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Sample records for atom probe study

  1. Atom probe tomography studies on the Cu(In,ga)Se2 grain boundaries.

    PubMed

    Cojocaru-Mirédin, Oana; Schwarz, Torsten; Choi, Pyuck-Pa; Herbig, Michael; Wuerz, Roland; Raabe, Dierk

    2013-01-01

    Compared with the existent techniques, atom probe tomography is a unique technique able to chemically characterize the internal interfaces at the nanoscale and in three dimensions. Indeed, APT possesses high sensitivity (in the order of ppm) and high spatial resolution (sub nm). Considerable efforts were done here to prepare an APT tip which contains the desired grain boundary with a known structure. Indeed, site-specific sample preparation using combined focused-ion-beam, electron backscatter diffraction, and transmission electron microscopy is presented in this work. This method allows selected grain boundaries with a known structure and location in Cu(In,Ga)Se2 thin-films to be studied by atom probe tomography. Finally, we discuss the advantages and drawbacks of using the atom probe tomography technique to study the grain boundaries in Cu(In,Ga)Se2 thin-film solar cells. PMID:23629452

  2. Atom Probe Tomography Studies on the Cu(In,Ga)Se2 Grain Boundaries

    PubMed Central

    Cojocaru-Mirédin, Oana; Schwarz, Torsten; Choi, Pyuck-Pa; Herbig, Michael; Wuerz, Roland; Raabe, Dierk

    2013-01-01

    Compared with the existent techniques, atom probe tomography is a unique technique able to chemically characterize the internal interfaces at the nanoscale and in three dimensions. Indeed, APT possesses high sensitivity (in the order of ppm) and high spatial resolution (sub nm). Considerable efforts were done here to prepare an APT tip which contains the desired grain boundary with a known structure. Indeed, site-specific sample preparation using combined focused-ion-beam, electron backscatter diffraction, and transmission electron microscopy is presented in this work. This method allows selected grain boundaries with a known structure and location in Cu(In,Ga)Se2 thin-films to be studied by atom probe tomography. Finally, we discuss the advantages and drawbacks of using the atom probe tomography technique to study the grain boundaries in Cu(In,Ga)Se2 thin-film solar cells. PMID:23629452

  3. Pulsed-laser atom probe studies of a precipitation hardened maraging TRIP steel.

    PubMed

    Dmitrieva, O; Choi, P; Gerstl, S S A; Ponge, D; Raabe, D

    2011-05-01

    A precipitation hardened maraging TRIP steel was analyzed using a pulsed laser atom probe. The laser pulse energy was varied from 0.3 to 1.9 nJ to study its effect on the measured chemical compositions and spatial resolution. Compositional analyses using proximity histograms did not show any significant variations in the average matrix and precipitate compositions. The only remarkable change in the atom probe data was a decrease in the ++/+ charge state ratios of the elements. The values of the evaporation field used for the reconstructions exhibit a linear dependence on the laser pulse energy. The adjustment of the evaporation fields used in the reconstructions for different laser pulse energies was based on the correlation of the obtained cluster shapes to the TEM observations. No influence of laser pulse energy on chemical composition of the precipitates and on the chemical sharpness of their interfaces was detected. PMID:21215524

  4. Atom probe, AFM, and STM studies on vacuum-fired stainless steels.

    PubMed

    Stupnik, A; Frank, P; Leisch, M

    2009-04-01

    The surface morphology of grades 304L and 316LN stainless steels, after low-temperature bake-out process and vacuum annealing, has been studied by atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). The local elemental composition on the surface before and after thermal treatment has been investigated by atom probe (AP) depth profiling measurements. After vacuum annealing, AFM and STM show significant changes in the surface structure and topology. Recrystallization and surface reconstruction is less pronounced on the 316LN stainless steel. AP depth profiling analyses result in noticeable nickel enrichment on the surface of grade 304L samples. Since hydrogen recombination is almost controlled by surface structure and composition, a strong influence on the outgassing behaviour by the particular surface microstructure can be deduced. PMID:19167824

  5. Atom probe study of grain boundary segregation in technically pure molybdenum

    SciTech Connect

    Babinsky, K.; Weidow, J.; Knabl, W.; Lorich, A.; Leitner, H.; Primig, S.

    2014-01-15

    Molybdenum, a metal with excellent physical, chemical and high-temperature properties, is an interesting material for applications in lighting-technology, high performance electronics, high temperature furnace construction and coating technology. However, its applicability as a structural material is limited because of the poor oxidation resistance at high temperatures and a brittle-to-ductile transition around room temperature, which is influenced by the grain size and the content of interstitial impurities at the grain boundaries. Due to the progress of the powder metallurgical production during the last decades, the amount of impurities in the current quality of molybdenum has become so small that surface sensitive techniques are not applicable anymore. Therefore, the atom probe, which allows the detection of small amounts of impurities as well as their location, seems to be a more suitable technique. However, a site-specific specimen preparation procedure for grain boundaries in refractory metals with a dual focused ion beam/scanning electron microscope is still required. The present investigation describes the development and successful application of such a site-specific preparation technique for grain boundaries in molybdenum, which is significantly improved by a combination with transmission electron microscopy. This complimentary technique helps to improve the visibility of grain boundaries during the last preparation steps and to evidence the presence of grain and subgrain boundaries without segregants in atom probe specimens. Furthermore, in industrially processed and recrystallized molybdenum sheets grain boundary segregation of oxygen, nitrogen and potassium is successfully detected close to segregated regions which are believed to be former sinter pores. - Highlights: • First study of grain boundary segregation in molybdenum by atom probe • Site-specific preparation technique by FIB and TEM successfully developed • Grain boundary segregation of

  6. Conducting Probe Atomic Force Microscope as a Relevant Tool for Studying Some Phenomena in MEMS Switches

    NASA Astrophysics Data System (ADS)

    Peschot, A.; Vincent, M.; Poulain, C.; Mariolle, D.; Houzé, F.; Delamare, J.

    2015-12-01

    As the reliability of electrical microcontacts has proved to be the main limitation to a fast-growing production of ultraminiaturized switches, a thorough understanding of their failure mechanisms is an all-important purpose. This paper aims at showing that conducting-probe Atomic Force Microscopy (cp-AFM) is an adequate tool to actuate and study electrical contacts. By choosing relevant cantilevers and operating mode of the cp-AFM, dimensions, gap and force level representative of existing microelectromechanical switches (MEMS switches) are obtained. With two examples, the advantages of using a cp-AFM in force mode for studying physical phenomena at very low scale are highlighted. The reported investigations concern material transfer between contact parts and contact bounces. Those two undesirable phenomena induce surface damages and impinge reliability of MEMS switches. In both cases an explanatory scenario of phenomena occurring at nanoscale is proposed and preventive recommendations for improving the lifetime of such devices are suggested.

  7. Pump-probe study of atoms and small molecules with laser driven high order harmonics

    NASA Astrophysics Data System (ADS)

    Cao, Wei

    A commercially available modern laser can emit over 1015 photons within a time window of a few tens of femtoseconds (10-15second), which can be focused into a spot size of about 10 mum, resulting in a peak intensity above 1014W/cm2. This paves the way for table-top strong field physics studies such as above threshold ionization (ATI), non-sequential double ionization (NSDI), high order harmonic generation (HHG), etc.. Among these strong laser-matter interactions, high order harmonic generation, which combines many photons of the fundamental laser field into a single photon, offers a unique way to generate light sources in the vacuum ultraviolet (VUV) or extreme ultraviolet (EUV) region. High order harmonic photons are emitted within a short time window from a few tens of femtoseconds down to a few hundreds of attoseconds (10 -18second). This highly coherent nature of HHG allows it to be synchronized with an infrared (IR) laser pulse, and the pump-probe technique can be adopted to study ultrafast dynamic processes in a quantum system. The major work of this thesis is to develop a table-top VUV(EUV) light source based on HHG, and use it to study dynamic processes in atoms and small molecules with the VUV(EUV)-pump IR-probe method. A Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) apparatus is used for momentum imaging of the interaction products. Two types of high harmonic pump pulses are generated and applied for pump-probe studies. The first one consists of several harmonics forming a short attosecond pulse train (APT) in the EUV regime (around 40 eV). We demonstrate that, (1) the auto-ionization process triggered by the EUV in cation carbon-monoxide and oxygen molecules can be modified by scanning the EUV-IR delay, (2) the phase information of quantum trajectories in bifurcated high harmonics can be extracted by performing an EUV-IR cross-correlation experiment, thus disclosing the macroscopic quantum control in HHG. The second type of high harmonic source

  8. Atomic Scale Characterization of Compound Semiconductors Using Atom Probe Tomography

    SciTech Connect

    Gorman, B. P.; Norman, A. G.; Lawrence, D.; Prosa, T.; Guthrey, H.; Al-Jassim, M.

    2011-01-01

    Internal interfaces are critical in determining the performance of III-V multijunction solar cells. Studying these interfaces with atomic resolution using a combination of transmission electron microscopy (TEM), atom probe tomography (APT), and density functional calculations enables a more fundamental understanding of carrier dynamics in photovoltaic (PV) device structures. To achieve full atomic scale spatial and chemical resolution, data acquisition parameters in laser pulsed APT must be carefully studied to eliminate surface diffusion. Atom probe data with minimized group V ion clustering and expected stoichiometry can be achieved by adjusting laser pulse power, pulse repetition rate, and specimen preparation parameters such that heat flow away from the evaporating surface is maximized. Applying these improved analysis conditions to III-V based PV gives an atomic scale understanding of compositional and dopant profiles across interfaces and tunnel junctions and the initial stages of alloy clustering and dopant accumulation. Details on APT experimental methods and future in-situ instrumentation developments are illustrated.

  9. Grain boundary segregation in neutron-irradiated 304 stainless steel studied by atom probe tomography

    NASA Astrophysics Data System (ADS)

    Toyama, T.; Nozawa, Y.; Van Renterghem, W.; Matsukawa, Y.; Hatakeyama, M.; Nagai, Y.; Al Mazouzi, A.; Van Dyck, S.

    2012-06-01

    Radiation-induced segregation (RIS) of solute atoms at a grain boundary (GB) in 304 stainless steel (SS), neutron-irradiated to a dose of 24 dpa at 300 °C in the fuel wrapper plates of a commercial pressurized water reactor, was investigated using laser-assisted atom probe tomography (APT). Ni, Si, and P enrichment and Cr and Fe depletion at the GB were evident. The full-width at half-maximum of the RIS region was ˜3 nm for the concentration profile peaks of Ni and Si. The atomic percentages of Ni, Si, and Cr at the GB were ˜19%, ˜7%, and ˜14%, respectively, in agreement with previously-reported values for neutron-irradiated SS. A high number density of intra-granular Ni-Si rich precipitates formed in the matrix. A precipitate-denuded zone with a width of ˜10 nm appeared on both sides of the GB.

  10. Thermal stability of TiAlN/CrN multilayer coatings studied by atom probe tomography.

    PubMed

    Choi, Pyuck-Pa; Povstugar, Ivan; Ahn, Jae-Pyeong; Kostka, Aleksander; Raabe, Dierk

    2011-05-01

    This study is about the microstructural evolution of TiAlN/CrN multilayers (with a Ti:Al ratio of 0.75:0.25 and average bilayer period of 9 nm) upon thermal treatment. Pulsed laser atom probe analyses were performed in conjunction with transmission electron microscopy and X-ray diffraction. The layers are found to be thermally stable up to 600 °C. At 700 °C TiAlN layers begin to decompose into Ti- and Al-rich nitride layers in the out-of-plane direction. Further increase in temperature to 1000 °C leads to a strong decomposition of the multilayer structure as well as grain coarsening. Layer dissolution and grain coarsening appear to begin at the surface. Domains of AlN and TiCrN larger than 100 nm are found, together with smaller nano-sized AlN precipitates within the TiCrN matrix. Fe and V impurities are detected in the multilayers as well, which diffuse from the steel substrate into the coating along columnar grain boundaries. PMID:21146308

  11. Fusion boundary precipitation in thermally aged dissimilar metal welds studied by atom probe tomography and nanoindentation

    NASA Astrophysics Data System (ADS)

    Choi, Kyoung Joon; Kim, Taeho; Yoo, Seung Chang; Kim, Seunghyun; Lee, Jae Hyuk; Kim, Ji Hyun

    2016-04-01

    In this study, microstructural and mechanical characterizations were performed to investigate the effect of long-term thermal aging on the fusion boundary region between low-alloy steel and Nickel-based weld metal in dissimilar metal welds used in operating power plant systems. The effects of thermal aging treatment on the low-alloy steel side near the fusion boundary were an increase in the ratio of Cr constituents and Cr-rich precipitates and the formation and growth of Cr23C6. Cr concentrations were calculated using atom probe tomography. The accuracy of simulations of thermal aging effects of heat treatment was verified, and the activation energy for Cr diffusion in the fusion boundary region was calculated. The mechanical properties of fusion boundary region changed based on the distribution of Cr-rich precipitates, where the material initially hardened with the formation of Cr-rich precipitates and then softened because of the reduction of residual strain or coarsening of Cr-rich precipitates.

  12. A theoretical study of dopant atom detection and probe behavior in STEM

    NASA Astrophysics Data System (ADS)

    Mittal, Anudha

    functional-based tight-binding model revealed that a stress-free single-walled (14,6) MoS2 nanotube has a torsional deformation of 0.87 °/nm. Comparison between simulated electron diffraction patterns and atomic-resolution ADF-STEM images of nanotubes with and without the small twist suggested that these experimental techniques are viable routes for detecting presence of the torsional deformation. 2. Development of theory to cast light on aspects of scattering behavior that affect STEM data.. STEM probe intensity oscillates as the probe transmits through a crystalline sample. The oscillatory behavior of the probe is extremely similar during transmission through 3-D crystals and the hypothetical structure of an isolated column of atoms, a 1-D crystal. This indicates that the physical origin of oscillation in intensity is not due to scattering of electrons away from one atomic column and subsequent scattering back from neighboring columns. It leaves in question what the physical origin or intensity oscillation is. This question was answered here by analysis of electron beam behavior in isolated atomic columns, examined via multislice-based simulations. Two physical origins, changes in angular distribution of the probe and phase shift between the angular components, were shown to cause oscillation in beam intensity. Sensitivity of frequency of oscillation to different probe and sample parameters was used to better understand the influence of the two physical origins on probe oscillation. 3. Acquisition of atomic-scale STEM data to answer specific questions about a material.. Graphene, due to its 2-Dimensionality, and due to its thermal, optical, electrical, and mechanical properties, which are conducive to providing a unique material for incorporation in devices, has gained a lot of interest in the research world and even spurred start-ups. There are several feasible routes of graphene synthesis, among which chemical exfoliation of graphite is a promising method for mass

  13. Atom probe tomography studies of Al₂O₃ gate dielectrics on GaN

    SciTech Connect

    Mazumder, Baishakhi Wu, Feng; Speck, James S.; Liu, Xiang; Yeluri, Ramya; Mishra, Umesh K.

    2014-10-07

    Atom probe tomography was used to achieve three-dimensional characterization of in situ Al₂O₃/GaN structures grown by metal organic chemical vapor deposition (MOCVD). Al₂O₃ dielectrics grown at three different temperatures of 700, 900, and 1000 °C were analyzed and compared. A low temperature GaN cap layer grown atop Al₂O₃ enabled a high success rate in the atom probe experiments. The Al₂O₃/GaN interfaces were found to be intermixed with Ga, N, and O over the distance of a few nm. Impurity measurements data showed that the 1000 °C sample contains higher amounts of C (4 × 10¹⁹/cm³) and lower amounts of H (7 × 10¹⁹/cm³), whereas the 700 °C sample exhibits lower C impurities (<10¹⁷/cm³) and higher H incorporation (2.2 × 10²⁰/cm³). On comparing with Al₂O₃ grown by atomic layer deposition (ALD), it was found that the MOCVD Al₂O₃/GaN interface is comparatively abrupt. Scanning transmission electron microscopy data showed that the 900 °C and 1000 °C MOCVD films exhibit polycrystalline nature, while the ALD films were found to be amorphous.

  14. Creating and probing coherent atomic states

    SciTech Connect

    Reinhold, C.O.; Burgdoerfer, J. |; Frey, M.T.; Dunning, F.B.

    1997-06-01

    The authors present a brief review of recent experimental and theoretical time resolved studies of the evolution of atomic wavepackets. In particular, wavepackets comprising a superposition of very-high-lying Rydberg states which are created either using a short half-cycle pulse (HCP) or by rapid application of a DC field. The properties of the wavepackets are probed using a second HCP that is applied following a variable time delay and ionizes a fraction of the atoms, much like a passing-by ion in atomic collisions.

  15. Atom-probe and field emission electron spectroscope studies of Ge on Ir

    NASA Astrophysics Data System (ADS)

    Ashino, Makoto; Tomitori, Masahiko; Nishikawa, Osamu

    1993-04-01

    The combination of an atom-probe (AP) and a field emission electron spectroscope (FEES) was employed to investigate the electronic structure of Ge layers on an Ir substrate. Germanium forms a thin film with a fairly uniform thickness, possibly owing to a small activation energy for diffusion on Ir or the lattice matching between Ge and Ir. The FEES spectrum obtained from Ge layers thicker than 8-9 ML exhibits a semiconductive energy gap and a peak at 0.7 eV below the Fermi level as for Si on Mo. However, the minimum layer thickness to exhibit the semiconductive spectrum profile is significantly thicker than that for Si on Mo. The observed difference could be attributed to the layer structure of the deposited Ge and to the narrower energy gap of Ge than that of Si.

  16. Atom probe and field emission electron spectroscopy studies of semiconductor films on metals

    NASA Astrophysics Data System (ADS)

    Ashino, Makoto; Tomitori, Masahiko; Nishikawa, Osamu

    1995-03-01

    The surface morphology and the electronic states of Ge overlayers deposited on Ir-and Mo-tips were investigated by a combined instrument of an atom probe (AP) and a field emission electron spectroscope (FEES). The overlayers were deposited on the tips while observing field emission microscope (FEM) images of the surfaces. The FEM images of thin Ge overlayers on the Ir-tips show layer-like structures. In field emission electron distribution (FEED) of a Ge overlayer on the Ir-tip, about 5 ML thick, an energy gap near the Fermi level was clearly widened by low temperature annealing. After the thickness was reduced to 3 ML by field evaporation, the energy gap still remained wide. The FEEDs of the Ge overlayers on the Mo-tips exhibit several peaks distinct from those on the Ir-tip. This may be attributed to the local strong electric field surrounding the Ge clusters formed on the Mo-tips.

  17. Atom Probe Tomography of Geomaterials

    NASA Astrophysics Data System (ADS)

    Parman, S. W.; Diercks, D.; Gorman, B.; Cooper, R. F.

    2013-12-01

    From the electron microprobe to the secondary ion microprobe to laser-ablation ICP-MS, steady improvements in the spatial resolution and detection limits of geochemical micro-analysis have been central to generating new discoveries. Atom probe tomography (APT) is a relatively new technology that promises nm-scale spatial resolution (in three dimensions) with ppm level detection limits. The method is substantially different from traditional beam-based (electron, ion, laser) methods. In APT, the sample is shaped (usually with a dual-beam FIB) into a needle with typical dimensions of 1-2 μm height and 100-200 nm diameter. Within the atom probe, the needle is evaporated one atom (ideally) at a time by a high electric field (ten's of V per square nm at the needle tip). A femtosecond laser (12 ps pulse width) is used to assist in evaporating non-conducting samples. The two-dimensional detector locates where the atom was released from the needle's surface and so can reconstruct the positions of all detected atoms in three dimensions. It also records the time of flight of the ion, which is used to calculate the mass/charge ratio of the ion. We will discuss our results analyzing a range of geologic materials. In one case, naturally occurring platinum group alloys (PGA) from the Josephine Ophiolite have been imaged. Such alloys are of interest as recorders of the Os heterogeneity of the mantle [1,2]. Optimal ablation was achieved with a laser power of 120-240 pJ and laser pulse rates 500 kHz. Runs were stopped after 10 million atoms were imaged. An example analysis is: Pt 61(1), Fe 26.1(9), Rh 1.20(4), Ir 7.0(7), Ni 2.65(8), Ru 0.20(9), Cu 1.22(8), Co 0.00029(5). Values are in atomic %; values in parentheses are one-sigma standard deviations on five separate needles from the same FIB lift-out, which was 30 μm long. Assuming the sample is homogenous over the 30 μm from which the needle was extracted, the analyses suggest relative errors for major elements below 5% and for

  18. Atom probe tomography study of alloying element distributions in Zr alloys and their oxides

    NASA Astrophysics Data System (ADS)

    Dong, Yan; Motta, Arthur T.; Marquis, Emmanuelle A.

    2013-11-01

    A detailed study of alloying element distributions in the metal and oxygen rich regions of corroded Zr alloys and of the phases formed ahead of the oxide front was conducted using atom probe tomography (APT). A consistent sequence of sub-oxide phases is observed ahead of the ZrO2 oxide front, consisting of (i) a thin layer of equiatomic ZrO (occasionally slightly over and under stoichiometric) (ii) saturated solid solution Zr(O)sat, and (iii) a slowly decreasing oxygen profile into the metal. The results also show that the distribution of the alloying elements in the metal is more inhomogeneous than previously thought and that in the oxygen-rich phases enhanced segregation is observed, compared to the metal. the stable oxide ZrO2 (which is in contact with water), the equiatomic suboxide ZrO (both slightly sub and superstoichiometric, denoted here ZrO1+x and ZrO1-x), a saturated solution of constant oxygen content at about 30% O, denoted Zr(O)sat, and an undersaturated solid solution of O in Zr, denoted Zr(O), the oxygen content of which decreases with distance from the oxide-metal interface. As stated above, the field evaporation behavior of these phases is drastically different, resulting in characteristic ions being evaporated from each phase. As a result, the phases can be identified both by atomic concentrations and by the nature of the ionic species evaporating from each phase. The latter method was also used to visualize the distribution of phases within needles. For example, it was found in the present study that oxygen was evaporated as O+, O2+, ZrO2+, ZrO3+, ZrO2+,ZrO22+,ZrO3+ with occasional instances of ZrO23+ and ZrO33+ observed. Zr ions (Zr2+, Zr3+) become significant in the Zr(O)sat phase. O2+ is only observed in the oxide (ZrO2) phase, so it is considered a marker for that phase. ZrO2+ and ZrO22+ are present both in the ZrO2 and ZrO1+x phases but absent in the ZrO1-x, Zr(O)sat and Zr(O) phase. the equiatomic ZrO phase (observed as both ZrO1+x and Zr

  19. Structural evolution and strain induced mixing in Cu–Co composites studied by transmission electron microscopy and atom probe tomography

    SciTech Connect

    Bachmaier, A.; Aboulfadl, H.; Pfaff, M.; Mücklich, F.; Motz, C.

    2015-02-15

    A Cu–Co composite material is chosen as a model system to study structural evolution and phase formations during severe plastic deformation. The evolving microstructures as a function of the applied strain were characterized at the micro-, nano-, and atomic scale-levels by combining scanning electron microscopy and transmission electron microscopy including energy-filtered transmission electron microscopy and electron energy-loss spectroscopy. The amount of intermixing between the two phases at different strains was examined at the atomic scale using atom probe tomography as complimentary method. It is shown that Co particles are dissolved in the Cu matrix during severe plastic deformation to a remarkable extent and their size, number, and volume fraction were quantitatively determined during the deformation process. From the results, it can be concluded that supersaturated solid solutions up to 26 at.% Co in a fcc Cu–26 at.% Co alloy are obtained during deformation. However, the distribution of Co was found to be inhomogeneous even at the highest degree of investigated strain. - Highlights: • Structural evolution in a deformed Cu–Co composite is studied on all length scales. • Amount of intermixing is examined by atom-probe tomography. • Supersaturated solid solutions up to 26 at.% Co in Cu are observed.

  20. Atom probe study of vanadium interphase precipitates and randomly distributed vanadium precipitates in ferrite.

    PubMed

    Nöhrer, M; Zamberger, S; Primig, S; Leitner, H

    2013-01-01

    Atom probe tomography and transmission electron microscopy were used to examine the precipitation reaction in the austenite and ferrite phases in vanadium micro-alloyed steel after a thermo-mechanical process. It was observed that only in the ferrite phase precipitates could be found, whereupon two different types were detected. Thus, the aim was to reveal the difference between these two types. The first type was randomly distributed precipitates from V supersaturated ferrite and the second type V interphase precipitates. Not only the arrangement of the particles was different also the chemical composition. The randomly distributed precipitates consisted of V, C and N in contrast to that the interphase precipitates showed a composition of V, C and Mn. Furthermore the randomly distributed precipitates had maximum size of 20 nm and the interphase precipitates a maximum size of 15 nm. It was assumed that the reason for these differences is caused by the site in which they were formed. The randomly distributed precipitates were formed in a matrix consisting mainly of 0.05 at% C, 0.68 at% Si, 0.03 at% N, 0.145 at% V and 1.51 at% Mn. The interphase precipitates were formed in a region with a much higher C, Mn and V content. PMID:24041583

  1. Structural evolution and strain induced mixing in Cu–Co composites studied by transmission electron microscopy and atom probe tomography

    PubMed Central

    Bachmaier, A.; Aboulfadl, H.; Pfaff, M.; Mücklich, F.; Motz, C.

    2015-01-01

    A Cu–Co composite material is chosen as a model system to study structural evolution and phase formations during severe plastic deformation. The evolving microstructures as a function of the applied strain were characterized at the micro-, nano-, and atomic scale-levels by combining scanning electron microscopy and transmission electron microscopy including energy-filtered transmission electron microscopy and electron energy-loss spectroscopy. The amount of intermixing between the two phases at different strains was examined at the atomic scale using atom probe tomography as complimentary method. It is shown that Co particles are dissolved in the Cu matrix during severe plastic deformation to a remarkable extent and their size, number, and volume fraction were quantitatively determined during the deformation process. From the results, it can be concluded that supersaturated solid solutions up to 26 at.% Co in a fcc Cu–26 at.% Co alloy are obtained during deformation. However, the distribution of Co was found to be inhomogeneous even at the highest degree of investigated strain. PMID:26523113

  2. Atom-probe tomographic study of interfaces of Cu{sub 2}ZnSnS{sub 4} photovoltaic cells

    SciTech Connect

    Tajima, S. Asahi, R.; Itoh, T.; Hasegawa, M.; Ohishi, K.; Isheim, D.; Seidman, D. N.

    2014-09-01

    The heterophase interfaces between the CdS buffer layer and the Cu{sub 2}ZnSnS{sub 4} (CZTS) absorption layers are one of the main factors affecting photovoltaic performance of CZTS cells. We have studied the compositional distributions at heterophase interfaces in CZTS cells using three-dimensional atom-probe tomography. The results demonstrate: (a) diffusion of Cd into the CZTS layer; (b) segregation of Zn at the CdS/CZTS interface; and (c) a change of oxygen and hydrogen concentrations in the CdS layer depending on the heat treatment. Annealing at 573 K after deposition of CdS improves the photovoltaic properties of CZTS cells probably because of the formation of a heterophase epitaxial junction at the CdS/CZTS interface. Conversely, segregation of Zn at the CdS/CZTS interface after annealing at a higher temperature deteriorates the photovoltaic properties.

  3. The Future of Atom Probe Tomography

    SciTech Connect

    Miller, Michael K; Kelly, T. F.; Rajan, Krishna; Ringer, S. P.

    2012-01-01

    The dream of the microscopy and materials science communities is to see, identify, accurately locate, and determine the fundamental physical properties of every atom in a specimen. With this knowledge together with modern computer models and simulations, a full understanding of the properties of a material can be determined. This fundamental knowledge leads to the design and development of more advanced materials for solving the needs of society. The technique of atom probe tomography is the closest to fulfilling this dream but is still significantly short of the goal. The future of atomic probe tomography, and the prospects for achieving this ultimate goal are outlined.

  4. Atom probe tomography study of internal interfaces in Cu2ZnSnSe4 thin-films

    NASA Astrophysics Data System (ADS)

    Schwarz, T.; Cojocaru-Mirédin, O.; Choi, P.; Mousel, M.; Redinger, A.; Siebentritt, S.; Raabe, D.

    2015-09-01

    We report on atom probe tomography studies of the composition at internal interfaces in Cu2ZnSnSe4 thin-films. For Cu2ZnSnSe4 precursors, which are deposited at 320 °C under Zn-rich conditions, grain boundaries are found to be enriched with Cu irrespective of whether Cu-poor or Cu-rich growth conditions are chosen. Cu2ZnSnSe4 grains are found to be Cu-poor and excess Cu atoms are found to be accumulated at grain boundaries. In addition, nanometer-sized ZnSe grains are detected at or near grain boundaries. The compositions at grain boundaries show different trends after annealing at 500 °C. Grain boundaries in the annealed absorber films, which are free of impurities, are Cu-, Sn-, and Se-depleted and Zn-enriched. This is attributed to dissolution of ZnSe at the Cu-enriched grain boundaries during annealing. Furthermore, some of the grain boundaries of the absorbers are enriched with Na and K atoms, stemming from the soda-lime glass substrate. Such grain boundaries show no or only small changes in composition of the matrix elements. Na and K impurities are also partly segregated at some of the Cu2ZnSnSe4/ZnSe interfaces in the absorber, whereas for the precursors, only Na was detected at such phase boundaries possibly due to a higher diffusivity of Na compared to K. Possible effects of the detected compositional fluctuations on cell performance are discussed.

  5. Advances in the calibration of atom probe tomographic reconstruction

    SciTech Connect

    Gault, Baptiste; Moody, Michael P.; La Fontaine, Alexandre; Stephenson, Leigh T.; Haley, Daniel; Ringer, Simon P.; Geuser, Frederic de; Tsafnat, Guy

    2009-02-01

    Modern wide field-of-view atom probes permit observation of a wide range of crystallographic features that can be used to calibrate the tomographic reconstruction of the analyzed volume. In this study, methodologies to determine values of the geometric parameters involved in the tomographic reconstruction of atom probe data sets are presented and discussed. The influence of the tip to electrode distance and specimen temperature on these parameters is explored. Significantly, their influence is demonstrated to be very limited, indicating a relatively wide regime of experimental parameters space for sound atom probe tomography (APT) experiments. These methods have been used on several specimens and material types, and the results indicate that the reconstruction parameters are specific to each specimen. Finally, it is shown how an accurate calibration of the reconstruction enables improvements to the quality and reliability of the microscopy and microanalysis capabilities of the atom probe.

  6. Optical probing of cold trapped atoms

    NASA Technical Reports Server (NTRS)

    Fox, R. W.; Gilbert, S. L.; Hollberg, L.; Marquardt, J. H.; Robinson, H. G.

    1993-01-01

    Transitions between excited states of laser-cooled and laser-trapped rubidium and cesium atoms are probed by use of fiber and diode lasers. High-resolution Doppler-free spectra are detected by observation of the absorption and fluorescence of light from the intermediate level of two-step cascade systems. The optical double-resonance spectra show Autler-Townes splitting in the weak probe limit and more complicated spectra for a strongly coupled three-level system.

  7. Study of modification methods of probes for critical-dimension atomic-force microscopy by the deposition of carbon nanotubes

    SciTech Connect

    Ageev, O. A.; Bykov, Al. V.; Kolomiitsev, A. S.; Konoplev, B. G.; Rubashkina, M. V.; Smirnov, V. A.; Tsukanova, O. G.

    2015-12-15

    The results of an experimental study of the modification of probes for critical-dimension atomicforce microscopy (CD-AFM) by the deposition of carbon nanotubes (CNTs) to improve the accuracy with which the surface roughness of vertical walls is determined in submicrometer structures are presented. Methods of the deposition of an individual CNT onto the tip of an AFM probe via mechanical and electrostatic interaction between the probe and an array of vertically aligned carbon nanotubes (VACNTs) are studied. It is shown that, when the distance between the AFM tip and a VACNT array is 1 nm and the applied voltage is within the range 20–30 V, an individual carbon nanotube is deposited onto the tip. On the basis of the results obtained in the study, a probe with a carbon nanotube on its tip (CNT probe) with a radius of 7 nm and an aspect ratio of 1:15 is formed. Analysis of the CNT probe demonstrates that its use improves the resolution and accuracy of AFM measurements, compared with the commercial probe, and also makes it possible to determine the roughness of the vertical walls of high-aspect structures by CD-AFM. The results obtained can be used to develop technological processes for the fabrication and reconditioning of special AFM probes, including those for CD-AFM, and procedures for the interoperational express monitoring of technological process parameters in the manufacturing of elements for micro- and nanoelectronics and micro- and nanosystem engineering.

  8. Coke Formation in a Zeolite Crystal During the Methanol-to-Hydrocarbons Reaction as Studied with Atom Probe Tomography.

    PubMed

    Schmidt, Joel E; Poplawsky, Jonathan D; Mazumder, Baishakhi; Attila, Özgün; Fu, Donglong; de Winter, D A Matthijs; Meirer, Florian; Bare, Simon R; Weckhuysen, Bert M

    2016-09-01

    Understanding the formation of carbon deposits in zeolites is vital to developing new, superior materials for various applications, including oil and gas conversion processes. Herein, atom probe tomography (APT) has been used to spatially resolve the 3D compositional changes at the sub-nm length scale in a single zeolite ZSM-5 crystal, which has been partially deactivated by the methanol-to-hydrocarbons reaction using (13) C-labeled methanol. The results reveal the formation of coke in agglomerates that span length scales from tens of nanometers to atomic clusters with a median size of 30-60 (13) C atoms. These clusters correlate with local increases in Brønsted acid site density, demonstrating that the formation of the first deactivating coke precursor molecules occurs in nanoscopic regions enriched in aluminum. This nanoscale correlation underscores the importance of carefully engineering materials to suppress detrimental coke formation. PMID:27485276

  9. Coke formation in a zeolite crystal during the methanol-to-hydrocarbons reaction as studied with atom probe tomography

    DOE PAGESBeta

    Schmidt, Joel E.; Poplawsky, Jonathan D.; Mazumder, Baishakhi; Attila, Özgün; Fu, Donglong; de Winter, D. A. Matthijs; Meirer, Florian; Bare, Simon R.; Weckhuysen, Bert M.

    2016-08-03

    Understanding the formation of carbon deposits in zeolites is vital to developing new, superior materials for various applications, including oil and gas conversion processes. Herein, atom probe tomography (APT) has been used to spatially resolve the 3D compositional changes at the sub-nm length scale in a single zeolite ZSM-5 crystal, which has been partially deactivated by the methanol-to-hydrocarbons reaction using 13C-labeled methanol. The results reveal the formation of coke in agglomerates that span length scales from tens of nanometers to atomic clusters with a median size of 30–60 13C atoms. These clusters correlate with local increases in Brønsted acid sitemore » density, demonstrating that the formation of the first deactivating coke precursor molecules occurs in nanoscopic regions enriched in aluminum. Here, this nanoscale correlation underscores the importance of carefully engineering materials to suppress detrimental coke formation.« less

  10. Atom probe study of irradiation-enhanced α' precipitation in neutron-irradiated Fe–Cr model alloys

    SciTech Connect

    Chen, Wei -Ying; Miao, Yinbin; Wu, Yaqiao; Tomchik, Carolyn A.; Mo, Kun; Gan, Jian; Okuniewski, Maria A.; Maloy, Stuart A.; Stubbins, James F.

    2015-07-01

    Atom probe tomography (APT) was performed to study the effects of Cr concentrations, irradiation doses and irradiation temperatures on a' phase formation in Fe-Cr model alloys (10-16 at.%) irradiated at 300 and 450°C to 0.01, 0.1 and 1 dpa. For 1 dpa specimens, α' precipitates with an average radius of 1.0-1.3 nm were observed. The precipitate density varied significantly from 1.1x10²³ to 2.7x10²⁴ 1/m³, depending on Cr concentrations and irradiation temperatures. The volume fraction of α' phase in 1 dpa specimens qualitatively agreed with the phase diagram prediction. For 0.01 dpa and 0.1 dpa, frequency distribution analysis detected slight Cr segregation in high-Cr specimens, but not in Fe-10Cr specimens. Proximity histogram analysis showed that the radial Cr concentration was highest at the center of a' precipitates. For most precipitates, the Cr contents were significantly lower than that predicted by the phase diagram. The Cr concentration at precipitate center increased with increasing precipitate size.

  11. Study of vertical Si/SiO2 interface using laser-assisted atom probe tomography and transmission electron microscopy.

    PubMed

    Lee, J H; Lee, B H; Kim, Y T; Kim, J J; Lee, S Y; Lee, K P; Park, C G

    2014-03-01

    Laser-assisted atom probe tomography has opened the way to three-dimensional visualization of nanostructures. However, many questions related to the laser-matter interaction remain unresolved. We demonstrate that the interface reaction can be activated by laser-assisted field evaporation and affects the quantification of the interfacial composition. At a vertical interface between Si and SiO2, a SiO2 molecule tends to combine with a Si atom and evaporate as a SiO molecule, reducing the evaporation field. The features of the reaction depend on the direction of the laser illumination and the inner structure of tip. A high concentration of SiO is observed at a vertical interface between Si and SiO2 when the Si column is positioned at the center of the tip, whereas no significant SiO is detected when the SiO2 layer is at the center. The difference in the interfacial compositions of two samples was due to preferential evaporation of the Si layer. This was explained using transmission electron microscopy observations before and after atom probe experiments. PMID:24411275

  12. Carbon nanotube atomic force microscopy probes

    NASA Astrophysics Data System (ADS)

    Yamanaka, Shigenobu; Okawa, Takashi; Akita, Seiji; Nakayama, Yoshikazu

    2005-05-01

    We have developed a carbon nanotube atomic force microscope probe. Because the carbon nanotube are well known to have high aspect ratios, small tip radii and high stiffness, carbon nanotube probes have a long lifetime and can be applied for the observation deep trenches. Carbon nanotubes were synthesized by a well-controlled DC arc discharge method, because this method can make nanotubes to have straight shape and high crystalline. The nanotubes were aligned on the knife-edge using an alternating current electrophoresis technique. A commercially available Si probe was used for the base of the nanotube probe. The nanotube probe was fabricated by the SEM manipulation method. The nanotube was then attached tightly to the Si probe by deposition of amorphous carbon. We demonstrate the measurement of a fine pith grating that has vertical walls. However, a carbon nanotube has a problem that is called "Sticking". The sticking is a chatter image on vertical like region in a sample. We solved this problem by applying 2 methods, 1. a large cantilever vibration amplitude in tapping mode, 2. an attractive mode measurement. We demonstrate the non-sticking images by these methods.

  13. Atom Probe Tomography of Nanoscale Electronic Materials

    SciTech Connect

    Larson, David J.; Prosa, Ty J.; Perea, Daniel E.; Inoue, Hidekazu; Mangelinck, D.

    2016-01-01

    Atom probe tomography (APT) is a mass spectrometry based on time-of-flight measurements which also concurrently produces 3D spatial information. The reader is referred to any of the other papers in this volume or to the following references for further information 4–8. The current capabilities of APT, such as detecting a low number of dopant atoms in nanoscale devices or segregation at a nanoparticle interface, make this technique an important component in the nanoscale metrology toolbox. In this manuscript, we review some of the applications of APT to nanoscale electronic materials, including transistors and finFETs, silicide contact microstructures, nanowires, and nanoparticles.

  14. Atom probe tomography analysis of WC powder.

    PubMed

    Weidow, Jonathan

    2013-09-01

    A tantalum doped tungsten carbide powder, (W,Ta)C, was prepared with the purpose to maximise the amount of Ta in the hexagonal mixed crystal carbide. Atom probe tomography (APT) was considered to be the best technique to quantitatively measure the amount of Ta within this carbide. As the carbide powder consisted in the form of very small particles (<1 μm), a method to produce APT specimens of such a powder was developed. The powder was at first embedded in copper and a FIB-SEM workstation was used to make an in-situ lift-out from a selected powder particle. The powder particle was then deposited on a post made from a WC-Co based cemented carbide specimen. With the use of a laser assisted atom probe, it was shown that the method is working and the Ta content of the (W,Ta)C could be measured quantitatively. PMID:23507029

  15. Mapping interfacial excess in atom probe data.

    PubMed

    Felfer, Peter; Scherrer, Barbara; Demeulemeester, Jelle; Vandervorst, Wilfried; Cairney, Julie M

    2015-12-01

    Using modern wide-angle atom probes, it is possible to acquire atomic scale 3D data containing 1000 s of nm(2) of interfaces. It is therefore possible to probe the distribution of segregated species across these interfaces. Here, we present techniques that allow the production of models for interfacial excess (IE) mapping and discuss the underlying considerations and sampling statistics. We also show, how the same principles can be used to achieve thickness mapping of thin films. We demonstrate the effectiveness on example applications, including the analysis of segregation to a phase boundary in stainless steel, segregation to a metal-ceramic interface and the assessment of thickness variations of the gate oxide in a fin-FET. PMID:26346774

  16. Atom probe tomographic mapping directly reveals the atomic distribution of phosphorus in resin embedded ferritin

    DOE PAGESBeta

    Perea, Daniel E.; Liu, Jia; Bartrand, Jonah A. G.; Dicken, Quinten G.; Thevuthasan, Suntharampillai Theva; Browning, Nigel D.; Evans, James E.

    2016-02-29

    In this study, we report the atomic-scale analysis of biological interfaces using atom probe tomography. Embedding the protein ferritin in an organic polymer resin lacking nitrogen provided chemical contrast to visualize atomic distributions and distinguish organic-organic and organic-inorganic interfaces. The sample preparation method can be directly extended to further enhance the study of biological, organic and inorganic nanomaterials relevant to health, energy or the environment.

  17. Mining information from atom probe data.

    PubMed

    Cairney, Julie M; Rajan, Krishna; Haley, Daniel; Gault, Baptiste; Bagot, Paul A J; Choi, Pyuck-Pa; Felfer, Peter J; Ringer, Simon P; Marceau, Ross K W; Moody, Michael P

    2015-12-01

    Whilst atom probe tomography (APT) is a powerful technique with the capacity to gather information containing hundreds of millions of atoms from a single specimen, the ability to effectively use this information creates significant challenges. The main technological bottleneck lies in handling the extremely large amounts of data on spatial-chemical correlations, as well as developing new quantitative computational foundations for image reconstruction that target critical and transformative problems in materials science. The power to explore materials at the atomic scale with the extraordinary level of sensitivity of detection offered by atom probe tomography has not been not fully harnessed due to the challenges of dealing with missing, sparse and often noisy data. Hence there is a profound need to couple the analytical tools to deal with the data challenges with the experimental issues associated with this instrument. In this paper we provide a summary of some key issues associated with the challenges, and solutions to extract or "mine" fundamental materials science information from that data. PMID:26095825

  18. EELS and atom probe tomography study of the evolution of the metal/oxide interface during zirconium alloy oxidation

    NASA Astrophysics Data System (ADS)

    de Gabory, Benoit; Dong, Yan; Motta, Arthur T.; Marquis, Emmanuelle A.

    2015-07-01

    In an effort to understand the mechanisms resulting in the variations of corrosion rate observed throughout corrosion including at the first kinetic transition when the oxide temporarily loses its protective character, the oxide/metal interfaces of autoclave corroded Zircaloy-4 and ZIRLO™ before and after the transition are characterized using electron energy loss spectroscopy and atom probe tomography. The results reveal a complex structure of different phases at different stages of corrosion. The oxide/metal interface exhibits an intermediate layer, with an oxygen content between 45 and 55 O at.% and a suboxide layer corresponding to an oxygen-saturated solid solution in the metal matrix side (∼30 O at.%). Local variations are observed in the width of these characteristic structural features, especially near the transition. Good agreement on the layers present as well as their order, composition, and width was seen with the two techniques.

  19. Data analysis and other considerations concerning the study of precipitation in Al–Mg–Si alloys by Atom Probe Tomography

    PubMed Central

    Zandbergen, M.W.; Xu, Q.; Cerezo, A.; Smith, G.D.W.

    2015-01-01

    Atom Probe Tomography (APT) analysis and hardness measurements were used to characterize the early stages of precipitation in an Al–0.51 at%Mg–0.94 at%Si alloy as reported in the accompanying Acta Materialia paper [1]. The changes in microstructure were investigated after single-stage or multi-stage heat treatments including natural ageing at 298 K (NA), pre-ageing at 353 K (PA), and automotive paint-bake ageing conditions at 453 K (PB). This article provides Supporting information and a detailed report on the experimental conditions and the data analysis methods used for this investigation. Careful design of experimental conditions and analysis methods was carried out to obtain consistent and reliable results. Detailed data on clustering for prolonged NA and PA treatments have been reported. PMID:26958619

  20. Full tip imaging in atom probe tomography.

    PubMed

    Du, Sichao; Burgess, Timothy; Loi, Shyeh Tjing; Gault, Baptiste; Gao, Qiang; Bao, Peite; Li, Li; Cui, Xiangyuan; Kong Yeoh, Wai; Tan, Hark Hoe; Jagadish, Chennupati; Ringer, Simon P; Zheng, Rongkun

    2013-01-01

    Atom probe tomography (APT) is capable of simultaneously revealing the chemical identities and three dimensional positions of individual atoms within a needle-shaped specimen, but suffers from a limited field-of-view (FOV), i.e., only the core of the specimen is effectively detected. Therefore, the capacity to analyze the full tip is crucial and much desired in cases that the shell of the specimen is also the region of interest. In this paper, we demonstrate that, in the analysis of III-V nanowires epitaxially grown from a substrate, the presence of the flat substrate positioned only micrometers away from the analyzed tip apex alters the field distribution and ion trajectories, which provides extra image compression that allows for the analysis of the entire specimen. An array of experimental results, including field desorption maps, elemental distributions, and crystallographic features clearly demonstrate the fact that the whole tip has been imaged, which is confirmed by electrostatic simulations. PMID:23142750

  1. Atomic Scale Characterization of Compound Semiconductors using Atom Probe Tomography: Preprint

    SciTech Connect

    Gorman, B. P.; Guthrey, H.; Norman, A. G.; Al-Jassim, M.; Lawrence, D.; Prosa, T.

    2011-07-01

    Internal interfaces are critical in determining the performance of III-V multijunction solar cells. Studying these interfaces with atomic resolution using a combination of transmission electron microscopy (TEM), atom probe tomography (APT), and density functional calculations enables a more fundamental understanding of carrier dynamics in photovoltaic (PV) device structures. To achieve full atomic scale spatial and chemical resolution, data acquisition parameters in laser pulsed APT must be carefully studied to eliminate surface diffusion. Atom probe data with minimized group V ion clustering and expected stoichiometry can be achieved by adjusting laser pulse power, pulse repetition rate, and specimen preparation parameters such that heat flow away from the evaporating surface is maximized. Applying these improved analysis conditions to III-V based PV gives an atomic scale understanding of compositional and dopant profiles across interfaces and tunnel junctions and the initial stages of alloy clustering and dopant accumulation. Details on APT experimental methods and future in-situ instrumentation developments are illustrated.

  2. Self-organization of Cu-based immiscible alloys under irradiation: An atom-probe tomography study

    NASA Astrophysics Data System (ADS)

    Stumphy, Brad D.

    The stability of materials subjected to prolonged irradiation has been a topic of renewed interest in recent years due to the projected growth of nuclear power as an alternative energy source. The irradiating particles impart energy into the material, thereby causing atomic displacements to occur. These displacements result in the creation of point defects and the random ballistic mixing of the atoms. Consequently, the material is driven away from its equilibrium structure. The supersaturation of defects can lead to the degradation of mechanical properties, but a high density of internal interfaces, which act as defect sinks, will suppress the supersaturation and long-range transport of defects. The microstructural evolution of the material is controlled by the ballistic mixing as well as the mobility of the point defects. In immiscible alloys, these two processes compete against one another, as the ballistic mixing acts to solutionize the alloy components, and the thermal diffusion of the large number of defects acts to phase separate the components. The work presented in this dissertation examines the effect of heavy-ion irradiation on immiscible, binary Cu-based alloys. Dilute alloys of Cu-Fe, Cu-V, and V-Cu have been subjected to irradiation, and atom-probe tomography has been utilized in order to better understand the complex nature of the response of these simple model systems to an irradiation environment. The results show that a steady-state, nano-scale patterning structure, with a high density of unsaturable defect sinks, can be maintained under prolonged irradiation. Additionally, precipitation from a supersaturated solid solution is shown to be a function of both the thermal diffusion and the ballistic mixing. Solvent-rich secondary precipitates, termed "cherry-pits," are observed inside of the solute-rich primary precipitates. Through a combination of simulation work and analyzing multiple alloys experimentally, it was determined that this cherry

  3. High-performance atom-probe field ion microscope study of segregation and hydrogen cracking in Fe-0. 29 Ti

    SciTech Connect

    Kuk, Y.; Pickering, H.W.; Sakurai, T.

    1980-01-01

    With the greatly improved resolution now available in energy focused atom probes, hydrogen can be readily resolved even when combined with metals having several isotopes. In addition to finding that H, H/sub 2/, FeH and TiH/sub 2/ accumulate at segregated grain boundaries in Fe-0.29 wt % Ti, a striking observation was made - the formation and propagation of a microcrack when the (field ion microscope) tip was exposed to hydrogen gas at elevated temperature. A small crack (approx. 200 A in length) was first noticed at a grain-boundary intersection during field ion imaging. This was an open crack, formed by detachment of metal between the intersecting grain boundaries, which was observed to be much larger after the tip was reheated to 1300/sup 0/K for 10 min. in the presence of 10/sup 2/ Pa (1 torr) H/sub 2/. This crack could be easily reduced in size by gradually field evaporating the surface. Its propagation was repeated several times and reproducible results were obtained. Hydrogen was identified in quantity in the crack surface, though not elsewhere. The observation of H/sub 2/ is taken to mean that H/sub 2/ gas was trapped in the grain boundary. The grain boundary was also observed to be enriched in Ti, O, C and S, in agreement with earlier results for Fe-Ti.

  4. Microstructural evolution of Fesbnd 22%Cr model alloy under thermal ageing and ion irradiation conditions studied by atom probe tomography

    NASA Astrophysics Data System (ADS)

    Korchuganova, Olesya A.; Thuvander, Mattias; Aleev, Andrey A.; Rogozhkin, Sergey V.; Boll, Torben; Kulevoy, Timur V.

    2016-08-01

    Nanostructure evolution during ion irradiation of two thermally aged binary Fee22Cr alloys has been investigated using atom probe tomography. Specimens aged at 500 °C for 50 and 200 h were irradiated by 5.6 MeV Fe ions at room temperature up to fluences of 0.3 × 1015 ions/cm2 and 1 × 1015 ions/cm2. The effect of irradiation on the material nanostructure was examined at a depth of 1 μm from the irradiated surface. The analysis of Cr radial concentration functions reveals that dense α‧-phase precipitates in the 200 h aged alloy become diffuse and thereby larger when subjected to irradiation. On the other hand, less Cr-enriched precipitates in the alloy aged for 50 h are less affected. The CreCr pair correlation function analysis shows that matrix inhomogeneity decreases under irradiation. Irradiation leads to a decrease in the number density of diffuse clusters, whereas in the case of well-developed precipitates it remains unchanged.

  5. Preparation of Regular Specimens for Atom Probes

    NASA Technical Reports Server (NTRS)

    Kuhlman, Kim; Wishard, James

    2003-01-01

    A method of preparation of specimens of non-electropolishable materials for analysis by atom probes is being developed as a superior alternative to a prior method. In comparison with the prior method, the present method involves less processing time. Also, whereas the prior method yields irregularly shaped and sized specimens, the present developmental method offers the potential to prepare specimens of regular shape and size. The prior method is called the method of sharp shards because it involves crushing the material of interest and selecting microscopic sharp shards of the material for use as specimens. Each selected shard is oriented with its sharp tip facing away from the tip of a stainless-steel pin and is glued to the tip of the pin by use of silver epoxy. Then the shard is milled by use of a focused ion beam (FIB) to make the shard very thin (relative to its length) and to make its tip sharp enough for atom-probe analysis. The method of sharp shards is extremely time-consuming because the selection of shards must be performed with the help of a microscope, the shards must be positioned on the pins by use of micromanipulators, and the irregularity of size and shape necessitates many hours of FIB milling to sharpen each shard. In the present method, a flat slab of the material of interest (e.g., a polished sample of rock or a coated semiconductor wafer) is mounted in the sample holder of a dicing saw of the type conventionally used to cut individual integrated circuits out of the wafers on which they are fabricated in batches. A saw blade appropriate to the material of interest is selected. The depth of cut and the distance between successive parallel cuts is made such that what is left after the cuts is a series of thin, parallel ridges on a solid base. Then the workpiece is rotated 90 and the pattern of cuts is repeated, leaving behind a square array of square posts on the solid base. The posts can be made regular, long, and thin, as required for samples

  6. Structural defect-dependent resistive switching in Cu-O/Si studied by Kelvin probe force microscopy and conductive atomic force microscopy.

    PubMed

    Kumar, Mohit; Som, Tapobrata

    2015-08-28

    In this study, we show structural defect-dependent presence or absence of resistive switching in Cu-O films. We use Kelvin probe force microscopy and conductive atomic force microscopy to show the presence of resistive switching. In addition, local current mapping provides direct evidence on the formation of nanoscale filament. These findings match well with the existing theoretical model on resistive switching. In particular, understanding the role of structural defects in resistive switching can be considered as critically important to take a step forward for designing advanced nanoscale memory devices. PMID:26243354

  7. Probe-rotating atomic force microscopy for determining material properties

    SciTech Connect

    Lee, Sang Heon

    2014-03-15

    In this paper, we propose a probe-rotating atomic force microscope that enables scan in an arbitrary direction in the contact imaging mode, which is difficult to achieve using a conventional atomic force microscope owing to the orientation-dependent probe and the inability to rotate the probe head. To enable rotation of the probe about its vertical axis, we employed a compact and light probe head, the sensor of which is made of an optical disk drive pickup unit. Our proposed mechanical configuration, operating principle, and control system enables axial and lateral scan in various directions.

  8. Interfacial chemistry in a ZnTe/CdSe superlattice studied by atom probe tomography and transmission electron microscopy strain measurements.

    PubMed

    Bonef, B; Haas, B; Rouvière, J-L; André, R; Bougerol, C; Grenier, A; Jouneau, P-H; Zuo, J-M

    2016-05-01

    The atomic scale analysis of a ZnTe/CdSe superlattice grown by molecular beam epitaxy is reported using atom probe tomography and strain measurements from high-resolution scanning transmission electron microscopy images. CdTe interfaces were grown by atomic layer epitaxy to prevent the spontaneous formation of ZnSe bonds. Both interfaces between ZnTe and CdSe are composed of alloyed layers of ZnSe. Pure CdTe interfaces are not observed and Zn atoms are also visible in the CdSe layers. This information is critical to design superlattices with the expected optoelectronic properties. PMID:26748639

  9. Embrittlement of RPV steels; An atom probe tomography perspective

    SciTech Connect

    Miller, Michael K; Russell, Kaye F

    2007-01-01

    Atom probe tomography has played a key role in the understanding of the embrittlement of neutron irradiated reactor pressure vessel steels through the atomic level characterization of the microstructure. Atom probe tomography has been used to demonstrate the importance of the post weld stress relief treatment in reducing the matrix copper content in high copper alloys, the formation of {approx}-nm-diameter copper-, nickel-, manganese- and silicon-enriched precipitates during neutron irradiation in copper containing RPV steels, and the coarsening of these precipitates during post irradiation heat treatments. Atom probe tomography has been used to detect {approx}2-nm-diameter nickel-, silicon- and manganese-enriched clusters in neutron irradiated low copper and copper free alloys. Atom probe tomography has also been used to quantify solute segregation to, and precipitation on, dislocations and grain boundaries.

  10. Atom probe tomography study of the nanoscale heterostructure around an Al20Mn3Cu2 dispersoid in aluminum alloy 2024.

    PubMed

    Parvizi, Reza; Marceau, Ross K W; Hughes, Anthony E; Tan, Mike Y; Forsyth, Maria

    2014-12-16

    Atom probe tomography (APT) has been used to investigate the surface and sub-surface microstructures of aluminum alloy 2024 (AA2024) in the T3 condition (solution heat treated, cold worked, and naturally aged to a substantially stable condition). This study revealed surface Cu enrichment on the alloy matrix, local chemical structure around a dispersoid Al20Mn3Cu2 particle including a Cu-rich particle and S-phase particle on its external surface. Moreover, there was a significant level of hydrogen within the dispersoid, indicating that it is a hydrogen sink. These observations of the nanoscale structure around the dispersoid particle have considerable implications for understanding both corrosion and hydrogen embrittlement in high-strength aluminum alloys. PMID:25415412

  11. Atom Probe Tomographic Mapping Directly Reveals the Atomic Distribution of Phosphorus in Resin Embedded Ferritin

    PubMed Central

    Perea, Daniel E.; Liu, Jia; Bartrand, Jonah; Dicken, Quinten; Thevuthasan, S. Theva; Browning, Nigel D.; Evans, James E.

    2016-01-01

    Here we report the atomic-scale analysis of biological interfaces within the ferritin protein using atom probe tomography that is facilitated by an advanced specimen preparation approach. Embedding ferritin in an organic polymer resin lacking nitrogen provided chemical contrast to visualise atomic distributions and distinguish the inorganic-organic interface of the ferrihydrite mineral core and protein shell, as well as the organic-organic interface between the ferritin protein shell and embedding resin. In addition, we definitively show the atomic-scale distribution of phosphorus as being at the surface of the ferrihydrite mineral with the distribution of sodium mapped within the protein shell environment with an enhanced distribution at the mineral/protein interface. The sample preparation method is robust and can be directly extended to further enhance the study of biological, organic and inorganic nanomaterials relevant to health, energy or the environment. PMID:26924804

  12. An Atom-Probe Tomographic Study of Arc Welds in a Multi-Component High-Strength Low-Alloy Steel

    NASA Astrophysics Data System (ADS)

    Hunter, Allen H.; Farren, Jeffrey D.; DuPont, John N.; Seidman, David N.

    2013-04-01

    An experimental plate steel with the composition Fe-1.39Cu-2.7Ni-0.58Al-0.48Mn-0.48Si-0.065Nb-0.05C (wt pct) or alternatively Fe-1.43Cu-2.61Ni-1.21Al-0.48Mn-0.98Si-0.039Nb-0.23C at. pct has been recently produced at Northwestern University for use in Naval hull and deck applications—it is designated NUCu-140. To understand the microstructural changes occurring in NUCu-140 steel after gas-metal arc welding (GMAW), a detailed study of the heat-affected and fusion zones was performed throughout the weld cross section using microhardness, metallographic, chemical, and atom-probe tomographic analyses. Local-electrode atom-probe (LEAP) tomography was employed to measure the morphology and compositions of Cu-rich precipitates from each region. The mean radius, number density, volume fraction, and compositions of the precipitates, as well as the interfacial concentration profiles, are measured. The Cu precipitates dissolve partially from the heat-affected zone (HAZ) thermal cycle, and freshly formed sub-nanometer radius Cu-rich precipitates nucleate in both the HAZ and fusion zone (FZ) during cooling; however, the precipitation of Cu during cooling in the HAZ and FZ is not sufficient to restore the lost strength. The precipitation in the FZ is reduced compared to the HAZ due to a mismatched Cu composition of the weld. Multi-pass welding is suggested to restore strength in the GMAW sample by promoting Cu precipitate nucleation and growth in the HAZ and FZ.

  13. Atom Probe Tomography Study of Multi-microalloyed Carbide and Carbo-Nitride Precipitates and the Precipitation Sequence in Nb-Ti HSLA Steels

    NASA Astrophysics Data System (ADS)

    Kapoor, Monica; O'Malley, Ronald; Thompson, Gregory B.

    2016-05-01

    Composition analysis of carbide and carbo-nitride precipitates was performed for two Nb-Ti microalloyed steels with yield strengths of 750 and 580 MPa using an atom probe study. In the high-Ti 750 MPa steel, Ti-rich (Ti,Nb)(C,N) and Ti-rich (Ti,Nb)(C) precipitates were observed. In the high-Nb 580 MPa steel, a Ti-rich (Ti,Nb)(C,N) precipitate and (Ti,Nb)(C) clusters were noted. These (Ti,Nb)(C) clusters in the high-Nb 580 MPa steel were smaller than the (Ti,Nb)(C) precipitates in high-Ti 750 MPa steel. In general, a larger number of precipitates were found in the high-Ti 750 MPa steel. This difference in the number density of the precipitates between the two steels is attributed to the difference in Ti content. Combining the atom probe tomography results and thermodynamic calculations, the precipitation sequence in these alloys was inferred to be the following: as the temperature decreases, TiN precipitates out of the solution with successive (Ti,Nb)(C,N) layers of varying composition forming on these Ti-rich precipitates. Once N is depleted from the solution, a second set of (Ti,Nb)(C) precipitates in a similar manner in the matrix and also onto the carbo-nitride phase. This observation is consistent with previous observations in high-strength low-alloy steels containing comparable amounts of only Nb. It was noted that the amount of Nb, Nb/(Nb + Ti), in the precipitates decreased from 0.20 to 0.04 with the size of the precipitate. We believe that this is due to the Nb supersaturation in the matrix when these precipitates nucleate.

  14. Atom chip microscopy: A novel probe for strongly correlated materials

    SciTech Connect

    Lev, Benjamin L

    2011-11-03

    Improved measurements of strongly correlated systems will enable the predicative design of the next generation of supermaterials. In this program, we are harnessing recent advances in the quantum manipulation of ultracold atomic gases to expand our ability to probe these technologically important materials in heretofore unexplored regions of temperature, resolution, and sensitivity parameter space. We are working to demonstrate the use of atom chips to enable single-shot, large area detection of magnetic flux at the 10^-7 flux quantum level and below. By harnessing the extreme sensitivity of atomic clocks and Bose-Einstein condensates (BECs) to external perturbations, the cryogenic atom chip technology developed here will provide a magnetic flux detection capability that surpasses other techniques---such as scanning SQUIDs---by a factor of 10--1000. We are testing the utility of this technique by using rubidium BECs to image the magnetic fields emanating from charge transport and magnetic domain percolation in strongly correlated materials as they undergo temperature-tuned metal--to--insulator phase transitions. Cryogenic atom chip microscopy introduces three very important features to the toolbox of high-resolution, strongly correlated material microscopy: simultaneous detection of magnetic and electric fields (down to the sub-single electron charge level); no invasive large magnetic fields or gradients; simultaneous micro- and macroscopic spatial resolution; freedom from 1/f flicker noise at low frequencies; and, perhaps most importantly, the complete decoupling of probe and sample temperatures. The first of these features will play an important role in studying the interplay between magnetic and electric domain structure. The last two are crucial for low frequency magnetic noise detection in, e.g., the cuprate pseudogap region and for precision measurements of transport in the high temperature, technologically relevant regime inaccessible to other techniques

  15. Clustered field evaporation of metallic glasses in atom probe tomography.

    PubMed

    Zemp, J; Gerstl, S S A; Löffler, J F; Schönfeld, B

    2016-03-01

    Field evaporation of metallic glasses is a stochastic process combined with spatially and temporally correlated events, which are referred to as clustered evaporation (CE). This phenomenon is investigated by studying the distance between consecutive detector hits. CE is found to be a strongly localized phenomenon (up to 3nm in range) which also depends on the type of evaporating ions. While a similar effect in crystals is attributed to the evaporation of crystalline layers, CE of metallic glasses presumably has a different - as yet unknown - physical origin. The present work provides new perspectives on quantification methods for atom probe tomography of metallic glasses. PMID:26724469

  16. He-diamond interaction probed by atom beam scattering

    NASA Astrophysics Data System (ADS)

    Vidali, G.; Frankl, D. R.

    1983-02-01

    A 4He atomic beam was used to probe the He-C (diamond) interaction. Selective adsorption features have been measured and three energy levels identified: 6.4, 3.0, and 1.1 meV with a standard deviation of 0.1 meV. Diffraction patterns showed weak diffraction up to the second order; a corrugation parameter of 0.021 Å was obtained with the use of a hard-wall model in the eikonal approximation. An extensive study of surface preparation was carried out and the results of 4He diffraction for different methods of surface cleaning are reported.

  17. Metastable atom probe for measuring electron beam density profiles

    NASA Technical Reports Server (NTRS)

    Lockhart, J. M.; Zorn, J. C.

    1972-01-01

    Metastable atom probe was developed for measuring current density in electron beam as function of two arbitrary coordinates, with spatial resolution better than 0.5 mm. Probe shows effects of space charge, magnetic fields, and other factors which influence electron current density, but operates with such low beam densities that introduced perturbation is very small.

