnan, Anandh

An Ultrasound assisted Atomization (UA) system has been developed and investigated to synthesize ˜20microm polyurethane thin films with uniform, repeatable thickness and microstructure. The UA system comprised a 20 kHz atomizer probe mounted on 750 W/cm2 transducer, a heated glass chamber and a rotating substrate. The rationale for the work has been built through a careful Design of Experiments (DoE) that sought to answer questions regarding the process-microstructure relationships from both the spray and material points of view. The independent variables chosen were the polymer solution weight percentage (0.2%, 2%, and 4%), power amplitude (energy) percentage supplied to the nozzle (23%, 29%, 37%, and 46%),the temperature of deposition (45°C, 80°C) and flow rate (50microL/min, 150microL/min). The research questions focused on influence of the process parameters on the microstructure and properties of the film. One of the problems involved fixing the trajectory of the spray and also making use of the droplet surfaces created by the spray. To achieve this, a simple air-draft attachment was devised and the influence of the same was evaluated through process and film characterization experiments. A mechanism for the draft has been schematically provided. The use of such a draft to fabricate thin polymer films via ultrasound atomization has not been achieved before and represents a 'first step' in advancing this ultrasound technology. The primary findings of the work were that the film microstructure and properties were heavily influenced by the flow rate, energy of atomization, and test temperature. In addition, the droplet diameters seemed to be readily amenable to change for the 0.2 and 2% solutions and the use of the air-draft made the process feasible, repeatable and accurate. For the 4% solutions, viscosity seemed to stabilize the liquid solution film at the tip requiring larger energies of atomization. In all, relative to the 0.2% films the fracture strengths, strains and toughness values had improved vastly for 4% and 2%. Calorimetric, Small Angle X-ray scattering and Atomic Force Microscopy (AFM) measurements showed a largely phase mixed hard segment-soft segment morphology. Calorimetry showed that the 0.2% specimens showed higher melting points (between 110--130°C) indicative of greater hard domain ordering in these samples. This is not evident in the 2% and 4% samples. This trend is supported by the Small Angle X-ray scattering and AFM data. The X-ray data show larger domain sizes and greater invariants for the 0.2% samples relative to the 2% and 4% samples. The AFM phase image measurements provided hard domain widths in the same range as the X-ray measurements (10--11 nm). All of the topographical trends from AFM showed that surface morphology was affected by i) increasing atomization energies from 29%--46% of energy (decreased surface roughness from 3 nm to 2 nm for 2% films and 1 nm to 0.5 nm for 4% films); ii) increasing film fabrication temperature from 45°C--80°C (increased roughness from 3nm to 4--5nm in local spots for 2% films and from 0.5nm to 0.6 nm for 4% films), iii) decreasing flow rate of the pump from 150microL/min to 50microL/min (comparable roughness for the case of the 2% films from 3nm to 2nm). These could explain the trends in mechanical responses as a f( energy of atomization and temperature). In order to examine sample crystallinity, we performed Wide Angle X-ray Scattering which showed a fully amorphous polymer structure. The lack of any reflections indicated that the melting points observed from calorimetry were not due to long range order in the material but due to pseudo crystalline behavior. This behavior could be ascribed to the formation of urethane-urethane ordering with hydrogen bonds between them. In general, ultrasonic energy of the capillary wave causes phase mixing and the extent of phase mixing was dependent on the weight percentage of polymer solution and the type of solvent. It was highest for the 4% samples and lowest for the 0.2% samples.

Characterization of sputtering deposited NiTi shape memory thin films using a temperature controllable atomic force microscope

NASA Astrophysics Data System (ADS)

He, Q.; Huang, W. M.; Hong, M. H.; Wu, M. J.; Fu, Y. Q.; Chong, T. C.; Chellet, F.; Du, H. J.

2004-10-01

NiTi shape memory thin films are potentially desirable for micro-electro-mechanical system (MEMS) actuators, because they have a much higher work output per volume and also a significantly improved response speed due to a larger surface-to-volume ratio. A new technique using a temperature controllable atomic force microscope (AFM) is presented in order to find the transformation temperatures of NiTi shape memory thin films of micrometer size, since traditional techniques, such as differential scanning calorimetry (DSC) and the curvature method, have difficulty in dealing with samples of such a scale as this. This technique is based on the surface relief phenomenon in shape memory alloys upon thermal cycling. The reliability of this technique is investigated and compared with the DSC result in terms of the transformation fraction (xgr). It appears that the new technique is nondestructive, in situ and capable of characterizing sputtering deposited very small NiTi shape memory thin films.

Nanostructured vanadium oxide thin film with high TCR at room temperature for microbolometer

NASA Astrophysics Data System (ADS)

Wang, Bin; Lai, Jianjun; Li, Hui; Hu, Haoming; Chen, Sihai

2013-03-01

In order to obtain high quality of thermal sensitive material, VOx thin film of high temperature coefficient of resistance (TCR) of 6.5%/K at room temperature has been deposited by reactive ion beam sputtering and post annealing method. AFM and XRD measurements indicate that the VOx thin film with nanostructured crystalline is composed of VO2 and V2O3. The nanostructured VOx microbolometer has been designed and fabricated. The measurement of the film system with TiN absorbing layer indicates that it has about 92% infrared absorption in the range of 8-14 μm. The performance of this bolometer, comparing with that of bolometer with common VOx, has a better result. At 20 Hz frequency and 10 μA bias current, the bolometer with high TCR has reached detectivity of 1.0 × 109 cm Hz1/2/W. It also indicates that this nanostructured VOx thin film has not only a higher TCR but also a lower noise than common VOx thin film without annealing.

Strong magnetic coupling in the hexagonal R5Pb3 compounds (R=Gd-Tm)

NASA Astrophysics Data System (ADS)

Marcinkova, Andrea; de la Cruz, Clarina; Yip, Joshua; Zhao, Liang L.; Wang, Jiakui K.; Svanidze, E.; Morosan, E.

2015-06-01

We have synthesized the R5Pb3 (R=Gd-Tm) compounds in polycrystalline form and performed neutron scattering and magnetization measurements. For all R5Pb3 reported here the Weiss temperatures θW are several times smaller than the ordering temperatures TORD, while the latter are remarkably high (TORD up to 275 K for R=Gd) compared to other known R-M binaries (M=Si, Ge, Sn and Sb). The magnetic order changes from ferromagnetic (FM) in R=Gd, Tb to antiferromagnetic (AFM) in R=Dy-Tm. Below TORD, the magnetization measurements together with neutron powder diffraction show complex magnetic behaviors and reveal the existence of up to three additional phase transitions, believed to be a result of large anisotropic exchange and/or crystal electric field effects, induced high anisotropy. The R5Pb3 magnetic unit cells for R=Tb-Tm can be described with incommensurate magnetic wave vectors with spin modulation either along the c axis in R=Tb, Er and Tm, or within the ab plane in R=Dy and Ho.

Various nanoparticle morphologies and surface properties of waterborne polyurethane controlled by water

PubMed Central

Zhou, Xing; Fang, Changqing; Lei, Wanqing; Du, Jie; Huang, Tingyi; Li, Yan; Cheng, Youliang

2016-01-01

Water plays important roles in organic reactions such as polyurethane synthesis, and the aqueous solution environment affects polymer morphology and other properties. This paper focuses on the morphology and surface properties of waterborne polyurethane resulting from the organic reaction in water involving different forms (solid and liquid), temperatures and aqueous solutions. We provide evidence from TEM observations that the appearance of polyurethane nanoparticles in aqueous solutions presents diverse forms, including imperfect spheres, perfect spheres, perfect and homogenous spheres and tubes. Based on the results on FTIR, GPC, AFM and XRD experiments, we suggest that the shape of the nanoparticles may be decided by the crimp degree (i.e., the degree of polyurethane chains intertangling in the water environment) and order degree, which are determined by the molecular weight (Mn) and hydrogen bonds. Meanwhile, solid water and high-temperature water can both reduce hard segments that gather on the polyurethane film surface to reduce hydrophilic groups and produce a soft surface. Our findings show that water may play key roles in aqueous polymer formation and bring order to molecular chains. PMID:27687001

Coercivity and Exchange Bias Study of Polycrystalline Hollow Nanoparticles

NASA Astrophysics Data System (ADS)

Bah, Mohamed Alpha

Magnetic nanoparticles (NPs) have the potential to be useful in a variety of applications such as biomedical instruments, catalysis, sensing, recording information, etc. These nanoparticles exhibit remarkably different properties compared to their bulk counter parts. Synthesis of magnetic NPs with the right morphology, phase, size and surface functionality, as well as their usage for specific applications are challenging in terms of efficiency and safety. Morphology wise, there have been numerous reports on magnetic nanoparticles where morphologies such as core/shell, hollow, solid, etc., have been explored. It has been shown that morphology affects the magnetic response. Achieving the right crystal structure with required morphology and the magnetic behavior of the nanoparticle phases determines the magnetic response of the structure. For example, in the case of core/shell NPs various ferromagnetic (FM), ferrimagnetic (FiM), and antiferromagnetic (AFM) core and shell combinations have been reported. In these cases, interesting and strikingly different features, such as unusually high spin glass transition temperature, large exchange bias, finite size effects, magnetic proximity effects, unusual trend of blocking temperature as function of average crystal size, etc., have been reported. More specifically, the morphology of core/shell nanoparticles provides added degrees of freedom compared to conventional solid magnetic nanoparticles, including variations in the size, phase and material of the core and shell of the particle, etc. which helps enhance their magnetic properties. Similar to traditional core/shell nanoparticles, inverted core/shell having a FiM or FM order above the Curie temperature (TC) of the shell has been reported where the Neel temperature (TN) is comparable with the bulk value and there is nonmonotonic dependence of the coercive field (HC) and exchange bias (HEB) on the core diameter. In addition to the core/shell morphology, nanoparticles with hollow morphology are also of interest to the scientific community. For such cases, surface spin glass transition enhancements have been reported due to the presence of the additional inner surface. CoFe2O4, NiFe 2O4 and gamma-Fe2O3 hollow nanoparticles exhibit strikingly contrasting magnetic behavior compared to bulk and conventional solid particles; similar behavior was also observed in core/shell nanoparticles. Structurally, hollow polycrystalline nanoparticles are composed of multiple crystallographic domains. This random orientation of the crystallographic domains also causes randomization of the local anisotropy axes. Hence the overall effect of this morphology on the magnetic properties is exhibited through the high coercivity, relatively high temperature magnetic irreversibility, lack of magnetic saturation, high blocking temperature, etc. Over the years, extensive work on core/shell nanoparticles have been carried out to understand their exchange bias phenomenon and the effect on coercivity. Recently, focus has been given to hollow polycrystalline nanoparticles for the reason mentioned above. This thesis investigates the root cause for the above-mentioned effects on the coercivity and exchange bias. Since hollow nanoparticles with polycrystalline structure have shown to exhibit different and improved magnetic behavior compared to bulk and other conventional solid particles, they will be the focus of our investigation. First, extensive field and temperature dependent magnetic study on polycrystalline hollow nickel ferrite (NiFe2O4) have revealed the effect of the presence of inner surface in a single oxide nanoparticle. Second, the effect of having multiple oxides with different magnetic properties (i.e. FM and AFM) in a single nanoparticle, while maintaining a hollow morphology was investigated by studying polycrystalline hollow gamma-Mn2O3 and MnO nanoparticles. Studies on various conventional solid manganese oxide nanoparticles have already been reported. Therefore, focus was only made on the fabrication and magnetic study of hollow polycrystalline manganese oxide, with a comparison of the results to those from solid nanoparticles already available in literature. A conclusion was drawn to the importance of the coupling of different magnetic phases (i.e. FM and AFM, FiM and AFM, or SG and AFM), in contrast to just having one single oxide in the hollow nanoparticles. Finally, the importance of this coupling as compared to the increase of surface-to-volume ratio was evaluated in CoO/Co3O4/CoFe2O4 polycrystalline hollow nanoparticles by varying the AFM phase (CoO/Co 3O4) in the nanoparticles and observing how the magnetic properties varied. This system helped address the effect of the coupling between different magnetic phases, super-exchange interaction, and proximity effect.

Magnetic, Electrical and Dielectric Properties of LaMnO3+η Perovskite Manganite.

NASA Astrophysics Data System (ADS)

v, Punith Kumar; Dayal, Vijaylakshmi

The high pure polycrystalline LaMnO3+η perovskite manganite has been synthesized using conventional solid state reaction method. The studied sample crystallizes into orthorhombic O', phase indexed with Pbnm space group. The magnetization measurement exhibits that the studied sample shows paramagnetic (PM) to ferromagnetic (FM) phase transition at TC = 191.6K followed with a frustration due to antiferromagnetic (AFM) kind of spin ordering at low temperature, Tf = 85.8K. The electrical resistivity measurements carried out at 0 tesla and 8 tesla magnetic field exhibits insulating kind of behavior throughout the measured temperature range. The resistivity at 0 tesla exhibits low temperature FM insulator to high temperature PM insulator type phase transition at TC = 191.6K similarly as observed from magnetization measurement. The application of the magnetic field (8 tesla) shifts TC to higher temperature side and the charge transport follows Shklovskii Efros variable range hopping (SE VRH) mechanism. The temperature and frequency dependent dielectric permittivity studied for the sample exhibits relaxation process explained based on Debye +Maxwell-Wagner relaxation mechanism. Department of Atomic Energy-Board of Research in Nuclear Sciences, Government of INDIA.

Nonlinear optical parameters of nanocrystalline AZO thin film measured at different substrate temperatures

NASA Astrophysics Data System (ADS)

Jilani, Asim; Abdel-wahab, M. Sh; Al-ghamdi, Attieh A.; Dahlan, Ammar sadik; Yahia, I. S.

2016-01-01

The 2.2 wt% of aluminum (Al)-doped zinc oxide (AZO) transparent and preferential c-axis oriented thin films were prepared by using radio frequency (DC/RF) magnetron sputtering at different substrate temperature ranging from room temperature to 200 °C. For structural analysis, X-ray Diffraction (XRD) and Atomic Force Electron Microscope (AFM) was used for morphological studies. The optical parameters such as, optical energy gap, refractive index, extinction coefficient, dielectric loss, tangent loss, first and third order nonlinear optical properties of transparent films were investigated. High transmittance above 90% and highly homogeneous surface were observed in all samples. The substrate temperature plays an important role to get the best transparent conductive oxide thin films. The substrate temperature at 150 °C showed the growth of highly transparent AZO thin film. Energy gap increased with the increased in substrate temperature of Al doped thin films. Dielectric constant and loss were found to be photon energy dependent with substrate temperature. The change in substrate temperature of Al doped thin films also affect the non-liner optical properties of thin films. The value of χ(3) was found to be changed with the grain size of the thin films that directly affected by the substrate temperature of the pure and Al doped ZnO thin films.

Construction of three-dimensional DNA hydrogels from linear building blocks.

PubMed

Nöll, Tanja; Schönherr, Holger; Wesner, Daniel; Schopferer, Michael; Paululat, Thomas; Nöll, Gilbert

2014-08-04

A three-dimensional DNA hydrogel was generated by self-assembly of short linear double-stranded DNA (dsDNA) building blocks equipped with sticky ends. The resulting DNA hydrogel is thermoresponsive and the length of the supramolecular dsDNA structures varies with temperature. The average diffusion coefficients of the supramolecular dsDNA structures formed by self-assembly were determined by diffusion-ordered NMR spectroscopy (DOSY NMR) for temperatures higher than 60 °C. Temperature-dependent rheological measurements revealed a gel point of 42±1 °C. Below this temperature, the resulting material behaved as a true gel of high viscosity with values for the storage modulus G' being significantly larger than that for the loss modulus G''. Frequency-dependent rheological measurements at 20 °C revealed a mesh size (ξ) of 15 nm. AFM analysis of the diluted hydrogel in the dry state showed densely packed structures of entangled chains, which are also expected to contain multiple interlocked rings and catenanes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High viscosity environments: an unexpected route to obtain true atomic resolution with atomic force microscopy.

PubMed

Weber, Stefan A L; Kilpatrick, Jason I; Brosnan, Timothy M; Jarvis, Suzanne P; Rodriguez, Brian J

2014-05-02

Atomic force microscopy (AFM) is widely used in liquid environments, where true atomic resolution at the solid-liquid interface can now be routinely achieved. It is generally expected that AFM operation in more viscous environments results in an increased noise contribution from the thermal motion of the cantilever, thereby reducing the signal-to-noise ratio (SNR). Thus, viscous fluids such as ionic and organic liquids have been generally avoided for high-resolution AFM studies despite their relevance to, e.g. energy applications. Here, we investigate the thermal noise limitations of dynamic AFM operation in both low and high viscosity environments theoretically, deriving expressions for the amplitude, phase and frequency noise resulting from the thermal motion of the cantilever, thereby defining the performance limits of amplitude modulation, phase modulation and frequency modulation AFM. We show that the assumption of a reduced SNR in viscous environments is not inherent to the technique and demonstrate that SNR values comparable to ultra-high vacuum systems can be obtained in high viscosity environments under certain conditions. Finally, we have obtained true atomic resolution images of highly ordered pyrolytic graphite and mica surfaces, thus revealing the potential of high-resolution imaging in high viscosity environments.

Spin pumping and inverse spin Hall effects in heavy metal/antiferromagnet/Permalloy trilayers

NASA Astrophysics Data System (ADS)

Saglam, Hilal; Zhang, Wei; Jungfleisch, M. Benjamin; Jiang, Wanjun; Pearson, John E.; Hoffmann, Axel

Recent work shows efficient spin transfer via spin waves in insulating antiferromagnets (AFMs), suggesting that AFMs can play a more active role in the manipulation of ferromagnets. We use spin pumping and inverse spin Hall effect experiments on heavy metal (Pt and W)/AFMs/Py (Ni80Fe20) trilayer structures, to examine the possible spin transfer phenomenon in metallic AFMs, i . e . , FeMn and PdMn. Previous work has studied electronic effects of the spin transport in these materials, yielding short spin diffusion length on the order of 1 nm. However, the work did not examine whether besides diffusive spin transport by the conduction electrons, there are additional spin transport contributions from spin wave excitations. We clearly observe spin transport from the Py spin reservoir to the heavy metal layer through the sandwiched AFMs with thicknesses well above the previously measured spin diffusion lengths, indicating that spin transport by spin waves may lead to non-negligible contributions This work was supported by US DOE, OS, Materials Sciences and Engineering Division. Lithographic patterning was carried out at the CNM, which is supported by DOE, OS under Contract No. DE-AC02-06CH11357.

High viscosity environments: an unexpected route to obtain true atomic resolution with atomic force microscopy

NASA Astrophysics Data System (ADS)

Weber, Stefan A. L.; Kilpatrick, Jason I.; Brosnan, Timothy M.; Jarvis, Suzanne P.; Rodriguez, Brian J.

2014-05-01

Atomic force microscopy (AFM) is widely used in liquid environments, where true atomic resolution at the solid-liquid interface can now be routinely achieved. It is generally expected that AFM operation in more viscous environments results in an increased noise contribution from the thermal motion of the cantilever, thereby reducing the signal-to-noise ratio (SNR). Thus, viscous fluids such as ionic and organic liquids have been generally avoided for high-resolution AFM studies despite their relevance to, e.g. energy applications. Here, we investigate the thermal noise limitations of dynamic AFM operation in both low and high viscosity environments theoretically, deriving expressions for the amplitude, phase and frequency noise resulting from the thermal motion of the cantilever, thereby defining the performance limits of amplitude modulation, phase modulation and frequency modulation AFM. We show that the assumption of a reduced SNR in viscous environments is not inherent to the technique and demonstrate that SNR values comparable to ultra-high vacuum systems can be obtained in high viscosity environments under certain conditions. Finally, we have obtained true atomic resolution images of highly ordered pyrolytic graphite and mica surfaces, thus revealing the potential of high-resolution imaging in high viscosity environments.

Atomic force microscopy imaging of macromolecular complexes.

PubMed

Santos, Sergio; Billingsley, Daniel; Thomson, Neil

2013-01-01

This chapter reviews amplitude modulation (AM) AFM in air and its applications to high-resolution imaging and interpretation of macromolecular complexes. We discuss single DNA molecular imaging and DNA-protein interactions, such as those with topoisomerases and RNA polymerase. We show how relative humidity can have a major influence on resolution and contrast and how it can also affect conformational switching of supercoiled DNA. Four regimes of AFM tip-sample interaction in air are defined and described, and relate to water perturbation and/or intermittent mechanical contact of the tip with either the molecular sample or the surface. Precise control and understanding of the AFM operational parameters is shown to allow the user to switch between these different regimes: an interpretation of the origins of topographical contrast is given for each regime. Perpetual water contact is shown to lead to a high-resolution mode of operation, which we term SASS (small amplitude small set-point) imaging, and which maximizes resolution while greatly decreasing tip and sample wear and any noise due to perturbation of the surface water. Thus, this chapter provides sufficient information to reliably control the AFM in the AM AFM mode of operation in order to image both heterogeneous samples and single macromolecules including complexes, with high resolution and with reproducibility. A brief introduction to AFM, its versatility and applications to biology is also given while providing references to key work and general reviews in the field.

Experimental investigations on potassium permanganate doped polyvinyl alcohol - polyvinyl pyrrolidone blend

NASA Astrophysics Data System (ADS)

Veena, G.; Lobo, Blaise

2018-04-01

Potassium permanganate (KMnO4) doped polyvinyl alcohol (PVA) - polyvinyl pyrrolidone (PVP) blend films were prepared by solution casting technique, in the doping range varying from 0.01 wt % up to 4.70 wt %. The microstructural changes caused by doping, and the modified properties of these films were studied using Atomic Force Microscope (AFM) and temperature dependent direct current (DC) electrical measurements. Temperature variation of electrical resistivity was found to obey Arrhenius relation, from which activation energy was determined. The study was supported by AFM scans, which showed an increase in surface roughness and the presence of spike-like structures, due to interaction of dopant with the polymeric blend. Differential Scanning Calorimetry (DSC) scans revealed two stages of degradation in KMnO4 doped PVA - PVP blend films.

Transport and magnetic properties of Fe doped CaMnO3

NASA Astrophysics Data System (ADS)

Neetika; Das, A.; Dhiman, I.; Nigam, A. K.; Yadav, A. K.; Bhattacharyya, D.; Meena, S. S.

2012-12-01

The structural, transport, and magnetic properties of CaMn1-xFexO3-δ (0.0 ≤ x ≤ 0.3) have been studied by using resistivity, magnetization, and neutron powder diffraction techniques. The compounds are found to be isostructural and crystallize in GdFeO3-type orthorhombic structure (space group Pnma). With Fe doping, no structural change is observed. Mössbauer and paramagnetic susceptibility measurements show that Fe substitutes in 4+ valence state, and XANES measurements indicate the presence of mixed valence state of Mn. The compounds exhibit insulating behavior in the studied temperature range. The temperature dependence of resistivity is found to be described by small polaron model for x = 0 and variable range hopping model for x = 0.1. For higher x values, it follows a parallel combination resistance model. A small reduction in TN from 120 K to 100 K with increase in x is found. The magnetic structure changes from Gz-type collinear antiferromagnetic (AFM) structure for x = 0.0 to canted AFM structure GZFY-type for Fe doped compounds. The AFM component of the moment progressively decreases with x while FM component exhibits a maximum at x = 0.2.

Magnetic ordering in intermetallic La1-xTbxMn2Si2 compounds

NASA Astrophysics Data System (ADS)

Korotin, Dm. M.; Streltsov, S. V.; Gerasimov, E. G.; Mushnikov, N. V.; Zhidkov, I. S.; Kukharenko, A. I.; Finkelstein, L. D.; Cholakh, S. O.; Kurmaev, E. Z.

2018-05-01

The magnetic structures and magnetic phase transitions in intermetallic layered La1-xTbxMn2Si2 compounds (the ThCr2Si2-type structure) are investigated using the first-principles method and XPS measurements. The experimentally observed transition from ferromagnetic (FM) to antiferromagnetic (AFM) ordering of Mn sublattice with increase of terbium concentration is successfully reproduced in calculations for collinear magnetic moments model. The FM →AFM change of interplane magnetic ordering at small x is irrelevant to the number of f-electrons of the rare-earth ion. In contrast it was shown to be related to the Mn-Mn in-plane distance. Calculated Tb critical concentration for this transition x ≈ 0.14 corresponds to the Mn-Mn in-plane distance 0.289 nm, very close to the experimentally observed transition distance 0.287 nm. The crystal cell compression due to substitution increases an overlap between Mndxz,yz and the rare-earth ion d orbitals. Resulting hybridized states manifest themselves as an additional peak in the density of states. We suggest that a corresponding interlayer Mn-R-Mn superexchange interaction stabilizes AFM magnetic ordering in these compounds with Tb doping level x > 0.2 . The results of DFT calculations are in agreement with X-ray photoemission spectra for La1-xTbxMn2Si2 .

Some aspects of pulsed laser deposition of Si nanocrystalline films

NASA Astrophysics Data System (ADS)

Polyakov, B.; Petruhins, A.; Butikova, J.; Kuzmin, A.; Tale, I.

2009-11-01

Nanocrystalline silicon films were deposited by a picosecond laser ablation on different substrates in vacuum at room temperature. A nanocrystalline structure of the films was evidenced by atomic force microscopy (AFM), optical and Raman spectroscopies. A blue shift of the absorption edge was observed in optical absorption spectra, and a decrease of the optical phonon energy at the Brillouin zone centre was detected by Raman scattering. Early stages of nanocrystalline film formation on mica and HOPG substrates were studied by AFM. Mechanism of nanocrystal growth on substrate is discussed. in here

A review of the current situation of aflatoxin M1 in cow's milk in Serbia: risk assessment and regulatory aspects.

PubMed

Milićević, Dragan R; Spirić, Danka; Radičević, Tatjana; Velebit, Branko; Stefanović, Srdjan; Milojević, Lazar; Janković, Saša

2017-09-01

The aim of this systematic review is to provide information regarding the incidence and levels of aflatoxin M 1 (AFM 1 ) in raw and heat processed cow's milk in Serbia during 2015-16 and to compare these with collected data on the occurrence of AFM 1 in raw milk and dairy products during the last decade in our region. Estimation of dietary exposure (EDI) and hazard index (HI) calculations for different age groups of the population were also carried out, based on the AFM 1 content of milk samples and on available food consumption data in Serbia. AFM 1 was detected in 69.9% (984/1408) of raw milk samples in 2015 versus 84.9% (3094/3646) in 2016, while in heat-processed milk, AFM 1 was detected in 77.8% (364/468) in 2015 versus 98.5% (753/765) in 2016. On the basis of the obtained results, 450 (9%) of raw and 14 (1.1%) of heat-processed milk samples were contaminated with AFM 1 levels above the maximum permitted level in Serbia (0.25 μg kg -1 ). However, a large percentage of raw and heat processed milk in Serbia (30.1% and 17.3%, respectively) was contaminated with AFM 1 levels above the maximum permitted level regulated in the European Union (0.05 μg kg -1 ). Therefore, in order to protect consumer health, it is extremely important to further control the level of aflatoxins in milk, and this should be considered as a high priority for risk management actions.

Quench of paramagnetic orbital selective Mott phase and appearance of antiferromagnetic orbital selective slater phase in multiorbital correlated systems

NASA Astrophysics Data System (ADS)

Quan, Ya-Min; Liu, Da-Yong; Lin, Hai-Qing; Zou, Liang-Jian

2018-06-01

We present the modulation of magnetic order on the orbital selective Mott phases (OSMP) and the metal-insulator transitions (MIT) of multi-orbital Hubbard models by employing the rotationally invariant slave-boson methods. We show that at half filling, the well-known paramagnetic (PM) OSMP is completely covered by an antiferromagnetic (AFM) Slater insulator, and the PM Mott phase by an AFM Mott insulator when electron correlation strength varies from intermediate to strong both in two- and three-orbitals Hubbard systems. Away from half-filling, we find that a partial-polarized AFM orbital-selective Slater phase appears in the intermediate correlation regime, and an almost full-polarized AFM OSMP fully covers the paramagnetic OSMP. In addition, the ferromagnetic phase in the three-orbital case is more robust than that in the two-orbital case. These results demonstrate that the modulation of magnetic correlation to the quasiparticle spectra leads to much rich and more interesting MIT scenario in multiorbital correlated systems.

Electrical switching of antiferromagnets via strongly spin-orbit coupled materials

NASA Astrophysics Data System (ADS)

Li, Xi-Lai; Duan, Xiaopeng; Semenov, Yuriy G.; Kim, Ki Wook

2017-01-01

Electrically controlled ultra-fast switching of an antiferromagnet (AFM) is shown to be realizable by interfacing it with a material of strong spin-orbit coupling. The proximity interaction between the sublattice magnetic moments of a layered AFM and the spin-polarized free electrons at the interface offers an efficient way to manipulate antiferromagnetic states. A quantitative analysis, using the combination with a topological insulator as an example, demonstrates highly reliable 90° and 180° rotations of AFM magnetic states under two different mechanisms of effective torque generation at the interface. The estimated switching speed and energy requirement are in the ps and aJ ranges, respectively, which are about two-three orders of magnitude better than the ferromagnetic counterparts. The observed differences in the magnetization dynamics may explain the disparate characteristic responses. Unlike the usual precessional/chiral motions in the ferromagnets, those of the AFMs can essentially be described as a damped oscillator with a more direct path. The impact of random thermal fluctuations is also examined.

A study of phase defect measurement on EUV mask by multiple detectors CD-SEM

NASA Astrophysics Data System (ADS)

Yonekura, Isao; Hakii, Hidemitsu; Morisaki, Shinya; Murakawa, Tsutomu; Shida, Soichi; Kuribara, Masayuki; Iwai, Toshimichi; Matsumoto, Jun; Nakamura, Takayuki

2013-06-01

We have studied MVM (Multi Vision Metrology) -SEM® E3630 to measure 3D shape of defects. The four detectors (Detector A, B, C and D) are independently set up in symmetry for the primary electron beam axis. Signal processing of four direction images enables not only 2D (width) measurement but also 3D (height) measurement. At last PMJ, we have investigated the relation between the E3630's signal of programmed defect on MoSi-HT and defect height measured by AFM (Atomic Force Microscope). It was confirmed that height of integral profile by this tool is correlated with AFM. It was tested that E3630 has capability of observing multilayer defect on EUV. We have investigated correlation with AFM of width and depth or height of multilayer defect. As the result of observing programmed defects, it was confirmed that measurement result by E3630 is well correlated with AFM. And the function of 3D view image enables to show nm order defect.

Positive exchange-bias and giant vertical hysteretic shift in La0.3Sr0.7FeO3/SrRuO3 bilayers

PubMed Central

Rana, Rakesh; Pandey, Parul; Singh, R. P.; Rana, D. S.

2014-01-01

The exchange-bias effects in the mosaic epitaxial bilayers of the itinerant ferromagnet (FM) SrRuO3 and the antiferromagnetic (AFM) charge-ordered La0.3Sr0.7FeO3 were investigated. An uncharacteristic low-field positive exchange bias, a cooling-field driven reversal of positive to negative exchange-bias and a layer thickness optimised unusual vertical magnetization shift were all novel facets of exchange bias realized for the first time in magnetic oxides. The successive magnetic training induces a transition from positive to negative exchange bias regime with changes in domain configurations. These observations are well corroborated by the hysteretic loop asymmetries which display the modifications in the AFM spin correlations. These exotic features emphasize the key role of i) mosaic disorder induced subtle interplay of competing AFM-superexchange and FM double exchange at the exchange biased interface and, ii) training induced irrecoverable alterations in the AFM spin structure. PMID:24569516

Unraveling DNA dynamics using atomic force microscopy.

PubMed

Suzuki, Yuki; Yoshikawa, Yuko; Yoshimura, Shige H; Yoshikawa, Kenichi; Takeyasu, Kunio

2011-01-01

The elucidation of structure-function relationships of biological samples has become important issue in post-genomic researches. In order to unveil the molecular mechanisms controlling gene regulations, it is essential to understand the interplay between fundamental DNA properties and the dynamics of the entire molecule. The wide range of applicability of atomic force microscopy (AFM) has allowed us to extract physicochemical properties of DNA and DNA-protein complexes, as well as to determine their topographical information. Here, we review how AFM techniques have been utilized to study DNA and DNA-protein complexes and what types of analyses have accelerated the understanding of the DNA dynamics. We begin by illustrating the application of AFM to investigate the fundamental feature of DNA molecules; topological transition of DNA, length dependent properties of DNA molecules, flexibility of double-stranded DNA, and capability of the formation of non-Watson-Crick base pairing. These properties of DNA are critical for the DNA folding and enzymatic reactions. The technical advancement in the time-resolution of AFM and sample preparation methods enabled visual analysis of DNA-protein interactions at sub-second time region. DNA tension-dependent enzymatic reaction and DNA looping dynamics by restriction enzymes were examined at a nanoscale in physiological environments. Contribution of physical properties of DNA to dynamics of nucleosomes and transition of the higher-order structure of reconstituted chromatin are also reviewed. Copyright © 2011 John Wiley & Sons, Inc.

On the use of SPM to probe the interplay between polymer surface chemistry and polymer surface mechanics

NASA Astrophysics Data System (ADS)

Brogly, Maurice; Noel, Olivier; Awada, Houssein; Castelein, Gilles

2007-03-01

Adhesive properties of a polymer surface results from the complex contribution of surface chemistry and activation of sliding and dissipating mechanisms within the polymer surface layer. The purpose of this study is to dissociate the different contributions (chemical and mechanical) included in an AFM force-distance curve in order to establish relationships between the surface viscoelastic properties of the polymer, the surface chemistry of functionalized polymer surfaces and the adhesive forces, as determined by C-AFM experiments. Indeed we are interested in the measurements of local attractive or adhesive forces in AFM contact mode, of controlled chemical and mechanical model substrates. In order to investigate the interplay between mechanical or viscoelastic mechanisms and surface chemistry during the tip - polymer contact, we achieved force measurements on model PDMS polymer networks, whose surfaces are chemically controlled with the same functional groups as before (silicon substrates). On the basis of AFM nano-indentation experiments, surface Young moduli have been determined. The results show that the viscoelastic contribution is dominating in the adhesion force measurement. We propose an original model, which express the local adhesion force to the energy dissipated within the contact and the surface properties of the material (thermodynamic work of adhesion). Moreover we show that the dissipation function is related to Mc, the mass between crosslinks of the network.

Silicon Carbide Epitaxial Films Studied by Atomic Force Microscopy

NASA Technical Reports Server (NTRS)

1996-01-01

Silicon carbide (SiC) holds great potential as an electronic material because of its wide band gap energy, high breakdown electric field, thermal stability, and resistance to radiation damage. Possible aerospace applications of high-temperature, high-power, or high-radiation SiC electronic devices include sensors, control electronics, and power electronics that can operate at temperatures up to 600 C and beyond. Commercially available SiC devices now include blue light-emitting diodes (LED's) and high-voltage diodes for operation up to 350 C, with other devices under development. At present, morphological defects in epitaxially grown SiC films limit their use in device applications. Research geared toward reducing the number of structural inhomogeneities can benefit from an understanding of the type and nature of problems that cause defects. The Atomic Force Microscope (AFM) has proven to be a useful tool in characterizing defects present on the surface of SiC epitaxial films. The in-house High-Temperature Integrated Electronics and Sensors (HTIES) Program at the NASA Lewis Research Center not only extended the dopant concentration range achievable in epitaxial SiC films, but it reduced the concentration of some types of defects. Advanced structural characterization using the AFM was warranted to identify the type and structure of the remaining film defects and morphological inhomogeneities. The AFM can give quantitative information on surface topography down to molecular scales. Acquired, in part, in support of the Advanced High Temperature Engine Materials Technology Program (HITEMP), the AFM had been used previously to detect partial fiber debonding in composite material cross sections. Atomic force microscopy examination of epitaxial SiC film surfaces revealed molecular-scale details of some unwanted surface features. Growth pits propagating from defects in the substrate, and hillocks due, presumably, to existing screw dislocations in the substrates, were imaged. Away from local defects, step bunching was observed to yield step heights of hundreds of angstroms, with possible implications for the uniformity of dopants incorporated in SiC devices during fabrication. The quantitative topographic data from the AFM allow the relevant defect information to be extracted, such as the size and distribution of step bunching and the Burgers vector of screw dislocations. These atomic force microscopy results have furthered the understanding of the dynamic epitaxial SiC growth process. A model describing the observed hillock step bunching has been proposed. This cooperation between researchers involved in crystal growth, electronic device fabrication, and surface structural characterization is likely to continue as atomic force microscopy is used to improve SiC films for high-temperature electronic devices for NASA's advanced turbine engines and space power devices, as well as for future applications in the automotive industry.

Thermopower behavior in the Gd5(Si0.1Ge0.9)4 magnetocaloric compound from 4 to 300 K

NASA Astrophysics Data System (ADS)

Sousa, J. B.; Braga, M. E.; Correia, F. C.; Carpinteiro, F.; Morellon, L.; Algarabel, P. A.; Ibarra, R.

2002-04-01

Recent studies on the orthorhombic Gd5(Si0.1Ge0.9)4 compound show, upon heating, a ferromagnetic to antiferromagnetic-like (AFM*) transition at TS=78 K, coupled with a first-order structural martensitic transformation keeping the orthorhombic symmetry but producing a large increase in the interlayer Si(Ge) distances leading to covalent bond-pair breaking. A second-order AFM*→(paramagnetic)PM transition occurs at TN=125 K. We report thermopower (S) measurements for the Gd5(SixGe1-x)4 series, performed on an x=0.1 sample, from 4 to 300 K, with increasing and decreasing temperatures through successive thermal cycling. Resistivity measurements show a systematic increase in the residual resistivity and a dramatic change in the ρ(T) behavior upon thermal cycling. In spite of this, the thermopower data show a common intrinsic behavior both in the ferromagnetic phase (T

Nature of the insulating ground state of the 5d postperovskite CaIrO 3

DOE PAGES

Kim, Sun -Woo; Liu, Chen; Kim, Hyun -Jung; ...

2015-08-26

In this study, the insulating ground state of the 5d transition metal oxide CaIrO 3 has been classified as a Mott-type insulator. Based on a systematic density functional theory (DFT) study with local, semilocal, and hybrid exchange-correlation functionals, we reveal that the Ir t 2g states exhibit large splittings and one-dimensional electronic states along the c axis due to a tetragonal crystal field. Our hybrid DFT calculation adequately describes the antiferromagnetic (AFM) order along the c direction via a superexchange interaction between Ir 4+ spins. Furthermore, the spin-orbit coupling (SOC) hybridizes the t 2g states to open an insulating gap.more » These results indicate that CaIrO 3 can be represented as a spin-orbit Slater insulator, driven by the interplay between a long-range AFM order and the SOC. Such a Slater mechanism for the gap formation is also demonstrated by the DFT + dynamical mean field theory calculation, where the metal-insulator transition and the paramagnetic to AFM phase transition are concomitant with each other.« less

First-principles investigation of competing magnetic interactions in (Mn ,Fe )Ru2Sn Heusler solid solutions

NASA Astrophysics Data System (ADS)

Decolvenaere, Elizabeth; Gordon, Michael; Seshadri, Ram; Van der Ven, Anton

2017-10-01

Many Heusler compounds possess magnetic properties well suited for applications as spintronic materials. The pseudobinary Mn0.5Fe0.5Ru2Sn , formed as a solid solution of two full Heuslers, has recently been shown to exhibit exchange hardening suggestive of two magnetic phases, despite existing as a single chemical phase. We have performed a first-principles study of the chemical and magnetic degrees of freedom in the Mn1 -xFexRu2Sn pseudobinary to determine the origin of the unique magnetic behavior responsible for exchange hardening within a single phase. We find a transition from antiferromagnetic (AFM) to ferromagnetic (FM) behavior upon replacement of Mn with Fe, consistent with experimental results. The lowest energy orderings in Mn1 -xFexRu2Sn consist of chemically and magnetically uniform (111) planes, with Fe-rich regions preferring FM ordering and Mn-rich regions preferring AFM ordering, independent of the overall composition. Analysis of the electronic structure suggests that the magnetic behavior of this alloy arises from a competition between AFM-favoring Sn-mediated superexchange and FM-favoring RKKY exchange mediated by spin-polarized conduction electrons. Changes in valency upon replacement of Mn with Fe shifts the balance from superexchange-dominated interactions to RKKY-dominated interactions.

Imaging the coexistence of superconductivity and antiferromagnetism in Fe1+yTe1-xSex (x=0.1) using spin-polarized scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Zhou, Haibiao; Aluru, Ramakrishna; Tsurkan, Vladimir; Loidl, Alois; Deisenhofer, Joachim; Wahl, Peter

Magnetism has been widely thought to play an important role in unconventional superconductivity. In iron chalcogenide Fe1+yTe, the bicollinear antiferromagnetim (AFM) can be suppressed by Se doping, and consequently superconductivity appears. Though a competition between the two orders is expected, their relation has never been shown in details. Here, using spin-polarized scanning tunneling microscopy, we explore their relation at the atomic scale in an Fe1+yTe1-xSex (x=0.1) single crystal with TC = 10 K, in a regime of the phase diagram where a spin-glass phase has been detected. We clearly observe the short-range AFM order with domains of a lateral size of 10 nm embedded in a non-magnetic matrix. In addition we observe a superconducting gap with prominent coherent peaks in differential conductance spectroscopy with a gap size 2 Δ 4 mV. Surprisingly, no correlation between the superconducting properties (gap size and zero bias conductance) and the local AFM order is observed, while the coherence peaks are weakened by the existence of excess iron atoms. Our observations put constraints on theories that are aimed at explaining the relation between magnetism and unconventional superconductivity.

Effects of deposition temperatures on structure and physical properties of Cd 1-xZn xTe films prepared by RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Zeng, Dongmei; Jie, Wanqi; Zhou, Hai; Yang, Yingge

2010-02-01

Cd 1-xZn xTe films were deposited by RF magnetron sputtering from Cd 0.9Zn 0.1Te crystals target at different substrate temperatures (100-400 °C). The effects of the deposition temperature on structure and physical properties of Cd 1-xZn xTe films have been studied using X-ray diffraction (XRD), step profilometer, atomic force microscopy (AFM), ultraviolet spectrophotometer and Hall effect measurements. X-ray studies suggest that the deposited films were polycrystalline with preferential (1 1 1) orientation. AFM micrographs show that the grain size was changed from 50 to 250 nm with the increase of deposition temperatures, the increased grain size may result from kinetic factors during sputtering growth. The optical transmission data indicate that shallow absorption edge occurs in the range of 744-835 nm and that the optical absorption coefficient is varied with the increase of deposition temperatures. In Hall Effect measurements, the sheet resistivities of the deposited films are 3.2×10 8, 3.0×10 8, 1.9×10 8 and 1.1×10 8 Ohm/sq, which were decreased with the increase of substrate temperatures. Analysis of the resistivity of films depended on the substrate temperatures is discussed.

Homoepitaxial growth of metal halide crystals investigated by reflection high-energy electron diffraction

DOE PAGES

Chen, Pei; Kuttipillai, Padmanaban S.; Wang, Lili; ...

2017-01-10

Here, we report the homoepitaxial growth of a metal halide on single crystals investigated with in situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM). Epitaxial growth of NaCl on NaCl (001) is explored as a function of temperature and growth rate which provides the first detailed report of RHEED oscillations for metal halide growth. Layer-by-layer growth is observed at room temperature accompanied by clear RHEED oscillations while the growth mode transitions to an island (3D) mode at low temperature. At higher temperatures (>100 °C), RHEED oscillations and AFM data indicate a transition to a step-flowmore » growth mode. To show the importance of such metal halide growth, green organic light-emitting diodes (OLEDs) are demonstrated using a doped NaCl film with a phosphorescent emitter as the emissive layer. This study demonstrates the ability to perform in situ and non-destructive RHEED monitoring even on insulating substrates and could enable doped single crystals and crystalline substrates for a range of optoelectronic applications.« less

Different Variations of Néel Temperature TN and Kondo Temperature TK in the Alloy System Ce(Ru1-xOsx)2Al10 under Uniaxial Pressure

NASA Astrophysics Data System (ADS)

Takeuchi, Takashi; Hayashi, Kyosuke; Umeo, Kazunori; Takabatake, Toshiro

2018-05-01

We report magnetic, transport, and specific-heat measurements for single crystals of the antiferromagnetic (AFM) Kondo semiconductor alloy series Ce(Ru1-xOsx)2Al10 (0 ≤ x ≤ 1), which crystallize into an orthorhombic structure. The specific-heat and resistivity data show that the isoelectronic substitution does not damage the hybridization gap or the AFM transition. The Kondo temperature TK increases linearly with x, whereas the Néel temperature TN exhibits a maximum value of 29.2 K for x = 0.71. Under increasing uniaxial pressure P || a, TN increases for x = 0 but decreases for x = 1, while TK increases in the entire range of x. Under P || b, in contrast, TN increases steadily in the whole range of x while TK remains unchanged for each x. The strongly anisotropic change in TN indicates the presence of another mechanism to enhance TN in this system in addition to the anisotropic hybridization of the 4f state with conduction bands.