  18. First data from a commercial local electrode atom probe (LEAP).

    PubMed

    Kelly, Thomas F; Gribb, Tye T; Olson, Jesse D; Martens, Richard L; Shepard, Jeffrey D; Wiener, Scott A; Kunicki, Thomas C; Ulfig, Robert M; Lenz, Daniel R; Strennen, Eric M; Oltman, Edward; Bunton, Joseph H; Strait, David R

    2004-06-01

    The first dedicated local electrode atom probes (LEAP [a trademark of Imago Scientific Instruments Corporation]) have been built and tested as commercial prototypes. Several key performance parameters have been markedly improved relative to conventional three-dimensional atom probe (3DAP) designs. The Imago LEAP can operate at a sustained data collection rate of 1 million atoms/minute. This is some 600 times faster than the next fastest atom probe and large images can be collected in less than 1 h that otherwise would take many days. The field of view of the Imago LEAP is about 40 times larger than conventional 3DAPs. This makes it possible to analyze regions that are about 100 nm diameter by 100 nm deep containing on the order of 50 to 100 million atoms with this instrument. Several example applications that illustrate the advantages of the LEAP for materials analysis are presented. PMID:15233856

  19. Neuron Biomechanics Probed by Atomic Force Microscopy

    PubMed Central

    Spedden, Elise; Staii, Cristian

    2013-01-01

    Mechanical interactions play a key role in many processes associated with neuronal growth and development. Over the last few years there has been significant progress in our understanding of the role played by the substrate stiffness in neuronal growth, of the cell-substrate adhesion forces, of the generation of traction forces during axonal elongation, and of the relationships between the neuron soma elastic properties and its health. The particular capabilities of the Atomic Force Microscope (AFM), such as high spatial resolution, high degree of control over the magnitude and orientation of the applied forces, minimal sample damage, and the ability to image and interact with cells in physiologically relevant conditions make this technique particularly suitable for measuring mechanical properties of living neuronal cells. This article reviews recent advances on using the AFM for studying neuronal biomechanics, provides an overview about the state-of-the-art measurements, and suggests directions for future applications. PMID:23921683

  20. Neuron biomechanics probed by atomic force microscopy.

    PubMed

    Spedden, Elise; Staii, Cristian

    2013-01-01

    Mechanical interactions play a key role in many processes associated with neuronal growth and development. Over the last few years there has been significant progress in our understanding of the role played by the substrate stiffness in neuronal growth, of the cell-substrate adhesion forces, of the generation of traction forces during axonal elongation, and of the relationships between the neuron soma elastic properties and its health. The particular capabilities of the Atomic Force Microscope (AFM), such as high spatial resolution, high degree of control over the magnitude and orientation of the applied forces, minimal sample damage, and the ability to image and interact with cells in physiologically relevant conditions make this technique particularly suitable for measuring mechanical properties of living neuronal cells. This article reviews recent advances on using the AFM for studying neuronal biomechanics, provides an overview about the state-of-the-art measurements, and suggests directions for future applications. PMID:23921683

  1. Dopant Diffusion and Activation in Silicon Nanowires Fabricated by ex Situ Doping: A Correlative Study via Atom-Probe Tomography and Scanning Tunneling Spectroscopy.

    PubMed

    Sun, Zhiyuan; Hazut, Ori; Huang, Bo-Chao; Chiu, Ya-Ping; Chang, Chia-Seng; Yerushalmi, Roie; Lauhon, Lincoln J; Seidman, David N

    2016-07-13

    Dopants play a critical role in modulating the electric properties of semiconducting materials, ranging from bulk to nanoscale semiconductors, nanowires, and quantum dots. The application of traditional doping methods developed for bulk materials involves additional considerations for nanoscale semiconductors because of the influence of surfaces and stochastic fluctuations, which may become significant at the nanometer-scale level. Monolayer doping is an ex situ doping method that permits the post growth doping of nanowires. Herein, using atom-probe tomography (APT) with subnanometer spatial resolution and atomic-ppm detection limit, we study the distributions of boron and phosphorus in ex situ doped silicon nanowires with accurate control. A highly phosphorus doped outer region and a uniformly boron doped interior are observed, which are not predicted by criteria based on bulk silicon. These phenomena are explained by fast interfacial diffusion of phosphorus and enhanced bulk diffusion of boron, respectively. The APT results are compared with scanning tunneling spectroscopy data, which yields information concerning the electrically active dopants. Overall, comparing the information obtained by the two methods permits us to evaluate the diffusivities of each different dopant type at the nanowire oxide, interface, and core regions. The combined data sets permit us to evaluate the electrical activation and compensation of the dopants in different regions of the nanowires and understand the details that lead to the sharp p-i-n junctions formed across the nanowire for the ex situ doping process. PMID:27351447

  2. Atom probe tomography study of internal interfaces in Cu{sub 2}ZnSnSe{sub 4} thin-films

    SciTech Connect

    Schwarz, T. Cojocaru-Mirédin, O.; Choi, P. Raabe, D.; Mousel, M.; Redinger, A.; Siebentritt, S.

    2015-09-07

    We report on atom probe tomography studies of the composition at internal interfaces in Cu{sub 2}ZnSnSe{sub 4} thin-films. For Cu{sub 2}ZnSnSe{sub 4} precursors, which are deposited at 320 °C under Zn-rich conditions, grain boundaries are found to be enriched with Cu irrespective of whether Cu-poor or Cu-rich growth conditions are chosen. Cu{sub 2}ZnSnSe{sub 4} grains are found to be Cu-poor and excess Cu atoms are found to be accumulated at grain boundaries. In addition, nanometer-sized ZnSe grains are detected at or near grain boundaries. The compositions at grain boundaries show different trends after annealing at 500 °C. Grain boundaries in the annealed absorber films, which are free of impurities, are Cu-, Sn-, and Se-depleted and Zn-enriched. This is attributed to dissolution of ZnSe at the Cu-enriched grain boundaries during annealing. Furthermore, some of the grain boundaries of the absorbers are enriched with Na and K atoms, stemming from the soda-lime glass substrate. Such grain boundaries show no or only small changes in composition of the matrix elements. Na and K impurities are also partly segregated at some of the Cu{sub 2}ZnSnSe{sub 4}/ZnSe interfaces in the absorber, whereas for the precursors, only Na was detected at such phase boundaries possibly due to a higher diffusivity of Na compared to K. Possible effects of the detected compositional fluctuations on cell performance are discussed.

  3. Atom probe tomography of a commercial light emitting diode

    NASA Astrophysics Data System (ADS)

    Larson, D. J.; Prosa, T. J.; Olson, D.; Lefebvre, W.; Lawrence, D.; Clifton, P. H.; Kelly, T. F.

    2013-11-01

    The atomic-scale analysis of a commercial light emitting diode device purchased at retail is demonstrated using a local electrode atom probe. Some of the features are correlated with transmission electron microscopy imaging. Subtle details of the structure that are revealed have potential significance for the design and performance of this device.

  4. Atom-probe and field emission electron spectroscopy studies of ordered structures and electronic properties of Ge overlayers on Ir-tips

    NASA Astrophysics Data System (ADS)

    Ashino, Makoto; Tomitori, Masahiko; Nishikawa, Osamu

    1994-03-01

    The combined instrument of an atom probe (AP) and a field emission electron spectroscope (FEES) was employed to investigate the crystallinity and the surface electronic state of Ge overlayers deposited on Ir tips. The crystallinity of Ge overlayers deposited at 300 and 420 K, and those annealed after the deposition, is better than that of the overlayers deposited at 50 K. The surface electronic state of the well-crystallized Ge overlayer is semiconductive at the thickness of ≈4 ML. When the degree of crystallinity is rather low or Ir atoms exist in the Ge overlayer, even a thick overlayer exhibits metallic surface electronic states. When an Ir atom exists on the overlayer surface, a small peak appears at ≈ 0.3 eV below the Fermi level in the field emission electron distribution (FEED), indicating a local state of the Ir atom.

  5. Quantum metrology with a scanning probe atom interferometer.

    PubMed

    Ockeloen, Caspar F; Schmied, Roman; Riedel, Max F; Treutlein, Philipp

    2013-10-01

    We use a small Bose-Einstein condensate on an atom chip as an interferometric scanning probe to map out a microwave field near the chip surface with a few micrometers resolution. With the use of entanglement between the atoms, our interferometer overcomes the standard quantum limit of interferometry by 4 dB and maintains enhanced performance for interrogation times up to 10 ms. This corresponds to a microwave magnetic field sensitivity of 77 pT/√Hz in a probe volume of 20 μm(3). Quantum metrology with entangled atoms is useful in measurements with high spatial resolution, since the atom number in the probe volume is limited by collisional loss. High-resolution measurements of microwave near fields, as demonstrated here, are important for the development of integrated microwave circuits for quantum information processing and applications in communication technology. PMID:24138235

  6. Probing dark energy with atom interferometry

    NASA Astrophysics Data System (ADS)

    Burrage, Clare; Copeland, Edmund J.; Hinds, E. A.

    2015-03-01

    Theories of dark energy require a screening mechanism to explain why the associated scalar fields do not mediate observable long range fifth forces. The archetype of this is the chameleon field. Here we show that individual atoms are too small to screen the chameleon field inside a large high-vacuum chamber, and therefore can detect the field with high sensitivity. We derive new limits on the chameleon parameters from existing experiments, and show that most of the remaining chameleon parameter space is readily accessible using atom interferometry.

  7. Nanoscale phase separation in epitaxial Cr-Mo and Cr-V alloy thin films studied using atom probe tomography: Comparison of experiments and simulation

    SciTech Connect

    Devaraj, A.; Ramanan, S.; Walvekar, S.; Bowden, M. E.; Shutthanandan, V.; Kaspar, T. C.; Kurtz, R. J.

    2014-11-21

    Tailored metal alloy thin film-oxide interfaces generated using molecular beam epitaxy (MBE) deposition of alloy thin films on a single crystalline oxide substrate can be used for detailed studies of irradiation damage response on the interface structure. However, the presence of nanoscale phase separation in the MBE grown alloy thin films can impact the metal-oxide interface structure. Due to nanoscale domain size of such phase separation, it is very challenging to characterize by conventional techniques. Therefore, laser assisted atom probe tomography (APT) was utilized to study the phase separation in epitaxial Cr{sub 0.61}Mo{sub 0.39}, Cr{sub 0.77}Mo{sub 0.23}, and Cr{sub 0.32}V{sub 0.68} alloy thin films grown by MBE on MgO(001) single crystal substrates. Statistical analysis, namely frequency distribution analysis and Pearson coefficient analysis of experimental data was compared with similar analyses conducted on simulated APT datasets with known extent of phase separation. Thus, the presence of phase separation in Cr-Mo films, even when phase separation was not clearly observed by x-ray diffraction, and the absence of phase separation in the Cr-V film were confirmed.

  8. Nanoscale Phase Separation In Epitaxial Cr-Mo and Cr-V Alloy Thin Films Studied Using Atom Probe Tomography. Comparison Of Experiments And Simulation

    SciTech Connect

    Devaraj, Arun; Kaspar, Tiffany C.; Ramanan, Sathvik; Walvekar, Sarita K.; Bowden, Mark E.; Shutthanandan, V.; Kurtz, Richard J.

    2014-11-21

    Tailored metal alloy thin film-oxide interfaces generated using molecular beam epitaxial (MBE) deposition of alloy thin films on a single crystalline oxide substrate can be used for detailed studies of irradiation damage response on the interface structure. However presence of nanoscale phase separation in the MBE grown alloy thin films can impact the metal-oxide interface structure. Due to nanoscale domain size of such phase separation it is very challenging to characterize by conventional techniques. Therefor laser assisted atom probe tomography (APT) was utilized to study the phase separation in epitaxial Cr0.61Mo0.39, Cr0.77Mo0.23, and Cr0.32V0.68 alloy thin films grown by MBE on MgO(001) single crystal substrates. Statistical analysis, namely frequency distribution analysis and Pearson coefficient analysis of experimental data was compared with similar analyses conducted on simulated APT datasets with known extent of phase separation. Thus the presence of phase separation in Cr-Mo films, even when phase separation was not clearly observed by x-ray diffraction, and the absence of phase separation in the Cr-V film were thus confirmed.

  9. Solid-state electrochemistry on the nanometer and atomic scales: the scanning probe microscopy approach.

    PubMed

    Strelcov, Evgheni; Yang, Sang Mo; Jesse, Stephen; Balke, Nina; Vasudevan, Rama K; Kalinin, Sergei V

    2016-08-01

    Energy technologies of the 21(st) century require an understanding and precise control over ion transport and electrochemistry at all length scales - from single atoms to macroscopic devices. This short review provides a summary of recent studies dedicated to methods of advanced scanning probe microscopy for probing electrochemical transformations in solids at the meso-, nano- and atomic scales. The discussion presents the advantages and limitations of several techniques and a wealth of examples highlighting peculiarities of nanoscale electrochemistry. PMID:27146961

  10. Solid-state electrochemistry on the nanometer and atomic scales: the scanning probe microscopy approach

    DOE PAGESBeta

    Strelcov, Evgheni; Yang, Sang Mo; Jesse, Stephen; Balke, Nina; Vasudevan, Rama K.; Kalinin, Sergei V.

    2016-04-21

    Energy technologies of the 21st century require an understanding and precise control over ion transport and electrochemistry at all length scales – from single atoms to macroscopic devices. Our short review provides a summary of recent studies dedicated to methods of advanced scanning probe microscopy for probing electrochemical transformations in solids at the meso-, nano- and atomic scales. In this discussion we present the advantages and limitations of several techniques and a wealth of examples highlighting peculiarities of nanoscale electrochemistry.

  11. Solid-state electrochemistry on the nanometer and atomic scales: the scanning probe microscopy approach

    NASA Astrophysics Data System (ADS)

    Strelcov, Evgheni; Yang, Sang Mo; Jesse, Stephen; Balke, Nina; Vasudevan, Rama K.; Kalinin, Sergei V.

    2016-07-01

    Energy technologies of the 21st century require an understanding and precise control over ion transport and electrochemistry at all length scales - from single atoms to macroscopic devices. This short review provides a summary of recent studies dedicated to methods of advanced scanning probe microscopy for probing electrochemical transformations in solids at the meso-, nano- and atomic scales. The discussion presents the advantages and limitations of several techniques and a wealth of examples highlighting peculiarities of nanoscale electrochemistry.

  12. Quantum metrology to probe atomic parity nonconservation

    SciTech Connect

    Mandal, P.; Mukherjee, M.

    2010-11-15

    An entangled state prepared in a decoherence-free subspace, together with a Ramsey-type measurement, can probe parity violation in heavy alkali-metal ions such as Ba{sup +} or Ra{sup +}. Here we propose an experiment with Ba{sup +} as an example to measure the small parity-violating effect in this system. It has been shown that a measurement on a maximally correlated system will reduce the uncertainty as compared to that on a single ion measurement, and also provides a feasible solution to measure the nuclear-spin-dependent part of the total parity-violating light shift in an ionic system.

  13. Detecting magnetic ordering with atomic size electron probes

    DOE PAGESBeta

    Idrobo, Juan Carlos; Rusz, Ján; Spiegelberg, Jakob; McGuire, Michael A.; Symons, Christopher T.; Vatsavai, Ranga Raju; Cantoni, Claudia; Lupini, Andrew R.

    2016-05-27

    While magnetism originates at the atomic scale, the existing spectroscopic techniques sensitive to magnetic signals only produce spectra with spatial resolution on a larger scale. However, recently, it has been theoretically argued that atomic size electron probes with customized phase distributions can detect magnetic circular dichroism. Here, we report a direct experimental real-space detection of magnetic circular dichroism in aberration-corrected scanning transmission electron microscopy (STEM). Using an atomic size-aberrated electron probe with a customized phase distribution, we reveal the checkerboard antiferromagnetic ordering of Mn moments in LaMnAsO by observing a dichroic signal in the Mn L-edge. The novel experimental setupmore » presented here, which can easily be implemented in aberration-corrected STEM, opens new paths for probing dichroic signals in materials with unprecedented spatial resolution.« less

  14. Laser-induced reversion of δ' precipitates in an Al-Li alloy: Study on temperature rise in pulsed laser atom probe.

    PubMed

    Khushaim, Muna; Gemma, Ryota; Al-Kassab, Talaat

    2016-08-01

    The influence of tuning the laser pulse energy during the analyses on the resulting microstructure in a specimen utilizing an ultra-fast laser assisted atom probe was demonstrated by a case study of a binary Al-Li alloy. The decomposition parameters, such as the size, number density, volume fraction, and composition of δ' precipitates, were carefully monitored after each analysis. A simple model was employed to estimate the corresponding specimen temperature for each value of the laser energy. The results indicated that the corresponding temperatures for the laser pulse energy in the range of 10 to 80 pJ are located inside the miscibility gap of the binary Al-Li phase diagram and fall into the metastable equilibrium field. In addition, the corresponding temperature for a laser pulse energy of 100 pJ was in fairly good agreement with reported range of  δ' solvus temperature, suggesting a result of reversion upon heating due to laser pulsing. Microsc. Res. Tech. 79:727-737, 2016. © 2016 Wiley Periodicals, Inc. PMID:27297621

  15. Imaging and force probing RNA by atomic force microscopy.

    PubMed

    Schön, Peter

    2016-07-01

    In the past 30years, the atomic force microscope (AFM) has become a true enabling platform in the life sciences opening entire novel avenues for structural and dynamic studies of biological systems. It enables visualization, probing and manipulation across the length scales, from single molecules to living cells in buffer solution under physiological conditions without the need for labeling or staining of the specimen. In particular, for structural studies of nucleic acids and assemblies thereof, the AFM has matured into a routinely used tool providing nanometer spatial resolution. This includes ssRNA, dsRNA and nucleoprotein complexes thereof, as well as RNA aggregates and 2D RNA assemblies. By AFM unique information can be obtained on RNA based assemblies which are becoming increasingly important as novel unique building blocks in the emerging field of RNA nanotechnology. In addition, the AFM is of fundamental relevance to study biological relevant RNA interactions and dynamics. In this short review first the basic functioning principles of commonly used AFM modes including AFM based force spectroscopy will be briefly described. Next a brief overview will be given on structural studies that have been done related to AFM topographic imaging of RNA, RNA assemblies and aggregates. Finally, an overview on AFM beyond imaging will be provided. This includes force spectroscopy of RNA under physiological conditions in aqueous buffer to probe RNA interaction with proteins and ligands as well as other AFM tip based RNA probing. The main intention of this short review to give the reader a flavor of what AFM contributes to RNA research and engineering. PMID:27222101

  16. Multiple dispersed phases in a high-strength low-carbon steel: An atom-probe tomographic and synchrotron X-ray diffraction study

    SciTech Connect

    Mulholland, Michael D.; Seidman, David N.

    2009-06-12

    The co-precipitation of Cu, M{sub 2}C (where M is any combination of Cr, Mo or Ti) and austenite (face-centered cubic) is characterized for 5 h isochronal aging times by synchrotron X-ray diffraction and three-dimensional atom-probe tomography for a high-strength low-carbon steel, BlastAlloy 160. High number densities, {approx}10{sup 23} m{sup 03}, of co-located Cu and M{sub 2}C preciptates were observed. Only small austenite volume percentages (<2.1%) were measured after aging at temperatures up to 625 C for 5 h.

  17. Atom-probe for FinFET dopant characterization.

    PubMed

    Kambham, A K; Mody, J; Gilbert, M; Koelling, S; Vandervorst, W

    2011-05-01

    With the continuous shrinking of transistors and advent of new transistor architectures to keep in pace with Moore's law and ITRS goals, there is a rising interest in multigate 3D-devices like FinFETs where the channel is surrounded by gates on multiple surfaces. The performance of these devices depends on the dimensions and the spatial distribution of dopants in source/drain regions of the device. As a result there is a need for new metrology approach/technique to characterize quantitatively the dopant distribution in these devices with nanometer precision in 3D. In recent years, atom probe tomography (APT) has shown its ability to analyze semiconductor and thin insulator materials effectively with sub-nm resolution in 3D. In this paper we will discuss the methodology used to study FinFET-based structures using APT. Whereas challenges and solutions for sample preparation linked to the limited fin dimensions already have been reported before, we report here an approach to prepare fin structures for APT, which based on their processing history (trenches filled with Si) are in principle invisible in FIB and SEM. Hence alternative solutions in locating and positioning them on the APT-tip are presented. We also report on the use of the atom probe results on FinFETs to understand the role of different dopant implantation angles (10° and 45°) when attempting conformal doping of FinFETs and provide a quantitative comparison with alternative approaches such as 1D secondary ion mass spectrometry (SIMS) and theoretical model values. PMID:21288644

  18. New approaches to nanoparticle sample fabrication for atom probe tomography.

    PubMed

    Felfer, P; Li, T; Eder, K; Galinski, H; Magyar, A P; Bell, D C; Smith, G D W; Kruse, N; Ringer, S P; Cairney, J M

    2015-12-01

    Due to their unique properties, nano-sized materials such as nanoparticles and nanowires are receiving considerable attention. However, little data is available about their chemical makeup at the atomic scale, especially in three dimensions (3D). Atom probe tomography is able to answer many important questions about these materials if the challenge of producing a suitable sample can be overcome. In order to achieve this, the nanomaterial needs to be positioned within the end of a tip and fixed there so the sample possesses sufficient structural integrity for analysis. Here we provide a detailed description of various techniques that have been used to position nanoparticles on substrates for atom probe analysis. In some of the approaches, this is combined with deposition techniques to incorporate the particles into a solid matrix, and focused ion beam processing is then used to fabricate atom probe samples from this composite. Using these approaches, data has been achieved from 10-20 nm core-shell nanoparticles that were extracted directly from suspension (i.e. with no chemical modification) with a resolution of better than ± 1 nm. PMID:25980894

  19. Impact of carbon co-implantation on boron distribution and activation in silicon studied by atom probe tomography and spreading resistance measurements

    NASA Astrophysics Data System (ADS)

    Shimizu, Yasuo; Takamizawa, Hisashi; Inoue, Koji; Yano, Fumiko; Kudo, Shuichi; Nishida, Akio; Toyama, Takeshi; Nagai, Yasuyoshi

    2016-02-01

    The impact of carbon (C) co-implantation on boron (B) activation in crystalline silicon was investigated. The detailed distribution of B and C atoms and B activation ratios dependent on the C ion-implantation energies were examined based on three-dimensional spatial mappings of B and C obtained by atom probe tomography and from depth profiles of their concentrations from secondary ion mass spectrometry and depth profiles of carrier concentrations with spreading resistance measurements. At all C implantation energies (8, 15, and 30 keV), B out-diffusion during activation annealing was reduced, so that more B atoms were observed in the C co-implanted samples. The carrier concentration was decreased throughout the entire implanted region for C implantation energies of 15 and 30 keV, although it was only increased at greater depths for C co-implantation at 8 keV. Two different effects of C co-implantation, (I) reduction of B out-diffusion and (II) influence of B activation, were confirmed.

  20. Probing the atomic structure of basaltic melts generated by partial melting of upper mantle peridotite (KLB-1): Insights from high-resolution solid-state NMR study

    NASA Astrophysics Data System (ADS)

    Park, S. Y.; Lee, S. K.

    2015-12-01

    Probing the structural disorder in multi-component silicate glasses and melts with varying composition is essential to reveal the change of macroscopic properties in natural silicate melts. While a number of NMR studies for the structure of multi-component silicate glasses and melts including basaltic and andesitic glasses have been reported (e.g., Park and Lee, Geochim. Cosmochim. Acta, 2012, 80, 125; Park and Lee, Geochim. Cosmochim. Acta, 2014, 26, 42), many challenges still remain. The composition of multi-component basaltic melts vary with temperature, pressure, and melt fraction (Kushiro, Annu. Rev. Earth Planet. Sci., 2001, 71, 107). Especially, the eutectic point (the composition of first melt) of nepheline-forsterite-quartz (the simplest model of basaltic melts) moves with pressure from silica-saturated to highly undersaturated and alkaline melts. The composition of basaltic melts generated by partial melting of upper mantle peridotite (KLB-1, the xenolith from Kilbourne Hole) also vary with pressure. In this study we report experimental results for the effects of composition on the atomic structure of Na2O-MgO-Al2O3-SiO2 (NMAS) glasses in nepheline (NaAlSiO4)-forsterite (Mg2SiO4)-quartz (SiO2) eutectic composition and basaltic glasses generated by partial melting of upper mantle peridotite (KLB-1) using high-resolution multi-nuclear solid-state NMR. The Al-27 3QMAS (triple quantum magic angle spinning) NMR spectra of NMAS glasses in nepheline-forsterite-quartz eutectic composition show only [4]Al. The Al-27 3QMAS NMR spectra of KLB-1 basaltic glasses show mostly [4]Al and a non-negligible fraction of [5]Al. The fraction of [5]Al, the degree of configurational disorder, increases from 0 at XMgO [MgO/(MgO+Al2O3)]=0.55 to ~3% at XMgO=0.79 in KLB-1 basaltic glasses while only [4]Al are observed in nepheline-forsterite-quartz eutectic composition. The current experimental results provide that the fraction of [5]Al abruptly increases by the effect of

  1. Phase-partitioning and site-substitution patterns of molybdenum in a model Ni-Al-Mo superalloy: An atom-probe tomographic and first-principles study

    NASA Astrophysics Data System (ADS)

    Tu, Yiyou; Mao, Zugang; Seidman, David N.

    2012-09-01

    Atom-probe tomography (APT) and first-principles calculations are employed to investigate the partitioning of Mo in the γ(f.c.c.)-and γ'(L12)-phases in a model Ni-6.5Al-9.9Mo at. % superalloy. Mo is experimentally observed to partition preferentially to the γ(f.c.c.)-matrix, which is consistent with the smaller value of the γ(f.c.c.)-matrix substitutional formation-energy, with a driving force of 0.707 eV for partitioning as determined by first-principles calculations. APT measurements of the γ'(L12)-precipitate-phase composition and Al-, Mo-centered partial radial distribution functions indicate that Mo occupies the Al sublattice sites of the Ni3Al(L12) phase. The preferential site-substitution of Mo at Al sublattice sites is confirmed by first-principles calculations.

  2. Probing stem cell differentiation using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Liang, Xiaobin; Shi, Xuetao; Ostrovidov, Serge; Wu, Hongkai; Nakajima, Ken

    2016-03-01

    A real-time method using atomic force microscopy (AFM) was developed to probe stem cell differentiation by measuring the mechanical properties of cells and the extracellular matrix (ECM). The mechanical properties of stem cells and their ECMs can be used to clearly distinguish specific stem cell-differentiated lineages. It is clear that AFM is a facile and useful tool for monitoring the differentiation of stem cells in a non-invasive manner.

  3. Probing the improbable: imaging carbon atoms in alumina

    SciTech Connect

    Marquis, E A; Yahia, Noor; Larson, David J.; Miller, Michael K; Todd, Richard

    2010-01-01

    Atom-probe tomography has proven very powerful to analyze the detailed structure and chemistry of metallic alloys and semiconductor structures while ceramic materials have remained outside its standard purview. In the current work, we demonstrate that bulk alumina can be quantitatively analyzed and microstructural features observed. The analysis of grain boundary carbon segregation - barely achievable by electron microscopy - opens the possibility of understanding the mechanistic effects of dopants on mechanical properties, fracture and wear properties of bulk oxides.

  4. Free vibrations of U-shaped atomic force microscope probes

    NASA Astrophysics Data System (ADS)

    Rezaei, E.; Turner, J. A.

    2014-05-01

    Contact resonance atomic force microscope (AFM) methods have been used to quantify the elastic and viscoelastic properties of a variety of materials such as polymers, ceramics, biological materials, and metals with spatial resolution on the order of tens of nanometers. This approach involves measurement of the resonant frequencies of the AFM probe both for the free case and the case for which the tip is in contact with a sample. Vibration models of the probe and tip-sample contact models are then used to determine the sample properties from the frequency behavior and to create images of the sample properties. This work has been primarily focused on rectangular, single-beam probes for which the vibration models are relatively simple. Recently, U-shaped AFM probes have been developed to allow local heating of samples and the resonances of these probes are much more complex. In this article, a simplified analytical model of these U-shaped probes is described. This three beam model includes two beams clamped at one end and connected with a perpendicular cross beam at the other end. The beams are assumed only to bend in flexure and twist but their coupling allows a wide range of possible dynamic behavior. Results are presented for the first ten modes and the mode shapes are shown to have complex coupling between the flexure and twisting of the beams, particularly for the higher modes. All resonant frequency results are in good agreement with finite element results for the three probe designs and two values of thickness considered (all wavenumbers are within 3.0%). This work is anticipated to allow U-shaped probes to be used eventually for quantitative measurements of sample material properties during heating using a contact resonance approach.

  5. Probing Atomic Dynamics and Structures Using Optical Patterns

    NASA Astrophysics Data System (ADS)

    Schmittberger, Bonnie L.; Gauthier, Daniel J.

    2015-05-01

    Pattern formation is a widely studied phenomenon that can provide fundamental insights into nonlinear systems. Emergent patterns in cold atoms are of particular interest in condensed matter physics and quantum information science because one can relate optical patterns to spatial structures in the atoms. In our experimental system, we study multimode optical patterns generated from a sample of cold, thermal atoms. We observe this nonlinear optical phenomenon at record low input powers due to the highly nonlinear nature of the spatial bunching of atoms in an optical lattice. We present a detailed study of the dynamics of these bunched atoms during optical pattern formation. We show how small changes in the atomic density distribution affect the symmetry of the generated patterns as well as the nature of the nonlinearity that describes the light-atom interaction. We gratefully acknowledge the financial support of the National Science Foundation through Grant #PHY-1206040.

  6. Distributed force probe bending model of critical dimension atomic force microscopy bias

    NASA Astrophysics Data System (ADS)

    Ukraintsev, Vladimir A.; Orji, Ndubuisi G.; Vorburger, Theodore V.; Dixson, Ronald G.; Fu, Joseph; Silver, Rick M.

    2013-04-01

    Critical dimension atomic force microscopy (CD-AFM) is a widely used reference metrology technique. To characterize modern semiconductor devices, small and flexible probes, often 15 to 20 nm in diameter, are used. Recent studies have reported uncontrolled and significant probe-to-probe bias variation during linewidth and sidewall angle measurements. To understand the source of these variations, tip-sample interactions between high aspect ratio features and small flexible probes, and their influence on measurement bias, should be carefully studied. Using theoretical and experimental procedures, one-dimensional (1-D) and two-dimensional (2-D) models of cylindrical probe bending relevant to carbon nanotube (CNT) AFM probes were developed and tested. An earlier 1-D bending model was refined, and a new 2-D distributed force (DF) model was developed. Contributions from several factors were considered, including: probe misalignment, CNT tip apex diameter variation, probe bending before snapping, and distributed van der Waals-London force. A method for extracting Hamaker probe-surface interaction energy from experimental probe-bending data was developed. Comparison of the new 2-D model with 1-D single point force (SPF) model revealed a difference of about 28% in probe bending. A simple linear relation between biases predicted by the 1-D SPF and 2-D DF models was found. The results suggest that probe bending can be on the order of several nanometers and can partially explain the observed CD-AFM probe-to-probe variation. New 2-D and three-dimensional CD-AFM data analysis software is needed to take full advantage of the new bias correction modeling capabilities.

  7. Developing detection efficiency standards for atom probe tomography

    NASA Astrophysics Data System (ADS)

    Prosa, Ty J.; Geiser, Brian P.; Lawrence, Dan; Olson, David; Larson, David J.

    2014-08-01

    Atom Probe Tomography (APT) is a near-atomic-scale analytical technique which, due to recent advances in instrumentation and sample preparation techniques, is being used on a variety of 3D applications. Total system detection efficiency is a key parameter for obtaining accurate spatial reconstruction of atomic coordinates from detected ions, but experimental determination of efficiency can be difficult. This work explores new ways to measure total system detection efficiency as well as the specimen characteristics necessary for such measurements. Composite specimens composed of a nickel/chromium multilayer core, National Institute of Standards and Technology Standard Reference Material 2135c, encapsulated with silver, silicon, or nickel were used to demonstrate the suitability of this approach for providing a direct measurement of APT efficiency. Efficiency measurements based on this multilayer encapsulated in nickel are reported.

  8. Contact resonances of U-shaped atomic force microscope probes

    NASA Astrophysics Data System (ADS)

    Rezaei, E.; Turner, J. A.

    2016-01-01

    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-AFM 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.

  9. Probing electronic transport of individual nanostructures with atomic precision

    SciTech Connect

    Qin, Shengyong; Li, An-Ping

    2012-01-01

    Accessing individual nanostructures with atomic precision is an important process in the bottom-up fabrication and characterization of electronic nanodevices. Local electrical contacts, namely nanoelectrodes, are often fabricated by using top-down lithography and chemical etching techniques. These processes however lack atomic precision and introduce the possibility of contamination. Here, we review recent reports on the application of a field-induced emission process in the fabrication of local contacts onto individual nanowires and nanotubes with atomic spatial precision. In this method, gold nanoislands are deposited onto nanostructures precisely by using a scanning tunneling microscope tip, which provides a clean and controllable process to ensure both electrically conductive and mechanically reliable contacts. The applicability of the technique has been demonstrated in a wide variety of nanostructures, including silicide atomic wires, carbon nanotubes, and copper nanowires. These local contacts bridge the nanostructures and the transport probes, allowing for the measurements of both electrical transport and scanning tunneling microscopy on the same nanostructures in situ. The direct correlation between electronic and transport properties and atomic structures can be explored on individual nanostructures at the unprecedented atomic level.

  10. Laboratory plasma probe studies

    NASA Technical Reports Server (NTRS)

    Heikkila, W. J.

    1975-01-01

    Diagnostic experiments performed in a collisionless plasma using CO2 as the working gas are described. In particular, simultaneous measurements that have been performed by means of Langmuir- and RF-probes are presented. A resonance occurring above the parallel resonance in the frequency characteristic of a two electrode system is interpreted as being due to the resonant excitation of electroacoustic waves.

  11. Nanoscale Cluster Detection in Massive Atom Probe Tomography Data

    SciTech Connect

    Seal, Sudip K; Yoginath, Srikanth B; Miller, Michael K

    2014-01-01

    Recent technological advances in atom probe tomography (APT) have led to unprecedented data acquisition capabilities that routinely generate data sets containing hundreds of millions of atoms. Detecting nanoscale clusters of different atom types present in these enormous amounts of data and analyzing their spatial correlations with one another are fundamental to understanding the structural properties of the material from which the data is derived. Extant algorithms for nanoscale cluster detection do not scale to large data sets. Here, a scalable, CUDA-based implementation of an autocorrelation algorithm is presented. It isolates spatial correlations amongst atomic clusters present in massive APT data sets in linear time using a linear amount of storage. Correctness of the algorithm is demonstrated using large synthetically generated data with known spatial distributions. Benefits and limitations of using GPU-acceleration for autocorrelation-based APT data analyses are presented with supporting performance results on data sets with up to billions of atoms. To our knowledge, this is the first nanoscale cluster detection algorithm that scales to massive APT data sets and executes on commodity hardware.

  12. Design and optimization of a harmonic probe with step cross section in multifrequency atomic force microscopy.

    PubMed

    Cai, Jiandong; Wang, Michael Yu; Zhang, Li

    2015-12-01

    In multifrequency atomic force microscopy (AFM), probe's characteristic of assigning resonance frequencies to integer harmonics results in a remarkable improvement of detection sensitivity at specific harmonic components. The selection criterion of harmonic order is based on its amplitude's sensitivity on material properties, e.g., elasticity. Previous studies on designing harmonic probe are unable to provide a large design capability along with maintaining the structural integrity. Herein, we propose a harmonic probe with step cross section, in which it has variable width in top and bottom steps, while the middle step in cross section is kept constant. Higher order resonance frequencies are tailored to be integer times of fundamental resonance frequency. The probe design is implemented within a structural optimization framework. The optimally designed probe is micromachined using focused ion beam milling technique, and then measured with an AFM. The measurement results agree well with our resonance frequency assignment requirement. PMID:26724066

  13. Multifunctional hydrogel nano-probes for atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Lee, Jae Seol; Song, Jungki; Kim, Seong Oh; Kim, Seokbeom; Lee, Wooju; Jackman, Joshua A.; Kim, Dongchoul; Cho, Nam-Joon; Lee, Jungchul

    2016-05-01

    Since the invention of the atomic force microscope (AFM) three decades ago, there have been numerous advances in its measurement capabilities. Curiously, throughout these developments, the fundamental nature of the force-sensing probe--the key actuating element--has remained largely unchanged. It is produced by long-established microfabrication etching strategies and typically composed of silicon-based materials. Here, we report a new class of photopolymerizable hydrogel nano-probes that are produced by bottom-up fabrication with compressible replica moulding. The hydrogel probes demonstrate excellent capabilities for AFM imaging and force measurement applications while enabling programmable, multifunctional capabilities based on compositionally adjustable mechanical properties and facile encapsulation of various nanomaterials. Taken together, the simple, fast and affordable manufacturing route and multifunctional capabilities of hydrogel AFM nano-probes highlight the potential of soft matter mechanical transducers in nanotechnology applications. The fabrication scheme can also be readily utilized to prepare hydrogel cantilevers, including in parallel arrays, for nanomechanical sensor devices.

  14. Multifunctional hydrogel nano-probes for atomic force microscopy.

    PubMed

    Lee, Jae Seol; Song, Jungki; Kim, Seong Oh; Kim, Seokbeom; Lee, Wooju; Jackman, Joshua A; Kim, Dongchoul; Cho, Nam-Joon; Lee, Jungchul

    2016-01-01

    Since the invention of the atomic force microscope (AFM) three decades ago, there have been numerous advances in its measurement capabilities. Curiously, throughout these developments, the fundamental nature of the force-sensing probe-the key actuating element-has remained largely unchanged. It is produced by long-established microfabrication etching strategies and typically composed of silicon-based materials. Here, we report a new class of photopolymerizable hydrogel nano-probes that are produced by bottom-up fabrication with compressible replica moulding. The hydrogel probes demonstrate excellent capabilities for AFM imaging and force measurement applications while enabling programmable, multifunctional capabilities based on compositionally adjustable mechanical properties and facile encapsulation of various nanomaterials. Taken together, the simple, fast and affordable manufacturing route and multifunctional capabilities of hydrogel AFM nano-probes highlight the potential of soft matter mechanical transducers in nanotechnology applications. The fabrication scheme can also be readily utilized to prepare hydrogel cantilevers, including in parallel arrays, for nanomechanical sensor devices. PMID:27199165

  15. Atom probe study of the carbon distribution in a hardened martensitic hot-work tool steel X38CrMoV5-1.

    PubMed

    Lerchbacher, Christoph; Zinner, Silvia; Leitner, Harald

    2012-07-01

    The microstructure of the hardened common hot-work tool steel X38CrMoV5-1 has been characterized by atom probe tomography with the focus on the carbon distribution. Samples quenched with technically relevant cooling parameters λ from 0.1 (30 K/s) to 12 (0.25 K/s) have been investigated. The parameter λ is an industrially commonly used exponential cooling parameter, representing the cooling time from 800 to 500 °C in seconds divided with hundred. In all samples pronounced carbon segregation to dislocations and cluster formation could be observed after quenching. Carbon enriched interlath films with peak carbon levels of 6-10 at.%, which have been identified to be retained austenite by TEM, show a thickness increase with increasing λ. Therefore, the fraction of total carbon staying in the austenite grows. This carbon is not available for the tempering induced precipitation of secondary carbides in the bulk. Through all samples no segregation of any substitutional elements takes place. Charpy impact testing and fracture surface analysis of the hardened samples reveal the cooling rate induced microstructural distinctions. PMID:22391101

  16. ESA Venus Entry Probe Study

    NASA Technical Reports Server (NTRS)

    vandenBerg, M. L.; Falkner, P.; Phipps, A.; Underwood, J. C.; Lingard, J. S.; Moorhouse, J.; Kraft, S.; Peacock, A.

    2005-01-01

    The Venus Entry Probe is one of ESA s Technology Reference Studies (TRS). The purpose of the Technology Reference Studies is to provide a focus for the development of strategically important technologies that are of likely relevance for future scientific missions. The aim of the Venus Entry Probe TRS is to study approaches for low cost in-situ exploration of Venus and other planetary bodies with a significant atmosphere. In this paper, the mission objectives and an outline of the mission concept of the Venus Entry Probe TRS are presented.

  17. Towards an accurate volume reconstruction in atom probe tomography.

    PubMed

    Beinke, Daniel; Oberdorfer, Christian; Schmitz, Guido

    2016-06-01

    An alternative concept for the reconstruction of atom probe data is outlined. It is based on the calculation of realistic trajectories of the evaporated ions in a recursive refinement process. To this end, the electrostatic problem is solved on a Delaunay tessellation. To enable the trajectory calculation, the order of reconstruction is inverted with respect to previous reconstruction schemes: the last atom detected is reconstructed first. In this way, the emitter shape, which controls the trajectory, can be defined throughout the duration of the reconstruction. A proof of concept is presented for 3D model tips, containing spherical precipitates or embedded layers of strongly contrasting evaporation thresholds. While the traditional method following Bas et al. generates serious distortions in these cases, a reconstruction with the proposed electrostatically informed approach improves the geometry of layers and particles significantly. PMID:27062338

  18. A Superconducting Ion Detection Scheme for Atom Probe Tomography

    NASA Astrophysics Data System (ADS)

    Suttle, Joseph; Kelly, Thomas; McDermott, Robert

    Superconducting detectors are a promising avenue for improving the performance of Atom Probe Microscopes. Many types of superconducting detectors have been developed within the past several decades, each with its own strengths and weaknesses. Many of these detectors are inherently slow, bulky, require complex multiplexing schemes to attain position sensitivity, or require complex read-out electronics. In response to the rigorous demands of atom probe technology, and with the goal of developing an elegant, simple to use solution, we have developed a novel superconducting delay line detector. The principal of detection is to use the kinetic energy of incoming ions to generate excess quasiparticles in a superconducting stripline. These quasiparticles generate a measurable signal which propagates along the delay line. By measuring the timing of the output signals from this delay line, we are able to measure the time of flight for the ion and the position of its impact on the detector. We will be presenting on the performance of this detector as measured in a Field Ion Microscope.

  19. Multifunctional hydrogel nano-probes for atomic force microscopy

    PubMed Central

    Lee, Jae Seol; Song, Jungki; Kim, Seong Oh; Kim, Seokbeom; Lee, Wooju; Jackman, Joshua A.; Kim, Dongchoul; Cho, Nam-Joon; Lee, Jungchul

    2016-01-01

    Since the invention of the atomic force microscope (AFM) three decades ago, there have been numerous advances in its measurement capabilities. Curiously, throughout these developments, the fundamental nature of the force-sensing probe—the key actuating element—has remained largely unchanged. It is produced by long-established microfabrication etching strategies and typically composed of silicon-based materials. Here, we report a new class of photopolymerizable hydrogel nano-probes that are produced by bottom-up fabrication with compressible replica moulding. The hydrogel probes demonstrate excellent capabilities for AFM imaging and force measurement applications while enabling programmable, multifunctional capabilities based on compositionally adjustable mechanical properties and facile encapsulation of various nanomaterials. Taken together, the simple, fast and affordable manufacturing route and multifunctional capabilities of hydrogel AFM nano-probes highlight the potential of soft matter mechanical transducers in nanotechnology applications. The fabrication scheme can also be readily utilized to prepare hydrogel cantilevers, including in parallel arrays, for nanomechanical sensor devices. PMID:27199165

  20. Mapping magnetism with atomic resolution using aberrated electron probes

    NASA Astrophysics Data System (ADS)

    Idrobo, Juan; Rusz, Ján; McGuire, Michael A.; Symons, Christopher T.; Vatsavai, Ranga Raju; Lupini, Andrew R.

    2015-03-01

    In this talk, we report a direct experimental real-space mapping of magnetic circular dichroism with atomic resolution in aberration-corrected scanning transmission electron microscopy (STEM). Using an aberrated electron probe with customized phase distribution, we reveal with electron energy-loss (EEL) spectroscopy the checkerboard antiferromagnetic ordering of Mn moments in LaMnAsO by observing a dichroic signal in the Mn L-edge. The aberrated probes allow the collection of EEL spectra using the transmitted beam, which results in a magnetic circular dichroic signal with intrinsically larger signal-to-noise ratios than those obtained via nanodiffraction techniques (where most of the transmitted electrons are discarded). The novel experimental setup presented here, which can easily be implemented in aberration-corrected STEM, opens new paths for probing dichroic signals in materials with unprecedented spatial resolution. This research was supported by DOE SUFD MSED, by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the US DOE, and by the Swedish Research Council and Swedish National Infrastructure for Computing (NSC center)

  1. Probing modified gravity with atom-interferometry: A numerical approach

    NASA Astrophysics Data System (ADS)

    Schlögel, Sandrine; Clesse, Sébastien; Füzfa, André

    2016-05-01

    Refined constraints on chameleon theories are calculated for atom-interferometry experiments, using a numerical approach consisting in solving for a four-region model the static and spherically symmetric Klein-Gordon equation for the chameleon field. By modeling not only the test mass and the vacuum chamber but also its walls and the exterior environment, the method allows one to probe new effects on the scalar field profile and the induced acceleration of atoms. In the case of a weakly perturbing test mass, the effect of the wall is to enhance the field profile and to lower the acceleration inside the chamber by up to 1 order of magnitude. In the thin-shell regime, results are found to be in good agreement with the analytical estimations, when measurements are realized in the immediate vicinity of the test mass. Close to the vacuum chamber wall, the acceleration becomes negative and potentially measurable. This prediction could be used to discriminate between fifth-force effects and systematic experimental uncertainties, by doing the experiment at several key positions inside the vacuum chamber. For the chameleon potential V (ϕ )=Λ4 +α/ϕα and a coupling function A (ϕ )=exp (ϕ /M ), one finds M ≳7 ×1016 GeV , independently of the power-law index. For V (ϕ )=Λ4(1 +Λ /ϕ ), one finds M ≳1014 GeV . A sensitivity of a ˜10-11 m /s2 would probe the model up to the Planck scale. Finally, a proposal for a second experimental setup, in a vacuum room, is presented. In this case, Planckian values of M could be probed provided that a ˜10-10 m /s2 , a limit reachable by future experiments. Our method can easily be extended to constrain other models with a screening mechanism, such as symmetron, dilaton and f(R) theories.

  2. Soft-Landing Ion Deposition of Isolated Radioactive Probe Atoms on Surfaces: A Novel Method

    SciTech Connect

    Laurens, C.R.; Rosu, M.F.; Pleiter, F.; Niesen, L.

    1997-05-01

    We present a method to deposit a wide range of radioactive probe atoms on surfaces, without introducing lattice damage or contaminating the surface with other elements or isotopes. In this method, the probe atoms are mass separated using an isotope separator, decelerated to 5eV, and directly deposited on the surface. The method allows for performing hyperfine interactions experiments using trace amounts of radioactive probes located at surfaces and interfaces. The characteristics of the deposition method were studied by performing perturbed angular correlation experiments on the system In on Cu(17,1,1). The results are in agreement with molecular dynamics simulations of the deposition process. The potential of this novel technique is briefly discussed. {copyright} {ital 1997} {ital The American Physical Society}

  3. Design and optimization of a harmonic probe with step cross section in multifrequency atomic force microscopy

    SciTech Connect

    Cai, Jiandong; Zhang, Li; Wang, Michael Yu

    2015-12-15

    In multifrequency atomic force microscopy (AFM), probe’s characteristic of assigning resonance frequencies to integer harmonics results in a remarkable improvement of detection sensitivity at specific harmonic components. The selection criterion of harmonic order is based on its amplitude’s sensitivity on material properties, e.g., elasticity. Previous studies on designing harmonic probe are unable to provide a large design capability along with maintaining the structural integrity. Herein, we propose a harmonic probe with step cross section, in which it has variable width in top and bottom steps, while the middle step in cross section is kept constant. Higher order resonance frequencies are tailored to be integer times of fundamental resonance frequency. The probe design is implemented within a structural optimization framework. The optimally designed probe is micromachined using focused ion beam milling technique, and then measured with an AFM. The measurement results agree well with our resonance frequency assignment requirement.

  4. Multivariate statistical analysis of atom probe tomography data

    SciTech Connect

    Parish, Chad M; Miller, Michael K

    2010-01-01

    The application of spectrum imaging multivariate statistical analysis methods, specifically principal component analysis (PCA), to atom probe tomography (APT) data has been investigated. The mathematical method of analysis is described and the results for two example datasets are analyzed and presented. The first dataset is from the analysis of a PM 2000 Fe-Cr-Al-Ti steel containing two different ultrafine precipitate populations. PCA properly describes the matrix and precipitate phases in a simple and intuitive manner. A second APT example is from the analysis of an irradiated reactor pressure vessel steel. Fine, nm-scale Cu-enriched precipitates having a core-shell structure were identified and qualitatively described by PCA. Advantages, disadvantages, and future prospects for implementing these data analysis methodologies for APT datasets, particularly with regard to quantitative analysis, are also discussed.

  5. Multivariate statistical analysis of atom probe tomography data.

    PubMed

    Parish, Chad M; Miller, Michael K

    2010-10-01

    The application of spectrum imaging multivariate statistical analysis methods, specifically principal component analysis (PCA), to atom probe tomography (APT) data has been investigated. The mathematical method of analysis is described and the results for two example datasets are analyzed and presented. The first dataset is from the analysis of a PM 2000 Fe-Cr-Al-Ti steel containing two different ultrafine precipitate populations. PCA properly describes the matrix and precipitate phases in a simple and intuitive manner. A second APT example is from the analysis of an irradiated reactor pressure vessel steel. Fine, nm-scale Cu-enriched precipitates having a core-shell structure were identified and qualitatively described by PCA. Advantages, disadvantages, and future prospects for implementing these data analysis methodologies for APT datasets, particularly with regard to quantitative analysis, are also discussed. PMID:20650566

  6. Characterization of Nanoporous Materials with Atom Probe Tomography.

    PubMed

    Pfeiffer, Björn; Erichsen, Torben; Epler, Eike; Volkert, Cynthia A; Trompenaars, Piet; Nowak, Carsten

    2015-06-01

    A method to characterize open-cell nanoporous materials with atom probe tomography (APT) has been developed. For this, open-cell nanoporous gold with pore diameters of around 50 nm was used as a model system, and filled by electron beam-induced deposition (EBID) to obtain a compact material. Two different EBID precursors were successfully tested-dicobalt octacarbonyl [Co2(CO)8] and diiron nonacarbonyl [Fe2(CO)9]. Penetration and filling depth are sufficient for focused ion beam-based APT sample preparation. With this approach, stable APT analysis of the nanoporous material can be performed. Reconstruction reveals the composition of the deposited precursor and the nanoporous material, as well as chemical information of the interfaces between them. Thus, it is shown that, using an appropriate EBID process, local chemical information in three dimensions with sub-nanometer resolution can be obtained from nanoporous materials using APT. PMID:25990813

  7. Accuracy of analyses of microelectronics nanostructures in atom probe tomography

    NASA Astrophysics Data System (ADS)

    Vurpillot, F.; Rolland, N.; Estivill, R.; Duguay, S.; Blavette, D.

    2016-07-01

    The routine use of atom probe tomography (APT) as a nano-analysis microscope in the semiconductor industry requires the precise evaluation of the metrological parameters of this instrument (spatial accuracy, spatial precision, composition accuracy or composition precision). The spatial accuracy of this microscope is evaluated in this paper in the analysis of planar structures such as high-k metal gate stacks. It is shown both experimentally and theoretically that the in-depth accuracy of reconstructed APT images is perturbed when analyzing this structure composed of an oxide layer of high electrical permittivity (higher-k dielectric constant) that separates the metal gate and the semiconductor channel of a field emitter transistor. Large differences in the evaporation field between these layers (resulting from large differences in material properties) are the main sources of image distortions. An analytic model is used to interpret inaccuracy in the depth reconstruction of these devices in APT.

  8. Implementing Transmission Electron Backscatter Diffraction for Atom Probe Tomography.

    PubMed

    Rice, Katherine P; Chen, Yimeng; Prosa, Ty J; Larson, David J

    2016-06-01

    There are advantages to performing transmission electron backscattering diffraction (tEBSD) in conjunction with focused ion beam-based specimen preparation for atom probe tomography (APT). Although tEBSD allows users to identify the position and character of grain boundaries, which can then be combined with APT to provide full chemical and orientation characterization of grain boundaries, tEBSD can also provide imaging information that improves the APT specimen preparation process by insuring proper placement of the targeted grain boundary within an APT specimen. In this report we discuss sample tilt angles, ion beam milling energies, and other considerations to optimize Kikuchi diffraction pattern quality for the APT specimen geometry. Coordinated specimen preparation and analysis of a grain boundary in a Ni-based Inconel 600 alloy is used to illustrate the approach revealing a 50° misorientation and trace element segregation to the grain boundary. PMID:27329309

  9. Characterization of microfabricated probes for combined atomic force and high-resolution scanning electrochemical microscopy.

    PubMed

    Gullo, Maurizio R; Frederix, Patrick L T M; Akiyama, Terunobu; Engel, Andreas; deRooij, Nico F; Staufer, Urs

    2006-08-01

    A combined atomic force and scanning electrochemical microscope probe is presented. The probe is electrically insulated except at the very apex of the tip, which has a radius of curvature in the range of 10-15 nm. Steady-state cyclic voltammetry measurements for the reduction of Ru(NH3)6Cl3 and feedback experiments showed a distinct and reproducible response of the electrode. These experimental results agreed with finite element simulations for the corresponding diffusion process. Sequentially topographical and electrochemical studies of Pt lines deposited onto Si3N4 and spaced 100 nm apart (edge to edge) showed a lateral electrochemical resolution of 10 nm. PMID:16878880

  10. Probe knots and Hopf insulators with ultracold atoms

    NASA Astrophysics Data System (ADS)

    Deng, Dong-Ling; Wang, Sheng-Tao; Sun, Kai; Duan, Lu-Ming

    2015-05-01

    Knots and links are fascinating and intricate topological objects that have played a prominent role in physical and life sciences. Their influence spans from DNA and molecular chemistry to vortices in superfluid helium, defects in liquid crystals and cosmic strings in the early universe. Here, we show that knotted structures also exist in a peculiar class of three dimensional topological insulators--the Hopf insulators. In particular, we demonstrate that the spin textures of Hopf insulators in momentum space are twisted in a nontrivial way, which implies various knot and link structures. We further illustrate that the knots and nontrivial spin textures can be probed via standard time-of-flight images in cold atoms as preimage contours of spin orientations in stereographic coordinates. The extracted Hopf invariants, knots, and links are validated to be robust to typical experimental imperfections. Our work establishes the existence of knotted structures in cold atoms and may have potential applications in spintronics and quantum information processings. We thank X.-J. Liu and G. Ortiz for helpful discussions. S.T.W., D.L.D., and L.M.D. are supported by the NBRPC 2011CBA00300, the IARPA MUSIQC program, the ARO and the AFOSR MURI program. K.S. acknowledges support from NSF under Grant No. PHY1402971.

  11. Atom probe field ion microscopy and related topics: A bibliography 1989

    SciTech Connect

    Miller, M.K.; Hawkins, A.R.; Russell, K.F.

    1990-12-01

    This bibliography includes references related to the following topics: atom probe field ion microscopy (APFIM), field ion spectroscopy (FIM), field emission microscopy (FEM), liquid metal ion sources (LMIS), scanning tunneling microscopy (STM), and theory. Technique-orientated studies and applications are included. This bibliography covers the period 1989. The references contained in this document were compiled from a variety of sources including computer searches and personal lists of publications.

  12. Mechanics of interaction and atomic-scale wear of amplitude modulation atomic force microscopy probes.

    PubMed

    Vahdat, Vahid; Grierson, David S; Turner, Kevin T; Carpick, Robert W

    2013-04-23

    Wear is one of the main factors that hinders the performance of probes for atomic force microscopy (AFM), including for the widely used amplitude modulation (AM-AFM) mode. Unfortunately, a comprehensive scientific understanding of nanoscale wear is lacking. We have developed a protocol for conducting consistent and quantitative AM-AFM wear experiments. The protocol involves controlling the tip-sample interaction regime during AM-AFM scanning, determining the tip-sample contact geometry, calculating the peak repulsive force and normal stress over the course of the wear test, and quantifying the wear volume using high-resolution transmission electron microscopy imaging. The peak repulsive tip-sample interaction force is estimated from a closed-form equation accompanied by an effective tip radius measurement procedure, which combines transmission electron microscopy and blind tip reconstruction. The contact stress is estimated by applying Derjaguin-Müller-Toporov contact mechanics model and also numerically solving a general contact mechanics model recently developed for the adhesive contact of arbitrary axisymmetric punch shapes. We discuss the important role that the assumed tip shape geometry plays in calculating both the interaction forces and the contact stresses. Contact stresses are significantly affected by the tip geometry while the peak repulsive force is mainly determined by experimentally controlled parameters, specifically, the free oscillation amplitude and amplitude ratio. The applicability of this protocol is demonstrated experimentally by assessing the performance of diamond-like carbon-coated and silicon-nitride-coated silicon probes scanned over ultrananocrystalline diamond substrates in repulsive mode AM-AFM. There is no sign of fracture or plastic deformation in the case of diamond-like carbon; wear could be characterized as a gradual atom-by-atom process. In contrast, silicon nitride wears through removal of the cluster of atoms and plastic

  13. Probing physical properties at the nanoscale using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Ditzler, Lindsay Rachel

    Techniques that measure physical properties at the nanoscale with high sensitivity are significantly limited considering the number of new nanomaterials being developed. The development of atomic force microscopy (AFM) has lead to significant advancements in the ability to characterize physical properties of materials in all areas of science: chemistry, physics, engineering, and biology have made great scientific strides do to the versatility of the AFM. AFM is used for quantification of many physical properties such as morphology, electrical, mechanical, magnetic, electrochemical, binding interactions, and protein folding. This work examines the electrical and mechanical properties of materials applicable to the field of nano-electronics. As electronic devices are miniaturized the demand for materials with unique electrical properties, which can be developed and exploited, has increased. For example, discussed in this work, a derivative of tetrathiafulvalene, which exhibits a unique loss of conductivity upon compression of the self-assembled monolayer could be developed into a molecular switch. This work also compares tunable organic (tetraphenylethylene tetracarboxylic acid and bis(pyridine)s assemblies) and metal-organic (Silver-stilbizole coordination compounds) crystals which show high electrical conductivity. The electrical properties of these materials vary depending on their composition allowing for the development of compositionally tunable functional materials. Additional work was done to investigate the effects of molecular environment on redox active 11-ferroceneyl-1 undecanethiol (Fc) molecules. The redox process of mixed monolayers of Fc and decanethiol was measured using conductive probe atomic force microscopy and force spectroscopy. As the concentration of Fc increased large, variations in the force were observed. Using these variations the number of oxidized molecules in the monolayer was determined. AFM is additionally capable of investigating

  14. Dicke superradiance as nondestructive probe for the state of atoms in optical lattices

    NASA Astrophysics Data System (ADS)

    ten Brinke, Nicolai; Schützhold, Ralf

    2016-04-01

    We present a proposal for a probing scheme utilizing Dicke superradiance to obtain information about ultracold atoms in optical lattices. A probe photon is absorbed collectively by an ensemble of lattice atoms generating a Dicke state. The lattice dynamics (e.g., tunneling) affects the coherence properties of that Dicke state and thus alters the superradiant emission characteristics - which in turn provides insight into the lattice (dynamics). Comparing the Bose-Hubbard and the Fermi-Hubbard model, we find similar superradiance in the strongly interacting Mott insulator regime, but crucial differences in the weakly interacting (superfluid or metallic) phase. Furthermore, we study the possibility to detect whether a quantum phase transition between the two regimes can be considered adiabatic or a quantum quench.

  15. Dicke superradiance as nondestructive probe for the state of atoms in optical lattices

    NASA Astrophysics Data System (ADS)

    Brinke, Nicolai ten; Schützhold, Ralf

    2016-05-01

    We present a proposal for a probing scheme utilizing Dicke superradiance to obtain information about ultracold atoms in optical lattices. A probe photon is absorbed collectively by an ensemble of lattice atoms generating a Dicke state. The lattice dynamics (e.g., tunneling) affects the coherence properties of that Dicke state and thus alters the superradiant emission characteristics - which in turn provides insight into the lattice (dynamics). Comparing the Bose-Hubbard and the Fermi-Hubbard model, we find similar superradiance in the strongly interacting Mott insulator regime, but crucial differences in the weakly interacting (superfluid or metallic) phase. Furthermore, we study the possibility to detect whether a quantum phase transition between the two regimes can be considered adiabatic or a quantum quench.

  16. Effect of Laser Power on Atom Probe Tomography of Silicates

    NASA Astrophysics Data System (ADS)

    Parman, S. W.; Gorman, B.; Jackson, C.; Cooper, R. F.; Diercks, D.

    2011-12-01

    Atom probe tomography (APT) is an emerging analytical method that has the potential to produce nm-scale spatial resolution of atom positions with ppm-level detection limits. Until recently, APT has been limited to analysis of conducting samples due to the high pulsed electrical fields previously required. The recent development of laser-assisted APT now allows much lower laser powers to be used, opening the door to analysis of geologic minerals. The potential applications are many, ranging from diffusion profiles to the distribution of nano-phases to grain boundary chemical properties. We reported the first analysis of natural olivine using APT last year (Parman et al, 2010). While the spatial resolution was good (nm-scale), the accuracy of the compositional analysis was not. Two of the primary barriers to accurate ion identification in APT are: 1) Specimen overheating - This is caused by the interaction of the laser with the low thermal conductivity insulating specimens. Ions are assumed to have left the surface of the sample at the time the laser is pulsed during the analysis (laser pulse width = 12 ps). If the laser power is too high, the surface remains heated for an appreciable time (greater than 5 ns in some cases) after the laser pulse, causing atoms to field evaporate from the surface well after the laser pulse. Since they hit the detector later than the atoms that were released during the pulse, they are interpreted to be higher mass. Thus overheating appears in the analysis as a smearing of mass/charge peaks to higher mass/charge ratios (thermal tails). For well separated peaks, this is not a substantial problem, but for closely spaced peaks, overheating causes artificial mass interferences. 2) Molecular evaporation or clustering - This is also caused by overheating by the laser. Ideally, atoms are field evaporated individually from the surface of the cylindrical specimen. However, if the absorbed energy is high enough, clusters of atoms will be formed

  17. RADMAP: Simple probes for rapid assessment of complex reactivity: A method and case studies on the reaction of hydrogen atoms with unsaturated organic molecules.

    PubMed

    Long, Andrew K; Fawcett, Jason A; Clyburne, Jason A C; Pye, Cory C

    2016-03-01

    RADMAP, an open source program, allows for rapid analysis and visualization of the earliest stages of reactions between any molecule and a monoatomic probe (i.e., H*, H(+), H(-), Br*, or any other monoatomic species) using ab initio methods. This program creates non-planar potential energy surfaces of the initial interaction between a molecule of interest and the monoatomic probe. These surfaces can be used to both predict the site of addition as well as provide a qualitative estimate for the relative proportion of the formation of adducts; therefore, it gives insight into both the reactivity and the kinetic stability of a molecule. The program presents a way to quickly predict the number of signals anticipated in transverse field muon spin resonance spectra as well as their relative intensities. PMID:26851865

  18. Conductive-probe atomic force microscopy characterization of silicon nanowire

    PubMed Central

    2011-01-01

    The electrical conduction properties of lateral and vertical silicon nanowires (SiNWs) were investigated using a conductive-probe atomic force microscopy (AFM). Horizontal SiNWs, which were synthesized by the in-plane solid-liquid-solid technique, are randomly deployed into an undoped hydrogenated amorphous silicon layer. Local current mapping shows that the wires have internal microstructures. The local current-voltage measurements on these horizontal wires reveal a power law behavior indicating several transport regimes based on space-charge limited conduction which can be assisted by traps in the high-bias regime (> 1 V). Vertical phosphorus-doped SiNWs were grown by chemical vapor deposition using a gold catalyst-driving vapor-liquid-solid process on higly n-type silicon substrates. The effect of phosphorus doping on the local contact resistance between the AFM tip and the SiNW was put in evidence, and the SiNWs resistivity was estimated. PMID:21711623

  19. New Methods of Sample Preparation for Atom Probe Specimens

    NASA Technical Reports Server (NTRS)

    Kuhlman, Kimberly, R.; Kowalczyk, Robert S.; Ward, Jennifer R.; Wishard, James L.; Martens, Richard L.; Kelly, Thomas F.

    2003-01-01

    Magnetite is a common conductive mineral found on Earth and Mars. Disk-shaped precipitates approximately 40 nm in diameter have been shown to have manganese and aluminum concentrations. Atom-probe field-ion microscopy (APFIM) is the only technique that can potentially quantify the composition of these precipitates. APFIM will be used to characterize geological and planetary materials, analyze samples of interest for geomicrobiology; and, for the metrology of nanoscale instrumentation. Prior to APFIM sample preparation was conducted by electropolishing, the method of sharp shards (MSS), or Bosch process (deep reactive ion etching) with focused ion beam (FIB) milling as a final step. However, new methods are required for difficult samples. Many materials are not easily fabricated using electropolishing, MSS, or the Bosch process, FIB milling is slow and expensive, and wet chemistry and the reactive ion etching are typically limited to Si and other semiconductors. APFIM sample preparation using the dicing saw is commonly used to section semiconductor wafers into individual devices following manufacture. The dicing saw is a time-effective method for preparing high aspect ratio posts of poorly conducting materials. Femtosecond laser micromachining is also suitable for preparation of posts. FIB time required is reduced by about a factor of 10 and multi-tip specimens can easily be fabricated using the dicing saw.

  20. Imaging of radiation damage using complementary field ion microscopy and atom probe tomography.

    PubMed

    Dagan, Michal; Hanna, Luke R; Xu, Alan; Roberts, Steve G; Smith, George D W; Gault, Baptiste; Edmondson, Philip D; Bagot, Paul A J; Moody, Michael P

    2015-12-01

    Radiation damage in tungsten and a tungsten-tantalum alloy, both of relevance to nuclear fusion research, has been characterized using a combination of field ion microscopy (FIM) imaging and atom probe tomography (APT). While APT provides 3D analytical imaging with sub-nanometer resolution, FIM is capable of imaging the arrangements of single atoms on a crystal lattice and has the potential to provide insights into radiation induced crystal damage, all the way down to its smallest manifestation--a single vacancy. This paper demonstrates the strength of combining these characterization techniques. In ion implanted tungsten, it was found that atomic scale lattice damage is best imaged using FIM. In certain cases, APT reveals an identifiable imprint in the data via the segregation of solute and impurities and trajectory aberrations. In a W-5at%Ta alloy, a combined APT-FIM study was able to determine the atomic distribution of tantalum inside the tungsten matrix. An indirect method was implemented to identify tantalum atoms inside the tungsten matrix in FIM images. By tracing irregularities in the evaporation sequence of atoms imaged with FIM, this method enables the benefit of FIM's atomic resolution in chemical distinction between the two species. PMID:25794822

  1. Comparison of atom probe tomography and transmission electron microscopy analysis of oxide dispersion strengthened steels

    NASA Astrophysics Data System (ADS)

    London, A. J.; Lozano-Perez, S.; Santra, S.; Amirthapandian, S.; Panigrahi, B. K.; Sundar, C. S.; Grovenor, C. R. M.