High temperature spin dynamics in linear magnetic chains, molecular rings, and segments by nuclear magnetic resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adelnia, Fatemeh; Lascialfari, Alessandro; Dipartimento di Fisica, Università degli Studi di Pavia and INSTM, Pavia

2015-05-07

We present the room temperature proton nuclear magnetic resonance (NMR) nuclear spin-lattice relaxation rate (NSLR) results in two 1D spin chains: the Heisenberg antiferromagnetic (AFM) Eu(hfac){sub 3}NITEt and the magnetically frustrated Gd(hfac){sub 3}NITEt. The NSLR as a function of external magnetic field can be interpreted very well in terms of high temperature spin dynamics dominated by a long time persistence of the decay of the two-spin correlation function due to the conservation of the total spin value for isotropic Heisenberg chains. The high temperature spin dynamics are also investigated in Heisenberg AFM molecular rings. In both Cr{sub 8} closed ringmore » and in Cr{sub 7}Cd and Cr{sub 8}Zn open rings, i.e., model systems for a finite spin segment, an enhancement of the low frequency spectral density is found consistent with spin diffusion but the high cut-off frequency due to intermolecular anisotropic interactions prevents a detailed analysis of the spin diffusion regime.« less

DESIGN NOTE: From nanometre to millimetre: a feasibility study of the combination of scanning probe microscopy and combined optical and x-ray interferometry

NASA Astrophysics Data System (ADS)

Yacoot, Andrew; Koenders, Ludger

2003-09-01

This feasibility study investigates the potential combination of an x-ray interferometer and optical interferometer as a one-dimensional long range high resolution scanning stage for an atomic force microscope (AFM) in order to overcome the problems of non-linearity associated with conventional AFMs and interferometers. Preliminary results of measurements of the uniformity of the period of a grating used as a transfer standards show variations in period at the nanometre level.

The investigation of smart magnetic nanoparticles for use in the hyperthermia treatment of cancer

NASA Astrophysics Data System (ADS)

Allyn, Megan; Kharel, Parashu; Vaishnava, Prem; Tackett, Ronald

The magnetic fluid hyperthermia (MFH) treatment of cancer has emerged as a possible low-side-effect alternative to traditional chemotherapy- and radiation-based therapy. As the nanoparticles absorb energy from a low amplitude RF magnetic field they heat up; however, currently used hyperthermia systems require external temperature monitoring as the nanoparticles can easily heat to temperature greater than the desired window between 42C and 46C. To combat this, we are investigating ``smart'' magnetic nanoparticles whose Curie temperatures fall within the desired range. In order to do this, we have doped non-magnetic cations onto the structure of the AFM LaMnO3. We report synthesis of LaxM1-xMnO3 (M = Ba, Ca, Sr; x = 0.10 - 0.25) nanoparticles via sol-gel method for use in temperature-controlled MFH. These nanoparticles were characterized via powder x-ray diffraction and found to have the expected R -3 c perovskite structure. For elemental analysis, energy dispersive spectroscopy was performed using scanning electron microscopy. The temperature dependence of the magnetization was investigated using vibrating sample magnetometry (VSM) to determine the Curie temperature of the ensembles. The results of the change in temperature vs time and SAR values will be presented.

High field induced magnetic transitions in the Y0.7E r0.3F e2D4.2 deuteride

NASA Astrophysics Data System (ADS)

Paul-Boncour, V.; Guillot, M.; Isnard, O.; Hoser, A.

2017-09-01

The influence of the partial Er for Y substitution on the crystal structure and magnetic properties of YF e2D4.2 has been investigated by high field magnetization and neutron diffraction experiments. Y0.7E r0.3F e2D4.2 compound crystallizes in the same monoclinic structure as YF e2D4.2 described in P c (P1c1) space group with D atoms located in 18 different tetrahedral interstitial sites. A cell volume contraction of 0.6% is observed upon Er substitution, inducing large modification of the magnetic properties. Electronic effect of D insertion as well as lowering of crystal symmetry are important factors determining the magnetic properties of Fe sublattice, which evolves towards more delocalized behavior and modifying the Er-Fe exchange interactions. In the ground state, the Er and Fe moments are arranged ferrimagnetically within the plane perpendicular to the monoclinic b axis and with average moments mEr=6.4 (3 ) μBEr-1 and mFe=2.0 (1 ) μBFe-1 at 10 K. Upon heating, mEr decreases progressively until TEr=55 K . Between 55 K and 75 K, the Fe sublattice undergoes a first-order ferromagnetic-antiferromagnetic (FM-AFM) transition with a cell volume contraction due to the itinerant metamagnetic behavior of one Fe site. In the AFM structure, mFe decreases until the Néel temperature TN=125 K . At high field, two different types of field induced transitions are observed. The Er moments become parallel to the Fe one and saturates to the E r3 + free ion value, leading to an unusual field induced FM arrangement at a transition field BTrans of only 78 kG below 30 K. Then above TM0=66 K , an AFM-FM transition of the Fe sublattice, accompanied by a cell volume increase is observed. BTrans increases linearly versus temperature and with a larger d BTrans/d T slope than for YF e2D4.2 . This has been explained by the additional contribution of Er induced moments above BTrans.

Strong magnetic correlations to 900 K in single crystals of the trigonal antiferromagnetic insulators SrMn 2 As 2 and CaMn 2 As 2

DOE PAGES

Sangeetha, N. S.; Pandey, Abhishek; Benson, Zackery A.; ...

2016-09-15

Crystallographic, electronic transport, thermal, and magnetic properties are reported for SrMn 2As 2 and CaMn 2As 2 single crystals grown using Sn flux. Rietveld refinements of powder x-ray diffraction data show that the two compounds are isostructural and crystallize in the trigonal CaAl 2Si 2-type structure (space groupmore » $$P\\bar{3}$$ m1), in agreement with the literature. Electrical resistivity ρ versus temperature T measurements demonstrate insulating ground states for both compounds with activation energies of 85 meV for SrMn 2As 2 and 61 meV for CaMn 2As 2. In a local-moment picture, the Mn +2 3d 5 ions are expected to have high-spin S=5/2 with spectroscopic splitting factor g≈2. Magnetic susceptibility χ and heat capacity Cp measurements versus T reveal antiferromagnetic (AFM) transitions at T N=120(2) K and 62(3) K for SrMn 2As 2 and CaMn 2As 2, respectively. The anisotropic χ(T≤T N) data indicate that the hexagonal c axis is the hard axis and hence that the ordered Mn moments are aligned in the ab plane. Finally, the χ(T) data for both compounds and the Cp(T) for SrMn 2As 2 show strong dynamic short-range AFM correlations from T N up to at least 900 K, likely associated with quasi-two-dimensional connectivity of strong AFM exchange interactions between the Mn spins within the corrugated honeycomb Mn layers parallel to the ab plane.« less

In situ probing the interior of single bacterial cells at nanometer scale

NASA Astrophysics Data System (ADS)

Liu, Boyin; Hemayet Uddin, Md; Ng, Tuck Wah; Paterson, David L.; Velkov, Tony; Li, Jian; Fu, Jing

2014-10-01

We report a novel approach to probe the interior of single bacterial cells at nanometre resolution by combining focused ion beam (FIB) and atomic force microscopy (AFM). After removing layers of pre-defined thickness in the order of 100 nm on the target bacterial cells with FIB milling, AFM of different modes can be employed to probe the cellular interior under both ambient and aqueous environments. Our initial investigations focused on the surface topology induced by FIB milling and the hydration effects on AFM measurements, followed by assessment of the sample protocols. With fine-tuning of the process parameters, in situ AFM probing beneath the bacterial cell wall was achieved for the first time. We further demonstrate the proposed method by performing a spatial mapping of intracellular elasticity and chemistry of the multi-drug resistant strain Klebsiella pneumoniae cells prior to and after it was exposed to the ‘last-line’ antibiotic polymyxin B. Our results revealed increased stiffness occurring in both surface and interior regions of the treated cells, suggesting loss of integrity of the outer membrane from polymyxin treatments. In addition, the hydrophobicity measurement using a functionalized AFM tip was able to highlight the evident hydrophobic portion of the cell such as the regions containing cell membrane. We expect that the proposed FIB-AFM platform will help in gaining deeper insights of bacteria-drug interactions to develop potential strategies for combating multi-drug resistance.

Thermal Noise Reduction of Mechanical Oscillators by Actively Controlled External Dissipative Forces

NASA Technical Reports Server (NTRS)

Liang, Shoudan; Medich, David; Czajkowsky, Daniel M.; Sheng, Sitong; Yuan, Jian-Yang; Shao, Zhifeng

1999-01-01

We show that the thermal fluctuations of very soft mechanical oscillators, such as the cantilever in an atomic force microscope (AFM), can be reduced without changing the stiffness of the spring or having to lower the environment temperature. We derive a theoretical relationship between the thermal fluctuations of an oscillator and an actively external-dissipative force. This relationship is verified by experiments with an AFM cantilever where the external active force is coupled through a magnetic field. With simple instrumentation, we have reduced the thermal noise amplitude of the cantilever by a factor of 3.4, achieving an apparent temperature of 25 K with the environment at 295K. This active noise reduction approach can significantly improve the accuracy of static position or static force measurements in a number of practical applications.

Ion-damage-free planarization or shallow angle sectioning of solar cells for mapping grain orientation and nanoscale photovoltaic properties

DOE PAGES

Kutes, Yasemin; Luria, Justin; Sun, Yu; ...

2017-04-11

Ion beam milling is the most common modern method for preparing specific features for microscopic analysis, even though concomitant ion implantation and amorphization remain persistent challenges, particularly as they often modify materials properties of interest. Atomic force microscopy (AFM), on the other hand, can mechanically mill specific nanoscale regions in plan-view without chemical or high energy ion damage, due to its resolution, directionality, and fine load control. As an example, AFM-nanomilling (AFM-NM) is implemented for top-down planarization of polycrystalline CdTe thin film solar cells, with a resulting decrease in the root mean square (RMS) roughness by an order of magnitude,more » even better than for a low incidence FIB polished surface. Subsequently AFM-based property maps reveal a substantially stronger contrast, in this case of the short-circuit current or open circuit voltage during light exposure. Furthermore, electron back scattering diffraction (EBSD) imaging also becomes possible upon AFM-NM, enabling direct correlations between the local materials properties and the polycrystalline microstructure. Smooth shallow-angle cross-sections are demonstrated as well, based on targeted oblique milling. As expected, this reveals a gradual decrease in the average short-circuit current and maximum power as the underlying CdS and electrode layers are approached, but a relatively consistent open-circuit voltage through the diminishing thickness of the CdTe absorber. AFM-based nanomilling is therefore a powerful tool for material characterization, uniquely providing ion-damage free, selective area, planar smoothing or low-angle sectioning of specimens while preserving their functionality. This then enables novel, co-located advanced AFM measurements, EBSD analysis, and investigations by related techniques that are otherwise hindered by surface morphology or surface damage.« less

Ion-damage-free planarization or shallow angle sectioning of solar cells for mapping grain orientation and nanoscale photovoltaic properties

NASA Astrophysics Data System (ADS)

Kutes, Yasemin; Luria, Justin; Sun, Yu; Moore, Andrew; Aguirre, Brandon A.; Cruz-Campa, Jose L.; Aindow, Mark; Zubia, David; Huey, Bryan D.

2017-05-01

Ion beam milling is the most common modern method for preparing specific features for microscopic analysis, even though concomitant ion implantation and amorphization remain persistent challenges, particularly as they often modify materials properties of interest. Atomic force microscopy (AFM), on the other hand, can mechanically mill specific nanoscale regions in plan-view without chemical or high energy ion damage, due to its resolution, directionality, and fine load control. As an example, AFM-nanomilling (AFM-NM) is implemented for top-down planarization of polycrystalline CdTe thin film solar cells, with a resulting decrease in the root mean square (RMS) roughness by an order of magnitude, even better than for a low incidence FIB polished surface. Subsequent AFM-based property maps reveal a substantially stronger contrast, in this case of the short-circuit current or open circuit voltage during light exposure. Electron back scattering diffraction (EBSD) imaging also becomes possible upon AFM-NM, enabling direct correlations between the local materials properties and the polycrystalline microstructure. Smooth shallow-angle cross-sections are demonstrated as well, based on targeted oblique milling. As expected, this reveals a gradual decrease in the average short-circuit current and maximum power as the underlying CdS and electrode layers are approached, but a relatively consistent open-circuit voltage through the diminishing thickness of the CdTe absorber. AFM-based nanomilling is therefore a powerful tool for material characterization, uniquely providing ion-damage free, selective area, planar smoothing or low-angle sectioning of specimens while preserving their functionality. This enables novel, co-located advanced AFM measurements, EBSD analysis, and investigations by related techniques that are otherwise hindered by surface morphology or surface damage.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kutes, Yasemin; Luria, Justin; Sun, Yu

Ion beam milling is the most common modern method for preparing specific features for microscopic analysis, even though concomitant ion implantation and amorphization remain persistent challenges, particularly as they often modify materials properties of interest. Atomic force microscopy (AFM), on the other hand, can mechanically mill specific nanoscale regions in plan-view without chemical or high energy ion damage, due to its resolution, directionality, and fine load control. As an example, AFM-nanomilling (AFM-NM) is implemented for top-down planarization of polycrystalline CdTe thin film solar cells, with a resulting decrease in the root mean square (RMS) roughness by an order of magnitude,more » even better than for a low incidence FIB polished surface. Subsequently AFM-based property maps reveal a substantially stronger contrast, in this case of the short-circuit current or open circuit voltage during light exposure. Furthermore, electron back scattering diffraction (EBSD) imaging also becomes possible upon AFM-NM, enabling direct correlations between the local materials properties and the polycrystalline microstructure. Smooth shallow-angle cross-sections are demonstrated as well, based on targeted oblique milling. As expected, this reveals a gradual decrease in the average short-circuit current and maximum power as the underlying CdS and electrode layers are approached, but a relatively consistent open-circuit voltage through the diminishing thickness of the CdTe absorber. AFM-based nanomilling is therefore a powerful tool for material characterization, uniquely providing ion-damage free, selective area, planar smoothing or low-angle sectioning of specimens while preserving their functionality. This then enables novel, co-located advanced AFM measurements, EBSD analysis, and investigations by related techniques that are otherwise hindered by surface morphology or surface damage.« less

Opposite Surface and Bulk Solvatochromic Effects in a Molecular Spin-Crossover Compound Revealed by Ambient Pressure X-ray Absorption Spectroscopy.

PubMed

Borgatti, Francesco; Torelli, Piero; Brucale, Marco; Gentili, Denis; Panaccione, Giancarlo; Castan Guerrero, Celia; Schäfer, Bernhard; Ruben, Mario; Cavallini, Massimiliano

2018-03-27

We investigate the solvatochromic effect of a Fe-based spin-crossover (SCO) compound via ambient pressure soft X-ray absorption spectroscopy (AP-XAS) and atomic force microscopy (AFM). AP-XAS provides the direct evidence of the spin configuration for the Fe(II) 3d states of the SCO material upon in situ exposure to specific gas or vapor mixtures; concurrent changes in nanoscale topography and mechanical characteristics are revealed via AFM imaging and AFM-based force spectroscopy, respectively. We find that exposing the SCO material to gaseous helium promotes an effective decrease of the transition temperature of its surface layers, while the exposure to methanol vapor causes opposite surfacial and bulk solvatochromic effects. Surfacial solvatochromism is accompanied by a dramatic reduction of the surface layers stiffness. We propose a rationalization of the observed effects based on interfacial dehydration and solvation phenomena.

Local oxidation using scanning probe microscope for fabricating magnetic nanostructures.

PubMed

Takemura, Yasushi

2010-07-01

Local oxidation technique using atomic force microscope (AFM) was studied. The local oxidation of ferromagnetic metal thin films was successfully performed by AFM under both contact and dynamic force modes. Modification of magnetic and electrical properties of magnetic devices fabricated by the AFM oxidation was achieved. Capped oxide layers deposited on the ferromagnetic metal films are advantageous for stable oxidation due to hydrophilic surface of oxide. The oxide layer is also expected to prevent magnetic devices from degradation by oxidation of ferromagnetic metal. As for modification of magnetic property, the isolated region of CoFe layer formed by nanowires of CoFe-oxide exhibited peculiar characteristic attributed to the isolated magnetization property and pinning of domain wall during magnetization reversal. Temperature dependence of current-voltage characteristic of the planar-type tunnel junction consisting of NiFe/NiFe-oxide/NiFe indicated that the observed current was dominated by intrinsic tunneling current at the oxide barrier.

Hydration states of AFm cement phases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baquerizo, Luis G., E-mail: luis.baquerizoibarra@holcim.com; Matschei, Thomas; Scrivener, Karen L.

2015-07-15

The AFm phase, one of the main products formed during the hydration of Portland and calcium aluminate cement based systems, belongs to the layered double hydrate (LDH) family having positively charged layers and water plus charge-balancing anions in the interlayer. It is known that these phases present different hydration states (i.e. varying water content) depending on the relative humidity (RH), temperature and anion type, which might be linked to volume changes (swelling and shrinkage). Unfortunately the stability conditions of these phases are insufficiently reported. This paper presents novel experimental results on the different hydration states of the most important AFmmore » phases: monocarboaluminate, hemicarboaluminate, strätlingite, hydroxy-AFm and monosulfoaluminate, and the thermodynamic properties associated with changes in their water content during absorption/desorption. This data opens the possibility to model the response of cementitious systems during drying and wetting and to engineer systems more resistant to harsh external conditions.« less

Nanomechanics of Protein Unfolding outside Protease Nanopores

NASA Astrophysics Data System (ADS)

Luan, Binquan; Zhou, Ruhong

Protein folding and unfolding have been the subject of active research for decades. Most of previous studies in protein unfolding were focused on temperature, chemical and/or force (such as in AFM) induced denaturations. Recent studies on the functional roles of proteasomes (such as ClpXP) revealed a novel unfolding process in cell, during which a target protein is mechanically unfolded and pulled into a confined, pore-like geometry for degradation. While the proteasome nanomachine has been extensively studied, the mechanism for unfolding proteins with the proteasome pore is still poorly understood. Here, we investigate the mechanical unfolding process of ubiquitin with (or really outside) an idealized proteasome pore, and compare such process with that in the AFM pulling experiment. Unexpectedly, the required force by a proteosome can be much smaller than that by the AFM. Simulation results also unveiled different nanomechanics, tearing fracture vs. shearing friction, in these two distinct types of mechanical unfoldings.

A low-noise measurement system for scanning thermal microscopy resistive nanoprobes based on a transformer ratio-arm bridge

NASA Astrophysics Data System (ADS)

Świątkowski, Michał; Wojtuś, Arkadiusz; Wielgoszewski, Grzegorz; Rudek, Maciej; Piasecki, Tomasz; Jóźwiak, Grzegorz; Gotszalk, Teodor

2018-04-01

Atomic force microscopy (AFM) is a widely used technology for the investigation and characterization of nanomaterials. Its functionality can be easily expanded by applying dedicated extension modules, which can measure the electrical conductivity or temperature of a sample. In this paper, we introduce a transformer ratio-arm bridge setup dedicated to AFM-based thermal imaging. One of the key features of the thermal module is the use of a low-power driving signal that prevents undesirable tip heating during resistance measurement, while the other is the sensor location in a ratio-arm transformer bridge working in the audio frequency range and ensuring galvanic isolation of the tip, enabling contact-mode scanning of electronic circuits. The proposed expansion module is compact and it can be integrated onto the AFM head close to the cantilever. The calibration process and the resolution of 11 mK of the proposed setup are shown.

Interfacial gas nanobubbles or oil nanodroplets?

PubMed

Wang, Xingya; Zhao, Binyu; Hu, Jun; Wang, Shuo; Tai, Renzhong; Gao, Xingyu; Zhang, Lijuan

2017-01-04

The existence of nanobubbles at a solid-liquid interface with high stability has been confirmed by myriad experimental studies, and their gaseous nature has also been extensively verified. However, nanodroplets of polydimethylsiloxane (PDMS) recently observed in the atomic force microscopy (AFM) measurement of nanobubbles plague the nanobubble community. It may easily lead to wrong interpretations of the AFM results and thus hinders further application of the already widely used AFM in nanobubble studies. Therefore, finding a direct experimental solution to distinguish nanobubbles from nanodroplets in AFM measurements is a matter of great urgency. Herein, we first developed an effective and reproducible method to produce PDMS nanodroplets at the highly ordered pyrolytic graphite (HOPG)/water interface. From their size, contact angle, and stiffness, the formed PDMS nanodroplets are not distinguishable from nanobubbles. However, the force curves on these two objects are strikingly different from each other, i.e., a peculiar plateau in both the approach and retraction curves was found on nanobubbles whereas they changed linearly between the jump-in and jump-off point on PDMS nanodroplets. Thus, the present study not only provided a simple and effective procedure to generate PDMS nanodroplets but also paved a simple practical and in situ way to discriminate nanobubbles from the PDMS nanodroplets by direct AFM force measurements.

On mapping subangstrom electron clouds with force microscopy.

PubMed

Wright, C Alan; Solares, Santiago D

2011-11-09

In 2004 Hembacher et al. (Science 2004, 305, 380-383) reported simultaneous higher-harmonics atomic force mocroscopy (AFM)/scanning tunneling microscopy (STM) images acquired while scanning a graphite surface with a tungsten tip. They interpreted the observed subatomic features in the AFM images as the signature of lobes of increased electron density at the tungsten tip apex. Although these intriguing images have stirred controversy, an in-depth theoretical feasibility study has not yet been produced. Here we report on the development of a method for simulating higher harmonics AFM images and its application to the same system. Our calculations suggest that four lobes of increased electron density are expected to be present at a W(001) tip apex atom and that the corresponding higher harmonics AFM images of graphite can exhibit 4-fold symmetry features. Despite these promising results, open questions remain since the calculated amplitudes of the higher harmonics generated by the short-range forces are on the order of hundredths of picometers, leading to very small corrugations in the theoretical images. Additionally, the complex, intermittent nature of the tip-sample interaction, which causes constant readjustment of the tip and sample orbitals as the tip approaches and retracts from the surface, prevents a direct quantitative connection between the electron density and the AFM image features.

Antiferromagnetism, structural instability and frustration in intermetallic AFe4X2 systems

NASA Astrophysics Data System (ADS)

Rosner, Helge; Bergmann, Christoph; Weber, Katharina; Kraft, Inga; Mufti, N.; Klauss, Hans-Henning; Dellmann, T.; Woike, T.; Geibel, Christoph

2013-03-01

Magnetic systems with reduced dimensionality or frustration attract strong interest because these features lead to an increase of quantum fluctuations and often result in unusual properties. Here, we present a detailed study of the magnetic, thermodynamic, and structural properties of the intermetallic AFe4X2 compounds (A=Sc,Y,Lu,Zr; X=Si,Ge) crystallizing in the ZrFe4Si2 structure type. Our results evidence that these compounds cover the whole regime from frustrated AFM order up to an AFM quantum critical point. Susceptibility χ(T), specific heat, resistivity, and T-dependent XRD measurements were performed on polycrystalline samples. In all compounds we observed a Curie-Weiss behavior in χ(T) at high T indicating a paramagnetic moment of about 3μB/Fe. Magnetic and structural transitions as previously reported for YFe4Ge2 occur in all compounds with trivalent A. However, transition temperatures, nature of the transition as well as the relation between structural and magnetic transitions change significantly with the A element. Low TN's and large θCW /TN ratios confirm the relevance of frustration. The results are analyzed and discussed with respect to electronic, structural and magnetic instabilities applying DFT calculations. Financial support from the DFG (GRK 1621) is acknowledged

Anisotropy of Spin Fluctuations in a Tetragonal Heavy Fermion Antiferromagnet CeRhAl 4 Si 2

DOE PAGES

Sakai, H.; Hattori, T.; Tokunaga, Y.; ...

2017-06-01

An antiferromagnetic (AFM) Kondo lattice compound CeRhAl 4Si 2, which exhibits successive AFM transitions at T N1=14 K and T N2=9 K in zero external field, has been microscopically investigated by means of 27Al nuclear magnetic resonance (NMR) technique. In the high temperature range, magnetic excitations of 4f electrons can be well explained by isotropic localized spin fluctuations. Below ~50 K, it begins to show a characteristic anisotropy of spin fluctuations, which suggests a competition between spin fluctuations and nesting instability in this system.

Direct and quantitative AFM measurements of the concentration and temperature dependence of the hydrophobic force law at nanoscopic contacts.

PubMed

Stock, Philipp; Utzig, Thomas; Valtiner, Markus

2015-05-15

By virtue of its importance for self-organization of biological matter the hydrophobic force law and the range of hydrophobic interactions (HI) have been debated extensively over the last 40 years. Here, we directly measure and quantify the hydrophobic force-distance law over large temperature and concentration ranges. In particular, we study the HI between molecularly smooth hydrophobic self-assembled monolayers, and similarly modified gold-coated AFM tips (radii∼8-50 nm). We present quantitative and direct evidence that the hydrophobic force is both long-ranged and exponential down to distances of about 1-2 nm. Therefore, we introduce a self-consistent radius-normalization for atomic force microscopy data. This approach allows quantitative data fitting of AFM-based experimental data to the recently proposed Hydra-model. With a statistical significance of r(2)⩾0.96 our fitting and data directly reveal an exponential HI decay length of 7.2±1.2 Å that is independent of the salt concentration up to 750 mM. As such, electrostatic screening does not have a significant influence on the HI in electrolyte concentrations ranging from 1 mM to 750 mM. In 1 M solutions the observed instability during approach shifts to longer distances, indicating ion correlation/adsorption effects at high salt concentrations. With increasing temperature the magnitude of HI decreases monotonically, while the range increases slightly. We compare our results to the large body of available literature, and shed new light into range and magnitude of hydrophobic interactions at very close distances and over wide temperature and concentration regimes. Copyright © 2015 Elsevier Inc. All rights reserved.

Lipid Bilayer Membrane in a Silicon Based Micron Sized Cavity Accessed by Atomic Force Microscopy and Electrochemical Impedance Spectroscopy

PubMed Central

Dosoky, Noura Sayed; Patel, Darayas; Weimer, Jeffrey; Williams, John Dalton

2017-01-01

Supported lipid bilayers (SLBs) are widely used in biophysical research to probe the functionality of biological membranes and to provide diagnoses in high throughput drug screening. Formation of SLBs at below phase transition temperature (Tm) has applications in nano-medicine research where low temperature profiles are required. Herein, we report the successful production of SLBs at above—as well as below—the Tm of the lipids in an anisotropically etched, silicon-based micro-cavity. The Si-based cavity walls exhibit controlled temperature which assist in the quick and stable formation of lipid bilayer membranes. Fusion of large unilamellar vesicles was monitored in real time in an aqueous environment inside the Si cavity using atomic force microscopy (AFM), and the lateral organization of the lipid molecules was characterized until the formation of the SLBs. The stability of SLBs produced was also characterized by recording the electrical resistance and the capacitance using electrochemical impedance spectroscopy (EIS). Analysis was done in the frequency regime of 10−2–105 Hz at a signal voltage of 100 mV and giga-ohm sealed impedance was obtained continuously over four days. Finally, the cantilever tip in AFM was utilized to estimate the bilayer thickness and to calculate the rupture force at the interface of the tip and the SLB. We anticipate that a silicon-based, micron-sized cavity has the potential to produce highly-stable SLBs below their Tm. The membranes inside the Si cavity could last for several days and allow robust characterization using AFM or EIS. This could be an excellent platform for nanomedicine experiments that require low operating temperatures. PMID:28678160

Lipid Bilayer Membrane in a Silicon Based Micron Sized Cavity Accessed by Atomic Force Microscopy and Electrochemical Impedance Spectroscopy.

PubMed

Khan, Muhammad Shuja; Dosoky, Noura Sayed; Patel, Darayas; Weimer, Jeffrey; Williams, John Dalton

2017-07-05

Supported lipid bilayers (SLBs) are widely used in biophysical research to probe the functionality of biological membranes and to provide diagnoses in high throughput drug screening. Formation of SLBs at below phase transition temperature ( Tm ) has applications in nano-medicine research where low temperature profiles are required. Herein, we report the successful production of SLBs at above-as well as below-the Tm of the lipids in an anisotropically etched, silicon-based micro-cavity. The Si-based cavity walls exhibit controlled temperature which assist in the quick and stable formation of lipid bilayer membranes. Fusion of large unilamellar vesicles was monitored in real time in an aqueous environment inside the Si cavity using atomic force microscopy (AFM), and the lateral organization of the lipid molecules was characterized until the formation of the SLBs. The stability of SLBs produced was also characterized by recording the electrical resistance and the capacitance using electrochemical impedance spectroscopy (EIS). Analysis was done in the frequency regime of 10 -2 -10⁵ Hz at a signal voltage of 100 mV and giga-ohm sealed impedance was obtained continuously over four days. Finally, the cantilever tip in AFM was utilized to estimate the bilayer thickness and to calculate the rupture force at the interface of the tip and the SLB. We anticipate that a silicon-based, micron-sized cavity has the potential to produce highly-stable SLBs below their Tm . The membranes inside the Si cavity could last for several days and allow robust characterization using AFM or EIS. This could be an excellent platform for nanomedicine experiments that require low operating temperatures.

Crystallographic order and decomposition of [MnIII 6CrIII]3+ single-molecule magnets deposited in submonolayers and monolayers on HOPG studied by means of molecular resolved atomic force microscopy (AFM) and Kelvin probe force microscopy in UHV

NASA Astrophysics Data System (ADS)

Gryzia, Aaron; Volkmann, Timm; Brechling, Armin; Hoeke, Veronika; Schneider, Lilli; Kuepper, Karsten; Glaser, Thorsten; Heinzmann, Ulrich

2014-02-01

Monolayers and submonolayers of [Mn III 6 Cr III ] 3+ single-molecule magnets (SMMs) adsorbed on highly oriented pyrolytic graphite (HOPG) using the droplet technique characterized by non-contact atomic force microscopy (nc-AFM) as well as by Kelvin probe force microscopy (KPFM) show island-like structures with heights resembling the height of the molecule. Furthermore, islands were found which revealed ordered 1D as well as 2D structures with periods close to the width of the SMMs. Along this, islands which show half the heights of intact SMMs were observed which are evidences for a decomposing process of the molecules during the preparation. Finally, models for the structure of the ordered SMM adsorbates are proposed to explain the observations.

Brownmillerite CaCoO2.5: Synthesis, Re-entrant Structural Transitions and Magnetic properties

NASA Astrophysics Data System (ADS)

Zhang, Junjie; Zheng, Hong; Malliakas, Christos; Allred, Jared; Ren, Yang; Li, Qing'an; Han, Tianheng; Mitchell, John

2015-03-01

Cobalt oxides attract both fundamental and technological attention due to their physical properties including thermoelectricity, giant magnetoresistance, superconductivity and multiferroicity. Here we report the first synthesis of CaCoO2.5 single crystals using a high pressure optical-image floating zone technique. We find that it is an ordered oxygen-deficient perovskite of the brownmillerite type, and it undergoes an unprecedented re-entrant structural phase transitions (Pcmb --> P2/c11 --> P121/m1 --> Pcmb) with decreasing temperature. We describe its temperature-dependent structural, thermal, and magnetic properties, including AFM ordering near 240 K, with a weakly spin canted ferromagnet ground state below 140 K. The magnetic response of CaCoO2.5 depends markedly on the cooling rate and field history. Magnetization data also imply the potential of a distinct, field-induced phase arising uniquely from the P121/m1 structure, revealed as kinetically trapped by a rapid-cooling protocol. Work in the Materials Science Division at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Division of Materials Science and Engineering.

AFM-porosimetry: density and pore volume measurements of particulate materials.

PubMed

Sörensen, Malin H; Valle-Delgado, Juan J; Corkery, Robert W; Rutland, Mark W; Alberius, Peter C

2008-06-01

We introduced the novel technique of AFM-porosimetry and applied it to measure the total pore volume of porous particles with a spherical geometry. The methodology is based on using an atomic force microscope as a balance to measure masses of individual particles. Several particles within the same batch were measured, and by plotting particle mass versus particle volume, the bulk density of the sample can be extracted from the slope of the linear fit. The pore volume is then calculated from the densities of the bulk and matrix materials, respectively. In contrast to nitrogen sorption and mercury porosimetry, this method is capable of measuring the total pore volume regardless of pore size distribution and pore connectivity. In this study, three porous samples were investigated by AFM-porosimetry: one ordered mesoporous sample and two disordered foam structures. All samples were based on a matrix of amorphous silica templated by a block copolymer, Pluronic F127, swollen to various degrees with poly(propylene glycol). In addition, the density of silica spheres without a template was measured by two independent techniques: AFM and the Archimedes principle.

Structural and electrical transport properties of La2Mo2O9 thin films prepared by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Paul, T.; Ghosh, A.

2017-04-01

We have studied the structure and electrical properties of La2Mo2O9 thin films of different thicknesses prepared by the laser deposition technique at different substrate temperatures. The structural properties of the thin films have been investigated using XRD, XPS, AFM, TEM, SEM, and Raman spectroscopy. The electrical transport properties of the thin films have been investigated in wide temperature and frequency ranges. The cubic nature of the thin films has been confirmed from structural analysis. An enhancement of the oxygen ion conductivity of the films up to five orders of magnitude is obtained compared to that of the bulk La2Mo2O9, suggesting usefulness of the thin films as electrolytes in micro-solid oxide fuel cells. The enhanced dc ionic conductivity of the thin films has been interpreted using the rule of the mixture model, while a power law model has been used to investigate the frequency and temperature dependences of the conductivity. The analysis of the results predicts the three-dimensional oxygen ion conduction in the thin films.

Microbial Cell Imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doktycz, Mitchel John; Sullivan, Claretta; Mortensen, Ninell P

Atomic force microscopy (AFM) is finding increasing application in a variety of fields including microbiology. Until the emergence of AFM, techniques for ivnestigating processes in single microbes were limited. From a biologist's perspective, the fact that AFM can be used to generate high-resolution images in buffers or media is its most appealing feature as live-cell imaging can be pursued. Imaging living cells by AFM allows dynamic biological events to be studied, at the nanoscale, in real time. Few areas of biological research have as much to gain as microbiology from the application of AFM. Whereas the scale of microbes placesmore » them near the limit of resolution for light microscopy. AFM is well suited for the study of structures on the order of a micron or less. Although electron microscopy techniques have been the standard for high-resolution imaging of microbes, AFM is quickly gaining favor for several reasons. First, fixatives that impair biological activity are not required. Second, AFM is capable of detecting forces in the pN range, and precise control of the force applied to the cantilever can be maintained. This combination facilitates the evaluation of physical characteristics of microbes. Third, rather than yielding the composite, statistical average of cell populations, as is the case with many biochemical assays, the behavior of single cells can be monitored. Despite the potential of AFM in microbiology, there are several limitations that must be considered. For example, the time required to record an image allows for the study of gross events such as cell division or membrane degradation from an antibiotic but precludes the evaluation of biological reactions and events that happen in just fractions of a second. Additionally, the AFM is a topographical tool and is restricted to imaging surfaces. Therefore, it cannot be used to look inside cells as with opticla and transmission electron microscopes. other practical considerations are the limitation on the maximum scan size (roughly 100 x 100 {mu}m) and the restricted movement of the cantilever in the Z (or height) direction. In most commercial AFMs, the Z range is restricted to roughly 10 {mu}m such that the height of cells to be imaged must be seriously considered. Nevertheless, AFM can provide structural-functional information at nanometer resolution and do so in physiologically relevant environments. Further, instrumentation for scanning probe microscopy continues to advance. Systems for high-speed imaging are becoming available, and techniques for looking inside the cells are being demonstrated. The ability to combine AFM with other imaging modalities is likely to have an even greater impact on microbiological studies. AFM studies of intact microbial cells started to appear in the literature in the 1990s. For example, AFM studies of Saccharomyces cerevisiae examined buddings cars after cell division and detailed changes related to cell growth processes. Also, the first AFM studies of bacterial biofilms appeared. In the late 1990s, AFM studies of intact fungal spores described clear changes in spore surfaces upon germination, and studies of individual bacterial cells were also described. These early bacterial imaging studies examined changes in bacterial morphology due to antimicrobial peptides exposure and bacterial adhesion properties. The majority of these early studies were carried out on dried samples and took advantage of the resolving power of AFM. The lack of cell mounting procedures presented an impediment for cell imaging studies. Subsequently, several approaches to mounting microbial cells have been developed, and these techniques are described later. Also highlighted are general considerations for microbial imaging and a description of some of the various applications of AFM to microbiology.« less

Energy dissipation unveils atomic displacement in the noncontact atomic force microscopy imaging of Si(111 )-(7 ×7 )

NASA Astrophysics Data System (ADS)

Arai, Toyoko; Inamura, Ryo; Kura, Daiki; Tomitori, Masahiko

2018-03-01

The kinetic energy of the oscillating cantilever of noncontact atomic force microscopy (nc-AFM) at room temperature was considerably dissipated over regions between a Si adatom and its neighboring rest atom for Si(111 )-(7 ×7 ) in close proximity to a Si tip on the cantilever. However, nc-AFM topographic images showed no atomic features over those regions, which were the hollow sites of the (7 ×7 ). This energy dissipation likely originated from displacement of Si adatoms with respect to the tip over the hollow sites, leading to a lateral shift of the adatoms toward the rest atom. This interaction led to hysteresis over each cantilever oscillation cycle; when the tip was retracted, the Si adatom likely returned to its original position. To confirm the atomic processes involved in the force interactions through Si dangling bonds, the Si(111 )-(7 ×7 ) surface was partly terminated with atomic hydrogen (H) and examined by nc-AFM. When the Si adatoms and/or the rest atoms were terminated with H, the hollow sites were not bright (less dissipation) in images of the energy dissipation channels by nc-AFM. The hollow sites acted as metastable sites for Si adatoms in surface diffusion and atom manipulation; thus, the dissipation energy which is saturated on the tip likely corresponds to the difference in the potential energy between the hollow site and the Si adatom site. In this study, we demonstrated the ability of dissipation channels of nc-AFM to enable visualization of the dynamics of atoms and molecules on surfaces, which cannot be revealed by nc-AFM topographic images alone.

Imaging modes of atomic force microscopy for application in molecular and cell biology.

PubMed

Dufrêne, Yves F; Ando, Toshio; Garcia, Ricardo; Alsteens, David; Martinez-Martin, David; Engel, Andreas; Gerber, Christoph; Müller, Daniel J

2017-04-06

Atomic force microscopy (AFM) is a powerful, multifunctional imaging platform that allows biological samples, from single molecules to living cells, to be visualized and manipulated. Soon after the instrument was invented, it was recognized that in order to maximize the opportunities of AFM imaging in biology, various technological developments would be required to address certain limitations of the method. This has led to the creation of a range of new imaging modes, which continue to push the capabilities of the technique today. Here, we review the basic principles, advantages and limitations of the most common AFM bioimaging modes, including the popular contact and dynamic modes, as well as recently developed modes such as multiparametric, molecular recognition, multifrequency and high-speed imaging. For each of these modes, we discuss recent experiments that highlight their unique capabilities.

Improving atomic force microscopy imaging by a direct inverse asymmetric PI hysteresis model.

PubMed

Wang, Dong; Yu, Peng; Wang, Feifei; Chan, Ho-Yin; Zhou, Lei; Dong, Zaili; Liu, Lianqing; Li, Wen Jung

2015-02-03

A modified Prandtl-Ishlinskii (PI) model, referred to as a direct inverse asymmetric PI (DIAPI) model in this paper, was implemented to reduce the displacement error between a predicted model and the actual trajectory of a piezoelectric actuator which is commonly found in AFM systems. Due to the nonlinearity of the piezoelectric actuator, the standard symmetric PI model cannot precisely describe the asymmetric motion of the actuator. In order to improve the accuracy of AFM scans, two series of slope parameters were introduced in the PI model to describe both the voltage-increase-loop (trace) and voltage-decrease-loop (retrace). A feedforward controller based on the DIAPI model was implemented to compensate hysteresis. Performance of the DIAPI model and the feedforward controller were validated by scanning micro-lenses and standard silicon grating using a custom-built AFM.

Magnetic Anisotropy by Rashba Spin-Orbit Coupling in Antiferromagnetic Thin Films

NASA Astrophysics Data System (ADS)

Ieda, Jun'ichi; Barnes, Stewart E.; Maekawa, Sadamichi

2018-05-01

Magnetic anisotropy in an antiferromagnet (AFM) with inversion symmetry breaking (ISB) is investigated. The magnetic anisotropy energy (MAE) resulting from the Rashba spin-orbit and s-d type exchange interactions is determined for two different models of AFMs. The global ISB model, representing the effect of a surface, an interface, or a gating electric field, results in an easy-plane magnetic anisotropy. In contrast, for a local ISB model, i.e., for a noncentrosymmetric AFM, perpendicular magnetic anisotropy (PMA) arises. Both results differ from the ferromagnetic case, in which the result for PMA depends on the band structure and dimensionality. These MAE contributions play a key role in determining the direction of the Néel order parameter in antiferromagnetic nanostructures, and reflect the possibility of electrical-field control of the Néel vector.

Effect of the deposition temperature on corrosion resistance and biocompatibility of the hydroxyapatite coatings

NASA Astrophysics Data System (ADS)

Vladescu, A.; Braic, M.; Azem, F. Ak; Titorencu, I.; Braic, V.; Pruna, V.; Kiss, A.; Parau, A. C.; Birlik, I.

2015-11-01

Hydroxyapatite (HAP) ceramics belong to a class of calcium phosphate-based materials, which have been widely used as coatings on titanium medical implants in order to improve bone fixation and thus to increase the lifetime of the implant. In this study, HAP coatings were deposited from pure HAP targets on Ti6Al4V substrates using the radio-frequency magnetron sputtering technique at substrate temperatures ranging from 400 to 800 °C. The surface morphology and the crystallographic structure of the films were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion resistance of the coatings in saliva solution at 37 °C was evaluated by potentiodynamic polarization. Additionally, the human osteosarcoma cell line (MG-63) was used to test the biocompatibility of the coatings. The results showed that all of the coatings grown uniformly and that the increasing substrate temperature induced an increase in their crystallinity. Corrosion performance of the coatings was improved with the increase of the substrate temperature from 400 °C to 800 °C. Furthermore, all the coatings support the attachment and growth of the osteosarcoma cells with regard to the in vitro test findings.

Hf{sub 3}Fe{sub 4}Sn{sub 4} and Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x}: Two stannide intermetallics with low-dimensional iron sublattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calta, Nicholas P.; Kanatzidis, Mercouri G., E-mail: m-kanatzidis@northwestern.edu; Materials Science Division, Argonne National Laboratory

This article reports two new Hf-rich intermetallics synthesized using Sn flux: Hf{sub 3}Fe{sub 4}Sn{sub 4} and Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x}. Hf{sub 3}Fe{sub 4}Sn{sub 4} adopts an ordered variant the Hf{sub 3}Cu{sub 8} structure type in orthorhombic space group Pnma with unit cell edges of a=8.1143(5) Å, b=8.8466(5) Å, and c=10.6069(6) Å. Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x}, on the other hand, adopts a new structure type in Cmc2{sub 1} with unit cell edges of a=5.6458(3) Å, b=35.796(2) Å, and c=8.88725(9) Å for x=0. It exhibits a small amount of phase width in which Sn substitutes on one of the Fe sites. Bothmore » structures are fully three-dimensional and are characterized by pseudo one- and two-dimensional networks of Fe–Fe homoatomic bonding. Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x} exhibits antiferromagnetic order at T{sub N}=46(2) K and its electrical transport behavior indicates that it is a normal metal with phonon-dictated resistivity. Hf{sub 3}Fe{sub 4}Sn{sub 4} is also an antiferromagnet with a rather high ordering temperature of T{sub N}=373(5) K. Single crystal resistivity measurements indicate that Hf{sub 3}Fe{sub 4}Sn{sub 4} behaves as a Fermi liquid at low temperatures, indicating strong electron correlation. - Graphical abstract: Slightly different growth conditions in Sn flux produce two new intermetallic compounds: Hf{sub 3}Fe{sub 4}Sn{sub 4} and Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x}. - Highlights: • Single crystals of both Hf{sub 3}Fe{sub 4}Sn{sub 4} and Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x} were grown using Sn flux. • The crystal structures were determined using single crystal X-ray diffraction. • The Fe moments in Hf{sub 3}Fe{sub 4}Sn{sub 4} display AFM order below T{sub N}=373 K. • The Fe moments in Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x} display AFM order below T{sub N}=46 K.« less

Controlled Atmosphere High Temperature SPM for electrochemical measurements

NASA Astrophysics Data System (ADS)

Vels Hansen, K.; Sander, C.; Koch, S.; Mogensen, M.