    2014-06-01

    Oxide dispersion strengthened steels owe part of their high temperature stability to the nano-scale oxides they contain. These yttrium-titanium oxides are notoriously difficult to characterise since they are embedded in a magnetic-ferritic matrix and often <10 nm across. This study uses correlated transmission electron microscopy and atom probe tomography on the same material to explore the kind of information that can be gained on the character of the oxide particles. The influence of chromium in these alloys is of interest, therefore two model ODS steels Fe-(14Cr)-0.2Ti-0.3Y2O3 are compared. TEM is shown to accurately measure the size of the oxide particles and atom probe tomography is necessary to observe the smallest sub-1.5 nm particles. Larger Y2Ti2O7 and Y2TiO5 structured particles were identified by high-resolution transmission electron microscopy, but the smallest oxides remain difficult to index. Chemical data from energy-filtered TEM agreed qualitatively with the atom probe findings. It was found that the majority of the oxide particles exhibit an unoxidised chromium shell which may be responsible for reducing the ultimate size of the oxide particles.

  2. Atomic-scale characterization of germanium isotopic multilayers by atom probe tomography

    SciTech Connect

    Shimizu, Y.; Takamizawa, H.; Toyama, T.; Inoue, K.; Nagai, Y.; Kawamura, Y.; Uematsu, M.; Itoh, K. M.; Haller, E. E.

    2013-01-14

    We report comparison of the interfacial sharpness characterization of germanium (Ge) isotopic multilayers between laser-assisted atom probe tomography (APT) and secondary ion mass spectrometry (SIMS). An alternating stack of 8-nm-thick naturally available Ge layers and 8-nm-thick isotopically enriched {sup 70}Ge layers was prepared on a Ge(100) substrate by molecular beam epitaxy. The APT mass spectra consist of clearly resolved peaks of five stable Ge isotopes ({sup 70}Ge, {sup 72}Ge, {sup 73}Ge, {sup 74}Ge, and {sup 76}Ge). The degree of intermixing at the interfaces between adjacent layers was determined by APT to be around 0.8 {+-} 0.1 nm which was much sharper than that obtained by SIMS.

  3. Networking strategies of the microscopy community for improved utilization of advanced instruments: (2) The national network for transmission electron microscopy and atom probe studies in France (METSA)

    NASA Astrophysics Data System (ADS)

    Épicier, Thierry; Snoeck, Étienne

    2014-02-01

    With the development, over the past ten years, of a new generation of electron microscopes with advanced performance, incorporating aberration correctors, monochromators, more sensitive detectors, and innovative specimen environments, quantitative measurements at the subnanometer and, in certain cases, at the unique atom level, are now accessible. However, an optimized use of these possibilities requires access to costly instruments and support by specialized trained experts. For these reasons, a national network (METSA) has been created in France with the support of CNRS and CEA in order to offer, in centres with complementary equipment and expertise, an open access to an enlarged and multidisciplinary community of academic and industrial users.

  4. C12/C13-ratio determination in nanodiamonds by atom-probe tomography.

    PubMed

    Lewis, Josiah B; Isheim, Dieter; Floss, Christine; Seidman, David N

    2015-12-01

    The astrophysical origins of ∼ 3 nm-diameter meteoritic nanodiamonds can be inferred from the ratio of C12/C13. It is essential to achieve high spatial and mass resolving power and minimize all sources of signal loss in order to obtain statistically significant measurements. We conducted atom-probe tomography on meteoritic nanodiamonds embedded between layers of Pt. We describe sample preparation, atom-probe tomography analysis, 3D reconstruction, and bias correction. We present new data from meteoritic nanodiamonds and terrestrial standards and discuss methods to correct isotopic measurements made with the atom-probe tomograph. PMID:26095824

  5. Atomization and Mixing Study

    NASA Technical Reports Server (NTRS)

    Ferrenberg, A.; Hunt, K.; Duesberg, J.

    1985-01-01

    The primary objective was the obtainment of atomization and mixing performance data for a variety of typical liquid oxygen/hydrocarbon injector element designs. Such data are required to establish injector design criteria and to provide critical inputs to liquid rocket engine combustor performance and stability analysis, and computational codes and methods. Deficiencies and problems with the atomization test equipment were identified, and action initiated to resolve them. Test results of the gas/liquid mixing tests indicated that an assessment of test methods was required. A series of 71 liquid/liquid tests were performed.

  6. Solar probe: an engineering study

    NASA Astrophysics Data System (ADS)

    Bedini, P.; Potocki, K.

    2003-04-01

    Solar Probe, a program to study the origins of the solar wind and the heating of the Sun’s corona, is currently a mission under study in NASA’s Sun-Earth Connection Theme. The availability of the Evolved Expendable Launch Vehicle (EELV) and Multi-Mission Radioisotope Thermoelectric Generators has enabled the development of an implementable Solar Probe mission concept that now offers substantial resources (55 kg and 47 W) for its science payload. The mission design assumes a launch on an EELV and uses a direct Jupiter Gravity Assist to reach a perihelion of 4 RS. The mission affords two polar solar passes with Earth in quadrature within 7.1 years from launch. A large (2.7-m diameter × 5.1-m), conical Carbon-Carbon thermal protection system harbors a complement of in situ and remote-sensing instruments (based on the 1999 Solar Probe Science Definition Team straw-man payload). A Ka-band telecommunications system allows uninterrupted real-time data downlink at perihelion (p) despite coronal scintillation effects, providing > 25 kbps even at closest approach. The 43.2 Gbits of data down-linked during each pass (p -- 10 days through p + 10 days) is augmented by as much as another 128 Gbits of data recorded on redundant solid-state recorders for post-perihelion playback. The capability exists to download cruise mode science as well. Fault tolerance is achieved using redundant avionics and a dedicated attitude control unit to assure that the proper orientation of the spacecraft is maintained throughout the passes. Viable opportunities begin with a 2010 launch, provided new start authority is obtained in FY-05.

  7. Geochemical Proxy Distribution at the Atomic-Scale: Atom Probe Tomography of Foraminiferal Calcite

    NASA Astrophysics Data System (ADS)

    Branson, O.; Perea, D. E.; Winters, M. A.; Fehrenbacher, J. S.; Russell, A. D.; Spero, H. J.; Gagnon, A. C.

    2014-12-01

    Biomineral composition reflects a complex interplay between minute-scale biological control, mineral growth processes, and the influence of environmental conditions. For this reason, the mechanisms responsible for the formation of these minerals, as well as the incorporation of trace elements during biomineral growth, are poorly understood. Potential mechanisms governing the production and composition of biominerals can be organized into two distinct groups: a) biological mechanisms controlling the calcifying environment and b) mineral growth processes from this controlled environment. Despite significant advances in both these areas, critical gaps remain in our understanding of biomineral production and geochemical tracer incorporation. We are adapting Atom Probe Tomography (APT), a technique that maps the arrangement and identity of individual atoms within a bulk material, to analyze foraminiferal calcite for the first time. These data-rich atom-scale chemical maps provide a unique opportunity to deconvolve the effects of biological and crystal growth processes in the incorporation of geochemical tracers. Our first experiments have examined the influence of the biological-mineral interface on geochemical proxy element incorporation. Preliminary measurements show that (1) we can successfully map impurities in calcite biominerals, while also distinguishing between mineral and organic zones, overcoming a major technical hurdle; and (2) that elements like sodium appear to be recruited to the organic-mineral interface. The high-resolution chemical data from the APT will further allow us to investigate the fundamental basis for geochemical proxy behavior. For example, we can determine for a certain set of conditions whether the substitution of trace elements into the calcite follows ideal solid-solution behavior, as tacitly assumed in many geochemical proxy systems, or is modulated by intra-shell organics, or coupled-substitution interactions. Collectively, the

  8. Atom probe field ion microscopy and related topics: A bibliography 1991

    SciTech Connect

    Russell, K.F.; Miller, M.K.

    1993-01-01

    This report contains a bibliography for 1991 on the following topics: Atom probe field ion microscopy; field desorption mass spectrometry; field emission; field ion microscopy; and field emission theory.

  9. Probing the rupture of a Ag atomic junction in a Ag-Au mixed electrode

    NASA Astrophysics Data System (ADS)

    Kim, Taekyeong

    2015-09-01

    We probed that the atomic junction in Ag part ruptures during stretching of atomic sized contacts of Ag-Au mixed electrodes, resulting in Ag-Ag electrodes through a scanning tunneling microscope breaking junction (STM-BJ) technique. We observed that the conductance and tunneling decay constant for a series of amine-terminated oligophenyl molecular junctions are essentially the same for the Ag-Au mixed and the Ag-Ag electrodes. We also found the molecular plateau length and the evolution patterns with the Ag-Au mixed electrodes are similar to those with Ag-Ag electrodes rather than the Au-Au electrodes in the molecular junction elongation. This result is attributed to the smaller binding energy of Ag atoms compared to that of Au atoms, so the Ag junction part is more easily broken than that of Au part in stretching of Ag-Au mixed electrodes. Furthermore, we successfully observed that the rupture force of the atomic junction for the Ag-Au mixed electrodes was identical to that for the Ag-Ag electrodes and smaller than that for the Au-Au electrodes. This study may advance the understanding of the electrical and the mechanical properties in molecular devices with Ag and Au electrodes in future.

  10. Aberrated electron probes for magnetic spectroscopy with atomic resolution: Theory and practical aspects

    DOE PAGESBeta

    Rusz, Ján; Idrobo, Juan Carlos

    2016-03-24

    It was recently proposed that electron magnetic circular dichroism (EMCD) can be measured in scanning transmission electron microscopy (STEM) with atomic resolution by tuning the phase distribution of a electron beam. Here, we describe the theoretical and practical aspects for the detection of out-of-plane and in-plane magnetization utilizing atomic size electron probes. Here we present the calculated optimized astigmatic probes and discuss how to achieve them experimentally.

  11. Aberrated electron probes for magnetic spectroscopy with atomic resolution: Theory and practical aspects

    NASA Astrophysics Data System (ADS)

    Rusz, Ján; Idrobo, Juan Carlos

    2016-03-01

    It was recently proposed that electron magnetic circular dichroism can be measured in scanning transmission electron microscopy with atomic resolution by tuning the phase distribution of an electron beam. Here, we describe the theoretical and practical aspects for the detection of out-of-plane and in-plane magnetization utilizing atomic size electron probes. We present the calculated optimized astigmatic probes and discuss how to achieve them experimentally.

  12. Aberrated electron probes for novel spectroscopy with atomic resolution: theory and practical aspects

    SciTech Connect

    Rusz, Jan; Idrobo Tapia, Juan Carlos

    2016-01-01

    It was recently proposed that electron magnetic circular dichroism (EMCD) can be measured in scanning transmission electron microscopy (STEM) with atomic resolution by tuning the phase distribution of a electron beam. Here, we describe the theoretical and practical aspects for the detection of out-of-plane and in-plane magnetization utilizing atomic size electron probes. We present the calculated optimized astigmatic probes and discuss how to achieve them experimentally.

  13. Pump-probe spectroscopy of cold rubidium atoms in an integrating sphere

    NASA Astrophysics Data System (ADS)

    Wang, Wen-Li; Dong, Ri-Chang; Deng, Jian-Liao; Wang, Yu-Zhu

    2016-05-01

    Absorption spectra of cold rubidium atoms in an integrating sphere under the influence of a diffuse laser field have been systematically investigated. A pronounced dispersionlike structure centered at the light-shifted pump frequency is observed with a subnatural linewidth. In particular, two clearly resolved absorption resonances on the 5 S1 /2(F =2 ) →5 P3 /2(F'=3 ) transitions occur with variable probe beam intensity, which is consistent with our proposed theoretical model. Based on the two absorption resonances,we measure the dependence of light shifts, from which we can directly extract the effective Rabi frequency in a diffuse laser field, on the probe laser intensity, pump laser intensity, and pump laser detuning. Our work helps to identify the physical mechanisms behind these spectral features and is beneficial for studying the corresponding effect in a cold sample.

  14. Atom probe field ion microscopy and related topics: A bibliography 1990

    SciTech Connect

    Russell, K.F.; Miller, M.K.

    1991-12-01

    This bibliography includes references related to the following topics: atom probe field ion microscopy (APFIM), field ion microscopy (FIM), field emission (FE), ion sources, and field desorption mass microscopy (FDMM). Technique-orientated studies and applications are included. The bibliography covers the period 1990. The references contained in this document were compiled from a variety of sources including computer searches and personal lists of publications. To reduce the length of this document, the references have been reduced to the minimum necessary to locate the articles. The references, listed alphabetically by authors, are subdivided into the categories listed in paragraph one above. An Addendum of references missed in previous bibliographies is included.

  15. Improved in situ spring constant calibration for colloidal probe atomic force microscopy

    SciTech Connect

    McBride, Sean P.; Law, Bruce M.

    2010-11-15

    In colloidal probe atomic force microscopy (AFM) surface forces cannot be measured without an accurate determination of the cantilever spring constant. The effective spring constant k depends upon the cantilever geometry and therefore should be measured in situ; additionally, k may be coupled to other measurement parameters. For example, colloidal probe AFM is frequently used to measure the slip length b at solid/liquid boundaries by comparing the measured hydrodynamic force with Vinogradova slip theory (V-theory). However, in this measurement k and b are coupled, hence, b cannot be accurately determined without knowing k to high precision. In this paper, a new in situ spring constant calibration method based upon the residuals, namely, the difference between experimental force-distance data and V-theory is presented and contrasted with two other popular spring constant determination methods. In this residuals calibration method, V-theory is fitted to the experimental force-distance data for a range of systematically varied spring constants where the only adjustable parameter in V-theory is the slip length b. The optimal spring constant k is that value where the residuals are symmetrically displaced about zero for all colloidal probe separations. This residual spring constant calibration method is demonstrated by studying three different liquids (n-decanol, n-hexadecane, and n-octane) and two different silane coated colloidal probe-silicon wafer systems (n-hexadecyltrichlorosilane and n-dodecyltrichlorosilane).

  16. Atomization and mixing study

    NASA Technical Reports Server (NTRS)

    Ferrenberg, A.; Jaqua, V. W.

    1983-01-01

    The state of the art in atomization and mixing for triplet, pentad, and coaxial injectors is described. Injectors that are applicable for LOX/hydrocarbon propellants and main chamber and fuel rich preburner/gas generator mixture ratios are of special interest. Various applicable correlating equations and parameters as well as test data found in the literature are presented. The validity, utility, and important aspects of these data and correlations are discussed and the measurement techniques used are evaluated. Propellant mixing tests performed are described and summarized, results are reported, and tentative conclusions are included.

  17. Probing the shape of atoms in real space

    NASA Astrophysics Data System (ADS)

    Herz, M.; Giessibl, F. J.; Mannhart, J.

    2003-07-01

    The structure of single atoms in real space is investigated by scanning tunneling microscopy. Very high resolution can be obtained by a dramatic reduction of the tip-sample distance. The instabilities which are normally encountered while using small tip-sample distances are avoided by oscillating the tip of the scanning tunneling microscope vertically with respect to the sample. The surface atoms of Si(111)-(7×7) with their well-known electronic configuration are used to image individual samarium, cobalt, iron, and silicon atoms. The resulting images resemble the charge density corresponding to 4f, 3d, and 3p atomic orbitals.

  18. Probing Local Ionic Dynamics in Functional Oxides: From Nanometer to Atomic Scale

    NASA Astrophysics Data System (ADS)

    Kalinin, Sergei

    2014-03-01

    Vacancy-mediated electrochemical reactions in oxides underpin multiple applications ranging from electroresistive memories, to chemical sensors to energy conversion systems such as fuel cells. Understanding the functionality in these systems requires probing reversible (oxygen reduction/evolution reaction) and irreversible (cathode degradation and activation, formation of conductive filaments) electrochemical processes. In this talk, I summarize recent advances in probing and controlling these transformations locally on nanometer level using scanning probe microscopy. The localized tip concentrates the electric field in the nanometer scale volume of material, inducing local transition. Measured simultaneously electromechanical response (piezoresponse) or current (conductive AFM) provides the information on the bias-induced changes in material. Here, I illustrate how these methods can be extended to study local electrochemical transformations, including vacancy dynamics in oxides such as titanates, LaxSr1-xCoO3, BiFeO3, and YxZr1-xO2. The formation of electromechanical hysteresis loops and their bias-, temperature- and environment dependences provide insight into local electrochemical mechanisms. In materials such as lanthanum-strontium cobaltite, mapping both reversible vacancy motion and vacancy ordering and static deformation is possible, and can be corroborated by post mortem STEM/EELS studies. In ceria, a broad gamut of electrochemical behaviors is observed as a function of temperature and humidity. The possible strategies for elucidation ionic motion at the electroactive interfaces in oxides using high-resolution electron microscopy and combined ex-situ and in-situ STEM-SPM studies are discussed. In the second part of the talk, probing electrochemical phenomena on in-situ grown surfaces with atomic resolution is illustrated. I present an approach based on the multivariate statistical analysis of the coordination spheres of individual atoms to reveal

  19. Determination of solute site occupancies within γ' precipitates in nickel-base superalloys via orientation-specific atom probe tomography

    SciTech Connect

    Meher, Subhashish; Rojhirunsakool, Tanaporn; Nandwana, Peeyush; Tiley, Jamie; Banerjee, Rajarshi

    2015-04-28

    In this study, the analytical limitations in atom probe tomography such as resolving a desired set of atomic planes, for solving complex materials science problems, have been overcome by employing a well-developed unique and reproducible crystallographic technique, involving synergetic coupling of orientation microscopy with atom probe tomography. The crystallographic information in atom probe reconstructions has been utilized to determine the solute site occupancies in Ni-Al-Cr based superalloys accurately. The structural information in atom probe reveals that both Al and Cr occupy the same sub-lattice within the L12-ordered g precipitates to form Ni3(Al,Cr) precipitates in a Ni-14Al-7Cr(at.%) alloy. Interestingly, the addition of Co, which is a solid solution strengthener, to a Ni-14Al-7Cr alloy results in the partial reversal of Al site occupancy within g precipitates to form (Ni,Al)3(Al,Cr,Co) precipitates. This unique evidence of reversal of Al site occupancy, resulting from the introduction of other solutes within the ordered structures, gives insights into the relative energetics of different sub-lattice sites when occupied by different solutes.

  20. Determination of solute site occupancies within γ' precipitates in nickel-base superalloys via orientation-specific atom probe tomography

    DOE PAGESBeta

    Meher, Subhashish; Rojhirunsakool, Tanaporn; Nandwana, Peeyush; Tiley, Jamie; Banerjee, Rajarshi

    2015-04-28

    In this study, the analytical limitations in atom probe tomography such as resolving a desired set of atomic planes, for solving complex materials science problems, have been overcome by employing a well-developed unique and reproducible crystallographic technique, involving synergetic coupling of orientation microscopy with atom probe tomography. The crystallographic information in atom probe reconstructions has been utilized to determine the solute site occupancies in Ni-Al-Cr based superalloys accurately. The structural information in atom probe reveals that both Al and Cr occupy the same sub-lattice within the L12-ordered g precipitates to form Ni3(Al,Cr) precipitates in a Ni-14Al-7Cr(at.%) alloy. Interestingly, the additionmore » of Co, which is a solid solution strengthener, to a Ni-14Al-7Cr alloy results in the partial reversal of Al site occupancy within g precipitates to form (Ni,Al)3(Al,Cr,Co) precipitates. This unique evidence of reversal of Al site occupancy, resulting from the introduction of other solutes within the ordered structures, gives insights into the relative energetics of different sub-lattice sites when occupied by different solutes.« less

  1. Resolving the morphology of niobium carbonitride nano-precipitates in steel using atom probe tomography.

    PubMed

    Breen, Andrew J; Xie, Kelvin Y; Moody, Michael P; Gault, Baptiste; Yen, Hung-Wei; Wong, Christopher C; Cairney, Julie M; Ringer, Simon P

    2014-08-01

    Atom probe is a powerful technique for studying the composition of nano-precipitates, but their morphology within the reconstructed data is distorted due to the so-called local magnification effect. A new technique has been developed to mitigate this limitation by characterizing the distribution of the surrounding matrix atoms, rather than those contained within the nano-precipitates themselves. A comprehensive chemical analysis enables further information on size and chemistry to be obtained. The method enables new insight into the morphology and chemistry of niobium carbonitride nano-precipitates within ferrite for a series of Nb-microalloyed ultra-thin cast strip steels. The results are supported by complementary high-resolution transmission electron microscopy. PMID:25410602

  2. Understanding proton-conducting perovskite interfaces using atom probe tomography

    NASA Astrophysics Data System (ADS)

    Clark, Daniel R.

    Proton-conducting ceramics are under intense scientific investigation for a number of exciting applications, including fuel cells, electrolyzers, hydrogen separation membranes, membrane reactors, and sensors. However, commercial application requires deeper understanding and improvement of proton conductivity in these materials. It is well-known that proton conductivity in these materials is often limited by highly resistive grain boundaries (GBs). While these conductivity-limiting GBs are still not well understood, it is hypothesized that their blocking nature stems from the formation of a positive (proton-repelling) space-charge zone. Furthermore, it has been observed that the strength of the blocking behavior can change dramatically depending on the fabrication process used to make the ceramic. This thesis applies laser-assisted atom probe tomography (LAAPT) to provide new insights into the GB chemistry and resulting space-charge behavior of BaZr0.9Y0.1O 3--delta (BZY10), a prototypical proton-conducting ceramic. LAAPT is an exciting characterization technique that allows for three-dimensional nm-scale spatial resolution and very high chemical resolution (up to parts-per-million). While it is challenging to quantitatively apply LAAPT to complex, multi-cation oxide materials, this thesis successfully develops a method to accurately quantify the stoichiometry of BZY10 and maintain minimal quantitative cationic deviation at a laser energies of approximately 10--20 pJ. With the analysis technique specifically optimized for BZY10, GB chemistry is then examined for BZY10 samples prepared using four differing processing methods: (1) spark plasma sintering (SPS), (2) conventional sintering using powder prepared by solid-state reaction followed by high-temperature annealing (HT), (3) conventional sintering using powder prepared by solid-state reaction with NiO used as a sintering aid (SSR-Ni), and (4) solid-state reactive sintering directly from BaCO3, ZrO2, and Y2O3

  3. Atomic Resolution Imaging with a sub-50 pm Electron Probe

    SciTech Connect

    Erni, Rolf P.; Rossell, Marta D.; Kisielowski, Christian; Dahmen, Ulrich

    2009-03-02

    Using a highly coherent focused electron probe in a 5th order aberration-corrected transmission electron microscope, we report on resolving a crystal spacing less than 50 pm. Based on the geometrical source size and residual coherent and incoherent axial lens aberrations, an electron probe is calculated, which is theoretically capable of resolving an ideal 47 pm spacing with 29percent contrast. Our experimental data show the 47 pm spacing of a Ge 114 crystal imaged with 11-18percent contrast at a 60-95percent confidence level, providing the first direct evidence for sub 50-pm resolution in ADF STEM imaging.

  4. Dopant distributions in n-MOSFET structure observed by atom probe tomography.

    PubMed

    Inoue, K; Yano, F; Nishida, A; Takamizawa, H; Tsunomura, T; Nagai, Y; Hasegawa, M

    2009-11-01

    The dopant distributions in an n-type metal-oxide-semiconductor field effect transistor (MOSFET) structure were analyzed by atom probe tomography. The dopant distributions of As, P, and B atoms in a MOSFET structure (gate, gate oxide, channel, source/drain extension, and halo) were obtained. P atoms were segregated at the interface between the poly-Si gate and the gate oxide, and on the grain boundaries of the poly-Si gate, which had an elongated grain structure along the gate height direction. The concentration of B atoms was enriched near the edge of the source/drain extension where the As atoms were implanted. PMID:19775815

  5. Bragg scattering as a probe of atomic wave functions and quantum phase transitions in optical lattices.

    PubMed

    Miyake, Hirokazu; Siviloglou, Georgios A; Puentes, Graciana; Pritchard, David E; Ketterle, Wolfgang; Weld, David M

    2011-10-21

    We have observed Bragg scattering of photons from quantum degenerate ^{87}Rb atoms in a three-dimensional optical lattice. Bragg scattered light directly probes the microscopic crystal structure and atomic wave function whose position and momentum width is Heisenberg limited. The spatial coherence of the wave function leads to revivals in the Bragg scattered light due to the atomic Talbot effect. The decay of revivals across the superfluid to Mott insulator transition indicates the loss of superfluid coherence. PMID:22107532

  6. Restoring the lattice of Si-based atom probe reconstructions for enhanced information on dopant positioning.

    PubMed

    Breen, Andrew J; Moody, Michael P; Ceguerra, Anna V; Gault, Baptiste; Araullo-Peters, Vicente J; Ringer, Simon P

    2015-12-01

    The following manuscript presents a novel approach for creating lattice based models of Sb-doped Si directly from atom probe reconstructions for the purposes of improving information on dopant positioning and directly informing quantum mechanics based materials modeling approaches. Sophisticated crystallographic analysis techniques are used to detect latent crystal structure within the atom probe reconstructions with unprecedented accuracy. A distortion correction algorithm is then developed to precisely calibrate the detected crystal structure to the theoretically known diamond cubic lattice. The reconstructed atoms are then positioned on their most likely lattice positions. Simulations are then used to determine the accuracy of such an approach and show that improvements to short-range order measurements are possible for noise levels and detector efficiencies comparable with experimentally collected atom probe data. PMID:26190007

  7. Study of alternative probe technologies

    NASA Technical Reports Server (NTRS)

    1977-01-01

    A number of implied technologies for a deep probe mission was examined; i.e., one that would provide the capability to scientifically examine planetary atmospheres at the 1000 bar level. Conditions imposed by current Jupiter, Saturn, and Uranus atmospheric models were considered. The major thrust of the measurements was to determine lower atmosphere composition, even to trace constituents of one part per billion. Two types of instruments having the necessary accuracy to meet the science objectives were considered and integrated into a deep probe configuration. One deep probe option that resulted was identified as a Minimum Technology Development approach. The significant feature of this option is that only three technology developments are required to enable the mission, i.e., (1) science instrument development, (2) advanced data processing, and (3) external high pressure/thermal insulation. It is concluded that a probe designed for a Jupiter mission could, with minor changes, be used for a Saturn or Uranus mission.

  8. Laser-cooled atomic ions as probes of molecular ions

    SciTech Connect

    Brown, Kenneth R.; Viteri, C. Ricardo; Clark, Craig R.; Goeders, James E.; Khanyile, Ncamiso B.; Vittorini, Grahame D.

    2015-01-22

    Trapped laser-cooled atomic ions are a new tool for understanding cold molecular ions. The atomic ions not only sympathetically cool the molecular ions to millikelvin temperatures, but the bright atomic ion fluorescence can also serve as a detector of both molecular reactions and molecular spectra. We are working towards the detection of single molecular ion spectra by sympathetic heating spectroscopy. Sympathetic heating spectroscopy uses the coupled motion of two trapped ions to measure the spectra of one ion by observing changes in the fluorescence of the other ion. Sympathetic heating spectroscopy is a generalization of quantum logic spectroscopy, but does not require ions in the motional ground state or coherent control of the ion internal states. We have recently demonstrated this technique using two isotopes of Ca{sup +} [Phys. Rev. A, 81, 043428 (2010)]. Limits of the method and potential applications for molecular spectroscopy are discussed.

  9. Generating and probing entangled states for optical atomic clocks

    NASA Astrophysics Data System (ADS)

    Braverman, Boris; Kawasaki, Akio; Vuletic, Vladan

    2016-05-01

    The precision of quantum measurements is inherently limited by projection noise caused by the measurement process itself. Spin squeezing and more complex forms of entanglement have been proposed as ways of surpassing this limitation. In our system, a high-finesse asymmetric micromirror-based optical cavity can mediate the atom-atom interaction necessary for generating entanglement in an 171 Yb optical lattice clock. I will discuss approaches for creating, characterizing, and optimally utilizing these nonclassical states for precision measurement, as well as recent progress toward their realization. This research is supported by DARPA QuASAR, NSF, and NSERC.

  10. Influence of probe contamination on recombination of atomic hydrogen

    NASA Technical Reports Server (NTRS)

    Collins, L. W.; Downs, W. R.

    1975-01-01

    Atomic hydrogen concentration profiles were measured through a screen-stabilized one-dimensional propane/oxygen front using a specially modified electron spin resonance (ESR) spectrometer. The ESR line occurring at 3075.5 G at 9261.2 MHz was monitored in the presence and absence of various halogenated hydrocarbons. A significant cumulative decrease in peak intensity occurred with addition of any halogenated compound. Further results suggest that the effect is due to inhibitor action on the transport tube walls followed by changes in atomic hydrogen interaction with the walls, and that hydrogen decay is nonlinear in the halogenated tube.

  11. Retained Austenite Decomposition and Carbide Formation During Tempering a Hot-Work Tool Steel X38CrMoV5-1 Studied by Dilatometry and Atom Probe Tomography

    NASA Astrophysics Data System (ADS)

    Lerchbacher, Christoph; Zinner, Silvia; Leitner, Harald

    2012-12-01

    The microstructural development of a hot-work tool steel X38CrMoV5-1 during continuous heating to tempering temperature has been investigated with the focus on the decomposition of retained austenite (Stage II) and carbide formation (Stages III and IV). Investigations have been carried out after heating to 673.15 K, 773.15 K, 883.15 K (400 °C, 500 °C, 610 °C) and after a dwell time of 600 seconds at 883.15 K (610 °C). Dilatometry and atom probe tomography were used to identify tempering reactions. A distinctive reaction takes place between 723.15 K and 823.15 K (450 °C and 550 °C) which is determined to be the formation of M3C from transition carbides. Stage II could be evidenced with the atom probe results and indirectly with dilatometry, indicating the formation of new martensite during cooling. Retained austenite decomposition starts with the precipitation of alloy carbides formed from nanometric interlath retained austenite films which are laminary arranged and cause a reduction of the carbon content within the retained austenite. Preceding enrichment of substitutes at the matrix/carbide interface in the early stages of Cr7C3 alloy carbide formation could be visualised on the basis of coarse M3C carbides within the matrix. Atom probe tomography has been found to be very useful to complement dilatational experiments in order to characterise and identify microstructural changes.

  12. Optical probes of atomic and molecular decay processes.

    SciTech Connect

    Pratt, S. T.

    2008-01-01

    characterize both the photoexcitation and subsequent decay processes. These techniques include mass spectrometry, dispersive and threshold photoelectron spectroscopy, laser-induced fluorescence, fluorescence-dip spectroscopy, and laser-induced grating spectroscopy. While the instrumentation is currently available for each of these techniques, two instruments deserve special mention. First, a high-resolution magnetic-bottle electron spectrometer has been developed that is equipped with a pulsed, skimmed molecular beam source. This instrument is capable of {approx}3-4 meV resolution in the electron kinetic energy while providing a collection efficiency of {approx}50%. Second, a time-of-flight mass spectrometer has been constructed with a similar molecular beam source. This instrument is currently being adapted to allow both ion- and electron-imaging studies. A typical experimental study is performed in three steps. First, resonant one-color multiphoton ionization is used to map out the transition between the ground state of the molecule of interest and the low-lying excited state to be used as an intermediate in the double-resonance process. The lasers used in these studies are Nd:YAG-pumped dye lasers with {approx}5 ns pulse durations. In general, this pump transition corresponds to a one- or two-photon process, and the laser output is frequency doubled, tripled, or mixed to generate light in the region of interest. In molecules such as ammonia and aniline, the pump transitions of interest are well characterized, allowing the unambiguous choice of pump transitions that access levels with the rovibronic character of interest. In other cases, the spectroscopy of the pump transition must be analyzed before it can be useful for the double-resonance experiments. In the second step, the pump laser is fixed on the pump transition of interest and a second laser is used to probe transitions from the upper state of the pump transition to the autoionizing or predissociating resonances in

  13. The effect orientation of features in reconstructed atom probe data on the resolution and measured composition of T1 plates in an A2198 aluminium alloy.

    PubMed

    Mullin, Maria A; Araullo-Peters, Vicente J; Gault, Baptiste; Cairney, Julie M

    2015-12-01

    Artefacts in atom probe tomography can impact the compositional analysis of microstructure in atom probe studies. To determine the integrity of information obtained, it is essential to understand how the positioning of features influences compositional analysis. By investigating the influence of feature orientation within atom probe data on measured composition in microstructural features within an AA2198 Al alloy, this study shows differences in the composition of T1 (Al2CuLi) plates that indicates imperfections in atom probe reconstructions. The data fits a model of an exponentially-modified Gaussian that scales with the difference in evaporation field between solutes and matrix. This information provides a guide for obtaining the most accurate information possible. PMID:25896290

  14. Probing atomic positions of adsorbed ammonia molecules in zeolite.

    PubMed

    Ye, Lin; Lo, Benedict T W; Qu, Jin; Wilkinson, Ian; Hughes, Tim; Murray, Claire A; Tang, Chiu C; Tsang, Shik Chi Edman

    2016-02-25

    Atomic positions and interactions between adsorbed guest molecules, such as ammonia in H-ZSM-5 microporous solids, are for the first time revealed by making use of the change in the periodical scattering parameter using in situ synchrotron powder X-ray diffraction combined with refinement within experimental errors. PMID:26833032

  15. Measurement of atomic oxygen in the middle atmosphere using solid electrolyte sensors and catalytic probes

    NASA Astrophysics Data System (ADS)

    Eberhart, M.; Löhle, S.; Steinbeck, A.; Binder, T.; Fasoulas, S.

    2015-09-01

    The middle- and upper-atmospheric energy budget is largely dominated by reactions involving atomic oxygen (O). Modeling of these processes requires detailed knowledge about the distribution of this oxygen species. Understanding the mutual contributions of atomic oxygen and wave motions to the atmospheric heating is the main goal of the rocket project WADIS (WAve propagation and DISsipation in the middle atmosphere). It includes, amongst others, our instruments for the measurement of atomic oxygen that have both been developed with the aim of resolving density variations on small vertical scales along the trajectory. In this paper the instrument based on catalytic effects (PHLUX: Pyrometric Heat Flux Experiment) is introduced briefly. The experiment employing solid electrolyte sensors (FIPEX: Flux φ(Phi) Probe Experiment) is presented in detail. These sensors were laboratory calibrated using a microwave plasma as a source of atomic oxygen in combination with mass spectrometer reference measurements. The spectrometer was in turn calibrated for O with a method based on methane. In order to get insight into the horizontal variability, the rocket payload had instrument decks at both ends. Each housed several sensor heads measuring during both the up- and downleg of the trajectory. The WADIS project comprises two rocket flights during different geophysical conditions. Results from WADIS-1 are presented, which was successfully launched in June 2013 from the Andøya Space Center, Norway. FIPEX data were sampled at 100 Hz and yield atomic oxygen density profiles with a vertical resolution better than 9 m. This allows density variations to be studied on very small spatial scales. Numerical simulations of the flow field around the rocket were done at several points of the trajectory to assess the influence of aerodynamic effects on the measurement results. Density profiles peak at 3 × 1010 cm-3 at altitudes of 93.6 and 96 km for the up- and downleg, respectively.

  16. Fabrication of specimens of metamorphic magnetite crystals for field ion microscopy and atom probe microanalysis.

    PubMed

    Kuhlman, K R; Martens, R L; Kelly, T F; Evans, N D; Miller, M K

    2001-10-01

    Field ion specimens have been successfully fabricated from samples of metamorphic magnetite crystals (Fe3O4) extracted from a polymetamorphosed, granulite-facies marble with the use of a focused ion beam. These magnetite crystals contain nanometer-scale, disk-shaped inclusions making this magnetite particularly attractive for investigating the capabilities of atom probe field ion microscopy (APFIM) for geological materials. Field ion microscope images of these magnetite crystals were obtained in which the observed size and morphology of the precipitates agree with previous results. Samples were analyzed in the energy compensated optical position-sensitive atom probe. Mass spectra were obtained in which peaks for singly ionized 16O, 56Fe and 56FeO and doubly ionized 54Fe, 56Fe and 57Fe peaks were fully resolved. Manganese and aluminum were observed in a limited analysis of a precipitate in an energy compensated position sensitive atom probe. PMID:11770743

  17. Preparation and Analysis of Atom Probe Tips by Xenon Focused Ion Beam Milling.

    PubMed

    Estivill, Robert; Audoit, Guillaume; Barnes, Jean-Paul; Grenier, Adeline; Blavette, Didier

    2016-06-01

    The damage and ion distribution induced in Si by an inductively coupled plasma Xe focused ion beam was investigated by atom probe tomography. By using predefined patterns it was possible to prepare the atom probe tips with a sub 50 nm end radius in the ion beam microscope. The atom probe reconstruction shows good agreement with simulated implantation profiles and interplanar distances extracted from spatial distribution maps. The elemental profiles of O and C indicate co-implantation during the milling process. The presence of small disc-shaped Xe clusters are also found in the three-dimensional reconstruction. These are attributed to the presence of Xe nanocrystals or bubbles that open during the evaporation process. The expected accumulated dose points to a loss of >95% of the Xe during analysis, which escapes undetected. PMID:27056544

  18. Probing starch-iodine interaction by atomic force microscopy.

    PubMed

    Du, Xiongwei; An, Hongjie; Liu, Zhongdong; Yang, Hongshun; Wei, Lijuan

    2014-01-01

    We explored the interaction of iodine with three crystalline type starches, corn, potato, and sweet potato starches using atomic force microscopy. Results revealed that starch molecules aggregated through interaction with iodine solution as well as iodine vapor. Detailed fine structures such as networks, chains, and super-helical structures were found in iodide solution tests. The nanostructures formed due to iodine adsorption could help to understand the formation and properties of the starch-iodine complex. PMID:24338992

  19. Tailored probes for atomic force microscopy fabricated by two-photon polymerization

    NASA Astrophysics Data System (ADS)

    Göring, Gerald; Dietrich, Philipp-Immanuel; Blaicher, Matthias; Sharma, Swati; Korvink, Jan G.; Schimmel, Thomas; Koos, Christian; Hölscher, Hendrik

    2016-08-01

    3D direct laser writing based on two-photon polymerization is considered as a tool to fabricate tailored probes for atomic force microscopy. Tips with radii of 25 nm and arbitrary shape are attached to conventionally shaped micro-machined cantilevers. Long-term scanning measurements reveal low wear rates and demonstrate the reliability of such tips. Furthermore, we show that the resonance spectrum of the probe can be tuned for multi-frequency applications by adding rebar structures to the cantilever.

  20. Laser assisted atom probe analysis of thin film on insulating substrate.

    PubMed

    Kodzuka, M; Ohkubo, T; Hono, K

    2011-05-01

    We demonstrate that the atom probe analyses of metallic thin films on insulating substrates are possible using laser assisted field evaporation. The tips with metallic thin film and insulating substrate (0.6-3 μm in thickness) were prepared by the lift-out and annular ion beam milling techniques on tungsten supports. In spite of the existence of thick insulating layer between the metallic film and the tungsten support, atom probe tomography with practical mass resolution, signal-to-noise ratio and spatial resolution was found to be possible using laser assisted field evaporation. PMID:21172729

  1. Design of a laser-assisted tomographic atom probe at Muenster University

    SciTech Connect

    Schlesiger, Ralf; Oberdorfer, Christian; Greiwe, Gerd; Stender, Patrick; Artmeier, Michael; Pelka, Patrick; Spaleck, Frank; Schmitz, Guido; Wuerz, Roland

    2010-04-15

    To benefit from the latest technical improvements in atom probe analysis, a new tomographic atom probe has been built at the University of Muenster, Germany. The instrument utilizes a femtosecond laser system with a high repetition rate combined with the ability of using a micrometer-sized extraction electrode and a wide angle configuration. Since field evaporation is triggered by laser pulses instead of high-voltage pulses, the instrument offers the ability to expand the range of analyzed materials to poorly conducting or insulating materials such as oxides, glasses, ceramics, and polymeric materials. The article describes the design of the instrument and presents characterizing measurements on metals, semiconductors, and oxide ceramic.

  2. Atomic oxygen studies on polymers

    NASA Technical Reports Server (NTRS)

    Morison, W. D.; Tennyson, R. C.; French, J. B.; Braithwaite, T.; Moisan, M.; Hubert, J.

    1988-01-01

    The purpose was to study the effects of atomic oxygen on the erosion of polymer based materials. The development of an atomic oxygen neutral beam facility using a SURFATRON surface wave launcher that can produce beam energies between 2 and 3 eV at flux levels as high as approx. 10 to the 17th power atoms/cm (2)-sec is described. Thin film dielectric materials were studied to determine recession rates and and reaction efficiencies as a function of incident beam energy and fluence. Accelerated testing was also accomplished and the values of reaction efficiency compared to available space flight data. Electron microscope photomicrographs of the samples' surface morphology were compared to flight test specimens.

  3. Atom-scale compositional distribution in InAlAsSb-based triple junction solar cells by atom probe tomography.

    PubMed

    Hernández-Saz, J; Herrera, M; Delgado, F J; Duguay, S; Philippe, T; Gonzalez, M; Abell, J; Walters, R J; Molina, S I

    2016-07-29

    The analysis by atom probe tomography (APT) of InAlAsSb layers with applications in triple junction solar cells (TJSCs) has shown the existence of In- and Sb-rich regions in the material. The composition variation found is not evident from the direct observation of the 3D atomic distribution and because of this a statistical analysis has been required. From previous analysis of these samples, it is shown that the small compositional fluctuations determined have a strong effect on the optical properties of the material and ultimately on the performance of TJSCs. PMID:27306098

  4. Atom-scale compositional distribution in InAlAsSb-based triple junction solar cells by atom probe tomography

    NASA Astrophysics Data System (ADS)

    Hernández-Saz, J.; Herrera, M.; Delgado, F. J.; Duguay, S.; Philippe, T.; Gonzalez, M.; Abell, J.; Walters, R. J.; Molina, S. I.

    2016-07-01

    The analysis by atom probe tomography (APT) of InAlAsSb layers with applications in triple junction solar cells (TJSCs) has shown the existence of In- and Sb-rich regions in the material. The composition variation found is not evident from the direct observation of the 3D atomic distribution and because of this a statistical analysis has been required. From previous analysis of these samples, it is shown that the small compositional fluctuations determined have a strong effect on the optical properties of the material and ultimately on the performance of TJSCs.

  5. Probing mechanical quantum coherence with an ultracold-atom meter

    SciTech Connect

    Lo Gullo, N.; Busch, Th.; Palma, G. M.; Paternostro, M.

    2011-12-15

    We propose a scheme to probe quantum coherence in the state of a nanocantilever based on its magnetic coupling (mediated by a magnetic tip) with a spinor Bose Einstein condensate (BEC). By mapping the BEC into a rotor, its coupling with the cantilever results in a gyroscopic motion whose properties depend on the state of the cantilever: the dynamics of one of the components of the rotor angular momentum turns out to be strictly related to the presence of quantum coherence in the state of the cantilever. We also suggest a detection scheme relying on Faraday rotation, which produces only a very small back-action on the BEC and is thus suitable for a continuous detection of the cantilever's dynamics.

  6. Magnetoencephalography with a two-color pump probe atomic magnetometer.

    SciTech Connect

    Johnson, Cort N.

    2010-07-01

    The authors have detected magnetic fields from the human brain with a compact, fiber-coupled rubidium spin-exchange-relaxation-free magnetometer. Optical pumping is performed on the D1 transition and Faraday rotation is measured on the D2 transition. The beams share an optical axis, with dichroic optics preparing beam polarizations appropriately. A sensitivity of <5 fT/{radical}Hz is achieved. Evoked responses resulting from median nerve and auditory stimulation were recorded with the atomic magnetometer. Recordings were validated by comparison with those taken by a commercial magnetoencephalography system. The design is amenable to arraying sensors around the head, providing a framework for noncryogenic, whole-head magnetoencephalography.

  7. Probing crystalline insulator surfaces with neutral helium atom scattering: A study of mixed potassium tantalate/niobate and thin films of potassium chloride and p-quaterphenyl on sodium chloride(001)

    NASA Astrophysics Data System (ADS)

    Trelenberg, Thomas Walter

    Results from experiments using a thermal-energy beam of helium atoms as a probe in studying three crystalline insulator surfaces are presented. The primary focus is the simple ferroelectric perovskite, KTa1- xNbxO3 (or KTN when not specifying an Nb concentration) with x = 0.06, 0.10, 0.20, 0.30, and 0.52. Thin films of KCl and p-quaterphenyl grown onto NaCl(001) were also studied. Extending an earlier work on potassium tantalate (KTaO3), freshly cleaved (001) surfaces of niobium-doped potassium tantalate (KTN) were studied. While KTaO3 is an incipient ferroelectric undergoing no bulk phase changes, KTN, with Nb concentration greater than ˜1.5%, is a tunable ferroelectric, existing in several bulk phases depending on the temperature of the material. A metastable feature observed in KTN immediately after cleaving results in satellite peaks around the specular peak which decay over time. Also, small, broad half-order peaks were observed when the surface temperature was cycled between 50 K and 270 K for the first time. Surface hysteresis effects and responses to electric fields were also studied. Surface dispersion curves for the two high-symmetry directions are given for various Nb doping levels and substrate temperatures. This work compares the above phenomena to similar occurrences observed previously in KTaO3, and notes how the responses differ as a function of niobium doping. Also building on previous experience, the growth of KCl on NaCl was studied. Several recent works have focused on the physical interpretation of 3/4-order peaks observed during LEED investigations of this system. A HAS study of this system revealed, at best, a weak indication of several n/4-order peaks, but at film thicknesses well above those reported. In our first attempt to examine the surfaces of films of large organic molecules using HAS, p-quaterphenyl (p-4P) was deposited onto an NaCl surface held at 300K. Diffraction intensities from the NaCl were reduced but produced no other

  8. Study of a wideband probe

    NASA Technical Reports Server (NTRS)

    Alexander, P., Jr.; Salwen, H.

    1972-01-01

    The design of an experiment to measure communication characteristics of wideband satellite-to-ground links is reported. Of special concern are the effects of rainstorms and atmospheric turbulence on path attenuation and phase fluctuation. Multi-tone and pulse probing are considered. A multi-tone technique which is a modification of ATS-5 and ATS-F hardware is recommended. Data extraction and data processing techniques and key hardware requirements for the experiment are reviewed.

  9. Simulation and signal analysis of Akiyama probe applied to atomic force microscope

    NASA Astrophysics Data System (ADS)

    Wang, Longlong; Lu, Mingzhen; Guo, Tong; Gao, Sitian; Zhang, Huakun

    2013-10-01

    Atomic force microscope is one of indispensable measurement tools in nano/micronano precision manufacture and critical dimension measurement. To expand its industry application, a novel head and system are newly designed combined with Nanosensors cooperation's patented probe — Akiyama probe, which is a self-sensing probe. The modal analysis and resonance frequency are obtained by finite element(FE) simulations. Using the Locked-in amplifier, the effective and available signal can be abtained. Through the experiment analysis, the retracting and extending curve reflects the tip and sample interaction. Furthermore, the measurement on the calibrated position system demonstrates that the whole system resolution can reach the nanometer scale.

  10. Probing non-Hermitian physics with flying atoms

    NASA Astrophysics Data System (ADS)

    Wen, Jianming; Xiao, Yanhong; Peng, Peng; Cao, Wanxia; Shen, Ce; Qu, Weizhi; Jiang, Liang

    2016-05-01

    Non-Hermtian optical systems with parity-time (PT) symmetry provide new means for light manipulation and control. To date, most of experimental demonstrations on PT symmetry rely on advanced nanotechnologies and sophisticated fabrication techniques to manmade solid-state materials. Here, we report the first experimental realization of optical anti-PT symmetry, a counterpart of conventional PT symmetry, in a warm atomic-vapor cell. By exploiting rapid coherence transport via flying atoms, we observe essential features of anti-PT symmetry with an unprecedented precision on phase-transition threshold. Moreover, our system allows nonlocal interference of two spatially-separated fields as well as anti-PT assisted four-wave mixing. Besides, another intriguing feature offered by the system is refractionless (or unit-refraction) light propagation. Our results thus represent a significant advance in non-Hermitian physics by bridging a firm connection with the AMO field, where novel phenomena and applications in quantum and nonlinear optics aided by (anti-)PT symmetry can be anticipated.

  11. Probing Individual Atoms and Molecules on Pt(111)

    NASA Astrophysics Data System (ADS)

    Liang, Zhu; Surface; Interface Science Laboratory, Riken, JAPAN Collaboration

    2015-03-01

    A low-temperature scanning tunneling microscopy (LT-STM) is used to investigate the structure and reactivity of atomic nitrogen on Pt surfaces, which is important to a variety of catalytic processes. The adsorption of ammonia on an oxygen covered Pt surface leads to the formation of an NH3-O2 complex. Such a complex serves as a precursor to ammonia oxydehydrogenation, which produces an ordered atomic N layer on the surface when annealed to temperatures above 300 K. (√{ 3} ×√{ 3})R30°-N and p(2 × 2)-N phases are found to coexist at temperatures between 360 and 400 K. After exposing the N-covered surface to hydrogen gas at 300 K, NH molecules are present as scattered molecules, as well as in dense islands. Mechanisms of dissociation of NH and lateral movement of H have been explored by examining the threshold energies and reaction rates. Measuring the response of the motion against applied bias voltage reveals the threshold energy, which is the energy of the vibrational mode that is responsible for activating a given motion. A theoretical model is used to fit the spectra, from which an estimate of reaction rate is obtained. ND dissociation and D hopping have also been investigated to examine the role of tunneling in these reactions. Hyowon Kim, Hyun Jin Yang, and Junepyo Oh are acknowledged for their contributions to this work. Support and supervision by professor Yousoo Kim and professor Michael Trenary are gratefully acknowledged.

  12. Probing the spin states of a single acceptor atom.

    PubMed

    van der Heijden, Joost; Salfi, Joe; Mol, Jan A; Verduijn, Jan; Tettamanzi, Giuseppe C; Hamilton, Alex R; Collaert, Nadine; Rogge, Sven

    2014-03-12

    We demonstrate a single-hole transistor using an individual acceptor dopant embedded in a silicon channel. Magneto-transport spectroscopy reveals that the ground state splits as a function of magnetic field into four states, which is unique for a single hole bound to an acceptor in a bulk semiconductor. The two lowest spin states are heavy (|m(j)| = 3/2) and light (|m(j)| = 1/2) hole-like, a two-level system that can be electrically driven and is characterized by a magnetic field dependent and long relaxation time, which are properties of interest for qubits. Although the bulklike spin splitting of a boron atom is preserved in our nanotransistor, the measured Landé g-factors, |g(hh)| = 0.81 ± 0.06 and |g(lh)| = 0.85 ± 0.21 for heavy and light holes respectively, are lower than the bulk value. PMID:24571637

  13. THERMAL EFFECTS ON MASS AND SPATIAL RESOLUTION DURING LASER PULSE ATOM PROBE TOMOGRAPHY OF CERIUM OXIDE

    SciTech Connect

    Rita Kirchhofer; Melissa C. Teague; Brian P. Gorman

    2013-05-01

    Cerium oxide (CeO2) is an ideal surrogate material for trans-uranic elements and fission products found in nuclear fuels due to similarities in their thermal properties; therefore, cerium oxide was used to determine the best run condition for atom probe tomography (APT). Laser pulse APT is a technique that allows for spatial resolution in the nm scale and isotopic/elemental chemical identification. A systematic study of the impact of laser pulse energy and specimen base temperature on the mass resolution, measurement of stoichiometry, multiples, and evaporation mechanisms are reported in this paper. It was demonstrated that using laser pulse APT stoichiometric field evaporation of cerium oxide was achieved at 1 pJ laser pulse energy and 20 K specimen base temperature.

  14. Real time drift measurement for colloidal probe atomic force microscope: a visual sensing approach

    SciTech Connect

    Wang, Yuliang Bi, Shusheng; Wang, Huimin

    2014-05-15

    Drift has long been an issue in atomic force microscope (AFM) systems and limits their ability to make long time period measurements. In this study, a new method is proposed to directly measure and compensate for the drift between AFM cantilevers and sample surfaces in AFM systems. This was achieved by simultaneously measuring z positions for beads at the end of an AFM colloidal probe and on sample surface through an off-focus image processing based visual sensing method. The working principle and system configuration are presented. Experiments were conducted to validate the real time drift measurement and compensation. The implication of the proposed method for regular AFM measurements is discussed. We believe that this technique provides a practical and efficient approach for AFM experiments requiring long time period measurement.

  15. Shape-dependent adhesion and friction of Au nanoparticles probed with atomic force microscopy.

    PubMed

    Yuk, Youngji; Hong, Jong Wook; Lee, Hyunsoo; Han, Sang Woo; Young Park, Jeong

    2015-03-27

    The relation between surface structure and friction and adhesion is a long-standing question in tribology. Tuning the surface structure of the exposed facets of metal nanoparticles is enabled by shape control. We investigated the effect of the shape of Au nanoparticles on friction and adhesion. Two nanoparticle systems, cubic nanoparticles with a low-index (100) surface and hexoctahedral nanoparticles with a high-index (321) surface, were used as model nanoparticle surfaces. Atomic force microscopy was used to probe the nanoscale friction and adhesion on the nanoparticle surface. Before removing the capping layers, the friction results include contributions from both the geometric factor and the presence of capping layers. After removing the capping layers, we can see the exclusive effect of the surface atomic structure while the geometric effect is maintained. We found that after removing the capping layer, the cubic Au nanoparticles exhibited higher adhesion and friction, compared with cubes capped with layers covering 25% and 70%, respectively. On the other hand, the adhesion and friction of hexoctahedral Au nanoparticles decreased after removing the capping layers, compared with nanoparticles with capping layers. The difference in adhesion and friction forces between the bare Au surfaces and Au nanoparticles with capping layers cannot be explained by geometric factors, such as the slope of the nanoparticle surfaces. The higher adhesion and friction forces on cubic nanoparticles after removing the capping layers is associated with the atomic structure of (100) and (321) (i.e., the flat (100) surfaces of the cubic nanoparticles have a larger contact area, compared with the rough (321) surfaces of the hexoctahedral nanoparticles). This study implies an intrinsic relation between atomic structure and nanomechanical properties, with potential applications for controlling nanoscale friction and adhesion via colloid chemistry. PMID:25765817

  16. Shape-dependent adhesion and friction of Au nanoparticles probed with atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Yuk, Youngji; Hong, Jong Wook; Lee, Hyunsoo; Han, Sang Woo; Park, Jeong Young

    2015-03-01

    The relation between surface structure and friction and adhesion is a long-standing question in tribology. Tuning the surface structure of the exposed facets of metal nanoparticles is enabled by shape control. We investigated the effect of the shape of Au nanoparticles on friction and adhesion. Two nanoparticle systems, cubic nanoparticles with a low-index (100) surface and hexoctahedral nanoparticles with a high-index (321) surface, were used as model nanoparticle surfaces. Atomic force microscopy was used to probe the nanoscale friction and adhesion on the nanoparticle surface. Before removing the capping layers, the friction results include contributions from both the geometric factor and the presence of capping layers. After removing the capping layers, we can see the exclusive effect of the surface atomic structure while the geometric effect is maintained. We found that after removing the capping layer, the cubic Au nanoparticles exhibited higher adhesion and friction, compared with cubes capped with layers covering 25% and 70%, respectively. On the other hand, the adhesion and friction of hexoctahedral Au nanoparticles decreased after removing the capping layers, compared with nanoparticles with capping layers. The difference in adhesion and friction forces between the bare Au surfaces and Au nanoparticles with capping layers cannot be explained by geometric factors, such as the slope of the nanoparticle surfaces. The higher adhesion and friction forces on cubic nanoparticles after removing the capping layers is associated with the atomic structure of (100) and (321) (i.e., the flat (100) surfaces of the cubic nanoparticles have a larger contact area, compared with the rough (321) surfaces of the hexoctahedral nanoparticles). This study implies an intrinsic relation between atomic structure and nanomechanical properties, with potential applications for controlling nanoscale friction and adhesion via colloid chemistry.

  17. Atom probe tomography of Ni-base superalloys Allvac 718Plus and Alloy 718.

    PubMed

    Viskari, L; Stiller, K

    2011-05-01

    Atom probe tomography (APT) allows near atomic scale compositional- and morphological studies of, e.g. matrix, precipitates and interfaces in a wide range of materials. In this work two Ni-base superalloys with similar compositions, Alloy 718 and its derivative Allvac 718Plus, are subject for investigation with special emphasis on the latter alloy. The structural and chemical nuances of these alloys are important for their properties. Of special interest are grain boundaries as their structure and chemistry are important for the materials' ability to resist rapid environmentally induced crack propagation. APT has proved to be suitable for analyses of these types of alloys using voltage pulsed APT. However, for investigations of specimens containing grain boundaries and other interfaces the risk for early specimen fracture is high. Analyses using laser pulsing impose lower electrical field on the specimen thereby significantly increasing the success rate of investigations. Here, the effect of laser pulsing was studied and the derived appropriate acquisition parameters were then applied for microstructural studies, from which initial results are shown. Furthermore, the influence of the higher evaporation field experienced by the hardening γ' Ni(3)(Al,Nb) precipitates on the obtained results is discussed. PMID:21295914

  18. Field Ion Microscopy and Atom Probe Tomography of Metamorphic Magnetite Crystals

    NASA Technical Reports Server (NTRS)

    Kuhlman, K.; Martens, R. L.; Kelly, T. F.; Evans, N. D.; Miller, M. K.

    2001-01-01

    Magnetite has been analysed using Field Ion Microscopy (FIM) and Atom Probe Tomography (APT), highly attractive techniques for the nanoanalysis of geological materials despite the difficulties inherent in analyzing semiconducting and insulating materials. Additional information is contained in the original extended abstract.

  19. Atom probe field ion microscopy and related topics: A bibliography 1992

    SciTech Connect

    Russell, K.F.; Godfrey, R.D.; Miller, M.K.

    1993-12-01

    This bibliography contains citations of books, conference proceedings, journals, and patents published in 1992 on the following types of microscopy: atom probe field ion microscopy (108 items); field emission microscopy (101 items); and field ion microscopy (48 items). An addendum of 34 items missed in previous bibliographies is included.

  20. Cavity-Enhanced Light Scattering in Optical Lattices to Probe Atomic Quantum Statistics

    SciTech Connect

    Mekhov, Igor B.; Maschler, Christoph; Ritsch, Helmut

    2007-03-09

    Different quantum states of atoms in optical lattices can be nondestructively monitored by off-resonant collective light scattering into a cavity. Angle resolved measurements of photon number and variance give information about atom-number fluctuations and pair correlations without single-site access. Observation at angles of diffraction minima provides information on quantum fluctuations insensitive to classical noise. For transverse probing, no photon is scattered into a cavity from a Mott insulator phase, while the photon number is proportional to the atom number for a superfluid.

  1. A variable-width harmonic probe for multifrequency atomic force microscopy

    SciTech Connect

    Cai, Jiandong; Zhang, Li; Xia, Qi E-mail: michael.wang@nus.edu.sg; Luo, Yangjun; Wang, Michael Yu E-mail: michael.wang@nus.edu.sg

    2015-02-16

    In multifrequency atomic force microscopy (AFM) to simultaneously measure topography and material properties of specimens, it is highly desirable that the higher order resonance frequencies of the cantilever probe are assigned to be integer harmonics of the excitation frequency. The harmonic resonances are essential for significant enhancement of the probe's response at the specified harmonic frequencies. In this letter, a structural optimization technique is employed to design cantilever probes so that the ratios between one or more higher order resonance frequencies and the fundamental natural frequency are ensured to be equal to specified integers and, in the meantime, that the fundamental natural frequency is maximized. Width profile of the cantilever probe is the design variable in optimization. Thereafter, the probes were prepared by modifying a commercial probe through the focused ion beam (FIB) milling. The resonance frequencies of the FIB fabricated probes were measured with an AFM. Results of the measurement show that the optimal design of probe is as effective as design prediction.

  2. Characterization of Probe Dynamic Behaviors in Critical Dimension Atomic Force Microscopy.

    PubMed

    Feng, Shaw C; Joung, Che Bong; Vorburger, Theodore V

    2009-01-01

    This paper describes a detailed computational model of the interaction between an atomic force microscope probe tip and a sample surface. The model provides analyses of dynamic behaviors of the tip to estimate the probe deflections due to surface intermittent contact and the resulting dimensional biases and uncertainties. Probe tip and cantilever beam responses to intermittent contact between the probe tip and sample surface are computed using the finite element method. Intermittent contacts with a wall and a horizontal surface are computed and modeled, respectively. Using a 75 nm Critical Dimension (CD) tip as an example, the responses of the probe to interaction forces between the sample surface and the probe tip are shown in both time and frequency domains. In particular, interaction forces between the tip and both a vertical wall and a horizontal surface of a silicon sample are modeled using Lennard-Jones theory. The Snap-in and Snap-out of the probe tip in surface scanning are calculated and shown in the time domain. Based on the given tip-sample interaction force model, the calculation includes the compliance of the probe and dynamic forces generated by an excitation. Cantilever and probe tip deflections versus interaction forces in the time domain can be derived for both vertical contact with a plateau and horizontal contact with a side wall. Dynamic analysis using the finite element method and Lennard-Jones model provide a unique means to analyze the interaction of the probe and sample, including calculation of the deflection and the gap between the probe tip and the measured sample surface. PMID:27504222

  3. Characterization of Probe Dynamic Behaviors in Critical Dimension Atomic Force Microscopy

    PubMed Central

    Feng, Shaw C.; Joung, Che Bong; Vorburger, Theodore V.

    2009-01-01

    This paper describes a detailed computational model of the interaction between an atomic force microscope probe tip and a sample surface. The model provides analyses of dynamic behaviors of the tip to estimate the probe deflections due to surface intermittent contact and the resulting dimensional biases and uncertainties. Probe tip and cantilever beam responses to intermittent contact between the probe tip and sample surface are computed using the finite element method. Intermittent contacts with a wall and a horizontal surface are computed and modeled, respectively. Using a 75 nm Critical Dimension (CD) tip as an example, the responses of the probe to interaction forces between the sample surface and the probe tip are shown in both time and frequency domains. In particular, interaction forces between the tip and both a vertical wall and a horizontal surface of a silicon sample are modeled using Lennard-Jones theory. The Snap-in and Snap-out of the probe tip in surface scanning are calculated and shown in the time domain. Based on the given tip-sample interaction force model, the calculation includes the compliance of the probe and dynamic forces generated by an excitation. Cantilever and probe tip deflections versus interaction forces in the time domain can be derived for both vertical contact with a plateau and horizontal contact with a side wall. Dynamic analysis using the finite element method and Lennard-Jones model provide a unique means to analyze the interaction of the probe and sample, including calculation of the deflection and the gap between the probe tip and the measured sample surface. PMID:27504222

  4. Phase stability and atom probe field ion microscopy of type 308 cre stainless steel weld metal

    NASA Astrophysics Data System (ADS)

    Babu, S. S.; David, S. A.; Vitek, J. M.; Miller, M. K.

    1996-03-01

    Improvement in high-temperature creep-rupture properties of type 308 stainless steel welds due to the controlled addition of boron is related to microstructural evolution during welding and thermal phase stability at creep service temperatures. The microstructure of boron-containing type 308 austenitic stainless steel welds, in the as-welded state, consisted of 8 to 10 pct ferrite in an austenite matrix. Atom probe field ion microscopy studies revealed segregation of boron and carbon to ferriteaustenite boundaries in the as-welded state; the segregation level was less than one monolayer coverage. On aging at 923 K for 100 hours, M23C6 carbides precipitated at ferrite-austenite boundaries. On further aging at 923 K for 1000 hours, the ferrite transformed into σ phase. Similar microstructural evolution was observed in a type 308 stainless steel weld without boron addition. The volume fractions of M23C6 carbides were identical in boron-containing and boron-free welds. Atom probe results from the welds with boron addition in the aged condition showed that the boron dissolved in the M23C6 carbides. However, lattice parameter analysis showed no apparent difference in the extracted carbides from the welds with and without boron. Creep property improvement due to boron addition could not be related to any change in the volume fraction of carbides. However, the results suggest that the incorporation of boron into M23C6 carbides may reduce the tendency for cavity formation along the M23C6 carbide-austenite boundaries and hence improve the resistance to creep fracture. The observed microstructural evolution in welds is consistent with thermodynamic calculations by THERMOCALC software.

  5. Submolecular Imaging by Noncontact Atomic Force Microscopy with an Oxygen Atom Rigidly Connected to a Metallic Probe.

    PubMed

    Mönig, Harry; Hermoso, Diego R; Díaz Arado, Oscar; Todorović, Milica; Timmer, Alexander; Schüer, Simon; Langewisch, Gernot; Pérez, Rubén; Fuchs, Harald

    2016-01-26

    In scanning probe microscopy, the imaging characteristics in the various interaction channels crucially depend on the chemical termination of the probe tip. Here we analyze the contrast signatures of an oxygen-terminated copper tip with a tetrahedral configuration of the covalently bound terminal O atom. Supported by first-principles calculations we show how this tip termination can be identified by contrast analysis in noncontact atomic force and scanning tunneling microscopy (NC-AFM, STM) on a partially oxidized Cu(110) surface. After controlled tip functionalization by soft indentations of only a few angstroms in an oxide nanodomain, we demonstrate that this tip allows imaging an organic molecule adsorbed on Cu(110) by constant-height NC-AFM in the repulsive force regime, revealing its internal bond structure. In established tip functionalization approaches where, for example, CO or Xe is deliberately picked up from a surface, these probe particles are only weakly bound to the metallic tip, leading to lateral deflections during scanning. Therefore, the contrast mechanism is subject to image distortions, artifacts, and related controversies. In contrast, our simulations for the O-terminated Cu tip show that lateral deflections of the terminating O atom are negligible. This allows a detailed discussion of the fundamental imaging mechanisms in high-resolution NC-AFM experiments. With its structural rigidity, its chemically passivated state, and a high electron density at the apex, we identify the main characteristics of the O-terminated Cu tip, making it a highly attractive complementary probe for the characterization of organic nanostructures on surfaces. PMID:26605698

  6. Nondestructive probing of means, variances, and correlations of ultracold-atomic-system densities via qubit impurities

    NASA Astrophysics Data System (ADS)

    Elliott, T. J.; Johnson, T. H.