2007-03-01

A new controlled atmosphere high temperature SPM has been designed and build for the purpose of performing electrochemical measurements on solid oxide fuel cell materials. The first tests show that images can be obtained at a surface temperature of 465°C in air with a standard AFM AC probe. The aim is to produce images at a surface temperature of 800°C with electrically conducting ceramic probes as working electrodes that can be positioned at desired locations at the surface for electrochemical measurements.

Use of atomic force microscopy in the forensic application of chronological order of toners and stamping inks in questioned documents.

PubMed

Kang, Tae-Yi; Lee, Joong; Park, Byung-Wook

2016-04-01

This paper describes the application of the atomic force microscopy (AFM) as a nano-indentation method and introduces a new method of identifying the chronological order of the application of the toner and stamping ink on the surface of documents by removing either of them. Various toners were used as samples for the AFM nano-indentation method. The chronological order of the application of the toner and stamping ink with either the toner placed over the stamping ink or the stamping ink placed over the toner, could be identified, regardless of the kinds of toners made by various companies. This paper provides the new approach for physically removing the toner and checking the material below it to identify questioned documents, which allows the method to be used to appraise documents forensically. Blind testing has shown that the method to analyze the chronological order of toner-printed documents and the seal stamping on them could accurately identify the order in all samples, while minimizing damage to the samples. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Study of mesoporous CdS-quantum-dot-sensitized TiO2 films by using X-ray photoelectron spectroscopy and AFM

PubMed Central

Wojcieszak, Robert; Raj, Gijo

2014-01-01

Summary CdS quantum dots were grown on mesoporous TiO2 films by successive ionic layer adsorption and reaction processes in order to obtain CdS particles of various sizes. AFM analysis shows that the growth of the CdS particles is a two-step process. The first step is the formation of new crystallites at each deposition cycle. In the next step the pre-deposited crystallites grow to form larger aggregates. Special attention is paid to the estimation of the CdS particle size by X-ray photoelectron spectroscopy (XPS). Among the classical methods of characterization the XPS model is described in detail. In order to make an attempt to validate the XPS model, the results are compared to those obtained from AFM analysis and to the evolution of the band gap energy of the CdS nanoparticles as obtained by UV–vis spectroscopy. The results showed that XPS technique is a powerful tool in the estimation of the CdS particle size. In conjunction with these results, a very good correlation has been found between the number of deposition cycles and the particle size. PMID:24605274

Temperature-Dependent Effect of Boric Acid Additive on Surface Roughness and Wear Rate

NASA Astrophysics Data System (ADS)

Ekinci, Şerafettin

Wear and friction hold an important place in engineering. Currently, scientific societies are struggling to control wear by means of studies on lubricants. Boric acid constitutes an important alternative with its good tribological properties similar to MO2S and graphite alongside with low environmental impacts. Boric acid can be used as a solid lubricant itself whereas it can be added or blended into mineral oils in order to yield better mechanical and tribological properties such as low shear stress due to the lamellar structure and low friction, wear and surface roughness rates. In this study, distinguishing from the literature, boric acid addition effect considering the temperature was investigated for the conventional ranges of internal combustion engines. Surface roughness, wear and friction coefficient values were used in order to determine tribological properties of boric acid as an environmentally friendly additive and mineral oil mixture in the present study. Wear experiments were conducted with a ball on disc experimental setup immersed in an oil reservoir at room temperature, 50∘C and 80∘C. The evolution of both the friction coefficient and wear behavior was determined under 10N load, at 2m/s sliding velocity and a total sliding distance of 9000m. Surface roughness was determined using atomic-force microscopy (AFM). Wear rate was calculated utilizing scanning electron microscope (SEM) visuals and data. The test results showed that wear resistance increased as the temperature increased, and friction coefficient decreased due to the presence of boric acid additive.

Anomalous temperature dependence of training effect in specular spin valve using ultrathin Cr2O3-nano-oxide layer with magnetoelectric effect

NASA Astrophysics Data System (ADS)

Sawada, Kazuya; Shimomura, Naoki; Doi, Masaaki; Sahashi, Masashi

2010-05-01

Exchange bias from antiferromagnetic (AFM) oxides with a magnetoelectric (ME) effect has been studied for controlling ferromagnetic (FM) magnetizations by an applying electric field. However, thick ME oxides are needed for realizing the electrically controlled exchange biasing. Therefore, in this study the temperature dependencies of the training effect for the Cr2O3-nano-oxide-layer (NOL) are investigated for confirming the ME effect of the Cr2O3-NOL. The anomalous temperature tendencies of system dependent constant for exchange bias and magnetoresistance (MR), κHex and κMR, were observed, which are probably originated from the ME effect of the Cr2O3-NOL because (1) these anomalous temperature tendencies could not be obtained in the CoO-NOL spin valve and (2) the κHex and κMR are defined as the strength of the coupling between FM and AFM spins. It is remarkable result for us to confirm the possibility of the ME effect from the ultrathin Cr2O3 layer (less than 1 nm) because the ME effect was observed in only thick ME materials.

Micro- and nano-scale characterization to study the thermal degradation of cement-based materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, Seungmin, E-mail: lim76@illinois.edu; Mondal, Paramita

2014-06-01

The degradation of hydration products of cement is known to cause changes in the micro- and nano-structure, which ultimately drive thermo-mechanical degradation of cement-based composite materials at elevated temperatures. However, a detailed characterization of these changes is still incomplete. This paper presents results of an extensive experimental study carried out to investigate micro- and nano-structural changes that occur due to exposure of cement paste to high temperatures. Following heat treatment of cement paste up to 1000 °C, damage states were studied by compressive strength test, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) atomic force microscopy (AFM) and AFM image analysis.more » Using experimental results and research from existing literature, new degradation processes that drive the loss of mechanical properties of cement paste are proposed. The development of micro-cracks at the interface between unhydrated cement particles and paste matrix, a change in C–S–H nano-structure and shrinkage of C–S–H, are considered as important factors that cause the thermal degradation of cement paste. - Highlights: • The thermal degradation of hydration products of cement is characterized at micro- and nano-scale using scanning electron microscopy (SEM) and atomic force microscopy (AFM). • The interface between unhydrated cement particles and the paste matrix is considered the origin of micro-cracks. • When cement paste is exposed to temperatures above 300 ºC, the nano-structure of C-S-H becomes a more loosely packed globular structure, which could be indicative of C-S-H shrinkage.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solares, Santiago D.

This study introduces a quasi-3-dimensional (Q3D) viscoelastic model and software tool for use in atomic force microscopy (AFM) simulations. The model is based on a 2-dimensional array of standard linear solid (SLS) model elements. The well-known 1-dimensional SLS model is a textbook example in viscoelastic theory but is relatively new in AFM simulation. It is the simplest model that offers a qualitatively correct description of the most fundamental viscoelastic behaviors, namely stress relaxation and creep. However, this simple model does not reflect the correct curvature in the repulsive portion of the force curve, so its application in the quantitative interpretationmore » of AFM experiments is relatively limited. In the proposed Q3D model the use of an array of SLS elements leads to force curves that have the typical upward curvature in the repulsive region, while still offering a very low computational cost. Furthermore, the use of a multidimensional model allows for the study of AFM tips having non-ideal geometries, which can be extremely useful in practice. Examples of typical force curves are provided for single- and multifrequency tappingmode imaging, for both of which the force curves exhibit the expected features. Lastly, a software tool to simulate amplitude and phase spectroscopy curves is provided, which can be easily modified to implement other controls schemes in order to aid in the interpretation of AFM experiments.« less

Quantum critical singularities in two-dimensional metallic XY ferromagnets

NASA Astrophysics Data System (ADS)

Varma, Chandra M.; Gannon, W. J.; Aronson, M. C.; Rodriguez-Rivera, J. A.; Qiu, Y.

2018-02-01

An important problem in contemporary physics concerns quantum-critical fluctuations in metals. A scaling function for the momentum, frequency, temperature, and magnetic field dependence of the correlation function near a 2D-ferromagnetic quantum-critical point (QCP) is constructed, and its singularities are determined by comparing to the recent calculations of the correlation functions of the dissipative quantum XY model (DQXY). The calculations are motivated by the measured properties of the metallic compound YFe2Al10 , which is a realization of the DQXY model in 2D. The frequency, temperature, and magnetic field dependence of the scaling function as well as the singularities measured in the experiments are given by the theory without adjustable exponents. The same model is applicable to the superconductor-insulator transitions, classes of metallic AFM-QCPs, and as fluctuations of the loop-current ordered state in hole-doped cuprates. The results presented here lend credence to the solution found for the 2D-DQXY model and its applications in understanding quantum-critical properties of diverse systems.

Interactions of collagen molecules in the presence of N-hydroxysuccinimide activated adipic acid (NHS-AA) as a crosslinking agent.

PubMed

Zhang, Min; Wu, Kun; Li, Guoying

2011-11-01

The effect of crosslinking agent on pepsin-soluble bovine collagen solution was examined using N-hydroxysuccinimide activated adipic acid (NHS-AA) as a crosslinker. Electrophoretic patterns indicated that crosslinks formed when NHS-AA was added. A higher polarity level deduced from the changes in the fluorescence emission spectrum of pyrene in the crosslinked collagen solution indicated that the formation of well-ordered aggregates was suppressed. The random aggregation of collagens was also observed by atomic force microscopy (AFM). Furthermore, the association of collagens into fibrils was influenced by crosslinking. Self-assembly was suppressed at 37°C; however, as temperature was increased to 39°C, a small amount of NHS-AA leaded to an improvement in the ability of self-aggregation. Although more random structure was brought about by crosslinking, self-aggregation might still be promoted as temperature was increased, accompanying by the thermal stability improvement of fibrils. Copyright © 2011 Elsevier B.V. All rights reserved.

Structural and magnetic analysis of Cu, Co substituted NiFe2O4 thin films

NASA Astrophysics Data System (ADS)

Sharma, Hakikat; Bala, Kanchan; Negi, N. S.

2016-05-01

In the present work we prepared NiFe2O4, Ni0.95Cu0.05Fe2O4 and Ni0.94Cu0.05Co0.01 Fe2O4 thin films by metallo-organic decomposition method (MOD) using spin coating technique. The thin films were analyzed by X-ray diffractometer (XRD) and Atomic force microscope (AFM) for structural studies. The XRD patterns confirmed the ferrite phase of thin films. From AFM, we analyzed surface morphology, calculated grain size (GS) and root mean square roughness (RMSR). Room temperature magnetic properties were investigated by vibrating sample magnetometer (VSM).

Mechanical Properties of Stable Glasses Using Nanoindentation

NASA Astrophysics Data System (ADS)

Wolf, Sarah; Liu, Tianyi; Jiang, Yijie; Ablajan, Keyume; Zhang, Yue; Walsh, Patrick; Turner, Kevin; Fakhraai, Zahra

Glasses with enhanced stability over ordinary, liquid quenched glasses have been formed via the process of Physical Vapor Deposition (PVD) by using a sufficiently slow deposition rate and a substrate temperature slightly below the glass transition temperature. These stable glasses have been shown to exhibit higher density, lower enthalpy, and better kinetic stability over ordinary glass, and are typically optically birefringent, due to packing and orientational anisotropy. Given these exceptional properties, it is of interest to further investigate how the properties of stable glasses compare to those of ordinary glass. In particular, the mechanical properties of stable glasses remain relatively under-investigated. While the speed of sound and elastic moduli have been shown to increase with increased stability, little is known about their hardness and fracture toughness compared to ordinary glasses. In this study, glasses of 9-(3,5-di(naphthalen-1-yl)phenyl)anthracene were deposited at varying temperatures relative to their glass transition temperature, and their mechanical properties measured by nanoindentation. Hardness and elastic modulus of the glasses were compared across substrate temperatures. After indentation, the topography of these films were studied using Atomic Force Microscopy (AFM) in order to further compare the relationship between thermodynamic and kinetic stability and mechanical failure. Z.F. and P.W. acknowledge funding from NSF(DMREF-1628407).

BOREAS AFM-1 NOAA/ATDD Long-EZ Aircraft Flux data Over the SSA

NASA Technical Reports Server (NTRS)

Crawford, Timothy L.; Baldocchi, Dennis; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Gunter, Laureen; Dumas, Ed; Smith, David E. (Technical Monitor)

2000-01-01

This data set contains measurements from the Airborne Flux and Meteorology (AFM)-1 National Oceanographic and Atmospheric Administration/Atmospheric Turbulence and Diffusion Division (NOAA/ATDD) Long-EZ Aircraft collected during the 1994 Intensive Field Campaigns (IFCs) at the southern study area (SSA). These measurements were made from various instruments mounted on the aircraft. The data that were collected include aircraft altitude, wind direction, wind speed, air temperature, potential temperature, water mixing ratio, U and V components of wind velocity, static pressure, surface radiative temperature, downwelling and upwelling total radiation, downwelling and upwelling longwave radiation, net radiation, downwelling and upwelling photosynthectically active radiation (PAR), greenness index, CO2 concentration, O3 concentration, and CH4 concentration. There are also various columns that indicate the standard deviation, skewness, kurtosis, and trend of some of these data. The data are stored in tabular ASCII files. The NOAA/ATDD Long-EZ aircraft flux data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

Universal aspects of sonolubrication in amorphous and crystalline materials

NASA Astrophysics Data System (ADS)

Pfahl, V.; Ma, C.; Arnold, W.; Samwer, K.

2018-01-01

We studied sonolubricity, a phenomenon reducing the friction between two sliding surfaces by ultrasound. Friction force measurements were performed using an atomic force microscope (AFM) when the tip-surface contact was excited to out-of-plane oscillations by a transducer attached to the rear of the sample or by oscillating the AFM cantilever by the built-in piezoelectric element in the cantilever holder. Experiments were carried out near or at the first cantilever contact-resonance. We studied friction on crystalline and amorphous Pd77.5Cu6Si16.5 ribbons, on a silicon wafer at room temperature, and on a La0.6Sr0.4MnO3 (LSMO) thin film at different temperatures. Measurements were carried out varying the cantilever amplitude, the ultrasonic frequency, and the normal static load. The effect of sonolubrication is explained by the non-linear force-distance curve between the sample and the tip due to the local interaction potential. The reduction of friction in LSMO as a function temperature is due to the direct coupling of the tip's stress-field to the electrons.

Effect of annealing temperature on the properties of copper oxide films prepared by dip coating technique

NASA Astrophysics Data System (ADS)

Raship, N. A.; Sahdan, M. Z.; Adriyanto, F.; Nurfazliana, M. F.; Bakri, A. S.

2017-01-01

Copper oxide films were grown on silicon substrates by sol-gel dip coating method. In order to study the effects of annealing temperature on the properties of copper oxide films, the temperature was varied from 200 °C to 450 °C. In the process of dip coating, the substrate is withdrawn from the precursor solution with uniform velocity to obtain a uniform coating before undergoing an annealing process to make the copper oxide film polycrystalline. The physical properties of the copper oxide films were measured by an X-ray diffraction (XRD), a field emission scanning electron microscope (FESEM), an atomic force microscopy (AFM) and a four point probe instrument. From the XRD results, we found that pure cuprite (Cu2O) phase can be obtained by annealing the films annealed at 200 °C. Films annealed at 300 °C had a combination phase which consists of tenorite (CuO) and cuprite (Cu2O) phase while pure tenorite (CuO) phase can be obtained at 450 °C annealing temperature. The surface microstructure showed that the grains size is increased whereas the surface roughness is increased and then decreases by increasing in annealing temperature. The films showed that the resistivity decreased with increasing annealing temperature. Consequently, it was observed that annealing temperature has strong effects on the structural, morphological and electrical properties of copper oxide films.

Impact of varying buffer thickness generated strain and threading dislocations on the formation of plasma assisted MBE grown ultra-thin AlGaN/GaN heterostructure on silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chowdhury, Subhra, E-mail: subhra1109@gmail.com; Biswas, Dhrubes; Department of E and E C E, Indian Institute of Technology Kharagpur, Kharagpur 721302

2015-05-15

Plasma-assisted molecular beam epitaxy (PAMBE) growth of ultra-thin Al{sub 0.2}Ga{sub 0.8}N/GaN heterostructures on Si(111) substrate with three buffer thickness (600 nm/400 nm/200 nm) have been reported. An unique growth process has been developed that supports lower temperature epitaxy of GaN buffer which minimizes thermally generated tensile strain through appropriate nitridation and AlN initiated epitaxy for achieving high quality GaN buffer which supports such ultra-thin heterostructures in the range of 10-15Å. It is followed by investigations of role of buffer thickness on formation of ultra-thin Al{sub 0.2}Ga{sub 0.8}N/GaN heterostructure, in terms of stress-strain and threading dislocation (TD). Structural characterization were performedmore » by High-Resolution X-Ray Diffraction (HRXRD), room-temperature Photoluminescence (RT-PL), High Resolution Transmission Electron Microscopy (HRTEM) and Atomic Force Microscopy (AFM). Analysis revealed increasing biaxial tensile stress of 0.6918 ± 0.04, 1.1084, 1.1814 GPa in heterostructures with decreasing buffer thickness of 600, 400, 200 nm respectively which are summed up with residual tensile strain causing red-shift in RT-PL peak. Also, increasing buffer thickness drastically reduced TD density from the order 10{sup 10} cm{sup −2} to 10{sup 8} cm{sup −2}. Surface morphology through AFM leads to decrease of pits and root mean square value with increasing buffer thickness which are resulted due to reduction of combined effect of strain and TDs.« less

Nano-Bio-Mechanics of Neuroblastoma Cells Using AFM

NASA Astrophysics Data System (ADS)

Bastatas, Lyndon; Matthews, James; Kang, Min; Park, Soyeun

2011-10-01

We have conducted an in vitro study to determine the elastic moduli of neurobalstoma cell lines using atomic force microscopy. Using a panel of cell lines established from neuroblastoma patients at different stages of disease progress and treatment, we have investigated the differences in elastic moduli during a course of cancer progression and chemotherapy. The cells were grown on the hard substrates that are chemically functionalized to enhance adhesion. We have performed the AFM indentation experiments with different applied forces from the AFM probe. For the purpose of the comparison between cell lines, the indentations were performed only on cell centers. The obtained force-distance curves were analyzed using the Hertz model in order to extract the elastic moduli. We have found that the elastic moduli of human neuroblastoma cells significantly varied during the disease progression. We postulate that the observed difference might be affected by the treatment and chemotherapy.

The long range voice coil atomic force microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barnard, H.; Randall, C.; Bridges, D.

2012-02-15

Most current atomic force microscopes (AFMs) use piezoelectric ceramics for scan actuation. Piezoelectric ceramics provide precision motion with fast response to applied voltage potential. A drawback to piezoelectric ceramics is their inherently limited ranges. For many samples this is a nonissue, as imaging the nanoscale details is the goal. However, a key advantage of AFM over other microscopy techniques is its ability to image biological samples in aqueous buffer. Many biological specimens have topography for which the range of piezoactuated stages is limiting, a notable example of which is bone. In this article, we present the use of voice coilsmore » in scan actuation for an actuation range in the Z-axis an order of magnitude larger than any AFM commercially available today. The increased scan size will allow for imaging an important new variety of samples, including bone fractures.« less

Ab initio simulations of subatomic resolution images in noncontact atomic force microscopy

NASA Astrophysics Data System (ADS)

Kim, Minjung; Chelikowsky, James R.

2015-03-01

Direct imaging of polycyclic aromatic molecules with a subatomic resolution has recently been achieved with noncontact atomic force microscopy (nc-AFM). Specifically, nc-AFM employing a CO functionalized tip has provided details of the chemical bond in aromatic molecules, including the discrimination of bond order. However, the underlying physics of such high resolution imaging remains problematic. By employing new, efficient algorithms based on real space pseudopotentials, we calculate the forces between the nc-AFM tip and specimen. We simulate images of planar organic molecules with two different approaches: 1) with a chemically inert tip and 2) with a CO functionalized tip. We find dramatic differences in the resulting images, which are consistent with recent experimental work. Our work is supported by the DOE under DOE/DE-FG02-06ER46286 and by the Welch Foundation under Grant F-1837. Computational resources were provided by NERSC and XSEDE.

Inverting dynamic force microscopy: From signals to time-resolved interaction forces

PubMed Central

Stark, Martin; Stark, Robert W.; Heckl, Wolfgang M.; Guckenberger, Reinhard

2002-01-01

Transient forces between nanoscale objects on surfaces govern friction, viscous flow, and plastic deformation, occur during manipulation of matter, or mediate the local wetting behavior of thin films. To resolve transient forces on the (sub) microsecond time and nanometer length scale, dynamic atomic force microscopy (AFM) offers largely unexploited potential. Full spectral analysis of the AFM signal completes dynamic AFM. Inverting the signal formation process, we measure the time course of the force effective at the sensing tip. This approach yields rich insight into processes at the tip and dispenses with a priori assumptions about the interaction, as it relies solely on measured data. Force measurements on silicon under ambient conditions demonstrate the distinct signature of the interaction and reveal that peak forces exceeding 200 nN are applied to the sample in a typical imaging situation. These forces are 2 orders of magnitude higher than those in covalent bonds. PMID:12070341

Finite element modeling of trolling-mode AFM.

PubMed

Sajjadi, Mohammadreza; Pishkenari, Hossein Nejat; Vossoughi, Gholamreza

2018-06-01

Trolling mode atomic force microscopy (TR-AFM) has overcome many imaging problems in liquid environments by considerably reducing the liquid-resonator interaction forces. The finite element model of the TR-AFM resonator considering the effects of fluid and nanoneedle flexibility is presented in this research, for the first time. The model is verified by ABAQUS software. The effect of installation angle of the microbeam relative to the horizon and the effect of fluid on the system behavior are investigated. Using the finite element model, frequency response curve of the system is obtained and validated around the frequency of the operating mode by the available experimental results, in air and liquid. The changes in the natural frequencies in the presence of liquid are studied. The effects of tip-sample interaction on the excitation of higher order modes of the system are also investigated in air and liquid environments. Copyright © 2018 Elsevier B.V. All rights reserved.

Improving Atomic Force Microscopy Imaging by a Direct Inverse Asymmetric PI Hysteresis Model

PubMed Central

Wang, Dong; Yu, Peng; Wang, Feifei; Chan, Ho-Yin; Zhou, Lei; Dong, Zaili; Liu, Lianqing; Li, Wen Jung

2015-01-01

A modified Prandtl–Ishlinskii (PI) model, referred to as a direct inverse asymmetric PI (DIAPI) model in this paper, was implemented to reduce the displacement error between a predicted model and the actual trajectory of a piezoelectric actuator which is commonly found in AFM systems. Due to the nonlinearity of the piezoelectric actuator, the standard symmetric PI model cannot precisely describe the asymmetric motion of the actuator. In order to improve the accuracy of AFM scans, two series of slope parameters were introduced in the PI model to describe both the voltage-increase-loop (trace) and voltage-decrease-loop (retrace). A feedforward controller based on the DIAPI model was implemented to compensate hysteresis. Performance of the DIAPI model and the feedforward controller were validated by scanning micro-lenses and standard silicon grating using a custom-built AFM. PMID:25654719

Nanospot soldering polystyrene nanoparticles with an optical fiber probe laser irradiating a metallic AFM probe based on the near-field enhancement effect.

PubMed

Cui, Jianlei; Yang, Lijun; Wang, Yang; Mei, Xuesong; Wang, Wenjun; Hou, Chaojian

2015-02-04

With the development of nanoscience and nanotechnology for the bottom-up nanofabrication of nanostructures formed from polystyrene nanoparticles, joining technology is an essential step in the manufacturing and assembly of nanodevices and nanostructures in order to provide mechanical integration and connection. To study the nanospot welding of polystyrene nanoparticles, we propose a new nanospot-soldering method using the near-field enhancement effect of a metallic atomic force microscope (AFM) probe tip that is irradiated by an optical fiber probe laser. On the basis of our theoretical analysis of the near-field enhancement effect, we set up an experimental system for nanospot soldering; this approach is carried out by using an optical fiber probe laser to irradiate the AFM probe tip to sinter the nanoparticles, providing a promising technical approach for the application of nanosoldering in nanoscience and nanotechnology.

Influence of growth temperature on laser molecular beam epitaxy and properties of GaN layers grown on c-plane sapphire

NASA Astrophysics Data System (ADS)

Dixit, Ripudaman; Tyagi, Prashant; Kushvaha, Sunil Singh; Chockalingam, Sreekumar; Yadav, Brajesh Singh; Sharma, Nita Dilawar; Kumar, M. Senthil

2017-04-01

We have investigated the influence of growth temperature on the in-plane strain, structural, optical and mechanical properties of heteroepitaxially grown GaN layers on sapphire (0001) substrate by laser molecular beam epitaxy (LMBE) technique in the temperature range 500-700 °C. The GaN epitaxial layers are found to have a large in-plane compressive stress of about 1 GPa for low growth temperatures but the strain drastically reduced in the layer grown at 700 °C. The nature of the in-plane strain has been analyzed using high resolution x-ray diffraction, atomic force microscopy (AFM), Raman spectroscopy and photoluminescence (PL) measurements. From AFM, a change in GaN growth mode from grain to island is observed at the high growth temperature above 600 °C. A blue shift of 20-30 meV in near band edge PL emission line has been noticed for the GaN layers containing the large in-plane strain. These observations indicate that the in-plane strain in the GaN layers is dominated by a biaxial strain. Using nanoindentation, it is found that the indentation hardness and Young's modulus of the GaN layers increases with increasing growth temperature. The results disclose the critical role of growth mode in determining the in-plane strain and mechanical properties of the GaN layers grown by LMBE technique.

Exchange bias in zinc ferrite-FeNiMoB based metallic glass composite thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

R, Lisha; P, Geetha; B, Aravind P.

2015-06-24

The Exchange bias phenomenon and methods to manipulate the bias field in a controlled manner are thrust areas in magnetism due to its sophisticated theoretical concepts as well as advanced technological utility in the field of spintronics. The Exchange bias effect is observed as a result of ferromagnetic-antiferromagnetic (FM-AFM) exchange interaction, usually observed as a loop shift on field cooling below the Neel temperature of AFM. In the present study, we have chosen zinc ferrite which is a well known antiferromagnet, and FeNiMoB based metallic glass as the ferromagnet. The films were prepared by RF sputtering technique. The thickness andmore » composition was obtained by RBS. The magnetic studies using SQUID VSM indicate exchange bias effect in the system. The effect of thermal annealing on exchange bias effect was studied. The observed exchange bias in the zinc ferrite-FeNiMoB system is not due to FM-AFM coupling but due to spin glass-ferromagnetic interaction.« less

Materials, Devices and Spin Transfer Torque in Antiferromagnetic Spintronics: A Concise Review

NASA Astrophysics Data System (ADS)

Coileáin, Cormac Ó.; Wu, Han Chun

From historical obscurity, antiferromagnets are recently enjoying revived interest, as antiferromagnetic (AFM) materials may allow the continued reduction in size of spintronic devices. They have the benefit of being insensitive to parasitic external magnetic fields, while displaying high read/write speeds, and thus poised to become an integral part of the next generation of logical devices and memory. They are currently employed to preserve the magnetoresistive qualities of some ferromagnetic based giant or tunnel magnetoresistance systems. However, the question remains how the magnetic states of an antiferromagnet can be efficiently manipulated and detected. Here, we reflect on AFM materials for their use in spintronics, in particular, newly recognized antiferromagnet Mn2Au with its in-plane anisotropy and tetragonal structure and high Néel temperature. These attributes make it one of the most promising candidates for AFM spintronics thus far with the possibility of architectures freed from the need for ferromagnetic (FM) elements. Here, we discuss its potential for use in ferromagnet-free spintronic devices.

Exchange bias in zinc ferrite-FeNiMoB based metallic glass composite thin films

NASA Astrophysics Data System (ADS)

R, Lisha; T, Hysen; P, Geetha; B, Aravind P.; Ojha, S.; Avasthi, D. K.; Ramanujan, R. V.; Anantharaman, M. R.

2015-06-01

The Exchange bias phenomenon and methods to manipulate the bias field in a controlled manner are thrust areas in magnetism due to its sophisticated theoretical concepts as well as advanced technological utility in the field of spintronics. The Exchange bias effect is observed as a result of ferromagnetic-antiferromagnetic (FM-AFM) exchange interaction, usually observed as a loop shift on field cooling below the Neel temperature of AFM. In the present study, we have chosen zinc ferrite which is a well known antiferromagnet, and FeNiMoB based metallic glass as the ferromagnet. The films were prepared by RF sputtering technique. The thickness and composition was obtained by RBS. The magnetic studies using SQUID VSM indicate exchange bias effect in the system. The effect of thermal annealing on exchange bias effect was studied. The observed exchange bias in the zinc ferrite-FeNiMoB system is not due to FM-AFM coupling but due to spin glass-ferromagnetic interaction.

Pressure effect on ferroelectricity of multiferroic Ho0.5Nd0.5Fe3(BO3)4

NASA Astrophysics Data System (ADS)

Poudel, Narayan; Gooch, Melissa; Lorenz, Bernd; Bezmaternykh, L. N.; Temerov, V. L.; Chu, C. W.

Ho0.5Nd0.5Fe3(BO3)4 becomes multiferroic below 33 K where it enters into the AFM1 phase and gives rise to a ferroelectric polarization along the a-axis. At 9.5 K, the polarization drops sharply and remains finite value of 40 μC/m2. This is due to the spin rotation from the a-b plane into the c-axis and gives rise to the AFM2 phase. The application of pressure suppresses the AFM2 phase and moves the spin rotation transition from 9.5 K to 4.8 K up to pressure of 18.8 kbar which is observed in both dielectric and pyroelectric measurements. The change in magnetic anisotropy of rare-earth moments and Fe ions under pressure drives the spin rotation transition of rare-earth at lower temperature. DOE, the AFOSR, the T.L.L Temple Foundation, the J.J. and R. Moores Endowment, and the State of Texas (TCSUH).

High-resolution AFM structure of DNA G-wires in aqueous solution.

PubMed

Bose, Krishnashish; Lech, Christopher J; Heddi, Brahim; Phan, Anh Tuân

2018-05-17

We investigate the self-assembly of short pieces of the Tetrahymena telomeric DNA sequence d[G 4 T 2 G 4 ] in physiologically relevant aqueous solution using atomic force microscopy (AFM). Wire-like structures (G-wires) of 3.0 nm height with well-defined surface periodic features were observed. Analysis of high-resolution AFM images allowed their classification based on the periodicity of these features. A major species is identified with periodic features of 4.3 nm displaying left-handed ridges or zigzag features on the molecular surface. A minor species shows primarily left-handed periodic features of 2.2 nm. In addition to 4.3 and 2.2 nm ridges, background features with periodicity of 0.9 nm are also observed. Using molecular modeling and simulation, we identify a molecular structure that can explain both the periodicity and handedness of the major G-wire species. Our results demonstrate the potential structural diversity of G-wire formation and provide valuable insight into the structure of higher-order intermolecular G-quadruplexes. Our results also demonstrate how AFM can be combined with simulation to gain insight into biomolecular structure.

Characterization of surface roughness of laser deposited titanium alloy and copper using AFM

NASA Astrophysics Data System (ADS)

Erinosho, M. F.; Akinlabi, E. T.; Johnson, O. T.

2018-03-01

Laser Metal Deposition (LMD) is the process of using the laser beam of a nozzle to produce a melt pool on a metal surface usually the substrate and metal powder is been deposited into it thereby creating a fusion bond with the substrate to form a new material layer against the force gravity. A good metal laminate is formed when the wettability between the dropping metal powder and the substrate adheres. This paper reports the surface roughness of laser deposited titanium alloy and copper (Ti6Al4V + Cu) using the Atomic Force Microscopy (AFM). This AFM is employed in order to sense the surface and produce different manipulated images using the micro-fabricated mechanical tip under a probe cartridge of high resolution. The process parameters employed during the deposition routine determines the output of the deposit. A careful attention is given to the laser deposited Ti6Al4V + Cu samples under the AFM probe because of their single tracked layers with semi-circular pattern of deposition. This research work can be applicable in the surface modification of laser deposited samples for the marine industry.

Direct Force Measurements of Receptor-Ligand Interactions on Living Cells

NASA Astrophysics Data System (ADS)

Eibl, Robert H.

The characterization of cell adhesion between two living cells at the level of single receptor-ligand bonds is an experimental challenge. This chapter describes how the extremely sensitive method of atomic force microscopy (AFM) based force spectroscopy can be applied to living cells in order to probe for cell-to-cell or cell-to-substrate interactions mediated by single pairs of adhesion receptors. In addition, it is outlined how single-molecule AFM force spectroscopy can be used to detect physiologic changes of an adhesion receptor in a living cell. This force spectroscopy allows us to detect in living cells rapidly changing, chemokine SDF-1 triggered activation states of single VLA-4 receptors. This recently developed AFM application will allow for the detailed investigation of the integrin-chemokine crosstalk of integrin activation mechanisms and on how other adhesion receptors are modulated in health and disease. As adhesion molecules, living cells and even bacteria can be studied by single-molecule AFM force spectroscopy, this method is set to become a powerful tool that can not only be used in biophysics, but in cell biology as well as in immunology and cancer research.

Formation of SIMOX-SOI structure by high-temperature oxygen implantation

NASA Astrophysics Data System (ADS)

Hoshino, Yasushi; Kamikawa, Tomohiro; Nakata, Jyoji

2015-12-01

We have performed oxygen ion implantation in silicon at very high substrate-temperatures (⩽1000 °C) for the purpose of forming silicon-on-insulator (SOI) structure. We have expected that the high-temperature implantation can effectively avoids ion-beam-induced damages in the SOI layer and simultaneously stabilizes the buried oxide (BOX) and SOI-Si layer. Such a high-temperature implantation makes it possible to reduce the post-implantation annealing temperature. In the present study, oxygen ions with 180 keV are incident on Si(0 0 1) substrates at various temperatures from room temperature (RT) up to 1000 °C. The ion-fluencies are in order of 1017-1018 ions/cm2. Samples have been analyzed by atomic force microscope, Rutherford backscattering, and micro-Raman spectroscopy. It is found in the AFM analysis that the surface roughness of the samples implanted at 500 °C or below are significantly small with mean roughness of less than 1 nm, and gradually increased for the 800 °C-implanted sample. On the other hand, a lot of dents are observed for the 1000 °C-implanted sample. RBS analysis has revealed that stoichiometric SOI-Si and BOX-SiO2 layers are formed by oxygen implantation at the substrate temperatures of RT, 500, and 800 °C. However, SiO2-BOX layer has been desorbed during the implantation. Raman spectra shows that the ion-beam-induced damages are fairly suppressed by such a high-temperatures implantation.

Electronic Transport Through Carbon Nanotubes: Effects of Structural Deformation and the Tube Chirality

NASA Technical Reports Server (NTRS)

Maiti, Amitesh; Svizhenko, Alexei; Anantram, M. P.; Biegel, Bryan (Technical Monitor)

2001-01-01

Atomistic simulations using a combination of classical force field and Density-Functional-Theory (DFT) show that carbon atoms remain essentially sp2 coordinated in either bent tubes or tubes pushed by an atomically sharp AFM tip. Subsequent Green's-function-based transport calculations reveal that for armchair tubes there is no significant drop in conductance, while for zigzag tubes the conductance can drop by several orders of magnitude in AFM-pushed tubes. The effect can be attributed to simple stretching of the tube under tip deformation, which opens up an energy gap at the Fermi surface.

Dynamic-force spectroscopy measurement with precise force control using atomic-force microscopy probe

NASA Astrophysics Data System (ADS)

Takeuchi, Osamu; Miyakoshi, Takaaki; Taninaka, Atsushi; Tanaka, Katsunori; Cho, Daichi; Fujita, Machiko; Yasuda, Satoshi; Jarvis, Suzanne P.; Shigekawa, Hidemi

2006-10-01

The accuracy of dynamic-force spectroscopy (DFS), a promising technique of analyzing the energy landscape of noncovalent molecular bonds, was reconsidered in order to justify the use of an atomic-force microscopy (AFM) cantilever as a DFS force probe. The advantages and disadvantages caused, for example, by the force-probe hardness were clarified, revealing the pivotal role of the molecular linkage between the force probe and the molecular bonds. It was shown that the feedback control of the loading rate of tensile force enables us a precise DFS measurement using an AFM cantilever as the force probe.

Nanostructured pyronin Y thin films as a new organic semiconductor: Linear/nonlinear optics, band gap and dielectric properties

NASA Astrophysics Data System (ADS)

Zahran, H. Y.; Yahia, I. S.; Alamri, F. H.

2017-05-01

Pyronin Y dye (PY) is a kind of xanthene derivatives. Thin films of pyronin Y were deposited onto highly cleaned glass substrates using low-cost/spin coating technique. The structure properties of pyronin Y thin films with different thicknesses were investigated by using X-ray diffraction (XRD) and atomic force microscope (AFM). PY thin films for all the studied thicknesses have an amorphous structure supporting the short range order of the grain size. AFM supports the nanostructure with spherical/clusters morphologies of the investigated thin films. The optical constants of pyronin Y thin films for various thicknesses were studied by using UV-vis-NIR spectrophotometer in the wavelength range 350-2500 nm. The transmittance T(λ), reflectance R(λ) spectral and absorbance (abs(λ)) were obtained for all film thicknesses at room temperature and the normal light incident. These films showed a high transmittance in the wide scale wavelengths. For different thicknesses of the studied thin films, the optical band gaps were determined and their values around 2 eV. Real and imaginary dielectric constants, dissipation factor and the nonlinear optical parameters were calculated in the wavelengths to the range 300-2500 nm. The pyronin Y is a new organic semiconductor with a good optical absorption in UV-vis regions and it is suitable for nonlinear optical applications.

Investigation of PDMS based bi-layer elasticity via interpretation of apparent Young's modulus.

PubMed

Sarrazin, Baptiste; Brossard, Rémy; Guenoun, Patrick; Malloggi, Florent

2016-02-21

As the need of new methods for the investigation of thin films on various kinds of substrates becomes greater, a novel approach based on AFM nanoindentation is explored. Substrates of polydimethylsiloxane (PDMS) coated by a layer of hard material are probed with an AFM tip in order to obtain the force profile as a function of the indentation. The equivalent elasticity of those composite systems is interpreted using a new numerical approach, the Coated Half-Space Indentation Model of Elastic Response (CHIMER), in order to extract the thicknesses of the upper layer. Two kinds of coating are investigated. First, chitosan films of known thicknesses between 30 and 200 nm were probed in order to test the model. A second type of samples is produced by oxygen plasma oxidation of the PDMS substrate, which results in the growth of a relatively homogeneous oxide layer. The local nature of this protocol enables measurements at long oxidation time, where the apparition of cracks prevents other kinds of measurements.

Multi-pole orders and Kondo screening: Implications for quantum phase transitions in multipolar heavy-fermion systems

NASA Astrophysics Data System (ADS)

Lai, Hsin-Hua; Nica, Emilian; Si, Qimiao

Motivated by the properties of the heavy-fermion Ce3Pd20Si6 compound which exhibits both antiferro-magnetic (AFM) and antiferro-quadrupolar (AFQ) orders, we study a simplified quantum non-linear sigma model for spin-1 systems, with generalized multi-pole Kondo couplings to conduction electrons. We first consider the case when an SU(3) symmetry relates the spin and quadrupolar channels. We then analyze the effect of breaking the SU(3) symmetry, so that the interaction parameters in the spin and quadrupolar sectors are no longer equivalent, and different stages of Kondo screenings are allowed. A renormalization group analysis is used to analyze the interplay between the Kondo effect and the AFM/AFQ orders. Our work paves the way for understanding the global phase diagram in settings beyond the prototypical spin-1/2 cases. We also discuss similar considerations in the non-Kramers systems such as the heavy fermion compound PrV2Al20

Mott criticality and multiferroicity in organic κ-(BEDT-TTF)2X salts

NASA Astrophysics Data System (ADS)

Lang, Michael

2014-03-01

Layered organic charge-transfer (CT) salts of the κ-(BEDT-TTF)2X family show a wealth of electronic phases resulting from the interplay of strong electron-electron correlations, reduced dimensions and magnetic frustration. Of particular interest has been the bandwidth-controlled Mott transition, separating an antiferromagnetic (afm) insulating state from a correlated metallic and superconducting state. Whereas the hydrogenated X = Cu[N(CN)2]Br salt is located on the metallic side, the deuterated variant, denoted κ-D8, is situated in splitting distance to the Mott transition, enabling the s-shaped transition line TMI to be crossed via temperature sweeps. The talk will address the following aspects: 1) Thermal expansion measurements on single crystalline κ-D8 reveal discontinuous changes of the lattice parameters on crossing the Mott transition line and a huge anomaly close to the second-order critical end point of TMI. By elaborating on a scaling theory, we found that (i) the latter effect is a consequence of an almost divergence of the Grüneisen parameter Γ at the finite- T critical end point, and (ii) that the expansivity data of are in excellent agreement with the Mott criticality lying within the 2D Ising universality class, at variance with results from conductivity measurements. Thermal expansion measurements under Helium-gas pressure are underway for providing thermodynamic information at variable pressure. 2) Surprisingly, for the isostructural X = Cu[N(CN)2]Cl salt, located close to the Mott transition on the insulating side, we found that besides the well-established afm order at TN ~ 27 K, the system also reveals a ferroelectric transition at TFE, making this material the first multiferroic CT salt. Most remarkably, the measurements reveal TFE ~TN , suggesting a close interrelation between both types of ferroic order. Work was supported by Deutsche Forschungsgemeinschaft through the Collaborative Research Centers TRR 49 and TRR 80.

A simple and efficient quasi 3-dimensional viscoelastic model and software for simulation of tapping-mode atomic force microscopy

DOE PAGES

Solares, Santiago D.

2015-11-26

This study introduces a quasi-3-dimensional (Q3D) viscoelastic model and software tool for use in atomic force microscopy (AFM) simulations. The model is based on a 2-dimensional array of standard linear solid (SLS) model elements. The well-known 1-dimensional SLS model is a textbook example in viscoelastic theory but is relatively new in AFM simulation. It is the simplest model that offers a qualitatively correct description of the most fundamental viscoelastic behaviors, namely stress relaxation and creep. However, this simple model does not reflect the correct curvature in the repulsive portion of the force curve, so its application in the quantitative interpretationmore » of AFM experiments is relatively limited. In the proposed Q3D model the use of an array of SLS elements leads to force curves that have the typical upward curvature in the repulsive region, while still offering a very low computational cost. Furthermore, the use of a multidimensional model allows for the study of AFM tips having non-ideal geometries, which can be extremely useful in practice. Examples of typical force curves are provided for single- and multifrequency tappingmode imaging, for both of which the force curves exhibit the expected features. Lastly, a software tool to simulate amplitude and phase spectroscopy curves is provided, which can be easily modified to implement other controls schemes in order to aid in the interpretation of AFM experiments.« less

A simple and efficient quasi 3-dimensional viscoelastic model and software for simulation of tapping-mode atomic force microscopy.

PubMed

Solares, Santiago D

2015-01-01

This paper introduces a quasi-3-dimensional (Q3D) viscoelastic model and software tool for use in atomic force microscopy (AFM) simulations. The model is based on a 2-dimensional array of standard linear solid (SLS) model elements. The well-known 1-dimensional SLS model is a textbook example in viscoelastic theory but is relatively new in AFM simulation. It is the simplest model that offers a qualitatively correct description of the most fundamental viscoelastic behaviors, namely stress relaxation and creep. However, this simple model does not reflect the correct curvature in the repulsive portion of the force curve, so its application in the quantitative interpretation of AFM experiments is relatively limited. In the proposed Q3D model the use of an array of SLS elements leads to force curves that have the typical upward curvature in the repulsive region, while still offering a very low computational cost. Furthermore, the use of a multidimensional model allows for the study of AFM tips having non-ideal geometries, which can be extremely useful in practice. Examples of typical force curves are provided for single- and multifrequency tapping-mode imaging, for both of which the force curves exhibit the expected features. Finally, a software tool to simulate amplitude and phase spectroscopy curves is provided, which can be easily modified to implement other controls schemes in order to aid in the interpretation of AFM experiments.