    2016-04-01

    We show how impurity atoms can measure moments of ultracold-atomic-gas densities, using the example of bosons in a one-dimensional lattice. This builds on a body of work regarding the probing of systems by measuring the dephasing of an immersed qubit. We show that this dephasing is captured by a function resembling characteristic functions of probability theory, of which the derivatives at short times reveal moments of the system operator to which the qubit couples. For a qubit formed by an impurity atom, in a system of ultracold atoms, this operator can be the density of the system at the location of the impurity, and thus means, variances, and correlations of the atomic densities are accessible.

  7. A new systematic framework for crystallographic analysis of atom probe data.

    PubMed

    Araullo-Peters, Vicente J; Breen, Andrew; Ceguerra, Anna V; Gault, Baptiste; Ringer, Simon P; Cairney, Julie M

    2015-07-01

    In this article, after a brief introduction to the principles behind atom probe crystallography, we introduce methods for unambiguously determining the presence of crystal planes within atom probe datasets, as well as their characteristics: location; orientation and interplanar spacing. These methods, which we refer to as plane orientation extraction (POE) and local crystallography mapping (LCM) make use of real-space data and allow for systematic analyses. We present here application of POE and LCM to datasets of pure Al, industrial aluminium alloys and doped-silicon. Data was collected both in DC voltage mode and laser-assisted mode (in the latter of which extracting crystallographic information is known to be more difficult due to distortions). The nature of the atomic planes in both datasets was extracted and analysed. PMID:25747179

  8. Investigation of material property influenced stoichiometric deviations as evidenced during UV laser-assisted atom probe tomography in fluorite oxides

    NASA Astrophysics Data System (ADS)

    Valderrama, Billy; Henderson, Hunter B.; Yablinsky, Clarissa A.; Gan, Jian; Allen, Todd R.; Manuel, Michele V.

    2015-09-01

    Oxide materials are used in numerous applications such as thermal barrier coatings, nuclear fuels, and electrical conductors and sensors, all applications where nanometer-scale stoichiometric changes can affect functional properties. Atom probe tomography can be used to characterize the precise chemical distribution of individual species and spatially quantify the oxygen to metal ratio at the nanometer scale. However, atom probe analysis of oxides can be accompanied by measurement artifacts caused by laser-material interactions. In this investigation, two technologically relevant oxide materials with the same crystal structure and an anion to cation ratio of 2.00, pure cerium oxide (CeO2) and uranium oxide (UO2) are studied. It was determined that electronic structure, optical properties, heat transfer properties, and oxide stability strongly affect their evaporation behavior, thus altering their measured stoichiometry, with thermal conductance and thermodynamic stability being strong factors.

  9. Switching surface polarization of atomic force microscopy probe utilizing photoisomerization of photochromic molecules

    SciTech Connect

    Aburaya, Yoshihiro; Nomura, Hikaru; Kageshima, Masami; Naitoh, Yoshitaka; Li, Yan Jun; Sugawara, Yasuhiro

    2011-03-15

    An attempt to develop an atomic force microscopy (AFM) probe with optically switchable polarization is described. Modification with a single molecular layer of photochromic molecules was attempted onto a Si substrate that is a prototype for a probe surface. Polarization switching caused by alternate irradiation of UV and visible lights were detected using the electrostatic force?>spectroscopy (EFS) technique. Si substrates modified with spiropyran and azobenzene exhibited reversible polarization switching that caused changes in CPD of about 100 and 50 mV, respectively. Modification with spiropyran was also attempted onto a Si probe and resulted in a CPD change of about 100 mV. It was confirmed that modification of an AFM probe or substrate with a single molecular layer of photochromic molecules can generate surface polarization switching of a mechanically detectable level.

  10. Prediction of atomic force microscope probe dynamics through the receptance coupling method

    SciTech Connect

    Mehrpouya, M.; Park, S. S.

    2011-12-15

    The increased growth in the use of tip-based sensing, manipulations, and fabrication of devices in atomic force microscopy (AFM) necessitates the accurate prediction of the dynamic behavior of the AFM probe. The chip holder, to which the micro-sensing device is attached, and the rest of the AFM system can affect the overall dynamics of the probe. In order to consider these boundary effects, we propose a novel receptance coupling method to mathematically combine the dynamics of the AFM setup and probe, based on the equilibrium and compatibility conditions at the joint. Once the frequency response functions of displacement over force at the tool tip are obtained, the dynamic interaction forces between the tip and the sample in nanoscale can be determined by measuring the probe tip displacement.

  11. Atom probe characterization of nano-scaled features in irradiated ODS Eurofer steel

    NASA Astrophysics Data System (ADS)

    Rogozhkin, S. V.; Aleev, A. A.; Zaluzhnyi, A. G.; Nikitin, A. A.; Iskandarov, N. A.; Vladimirov, P.; Lindau, R.; Möslang, A.

    2011-02-01

    Our previous investigations of unirradiated ODS Eurofer by tomographic atom probe (TAP) revealed numerous nano-scaled features (nanoclusters) enriched in vanadium, yttrium and oxygen. In this work the effect of neutron irradiation on nanostructure behaviour of ODS Eurofer (9%-CrWVTa) was investigated. The irradiation was performed in the research reactor BOR-60 (Dimitrovgrad, Russia) where materials were irradiated at 330 °С to 32 dpa. TAP studies were performed on the needles prepared from parts of broken Charpy specimens. For all specimens except one, which was tested at 500 °C, the Charpy tests were performed at temperatures not exceeding the irradiation temperature. A high number density 2-4 × 10 24 m -3 of ultra fine 1-3 nm diameter nanoclusters enriched in yttrium, oxygen, manganese and chromium was observed in the irradiated state. The composition of detected clusters differs from that for unirradiated ODS Eurofer. It was observed in this work that after neutron irradiation vanadium atoms had left the clusters, moving from the core into solid solution. The concentrations of yttrium and oxygen in the matrix, as it was detected, increase several times under irradiation. In the samples tested at 500 °C both the number density of clusters and the yttrium concentration in the matrix decrease by a factor of two.

  12. Fabrication of tungsten probe for hard tapping operation in atomic force microscopy.

    PubMed

    Han, Guebum; Ahn, Hyo-Sok

    2016-02-01

    We propose a method of producing a tungsten probe with high stiffness for atomic force microscopy (AFM) in order to acquire enhanced phase contrast images and efficiently perform lithography. A tungsten probe with a tip radius between 20nm and 50nm was fabricated using electrochemical etching optimized by applying pulse waves at different voltages. The spring constant of the tungsten probe was determined by finite element analysis (FEA), and its applicability as an AFM probe was evaluated by obtaining topography and phase contrast images of a Si wafer sample partly coated with Au. Enhanced hard tapping performance of the tungsten probe compared with a commercial Si probe was confirmed by conducting hard tapping tests at five different oscillation amplitudes on single layer graphene grown by chemical vapor deposition (CVD). To analyze the damaged graphene sample, the test areas were investigated using tip-enhanced Raman spectroscopy (TERS). The test results demonstrate that the tungsten probe with high stiffness was capable of inducing sufficient elastic and plastic deformation to enable obtaining enhanced phase contrast images and performing lithography, respectively. PMID:26630069

  13. Lateral force calibration: accurate procedures for colloidal probe friction measurements in atomic force microscopy.

    PubMed

    Chung, Koo-Hyun; Pratt, Jon R; Reitsma, Mark G

    2010-01-19

    The colloidal probe technique for atomic force microscopy (AFM) has allowed the investigation of an extensive range of surface force phenomena, including the measurement of frictional (lateral) forces between numerous materials. The quantitative accuracy of such friction measurements is often debated, in part due to a lack of confidence in existing calibration strategies. Here we compare three in situ AFM lateral force calibration techniques using a single colloidal probe, seeking to establish a foundation for quantitative measurement by linking these techniques to accurate force references available at the National Institute of Standards and Technology. We introduce a procedure for calibrating the AFM lateral force response to known electrostatic forces applied directly to the conductive colloidal probe. In a second procedure, we apply known force directly to the colloidal probe using a precalibrated piezo-resistive reference cantilever. We found agreement between these direct methods on the order of 2% (within random uncertainty for both measurements). In a third procedure, we performed a displacement-based calibration using the piezo-resistive reference cantilever as a stiffness reference artifact. The method demonstrated agreement on the order of 7% with the direct force methods, with the difference attributed to an expected systematic uncertainty, caused by in-plane deflection in the cantilever during loading. The comparison establishes the existing limits of instrument accuracy and sets down a basis for selection criteria for materials and methods in colloidal probe friction (lateral) force measurements via atomic force microscopy. PMID:19827782

  14. Diamond-modified AFM probes: from diamond nanowires to atomic force microscopy-integrated boron-doped diamond electrodes.

    PubMed

    Smirnov, Waldemar; Kriele, Armin; Hoffmann, René; Sillero, Eugenio; Hees, Jakob; Williams, Oliver A; Yang, Nianjun; Kranz, Christine; Nebel, Christoph E

    2011-06-15

    In atomic force microscopy (AFM), sharp and wear-resistant tips are a critical issue. Regarding scanning electrochemical microscopy (SECM), electrodes are required to be mechanically and chemically stable. Diamond is the perfect candidate for both AFM probes as well as for electrode materials if doped, due to diamond's unrivaled mechanical, chemical, and electrochemical properties. In this study, standard AFM tips were overgrown with typically 300 nm thick nanocrystalline diamond (NCD) layers and modified to obtain ultra sharp diamond nanowire-based AFM probes and probes that were used for combined AFM-SECM measurements based on integrated boron-doped conductive diamond electrodes. Analysis of the resonance properties of the diamond overgrown AFM cantilevers showed increasing resonance frequencies with increasing diamond coating thicknesses (i.e., from 160 to 260 kHz). The measured data were compared to performed simulations and show excellent correlation. A strong enhancement of the quality factor upon overgrowth was also observed (120 to 710). AFM tips with integrated diamond nanowires are shown to have apex radii as small as 5 nm and where fabricated by selectively etching diamond in a plasma etching process using self-organized metal nanomasks. These scanning tips showed superior imaging performance as compared to standard Si-tips or commercially available diamond-coated tips. The high imaging resolution and low tip wear are demonstrated using tapping and contact mode AFM measurements by imaging ultra hard substrates and DNA. Furthermore, AFM probes were coated with conductive boron-doped and insulating diamond layers to achieve bifunctional AFM-SECM probes. For this, focused ion beam (FIB) technology was used to expose the boron-doped diamond as a recessed electrode near the apex of the scanning tip. Such a modified probe was used to perform proof-of-concept AFM-SECM measurements. The results show that high-quality diamond probes can be fabricated, which are

  15. An atom probe investigation of the influence of trace impurities on the mechanical behavior of NiAl

    SciTech Connect

    Jayaram, R.; Liu, C.T.; Miller, M.K.

    1993-11-01

    Atom probe field ion microscopy (APFIM) and transmission electron microscopy (TEM) have been used to investigate the influence of trace metallic impurities on the enormous increase in the yield stress of boron-doped NiAl. Previous atom probe studies of NiAl containing 0.12 at. % boron had demonstrated that 0.026 at. % of the boron was in solid solution. The remainder reacted with trace metallic impurities, presumably present in high purity Ni, to form ultrafine MB{sub 2} precipitates ranging in size from less than 2 nm to 20 nm. Atom probe measurements had shown that their number densities were significant enough to make the dominant contribution to the observed increase in yield stress. An attempt was made in the present work to minimize the effect of these precipitates by an additional aging treatment. Field ion microscope (FIM) and TEM micrographs revealed that 2 nm precipitates coarsened significantly during aging. Microstructure of aged NiAl was consistent with observed mechanical behavior showing a significantly smaller increase in the yield stress. An approximate value of the Orowan stress, based on TEM estimates of the size and number density of the precipitates, is in reasonable agreement with the measured value. This APFIM/TEM investigation has indicated a practical approach to minimize the detrimental role of trace impurities in NiAl.

  16. Outer planet entry probe system study. Volume 4: Common Saturn/Uranus probe studies

    NASA Technical Reports Server (NTRS)

    1973-01-01

    Results are summarized of a common scientific probe study to explore the atmospheres of Saturn and Uranus. This was a three-month follow-on effort to the Outer Planet Entry Probe System study. The report presents: (1) a summary, conclusions and recommendations of this study, (2) parametric analysis conducted to support the two system definitions, (3) common Saturn/Uranus probe system definition using the Science Advisory Group's exploratory payload and, (4) common Saturn/Uranus probe system definition using an expanded science complement. Each of the probe system definitions consists of detailed discussions of the mission, science, system and subsystems including telecommunications, data handling, power, pyrotechnics, attitude control, structures, propulsion, thermal control and probe-to-spacecraft integration. References are made to the contents of the first three volumes where it is feasible to do so.

  17. Probing biofouling resistant polymer brush surfaces by atomic force microscopy based force spectroscopy.

    PubMed

    Schön, Peter; Kutnyanszky, Edit; ten Donkelaar, Bas; Santonicola, M Gabriella; Tecim, Tugba; Aldred, Nick; Clare, Anthony S; Vancso, G Julius

    2013-02-01

    The protein repellency and biofouling resistance of zwitterionic poly(sulfobetaine methacrylate)(pSBMA) brushes grafted via surface initiated polymerization (SIP) from silicon and glass substrata was assessed using atomic force microscopy (AFM) adherence experiments. Laboratory settlement assays were conducted with cypris larvae of the barnacle Balanus amphitrite. AFM adherence includes the determination of contact rupture forces when AFM probe tips are withdrawn from the substratum. When the surface of the AFM tip is modified, adherence can be assessed with chemical specifity using a method known as chemical force microscopy (CFM). In this study, AFM tips were chemically functionalized with (a) fibronectin- here used as model for a nonspecifically adhering protein - and (b) arginine-glycine-aspartic acid (RGD) peptide motifs covalently attached to poly(methacrylic acid) (PMAA) brushes as biomimics of cellular adhesion receptors. Fibronectin functionalized tips showed significantly reduced nonspecific adhesion to pSBMA-modified substrata compared to bare gold (2.3±0.75 nN) and octadecanethiol (ODT) self-assembled monolayers (1.3±0.75 nN). PMAA and PMAA-RGD modified probes showed no significant adhesion to pSBMA modified silicon substrata. The results gathered through AFM protein adherence studies were complemented by laboratory fouling studies, which showed no adhesion of cypris larvae of Balanus amphitrite on pSBMA. With regard to its unusually high non-specific adsorption to a wide variety of materials the behavior of fibronectin is analogous to the barnacle cyprid temporary adhesive that also binds well to surfaces differing in polarity, charge and free energy. The antifouling efficacy of pSBMA may, therefore, be directly related to the ability of this surface to resist nonspecific protein adsorption. PMID:23138001

  18. Spatial decomposition of molecular ions within 3D atom probe reconstructions.

    PubMed

    Breen, Andrew; Moody, Michael P; Gault, Baptiste; Ceguerra, Anna V; Xie, Kelvin Y; Du, Sichao; Ringer, Simon P

    2013-09-01

    Two methods for separating the constituent atoms of molecular ions within atom probe tomography reconstructions are presented. The Gaussian Separation Method efficiently deconvolutes molecular ions containing two constituent atoms and is tested on simulated data before being applied to an experimental HSLA steel dataset containing NbN. The Delaunay Separation Method extends separation to larger complex ions and is also tested on simulated data before being applied to an experimental GaAs dataset containing many large (>3 atoms) complex ions. First nearest neighbour (1NN) distributions and images of the reconstruction before and after the separations are used to show the effect of the algorithms and their validity and practicality are also discussed. PMID:23522847

  19. A filtering method to reveal crystalline patterns from atom probe microscopy desorption maps

    PubMed Central

    Yao, Lan

    2016-01-01

    A filtering method to reveal the crystallographic information present in Atom Probe Microscopy (APM) data is presented. The method filters atoms based on the time difference between their evaporation and the evaporation of the previous atom. Since this time difference correlates with the location and the local structure of the evaporating atoms on the surface, it can be used to reveal any crystallographic information contained within APM data. The demonstration of this method is illustrated on: • A pure Al specimen for which crystallographic poles are clearly visible on the desorption patterns easily indexed. • Three Fe-15at.% Cr datasets where crystallographic patterns are less obvious and require this filtering method. PMID:27104149

  20. Dynamics of Hollow Atom Formation in Intense X-Ray Pulses Probed by Partial Covariance Mapping

    NASA Astrophysics Data System (ADS)

    Frasinski, L. J.; Zhaunerchyk, V.; Mucke, M.; Squibb, R. J.; Siano, M.; Eland, J. H. D.; Linusson, P.; v. d. Meulen, P.; Salén, P.; Thomas, R. D.; Larsson, M.; Foucar, L.; Ullrich, J.; Motomura, K.; Mondal, S.; Ueda, K.; Osipov, T.; Fang, L.; Murphy, B. F.; Berrah, N.; Bostedt, C.; Bozek, J. D.; Schorb, S.; Messerschmidt, M.; Glownia, J. M.; Cryan, J. P.; Coffee, R. N.; Takahashi, O.; Wada, S.; Piancastelli, M. N.; Richter, R.; Prince, K. C.; Feifel, R.

    2013-08-01

    When exposed to ultraintense x-radiation sources such as free electron lasers (FELs) the innermost electronic shell can efficiently be emptied, creating a transient hollow atom or molecule. Understanding the femtosecond dynamics of such systems is fundamental to achieving atomic resolution in flash diffraction imaging of noncrystallized complex biological samples. We demonstrate the capacity of a correlation method called “partial covariance mapping” to probe the electron dynamics of neon atoms exposed to intense 8 fs pulses of 1062 eV photons. A complete picture of ionization processes competing in hollow atom formation and decay is visualized with unprecedented ease and the map reveals hitherto unobserved nonlinear sequences of photoionization and Auger events. The technique is particularly well suited to the high counting rate inherent in FEL experiments.

  1. Probing effective slippage on superhydrophobic stripes by atomic force microscopy.

    PubMed

    Nizkaya, Tatiana V; Dubov, Alexander L; Mourran, Ahmed; Vinogradova, Olga I

    2016-08-17

    While the effective slippage of water past superhydrophobic surfaces has been studied over a decade, theoretical predictions have never been properly confirmed by experiments. Here we measure a drag force on a sphere approaching a plane decorated by superhydrophobic grooves and compare the results with the predictions of semi-analytical theory developed here, which employs the gas cushion model to calculate the local slip length at the gas sectors. We demonstrate that at intermediate and large (compared to a texture period) separations the half-sum of longitudinal and transverse effective slip lengths can be deduced from the force-distance curve by using the known analytical theory of hydrodynamic interaction of a sphere with a homogeneous slipping plane. This half-sum is shown to depend on the fraction of gas sectors and its value is in excellent agreement with theoretical predictions. At small distances the half-sum of effective longitudinal and transverse slip lengths becomes separation-dependent, and is in quantitative agreement with the predictions of our semi-analytical theory. PMID:27476481

  2. Probing Charges on the Atomic Scale by Means of Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Albrecht, F.; Repp, J.; Fleischmann, M.; Scheer, M.; Ondráček, M.; Jelínek, P.

    2015-08-01

    Kelvin probe force spectroscopy was used to characterize the charge distribution of individual molecules with polar bonds. Whereas this technique represents the charge distribution with moderate resolution for large tip-molecule separations, it fails for short distances. Here, we introduce a novel local force spectroscopy technique which allows one to better disentangle electrostatic from other contributions in the force signal. It enables one to obtain charge-related maps at even closer tip-sample distances, where the lateral resolution is further enhanced. This enhanced resolution allows one to resolve contrast variations along individual polar bonds.

  3. Probing Charges on the Atomic Scale by Means of Atomic Force Microscopy.

    PubMed

    Albrecht, F; Repp, J; Fleischmann, M; Scheer, M; Ondráček, M; Jelínek, P

    2015-08-14

    Kelvin probe force spectroscopy was used to characterize the charge distribution of individual molecules with polar bonds. Whereas this technique represents the charge distribution with moderate resolution for large tip-molecule separations, it fails for short distances. Here, we introduce a novel local force spectroscopy technique which allows one to better disentangle electrostatic from other contributions in the force signal. It enables one to obtain charge-related maps at even closer tip-sample distances, where the lateral resolution is further enhanced. This enhanced resolution allows one to resolve contrast variations along individual polar bonds. PMID:26317733

  4. Atom-surface studies with Rb Rydberg atoms

    NASA Astrophysics Data System (ADS)

    Chao, Yuanxi; Sheng, Jiteng; Sedlacek, Jonathon; Shaffer, James

    2015-05-01

    We report on experimental and theoretical progress studying atom-surface interactions using rubidium Rydberg atoms. Rydberg atoms can be strongly coupled to surface phonon polariton (SPhP) modes of a dielectric material. The coherent interaction between Rydberg atoms and SPhPs has potential applications for quantum hybrid devices. Calculations of TM-mode SPhPs on engineered surfaces of periodically poled lithium niobate (PPLN) and lithium tantalate (PPLT) for different periodic domains and surface orientations, as well as natural materials such as quartz, are presented. Our SPhP calculations account for the semi-infinite anisotropic nature of the materials. In addition to theoretical calculations, we show experimental results of measurements of adsorbate fields and coupling of Rydberg atoms to SPhPs on quartz.

  5. Quantitative dopant distributions in GaAs nanowires using atom probe tomography.

    PubMed

    Du, Sichao; Burgess, Timothy; Gault, Baptiste; Gao, Qiang; Bao, Peite; Li, Li; Cui, Xiangyuan; Kong Yeoh, Wai; Liu, Hongwei; Yao, Lan; Ceguerra, Anna V; Hoe Tan, Hark; Jagadish, Chennupati; Ringer, Simon P; Zheng, Rongkun

    2013-09-01

    Controllable doping of semiconductor nanowires is critical to realize their proposed applications, however precise and reliable characterization of dopant distributions remains challenging. In this article, we demonstrate an atomic-resolution three-dimensional elemental mapping of pristine semiconductor nanowires on growth substrates by using atom probe tomography to tackle this major challenge. This highly transferrable method is able to analyze the full diameter of a nanowire, with a depth resolution better than 0.17 nm thanks to an advanced reconstruction method exploiting the specimen's crystallography, and an enhanced chemical sensitivity of better than 8-fold increase in the signal-to-noise ratio. PMID:23489910

  6. Methodology exploration of specimen preparation for atom probe tomography from nanowires.

    PubMed

    Qu, Jiangtao; Wong, Derek; Du, Sichao; Yang, Limei; Ringer, Simon; Zheng, Rongkun

    2015-12-01

    Semiconductor nanowires have been intensively explored for applications in electronics, photonics, energy conversion and storage. A fundamental and quantitative understanding of growth-structure-property relationships is central to applications where nanowires exhibit clear advantages. Atom Probe Tomography (APT) is able to provide 3 dimensional quantitative elemental distributions at atomic-resolution and is therefore unique in understanding the growth-structure-property relationships. However, the specimen preparation with nanowires is extremely challenging. In this paper, two ion beam free specimen preparation methods for APT are presented which are efficient for various nanowires. PMID:26119926

  7. Atom probe field ion microscopy investigation of boron containing martensitic 9 Pct chromium steel

    NASA Astrophysics Data System (ADS)

    Hofer, P.; Miller, M. K.; Babu, S. S.; David, S. A.; Cerjak, H.

    2000-03-01

    The chemical compositions of the ferrite matrix and various other phases in an Fe-0.17 C-9 Cr-1.55 Mo-0.27 V-0.015 N-0.01B (mass pct) steel in as-received and crept conditions were measured with atom probe field ion microscopy (APFIM). The results showed the presence of some residual boron within the ferrite matrix. Analyses showed that boron was distributed within M23C6, M6C, MX, and Laves phases. Phosphor atoms were detected at the M23C6-ferrite interface in the crept condition. The results are compared to predictions from thermodynamic calculations.

  8. Acoustic Attenuation Probe for Fermion Superfluidity in Ultracold-Atom Gases

    SciTech Connect

    Gaudio, Sergio; Mihaila, Bogdan; Blagoev, Krastan B.; Timmermans, Eddy; Bedell, Kevin S.

    2007-03-16

    Dilute gas Bose-Einstein condensates (BEC's), currently used to cool fermionic atoms in atom traps, can also probe the superfluidity of these fermions. The damping rate of BEC-acoustic excitations (phonon modes), measured in the middle of the trap as a function of the phonon momentum, yields an unambiguous signature of BCS-like superfluidity, provides a measurement of the superfluid gap parameter, and gives an estimate of the size of the Cooper pairs in the BEC-BCS crossover regime. We also predict kinks in the momentum dependence of the damping rate which can reveal detailed information about the fermion quasiparticle dispersion relation.

  9. A computational geometry framework for the optimisation of atom probe reconstructions.

    PubMed

    Felfer, Peter; Cairney, Julie

    2016-10-01

    In this paper, we present pathways for improving the reconstruction of atom probe data on a coarse (>10nm) scale, based on computational geometry. We introduce a way to iteratively improve an atom probe reconstruction by adjusting it, so that certain known shape criteria are fulfilled. This is achieved by creating an implicit approximation of the reconstruction through a barycentric coordinate transform. We demonstrate the application of these techniques to the compensation of trajectory aberrations and the iterative improvement of the reconstruction of a dataset containing a grain boundary. We also present a method for obtaining a hull of the dataset in both detector and reconstruction space. This maximises data utilisation, and can be used to compensate for ion trajectory aberrations caused by residual fields in the ion flight path through a 'master curve' and correct for overall shape deviations in the data. PMID:27449275

  10. Achieving atomic resolution magnetic dichroism by controlling the phase symmetry of an electron probe

    DOE PAGESBeta

    Rusz, Jan; Idrobo, Juan -Carlos; Bhowmick, Somnath

    2014-09-30

    The calculations presented here reveal that an electron probe carrying orbital angular momentum is just a particular case of a wider class of electron beams that can be used to measure electron magnetic circular dichroism (EMCD) with atomic resolution. It is possible to obtain an EMCD signal with atomic resolution by simply breaking the symmetry of the electron probe phase front using the aberration-corrected optics of a scanning transmission electron microscope. The probe’s required phase distribution depends on the sample’s magnetic symmetry and crystal structure. The calculations indicate that EMCD signals that use the electron probe’s phase are as strongmore » as those obtained by nanodiffraction methods.« less

  11. Achieving atomic resolution magnetic dichroism by controlling the phase symmetry of an electron probe

    SciTech Connect

    Rusz, Jan; Idrobo, Juan -Carlos; Bhowmick, Somnath

    2014-09-30

    The calculations presented here reveal that an electron probe carrying orbital angular momentum is just a particular case of a wider class of electron beams that can be used to measure electron magnetic circular dichroism (EMCD) with atomic resolution. It is possible to obtain an EMCD signal with atomic resolution by simply breaking the symmetry of the electron probe phase front using the aberration-corrected optics of a scanning transmission electron microscope. The probe’s required phase distribution depends on the sample’s magnetic symmetry and crystal structure. The calculations indicate that EMCD signals that use the electron probe’s phase are as strong as those obtained by nanodiffraction methods.

  12. Nanomanipulation and nanofabrication with multi-probe STM: From individual atoms to nanowires

    SciTech Connect

    Qin, Shengyong; Kim, Tae Hwan; Wang, Zhouhang; Li, An-Ping

    2012-01-01

    The wide variety of nanoscale structures and devices demands novel tools for handling, assembly, and fabrication at nanoscopic positioning precision. The manipulation tools should allow for in situ characterization and testing of fundamental building blocks, such as nanotubes and nanowires, as they are built into functional devices. In this paper, a bottom-up technique for nanomanipulation and nanofabrication is reported by using a 4-probe scanning tunneling microscope (STM) combined with a scanning electron microscope (SEM). The applications of this technique are demonstrated in a variety of nanosystems, from manipulating individual atoms to bending, cutting, breaking carbon nanofibers, and constructing nanodevices for electrical characterizations. The combination of the wide field of view of SEM, the atomic position resolution of STM, and the flexibility of multiple scanning probes is expected to be a valuable tool for rapid prototyping in the nanoscience and nanotechnology.

  13. Atomic probes of surface structure and dynamics. Technical progress report, September 15, 1991--September 14, 1992

    SciTech Connect

    Heller, E.J.; Jonsson, H.

    1992-12-31

    The following were studied: New semiclassical method for scattering calculations, He atom scattering from defective Pt surfaces, He atom scattering from Xe overlayers, thermal dissociation of H{sub 2} on Cu(110), spin flip scattering of atoms from surfaces, and Car-Parrinello simulations of surface processes.

  14. New atomic probes for dark matter detection: Axions, axion-like particles and topological defects

    NASA Astrophysics Data System (ADS)

    Stadnik, Yevgeny V.; Flambaum, Victor V.

    2014-11-01

    We present a brief overview of recently proposed detection schemes for axion, axion-like pseudoscalar particle and topological defect dark matter. We focus mainly on the possibility of using atomic and molecular systems for dark matter detection. For axions and axion-like particles, these methods are complementary probes to ongoing photon-axion interconversion experiments and astrophysical observations. For topological defects, these methods are complementary to conventional astrophysical search schemes based on gravitational signatures.

  15. Accurate noncontact calibration of colloidal probe sensitivities in atomic force microscopy

    SciTech Connect

    Chung, Koo-Hyun; Shaw, Gordon A.; Pratt, Jon R.

    2009-06-15

    The absolute force sensitivities of colloidal probes comprised of atomic force microscope, or AFM, cantilevers with microspheres attached to their distal ends are measured. The force sensitivities are calibrated through reference to accurate electrostatic forces, the realizations of which are described in detail. Furthermore, the absolute accuracy of a common AFM force calibration scheme, known as the thermal noise method, is evaluated. It is demonstrated that the thermal noise method can be applied with great success to colloidal probe calibration in air and in liquid to yield force measurements with relative standard uncertainties below 5%. Techniques to combine the electrostatics-based determination of the AFM force sensitivity with measurements of the colloidal probe's thermal noise spectrum to compute noncontact estimates of the displacement sensitivity and spring constant are also developed.

  16. Resistance of single polyaniline fibers and their junctions measured by double-probe atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Higuchi, Rintaro; Shingaya, Yoshitaka; Nakayama, Tomonobu

    2016-08-01

    Electrical properties of polyaniline (PANI) fibers are of our interest as a component of network materials. Using a multiple-probe atomic force microscope with tuning fork probes, we investigated the resistance of single PANI fibers and their cross-point junction where the fibers contact each other. The resistivity of single PANI fibers was measured to be on the order of 10 Ω cm, and the contact resistance between PANI fibers was on the order of GΩ. The resistances through single cross-point junctions between two PANI fibers were very much dependent on the experimental condition, that is, the cross-point junction is stabilized or destabilized by physically placing the probes onto the two fibers. This suggests the nanomechanical instability of the cross-point junctions and a possibility to construct strain-responsive PANI fiber networks.

  17. Proposal for efficient two-dimensional atom localization using probe absorption in a microwave-driven four-level atomic system

    SciTech Connect

    Ding Chunling; Li Jiahua; Yang Xiaoxue; Xiong Hao; Zhang Duo

    2011-10-15

    The behavior of two-dimensional (2D) atom localization is explored by monitoring the probe absorption in a microwave-driven four-level atomic medium under the action of two orthogonal standing-wave fields. Because of the position-dependent atom-field interaction, the information about the position of the atom can be obtained via the absorption measurement of the weak probe field. It is found that the localization behavior is significantly improved due to the joint quantum interference induced by the standing-wave and microwave-driven fields. Most importantly, the atom can be localized at a particular position and the maximal probability of finding the atom in one period of the standing-wave fields reaches unity by properly adjusting the system parameters. The proposed scheme may provide a promising way to achieve high-precision and high-resolution 2D atom localization.

  18. Polarisation response of delay dependent absorption modulation in strong field dressed helium atoms probed near threshold

    NASA Astrophysics Data System (ADS)

    Simpson, E. R.; Sanchez-Gonzalez, A.; Austin, D. R.; Diveki, Z.; Hutchinson, S. E. E.; Siegel, T.; Ruberti, M.; Averbukh, V.; Miseikis, L.; Strüber, C. S.; Chipperfield, L.; Marangos, J. P.

    2016-08-01

    We present the first measurement of the vectorial response of strongly dressed helium atoms probed by an attosecond pulse train (APT) polarised either parallel or perpendicular to the dressing field polarisation. The transient absorption is probed as a function of delay between the APT and the linearly polarised 800 nm field of peak intensity 1.3× {10}14 {{W}} {{cm}}-2. The APT spans the photon energy range 16–42 eV, covering the first ionisation energy of helium (24.59 eV). With parallel polarised dressing and probing fields, we observe modulations with periods of one half and one quarter of the dressing field period. When the polarisation of the dressing field is altered from parallel to perpendicular with respect to the APT polarisation we observe a large suppression in the modulation depth of the above ionisation threshold absorption. In addition to this we present the intensity dependence of the harmonic modulation depth as a function of delay between the dressing and probe fields, with dressing field peak intensities ranging from 2 × 1012 to 2 × 1014 {{W}} {{cm}}-2. We compare our experimental results with a full-dimensional solution of the single-atom time-dependent (TD) Schrödinger equation obtained using the recently developed abinitio TD B-spline ADC method and find good qualitative agreement for the above threshold harmonics.

  19. Impact of Dynamic Specimen Shape Evolution on the Atom Probe Tomography Results of Doped Epitaxial Oxide Multilayers: Comparison of Experiment and Simulation

    SciTech Connect

    Madaan, Nitesh; Bao, Jie; Nandasiri, Manjula I.; Xu, Zhijie; Thevuthasan, Suntharampillai; Devaraj, Arun

    2015-08-31

    The experimental atom probe tomography results from two different specimen orientations (top-down and side-ways) of a high oxygen ion conducting Samaria-doped-ceria/Scandia-stabilized-zirconia multilayer thin film solid oxide fuel cell electrolyte was correlated with level-set method based field evaporation simulations for the same specimen orientations. This experiment-theory correlation explains the dynamic specimen shape evolution and ion trajectory aberrations that can induce density artifacts in final reconstruction leading to inaccurate estimation of interfacial intermixing. This study highlights the need and importance of correlating experimental results with field evaporation simulations when using atom probe tomography for studying oxide heterostructure interfaces.

  20. Trapping, cooling and probing fermionic atoms into the Mott and Neel states

    NASA Astrophysics Data System (ADS)

    Georges, Antoine

    2011-03-01

    A new form of quantum condensed matter physics has emerged from the study of ultra-cold fermionic atoms in optical lattices. Experiments have recently reached the incompressible Mott regime. Detailed comparison to theory and computational studies at intermediate temperatures have validated the concept of optical lattice emulation of many-body fermionic systems. Cooling these systems deeper into the quantum degenerate regime, and devising new spectroscopic probes to investigate physical issues of interest such as quasiparticle properties, are key challenges in this context. The presentation will be based in part on the following references: L. De Leo, C.Kollath, A.Georges, M.Ferrero and O.Parcollet Phys. Rev. Lett. 101, 210403(2008); J.-S. Bernier et al. Phys. Rev. A 79, 061601 (2009); R. Jördens et al. Phys. Rev. Lett. 104, 180401 (2010); J.-S. Bernier et al., Phys. Rev. A 81, 063618 (2010); L. De Leo et al., arXiv:1009.2761 Collaboration with J.S. Bernier, L. De Leo and C.Kollath is especially acknowledged. Work supported in part by CNRS, the ``Triangle de la Physique'' and the DARPA-OLE program.

  1. Nanomechanical properties of lithiated Si nanowires probed with atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Lee, Hyunsoo; Shin, Weonho; Choi, Jang Wook; Park, Jeong Young

    2012-07-01

    The nanomechanical properties of fully lithiated and pristine Si nanowires (NWs) deposited on a Si substrate were studied with atomic force microscopy (AFM). Si NWs were synthesized using the vapour-liquid-solid process on stainless-steel substrates using an Au catalyst. Fully lithiated Si NWs were obtained using the electrochemical method, followed by drop-casting on a Si substrate. The roughness of the Si NWs, which was derived from AFM images, is greater for the lithiated Si NWs than for the pristine Si NWs. Force spectroscopy was used to study the influence of lithiation on the tip-surface adhesion force. The lithiated Si NWs revealed a smaller tip-surface adhesion force than the Si substrate by a factor of two, while the adhesion force of the Si NWs is similar to that of the Si substrate. Young's modulus, obtained from the force-distance curve, also shows that the pristine Si NWs have a relatively higher value than the lithiated Si NWs due to the elastically soft and amorphous structures of the lithiated region. These results suggest that force spectroscopy can be used to probe the degree of lithiation at nanometer scale during the charging and discharging processes.

  2. Study of nuclear matter density distributions using hadronic probes

    SciTech Connect

    Kohama, Akihisa; Iida, Kei; Oyamatsu, Kazuhiro

    2011-05-06

    We briefly review our formula for a proton-nucleus total reaction cross section, {sigma}{sub R}, constructed in the black-sphere approximation of nuclei, in which a nucleus is viewed as a 'black' sphere of radius 'a'. Some years ago, using the Glauber model, one of the authors (A.K.) and his collaborators performed numerical simulations to examine the possibility to probe the nuclear matter density distributions of neutron-rich unstable nuclei from proton elastic scatterings 'model-independently'. The present study is another attempt to seek a 'model-independent' framework for systematically analyzing scattering data for studying the matter density distributions of atomic nuclei.

  3. Probing three-dimensional surface force fields with atomic resolution: Measurement strategies, limitations, and artifact reduction

    PubMed Central

    Dagdeviren, Omur E; Schwendemann, Todd C; Mönig, Harry; Altman, Eric I

    2012-01-01

    Summary Noncontact atomic force microscopy (NC-AFM) is being increasingly used to measure the interaction force between an atomically sharp probe tip and surfaces of interest, as a function of the three spatial dimensions, with picometer and piconewton accuracy. Since the results of such measurements may be affected by piezo nonlinearities, thermal and electronic drift, tip asymmetries, and elastic deformation of the tip apex, these effects need to be considered during image interpretation. In this paper, we analyze their impact on the acquired data, compare different methods to record atomic-resolution surface force fields, and determine the approaches that suffer the least from the associated artifacts. The related discussion underscores the idea that since force fields recorded by using NC-AFM always reflect the properties of both the sample and the probe tip, efforts to reduce unwanted effects of the tip on recorded data are indispensable for the extraction of detailed information about the atomic-scale properties of the surface. PMID:23019560

  4. Measuring excited state lifetime of Rb atoms with pump-probe technique

    SciTech Connect

    Zeng, X.; Boiko, D. L.

    2015-08-31

    A technique for measuring the excited state lifetime τ{sub ex} of optical transitions in alkali atoms is presented. It is a form of pump-probe technique based on time-resolved optical transmission through the atomic vapor cell. This technique can serve as an alternative to the traditionally used time-resolved photofluorescence methods when measuring alkali vapor cells with heavily quenched fluorescence, where the τ{sub ex} is expected to be on the order of a few nanoseconds, and the highly sensitive fluorescence detectors with sub-nanosecond temporal resolution that are required may not be available. We use this technique to measure the τ{sub ex} of Rb atoms in vapor cells with different buffer gas pressures.

  5. Detecting and extracting clusters in atom probe data: a simple, automated method using Voronoi cells.

    PubMed

    Felfer, P; Ceguerra, A V; Ringer, S P; Cairney, J M

    2015-03-01

    The analysis of the formation of clusters in solid solutions is one of the most common uses of atom probe tomography. Here, we present a method where we use the Voronoi tessellation of the solute atoms and its geometric dual, the Delaunay triangulation to test for spatial/chemical randomness of the solid solution as well as extracting the clusters themselves. We show how the parameters necessary for cluster extraction can be determined automatically, i.e. without user interaction, making it an ideal tool for the screening of datasets and the pre-filtering of structures for other spatial analysis techniques. Since the Voronoi volumes are closely related to atomic concentrations, the parameters resulting from this analysis can also be used for other concentration based methods such as iso-surfaces. PMID:25497494

  6. Electron Affinity Calculations for Atoms: Sensitive Probe of Many-Body Effects

    NASA Astrophysics Data System (ADS)

    Felfli, Z.; Msezane, A. Z.

    2016-05-01

    Electron-electron correlations and core-polarization interactions are crucial for the existence and stability of most negative ions. Therefore, they can be used as a sensitive probe of many-body effects in the calculation of the electron affinities (EAs) of atoms. The importance of relativistic effects in the calculation of the EAs of atoms has recently been assessed to be insignificant up to Z of 85. Here we use the complex angular momentum (CAM) methodology wherein is embedded fully the electron-electron correlations, to investigate core-polarization interactions in low-energy electron elastic scattering from the atoms In, Sn, Eu, Au and At through the calculation of their EAs. For the core-polarization interaction we use the rational function approximation of the Thomas-Fermi potential, which can be analytically continued into the complex plane. The EAs are extracted from the large resonance peaks in the CAM calculated low-energy electron-atom scattering total cross sections and compared with those from measurements and sophisticated theoretical methods. It is concluded that when the electron-electron correlations and core polarization interactions (both major many-body effects) are accounted for adequately the importance of relativity on the calculation of the EAs of atoms can be assessed. Even for the high Z (85) At atom relativistic effects are estimated to contribute a maximum of 3.6% to its EA calculation.

  7. Practical Issues for Atom Probe Tomography Analysis of III-Nitride Semiconductor Materials.

    PubMed

    Tang, Fengzai; Moody, Michael P; Martin, Tomas L; Bagot, Paul A J; Kappers, Menno J; Oliver, Rachel A

    2015-06-01

    Various practical issues affecting atom probe tomography (APT) analysis of III-nitride semiconductors have been studied as part of an investigation using a c-plane InAlN/GaN heterostructure. Specimen preparation was undertaken using a focused ion beam microscope with a mono-isotopic Ga source. This enabled the unambiguous observation of implantation damage induced by sample preparation. In the reconstructed InAlN layer Ga implantation was demonstrated for the standard "clean-up" voltage (5 kV), but this was significantly reduced by using a lower voltage (e.g., 1 kV). The characteristics of APT data from the desorption maps to the mass spectra and measured chemical compositions were examined within the GaN buffer layer underlying the InAlN layer in both pulsed laser and pulsed voltage modes. The measured Ga content increased monotonically with increasing laser pulse energy and voltage pulse fraction within the examined ranges. The best results were obtained at very low laser energy, with the Ga content close to the expected stoichiometric value for GaN and the associated desorption map showing a clear crystallographic pole structure. PMID:25926083

  8. Atom Probe Tomography Examination of Carbon Redistribution in Quenched and Tempered 4340 Steel

    SciTech Connect

    Clarke, Amy J.; Miller, Michael K.; Alexander, David J.; Field, Robert D.; Clarke, Kester D.

    2012-08-07

    Quenching and tempering produces a wide range of mechanical properties in medium carbon, low alloyed steels - Study fragmentation behavior as a function of heat-treatment. Subtle microstructural changes accompany the mechanical property changes that result from quenching and tempering - Characterize the location and distribution of carbon and alloying elements in the microstructure using atom probe tomography (APT). Perform complementary transmission electron microscopy (TEM). Tempering influences the mechanical properties and fragmentation of quenched 4340 (hemi-shaped samples). APT revealed carbon-enriched features that contain a maximum of {approx}12-14 at.% carbon after quenching to RT (the level of carbon is perhaps associated with the extent of autotempering). TEM confirmed the presence of twinned martensite and indicates {var_epsilon} ({eta}) transition carbides after oil quenching to RT. Tempering at 325 C resulted in carbon-enriched plates (> 25 at.% C) with no significant element partitioning (transition carbides?). Tempering at 450 C and 575 C resulted in cementite ({approx} 25 at.% C) during late stage tempering; Cr, Mn, Mo partitioned to cementite and Si partitioned to ferrite. Tempering at 575 C resulted in P segregation at cementite interfaces and the formation of Cottrell atmospheres.

  9. Atom-probe investigation of precipitation in 12% Cr steel weld metals

    NASA Astrophysics Data System (ADS)

    Cai, Guang-Jun; Lundin, Lars; Andrén, Hans-Olof; Svensson, Lars-Erik

    1994-03-01

    The microstructure of two types of 12% Cr steel weld metals, one with the composition of a common 12% Cr steel and the other with a higher nitrogen content, was studied using TEM (transmission electron microscopy) and APFIM (atom-probe field-ion microscopy) in post-weld heat-treated condition. The microstructure of the 12% Cr weld metals consisted of tempered martensite, retained δ-ferrite, an irregular low-dislocation α-ferrite and precipitates. Precipitates in the weld metals were dominantly M 23C 6 on different boundaries. Plate-like and fine cubic MN and M 2N were found inside the α-ferrite. APFIM analysis showed that M 23C 6 was almost a pure carbide and MN was almost a pure nitride. Carbon and nitrogen in the weld metals mainly existed in the precipitates. High nitrogen content did not change the composition of the precipitates, but increased the quantity of nitrides. Therefore, in the high nitrogen weld metal, the content of strong nitride-forming elements in the matrix decreased. These results are important in order to understand the strengthening mechanism of the high Cr steel weld metals, as well as of other high Cr heat-resistant steels.

  10. Large-Scale Fabrication of Carbon Nanotube Probe Tips For Atomic Force Microscopy Critical Dimension Imaging Applications

    NASA Technical Reports Server (NTRS)

    Ye, Qi Laura; Cassell, Alan M.; Stevens, Ramsey M.; Meyyappan, Meyya; Li, Jun; Han, Jie; Liu, Hongbing; Chao, Gordon

    2004-01-01

    Carbon nanotube (CNT) probe tips for atomic force microscopy (AFM) offer several advantages over Si/Si3N4 probe tips, including improved resolution, shape, and mechanical properties. This viewgraph presentation discusses these advantages, and the drawbacks of existing methods for fabricating CNT probe tips for AFM. The presentation introduces a bottom up wafer scale fabrication method for CNT probe tips which integrates catalyst nanopatterning and nanomaterials synthesis with traditional silicon cantilever microfabrication technology. This method makes mass production of CNT AFM probe tips feasible, and can be applied to the fabrication of other nanodevices with CNT elements.

  11. Inhomogeneous distribution of manganese atoms in ferromagnetic ZnSnAs{sub 2}:Mn thin films on InP revealed by three-dimensional atom probe investigation

    SciTech Connect

    Uchitomi, Naotaka Inoue, Hiroaki; Kato, Takahiro; Toyota, Hideyuki; Uchida, Hiroshi

    2015-05-07

    Atomic-scale Mn distributions in ferromagnetic ZnSnAs{sub 2}:Mn thin films grown on InP substrates have been studied by applying three-dimensional atom probe (3DAP) microscopy. It is found that Mn atoms in cross-sectional 3DAP maps show the presence of inhomogeneities in Mn distribution, which is characteristic patterns of a spinoidal decomposition phase with slightly high and low concentration regions. The high Mn concentration regions are expected to be coherently clustered MnAs in the zinc-blende structure, resulting in the formation of Mn-As random connecting patterns. The origin of room-temperature ferromagnetism in ZnSnAs{sub 2}:Mn on InP can be well explained by the formation of atomic-scale magnetic clustering by spinoidal decomposition without breaking the continuity of the zinc-blende structure, which has been suggested by previous theoretical works. The lattice-matching between magnetic epi-layers and substrates should be one of the most important factors to avoid the formation of secondary hexagonal MnAs phase precipitates in preparing ferromagnetic semiconductor thin films.

  12. Sodium distribution in solar-grade Cu2ZnSnS4 layers using atom-probe tomographic technique

    NASA Astrophysics Data System (ADS)

    Tajima, Shin; Asahi, Ryoji; Isheim, Dieter; Seidman, David N.; Itoh, Tadayoshi; Ohishi, Kei-ichiro

    2015-11-01

    To investigate the effect of alkali doping on Cu2ZnSnS4 (CZTS) photovoltaic cells, we studied compositional distributions in CZTS layers using three-dimensional atom-probe tomography. The segregation of Na at a concentration of approximately 1 at. % was observed predominantly at CZTS grain boundaries. The concentration of Na in the interior of the CZTS grains was below the detection limit (approximately 40 ppm). Na ions may exist as sulfide compounds at CZTS grain boundaries, independent of the presence of oxygen.

  13. Cosmic ray studies with an Interstellar Probe

    NASA Technical Reports Server (NTRS)

    Mewaldt, R. A.; Stone, E. C.

    1990-01-01

    Among the NASA mission concepts that have been suggested for the 21st century is an Interstellar Probe that might be accelerated to a velocity of about 10 to 20 AU/yr, allowing it to leave the heliosphere, ultimately reaching a radial distance of about 500 to 1000 AU in about 50 years. Previous studies of such a mission, and its potential significance for cosmic ray studies, both within the heliosphere, and beyond, in interstellar space are discussed.

  14. Atomic Force Microscope Controlled Topographical Imaging and Proximal Probe Thermal Desorption/Ionization Mass Spectrometry Imaging

    SciTech Connect

    Ovchinnikova, Olga S; Kjoller, Kevin; Hurst, Gregory {Greg} B; Pelletier, Dale A; Van Berkel, Gary J

    2014-01-01

    This paper reports on the development of a hybrid atmospheric pressure atomic force microscopy/mass spectrometry imaging system utilizing nano-thermal analysis probes for thermal desorption surface sampling with subsequent atmospheric pressure chemical ionization and mass analysis. The basic instrumental setup and the general operation of the system were discussed and optimized performance metrics were presented. The ability to correlate topographic images of a surface with atomic force microscopy and a mass spectral chemical image of the same surface, utilizing the same probe without moving the sample from the system, was demonstrated. Co-registered mass spectral chemical images and atomic force microscopy topographical images were obtained from inked patterns on paper as well as from a living bacterial colony on an agar gel. Spatial resolution of the topography images based on pixel size (0.2 m x 0.8 m) was better than the resolution of the mass spectral images (2.5 m x 2.0 m), which were limited by current mass spectral data acquisition rate and system detection levels.

  15. Variation of local atomic structure due to devitrification of Ni-Zr alloy thin films probed by EXAFS measurements

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Debarati; Tiwari, Nidhi; Bhattacharyya, Dibyendu; Jha, S. N.; Basu, S.

    2016-05-01

    Thin film metallic glasses (TFMGs) exhibit properties superior to their bulk counterparts allowing them to be potentially useful in many practical applications. Apart from their technological interest, when converted to crystallized state (devitrification) TFMGs can also act as precursors for partially crystallized or fully crystallized forms. Such devitrified forms are attractive due to their novel structural and magnetic properties. The amorphous-to-crystalline transformation of co-sputtered Ni-Zr alloy thin films through annealing was studied using EXAFS (Extended X-ray Absorption Fine Structure) measurements. Investigation through an atomic probe gives a better insight into the local environment of the atomic species, rendering a deeper understanding of thermal evolution of such materials.

  16. Pressure/temperature fluid cell apparatus for the neutron powder diffractometer instrument: Probing atomic structure in situ

    NASA Astrophysics Data System (ADS)

    Wang, Hsiu-Wen; Fanelli, Victor R.; Reiche, Helmut M.; Larson, Eric; Taylor, Mark A.; Xu, Hongwu; Zhu, Jinlong; Siewenie, Joan; Page, Katharine

    2014-12-01

    This contribution describes a new local structure compatible gas/liquid cell apparatus for probing disordered materials at high pressures and variable temperatures in the Neutron Powder Diffraction instrument at the Lujan Neutron Scattering Center, Los Alamos National Laboratory. The new sample environment offers choices for sample canister thickness and canister material type. Finite element modeling is utilized to establish maximum allowable working pressures of 414 MPa at 15 K and 121 MPa at 600 K. High quality atomic pair distribution function data extraction and modeling have been demonstrated for a calibration standard (Si powder) and for supercritical and subcritical CO2 measurements. The new sample environment was designed to specifically target experimental studies of the local atomic structures involved in geologic CO2 sequestration, but will be equally applicable to a wide variety of energy applications, including sorption of fluids on nano/meso-porous solids, clathrate hydrate formation, catalysis, carbon capture, and H2 and natural gas uptake/storage.

  17. Comet nucleus impact probe feasibility study

    NASA Technical Reports Server (NTRS)

    Castro, A. J.

    1980-01-01

    A top level listing of the comet nucleus impact probe (CNIP) feasibility experiments requirements are presented. A conceptual configuration which shows that the feasibility of engineering the experiment is possible and describes the candidate hardware is discussed. The design studies required in order to design the operating experiment are outlined. An overview of a program plan used to estimate a rough order of magnitude cost for the CNIP experiment is given.

  18. Note: Seesaw actuation of atomic force microscope probes for improved imaging bandwidth and displacement range

    SciTech Connect

    Torun, H.; Torello, D.; Degertekin, F. L.

    2011-08-15

    The authors describe a method of actuation for atomic force microscope (AFM) probes to improve imaging speed and displacement range simultaneously. Unlike conventional piezoelectric tube actuation, the proposed method involves a lever and fulcrum ''seesaw'' like actuation mechanism that uses a small, fast piezoelectric transducer. The lever arm of the seesaw mechanism increases the apparent displacement range by an adjustable gain factor, overcoming the standard tradeoff between imaging speed and displacement range. Experimental characterization of a cantilever holder implementing the method is provided together with comparative line scans obtained with contact mode imaging. An imaging bandwidth of 30 kHz in air with the current setup was demonstrated.

  19. Probing Non-Abelian Statistics of Majorana Fermions in Ultracold Atomic Superfluid

    SciTech Connect

    Zhu Shiliang; Shao, L.-B.; Wang, Z. D.; Duan, L.-M.

    2011-03-11

    We propose an experiment to directly probe the non-Abelian statistics of Majorana fermions by braiding them in an s-wave superfluid of ultracold atoms. We show that different orders of braiding operations give orthogonal output states that can be distinguished through Raman spectroscopy. Realization of Majorana states in an s-wave superfluid requires strong spin-orbital coupling and a controllable Zeeman field in the perpendicular direction. We present a simple laser configuration to generate the artificial spin-orbital coupling and the required Zeeman field in the dark-state subspace.

  20. Investigation of dopant clustering and segregation to defects in semiconductors using atom probe tomography

    NASA Astrophysics Data System (ADS)

    Blavette, D.; Duguay, S.

    2016-05-01

    The role of atom probe tomography in the investigation of clustering and segregation of dopants to lattice defects in semiconductors is highlighted on the basis of some selected salient illustrations obtained at the Groupe de Physique des Matériaux of Rouen (France). The instrument is shown to be able to map out the 3D distribution of chemical species in the three dimensions of space at the ultimate scale. Results related to clustering, segregation of dopants (As, B, and P) to grain boundaries, dislocation loops, and extended defects in silicon are discussed.

  1. The mystery of missing species in atom probe tomography of composite materials

    SciTech Connect

    Karahka, M.; Xia, Y.; Kreuzer, H. J.

    2015-08-10

    There is a serious problem in atom probe tomography of composite materials such as oxides that even from stoichiometric samples one observes non-stoichiometric ion yields. We present a quantitative model that explains the non-stoichiometry allowing a fit to experimental data of ion yields as a function of applied field to extract activation barriers and prefactors. The numbers are confirmed by density functional theory. We also show that for oxides the missing oxygen is thermally desorbed as neutral O{sub 2}, either directly or associatively. Finally, we suggest methods to improve the experimental setup.

  2. Atomic probe microscopy of 3C SiC films grown on 6H SiC substrates

    NASA Technical Reports Server (NTRS)

    Steckl, A. J.; Roth, M. D.; Powell, J. A.; Larkin, D. J.

    1993-01-01

    The surface of 3C SiC films grown on 6H SiC substrates has been studied by atomic probe microscopy in air. Atomic-scale images of the 3C SiC surface have been obtained by STM which confirm the 111 line type orientation of the cubic 3C layer grown on the 0001 plane type surface of the hexagonal 6H substrate. The nearest-neighbor atomic spacing for the 3C layer has been measured to be 3.29 +/- 0.2 A, which is within 7 percent of the bulk value. Shallow terraces in the 3C layer have been observed by STM to separate regions of very smooth growth in the vicinity of the 3C nucleation point from considerably rougher 3C surface regions. These terraces are oriented at right angles to the growth direction. Atomic force microscopy has been used to study etch pits present on the 6H substrate due to high temperature HCl cleaning prior to CVD growth of the 3C layer. The etch pits have hexagonal symmetry and vary in depth from 50 nm to 1 micron.

  3. SISGR: Atom chip microscopy: A novel probe for strongly correlated materials

    SciTech Connect

    Lev, Benjamin L.

    2014-05-31

    Microscopy techniques co-opted from nonlinear optics and high energy physics have complemented solid-state probes in elucidating the order manifest in condensed matter materials. Up until now, however, no attempts have been made to use modern techniques of ultracold atomic physics to directly explore properties of strongly correlated or topologically protected materials. Our current program is focused on introducing a novel magnetic field microscopy technique into the toolbox of imaging probes. Our prior DOE ESPM program funded the development of a novel instrument using a dilute gas Bose-Einstein condensate (BEC) as a scanning probe capable of measuring tiny magnetic (and electric) DC and AC fields above materials. We successfully built the world's first “scanning cryogenic atom chip microscope” [1], and we now are in the process of characterizing its performance before using the instrument to take the first wide-area images of transport flow within unconventional superconductors, pnictides and oxide interfaces (LAO/STO), topological insulators, and colossal magnetoresistive manganites. We will do so at temperatures outside the capability of scanning SQUIDs, with ~10x better resolution and without 1/f-noise. A notable goal will be to measure the surface-to-bulk conductivity ratio in topological insulators in a relatively model-independent fashion [2]. We have completed the construction of this magnetic microscope, shown in Figure 1. The instrument uses atom chips—substrates supporting micron-sized current-carrying wires that create magnetic microtraps near surfaces for ultracold thermal gases and BECs—to enable single-shot and raster-scanned large-field-of-view detection of magnetic fields. The fields emanating from electronic transport may be detected at the 10-7 flux quantum (Φ0) level and below (see Fig. 2); that is, few to sub-micron resolution of sub-nanotesla fields over single-shot, millimeter-long detection lengths. By harnessing the extreme

  4. Probing atomic-scale friction on reconstructed surfaces of single-crystal semiconductors

    NASA Astrophysics Data System (ADS)

    Goryl, M.; Budzioch, J.; Krok, F.; Wojtaszek, M.; Kolmer, M.; Walczak, L.; Konior, J.; Gnecco, E.; Szymonski, M.

    2012-02-01

    Friction force microscopy (FFM) investigations have been performed on reconstructed (001) surfaces of InSb and Ge in an ultrahigh vacuum. On the c(8×2) reconstruction of InSb(001) atomic resolution is achieved under superlubric conditions, and the features observed in the lateral force images are precisely reproduced by numerical simulations, taking into account possible decorations of the probing tip. On the simultaneously acquired (1×3) reconstruction a significant disorder of the surface atoms is observed. If the loading force increases, friction becomes much larger on this reconstruction compared to the c(8×2) one. In FFM images acquired on the Ge(001)(2×1) characteristic substructures are resolved within the unit cells. In such a case, a strong dependence of the friction pattern on the scan direction is observed.

  5. Microstructural characterization of irradiated PWR steels using the atom probe field-ion microscope

    SciTech Connect

    Miller, M.K.; Burke, M.G.

    1987-08-01

    Atom probe field-ion microscopy has been used to characterize the microstructure of a neutron-irradiated A533B pressure vessel steel weld. The atomic spatial resolution of this technique permits a complete structural and chemical description of the ultra-fine features that control the mechanical properties to be made. A variety of fine scale features including roughly spherical copper precipitates and clusters, spherical and rod-shaped molybdenum carbide and disc-shaped molybdenum nitride precipitates were observed to be inhomogeneously distributed in the ferrite. The copper content of the ferrite was substantially reduced from the nominal level. A thin film of molybdenum carbides and nitrides was observed on grain boundaries in addition to a coarse copper-manganese precipitate. Substantial enrichment of manganese and nickel were detected at the copper-manganese precipitate-ferrite interface and this enrichment extended into the ferrite. Enrichment of nickel, manganese and phosphorus were also measured at grain boundaries.

  6. Atom probe tomography characterisation of a laser diode structure grown by molecular beam epitaxy

    SciTech Connect

    Bennett, Samantha E.; Humphreys, Colin J.; Oliver, Rachel A.; Smeeton, Tim M.; Hooper, Stewart E.; Heffernan, Jonathan; Saxey, David W.; Smith, George D. W.

    2012-03-01

    Atom probe tomography (APT) has been used to achieve three-dimensional characterization of a III-nitride laser diode (LD) structure grown by molecular beam epitaxy (MBE). Four APT data sets have been obtained, with fields of view up to 400 nm in depth and 120 nm in diameter. These data sets contain material from the InGaN quantum well (QW) active region, as well as the surrounding p- and n-doped waveguide and cladding layers, enabling comprehensive study of the structure and composition of the LD structure. Two regions of the same sample, with different average indium contents (18% and 16%) in the QW region, were studied. The APT data are shown to provide easy access to the p-type dopant levels, and the composition of a thin AlGaN barrier layer. Next, the distribution of indium within the InGaN QW was analyzed, to assess any possible inhomogeneity of the distribution of indium (''indium clustering''). No evidence for a statistically significant deviation from a random distribution was found, indicating that these MBE-grown InGaN QWs do not require indium clusters for carrier localization. However, the APT data show steps in the QW interfaces, leading to well-width fluctuations, which may act to localize carriers. Additionally, the unexpected presence of a small amount (x = 0.005) of indium in a layer grown intentionally as GaN was revealed. Finally, the same statistical method applied to the QW was used to show that the indium distribution within a thick InGaN waveguide layer in the n-doped region did not show any deviation from randomness.

  7. Nanoscale isotope mapping of terrestrial and lunar zircons by atom probe tomography

    NASA Astrophysics Data System (ADS)

    Blum, T.; Reinhard, D. A.; Spicuzza, M. J.; Olson, D.; Coble, M. A.; Cavosie, A. J.; Ushikubo, T.; Larson, D. J.; Kelly, T. F.; Valley, J. W.

    2014-12-01

    Atom Probe Tomography (APT) allows 3D mapping of elements and isotopes with near atomic resolution, at concentrations down to the 10's of ppma. Direct characterization of nanoscale chemical heterogeneity down to trace element levels permits novel interrogations of geochemical processes acting at the nm-scale, and further informs us about elemental or isotopic data gathered by larger-scale techniques. We have studied four zircons including a 2.5 Ga xenocryst from a 29 Ma granitoid (ARG2.5), a 4.3 Ga zircon from the quartz monzodiorite clast of lunar sample 15405 (15Q4), and two Jack Hills zircons dated at 4.0 Ga (JH4.0) and 4.4 Ga (JH4.4) (Valley et al. 2014, Nat. Geosci.). JH4.4 and ARG2.5 contain enrichments of Y, REE, and Pb in ~10 nm clusters, in contrast to the uniform distribution of these elements in JH4.0 and 15Q4. Despite varying amounts of nanoscale trace element heterogeneity, all terrestrial zircons have total 207Pb/206Pb ratios consistent with concordant U-Pb ages obtained by SIMS. This proves that zircon cores remained closed U-Pb systems at the micron scale. In JH4.4 and ARG2.5, the 207Pb/206Pb ratio within clusters is a function of the timing of cluster formation, and precludes clusters from being primary features. Instead, the timing of element mobility and cluster formation is linked with known high temperature geological events. The lack of clustering within JH4.0 and lunar zircon 15Q4 suggests no nm-scale element mobility has occurred, and supports the concordant ages obtained by SIMS. The size, shape, distribution and composition of clusters reflect the time-integrated influence of radiation damage, annealing, and temperature on intracrystalline trace element mobility, and can be used to further understand the thermal history of zircons and their structural evolution since crystallization. The combination of spatial resolution and detection limits for APT has exciting potential for many geochemistry and mineralogy studies.

  8. Probing the nanoscale Schottky barrier of metal/semiconductor interfaces of Pt/CdSe/Pt nanodumbbells by conductive-probe atomic force microscopy.

    PubMed

    Kwon, Sangku; Lee, Seon Joo; Kim, Sun Mi; Lee, Youngkeun; Song, Hyunjoon; Park, Jeong Young

    2015-08-01

    The electrical nature of the nanoscale contact between metal nanodots and semiconductor rods has drawn significant interest because of potential applications for metal-semiconductor hybrid nanostructures in energy conversion or heterogeneous catalysis. Here, we studied the nanoscale electrical character of the Pt/CdSe junction in Pt/CdSe/Pt nanodumbbells on connected Au islands by conductive-probe atomic force microscopy under ultra-high vacuum. Current-voltage plots measured in contact mode revealed Schottky barrier heights of individual nanojunctions of 0.41 ± 0.02 eV. The measured value of the Schottky barrier is significantly lower than that of planar thin-film diodes because of a reduction in the barrier width and enhanced tunneling probability at the interface. PMID:26136054

  9. Probing the nanoscale Schottky barrier of metal/semiconductor interfaces of Pt/CdSe/Pt nanodumbbells by conductive-probe atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Kwon, Sangku; Lee, Seon Joo; Kim, Sun Mi; Lee, Youngkeun; Song, Hyunjoon; Park, Jeong Young

    2015-07-01

    The electrical nature of the nanoscale contact between metal nanodots and semiconductor rods has drawn significant interest because of potential applications for metal-semiconductor hybrid nanostructures in energy conversion or heterogeneous catalysis. Here, we studied the nanoscale electrical character of the Pt/CdSe junction in Pt/CdSe/Pt nanodumbbells on connected Au islands by conductive-probe atomic force microscopy under ultra-high vacuum. Current-voltage plots measured in contact mode revealed Schottky barrier heights of individual nanojunctions of 0.41 +/- 0.02 eV. The measured value of the Schottky barrier is significantly lower than that of planar thin-film diodes because of a reduction in the barrier width and enhanced tunneling probability at the interface.The electrical nature of the nanoscale contact between metal nanodots and semiconductor rods has drawn significant interest because of potential applications for metal-semiconductor hybrid nanostructures in energy conversion or heterogeneous catalysis. Here, we studied the nanoscale electrical character of the Pt/CdSe junction in Pt/CdSe/Pt nanodumbbells on connected Au islands by conductive-probe atomic force microscopy under ultra-high vacuum. Current-voltage plots measured in contact mode revealed Schottky barrier heights of individual nanojunctions of 0.41 +/- 0.02 eV. The measured value of the Schottky barrier is significantly lower than that of planar thin-film diodes because of a reduction in the barrier width and enhanced tunneling probability at the interface. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02285a

  10. Atom probe tomography characterization of radiation-sensitive KS-01 weld

    NASA Astrophysics Data System (ADS)

    Miller, M. K.; Russell, K. F.; Sokolov, M. A.; Nanstad, R. K.

    2003-08-01

    The microstructure of a radiation-sensitive KS-01 test weld has been characterized by atom probe tomography. The levels of copper, manganese, nickel and chromium in this weld were amongst the highest of all the steels used in Western reactor pressure vessels. After neutron irradiation to a fluence of 0.8 × 10 23 n m -2 ( E>1 MeV) at a temperature of 288 °C, this weld exhibited a large Charpy T41J shift of 169 K, a large shift of the fracture toughness transition temperature of 160 K, a decrease in upper shelf energy from 118 to ˜78 J, and an increase in the yield strength from 600 to 826 MPa. However, the mechanical properties data conformed to the master curve. Atom probe tomography revealed a high number density (˜3 × 10 24 m -3) of Cu-, Mn-, Ni-, Si- and P-enriched precipitates and a lower number density (˜1 × 10 23 m -3) of P clusters.

  11. Atom probe field ion microscopy of type 308 CRE stainless steel welds

    SciTech Connect

    Babu, S.S.; David, S.A.; Vitek, J.M.; Miller, M.K.

    1994-09-01

    Additions of controlled residual elements (CRE) such as titanium, boron and phosphorus, to the commercial 308 type stainless steel welds have been found to improve the creep-rupture properties. In both conventional and CRE-type stainless steel welds, during high temperature service, various microstructural changes take place such as the formation of M{sub 23}C{sub 6} carbide networks along austenite({gamma})-ferrite ({delta}) interface, the formation of sigma ({sigma}) phase, and the dissolution of ferrite. Boron-containing CRE welds exhibit similar microstructural evolution as that of conventional types 308 stainless steel welds. As boron may segregate to ferrite-austenite interface and thereby modify the austenite-M{sub 23}C{sub 6} carbide interface, the distribution of boron was measured with an atom probe field ion microscope. Atom probe analysis revealed significant boron and carbon enrichments along the ferrite-austenite boundary in the as-welded state. The ratio of carbon to boron concentration at the interface was found to be {approximately} 4.

  12. Attosecond probing of state-resolved ionization and superpositions of atoms and molecules

    NASA Astrophysics Data System (ADS)

    Leone, Stephen

    2016-05-01

    Isolated attosecond pulses in the extreme ultraviolet are used to probe strong field ionization and to initiate electronic and vibrational superpositions in atoms and small molecules. Few-cycle 800 nm pulses produce strong-field ionization of Xe atoms, and the attosecond probe is used to measure the risetimes of the two spin orbit states of the ion on the 4d inner shell transitions to the 5p vacancies in the valence shell. Step-like features in the risetimes due to the subcycles of the 800 nm pulse are observed and compared with theory to elucidate the instantaneous and effective hole dynamics. Isolated attosecond pulses create massive superpositions of electronic states in Ar and nitrogen as well as vibrational superpositions among electronic states in nitrogen. An 800 nm pulse manipulates the superpositions, and specific subcycle interferences, level shifting, and quantum beats are imprinted onto the attosecond pulse as a function of time delay. Detailed outcomes are compared to theory for measurements of time-dynamic superpositions by attosecond transient absorption. Supported by DOE, NSF, ARO, AFOSR, and DARPA.

  13. Probing poly(N-isopropylacrylamide-co-butylacrylate)/cell interactions by atomic force microscopy.

    PubMed

    Natalia, Becerra; Henry, Andrade; Betty, López; Marina, Restrepo Luz; Roberto, Raiteri

    2015-01-01

    Poly(N-isopropylacrylamide) based hydrogels have been proposed as cell culture supports in cell sheet engineering. Toward this goal, we characterized the poly(N-isopropylacrylamide-co-butylacrylate) copolymer thermo-sensitivity and the cell/copolymer interactions above and below the copolymer lower critical solution temperature. We did that by direct force measurements at different temperatures using an atomic force microscope with either a polystyrene or a glass microbead as probes. We used a copolymer-coated microbead to measure adhesion after a short contact time with a single fibroblast in culture. Statistical analysis of the maximum adhesion force and the mechanical work necessary to separate the probe from the cell surface confirmed the hydrophilic/hydrophobic behavior of poly(N-isopropylacrylamide-co-butylacrylate) as a function of temperature in the range 20-37°C and, consequently, a reversible increase/decrease in cell adhesion with the copolymer. As control experiments we measured interactions between uncoated microbeads with the copolymer hydrogel or cells as well as interaction of the Poly(N-isopropylacrylamide) homopolymer with cells. These results show the potential of an assay based on atomic force microscopy for an in situ and quantitative assessment of cell/substrate interactions and support the use of poly(N-isopropylacrylamide-co-butylacrylate) copolymer as an efficient culture substrate in cell sheet engineering. PMID:24619976

  14. Boosting the local anodic oxidation of silicon through carbon nanofiber atomic force microscopy probes

    PubMed Central

    Lorenzoni, Matteo; Matsui, Soichiro; Tanemura, Masaki; Perez-Murano, Francesc

    2015-01-01

    Summary Many nanofabrication methods based on scanning probe microscopy have been developed during the last decades. Local anodic oxidation (LAO) is one of such methods: Upon application of an electric field between tip and surface under ambient conditions, oxide patterning with nanometer-scale resolution can be performed with good control of dimensions and placement. LAO through the non-contact mode of atomic force microscopy (AFM) has proven to yield a better resolution and tip preservation than the contact mode and it can be effectively performed in the dynamic mode of AFM. The tip plays a crucial role for the LAO-AFM, because it regulates the minimum feature size and the electric field. For instance, the feasibility of carbon nanotube (CNT)-functionalized tips showed great promise for LAO-AFM, yet, the fabrication of CNT tips presents difficulties. Here, we explore the use of a carbon nanofiber (CNF) as the tip apex of AFM probes for the application of LAO on silicon substrates in the AFM amplitude modulation dynamic mode of operation. We show the good performance of CNF-AFM probes in terms of resolution and reproducibility, as well as demonstration that the CNF apex provides enhanced conditions in terms of field-induced, chemical process efficiency. PMID:25671165

  15. Customized atomic force microscopy probe by focused-ion-beam-assisted tip transfer

    PubMed Central

    Wang, Andrew; Butte, Manish J.

    2014-01-01

    We present a technique for transferring separately fabricated tips onto tipless atomic force microscopy (AFM) cantilevers, performed using focused ion beam-assisted nanomanipulation. This method addresses the need in scanning probe microscopy for certain tip geometries that cannot be achieved by conventional lithography. For example, in probing complex layered materials or tall biological cells using AFM, a tall tip with a high-aspect-ratio is required to avoid artifacts caused by collisions of the tip's sides with the material being probed. We show experimentally that tall (18 μm) cantilever tips fabricated by this approach reduce squeeze-film damping, which fits predictions from hydrodynamic theory, and results in an increased quality factor (Q) of the fundamental flexural mode. We demonstrate that a customized tip's well-defined geometry, tall tip height, and aspect ratio enable improved measurement of elastic moduli by allowing access to low-laying portions of tall cells (T lymphocytes). This technique can be generally used to attach tips to any micromechanical device when conventional lithography of tips cannot be accomplished. PMID:25161320

  16. Customized atomic force microscopy probe by focused-ion-beam-assisted tip transfer.

    PubMed

    Wang, Andrew; Butte, Manish J

    2014-08-01

    We present a technique for transferring separately fabricated tips onto tipless atomic force microscopy (AFM) cantilevers, performed using focused ion beam-assisted nanomanipulation. This method addresses the need in scanning probe microscopy for certain tip geometries that cannot be achieved by conventional lithography. For example, in probing complex layered materials or tall biological cells using AFM, a tall tip with a high-aspect-ratio is required to avoid artifacts caused by collisions of the tip's sides with the material being probed. We show experimentally that tall (18 μm) cantilever tips fabricated by this approach reduce squeeze-film damping, which fits predictions from hydrodynamic theory, and results in an increased quality factor (Q) of the fundamental flexural mode. We demonstrate that a customized tip's well-defined geometry, tall tip height, and aspect ratio enable improved measurement of elastic moduli by allowing access to low-laying portions of tall cells (T lymphocytes). This technique can be generally used to attach tips to any micromechanical device when conventional lithography of tips cannot be accomplished. PMID:25161320

  17. Customized atomic force microscopy probe by focused-ion-beam-assisted tip transfer

    SciTech Connect

    Wang, Andrew; Butte, Manish J.

    2014-08-04

    We present a technique for transferring separately fabricated tips onto tipless atomic force microscopy (AFM) cantilevers, performed using focused ion beam-assisted nanomanipulation. This method addresses the need in scanning probe microscopy for certain tip geometries that cannot be achieved by conventional lithography. For example, in probing complex layered materials or tall biological cells using AFM, a tall tip with a high-aspect-ratio is required to avoid artifacts caused by collisions of the tip's sides with the material being probed. We show experimentally that tall (18 μm) cantilever tips fabricated by this approach reduce squeeze-film damping, which fits predictions from hydrodynamic theory, and results in an increased quality factor (Q) of the fundamental flexural mode. We demonstrate that a customized tip's well-defined geometry, tall tip height, and aspect ratio enable improved measurement of elastic moduli by allowing access to low-laying portions of tall cells (T lymphocytes). This technique can be generally used to attach tips to any micromechanical device when conventional lithography of tips cannot be accomplished.

  18. Probing the quantum vacuum with an artificial atom in front of a mirror

    NASA Astrophysics Data System (ADS)

    Hoi, I.-C.; Kockum, A. F.; Tornberg, L.; Pourkabirian, A.; Johansson, G.; Delsing, P.; Wilson, C. M.

    2015-12-01

    Quantum fluctuations of the vacuum are both a surprising and fundamental phenomenon of nature. Understood as virtual photons, they still have a very real impact, for instance, in the Casimir effects and the lifetimes of atoms. Engineering vacuum fluctuations is therefore becoming increasingly important to emerging technologies. Here, we shape vacuum fluctuations using a superconducting circuit analogue of a mirror, creating regions in space where they are suppressed. Moving an artificial atom through these regions and measuring the spontaneous emission lifetime of the atom provides us with the spectral density of the vacuum fluctuations. Using the paradigm of waveguide quantum electrodynamics, we significantly improve over previous studies of the interaction of an atom with its mirror image, observing a spectral density as low as 0.02 quanta, a factor of 50 below the mirrorless result. This demonstrates that we can hide the atom from the vacuum, even though it is exposed in free space.

  19. Investigations of ion-irradiated uranium dioxide nuclear fuel with laser-assisted atom probe tomography

    NASA Astrophysics Data System (ADS)

    Valderrama, Billy

    Performance in commercial light water reactors is dictated by the ability of its fuel material, uranium dioxide (UO2), to transport heat generated during the fission process. It is widely known that the service lifetime is limited by irradiation-induced microstructural changes that degrade the thermal performance of UO2. Studying the role of complex, often interacting mechanisms that occur during the early stages of microstructural evolution presents a challenge. Phenomena of particular interest are the segregation of fission products to form bubbles and their resultant effect on grain boundary (GB) mobility, and the effect of irradiation on fuel stoichiometry. Each mechanism has a profound consequence on fuel thermal conductivity. Several advanced analytical techniques, such as transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, etc. have been used to study these mechanisms. However, they each have limitations and cannot individually provide the necessary information for deeper understanding. One technique that has been under utilized is atom probe tomography (APT), which has a unique ability to spatially resolve small-scale chemical variations. APT uses the principle of field ionization to evaporate surface ions for chemical analysis. For low electrical conductivity systems, a pulsed laser is used to thermally assist in the evaporation process. One factor complicating the analysis is that laser-material interactions are poorly understood for oxide materials and literature using this technique with UO2 is lacking. Therefore, an initial systematic study to identify the optimal conditions for the analysis of UO2 using laser-assisted APT was conducted. A comparative study on the evaporation behavior between CeO2 and UO2 was followed. CeO2 was chosen due to its technological relevancy and availability of comparative studies with laser-assisted APT. Dissimilar evaporation behavior between these materials was identified and attributed

  20. Development of dual-probe atomic force microscopy system using optical beam deflection sensors with obliquely incident laser beams

    NASA Astrophysics Data System (ADS)

    Tsunemi, Eika; Kobayashi, Kei; Matsushige, Kazumi; Yamada, Hirofumi

    2011-03-01

    We developed a dual-probe (DP) atomic force microscopy (AFM) system that has two independently controlled probes. The deflection of each cantilever is measured by the optical beam deflection (OBD) method. In order to keep a large space over the two probes for an objective lens with a large numerical aperture, we employed the OBD sensors with obliquely incident laser beams. In this paper, we describe the details of our developed DP-AFM system, including analysis of the sensitivity of the OBD sensor for detection of the cantilever deflection. We also describe a method to eliminate the crosstalk caused by the vertical translation of the cantilever. In addition, we demonstrate simultaneous topographic imaging of a test sample by the two probes and surface potential measurement on an α-sexithiophene (α-6T) thin film by one probe while electrical charges were injected by the other probe.

  1. Development of dual-probe atomic force microscopy system using optical beam deflection sensors with obliquely incident laser beams.

    PubMed

    Tsunemi, Eika; Kobayashi, Kei; Matsushige, Kazumi; Yamada, Hirofumi

    2011-03-01

    We developed a dual-probe (DP) atomic force microscopy (AFM) system that has two independently controlled probes. The deflection of each cantilever is measured by the optical beam deflection (OBD) method. In order to keep a large space over the two probes for an objective lens with a large numerical aperture, we employed the OBD sensors with obliquely incident laser beams. In this paper, we describe the details of our developed DP-AFM system, including analysis of the sensitivity of the OBD sensor for detection of the cantilever deflection. We also describe a method to eliminate the crosstalk caused by the vertical translation of the cantilever. In addition, we demonstrate simultaneous topographic imaging of a test sample by the two probes and surface potential measurement on an α-sexithiophene (α-6T) thin film by one probe while electrical charges were injected by the other probe. PMID:21456752

  2. What Is a pH Probe Study?

    MedlinePlus

    What is a pH Probe Study ? What is pH a probe study? M easuring the pH in the esophagus helps determine whether or not acid is coming up from the stomach. A pH probe study is usually done in patients where ...

  3. Determining the location and nearest neighbours of aluminium in zeolites with atom probe tomography

    SciTech Connect

    Perea, Daniel E.; Arslan, Ilke; Liu, Jia; Ristanović, Zoran; Kovarik, Libor; Arey, Bruce W.; Lercher, Johannes A.; Bare, Simon R.; Weckhuysen, Bert M.

    2015-07-02

    Zeolite catalysis is determined by a combination of pore architecture and Brønsted acidity. As Brønsted acid sites are formed by the substitution of AlO4 for SiO4 tetrahedra, it is of utmost importance to have information on the number as well as the location and neighbouring sites of framework aluminium. Unfortunately, such detailed information has not yet been obtained, mainly due to the lack of suitable characterization methods. Here we report, using the powerful atomic-scale analysis technique known as atom probe tomography, the quantitative spatial distribution of individual aluminium atoms, including their three-dimensional extent of segregation. Ultimately, using a nearest-neighbour statistical analysis, we precisely determine the short-range distribution of aluminium over the different T-sites and determine the most probable Al–Al neighbouring distance within parent and steamed ZSM-5 crystals, as well as assess the long-range redistribution of aluminium upon zeolite steaming.

  4. Determining the location and nearest neighbours of aluminium in zeolites with atom probe tomography

    PubMed Central

    Perea, Daniel E.; Arslan, Ilke; Liu, Jia; Ristanović, Zoran; Kovarik, Libor; Arey, Bruce W.; Lercher, Johannes A.; Bare, Simon R.; Weckhuysen, Bert M.

    2015-01-01

    Zeolite catalysis is determined by a combination of pore architecture and Brønsted acidity. As Brønsted acid sites are formed by the substitution of AlO4 for SiO4 tetrahedra, it is of utmost importance to have information on the number as well as the location and neighbouring sites of framework aluminium. Unfortunately, such detailed information has not yet been obtained, mainly due to the lack of suitable characterization methods. Here we report, using the powerful atomic-scale analysis technique known as atom probe tomography, the quantitative spatial distribution of individual aluminium atoms, including their three-dimensional extent of segregation. Using a nearest-neighbour statistical analysis, we precisely determine the short-range distribution of aluminium over the different T-sites and determine the most probable Al–Al neighbouring distance within parent and steamed ZSM-5 crystals, as well as assess the long-range redistribution of aluminium upon zeolite steaming. PMID:26133270

  5. Determining the location and nearest neighbours of aluminium in zeolites with atom probe tomography.

    PubMed

    Perea, Daniel E; Arslan, Ilke; Liu, Jia; Ristanović, Zoran; Kovarik, Libor; Arey, Bruce W; Lercher, Johannes A; Bare, Simon R; Weckhuysen, Bert M

    2015-01-01

    Zeolite catalysis is determined by a combination of pore architecture and Brønsted acidity. As Brønsted acid sites are formed by the substitution of AlO4 for SiO4 tetrahedra, it is of utmost importance to have information on the number as well as the location and neighbouring sites of framework aluminium. Unfortunately, such detailed information has not yet been obtained, mainly due to the lack of suitable characterization methods. Here we report, using the powerful atomic-scale analysis technique known as atom probe tomography, the quantitative spatial distribution of individual aluminium atoms, including their three-dimensional extent of segregation. Using a nearest-neighbour statistical analysis, we precisely determine the short-range distribution of aluminium over the different T-sites and determine the most probable Al-Al neighbouring distance within parent and steamed ZSM-5 crystals, as well as assess the long-range redistribution of aluminium upon zeolite steaming. PMID:26133270

  6. Determining the location and nearest neighbours of aluminium in zeolites with atom probe tomography

    NASA Astrophysics Data System (ADS)

    Perea, Daniel E.; Arslan, Ilke; Liu, Jia; Ristanović, Zoran; Kovarik, Libor; Arey, Bruce W.; Lercher, Johannes A.; Bare, Simon R.; Weckhuysen, Bert M.

    2015-07-01

    Zeolite catalysis is determined by a combination of pore architecture and Brønsted acidity. As Brønsted acid sites are formed by the substitution of AlO4 for SiO4 tetrahedra, it is of utmost importance to have information on the number as well as the location and neighbouring sites of framework aluminium. Unfortunately, such detailed information has not yet been obtained, mainly due to the lack of suitable characterization methods. Here we report, using the powerful atomic-scale analysis technique known as atom probe tomography, the quantitative spatial distribution of individual aluminium atoms, including their three-dimensional extent of segregation. Using a nearest-neighbour statistical analysis, we precisely determine the short-range distribution of aluminium over the different T-sites and determine the most probable Al-Al neighbouring distance within parent and steamed ZSM-5 crystals, as well as assess the long-range redistribution of aluminium upon zeolite steaming.

  7. Determining the location and nearest neighbours of aluminium in zeolites with atom probe tomography

    DOE PAGESBeta

    Perea, Daniel E.; Arslan, Ilke; Liu, Jia; Ristanović, Zoran; Kovarik, Libor; Arey, Bruce W.; Lercher, Johannes A.; Bare, Simon R.; Weckhuysen, Bert M.

    2015-07-02

    Zeolite catalysis is determined by a combination of pore architecture and Brønsted acidity. As Brønsted acid sites are formed by the substitution of AlO4 for SiO4 tetrahedra, it is of utmost importance to have information on the number as well as the location and neighbouring sites of framework aluminium. Unfortunately, such detailed information has not yet been obtained, mainly due to the lack of suitable characterization methods. Here we report, using the powerful atomic-scale analysis technique known as atom probe tomography, the quantitative spatial distribution of individual aluminium atoms, including their three-dimensional extent of segregation. Ultimately, using a nearest-neighbour statisticalmore » analysis, we precisely determine the short-range distribution of aluminium over the different T-sites and determine the most probable Al–Al neighbouring distance within parent and steamed ZSM-5 crystals, as well as assess the long-range redistribution of aluminium upon zeolite steaming.« less

  8. PROBE: Empowering the Individual (A Case Study).

    ERIC Educational Resources Information Center

    Towns, Kathryn; And Others

    The Potential Reentry Opportunities in Business and Education (PROBE) counseling and referral system is intended to help single parents and displaced homemakers gain greater control over their own lives, careers, and futures. PROBE began in 1975 as a campus-based program at Pennsylvania State University and became community based in 1977. PROBE,…

  9. Theoretical Studies of Atomic Transitions

    SciTech Connect

    Charlotte Froese Fischer

    2005-07-08

    Atomic structure calculations were performed for properties such as energy levels, binding energies, transition probabilities, lifetimes, hyperfine structure, and isotope shifts. Accurate computational procedures were devised so that properties could be predicted even when they could not be obtained from experiment, and to assist in the identification of observed data. The method used was the multiconfiguration Hartree-Fock (MCHF) method, optionally corrected for relativistic effects in the Breit-Pauli approximation. Fully relativistic Dirac-Fock calculations also were performed using the GRASP code A database of energy levels, lifetimes, and transition probabilities was designed and implemented and, at present, includes many results for Be-like to Ar-like.

  10. Resonant enhanced multiphoton ionization studies of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Dixit, S. N.; Levin, D.; Mckoy, V.

    1987-01-01

    In resonant enhanced multiphoton ionization (REMPI), an atom absorbs several photons making a transition to a resonant intermediate state and subsequently ionizing out of it. With currently available tunable narrow-band lasers, the extreme sensitivity of REMPI to the specific arrangement of levels can be used to selectively probe minute amounts of a single species (atom) in a host of background material. Determination of the number density of atoms from the observed REMPI signal requires a knowledge of the multiphoton ionization cross sections. The REMPI of atomic oxygen was investigated through various excitation schemes that are feasible with available light sources. Using quantum defect theory (QDT) to estimate the various atomic parameters, the REMPI dynamics in atomic oxygen were studied incorporating the effects of saturation and a.c. Stark shifts. Results are presented for REMPI probabilities for excitation through various 2p(3) (4S sup o) np(3)P and 2p(3) (4S sup o) nf(3)F levels.

  11. Implementation and characterization of a quartz tuning fork based probe consisted of discrete resonators for dynamic mode atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Akiyama, Terunobu; de Rooij, Nicolaas F.; Staufer, Urs; Detterbeck, Manfred; Braendlin, Dominik; Waldmeier, Simon; Scheidiger, Martin

    2010-06-01

    The quartz tuning fork based probe {e.g., Akiyama et al. [Appl. Surf. Sci. 210, 18 (2003)]}, termed "A-Probe," is a self-sensing and self-actuating (exciting) probe for dynamic mode atomic force microscope (AFM) operation. It is an oscillatory force sensor consisting of the two discrete resonators. This paper presents the investigations on an improved A-Probe: its batch fabrication and assembly, mounting on an AFM head, electrical setup, characterization, and AFM imaging. The fundamental features of the A-Probe are electrically and optically characterized in "approach-withdraw" experiments. Further investigations include the frequency response of an A-Probe to small mechanical vibrations externally applied to the tip and the effective loading force yielding between the tip and the sample during the periodic contact. Imaging of an electronic chip, a compact disk stamper, carbon nanotubes, and Si beads is demonstrated with this probe at ambient conditions in the so-called frequency modulation mode. A special probe substrate, which can snap on a receptacle fixed on an AFM head, and a special holder including a preamplifier electronic are introduced. We hope that the implementation and characterization of the A-Probe described in this paper will provide hints for new scanning probe techniques.

  12. Light scattering from ultracold atoms in optical lattices as an optical probe of quantum statistics

    SciTech Connect

    Mekhov, Igor B.; Maschler, Christoph; Ritsch, Helmut

    2007-11-15

    We study off-resonant collective light scattering from ultracold atoms trapped in an optical lattice. Scattering from different atomic quantum states creates different quantum states of the scattered light, which can be distinguished by measurements of the spatial intensity distribution, quadrature variances, photon statistics, or spectral measurements. In particular, angle-resolved intensity measurements reflect global statistics of atoms (total number of radiating atoms) as well as local statistical quantities (single-site statistics even without optical access to a single site) and pair correlations between different sites. As a striking example we consider scattering from transversally illuminated atoms into an optical cavity mode. For the Mott-insulator state, similar to classical diffraction, the number of photons scattered into a cavity is zero due to destructive interference, while for the superfluid state it is nonzero and proportional to the number of atoms. Moreover, we demonstrate that light scattering into a standing-wave cavity has a nontrivial angle dependence, including the appearance of narrow features at angles, where classical diffraction predicts zero. The measurement procedure corresponds to the quantum nondemolition measurement of various atomic variables by observing light.

  13. The extended wedge method: Atomic force microscope friction calibration for improved tolerance to instrument misalignments, tip offset, and blunt probes

    NASA Astrophysics Data System (ADS)

    Khare, H. S.; Burris, D. L.

    2013-05-01

    One of the major challenges in understanding and controlling friction is the difficulty in bridging the length and time scales of macroscale contacts and those of the single asperity interactions they comprise. While the atomic force microscope (AFM) offers a unique ability to probe tribological surfaces in a wear-free single-asperity contact, instrument calibration challenges have limited the usefulness of this technique for quantitative nanotribological studies. A number of lateral force calibration techniques have been proposed and used, but none has gained universal acceptance due to practical considerations, configuration limitations, or sensitivities to unknowable error sources. This paper describes a simple extension of the classic wedge method of AFM lateral force calibration which: (1) allows simultaneous calibration and measurement on any substrate, thus eliminating prior tip damage and confounding effects of instrument setup adjustments; (2) is insensitive to adhesion, PSD cross-talk, transducer/piezo-tube axis misalignment, and shear-center offset; (3) is applicable to integrated tips and colloidal probes; and (4) is generally applicable to any reciprocating friction coefficient measurement. The method was applied to AFM measurements of polished carbon (99.999% graphite) and single crystal MoS2 to demonstrate the technique. Carbon and single crystal MoS2 had friction coefficients of μ = 0.20 ± 0.04 and μ = 0.006 ± 0.001, respectively, against an integrated Si probe. Against a glass colloidal sphere, MoS2 had a friction coefficient of μ = 0.005 ± 0.001. Generally, the measurement uncertainties ranged from 10%-20% and were driven by the effect of actual frictional variation on the calibration rather than calibration error itself (i.e., due to misalignment, tip-offset, or probe radius).

  14. RF Pulse Signal Integrity Analysis for Nonlinear Ended Microstrip Line Atom-Probe Tomography

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Delamare, A.; Normand, A.; Delaroche, F.; Latry, O.; Vurpillot, F.; Ravelo, B.

    2016-03-01

    A signal integrity (SI) analysis of high voltage rectangular short pulses for the atom- probe system is explored in this paper. The operated RF transient pulse is considered for exciting on material sample inside an ultra-high vacuum (UHV) cryogenic chamber. The ns- duration pulse signal is injected into the cryogenic analysis chamber through the transmitting system mainly constituted by a microstrip interconnect line ended by optical controlled nonlinear load. The whole system frequency characterization is performed based on the S- parameter measurements. As expected, a challenging ultra-short rectangular shape pulse is exhibited by the pulser. Promising experimental results with the improvement of ion mass spectrum is demonstrated with the designed RF pulser.

  15. Atom probe tomography of compositional fluctuation in GaInN layers

    NASA Astrophysics Data System (ADS)

    Kanitani, Yuya; Tanaka, Shinji; Tomiya, Shigetaka; Ohkubo, Tadakatsu; Hono, Kazuhiro

    2016-05-01

    Thin Ga1‑ x In x N layers with various indium compositions x (0.08,0.15,0.25) were examined by high-angle annular dark-field scanning transmission electron microscopy and atom probe tomography. Although nanoscale compositional fluctuation was observed in all Ga1‑ x In x N layers, no appreciable phase separation was observed. Since Ga1‑ x In x N layers were coherently grown on underlying GaN layers, it is considered that the elastic strain constrains phase separation in the Ga1‑ x In x N layers and that compositional fluctuations develop in order to minimize the local strain energy. The measured period of compositional fluctuations ranged from 3.4 to 4.9 nm and decreased with growth temperature (T growth). This tendency is suggested to be dominated by the surface migration length of the adatom during the crystal growth.

  16. Atom Probe Tomography Analysis of the Distribution of Rhenium in Nickel Alloys

    SciTech Connect

    Mottura, A.; Warnken, N; Miller, Michael K; Reed, R. C.; Finnis, M.

    2010-01-01

    Atom probe tomography (APT) is used to characterise the distributions of rhenium in a binary Ni-Re alloy and the nickel-based single-crystal CMSX-4 superalloy. A purpose-built algorithm is developed to quantify the size distribution of solute clusters, and applied to the APT datasets to critique the hypothesis that rhenium is prone to the formation of clusters in these systems. No evidence is found to indicate that rhenium forms solute clusters above the level expected from random fluctuations. In CMSX-4, enrichment of Re is detected in the matrix phase close to the matrix/precipitate ({gamma}/{gamma}{prime}) phase boundaries. Phase field modelling indicates that this is due to the migration of the {gamma}/{gamma}{prime} interface during cooling from the temperature of operation. Thus, neither clustering of rhenium nor interface enrichments can be the cause of the enhancement in high temperature mechanical properties conferred by rhenium alloying.

  17. Information storage materials: nanoscale characterisation by three-dimensional atom probe analysis

    SciTech Connect

    Larson, D.J.; Petford-Long, A.K.; Ma, Y.Q; Cerezo, A

    2004-06-07

    The development of nanoscale magnetic materials for applications in information storage systems relies heavily on the ability to engineer the properties of the layered structures from which such materials are fabricated. These properties are strongly dependent on the nature of the interfaces between the individual nanoscale magnetic layers, so knowledge of the interface chemistry is crucial. In this paper, we discuss the application of three-dimensional atom probe analysis to the characterisation of layered magnetic materials, including details of specimen preparation techniques required for this type of analysis. Recent results are presented on the characterisation of interfaces in Co/Cu or CoFe/Cu multilayers, which form part of the read sensor in magnetic recording heads, and Co/Pd multilayers, which are being considered for use as perpendicular recording media.

  18. Quantitative analysis of Si/SiGeC superlattices using atom probe tomography.

    PubMed

    Estivill, Robert; Grenier, Adeline; Duguay, Sébastien; Vurpillot, François; Terlier, Tanguy; Barnes, Jean-Paul; Hartmann, Jean-Michel; Blavette, Didier

    2015-12-01

    SiGe and its alloys are used as key materials in innovative electronic devices. The analysis of these materials together with the localisation of dopants and impurities on a very fine scale is of crucial importance for better understanding their electronic properties. The quantification of carbon and germanium in an as-grown Si/SiGeC superlattice has been investigated using Atom Probe Tomography as a function of analysis conditions and sample anneal temperature. The mass spectrum is heavily influenced by the analysis conditions and chemical identification is needed. It was found that quantitative results are obtained using a intermediate electric field. The evaporation of carbon ions shows a strong spatial and temporal correlation. A series of annealed samples have been analysed, presenting an inhomogeneous carbon distribution, appearing in the shape of small clusters. These findings confirm previous results and give a better understanding of the processes occurring in these technologically important materials. PMID:25814020

  19. Probing dark energy with an atom interferometer in an optical cavity

    NASA Astrophysics Data System (ADS)

    Jaffe, Matthew; Haslinger, Philipp; Hamilton, Paul; Mueller, Holger; Khoury, Justin; Elder, Benjamin

    2016-05-01

    If dark energy -- which drives the accelerated expansion of the universe -- consists of a light scalar field, it might be detectable as a ``fifth force'' between normal-matter objects, in potential conflict with precision tests of gravity. Chameleon fields and other theories with screening mechanisms can evade such tests by suppressing this force in regions of high density, such as the laboratory. Our experiments constrain these dark energy models using atoms in an ultrahigh-vacuum chamber as probes to expose the screened fields. Using a cesium matter wave interferometer in an optical cavity, we set stringent bounds on coupling screened theories to matter. A further 4 to 5 orders of magnitude would completely rule out chameleon and f(R) theories. I will describe this first tabletop dark energy search, and present the hundredfold boost in sensitivity we have since achieved.

  20. Atom Probe Tomography Analysis of Precipitation during Tempering of a Nanostructured Bainitic Steel

    SciTech Connect

    Caballero, Francesca G.; Miller, Michael K; Garcia-Mateo, C.

    2011-01-01

    Carbon distribution during tempering of a nanostructured bainitic steel was analyzed by atom probe tomography (APT). Three different types of particles are detected on samples tempered at 673 K (400 C) for 30 minutes: lower bainite cementite with a carbon content of {approx}25 at. pct, {var_epsilon}-carbides with a carbon content close to 30 at. pct, and carbon clusters, small features with a carbon content of {approx}14 at. pct indicative of a stage of tempering prior to precipitation of {var_epsilon}-carbide. After tempering at 773 K (500 C) for 30 minutes, the {var_epsilon}-carbide-to-cementite transition was observed. Solute concentration profiles across carbide/ferrite interfaces showed the distribution of substitutional elements in {var_epsilon}-carbide and cementite for all the tempering conditions.

  1. Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops

    PubMed Central

    Peterman, Emily M.; Reddy, Steven M.; Saxey, David W.; Snoeyenbos, David R.; Rickard, William D. A.; Fougerouse, Denis; Kylander-Clark, Andrew R. C.

    2016-01-01

    Isotopic discordance is a common feature in zircon that can lead to an erroneous age determination, and it is attributed to the mobilization and escape of radiogenic Pb during its post-crystallization geological evolution. The degree of isotopic discordance measured at analytical scales of ~10 μm often differs among adjacent analysis locations, indicating heterogeneous distributions of Pb at shorter length scales. We use atom probe microscopy to establish the nature of these sites and the mechanisms by which they form. We show that the nanoscale distribution of Pb in a ~2.1 billion year old discordant zircon that was metamorphosed c. 150 million years ago is defined by two distinct Pb reservoirs. Despite overall Pb loss during peak metamorphic conditions, the atom probe data indicate that a component of radiogenic Pb was trapped in 10-nm dislocation loops that formed during the annealing of radiation damage associated with the metamorphic event. A second Pb component, found outside the dislocation loops, represents homogeneous accumulation of radiogenic Pb in the zircon matrix after metamorphism. The 207Pb/206Pb ratios measured from eight dislocation loops are equivalent within uncertainty and yield an age consistent with the original crystallization age of the zircon, as determined by laser ablation spot analysis. Our results provide a specific mechanism for the trapping and retention of radiogenic Pb during metamorphism and confirm that isotopic discordance in this zircon is characterized by discrete nanoscale reservoirs of Pb that record different isotopic compositions and yield age data consistent with distinct geological events. These data may provide a framework for interpreting discordance in zircon as the heterogeneous distribution of discrete radiogenic Pb populations, each yielding geologically meaningful ages. PMID:27617295

  2. Probing interlayer interactions between graphene and metal substrates by supersonic rare-gas atom scattering

    NASA Astrophysics Data System (ADS)

    Shichibe, H.; Satake, Y.; Watanabe, K.; Kinjyo, A.; Kunihara, A.; Yamada, Y.; Sasaki, M.; Hayes, W. W.; Manson, J. R.

    2015-04-01

    We demonstrate that highly surface-sensitive supersonic rare-gas (He, Ar, and Xe) atom scattering, in both the quantum and classical regimes, can probe and quantify the interlayer interactions between graphene monolayers and metal substrates in terms of the Debye temperature corresponding to the surface normal vibration, and the surface effective mass. As models of the strongly and weakly interacting graphene, we investigated two systems, graphene on Ru(0001) and Pt(111), respectively. The experimental data for Ar and Xe are compared with the results from theoretical simulations based on the classical smooth surface model. For gr/Pt(111) we find that the scattering pattern of the rare-gas beam, including the Debye-Waller attenuation of the He beam, are quite similar to that from highly oriented pyrolytic graphite (HOPG); this suggests that the graphene-Pt(111) interaction is much like a van der Waals interaction. On the contrary, for the gr/Ru(0001) system, we find a smaller Debye-Waller attenuation and a larger surface effective mass, indicating that graphene on Ru(0001) is tightly bonded to the substrate. Furthermore, asymmetrical spectral shapes in the Ar and Xe scattering spectra from gr/Ru(0001) are interpreted as a result of the lateral distribution of the interlayer interaction corresponding to the moiré pattern. It is found that the "valley" region of the moiré pattern has high effective mass reflecting stronger bonding to the substrate, contributing to the high reflectivity of the He beam reported for this system. On the other hand, the effective mass of the "hill" region is found to be similar to that of HOPG, indicating that this region is well decoupled from the substrate. These results demonstrate a unique capability of atom scattering to probe and evaluate the molecule-substrate interaction and its spatial distributions.

  3. Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops.

    PubMed

    Peterman, Emily M; Reddy, Steven M; Saxey, David W; Snoeyenbos, David R; Rickard, William D A; Fougerouse, Denis; Kylander-Clark, Andrew R C

    2016-09-01

    Isotopic discordance is a common feature in zircon that can lead to an erroneous age determination, and it is attributed to the mobilization and escape of radiogenic Pb during its post-crystallization geological evolution. The degree of isotopic discordance measured at analytical scales of ~10 μm often differs among adjacent analysis locations, indicating heterogeneous distributions of Pb at shorter length scales. We use atom probe microscopy to establish the nature of these sites and the mechanisms by which they form. We show that the nanoscale distribution of Pb in a ~2.1 billion year old discordant zircon that was metamorphosed c. 150 million years ago is defined by two distinct Pb reservoirs. Despite overall Pb loss during peak metamorphic conditions, the atom probe data indicate that a component of radiogenic Pb was trapped in 10-nm dislocation loops that formed during the annealing of radiation damage associated with the metamorphic event. A second Pb component, found outside the dislocation loops, represents homogeneous accumulation of radiogenic Pb in the zircon matrix after metamorphism. The (207)Pb/(206)Pb ratios measured from eight dislocation loops are equivalent within uncertainty and yield an age consistent with the original crystallization age of the zircon, as determined by laser ablation spot analysis. Our results provide a specific mechanism for the trapping and retention of radiogenic Pb during metamorphism and confirm that isotopic discordance in this zircon is characterized by discrete nanoscale reservoirs of Pb that record different isotopic compositions and yield age data consistent with distinct geological events. These data may provide a framework for interpreting discordance in zircon as the heterogeneous distribution of discrete radiogenic Pb populations, each yielding geologically meaningful ages. PMID:27617295

  4. Probing quantum confinement at the atomic scale with optically detected nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Kempf, James G.

    2001-09-01

    either donor-bound electrons or excitons indicate differences, where the bound-exciton model provides a significantly better fit to the data. The same spin physics enabled our measurement of the heterojunction interfacial field, which we find to be less than 1.3 kV/cm at the sites responsible for optical NMR. Other simulations show the promise of optical NMR as a tool in future studies aimed at atomic-level characterization of quantum-confined systems such as quantum dots and wells.

  5. Probing the interaction between air bubble and sphalerite mineral surface using atomic force microscope.

    PubMed

    Xie, Lei; Shi, Chen; Wang, Jingyi; Huang, Jun; Lu, Qiuyi; Liu, Qingxia; Zeng, Hongbo

    2015-03-01

    The interaction between air bubbles and solid surfaces plays important roles in many engineering processes, such as mineral froth flotation. In this work, an atomic force microscope (AFM) bubble probe technique was employed, for the first time, to directly measure the interaction forces between an air bubble and sphalerite mineral surfaces of different hydrophobicity (i.e., sphalerite before/after conditioning treatment) under various hydrodynamic conditions. The direct force measurements demonstrate the critical role of the hydrodynamic force and surface forces in bubble-mineral interaction and attachment, which agree well with the theoretical calculations based on Reynolds lubrication theory and augmented Young-Laplace equation by including the effect of disjoining pressure. The hydrophobic disjoining pressure was found to be stronger for the bubble-water-conditioned sphalerite interaction with a larger hydrophobic decay length, which enables the bubble attachment on conditioned sphalerite at relatively higher bubble approaching velocities than that of unconditioned sphalerite. Increasing the salt concentration (i.e., NaCl, CaCl2) leads to weakened electrical double layer force and thereby facilitates the bubble-mineral attachment, which follows the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory by including the effects of hydrophobic interaction. The results provide insights into the basic understanding of the interaction mechanism between bubbles and minerals at nanoscale in froth flotation processes, and the methodology on probing the interaction forces of air bubble and sphalerite surfaces in this work can be extended to many other mineral and particle systems. PMID:25675101

  6. Probing mechanical properties of living cells by atomic force microscopy with blunted pyramidal cantilever tips.

    PubMed

    Rico, Félix; Roca-Cusachs, Pere; Gavara, Núria; Farré, Ramon; Rotger, Mar; Navajas, Daniel

    2005-08-01

    Atomic force microscopy (AFM) allows the acquisition of high-resolution images and the measurement of mechanical properties of living cells under physiological conditions. AFM cantilevers with blunted pyramidal tips are commonly used to obtain images of living cells. Measurement of mechanical properties with these tips requires a contact model that takes into account their blunted geometry. The aim of this work was to develop a contact model of a blunted pyramidal tip and to assess the suitability of pyramidal tips for probing mechanical properties of soft gels and living cells. We developed a contact model of a blunted pyramidal tip indenting an elastic half-space. We measured Young's modulus (E) and the complex shear modulus (G*= G' +i G" ) of agarose gels and A549 alveolar epithelial cells with pyramidal tips and compared them with those obtained with spherical tips. The gels exhibited an elastic behavior with almost coincident loading and unloading force curves and negligible values of G". E fell sharply with indentation up to approximately 300 nm , showing a linear regime for deeper indentations. A similar indentation dependence of E with twofold lower values at the linear regime was obtained with the spherical tip fitted with Hertz's model. The dependence of E on indentation in cells paralleled that found in gels. Cells exhibited viscoelastic behavior with G"/G' approximately 1/4 . Pyramidal tips commonly used for AFM imaging are suitable for probing mechanical properties of soft gels and living cells. PMID:16196611

  7. Nanomechanical and topographical imaging of living cells by atomic force microscopy with colloidal probes

    NASA Astrophysics Data System (ADS)

    Puricelli, Luca; Galluzzi, Massimiliano; Schulte, Carsten; Podestà, Alessandro; Milani, Paolo

    2015-03-01

    Atomic Force Microscopy (AFM) has a great potential as a tool to characterize mechanical and morphological properties of living cells; these properties have been shown to correlate with cells' fate and patho-physiological state in view of the development of novel early-diagnostic strategies. Although several reports have described experimental and technical approaches for the characterization of cellular elasticity by means of AFM, a robust and commonly accepted methodology is still lacking. Here, we show that micrometric spherical probes (also known as colloidal probes) are well suited for performing a combined topographic and mechanical analysis of living cells, with spatial resolution suitable for a complete and accurate mapping of cell morphological and elastic properties, and superior reliability and accuracy in the mechanical measurements with respect to conventional and widely used sharp AFM tips. We address a number of issues concerning the nanomechanical analysis, including the applicability of contact mechanical models and the impact of a constrained contact geometry on the measured Young's modulus (the finite-thickness effect). We have tested our protocol by imaging living PC12 and MDA-MB-231 cells, in order to demonstrate the importance of the correction of the finite-thickness effect and the change in Young's modulus induced by the action of a cytoskeleton-targeting drug.

  8. Nanomechanical and topographical imaging of living cells by atomic force microscopy with colloidal probes

    SciTech Connect

    Puricelli, Luca; Galluzzi, Massimiliano; Schulte, Carsten; Podestà, Alessandro Milani, Paolo

    2015-03-15

    Atomic Force Microscopy (AFM) has a great potential as a tool to characterize mechanical and morphological properties of living cells; these properties have been shown to correlate with cells’ fate and patho-physiological state in view of the development of novel early-diagnostic strategies. Although several reports have described experimental and technical approaches for the characterization of cellular elasticity by means of AFM, a robust and commonly accepted methodology is still lacking. Here, we show that micrometric spherical probes (also known as colloidal probes) are well suited for performing a combined topographic and mechanical analysis of living cells, with spatial resolution suitable for a complete and accurate mapping of cell morphological and elastic properties, and superior reliability and accuracy in the mechanical measurements with respect to conventional and widely used sharp AFM tips. We address a number of issues concerning the nanomechanical analysis, including the applicability of contact mechanical models and the impact of a constrained contact geometry on the measured Young’s modulus (the finite-thickness effect). We have tested our protocol by imaging living PC12 and MDA-MB-231 cells, in order to demonstrate the importance of the correction of the finite-thickness effect and the change in Young’s modulus induced by the action of a cytoskeleton-targeting drug.

  9. Determination of solute site occupancies within γ' precipitates in nickel-base superalloys via orientation-specific atom probe tomography.

    PubMed

    Meher, S; Rojhirunsakool, T; Nandwana, P; Tiley, J; Banerjee, R

    2015-12-01

    The analytical limitations in atom probe tomography such as resolving a desired set of atomic planes, for solving complex materials science problems, have been overcome by employing a well-developed unique and reproducible crystallographic technique, involving synergetic coupling of orientation microscopy with atom probe tomography. The crystallographic information in atom probe reconstructions has been utilized to determine the solute site occupancies in Ni-Al-Cr based superalloys accurately. The structural information in atom probe reveals that both Al and Cr occupy the same sub-lattice within the L12-ordered γ' precipitates to form Ni3(Al,Cr) precipitates in a Ni-14Al-7Cr (at%) alloy. Interestingly, the addition of Co, which is a solid solution strengthener, to a Ni-14Al-7Cr alloy results in the partial reversal of Al site occupancy within γ' precipitates to form (Ni,Al)3(Al,Cr,Co) precipitates. This unique evidence of reversal of Al site occupancy, resulting from the introduction of other solutes within the ordered structures, gives insights into the relative energetics of different sub-lattice sites when occupied by different solutes. PMID:25952611

  10. Energetic oxygen atom material degradation studies

    NASA Technical Reports Server (NTRS)

    Caledonia, George E.; Krech, Robert H.

    1987-01-01

    As part of a study designed to test potential Shuttle surface materials for the extents of degradation and mass loss expected to be suffered in space from the velocity impacts of ambient oxygen atoms, a novel technique was developed for generation of a high flux of energetic oxygen atoms. The generation technique involves laser-induced breakdown of molecular oxygen followed by a rapid expansion of energetic oxygen atoms. The high-velocity streams developed in an evacuated hypersonic nozzle have average O-atom velocities of about 5 to 13 km/s, with an estimated total production of 10 to the 18th atoms per pulse over pulse durations of several microseconds. Results on preliminary material degradation tests conducted with this test facility have been reported by Caledonia et al. (1987). Diagrams of the experimental setup are included.

  11. Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography

    NASA Astrophysics Data System (ADS)

    Valley, John W.; Cavosie, Aaron J.; Ushikubo, Takayuki; Reinhard, David A.; Lawrence, Daniel F.; Larson, David J.; Clifton, Peter H.; Kelly, Thomas F.; Wilde, Simon A.; Moser, Desmond E.; Spicuzza, Michael J.

    2014-03-01

    The only physical evidence from the earliest phases of Earth's evolution comes from zircons, ancient mineral grains that can be dated using the U-Th-Pb geochronometer. Oxygen isotope ratios from such zircons have been used to infer when the hydrosphere and conditions habitable to life were established. Chemical homogenization of Earth's crust and the existence of a magma ocean have not been dated directly, but must have occurred earlier. However, the accuracy of the U-Pb zircon ages can plausibly be biased by poorly understood processes of intracrystalline Pb mobility. Here we use atom-probe tomography to identify and map individual atoms in the oldest concordant grain from Earth, a 4.4-Gyr-old Hadean zircon with a high-temperature overgrowth that formed about 1 Gyr after the mineral's core. Isolated nanoclusters, measuring about 10 nm and spaced 10-50 nm apart, are enriched in incompatible elements including radiogenic Pb with unusually high 207Pb/206Pb ratios. We demonstrate that the length scales of these clusters make U-Pb age biasing impossible, and that they formed during the later reheating event. Our tomography data thereby confirm that any mixing event of the silicate Earth must have occurred before 4.4 Gyr ago, consistent with magma ocean formation by an early moon-forming impact about 4.5 Gyr ago.

  12. Deformation-induced trace element redistribution in zircon revealed using atom probe tomography

    PubMed Central

    Piazolo, Sandra; La Fontaine, Alexandre; Trimby, Patrick; Harley, Simon; Yang, Limei; Armstrong, Richard; Cairney, Julie M.

    2016-01-01

    Trace elements diffuse negligible distances through the pristine crystal lattice in minerals: this is a fundamental assumption when using them to decipher geological processes. For example, the reliable use of the mineral zircon (ZrSiO4) as a U-Th-Pb geochronometer and trace element monitor requires minimal radiogenic isotope and trace element mobility. Here, using atom probe tomography, we document the effects of crystal–plastic deformation on atomic-scale elemental distributions in zircon revealing sub-micrometre-scale mechanisms of trace element mobility. Dislocations that move through the lattice accumulate U and other trace elements. Pipe diffusion along dislocation arrays connected to a chemical or structural sink results in continuous removal of selected elements (for example, Pb), even after deformation has ceased. However, in disconnected dislocations, trace elements remain locked. Our findings have important implications for the use of zircon as a geochronometer, and highlight the importance of deformation on trace element redistribution in minerals and engineering materials. PMID:26868040

  13. Deformation-induced trace element redistribution in zircon revealed using atom probe tomography.

    PubMed

    Piazolo, Sandra; La Fontaine, Alexandre; Trimby, Patrick; Harley, Simon; Yang, Limei; Armstrong, Richard; Cairney, Julie M

    2016-01-01

    Trace elements diffuse negligible distances through the pristine crystal lattice in minerals: this is a fundamental assumption when using them to decipher geological processes. For example, the reliable use of the mineral zircon (ZrSiO4) as a U-Th-Pb geochronometer and trace element monitor requires minimal radiogenic isotope and trace element mobility. Here, using atom probe tomography, we document the effects of crystal-plastic deformation on atomic-scale elemental distributions in zircon revealing sub-micrometre-scale mechanisms of trace element mobility. Dislocations that move through the lattice accumulate U and other trace elements. Pipe diffusion along dislocation arrays connected to a chemical or structural sink results in continuous removal of selected elements (for example, Pb), even after deformation has ceased. However, in disconnected dislocations, trace elements remain locked. Our findings have important implications for the use of zircon as a geochronometer, and highlight the importance of deformation on trace element redistribution in minerals and engineering materials. PMID:26868040

  14. Deformation-induced trace element redistribution in zircon revealed using atom probe tomography

    NASA Astrophysics Data System (ADS)

    Piazolo, Sandra; La Fontaine, Alexandre; Trimby, Patrick; Harley, Simon; Yang, Limei; Armstrong, Richard; Cairney, Julie M.

    2016-02-01

    Trace elements diffuse negligible distances through the pristine crystal lattice in minerals: this is a fundamental assumption when using them to decipher geological processes. For example, the reliable use of the mineral zircon (ZrSiO4) as a U-Th-Pb geochronometer and trace element monitor requires minimal radiogenic isotope and trace element mobility. Here, using atom probe tomography, we document the effects of crystal-plastic deformation on atomic-scale elemental distributions in zircon revealing sub-micrometre-scale mechanisms of trace element mobility. Dislocations that move through the lattice accumulate U and other trace elements. Pipe diffusion along dislocation arrays connected to a chemical or structural sink results in continuous removal of selected elements (for example, Pb), even after deformation has ceased. However, in disconnected dislocations, trace elements remain locked. Our findings have important implications for the use of zircon as a geochronometer, and highlight the importance of deformation on trace element redistribution in minerals and engineering materials.

  15. Reduced-density-matrix description for pump-probe optical phenomena in moving atomic systems

    NASA Astrophysics Data System (ADS)

    Jacobs, V. L.

    2014-09-01

    Linear and nonlinear (especially coherent) electromagnetic interactions of moving many-electron atoms are investigated using a reduced-density-matrix description, which is applied to electromagnetically induced transparency and related resonant pump-probe optical phenomena. External magnetic fields are included on an equal footing with the electromagnetic fields and spin-Zeeman interactions are taken into account. Complimentary time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations of the reduced-density-matrix description are self-consistently developed. The general nonperturbative and non-Markovian formulations provide a fundamental framework for systematic evaluations of corrections to the standard Born (lowest-order-perturbation) and Markov (short-memory-time) approximations. The macroscopic electromagnetic response is described semiclassically, employing a perturbation expansion of the reduced-density operator in powers of the classical electromagnetic field. Our primary results are compact Liouville-space operator expressions for the linear and general (nth-order) nonlinear macroscopic electromagnetic-response tensors, which can be evaluated for nonlocal and nonstationary optical media described by multilevel atomic-system representations. Interactions among atoms and with environmental photons are treated as line-broadening effects by means of a general Liouville-space self-energy operator, for which the tetradic-matrix elements are explicitly evaluated in the diagonal, lowest-order, and Markov approximations. The compact Liouville-space operator expressions that are derived for the macroscopic electromagnetic-response tensors are introduced into the dynamical description of the electromagnetic-field propagation. It is pointed out that a quantized-electromagnetic-field approach will be required for a fully self-consistent quantum-mechanical treatment of local-field effects and radiative corrections.

  16. Electrical transport and mechanical properties of alkylsilane self-assembled monolayers on silicon surfaces probed by atomic force microscopy

    SciTech Connect

    Park, Jeong Young; Qi, Yabing; Ashby, Paul D.; Hendriksen, Bas L.M.; Salmeron, Miquel

    2009-02-06

    The correlation between molecular conductivity and mechanical properties (molecular deformation and frictional responses) of hexadecylsilane self-assembled monolayers was studied with conductive probe atomic force microscopy/friction force microscopy in ultrahigh vacuum. Current and friction were measured as a function of applied pressure, simultaneously, while imaging the topography of self-assembled monolayer molecule islands and silicon surfaces covered with a thin oxide layer. Friction images reveal lower friction over the molecules forming islands than over the bare silicon surface, indicating the lubricating functionality of alkylsilane molecules. By measuring the tunneling current change due to changing of the height of the molecular islands by tilting the molecules under pressure from the tip, we obtained an effective conductance decay constant ({beta}) of 0.52/{angstrom}.

  17. Stability of nanoclusters in 14YWT oxide dispersion strengthened steel under heavy ion-irradiation by atom probe tomography

    SciTech Connect

    Jianchao He; Farong Wan; Kumar Sridharan; Todd R. Allen; A. Certain; V. Shutthanandan; Y.Q. Wu

    2014-12-01

    14YWT oxide dispersion strengthened (ODS) ferritic steel was irradiated with of 5 MeV Ni2+ ions, at 300 C, 450 C, and 600 C to a damage level of 100 dpa. The stability of Ti–Y–O nanoclusters was investigated by applying atom probe tomography (APT) in voltage mode, of the samples before and after irradiations. The average size and number density of the nanoclusters was determined using the maximum separation method. These techniques allowed for the imaging of nanoclusters to sizes well below the resolution limit of conventional transmission electron microscopy techniques. The most significant changes were observed for samples irradiated at 300 C where the size (average Guinier radius) and number density of nanoclusters were observed to decrease from 1.1 nm to 0.8 nm and 12 1023 to 3.6 1023, respectively. In this study, the nanoclusters are more stable at higher temperature.

  18. Computational comparative study of microwave probes for plasma density measurement

    NASA Astrophysics Data System (ADS)

    Kim, D. W.; You, S. J.; Kim, J. H.; Chang, H. Y.; Oh, W. Y.

    2016-06-01

    A microwave probe is known to be a suitable method to measure plasma density, even in the processing condition and is widely used in various environments of low-temperature processing plasmas. Various types of microwave probes have been researched and developed to measure the precise plasma density. Extensive research has been conducted to investigate each probes characteristic responding to the plasma parameters (plasma density, electron temperature, pressure, sheath width, and so forth) based on both experiments and simulations. However, a comparative study elucidating the relative characteristics of each probe has not been completed yet, despite the wide applications of the probes in processing plasma. We conduct a comparative study among the microwave probes using the numerical method of three-dimensional finite-difference time-domain simulation. In this study, the microwave probes are compared by investigating the precision of plasma density measurement under a comprehensive range of plasma parameters (plasma density, pressure, and sheath width).

  19. Probing quantum phases of ultracold atoms in optical lattices by transmission spectra in cavity quantum electrodynamics

    NASA Astrophysics Data System (ADS)

    Mekhov, Igor B.; Maschler, Christoph; Ritsch, Helmut

    2007-05-01

    Studies of ultracold gases in optical lattices provide a means for testing fundamental and application-oriented quantum many-body concepts of condensed-matter physics in well controllable atomic systems; examples include strongly correlated phases and quantum-information processing. Standard methods to observe quantum properties of Bose-Einstein condensates are based on matter-wave interference between atoms released from traps, a method that ultimately destroys the system. Here, we propose a new approach on the basis of optical measurements that conserves the number of atoms. We prove that atomic quantum statistics can be mapped on transmission spectra of high-Q cavities, where atoms create a quantum refractive index. This can be useful for studying phase transitions-for example, between Mott insulator and superfluid states-as various phases show qualitatively distinct light scattering. Joining the paradigms of cavity quantum electrodynamics and ultracold gases could enable conceptually new investigations of both light and matter at ultimate quantum levels. We predict effects accessible in experiments that recently became possible.

  20. On the interplay between relaxation, defect formation, and atomic Sn distribution in Ge{sub (1−x)}Sn{sub (x)} unraveled with atom probe tomography

    SciTech Connect

    Kumar, A. Bran, J. Melkonyan, D. Shimura, Y. Vandervorst, W.; Demeulemeester, J. Bogdanowicz, J. Fleischmann, C. Loo, R.; Gencarelli, F. Wang, W.

    2015-07-14

    Ge{sub (1−x)}Sn{sub (x)} has received a lot of interest for opto-electronic applications and for strain engineering in advanced complementary-metal-oxide-semiconductor technology, because it enables engineering of the band gap and inducing strain in the alloy. To target a reliable technology for mass application in microelectronic devices, the physical problem to be addressed is to unravel the complex relationship between strain relaxation (as induced by the growth of large layer thicknesses or a thermal anneal) and defect formation, and/or stable Sn-cluster formation. In this paper, we study the onset of Sn-cluster formation and its link to strain relaxation using Atom Probe Tomography (APT). To this end, we also propose a modification of the core-linkage [Stephenson et al., Microsc. Microanal. 13, 448 (2007)] cluster analysis method, to overcome the challenges of limited detection efficiency and lateral resolution of APT, and the quantitative assessment for very small clusters (<40 atoms) embedded in a random distribution of Sn-atoms. We concluded that the main relaxation mechanism for these layers is defect generation (misfit dislocations, threading dislocations, etc.), irrespective of the cause (thickness of layer or thermal anneal) of relaxation and is independent of the cluster formation. The low thermodynamic solubility limit of Sn in Ge seems to be the driving force for Sn-cluster formation. Finally, we also discuss the spatial distribution of Sn in clusters and relate them to the theoretically predicted stable Sn clusters [Ventura et al., Phys. Rev. B 79, 155202 (2009)].

  1. Beyond the single-atom response in absorption line shapes: probing a dense, laser-dressed helium gas with attosecond pulse trains.

    PubMed

    Liao, Chen-Ting; Sandhu, Arvinder; Camp, Seth; Schafer, Kenneth J; Gaarde, Mette B

    2015-04-10

    We investigate the absorption line shapes of laser-dressed atoms beyond the single-atom response, by using extreme ultraviolet (XUV) attosecond pulse trains to probe an optically thick helium target under the influence of a strong infrared (IR) field. We study the interplay between the IR-induced phase shift of the microscopic time-dependent dipole moment and the resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our experimental and theoretical results show that as the optical depth increases, this interplay leads initially to a broadening of the IR-modified line shape, and subsequently, to the appearance of new, narrow features in the absorption line. PMID:25910116

  2. Probing the initiation of voltage decay in Li-rich layered cathode materials at the atomic scale

    SciTech Connect

    Wu, Yan; Ma, Cheng; Yang, Jihui; Li, Zicheng; Allard, Jr., Lawrence Frederick; Liang, Chengdu; Chi, Miaofang

    2015-01-01

    Li-rich layered oxides hold great promise for improving the energy density of present-day Li-ion batteries. However, their application is limited by the voltage decay upon cycling, and the origin of such a phenomenon is poorly understood. A major issue is determining the voltage range over which detrimental reactions originate. In the present study, a unique yet effective approach was employed to probe this issue. Instead of studying the materials during the first cycle, electrochemical behavior and evolution of the atomic structures were compared in extensively cycled specimens under varied charge/discharge voltages. With the upper cutoff voltage lowered from 4.8 to 4.4 V, the voltage decay ceased to occur even after 60 cycles. In the meantime, the material maintained its layered structure without any spinel phase emerging at the surface, which is unambiguously shown by the atomic-resolution Z-contrast imaging and electron energy loss spectroscopy. These results have conclusively demonstrated that structural/chemical changes responsible for the voltage decay began between 4.4 and 4.8 V, where the layered-to-spinel transition was the most dramatic structural change observed. Thus, this discovery lays important groundwork for the mechanistic understanding of the voltage decay in Li-rich layered cathode materials.

  3. Probing the initiation of voltage decay in Li-rich layered cathode materials at the atomic scale

    DOE PAGESBeta

    Wu, Yan; Ma, Cheng; Yang, Jihui; Li, Zicheng; Allard, Jr., Lawrence Frederick; Liang, Chengdu; Chi, Miaofang

    2015-01-01

    Li-rich layered oxides hold great promise for improving the energy density of present-day Li-ion batteries. However, their application is limited by the voltage decay upon cycling, and the origin of such a phenomenon is poorly understood. A major issue is determining the voltage range over which detrimental reactions originate. In the present study, a unique yet effective approach was employed to probe this issue. Instead of studying the materials during the first cycle, electrochemical behavior and evolution of the atomic structures were compared in extensively cycled specimens under varied charge/discharge voltages. With the upper cutoff voltage lowered from 4.8 tomore » 4.4 V, the voltage decay ceased to occur even after 60 cycles. In the meantime, the material maintained its layered structure without any spinel phase emerging at the surface, which is unambiguously shown by the atomic-resolution Z-contrast imaging and electron energy loss spectroscopy. These results have conclusively demonstrated that structural/chemical changes responsible for the voltage decay began between 4.4 and 4.8 V, where the layered-to-spinel transition was the most dramatic structural change observed. Thus, this discovery lays important groundwork for the mechanistic understanding of the voltage decay in Li-rich layered cathode materials.« less

  4. The interstellar heliopause probe technology reference study

    NASA Astrophysics Data System (ADS)

    Lyngvi, A.; Falkner, P.; Peacock, A.

    The interstellar heliopause probe (IHP) is one of ESA's technology reference studies (TRS). The TRS aim to focus the development of strategically important technologies of relevance to future science missions by studying technologically demanding and scientifically interesting missions that are currently not part of the science mission programme. Equipped with a highly integrated payload suite (HIPS), the IHP will perform in situ exploration of the heliopause and the heliospheric interface. The HIPS, which is a standard element in all TRSs, miniaturize payloads through resource reduction by using miniaturized components and sensors, and by sharing common structures and payload functionality. To achieve the scientific requirements of the mission, the spacecraft is to leave the heliosphere as close to the heliosphere nose as possible and reach a distance of 200 AU from the Sun within 25 years. This is possible by using a trajectory with two solar flybys and a solar sail with characteristic acceleration of 1.1 mm/s 2, which corresponds to a 245 × 245 m 2 solar sail and a sail thickness of 1-2 μm. The trajectory facilitates a modest sail design that could potentially be developed in a reasonable timeframe. In this paper, an update to the results of studies being performed on this mission will be given and the current mission baseline and spacecraft design will be described. Furthermore, alternative solar sail systems and enabling technologies will be discussed.

  5. Titanium pigmentation. An electron probe microanalysis study

    SciTech Connect

    Dupre, A.; Touron, P.; Daste, J.; Lassere, J.; Bonafe, J.L.; Viraben, R.

    1985-05-01

    A patient had an unusual pigmentary disease induced by titanium dioxide. The use of a topical cream containing titanium dioxide caused a xanthomalike appearance on the patient's penis. Electron probe microanalysis was valuable in establishing the cause of this balanitis.