Magnetic interaction reversal in watermelon nanostructured Cr-doped Fe nanoclusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaur, Maninder; Dai, Qilin; Bowden, Mark

2013-01-01

Cr-doped core-shell Fe/Fe-oxide nanoclusters (NCs) were synthesized at varied atomic percentages of Cr from 0 at. % to 8 at. %. The low concentrations of Cr (<10 at. %) were selected in order to inhibit the complete conversion of the Fe-oxide shell to Cr2O3 and the Fe core to FeCr alloy. The magnetic interaction in Fe/Fe-oxide NCs (rv25 nm) can be controlled by antiferromagnetic Cr-dopant. We report the origin of r-FeCr phase at very low Cr concentration (2 at. %) unlike in previous studies, and the interaction reversal from dipolar to exchange interaction in watermelon-like Cr-doped core-shell NCs. The giantmore » magnetoresistance (GMR) effect,1,2 where an antiferromagnetic (AFM) exchange coupling exists between two ferromagnetic (FM) layers separated by a certain type of magnetic or non-magnetic spacer,3 has significant potential for application in the magnetic recording industry. Soon after the discovery of the GMR, the magnetic properties of multilayer systems (FeCr) became a subject of intensive study. The application of bulk iron-chromium (Fe-Cr) alloys has been of great interest, as these alloys exhibit favorable prop- erties including corrosion resistance, high strength, hardness, low oxidation rate, and strength retention at elevated temper- ature. However, the structural and magnetic properties of Cr-doped Fe nanoclusters (NCs) have not been investigated in-depth. Of all NCs, Fe-based clusters have unique magnetic properties as well as favorable catalytic characteristics in reactivity, selectivity, and durability.4 The incorporation of dopant of varied type and concentration in Fe can modify its chemical ordering, thereby optimizing its electrical, optical, and magnetic properties and opening up many new applications. The substitution of an Fe atom (1.24 A°) by a Cr atom (1.25 A° ) can easily modify the magnetic properties, since (i) the curie temperature (Tc ) of Fe is 1043 K, while Cr is an itinerant AFM with a bulk Neel temperature TN =311 K, and (ii) Fe and Cr share the same crystal structure (bcc) with only 0.5% difference between their lattice constants.« less

Synthesis, crystal structure and magnetic properties of the two polymorphs of novel S=1 osmate; Li{sub 4}MgOsO{sub 6}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Phoung-Hieu T.; Kemei, Moureen C.; Tan, Malinda S.

2016-10-15

Li{sub 4}MgOsO{sub 6} was synthesized by two different solid-state reaction procedures. The crystal structures were determined by X-ray powder diffraction technique and it was revealed that Li{sub 4}MgOsO{sub 6} crystallizes in two different crystal symmetries in ordered rock salt structure type, namely monoclinic C2/m and orthorhombic Fddd. The unit cell constants for the monoclinic system are a=5.1074(4) Å, b=8.8182(4) Å, c=5.0902(2) Å, and β=109.845(4)° and those of the orthorhombic structure are a=5.8485(1) Å, b=8.3821(1) Å, and c=17.6212(3) Å. In both systems, Os{sup 6+} ions reside exclusively in a specific crystallographic position while Li{sup +} and Mg{sup 2+} ions exhibit mixmore » occupancy. The temperature dependent magnetic susceptibility data for both S=1 osmate systems do not support the occurrence of any magnetic transition down to 2 K. The Curie–Weiss fit to the paramagnetic regime of the magnetic susceptibility data reveal highly negative θ value (−114.81 K and −121.87 K for C2/m and for Fddd systems, respectively), which are indicative of predominant antiferromagnetic (AFM) interactions in both systems. The experimental effective magnetic moment (μ{sub eff}) value for the monoclinic phase is 2.13 μB and that of the orthorhombic system is 2.34 μB. Due to the rather strong AFM interactions and lack of magnetic transition down to 2 K, both of these novel osmates are placed in the class of highly frustrated magnets. Low temperature magnetic susceptibility (below 2 K) and dynamic magnetic properties studies (μsr studies) are in order to better understand the magnetic ground states of these two polymorphs of Li{sub 4}MgOsO{sub 6}. - Graphical abstract: The structural transformation between two modifications of highly frustrated Li{sub 4}MgOsO{sub 6}. - Highlights: • Li4MgOsO{sub 6} was synthesized in two different crystal systems. • The monoclinic variant crystallizes in C2/m space group, while the orthorhombic version forms in Fddd space group. • The Os{sup 6+} ions are fully ordered while Li{sup +} and Mg{sup 2+} are mixed occupied. • These systems are the first Os{sup 6+} compounds in ordered NaCl structure type. • Both compounds exhibit high degree of geometric magnetic frustration.« less

Multiferroic Polar Metals

NASA Astrophysics Data System (ADS)

Lei, Shiming; Chikara, Shalinee; Puggioni, Danilo; Ke, Xianglin; Mao, Z. Q.; Rondinelli, J. M.; Jaime, Marcelo; Singleton, John; Zapf, Vivien; Gopalan, Venkatraman

Ca3Ru2O7 undergoes a second-order magnetic phase transition to AFM-a (ferromagnetic bilayers antiferromagnetically stack along c-axis with magnetic easy axis along a) at TN = 56 K, followed by a concomitant first-order structural and magnetic phase transition to an AFM-b (antiferromagnetic with magnetic easy axis along b) at TS = 48 K. For T<30 K, a quasi-two-dimensional (2D) metallic state exists due to the survival of small non-nested Fermi pockets. With a proper magnetic field applied along b-axis, an additional phase of canted-AFM is induced. Here we propose a new strategy to tune the polar metal Ca3Ru2O7 into insulating state by chemical doping. In the meantime, the superexchange interaction is significantly weakened to allow the existence of a weak ferromagnetic state. Combined with its robust polar nature, we offer an experimental demonstration of a new multiferroic material. The mechanism is further discussed in the framework of hybrid improper ferroelectricity proposed by Benedek and Fennie. This new strategy proposed here may be utilized as a general approach for new multiferroics starting from a material on the verge of the Mott insulating. Here we will discuss our comprehensive magnetization and magnetostriction, and magnetic field dependent SHG study on this material

Pinned orbital moments in uncompensated antiferromagnetic Co doped ZnO

NASA Astrophysics Data System (ADS)

Buchner, Martin; Henne, Bastian; Ney, Verena; Lumetzberger, Julia; Wilhelm, Fabrice; Rogalev, Andrei; Hen, Amir; Ney, Andreas

2018-05-01

Low temperature Co K-edge x-ray magnetic circular dichroism spectra at different field cooling conditions were recorded to study the imprinted magnetization in antiferromagnetic (AFM) Co doped ZnO (Co:ZnO) films which manifests itself in a vertical exchange bias effect. Co:ZnO films with 50% and 60% doping concentrations were investigated to provide a high degree of pinned magnetic moments. The measurements reveal a change at the main absorption energy of the spectra, while the signal obtained at the pre-edge stays unaffected by the cooling conditions. Therefore, the pinned uncompensated AFM moments, resulting in an imprinted magnetization, are predominantly of orbital character and are independent of ferromagnetic layers.

Theory of the Interfacial Dzyaloshinskii-Moriya Interaction in Rashba Antiferromagnets

NASA Astrophysics Data System (ADS)

Qaiumzadeh, Alireza; Ado, Ivan A.; Duine, Rembert A.; Titov, Mikhail; Brataas, Arne

2018-05-01

In antiferromagnetic (AFM) thin films, broken inversion symmetry or coupling to adjacent heavy metals can induce Dzyaloshinskii-Moriya (DM) interactions. Knowledge of the DM parameters is essential for understanding and designing exotic spin structures, such as hedgehog Skyrmions and chiral Néel walls, which are attractive for use in novel information storage technologies. We introduce a framework for computing the DM interaction in two-dimensional Rashba antiferromagnets. Unlike in Rashba ferromagnets, the DM interaction is not suppressed even at low temperatures. The material parameters control both the strength and the sign of the interfacial DM interaction. Our results suggest a route toward controlling the DM interaction in AFM materials by means of doping and electric fields.

Oxygen sorption and desorption properties of selected lanthanum manganites and lanthanum ferrite manganites.

PubMed

Nielsen, Jimmi; Skou, Eivind M; Jacobsen, Torben

2015-06-08

Temperature-programmed desorption (TPD) with a carrier gas was used to study the oxygen sorption and desorption properties of oxidation catalysts and solid-oxide fuel cell (SOFC) cathode materials (La(0.85) Sr(0.15)0.95 MnO(3+δ) (LSM) and La(0.60) Sr(0.40) Fe(0.80) Mn(0.20) O(3-δ) (LSFM). The powders were characterized by X-ray diffractometry, atomic force microscopy (AFM), and BET surface adsorption. Sorbed oxygen could be distinguished from oxygen originating from stoichiometry changes. The results indicated that there is one main site for oxygen sorption/desorption. The amount of sorbed oxygen was monitored over time at different temperatures. Furthermore, through data analysis it was shown that the desorption peak associated with oxygen sorption is described well by second-order desorption kinetics. This indicates that oxygen molecules dissociate upon adsorption and that the rate-determining step for the desorption reaction is a recombination of monatomic oxygen. Typical problems with re-adsorption in this kind of TPD setup were revealed to be insignificant by using simulations. Finally, different key parameters of sorption and desorption were determined, such as desorption activation energies, density of sorption sites, and adsorption and desorption reaction order. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A thermal microprobe fabricated with wafer-stage processing

NASA Astrophysics Data System (ADS)

Zhang, Yongxia; Zhang, Yanwei; Blaser, Juliana; Sriram, T. S.; Enver, Ahsan; Marcus, R. B.

1998-05-01

A thermal microprobe has been designed and built for high resolution temperature sensing. The thermal sensor is a thin-film thermocouple junction at the tip of an atomic force microprobe (AFM) silicon probe needle. Only wafer-stage processing steps are used for the fabrication. For high resolution temperature sensing it is essential that the junction be confined to a short distance at the AFM tip. This confinement is achieved by a controlled photoresist coating process. Experiment prototypes have been made with an Au/Pd junction confined to within 0.5 μm of the tip, with the two metals separated elsewhere by a thin insulating oxide layer. Processing begins with double-polished, n-type, 4 in. diameter, 300-μm-thick silicon wafers. Atomically sharp probe tips are formed by a combination of dry and wet chemical etching, and oxidation sharpening. The metal layers are sputtering deposited and the cantilevers are released by a combination of KOH and dry etching. A resistively heated calibration device was made for temperature calibration of the thermal microprobe over the temperature range 25-110 °C. Over this range the thermal outputs of two microprobes are 4.5 and 5.6 μV/K and is linear. Thermal and topographical images are also obtained from a heated tungsten thin film fuse.

In vitro behavior of MC3T3-E1 preosteoblast with different annealing temperature titania nanotubes.

PubMed

Yu, W Q; Zhang, Y L; Jiang, X Q; Zhang, F Q

2010-10-01

Titanium oxide nanotube layers by anodization have excellent potential for dental implants because of good bone cell promotion. It is necessary to evaluate osteoblast behavior on different annealing temperature titania nanotubes for actual implant designs.  Scanning Electron Microscopy, X-Ray polycrystalline Diffractometer (XRD), X-ray photoelectron Spectroscope, and Atomic Force Microscopy (AFM) were used to characterize the different annealing temperature titania nanotubes. Confocal laser scanning microscopy, MTT, and Alizarin Red-S staining were used to evaluate the MC3T3-E1 preosteoblast behavior on different annealing temperature nanotubes.  The tubular morphology was constant when annealed at 450°C and 550°C, but collapsed when annealed at 650°C. XRD exhibited the crystal form of nanotubes after formation (amorphous), after annealing at 450°C (anatase), and after annealing at 550°C (anatase/rutile). Annealing led to the complete loss of fluorine on nanotubes at 550°C. Average surface roughness of different annealing temperature nanotubes showed no difference by AFM analysis. The proliferation and mineralization of preostoblasts cultured on anatase or anatase/rutile nanotube layers were shown to be significantly higher than smooth, amorphous nanotube layers.  Annealing can change the crystal form and composition of nanotubes. The nanotubes after annealing can promote osteoblast proliferation and mineralization in vitro. © 2010 John Wiley & Sons A/S.

Determination of the Activation Energy of the Enzymatic Biodegradation Process in Microfabricated Polyhydroxyalkanoate Thin Films Using In-Situ, Real Time Atomic Force Microscopy

NASA Astrophysics Data System (ADS)

Morse, Clinton; Latuga, Brian M.; Delfaus, Stephen; Devore, Thomas C.; Augustine, Brian H.; Hughes, W. Christopher; Warne, Paul G.

2003-11-01

Using the liquid cell capability of the atomic force microscope (AFM), we report the determination of the activation energy of the biodegradation process of the enzymatic biodegradation of poly 3-hydroxybutyrate / poly 3-hydroxyvalerate [P(3HB-HV)] thin films. We have prepared P(3HB-3HV) copolymer microstructures by the selective dewetting of soft lithographically patterned gold substrates with features sizes down to 10 mm. These have been then used as an internal height standard to measure the volume of material as a function of biodegradation time. Biodegradation is measured in-situ and real time using contact mode AFM in an enzymatic solution produced from Streptomyces sp. bacteria. The temperature dependent biodegradation has been measured over a temperature range from 23oC to 40oC. We will discuss the calculation of the activation energy of this process as well as a physical model to describe three distinct regions in the biodegradation process that have been observed.

Development of in-situ high-voltage and high-temperature stressing capability on atomic force microscopy platform

DOE PAGES

Xiao, Chuanxiao; Jiang, Chun-Sheng; Johnston, Steve; ...

2017-10-18

Reliability has become an increasingly important issue as photovoltaic technologies mature. However, researching reliability at the nanometer scale is in its infancy; in particular, in-situ studies have not been reported to date. Here, to investigate potential-induced degradation (PID) of solar cell modules, we have developed an in-situ stressing capability with applied high voltage (HV) and high temperature (HT) on an atomic force microscopy (AFM) platform. We designed a sample holder to simultaneously accommodate 1000-V HV and 200 degrees C HT stressing. Three technical challenges have been overcome along with the development: thermal drift at HT, HV interference with measurement, andmore » arc discharge caused by HV. We demonstrated no observable measurement artifact under the stress conditions. Based on our in-situ stressing AFM, Kelvin probe force microscopy potential imaging revealed the evolution of electrical potential across the junction along with the PID stressing time, which provides vital information to further study the PID mechanism.« less

Tip-induced domain structures and polarization switching in ferroelectric amino acid glycine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seyedhosseini, E., E-mail: Seyedhosseini@ua.pt; Ivanov, M.; Bdikin, I.

2015-08-21

Bioorganic ferroelectrics and piezoelectrics are becoming increasingly important in view of their intrinsic compatibility with biological environment and biofunctionality combined with strong piezoelectric effect and a switchable polarization at room temperature. Here, we study tip-induced domain structures and polarization switching in the smallest amino acid β-glycine, representing a broad class of non-centrosymmetric amino acids. We show that β-glycine is indeed a room-temperature ferroelectric and polarization can be switched by applying a bias to non-polar cuts via a conducting tip of atomic force microscope (AFM). Dynamics of these in-plane domains is studied as a function of an applied voltage and pulsemore » duration. The domain shape is dictated by polarization screening at the domain boundaries and mediated by growth defects. Thermodynamic theory is applied to explain the domain propagation induced by the AFM tip. Our findings suggest that the properties of β-glycine are controlled by the charged domain walls which in turn can be manipulated by an external bias.« less

Nucleation and growth of oxide islands during the initial-stage oxidation of (100)Cu-Pt alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Langli; Zhou, Guangwen, E-mail: gzhou@binghamton.edu; Kang, Yihong

2015-02-14

The initial-stage oxidation of (100) Cu-Pt alloys has been examined by in situ environmental transmission electron microscopy and ex situ atomic force microscopy (AFM). It is shown that the oxidation proceeds via the nucleation and growth of Cu{sub 2}O islands that show dependence on the alloy composition and oxidation temperature. The kinetic measurements on the oxide nucleation reveal that both the nucleation density and surface coverage of Cu{sub 2}O islands can be promoted by alloying more Pt in the Cu-Pt alloys. Increasing the oxidation temperature above 700 °C results in the growth of large Cu{sub 2}O islands that transits to amore » dendritic growth morphology. The ex situ AFM studies reveal that the nucleation of oxide islands can occur on surface terraces and the subsequent oxide growth depletes local terrace Cu atoms that results in the formation of surface pits.« less

Reduced graphene oxide composites with water soluble copolymers having tailored lower critical solution temperatures and unique tube-like structure

NASA Astrophysics Data System (ADS)

Namvari, Mina; Biswas, Chandra S.; Galluzzi, Massimiliano; Wang, Qiao; Du, Bing; Stadler, Florian J.

2017-03-01

Nanohybrids of graphene with water soluble polymer were synthesized using ‘grafting from’ method. GO, prepared by modified Hummers’ method, was first reacted with sodium azide. Alkyne-terminated RAFT-CTA was synthesized by reaction of propargyl alcohol and S-1-dodecyl-S’-(α,α‘-dimethyl-α”-acetic acid) trithiocarbonate. RAFT-CTA was grafted onto the GO sheets by facile click-reaction and subsequently, N-isopropylacrylamide (NIPAM) and N-ethyleacrylamide (NEAM) were polymerized on graphene sheets via RAFT polymerization method. The respective copolymers with different ratios were also prepared. The nanohybrids were characterized by FTIR, XRD, TGA, Raman, SEM, and AFM. Both SEM and AFM clearly showed rod-like structures for rGO-PNEAM. XRD showed a small peak at 2θ = 19.21°, corresponding to d-spacing ≈ 4.6 Å. In addition, the nanohybrids showed a very broad temperature range for the LCST in water between ca. 30 and 70 °C.

Development of in-situ high-voltage and high-temperature stressing capability on atomic force microscopy platform

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiao, Chuanxiao; Jiang, Chun-Sheng; Johnston, Steve

Reliability has become an increasingly important issue as photovoltaic technologies mature. However, researching reliability at the nanometer scale is in its infancy; in particular, in-situ studies have not been reported to date. Here, to investigate potential-induced degradation (PID) of solar cell modules, we have developed an in-situ stressing capability with applied high voltage (HV) and high temperature (HT) on an atomic force microscopy (AFM) platform. We designed a sample holder to simultaneously accommodate 1000-V HV and 200 degrees C HT stressing. Three technical challenges have been overcome along with the development: thermal drift at HT, HV interference with measurement, andmore » arc discharge caused by HV. We demonstrated no observable measurement artifact under the stress conditions. Based on our in-situ stressing AFM, Kelvin probe force microscopy potential imaging revealed the evolution of electrical potential across the junction along with the PID stressing time, which provides vital information to further study the PID mechanism.« less

Investigations on Substrate Temperature-Induced Growth Modes of Organic Semiconductors at Dielectric/semiconductor Interface and Their Correlation with Threshold Voltage Stability in Organic Field-Effect Transistors.

PubMed

Padma, Narayanan; Maheshwari, Priya; Bhattacharya, Debarati; Tokas, Raj B; Sen, Shashwati; Honda, Yoshihide; Basu, Saibal; Pujari, Pradeep Kumar; Rao, T V Chandrasekhar

2016-02-10

Influence of substrate temperature on growth modes of copper phthalocyanine (CuPc) thin films at the dielectric/semiconductor interface in organic field effect transistors (OFETs) is investigated. Atomic force microscopy (AFM) imaging at the interface reveals a change from 'layer+island' to "island" growth mode with increasing substrate temperatures, further confirmed by probing the buried interfaces using X-ray reflectivity (XRR) and positron annihilation spectroscopic (PAS) techniques. PAS depth profiling provides insight into the details of molecular ordering while positron lifetime measurements reveal the difference in packing modes of CuPc molecules at the interface. XRR measurements show systematic increase in interface width and electron density correlating well with the change from layer + island to coalesced huge 3D islands at higher substrate temperatures. Study demonstrates the usefulness of XRR and PAS techniques to study growth modes at buried interfaces and reveals the influence of growth modes of semiconductor at the interface on hole and electron trap concentrations individually, thereby affecting hysteresis and threshold voltage stability. Minimum hole trapping is correlated to near layer by layer formation close to the interface at 100 °C and maximum to the island formation with large voids between the grains at 225 °C.

3-Dimensional atomic scale structure of the ionic liquid-graphite interface elucidated by AM-AFM and quantum chemical simulations

NASA Astrophysics Data System (ADS)

Page, Alister J.; Elbourne, Aaron; Stefanovic, Ryan; Addicoat, Matthew A.; Warr, Gregory G.; Voïtchovsky, Kislon; Atkin, Rob

2014-06-01

In situ amplitude modulated atomic force microscopy (AM-AFM) and quantum chemical simulations are used to resolve the structure of the highly ordered pyrolytic graphite (HOPG)-bulk propylammonium nitrate (PAN) interface with resolution comparable with that achieved for frozen ionic liquid (IL) monolayers using STM. This is the first time that (a) molecular resolution images of bulk IL-solid interfaces have been achieved, (b) the lateral structure of the IL graphite interface has been imaged for any IL, (c) AM-AFM has elucidated molecular level structure immersed in a viscous liquid and (d) it has been demonstrated that the IL structure at solid surfaces is a consequence of both thermodynamic and kinetic effects. The lateral structure of the PAN-graphite interface is highly ordered and consists of remarkably well-defined domains of a rhomboidal superstructure composed of propylammonium cations preferentially aligned along two of the three directions in the underlying graphite lattice. The nanostructure is primarily determined by the cation. Van der Waals interactions between the propylammonium chains and the surface mean that the cation is enriched in the surface layer, and is much less mobile than the anion. The presence of a heterogeneous lateral structure at an ionic liquid-solid interface has wide ranging ramifications for ionic liquid applications, including lubrication, capacitive charge storage and electrodeposition.In situ amplitude modulated atomic force microscopy (AM-AFM) and quantum chemical simulations are used to resolve the structure of the highly ordered pyrolytic graphite (HOPG)-bulk propylammonium nitrate (PAN) interface with resolution comparable with that achieved for frozen ionic liquid (IL) monolayers using STM. This is the first time that (a) molecular resolution images of bulk IL-solid interfaces have been achieved, (b) the lateral structure of the IL graphite interface has been imaged for any IL, (c) AM-AFM has elucidated molecular level structure immersed in a viscous liquid and (d) it has been demonstrated that the IL structure at solid surfaces is a consequence of both thermodynamic and kinetic effects. The lateral structure of the PAN-graphite interface is highly ordered and consists of remarkably well-defined domains of a rhomboidal superstructure composed of propylammonium cations preferentially aligned along two of the three directions in the underlying graphite lattice. The nanostructure is primarily determined by the cation. Van der Waals interactions between the propylammonium chains and the surface mean that the cation is enriched in the surface layer, and is much less mobile than the anion. The presence of a heterogeneous lateral structure at an ionic liquid-solid interface has wide ranging ramifications for ionic liquid applications, including lubrication, capacitive charge storage and electrodeposition. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr01219d

Layer and doping tunable ferromagnetic order in two-dimensional Cr S2 layers

NASA Astrophysics Data System (ADS)

Wang, Cong; Zhou, Xieyu; Pan, Yuhao; Qiao, Jingsi; Kong, Xianghua; Kaun, Chao-Cheng; Ji, Wei

2018-06-01

Interlayer coupling is of vital importance for manipulating physical properties, e.g., electronic band gap, in two-dimensional materials. However, tuning magnetic properties in these materials is yet to be addressed. Here, we found the in-plane magnetic orders of Cr S2 mono and few layers are tunable between striped antiferromagnetic (sAFM) and ferromagnetic (FM) orders by manipulating charge transfer between Cr t2 g and eg orbitals. Such charge transfer is realizable through interlayer coupling, direct charge doping, or substituting S with Cl atoms. In particular, the transferred charge effectively reduces a portion of Cr4 + to Cr3 +, which, together with delocalized S p orbitals and their resulting direct S-S interlayer hopping, enhances the double-exchange mechanism favoring the FM rather than sAFM order. An exceptional interlayer spin-exchange parameter was revealed over -10 meV , an order of magnitude stronger than available results of interlayer magnetic coupling. It addition, the charge doping could tune Cr S2 between p - and n -doped magnetic semiconductors. Given these results, several prototype devices were proposed for manipulating magnetic orders using external electric fields or mechanical motion. These results manifest the role of interlayer coupling in modifying magnetic properties of layered materials and shed considerable light on manipulating magnetism in these materials.

Infrared nanoscopy down to liquid helium temperatures

NASA Astrophysics Data System (ADS)

Lang, Denny; Döring, Jonathan; Nörenberg, Tobias; Butykai, Ádám; Kézsmárki, István; Schneider, Harald; Winnerl, Stephan; Helm, Manfred; Kehr, Susanne C.; Eng, Lukas M.

2018-03-01

We introduce a scattering-type scanning near-field infrared microscope (s-SNIM) for the local scale near-field sample analysis and spectroscopy from room temperature down to liquid helium (LHe) temperature. The extension of s-SNIM down to T = 5 K is in particular crucial for low-temperature phase transitions, e.g., for the examination of superconductors, as well as low energy excitations. The low temperature (LT) s-SNIM performance is tested with CO2-IR excitation at T = 7 K using a bare Au reference and a structured Si/SiO2-sample. Furthermore, we quantify the impact of local laser heating under the s-SNIM tip apex by monitoring the light-induced ferroelectric-to-paraelectric phase transition of the skyrmion-hosting multiferroic material GaV4S8 at Tc = 42 K. We apply LT s-SNIM to study the spectral response of GaV4S8 and its lateral domain structure in the ferroelectric phase by the mid-IR to THz free-electron laser-light source FELBE at the Helmholtz-Zentrum Dresden-Rossendorf, Germany. Notably, our s-SNIM is based on a non-contact atomic force microscope (AFM) and thus can be complemented in situ by various other AFM techniques, such as topography profiling, piezo-response force microscopy (PFM), and/or Kelvin-probe force microscopy (KPFM). The combination of these methods supports the comprehensive study of the mutual interplay in the topographic, electronic, and optical properties of surfaces from room temperature down to 5 K.

A New "Quasi-Dynamic" Method for Determining the Hamaker Constant of Solids Using an Atomic Force Microscope.

PubMed

Fronczak, Sean G; Dong, Jiannan; Browne, Christopher A; Krenek, Elizabeth C; Franses, Elias I; Beaudoin, Stephen P; Corti, David S

2017-01-24

In order to minimize the effects of surface roughness and deformation, a new method for estimating the Hamaker constant, A, of solids using the approach-to-contact regime of an atomic force microscope (AFM) is presented. First, a previous "jump-into-contact" quasi-static method for determining A from AFM measurements is analyzed and then extended to include various AFM tip-surface force models of interest. Then, to test the efficacy of the "jump-into-contact" method, a dynamic model of the AFM tip motion is developed. For finite AFM cantilever-surface approach speeds, a true "jump" point, or limit of stability, is found not to appear, and the quasi-static model fails to represent the dynamic tip behavior at close tip-surface separations. Hence, a new "quasi-dynamic" method for estimating A is proposed that uses the dynamically well-defined deflection at which the tip and surface first come into contact, d c , instead of the dynamically ill-defined "jump" point. With the new method, an apparent Hamaker constant, A app , is calculated from d c and a corresponding quasi-static-based equation. Since A app depends on the cantilever's approach speed, v c , and the AFM's sampling resolution, δ, a double extrapolation procedure is used to determine A app in the quasi-static (v c → 0) and continuous sampling (δ → 0) limits, thereby recovering the "true" value of A. The accuracy of the new method is validated using simulated AFM data. To enable the experimental implementation of this method, a new dimensionless parameter τ is introduced to guide cantilever selection and the AFM operating conditions. The value of τ quantifies how close a given cantilever is to its quasi-static limit for a chosen cantilever-surface approach speed. For sufficiently small values of τ (i.e., a cantilever that effectively behaves "quasi-statically"), simulated data indicate that A app will be within ∼3% or less of the inputted value of the Hamaker constant. This implies that Hamaker constants can be reliably estimated using a single measurement taken with an appropriately chosen cantilever and a slow, yet practical, approach speed (with no extrapolation required). This result is confirmed by the very good agreement found between the experimental AFM results obtained using this new method and previously reported predictions of A for amorphous silica, polystyrene, and α-Al 2 O 3 substrates obtained using the Lifshitz method.

BOREAS AFM-2 Wyoming King Air 1994 Aircraft Sounding Data

NASA Technical Reports Server (NTRS)

Kelly, Robert D.; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Smith, David E. (Technical Monitor)

2000-01-01

The BOREAS AFM-2 team used the University of Wyoming King Air aircraft during IFCs 1, 2, and 3 in 1994 to collected pass-by-pass fluxes (and many other statistics) for the large number of level (constant altitude), straight-line passes used in a variety of flight patterns over the SSA and NSA and areas along the transect between these study areas. The data described here form a second set, namely soundings that were incorporated into nearly every research flight by the King Air in 1994. These soundings generally went from near the surface to above the inversion layer. Most were flown immediately after takeoff or immediately after finishing the last flux pattern of that particular day's flights. The parameters that were measured include wind direction, wind speed, west wind component (u), south wind component (v), static pressure, air dry bulb temperature, potential temperature, dewpoint, temperature, water vapor mixing ratio, and CO2 concentration. Data on the aircraft's location, attitude, and altitude during data collection are also provided. These data are stored in tabular ASCH files. The data files are available on a CD-ROM (see document number 20010000884) or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Growth and adhesion properties of monosodium urate monohydrate (MSU) crystals

NASA Astrophysics Data System (ADS)

Perrin, Clare M.

The presence of monosodium urate monohydrate (MSU) crystals in the synovial fluid has long been associated with the joint disease gout. To elucidate the molecular level growth mechanism and adhesive properties of MSU crystals, atomic force microscopy (AFM), scanning electron microscopy, and dynamic light scattering (DLS) techniques were employed in the characterization of the (010) and (1-10) faces of MSU, as well as physiologically relevant solutions supersaturated with urate. Topographical AFM imaging of both MSU (010) and (1-10) revealed the presence of crystalline layers of urate arranged into v-shaped features of varying height. Growth rates were measured for both monolayers (elementary steps) and multiple layers (macrosteps) on both crystal faces under a wide range of urate supersaturation in physiologically relevant solutions. Step velocities for monolayers and multiple layers displayed a second order polynomial dependence on urate supersaturation on MSU (010) and (1-10), with step velocities on (1-10) generally half of those measured on MSU (010) in corresponding growth conditions. Perpendicular step velocities on MSU (010) were obtained and also showed a second order polynomial dependence of step velocity with respect to urate supersaturation, which implies a 2D-island nucleation growth mechanism for MSU (010). Extensive topographical imaging of MSU (010) showed island adsorption from urate growth solutions under all urate solution concentrations investigated, lending further support for the determined growth mechanism. Island sizes derived from DLS experiments on growth solutions were in agreement with those measured on MSU (010) topographical images. Chemical force microscopy (CFM) was utilized to characterize the adhesive properties of MSU (010) and (1-10). AFM probes functionalized with amino acid derivatives and bio-macromolecules found in the synovial fluid were brought into contact with both crystal faces and adhesion forces were tabulated into histograms for comparison. AFM probes functionalized with -COO-, -CH3, and -OH functionalities displayed similar adhesion force with both crystal surfaces of MSU, while adhesion force on (1-10) was three times greater than (010) for -NH2+ probes. For AFM probes functionalized with bovine serum albumin, adhesion force was three times greater on MSU (1-10) than (010), most likely due to the more ionic nature of (1-10).

Study of thermal-field emission properties and investigation of temperature dependent noise in the field emission current from vertical carbon nanotube emitters

NASA Astrophysics Data System (ADS)

Kolekar, Sadhu; Patole, S. P.; Patil, Sumati; Yoo, J. B.; Dharmadhikari, C. V.

2017-10-01

We have investigated temperature dependent field electron emission characteristics of vertical carbon nanotubes (CNTs). The generalized expression for electron emission from well-defined cathode surface is given by Millikan and Lauritsen [1] for the combination of temperature and electric field effect. The same expression has been used to explain the electron emission characteristics from vertical CNT emitters. Furthermore, this has been applied to explain the electron emission for different temperatures ranging from room temperature to 1500 K. The real-time field electron emission images at room temperature and 1500 K are recorded by using Charge Coupled Device (CCD) in order to understand the effect of temperature on distribution of electron emission spots and ring like structures in Field Emission Microscope (FEM) image. The FEM images could be used to calculate the total number of emitters per cm2 for electron emission. The calculated number of emitters per cm2 from FEM image is typically, 4.5 × 107 and the actual number emitters per cm2 present as per Atomic Force Microscopy (AFM) data is 1.2 × 1012. The measured Current-Voltage (I-V) characteristics exhibit non linear Folwer-Nordheim (F-N) type behavior. The fluctuations in the emission current were recorded at different temperatures and Fast Fourier transformed into temperature dependent power spectral density. The latter was found to obey power law relation S(f) = A(Iδ/fξ), where δ and ξ are temperature dependent current and frequency exponents respectively.

Actuation of atomic force microscopy microcantilevers using contact acoustic nonlinearities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Torello, D.; Degertekin, F. Levent, E-mail: levent.degertekin@me.gatech.edu

2013-11-15

A new method of actuating atomic force microscopy (AFM) cantilevers is proposed in which a high frequency (>5 MHz) wave modulated by a lower frequency (∼300 kHz) wave passes through a contact acoustic nonlinearity at the contact interface between the actuator and the cantilever chip. The nonlinearity converts the high frequency, modulated signal to a low frequency drive signal suitable for actuation of tapping-mode AFM probes. The higher harmonic content of this signal is filtered out mechanically by the cantilever transfer function, providing for clean output. A custom probe holder was designed and constructed using rapid prototyping technologies and off-the-shelfmore » components and was interfaced with an Asylum Research MFP-3D AFM, which was then used to evaluate the performance characteristics with respect to standard hardware and linear actuation techniques. Using a carrier frequency of 14.19 MHz, it was observed that the cantilever output was cleaner with this actuation technique and added no significant noise to the system. This setup, without any optimization, was determined to have an actuation bandwidth on the order of 10 MHz, suitable for high speed imaging applications. Using this method, an image was taken that demonstrates the viability of the technique and is compared favorably to images taken with a standard AFM setup.« less

Thermal effect on structure organizations in cobalt-fullerene nanocomposition.

PubMed

Lavrentiev, Vasily; Vacik, Jiri; Naramoto, Hiroshi; Sakai, Seiji

2010-04-01

Effect of deposition temperature (Ts) on structure of Co-C60 nanocomposite (NC) prepared by simultaneous deposition of cobalt and fullerene on sapphire is presented. The NC structure variations with Ts increasing from room temperature (RT) to 400 degrees C have been analyzed using scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy. AFM and SEM show granule-like structure of the Co-C60 film. The mixture film deposited at RT includes the hills on the surface suggesting accumulation of internal stress during phase separation. Raman spectra show 25 cm(-1) downshift of Ag(2) C60 peak suggesting -Co-C60- polymerization in C60-based matrix of the NC film. Analysis of Raman spectra has revealed existence of amorphous carbon (a-C) in the NC matrix that argues C60 decomposition. The Ts increase to 200 degrees C causes the surface hills smoothing. In parallel, downshift of the Ag(2) peak decreases to 16 cm(-1) that implies more pronounced phase separation and lower -Co-C60- polymerization efficiency. Also, amount of a-C content slightly increases. Further Ts increasing to 400 degrees C changes the NC structure dramatically. AFM shows evident enlargement of the granules. According to Raman spectra the high Ts deposition yields pronounced C60 decomposition increasing the a-C content. Features of a-C Raman peak imply nucleation of graphitic islands at the NC interfaces. Abundant decomposition of C60 in the mixture film deposited at 400 degrees C is referred to cobalt catalytic effect.

Computationally-efficient optical coherence elastography to assess degenerative osteoarthritis based on ultrasound-induced fringe washout (Conference Presentation)

NASA Astrophysics Data System (ADS)

Tong, Minh Q.; Hasan, M. Monirul; Gregory, Patrick D.; Shah, Jasmine; Park, B. Hyle; Hirota, Koji; Liu, Junze; Choi, Andy; Low, Karen; Nam, Jin

2017-02-01

We demonstrate a computationally-efficient optical coherence elastography (OCE) method based on fringe washout. By introducing ultrasound in alternating depth profile, we can obtain information on the mechanical properties of a sample within acquisition of a single image. This can be achieved by simply comparing the intensity in adjacent depth profiles in order to quantify the degree of fringe washout. Phantom agar samples with various densities were measured and quantified by our OCE technique, the correlation to Young's modulus measurement by atomic force micrscopy (AFM) were observed. Knee cartilage samples of monoiodo acetate-induced arthiritis (MIA) rat models were utilized to replicate cartilage damages where our proposed OCE technique along with intensity and birefringence analyses and AFM measurements were applied. The results indicate that our OCE technique shows a correlation to the techniques as polarization-sensitive OCT, AFM Young's modulus measurements and histology were promising. Our OCE is applicable to any of existing OCT systems and demonstrated to be computationally-efficient.

Frequency modulation atomic force microscopy: a dynamic measurement technique for biological systems

NASA Astrophysics Data System (ADS)

Higgins, Michael J.; Riener, Christian K.; Uchihashi, Takayuki; Sader, John E.; McKendry, Rachel; Jarvis, Suzanne P.

2005-03-01

Frequency modulation atomic force microscopy (FM-AFM) has been modified to operate in a liquid environment within an atomic force microscope specifically designed for investigating biological samples. We demonstrate the applicability of FM-AFM to biological samples using the spectroscopy mode to measure the unbinding forces of a single receptor-ligand (biotin-avidin) interaction. We show that quantitative adhesion force measurements can only be obtained provided certain modifications are made to the existing theory, which is used to convert the detected frequency shifts to an interaction force. Quantitative force measurements revealed that the unbinding forces for the biotin-avidin interaction were greater than those reported in previous studies. This finding was due to the use of high average tip velocities, which were calculated to be two orders of magnitude greater than those typically used in unbinding receptor-ligand experiments. This study therefore highlights the potential use of FM-AFM to study a range of biological systems, including living cells and/or single biomolecule interactions.

Cell mechanics as a marker for diseases: Biomedical applications of AFM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rianna, Carmela; Radmacher, Manfred, E-mail: mr@biophysik.uni-bremen.de

Many diseases are related to changes in cell mechanics. Atomic Force Microscopy (AFM) is one of the most suitable techniques allowing the investigation of both topography and mechanical properties of adherent cells with high spatial resolution under physiological conditions. Over the years the use of this technique in medical and clinical applications has largely increased, resulting in the notion of cell mechanics as a biomarker to discriminate between different physiological and pathological states of cells. Cell mechanics has proven to be a biophysical fingerprint able discerning between cell phenotypes, unraveling processes in aging or diseases, or even detecting and diagnosingmore » cellular pathologies. We will review in this report some of the works on cell mechanics investigated by AFM with clinical and medical relevance in order to clarify the state of research in this field and to highlight the role of cell mechanics in the study of pathologies, focusing on cancer, blood and cardiovascular diseases.« less

AFM of the ultrastructural and mechanical properties of lipid-raft-disrupted and/or cold-treated endothelial cells.

PubMed

Wu, Li; Huang, Jie; Yu, Xiaoxue; Zhou, Xiaoqing; Gan, Chaoye; Li, Ming; Chen, Yong

2014-02-01

The nonionic detergent extraction at 4 °C and the cholesterol-depletion-induced lipid raft disruption are the two widely used experimental strategies for lipid raft research. However, the effects of raft disruption and/or cold treatment on the ultrastructural and mechanical properties of cells are still unclear. Here, we evaluated the effects of raft disruption and/or cold (4 °C) treatment on these properties of living human umbilical vein endothelial cells (HUVECs). At first, the cholesterol-depletion-induced raft disruption was visualized by confocal microscopy and atomic force microscopy (AFM) in combination with fluorescent quantum dots. Next, the cold-induced cell contraction and the formation of end-branched filopodia were observed by confocal microscopy and AFM. Then, the cell-surface ultrastructures were imaged by AFM, and the data showed that raft disruption and cold treatment induced opposite effects on cell-surface roughness (a significant decrease and a significant increase, respectively). Moreover, the cell-surface mechanical properties (stiffness and adhesion force) of raft-disrupted- and/or cold-treated HUVECs were measured by the force measurement function of AFM. We found that raft disruption and cold treatment induced parallel effects on cell stiffness (increase) or adhesion force (decrease) and that the combination of the two treatments caused dramatically strengthened effects. Finally, raft disruption was found to significantly impair cell migration as previously reported, whereas temporary cold treatment only caused a slight but nonsignificant decrease in cell migration performed at physiological temperature. Although the mechanisms for causing these results might be complicated and more in-depth studies will be needed, our data may provide important information for better understanding the effects of raft disruption or cold treatment on cells and the two strategies for lipid raft research.

Exploratory Study of RNA Polymerase II Using Dynamic Atomic Force Microscopy

NASA Astrophysics Data System (ADS)

Rhodin, Thor; Umemura, Kazuo; Gad, Mohammed; Jarvis, Suzanne; Ishikawa, Mitsuru; Fu, Jianhua

2002-03-01

An exploratory study of the microtopological dimensions and shape features of yeast RNA polymerase II (y-poly II) on freshly cleaved mica was made in phosphate aqueous buffer solution at room temperature following previous work by Hansma and others. The molecules were imaged by stabilization on freshly cleaved mica at a limiting resolution of 10 Å and scanned using dynamical atomic force microscopy with a 10 nm multi-wall carbon nanotube in the resonance frequency modulation mode. They indicated microtopological shape and dimensional features similar to those predicted by electron density plots derived from the X-ray crystallographic model. It is concluded that this is considered primarily a feasibility study with definitive conclusions subject to more detailed systematic measurements of the 3D microtopology. These measurements appear to establish validity of the noncontact atomic force microscopy (nc-AFM) approach into defining the primary microtopology and biochemical functionality of RNA polymerase II. Further nc-AFM studies at higher resolution using dynamical nc-AFM will be required to clearly define the detailed 3D microtopology of RNA polymerase II in anaerobic aqueous environments for both static and dynamic conditions.

Structure and Magnetic Properties in Ruthenium-Based Full-Heusler Alloys: AB INITIO Calculations

NASA Astrophysics Data System (ADS)

Bahlouli, S.; Aarizou, Z.; Elchikh, M.

2013-12-01

In this paper, we present ab initio calculations within density functional theory (DFT) to investigate structure, electronic and magnetic properties of Ru2CrZ (Z = Si, Ge and Sn) full-Heusler alloys. We have used the developed full-potential linearized muffin tin orbitals (FP-LMTO) based on the local spin density approximation (LSDA) with the PLane Wave expansion (PLW). In particular, we found that these Ruthenium-based Heusler alloys have the antiferromagnetic (AFM) type II as ground state. Then, we studied and discussed the magnetic properties belonging to our different magnetic structures: AFM type II, AFM type I and ferromagnetic (FM) phase. We also found that Ru2CrSi and Ru2CrGe exhibit a semiconducting behavior whereas Ru2CrSn has a semimetallic-like behavior as it is experimentally found. We made an estimation of Néel temperatures (TN) in the framework of the mean-field theory and used the energy differences approach to deduce the relevant short-range nearest-neighbor (J1) and next-nearest-neighbor (J2) interactions. The calculated TN are somewhat overestimated to the available experimental ones.

Characterization of Bitumen Micro-Mechanical Behaviors Using AFM, Phase Dynamics Theory and MD Simulation.

PubMed

Hou, Yue; Wang, Linbing; Wang, Dawei; Guo, Meng; Liu, Pengfei; Yu, Jianxin

2017-02-21

Fundamental understanding of micro-mechanical behaviors in bitumen, including phase separation, micro-friction, micro-abrasion, etc., can help the pavement engineers better understand the bitumen mechanical performances at macroscale. Recent researches show that the microstructure evolution in bitumen will directly affect its surface structure and micro-mechanical performance. In this study, the bitumen microstructure and micro-mechanical behaviors are studied using Atomic Force Microscopy (AFM) experiments, Phase Dynamics Theory and Molecular Dynamics (MD) Simulation. The AFM experiment results show that different phase-structure will occur at the surface of the bitumen samples under certain thermodynamic conditions at microscale. The phenomenon can be explained using the phase dynamics theory, where the effects of stability parameter and temperature on bitumen microstructure and micro-mechanical behavior are studied combined with MD Simulation. Simulation results show that the saturates phase, in contrast to the naphthene aromatics phase, plays a major role in bitumen micro-mechanical behavior. A high stress zone occurs at the interface between the saturates phase and the naphthene aromatics phase, which may form discontinuities that further affect the bitumen frictional performance.