  6. Optimisation of mass ranging for atom probe microanalysis and application to the corrosion processes in Zr alloys.

    PubMed

    Hudson, D; Smith, G D W; Gault, B

    2011-05-01

    Atom probe tomography uses time-of-flight mass spectrometry to identify the chemical nature of atoms from their mass-to-charge-state ratios. Within a mass spectrum, ranges are defined so as to attribute a chemical identity to each peak. The accuracy of atom probe microanalysis relies on the definition of these ranges. Here we propose and compare several automated ranging techniques, tested against simulated mass spectra. The performance of these metrics compare favourably with a trial of users asked to manually range a simplified simulated dataset. The optimised automated ranging procedure was then used to precisely evaluate the very low iron concentration (0.003-0.018 at%) in a zirconium alloy to reveal its behaviour in the matrix during corrosion; oxygen is injected into solution and has the effect of increasing the local iron concentration near the oxide-metal interface, which in turn affects the corrosion properties of the metal substrate. PMID:21163577

  7. Influence of the Electronic Structure and Optical Properties of CeO2 and UO2 for Characterization with UV-Laser Assisted Atom Probe Tomography

    SciTech Connect

    Billy Valderrama; H.B. Henderson; C. Yablinsky; J. Gan; T.R. Allen; M.V. Manuel

    2015-09-01

    Oxide materials are used in numerous applications such as thermal barrier coatings, nuclear fuels, and electrical conductors and sensors, all applications where nanometer-scale stoichiometric changes can affect functional properties. Atom probe tomography can be used to characterize the precise chemical distribution of individual species and spatially quantify the oxygen to metal ratio at the nanometer scale. However, atom probe analysis of oxides can be accompanied by measurement artifacts caused by laser-material interactions. In this investigation, two technologically relevant oxide materials with the same crystal structure and an anion to cation ratio of 2.00, pure cerium oxide (CeO2) and uranium oxide (UO2) are studied. It was determined that electronic structure, optical properties, heat transfer properties, and oxide stability strongly affect their evaporation behavior, thus altering their measured stoichiometry, with thermal conductance and thermodynamic stability being strong factors.

  8. An atom probe perspective on phase separation and precipitation in duplex stainless steels

    NASA Astrophysics Data System (ADS)

    Guo, Wei; Garfinkel, David A.; Tucker, Julie D.; Haley, Daniel; Young, George A.; Poplawsky, Jonathan D.

    2016-06-01

    Three-dimensional chemical imaging of Fe–Cr alloys showing Fe-rich (α)/Cr-rich (α‧) phase separation is reported using atom probe tomography techniques. The extent of phase separation, i.e., amplitude and wavelength, has been quantitatively assessed using the Langer-Bar-on-Miller, proximity histogram, and autocorrelation function methods for two separate Fe–Cr alloys, designated 2101 and 2205. Although the 2101 alloy possesses a larger wavelength and amplitude after annealing at 427 °C for 100–10 000 h, it exhibits a lower hardness than the 2205 alloy. In addition to this phase separation, ultra-fine Ni–Mn–Si–Cu-rich G-phase precipitates form at the α/α‧ interfaces in both alloys. For the 2101 alloy, Cu clusters act to form a nucleus, around which a Ni–Mn–Si shell develops during the precipitation process. For the 2205 alloy, the Ni and Cu atoms enrich simultaneously and no core–shell chemical distribution was found. This segregation phenomenon may arise from the exact Ni/Cu ratio inside the ferrite. After annealing for 10 000 h, the number density of the G-phase within the 2205 alloy was found to be roughly one order of magnitude higher than in the 2101 alloy. The G-phase precipitates have an additional deleterious effect on the thermal embrittlement, as evaluated by the Ashby–Orowan equation, which explains the discrepancy between the hardness and the rate of phase separation with respect to annealing time (Gladman T 1999 Mater. Sci. Tech. Ser. 15 30–36). ).

  9. An atom probe perspective on phase separation and precipitation in duplex stainless steels

    DOE PAGESBeta

    Garfinkel, David A.; Tucker, Julie D.; Haley, Daniel A.; Young, George A.; Guo, Wei; Poplawsky, Jonathan D.

    2016-05-16

    Here, three-dimensional chemical imaging of Fe–Cr alloys showing Fe-rich (α)/Cr-rich (α') phase separation is reported using atom probe tomography techniques. The extent of phase separation, i.e., amplitude and wavelength, has been quantitatively assessed using the Langer-Bar-on-Miller, proximity histogram, and autocorrelation function methods for two separate Fe–Cr alloys, designated 2101 and 2205. Although the 2101 alloy possesses a larger wavelength and amplitude after annealing at 427 °C for 100–10 000 h, it exhibits a lower hardness than the 2205 alloy. In addition to this phase separation, ultra-fine Ni–Mn–Si–Cu-rich G-phase precipitates form at the α/α' interfaces in both alloys. For the 2101more » alloy, Cu clusters act to form a nucleus, around which a Ni–Mn–Si shell develops during the precipitation process. For the 2205 alloy, the Ni and Cu atoms enrich simultaneously and no core–shell chemical distribution was found. This segregation phenomenon may arise from the exact Ni/Cu ratio inside the ferrite. After annealing for 10 000 h, the number density of the G-phase within the 2205 alloy was found to be roughly one order of magnitude higher than in the 2101 alloy. The G-phase precipitates have an additional deleterious effect on the thermal embrittlement, as evaluated by the Ashby–Orowan equation, which explains the discrepancy between the hardness and the rate of phase separation with respect to annealing time (Gladman T 1999 Mater. Sci. Tech. Ser. 15 30–36).« less

  10. An atom probe perspective on phase separation and precipitation in duplex stainless steels.

    PubMed

    Guo, Wei; Garfinkel, David A; Tucker, Julie D; Haley, Daniel; Young, George A; Poplawsky, Jonathan D

    2016-06-24

    Three-dimensional chemical imaging of Fe-Cr alloys showing Fe-rich (α)/Cr-rich (α') phase separation is reported using atom probe tomography techniques. The extent of phase separation, i.e., amplitude and wavelength, has been quantitatively assessed using the Langer-Bar-on-Miller, proximity histogram, and autocorrelation function methods for two separate Fe-Cr alloys, designated 2101 and 2205. Although the 2101 alloy possesses a larger wavelength and amplitude after annealing at 427 °C for 100-10 000 h, it exhibits a lower hardness than the 2205 alloy. In addition to this phase separation, ultra-fine Ni-Mn-Si-Cu-rich G-phase precipitates form at the α/α' interfaces in both alloys. For the 2101 alloy, Cu clusters act to form a nucleus, around which a Ni-Mn-Si shell develops during the precipitation process. For the 2205 alloy, the Ni and Cu atoms enrich simultaneously and no core-shell chemical distribution was found. This segregation phenomenon may arise from the exact Ni/Cu ratio inside the ferrite. After annealing for 10 000 h, the number density of the G-phase within the 2205 alloy was found to be roughly one order of magnitude higher than in the 2101 alloy. The G-phase precipitates have an additional deleterious effect on the thermal embrittlement, as evaluated by the Ashby-Orowan equation, which explains the discrepancy between the hardness and the rate of phase separation with respect to annealing time (Gladman T 1999 Mater. Sci. Tech. Ser. 15 30-36). PMID:27181108

  11. Atom probe tomography characterizations of high nickel, low copper surveillance RPV welds irradiated to high fluences

    NASA Astrophysics Data System (ADS)

    Miller, M. K.; Powers, K. A.; Nanstad, R. K.; Efsing, P.

    2013-06-01

    The Ringhals Units 3 and 4 reactors in Sweden are pressurized water reactors (PWRs) designed and supplied by Westinghouse Electric Company, with commercial operation in 1981 and 1983, respectively. The reactor pressure vessels (RPVs) for both reactors were fabricated with ring forgings of SA 508 class 2 steel. Surveillance blocks for both units were fabricated using the same weld wire heat, welding procedures, and base metals used for the RPVs. The primary interest in these weld metals is because they have very high nickel contents, with 1.58 and 1.66 wt.% for Unit 3 and Unit 4, respectively. The nickel content in Unit 4 is the highest reported nickel content for any Westinghouse PWR. Although both welds contain less than 0.10 wt.% copper, the weld metals have exhibited high irradiation-induced Charpy 41-J transition temperature shifts in surveillance testing. The Charpy impact 41-J shifts and corresponding fluences are 192 °C at 5.0 × 1023 n/m2 (>1 MeV) for Unit 3 and 162 °C at 6.0 × 1023 n/m2 (>1 MeV) for Unit 4. These relatively low-copper, high-nickel, radiation-sensitive welds relate to the issue of so-called late-blooming nickel-manganese-silicon phases. Atom probe tomography measurements have revealed ˜2 nm-diameter irradiation-induced precipitates containing manganese, nickel, and silicon, with phosphorus evident in some of the precipitates. However, only a relatively few number of copper atoms are contained within the precipitates. The larger increase in the transition temperature shift in the higher copper weld metal from the Ringhals R3 Unit is associated with copper-enriched regions within the manganese-nickel-silicon-enriched precipitates rather than changes in their size or number density.

  12. Pressure/temperature fluid cell apparatus for the neutron powder diffractometer instrument: Probing atomic structure in situ

    DOE PAGESBeta

    Wang, Hsiu -Wen; Fanelli, Victor R.; Reiche, Helmut M.; Larson, Eric; Taylor, Mark A.; Xu, Hongwu; Zhu, Jinlong; Siewenie, Joan; Page, Katharine

    2014-12-01

    This contribution describes a new local structure compatible gas/liquid cell apparatus for probing disordered materials at high pressures and variable temperatures in the Neutron Powder Diffraction instrument at the Lujan Neutron Scattering Center, Los Alamos National Laboratory. The new sample environment offers choices for sample canister thickness and canister material type. Finite element modeling is utilized to establish maximum allowable working pressures of 414 MPa at 15 K and 121 MPa at 600 K. High quality atomic pair distribution function data extraction and modeling have been demonstrated for a calibration standard (Si powder) and for supercritical and subcritical CO2measurements. Asmore » a result, the new sample environment was designed to specifically target experimental studies of the local atomic structures involved in geologic CO2 sequestration, but will be equally applicable to a wide variety of energy applications, including sorption of fluids on nano/meso-porous solids, clathrate hydrate formation, catalysis, carbon capture, and H2 and natural gas uptake/storage.« less

  13. Influence of instrument conditions on the evaporation behavior of uranium dioxide with UV laser-assisted atom probe tomography

    SciTech Connect

    Valderrama, B.; Henderson, H.B.; Gan, J.; Manuel, M.V.

    2015-04-01

    Atom probe tomography (APT) provides the ability to detect subnanometer chemical variations spatially, with high accuracy. However, it is known that compositional accuracy can be affected by experimental conditions. A study of the effect of laser energy, specimen base temperature, and detection rate is performed on the evaporation behavior of uranium dioxide (UO2). In laser-assisted mode, tip geometry and standing voltage also contribute to the evaporation behavior. In this investigation, it was determined that modifying the detection rate and temperature did not affect the evaporation behavior as significantly as laser energy. It was also determined that three laser evaporation regimes are present in UO2. Very low laser energy produces a behavior similar to DC-field evaporation, moderate laser energy produces the desired laser-assisted field evaporation characteristic and high laser energy induces thermal effects, negatively altering the evaporation behavior. The need for UO2 to be analyzed under moderate laser energies to produce accurate stoichiometry distinguishes it from other oxides. The following experimental conditions providing the best combination of mass resolving power, accurate stoichiometry, and uniform evaporation behavior: 50 K, 10 pJ laser energy, a detection rate of 0.003 atoms per pulse, and a 100 kHz repetition rate.

  14. Pressure/temperature fluid cell apparatus for the neutron powder diffractometer instrument: Probing atomic structure in situ

    SciTech Connect

    Wang, Hsiu-Wen; Fanelli, Victor R.; Reiche, Helmut M.; Larson, Eric; Taylor, Mark A.; Siewenie, Joan; Xu, Hongwu; Zhu, Jinlong; Page, Katharine

    2014-12-15

    This contribution describes a new local structure compatible gas/liquid cell apparatus for probing disordered materials at high pressures and variable temperatures in the Neutron Powder Diffraction instrument at the Lujan Neutron Scattering Center, Los Alamos National Laboratory. The new sample environment offers choices for sample canister thickness and canister material type. Finite element modeling is utilized to establish maximum allowable working pressures of 414 MPa at 15 K and 121 MPa at 600 K. High quality atomic pair distribution function data extraction and modeling have been demonstrated for a calibration standard (Si powder) and for supercritical and subcritical CO{sub 2} measurements. The new sample environment was designed to specifically target experimental studies of the local atomic structures involved in geologic CO{sub 2} sequestration, but will be equally applicable to a wide variety of energy applications, including sorption of fluids on nano/meso-porous solids, clathrate hydrate formation, catalysis, carbon capture, and H{sub 2} and natural gas uptake/storage.

  15. Simulation of Heterogeneous Atom Probe Tip Shapes Evolution during Field Evaporation Using a Level Set Method and Different Evaporation Models

    SciTech Connect

    Xu, Zhijie; Li, Dongsheng; Xu, Wei; Devaraj, Arun; Colby, Robert J.; Thevuthasan, Suntharampillai; Geiser, B. P.; Larson, David J.

    2015-04-01

    In atom probe tomography (APT), accurate reconstruction of the spatial positions of field evaporated ions from measured detector patterns depends upon a correct understanding of the dynamic tip shape evolution and evaporation laws of component atoms. Artifacts in APT reconstructions of heterogeneous materials can be attributed to the assumption of homogeneous evaporation of all the elements in the material in addition to the assumption of a steady state hemispherical dynamic tip shape evolution. A level set method based specimen shape evolution model is developed in this study to simulate the evaporation of synthetic layered-structured APT tips. The simulation results of the shape evolution by the level set model qualitatively agree with the finite element method and the literature data using the finite difference method. The asymmetric evolving shape predicted by the level set model demonstrates the complex evaporation behavior of heterogeneous tip and the interface curvature can potentially lead to the artifacts in the APT reconstruction of such materials. Compared with other APT simulation methods, the new method provides smoother interface representation with the aid of the intrinsic sub-grid accuracy. Two evaporation models (linear and exponential evaporation laws) are implemented in the level set simulations and the effect of evaporation laws on the tip shape evolution is also presented.

  16. Pressure/temperature fluid cell apparatus for the neutron powder diffractometer instrument: probing atomic structure in situ.

    PubMed

    Wang, Hsiu-Wen; Fanelli, Victor R; Reiche, Helmut M; Larson, Eric; Taylor, Mark A; Xu, Hongwu; Zhu, Jinlong; Siewenie, Joan; Page, Katharine

    2014-12-01

    This contribution describes a new local structure compatible gas/liquid cell apparatus for probing disordered materials at high pressures and variable temperatures in the Neutron Powder Diffraction instrument at the Lujan Neutron Scattering Center, Los Alamos National Laboratory. The new sample environment offers choices for sample canister thickness and canister material type. Finite element modeling is utilized to establish maximum allowable working pressures of 414 MPa at 15 K and 121 MPa at 600 K. High quality atomic pair distribution function data extraction and modeling have been demonstrated for a calibration standard (Si powder) and for supercritical and subcritical CO2 measurements. The new sample environment was designed to specifically target experimental studies of the local atomic structures involved in geologic CO2 sequestration, but will be equally applicable to a wide variety of energy applications, including sorption of fluids on nano/meso-porous solids, clathrate hydrate formation, catalysis, carbon capture, and H2 and natural gas uptake/storage. PMID:25554335

  17. Influence of instrument conditions on the evaporation behavior of uranium dioxide with UV laser-assisted atom probe tomography

    NASA Astrophysics Data System (ADS)

    Valderrama, B.; Henderson, H. B.; Gan, J.; Manuel, M. V.

    2015-04-01

    Atom probe tomography (APT) provides the ability to detect subnanometer chemical variations spatially, with high accuracy. However, it is known that compositional accuracy can be affected by experimental conditions. A study of the effect of laser energy, specimen base temperature, and detection rate is performed on the evaporation behavior of uranium dioxide (UO2). In laser-assisted mode, tip geometry and standing voltage also contribute to the evaporation behavior. In this investigation, it was determined that modifying the detection rate and temperature did not affect the evaporation behavior as significantly as laser energy. It was also determined that three laser evaporation regimes are present in UO2. Very low laser energy produces a behavior similar to DC-field evaporation, moderate laser energy produces the desired laser-assisted field evaporation characteristic and high laser energy induces thermal effects, negatively altering the evaporation behavior. The need for UO2 to be analyzed under moderate laser energies to produce accurate stoichiometry distinguishes it from other oxides. The following experimental conditions providing the best combination of mass resolving power, accurate stoichiometry, and uniform evaporation behavior: 50 K, 10 pJ laser energy, a detection rate of 0.003 atoms per pulse, and a 100 kHz repetition rate.

  18. Atom probe microscopy of three-dimensional distribution of silicon isotopes in {sup 28}Si/{sup 30}Si isotope superlattices with sub-nanometer spatial resolution

    SciTech Connect

    Shimizu, Yasuo; Kawamura, Yoko; Uematsu, Masashi; Itoh, Kohei M.; Tomita, Mitsuhiro; Sasaki, Mikio; Uchida, Hiroshi; Takahashi, Mamoru

    2009-10-01

    Laser-assisted atom probe microscopy of 2 nm period {sup 28}Si/{sup 30}Si isotope superlattices (SLs) is reported. Three-dimensional distributions of {sup 28}Si and {sup 30}Si stable isotopes are obtained with sub-nanometer spatial resolution. The depth resolution of the present atom probe analysis is much higher than that of secondary ion mass spectrometry (SIMS) even when SIMS is performed with a great care to reduce the artifact due to atomic mixing. Outlook of Si isotope SLs as ideal depth scales for SIMS and three-dimensional position standards for atom probe microscopy is discussed.

  19. Atom probe tomography analysis of high dose MA957 at selected irradiation temperatures

    NASA Astrophysics Data System (ADS)

    Bailey, Nathan A.; Stergar, Erich; Toloczko, Mychailo; Hosemann, Peter

    2015-04-01

    Oxide dispersion strengthened (ODS) alloys are meritable structural materials for nuclear reactor systems due to the exemplary resistance to radiation damage and high temperature creep. Summarized in this work are atom probe tomography (APT) investigations on a heat of MA957 that underwent irradiation in the form of in-reactor creep specimens in the Fast Flux Test Facility-Materials Open Test Assembly (FFTF-MOTA) for the Liquid Metal Fast Breeder Reactor (LMFBR) program. The oxide precipitates appear stable under irradiation at elevated temperature over extended periods of time. Nominally, the precipitate chemistry is unchanged by the accumulated dose; although, evidence suggests that ballistic dissolution and reformation processes are occurring at all irradiation temperatures. At 412 °C-109 dpa, chromium enrichments - consistent with the α‧ phase - appear between the oxide precipitates, indicating radiation induced segregation. Grain boundaries, enriched with several elements including nickel and titanium, are observed at all irradiation conditions. At 412 °C-109 dpa, the grain boundaries are also enriched in molecular titanium oxide (TiO).

  20. Uranium isotopic ratio measurements of U3O8 reference materials by atom probe tomography.

    PubMed

    Fahey, Albert J; Perea, Daniel E; Bartrand, Jonah; Arey, Bruce W; Thevuthasan, Suntharampillai

    2016-03-01

    We report results of measurements of isotopic ratios obtained with atom probe tomography on U3O8 reference materials certified for their isotopic abundances of uranium. The results show good agreement with the certified values. High backgrounds due to tails from adjacent peaks complicate the measurement of the integrated peak areas as well as the fact that only oxides of uranium appear in the spectrum, the most intense of which is doubly charged. In addition, lack of knowledge of other instrumental parameters, such as the dead time, may bias the results. Isotopic ratio measurements can be performed at the nanometer-scale with the expectation of sensible results. The abundance sensitivity and mass resolving power of the mass spectrometer are not sufficient to compete with magnetic-sector instruments but are not far from measurements made by ToF-SIMS of other isotopic systems. The agreement of the major isotope ratios is more than sufficient to distinguish most anthropogenic compositions from natural. PMID:26774651

  1. Blind deconvolution of time-of-flight mass spectra from atom probe tomography.

    PubMed

    Johnson, L J S; Thuvander, M; Stiller, K; Odén, M; Hultman, L

    2013-09-01

    A major source of uncertainty in compositional measurements in atom probe tomography stems from the uncertainties of assigning peaks or parts of peaks in the mass spectrum to their correct identities. In particular, peak overlap is a limiting factor, whereas an ideal mass spectrum would have peaks at their correct positions with zero broadening. Here, we report a method to deconvolute the experimental mass spectrum into such an ideal spectrum and a system function describing the peak broadening introduced by the field evaporation and detection of each ion. By making the assumption of a linear and time-invariant behavior, a system of equations is derived that describes the peak shape and peak intensities. The model is fitted to the observed spectrum by minimizing the squared residuals, regularized by the maximum entropy method. For synthetic data perfectly obeying the assumptions, the method recovered peak intensities to within ±0.33 at%. The application of this model to experimental APT data is exemplified with Fe-Cr data. Knowledge of the peak shape opens up several new possibilities, not just for better overall compositional determination, but, e.g., for the estimation of errors of ranging due to peak overlap or peak separation constrained by isotope abundances. PMID:23607992

  2. Atom probe tomography investigation of lath boundary segregation and precipitation in a maraging stainless steel.

    PubMed

    Thuvander, Mattias; Andersson, Marcus; Stiller, Krystyna

    2013-09-01

    Lath boundaries in a maraging stainless steel of composition 13Cr-8Ni-2Mo-2Cu-1Ti-0.7Al-0.3Mn-0.2Si-0.03C (at%) have been investigated using atom probe tomography following aging at 475 °C for up to 100 h. Segregation of Mo, Si and P to the lath boundaries was observed already after 5 min of aging, and the amount of segregation increases with aging time. At lath boundaries also precipitation of η-Ni₃(Ti, Al) and Cu-rich 9R, in contact with each other, takes place. These co-precipitates grow with time and because of coarsening the area number density decreases. After 100 h of aging a ∼5 nm thick film-like precipitation of a Mo-rich phase was observed at the lath boundaries. From the composition of the film it is suggested that the phase in question is the quasicrystalline R' phase. The film is perforated with Cu-rich 9R and η-Ni₃(Ti, Al) co-precipitates. Not all precipitate types present in the matrix do precipitate at the lath boundaries; the Si-containing G phase and γ'-Ni₃(Ti, Al, Si) and the Cr-rich α' phase were not observed at the lath boundaries. PMID:23234833

  3. Atomic force microscopy deep trench and sidewall imaging with an optical fiber probe

    SciTech Connect

    Xie, Hui Hussain, Danish; Yang, Feng; Sun, Lining

    2014-12-15

    We report a method to measure critical dimensions of micro- and nanostructures using the atomic force microscope (AFM) with an optical fiber probe (OFP). This method is capable of scanning narrow and deep trenches due to the long and thin OFP tip, as well as imaging of steep sidewalls with unique profiling possibilities by laterally tilting the OFP without any modifications of the optical lever. A switch control scheme is developed to measure the sidewall angle by flexibly transferring feedback control between the Z- and Y-axis, for a serial scan of the horizontal surface (raster scan on XY-plane) and sidewall (raster scan on the YZ-plane), respectively. In experiments, a deep trench with tapered walls (243.5 μm deep) and a microhole (about 14.9 μm deep) have been imaged with the orthogonally aligned OFP, as well as a silicon sidewall (fabricated by deep reactive ion etching) has been characterized with the tilted OFP. Moreover, the sidewall angle of TGZ3 (AFM calibration grating) was accurately measured using the switchable scan method.

  4. Uranium Isotopic Ratio Measurements of U3O8 Reference Materials by Atom Probe Tomography

    SciTech Connect

    Fahey, Albert J.; Perea, Daniel E.; Bartrand, Jonah AG; Arey, Bruce W.; Thevuthasan, Suntharampillai

    2016-01-01

    We report results of measurements of isotopic ratios obtained with atom probe tomography on U3O8 reference materials certified for their isotopic abundances of uranium. The results show good agreement with the certified values. High backgrounds due to tails from adjacent peaks complicate the measurement of the integrated peak areas as well as the fact that only oxides of uranium appear in the spectrum, the most intense of which is doubly charged. In addition, lack of knowledge of other instrumental parameters, such as the dead time, may bias the results. Isotopic ratio measurements can be performed at the nanometer-scale with the expectation of sensible results. The abundance sensitivity and mass resolving power of the mass spectrometer are not sufficient to compete with magnetic-sector instruments but are not far from measurements made by ToF-SIMS of other isotopic systems. The agreement of the major isotope ratios is more than sufficient to distinguish most anthropogenic compositions from natural.

  5. Roles of Atomic Injection Rate and External Magnetic Field on Optical Properties of Elliptical Polarized Probe Light

    NASA Astrophysics Data System (ADS)

    Karimi, R.; Asadpour, S. H.; Batebi, S.; Rahimpour Soleimani, H.

    2016-01-01

    In this paper we investigate the optical properties of an open four-level tripod atomic system driven by an elliptically polarized probe field in the presence of the external magnetic field and compare its properties with the corresponding closed system. Our result reveals that absorption, dispersion and group velocity of probe field can be manipulated by adjusting the phase difference between the two circularly polarized components of a single coherent field, magnetic field and cavity parameters i.e. the atomic exit rate from cavity and atomic injection rates. We show that the system can exhibit multiple electromagnetically induced transparency windows in the presence of the external magnetic field. The numerical result shows that the probe field in the open system can be amplified by appropriate choice of cavity parameters, while in the closed system with introduce appropriate phase difference between fields the probe field can be enhanced. Also it is shown that the group velocity of light pulse can be controlled by external magnetic field, relative phase of applied fields and cavity parameters. By changing the parameters the group velocity of light pulse changes from subluminal to superluminal light propagation and vice versa.

  6. Development of Two-Photon Pump Polarization Spectroscopy Probe Technique Tpp-Psp for Measurements of Atomic Hydrogen .

    NASA Astrophysics Data System (ADS)

    Satija, Aman; Lucht, Robert P.

    2015-06-01

    Atomic hydrogen (H) is a key radical in combustion and plasmas. Accurate knowledge of its concentration can be used to better understand transient phenomenon such as ignition and extinction in combustion environments. Laser induced polarization spectroscopy is a spatially resolved absorption technique which we have adapted for quantitative measurements of H atom. This adaptation is called two-photon pump, polarization spectroscopy probe technique (TPP-PSP) and it has been implemented using two different laser excitation schemes. The first scheme involves the two-photon excitation of 1S-2S transitions using a linearly polarized 243-nm beam. An anisotropy is created amongst Zeeman states in 2S-3P levels using a circularly polarized 656-nm pump beam. This anisotropy rotates the polarization of a weak, linearly polarized probe beam at 656 nm. As a result, the weak probe beam "leaks" past an analyzer in the detection channel and is measured using a PMT. This signal can be related to H atom density in the probe volume. The laser beams were created by optical parametric generation followed by multiple pulse dye amplification stages. This resulted in narrow linewidth beams which could be scanned in frequency domain and varied in energy. This allowed us to systematically investigate saturation and Stark effect in 2S-3P transitions with the goal of developing a quantitative H atom measurement technique. The second scheme involves the two-photon excitation of 1S-2S transitions using a linearly polarized 243-nm beam. An anisotropy is created amongst Zeeman states in 2S-4P transitions using a circularly polarized 486-nm pump beam. This anisotropy rotates the polarization of a weak, linearly polarized probe beam at 486 nm. As a result the weak probe beam "leaks" past an analyzer in the detection channel and is measured using a PMT. This signal can be related to H atom density in the probe volume. A dye laser was pumped by third harmonic of a Nd:YAG laser to create a laser beam

  7. Study of new systems concepts for a Titan atmospheric probe

    NASA Technical Reports Server (NTRS)

    Bernard, Doug; Citron, Todd; Drean, Robert; Lewis, Scott; Lo, Martin; Mccarthy, John; Soderblom, Robert; Steffy, Dave; Vargas, Tina; Wolff, Marty

    1986-01-01

    Results of a systems concepts study for a Titan Probe were examined. The key tradeoffs performed are described in detail. Mass breakdown of each Probe subsystem or major element were given. The mission analysis performed to determine compliance with the high altitude sampling and descent time requirements are described. The baseline Descent Module design was derived. The element of the Probe System left on the Carrier after separation were described.

  8. Measuring Young's modulus of biological objects in a liquid medium using an atomic force microscope with a special probe

    NASA Astrophysics Data System (ADS)

    Lebedev, D. V.; Chuklanov, A. P.; Bukharaev, A. A.; Druzhinina, O. S.

    2009-04-01

    A special probe with a 5-μm-diameter ball fixed at the end is developed for an atomic force microscope (AFM), with the use of which it is possible to obtain more correct values of the Young’s moduli of biological objects in liquid media and eliminate the risk of damaging the sample surface. In particular, the AFM measurements with this probe in situ revealed an increase in the Young’s modulus of rat blood vessel under the action of chlorhexidine.

  9. Atomic arrangement at ZnTe/CdSe interfaces determined by high resolution scanning transmission electron microscopy and atom probe tomography

    SciTech Connect

    Bonef, Bastien; Rouvière, Jean-Luc; Jouneau, Pierre-Henri; Bellet-Amalric, Edith; Gérard, Lionel; Mariette, Henri; André, Régis; Bougerol, Catherine; Grenier, Adeline

    2015-02-02

    High resolution scanning transmission electron microscopy and atom probe tomography experiments reveal the presence of an intermediate layer at the interface between two binary compounds with no common atom, namely, ZnTe and CdSe for samples grown by Molecular Beam Epitaxy under standard conditions. This thin transition layer, of the order of 1 to 3 atomic planes, contains typically one monolayer of ZnSe. Even if it occurs at each interface, the direct interface, i.e., ZnTe on CdSe, is sharper than the reverse one, where the ZnSe layer is likely surrounded by alloyed layers. On the other hand, a CdTe-like interface was never observed. This interface knowledge is crucial to properly design superlattices for optoelectronic applications and to master band-gap engineering.

  10. Charge transport and contact effects in nanoscale electrical junctions formed via conducting probe atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Beebe, Jeremy Matthew

    This thesis describes the fabrication and characterization of nanoscale molecular junctions using conducting probe atomic force microscopy (CP-AFM). This technique involves using a metal-coated AFM tip to contact a self-assembled monolayer (SAM) of an organic molecule tethered to a metal surface. This is one of several strategies for the formation of nanoscale electrical junctions designed to probe the current-voltage characteristics of very small numbers of organic molecules. The general goals of this research are to gain a better understanding of the nature of charge transport through molecules, and to begin to pave the way for their use in commercial electronic devices. Important concerns in molecular electronic research can be broken into two general categories, those being the metal contacts and the molecules themselves. In the contact subcategory, issues such as metal work function, electrode roughness, and electrode cleanliness are all important in determining the resistance of a given junction. The physical details of monolayer formation, such as surface coverage, tilt angle, and surface functionality combine with the electronic structure of the molecules to dictate how a given molecule performs in a junction. Included in this thesis is the first direct evidence that resistance in molecular junctions comprised of alkyl repeat units depends on the work function of the metal electrodes. Because an increase in metal work function corresponds to a smaller offset between the molecular HOMO and the junction Fermi level, this dependence also suggests that transport in these aliphatic systems occurs chiefly via hole tunneling. Also included is an analysis of the contribution to junction resistance that arises from each metal-molecule contact, and across the molecule in alkanethiol and alkanedithiol junctions. The aromatic phenylene and acene systems are examined briefly, and phenylenes are shown to be more efficient conduits for charge transport, contrary to

  11. Atomic structure and surface defects at mineral-water interfaces probed by in situ atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Siretanu, Igor; van den Ende, Dirk; Mugele, Frieder

    2016-04-01

    Atomic scale details of surface structure play a crucial role for solid-liquid interfaces. While macroscopic characterization techniques provide averaged information about bulk and interfaces, high resolution real space imaging reveals unique insights into the role of defects that are believed to dominate many aspects of surface chemistry and physics. Here, we use high resolution dynamic Atomic Force Microscopy (AFM) to visualize and characterize in ambient water the morphology and atomic scale structure of a variety of nanoparticles of common clay minerals adsorbed to flat solid surfaces. Atomically resolved images of the (001) basal planes are obtained on all materials investigated, namely gibbsite, kaolinite, illite, and Na-montmorillonite of both natural and synthetic origin. Next to regions of perfect crystallinity, we routinely observe extended regions of various types of defects on the surfaces, including vacancies of one or few atoms, vacancy islands, atomic steps, apparently disordered regions, as well as strongly adsorbed seemingly organic and inorganic species. While their exact nature is frequently difficult to identify, our observations clearly highlight the ubiquity of such defects and their relevance for the overall physical and chemical properties of clay nanoparticle-water interfaces.Atomic scale details of surface structure play a crucial role for solid-liquid interfaces. While macroscopic characterization techniques provide averaged information about bulk and interfaces, high resolution real space imaging reveals unique insights into the role of defects that are believed to dominate many aspects of surface chemistry and physics. Here, we use high resolution dynamic Atomic Force Microscopy (AFM) to visualize and characterize in ambient water the morphology and atomic scale structure of a variety of nanoparticles of common clay minerals adsorbed to flat solid surfaces. Atomically resolved images of the (001) basal planes are obtained on all

  12. Imaging of a soft, weakly adsorbing, living cell with a colloid probe tapping atomic force microscope technique.

    PubMed

    McNamee, Cathy E; Pyo, Nayoung; Tanaka, Saaya; Kanda, Yoichi; Higashitani, Ko

    2006-01-15

    Here, we propose a new method to improve the atomic force microscopy (AFM) image resolution of soft samples, such as cells, in liquid. Attaching a colloid probe to a cantilever was seen improve the image resolution of a living cell in a physiological buffer solution, obtained by the normal tapping mode, when compared to an image obtained using a regular cantilever tip. This may be due to the averaging out of the cantilever tip swinging caused by the visco-elasticity of the cell. The resolution was best, when silica spheres with a 3.3 microm diameter were attached. Although larger spheres gave a resolution better than a bare cantilever tip, their resolution was less than that obtained for the 3.3 microm diameter silica colloid. This dependency of the image resolution on the colloid probe size may be a result of the increased macroscopic van der Waals attraction between the cell and probe, the decreased repulsive force dependence on the cantilever probe radius, and the decrease in resolution due to the increased probe size. The size of the colloid probe, which should be attached to the cantilever to give the best image resolution, would be the one that optimises the combined result of these facts. PMID:16406494

  13. Ordering and site occupancy of D03 ordered Fe3Al-5 at%Cr evaluated by means of atom probe tomography.

    PubMed

    Rademacher, Thomas; Al-Kassab, Talaat; Deges, Johannes; Kirchheim, Reiner

    2011-05-01

    Addition of ternary elements to the D0(3) ordered Fe(3)Al intermetallic phase is a general approach to optimise its mechanical properties. To understand the physical influences of such additions the determination of the probability of site occupancies of these additions on the lattice site and ordering parameters is of high interest. Some common experimental techniques such as X-ray diffraction or Atom Location by Channelling Enhanced Microanalysis (ALCHEMI) are usually applied to explore this interplay. Unfortunately, certain published results are partly inconsistent, imprecise or even contradictory. In this study, these aspects are evaluated systematically by atom probe tomography (APT) and a special data analysis method. Additionally, to account for possible field evaporation effects that can falsify the estimation of site occupancy and induce misinterpretations, APT evaporation sequences were also simulated. As a result, chromium occupies most frequently the next nearest neighbour sites of Al atoms and local ordering parameters could be achieved. PMID:21247699

  14. Dopant characterization in self-regulatory plasma doped fin field-effect transistors by atom probe tomography

    SciTech Connect

    Takamizawa, H.; Shimizu, Y.; Nozawa, Y.; Toyama, T.; Nagai, Y.; Morita, H.; Yabuuchi, Y.; Ogura, M.

    2012-02-27

    Fin field-effect transistors are promising next-generation electronic devices, and the identification of dopant positions is important for their accurate characterization. We report atom probe tomography (APT) of silicon fin structures prepared by a recently developed self-regulatory plasma doping (SRPD) technique. Trenches between fin-arrays were filled using a low-energy focused ion beam to directly deposit silicon, which allowed the analysis of dopant distribution by APT near the surface of an actual fin transistor exposed to air. We directly demonstrate that SRPD can achieve a boron concentration above 1 x 10{sup 20} atoms/cm{sup 3} at the fin sidewall.

  15. Studies of atomic properties of francium and rubidium

    NASA Astrophysics Data System (ADS)

    Perez Galvan, Adrian

    High precision measurements of atomic properties are excellent probes for electroweak interaction studies at the lowest possible energy range. The extraction of standard model coupling constants relies on a unique combination of experimental measurements and theoretical atomic structure calculations. It is only through stringent comparison between experimental and theoretical values of atomic properties that a successful experiment can take place. Francium, with its heavy nucleus and alkali structure that makes it amenable to laser cooling and trapping, stands as an ideal test bed for such studies. Our group has successfully created, trapped and cooled several isotopes of francium, the heaviest of the alkalies, and demonstrated that precision studies of atomic properties, such as the measurement of the 8S 1/2 excited state lifetime of 210Fr presented here, are feasible. Further work in our program of electroweak studies requires a better control of the electromagnetic environment observed by the sample of cold atoms as well as a lower background pressure (10-10 torr or better). We have designed and adapted to our previous setup a new "science" vacuum chamber that fulfills these requirements and the transport system that will transfer the francium atoms to the new chamber. We use this new experimental setup as well as a rubidium glass cell to perform precision studies of atomic and nuclear properties of rubidium. Spectroscopic studies of the most abundant isotopes of rubidium, 85Rb and 87Rb, are a vital component in our program. Performing measurements in rubidium allows us to do extensive and rigorous searches of systematics that can be later extrapolated to francium. We present a precision lifetime measurement of the 5D 3/2 state of 87Rb and a measurement of hyperfine splittings of the 6S1/2 level of 87Rb and 85Rb. The quality of the data of the latter allows us to observe a hyperfine anomaly attributed to an isotopic difference of the magnetization distribution

  16. X-ray phase computed tomography for nanoparticulated imaging probes and therapeutics: preliminary feasibility study

    NASA Astrophysics Data System (ADS)

    Tang, Xiangyang; Yang, Yi; Tang, Shaojie

    2011-03-01

    With the scientific progress in cancer biology, pharmacology and biomedical engineering, the nano-biotechnology based imaging probes and therapeutical agents (namely probes/agents) - a form of theranostics - are among the strategic solutions bearing the hope for the cure of cancer. The key feature distinguishing the nanoparticulated probes/agents from their conventional counterparts is their targeting capability. A large surface-to-volume ratio in nanoparticulated probes/agents enables the accommodation of multiple targeting, imaging and therapeutic components to cope with the intra- and inter-tumor heterogeneity. Most nanoparticulated probes/agents are synthesized with low atomic number materials and thus their x-ray attenuation are very similar to biological tissues. However, their microscopic structures are very different, which may result in significant differences in their refractive properties. Recently, the investigation in the x-ray grating-based differential phase contrast (DPC) CT has demonstrated its advantages in differentiating low-atomic materials over the conventional attenuation-based CT. We believe that a synergy of x-ray grating-based DPC CT and nanoparticulated imaging probes and therapeutic agents may play a significant role in extensive preclinical and clinical applications, or even become a modality for molecular imaging. Hence, we propose to image the refractive property of nanoparticulated imaging probes and therapeutical agents using x-ray grating-based DPC CT. In this work, we conduct a preliminary feasibility study with a focus to characterize the contrast-to-noise ratio (CNR) and contrast-detail behavior of the x-ray grating-based DPC CT. The obtained data may be instructive to the architecture design and performance optimization of the x-ray grating-based DPC CT for imaging biomarker-targeted imaging probes and therapeutic agents, and even informative to the translation of preclinical research in theranostics into clinical applications.

  17. Atomic structure and surface defects at mineral-water interfaces probed by in situ atomic force microscopy.

    PubMed

    Siretanu, Igor; van den Ende, Dirk; Mugele, Frieder

    2016-04-21

    Atomic scale details of surface structure play a crucial role for solid-liquid interfaces. While macroscopic characterization techniques provide averaged information about bulk and interfaces, high resolution real space imaging reveals unique insights into the role of defects that are believed to dominate many aspects of surface chemistry and physics. Here, we use high resolution dynamic Atomic Force Microscopy (AFM) to visualize and characterize in ambient water the morphology and atomic scale structure of a variety of nanoparticles of common clay minerals adsorbed to flat solid surfaces. Atomically resolved images of the (001) basal planes are obtained on all materials investigated, namely gibbsite, kaolinite, illite, and Na-montmorillonite of both natural and synthetic origin. Next to regions of perfect crystallinity, we routinely observe extended regions of various types of defects on the surfaces, including vacancies of one or few atoms, vacancy islands, atomic steps, apparently disordered regions, as well as strongly adsorbed seemingly organic and inorganic species. While their exact nature is frequently difficult to identify, our observations clearly highlight the ubiquity of such defects and their relevance for the overall physical and chemical properties of clay nanoparticle-water interfaces. PMID:27030282

  18. Characterization of phosphorus segregation in neutron-irradiated pressure vessel steels by atom probe field ion microscopy

    SciTech Connect

    Miller, M.K.; Jayaram, R.; Russell, K.F.

    1995-04-01

    An atom probe field ion microscopy characterization of A533B and Russian VVER 440 and 1000 pressure vessel steels has been performed to determine the phosphorus coverage of grain and lath boundaries. Field ion micrographs of grain and lath boundaries have revealed that they are decorated with a semi-continuous film of discrete brightly-imaging precipitates that were identified as molybdenum carbonitride precipitates. In addition, extremely high phosphorus levels were measured at the boundaries. The phosphorus segregation was found to be confined to an extremely narrow region indicative of monolayer-type segregation. The phosphorus coverages determined from the atom probe results of the unirradiated materials were in excellent agreement with predictions based on McLean`s equilibrium model of grain boundary segregation. The boundary phosphorus coverage of a neutron-irradiated weld material was significantly higher than that observed in the unirradiated material.

  19. Reaction studies of hot silicon, germanium and carbon atoms

    SciTech Connect

    Gaspar, P.P.

    1986-11-15

    Research has been continued on hot silicon, germanium and carbon atoms. Progress in the period November 16, 1985 to November 15, 1986 is reviewed in the following areas: (1) Recoil atom reaction studies. (2) Reactions of thermally generated free atoms.

  20. Cryogen free scanning probe microscope: the solution for atomic scale surface science below 10 Kelvin without liquid helium

    NASA Astrophysics Data System (ADS)

    Choi, Byoung; Venegas, Miguel; RHK Team

    We present a cryogen free low temperature scanning probe microscope (LT-SPM) working at 9K on both tip and sample. The performance of the microscope was validated in various conditions such as noisy environment and modulated temperature as well as the long time elapsed measurements. Building on the stability and consistency of the closed cycle refrigerator, time extended measurements are available with this state-of-the-art LT-SPM. Studies can now be performed without interrupting the critical moment of the tip on the surface while refilling the conventional liquid cryogen tank. We will present the time evolution of the dopant induced topographic and spectroscopic properties of some topological insulators such as Bi2Se3 and Bi2Te3. The compact and rigid design of the microscope also allows this instrument to work as a practical variable temperature microscope without the hassle of liquid cryogen consumption. We will present temperature dependent STM/STS results on a TiSe2 surface at the temperature between 10K and 350K. Finally, we will discuss how the cryogen free LT-SPM will make the study of the atomic scale phenomenon at low temperature both economical and easy, opening promising new capabilities to surface scientists and researchers in nanotechnology.

  1. Three-Dimensional (3-D) Atom Probe Tomography of a Cu-Precipitation-Strengthened, Ultrahigh-Strength Carburized Steel

    NASA Astrophysics Data System (ADS)

    Tiemens, Benjamin L.; Sachdev, Anil K.; Mishra, Raja K.; Olson, Gregory B.

    2012-10-01

    In an effort to reduce material cost, experimental steel alloys were developed that incorporated Cu precipitation in lieu of costly Co alloying additions in secondary hardening carburizing gear steels. This work utilizes three-dimensional atom probe tomography to study one of these prototype alloys and quantify the nanoscale dispersions of body-centered cubic (bcc) Cu and M2C alloy carbides used to strengthen these steels. The temporal evolution of precipitate, size, morphology, and interprecipitate interactions were studied for various tempering times. Findings suggest that Cu precipitation does act as a catalyst for heterogeneous nucleation of M2C carbides at relatively high hardness levels; however, the resultant volume fraction of strengthening carbides was noticeably less than that predicted by thermodynamic equilibrium calculations, indicating a reduced potency compared with Co-assisted precipitation. Microstructural information such as precipitate size and volume fraction was measured at the peak hardness condition and successfully used to recalibrate alloy design models for subsequent alloy design iterations.

  2. Toward single atom qubits on a surface: Pump-probe spectroscopy and electrically-driven spin resonance

    NASA Astrophysics Data System (ADS)

    Paul, William

    We will discuss the characterization of spin dynamics by pump-probe spectroscopy and the use of gigahertz-frequency electric fields to drive spin resonance of a Fe atom on a MgO/Ag(001) surface. In the spirit of this session, the technical challenges in applying a precise voltage to the tip sample junction across a wide radio-frequency bandwidth will be described. The energy relaxation time, T1, of single spins on surfaces can be measured by spin-polarized pump-probe STM (scanning tunneling microscopy). To date, the relaxation times reported for Fe-Cu dimers on Cu2N insulating films have been of the order ~100 ns. A three-order-of-magnitude enhancement of lifetime, to ~200 μs, was recently demonstrated for Co on a single-monolayer of MgO. Here, we report on the tailoring of the T1 lifetime of single Fe atoms on single- and multi- layer MgO films grown on Ag(001). Next, we demonstrate electron spin resonance of an individual single Fe atom, driven by a gigahertz-frequency electric field applied across the tip-sample junction, and detected by a spin-polarized tunneling current. The principle parameters of the spin resonance experiment, namely the phase coherence time T2 and the Rabi rate, are characterized for Fe atoms adsorbed to the monolayer MgO film.

  3. Atomic resolution studies of carbonic anhydrase II

    SciTech Connect

    Behnke, Craig A.; Le Trong, Isolde; Godden, Jeff W.; Merritt, Ethan A.; Teller, David C.; Bajorath, Jürgen; Stenkamp, Ronald E.

    2010-05-01

    The structure of human carbonic anhydrase II has been solved with a sulfonamide inhibitor at 0.9 Å resolution. Structural variation and flexibility is seen on the surface of the protein and is consistent with the anisotropic ADPs obtained from refinement. Comparison with 13 other atomic resolution carbonic anhydrase structures shows that surface variation exists even in these highly ordered isomorphous crystals. Carbonic anhydrase has been well studied structurally and functionally owing to its importance in respiration. A large number of X-ray crystallographic structures of carbonic anhydrase and its inhibitor complexes have been determined, some at atomic resolution. Structure determination of a sulfonamide-containing inhibitor complex has been carried out and the structure was refined at 0.9 Å resolution with anisotropic atomic displacement parameters to an R value of 0.141. The structure is similar to those of other carbonic anhydrase complexes, with the inhibitor providing a fourth nonprotein ligand to the active-site zinc. Comparison of this structure with 13 other atomic resolution (higher than 1.25 Å) isomorphous carbonic anhydrase structures provides a view of the structural similarity and variability in a series of crystal structures. At the center of the protein the structures superpose very well. The metal complexes superpose (with only two exceptions) with standard deviations of 0.01 Å in some zinc–protein and zinc–ligand bond lengths. In contrast, regions of structural variability are found on the protein surface, possibly owing to flexibility and disorder in the individual structures, differences in the chemical and crystalline environments or the different approaches used by different investigators to model weak or complicated electron-density maps. These findings suggest that care must be taken in interpreting structural details on protein surfaces on the basis of individual X-ray structures, even if atomic resolution data are available.

  4. Noncontact atomic force and Kelvin probe force microscopy on MgO(100) and MgO(100)-supported Ba

    NASA Astrophysics Data System (ADS)

    Pang, Chi Lun; Sasahara, Akira; Onishi, Hiroshi

    2016-08-01

    Atomically-flat MgO(100) surfaces were prepared by sputtering and annealing. Noncontact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM) were used to characterize the MgO(100) surfaces. The NC-AFM images revealed the presence of point defects on an atomically-resolved surface. The surface potential at these point defects, as well as features such as step edges and deposited Ba nanoparticles were mapped using KPFM. The Kelvin images show that the surface potential increases at the point defects and at the step edges. On the other hand, a decrease in the potential was found over Ba nanoparticles which can be explained by electron charge transfer from the Ba to the MgO.

  5. Impact of dynamic specimen shape evolution on the atom probe tomography results of doped epitaxial oxide multilayers: Comparison of experiment and simulation

    SciTech Connect

    Madaan, Nitesh; Nandasiri, Manjula; Devaraj, Arun; Bao, Jie; Xu, Zhijie; Thevuthasan, Suntharampillai

    2015-08-31

    The experimental atom probe tomography (APT) results from two different specimen orientations (top-down and sideways) of a high oxygen ion conducting Samaria-doped-ceria/Scandia-stabilized-zirconia multilayer thin film solid oxide fuel cell electrolyte was compared with level-set method based field evaporation simulations for the same specimen orientations. This experiment-simulation comparison explains the dynamic specimen shape evolution and ion trajectory aberrations that can induce density artifacts in final reconstruction, leading to inaccurate estimation of interfacial intermixing. This study highlights the importance of comparing experimental results with field evaporation simulations when using APT to study oxide heterostructure interfaces.

  6. Atom probe tomography evidence for uniform incorporation of Bi across the growth front in GaAs1-xBix/GaAs superlattice

    NASA Astrophysics Data System (ADS)

    Chen, Weixin; Ronsheim, Paul A.; Wood, Adam W.; Forghani, Kamran; Guan, Yingxin; Kuech, Thomas F.; Babcock, Susan E.

    2016-07-01

    The three-dimensional distribution of Bi atoms in a GaAs1-xBix/GaAs superlattice grown by metalorganic vapor phase epitaxy (MOVPE) was studied using atom probe tomography (APT). The Bi distribution in the growth direction deduced from APT agreed quantitatively with the complex Bi concentration profile that was discovered using high-angle annular dark-field scanning transmission electron microscopy in a previous study. More importantly, APT revealed the Bi atom distribution in the growth planes at near atomic resolution. Bi nearest neighbor distribution and concentration frequency distribution analysis of the APT data indicated a statistically random distribution of Bi atoms in 1-2 nm thick layers oriented perpendicular to the growth direction. These results provide evidence that Bi is incorporated homogeneously across the growth front even when the concentration profile in the growth direction is complex. They also suggest that MOVPE growth conditions can promote uniform Bi distribution within GaAs1-xBix layers, opening a path for application of these materials in the optoelectronic devices for which they show much promise.

  7. Stability Of Nanoclusters In 14YWT Oxide Dispersion Strengthened Steel Under Heavy Ion-irradiation By Atom Probe Tomography

    SciTech Connect

    He, Jianchao; Wan, F.; Sridharan, Kumar; Allen, Todd R.; Certain, Alicia G.; Shutthanandan, V.; Wu, Yaqiao

    2014-12-01

    14YWT oxide dispersion strengthened (ODS) ferritic steel was irradiated with of 5 MeV Ni2+ ions, at 300 °C, 450 °C, and 600 °C to a damage level of 100 dpa. The stability of Ti–Y–O nanoclusters was investigated by applying atom probe tomography (APT) in voltage mode, of the samples before and after irradiations. The average size and number density of the nanoclusters was determined using the maximum separation method. These techniques allowed for the imaging of nanoclusters to sizes well below the resolution limit of conventional transmission electron microscopy techniques. The most significant changes were observed for samples irradiated at 300 °C where the size (average Guinier radius) and number density of nanoclusters were observed to decrease from 1.1 nm to 0.8 nm and 12 × 1023 to 3.6 × 1023, respectively. In this study, the nanoclusters are more stable at higher temperature.

  8. Electrical conductivity studies on individual conjugated polymer nanowires: two-probe and four-probe results.

    PubMed

    Long, Yunze; Duvail, Jeanluc; Li, Mengmeng; Gu, Changzhi; Liu, Zongwen; Ringer, Simon P

    2009-01-01

    Two- and four-probe electrical measurements on individual conjugated polymer nanowires with different diameters ranging from 20 to 190 nm have been performed to study their conductivity and nanocontact resistance. The two-probe results reveal that all the measured polymer nanowires with different diameters are semiconducting. However, the four-probe results show that the measured polymer nanowires with diameters of 190, 95-100, 35-40 and 20-25 nm are lying in the insulating, critical, metallic and insulting regimes of metal-insulator transition, respectively. The 35-40 nm nanowire displays a metal-insulator transition at around 35 K. In addition, it was found that the nanocontact resistance is in the magnitude of 104Ω at room temperature, which is comparable to the intrinsic resistance of the nanowires. These results demonstrate that four-probe electrical measurement is necessary to explore the intrinsic electronic transport properties of isolated nanowires, especially in the case of metallic nanowires, because the metallic nature of the measured nanowires may be coved by the nanocontact resistance that cannot be excluded by a two-probe technique. PMID:20652139

  9. Probing deviations from traditional colloid filtration theory by atomic forces microscopy.

    SciTech Connect

    Reno, Marissa Devan

    2005-12-01

    Colloid transport through saturated media is an integral component of predicting the fate and transport of groundwater contaminants. Developing sound predictive capabilities and establishing effective methodologies for remediation relies heavily on our ability to understand the pertinent physical and chemical mechanisms. Traditionally, colloid transport through saturated media has been described by classical colloid filtration theory (CFT), which predicts an exponential decrease in colloid concentration with travel distance. Furthermore, colloid stability as determined by Derjaguin-Landau-Veney-Overbeek (DLVO) theory predicts permanent attachment of unstable particles in a primary energy minimum. However, recent studies show significant deviations from these traditional theories. Deposition in the secondary energy minimum has been suggested as a mechanism by which observed deviations can occur. This work investigates the existence of the secondary energy minimum as predicted by DLVO theory using direct force measurements obtained by Atomic Forces Microscopy. Interaction energy as a function of separation distance between a colloid and a quartz surface in electrolyte solutions of varying ionic strength are obtained. Preliminary force measurements show promise and necessary modifications to the current experimental methodology have been identified. Stringent surface cleaning procedures and the use of high-purity water for all injectant solutions is necessary for the most accurate and precise measurements. Comparisons between direct physical measurements by Atomic Forces Microscopy with theoretical calculations and existing experimental findings will allow the evaluation of the existence or absence of a secondary energy minimum.

  10. Development of laser optogalvanic spectroscopy as a probe of alkali atoms in an MHD environment

    SciTech Connect

    Monts, D.L.; Qian, S.; Cook, R.L.; Shepard, W.S.

    1995-02-01

    Application of Laser Optogalvanic Spectroscopy (LOGS) to MHD combustion systems requires selection of an appropriate alkali atom electronic transition to monitor. These studies suggest that in MHD combustion systems, it is desirable to use cesium, which occurs as an impurity in potassium compounds, as a surrogate for potassium rather than to directly monitor potassium in order to obtain reliable determinations of seed concentration. Studies were also performed to investigate the effect of electrode corrosion on the normalized LOGS signal intensity at a fixed wavelength (578.238 nm). During six-hour experiments in a near-stoichiometric flame, the normalized LOGS signal intensity decreased by 40-50% for a -960 V rod electrode and by 10-20% for a -500 V rod electrode. These changes are attributed to buildup of an oxide coating on the electrode, reducing the collection efficiency of the electrode.

  11. Study of wear of diamond-coated probe tips when scanning on different materials

    NASA Astrophysics Data System (ADS)

    Küng, A.; Nicolet, A.; Meli, F.

    2015-08-01

    The accuracy of today’s coordinate measuring machines (CMM) has reached a level at which the exact knowledge of each component is required. The role of the probe tip is particularly crucial because it is in contact with the sample surface. Understanding how the probe tip wears off will help to narrow the measurement errors. Today, diamond-coated probes of excellent quality are becoming commercially available. In the present work, the wear of those probes was studied when scanning on different sample materials and under different measuring conditions. The wear rate was quantified in terms of the rate of the removed diamond volume per meter scan length. It cannot be simply derived from material properties or scanning conditions. A simple calculation also shows that only a very small fraction of the friction energy is devoted to the removal of atoms from the diamond crystal. The wear rate of diamond-coated probes was found to be orders of magnitude smaller compared with the wear of traditional sapphire probes.

  12. Atom-interferometric studies of light scattering

    SciTech Connect

    Beattie, S.; Barrett, B.; Chan, I.; Mok, C.; Kumarakrishnan, A.; Yavin, I.

    2009-07-15

    larger than the recoil velocity. These measurements are consistent with Monte Carlo wave-function simulations. If the additional pulse is a traveling wave, we find that the grating contrast measured as a function of {delta}T can be modeled by a quasiperiodic coherence function as in previous experiments that utilized atomic beams. In this work, we investigate the dependence of the photon scattering rate on the intensity and detuning of the traveling wave. We also study the effects of perturbing the interferometer with continuous-wave light and find that the dependence of the photon scattering rate on the intensity and detuning of the perturbing field is consistent with expectations.

  13. Study of entry and landing probes for exploration of Titan

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Saturn's largest moon, Titan, is a totally unique planetary body which is certain to yield exciting new phenomena. Current information is lacking in detail to distinguish between a thin methane rich atmosphere and a thick nitrogen rich atmosphere. Therefore, both the thin and thick atmospheric models were used for the study of various Titan probe classes described in this report. The technical requirements, conceptual design, science return, schedule, cost and mission implications of three probe classes that could be used for exploration of Titan are defined. The three probe classes were based on a wide range of exploration mission possibilities.

  14. Local Probes of Strain Texture and Individual Atomic Dopant Sites in Monolayer MoS2

    NASA Astrophysics Data System (ADS)

    Fragapane, Alex H.; Contryman, Alex W.; Li, Hong; Qian, Xiaofeng; Ardakani, Sina Moeini; Gong, Yongji; Wang, Xingli; Weisse, Jeffrey M.; Lee, Chi Hwan; Zhao, Jiheng; Ajayan, Pulickel M.; Li, Ju; Zheng, Xiaolin; Manoharan, Hari C.

    The 2D semiconductor MoS2 is an optically active material uniquely responsive to local perturbations. As an atomically thin membrane with exceptional strength, it can embed wide band gap variations overlapping the visible light spectrum when subjected to biaxial strain, where the modified electronic potential emanating from point-induced tensile strain perturbations mimics the Coulomb potential in a mesoscopic atom. We have realized this ``artificial atom'' concept via monolayer nanoindentation, and demonstrate that a synthetic superlattice of these building blocks forms an optoelectronic crystal capable of broadband light absorption and efficient funneling of photogenerated excitons to points of maximum strain at the artificial-atom nuclei. We also investigate the effects of individual atomic dopant sites through STM/STS, and visualize the atomic-scale local band structure changes. The modification of 2D semiconductors through methods such as strain texturing and doping connects to applications in next generation optoelectronics and photovoltaics.

  15. Understanding Atom Probe Tomography of Oxide-Supported Metal Nanoparticles by Correlation with Atomic Resolution Electron Microscopy and Field Evaporation Simulation

    SciTech Connect

    Devaraj, Arun; Colby, Robert J.; Vurpillot, F.; Thevuthasan, Suntharampillai

    2014-03-26

    Metal-dielectric composite materials, specifically metal nanoparticles supported on or embedded in metal oxides, are widely used in catalysis. The accurate optimization of such nanostructures warrants the need for detailed three-dimensional characterization. Atom probe tomography is uniquely capable of generating sub-nanometer structural and compositional data with part-per-million mass sensitivity, but there are reconstruction artifacts for composites containing materials with strongly differing fields of evaporation, as for oxide-supported metal nanoparticles. By correlating atom probe tomography with scanning transmission electron microscopy for Au nanoparticles embedded in an MgO support, deviations from an ideal topography during evaporation are demonstrated directly, and correlated with compositional errors in the reconstructed data. Finite element simulations of the field evaporation process confirm that protruding Au nanoparticles will evolve on the tip surface, and that evaporation field variations lead to an inaccurate assessment of the local composition, effectively lowering the spatial resolution of the final reconstructed dataset. Cross-correlating the experimental data with simulations results in a more detailed understanding of local evaporation aberrations during APT analysis of metal-oxide composites, paving the way towards a more accurate three-dimensional characterization of this technologically important class of materials.

  16. Concept and Demonstration of Individual Probe Actuation in Two-Dimensional Parallel Atomic Force Microscope System

    NASA Astrophysics Data System (ADS)

    Akiyama, Terunobu; Aeschimann, Laure; Chantada, Laura; de Rooij, Nico. F.; Heinzelmann, Harry; Herzig, Hans P.; Manzardo, Omar; Meister, André; Polesel-Maris, Jérôme; Pugin, Raphaël; Staufer, Urs; Vettiger, Peter

    2007-09-01

    A concept of an array actuator that is used to control the tip-sample separation of cantilevers in a two-dimensional (2D) probe array scanning system is proposed in this article. The feasibility of the concept is demonstrated with a 10× 10 array actuator with 500 μm xy-pitches. The array actuator is made by slicing a bulk piezoceramic block. The obtained maximum actuation of a single probe was 2.19 μmp-p at ± 168 Vp-p. A major issue for the actuator was the insufficient strength of the frame of the probe array chip. The demonstrated array actuator is highly compatible with previously developed parallel readout modules that use either a parallel optical beam or integrated piezoresistive deflection sensing. A large-scale 2D probe array is our ultimate target.

  17. MESUR probe aerobrake preliminary design study

    NASA Technical Reports Server (NTRS)

    Tauber, M.; Henline, W.; Chargin, M.; Papadopoulos, P.; Chen, Y.; Yang, L.; Hamm, K.

    1992-01-01

    Aerobrake design for the Mars Environmental Survey (MESUR) vehicles is considered which is intended for both a nominal entry velocity of 7 km/sec and a high-speed case of 9 km/sec. Topics discussed include the entry environment, the thermal protection requirements for several types of heat shield materials, the structural design of the aeroshell, and the total aerobrake masses and mass fractions. For the nominal 7 km/sec entry, a silicone elastometric charring ablator, SLA-561, was found to be the lightest heat shield material. For the 7 km/sec entry, the mass fraction of the aerobrake was 13.2 percent. For the 9 km/sec entry, the heat shield consisted of the medium-density ablator AVCOAT-5026; SLA-561 was used on part of the conical skirt. The aerobrake mass fraction in this case was 18 percent. It is recommended that separate aerobrakes be designed for probes entering at 7 and 9 km/sec.

  18. MESUR probe aerobrake preliminary design study

    NASA Astrophysics Data System (ADS)

    Tauber, M.; Henline, W.; Chargin, M.; Papadopoulos, P.; Chen, Y.; Yang, L.; Hamm, K.

    1992-07-01

    Aerobrake design for the Mars Environmental Survey (MESUR) vehicles is considered which is intended for both a nominal entry velocity of 7 km/sec and a high-speed case of 9 km/sec. Topics discussed include the entry environment, the thermal protection requirements for several types of heat shield materials, the structural design of the aeroshell, and the total aerobrake masses and mass fractions. For the nominal 7 km/sec entry, a silicone elastometric charring ablator, SLA-561, was found to be the lightest heat shield material. For the 7 km/sec entry, the mass fraction of the aerobrake was 13.2 percent. For the 9 km/sec entry, the heat shield consisted of the medium-density ablator AVCOAT-5026; SLA-561 was used on part of the conical skirt. The aerobrake mass fraction in this case was 18 percent. It is recommended that separate aerobrakes be designed for probes entering at 7 and 9 km/sec.

  19. Cross-Sectional Investigations on Epitaxial Silicon Solar Cells by Kelvin and Conducting Probe Atomic Force Microscopy: Effect of Illumination.

    PubMed

    Narchi, Paul; Alvarez, Jose; Chrétien, Pascal; Picardi, Gennaro; Cariou, Romain; Foldyna, Martin; Prod'homme, Patricia; Kleider, Jean-Paul; I Cabarrocas, Pere Roca

    2016-12-01

    Both surface photovoltage and photocurrent enable to assess the effect of visible light illumination on the electrical behavior of a solar cell. We report on photovoltage and photocurrent measurements with nanometer scale resolution performed on the cross section of an epitaxial crystalline silicon solar cell, using respectively Kelvin probe force microscopy and conducting probe atomic force microscopy. Even though two different setups are used, the scans were performed on locations within 100-μm distance in order to compare data from the same area and provide a consistent interpretation. In both measurements, modifications under illumination are observed in accordance with the theory of PIN junctions. Moreover, an unintentional doping during the deposition of the epitaxial silicon intrinsic layer in the solar cell is suggested from the comparison between photovoltage and photocurrent measurements. PMID:26831693

  20. Cross-Sectional Investigations on Epitaxial Silicon Solar Cells by Kelvin and Conducting Probe Atomic Force Microscopy: Effect of Illumination

    NASA Astrophysics Data System (ADS)

    Narchi, Paul; Alvarez, Jose; Chrétien, Pascal; Picardi, Gennaro; Cariou, Romain; Foldyna, Martin; Prod'homme, Patricia; Kleider, Jean-Paul; i Cabarrocas, Pere Roca

    2016-02-01

    Both surface photovoltage and photocurrent enable to assess the effect of visible light illumination on the electrical behavior of a solar cell. We report on photovoltage and photocurrent measurements with nanometer scale resolution performed on the cross section of an epitaxial crystalline silicon solar cell, using respectively Kelvin probe force microscopy and conducting probe atomic force microscopy. Even though two different setups are used, the scans were performed on locations within 100-μm distance in order to compare data from the same area and provide a consistent interpretation. In both measurements, modifications under illumination are observed in accordance with the theory of PIN junctions. Moreover, an unintentional doping during the deposition of the epitaxial silicon intrinsic layer in the solar cell is suggested from the comparison between photovoltage and photocurrent measurements.

  1. Nanopatterning on silicon surface using atomic force microscopy with diamond-like carbon (DLC)-coated Si probe

    PubMed Central

    2011-01-01

    Atomic force microscope (AFM) equipped with diamond-like carbon (DLC)-coated Si probe has been used for scratch nanolithography on Si surfaces. The effect of scratch direction, applied tip force, scratch speed, and number of scratches on the size of the scratched geometry has been investigated. The size of the groove differs with scratch direction, which increases with the applied tip force and number of scratches but decreases slightly with scratch speed. Complex nanostructures of arrays of parallel lines and square arrays are further fabricated uniformly and precisely on Si substrates at relatively high scratch speed. DLC-coated Si probe has the potential to be an alternative in AFM-based scratch nanofabrication on hard surfaces. PMID:21888633

  2. The `Carina Flare' supershell: probing the atomic and molecular ISM in a Galactic chimney

    NASA Astrophysics Data System (ADS)

    Dawson, J. R.; Mizuno, N.; Onishi, T.; McClure-Griffiths, N. M.; Fukui, Y.

    2008-06-01

    The `Carina Flare' supershell, GSH 287+04-17, is a molecular supershell originally discovered in 12CO(J = 1-0) with the NANTEN 4m telescope. We present the first study of the shell's atomic ISM, using HI 21-cm line data from the Parkes 64-m telescope Southern Galactic Plane Survey. The data reveal a gently expanding, ~230 × 360 pc HI supershell that shows strong evidence of Galactic Plane blowout, with a break in its main body at z ~ 280 pc and a capped high-latitude extension reaching z ~ 450 pc. The molecular clouds form comoving parts of the atomic shell, and the morphology of the two phases reflects the supershell's influence on the structure of the ISM. We also report the first discovery of an ionized component of the supershell, in the form of delicate, streamer-like filaments aligned with the proposed direction of blowout. The distance estimate to the shell is re-examined, and we find strong evidence to support the original suggestion that it is located in the Carina Arm at a distance of 2.6 +/- 0.4 kpc. Associated HI and H2 masses are estimated as MHI ~ 7 +/- 3 × 105Msolar and , and the kinetic energy of the expanding shell as EK ~ 1 × 1051 erg. We examine the results of analytical and numerical models to estimate a required formation energy of several 1051 to ~1052 erg, and an age of ~107 yr. This age is compatible with molecular cloud formation time-scales, and we briefly consider the viability of a supershell-triggered origin for the molecular component.

  3. Nanoscale isotope mapping of terrestrial and lunar zircons by atom probe tomography

    NASA Astrophysics Data System (ADS)

    Blum, T.; Reinhard, D. A.; Spicuzza, M. J.; Olson, D.; Coble, M. A.; Cavosie, A. J.; Ushikubo, T.; Larson, D. J.; Kelly, T. F.; Valley, J. W.

    2014-12-01

    Microscopic mobility of atoms in minerals controls macroscopic metamorphic and tectonic processes in Earth's crust. Deformation and diffusion, each an expression of this mobility, are both processes of breaking and reforming bonds and take energy to proceed. Deformation can facilitate diffusion by supplying strain energy that facilitates breaking bonds and enhance diffusion rates by mobilizing dislocations, which localize atomic migration. Deformation-enhanced diffusion may therefore lower closure temperatures for geochronometers and thermobarometers. If the effect of deformation on diffusion is measurable, we must reevaluate these tools for deformed rocks. We explore this effect and its potential as the basis for estimating duration and rate of strain in the rock record. We focus on feldspar, a rheologically and modally dominant mineral in Earth's crust for which deformation and diffusion parameters are well known. Different elements have different diffusion rates within each mineral, which are differentially accelerated by a deformation-induced reduction of their activation energies for diffusion. We present the first comprehensive study of strain enhancement of diffusion in plagioclase, a combination of km-scale, thin-section-scale, and grain-scale strain and chemical measurements for major and trace elements in naturally deformed plagioclase phenocrysts from the San José Pluton, Peninsular Ranges Batholith, México. Our samples had low initial compositional contrasts and experienced low strain. Under these conditions, the effect of strain-enhanced element mobility, as predicted from our model, is below analytical detection limits. For these rocks, a static diffusion model is sufficient, and thermobarometers and geochronometers can still be applied to yield accurate results.

  4. Investigation of the interaction of atoms with lattice defects using probe methods

    NASA Astrophysics Data System (ADS)

    Bruessler, M.; Groeger, V.; Ecker, K.; Petry, W.; Sakamoto, J.; Sassa, K.; Stehr, R.; Vogl, G.

    1984-03-01

    The physics of atomic vacancies were investigated using Mossbauer spectroscopy, perturbed gamma-gamma angular correlation and the backscattering of protons (channeling). Trapped interstitial atoms in the diluted alloy AgFe displace the Fe-atom in an interstitial cage which contributes essentially to radiation induced diffusion. The combination of alloy formation by ion implantation, defect production by particle radiation, and channeling measurements shows that interstitial atoms in Mo are trapped by Co strange atoms and form 110 dump-bells. The investigation of point defects shows that after cold working of Al and Ag no freely moving interstitial atoms are found. The anomalously fast diffusion of impurity atoms was investigated in the polycrystalline ZrFe by quasielastic Mossbauer spectroscopy, and in ZrCo by quasielastic incoherent neutron scattering. It is found that all Fe and Co atoms respectively, take part in the diffusion process. The evolution of the diffusion is divided in at least two jump mechanisms with strongly different jump probabilities.

  5. Parameter sensitivity analysis of nonlinear piezoelectric probe in tapping mode atomic force microscopy for measurement improvement

    SciTech Connect

    McCarty, Rachael; Nima Mahmoodi, S.

    2014-02-21

    The equations of motion for a piezoelectric microcantilever are derived for a nonlinear contact force. The analytical expressions for natural frequencies and mode shapes are obtained. Then, the method of multiple scales is used to analyze the analytical frequency response of the piezoelectric probe. The effects of nonlinear excitation force on the microcantilever beam's frequency and amplitude are analytically studied. The results show a frequency shift in the response resulting from the force nonlinearities. This frequency shift during contact mode is an important consideration in the modeling of AFM mechanics for generation of more accurate imaging. Also, a sensitivity analysis of the system parameters on the nonlinearity effect is performed. The results of a sensitivity analysis show that it is possible to choose parameters such that the frequency shift minimizes. Certain parameters such as tip radius, microcantilever beam dimensions, and modulus of elasticity have more influence on the nonlinearity of the system than other parameters. By changing only three parameters—tip radius, thickness, and modulus of elasticity of the microbeam—a more than 70% reduction in nonlinearity effect was achieved.

  6. Role of Photoexcitation and Field Ionization in the Measurement of Accurate Oxide Stoichiometry by Laser-Assisted Atom Probe Tomography

    SciTech Connect

    Devaraj, Arun; Colby, Robert J.; Hess, Wayne P.; Perea, Daniel E.; Thevuthasan, Suntharampillai

    2013-03-06

    Pulsed lasers extend the high spatial and mass resolution of atom probe tomography (APT) to non-conducting materials, such as oxides. For prototypical metal oxide MgO, measured stoichiometry depends strongly upon pulse energy and applied voltage. Very low laser energies (0.02 pJ) and high electric fields yield optimal stoichiometric accuracy, attributed to the field-dependent ionization of photo-desorbed O or O2 neutrals. This emphasizes the importance of considering electronic excitations in APT analysis of oxides ionic materials.

  7. Development of multi-environment dual-probe atomic force microscopy system using optical beam deflection sensors with vertically incident laser beams.

    PubMed

    Tsunemi, Eika; Kobayashi, Kei; Oyabu, Noriaki; Hirose, Masaharu; Takenaka, Yoshiko; Matsushige, Kazumi; Yamada, Hirofumi

    2013-08-01

    We developed a dual-probe atomic force microscopy (DP-AFM) system with two cantilever probes that can be operated in various environments such as in air, vacuum, and liquid. The system employs the optical beam deflection method for measuring the deflection of each cantilever mounted on a probe scanner. The cantilever probes mounted on the probe scanners are attached to inertia sliders, which allow independent control of the probe positions. We constructed three types of probe scanners (tube, shear-piezo, and tripod types) and characterized their performance. We demonstrated AFM imaging in ambient air, vacuum, and ultrapure water, and also performed electrical measurement and pick-up manipulation of a Au nanorod using the DP-AFM system. PMID:24007067

  8. Development of multi-environment dual-probe atomic force microscopy system using optical beam deflection sensors with vertically incident laser beams

    NASA Astrophysics Data System (ADS)

    Tsunemi, Eika; Kobayashi, Kei; Oyabu, Noriaki; Hirose, Masaharu; Takenaka, Yoshiko; Matsushige, Kazumi; Yamada, Hirofumi

    2013-08-01

    We developed a dual-probe atomic force microscopy (DP-AFM) system with two cantilever probes that can be operated in various environments such as in air, vacuum, and liquid. The system employs the optical beam deflection method for measuring the deflection of each cantilever mounted on a probe scanner. The cantilever probes mounted on the probe scanners are attached to inertia sliders, which allow independent control of the probe positions. We constructed three types of probe scanners (tube, shear-piezo, and tripod types) and characterized their performance. We demonstrated AFM imaging in ambient air, vacuum, and ultrapure water, and also performed electrical measurement and pick-up manipulation of a Au nanorod using the DP-AFM system.

  9. Absorption spectra of two-level atoms interacting with a strong polychromatic pump field and an arbitrarily intense probe field

    NASA Astrophysics Data System (ADS)

    Yoon, Tai Hyun; Chung, Myung Sai; Lee, Hai-Woong

    1999-09-01

    A numerical method is introduced that solves the optical Bloch equations describing a two-level atom interacting with a strong polychromatic pump field with an equidistant spectrum and an arbitrarily intense monochromatic probe field. The method involves a transformation of the optical Bloch equations into a system of equations with time-independent coefficients at steady state via double harmonic expansion of the density-matrix elements, which is then solved by the method of matrix inversion. The solutions so obtained lead immediately to the determination of the polarization of the atomic medium and of the absorption and dispersion spectra. The method is applied to the case when the pump field is bichromatic and trichromatic, and the physical interpretation of the numerically computed spectra is given.

  10. Probing Membrane Order and Topography in Supported Lipid Bilayers by Combined Polarized Total Internal Reflection Fluorescence-Atomic Force Microscopy

    PubMed Central

    Oreopoulos, John; Yip, Christopher M.

    2009-01-01

    Determining the local structure, dynamics, and conformational requirements for protein-protein and protein-lipid interactions in membranes is critical to understanding biological processes ranging from signaling to the translocating and membranolytic action of antimicrobial peptides. We report here the application of a combined polarized total internal reflection fluorescence microscopy-in situ atomic force microscopy platform. This platform's ability to image membrane orientational order was demonstrated on DOPC/DSPC/cholesterol model membranes containing the fluorescent membrane probe, DiI-C20 or BODIPY-PC. Spatially resolved order parameters and fluorophore tilt angles extracted from the polarized total internal reflection fluorescence microscopy images were in good agreement with the topographical details resolved by in situ atomic force microscopy, portending use of this technique for high-resolution characterization of membrane domain structures and peptide-membrane interactions. PMID:19254557

  11. Probing of multiple magnetic responses in magnetic inductors using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Park, Seongjae; Seo, Hosung; Seol, Daehee; Yoon, Young-Hwan; Kim, Mi Yang; Kim, Yunseok

    2016-02-01

    Even though nanoscale analysis of magnetic properties is of significant interest, probing methods are relatively less developed compared to the significance of the technique, which has multiple potential applications. Here, we demonstrate an approach for probing various magnetic properties associated with eddy current, coil current and magnetic domains in magnetic inductors using multidimensional magnetic force microscopy (MMFM). The MMFM images provide combined magnetic responses from the three different origins, however, each contribution to the MMFM response can be differentiated through analysis based on the bias dependence of the response. In particular, the bias dependent MMFM images show locally different eddy current behavior with values dependent on the type of materials that comprise the MI. This approach for probing magnetic responses can be further extended to the analysis of local physical features.

  12. Probing of multiple magnetic responses in magnetic inductors using atomic force microscopy.

    PubMed

    Park, Seongjae; Seo, Hosung; Seol, Daehee; Yoon, Young-Hwan; Kim, Mi Yang; Kim, Yunseok

    2016-01-01

    Even though nanoscale analysis of magnetic properties is of significant interest, probing methods are relatively less developed compared to the significance of the technique, which has multiple potential applications. Here, we demonstrate an approach for probing various magnetic properties associated with eddy current, coil current and magnetic domains in magnetic inductors using multidimensional magnetic force microscopy (MMFM). The MMFM images provide combined magnetic responses from the three different origins, however, each contribution to the MMFM response can be differentiated through analysis based on the bias dependence of the response. In particular, the bias dependent MMFM images show locally different eddy current behavior with values dependent on the type of materials that comprise the MI. This approach for probing magnetic responses can be further extended to the analysis of local physical features. PMID:26852801

  13. Probing of multiple magnetic responses in magnetic inductors using atomic force microscopy

    PubMed Central

    Park, Seongjae; Seo, Hosung; Seol, Daehee; Yoon, Young-Hwan; Kim, Mi Yang; Kim, Yunseok

    2016-01-01

    Even though nanoscale analysis of magnetic properties is of significant interest, probing methods are relatively less developed compared to the significance of the technique, which has multiple potential applications. Here, we demonstrate an approach for probing various magnetic properties associated with eddy current, coil current and magnetic domains in magnetic inductors using multidimensional magnetic force microscopy (MMFM). The MMFM images provide combined magnetic responses from the three different origins, however, each contribution to the MMFM response can be differentiated through analysis based on the bias dependence of the response. In particular, the bias dependent MMFM images show locally different eddy current behavior with values dependent on the type of materials that comprise the MI. This approach for probing magnetic responses can be further extended to the analysis of local physical features. PMID:26852801

  14. Mg I as a probe of the solar chromosphere - The atomic model

    NASA Technical Reports Server (NTRS)

    Mauas, Pablo J.; Avrett, Eugene H.; Loeser, Rudolf

    1988-01-01

    This paper presents a complete atomic model for Mg I line synthesis, where all the atomic parameters are based on recent experimental and theoretical data. It is shown how the computed profiles at 4571 A and 5173 A are influenced by the choice of these parameters and the number of levels included in the model atom. In addition, observed profiles of the 5173 A b2 line and theoretical profiles for comparison (based on a recent atmospheric model for the average quiet sun) are presented.

  15. Slow-light probe of Fermi pairing through an atom-molecule dark state

    SciTech Connect

    Jing, H.; Deng, Y.; Meystre, P.

    2011-06-15

    We consider the two-color photoassociation of a quantum degenerate atomic gas into ground-state diatomic molecules via a molecular dark state. This process can be described in terms of a {Lambda} level scheme that is formally analogous to the situation in electromagnetically induced transparency in atomic systems and therefore can result in slow-light propagation. We show that the group velocity of the light field depends explicitly on whether the atoms are bosons or fermions, as well as on the existence or absence of a pairing gap in the case of fermions, so that the measurement of the group velocity realizes a nondestructive diagnosis of the atomic state and the pairing gap.

  16. Shot Noise as a Probe of Spin-Polarized Transport through Single Atoms

    NASA Astrophysics Data System (ADS)

    Burtzlaff, Andreas; Weismann, Alexander; Brandbyge, Mads; Berndt, Richard

    2015-01-01

    Single atoms on Au(111) surfaces have been contacted with the Au tip of a low temperature scanning tunneling microscope. The shot noise of the current through these contacts has been measured up to frequencies of 120 kHz and Fano factors have been determined to characterize the transport channels. The noise at Fe and Co atoms, the latter displaying a Kondo effect, indicates spin-polarized transport through a single channel. Transport calculations reproduce this observation.

  17. Understanding of the field evaporation of surface modified oxide materials through transmission electron microscopy and atom probe tomography

    NASA Astrophysics Data System (ADS)

    Seol, Jae-Bok; Kwak, Chang-Min; Kim, Y.-T.; Park, Chan-Gyung

    2016-04-01

    Understanding of triggering the field evaporation of surface ions on the non-conductive materials enables improvement in the mass resolution in laser-pulsed atom probe tomography. This study addresses the influence of surface modification through metallic-capped layers, such as Co, Ni, and Ag, with surrounding bulk MgO tips on the physical mechanisms responsible for field evaporation and on the mass resolving power compared to uncapped bulk MgO. In particular, the field evaporation on the surface regions of Ag-capped bulk MgO tips during analysis was extensively observed by transmission electron microscopy to confirm the overall evaporation sequences occurring at the tip surface. We found that the introduction of such capping layers, especially for Ag-capping, controls both symmetric tip geometry at the surface of the specimens and the mass resolving power of ion species consisting of MgO materials. This implies the improvements in the symmetries of local field distributions and the isotropy of thermal heating across the tip surface. It reveals that Ag-capping with high thermal diffusivity promotes the compositional uniformities between the laser illumination side and the opposite side for MgO samples as well as the reduced fraction of multiple events for oxygen ions between both sides. Moreover, a variation in the thickness of the Ag-capping layer is an additional factor governing a thermal-assisted mechanism of MgO evaporation. Based on our findings, homogeneous thermal heat transfer for MgO emission along the tip axis by Ag-capping layers may be significant in potential methods for improvement.

  18. An Atom Probe Tomographic Investigation of High-Strength, High-Toughness Precipitation Strengthened Steels for Naval Applications

    NASA Astrophysics Data System (ADS)

    Hunter, Allen H.

    Novel high-strength high-toughness alloys strengthened by precipitation are investigated for use in naval applications. The mechanical properties of an experimental steel alloy, NUCu-140, are evaluated and are not suitable for the naval requirements due to poor impact toughness at -40°C. An investigation is conducted to determine optimum processing conditions to restore toughness. A detailed aging study is conducted at 450, 500, and 550°C to determine the evolution of the microstructure and mechanical properties. A combination of transmission electron microscopy (TEM), synchrotron X-ray Diffraction (XRD), and Local electrode atom probe (LEAP) tomography are used to measure the evolution of the Cu precipitates, austenite, NbC, and cementite phases during aging. The evolution of the Cu precipitates significantly affects the yield strength of the steel, but low temperature toughness is controlled by the cementite precipitates. Extended aging is effective at improving the impact toughness but the yield strength is also decreased due to coarsening of the Cu precipitates. To provide a foundation for successful welding of NUCu-140 steel, an investigation of the effects of gas metal arc welding (GMAW) are performed. The microstructures in the base metal (BM), heat affected zone (HAZ), and fusion zone (FZ) of a GMAW sample are analyzed to determine the effects of the welding thermal cycle. Weld simulation samples with known thermal histories are prepared and analyzed by XRD and LEAP tomography. A significant loss in microhardness is observed as a result of dissolution of the Cu precipitates after the weld thermal cycle. The cooling time is too rapid to allow significant precipitation of Cu. In addition to the NUCu-140 alloy, a production HSLA-115 steel alloy is investigated using TEM, XRD, and LEAP tomography. The strength of the HSLA-115 is found to be derived primarily from Cu precipitates. The volume fractions of cementite, austenite, and NbC are measured by XRD

  19. Quantitative analysis of doped/undoped ZnO nanomaterials using laser assisted atom probe tomography: Influence of the analysis parameters

    NASA Astrophysics Data System (ADS)

    Amirifar, Nooshin; Lardé, Rodrigue; Talbot, Etienne; Pareige, Philippe; Rigutti, Lorenzo; Mancini, Lorenzo; Houard, Jonathan; Castro, Celia; Sallet, Vincent; Zehani, Emir; Hassani, Said; Sartel, Corine; Ziani, Ahmed; Portier, Xavier

    2015-12-01

    In the last decade, atom probe tomography has become a powerful tool to investigate semiconductor and insulator nanomaterials in microelectronics, spintronics, and optoelectronics. In this paper, we report an investigation of zinc oxide nanostructures using atom probe tomography. We observed that the chemical composition of zinc oxide is strongly dependent on the analysis parameters used for atom probe experiments. It was observed that at high laser pulse energies, the electric field at the specimen surface is strongly dependent on the crystallographic directions. This dependence leads to an inhomogeneous field evaporation of the surface atoms, resulting in unreliable measurements. We show that the laser pulse energy has to be well tuned to obtain reliable quantitative chemical composition measurements of undoped and doped ZnO nanomaterials.

  20. Quantitative analysis of doped/undoped ZnO nanomaterials using laser assisted atom probe tomography: Influence of the analysis parameters

    SciTech Connect

    Amirifar, Nooshin; Lardé, Rodrigue Talbot, Etienne; Pareige, Philippe; Rigutti, Lorenzo; Mancini, Lorenzo; Houard, Jonathan; Castro, Celia; Sallet, Vincent; Zehani, Emir; Hassani, Said; Sartel, Corine; Ziani, Ahmed; Portier, Xavier

    2015-12-07

    In the last decade, atom probe tomography has become a powerful tool to investigate semiconductor and insulator nanomaterials in microelectronics, spintronics, and optoelectronics. In this paper, we report an investigation of zinc oxide nanostructures using atom probe tomography. We observed that the chemical composition of zinc oxide is strongly dependent on the analysis parameters used for atom probe experiments. It was observed that at high laser pulse energies, the electric field at the specimen surface is strongly dependent on the crystallographic directions. This dependence leads to an inhomogeneous field evaporation of the surface atoms, resulting in unreliable measurements. We show that the laser pulse energy has to be well tuned to obtain reliable quantitative chemical composition measurements of undoped and doped ZnO nanomaterials.

  1. Regulation of muscle contraction by Drebrin-like protein 1 probed by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Garces, Renata; Butkevich, Eugenia; Platen, Mitja; Schmidt, Christoph F.; Biophysics Team

    Sarcomeres are the fundamental contractile units of striated muscle cells. They are composed of a variety of structural and regulatory proteins functioning in a precisely orchestrated fashion to enable coordinated force generation in striated muscles. Recently, we have identified a C. elegans drebrin-like protein 1 (DBN-1) as a novel sarcomere component, which stabilizes actin filaments during muscle contraction. To further characterize the function of DBN-1 in muscle cells, we generated a new dbn-1 loss-of-function allele. Absence of DBN-1 resulted in a unique worm movement phenotype, characterized by hyper-bending. It is not clear yet if DBN-1 acts to enhance or reduce the capacity for contraction. We present here an experimental mechanical study on C. elegans muscle mechanics. We measured the stiffness of the worm by indenting living C. eleganswith a micron-sized sphere adhered to the cantilever of an atomic force microscope (AFM). Modeling the worm as a pressurized elastic shell allows us to monitor the axial tension in the muscle through the measured stiffness. We compared responses of wild-type and mutant C. elegans in which DBN-1 is not expressed..

  2. Probing the compressibility of tumor cell nuclei by combined atomic force-confocal microscopy

    NASA Astrophysics Data System (ADS)

    Krause, Marina; te Riet, Joost; Wolf, Katarina

    2013-12-01

    The cell nucleus is the largest and stiffest organelle rendering it the limiting compartment during migration of invasive tumor cells through dense connective tissue. We here describe a combined atomic force microscopy (AFM)-confocal microscopy approach for measurement of bulk nuclear stiffness together with simultaneous visualization of the cantilever-nucleus contact and the fate of the cell. Using cantilevers functionalized with either tips or beads and spring constants ranging from 0.06-10 N m-1, force-deformation curves were generated from nuclear positions of adherent HT1080 fibrosarcoma cell populations at unchallenged integrity, and a nuclear stiffness range of 0.2 to 2.5 kPa was identified depending on cantilever type and the use of extended fitting models. Chromatin-decondensating agent trichostatin A (TSA) induced nuclear softening of up to 50%, demonstrating the feasibility of our approach. Finally, using a stiff bead-functionalized cantilever pushing at maximal system-intrinsic force, the nucleus was deformed to 20% of its original height which after TSA treatment reduced further to 5% remaining height confirming chromatin organization as an important determinant of nuclear stiffness. Thus, combined AFM-confocal microscopy is a feasible approach to study nuclear compressibility to complement concepts of limiting nuclear deformation in cancer cell invasion and other biological processes.

  3. Nuclear structure studies with intermediate energy probes

    SciTech Connect

    Lee, T.S.H.

    1993-10-01

    Nuclear structure studies with pions are reviewed. Results from a recent study of 1 p-shell nuclei using (e,e{prime}), ({pi}, {pi}{prime}), and ({gamma},{pi}) reactions are reported. Future nuclear structure studies with GeV electrons at CEBAF are also briefly discussed.

  4. Future studies of planetary rings by space probes

    NASA Technical Reports Server (NTRS)

    Stone, E. C.

    1984-01-01

    Recent space probe observations of the rings of Jupiter and Saturn have furnished a substantial enhancement of the current understanding of the outer planets' rings. Voyager 2 offers further opportunities for the study of the Neptune and Uranus ring systems. The Galileo mission to Jupiter furnishes the first opportunity for long term space probe studies of a planetary ring system. It is suggested that an appropriately instrumented Saturn orbiter would not only provide a similar opportunity for the study of the Saturn rings, but may also be the only means by which to adequately address the nature of the diverse phenomena displayed by this prototypical planetary ring system.

  5. Atom probe tomography evaporation behavior of C-axis GaN nanowires: Crystallographic, stoichiometric, and detection efficiency aspects

    SciTech Connect

    Diercks, David R. Gorman, Brian P.; Kirchhofer, Rita; Sanford, Norman; Bertness, Kris; Brubaker, Matt

    2013-11-14

    The field evaporation behavior of c-axis GaN nanowires was explored in two different laser-pulsed atom probe tomography (APT) instruments. Transmission electron microscopy imaging before and after atom probe tomography analysis was used to assist in reconstructing the data and assess the observed evaporation behavior. It was found that the ionic species exhibited preferential locations for evaporation related to the underlying crystal structure of the GaN and that the species which evaporated from these locations was dependent on the pulsed laser energy. Additionally, the overall stoichiometry measured by APT was significantly correlated with the energy of the laser pulses. At the lowest laser energies, the apparent composition was nitrogen-rich, while higher laser energies resulted in measurements of predominantly gallium compositions. The percent of ions detected (detection efficiency) for these specimens was found to be considerably below that shown for other materials, even for laser energies which produced the expected Ga:N ratio. The apparent stoichiometry variation and low detection efficiency appear to be a result of evaporation of Ga ions between laser pulses at the lowest laser energies and evaporation of neutral N{sub 2} species at higher laser energies. All of these behaviors are tied to the formation of nitrogen-nitrogen bonds on the tip surface, which occurred under all analysis conditions. Similar field evaporation behaviors are therefore expected for other materials where the anionic species readily form a strong diatomic bond.

  6. Fe-implanted 6H-SiC: Direct evidence of Fe{sub 3}Si nanoparticles observed by atom probe tomography and {sup 57}Fe Mössbauer spectroscopy

    SciTech Connect

    Diallo, M. L.; Fnidiki, A. Lardé, R.; Cuvilly, F.; Blum, I.; Lechevallier, L.; Debelle, A.; Thomé, L.; Viret, M.; Marteau, M.; Eyidi, D.; Declémy, A.

    2015-05-14

    In order to understand ferromagnetic ordering in SiC-based diluted magnetic semiconductors, Fe-implanted 6H-SiC subsequently annealed was studied by Atom Probe Tomography, {sup 57}Fe Mössbauer spectroscopy and SQUID magnetometry. Thanks to its 3D imaging capabilities at the atomic scale, Atom Probe Tomography appears as the most suitable technique to investigate the Fe distribution in the 6H-SiC host semiconductor and to evidence secondary phases. This study definitely evidences the formation of Fe{sub 3}Si nano-sized clusters after annealing. These clusters are unambiguously responsible for the main part of the magnetic properties observed in the annealed samples.

  7. Atomic force microscope based near-field imaging for probing cell surface interactions

    NASA Astrophysics Data System (ADS)

    Amini, Sina

    Near-membrane and trans-membrane proteins and their interactions with the extracellular matrix (ECM) can yield valuable information about cell dynamics. However, advances in the field of nanoscale cellular processes have been hindered, in part, due to limits imposed by current technology. In this work, a novel evanescent field (EF) imaging technique is designed, modeled, created and tested for near-field imaging in the apical surface of cells. This technique and Forster resonance energy transfer (FRET) were used to investigate interactions between integrins on the cell surface and the ECM protein, fibronectin. The goal was to monitor changes in the integrin density at the cell surface as a function of clustering after binding to fibronectin on the microsphere surface. For the EF technique, quantum dot (QD)-embedded polystyrene microspheres were used to couple light into whispering gallery modes (WGMs) inside the microspheres; the resulting EF at the surface of the microsphere was used as a near-field excitation source with ~50 nm axial resolution for exciting fluorescently-labeled integrins. For FRET measurements (~10 nm axial resolution), QDs (donors) were coated on the surface of microspheres and energy transfer to red fluorescent protein (RFP)-integrin constructs (acceptors) studied. In both techniques, the QD-modified microspheres were mounted on atomic force microscope (AFM) cantilevers, functionalized with fibronectin, and brought into contact with fluorescently-labeled HeLa or vascular smooth muscle (VSM) cells. The results obtained from both methods show the clustering and activity of the integrins and are in good agreement with each other. Amsterdam discrete dipole approximation (ADDA) was used to study the effects of inhomogeneous surrounding refractive index on the quality factor and position of the WGMs due to the attachment of a microsphere to an AFM cantilever. WGMs of various QD-embedded microspheres mounted on AFM cantilevers were experimentally

  8. Combined Impedance Probe and Langmuir Probe Studies of the Low-Latitude E Region

    NASA Technical Reports Server (NTRS)

    Rowland, D. E.; Pfaff, R. F.; Steigies, C. T.

    2008-01-01

    The EQUIS-2 sounding rocket and radar campaign, launched from Kwajalein Atoll in 2004, included a mission to study low-latitude irregularities and electrodynamics, led by NASA GSFC. This mission included two instrumented rockets launched into the nighttime E region (apogee near 120 km), which included comprehensive electrodynamics and neutral density instrumentation. These rockets carried the first of a new generation of impedance probes, that utilize a wide-band drive signal to simultaneously measure the impedance of an antenna in a plasma as a function of frequency from 7 kEIz to 4 MHz. at a rapid cadence. This technique promises to permit true plasma spectroscopy, and resulted in the identification of multiple plasma resonances and accurate measurements of the plasma density, even in the low density nighttime E region. We present analyses of the technique and resulting spectra, and show how these data may be combined with fixed-bias Langmuir Probe data to infer the temperature structure of the E region as well as providing accurate absolute calibrations for the very high time resolution fixed-bias probe data. The data is shown to agree well with data from ionosonde, the ALTAIR radar, and the Peruvian beacon experiment.

  9. Probing the electronic properties of atomically thin graphitic layers with optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Mak, Kin Fai

    Since its discovery, graphene (a mono-layer of graphitic layer) has attracted tremendous attention from the physics community. Being one-atom thick, Single Layer Graphene (SLG) is an ideal model for fundamental studies of 2-Dimensional (2D) systems. One of the most interesting aspects of SLG is the resemblance of its electronic structure to an important class of particles in high energy physics, the Dirac massless Fermions, i.e., massless Fermions with 4 flavors. Such an electronic structure leads to many peculiar phenomena in fundamental physics and many desirable properties for technological applications of this new material. Therefore, a basic understanding of the electronic properties of SLG is of the greatest importance in this field. In this thesis, the electronic structure of single- and few-layer graphene is investigated with optical spectroscopic techniques. In the first part, the optical absorption spectrum of SLG is measured. In the mid/near infrared range, the absorbance is a universal constant equal to pialpha = 2.29%, a being the fine structure constant, independent of photon energies, the particular sample characteristics and all parameters describing the band structure of SLG. This reflects a fundamental fact that the charge carriers in SLG indeed behave as 2D Dirac massless Fermions at low energies. Since each Fermionic species absorbs by pialpha/4, the 4 spin-nodal flavors of Fermions in SLG gives an absorbance of pialpha. On the other hand, strong modifications of optical absorption in the visible/UV range due to many body interactions are observed. Such effects give rise to a breakdown of the universal absorbance and experimental signatures of saddle point excitons. In the second part, the electronic structure of Bi-Layer Graphene (BLG) is studied in the presence of strong applied electric fields. In contrast to SLG, the low-energy electrons in BLG are described as chiral massive Fermions. The linearly dispersing bands in SLG are replaced by

  10. Strong interaction studies with kaonic atoms

    NASA Astrophysics Data System (ADS)

    Marton, J.; Bazzi, M.; Beer, G.; Berucci, C.; Bosnar, D.; Bragadireanu, A. M.; Cargnelli, M.; Clozza, A.; Curceanu, C.; d'Uffizi, A.; Fiorini, C.; Ghio, F.; Guaraldo, C.; Hayano, R.; Iliescu, M.; Ishiwatari, T.; Iwasaki, M.; Levi Sandri, P.; Okada, S.; Pietreanu, D.; Piscicchia, K.; Ponta, T.; Quaglia, R.; Romero Vidal, A.; Sbardella, E.; Scordo, A.; Shi, H.; Sirghi, D. L.; Sirghi, F.; Tatsuno, H.; Vazquez Doce, O.; Widmann, E.; Zmeskal, J.

    2016-03-01

    The strong interaction of antikaons (K-) with nucleons and nuclei in the low-energy regime represents an active research field connected intrinsically with few-body physics. There are important open questions like the question of antikaon nuclear bound states - the prototype system being K-pp. A unique and rather direct experimental access to the antikaon-nucleon scattering lengths is provided by precision X-ray spectroscopy of transitions in low-lying states of light kaonic atoms like kaonic hydrogen isotopes. In the SIDDHARTA experiment at the electron-positron collider DAΦNE of LNF-INFN we measured the most precise values of the strong interaction observables, i.e. the strong interaction on the 1s ground state of the electromagnetically bound K-p atom leading to a hadronic shift ɛ1s and a hadronic broadening Γ1s of the 1s state. The SIDDHARTA result triggered new theoretical work which achieved major progress in the understanding of the low-energy strong interaction with strangeness. Antikaon-nucleon scattering lengths have been calculated constrained by the SIDDHARTA data on kaonic hydrogen. For the extraction of the isospin-dependent scattering lengths a measurement of the hadronic shift and width of kaonic deuterium is necessary. Therefore, new X-ray studies with the focus on kaonic deuterium are in preparation (SIDDHARTA2). Many improvements in the experimental setup will allow to measure kaonic deuterium which is challenging due to the anticipated low X-ray yield. Especially important are the data on the X-ray yields of kaonic deuterium extracted from a exploratory experiment within SIDDHARTA.

  11. Studying Atomic Dynamics with Designer Pulses

    SciTech Connect

    Reinhold, C.O.; Burgdorfer, J.; Frey, M.T.; Dunning, F.B.

    1997-09-01

    We present a brief review of recent experimental and theoretical progress on the dynamics of Rydberg atoms using short half cycle pulses. We discuss new possibilities in coherent control and non-linear dynamics of atoms which have lately become possible using various superpositions of such pulses.

  12. Adhesion properties of hydrogen on Sb(111) probed by helium atom scattering

    NASA Astrophysics Data System (ADS)

    Kraus, P.; Gösweiner, Ch.; Tamtögl, A.; Apolloner, F.; Ernst, W. E.

    2016-06-01

    We have carried out a series of helium atom scattering measurements in order to characterise the adsorption properties of hydrogen on antimony(111). Molecular hydrogen does not adsorb at temperatures above 110 K in contrast to pre-dissociated atomic hydrogen. Depending on the substrate temperature, two different adlayer phases of atomic hydrogen on Sb(111) occur. At low substrate temperatures (110 K), the deposited hydrogen layer does not show any ordering while we observe a perfectly ordered (1× 1) H/Sb(111) structure for deposition at room temperature. Furthermore, the amorphous hydrogen layer deposited at low temperature forms an ordered overlayer upon heating the crystal to room temperature. Hydrogen starts to desorb at Tm = 430 \\text{K} which corresponds to a desorption energy of Edes=(1.33+/-0.06) \\text{eV} . Using measurements of the helium reflectivity during hydrogen exposure at different surface temperatures, we conclude that the initial sticking coefficient of atomic hydrogen on Sb(111) decreases with increasing surface temperature. Furthermore, the scattering cross-section for the diffuse scattering of helium from hydrogen on Sb(111) is determined as Σ = (12 +/- 1) \\unicode{8491}2 .

  13. 3D compositional characterization of Si/SiO2 vertical interface structure by atom probe tomography

    NASA Astrophysics Data System (ADS)

    Lee, J. H.; Kim, Y. T.; Kim, J. J.; Lee, S. Y.; Park, C. G.

    2013-11-01

    Precise interpretation of three-dimensional atom probe tomography (3D-APT) data is necessary to reconstruct semiconductor-device structures. In particular, it is difficult to reconstruct the hetero-structure of conductors and insulators using APT analysis, due to the preferential evaporation of low-evaporation field-material. In this paper, shallow-trench isolation (STI) structure, consisting of a Si column and a SiO2 region, is analyzed using APT. The dimensional artifact known as the local-magnification-effect occurring as a result of the geometric deviation from the ideal hemisphere was successfully calibrated by `high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) tomography' and Electron Energy Loss Spectroscopy (EELS). In the direction of the width, the Si layer was compressed by 50%, and the interface was expanded by 250% with respect to the reference data obtained for the same sample. A 5-nm-thick transition layer was observed at the interface between Si and SiO2. The composition of the transition layer follows the well-developed sequence Si-Si2O-SiO-SiO2 from the Si area to the SiO2 area. Atoms at the interface were likely to evaporate with a bit wider angle than atoms in the Si area due to the preferentially evaporated Si layer, which caused the interface area to appear locally magnified.

  14. Quantitative analysis of hydrogen in SiO2/SiN/SiO2 stacks using atom probe tomography

    NASA Astrophysics Data System (ADS)

    Kunimune, Yorinobu; Shimada, Yasuhiro; Sakurai, Yusuke; Inoue, Masao; Nishida, Akio; Han, Bin; Tu, Yuan; Takamizawa, Hisashi; Shimizu, Yasuo; Inoue, Koji; Yano, Fumiko; Nagai, Yasuyoshi; Katayama, Toshiharu; Ide, Takashi

    2016-04-01

    We have demonstrated that it is possible to reproducibly quantify hydrogen concentration in the SiN layer of a SiO2/SiN/SiO2 (ONO) stack structure using ultraviolet laser-assisted atom probe tomography (APT). The concentration of hydrogen atoms detected using APT increased gradually during the analysis, which could be explained by the effect of hydrogen adsorption from residual gas in the vacuum chamber onto the specimen surface. The amount of adsorbed hydrogen in the SiN layer was estimated by analyzing another SiN layer with an extremely low hydrogen concentration (<0.2 at. %). Thus, by subtracting the concentration of adsorbed hydrogen, the actual hydrogen concentration in the SiN layer was quantified as approximately 1.0 at. %. This result was consistent with that obtained by elastic recoil detection analysis (ERDA), which confirmed the accuracy of the APT quantification. The present results indicate that APT enables the imaging of the three-dimensional distribution of hydrogen atoms in actual devices at a sub-nanometer scale.

  15. Measurement of atomic oxygen in the middle atmosphere using solid electrolyte sensors and catalytic probes

    NASA Astrophysics Data System (ADS)

    Eberhart, M.; Löhle, S.; Steinbeck, A.; Binder, T.; Fasoulas, S.

    2015-03-01

    The atmospheric energy budget is largely dominated by reactions involving atomic oxygen (O). Modeling of these processes requires detailed knowledge about the distribution of this oxygen species. Understanding the mutual contributions of atomic oxygen and wave motions to the atmospheric heating is the main goal of the rocket campaign WADIS. It includes, amongst others, two of our instruments for the measurement of atomic oxygen that have both been developed with the aim of resolving density variations on small vertical scales along the trajectory. In this paper the instrument based on catalytic effects (PHLUX) is introduced briefly. The experiment employing solid electrolyte sensors (FIPEX) is presented in detail. These sensors were laboratory calibrated using a microwave plasma as a source for atomic oxygen in combination with mass spectrometer reference measurements. The spectrometer was in turn calibrated for O with a method based on methane. In order to get insight into the horizontal variability the rocket payload had instrument decks at both ends. Each housed several sensor heads measuring during both the up- and downleg of the trajectory. The WADIS campaign comprises two rocket flights during different geophysical conditions. Results from WADIS-1 are presented which was successfully launched in June 2013 from Andøya Rocket Range, Norway. FIPEX data was sampled with 100 Hz and yield atomic oxygen density profiles with a vertical resolution better than 10 m. Numerical simulations of the flow field around the rocket were done at several points of the trajectory to assess the influence of aerodynamic effects on the measurement results. Density profiles peak at 3 × 1010 cm-3 at altitudes of 93.6 and 96 km for up- and downleg respectively.

  16. Studies of enzyme mechanism using isotopic probes

    SciTech Connect

    Chen, C.

    1987-01-01

    The isotope partitioning studies of the Ascaris suum NAD-malic enzyme reaction were examined with five transitory complexes including E:NAD, E:NAD:Mg, E:malate, E:Mg:malate, and E:NAD:malate. Three productive complexes, E:NAD, E:NAD:Mg, and E:Mg:malate, were obtained, suggesting a steady-state random mechanism. Data for trapping with E:/sup 14/C-NAD indicate a rapid equilibrium addition of Mg/sup 2 +/ prior to the addition of malate. Trapping with /sup 14/C-malate could only be obtained from the E:Mg/sup 2 +/:/sup 14/C-malate complex, while no trapping from E:/sup 14/C-malate was obtained under feasible experimental conditions. The equations for the isotope partitioning studies varying two substrates in the chase solution in an ordered terreactant reaction were derived, allowing a determination of the relative rates of substrate dissociation to the catalytic reaction for each of the productive transitory complexes. NAD and malate are released from the central complex at an identical rate, equal to the catalytic rate. The release of NAD from E:NAD and E:NAD:Mg complexes is 2- to 4-fold and 5- to 9-fold V/sub max//E/sub t/, respectively. The release of malate from the E:Mg:malate complex is 0.1- to 0.3-fold of V/sub max//E/sub t/. The individual rate constants for association and dissociation of the substrates, NAD and malate have been estimated.

  17. Probing deeper into first American studies

    PubMed Central

    Dillehay, Tom D.

    2009-01-01

    The initial peopling of the Americas has proved one of the most challenging episodes in reconstructing global prehistory, challenging because researchers struggle with the vagaries of early archaeological site preservation, and debates continue over the date and place of human entry, the rapidity and direction of dispersion, and the variety of cultural responses to climatic change during the terminal Pleistocene period. Despite many recent advances in our understanding of these issues, especially in the areas of genetics and new archaeological discoveries, the field continues facing limitations in the sampling and quality of data, the research problems defined, and the epistemologies and theories applied. Theoretical development of first American studies has been uneven, and its contribution to global issues of early human migration has been restricted. This essay discusses what is known and not known about the process of the first peopling of the Americas from the perspective of archaeology, genetics, and bioanthropology. Some approaches to fill voids in data, methods, and the broader conceptualization of the process also are considered. PMID:19164556

  18. On the interaction of an ultra-fast laser with a nanometric tip by laser assisted atom probe tomography: a review.

    PubMed

    Vella, A

    2013-09-01

    The evaporation mechanisms of surface atoms in laser assisted atom probe tomography (LA-APT) are reviewed with an emphasis on the changes in laser-matter interaction when the sample is a nanometric tip submitted to a high electric field. The nanometric dimensions induce light diffraction, the tip shape induces field enhancement and these effects together completely change the absorption properties of the sample from those of macroscopic bulk materials. Moreover, the high electric field applied to the sample during LA-APT analysis strongly modifies the surface optical properties of band gap materials, due to the band bending induced at the surface. All these effects are presented and studied in order to determine the physical mechanisms of atoms evaporation in LA-APT. Moreover, LA-APT is used as an original experimental setup to study: (a) the absorption of nanometric tips; (b) the contribution of the standing field to this laser energy absorption and (c) the heating and cooling process of nanometric sample after the interaction with ultra fast laser. PMID:23822883

  19. Investigation of the hybrid molecular probe for intracellular studies

    PubMed Central

    Martinez, Karen; Medley, Colin D.; Yang, Chaoyong James; Tan, Weihong

    2009-01-01

    Monitoring gene expression in vivo is essential to the advancement of biological studies, medical diagnostics, and drug discovery. Adding to major efforts in developing molecular probes for mRNA monitoring, we have recently developed an alternative tool, the hybrid molecular probe (HMP). To optimize the probe, a series of experiments were performed to study the properties of HMP hybridization kinetics and stability. The results demonstrated the potential of the HMP as a prospective tool for use in both hybridization studies and in vitro and in vivo analyses. The HMP has shown no tendency to produce false positive signals, which is a major concern for living cell studies. Moreover, HMP has shown the ability to detect the mRNA expression of different genes inside single cells from both basal and stimulated genes. As an effective alternative to conventional molecular probes, the proven sensitivity, simplicity, and stability of HMPs show promise for their use in monitoring mRNA expression in living cells. PMID:18421445

  20. Probe Studies of a Hall Thruster at Low Voltages

    NASA Astrophysics Data System (ADS)

    Ross, Jerry L.

    Internal and external probe studies were performed on a Hall thruster operating at low discharge voltages. At nominal magnet current levels ionization and acceleration regions were found to have shifted downstream axially outside the exit plane. Reducing the magnet current partially reversed the situation by inducing a fractional axial upstream shift in both regions.

  1. Novel Diubiquitin Probes Expand the Chemical Toolkit to Study DUBs.

    PubMed

    Kulathu, Yogesh

    2016-04-21

    Linkage-specific DUBs employ different mechanisms to recognize and cleave polyubiquitin chains of specific linkage types. In this issue of Cell Chemical Biology, Flierman et al. (2016) develop a new family of novel non-hydrolyzable diubiquitin probes that will be valuable tools to study how DUBs achieve specificity. PMID:27105279

  2. The use of analytical surface tools in the fundamental study of wear. [atomic nature of wear

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1977-01-01

    Various techniques and surface tools available for the study of the atomic nature of the wear of materials are reviewed These include chemical etching, x-ray diffraction, electron diffraction, scanning electron microscopy, low-energy electron diffraction, Auger emission spectroscopy analysis, electron spectroscopy for chemical analysis, field ion microscopy, and the atom probe. Properties of the surface and wear surface regions which affect wear, such as surface energy, crystal structure, crystallographic orientation, mode of dislocation behavior, and cohesive binding, are discussed. A number of mechanisms involved in the generation of wear particles are identified with the aid of the aforementioned tools.

  3. Atomic Bomb Survivors Life-Span Study

    PubMed Central

    Dobrzyński, Ludwik

    2015-01-01

    The atomic bomb survivors life-span study (LSS) is often claimed to support the linear no-threshold hypothesis (LNTH) of radiation carcinogenesis. This paper shows that this claim is baseless. The LSS data are equally or better described by an s-shaped dependence on radiation exposure with a threshold of about 0.3 Sievert (Sv) and saturation level at about 1.5 Sv. A Monte-Carlo simulation of possible LSS outcomes demonstrates that, given the weak statistical power, LSS cannot provide support for LNTH. Even if the LNTH is used at low dose and dose rates, its estimation of excess cancer mortality should be communicated as 2.5% per Sv, i.e., an increase of cancer mortality from about 20% spontaneous mortality to about 22.5% per Sv, which is about half of the usually cited value. The impact of the “neutron discrepancy problem” – the apparent difference between the calculated and measured values of neutron flux in Hiroshima – was studied and found to be marginal. Major revision of the radiation risk assessment paradigm is required. PMID:26673526

  4. Laser spectroscopic probing of coexisting superfluid and insulating states of an atomic Bose-Hubbard system

    NASA Astrophysics Data System (ADS)

    Kato, Shinya; Inaba, Kensuke; Sugawa, Seiji; Shibata, Kosuke; Yamamoto, Ryuta; Yamashita, Makoto; Takahashi, Yoshiro

    2016-04-01

    A system of ultracold atoms in an optical lattice has been regarded as an ideal quantum simulator for a Hubbard model with extremely high controllability of the system parameters. While making use of the controllability, a comprehensive measurement across the weakly to strongly interacting regimes in the Hubbard model to discuss the quantum many-body state is still limited. Here we observe a great change in the excitation energy spectra across the two regimes in an atomic Bose-Hubbard system by using a spectroscopic technique, which can resolve the site occupancy in the lattice. By quantitatively comparing the observed spectra and numerical simulations based on sum rule relations and a binary fluid treatment under a finite temperature Gutzwiller approximation, we show that the spectra reflect the coexistence of a delocalized superfluid state and a localized insulating state across the two regimes.

  5. Laser spectroscopic probing of coexisting superfluid and insulating states of an atomic Bose–Hubbard system

    PubMed Central

    Kato, Shinya; Inaba, Kensuke; Sugawa, Seiji; Shibata, Kosuke; Yamamoto, Ryuta; Yamashita, Makoto; Takahashi, Yoshiro

    2016-01-01

    A system of ultracold atoms in an optical lattice has been regarded as an ideal quantum simulator for a Hubbard model with extremely high controllability of the system parameters. While making use of the controllability, a comprehensive measurement across the weakly to strongly interacting regimes in the Hubbard model to discuss the quantum many-body state is still limited. Here we observe a great change in the excitation energy spectra across the two regimes in an atomic Bose–Hubbard system by using a spectroscopic technique, which can resolve the site occupancy in the lattice. By quantitatively comparing the observed spectra and numerical simulations based on sum rule relations and a binary fluid treatment under a finite temperature Gutzwiller approximation, we show that the spectra reflect the coexistence of a delocalized superfluid state and a localized insulating state across the two regimes. PMID:27094083

  6. Reaction ({gamma},2e) and (e,3e) as probe of electron correlation in atoms

    SciTech Connect

    Amusia, M.Y.

    1995-08-01

    Cross sections of the ({gamma},2e) and (e,3e) reactions contain information about the two vacancy-energy spectrum and electron-pair correlations in initial and final states of the target atom. Physical pictures of these processes are presented for two- and many-electron atoms. The simplest mechanisms are discussed, demonstrating some features which await experimental confirmation. Attention is given to high photon energy and the relativistic energy region of these reactions. The energy distribution of outgoing relativistic electrons is qualitatively different from the nonrelativistic case. The origin and types of corrections to the simplest mechanisms, and possible means of their detection, are discussed. In addition, the role of different resonances: shape, giant, autoionizational, and Feshbach-type are considered. Results of calculations are compared with experimental data, mainly on double photoionization cross sections. Different possible objects as targets for the reactions are considered, including negative ions, excited atoms, molecules, and clusters. The modification of these reactions due to photon emission is discussed. The future of the domain is outlined.

  7. Characterization of nanoscale NiAl-type precipitates in a ferritic steel by electron microscopy and atom probe tomography

    SciTech Connect

    Teng, Zhenke; Miller, Michael K; Ghosh, Gautam; Liu, Chain T; Huang, Shenyan; Russell, Kaye F; Fine, Morris E; Liaw, Peter K

    2010-01-01

    The microstructure of NiAl-type ({beta}{prime}) precipitates in an aged ferritic steel (Fe-12.7Al-9Ni-10.2Cr-1.9Mo, at.%) is characterized by transmission and analytical electron microscopy (AEM) and atom probe tomography (APT). The alloy shows a duplex precipitation of {beta}{prime} particles: primary with an average diameter of 130 nm and secondary with an average diameter of 3 nm. Based on APT, the primary and secondary {beta}{prime} have compositions of Ni{sub 41.2}Al{sub 43.6}Fe{sub 12.7}Cr{sub 0.8}Mo{sub 1.4} and Ni{sub 26.3}Al{sub 41.6}Fe{sub 26.9}Cr{sub 3.3}Mo{sub 1.7}, respectively.

  8. Probing the influence of the Coulomb field on atomic ionization by sculpted two-color laser fields

    NASA Astrophysics Data System (ADS)

    Xie, Xinhua; Roither, Stefan; Gräfe, Stefanie; Kartashov, Daniil; Persson, Emil; Lemell, Christoph; Zhang, Li; Schöffler, Markus S.; Baltuška, Andrius; Burgdörfer, Joachim; Kitzler, Markus

    2013-04-01

    Interpretation of electron or photon spectra obtained with strong laser pulses that may carry attosecond dynamical and Ångström structural information about atoms or molecules usually relies on variants of the strong-field approximation (SFA) within which the influence of the Coulomb potential on the electron trajectory is neglected. We employ two-color sculpted laser fields to experimentally tune and probe the influence of the Coulomb field on the strong-field-driven wavepacket as observed by two-dimensional electron and ion momentum spectra. By comparison of measured spectra with predictions of the three-dimensional time-dependent Schrödinger equation as well as the quasi-classical limit of the SFA, the strong-field classical trajectory model, we are able to trace back the influence of the Coulomb field to the timing of the wavepacket release with sub-cycle precision.

  9. Rydberg gas theory of a glow discharge plasma: II. Electrode kinetics (probe theory) and the thermal rate constant for Symmetrical charge transfer involving Rydberg atoms of Ar.

    PubMed

    Mason, Rod S

    2010-04-21

    A steady state chemical kinetic model is developed to describe the conduction of electrical current between two probes, of relatively large surface area, immersed in a fast flowing plasma by the mechanism of charge transfer through a gas of Rydberg atoms. It correctly predicts the shape of current-voltage profiles which are similar to those of Langmuir, or floating double probe measurements. The difference is that the plateau current at the probe reflects the transport limited ion current at the cathodic electrode, even when the probe is being scanned in the anodic region. The sharp gradient leading up to the plateau of the I-V curve is associated with the field dependence of the efficiency of Rydberg atom ionisation, not the electron temperature. This approach gives a good qualitative explanation of experimental behaviour over a wide range of probe bias voltages and includes the occurrence of electron impact ionisation at the anode. It also gives a value for the thermal rate coefficient of symmetrical charge transfer between Rydberg atoms of Ar (8.2 x 10(-7) molecule(-1) cm(3) s(-1), at 313 K; plasma density approximately = 10(10) atoms cm(-3), total pressure = 2.7 mbar). PMID:20358036

  10. A comparative study of electrical probe techniques for plasma diagnostics

    NASA Technical Reports Server (NTRS)

    Szuszczewicz, E. P.

    1972-01-01

    Techniques for using electrical probes for plasma diagnostics are reviewed. Specific consideration is given to the simple Langmuir probe, the symmetric double probe of Johnson and Malter, the variable-area probe of Fetz and Oeschsner, and a floating probe technique. The advantages and disadvantages of each technique are discussed.

  11. Nanoscale electrical property studies of individual GeSi quantum rings by conductive scanning probe microscopy

    PubMed Central

    2012-01-01

    The nanoscale electrical properties of individual self-assembled GeSi quantum rings (QRs) were studied by scanning probe microscopy-based techniques. The surface potential distributions of individual GeSi QRs are obtained by scanning Kelvin microscopy (SKM). Ring-shaped work function distributions are observed, presenting that the QRs' rim has a larger work function than the QRs' central hole. By combining the SKM results with those obtained by conductive atomic force microscopy and scanning capacitance microscopy, the correlations between the surface potential, conductance, and carrier density distributions are revealed, and a possible interpretation for the QRs' conductance distributions is suggested. PMID:23194252

  12. Directly correlated transmission electron microscopy and atom probe tomography of grain boundary oxidation in a Ni-Al binary alloy exposed to high-temperature water

    SciTech Connect

    Schreiber, Daniel K.; Olszta, Matthew J.; Bruemmer, Stephen M.

    2013-06-14

    Intergranular oxidation of a Ni-4Al alloy exposed to hydrogenated, high-temperature water was characterized using directly correlated transmission electron microscopy and atom probe tomography. These combined analyses revealed that discrete, well-separated oxides (NiAl2O4) precipitated along grain boundaries in the metal. Aluminum was depleted from the grain boundary between oxides and also from one side of the boundary as a result of grain boundary migration. The discrete oxide morphology, disconnected from the continuous surface oxidation, suggests intergranular solid-state internal oxidation of Al. Keywords: oxidation; grain boundaries; nickel alloys; atom probe tomography; transmission electron microscopy (TEM)

  13. Probing ultrafast molecular dynamics in O2 using XUV/IR pump-probe studies

    NASA Astrophysics Data System (ADS)

    Ray, D.; Sturm, F. P.; Wright, T. W.; Ranitovic, P.; Shivaram, N. H.; Bocharova, I.; Belkacem, A.; Weber, Th.

    2015-05-01

    We investigate the molecular dynamics via different dissociative and autoionizing pathways in molecular oxygen using a pump-probe scheme with ultrashort extreme ultraviolet (XUV) laser pulses. Our primary focus is to study the molecular dynamics in the superexcited Rydberg states in a time-resolved manner. The O2 molecules are pumped by 20.2 eV and 23.1 eV XUV pulses (13th and 15th harmonics). Probing the relaxation dynamics with an infrared (IR) pulse at very long delays (100s of fs) enables us to measure the lifetimes of these Rydberg states. We also observe an enhancement and suppression of vibrational levels of the O2+ion due to the presence of IR. The high flux XUV pulses used for this experiment are generated in an Ar gas by IR pulses from our state-of-the-art 30 mJ, 50 Hz laser system. The pulses are overlapped with the supersonic jet in our Momentum Imaging for TimE Resolved Studies (MISTERS) setup. The cold target in our setup, combined with a very tight focussing geometry and a 3D momentum detection capability gives a high kinetic energy resolution. Molecular dynamics in other polyatomic molecules are also under investigation. Chemical Sciences Division, Lawrence Berkeley National Laboratory.

  14. Probing the surface of a sweet protein: NMR study of MNEI with a paramagnetic probe

    PubMed Central

    Niccolai, Neri; Spadaccini, Roberta; Scarselli, Maria; Bernini, Andrea; Crescenzi, Orlando; Spiga, Ottavia; Ciutti, Arianna; Di Maro, Daniela; Bracci, Luisa; Dalvit, Claudio; Temussi, Piero A.

    2001-01-01

    The design of safe sweeteners is very important for people who are affected by diabetes, hyperlipemia, and caries and other diseases that are linked to the consumption of sugars. Sweet proteins, which are found in several tropical plants, are many times sweeter than sucrose on a molar basis. A good understanding of their structure–function relationship can complement traditional SAR studies on small molecular weight sweeteners and thus help in the design of safe sweeteners. However, there is virtually no sequence homology and very little structural similarity among known sweet proteins. Studies on mutants of monellin, the best characterized of sweet proteins, proved not decisive in the localization of the main interaction points of monellin with its receptor. Accordingly, we resorted to an unbiased approach to restrict the search of likely areas of interaction on the surface of a typical sweet protein. It has been recently shown that an accurate survey of the surface of proteins by appropriate paramagnetic probes may locate interaction points on protein surface. Here we report the survey of the surface of MNEI, a single chain monellin, by means of a paramagnetic probe, and a direct assessment of bound water based on an application of ePHOGSY, an NMR experiment that is ideally suited to detect interactions of small ligands to a protein. Detailed surface mapping reveals the presence, on the surface of MNEI, of interaction points that include residues previously predicted by ELISA tests and by mutagenesis. PMID:11468346

  15. PROBING THE NATURE OF THE HELIOSHEATH WITH THE NEUTRAL ATOM SPECTRA MEASURED BY IBEX IN THE VOYAGER 1 DIRECTION

    SciTech Connect

    Opher, M.; Prested, C.; McComas, D. J.; Schwadron, N. A.; Drake, J. F.

    2013-10-20

    We are able to show by comparing modeled energetic neutral atoms (ENAs) spectra to those measured by Interstellar Boundary Explorer (IBEX) that the models along the Voyager 1 (V1) trajectory that best agree with the low energy IBEX data include extra heating due to ram and magnetic energy in the quasi-stagnation region or a kappa ion distribution (with κ = 2.0) in the outer heliosheath. The model explored is the multi-ion, multi-fluid (MI-MF) which treats the pick-up ions and the thermal ion fluids with separate Maxwellian distributions. These effects are included ad hoc in the modeled ENA since they are not present in the model. These results indicate that the low energy spectra of ENAs as measured by IBEX is sensitive to the physical nature of the heliosheath and to effects not traditionally present in current global models. Therefore, by comparing the low energy ENA spectra to models, we can potentially probe the heliosheath in locations beyond those probed by V1 and Voyager 2 (V2)

  16. Pyrenyl Derivative with a Four-Atom Linker That Can Probe the Local Polarity of Pyrene-Labeled Macromolecules.

    PubMed

    Farhangi, Shiva; Duhamel, Jean

    2016-02-01

    The fluorescent probe 1-pyrenemethoxyethanol (PyMeEGOH) was designed to replace commercially available 1-pyrenebutanol (PyButOH) as an alternative fluorescent label to probe the internal dynamics and interior polarity of macromolecules by steady-state and time-resolved fluorescence. While excimer formation and sensitivity to solvent polarity are two well-recognized properties of pyrene, much less known is that these properties are often mutually exclusive when a 1-pyrenebutyl derivative is used to prepare pyrene-labeled macromolecules (PyLMs). As the sensitivity of pyrene to solvent polarity is a result of its symmetry, attaching a butyl group to pyrene breaks the symmetry of pyrene, so that the 1-pyrenebutyl derivatives are much less sensitive to the polarity of their environment compared to unmodified pyrene. This report demonstrates that replacement of a methylene group in the β-position of PyButOH by an oxygen atom, such as in PyMeEGOH, restores the sensitivity of this pyrene derivative to the polarity of its local environment to the same level as that of molecular pyrene without impeding pyrene excimer formation upon incorporation into PyLMs. PMID:26734846

  17. Native Escherichia coli OmpF Porin Surfaces Probed by Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Schabert, Frank A.; Henn, Christian; Engel, Andreas

    1995-04-01

    Topographs of two dimensional porin OmpF crystals reconstituted in the presence of lipids were recorded in solution by atomic force microscopy (AFM) to a lateral resolution of 10 angstroms and a vertical resolution of 1 angstrom. Protein-protein interactions were demonstrated on the basis of the AFM results and earlier crystallographic findings. To assess protein-lipid interactions, the bilayer was modeled with kinked lipids by fitting the head groups to contours determined with AFM. Finally, two conformations of the extracellular porin surface were detected at forces of 0.1 nanonewton, demonstrating the potential of AFM to monitor conformational changes with high resolution.

  18. Molecular Beam Studies of Hot Atom Chemical Reactions: Reactive Scattering of Energetic Deuterium Atoms

    DOE R&D Accomplishments Database

    Continetti, R. E.; Balko, B. A.; Lee, Y. T.

    1989-02-01

    A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H{sub 2} -> DH + H and the substitution reaction D + C{sub 2}H{sub 2} -> C{sub 2}HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible.

  19. Molecular beam studies of hot atom chemical reactions: Reactive scattering of energetic deuterium atoms

    SciTech Connect

    Continetti, R.E.; Balko, B.A.; Lee, Y.T.

    1989-02-01

    A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H/sub 2/ /minus/> DH + H and the substitution reaction D + C/sub 2/H/sub 2/ /minus/> C/sub 2/HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible. 18 refs., 9 figs.

  20. New BODIPY lipid probes for fluorescence studies of membranes

    PubMed Central

    Momsen, Maureen M.; Brockman, Howard L.; Brown, Rhoderick E.; Molotkovsky, Julian G.

    2007-01-01

    Many fluorescent lipid probes tend to loop back to the membrane interface when attached to a lipid acyl chain rather than embedding deeply into the bilayer. To achieve maximum embedding of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) fluorophore into the bilayer apolar region, a series of sn-2 acyl-labeled phosphatidylcholines was synthesized bearing 4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene-8-yl (Me4-BODIPY-8) at the end of C3-, C5-, C7-, or C9-acyl. A strategy was used of symmetrically dispersing the methyl groups at BODIPY ring positions 1, 3, 5, and 7 to decrease fluorophore polarity. Iodide quenching of the phosphatidylcholine probes in bilayer vesicles confirmed that the Me4-BODIPY-8 fluorophore was embedded in the bilayer. Parallax analysis of Me4-BODIPY-8 fluorescence quenching by phosphatidylcholines containing iodide at different positions along the sn-2 acyl chain indicated that the penetration depth of Me4-BODIPY-8 into the bilayer was determined by the length of the linking acyl chain. Evaluation using monolayers showed minimal perturbation of <10 mol% probe in fluid-phase and cholesterol-enriched phosphatidylcholine. Spectral characterization in monolayers and bilayers confirmed the retention of many features of other BODIPY derivatives (i.e., absorption and emission wavelength maxima near 498 nm and ∼506−515 nm) but also showed the absence of the 620−630 nm peak associated with BODIPY dimer fluorescence and the presence of a 570 nm emission shoulder at high Me4-BODIPY-8 surface concentrations. We conclude that the new probes should have versatile utility in membrane studies, especially when precise location of the reporter group is needed.—Boldyrev, I. A., X. Zhai, M. M. Momsen, H. L. Brockman, R. E. Brown, and J. G. Molotkovsky. New BODIPY lipid probes for fluorescence studies of membranes. PMID:17416929

  1. Atomic and Molecular Data for Interstellar Studies: A Status Report

    NASA Technical Reports Server (NTRS)

    Federman, Steven R.; Cardelli, Jason A.

    1996-01-01

    Most interstellar species have a large fraction of their electronic transitions at far ultraviolet wavelengths. Observations at these wavelengths reveal spectra rich in absorption lines seen against the continuum of a background source, such as a hot star in our Galaxy, a supernova in a nearby galaxy, or even a bright nucleus in an active galaxy. Most of the observations continue to be made with space-borne instruments, but recent work includes measurements of extragalactic material at large redshifts obtained at high resolution with large ground-based telescopes (e.g., the Keck Telescope). The combination of precise experimental oscillator strengths, large-scale computations, and astronomical spectra with high signal-to-noise ratios are yielding a set of self-consistent-values that span a range in strength in excess of 100 for more and more species. The large range is important for studies involving the different environments probed by the various background sources. This review highlights recent work on the atomic species. Si II, S I, and Fe II, and on the molecules, CO and C2.

  2. Indium clustering in a-plane InGaN quantum wells as evidenced by atom probe tomography

    SciTech Connect

    Tang, Fengzai; Zhu, Tongtong; Oehler, Fabrice; Fu, Wai Yuen; Griffiths, James T.; Massabuau, Fabien C.-P.; Kappers, Menno J.; Oliver, Rachel A.; Martin, Tomas L.; Bagot, Paul A. J.; Moody, Michael P.