Characterization of Bitumen Micro-Mechanical Behaviors Using AFM, Phase Dynamics Theory and MD Simulation

PubMed Central

Hou, Yue; Wang, Linbing; Wang, Dawei; Guo, Meng; Liu, Pengfei; Yu, Jianxin

2017-01-01

Fundamental understanding of micro-mechanical behaviors in bitumen, including phase separation, micro-friction, micro-abrasion, etc., can help the pavement engineers better understand the bitumen mechanical performances at macroscale. Recent researches show that the microstructure evolution in bitumen will directly affect its surface structure and micro-mechanical performance. In this study, the bitumen microstructure and micro-mechanical behaviors are studied using Atomic Force Microscopy (AFM) experiments, Phase Dynamics Theory and Molecular Dynamics (MD) Simulation. The AFM experiment results show that different phase-structure will occur at the surface of the bitumen samples under certain thermodynamic conditions at microscale. The phenomenon can be explained using the phase dynamics theory, where the effects of stability parameter and temperature on bitumen microstructure and micro-mechanical behavior are studied combined with MD Simulation. Simulation results show that the saturates phase, in contrast to the naphthene aromatics phase, plays a major role in bitumen micro-mechanical behavior. A high stress zone occurs at the interface between the saturates phase and the naphthene aromatics phase, which may form discontinuities that further affect the bitumen frictional performance. PMID:28772570

Studying post-etching silicon crystal defects on 300mm wafer by automatic defect review AFM

NASA Astrophysics Data System (ADS)

Zandiatashbar, Ardavan; Taylor, Patrick A.; Kim, Byong; Yoo, Young-kook; Lee, Keibock; Jo, Ahjin; Lee, Ju Suk; Cho, Sang-Joon; Park, Sang-il

2016-03-01

Single crystal silicon wafers are the fundamental elements of semiconductor manufacturing industry. The wafers produced by Czochralski (CZ) process are very high quality single crystalline materials with known defects that are formed during the crystal growth or modified by further processing. While defects can be unfavorable for yield for some manufactured electrical devices, a group of defects like oxide precipitates can have both positive and negative impacts on the final device. The spatial distribution of these defects may be found by scattering techniques. However, due to limitations of scattering (i.e. light wavelength), many crystal defects are either poorly classified or not detected. Therefore a high throughput and accurate characterization of their shape and dimension is essential for reviewing the defects and proper classification. While scanning electron microscopy (SEM) can provide high resolution twodimensional images, atomic force microscopy (AFM) is essential for obtaining three-dimensional information of the defects of interest (DOI) as it is known to provide the highest vertical resolution among all techniques [1]. However AFM's low throughput, limited tip life, and laborious efforts for locating the DOI have been the limitations of this technique for defect review for 300 mm wafers. To address these limitations of AFM, automatic defect review AFM has been introduced recently [2], and is utilized in this work for studying DOI on 300 mm silicon wafer. In this work, we carefully etched a 300 mm silicon wafer with a gaseous acid in a reducing atmosphere at a temperature and for a sufficient duration to decorate and grow the crystal defects to a size capable of being detected as light scattering defects [3]. The etched defects form a shallow structure and their distribution and relative size are inspected by laser light scattering (LLS). However, several groups of defects couldn't be properly sized by the LLS due to the very shallow depth and low light scattering. Likewise, SEM cannot be used effectively for post-inspection defect review and classification of these very shallow types of defects. To verify and obtain accurate shape and three-dimensional information of those defects, automatic defect review AFM (ADR AFM) is utilized for accurate locating and imaging of DOI. In ADR AFM, non-contact mode imaging is used for non-destructive characterization and preserving tip sharpness for data repeatability and reproducibility. Locating DOI and imaging are performed automatically with a throughput of many defects per hour. Topography images of DOI has been collected and compared with SEM images. The ADR AFM has been shown as a non-destructive metrology tool for defect review and obtaining three-dimensional topography information.

Toward tunable doping in graphene FETs by molecular self-assembled monolayers

NASA Astrophysics Data System (ADS)

Li, Bing; Klekachev, Alexander V.; Cantoro, Mirco; Huyghebaert, Cedric; Stesmans, André; Asselberghs, Inge; de Gendt, Stefan; de Feyter, Steven

2013-09-01

In this paper, we report the formation of self-assembled monolayers (SAMs) of oleylamine (OA) on highly oriented pyrolytic graphite (HOPG) and graphene surfaces and demonstrate the potential of using such organic SAMs to tailor the electronic properties of graphene. Molecular resolution Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) images reveal the detailed molecular ordering. The electrical measurements show that OA strongly interacts with graphene leading to n-doping effects in graphene devices. The doping levels are tunable by varying the OA deposition conditions. Importantly, neither hole nor electron mobilities are decreased by the OA modification. As a benefit from this noncovalent modification strategy, the pristine characteristics of the device are recoverable upon OA removal. From this study, one can envision the possibility to correlate the graphene-based device performance with the molecular structure and supramolecular ordering of the organic dopant.In this paper, we report the formation of self-assembled monolayers (SAMs) of oleylamine (OA) on highly oriented pyrolytic graphite (HOPG) and graphene surfaces and demonstrate the potential of using such organic SAMs to tailor the electronic properties of graphene. Molecular resolution Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) images reveal the detailed molecular ordering. The electrical measurements show that OA strongly interacts with graphene leading to n-doping effects in graphene devices. The doping levels are tunable by varying the OA deposition conditions. Importantly, neither hole nor electron mobilities are decreased by the OA modification. As a benefit from this noncovalent modification strategy, the pristine characteristics of the device are recoverable upon OA removal. From this study, one can envision the possibility to correlate the graphene-based device performance with the molecular structure and supramolecular ordering of the organic dopant. Electronic supplementary information (ESI) available: AFM images of self-assembled monolayers of OA on HOPG; AFM height image of the graphene surface on a SiC substrate; high resolution STM image of a self-assembled monolayer of OA on HOPG; transfer curves of a graphene FET with and without baking steps; transfer curves of a graphene FET under high vacuum conditions; transfer curves of a graphene FET and its Raman response before and after OA treatment; transfer curves of a graphene FET before and after rinsing with n-hexane. See DOI: 10.1039/c3nr01255g

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin, L. H., E-mail: lhyin@issp.ac.cn, E-mail: ypsun@issp.ac.cn; Yang, J.; Dai, J. M.

We have investigated the detailed magnetic, magnetoelectric (ME), magnetodielectric (MD) and thermal expansion properties in Co{sub 4}Nb{sub 2}O{sub 9} crystal. A magnetic-field-induced spin flop was observed below antiferromagnetic (AFM) transition temperature T{sub N}. Dielectric constant at applied magnetic field nearly diverges around the AFM transition, giving rise to a colossal MD effect as high as ∼138% around T{sub N}. Theoretical analysis of the ME and MD data revealed a major contribution of critical spin fluctuation to the colossal MD effect in Co{sub 4}Nb{sub 2}O{sub 9}. These results suggest that linear ME materials with large ME coupling might be potentially usedmore » to realize large MD effect for future application.« less

Simulation of Tip-Sample Interaction in the Atomic Force Microscope

NASA Technical Reports Server (NTRS)

Good, Brian S.; Banerjea, Amitava

1994-01-01

Recent simulations of the interaction between planar surfaces and model Atomic Force Microscope (AFM) tips have suggested that there are conditions under which the tip may become unstable and 'avalanche' toward the sample surface. Here we investigate via computer simulation the stability of a variety of model AFM tip configurations with respect to the avalanche transition for a number of fcc metals. We perform Monte-Carlo simulations at room temperature using the Equivalent Crystal Theory (ECT) of Smith and Banerjea. Results are compared with recent experimental results as well as with our earlier work on the avalanche of parallel planar surfaces. Our results on a model single-atom tip are in excellent agreement with recent experiments on tunneling through mechanically-controlled break junctions.

Structural and magnetic analysis of Cu, Co substituted NiFe{sub 2}O{sub 4} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Hakikat; Bala, Kanchan; Negi, N. S.

2016-05-23

In the present work we prepared NiFe{sub 2}O{sub 4}, Ni{sub 0.95}Cu{sub 0.05}Fe{sub 2}O{sub 4} and Ni{sub 0.94}Cu{sub 0.05}Co{sub 0.01} Fe{sub 2}O{sub 4} thin films by metallo-organic decomposition method (MOD) using spin coating technique. The thin films were analyzed by X-ray diffractometer (XRD) and Atomic force microscope (AFM) for structural studies. The XRD patterns confirmed the ferrite phase of thin films. From AFM, we analyzed surface morphology, calculated grain size (GS) and root mean square roughness (RMSR). Room temperature magnetic properties were investigated by vibrating sample magnetometer (VSM).

Synthesis of TiN/a-Si3N4 thin film by using a Mather type dense plasma focus system

NASA Astrophysics Data System (ADS)

Hussain, T.; R., Ahmad; Khalid, N.; A. Umar, Z.; Hussnain, A.

2013-05-01

A 2.3 kJ Mather type pulsed plasma focus device was used for the synthesis of a TiN/a-Si3N4 thin film at room temperature. The film was characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The XRD pattern confirms the growth of polycrystalline TiN thin film. The XPS results indicate that the synthesized film is non-stoichiometric and contains titanium nitride, silicon nitride, and a phase of silicon oxy-nitride. The SEM and AFM results reveal that the surface of the synthesized film is quite smooth with 0.59 nm roughness (root-mean-square).

Nanoscale multiple gaseous layers on a hydrophobic surface.

PubMed

Zhang, Lijuan; Zhang, Xuehua; Fan, Chunhai; Zhang, Yi; Hu, Jun

2009-08-18

The nanoscale gas state at the interfaces of liquids (water, acid, and salt solutions) and highly oriented pyrolytic graphite (HOPG) was investigated via tapping-mode atomic force microscopy (AFM). For the first time, we report that the interfacial gases could form bilayers and trilayers, i.e., on the top of a flat gas layer, there are one or two more gas layers. The formation of these gas layers could be induced by a local supersaturation of gases, which can be achieved by (1) temperature difference between the liquids and the HOPG substrates or (2) exchange ethanol with water. Furthermore, we found that the gas layers were less stable than spherical bubbles. They could transform to bubbles with time or under the perturbation of the AFM tip.

Size-dependent single electron transfer and semi-metal-to-insulator transitions in molecular metal oxide electronics

NASA Astrophysics Data System (ADS)

Balliou, Angelika; Bouroushian, Mirtat; Douvas, Antonios M.; Skoulatakis, George; Kennou, Stella; Glezos, Nikos

2018-07-01

All-inorganic self-arranged molecular transition metal oxide hyperstructures based on polyoxometalate molecules (POMs) are fabricated and tested as electronically tunable components in emerging electronic devices. POM hyperstructures reveal great potential as charging nodes of tunable charging level for molecular memories and as enhancers of interfacial electron/hole injection for photovoltaic stacks. STM, UPS, UV–vis spectroscopy and AFM measurements show that this functionality stems from the films’ ability to structurally tune their HOMO–LUMO levels and electron localization length at room temperature. By adapting POM nanocluster size in solution, self-doping and current modulation of four orders of magnitude is monitored on a single nanocluster on SiO2 at voltages as low as 3 Volt. Structurally driven insulator-to-semi-metal transitions and size-dependent current regulation through single electron tunneling are demonstrated and examined with respect to the stereochemical and electronic structure of the molecular entities. This extends the value of self-assembly as a tool for correlation length and electronic properties tuning and demonstrate POM hyperstructures’ plausibility for on-chip molecular electronics operative at room temperature.

Drying of polymer films: study of demixing phenomena

NASA Astrophysics Data System (ADS)

Fichot, Julie; Heyd, Rodolphe; Saboungi, Marie-Louise; Josserend, Christophe; Combard, Emilie; Tranchant, Jean Francois

2011-03-01

Understanding the mechanisms that control the stability of polymeric films is important in beauty care. We have prepared films starting from a water-soluble organic polymer, a preservative and water. We study the drying of these films as a function of several physicochemical parameters that control their interfaces such as temperature, humidity and the nature of the support. The viscoelastic properties of the solutions before spreading out are analyzed with a rheometer in order to adjust the temperature. The topography of the films is observed by optical microscopy and the evolution of the drying is determined with a precision gravimetric balance. The behavior of the films on a nanometric scale is followed by AFM. During the drying process, droplets appear on the surface of the film, made up of water surrounded by a shell of preservative. As the films dries, the water evaporates from the droplets and the preservative spreads on the surface of the film, leading to the formation of craters on the surface of the dried film. The dimensions and numbers of the craters depend strongly on the type and concentration of the preservative employed.

Contrast and Raman spectroscopy study of single- and few-layered charge density wave material: 2H-TaSe2

PubMed Central

Hajiyev, Parviz; Cong, Chunxiao; Qiu, Caiyu; Yu, Ting

2013-01-01

In this article, we report the first successful preparation of single- and few-layers of tantalum diselenide (2H-TaSe2) by mechanical exfoliation technique. Number of layers is confirmed by white light contrast spectroscopy and atomic force microscopy (AFM). Vibrational properties of the atomically thin layers of 2H-TaSe2 are characterized by micro-Raman spectroscopy. Room temperature Raman measurements demonstrate MoS2-like spectral features, which are reliable for thickness determination. E1g mode, usually forbidden in backscattering Raman configuration is observed in the supported TaSe2 layers while disappears in the suspended layers, suggesting that this mode may be enabled because of the symmetry breaking induced by the interaction with the substrate. A systematic in-situ low temperature Raman study, for the first time, reveals the existence of incommensurate charge density wave phase transition in single and double-layered 2H-TaSe2 as reflected by a sudden softening of the second-order broad Raman mode resulted from the strong electron-phonon coupling (Kohn anomaly). PMID:24005335

Size-dependent single electron transfer and semi-metal-to-insulator transitions in molecular metal oxide electronics.

PubMed

Balliou, Angelika; Bouroushian, Mirtat; Douvas, Antonios M; Skoulatakis, George; Kennou, Stella; Glezos, Nikos

2018-07-06

All-inorganic self-arranged molecular transition metal oxide hyperstructures based on polyoxometalate molecules (POMs) are fabricated and tested as electronically tunable components in emerging electronic devices. POM hyperstructures reveal great potential as charging nodes of tunable charging level for molecular memories and as enhancers of interfacial electron/hole injection for photovoltaic stacks. STM, UPS, UV-vis spectroscopy and AFM measurements show that this functionality stems from the films' ability to structurally tune their HOMO-LUMO levels and electron localization length at room temperature. By adapting POM nanocluster size in solution, self-doping and current modulation of four orders of magnitude is monitored on a single nanocluster on SiO 2 at voltages as low as 3 Volt. Structurally driven insulator-to-semi-metal transitions and size-dependent current regulation through single electron tunneling are demonstrated and examined with respect to the stereochemical and electronic structure of the molecular entities. This extends the value of self-assembly as a tool for correlation length and electronic properties tuning and demonstrate POM hyperstructures' plausibility for on-chip molecular electronics operative at room temperature.

Low-temperature magnetoelectric effect in multiferroic h-Yb1-xHoxMnO3

NASA Astrophysics Data System (ADS)

Zhang, Jincang; Gang, Qiang; Fang, Yifei

In this work, we study the low-temperature ferroelectricity, magnetic property and ME effect in Yb1-xHoxMnO3. In YbMnO3, ferroelectric polarization (P) is closely related with the structure change derived from spin-reorientation process. The initial symmetric relationship of P between the upper and lower half of magnetic sublattice will be broken, which gives rise to the detectable polarization. Additionally, the asymmetry of the P - T curves revealed the pinning effect of the defects in the material. In Ho-doped samples 2D antiferromagnetic perturbation as well as the second AFM ordering have been observed. Substitution of Yb by Ho atoms shows great influences on electric properties and the lowdoping concentration tend to be more favorable for the enhancement of P. The maximum polarization has been promoted hugely in Yb0.8Ho0.2MnO3. We suggested the variation of P is closely related with the stronger exchange interaction in Mn-O-Ho as well as the establishment of new Ho layers with the increase of Ho.

Magnetic transition in Y-site doped multiferroic YMnO3

NASA Astrophysics Data System (ADS)

Thakur, Rajesh K.; Thakur, Rasna; Gaur, N. K.

2016-05-01

We have synthesized polycrystalline hexagonal Y1-xSrxMnO3 (x=0.02, 0.1) compounds by using conventional solid state reaction method. The detailed structural investigations are carried out by using XRD studies which reveals the single phase formation of the reported compounds with hexagonal structure and space group P63cm (JCPDS: 25-1079). Further the XRD data of reported compounds were analyzed by RIETVELD (FULLPROFF) method which shows the decrease in the lattice parameter with increasing concentration of divalent strontium to Y-site. The observed pointed kinks in the specific heat study are indicative of the probable coupling in between the electric and magnetic orders in this class of materials. The reported systematic specific heat studies shows that the antiferromagnetic (AFM) transition temperature (TN) shifts to higher value with increasing concentration of Sr2+ ion in the YMnO3 compound which is attributed to the enhanced lattice contribution to the specific heat in the this compound. The present compound shows the independence of specific heat and magnetic transition temperature with applied magnetic field of 8T and 12T.

Cohesiveness and hydrodynamic properties of young drinking water biofilms.

PubMed

Abe, Yumiko; Skali-Lami, Salaheddine; Block, Jean-Claude; Francius, Grégory

2012-03-15

Drinking water biofilms are complex microbial systems mainly composed of clusters of different size and age. Atomic force microscopy (AFM) measurements were performed on 4, 8 and 12 weeks old biofilms in order to quantify the mechanical detachment shear stress of the clusters, to estimate the biofilm entanglement rate ξ. This AFM approach showed that the removal of the clusters occurred generally for mechanical shear stress of about 100 kPa only for clusters volumes greater than 200 μm3. This value appears 1000 times higher than hydrodynamic shear stress technically available meaning that the cleaning of pipe surfaces by water flushing remains always incomplete. To predict hydrodynamic detachment of biofilm clusters, a theoretical model has been developed regarding the averaging of elastic and viscous stresses in the cluster and by including the entanglement rate ξ. The results highlighted a slight increase of the detachment shear stress with age and also the dependence between the posting of clusters and their volume. Indeed, the experimental values of ξ allow predicting biofilm hydrodynamic detachment with same order of magnitude than was what reported in the literature. The apparent discrepancy between the mechanical and the hydrodynamic detachment is mainly due to the fact that AFM mechanical experiments are related to the clusters local properties whereas hydrodynamic measurements reflected the global properties of the whole biofilm. Copyright © 2011 Elsevier Ltd. All rights reserved.

Influence of smectite suspension structure on sheet orientation in dry sediments: XRD and AFM applications.

PubMed

Zbik, Marek S; Frost, Ray L

2010-06-15

The structure-building phenomena within clay aggregates are governed by forces acting between clay particles. Measurements of such forces are important to understand in order to manipulate the aggregate structure for applications such as dewatering of mineral processing tailings. A parallel particle orientation is required when conducting XRD investigation on the oriented samples and conduct force measurements acting between basal planes of clay mineral platelets using atomic force microscopy (AFM). To investigate how smectite clay platelets were oriented on silicon wafer substrate when dried from suspension range of methods like SEM, XRD and AFM were employed. From these investigations, we conclude that high clay concentrations and larger particle diameters (up to 5 microm) in suspension result in random orientation of platelets in the substrate. The best possible laminar orientation in the clay dry film, represented in the XRD 001/020 intensity ratio of 47 was obtained by drying thin layers from 0.02 wt.% clay suspensions of the natural pH. Conducted AFM investigations show that smectite studied in water based electrolytes show very long-range repulsive forces lower in strength than electrostatic forces from double-layer repulsion. It was suggested that these forces may have structural nature. Smectite surface layers rehydrate in water environment forms surface gel with spongy and cellular texture which cushion approaching AFM probe. This structural effect can be measured in distances larger than 1000 nm from substrate surface and when probe penetrate this gel layer, structural linkages are forming between substrate and clay covered probe. These linkages prevent subsequently smooth detachments of AFM probe on way back when retrieval. This effect of tearing new formed structure apart involves larger adhesion-like forces measured in retrieval. It is also suggested that these effect may be enhanced by the nano-clay particles interaction. 2010 Elsevier Inc. All rights reserved.

Study of the highly ordered TiO2 nanotubes physical properties prepared with two-step anodization

NASA Astrophysics Data System (ADS)

Pishkar, Negin; Ghoranneviss, Mahmood; Ghorannevis, Zohreh; Akbari, Hossein

2018-06-01

Highly ordered hexagonal closely packed titanium dioxide nanotubes (TiO2 NTs) were successfully grown by a two-step anodization process. The TiO2 NTs were synthesized by electrochemical anodization of titanium foils in an ethylene glycol based electrolyte solution containing 0.3 wt% NH4F and 2 vol% deionized (DI) water at constant potential (50 V) for 1 h at room temperature. Physical properties of the TiO2 NTs, which were prepared via one and two-step anodization, were investigated. Atomic Force Microscopy (AFM) analysis revealed that anodization and subsequently peeled off the TiO2 NTs caused to the periodic pattern on the Ti surface. In order To study the nanotubes morphology, Field Emission Scanning Electron Microscopy (FESEM) was used, which was revealed that the two-step anodization resulted highly ordered hexagonal TiO2 NTs. Crystal structures of the TiO2 NTs were mainly anatase, determined by X-ray diffraction analysis. Optical studies were performed by Diffuse Reflection Spectra (DRS) and Photoluminescence (PL) analysis showed that the band gap of TiO2 NTs prepared via two-step anodization was lower than the band gap of samples prepared by one-step anodization process.

Tracing the beginning of crystallization of amorphous forsterite thin films using AFM and IR spectroscopy

NASA Astrophysics Data System (ADS)

Oehm, B.; Burchard, M.; Lattard, D.; Dohmen, R.; Chakraborty, S.

2009-12-01

Observations of accretion disks of Young Stellar Objects revealed dust of crystalline Mg-silicates, in particular of forsterite, which is assumed to result from high temperature annealing of amorphous cosmic dust particles. We are performing annealing experiments to obtain kinetic parameters of the crystallization that are necessary for the numerical modeling of accretion disks. We use thin films obtained by Pulsed Laser Deposition (PLD) on Si (111) wafers. The thin films are completely amorphous, chemically homogeneous (on the Mg2SiO4 composition) and with a continuous and flat surface. They are annealed for 1 to 260 h at 1073K in a vertical furnace and drop-quenched. To monitor the progress of crystallization, the samples are characterized by AFM and SEM imaging and IR spectroscopy. After 2.5 h of annealing AFM images reveal elliptical features, below 1 µm in diameter, with a central elevation and surrounded by a lowering of the surface which indicate material transport within the elliptical domains. These elliptical features most probably represent early nucleation sites in an amorphous matrix. The IR spectra still show the broad bands of Si-O stretching modes typical of amorphous silica without clear evidence for crystalline forsterite. After 6 h of annealing, AFM and SEM images show circular and square features both with a central elevation in the range of 80 to 120 nm. IR spectra show a few weak bands that can be assigned to crystalline forsterite (bending and stretching of tetrahedra). After 10 h of annealing planar faces appear in the former pyramidal features and the surrounding matrix evolves into domains with spherolitic appearance. IR spectra of these samples display typical bands of crystalline forsterite. With increasing annealing time AFM images picture the further growth of the planar faces towards idiomorphic crystals. SEM imaging shows surface roughening with increasing annealing time. The quantitative evaluation of the surface roughness of AFM images point to three evolutionary stages during annealing. The quantitative evaluation of IR spectra reveals that the forsterite bands continuously grow with increasing annealing time up to 64 h but that no significant change appears for longer run durations. AFM imaging proves to be a powerful tool to detect the very first signs of crystallization and to trace its further evolution.

Electrical Measurements and Nanomechanics Using Scanning Probe Microscopy

NASA Astrophysics Data System (ADS)

Chang, Yong

2002-10-01

In the early 1980s, G. Binnig et al. invented the Scanning Tunneling Microscopy (STM) [1], making it possible to obtain atomic resolution images of conducting surfaces. After that, many different types of Scanning Probe Microscopy (SPM) were invented and some of the most useful representatives are Atomic Force Microscopy (AFM) [2], Electrostatic Force Microscopy (EFM) [3] and Kelvin Probe Force Microscopy (KPFM) [4,5]. In 1985, G. Binnig et al. [2] invented the AFM, which now is used as a fundamental tool in many fields of research. Developed from AFM, Y. Martin et al. [3] invented EFM in 1987. The development of AC mode AFM allows the detection of weak long-range forces. EFM has also been used to study other systems and phenomena, such as thin liquid films on solid surfaces [6], electrically stressed gold nanowires [7], and spatial charge distribution in quantum wires [8]. In 1991, M. Nonnenmacher et al. [5] invented Kelvin Probe Force Microscopy. KPFM is used to study any property that affects the tip-surface Contact Potential Difference (CPD), such as voltage signals in integrated circuits (IC) [9], charged grain boundaries in polycrystalline silicon [10] and surface potential variations in multilayer semiconductor devices [11]. The aim of this poster is to discuss the application of SPM to electrical measurements. The theory of SPM was presented. The AFM was firstly introduced as it was developed before the other two. The design and theory were discussed. The force-distance curve was introduced. After this EFM was presented. EFM was developed from AC mode AFM. The technique was achieved by applying a DC voltage between the tip and the sample. The design, theory and features of it were surveyed. KPFM was also discussed. KPFM was developed from EFM. The central part of this technique is to measure the CPD. Experimental measurements of SPM were described after theory part. Research work using AFM was presented. The newest technique of AFM, UHV-AFM has been used in investigating the nano-mechanical properties of different materials. Normally common AFM has shortcomings as it has either strict limit resolution or difficulties in interpreting the data from the measurements. In order to solve these problems, Ultra High Vacuum (UHV) conditions were applied to acquire quantitative results. A typical UHV-AFM uses a cantilever whose spring constant is relatively high (>100 N/m) to obtain high-resolution image. Experimental measurements using KPFM was presented after AFM. Researchers are using KPFM to acquire the topography and measuring the CPD of semiconductor or metal surfaces. Similarly as in AFM, KPFM works best in UHV environment. A typical UHV-KPFM also uses a cantilever whose spring constant is relatively high. A UHV-KPFM may be able to achieve a high resolution in CPD images. In the past 20 years many different kinds of SPM were invented and used. AFM, EFM, and KPFM are representatives of them. Researchers are still developing new techniques. However, in recent years, they pay more attention in improving the measurement accuracy instead of trying to invent new SPM. These three SPM continue to be frequently used. The current capabilities of SPM do not satisfy us completely. We still cant measure the Electrical field directly. We actually measure the capacitance gradient. There are also some other questions. This is because the electrostatic force depends very strongly on the geometry of the probe at all length scales, so any model is subject to two big problems. First, the geometry is not known with complete accuracy; and second, the tip shape can change during an experiment due to wear. In the future, maybe the problems could be overcome by using a tip with a very well defined shape, such as a carbon nanotube, for which a realistic geometrical model could be more easily constructed, and the wear could be avoided or reduced.

Spin liquid state in the disordered triangular lattice Sc 2Ga 2CuO 7 revealed by NMR

DOE PAGES

Khuntia, P.; Kumar, R.; Mahajan, A. V.; ...

2016-04-18

We present microscopic magnetic properties of a two-dimensional triangular lattice Sc 2Ga 2CuO 7, consisting of single and double triangular Cu planes. An antiferromagnetic (AFM) exchange interaction J/k B ≈ 35 K between Cu 2+ (S = 1/2) spins in the triangular biplane is obtained from the analysis of intrinsic magnetic susceptibility data. The intrinsic magnetic susceptibility, extracted from 71Ga NMR shift data, displays the presence of AFM short range spin correlations and remains finite down to 50 mK, suggesting a nonsinglet ground state. The nuclear spin-lattice relaxation rate (1/T 1) reveals a slowing down of Cu 2+ spin fluctuationsmore » with decreasing T down to 100 mK. Magnetic specific heat (C m) and 1/T 1 exhibit power law behavior at low temperatures, implying the gapless nature of the spin excitation spectrum. The absence of long range magnetic ordering down to ~J/700, nonzero spin susceptibility at low T, and the power law behavior of C m and 1/T 1 suggest a gapless quantum spin liquid (QSL) state. Our results demonstrate that persistent spin dynamics induced by frustration maintain a quantum-disordered state at T → 0 in this triangular lattice antiferromagnet. Furthermore, this suggests that the low energy modes are dominated by spinon excitations in the QSL state due to randomness engendered by disorder and frustration.« less

"Un-annealed and Annealed Pd Ultra-Thin Film on SiC Characterized by Scanning Probe Microscopy and X-ray Photoelectron Spectroscopy"

NASA Technical Reports Server (NTRS)

Lu, W. J.; Shi, D. T.; Elshot, K.; Bryant, E.; Lafate, K.; Chen, H.; Burger, A.; Collins, W. E.

1998-01-01

Pd/SiC has been used as a hydrogen and a hydrocarbon gas sensor operated at high temperature. UHV (Ultra High Vacuum)-Scanning Tunneling Microscopy (STM), Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) techniques were applied to study the relationship between the morphology and chemical compositions for Pd ultra-thin films on SiC (less than 30 angstroms) at different annealing temperatures. Pd ultra-thin film on 6H-SiC was prepared by the RF sputtering method. The morphology from UHV-STM and AFM shows that the Pd thin film was well deposited on SiC substrate, and the Pd was partially aggregated to round shaped participates at an annealing temperature of 300 C. At 400 C, the amount of surface participates decreases, and some strap shape participates appear. From XPS, Pd2Si was formed on the surface after annealing at 300 C, and all Pd reacted with SiC to form Pd2Si after annealing at 400 C. The intensity of the XPS Pd peak decreases enormously at 400 C. The Pd film diffused into SiC, and the Schottky barrier height has almost no changes. The work shows the Pd sicilides/SiC have the same electronic properties with Pd/SiC, and explains why the Pd/SiC sensor still responds to hydrogen at high operating temperatures.

Single Spin Superconductivity: Bulk and Junction Effects

NASA Astrophysics Data System (ADS)

Rudd, Robert E.; Pickett, Warren E.

1998-03-01

The Josephson Effect provides a primary signature of single spin superconductivity (SSS), the as yet unobserved superconducting state which was proposed recently(W.E. Pickett, Phys. Rev. Lett. 77), 3185 (1996). as a low temperature phase of half-metallic antiferromagnets.(W.E. Pickett, ``Spin Density Functional Based Search for Half-Metallic Antiferromagnets,'' cond-mat/9709100 (1997).) These materials are insulating in the spin-down channel but are metallic in the spin-up channel. The SSS state is characterized by a unique form of p-wave pairing within a single spin channel.(R.E. Rudd and W.E. Pickett, ``Single Spin Superconductivity:Formulation and Ginzburg-Landau Theory,'' Phys. Rev. B. in press) We develop the theory of a rich variety of Josephson effects that arise due to the form of the SSS order parameter. Tunneling is allowed at a SSS-SSS^' junction depending on the relative orientation of each of their order parameters (SSS and HM AFM). No current flows between an SSS and an s-wave BCS system, which provides a powerful method to distinguish SSS from other superconducting states.

Work function and temperature dependence of electron tunneling through an N-type perylene diimide molecular junction with isocyanide surface linkers.

PubMed

Smith, Christopher E; Xie, Zuoti; Bâldea, Ioan; Frisbie, C Daniel

2018-01-18

Conducting probe atomic force microscopy (CP-AFM) was employed to examine electron tunneling in self-assembled monolayer (SAM) junctions. A 2.3 nm long perylene tetracarboxylic acid diimide (PDI) acceptor molecule equipped with isocyanide linker groups was synthesized, adsorbed onto Ag, Au and Pt substrates, and the current-voltage (I-V) properties were measured by CP-AFM. The dependence of the low-bias resistance (R) on contact work function indicates that transport is LUMO-assisted ('n-type behavior'). A single-level tunneling model combined with transition voltage spectroscopy (TVS) was employed to analyze the experimental I-V curves and to extract the effective LUMO position ε l = E LUMO - E F and the effective electronic coupling (Γ) between the PDI redox core and the contacts. This analysis revealed a strong Fermi level (E F ) pinning effect in all the junctions, likely due to interface dipoles that significantly increased with increasing contact work function, as revealed by scanning Kelvin probe microscopy (SKPM). Furthermore, the temperature (T) dependence of R was found to be substantial. For Pt/Pt junctions, R varied more than two orders of magnitude in the range 248 K < T < 338 K. Importantly, the R(T) data are consistent with a single step electron tunneling mechanism and allow independent determination of ε l , giving values compatible with estimates of ε l based on analysis of the full I-V data. Theoretical analysis revealed a general criterion to unambiguously rule out a two-step transport mechanism: namely, if measured resistance data exhibit a pronounced Arrhenius-type temperature dependence, a two-step electron transfer scenario should be excluded in cases where the activation energy depends on contact metallurgy. Overall, our results indicate (1) the generality of the Fermi level pinning phenomenon in molecular junctions, (2) the utility of employing the single level tunneling model for determining essential electronic structure parameters (ε l and Γ), and (3) the importance of changing the nature of the contacts to verify transport mechanisms.

From molecular to macroscopic engineering: shaping hydrogen-bonded organic nanomaterials.

PubMed

Yoosaf, K; Llanes-Pallas, Anna; Marangoni, Tomas; Belbakra, Abdelhalim; Marega, Riccardo; Botek, Edith; Champagne, Benoît; Bonifazi, Davide; Armaroli, Nicola

2011-03-07

The self-assembly and self-organization behavior of chromophoric acetylenic scaffolds bearing 2,6-bis(acetylamino)pyridine (1, 2) or uracyl-type (3-9) terminal groups has been investigated by photophysical and microscopic methods. Systematic absorption and luminescence studies show that 1 and 2, thanks to a combination of solvophilic/solvophobic forces and π-π stacking interactions, undergo self-organization in apolar solvents (i.e., cyclohexane) and form spherical nanoparticles, as evidenced by wide-field optical microscopy, TEM, and AFM analysis. For the longer molecular module, 2, a more uniform size distribution is found (80-200 nm) compared to 1 (20-1000 nm). Temperature scans in the range 283-353 K show that the self-organized nanoparticles are reversibly formed and destroyed, being stable at lower temperatures. Molecular modules 1 and 2 were then thoroughly mixed with the complementary triply hydrogen-bonding units 3-9. Depending on the specific geometrical structure of 3-9, different nanostructures are evidenced by microscopic investigations. Combination of modules 1 or 2 with 3, which bears only one terminal uracyl unit, leads to the formation of vesicular structures; instead, when 1 is combined with bis-uracyl derivative 4 or 5, a structural evolution from nanoparticles to nanowires is observed. The length of the wires obtained by mixing 1 and 4 or 1 and 5 can be controlled by addition of 3, which prompts transformation of the wires into shorter rods. The replacement of linear system 5 with the related angular modules 6 and 7 enables formation of helical nanostructures, unambiguously evidenced by AFM. Finally, thermally induced self-assembly was studied in parallel with modules 8 and 9, in which the uracyl recognition sites are protected with tert-butyloxycarbonyl (BOC) groups. This strategy allows further control of the self-assembly/self-organization process by temperature, since the BOC group is completely removed on heating. Microscopy studies show that the BOC-protected ditopic modules 8 self-assemble and self-organize with 1 into ordered linear nanostructures, whereas BOC-protected tritopic system 9 gives rise to extended domains of circular nano-objects in combination with 1. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Force spectroscopy of quadruple H-bonded dimers by AFM: dynamic bond rupture and molecular time-temperature superposition.

PubMed

Zou, Shan; Schönherr, Holger; Vancso, G Julius

2005-08-17

We report on the application of the time-temperature superposition principle to supramolecular bond-rupture forces on the single-molecule level. The construction of force-loading rate master curves using atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS) experiments carried out in situ at different temperatures allows one to extend the limited range of the experimentally accessible loading rates and hence to cross from thermodynamic nonequilibrium to quasi-equilibrium states. The approach is demonstrated for quadruple H-bonded ureido-4[1H]-pyrimidinone (UPy) moieties studied by variable-temperature SMFS in organic media. The unbinding forces of single quadruple H-bonding (UPy)2 complexes, which were identified based on a polymeric spacer strategy, were found to depend on the loading rate in the range of 5 nN/s to 500 nN/s at 301 K in hexadecane. By contrast, these rupture forces were independent of the loading rate from 5 to 200 nN/s at 330 K. These results indicate that the unbinding behavior of individual supramolecular complexes can be directly probed under both thermodynamic nonequilibrium and quasi-equilibrium conditions. On the basis of the time-temperature superposition principle, a master curve was constructed for a reference temperature of 301 K, and the crossover force (from loading-rate independent to -dependent regimes) was determined as approximately 145 pN (at a loading rate of approximately 5.6 nN/s). This approach significantly broadens the accessible loading-rate range and hence provides access to fine details of potential energy landscape of supramolecular complexes based on SMFS experiments.

Using Polarized Spectroscopy to Investigate Order in Thin-Films of Ionic Self-Assembled Materials Based on Azo-Dyes

PubMed Central

Ahmad, Mariam; Andersen, Frederik; Brend Bech, Ári; Bendixen, H. Krestian L.; Nawrocki, Patrick R.; Bloch, Anders J.; Bora, Ilkay; Bukhari, Tahreem A.; Bærentsen, Nicolai V.; Carstensen, Jens; Chima, Smeeah; Colberg, Helene; Dahm, Rasmus T.; Daniels, Joshua A.; Dinckan, Nermin; El Idrissi, Mohamed; Erlandsen, Ricci; Førster, Marc; Ghauri, Yasmin; Gold, Mikkel; Hansen, Andreas; Hansen, Kenn; Helmsøe-Zinck, Mathias; Henriksen, Mathias; Hoffmann, Sophus V.; Hyllested, Louise O. H.; Jensen, Casper; Kallenbach, Amalie S.; Kaur, Kirandip; Khan, Suheb R.; Kjær, Emil T. S.; Kristiansen, Bjørn; Langvad, Sylvester; Lund, Philip M.; Munk, Chastine F.; Møller, Theis; Nehme, Ola M. Z.; Nejrup, Mathilde Rove; Nexø, Louise; Nielsen, Simon Skødt Holm; Niemeier, Nicolai; Nikolajsen, Lasse V.; Nøhr, Peter C. T.; Skaarup Ovesen, Jacob; Paustian, Lucas; Pedersen, Adam S.; Petersen, Mathias K.; Poulsen, Camilla M.; Praeger-Jahnsen, Louis; Qureshi, L. Sonia; Schiermacher, Louise S.; Simris, Martin B.; Smith, Gorm; Smith, Heidi N.; Sonne, Alexander K.; Zenulovic, Marko R.; Winther Sørensen, Alma; Vogt, Emil; Væring, Andreas; Westermann, Jonas; Özcan, Sevin B.

2018-01-01

Three series of ionic self-assembled materials based on anionic azo-dyes and cationic benzalkonium surfactants were synthesized and thin films were prepared by spin-casting. These thin films appear isotropic when investigated with polarized optical microscopy, although they are highly anisotropic. Here, three series of homologous materials were studied to rationalize this observation. Investigating thin films of ordered molecular materials relies to a large extent on advanced experimental methods and large research infrastructure. A statement that in particular is true for thin films with nanoscopic order, where X-ray reflectometry, X-ray and neutron scattering, electron microscopy and atom force microscopy (AFM) has to be used to elucidate film morphology and the underlying molecular structure. Here, the thin films were investigated using AFM, optical microscopy and polarized absorption spectroscopy. It was shown that by using numerical method for treating the polarized absorption spectroscopy data, the molecular structure can be elucidated. Further, it was shown that polarized optical spectroscopy is a general tool that allows determination of the molecular order in thin films. Finally, it was found that full control of thermal history and rigorous control of the ionic self-assembly conditions are required to reproducibly make these materials of high nanoscopic order. Similarly, the conditions for spin-casting are shown to be determining for the overall thin film morphology, while molecular order is maintained. PMID:29462883

Using Polarized Spectroscopy to Investigate Order in Thin-Films of Ionic Self-Assembled Materials Based on Azo-Dyes.

PubMed

Kühnel, Miguel R Carro-Temboury Martin; Ahmad, Mariam; Andersen, Frederik; Bech, Ári Brend; Bendixen, H Krestian L; Nawrocki, Patrick R; Bloch, Anders J; Bora, Ilkay; Bukhari, Tahreem A; Bærentsen, Nicolai V; Carstensen, Jens; Chima, Smeeah; Colberg, Helene; Dahm, Rasmus T; Daniels, Joshua A; Dinckan, Nermin; Idrissi, Mohamed El; Erlandsen, Ricci; Førster, Marc; Ghauri, Yasmin; Gold, Mikkel; Hansen, Andreas; Hansen, Kenn; Helmsøe-Zinck, Mathias; Henriksen, Mathias; Hoffmann, Sophus V; Hyllested, Louise O H; Jensen, Casper; Kallenbach, Amalie S; Kaur, Kirandip; Khan, Suheb R; Kjær, Emil T S; Kristiansen, Bjørn; Langvad, Sylvester; Lund, Philip M; Munk, Chastine F; Møller, Theis; Nehme, Ola M Z; Nejrup, Mathilde Rove; Nexø, Louise; Nielsen, Simon Skødt Holm; Niemeier, Nicolai; Nikolajsen, Lasse V; Nøhr, Peter C T; Orlowski, Dominik B; Overgaard, Marc; Ovesen, Jacob Skaarup; Paustian, Lucas; Pedersen, Adam S; Petersen, Mathias K; Poulsen, Camilla M; Praeger-Jahnsen, Louis; Qureshi, L Sonia; Ree, Nicolai; Schiermacher, Louise S; Simris, Martin B; Smith, Gorm; Smith, Heidi N; Sonne, Alexander K; Zenulovic, Marko R; Sørensen, Alma Winther; Sørensen, Karina; Vogt, Emil; Væring, Andreas; Westermann, Jonas; Özcan, Sevin B; Sørensen, Thomas Just

2018-02-15

Three series of ionic self-assembled materials based on anionic azo-dyes and cationic benzalkonium surfactants were synthesized and thin films were prepared by spin-casting. These thin films appear isotropic when investigated with polarized optical microscopy, although they are highly anisotropic. Here, three series of homologous materials were studied to rationalize this observation. Investigating thin films of ordered molecular materials relies to a large extent on advanced experimental methods and large research infrastructure. A statement that in particular is true for thin films with nanoscopic order, where X-ray reflectometry, X-ray and neutron scattering, electron microscopy and atom force microscopy (AFM) has to be used to elucidate film morphology and the underlying molecular structure. Here, the thin films were investigated using AFM, optical microscopy and polarized absorption spectroscopy. It was shown that by using numerical method for treating the polarized absorption spectroscopy data, the molecular structure can be elucidated. Further, it was shown that polarized optical spectroscopy is a general tool that allows determination of the molecular order in thin films. Finally, it was found that full control of thermal history and rigorous control of the ionic self-assembly conditions are required to reproducibly make these materials of high nanoscopic order. Similarly, the conditions for spin-casting are shown to be determining for the overall thin film morphology, while molecular order is maintained.

AFM-IR: Technology and Applications in Nanoscale Infrared Spectroscopy and Chemical Imaging.

PubMed

Dazzi, Alexandre; Prater, Craig B

2016-12-13

Atomic force microscopy-based infrared spectroscopy (AFM-IR) is a rapidly emerging technique that provides chemical analysis and compositional mapping with spatial resolution far below conventional optical diffraction limits. AFM-IR works by using the tip of an AFM probe to locally detect thermal expansion in a sample resulting from absorption of infrared radiation. AFM-IR thus can provide the spatial resolution of AFM in combination with the chemical analysis and compositional imaging capabilities of infrared spectroscopy. This article briefly reviews the development and underlying technology of AFM-IR, including recent advances, and then surveys a wide range of applications and investigations using AFM-IR. AFM-IR applications that will be discussed include those in polymers, life sciences, photonics, solar cells, semiconductors, pharmaceuticals, and cultural heritage. In the Supporting Information , the authors provide a theoretical section that reviews the physics underlying the AFM-IR measurement and detection mechanisms.

Contaminants in milk and impact of heating: an assessment study.

PubMed

Awasthi, Vandana; Bahman, Sanjivan; Thakur, Lalit K; Singh, Santosh Kumar; Dua, Ajit; Ganguly, Sanjeev

2012-01-01

The major contaminants usually encountered in milk and milk products include pesticide residues, heavy metals, and aflatoxin M1 (AFM1). Primarily, milk get contaminated before milching, from the cattle feed, from sources/materials used during the processing of milk as well as improper handling of the milk during the pre- and postprocessing period. The purpose of this study was to evaluate the effect of household practices on milk contaminants. Samples of pasteurized as well as unpasteurized milk (Vendor's milk) were analyzed for AFM1, pesticide residues, and heavy metals. Simulating the household practices, the impact of boiling on these contaminants was assessed. The contaminant Aflatoxin M1 (AFM1) was detected at a concentration ranging from 0.071-0.075 ppb in unpasteurized as well as pasteurized milk samples analyzed during the course of study. Moreover, boiling had no impact on the quantity of AFM1 present in the milk. Pesticides and heavy metal contents were found to be within acceptable limits in all the milk samples tested. Mycotoxins especially aflatoxins in cattle feed and their consequential presence in milk and milk products is a serious concern world over as they are reported carcinogens. These fungal toxins are resistant to high temperatures and may lead to various health hazards. Preventive steps must be taken at each stage to ensure good quality of milk and milk products free from these contaminants. Awareness programs and education for the dairy farmers and milk processors may be helpful in this regard.

Nanoscale effects in the characterization of viscoelastic materials with atomic force microscopy: coupling of a quasi-three-dimensional standard linear solid model with in-plane surface interactions.

PubMed

Solares, Santiago D

2016-01-01

Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip-sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surface as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young's modulus. Relevant cases are discussed for single- and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip-sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. A multifrequency AFM simulation tool based on the above sample model is provided as supporting information.

A New Method for Single-Epoch Ambiguity Resolution with Indoor Pseudolite Positioning.

PubMed

Li, Xin; Zhang, Peng; Guo, Jiming; Wang, Jinling; Qiu, Weining

2017-04-21

Ambiguity resolution (AR) is crucial for high-precision indoor pseudolite positioning. Due to the existing characteristics of the pseudolite positioning system, such as the geometry structure of the stationary pseudolite which is consistently invariant, the indoor signal is easy to interrupt and the first order linear truncation error cannot be ignored, and a new AR method based on the idea of the ambiguity function method (AFM) is proposed in this paper. The proposed method is a single-epoch and nonlinear method that is especially well-suited for indoor pseudolite positioning. Considering the very low computational efficiency of conventional AFM, we adopt an improved particle swarm optimization (IPSO) algorithm to search for the best solution in the coordinate domain, and variances of a least squares adjustment is conducted to ensure the reliability of the solving ambiguity. Several experiments, including static and kinematic tests, are conducted to verify the validity of the proposed AR method. Numerical results show that the IPSO significantly improved the computational efficiency of AFM and has a more elaborate search ability compared to the conventional grid searching method. For the indoor pseudolite system, which had an initial approximate coordinate precision better than 0.2 m, the AFM exhibited good performances in both static and kinematic tests. With the corrected ambiguity gained from our proposed method, indoor pseudolite positioning can achieve centimeter-level precision using a low-cost single-frequency software receiver.

Synthesis of nano-sized lithium cobalt oxide via a sol-gel method

NASA Astrophysics Data System (ADS)

Li, Guangfen; Zhang, Jing

2012-07-01

In this study, nano-structured LiCoO2 thin film were synthesized by coupling a sol-gel process with a spin-coating method using polyacrylic acid (PAA) as chelating agent. The optimized conditions for obtaining a better gel formulation and subsequent homogenous dense film were investigated by varying the calcination temperature, the molar mass of PAA, and the precursor's molar ratios of PAA, lithium, and cobalt ions. The gel films on the silicon substrate surfaces were deposited by multi-step spin-coating process for either increasing the density of the gel film or adjusting the quantity of PAA in the film. The gel film was calcined by an optimized two-step heating procedure in order to obtain regular nano-structured LiCoO2 materials. Both atomic force microscopy (AFM) and scanning electron microscopy (SEM) were utilized to analyze the crystalline and the morphology of the films, respectively.

Surface morphology and interdiffusion of LiF in Alq3-based organic light-emitting devices.

PubMed

Lee, Young Joo; Li, Xiaolong; Kang, Da-Yeon; Park, Seong-Sik; Kim, Jinwoo; Choi, Jeong-Woo; Kim, Hyunjung

2008-09-01

Highly efficient organic light-emitting devices (OLEDs) have been realized by insertion of a thin insulating lithium fluoride (LiF) layer between aluminum (Al) cathode and an electron transport layer, tris-(8-hydroxyquinoline) aluminum (Alq(3)). In this paper, we study the surface morphology of LiF on Alq(3) by synchrotron X-ray scattering and atomic force microscopy (AFM) as a function of thickness of LiF. We also study the interdiffusion of LiF into Al cathode as well as into Alq(3) layer as a function of temperature. Initially, LiF molecules are distributed randomly as clusters on the Alq(3) layer and then gradually form a layer as increasing LiF thickness. The interdiffusion of LiF into Al occurs more actively than into Alq(3) in annealing process. LiF on Alq(3) induces the ordering of Al to (111) direction strongly with increasing LiF thickness.

Adsorptive removal of patulin from aqueous solution using thiourea modified chitosan resin.

PubMed

Liu, Bingjie; Peng, Xiaoning; Chen, Wei; Li, Yang; Meng, Xianghong; Wang, Dongfeng; Yu, Guangli

2015-09-01

In the present paper, thiourea modified chitosan resin (TMCR) was firstly prepared through converting hydroxyl groups of chitosan resin into thiol groups, using glutaraldehyde as cross-linking agent and thiourea as modification agent. TMCR was characterized by FTIR, EDXS, SEM, XRD and AFM technologies. Batch adsorption experiments were performed to study the adsorption capacity of TMCR for patulin at different pH, temperature, contact time and patulin concentration. The result showed that TMCR was effective in removal of patulin from aqueous solution. The adsorption capacity of TMCR for patulin was 1.0 mg/g at pH 4.0, 25 °C for 24 h. Adsorption process could be well described by pseudo-first order model, Freundlich isotherm model and intraparticle diffusion model. It indicated that TMCR is expected to be a new material for patulin adsorption from aqueous solutions. Copyright © 2015 Elsevier B.V. All rights reserved.

Synthesis, magnetic and electrical properties of R3AlCx (R = Ce, Pr and Nd)

NASA Astrophysics Data System (ADS)

Ghule, S. S.; Garde, C. S.; Ramakrishnan, S.; Singh, S.; Rajarajan, A. K.; Laad, Meena; Karmakar, Koushik

2017-09-01

R3AlCx (R = Ce, Pr and Nd; x = 0-1) series has been synthesized by arc melting. Rietveld analysis of x-ray powder diffraction reveals cubic (Pm-3m) structure. A Kondo temperature TK 1 K is estimated for Ce3AlC0.65 from the susceptibility and resistivity data. Magnetic susceptibility measurements indicate antiferromagnetic (AFM) order for R = Pr (x = 0.8 and 1) and Nd (x = 0.6, 0.8 and 1) and ferromagnetic (FM) for Nd3Al. Metamagnetic behaviour in the magnetization curve indicates complex magnetic structure. Band structure calculations indicate growth of a pseudo-gap in the density of states (DOS) from Ce3AlC to Pr3AlC to Nd3AlC. The DOS calculations predict a metallic behaviour which is consistent with the resistivity measurements.

Using 2D correlation analysis to enhance spectral information available from highly spatially resolved AFM-IR spectra

NASA Astrophysics Data System (ADS)

Marcott, Curtis; Lo, Michael; Hu, Qichi; Kjoller, Kevin; Boskey, Adele; Noda, Isao

2014-07-01

The recent combination of atomic force microscopy and infrared spectroscopy (AFM-IR) has led to the ability to obtain IR spectra with nanoscale spatial resolution, nearly two orders-of-magnitude better than conventional Fourier transform infrared (FT-IR) microspectroscopy. This advanced methodology can lead to significantly sharper spectral features than are typically seen in conventional IR spectra of inhomogeneous materials, where a wider range of molecular environments are coaveraged by the larger sample cross section being probed. In this work, two-dimensional (2D) correlation analysis is used to examine position sensitive spectral variations in datasets of closely spaced AFM-IR spectra. This analysis can reveal new key insights, providing a better understanding of the new spectral information that was previously hidden under broader overlapped spectral features. Two examples of the utility of this new approach are presented. Two-dimensional correlation analysis of a set of AFM-IR spectra were collected at 200-nm increments along a line through a nucleation site generated by remelting a small spot on a thin film of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). There are two different crystalline carbonyl band components near 1720 cm-1 that sequentially disappear before a band at 1740 cm-1 due to more disordered material appears. In the second example, 2D correlation analysis of a series of AFM-IR spectra spaced every 1 μm of a thin cross section of a bone sample measured outward from an osteon center of bone growth. There are many changes in the amide I and phosphate band contours, suggesting changes in the bone structure are occurring as the bone matures.

Breaking the Time Barrier in Kelvin Probe Force Microscopy: Fast Free Force Reconstruction Using the G-Mode Platform

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collins, Liam; Ahmadi, Mahshid; Wu, Ting

The atomic force microscope (AFM) offers unparalleled insight into structure and material functionality across nanometer length scales. However, the spatial resolution afforded by the AFM tip is counterpoised by slow detection speeds compared to other common microscopy techniques (e.g. optical, scanning electron microscopy etc.). In this work, we develop an AFM imaging approach allowing ultrafast reconstruction of the tip-sample forces having ~2 orders of magnitude higher time resolution than standard detection methods. Fast free force recovery (F3R) overcomes the widely-viewed temporal bottleneck in AFM, i.e. the mechanical bandwidth of the cantilever, enabling time-resolved imaging at sub-bandwidth speeds. We demonstrate quantitativemore » recovery of electrostatic forces with ~10 µs temporal resolution, free from cantilever ring-down effects. We further apply the F3R method to Kelvin probe force microscopy (KPFM) measurements. F3R-KPFM is an open loop imaging approach (i.e. no bias feedback), allowing ultrafast surface potential measurements (e.g. < 20 µs) to be performed at regular KPFM scan speeds. F3R-KPFM is demonstrated for exploration of ion migration in organometallic halide perovskites materials and shown to allow spatio-temporal imaging of positively charged ion migration under applied electric field, as well as subsequent formation of accumulated charges at the perovskite/electrode interface. In this work we demonstrate quantitative F3R-KPFM measurements – however, we fully expect the F3R approach to be valid for all modes of non-contact AFM operation, including non-invasive probing of ultrafast electrical and magnetic dynamics.« less

Staphylococcus aureus-Fibronectin Interactions with and without Fibronectin-Binding Proteins and Their Role in Adhesion and Desorption ▿

PubMed Central

Xu, Chun-Ping; Boks, Niels P.; de Vries, Joop; Kaper, Hans J.; Norde, Willem; Busscher, Henk J.; van der Mei, Henny C.

2008-01-01

Adhesion and residence-time-dependent desorption of two Staphylococcus aureus strains with and without fibronectin (Fn) binding proteins (FnBPs) on Fn-coated glass were compared under flow conditions. To obtain a better understanding of the role of Fn-FnBP binding, the adsorption enthalpies of Fn with staphylococcal cell surfaces were determined using isothermal titration calorimetry (ITC). Interaction forces between staphylococci and Fn coatings were measured using atomic force microscopy (AFM). The strain with FnBPs adhered faster and initially stronger to an Fn coating than the strain without FnBPs, and its Fn adsorption enthalpies were higher. The initial desorption was high for both strains but decreased substantially within 2 s. These time scales of staphylococcal bond ageing were confirmed by AFM adhesion force measurement. After exposure of either Fn coating or staphylococcal cell surfaces to bovine serum albumin (BSA), the adhesion of both strains to Fn coatings was reduced, suggesting that BSA suppresses not only nonspecific but also specific Fn-FnBP interactions. Adhesion forces and adsorption enthalpies were only slightly affected by BSA adsorption. This implies that under the mild contact conditions of convective diffusion in a flow chamber, adsorbed BSA prevents specific interactions but does allow forced Fn-FnBP binding during AFM or stirring in ITC. The bond strength energies calculated from retraction force-distance curves from AFM were orders of magnitude higher than those calculated from desorption data, confirming that a penetrating Fn-coated AFM tip probes multiple adhesins in the outermost cell surface that remain hidden during mild landing of an organism on an Fn-coated substratum, like that during convective diffusional flow. PMID:18952882

Breaking the Time Barrier in Kelvin Probe Force Microscopy: Fast Free Force Reconstruction Using the G-Mode Platform

DOE PAGES

Collins, Liam; Ahmadi, Mahshid; Wu, Ting; ...

2017-08-06

The atomic force microscope (AFM) offers unparalleled insight into structure and material functionality across nanometer length scales. However, the spatial resolution afforded by the AFM tip is counterpoised by slow detection speeds compared to other common microscopy techniques (e.g. optical, scanning electron microscopy etc.). In this work, we develop an AFM imaging approach allowing ultrafast reconstruction of the tip-sample forces having ~2 orders of magnitude higher time resolution than standard detection methods. Fast free force recovery (F3R) overcomes the widely-viewed temporal bottleneck in AFM, i.e. the mechanical bandwidth of the cantilever, enabling time-resolved imaging at sub-bandwidth speeds. We demonstrate quantitativemore » recovery of electrostatic forces with ~10 µs temporal resolution, free from cantilever ring-down effects. We further apply the F3R method to Kelvin probe force microscopy (KPFM) measurements. F3R-KPFM is an open loop imaging approach (i.e. no bias feedback), allowing ultrafast surface potential measurements (e.g. < 20 µs) to be performed at regular KPFM scan speeds. F3R-KPFM is demonstrated for exploration of ion migration in organometallic halide perovskites materials and shown to allow spatio-temporal imaging of positively charged ion migration under applied electric field, as well as subsequent formation of accumulated charges at the perovskite/electrode interface. In this work we demonstrate quantitative F3R-KPFM measurements – however, we fully expect the F3R approach to be valid for all modes of non-contact AFM operation, including non-invasive probing of ultrafast electrical and magnetic dynamics.« less

Functionalized AFM probes for force spectroscopy: eigenmode shapes and stiffness calibration through thermal noise measurements.

PubMed

Laurent, Justine; Steinberger, Audrey; Bellon, Ludovic

2013-06-07

The functionalization of an atomic force microscope (AFM) cantilever with a colloidal bead is a widely used technique when the geometry between the probe and the sample must be controlled, particularly in force spectroscopy. But some questions remain: how does a bead glued at the end of a cantilever influence its mechanical response? And more importantly for quantitative measurements, can we still determine the stiffness of the AFM probe with traditional techniques?In this paper, the influence of the colloidal mass loading on the eigenmode shape and resonant frequency is investigated by measuring the thermal noise on rectangular AFM microcantilevers with and without beads attached at their extremities. The experiments are performed with a home-made ultra-sensitive AFM, based on differential interferometry. The focused beam from the interferometer probes the cantilever at different positions and the spatial shapes of the modes are determined up to the fifth resonance, without external excitation. The results clearly demonstrate that the first eigenmode is almost unchanged by mass loading. However the oscillation behavior of higher resonances presents a marked difference: with a particle glued at its extremity, the nodes of the modes are displaced towards the free end of the cantilever. These results are compared to an analytical model taking into account the mass and inertial moment of the load in an Euler-Bernoulli framework, where the normalization of the eigenmodes is explicitly worked out in order to allow a quantitative prediction of the thermal noise amplitude of each mode. A good agreement between the experimental results and the analytical model is demonstrated, allowing a clean calibration of the probe stiffness.

On CD-AFM bias related to probe bending

NASA Astrophysics Data System (ADS)

Ukraintsev, V. A.; Orji, N. G.; Vorburger, T. V.; Dixson, R. G.; Fu, J.; Silver, R. M.

2012-03-01

Critical Dimension AFM (CD-AFM) is a widely used reference metrology. To characterize modern semiconductor devices, very small and flexible probes, often 15 nm to 20 nm in diameter, are now frequently used. Several recent publications have reported on uncontrolled and significant probe-to-probe bias variation during linewidth and sidewall angle measurements [1,2]. Results obtained in this work suggest that probe bending can be on the order of several nanometers and thus potentially can explain much of the observed CD-AFM probe-to-probe bias variation. We have developed and experimentally tested one-dimensional (1D) and two-dimensional (2D) models to describe the bending of cylindrical probes. An earlier 1D bending model reported by Watanabe et al. [3] was refined. Contributions from several new phenomena were considered, including: probe misalignment, diameter variation near the carbon nanotube tip (CNT) apex, probe bending before snapping, distributed van der Waals-London force, etc. The methodology for extraction of the Hamaker probe-surface interaction energy from experimental probe bending data was developed. To overcome limitations of the 1D model, a new 2D distributed force (DF) model was developed. Comparison of the new model with the 1D single point force (SPF) model revealed about 27 % difference in probe bending bias between the two. A simple linear relation between biases predicted by the 1D SPF and 2D DF models was found. This finding simplifies use of the advanced 2D DF model of probe bending in various CD-AFM applications. New 2D and three-dimensional (3D) CDAFM data analysis software is needed to take full advantage of the new bias correction modeling capabilities.

Preparation and characterization of nanocrystalline cellulose/Eucommia ulmoides gum nanocomposite film.

PubMed

Sun, Qianqian; Zhao, Xinkun; Wang, Dongmei; Dong, Juane; She, Diao; Peng, Pai

2018-02-01

The nanocomposite films were prepared using Eucommia ulmoides gum (EUG) matrix reinforced with nanocrystalline cellulose (NCC) at different concentrations. Subsequently, the obtained films were characterized by Raman spectra, AFM, XRD, TGA, and DSC. Meanwhile, the wettability, mechanical, and water vapor barrier properties of these films were analyzed. AFM noticed that the average sizes of NCC were 81.95×50.17×13.06nm, while the size of molecular chain for EUG was 2530×57.33×1.28nm. In comparison with control film, a certain amount of NCC obviously improved elongation at break and enhanced their crystallinity and ΔH m . More importantly, NCC/EUG nanocomposite films presented lower thermal stability, glass transition temperature (T g ), melting temperature (T m ), and water vapor permeability (WVP) values, especially the WVP values of 4% NCC film were the lowest as 0.28×10 -9 , 0.30×10 -9 , and 0.58×10 -9 g/m/h/Pa at RH 34%, 55%, and 76%, respectively. Copyright © 2017 Elsevier Ltd. All rights reserved.

Competing exchanges and spin-phonon coupling in Eu(1-x)R(x)MnO3 (R=Y, Lu).

PubMed

Mota, D A; Barcelay, Y Romaguera; Tavares, P B; Chaves, M R; Almeida, A; Oliveira, J; Ferreira, W S; Moreira, J Agostinho

2013-06-12

This work is focused on the phase diagrams and physical properties of Y-doped and Lu-doped EuMnO3. The differences in the corresponding phase boundaries in the (x,T) phase diagram could be overcome by considering a scaling of the Y(3+) and Lu(3+) concentrations to the tolerance factor. This outcome evidences that the tolerance factor is in fact a more reliable representative of the lattice deformation induced by doping. The normalization of the phase boundaries using the tolerance factor corroborates previous theoretical outcomes regarding the key role of competitive FM and AFM exchanges in determining the phase diagrams of manganite perovskites. However, significant differences in the nature and number of phases at low temperatures and concentrations could not be explained by just considering the normalization to the tolerance factor. The vertical phase boundary observed just for Lu-doped EuMnO3, close to 10% Lu, is understood by considering a low temperature Peierls-type spin-phonon coupling, which stabilizes the AFM-4 phase in Lu-doped EuMnO3.

Structural, morphological and optical properties of pulsed laser deposited ZnSe/ZnSeO3 thin films

NASA Astrophysics Data System (ADS)

Hassan, Syed Ali; Bashir, Shazia; Zehra, Khushboo; Salman Ahmed, Qazi

2018-04-01

The effect of varying laser pulses on structural, morphological and optical behavior of Pulsed Laser Deposited (PLD) ZnSe/ZnSeO3 thin films has been investigated. The films were grown by employing Excimer laser (100 mJ, 248 nm, 18 ns, 30 Hz) at various number of laser pulses i.e. 3000, 4000, 5000 and 6000 with elevated substrate temperature of 300 °C. One film was grown at Room Temperature (RT) by employing 3000 number of laser pulses. In order to investigate the structural analysis of deposited films, XRD analysis was performed. It was observed that the room temperature is not favorable for the growth of crystalline film. However, elevated substrate temperature to 300°C, two phases with preferred orientation of ZnSeO3 (2 1 2) and ZnSe (3 3 1) were identified. AFM and SEM analysis were performed to explore the surface morphology of grown films. Morphological analysis also confirmed the non-uniform film growth at room temperature. At elevated substrate temperature (300 °C), the growth of dendritic rods and cubical crystalline structures are observed for lower number of laser pulses i.e. 3000 and 4000 respectively. With increased number of pulses i.e. 5000 and 6000, the films surface morphology becomes smooth which is confirmed by measurement of surface RMS roughness. Number of grains, skewness, kurtosis and other parameters have been evaluated by statistical analysis. In order to investigate the thickness, and optical properties of deposited films, ellipsometery and UV–Vis spectroscopy techniques were employed. The estimated band gap energy is 2.67 eV for the film grown at RT, whereas band gap values varies from 2.80 eV to 3.01 eV for the films grown at 300 °C with increasing number of laser pulses.

Heating Plant Options Economic Analysis System (HPECON): User’s Manual and Technical Reference

DTIC Science & Technology

1991-03-01

Bulb Temperature: The temperature of dry air. Dry Scrubber: A flue gas desulfurization system in which sulfur dioxide is collected by a solid medium...method of solution of a problem. Flue Gas : The gaseous products of combustion. Fly Ash: The fine particles of ash which are carried by the products...AFM 88-29 (U.S. Air Force, July 1978); TM 5-785 (U.S. Army, July 1978); NAVFAC P-89 (Naval Facilities Engineering Command, July 1978). " Flue Gas

Negative Thermal Expansion over a Wide Temperature Range in Fe-doped MnNiGe Composites

NASA Astrophysics Data System (ADS)

Zhao, Wenjun; Sun, Ying; Liu, Yufei; Shi, Kewen; Lu, Huiqing; Song, Ping; Wang, Lei; Han, Huimin; Yuan, Xiuliang; Wang, Cong

2018-02-01

Fe-doped MnNiGe alloys were successfully synthesized by solid-state reaction. Giant negative thermal expansion (NTE) behaviors with the coefficients of thermal expansion (CTE) of -285.23×10-6 K-1 (192-305 K) and -1167.09×10-6 K-1 (246-305 K) have been obtained in Mn0.90Fe0.10NiGe and MnNi0.90Fe0.10Ge, respectively. Furthermore, these materials were combined with Cu in order to control the NTE properties. The results indicate that the absolute value of CTE gradually decreases with increasing Cu contents. In Mn0.92Fe0.08NiGe/x%Cu, the CTE gradually changes from -64.92×10-6 K-1 (125-274 K) to -4.73×10-6 K-1 (173-229 K) with increasing value of x from 15 to 70. The magnetic measurements reveal that the NTE behaviors in this work are strongly correlated with the process of the magnetic phase transition and the introduction of Fe atoms could also change the spiral anti-ferromagnetic (s-AFM) state into ferromagnetic (FM) state at low temperature. Our study launches a new candidate for controlling thermal expansion properties of metal matrix materials which could have potential application in variable temperature environment.

The LER/LWR metrology challenge for advance process control through 3D-AFM and CD-SEM

NASA Astrophysics Data System (ADS)

Faurie, P.; Foucher, J.; Foucher, A.-L.

2009-12-01

The continuous shrinkage in dimensions of microelectronic devices has reached such level, with typical gate length in advance R&D of less than 20nm combine with the introduction of new architecture (FinFET, Double gate...) and new materials (porous interconnect material, 193 immersion resist, metal gate material, high k materials...), that new process parameters have to be well understood and well monitored to guarantee sufficient production yield in a near future. Among these parameters, there are the critical dimensions (CD) associated to the sidewall angle (SWA) values, the line edge roughness (LER) and the line width roughness (LWR). Thus, a new metrology challenge has appeared recently and consists in measuring "accurately" the fabricated patterns on wafers in addition to measure the patterns on a repeatable way. Therefore, a great effort has to be done on existing techniques like CD-SEM, Scatterometry and 3D-AFM in order to develop them following the two previous criteria: Repeatability and Accuracy. In this paper, we will compare the 3D-AFM and CD-SEM techniques as a mean to measure LER and LWR on silicon and 193 resist and point out CD-SEM impact on the material during measurement. Indeed, depending on the material type, the interaction between the electron beam and the material or between the AFM tip and the material can vary a lot and subsequently can generate measurements bias. The first results tend to show that depending on CD-SEM conditions (magnification, number of acquisition frames) the final outputs can vary on a large range and therefore show that accuracy in such measurements are really not obvious to obtain. On the basis of results obtained on various materials that present standard sidewall roughness, we will show the limit of each technique and will propose different ways to improve them in order to fulfil advance roadmap requirements for the development of the next IC generation.

Physical and Occupational Therapy for a Teenager with Acute Flaccid Myelitis: A Case Report.

PubMed

Kornafel, Tracy; Tsao, Elaine Y; Sabelhaus, Emily; Surges, Lori; Apkon, Susan D

2017-10-20

The purpose of this case report is to describe the inpatient rehabilitation program of a 13-year-old boy with acute flaccid myelitis (AFM), specific to physical and occupational therapy examination, treatment, and outcomes. AFM is a rare, acute neurologic illness in children and young adults who present with weakness and/or paralysis of unknown etiology. The teenager was admitted to the program, dependent for all mobility and self-care. Interventions focused on range of motion, transfer training, self-care, power wheelchair mobility, and environmental adaptations. Weekly re-evaluations and the WeeFIM were used at admission and discharge to measure the teenager's progress. At discharge, the teenager had made small gains in his passive and active range of motion. He was independent in directing his care and able to drive his power wheelchair with supervision. Due to the scarcity of published data describing AFM, this report describes an individual's response to a rehabilitation program and will hopefully add to future research in order to provide patients and families with expectations for their recovery and ultimate level of function.

Analysis of effect of nanoporous alumina substrate coated with polypyrrole nanowire on cell morphology based on AFM topography.

PubMed

El-Said, Waleed Ahmed; Yea, Cheol-Heon; Jung, Mi; Kim, Hyuncheol; Choi, Jeong-Woo

2010-05-01

In this study, in situ electrochemical synthesis of polypyrrole nanowires with nanoporous alumina template was described. The formation of highly ordered porous alumina substrate was demonstrated with Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). In addition, Fourier transform infrared analysis confirmed that polypyrrole (PP) nanowires were synthesized by direct electrochemical oxidation of pyrrole. HeLa cancer cells and HMCF normal cells were immobilized on the polypyrrole nanowires/nanoporous alumina substrates to determine the effects of the substrate on the cell morphology, adhesion and proliferation as well as the biocompatibility of the substrate. Cell adhesion and proliferation were characterized using a standard MTT assay. The effects of the polypyrrole nanowires/nanoporous alumina substrate on the cell morphology were studied by AFM. The nanoporous alumina coated with polypyrrole nanowires was found to exhibit better cell adhesion and proliferation than polystyrene petridish, aluminum foil, 1st anodized and uncoated 2nd anodized alumina substrate. This study showed the potential of the polypyrrole nanowires/nanoporous alumina substrate as biocompatibility electroactive polymer substrate for both healthy and cancer cell cultures applications.

UV-induced reaction kinetics of dilinoleoylphosphatidylethanolamine monolayers.

PubMed Central

Viitala, T; Peltonen, J

1999-01-01

The UV-induced reactivity of dilinoleoylphosphatidylethanolamine (DLiPE) Langmuir and Langmuir-Blodgett films has been studied by in situ measurements of the changes in the mean molecular area, UV-vis and Fourier transform infrared spectroscopy, and atomic force microscopy (AFM). Optimum orientation and packing density of the DLiPE molecules in the monolayer were achieved by adding uranyl acetate to the subphase. A first-order reaction kinetic model was successfully fitted to the experimental reaction kinetics data obtained at a surface pressure of 30 mN/m. Topographical studies of LB films by AFM were performed on bilayer structures as a function of subphase composition and UV irradiation time. The orientational effect of the uranyl ions on the monolayer molecules was observed as an enhanced homogeneity of the freshly prepared monomeric LB films. However, the long-term stability of these films proved to be bad; clear reorganization and loss of a true monolayer structure were evidenced by the AFM images. This instability was inhibited for the UV-irradiated films, indicating that the UV irradiation gave rise to a cross-linked structure. PMID:10233096

Characterization of opto-electrical enhancement of tandem photoelectrochemical cells by using photoconductive-AFM

NASA Astrophysics Data System (ADS)

Park, Sun-Young; Elbersen, Rick; Huskens, Jurriaan; Gardeniers, Han; Lee, Joo-Yul; Mul, Guido; Heo, Jinhee

2017-07-01

Solar-to-hydrogen conversion by water splitting in photoelectrochemical cells (PECs) is a promising approach to alleviate problems associated with intermittency in solar energy supply and demand. Several interfacial resistances in photoelectrodes limit the performance of such cells, while the properties of interfaces are not easy to analyze in situ. We applied photoconductive-AFM to analyze the performance of WO3/p+n Si photoanodes, containing an ultra-thin metal interface of either Au or Pt. The Au interface consisted of Au nanoparticles with well-ordered interspacing, while Pt was present in the form of a continuous film. Photoconductive-AFM data show that upon illumination significantly larger currents are measured for the WO3/p+n Si anode equipped with the Au interface, as compared to the WO3/p+n Si anode with the Pt interface, in agreement with the better performance of the former electrode in a photoelectrochemical cell. The remarkable performance of the Au-containing electrode is proposed to be the result of favorable electron-hole recombination rates induced by the Au nanoparticles in a plasmon resonance excited state.

Direct Measurement of Optical Force Induced by Near-Field Plasmonic Cavity Using Dynamic Mode AFM

PubMed Central

Guan, Dongshi; Hang, Zhi Hong; Marcet, Zsolt; Liu, Hui; Kravchenko, I. I.; Chan, C. T.; Chan, H. B.; Tong, Penger

2015-01-01

Plasmonic nanostructures have attracted much attention in recent years because of their potential applications in optical manipulation through near-field enhancement. Continuing experimental efforts have been made to develop accurate techniques to directly measure the near-field optical force induced by the plasmonic nanostructures in the visible frequency range. In this work, we report a new application of dynamic mode atomic force microscopy (DM-AFM) in the measurement of the enhanced optical force acting on a nano-structured plasmonic resonant cavity. The plasmonic cavity is made of an upper gold-coated glass sphere and a lower quartz substrate patterned with an array of subwavelength gold disks. In the near-field when the sphere is positioned close to the disk array, plasmonic resonance is excited in the cavity and the induced force by a 1550 nm infrared laser is found to be increased by an order of magnitude compared with the photon pressure generated by the same laser light. The experiment demonstrates that DM-AFM is a powerful tool for the study of light induced forces and their enhancement in plasmonic nanostructures. PMID:26586455

Combined frequency modulated atomic force microscopy and scanning tunneling microscopy detection for multi-tip scanning probe microscopy applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morawski, Ireneusz; Institute of Experimental Physics, University of Wrocław, pl. M. Borna 9, 50-204 Wrocław; Spiegelberg, Richard

A method which allows scanning tunneling microscopy (STM) tip biasing independent of the sample bias during frequency modulated atomic force microscopy (AFM) operation is presented. The AFM sensor is supplied by an electronic circuit combining both a frequency shift signal and a tunneling current signal by means of an inductive coupling. This solution enables a control of the tip potential independent of the sample potential. Individual tip biasing is specifically important in order to implement multi-tip STM/AFM applications. An extensional quartz sensor (needle sensor) with a conductive tip is applied to record simultaneously topography and conductivity of the sample. Themore » high resonance frequency of the needle sensor (1 MHz) allows scanning of a large area of the surface being investigated in a reasonably short time. A recipe for the amplitude calibration which is based only on the frequency shift signal and does not require the tip being in contact is presented. Additionally, we show spectral measurements of the mechanical vibration noise of the scanning system used in the investigations.« less

Interface electronic structure and morphology of 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on Au film

NASA Astrophysics Data System (ADS)

Wang, Shitan; Niu, Dongmei; Lyu, Lu; Huang, Yingbao; Wei, Xuhui; Wang, Can; Xie, Haipeng; Gao, Yongli

2017-09-01

The interfacial electronic structure and morphology of 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene(C8-BTBT) on polycrystalline Au film was investigated with photoemission spectroscopy (PES), atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXRD). The transport barriers of holes and electrons at the interface are 1.72 eV and 2.12 eV, respectively, from the UPS measurement. There is no chemical reaction of C8-BTBT with Au from the XPS investigation of core levels Au 4f, C 1s and S 2p. The upmost molecules adopt a standing up configuration deduced from the diffraction peaks in GIXRD and the step height in AFM. Increasing order of the upright orientation of C8-BTBT molecules with film growth result in decreasing work function of the C8-BTBT thin film by forming an outward pointing dipole layer with the ordered end Csbnd H bonds.

Optical nanoscopy of high T c cuprate nanoconstriction devices patterned by helium ion beams

DOE PAGES

Gozar, Adrian; Litombe, N. E.; Hoffman, Jennifer E.; ...

2017-02-06

Helium ion beams (HIB) focused to subnanometer scales have emerged as powerful tools for high-resolution imaging as well as nanoscale lithography, ion milling, or deposition. Quantifying irradiation effects is an essential step toward reliable device fabrication, but most of the depth profiling information is provided by computer simulations rather than the experiment. Here, we demonstrate the use of atomic force microscopy (AFM) combined with scanning near-field optical microscopy (SNOM) to provide three-dimensional (3D) dielectric characterization of high-temperature superconductor devices fabricated by HIB. By imaging the infrared dielectric response obtained from light demodulation at multiple harmonics of the AFM tapping frequency,more » we find that amorphization caused by the nominally 0.5 nm HIB extends throughout the entire 26.5 nm thickness of the cuprate film and by ~500 nm laterally. This unexpectedly widespread damage in morphology and electronic structure can be attributed to a helium depth distribution substantially modified by the internal device interfaces. Lastly, our study introduces AFM-SNOM as a quantitative tomographic technique for noninvasive 3D characterization of irradiation damage in a wide variety of nanoscale devices.« less

Quasistatic remanence in Dzyaloshinskii-Moriya interaction driven weak ferromagnets and piezomagnets

NASA Astrophysics Data System (ADS)

Pattanayak, Namrata; Bhattacharyya, Arpan; Nigam, A. K.; Cheong, Sang-Wook; Bajpai, Ashna

2017-09-01

We explore remanent magnetization (μ ) as a function of time and temperature, in a variety of rhombohedral antiferromagnets (AFMs) which are also weak ferromagnets (WFMs) and piezomagnets (PzMs). These measurements, across samples with length scales ranging from nano to bulk, firmly establish the presence of a remanence that is quasistatic in nature and exhibits a counterintuitive magnetic field dependence. These observations unravel an ultraslow magnetization relaxation phenomenon related to this quasistatic remanence. This feature is also observed in a defect-free single crystal of α -Fe2O3 , which is a canonical WFM and PzM. Notably, α -Fe2O3 is not a typical geometrically frustrated AFM, and in single crystal form it is also devoid of any size or interface effects, which are the usual suspects for a slow magnetization relaxation phenomenon. The underlying pinning mechanism appears exclusive to those AFMs which either are symmetry allowed WFMs, driven by Dzyaloshinskii-Moriya interaction, or can generate this trait by tuning of size and interface. The qualitative features of the quasistatic remanence indicate that such WFMs are potential piezomagnets, in which magnetization can be tuned by stress alone.

Electron beam detection of a Nanotube Scanning Force Microscope.

PubMed

Siria, Alessandro; Niguès, Antoine

2017-09-14

Atomic Force Microscopy (AFM) allows to probe matter at atomic scale by measuring the perturbation of a nanomechanical oscillator induced by near-field interaction forces. The quest to improve sensitivity and resolution of AFM forced the introduction of a new class of resonators with dimensions at the nanometer scale. In this context, nanotubes are the ultimate mechanical oscillators because of their one dimensional nature, small mass and almost perfect crystallinity. Coupled to the possibility of functionalisation, these properties make them the perfect candidates as ultra sensitive, on-demand force sensors. However their dimensions make the measurement of the mechanical properties a challenging task in particular when working in cavity free geometry at ambient temperature. By using a focused electron beam, we show that the mechanical response of nanotubes can be quantitatively measured while approaching to a surface sample. By coupling electron beam detection of individual nanotubes with a custom AFM we image the surface topography of a sample by continuously measuring the mechanical properties of the nanoresonators. The combination of very small size and mass together with the high resolution of the electron beam detection method offers unprecedented opportunities for the development of a new class of nanotube-based scanning force microscopy.

Principles and Applications of the qPlus Sensor

NASA Astrophysics Data System (ADS)

Giessibl, Franz J.

The concept of the atomic force microscope (AFM) is a very simple one: map the surface of a sample by a sharp probe that scans over the surface similar to the finger of a blind person that reads Braille characters. In AFM, the role of that finger is taken by the probe tip that senses the presence of the sample surface by detecting the force between the tip of the probe and a sample. The qPlus sensor is a self sensing cantilever based on a quartz tuning fork that supplements the traditional microfabricated cantilevers made of silicon. Quartz tuning forks are used in the watch industry in quantities of billions annually, with the positive effects on quality and perfection. Three properties of these quartz-based sensors simplify the AFM significantly: (1) the piezoelectricity of quartz allows simple self sensing, (2) the mechanical properties of quartz show very small variations with temperature, and (3) the given stiffness of many quartz tuning forks is close to the ideal stiffness of cantilevers. The key properties of the qPlus sensor are a large stiffness that allows small amplitude operation, the large size that allows to mount single-crystal probe tips, and the self-sensing piezoelectric detection mechanism.

The correlations of the electronic structure and film growth of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on SiO2.

PubMed

Lyu, Lu; Niu, Dongmei; Xie, Haipeng; Zhao, Yuan; Cao, Ningtong; Zhang, Hong; Zhang, Yuhe; Liu, Peng; Gao, Yongli

2017-01-04

Combining ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM) and small angle X-ray diffraction (SAXD) measurements, we perform a systematic investigation on the correlations of the electronic structure, film growth and molecular orientation of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on silicon oxide (SiO 2 ). AFM analysis reveals a phase transition of disorderedly oriented molecules in clusters in thinner films to highly ordered standing-up molecules in islands in thicker films. SAXD peaks consistently support the standing-up configuration in islands. The increasing ordering of the molecular orientation with film thickness contributes to the changing of the shape and lowering of the leading edge of the highest occupied molecular orbital (HOMO). The end methyl of the highly ordered standing molecules forms an outward pointing dipole layer which makes the work function (WF) decrease with increasing thickness. The downward shift of the HOMO and a decrease of WF result in unconventional downward band bending and decreased ionization potential (IP). The correlations of the orientation ordering of molecules, film growth and interface electronic structures provide a useful design strategy to improve the performance of C8-BTBT thin film based field effect transistors.

Antiferromagnetism in semiconducting SrMn 2 Sb 2 and BaMn 2 Sb 2 single crystals

DOE PAGES

Sangeetha, N. S.; Smetana, V.; Mudring, A. -V.; ...

2018-01-03

Here, crystals of SrMn 2Sb 2 and BaMn 2Sb 2 were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity ρ, heat capacity C p, and magnetic susceptibility χ measurements versus temperature T, and magnetization versus field M(H) isotherm measurements. SrMn 2Sb 2 adopts the trigonal CaAl 2Si 2-type structure, whereas BaMn 2Sb 2 crystallizes in the tetragonal ThCr 2Si 2-type structure. The ρ(T) data indicate semiconducting behaviors for both compounds with activation energies of ≳0.35 eV for SrMn 2Sb 2 and 0.16 eV for BaMn 2Sb 2. The χ(T) andmore » C p(T) data reveal antiferromagnetic (AFM) ordering at T N = 110 K for SrMn 2Sb 2 and 450 K for BaMn 2Sb 2. The anisotropic χ(T≤T N) data also show that the ordered moments in SrMn 2Sb 2 are aligned in the hexagonal ab plane, whereas the ordered moments in BaMn 2Sb 2 are aligned collinearly along the tetragonal c axis. The ab-plane M(H) data for SrMn 2Sb 2 exhibit a continuous metamagnetic transition at low fields 02Sb 2 exhibits no metamagnetic transitions up to 5.5 T. The χ(T) and C p(T) data for both SrMn 2Sb 2 and BaMn 2Sb 2 indicate strong dynamic short-range AFM correlations above their respective T N up to at least 900 K within a local-moment picture, corresponding to quasi-two-dimensional magnetic behavior. The present results and a survey of the literature for Mn pnictides with the CaAl 2Si 2 and ThCr 2Si 2 crystal structures show that the T N values for the CaAl 2Si 2-type compounds are much smaller than those for the ThCr 2Si 2-type materials.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sangeetha, N. S.; Smetana, V.; Mudring, A. -V.

Here, crystals of SrMn 2Sb 2 and BaMn 2Sb 2 were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity ρ, heat capacity C p, and magnetic susceptibility χ measurements versus temperature T, and magnetization versus field M(H) isotherm measurements. SrMn 2Sb 2 adopts the trigonal CaAl 2Si 2-type structure, whereas BaMn 2Sb 2 crystallizes in the tetragonal ThCr 2Si 2-type structure. The ρ(T) data indicate semiconducting behaviors for both compounds with activation energies of ≳0.35 eV for SrMn 2Sb 2 and 0.16 eV for BaMn 2Sb 2. The χ(T) andmore » C p(T) data reveal antiferromagnetic (AFM) ordering at T N = 110 K for SrMn 2Sb 2 and 450 K for BaMn 2Sb 2. The anisotropic χ(T≤T N) data also show that the ordered moments in SrMn 2Sb 2 are aligned in the hexagonal ab plane, whereas the ordered moments in BaMn 2Sb 2 are aligned collinearly along the tetragonal c axis. The ab-plane M(H) data for SrMn 2Sb 2 exhibit a continuous metamagnetic transition at low fields 02Sb 2 exhibits no metamagnetic transitions up to 5.5 T. The χ(T) and C p(T) data for both SrMn 2Sb 2 and BaMn 2Sb 2 indicate strong dynamic short-range AFM correlations above their respective T N up to at least 900 K within a local-moment picture, corresponding to quasi-two-dimensional magnetic behavior. The present results and a survey of the literature for Mn pnictides with the CaAl 2Si 2 and ThCr 2Si 2 crystal structures show that the T N values for the CaAl 2Si 2-type compounds are much smaller than those for the ThCr 2Si 2-type materials.« less

Antiferromagnetism in semiconducting SrMn2Sb2 and BaMn2Sb2 single crystals

NASA Astrophysics Data System (ADS)

Sangeetha, N. S.; Smetana, V.; Mudring, A.-V.; Johnston, D. C.

2018-01-01

Crystals of SrMn2Sb2 and BaMn2Sb2 were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity ρ , heat capacity Cp, and magnetic susceptibility χ measurements versus temperature T , and magnetization versus field M (H ) isotherm measurements. SrMn2Sb2 adopts the trigonal CaAl2Si2 -type structure, whereas BaMn2Sb2 crystallizes in the tetragonal ThCr2Si2 -type structure. The ρ (T ) data indicate semiconducting behaviors for both compounds with activation energies of ≳0.35 eV for SrMn2Sb2 and 0.16 eV for BaMn2Sb2 . The χ (T ) and Cp(T ) data reveal antiferromagnetic (AFM) ordering at TN = 110 K for SrMn2Sb2 and 450 K for BaMn2Sb2 . The anisotropic χ (T ≤TN) data also show that the ordered moments in SrMn2Sb2 are aligned in the hexagonal a b plane, whereas the ordered moments in BaMn2Sb2 are aligned collinearly along the tetragonal c axis. The a b -plane M (H ) data for SrMn2Sb2 exhibit a continuous metamagnetic transition at low fields 0

Design and evaluation of precise current integrator for scanning probe microscopy

NASA Astrophysics Data System (ADS)

Raczkowski, Kamil; Piasecki, Tomasz; Rudek, Maciej; Gotszalk, Teodor

2017-03-01

Several of the scanning probe microscopy (SPM) techniques, such as the scanning tunnelling microscopy (STM) or conductive atomic force microscopy (C-AFM), rely on precise measurements of current flowing between the investigated sample and the conductive nanoprobe. The parameters of current-to-voltage converter (CVC), which should detect current in the picompere range, are of utmost importance to those systems as they determine the microscopes’ measuring capabilities. That was the motivation for research on the precise current integrator (PCI), described in this paper, which could be used as the CVC in the C-AFM systems. The main design goal of the PCI was to provide a small and versatile device with the sub-picoampere level resolution with high dynamic range in the order of nanoamperes. The PCI was based on the integrating amplifier (Texas Instruments DDC112) paired with a STM32F4 microcontroller unit (MCU).The gain and bandwidth of the PCI might be easily changed by varying the integration time and the feedback capacitance. Depending on these parameters it was possible to obtain for example the 2.15 pA resolution at 688 nA range with 1 kHz bandwidth or 7.4 fA resolution at 0.98 nA range with 10 Hz bandwidth. The measurement of sinusoidal current with 28 fA amplitude was also presented. The PCI was integrated with the C-AFM system and used in the highly ordered pyrolytic graphite (HOPG) and graphene samples imaging.

Adsorption orientations and immunological recognition of antibodies on graphene

NASA Astrophysics Data System (ADS)

Vilhena, J. G.; Dumitru, A. C.; Herruzo, Elena T.; Mendieta-Moreno, Jesús I.; Garcia, Ricardo; Serena, P. A.; Pérez, Rubén

2016-07-01

Large-scale molecular dynamics (MD) simulations and atomic force microscopy (AFM) in liquid are combined to characterize the adsorption of Immunoglobulin G (IgG) antibodies over a hydrophobic surface modeled with a three-layer graphene slab. We consider explicitly the water solvent, simulating systems with massive sizes (up to 770 000 atoms), for four different adsorption orientations. Protocols based on steered MD to speed up the protein diffusion stage and to enhance the dehydration process are combined with long simulation times (>150 ns) in order to make sure that the final adsorption states correspond to actual stable configurations. Our MD results and the AFM images demonstrate that the IgG antibodies are strongly adsorbed, do not unfold, and retain their secondary and tertiary structures upon deposition. Statistical analysis of the AFM images shows that many of the antibodies adopt vertical orientations, even at very small coverages, which expose at least one Fab binding site for recognition events. Single molecule force spectroscopy experiments demonstrate the immunological response of the deposited antibodies by recognizing its specific antigens. The above properties together with the strong anchoring and preservation of the secondary structure, make graphene an excellent candidate for the development of immunosensors.Large-scale molecular dynamics (MD) simulations and atomic force microscopy (AFM) in liquid are combined to characterize the adsorption of Immunoglobulin G (IgG) antibodies over a hydrophobic surface modeled with a three-layer graphene slab. We consider explicitly the water solvent, simulating systems with massive sizes (up to 770 000 atoms), for four different adsorption orientations. Protocols based on steered MD to speed up the protein diffusion stage and to enhance the dehydration process are combined with long simulation times (>150 ns) in order to make sure that the final adsorption states correspond to actual stable configurations. Our MD results and the AFM images demonstrate that the IgG antibodies are strongly adsorbed, do not unfold, and retain their secondary and tertiary structures upon deposition. Statistical analysis of the AFM images shows that many of the antibodies adopt vertical orientations, even at very small coverages, which expose at least one Fab binding site for recognition events. Single molecule force spectroscopy experiments demonstrate the immunological response of the deposited antibodies by recognizing its specific antigens. The above properties together with the strong anchoring and preservation of the secondary structure, make graphene an excellent candidate for the development of immunosensors. Electronic supplementary information (ESI) available: Further details concerning the experimental methods, the MD simulation protocols, and the characterization and stability of the different adsorption configurations. See DOI: 10.1039/C5NR07612A

PECVD based silicon oxynitride thin films for nano photonic on chip interconnects applications.

PubMed

Sharma, Satinder K; Barthwal, Sumit; Singh, Vikram; Kumar, Anuj; Dwivedi, Prabhat K; Prasad, B; Kumar, Dinesh

2013-01-01

Thin silicon oxynitride (SiO(x)N(y)) films were deposited by low temperature (~300°C) plasma enhanced chemical vapour deposition (PECVD), using SiH(4), N(2)O, NH(3) precursor of the flow rate 25, 100, 30 sccm and subjected to the post deposition annealing (PDA) treatment at 400°C and 600°C for nano optical/photonics on chip interconnects applications. AFM result reveals the variation of roughness from 60.9 Å to 23.4 Å after PDA treatment with respect to the as-deposited films, favourable surface topography for integrated waveguide applications. A model of decrease in island height with the effect of PDA treatment is proposed in support of AFM results. Raman spectroscopy and FTIR measurements are performed in order to define the change in crystallite and chemical bonding of as-deposited as well as PDA treated samples. These outcomes endorsed to the densification of SiO(x)N(y) thin films, due to decrease in Si-N and Si-O bonds strain, as well the O-H, N-H bonds with in oxynitride network. The increase in refractive index and PL intensity of as deposited SiO(x)N(y) thin films to the PDA treated films at 400°C and 600°C are observed. The significant shift of PL spectra peak positions indicate the change in cluster size as the result of PDA treatment, which influence the optical properties of thin films. It might be due to out diffusion of hydrogen containing species from silicon oxynitride films after PDA treatment. In this way, the structural and optical, feasibility of SiO(x)N(y) films are demonstrated in order to obtain high quality thin films for nano optical/photonics on chip interconnects applications. Copyright © 2012 Elsevier Ltd. All rights reserved.

MBE grown III-V strain relaxed buffer layers and superlattices characterized by atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howard, A.J.; Fritz, I.J.; Drummond, T.J.

1993-11-01

Using atomic force microscopy (AFM), the authors have investigated the effects of growth temperature and dopant incorporation on the surface morphology of MBE grown graded buffer layers and strained layer superlattices (SLSs) in the InGaAlAs/GaAs and InAsSb/InSb material systems. The AFM results show quantitatively that over the temperature range from 380 to 545 C, graded in{sub x}Al{sub 1{minus}x}As(x = 0.05 {minus} 0.32) buffer layers grown at high temperatures ({approximately}520 C), and graded In{sub x}Ga{sub 1{minus}x}As (x = 0.05 {minus} 0.33) buffer layers and In{sub 0.4}Ga{sub 0.6}As/In{sub 0.26}Al{sub 0.35}Ga{sub 0.39}As SLSs grown at low temperatures ({approximately}400 C) have the lowest RMSmore » roughness. Also, for SLSs InAs{sub 0.21}Sb{sub 0.79}/InSb, undoped layers grown at 470 C were smoother than undoped layers grown at 420 C and Be-doped layers grown at 470 C. These results illustrate the role of surface tension in the growth of strained layer materials near the melting temperature of the InAs{sub x}Sb{sub {minus}x}/InSb superlattice. Nomarski interference and transmission electron microscopies, IR photoluminescence, x-ray diffraction, and photocurrent spectroscopy were also used to evaluate the relative quality of the material but usually, the results were not conclusive.« less

Anisotropic dependence of the magnetic transition on uniaxial pressure in the Kondo semiconductors Ce T2A l10 (T =Ru and Os)

NASA Astrophysics Data System (ADS)

Hayashi, K.; Umeo, K.; Takeuchi, T.; Kawabata, J.; Muro, Y.; Takabatake, T.

2017-12-01

We have measured the strain, magnetization, and specific heat of the antiferromagnetic (AFM) Kondo semiconductors Ce T2A l10 (T =Ru and Os) under uniaxial pressures applied along the orthorhombic axes. We found a linear dependence of TN on the b -axis parameter for both compounds under uniaxial pressure P ∥b and hydrostatic pressure. This relation indicates that the distance between the Ce-T layers along the b axis is the key structural parameter determining TN. Furthermore, the pressure dependence of the spin-flop transition field indicates that Ce-Ce interchain interactions stabilize the AFM state with the ordered moments pointing to the c axis.

Silk fibroin/gold nanocrystals: a new example of biopolymer-based nanocomposites

NASA Astrophysics Data System (ADS)

Noinville, S.; Garnier, A.; Courty, A.

2017-05-01

The dispersion of nanoparticles in ordered polymer nanostructures can provide control over particle location and orientation, and pave the way for tailored nanomaterials that have enhanced mechanical, electrical, or optical properties. Here we used silk fibroin, a natural biopolymer, to embed gold nanocrystals (NCs), so as to obtain well-ordered structures such as nanowires and self-assembled triangular nanocomposites. Monodisperse gold NCs synthesized in organic media are mixed to silk fibroin and the obtained nanocomposites are characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and Infrared spectroscopy. The optical properties study of gold NCs and silk-gold nanocomposites shows that the Surface Plasmon band is blue shifted compared to gold NCs. The size and shape of NCs gold superlattices can be well controlled by the presence of silk fibroin giving nanowires and also self-assembled triangular nanocomposites as characterized by TEM, FE-SEM and AFM. The strong interaction between gold NCs and silk fibroin is also revealed by the conformation change of silk protein in presence of gold NCs, as shown by FTIR analysis. The formation of such ordered nanocomposites (gold NCs/silk fibroin) will provide new nanoplasmonic devices.

Breakdown of antiferromagnet order in polycrystalline NiFe/NiO bilayers probed with acoustic emission

NASA Astrophysics Data System (ADS)

Lebyodkin, M. A.; Lebedkina, T. A.; Shashkov, I. V.; Gornakov, V. S.

2017-07-01

Magnetization reversal of polycrystalline NiFe/NiO bilayers was investigated using magneto-optical indicator film imaging and acoustic emission techniques. Sporadic acoustic signals were detected in a constant magnetic field after the magnetization reversal. It is suggested that they are related to elastic waves excited by sharp shocks in the NiO layer with strong magnetostriction. Their probability depends on the history and number of repetitions of the field cycling, thus testifying the thermal-activation nature of the long-time relaxation of an antiferromagnetic order. These results provide evidence of spontaneous thermally activated switching of the antiferromagnetic order in NiO grains during magnetization reversal in ferromagnet/antiferromagnet (FM/AFM) heterostructures. The respective deformation modes are discussed in terms of the thermal fluctuation aftereffect in the Fulcomer and Charap model which predicts that irreversible breakdown of the original spin orientation can take place in some antiferromagnetic grains with disordered anisotropy axes during magnetization reversal of exchange-coupled FM/AFM structures. The spin reorientation in the saturated state may induce abrupt distortion of isolated metastable grains because of the NiO magnetostriction, leading to excitation of shock waves and formation of plate (or Lamb) waves.

Visualizing molecular polar order in tissues via electromechanical coupling

PubMed Central

Denning, Denise; Alilat, Sofiane; Habelitz, Stefan; Fertala, Andrzej; Rodriguez, Brian J.

2015-01-01

Electron microscopy (EM) and atomic force microscopy (AFM) techniques have long been used to characterize collagen fibril ordering and alignment in connective tissues. These techniques, however, are unable to map collagen fibril polarity, i.e., the polar orientation that is directed from the amine to the carboxyl termini. Using a voltage modulated AFM-based technique called piezoresponse force microscopy (PFM), we show it is possible to visualize both the alignment of collagen fibrils within a tissue and the polar orientation of the fibrils with minimal sample preparation. We demonstrate the technique on rat tail tendon and porcine eye tissues in ambient conditions. In each sample, fibrils are arranged into domains whereby neighboring domains exhibit opposite polarizations, which in some cases extend to the individual fibrillar level. Uniform polarity has not been observed in any of the tissues studied. Evidence of anti-parallel ordering of the amine to carboxyl polarity in bundles of fibrils or in individual fibrils is found in all tissues, which has relevance for understanding mechanical and biofunctional properties and the formation of connective tissues. The technique can be applied to any biological material containing piezoelectric biopolymers or polysaccharides. PMID:22985991

Morphological evolution in dewetting polystyrene/polyhedral oligomeric silsesquioxane thin film bilayers.

PubMed

Paul, Rituparna; Karabiyik, Ufuk; Swift, Michael C; Hottle, John R; Esker, Alan R

2008-05-06

Morphological evolution in dewetting thin film bilayers of polystyrene (PS) and a polyhedral oligomeric silsesquioxane (POSS), trisilanolphenyl-POSS (TPP), was studied as a function of annealing temperature and annealing time. The results demonstrate unique dewetting morphologies in PS/TPP bilayers at elevated temperatures that are significantly different from those typically observed in dewetting polymer/polymer bilayers. During temperature ramp studies by optical microscopy (OM) in the reflection mode, PS/TPP bilayers form cracks with a weak optical contrast at approximately 130 degrees C. The crack formation is attributed to tensile stresses within the upper TPP layer. The weak optical contrast of the cracks observed in the bilayers for annealing temperatures below approximately 160 degrees C is consistent with the cracking and dewetting of only the upper TPP layer from the underlying PS layer. The optical contrast of the morphological features is significantly enhanced at annealing temperatures of >160 degrees C. This observation suggests dewetting of both the upper TPP and the lower PS layers that results in the exposure of the silicon substrate. Upon annealing the PS/TPP bilayers at 200 degrees C in a temperature jump experiment, the upper TPP layer undergoes instantaneous cracking as observed by OM. These cracks in the upper TPP layer serve as nucleation sites for rapid dewetting and aggregation of the TPP layer, as revealed by OM and atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) results indicated that dewetting of the lower PS layer ensued for annealing times >5 min and progressed up to 90 min. For annealing times >90 min, OM, AFM, and XPS results revealed complete dewetting of both the layers with the formation of TPP encapsulated PS droplets.

Influence of deposition substrate temperature on the morphology and molecular orientation of chloroaluminum phthalocyanine films as well the performance of organic photovoltaic cells.

PubMed

Zheng, Yan-Qiong; Zhang, Jing; Yang, Fang; Komino, Takeshi; Wei, Bin; Zhang, Jianhua; Wang, Zixing; Pu, Wenhong; Yang, Changzhu; Adachi, Chihaya

2015-10-09

The dependence of the morphology of neat chloroaluminum phthalocyanine (ClAlPc) films on substrate temperature (Tsub) during deposition is investigated by variable angle spectroscopic ellipsometry (VASE), x-ray diffraction (XRD), and atomic force microscopy (AFM) to obtain detailed information about the molecular orientation, phase separation, and crystallinity. AFM images indicate that both grain size and root mean square (RMS) roughness noticeably increase with Tsub both in neat and blend films. Increasing Tsub from room temperature to 420 K increases the horizontal orientation of the ClAlPc molecules with an increase of the mean molecular tilt angle from 60.13° (300 K) to 65.86° (420 K). The UV-vis absorption band of the corresponding films increases and the peak wavelength slightly red shifts with the Tsub increase. XRD patterns show a clear diffraction peak at Tsub over 390 K, implying the π-stacking of interconnected ClAlPc molecules at high Tsub. Planar and bulk heterojunction (BHJ) photovoltaic cells containing pristine ClAlPc films and ClAlPc:C60 blend films fabricated at Tsub of 390 K show increases in the power conversion efficiency (ηPCE) of 28% (ηPCE = 3.12%) and 36% (ηPCE = 3.58%), respectively, relative to devices as-deposited at room temperature. The maximum short circuit current in BHJs is obtained at 390 K in the Tsub range from 300 K to 450 K.

Measurement of nanoscale molten polymer droplet spreading using atomic force microscopy

NASA Astrophysics Data System (ADS)

Soleymaniha, Mohammadreza; Felts, Jonathan R.

2018-03-01

We present a technique for measuring molten polymer spreading dynamics with nanometer scale spatial resolution at elevated temperatures using atomic force microscopy (AFM). The experimental setup is used to measure the spreading dynamics of polystyrene droplets with 2 μm diameters at 115-175 °C on sapphire, silicon oxide, and mica. Custom image processing algorithms determine the droplet height, radius, volume, and contact angle of each AFM image over time to calculate the droplet spreading dynamics. The contact angle evolution follows a power law with time with experimentally determined values of -0.29 ± 0.01, -0.08 ± 0.02, and -0.21 ± 0.01 for sapphire, silicon oxide, and mica, respectively. The non-zero steady state contact angles result in a slower evolution of contact angle with time consistent with theories combining molecular kinetic and hydrodynamic models. Monitoring the cantilever phase provides additional information about the local mechanics of the droplet surface. We observe local crystallinity on the molten droplet surface, where crystalline structures appear to nucleate at the contact line and migrate toward the top of the droplet. Increasing the temperature from 115 °C to 175 °C reduced surface crystallinity from 35% to 12%, consistent with increasingly energetically favorable amorphous phase as the temperature approaches the melting temperature. This platform provides a way to measure spreading dynamics of extremely small volumes of heterogeneously complex fluids not possible through other means.

Magnetic Structure and Exchange Interactions in Quasi-One-Dimensional MnCl 2(urea) 2

DOE PAGES

Manson, Jamie L.; Huang, Qing-zhen; Brown, Craig M.; ...

2015-12-08

MnCl 2(urea) 2 is a new linear chain coordination polymer that exhibits slightly counter-rotated Mn 2Cl 2 rhomboids along the chain-axis. The material crystallizes in the noncentrosymmetric orthorhombic space group Iba2, with each Mn(II) ion equatorially surrounded by four Cl – that lead to bibridged ribbons. Additionally, urea ligands coordinate via O atoms in the axial positions. Hydrogen bonds of the Cl···H–N and O···H–N type link the chains into a quasi-3D network. Magnetic susceptibility data reveal a broad maximum at 9 K that is consistent with short-range magnetic order. Pulsed-field magnetization measurements conducted at 0.6 K show that a fullymore » polarized magnetic state is achieved at B sat = 19.6 T with another field-induced phase transition occurring at 2.8 T. Zero-field neutron diffraction studies made on a powdered sample of MnCl 2(urea) 2 reveal that long-range magnetic order occurs below T N = 3.2(1) K. Additional Bragg peaks due to antiferromagnetic (AFM) ordering can be indexed according to the Ib'a2' magnetic space group and propagation vector τ = [0, 0, 0]. Rietveld profile analysis of these data revealed a Néel-type collinear ordering of Mn(II) ions with an ordered magnetic moment of 4.06(6) μ B (5 μ B is expected for isotropic S = 5/2) oriented along the b-axis, i.e., perpendicular to the chain-axis that runs along the c-direction. Owing to the potential for spatial exchange anisotropy and the pitfalls in modeling bulk magnetic data, we analyzed inelastic neutron scattering data to retrieve the exchange constants: J c = 2.22 K (intrachain), J a = -0.10 K (interchain), and D = -0.14 K with J > 0 assigned to AFM coupling. Lastly, this J configuration is most unusual and contrasts the more commonly observed AFM interchain coupling of 1D chains.« less

Structural, magnetic, and dielectric properties of multiferroic Co1-xMgxCr2O4 nanoparticles

NASA Astrophysics Data System (ADS)

Kamran, M.; Ullah, A.; Rahman, S.; Tahir, A.; Nadeem, K.; Anis ur Rehman, M.; Hussain, S.

2017-07-01

We examined the structural, magnetic, and dielectric properties of Co1-xMgxCr2O4 nanoparticles with composition x = 0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1 in detail. X-ray diffraction (XRD) revealed normal spinel structure for all the samples. Rietveld refinement fitting results of the XRD showed no impurity phases which signifies the formation of single phase Co1-xMgxCr2O4 nanoparticles. The average crystallite size showed a peak behaviour with maxima at x = 0.6. Raman and Fourier transform infrared (FTIR) spectroscopy also confirmed the formation of single phase normal spinel for all the samples and exhibited dominant vibrational changes for x ≥ 0.6. For x = 0 (CoCr2O4), zero field cooled/field cooled (ZFC/FC) magnetization curves showed paramagnetic (PM) to ferrimagnetic (FiM) transition at Tc = 97 K and a conical spiral magnetic order at Ts = 30 K. The end members CoCr2O4 (x = 0) and MgCr2O4 (x = 1) are FiM and antiferromagnetic (AFM), respectively. Tc and Ts showed decreasing trend with increasing x, followed by an additional AFM transition at TN = 15 K for x = 0.6. The system finally stabilized and changed to highly frustrated AFM structure at x = 1 due to formation of pure MgCr2O4. High field FC curves (5T) depicted nearly no effect on spiral magnetic state, which is attributed to strong exchange B-B magnetic interactions at low temperatures. Dielectric parameters showed a non-monotonous behaviour with Mg concentration and were explained with the help of Maxwell-Wagner model and Koop's theory. Dielectric properties were improved for nanoparticles with x = 0.6 and is attributed to their larger average crystallite size. In summary, Mg doping has significantly affects the structural, magnetic, and dielectric properties of CoCr2O4 nanoparticles, which can be attributed to variations in local magnetic exchange interactions and variation in average crystallite size of these chromite nanoparticles.

Dynamical studies of confined fluids and polymers

NASA Astrophysics Data System (ADS)

Grabowski, Christopher A.

Soft matter, a class of materials including polymers, colloids, and surfactant molecules, are ubiquitous in our everyday lives. Plastics, soaps, foods and living organisms are mostly comprised of soft materials. Research conducted to understand soft matter behavior at the molecular level is essential to create new materials with unique properties. Self-healing plastics, targeted drug delivery, and nanowire assemblies have all been further advanced by soft matter research. The author of this dissertation investigates fundamental soft matter systems, including polymer solutions and melts, colloid dispersions in polymer melts, and interfacial fluids. The dynamics of polymers and confined fluids were studied using the single-molecule sensitive technique of fluorescence correlation spectroscopy (FCS). Here, fluorescent dyes are attached to polymer coils or by introducing free dyes directly into the solution/film. Complementary experiments were also performed, utilizing atomic force microscopy (AFM) and ellipsometry. FCS and AFM experiments demonstrated the significant difference in properties of thin fluid films of the nearly spherical, nonpolar molecule TEHOS (tetrakis(2-ethylhexoxy)silane) when compared to its bulk counterpart. AFM experiments confirmed TEHOS orders in layers near a solid substrate. FCS experiments show that free dyes introduced in these thin films do not have a single diffusion coefficient, indicating that these films have heterogeneity at the molecular level. FCS experiments have been applied to study the diffusion of gold colloids. The diffusion of gold colloids in polymer melts was found to dramatically depart from the Stokes-Einstein prediction when colloid size was smaller than the surrounding polymer mesh size. This effect is explained by noting the viscosity experienced by the colloid is not equivalent to the overall bulk viscosity of the polymer melt. The conformational change of polymers immersed in a binary solvent was measured via FCS. This experiment was conducted to test a theory proposed by Brochard and de Gennes, who postulated a polymer chain undergoes a collapse and a dramatic re-swelling as the critical point of the binary mixture is approached. Measuring polymer chain diffusion as a function of temperature, this theory was confirmed. To my knowledge, this was the first experimental evidence of contraction/re-swelling for polymers in critical binary solvents.

Extending the Cutoff Wavelength of Thermophotovoltaic Devices via Band Structure Engineering

NASA Astrophysics Data System (ADS)

Lee, Michael Steven

Complex oxides, solid-state compounds comprised of oxygen and at least two metal cations, are an intriguing class of materials for implementation into future microelectronic devices. They possess a wide range of functional properties, such as magnetism, ferroelectricity, and superconductivity, that can all be readily modified by their sensitivity to lattice strain, electronic and magnetic fields, chemical doping, and other external stimuli. This sensitivity makes complex oxides highly capable materials, but also introduces many technical challenges. The work of this dissertation has focused on extending our current knowledge of the magnetic materials properties and interfacial effects present in epitaxial films into micro- and nanoscale features. Ferromagnetic (FM) spin textures are arrangements of magnetic moments within such patterned features. Their switching behaviors are essential components of current data storage applications, and complex oxides are ideal candidates for future designs. In any materials system, the deviation from bulk or thin film properties when scaling down to nanostructures can be difficult to predict due to either size induced effects or consequences of the fabrication process itself. Therefore, these magnetic films and multilayers must be studied in the modified state to understand the challenges and opportunities associated with designing practical structures. Soft x-ray photoemission electron microscopy (X-PEEM) was used to observe and characterize the evolution of magnetic domain structure as a function of temperature in micromagnets patterned into epitaxial films of La0.7 Sr0.3MnO3 (LSMO). These images reveal the formation of novel spin textures that are a hybridization of well-described configurations, vortex and Landau, and emerge from the balance between fundamental materials parameters, micromagnet geometries, and epitaxial strain. Furthermore, slight perturbations to the lattice near the lithographically defined microstructure edges are shown to induce long range suppression of the magnetocrystalline anisotropy while other magnetic parameters, such as the saturation magnetization, remain unchanged. The results demonstrate how the magnetic domain state can be tailored through careful incorporation of these factors. Additional complexity is added to the system by interfacing LSMO with antiferromagnetic (AFM) LaFeO3 (LFO) or La0.7Sr 0.3FeO3 (LSFO). In unpatterned bilayers and superlattices, exchange coupling across the FM/AFM interface promotes a perpendicular alignment of the FM and AFM spin axes. Within patterned bilayers the alignment can be driven into a parallel configuration through changes in the micromagnet width, crystallographic orientation, and temperature. The importance of FM/AFM spin alignment is emphasized by magnetic reversal experiments of individual magnetic bits that demonstrate the coercivity can be adjusted over a wide range relative to LSMO single-layer micromagnets. In a superlattice of FM/AFM interfaces, the relative influence of the LSMO is reduced as the TC drops from 360 K to 80 K due to the ultra-thin sublayer thickness. Like the initial study on LSMO, the magnetocrystalline anisotropy of the LSFO layer is fully suppressed near microstructure edges, and the AFM domain configuration is entirely dictated by a magnetostatic-type effect in that region. This behavior persists both above and below the TC (with spin-flop coupling preserved) suggesting a new method to control AFM spin textures which are typically pinned to stochastic structural domains and defects and require large fields to manipulate.

Needs and workflow assessment prior to implementation of a digital pathology infrastructure for the US Air Force Medical Service

PubMed Central

Ho, Jonhan; Aridor, Orly; Glinski, David W.; Saylor, Christopher D.; Pelletier, Joseph P.; Selby, Dale M.; Davis, Steven W.; Lancia, Nicholas; Gerlach, Christopher B.; Newberry, Jonathan; Anthony, Leslie; Pantanowitz, Liron; Parwani, Anil V.

2013-01-01

Background: Advances in digital pathology are accelerating integration of this technology into anatomic pathology (AP). To optimize implementation and adoption of digital pathology systems within a large healthcare organization, initial assessment of both end user (pathologist) needs and organizational infrastructure are required. Contextual inquiry is a qualitative, user-centered tool for collecting, interpreting, and aggregating such detailed data about work practices that can be employed to help identify specific needs and requirements. Aim: Using contextual inquiry, the objective of this study was to identify the unique work practices and requirements in AP for the United States (US) Air Force Medical Service (AFMS) that had to be targeted in order to support their transition to digital pathology. Subjects and Methods: A pathology-centered observer team conducted 1.5 h interviews with a total of 24 AFMS pathologists and histology lab personnel at three large regional centers and one smaller peripheral AFMS pathology center using contextual inquiry guidelines. Findings were documented as notes and arranged into a hierarchal organization of common themes based on user-provided data, defined as an affinity diagram. These data were also organized into consolidated graphic models that characterized AFMS pathology work practices, structure, and requirements. Results: Over 1,200 recorded notes were grouped into an affinity diagram composed of 27 third-level, 10 second-level, and five main-level (workflow and workload distribution, quality, communication, military culture, and technology) categories. When combined with workflow and cultural models, the findings revealed that AFMS pathologists had needs that were unique to their military setting, when compared to civilian pathologists. These unique needs included having to serve a globally distributed patient population, transient staff, but a uniform information technology (IT) structure. Conclusions: The contextual inquiry method helped reveal similarities and key differences with civilian pathologists. Such an analysis helped identify specific instances that would benefit from implementing digital pathology in a military environment. Employing digital pathology to facilitate workload distribution, secondary consultations, and quality assurance (over-reads) could help the AFMS deliver more accurate, efficient, and timely AP services at a global level. PMID:24392246

Wettability of natural root mucilage studied by atomic force microscopy and contact angle: Links between nanoscale and macroscale surface properties

NASA Astrophysics Data System (ADS)

Kaltenbach, Robin; Diehl, Dörte; Schaumann, Gabriele E.

2017-04-01

Organic coatings are considered as main cause of soil water repellency (SWR). This phenomenon plays a crucial role in the rhizosphere, at the interface of plant water uptake and soil hydraulics. Still, there is little knowledge about the nanoscale properties of natural soil compounds such as root-mucilage and its mechanistic effect on wettability. In this study, dried films of natural root-mucilage from Sorghum (Sorghum sp., MOENCH) on glass substrates were studied in order to explore experimental and evaluation methods that allow to link between macroscopic wettability and nano-/microscopic surface properties in this model soil system. SWR was assessed by optical contact angle (CA) measurements. The nanostructure of topography and adhesion forces of the mucilage surfaces was revealed by atomic force microscopy (AFM) measurements in ambient air, using PeakForce Quantitative Nanomechanical Mapping (PFQNM). Undiluted mucilage formed hydrophobic films on the substrate with CA > 90° and rather homogeneous nanostructure. Contact angles showed reduced water repellency of surfaces, when concentration of mucilage was decreased by dilution. AFM height and adhesion images displayed incomplete mucilage surface coverage for diluted samples. Hole-like structures in the film frequently exhibited increased adhesion forces. Spatial analysis of the AFM data via variograms enabled a numerical description of such 'adhesion holes'. The use of geostatistical approaches in AFM studies of the complex surface structure of soil compounds was considered meaningful in view of the need of comprehensive analysis of large AFM image data sets that exceed the capability of comparative visual inspection. Furthermore, force curves measured with the AFM showed increased break-free distances and pull-off forces inside the observed 'adhesion holes', indicating enhanced capillary forces due to adsorbed water films at hydrophilic domains for ambient RH (40 ± 2 %). This offers the possibility of mapping the nanostructure of water layers on soil surfaces and assessing the consequences for wettability. The collected information on macroscopic wetting properties, nanoscale roughness and adhesion structure of the investigated surfaces in this study are discussed in view of the applicability of the mechanistic wetting models given by Wenzel and Cassie-Baxter.

Nanoscale effects in the characterization of viscoelastic materials with atomic force microscopy: Coupling of a quasi-three-dimensional standard linear solid model with in-plane surface interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solares, Santiago D.

Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip-sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surfacemore » as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young's modulus. Relevant cases are discussed for single-and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip-sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. As a result, a multifrequency AFM simulation tool based on the above sample model is provided as supporting information.« less

Gaining insight into the physics of dynamic atomic force microscopy in complex environments using the VEDA simulator

NASA Astrophysics Data System (ADS)

Kiracofe, Daniel; Melcher, John; Raman, Arvind

2012-01-01

Dynamic atomic force microscopy (dAFM) continues to grow in popularity among scientists in many different fields, and research on new methods and operating modes continues to expand the resolution, capabilities, and types of samples that can be studied. But many promising increases in capability are accompanied by increases in complexity. Indeed, interpreting modern dAFM data can be challenging, especially on complicated material systems, or in liquid environments where the behavior is often contrary to what is known in air or vacuum environments. Mathematical simulations have proven to be an effective tool in providing physical insight into these non-intuitive systems. In this article we describe recent developments in the VEDA (virtual environment for dynamic AFM) simulator, which is a suite of freely available, open-source simulation tools that are delivered through the cloud computing cyber-infrastructure of nanoHUB (www.nanohub.org). Here we describe three major developments. First, simulations in liquid environments are improved by enhancements in the modeling of cantilever dynamics, excitation methods, and solvation shell forces. Second, VEDA is now able to simulate many new advanced modes of operation (bimodal, phase-modulation, frequency-modulation, etc.). Finally, nineteen different tip-sample models are available to simulate the surface physics of a wide variety different material systems including capillary, specific adhesion, van der Waals, electrostatic, viscoelasticity, and hydration forces. These features are demonstrated through example simulations and validated against experimental data, in order to provide insight into practical problems in dynamic AFM.

Electrical characterization of FIB processed metal layers for reliable conductive-AFM on ZnO microstructures

NASA Astrophysics Data System (ADS)

Pea, M.; Maiolo, L.; Giovine, E.; Rinaldi, A.; Araneo, R.; Notargiacomo, A.

2016-05-01

We report on the conductive-atomic force microscopy (C-AFM) study of metallic layers in order to find the most suitable configuration for electrical characterization of individual ZnO micro-pillars fabricated by focused ion beam (FIB). The electrical resistance between the probe tip and both as deposited and FIB processed metal layers (namely, Cr, Ti, Au and Al) has been investigated. Both chromium and titanium evidenced a non homogenous and non ohmic behaviour, non negligible scanning probe induced anodic oxidation associated to electrical measurements, and after FIB milling they exhibited significantly higher tip-sample resistance. Aluminium had generally a more apparent non conductive behaviour. Conversely, gold films showed very good tip-sample conduction properties being less sensitive to FIB processing than the other investigated metals. We found that a reliable C-AFM electrical characterization of ZnO microstructures obtained by FIB machining is feasible by using a combination of metal films as top contact layer. An Au/Ti bilayer on top of ZnO was capable to sustain the FIB fabrication process and to form a suitable ohmic contact to the semiconductor, allowing for reliable C-AFM measurement. To validate the consistency of this approach, we measured the resistance of ZnO micropillars finding a linear dependence on the pillar height, as expected for an ohmic conductor, and evaluated the resistivity of the material. This procedure has the potential to be downscaled to nanometer size structures by a proper choice of metal films type and thickness.

Gaining insight into the physics of dynamic atomic force microscopy in complex environments using the VEDA simulator.

PubMed

Kiracofe, Daniel; Melcher, John; Raman, Arvind

2012-01-01

Dynamic atomic force microscopy (dAFM) continues to grow in popularity among scientists in many different fields, and research on new methods and operating modes continues to expand the resolution, capabilities, and types of samples that can be studied. But many promising increases in capability are accompanied by increases in complexity. Indeed, interpreting modern dAFM data can be challenging, especially on complicated material systems, or in liquid environments where the behavior is often contrary to what is known in air or vacuum environments. Mathematical simulations have proven to be an effective tool in providing physical insight into these non-intuitive systems. In this article we describe recent developments in the VEDA (virtual environment for dynamic AFM) simulator, which is a suite of freely available, open-source simulation tools that are delivered through the cloud computing cyber-infrastructure of nanoHUB (www.nanohub.org). Here we describe three major developments. First, simulations in liquid environments are improved by enhancements in the modeling of cantilever dynamics, excitation methods, and solvation shell forces. Second, VEDA is now able to simulate many new advanced modes of operation (bimodal, phase-modulation, frequency-modulation, etc.). Finally, nineteen different tip-sample models are available to simulate the surface physics of a wide variety different material systems including capillary, specific adhesion, van der Waals, electrostatic, viscoelasticity, and hydration forces. These features are demonstrated through example simulations and validated against experimental data, in order to provide insight into practical problems in dynamic AFM.

In situ observation of fluoride-ion-induced hydroxyapatite collagen detachment on bone fracture surfaces by atomic force microscopy

NASA Astrophysics Data System (ADS)

Kindt, J. H.; Thurner, P. J.; Lauer, M. E.; Bosma, B. L.; Schitter, G.; Fantner, G. E.; Izumi, M.; Weaver, J. C.; Morse, D. E.; Hansma, P. K.

2007-04-01

The topography of freshly fractured bovine and human bone surfaces was determined by the use of atomic force microscopy (AFM). Fracture surfaces from both kinds of samples exhibited complex landscapes formed by hydroxyapatite mineral platelets with lateral dimensions ranging from ~90 nm × 60 nm to ~20 nm × 20 nm. Novel AFM techniques were used to study these fracture surfaces during various chemical treatments. Significant topographical changes were observed following exposure to aqueous solutions of ethylenediaminetetraacetic acid (EDTA) or highly concentrated sodium fluoride (NaF). Both treatments resulted in the apparent loss of the hydroxyapatite mineral platelets on a timescale of a few seconds. Collagen fibrils situated beneath the overlying mineral platelets were clearly exposed and could be resolved with high spatial resolution in the acquired AFM images. Time-dependent mass loss experiments revealed that the applied agents (NaF or EDTA) had very different resulting effects. Despite the fact that the two treatments exhibited nearly identical results following examination by AFM, bulk bone samples treated with EDTA exhibited a ~70% mass loss after 72 h, whereas for the NaF-treated samples, the mass loss was only of the order of ~10%. These results support those obtained from previous mechanical testing experiments, suggesting that enhanced formation of superficial fluoroapatite dramatically weakens the protein-hydroxyapatite interfaces. Additionally, we discovered that treatment with aqueous solutions of NaF resulted in the effective extraction of noncollagenous proteins from bone powder.

Nanoscale effects in the characterization of viscoelastic materials with atomic force microscopy: Coupling of a quasi-three-dimensional standard linear solid model with in-plane surface interactions

DOE PAGES

Solares, Santiago D.

2016-04-15

Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip-sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surfacemore » as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young's modulus. Relevant cases are discussed for single-and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip-sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. As a result, a multifrequency AFM simulation tool based on the above sample model is provided as supporting information.« less

Enhanced electrical properties in sub-10-nm WO3 nanoflakes prepared via a two-step sol-gel-exfoliation method

PubMed Central

2014-01-01

The morphology and electrical properties of orthorhombic β-WO3 nanoflakes with thickness of ~7 to 9 nm were investigated at the nanoscale with a combination of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), current sensing force spectroscopy atomic force microscopy (CSFS-AFM, or PeakForce TUNA™), Fourier transform infra-red absorption spectroscopy (FTIR), linear sweep voltammetry (LSV) and Raman spectroscopy techniques. CSFS-AFM analysis established good correlation between the topography of the developed nanostructures and various features of WO3 nanoflakes synthesized via a two-step sol-gel-exfoliation method. It was determined that β-WO3 nanoflakes annealed at 550°C possess distinguished and exceptional thickness-dependent properties in comparison with the bulk, micro and nanostructured WO3 synthesized at alternative temperatures. PMID:25221453

Studies on solid solutions based on layered honeycomb-ordered phases P2-Na{sub 2}M{sub 2}TeO{sub 6} (M=Co, Ni, Zn)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berthelot, Romain; Schmidt, Whitney; Sleight, A.W.

2012-12-15

Three complete solid solutions between the layered phases P2-Na{sub 2}M{sub 2}TeO{sub 6} (M=Co, Ni, Zn) have been prepared by conventional solid state method and investigated through X-ray diffraction, magnetism and optical measurements. All compositions are characterized by a M{sup 2+}/X{sup 6+} honeycomb ordering within the slabs and crystallize in a hexagonal unit cell. However, a structural transition based on a different stacking is observed as nickel (space group P6{sub 3}/mcm) is substituted by zinc or cobalt (space group P6{sub 3}22). All compositions exhibit a paramagnetic Curie-Weiss behavior at high temperatures; and the magnetic moment values confirm the presence of Ni{supmore » 2+} and/or Co{sup 2+} cations. The low-temperature antiferromagnetic order of Na{sub 2}Ni{sub 2}TeO{sub 6} and Na{sub 2}Co{sub 2}TeO{sub 6} is suppressed by zinc substitution. The color of the obtained compositions varies from pink, to light green and white when M=Co, Ni, Zn, respectively. - Graphical abstract: The comparison between the structure of Na{sub 2}Ni{sub 2}TeO{sub 6} (left) and Na{sub 2}M{sub 2}TeO{sub 6} (M=Co, Zn) (right) evidences the stacking difference with distinct atom sequences along the hexagonal c-axis. Highlights: Black-Right-Pointing-Pointer Solid solutions between lamellar phases Na{sub 2}M{sub 2}TeO{sub 6} (M=Co, Ni, Zn) are investigated. Black-Right-Pointing-Pointer A M{sup 2+}/X{sup 6+} honeycomb ordering characterized all the compositions. Black-Right-Pointing-Pointer A structural transition is shown when Ni is replaced by Co or Zn. Black-Right-Pointing-Pointer The low-temperature AFM ordering of Na{sub 2}Ni{sub 2}TeO{sub 6} and Na{sub 2}Co{sub 2}TeO{sub 6} is suppressed by zinc substitution. Black-Right-Pointing-Pointer Color changes from pink to light green and white when M=Co, Ni, Zn, respectively.« less

Investigating the effect of an arterial hypertension drug on the structural properties of plasma protein.

PubMed

Hassan, Natalia; Maldonado-Valderrama, Julia; Gunning, A Patrick; Morris, V J; Ruso, Juan M

2011-10-15

Propanolol is a betablocker drug used in the treatment of arterial hypertension related diseases. In order to achieve an optimal performance of this drug it is important to consider the possible interactions of propanolol with plasma proteins. In this work, we have used several experimental techniques to characterise the effect of addition of the betablocker propanolol on the properties of bovine plasma fibrinogen (FB). Differential scanning calorimeter (DSC), circular dichroism (CD), dynamic light scattering (DLS), surface tension techniques and atomic force microscopy (AFM) measurements have been combined to carry out a detailed physicochemical and surface characterization of the mixed system. As a result, DSC measurements show that propranolol can play two opposite roles, either acting as a structure stabilizer at low molar concentrations or as a structure destabilizer at higher concentrations, in different domains of fibrinogen. CD measurements have revealed that the effect of propanolol on the secondary structure of fibrinogen depends on the temperature and the drug concentration and the DLS analysis showed evidence for protein aggregation. Interestingly, surface tension measurements provided further evidence of the conformational change induced by propanolol on the secondary structure of FB by importantly increasing the surface tension of the system. Finally, AFM imaging of the fibrinogen system provided direct visualization of the protein structure in the presence of propanolol. Combination of these techniques has produced complementary information on the behavior of the mixed system, providing new insights into the structural properties of proteins with potential medical interest. Copyright © 2011 Elsevier B.V. All rights reserved.

Magnetic transition in Y-site doped multiferroic YMnO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thakur, Rajesh K., E-mail: thakur.rajesh2009@gmail.com; Thakur, Rasna, E-mail: rasnathakur@yahoo.com; Gaur, N. K., E-mail: srl-nkgaur@yahoo.co.in

2016-05-06

We have synthesized polycrystalline hexagonal Y{sub 1-x}Sr{sub x}MnO{sub 3} (x=0.02, 0.1) compounds by using conventional solid state reaction method. The detailed structural investigations are carried out by using XRD studies which reveals the single phase formation of the reported compounds with hexagonal structure and space group P6{sub 3}cm (JCPDS: 25-1079). Further the XRD data of reported compounds were analyzed by RIETVELD (FULLPROFF) method which shows the decrease in the lattice parameter with increasing concentration of divalent strontium to Y-site. The observed pointed kinks in the specific heat study are indicative of the probable coupling in between the electric and magneticmore » orders in this class of materials. The reported systematic specific heat studies shows that the antiferromagnetic (AFM) transition temperature (T{sub N}) shifts to higher value with increasing concentration of Sr{sup 2+} ion in the YMnO{sub 3} compound which is attributed to the enhanced lattice contribution to the specific heat in the this compound. The present compound shows the independence of specific heat and magnetic transition temperature with applied magnetic field of 8T and 12T.« less

Morphological, structural and optical properties of MEH-PPV: PC70BM nanocomposite film

NASA Astrophysics Data System (ADS)

Mhamdi, Asya; Sweii, Fatma ben Slama; Saidi, Hamza; Saidi, Faouzi; Bouazizi, Abdelaziz

2018-05-01

In this report, the influence of annealing temperature and spin coating speed on the structural and morphological properties of a blend of poly (2-methoxy-5-(2-ethyl-oxy)-p-phenylene-vinylene) (MEH-PPV) and [6-6]-phenyl-C71-butyric acid methyl ester (PC70BM) layer has been investigated. The photoactive layer (MEH-PPV: PC70BM) was deposited on ZnO film deposited on top of indium tin oxide (ITO) substrate by spin-coating. The effect of spin coating speed via atomic force microscope (AFM) leads to conclude that high speed is favorable for a good homogeneity of the film surface and good aggregates dispersion. The optimized structure was studied by varying the annealing temperatures using X-ray diffraction (XRD). The XRD analysis indicates that annealing treatment promoted the ordered aggregation and crystallization of MEH-PPV: PC70BM films. Indeed, the blend ratio effect on the optical properties of MEH-PPV: PC70BM thin film was investigated. While, the effect of incorporation of PC70BM on the optical properties was studied using UV-Vis and photoluminescence (PL) measurement. We conclude that MEH-PPV: PC70BM (1:3) film leads to high charge transfer rate.

Phase diagram of pressure-induced superconductor β-(BDA-TTP)2MX4 (M=Fe, Ga and X=Cl, Br) with localized magnetic moments

NASA Astrophysics Data System (ADS)

Choi, E. S.; Graf, D.; Tokumoto, T.; Brooks, J. S.; Yamada, Jun-Ichi

2007-03-01

We have investigated transport and magnetization properties of β-(BDA-TTP)2MX4 (M=Fe, Ga and X=Cl, Br) as a function of pressure, temperature and magnetic field. The title material undergoes metal-insulator transitions above 100 K at ambient pressure. The insulating phase is suppressed with pressure and superconductivity eventually appears above Pc= 4.5 kbar (X=Cl) and 13 kbar (X=Br). The general temperature-pressure (TP) phase diagram is similar each other, while higher pressure is required for X=Br compounds to suppress the insulating state and induce the superconductivity. Pressure dependent DC magnetization studies on β-(BDA-TTP)2FeCl4 compound revealed that the AFM ordering persist well above Pc. In spite of similarity of phase diagram between M=Fe and M=Ga compounds, magnetoresistance results show distinct behaviors, which indicates the magnetic interaction with the conduction electrons are still effective. The comparison between X=Cl and X=Br compounds suggests the anion-size effect rather than the existence of localized magnetic moments plays more important role in determining the ground state.

The coupled effects of environmental composition, temperature and contact size-scale on the tribology of molybdenum disulfide

NASA Astrophysics Data System (ADS)

Khare, Harmandeep S.

Liquid lubricants are precluded in an exceedingly large number of consumer as well as extreme applications as a means to reduce friction and wear at the sliding interface of two bodies. The extraterrestrial environment is one such example of an extreme environment which has motivated the development of advanced solid lubricant materials. Mechanical systems for space require fabrication, assembly, transportation and testing on earth before launch and deployment. Solid lubricants for space are expected to not only operate efficiently in the hard vacuum of space but also withstand interactions with moisture or oxygen during the terrestrial storage, transportation and assembly prior to deployment and launch. Molybdenum disulfide (MoS2) is considered the gold standard in solid lubricants for space due to its excellent tribological properties in ultra-high vacuum. However in the presence of environmental species such as water and oxygen or at elevated temperatures, the lubricity and endurance of MoS2 is severely limited. Past studies have offered several hypotheses for the breakdown of lubrication of MoS2 under the influence of water and oxygen, although exact mechanisms remain unknown. Furthermore, it is unclear if temperature acts as a driver solely for oxidation or for thermally activated slip and thermally activated desorption as well. The answers to these questions are of fundamental importance to improving the reliability of existing MoS2-based solid lubricants for space, as well as for guiding the design of advanced lamellar solid lubricant coatings. This dissertation aims to elucidate: (1) the role of water on MoS2 oxidation, (2) the role of water on MoS2 friction, (3) the role of oxygen on MoS2 friction, (4) the contribution of thermal activation to ambient-temperature friction, and (5) effects of length-scale. The results of this study showed that water does not cause oxidation of MoS2. Water increases ambient-temperature friction of MoS2 directly through a combination of both surface adsorption and diffusion into the coating subsurface. Thermally activated desiccation effectively dries the bulk of the coating, yielding low values of friction coefficient even at ambient humidity and temperature. Friction of MoS2 decreases with increasing temperature between 25°C and 100°C in the presence of environmental water and increases in the presence of oxygen alone. At temperatures greater than 100°C, friction generally increases with temperature only in the presence of environmental oxygen; at these elevated temperatures, friction decreases with increasing humidity. The transition from room-temperature increase to elevated-temperature decrease in friction with increasing humidity is found to be a strong function of the contact history as well as coating microstructure. Lastly, the contribution of nanoscale tribofilms to macroscale friction was studied through nanotribometry. Friction measured on the worn MoS2 coating with a nano-scale AFM probe showed direct and quantifiable evidence of sliding-induced surface modification of MoS2; friction measured on the perfectly ordered single crystal MoS2 was nearly an order of magnitude lower than friction on worn MoS2. Although friction coefficients measured with a nanoscale probe showed high surface sensitivity, micron-sized AFM probes gave friction coefficients similar to those obtained in the macroscale, suggesting the formation of surface films in-situ during sliding with the colloidal probe. A reduction in friction is observed after annealing for both the nanoscale and microscale probes, suggesting a strong overriding effect of the desiccated bulk over surface adsorption in driving the friction response at these length-scales.

Application of atomic force microscopy as a nanotechnology tool in food science.

PubMed

Yang, Hongshun; Wang, Yifen; Lai, Shaojuan; An, Hongjie; Li, Yunfei; Chen, Fusheng

2007-05-01

Atomic force microscopy (AFM) provides a method for detecting nanoscale structural information. First, this review explains the fundamentals of AFM, including principle, manipulation, and analysis. Applications of AFM are then reported in food science and technology research, including qualitative macromolecule and polymer imaging, complicated or quantitative structure analysis, molecular interaction, molecular manipulation, surface topography, and nanofood characterization. The results suggested that AFM could bring insightful knowledge on food properties, and the AFM analysis could be used to illustrate some mechanisms of property changes during processing and storage. However, the current difficulty in applying AFM to food research is lacking appropriate methodology for different food systems. Better understanding of AFM technology and developing corresponding methodology for complicated food systems would lead to a more in-depth understanding of food properties at macromolecular levels and enlarge their applications. The AFM results could greatly improve the food processing and storage technologies.

Ripple formation in unilamellar-supported lipid bilayer revealed by FRAPP.

PubMed

Harb, Frédéric; Simon, Anne; Tinland, Bernard

2013-12-01

The mechanisms of formation and conditions of the existence of the ripple phase are fundamental thermodynamic questions with practical implications for medicine and pharmaceuticals. We reveal a new case of ripple formation occurring in unilamellar-supported bilayers in water, which results solely from the bilayer/support interaction, without using lipid mixtures or specific ions. This ripple phase is detected by FRAPP using diffusion coefficient measurements as a function of temperature: a diffusivity plateau is observed. It occurs in the same temperature range where ripple phase existence has been observed using other methods. When AFM experiments are performed in the appropriate temperature range the ripple phase is confirmed.

Materials Research Society Spring Meeting Symposium KK: Microbial Life on Surfaces: Biofilm-Material Interactions: Life at Interfaces. Held in San Francisco, California on 25-27 April 2011 (Abstracts)

DTIC Science & Technology

2012-05-24

distribution of protein molecules on the cell surface and relative to the substrate on which the bacteria were growing. 9:30AMKKLL3 Effects of the... Temperature and Ionic Strength of Growth Conditions on the Nanoscale Adhesion of L. monocytogenes EGDe to Silicon Nitride. Pinar Gordesli and Nehal Abu...microscopy (AFM) for bacterial cells grown under five different temperatures (10, 20, 30, 37 and 40°C) and five different ionic strengths (0.005

Photomask applications of traceable atomic force microscope dimensional metrology at NIST

NASA Astrophysics Data System (ADS)

Dixson, Ronald; Orji, Ndubuisi G.; Potzick, James; Fu, Joseph; Allen, Richard A.; Cresswell, Michael; Smith, Stewart; Walton, Anthony J.; Tsiamis, Andreas

2007-10-01

The National Institute of Standards and Technology (NIST) has a multifaceted program in atomic force microscope (AFM) dimensional metrology. Three major instruments are being used for traceable measurements. The first is a custom in-house metrology AFM, called the calibrated AFM (C-AFM), the second is the first generation of commercially available critical dimension AFM (CD-AFM), and the third is a current generation CD-AFM at SEMATECH - for which NIST has established the calibration and uncertainties. All of these instruments have useful applications in photomask metrology. Linewidth reference metrology is an important application of CD-AFM. We have performed a preliminary comparison of linewidths measured by CD-AFM and by electrical resistance metrology on a binary mask. For the ten selected test structures with on-mask linewidths between 350 nm and 600 nm, most of the observed differences were less than 5 nm, and all of them were less than 10 nm. The offsets were often within the estimated uncertainties of the AFM measurements, without accounting for the effect of linewidth roughness or the uncertainties of electrical measurements. The most recent release of the NIST photomask standard - which is Standard Reference Material (SRM) 2059 - was also supported by CD-AFM reference measurements. We review the recent advances in AFM linewidth metrology that will reduce the uncertainty of AFM measurements on this and future generations of the NIST photomask standard. The NIST C-AFM has displacement metrology for all three axes traceable to the 633 nm wavelength of the iodine-stabilized He-Ne laser. One of the important applications of the C-AFM is step height metrology, which has some relevance to phase shift calibration. In the current generation of the system, the approximate level of relative standard uncertainty for step height measurements at the 100 nm scale is 0.1 %. We discuss the monitor history of a 290 nm step height, originally measured on the C-AFM with a 1.9 nm (k = 2) expanded uncertainty, and describe advances that bring the step height uncertainty of recent measurements to an estimated 0.6 nm (k = 2). Based on this work, we expect to be able to reduce the topographic component of phase uncertainty in alternating aperture phase shift masks (AAPSM) by a factor of three compared to current calibrations based on earlier generation step height references.

Surface topography and ordering-variant segregation in GaInP[sub 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Friedman, D.J.; Zhu, J.G.; Kibbler, A.E.

1993-09-27

Using transmission electron diffraction dark-field imaging, atomic force microscopy (AFM), and Nomarski microscopy, we demonstrate a direct connection between surface topography and cation site ordering in GaInP[sub 2]. We study epilayers grown by organometallic vapor-phase epitaxy on GaAs substrates oriented 2[degree] off (100) towards (110). Nomarski microscopy shows that, as growth proceeds, the surface of ordered material forms faceted structures aligned roughly along [011]. A comparison with the dark-field demonstrates that the [1[bar 1]1] and [11[bar 1

DNA-Templated Fabrication of Arbitrary-Structured Porous Carbon Materials

DTIC Science & Technology

2016-07-11

same as the DNA nanostructure. Conductive AFM measurement shows that the carbon nanostructures are electrically conductive. These research activities ...surface chemistry. These research activities revealed a rich These research activities have resulted in 24 peer reviewed journal articles (23 published...of the intrinsic wettability of graphitic materials; and (c) high temperature carbonization of DNA. These activities are detailed below (Note that

Syntheses of Eu-Activated Alkaline Earth Fluoride MF2 (M=Ca, Sr) Nanoparticles

NASA Astrophysics Data System (ADS)

Hong, Byung-Chul; Kawano, Katsuyasu

2007-09-01

The Eu2+ ion-activated CaF2 and SrF2 nanoparticles were prepared by the sol-gel technique assisted with the trifluoro-acetic acid (TFA), and were evaluated by X-ray diffraction (XRD), photoluminescence (PL), photoluminescence excitation (PLE) measurements and atomic force microscopy (AFM) observation. A modified reducing method based on the thermal-carbon reducing atmosphere (TCRA) treatment using activated carbon was proposed to realize the effective reduction from Eu3+ to Eu2+ ions, in which the nanoparticles showed a strong and broad luminescence due to the parity allowed 4f7-4f65d1 transition. From the XRD results, it was found that the average particle size proportionally increased in the range of 15 to 120 nm and 10 to 100 nm for CaF2 and SrF2, respectively, with increasing sintering temperatures 300-700 °C. The surface images of nanoparticles obtained by the AFM revealed that the grains with high uniformity grew with increasing TCRA temperatures. It was confirmed that the reduced Eu2+ ions were homogeneously dispersed with the critical distance 16-17 Å in the fluoride nanoparticles from the concentration quenching results.

Observation of multicellular spinning behavior of Proteus mirabilis by atomic force microscopy and multifunctional microscopy.

PubMed

Liu, Yanxia; Deng, Yuanxin; Luo, Shuxiu; Deng, Yu; Guo, Linming; Xu, Weiwei; Liu, Lei; Liu, Junkang

2014-01-01

This study aimed to observe the multicellular spinning behavior of Proteus mirabilis by atomic force microscopy (AFM) and multifunctional microscopy in order to understand the mechanism underlying this spinning movement and its biological significance. Multifunctional microscopy with charge-coupled device (CCD) and real-time AFM showed changes in cell structure and shape of P. mirabilis during multicellular spinning movement. Specifically, the morphological characteristics of P. mirabilis, multicellular spinning dynamics, and unique movement were observed. Our findings indicate that the multicellular spinning behavior of P. mirabilis may be used to collect nutrients, perform colonization, and squeeze out competitors. The movement characteristics of P. mirabilis are vital to the organism's biological adaptability to the surrounding environment. Copyright © 2013 Elsevier Ltd. All rights reserved.

Study of half-metallicity in BiMnxFe1-xO3

NASA Astrophysics Data System (ADS)

Ameer, Shaan; Jindal, Kajal; Tomar, Monika; Jha, Pradip K.; Gupta, Vinay

2018-05-01

Spin polarized calculations are performed to study the structural and electronic properties of Mn doped BiFeO3 (BMFO) using simplified local spin density approximation (LSDA) functional under density functional theory (DFT). The B-site doping concentration of Mn in BMFO considered to be 16.7 % (BiMn0.167Fe0.833O3). Density of states calculations are carried out for both ferromagnetic (FM) and anti-ferromagnetic (AFM) order in BMFO. The results predict that BMFO is a half metal for both FM and AFM BMFO with magnetization of 29.0000 µB/cell and 1.0000 µB/cell respectively. The ground state of BMFO is found to be antiferromagnetic and demonstrates BMFO to be a potential candidate for spintronic applications.

Micromorphological characterization of zinc/silver particle composite coatings.

PubMed

Méndez, Alia; Reyes, Yolanda; Trejo, Gabriel; StĘpień, Krzysztof; Ţălu, Ştefan

2015-12-01

The aim of this study was to evaluate the three-dimensional (3D) surface micromorphology of zinc/silver particles (Zn/AgPs) composite coatings with antibacterial activity prepared using an electrodeposition technique. These 3D nanostructures were investigated over square areas of 5 μm × 5 μm by atomic force microscopy (AFM), fractal, and wavelet analysis. The fractal analysis of 3D surface roughness revealed that (Zn/AgPs) composite coatings have fractal geometry. Triangulation method, based on the linear interpolation type, applied for AFM data was employed in order to characterise the surfaces topographically (in amplitude, spatial distribution and pattern of surface characteristics). The surface fractal dimension Df , as well as height values distribution have been determined for the 3D nanostructure surfaces. © 2015 The Authors published by Wiley Periodicals, Inc.

Electric-field switching of two-dimensional van der Waals magnets

NASA Astrophysics Data System (ADS)

Jiang, Shengwei; Shan, Jie; Mak, Kin Fai

2018-05-01

Controlling magnetism by purely electrical means is a key challenge to better information technology1. A variety of material systems, including ferromagnetic (FM) metals2-4, FM semiconductors5, multiferroics6-8 and magnetoelectric (ME) materials9,10, have been explored for the electric-field control of magnetism. The recent discovery of two-dimensional (2D) van der Waals magnets11,12 has opened a new door for the electrical control of magnetism at the nanometre scale through a van der Waals heterostructure device platform13. Here we demonstrate the control of magnetism in bilayer CrI3, an antiferromagnetic (AFM) semiconductor in its ground state12, by the application of small gate voltages in field-effect devices and the detection of magnetization using magnetic circular dichroism (MCD) microscopy. The applied electric field creates an interlayer potential difference, which results in a large linear ME effect, whose sign depends on the interlayer AFM order. We also achieve a complete and reversible electrical switching between the interlayer AFM and FM states in the vicinity of the interlayer spin-flip transition. The effect originates from the electric-field dependence of the interlayer exchange bias.

Stretching of Single Polymer Chains Using the Atomic Force Microscope

NASA Astrophysics Data System (ADS)

Ortiz, C.; van der Vegte, E. W.; van Swieten, E.; Robillard, G. T.; Hadziioannou, G.

1998-03-01

A variety of macroscopic phenomenon involve "nanoscale" polymer deformation including rubber elasticity, shear yielding, strain hardening, stress relaxation, fracture, and flow. With the advent of new and improved experimental techniques, such as the atomic force microscope (AFM), the probing of physical properties of polymers has reached finer and finer scales. The development of mixed self-assembling monolayer techniques and the chemical functionalization of AFM probe tips has allowed for mechanical experiments on single polymer chains of molecular dimensions. In our experiments, mixed monolayers are prepared in which end-functionalized, flexible polymer chains of thiol-terminated poly(methacrylic acid) are covalently bonded, isolated, and randomly distributed on gold substrates. The coils are then imaged, tethered to a gold-coated AFM tip, and stretched between the tip and the substrate in a conventional force / distance experiment. An increase in the attractive force due to entropic, elastic resistance to stretching, as well as fracture of the polymer chain is observed. The effect of chain stiffness, topological constraints, strain rate, mechanical hysteresis, and stress relaxation were investigated. Force modulation techniques were also employed in order to image the viscoelastic character of the polymer chains. Parallel work includes similar studies of biological systems such as wheat gluten proteins and polypeptides.

Predicting hidden bulk phases from surface phases in bilayered Sr 3Ru 2O 7

DOE PAGES

Rivero, Pablo; Jin, Rongying; Chen, Chen; ...

2017-08-31

The ability to predict hidden phases under extreme conditions is not only crucial to understanding and manipulating materials but it could also lead to insight into new phenomena and novel routes to synthesize new phases. This is especially true for Ruddlesden-Popper perovskite phases that possess interesting properties ranging from superconductivity and colossal magnetoresistance to photovoltaic and catalytic activities. In particular, the physical properties of the bilayer perovskite Sr 3Ru 2O 7 at the surface are intimately tied to the rotation and tilt of the RuO 6 octahedra. In order to take advantage of the extra degree of freedom associated withmore » tilting we have performed first principles hybrid density functional simulations of uniaxial pressure applied along the c-axis of bulk Sr 3Ru 2O 7 where we find that the octahedra become tilted, leading to two phase transitions. One is a structural transition at ~1.5 GPa, and the other is from a ferromagnetic (FM) metal to an antiferromagnetic (AFM) insulator at ~21 GPa whose AFM spin configuration is different from the AFM state near the FM ground state.« less

Investigating cell mechanics with atomic force microscopy

PubMed Central

Haase, Kristina; Pelling, Andrew E.

2015-01-01

Transmission of mechanical force is crucial for normal cell development and functioning. However, the process of mechanotransduction cannot be studied in isolation from cell mechanics. Thus, in order to understand how cells ‘feel’, we must first understand how they deform and recover from physical perturbations. Owing to its versatility, atomic force microscopy (AFM) has become a popular tool to study intrinsic cellular mechanical properties. Used to directly manipulate and examine whole and subcellular reactions, AFM allows for top-down and reconstitutive approaches to mechanical characterization. These studies show that the responses of cells and their components are complex, and largely depend on the magnitude and time scale of loading. In this review, we generally describe the mechanotransductive process through discussion of well-known mechanosensors. We then focus on discussion of recent examples where AFM is used to specifically probe the elastic and inelastic responses of single cells undergoing deformation. We present a brief overview of classical and current models often used to characterize observed cellular phenomena in response to force. Both simple mechanistic models and complex nonlinear models have been used to describe the observed cellular behaviours, however a unifying description of cell mechanics has not yet been resolved. PMID:25589563

Direct Single-Molecule Observation of Mode and Geometry of RecA-Mediated Homology Search.

PubMed

Lee, Andrew J; Endo, Masayuki; Hobbs, Jamie K; Wälti, Christoph

2018-01-23

Genomic integrity, when compromised by accrued DNA lesions, is maintained through efficient repair via homologous recombination. For this process the ubiquitous recombinase A (RecA), and its homologues such as the human Rad51, are of central importance, able to align and exchange homologous sequences within single-stranded and double-stranded DNA in order to swap out defective regions. Here, we directly observe the widely debated mechanism of RecA homology searching at a single-molecule level using high-speed atomic force microscopy (HS-AFM) in combination with tailored DNA origami frames to present the reaction targets in a way suitable for AFM-imaging. We show that RecA nucleoprotein filaments move along DNA substrates via short-distance facilitated diffusions, or slides, interspersed with longer-distance random moves, or hops. Importantly, from the specific interaction geometry, we find that the double-stranded substrate DNA resides in the secondary DNA binding-site within the RecA nucleoprotein filament helical groove during the homology search. This work demonstrates that tailored DNA origami, in conjunction with HS-AFM, can be employed to reveal directly conformational and geometrical information on dynamic protein-DNA interactions which was previously inaccessible at an individual single-molecule level.

Electronic Structures of Silicene Nanoribbons: Two-Edge-Chemistry Modification and First-Principles Study.

PubMed

Yao, Yin; Liu, Anping; Bai, Jianhui; Zhang, Xuanmei; Wang, Rui

2016-12-01

In this paper, we investigate the structural and electronic properties of zigzag silicene nanoribbons (ZSiNRs) with edge-chemistry modified by H, F, OH, and O, using the ab initio density functional theory method and local spin-density approximation. Three kinds of spin polarized configurations are considered: nonspin polarization (NM), ferromagnetic spin coupling for all electrons (FM), ferromagnetic ordering along each edge, and antiparallel spin orientation between the two edges (AFM). The H, F, and OH groups modified 8-ZSiNRs have the AFM ground state. The directly edge oxidized (O1) ZSiNRs yield the same energy and band structure for NM, FM, and AFM configurations, owning to the same s p (2) hybridization. And replacing the Si atoms on the two edges with O atoms (O2) yields FM ground state. The edge-chemistry-modified ZSiNRs all exhibit metallic band structures. And the modifications introduce special edge state strongly localized at the Si atoms in the edge, except for the O1 form. The modification of the zigzag edges of silicene nanoribbons is a key issue to apply the silicene into the field effect transistors (FETs) and gives more necessity to better understand the experimental findings.

Direct measurement of optical force induced by near-field plasmonic cavity using dynamic mode AFM

DOE PAGES

Guan, Dongshi; Hang, Zhi Hong; Marset, Zsolt; ...

2015-11-20

Plasmonic nanostructures have attracted much attention in recent years because of their potential applications in optical manipulation through near-field enhancement. Continuing experimental efforts have been made to develop accurate techniques to directly measure the near-field optical force induced by the plasmonic nanostructures in the visible frequency range. In this work, we report a new application of dynamic mode atomic force microscopy (DM-AFM) in the measurement of the enhanced optical force acting on a nano-structured plasmonic resonant cavity. The plasmonic cavity is made of an upper gold-coated glass sphere and a lower quartz substrate patterned with an array of subwavelength goldmore » disks. In the near-field when the sphere is positioned close to the disk array, plasmonic resonance is excited in the cavity and the induced force by a 1550 nm infrared laser is found to be increased by an order of magnitude compared with the photon pressure generated by the same laser light. Lastly, the experiment demonstrates that DM-AFM is a powerful tool for the study of light induced forces and their enhancement in plasmonic nanostructures.« less

Double minute chromosomes in mouse methotrexate-resistant cells studied by atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng Xinyu; Zhang Liangyu; Zhang Yu

2006-08-11

Double minute chromosomes (DMs) are acentric, autonomously replicating extra-chromosomes and frequently mediate gene amplification in tumor and drug resistant cells. Atomic force microscopy (AFM) is a powerful tool in microbiology. We used AFM to explore the ultrastructure of DMs in mouse fibroblasts 3T3R500. DMs in various phases of cell cycle were also studied in order to elucidate the mechanisms of their duplication and separation. Metaphase spread and induced premature condensed chromosomes (PCCs) were observed under the AFM. DMs were detected to be composed of two compact spheres linked by fibers. The fibers of DMs directly connected with metaphase chromosomes weremore » observed. Many single-minutes and few DMs were detected in G1 PCCs, while more DMs were detected in S PCCs than in G1 PCCs. Besides, all of the DMs in G2 PCCs were coupled. Our present results suggested that DMs might divide into single-minutes during or before G1-phase, followed by duplication of the single-minutes in S-phase. Moreover, we introduced a new powerful tool to study DMs and got some ideal results.« less

Fabrication of nanochannels on polyimide films using dynamic plowing lithography

NASA Astrophysics Data System (ADS)

Stoica, Iuliana; Barzic, Andreea Irina; Hulubei, Camelia

2017-12-01

Three distinct polyimide films were analyzed from the point of view of their morphology in order to determine if their surface features can be adapted for applications where surface anisotropy is mandatory. Channels of nanometric dimensions were created on surface of the specimens by using a less common atomic force microscopy (AFM) method, namely Dynamic Plowing Lithography (DPL). The changes generated by DPL procedure were monitored through the surface texture and other functional parameters, denoting the surface orientation degree and also bearing and fluid retention properties. The results revealed that in the same nanolithography conditions, the diamine and dianhydride moieties have affected the characteristics of the nanochannels. This was explained based on the aliphatic/aromatic nature of the monomers and the backbone flexibility. The reported data are of great importance in designing custom nanostructures with enhanced anisotropy on surface of polyimide films for liquid crystal orientation or guided cell growth purposes. At the end, to track the effect of the nanolithography process on the tip sharpness, degradation and contamination, the blind tip reconstruction was performed on AFM probe, before and after lithography experiments, using TGT1 test grating AFM image.

Observation of molecular level behavior in molecular electronic junction device

NASA Astrophysics Data System (ADS)

Maitani, Masato

In this dissertation, I utilize AFM based scanning probe measurement and surface enhanced Raman scattering based vibrational spectroscopic analysis to directly characterize topographic, electronic, and chemical properties of molecules confined in the local area of M3 junction to elucidate the molecular level behavior of molecular junction electronic devices. In the introduction, the characterization of molecular electronic devices with different types of metal-molecule-metal (M3) structures based upon self-assembled monolayers (SAMs) is reviewed. A background of the characterization methods I use in this dissertation, conducting probe atomic force microscopy (cp-AFM) and surface enhanced Raman spectroscopy (SERS), is provided in chapter 1. Several attempts are performed to create the ideal top metal contacts on SAMs by metal vapor phase deposition in order to prevent the metal penetration inducing critical defects of the molecular electronic devices. The scanning probe microscopy (SPM), such as cp-AFM, contact mode (c-) AFM and non-contact mode (nc-) AFM, in ultra high vacuum conditions are utilized to study the process of the metal-SAM interface construction in terms of the correlation between the morphological and electrical properties including the metal nucleation and filament generation as a function of the functionalization of long-chain alkane thiolate SAMs on Au. In chapter 2, the nascent condensation process of vapor phase Al deposition on inert and reactive SAMs are studied by SPM. The results of top deposition, penetration, and filament generation of deposited Al are discussed and compared to the results previously observed by spectroscopic measurements. Cp-AFM was shown to provide new insights into Al filament formation which has not been observed by conventional spectroscopic analysis. Additionally, the electronic characteristics of individual Al filaments are measured. Chapter 3 reveals SPM characterization of Au deposition onto --COOH terminated SAMs utilized with strong surface dipole-dipole intermolecular interaction based on hydrogen bonding and ionic bonding potentially preventing the metal penetration. The observed results are discussed with kinetic paths of metal atoms on each SAM including temporal vacancies controlled by the intermolecular interactions in SAM upon the comparison with the spectroscopic results previously reported. The results in chapter 2 and 3 strongly suggests that AFM based characterization technique is powerful tool especially for detecting molecular-size local phenomena in vapor phase metal deposition process, especially, the electric short-circuit filaments growing through SAMs, which may induce critical misinterpretation of M3 junction device properties. In Chapter 4, an altered metal deposition process on inert SAM with using a buffer layer is performed to diminish the kinetic energy of impinging metal atoms. SPM characterization reveals an abrupt metal-SAM interface without any metal penetration. Examined electric characteristics also revealed typical non-resonant tunneling characteristics of long chain alkane thiolate SAMs. In chapter 5, the buffer layer assisted growth process is used to prepare a nano particles-SAM pristine interface on SAMs to control the metal-SAM interaction in order to study the fundamental issue of chemical enhancement mechanism of SERS. Identical Au nanoparticles-SAM-Au M3 structures with different Au-SAM interactions reveal a large discrepancy of enhancement factors of ˜100 attributed to the chemical interaction. In chapter 6, Raman spectroscopy of M3 junction is applied to the characterization of molecular electronics devices. A crossed nanowire junction (X-nWJ) device is employed for in-situ electronic-spectroscopic simultaneous characterization using Raman spectroscopy. A detailed study reveals the multi-probe capability of X-nWJ for in-situ Raman and in-elastic electron tunneling spectroscopy (IETS) as vibrational spectroscopies to diagnose molecular electronic devices. In chapter 7, aniline oligomer (OAn) based redox SAMs are characterized by spectroscopic and microscopic methods under different chemical redox states by reflection absorption infrared spectroscopy (RAIRS), Raman, x-ray photoelectron spectroscopy (XPS), and AFM in order to elucidate the mechanism of electric switching molecular junctions previously reported. Obtained results are discussed in terms of the chemical and geometrical conformations of molecules in closely packed SAM domains. In chapter 8, in-situ Raman spectroscopy and cp-AFM microscopic techniques are applied to study the electric switching characteristics of X-nWJ incorporating OAn based SAM. The results of tunneling current and in-situ Raman spectroscopy are discussed with the conformational change of OAn component. The conductance switching mechanism associated with domain conformation change of OAn SAM is proposed and evaluated based on the results.

Competing charge density wave and antiferromagnetism of metallic atom wires in GaN(10 1 ¯ ) and ZnO(10 1 ¯ )

NASA Astrophysics Data System (ADS)

Kang, Yoon-Gu; Kim, Sun-Woo; Cho, Jun-Hyung

2017-12-01

Low-dimensional electron systems often show a delicate interplay between electron-phonon and electron-electron interactions, giving rise to interesting quantum phases such as the charge density wave (CDW) and magnetism. Using the density-functional theory (DFT) calculations with the semilocal and hybrid exchange-correlation functionals as well as the exact-exchange plus correlation in the random-phase approximation (EX + cRPA), we systematically investigate the ground state of the metallic atom wires containing dangling-bond (DB) electrons, fabricated by partially hydrogenating the GaN(10 1 ¯0 ) and ZnO(10 1 ¯0 ) surfaces. We find that the CDW or antiferromagnetic (AFM) order has an electronic energy gain due to a band-gap opening, thereby being more stabilized compared to the metallic state. Our semilocal DFT calculation predicts that both DB wires in GaN(10 1 ¯0 ) and ZnO(10 1 ¯0 ) have the same CDW ground state, whereas the hybrid DFT and EX + cRPA calculations predict the AFM ground state for the former DB wire and the CDW ground state for the latter one. It is revealed that more localized Ga DB electrons in GaN(10 1 ¯0 ) prefer the AFM order, while less localized Zn DB electrons in ZnO(10 1 ¯0 ) the CDW formation. Our findings demonstrate that the drastically different ground states are competing in the DB wires created on the two representative compound semiconductor surfaces.

Occurrence of aflatoxin M(1) in raw and market milk commercialized in Greece.

PubMed

Roussi, V; Govaris, A; Varagouli, A; Botsoglou, N A

2002-09-01

From December 1999 to May 2000, 114 samples of pasteurized, ultrahigh temperature-treated (UHT) and concentrated milk were collected in supermarkets, whereas 52 raw milk samples from cow, sheep and goat were obtained from different milk producers all over Greece. Sample collection was repeated from December 2000 to May 2001 and concerned 54 samples of pasteurized milk, 23 samples of bulk-tank raw milk and 55 raw milk samples from cow, sheep and goat. The total number of samples analysed for aflatoxin M(1) (AFM(1)) contamination by immunoaffinity column extraction and liquid chromatography was 297. In the first sampling, the incidence rates of AFM(1) contamination in pasteurized, UHT, concentrated and cow, sheep and goat raw milk were 85.4, 82.3, 93.3, 73.3, 66.7 and 40%, respectively, with only one cow raw milk and two concentrated milk samples exceeding the EU limit of 50 ng l(-1). In the second sampling, the incidence rates of AFM(1) contamination in pasteurized, bulk-tank and cow, sheep and goat raw milk were 79.6, 78.3, 64.3, 73.3 and 66.7%, respectively, with only one cow and one sheep raw milk samples exceeding the limit of 50 ng l(-1). The results suggest that the current regulatory status in Greece is effective.

On the occurrence of aflatoxin M1 in milk and dairy products.

PubMed

Prandini, A; Tansini, G; Sigolo, S; Filippi, L; Laporta, M; Piva, G

2009-05-01

Aflatoxins are toxic fungal metabolites found in foods and feeds. When ruminants eat AFB(1)-feedstuffs, they metabolise the toxin and excrete AFM(1) in milk. To control AFM(1) in foods it is necessary to reduce AFB(1) contamination of feeds for dairy cattle by preventing fungal growth and AFB(1) formation in agricultural commodities intended for animal use. Corn and corn-based products are one of the most contaminated feedstuffs; therefore risk factor analysis of AFB(1) contamination in corn is necessary to evaluate risk of AFM(1) contamination in milk and milk products. During the corn silage production, the aflatoxins production is mostly influenced by: harvest time; fertilization; irrigation; pest control; silage moisture; and storage practices. Due to the lower moisture at harvest and to the conservation methods, the corn grain is mostly exposed to the contamination by Aspergillus species. Therefore, it is necessary to reduce the probability of this contaminant through choice of: hybrids; seeding time and density; suitable ploughing and fertirrigation; and chemical or biological control. Grains harvested with the lowest possible moisture and conservation moisture close to or less than 14% are necessary to reduce contamination risks, as is maintaining mass to homogeneous moisture. Kernel mechanical damage, grain cleaning practices and conservation temperature are also factors which need to be carefully controlled.

Structural, electronic and magnetic properties of layered REB{sub 2}C compounds (RE=Dy, Tm, Lu)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Babizhetskyy, Volodymyr, E-mail: v.babizhetskyy@googlemail.com; Department of Inorganic Chemistry, Ivan Franko National University of L'viv, Kyryla and Mefodiya Str. 6, UA-79005 Lviv; Simon, Arndt

2012-07-15

The crystal structure of LuB{sub 2}C has been determined from single crystal and powder X-ray diffraction data. It crystallizes in the orthorhombic space group Pbam (a=6.7429(1) A, b=6.7341(1) A, c=3.5890(1) A, Z=4, R1=0.024 (wR2=0.059) for 436 reflections with I{sub o}>2{sigma}(I{sub o})). The compounds REB{sub 2}C (RE=Y, Tb-Lu) are isotypic. The boron and carbon atoms form infinite, planar two-dimensional nets which alternate with sheets of rare-earth metal atoms. Inside the nonmetal atom nets, a coloring with fused B{sub 2}C{sub 2} rhombuses and B{sub 5}C{sub 2} heptagons is proposed, supported by NMR experiments and density functional theory calculations. The calculated density ofmore » states of LuB{sub 2}C indicates this compound to be metallic. The magnetic properties of the isotypic compound TmB{sub 2}C, has been measured in the temperature range 2 K3 T a metamagnetic transition is encountered. The temperature dependence of the electrical resistivity proves the metallic character of the TmB{sub 2}C compound as well as the AFM ordering. - Graphical abstract: The crystal structure of LuB{sub 2}C has been determined from single crystal and powder X-ray diffraction data. It crystallizes in the orthorhombic space group Pbam. The compounds REB{sub 2}C (RE=Y, Tb-Lu) are isotypic. The boron and carbon atoms form infinite, planar two-dimensional nets which alternate with sheets of rare-earth metal atoms. Inside the nonmetal atom nets, a coloring with fused B{sub 2}C{sub 2} rhombuses and B{sub 5}C{sub 2} heptagons is proposed, supported by NMR experiments and density functional theory calculations. The magnetic properties of the isotypic compound TmB{sub 2}C, has been measured in the temperature range 2 K3 T a metamagnetic transition is encountered. The temperature dependence of the electrical resistivity proves the metallic character of the TmB{sub 2}C compound as well as the AFM ordering. Highlights: Black-Right-Pointing-Pointer LuB{sub 2}C compound crystallizes in orthorhombic symmetry. Black-Right-Pointing-Pointer In the structure the B{sub 2}C layers are stacked directly on top of each other. Black-Right-Pointing-Pointer A coloring with fused B{sub 2}C{sub 2} rhombuses and B{sub 5}C{sub 2} heptagons is proposed. Black-Right-Pointing-Pointer The coloring is supported by NMR experiments and theoretical calculations. Black-Right-Pointing-Pointer TmB{sub 2}C undergoes an antiferromagnetic transition at T{sub N}=12 K at elevated fields.« less

The effect of physiological conditions on the surface structure of proteins: Setting the scene for human digestion of emulsions

NASA Astrophysics Data System (ADS)

Maldonado-Valderrama, J.; Gunning, A. P.; Ridout, M. J.; Wilde, P. J.; Morris, V. J.

2009-10-01

Understanding and manipulating the interfacial mechanisms that control human digestion of food emulsions is a crucial step towards improved control of dietary intake. This article reports initial studies on the effects of the physiological conditions within the stomach on the properties of the film formed by the milk protein ( β -lactoglobulin) at the air-water interface. Atomic force microscopy (AFM), surface tension and surface rheology techniques were used to visualize and examine the effect of gastric conditions on the network structure. The effects of changes in temperature, pH and ionic strength on a pre-formed interfacial structure were characterized in order to simulate the actual digestion process. Changes in ionic strength had little effect on the surface properties. In isolation, acidification reduced both the dilatational and the surface shear modulus, mainly due to strong repulsive electrostatic interactions within the surface layer and raising the temperature to body temperature accelerated the rearrangements within the surface layer, resulting in a decrease of the dilatational response and an increase of surface pressure. Together pH and temperature display an unexpected synergism, independent of the ionic strength. Thus, exposure of a pre-formed interfacial β -lactoglobulin film to simulated gastric conditions reduced the surface dilatational modulus and surface shear moduli. This is attributed to a weakening of the surface network in which the surface rearrangements of the protein prior to exposure to gastric conditions might play a crucial role.

Prototypical Organic–Oxide Interface: Intramolecular Resolution of Sexiphenyl on In 2O 3 (111)

DOE PAGES

Wagner, Margareta; Hofinger, Jakob; Setvin, Martin; ...

2018-03-28

The performance of an organic semiconductor device is critically determined by the geometric alignment, orientation, and ordering of the organic molecules. Although an organic multilayer eventually adopts the crystal structure of the organic material, the alignment and configuration at the interface with the substrate/electrode material are essential for charge injection into the organic layer. This work focuses on the prototypical organic semiconductor para-sexiphenyl (6P) adsorbed on In 2O 3(111), the thermodynamically most stable surface of the material that the most common transparent conducting oxide, indium tin oxide, is based on. The onset of nucleation and formation of the first monolayermore » are followed with atomically resolved scanning tunneling microscopy and noncontact atomic force microscopy (nc-AFM). Annealing to 200 °C provides sufficient thermal energy for the molecules to orient themselves along the high-symmetry directions of the surface, leading to a single adsorption site. The AFM data suggests an essentially planar adsorption geometry. With increasing coverage, the 6P molecules first form a loose network with a poor long-range order. Eventually, the molecules reorient into an ordered monolayer. In conclusion, this first monolayer has a densely packed, well-ordered (2 × 1) structure with one 6P per In 2O 3(111) substrate unit cell, that is, a molecular density of 5.64 × 10 13 cm –2.« less

Prototypical Organic–Oxide Interface: Intramolecular Resolution of Sexiphenyl on In 2O 3 (111)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wagner, Margareta; Hofinger, Jakob; Setvin, Martin

The performance of an organic semiconductor device is critically determined by the geometric alignment, orientation, and ordering of the organic molecules. Although an organic multilayer eventually adopts the crystal structure of the organic material, the alignment and configuration at the interface with the substrate/electrode material are essential for charge injection into the organic layer. This work focuses on the prototypical organic semiconductor para-sexiphenyl (6P) adsorbed on In 2O 3(111), the thermodynamically most stable surface of the material that the most common transparent conducting oxide, indium tin oxide, is based on. The onset of nucleation and formation of the first monolayermore » are followed with atomically resolved scanning tunneling microscopy and noncontact atomic force microscopy (nc-AFM). Annealing to 200 °C provides sufficient thermal energy for the molecules to orient themselves along the high-symmetry directions of the surface, leading to a single adsorption site. The AFM data suggests an essentially planar adsorption geometry. With increasing coverage, the 6P molecules first form a loose network with a poor long-range order. Eventually, the molecules reorient into an ordered monolayer. In conclusion, this first monolayer has a densely packed, well-ordered (2 × 1) structure with one 6P per In 2O 3(111) substrate unit cell, that is, a molecular density of 5.64 × 10 13 cm –2.« less

Structural and Electrical Characterization of SiO2 Gate Dielectrics Deposited from Solutions at Moderate Temperatures in Air.

PubMed

Esro, Mazran; Kolosov, Oleg; Jones, Peter J; Milne, William I; Adamopoulos, George

2017-01-11

Silicon dioxide (SiO 2 ) is the most widely used dielectric for electronic applications. It is usually produced by thermal oxidation of silicon or by using a wide range of vacuum-based techniques. By default, the growth of SiO 2 by thermal oxidation of silicon requires the use of Si substrates whereas the other deposition techniques either produce low quality or poor interface material and mostly require high deposition or annealing temperatures. Recent investigations therefore have focused on the development of alternative deposition paradigms based on solutions. Here, we report the deposition of SiO 2 thin film dielectrics deposited by spray pyrolysis in air at moderate temperatures of ≈350 °C from pentane-2,4-dione solutions of SiCl 4 . SiO 2 dielectrics were investigated by means of UV-vis absorption spectroscopy, spectroscopic ellipsometry, XPS, XRD, UFM/AFM, admittance spectroscopy, and field-effect measurements. Data analysis reveals smooth (R RMS < 1 nm) amorphous films with a dielectric constant of about 3.8, an optical band gap of ≈8.1 eV, leakage current densities in the order of ≈10 -7 A/cm 2 at 1 MV/cm, and high dielectric strength in excess of 5 MV/cm. XPS measurements confirm the SiO 2 stoichiometry and FTIR spectra reveal features related to SiO 2 only. Thin film transistors implementing spray-coated SiO 2 gate dielectrics and C 60 and pentacene semiconducting channels exhibit excellent transport characteristics, i.e., negligible hysteresis, low leakage currents, high on/off current modulation ratio on the order of 10 6 , and high carrier mobility.

Nanoscale Infrared Spectroscopy of Biopolymeric Materials

Treesearch

Curtis Marcott; Michael Lo; Kevin Kjoller; Craig Prater; Roshan Shetty; Joseph Jakes; Isao Noda

2012-01-01

Atomic Force Microscopy (AFM) and infrared (IR) spectroscopy have been combined in a single instrument capable of producing 100 nm spatial resolution IR spectra and images. This new capability enables the spectroscopic characterization of biomaterial domains at levels not previously possible. A tunable IR laser source generating pulses on the order of 10 ns was used...

Demonstration of correlative atomic force and transmission electron microscopy using actin cytoskeleton

PubMed Central

Yamada, Yutaro; Konno, Hiroki; Shimabukuro, Katsuya

2017-01-01

In this study, we present a new technique called correlative atomic force and transmission electron microscopy (correlative AFM/TEM) in which a targeted region of a sample can be observed under AFM and TEM. The ultimate goal of developing this new technique is to provide a technical platform to expand the fields of AFM application to complex biological systems such as cell extracts. Recent advances in the time resolution of AFM have enabled detailed observation of the dynamic nature of biomolecules. However, specifying molecular species, by AFM alone, remains a challenge. Here, we demonstrate correlative AFM/TEM, using actin filaments as a test sample, and further show that immuno-electron microscopy (immuno-EM), to specify molecules, can be integrated into this technique. Therefore, it is now possible to specify molecules, captured under AFM, by subsequent observation using immuno-EM. In conclusion, correlative AFM/TEM can be a versatile method to investigate complex biological systems at the molecular level. PMID:28828286

Studies of chain substitution caused sub-fibril level differences in stiffness and ultrastructure of wildtype and oim/oim collagen fibers using multifrequency-AFM and molecular modeling.

PubMed

Li, Tao; Chang, Shu-Wei; Rodriguez-Florez, Naiara; Buehler, Markus J; Shefelbine, Sandra; Dao, Ming; Zeng, Kaiyang

2016-11-01

Molecular alteration in type I collagen, i.e., substituting the α2 chain with α1 chain in tropocollagen molecule, can cause osteogenesis imperfecta (OI), a brittle bone disease, which can be represented by a mouse model (oim/oim). In this work, we use dual-frequency Atomic Force Microscopy (AFM) and incorporated with molecular modeling to quantify the ultrastructure and stiffness of the individual native collagen fibers from wildtype (+/+) and oim/oim diseased mice humeri. Our work presents direct experimental evidences that the +/+ fibers have highly organized and compact ultrastructure and corresponding ordered stiffness distribution. In contrast, oim/oim fibers have ordered but loosely packed ultrastructure with uncorrelated stiffness distribution, as well as local defects. The molecular model also demonstrates the structural and molecular packing differences between +/+ and oim/oim collagens. The molecular mutation significantly altered sub-fibril structure and mechanical property of collagen fibers. This study can give the new insight for the mechanisms and treatment of the brittle bone disease. Copyright © 2016 Elsevier Ltd. All rights reserved.

Electronic disorder and magnetic-field-induced superconductivity enhancement in Fe1+y(Te1-xSex)

NASA Astrophysics Data System (ADS)

Hu, Jin; Liu, Tijiang; Qian, Bin; Mao, Zhiqiang

2012-02-01

The iron chalcogenide Fe1+y(Te1-xSex) superconductor system exhibits a unique electronic and magnetic phase diagram distinct from those seen in iron pnictides: bulk superconductivity does not appear immediately following the suppression of long-range (π,0) AFM order. Instead, an intermediate phase with weak charge carrier localization appears between AFM order and bulk superconductivity (Liu et al., Nat. Mater. 9, 719 (2010)). In this talk, we report our recent studies on the relationship between the normal state and superconducting properties in Fe1+y(Te1-xSex). We show that the superconducting volume fraction VSC and normal state metallicity significantly increase while the normal state Sommerfeld coefficient γ and Hall coefficient RH drop drastically with increasing Se content in the underdoped superconducting region. Additionally, VSC is surprisingly enhanced by magnetic field in heavily underdoped superconducting samples. The implications of these results will be discussed. Our analyses suggest that the suppression of superconductivity in the underdoped region is associated with electronic disorder caused by incoherent magnetic scattering arising from (π,0) magnetic fluctuations.