    2015-02-16

    Atom probe tomography (APT) has been used to characterize the distribution of In atoms within non-polar a-plane InGaN quantum wells (QWs) grown on a GaN pseudo-substrate produced using epitaxial lateral overgrowth. Application of the focused ion beam microscope enabled APT needles to be prepared from the low defect density regions of the grown sample. A complementary analysis was also undertaken on QWs having comparable In contents grown on polar c-plane sample pseudo-substrates. Both frequency distribution and modified nearest neighbor analyses indicate a statistically non-randomized In distribution in the a-plane QWs, but a random distribution in the c-plane QWs. This work not only provides insights into the structure of non-polar a-plane QWs but also shows that APT is capable of detecting as-grown nanoscale clustering in InGaN and thus validates the reliability of earlier APT analyses of the In distribution in c-plane InGaN QWs which show no such clustering.

  3. Micro-wilhelmy and related liquid property measurements using constant-diameter nanoneedle-tipped atomic force microscope probes.

    PubMed

    Yazdanpanah, Mehdi M; Hosseini, Mahdi; Pabba, Santosh; Berry, Scott M; Dobrokhotov, Vladimir V; Safir, Abdelilah; Keynton, Robert S; Cohn, Robert W

    2008-12-01

    The micro-Wilhelmy method is a well-established method of determining surface tension by measuring the force of withdrawing a tens of microns to millimeters in diameter cylindrical wire or fiber from a liquid. A comparison of insertion force to retraction force can also be used to determine the contact angle with the fiber. Given the limited availability of atomic force microscope (AFM) probes that have long constant diameter tips, force-distance (F-D) curves using probes with standard tapered tips have been difficult to relate to surface tension. In this report, constant diameter metal alloy nanowires (referred to as "nanoneedles") between 7.2 and 67 microm in length and 108 and 1006 nm in diameter were grown on AFM probes. F-D and Q damping AFM measurements of wetting and drag forces made with the probes were compared against standard macroscopic models of these forces on slender cylinders to estimate surface tension, contact angle, meniscus height, evaporation rate, and viscosity. The surface tensions for several low molecular weight liquids that were measured with these probes were between -4.2% and +8.3% of standard reported values. Also, the F-D curves show well-defined stair-step events on insertion and retraction from partial wetting liquids, compared to the continuously growing attractive force of standard tapered AFM probe tips. In the AFM used, the stair-step feature in F-D curves was repeatably monitored for at least 0.5 h (depending on the volatility of the liquid), and this feature was then used to evaluate evaporation rates (as low as 0.30 nm/s) through changes in the surface height of the liquid. A nanoneedle with a step change in diameter at a known distance from its end produced two steps in the F-D curve from which the meniscus height was determined. The step features enable meniscus height to be determined from distance between the steps, as an alternative to calculating the height corresponding to the AFM measured values of surface tension and

  4. Local Probe into the Atomic Structure of Metallic Glasses using EELS

    SciTech Connect

    Alamgir, F.M.; Ito, Y. Schwarz, R.B.

    1999-11-30

    Electron energy loss spectroscopy (EELS) is used to extract information on the topological arrangement of atoms around Pd in the bulk-glass-forming Pd{sub 60}Ni{sub 20}P{sub 20}. It is found that the environment around Pd in the glass is only a slight modification of the Pd crystalline structure. However, the modification is enough to allow this alloy to form a glass in bulk. In examining the differences between the structure of crystalline Pd and glassy Pd{sub 60}Ni{sub 20}P{sub 20} it is concluded that incorporation of Ni and P into the structure frustrates the structure enough that glass formation becomes easy.

  5. 158 micrometers (CII) mapping of NGC 6946: Probing the atomic medium

    NASA Technical Reports Server (NTRS)

    Madden, S. C.; Geis, N.; Genzel, R.; Herrmann, F.; Jackson, J. M.; Poglitsch, A.; Stacey, G. J.; Townes, C. H.

    1992-01-01

    The strong 158 micrometers (C2) cooling line of the NGC 6946 galaxy is investigated. The data was acquired with a far infrared imaging Fabry-Perot interferometer with 55 minutes resolution. About 1 percent of the total far infrared luminosity of the galaxy is analyzed. The (C2) emission comes from a mizture of components of interstellar gas. The brightest emission is associated with the nucleus, a second component traces the spiral arms and the largest star forming/H2 regions contained within them, and a third extended component of low brightness can be detected at least 12 kpc from the nucleus. The nuclear and spiral arm components are most likely associated with dense photon dominated regions at molecular cloud surfaces that are exposed to ultraviolet radiation produced by young massive stars. The (C2) emission is analyzed and the cooling rate in the atomic medium is consistent with photoelectric heating by diffuse ultraviolet radiation.

  6. Nanoscale mechanical probing of supported lipid bilayers with atomic force microscopy.

    PubMed

    Das, Chinmay; Sheikh, Khizar H; Olmsted, Peter D; Connell, Simon D

    2010-10-01

    We present theory and experiments for the force-distance curve F(z(0)) of an atomic force microscope (AFM) tip (radius R) indenting a supported fluid bilayer (thickness 2d). For realistic conditions the force is dominated by the area compressibility modulus κ(A) of the bilayer and, to an excellent approximation, given by F=πκ(A)Rz(0)(2)/(2d-z(0))(2). The experimental AFM force curves from coexisting liquid ordered and liquid disordered domains in three-component lipid bilayers are well described by our model, which provides κ(A) in agreement with literature values. The liquid ordered phase has a yieldlike response that we model as due to the breaking of hydrogen bonds. PMID:21230326

  7. Characterization of ion-irradiation-induced nanodot structures on InP surfaces by atom probe tomography.

    PubMed

    Gnaser, Hubert; Radny, Tobias

    2015-12-01

    Surfaces of InP were bombarded by 1.9 keV Ar(+) ions under normal incidence. The total accumulated ion fluence the samples were exposed to was varied from 1 × 10(17) cm(-2) to 3 × 10(18)cm(-2) and ion flux densities f of (0.4-2) × 10(14) cm(-2) s(-1) were used. Nanodot structures were found to evolve on the surface from these ion irradiations, their dimensions however, depend on the specific bombardment conditions. The resulting surface morphology was examined by atomic force microscopy (AFM). As a function of ion fluence, the mean radius, height, and spacing of the dots can be fitted by power-law dependences. In order to determine possible local compositional changes in these nanostructures induced by ion impact, selected samples were prepared for atom probe tomography (APT). The results indicate that by APT the composition of individual InP nanodots evolving under ion bombardment could be examined with atomic spatial resolution. At the InP surface, the values of the In/P concentration ratio are distinctly higher over a distance of ~1 nm and amount to 1.3-1.8. However, several aspects critical for the analyses were identified: (i) because of the small dimensions of these nanostructures a successful tip preparation proved very challenging. (ii) The elemental compositions obtained from APT were found to be influenced pronouncedly by the laser pulse energy; typically, low energies result in the correct stoichiometry whereas high ones lead to an inhomogeneous evaporation from the tips and deviations from the nominal composition. (iii) Depending again on the laser energy, a prolific emission of Pn cluster ions was observed, with n ≤ 11. PMID:25980895

  8. Damage behavior and atomic migration in MgAl2O4 under an 80 keV scanning focused probe in a STEM.

    PubMed

    Zhu, Guo-zhen; Botton, Gianluigi A

    2015-01-01

    With the dramatic improvement in the spatial resolution of scanning transmission electron microscopes over the past few decades, the tolerance of a specimen to the high-energy electron beam becomes the limiting factor for the quality of images and spectra obtained. Therefore, a deep understanding of the beam irradiation processes is crucial to extend the applications of electron microscopy. In this paper, we report the structural evolution of a selected oxide, MgAl2O4, under an 80 keV focused electron probe so that the beam irradiation process is not dominated by the knock-on mechanism. The formation of peroxyl bonds and the assisted atomic migration were studied using imaging and electron energy-loss spectroscopic techniques. PMID:25043440

  9. Correlated high-resolution x-ray diffraction photoluminescence and atom probe tomography analysis of continuous and discontinuous InxGa1-xN quantum wells

    DOE PAGESBeta

    Ren, Xiaochen; Riley, James R.; Koleske, Daniel; Lauhon, Lincoln J.

    2015-07-14

    In this study, atom probe tomography (APT) is used to characterize the influence of hydrogen dosing duringGaN barrier growth on the indium distribution of InxGa1-xN quantum wells, and correlatedmicro-photoluminescence is used to measure changes in the emission spectrum and efficiency. We found that relative to the control growth, hydrogen dosing leads to a 50% increase in emission intensity arising from discontinuous quantum wells that are narrower, of lower indium content, and with more abrupt interfaces. Additionally, simulations of carrier distributions based on APT composition profiles indicate that the greater carrier confinement leads to an increased radiative recombination rate. Furthermore, APTmore » analysis of quantum well profiles enables refinement of x-ray diffractionanalysis for more accurate nondestructive measurements of composition.« less

  10. Ink-on-probe hydrodynamics in atomic force microscope deposition of liquid inks.

    PubMed

    O'Connell, Cathal D; Higgins, Michael J; Sullivan, Ryan P; Moulton, Simon E; Wallace, Gordon G

    2014-09-24

    The controlled deposition of attolitre volumes of liquids may engender novel applications such as soft, nano-tailored cell-material interfaces, multi-plexed nano-arrays for high throughput screening of biomolecular interactions, and localized delivery of reagents to reactions confined at the nano-scale. Although the deposition of small organic molecules from an AFM tip, known as dip-pen nanolithography (DPN), is being continually refined, AFM deposition of liquid inks is not well understood, and is often fraught with inconsistent deposition rates. In this work, the variation in feature-size over long term printing experiments for four model inks of varying viscosity is examined. A hierarchy of recurring phenomena is uncovered and there are attributed to ink movement and reorganisation along the cantilever itself. Simple analytical approaches to model these effects, as well as a method to gauge the degree of ink loading using the cantilever resonance frequency, are described. In light of the conclusions, the various parameters which need to be controlled in order to achieve uniform printing are dicussed. This work has implications for the nanopatterning of viscous liquids and hydrogels, encompassing ink development, the design of probes and printing protocols. PMID:24861023

  11. Experimental studies on effervescent atomizers with wide spray angles

    NASA Astrophysics Data System (ADS)

    Whitlow, J. D.; Lefebvre, A. H.; Rollbuhler, R. J.

    1993-09-01

    An experimental investigation was conducted to examine the operating and spray characteristics of two internal-mixing twin-fluid atomizers that were designed to produce effervescent atomization at low air/liquid mass ratios (ALR's). These two experimental atomizers ejected the two phase flow so as to produce a wide spray angle. One atomizer was a plain orifice design that used a four-hole exit orifice which divided and turned the two phase flow just prior to ejection. The other atomizer, called the conical sheet atomizer, ejected the two phase flow through an annular passage in such a way as to form a hollow cone spray. The atomizer operating parameters varied during this investigation were the air/liquid mass ratio, atomizer operating pressure, and, in the case of the conical sheet atomizer, the exit gap width. Studies of spray characteristics included measurements of the spray Sauter mean diameter (SMD), drop size distribution, and, for the conical sheet atomizer, circumferential distribution of the liquid mass within the spray. For both atomizers it was found that SMD decreases with an increase in either ALR or operating pressure. The effect of ALR on SMD diminishes as the value of ALR increases. For the conical sheet atomizer, when operating at low values of pressure and ALR, SMD increases with increase in gap width, but the influence of gap width on SMD diminishes with an increase in either pressure or ALR. At the highest operating pressure of the conical sheet atomizer (552 kPa), SMD is independent of gap width at all ALR's. For both atomizers, changes in operating pressure and ALR have little effect on the distribution of drop sizes in the spray.

  12. European Space Agency studies of the solar probe

    NASA Technical Reports Server (NTRS)

    Roxburgh, I. W.

    1978-01-01

    The feasibility and scientific objectives of a solar probe were studied by a Mission Definition Group in 1975 and 1976. The orbit analysis program was developed and an extended study of the orbit analysis was done in 1977. The results of these studies are in the Report of the Mission Definition Study (1976) and an E.S.O.C. report (1978), and the reader is referred to these sources for greater details. In this report, only brief discussion on mission concept and objectives, satellite design, orbit, orbit analysis, are presented.

  13. Probing the nanoadhesion of Streptococcus sanguinis to titanium implant surfaces by atomic force microscopy.

    PubMed

    Aguayo, Sebastian; Donos, Nikolaos; Spratt, Dave; Bozec, Laurent

    2016-01-01

    As titanium (Ti) continues to be utilized in great extent for the fabrication of artificial implants, it is important to understand the crucial bacterium-Ti interaction occurring during the initial phases of biofilm formation. By employing a single-cell force spectroscopy technique, the nanoadhesive interactions between the early-colonizing Streptococcus sanguinis and a clinically analogous smooth Ti substrate were explored. Mean adhesion forces between S. sanguinis and Ti were found to be 0.32±0.00, 1.07±0.06, and 4.85±0.56 nN for 0, 1, and 60 seconds contact times, respectively; while adhesion work values were reported at 19.28±2.38, 104.60±7.02, and 1,317.26±197.69 aJ for 0, 1, and 60 seconds, respectively. At 60 seconds surface delays, minor-rupture events were modeled with the worm-like chain model yielding an average contour length of 668±12 nm. The mean force for S. sanguinis minor-detachment events was 1.84±0.64 nN, and Poisson analysis decoupled this value into a short-range force component of -1.60±0.34 nN and a long-range force component of -0.55±0.47 nN. Furthermore, a solution of 2 mg/mL chlorhexidine was found to increase adhesion between the bacterial probe and substrate. Overall, single-cell force spectroscopy of living S. sanguinis cells proved to be a reliable way to characterize early-bacterial adhesion onto machined Ti implant surfaces at the nanoscale. PMID:27103802

  14. Probing the nanoadhesion of Streptococcus sanguinis to titanium implant surfaces by atomic force microscopy

    PubMed Central

    Aguayo, Sebastian; Donos, Nikolaos; Spratt, Dave; Bozec, Laurent

    2016-01-01

    As titanium (Ti) continues to be utilized in great extent for the fabrication of artificial implants, it is important to understand the crucial bacterium–Ti interaction occurring during the initial phases of biofilm formation. By employing a single-cell force spectroscopy technique, the nanoadhesive interactions between the early-colonizing Streptococcus sanguinis and a clinically analogous smooth Ti substrate were explored. Mean adhesion forces between S. sanguinis and Ti were found to be 0.32±0.00, 1.07±0.06, and 4.85±0.56 nN for 0, 1, and 60 seconds contact times, respectively; while adhesion work values were reported at 19.28±2.38, 104.60±7.02, and 1,317.26±197.69 aJ for 0, 1, and 60 seconds, respectively. At 60 seconds surface delays, minor-rupture events were modeled with the worm-like chain model yielding an average contour length of 668±12 nm. The mean force for S. sanguinis minor-detachment events was 1.84±0.64 nN, and Poisson analysis decoupled this value into a short-range force component of −1.60±0.34 nN and a long-range force component of −0.55±0.47 nN. Furthermore, a solution of 2 mg/mL chlorhexidine was found to increase adhesion between the bacterial probe and substrate. Overall, single-cell force spectroscopy of living S. sanguinis cells proved to be a reliable way to characterize early-bacterial adhesion onto machined Ti implant surfaces at the nanoscale. PMID:27103802

  15. Studies of Interstellar and Circumstellar Magnetic Field with Aligned Atoms

    NASA Astrophysics Data System (ADS)

    Lazarian, A.; Yan, H.

    2004-12-01

    Population of levels of the hyperfine and fine split ground state of an atom is affected by radiative transitions induced by anisotropic radiation flux. Such aligned atoms precess in the external magnetic field and this affects properties of polarized radiation arising from both scattering and absorption by atoms. As the result the degree of light polarization depends on the direction of the magnetic field. This provides a new tool for studies of astrophysical magnetic fields using optical and UV polarimetry. We provide calculations for several atoms and ions that can be used to study magnetic fields in interplanetary medium, interstellar medius, circumstellar regions and quasars.

  16. Mechanical properties of poly(dimethylsiloxane)-block-poly(2-methyloxazoline) polymersomes probed by atomic force microscopy.

    PubMed

    Jaskiewicz, Karmena; Makowski, Marcin; Kappl, Michael; Landfester, Katharina; Kroeger, Anja

    2012-08-28

    Poly(dimethylsiloxane)-block-poly(2-methyloxazoline) (PDMS-b-PMOXA) vesicles were characterized by a combination of dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), and atomic force microscopy imaging and force spectroscopy (AFM). From DLS data, a hydrodynamic radius of ~150 nm was determined, and cryo-TEM micrographs revealed a bilayer thickness of ~16 nm. In AFM experiments on a silicon wafer substrate, adsorption led to a stable spherical caplike conformation of the polymersomes, whereas on mica, adsorption resulted also in vesicle fusion and formation of bilayer patches or multilayer stacks. This indicates a delicate balance between the mechanical stability of PDMS-b-PMOXA polymersomes on one hand and the driving forces for spreading on the other. A Young's modulus of 17 ± 11 MPa and a bending modulus of 7 ± 5 × 10(-18) J were derived from AFM force spectroscopy measurements. Therefore, the elastic response of the PDMS-b-PMOXA polymersomes to external stimuli is much closer to that of lipid vesicles compared to other types of polymersomes, such as polystyrene-block-poly(acrylic acid) (PS-b-PAA). PMID:22860888

  17. Viscous nature of the bond between adhering bacteria and substratum surfaces probed by atomic force microscopy.

    PubMed

    Chen, Yun; van der Mei, Henny C; Busscher, Henk J; Norde, Willem

    2014-03-25

    Here we report on the viscous nature of the bond between adhering bacteria and a substratum surface. A tailor-made script was written for an atomic force microscope, that enabled a constant loading force of 1 or 5 nN to act for 30 s upon a bacterium compressed between a cantilever and a glass surface, while measuring its deformation. Time-dependent deformation was fitted to a one element Kelvin-Voigt analogue of the bond to yield a characteristic relaxation time and viscosity of the bond. Viscosities of streptococcal bonds were smaller (<20 kPa s) than those of staphylococcal bonds (>31 kPa s). Since staphylococci are relatively rich in extracellular polymeric substances, it can be inferred that the presence of extracellular polymeric substances yields the major contribution to the viscous response. The viscous nature of the bond between adhering bacteria and substratum surfaces provides the bacteria with more time to respond and protect themselves against external stresses. PMID:24588204

  18. Interaction forces between talc and pitch probed by atomic force microscopy.

    PubMed

    Wallqvist, Viveca; Claesson, Per M; Swerin, Agne; Schoelkopf, Joachim; Gane, Patrick A C

    2007-04-10

    Colloidal wood resin components present in pulp are collectively called "pitch". The presence of pitch may cause severe problems due to deposits in and on the paper machine. There is thus a need for controlling pitch aggregation and adsorption. To be able to develop more efficient pitch control systems, one needs to develop the understanding of pitch-pitch interactions and of the interactions between pitch and other materials. With this general goal in mind, we present methods for preparing geometrically well-defined pitch particles attached to atomic force microscopy tips. This has enabled us to investigate the interactions between pitch and talc, an additive commonly used for pitch control. We have used model pitch particles consisting of one component only (abietic acid), a mixture of components (collophonium), and particles prepared from real pitch deposits. We show that the forces acting between pitch and talc are attractive and, once the initial approach is made, exert this attraction out to large distances of separation. We present evidence that the formation of bridging air bubbles or cavities is responsible for this interaction. PMID:17352501

  19. 158 micron forbidden C II mapping of NGC 6946 - Probing the atomic medium

    NASA Technical Reports Server (NTRS)

    Madden, S. C.; Geis, N.; Genzel, R.; Herrmann, F.; Jackson, J.; Poglitsch, A.; Stacey, G. J.; Townes, C. H.

    1993-01-01

    A well-sampled map (23 x 17 kpc) of the strong 158 micron forbidden C II cooling line in the Scd galaxy NGC 6946 at 55 arcsec resolution is presented which was taken with the MPE/UCB Far-infrared Imaging Fabry-Perot Interferometer (FIFI) in the Kuiper Airborne Observatory. It is concluded that the line emission in NGC 6946 is present in three spatially distinct components including nucleus, spiral arms, and extended region. An extended emission region is a source of most of the forbidden C II luminosity in NGC 6946. The 1 arcmin nuclear component has a line luminosity of 1.5 x 10 exp 7 solar luminosity and contributes 0.15 percent of the galaxy's total FIR luminosity. An extended component of forbidden C II emission is found to exist past the molecular extent of the galaxy and to be present to at least the full dimensions of the map. This component is attributed to a mixture of neutral and atomic clouds.

  20. Chemical probing of RNA with the hydroxyl radical at single-atom resolution

    PubMed Central

    Ingle, Shakti; Azad, Robert N.; Jain, Swapan S.; Tullius, Thomas D.

    2014-01-01

    While hydroxyl radical cleavage is widely used to map RNA tertiary structure, lack of mechanistic understanding of strand break formation limits the degree of structural insight that can be obtained from this experiment. Here, we determine how individual ribose hydrogens of sarcin/ricin loop RNA participate in strand cleavage. We find that substituting deuterium for hydrogen at a ribose 5′-carbon produces a kinetic isotope effect on cleavage; the major cleavage product is an RNA strand terminated by a 5′-aldehyde. We conclude that hydroxyl radical abstracts a 5′-hydrogen atom, leading to RNA strand cleavage. We used this approach to obtain structural information for a GUA base triple, a common tertiary structural feature of RNA. Cleavage at U exhibits a large 5′ deuterium kinetic isotope effect, a potential signature of a base triple. Others had noted a ribose-phosphate hydrogen bond involving the G 2′-OH and the U phosphate of the GUA triple, and suggested that this hydrogen bond contributes to backbone rigidity. Substituting deoxyguanosine for G, to eliminate this hydrogen bond, results in a substantial decrease in cleavage at G and U of the triple. We conclude that this hydrogen bond is a linchpin of backbone structure around the triple. PMID:25313156

  1. Molecular self-assembly of conducting polymer by Conducting Probe Technique in Atomic Force Microscope

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shin-ichi; Ogawa, Kazufumi

    2007-04-01

    A polypyrrole derivative monolayer was investigated for the application as a wire. First, a pyrrole derivative monolayer was prepared by chemically adsorbing (self-assembling) monolayer (CAM) of 6-pyrrolylhexyl-12,12,12-trichloro-12- siladodecanoate (PEN) on a glass substrate. Then, the monolayer was polymerized in the presence of pure water by electrooxidation. The surface characterization of the molecular interaction was investigated by measuring the properties of CAMs attached to the glass substrate in the lateral direction. We formed PEN having polypyrrolyl groups, using Pt-patterned electrodes on glass surfaces and measured the conductance under a small bias voltage, using a conductive cantilever of atomic force microscopy (AFM). The polypyrrole derivative monolayer thus synthesized was covalently bonded to the glass substrate and showed conductivity as high as 3.05..103 S/cm after electro-oxidized. The method of preparing a conductive polymer monolayer by the combining chemical adsorption and electro-oxidation leads to a lot molecular wire to perpendicular to the Pt electrodes, and it is one of the key technologies for molecular devices.

  2. Outer planet entry probe system study. Volume 1: Summary

    NASA Technical Reports Server (NTRS)

    1972-01-01

    General mission considerations and science prospectus, which are of a general nature that applies to several or all planetary applications, are presented. Five probe systems are defined: nominal Jupiter probe system, and Jupiter probe-dedicated alternative probe system, Jupiter spacecraft radiation-compatible alternative probe system, Saturn probe system, and Saturn probe applicability for Uranus. Parametric analysis is summarized for mission analysis of a general nature, and then for specific missions to Jupiter, Saturn, Uranus, and Neptune. The program is also discussed from the hardware availability viewpoint and the aspect of commonality.

  3. Multifrequency scanning probe microscopy study of nanodiamond agglomerates

    NASA Astrophysics Data System (ADS)

    Aravind, Vasudeva; Lippold, Stephen; Li, Qian; Strelcov, Evgheny; Okatan, Baris; Legum, Benjamin; Kalinin, Sergei; Clarion University Team; Oak Ridge National Laboratory Team

    Due to their rich surface chemistry and excellent mechanical properties and non-toxic nature, nanodiamond particles have found applications such as biomedicine, tribology and lubrication, targeted drug delivery systems, tissue scaffolds and surgical implants. Although single nanodiamond particles have diameters about 4-5nm, they tend to form agglomerates. While these agglomerates can be useful for some purposes, many applications of nanodiamonds require single particle, disaggregated nanodiamonds. This work is oriented towards studying forces and interactions that contribute to agglomeration in nanodiamonds. In this work, using multifrequency scanning probe microscopy techniques, we show that agglomerate sizes can vary between 50-100nm in raw nanodiamonds. Extremeties of particles and Interfaces between agglomerates show dissipative forces with scanning probe microscope tip, indicating agglomerates could act as points of increased adhesion, thus reducing lubricating efficiency when nanodiamonds are used as lubricant additives. This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

  4. THz pump-THz probe study of electrostatically gated graphene

    NASA Astrophysics Data System (ADS)

    Zhang, Jingdi; Liu, Mengkun; Wagner, Martin; Basov, D. N.; Averitt, Richard D.

    2015-03-01

    We investigate ultrafast carrier dynamics in graphene using THz-pump THz-probe spectroscopy. In contrast to recent studies using optical excitation, THz excitation exclusively initiates intra-band transitions, resulting in an increase in the carrier scattering rate. The corresponding transient peak of the transmitted probe signal scales linearly with the E-field of the incident THz pump pulse. Further, the decay time of the excited carriers is independent of the gating voltage. As the Fermi level is tuned toward the charge neutral point (CNP) by varying the electrostatic gate voltage, the induced increase in transmission is strongly suppressed. We believe that the low density of states near the CNP is responsible for this suppression. Work supported by DOE-BES. RDA and JZ also with Boston University. ML also with Stony Brook University.

  5. Atomic jump frequencies in intermetallic compounds studied using perturbed angular correlation of gamma rays

    NASA Astrophysics Data System (ADS)

    Newhouse, Randal Leslie

    Atomic jump frequencies were determined in a variety of intermetallic compounds through analysis of nuclear relaxation of spectra measured using the nuclear hyperfine technique, perturbed angular correlation (PAC) of gamma rays. Observed at higher temperatures, this relaxation is attributed to fluctuations in the orientation or magnitude of electric field gradients (EFG) at nuclei of 111In/Cd probe atoms as the atoms make diffusive jumps. Jump frequencies were obtained by fitting dynamically relaxed PAC spectra using either an empirical relaxation function or using ab initio relaxation models created using the program PolyPacFit. Jump frequency activation enthalpies were determined from measurements over a range of temperatures. Diffusion was studied in the following systems: 1) Pseudo-binary alloys having the L12 crystal structure such as In3(La1-xPrx). The goal was to see how jump frequencies were affected by random disorder. 2) The family of layered phases, LanCoIn3n+2 ( n=0,1,2,3…∞). The goal was to see how jump frequencies varied with the spacing of Co layers, which were found to block diffusion. 3) Phases having the FeGa3 structure. The goal was to analyze dynamical relaxation for probe atoms having multiple inequivalent jump vectors. 4) Phases having the tetragonal Al4Ba structure. The goal was to search for effects in the PAC spectra caused by fluctuations in magnitudes of EFGs without fluctuations in orientations. Ab initio relaxation models were developed to simulate and fit dynamical relaxation for PAC spectra of FeGa3, and several phases with the Al4Ba structure in order to determine underlying microscopic jump frequencies. In the course of this work, site preferences also were observed for 111In/Cd probe atoms in several FeGa 3 and Al4Ba phases.

  6. Reassessing critiques of the independent probe method for studying inhibition.

    PubMed

    Huddleston, Ean; Anderson, Michael C

    2012-09-01

    Inhibitory processes have been proposed to play an important role in resolving interference during retrieval (M. C. Anderson, 2003; M. C. Anderson & Spellman, 1995). Supporting this view, retrieval induces a negative aftereffect on competing items known as retrieval-induced forgetting (M. C. Anderson, Bjork, & Bjork, 1994). Retrieval-induced forgetting often generalizes to novel cues used to test the forgotten items, and this cue independence is considered diagnostic of inhibition. This interpretation of cue independence assumes, however, that these novel cues (i.e., independent probes) are truly independent of the original cues. Challenging this assumption, Camp, Pecher, Schmidt, and Zeelenberg (2009) reported that extralist cuing test performance can be influenced by increasing the accessibility of other nonpresented cues. Here we consider this evidence for nonindependence and the conditions under which it occurs. We present two experiments demonstrating that this cue enhancement effect arises exclusively whenever independent probes have uncontrolled semantic relationships to the study cues of the sort that are specifically proscribed by the method--relationships not at all detected by association norms. When such relationships are controlled, as they are in many studies of inhibition, cue enhancement effects disappear. These findings highlight the importance of carefully controlling probe-cue relatedness in research on cue-independent forgetting and suggest that cue independence is diagnostic of inhibition. PMID:22329790

  7. Laser Methods in the Study of Nuclei, Atoms and Molecules

    NASA Astrophysics Data System (ADS)

    Inamura, Takashi T.

    2005-01-01

    The VIth International Workshop on Application of Lasers in Atomic Nuclei Research was held at Adam Mickiewicz University, Poznan in Poland from May 24 to 27, 2004. Its title this year was "Laser methods in the study of nuclei, atoms and molecules". Some topics are reviewed from a viewpoint of the atomic physics contribution to nuclear physics and its applications. It is suggested how this meeting should be organized in the future by taking the new geopolitics into account.

  8. Reaction studies of hot silicon, germanium and carbon atoms

    SciTech Connect

    Gaspar, P.P.

    1990-11-01

    The goal of this project was to increase the authors understanding of the interplay between the kinetic and electronic energy of free atoms and their chemical reactivity by answering the following questions: (1) what is the chemistry of high-energy carbon silicon and germanium atoms recoiling from nuclear transformations; (2) how do the reactions of recoiling carbon, silicon and germanium atoms take place - what are the operative reaction mechanisms; (3) how does the reactivity of free carbon, silicon and germanium atoms vary with energy and electronic state, and what are the differences in the chemistry of these three isoelectronic atoms This research program consisted of a coordinated set of experiments capable of achieving these goals by defining the structures, the kinetic and internal energy, and the charge states of the intermediates formed in the gas-phase reactions of recoiling silicon and germanium atoms with silane, germane, and unsaturated organic molecules, and of recoiling carbon atoms with aromatic molecules. The reactions of high energy silicon, germanium, and carbon atoms created by nuclear recoil were studied with substrates chosen so that their products illuminated the mechanism of the recoil reactions. Information about the energy and electronic state of the recoiling atoms at reaction was obtained from the variation in end product yields and the extent of decomposition and rearrangement of primary products (usually reactive intermediates) as a function of total pressure and the concentration of inert moderator molecules that remove kinetic energy from the recoiling atoms and can induce transitions between electronic spin states. 29 refs.

  9. A portable microevaporator for low temperature single atom studies by scanning tunneling and dynamic force microscopy

    NASA Astrophysics Data System (ADS)

    Rust, H.-P.; König, T.; Simon, G. H.; Nowicki, M.; Simic-Milosevic, V.; Thielsch, G.; Heyde, M.; Freund, H.-J.

    2009-11-01

    Here, we present a microevaporator setup for single adatom deposition at low temperature, which is a prerequisite for most single atom studies with scanning probe techniques. The construction of the microevaporator is based on the tungsten filament of a modified halogen lamp, covered with the required adsorbate. Very stable evaporation conditions were obtained, which were controlled by the filament current. The installation of this microevaporator on a manipulator enabled its transportation directly to the sample at the microscope kept at 5 K. In this way, the controlled deposition of Li onto Ag(100), Li, Pd, and Au onto MgO/Ag(001) as well as Au onto alumina/NiAl(110) at low temperature has been performed. The obtained images recorded after the deposition show the presence of single Li/Au atoms on the sample surfaces as a prove for successful dispersion of single atoms onto the sample surface using this technique.

  10. Preentry communications study. Outer planets atmospheric entry probe

    NASA Technical Reports Server (NTRS)

    Hinrichs, C. A.

    1976-01-01

    A pre-entry communications study is presented for a relay link between a Jupiter entry probe and a spacecraft in hyperbolic orbit. Two generic communications links of interest are described: a pre-entry link to a spun spacecraft antenna, and a pre-entry link to a despun spacecraft antenna. The propagation environment of Jupiter is defined. Although this is one of the least well known features of Jupiter, enough information exists to reasonably establish bounds on the performance of a communications link. Within these bounds, optimal carrier frequencies are defined. The next step is to identify optimal relative geometries between the probe and the spacecraft. Optimal trajectories are established for both spun and despun spacecraft antennas. Given the optimal carrier frequencies, and the optimal trajectories, the data carrying capacities of the pre-entry links are defined. The impact of incorporating pre-entry communications into a basic post entry probe is then assessed. This assessment covers the disciplines of thermal control, power source, mass properties and design layout. A conceptual design is developed of an electronically despun antenna for use on a Pioneer class of spacecraft.

  11. ATOMIC BEAM STUDIES IN THE RHIC H-JET POLARIMETER.

    SciTech Connect

    MAKDISI,Y.; ZELENSKI,A.; GRAHAM,D.; KOKHANOVSKI,S.; MAHLER,G.; NASS,A.; RITTER,J.; ZUBETS,V.; ET AL.

    2005-01-28

    The results of atomic beam production studies are presented. Improved cooling of the atoms before jet formation in the dissociator cold nozzle apparently reduces the atomic beam velocity spread and improves beam focusing conditions. A carefully designed sextupole separating (and focusing) magnet system takes advantage of the high brightness source. As a result a record beam intensity of a 12.4 {center_dot} 10{sup 16} atoms/s was obtained within 10 mm acceptance at the collision point. The results of the polarization dilution factor measurements (by the hydrogen molecules at the collision point) are also presented.

  12. X-ray pump optical probe cross-correlation study of GaAs

    SciTech Connect

    Durbin, S.M.; Clevenger, T.; Graber, T.; Henning, R.

    2012-09-10

    Ultrafast dynamics in atomic, molecular and condensed-matter systems are increasingly being studied using optical-pump, X-ray probe techniques where subpicosecond laser pulses excite the system and X-rays detect changes in absorption spectra and local atomic structure. New opportunities are appearing as a result of improved synchrotron capabilities and the advent of X-ray free-electron lasers. These source improvements also allow for the reverse measurement: X-ray pump followed by optical probe. We describe here how an X-ray pump beam transforms a thin GaAs specimen from a strong absorber into a nearly transparent window in less than 100 ps, for laser photon energies just above the bandgap. We find the opposite effect - X-ray induced optical opacity - for photon energies just below the bandgap. This raises interesting questions about the ultrafast many-body response of semiconductors to X-ray absorption, and provides a new approach for an X-ray/optical cross-correlator for synchrotron and X-ray free-electron laser applications.

  13. Pressure/temperature fluid cell apparatus for the neutron powder diffractometer instrument: Probing atomic structure in situ

    SciTech Connect

    Wang, Hsiu -Wen; Fanelli, Victor R.; Reiche, Helmut M.; Larson, Eric; Taylor, Mark A.; Xu, Hongwu; Zhu, Jinlong; Siewenie, Joan; Page, Katharine

    2014-12-01

    This contribution describes a new local structure compatible gas/liquid cell apparatus for probing disordered materials at high pressures and variable temperatures in the Neutron Powder Diffraction instrument at the Lujan Neutron Scattering Center, Los Alamos National Laboratory. The new sample environment offers choices for sample canister thickness and canister material type. Finite element modeling is utilized to establish maximum allowable working pressures of 414 MPa at 15 K and 121 MPa at 600 K. High quality atomic pair distribution function data extraction and modeling have been demonstrated for a calibration standard (Si powder) and for supercritical and subcritical CO2measurements. As a result, the new sample environment was designed to specifically target experimental studies of the local atomic structures involved in geologic CO2 sequestration, but will be equally applicable to a wide variety of energy applications, including sorption of fluids on nano/meso-porous solids, clathrate hydrate formation, catalysis, carbon capture, and H2 and natural gas uptake/storage.

  14. Nitrile and thiocyanate IR probes: Molecular dynamics simulation studies

    NASA Astrophysics Data System (ADS)

    Oh, Kwang-Im; Choi, Jun-Ho; Lee, Joo-Hyun; Han, Jae-Beom; Lee, Hochan; Cho, Minhaeng

    2008-04-01

    Nitrile- and thiocyanate-derivatized amino acids have been found to be useful IR probes for investigating their local electrostatic environments in proteins. To shed light on the CN stretch frequency shift and spectral lineshape change induced by interactions with hydrogen-bonding solvent molecules, we carried out both classical and quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulations for MeCN and MeSCN in water. These QM/MM and conventional force field MD simulation results were found to be inconsistent with the experimental results as well as with the high-level ab initio calculation results of MeCN-water and MeSCN-water potential energies. Thus, a new set of atomic partial charges of MeCN and MeSCN is obtained. By using the MD simulation trajectories and the electrostatic potential model recently developed, the CN and SCN stretching mode frequency trajectories were obtained and used to simulate the IR spectra. The C N frequency blueshifts of MeCN and MeSCN in water are estimated to be 9.0 and 1.9cm-1, respectively, in comparison with those of gas phase values. These values are found to be in reasonable agreement with the experimentally measured IR spectra of MeCN, MeSCN, β-cyano-L-alanine, and cyanylated cysteine in water and other polar solvents.

  15. [Connection of magnetic antisense probe with SK-Br-3 oncocyte mRNA nucleotide detected by high resolution atomic force microscope].

    PubMed

    Tan, Shude; Ouyang, Yu; Li, Xinyou; Wen, Ming; Li, Shaolin

    2011-06-01

    The present paper is aimed to detect superparamagnetic iron oxide labeled c-erbB2 oncogene antisense oligonucleotide probe (magnetic antisense probe) connected with SK-Br-3 oncocyte mRNA nucleotide by high resolution atomic force microscope (AFM). We transfected SK-Br-3 oncocyte with magnetic antisense probe, then observed the cells by AFM with high resolution and detected protein expression and magnetic resonance imagine (MRI). The high resolution AFM clearly showed the connection of the oligonucleotide remote end of magnetic antisense probe with the mRNA nucleotide of oncocyte. The expression of e-erbB2 protein in SK-Br3 cells were highly inhibited by using magnetic antisense probe. We then obtained the lowest signal to noise ratio (SNR) of SK-Br-3 oncocyte transfected with magnetic antisense probe by MRI (P<0.05). These experiments demonstrated that the high resolution AFM could be used to show the binding of magnetic antisense probe and SK-Br-3 mRNA of tumor cell nuclear. PMID:21774198

  16. Optimisation of sample preparation and analysis conditions for atom probe tomography characterisation of low concentration surface species

    NASA Astrophysics Data System (ADS)

    Douglas, J. O.; Bagot, P. A. J.; Johnson, B. C.; Jamieson, D. N.; Moody, M. P.

    2016-08-01

    The practicalities for atom probe tomography (APT) analysis of near-surface chemistry, particularly the distribution of low concentration elements, are presented in detail. Specifically, the challenges of surface analysis using APT are described through the characterisation of near-surface implantation profiles of low concentration phosphorus into single crystal silicon. This material system was chosen to illustrate this surface specific approach as low concentration phosphorus has significant mass spectra overlaps with silicon species and the near surface location requires particular attention to focused ion beam specimen preparation and deposition of various capping layers. Required changes to standard sample preparation procedure are described and the effects of changes in APT analysis parameters are discussed with regards to this specific material system. Implantation profiles of 14 kV phosphorus ions with a predicted peak concentration of 0.2 at .% were successfully analysed using APT using pulsed laser assisted evaporation. It is demonstrated that the most important factor in obtaining the most accurate implantation profile was to ensure all phosphorus mass peaks were as free of background noise as possible, with thermal tails from the Si2+ ions obscuring the P2+ ions being the major overlap in the mass spectrum. The false positive contribution to the phosphorus profiles from hydride species appears minimal at the capping layer/substrate interface. The initial capping layer selection of nickel was successful in allowing the analysis of the majority of the phosphorus profile but nickel and phosphorus mass spectra overlaps prevent optimum quantification of phosphorus at the surface.

  17. Atom probe tomography of a Ti-Si-Al-C-N coating grown on a cemented carbide substrate.

    PubMed

    Thuvander, M; Östberg, G; Ahlgren, M; Falk, L K L

    2015-12-01

    The elemental distribution within a Ti-Si-Al-C-N coating grown by physical vapour deposition on a Cr-doped WC-Co cemented carbide substrate has been investigated by atom probe tomography. Special attention was paid to the coating/substrate interface region. The results indicated a diffusion of substrate binder phase elements into the Ti-N adhesion layer. The composition of this layer, and the Ti-Al-N interlayer present between the adhesion layer and the main Ti-Si-Al-C-N layer, appeared to be sub-stoichiometric. The analysis of the interlayer showed the presence of internal surfaces, possibly grain boundaries, depleted in Al. The composition of the main Ti-Al-Si-C-N layer varied periodically in the growth direction; layers enriched in Ti appeared with a periodicity of around 30 nm. Laser pulsing resulted in a good mass resolution that made it possible to distinguish between N(+) and Si(2+) at 14 Da. PMID:25956619

  18. High Resolution Dopant Profiles Revealed by Atom Probe Tomography and STEM-EBIC for CdTe Based Solar Cells

    SciTech Connect

    Poplawsky, Jonathan D.; Li, Chen; Paudel, Naba; Guo, Wei; Yan, Yanfa; Pennycook, Stephen J.

    2016-01-01

    Segregated elements and their diffusion profiles within grain boundaries and interfaces resulting from post deposition heat treatments are revealed using atom probe tomography (APT), scanning transmission electron microscopy (STEM), and electron beam induced current (EBIC) techniques. The results demonstrate how these techniques complement each other to provide conclusive evidence for locations of space charge regions and mechanisms that create them at the nanoscale. Most importantly, a Cl dopant profile that extends ~5 nm into CdTe grains interfacing the CdS is shown using APT and STEM synergy, which has been shown to push the pn-junction into the CdTe layer indicative of a homojunction (revealed by STEM EBIC). In addition, Cu and Cl concentrations within grain boundaries within several nms and µms from the CdS/CdTe interface are compared, Na segregation of <0.1% is detected, and S variations of ~1–3% are witnessed between CdTe grains close to the CdS/CdTe interface. The segregation and diffusion of these elements directly impacts on the material properties, such as band gap energy and n/p type properties. Optimization of the interfacial and grain boundary doping will lead to higher efficiency solar cells.

  19. High Resolution Dopant Profiles Revealed by Atom Probe Tomography and STEM-EBIC for CdTe Based Solar Cells

    DOE PAGESBeta

    Poplawsky, Jonathan D.; Li, Chen; Paudel, Naba; Guo, Wei; Yan, Yanfa; Pennycook, Stephen J.

    2016-01-01

    Segregated elements and their diffusion profiles within grain boundaries and interfaces resulting from post deposition heat treatments are revealed using atom probe tomography (APT), scanning transmission electron microscopy (STEM), and electron beam induced current (EBIC) techniques. The results demonstrate how these techniques complement each other to provide conclusive evidence for locations of space charge regions and mechanisms that create them at the nanoscale. Most importantly, a Cl dopant profile that extends ~5 nm into CdTe grains interfacing the CdS is shown using APT and STEM synergy, which has been shown to push the pn-junction into the CdTe layer indicative ofmore » a homojunction (revealed by STEM EBIC). In addition, Cu and Cl concentrations within grain boundaries within several nms and µms from the CdS/CdTe interface are compared, Na segregation of <0.1% is detected, and S variations of ~1–3% are witnessed between CdTe grains close to the CdS/CdTe interface. The segregation and diffusion of these elements directly impacts on the material properties, such as band gap energy and n/p type properties. Optimization of the interfacial and grain boundary doping will lead to higher efficiency solar cells.« less

  20. Effects of laser energy and wavelength on the analysis of LiFePO₄ using laser assisted atom probe tomography

    DOE PAGESBeta

    Santhanagopalan, Dhamodaran; Schreiber, Daniel K.; Perea, Daniel E.; Martens, Richard L.; Janssen, Yuri; Khalifah, Peter; Meng, Ying Shirley

    2014-09-21

    The effects of laser wavelength (355 nm and 532 nm) and laser pulse energy on the quantitative analysis of LiFePO₄ by atom probe tomography are considered. A systematic investigation of ultraviolet (UV, 355 nm) and green (532 nm) laser assisted field evaporation has revealed distinctly different behaviors. With the use of a UV laser, the major issue was identified as the preferential loss of oxygen (up to 10 at%) while other elements (Li, Fe and P) were observed to be close to nominal ratios. Lowering the laser energy per pulse to 1 pJ/pulse from 50 pJ/pulse increased the observed oxygenmore » concentration to nearer its correct stoichiometry, which was also well correlated with systematically higher concentrations of ¹⁶O₂⁺ ions. Green laser assisted field evaporation led to the selective loss of Li (33% deficiency) and a relatively minor O deficiency. The loss of Li is likely a result of selective dc evaporation of Li between or after laser pulses. Comparison of the UV and green laser data suggests that the green wavelength energy was absorbed less efficiently than the UV wavelength because of differences in absorption at 355 and 532 nm for LiFePO₄. Plotting of multihit events on Saxey plots also revealed a strong neutral O₂ loss from molecular dissociation, but quantification of this loss was insufficient to account for the observed oxygen deficiency.« less

  1. Effects of laser energy and wavelength on the analysis of LiFePO₄ using laser assisted atom probe tomography

    SciTech Connect

    Santhanagopalan, Dhamodaran; Schreiber, Daniel K.; Perea, Daniel E.; Martens, Richard L.; Janssen, Yuri; Khalifah, Peter; Meng, Ying Shirley

    2014-09-21

    The effects of laser wavelength (355 nm and 532 nm) and laser pulse energy on the quantitative analysis of LiFePO₄ by atom probe tomography are considered. A systematic investigation of ultraviolet (UV, 355 nm) and green (532 nm) laser assisted field evaporation has revealed distinctly different behaviors. With the use of a UV laser, the major issue was identified as the preferential loss of oxygen (up to 10 at%) while other elements (Li, Fe and P) were observed to be close to nominal ratios. Lowering the laser energy per pulse to 1 pJ/pulse from 50 pJ/pulse increased the observed oxygen concentration to nearer its correct stoichiometry, which was also well correlated with systematically higher concentrations of ¹⁶O₂⁺ ions. Green laser assisted field evaporation led to the selective loss of Li (33% deficiency) and a relatively minor O deficiency. The loss of Li is likely a result of selective dc evaporation of Li between or after laser pulses. Comparison of the UV and green laser data suggests that the green wavelength energy was absorbed less efficiently than the UV wavelength because of differences in absorption at 355 and 532 nm for LiFePO₄. Plotting of multihit events on Saxey plots also revealed a strong neutral O₂ loss from molecular dissociation, but quantification of this loss was insufficient to account for the observed oxygen deficiency.

  2. Conductivity Measurements of Pyrrole Molecules Incorporated into Chemically Adsorbed Monolayer by Conducting Probe Technique in Atomic Force Microscope

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shin‑ichi; Ogawa, Kazufumi

    2006-03-01

    A monomolecular layer containing pyrrolyl groups at the surface was prepared between two parallel Pt electrodes on a glass substrate by a chemical adsorption technique using N-[11-(trichlorosilyl)undecyl] pyrrole (PNN). Then, the pyrrolyl was polymerized with pure water by applying a DC voltage of 10 V between the two Pt electrodes. It was confirmed using an optical microscope that many electric paths were formed between the two Pt electrodes by a decoration technique using electrochemical polymerization in an aqueous medium containing pyrrole after the polymerization. Next, a conductive probe of an atomic force microscope (AFM) was used to examine an electrical polymerized path through the surface of the polypyrrolyl group in a chemically adsorbed monomolecular layer. The resistance of one electric path in the monomolecular layer was measured using an AFM with an attached Au-covered tip at room temperature. With a measurement volume of about 0.2 nm (the thickness of the electric path in the monomolecular layer) × 200 μm (the average width of the electric path) × 100 μm (the distance between the Pt electrode and the Au-covered AFM tip), the resistance at room temperature of one electric path was 4 k Ω under ambient conditions. From the results in the atmosphere, the conductivity of a super long conjugated polypyrrolyl group without any dopant in a lateral direction was ohmically estimated to be at least 6.0 × 105 S/m.

  3. A sputtering derived atomic oxygen source for studying fast atom reactions

    NASA Technical Reports Server (NTRS)

    Ferrieri, Richard A.; Yung, Y. Chu; Wolf, Alfred P.

    1987-01-01

    A technique for the generation of fast atomic oxygen was developed. These atoms are created by ion beam sputtering from metal oxide surfaces. Mass resolved ion beams at energies up to 60 KeV are produced for this purpose using a 150 cm isotope separator. Studies have shown that particles sputtered with 40 KeV Ar(+) on Ta2O5 were dominantly neutral and exclusively atomic. The atomic oxygen also resided exclusively in its 3P ground state. The translational energy distribution for these atoms peaked at ca 7 eV (the metal-oxygen bond energy). Additional measurements on V2O5 yielded a bimodal distribution with the lower energy peak at ca 5 eV coinciding reasonably well with the metal-oxygen bond energy. The 7 eV source was used to investigate fast oxygen atom reactions with the 2-butene stereoisomers. Relative excitation functions for H-abstraction and pi-bond reaction were measured with trans-2-butene. The abstraction channel, although of minor relative importance at thermal energy, becomes comparable to the addition channel at 0.9 eV and dominates the high-energy regime. Structural effects on the specific channels were also found to be important at high energy.

  4. Ultrafast Pump-Probe Experimental Studies of Heme Proteins

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Demidov, Andrey; Ye, Xiong; Christian, James F.; Champion, Paul M.

    1998-03-01

    Femtosecond time-resovled spectroscopy has been applied to explore coherent dynamics of cytochrome c and myoglobin with different diatomic ligands (NO, O2, CO) using amplified 50fs laser pulses which are generated by a regenerative amplifier and optical parametric amplifier laser system at a repetition rate of 250KHz. Signals associated with ``field driven'' coherence and ``reaction driven'' coherence are studied using both single-color and two-color pump-probe schemes. The combination of the two schemes helps us to further understand electronic relaxation, ligand photodissociation and protein relaxation processes in heme proteins.

  5. The study on the atomic force microscopy base nanoscale electrical discharge machining.

    PubMed

    Huang, Jen-Ching; Chen, Chung-Ming

    2012-01-01

    This study proposes an innovative atomic force microscopy (AFM) based nanoscale electrical discharge machining (AFM-based nanoEDM) system which combines an AFM with a self-produced metallic probe and a high-voltage generator to create an atmospheric environment AFM-based nanoEDM system and a deionized water (DI water) environment AFM-based nanoEDM system. This study combines wire-cut processing and electrochemical tip sharpening techniques on a 40-µm thick stainless steel sheet to produce a high conductive AFM probes, the production can withstand high voltage and large current. The tip radius of these probes is approximately 40 nm. A probe test was executed on the AFM using probes to obtain nanoscales morphology of Si wafer surface. The silicon wafer was as a specimen to carry out AFM-base nanoEDM process in atmospheric and DI water environments by AFM-based nanoEDM system. After experiments, the results show that the atmospheric and DI water environment AFM-based nanoEDM systems operate smoothly. From experimental results, it can be found that the electric discharge depth of the silicon wafer at atmospheric environments is a mere 14.54 nm. In a DI water environment, the depth of electric discharge of the silicon wafer can reach 25.4 nm. This indicates that the EDM ability of DI water environment AFM-based nanoEDM system is higher than that of atmospheric environment AFM-based nanoEDM system. After multiple nanoEDM process, the tips become blunt. After applying electrochemical tip sharpening techniques, the tip radius can return to approximately 40 nm. Therefore, AFM probes produced in this study can be reused. PMID:21898457

  6. The 158 micron (CII) mapping of galaxies: Probing the atomic medium

    NASA Technical Reports Server (NTRS)

    Madden, S. C.; Geis, N.; Genzel, R.; Herrmann, F.; Jackson, J.; Poglitsch, A.; Stacey, G. J.; Townes, C. H.

    1993-01-01

    Using the MPE/UCB Far-infrared Imaging Fabry-Perot Interferometer (FIFI) on the Kuiper Airborne Observatory (KAO), we have made large scale maps of (CII) in the spiral galaxies NGC 6946, NGC 891, M83 and the peculiar elliptical Cen A, thus allowing for the first time, detailed studies of the spatial distribution of the FIR line emission in external galaxies. We find that the (CII) emission comes from a mixture of components of interstellar gas. The brightest emission is associated with the nuclear regions, a second component traces the spiral arms as seen in the nearly face on spiral galaxies NGC 6946 and M83 and the largest star forming/H2 regions contained within them, and another extended component of low brightness can be detected in all of the galaxies far from the nucleus, beyond the extent of CO emission.

  7. Probing Electron Transfer Dynamics at MgO Surfaces by Mg-Atom Desorption

    SciTech Connect

    Joly, Alan G.; Henyk, Matthias; Beck, Kenneth M.; Trevisanutto, P. E.; Sushko, Petr V.; Hess, Wayne P.; Shluger, Alexander L.

    2006-08-14

    Desorption of a weakly bound adsorbate from a porous solid was studied for the case of N2 on amorphous solid water (ASW). Porous ASW films of different thickness were grown on Pt(111) by ballistic deposition. N2 adsorption and desorption kinetics were monitored mass-spectrometrically. Temperature programmed desorption spectra show that with the increasing film thickness, the N2 desorption peak systematically shifts to higher temperatures. The results are explained and quantitatively reproduced by a simple model, which assumes that the N2 transport within the film is faster than the depletion rate to vacuum. The local coverage at the pore mouth determines the desorption rate. For thick ASW films (>1 μm), the assumption of the fast equilibration within the film is shown to be no longer valid due to diffusion limitations. The mechanisms of the adsorbate transport are discussed.

  8. Outer planet entry probe system study. Volume 2: Supporting technical studies

    NASA Technical Reports Server (NTRS)

    1972-01-01

    The environment, science investigations, and general mission analysis considerations are given first. These data are followed by discussions of the studies pertaining to the planets Jupiter, Saturn, Uranus, and Neptune. Except for Neptune, each planet discussion is divided into two parts: (1) parametric activities and (2) probe definition for that planet, or the application of a given probe for that planet. The Neptune discussion is limited to parametrics in the area of science and mission analysis. Each of the probe system definitions consists of system and subsystem details including telecommunications, data handling, power pyrotechnics, attitude control, structures, propulsion, thermal control, and probe to spacecraft integration. The first configuration is discussed in detail and the subsequent configuration discussions are limited to the differences. Finally, the hardware availability to support a probe system and commonality of science, missions, and subsystems for use at the various planets are considered.

  9. Probing Spin-Orbit Coupling and Interlayer Coupling in Atomically Thin Molybdenum Disulfide Using Hydrostatic Pressure.

    PubMed

    Dou, Xiuming; Ding, Kun; Jiang, Desheng; Fan, Xiaofeng; Sun, Baoquan

    2016-01-26

    In two-dimensional transition-metal dichalcogenides, both spin-orbit coupling and interlayer coupling play critical roles in the electronic band structure and are desirable for the potential applications in spin electronics. Here, we demonstrate the pressure characteristics of the exciton absorption peaks (so-called excitons A, B and C) in monolayer, bilayer, and trilayer molybdenum disulfide (MoS2) by studying the reflectance spectra under hydrostatic pressure and performing the electronic band structure calculations based on density functional theory to account for the experimental observations. We find that the valence band maximum splitting at the K point in monolayer MoS2, induced by spin-orbit coupling, remains almost unchanged with increasing pressure applied up to 3.98 GPa, indicating that the spin-orbit coupling is insensitive to the pressure. For bilayer and trilayer MoS2, however, the splitting shows an increase with increasing pressure due to the pressure-induced strengthening of the interlayer coupling. The experimental results are in good agreement with the theoretical calculations. Moreover, the exciton C is identified to be the interband transition related to the van Hove singularity located at a special point which is approximately 1/4 of the total length of Γ-K away from the Γ point in the Brillouin zone. PMID:26745440

  10. A Preliminary Study of a Solar-Probe Mission

    NASA Technical Reports Server (NTRS)

    Dugan, Duane W.

    1961-01-01

    A preliminary study is made of some problems associated with the sending of an instrumented probe close to the Sun for the purpose of gathering and telemetering back to Earth information concerning solar phenomena and circumsolar space. The problems considered are primarily those relating to heating and to launch requirements. A nonanalytic discussion of the communications problem of a solar-probe mission is presented to obtain order-of-magnitude estimates of the output and weight of an auxiliary power supply which might be required. From the study it is believed that approaches to the Sun as close as about 4 or 5 million miles do not present insuperable difficulties insofar as heating and communications are concerned. Guidance requirements, in general, do not appear to be stringent. However, in terms of current experience, velocity requirements may be large. It is found, for example, that to achieve perihelion distances between the orbit of Mercury and the visible disc of the Sun, total burnout velocities ranging between 50,000 and 100,000 feet per second are required.

  11. Oxygen-18 tracer studies of enzyme reactions with radical/cation diagnostic probes

    SciTech Connect

    Moe, Luke A.; Fox, Brian G. . E-mail: bgfox@biochem.wisc.edu

    2005-12-09

    This review considers reactions of enzymes with the cyclopropanoid radical/cation diagnostic probes norcarane, 1,1-dimethylcyclopropane, and 1,1-diethylcyclopropane as elaborated by the use of {sup 18}O{sub 2} and {sup 18}OH{sub 2} to trace the origin of O-atoms incorporated during catalysis. The reactions of soluble and integral membrane diiron enzymes are summarized and compared to results obtained from cytochrome P450 studies. Norcarane proved to be an excellent substrate for the diiron enzyme toluene 4-monooxygenase and its engineered isoforms, with k {sub cat} and coupling between NADH utilization and total hydroxylated products comparable to that determined for toluene, the natural substrate. Results obtained with toluene 4-monooxygenase show that the un-rearranged and radical-rearranged alcohol products have a high percentage of O-atom incorporation (>80-95%) from O{sub 2}, while the cation-derived ring-expansion products have O-atom incorporation primarily derived from solvent water. Mechanistic possibilities accounting for this difference are discussed.

  12. Nuclear structure studies with medium energy probes. [Northwestern Univ

    SciTech Connect

    Seth, Kamal K.

    1980-01-01

    Progress in the continuing program of experimental research in nuclear structure with medium-energy probes during the year 1979-1980 is reviewed, and the research activities planned for the year 1980-1981 are discussed. In the study of pion-induced reactions emphasis is placed on investigation of isovector characteristics of nuclear excitations and on double charge exchange reactions. Pion production studies form the major part of the program of experiments with proton beams of 400 to 800 MeV at LAMPF. Current emphasis is on the bearing of these investigations on di-baryon existence. The study of high-spin states and magnetic scattering constitute the main goals of the electron scattering program at Bates. Representative results are presented; completed work is reported in the usual publications. (RWR)

  13. Probing microplatform for the study of biological adhesion forces

    NASA Astrophysics Data System (ADS)

    Whisman, N.; York, D.; Manning, L.; Brant, J.; Dyer, R.; Childress, A.; Marchand, E. A.; Adams, J. D.

    2003-10-01

    A tool for the study of biological adhesion forces with the atomic force microscope (AFM) is introduced. The tool, a "microplatform," can be functionalized with variety of specimens such as bacterial cells and used to study adhesion between the specimen and a surface. This tool is easily created using commercially available silicon AFM tips and an AFM, and can be customized in size to fit specific applications. Two custom fabricated microplatforms, ˜1 and ˜2.5 μm were tested. The method of microplatform fabrication, as well as adhesion force data between E. coli bacteria and a nanofiltration membrane is presented.

  14. Statistical correction of atom probe tomography data of semiconductor alloys combined with optical spectroscopy: The case of Al0.25Ga0.75N

    NASA Astrophysics Data System (ADS)

    Rigutti, L.; Mancini, L.; Hernández-Maldonado, D.; Lefebvre, W.; Giraud, E.; Butté, R.; Carlin, J. F.; Grandjean, N.; Blavette, D.; Vurpillot, F.

    2016-03-01

    The ternary semiconductor alloy Al0.25Ga0.75N has been analyzed by means of correlated photoluminescence spectroscopy and atom probe tomography (APT). We find that the composition measured by APT is strongly dependent on the surface electric field, leading to erroneous measurements of the alloy composition at high field, due to the different evaporation behaviors of Al and Ga atoms. After showing how a biased measurement of the alloy content leads to inaccurate predictions on the optical properties of the material, we develop a correction procedure which yields consistent transition and localization energies for the alloy photoluminescence.

  15. Atom probe tomography characterization of neutron irradiated surveillance samples from the R. E. Ginna reactor pressure vessel

    NASA Astrophysics Data System (ADS)

    Edmondson, P. D.; Miller, M. K.; Powers, K. A.; Nanstad, R. K.

    2016-03-01

    Surveillance samples of a low copper (nominally 0.05 wt.% Cu) forging and a higher copper (0.23 wt.% Cu) submerged arc weld from the R. E. Ginna reactor pressure vessel have been characterized by atom probe tomography (APT) after exposure to three levels of neutron irradiation, i.e., fluences of 1.7, 3.6 and 5.8 × 1023 n.m-2 (E > 1 MeV), and inlet temperatures of ∼289 °C (∼552 °F). As no copper-enriched precipitates were observed in the low copper forging, and the measured copper content in the ferrite matrix was 0.04± <0.01 at.% Cu, after neutron irradiation to a fluence of 1.7 × 1023 n.m-3, this copper level was below the solubility limit. A number density of 2 × 1022 m-3 of Ni-, Mn- Si-enriched precipitates with an equivalent radius of gyration of 1.7 ± 0.4 nm were detected in the sample. However, Cu-, Ni-, Mn-enriched precipitates were observed in specimens cut from different surveillance specimens from the same forging material in which the overall measured copper level was 0.08± <0.01 at.% (fluence of 3.6 × 1023 n.m-3) and 0.09± <0.01 at.% Cu (fluence of 5.8 × 1023 n.m-3). Therefore, these slightly higher copper contents were above the solubility limit of Cu under these irradiation conditions. A best fit of all the composition data indicated that the size and number density of the Cu-enriched precipitates increased slightly in both size and number density by additional exposure to neutron irradiation. High number densities of Cu-enriched precipitates were observed in the higher Cu submerged arc weld for all irradiated conditions. The size and number density of the precipitates in the welds were higher than in the same fluence forgings. Some Cu-enriched precipitates were found to have Ni-, Mn- Si-, and P-enriched regions on their surfaces suggesting a preferential nucleation site. Atom maps revealed P, Ni, and Mn segregation to, and preferential precipitation of, Cu-enriched precipitates over the surface of a grain boundary in the low fluence

  16. Atom probe tomography characterization of neutron irradiated surveillance samples from the R. E. Ginna reactor pressure vessel

    DOE PAGESBeta

    Edmondson, Philip D.; Miller, Michael K.; Powers, Kathy A.; Nanstad, Randy K.

    2015-12-29

    Surveillance samples of a low copper (nominally 0.05 wt.% Cu) forging and a higher copper (0.23 wt.% Cu) submerged arc weld from the R. E. Ginna reactor pressure vessel have been characterized by atom probe tomography (APT) after exposure to three levels of neutron irradiation, i.e., fluences of 1.7, 3.6 and 5.8 × 1023 n.m–2 (E > 1 MeV), and inlet temperatures of ~289 °C (~552 °F). As no copper-enriched precipitates were observed in the low copper forging, and the measured copper content in the ferrite matrix was 0.04± <0.01 at.% Cu, after neutron irradiation to a fluence of 1.7more » × 1023 n.m–3, this copper level was below the solubility limit. A number density of 2 × 1022 m–3 of Ni–, Mn– Si-enriched precipitates with an equivalent radius of gyration of 1.7 ± 0.4 nm were detected in the sample. However, Cu-, Ni-, Mn-enriched precipitates were observed in specimens cut from different surveillance specimens from the same forging material in which the overall measured copper level was 0.08± <0.01 at.% (fluence of 3.6 × 1023 n.m–3) and 0.09± <0.01 at.% Cu (fluence of 5.8 × 1023 n.m–3). Therefore, these slightly higher copper contents were above the solubility limit of Cu under these irradiation conditions. A best fit of all the composition data indicated that the size and number density of the Cu-enriched precipitates increased slightly in both size and number density by additional exposure to neutron irradiation. High number densities of Cu-enriched precipitates were observed in the higher Cu submerged arc weld for all irradiated conditions. The size and number density of the precipitates in the welds were higher than in the same fluence forgings. Some Cu-enriched precipitates were found to have Ni-, Mn- Si-, and P-enriched regions on their surfaces suggesting a preferential nucleation site. Furthermore, atom maps revealed P, Ni, and Mn segregation to, and preferential precipitation of, Cu-enriched precipitates over the surface of a grain

  17. Atom probe tomography characterization of neutron irradiated surveillance samples from the R. E. Ginna reactor pressure vessel

    SciTech Connect

    Edmondson, Philip D.; Miller, Michael K.; Powers, Kathy A.; Nanstad, Randy K.

    2015-12-29

    Surveillance samples of a low copper (nominally 0.05 wt.% Cu) forging and a higher copper (0.23 wt.% Cu) submerged arc weld from the R. E. Ginna reactor pressure vessel have been characterized by atom probe tomography (APT) after exposure to three levels of neutron irradiation, i.e., fluences of 1.7, 3.6 and 5.8 × 1023 n.m–2 (E > 1 MeV), and inlet temperatures of ~289 °C (~552 °F). As no copper-enriched precipitates were observed in the low copper forging, and the measured copper content in the ferrite matrix was 0.04± <0.01 at.% Cu, after neutron irradiation to a fluence of 1.7 × 1023 n.m–3, this copper level was below the solubility limit. A number density of 2 × 1022 m–3 of Ni–, Mn– Si-enriched precipitates with an equivalent radius of gyration of 1.7 ± 0.4 nm were detected in the sample. However, Cu-, Ni-, Mn-enriched precipitates were observed in specimens cut from different surveillance specimens from the same forging material in which the overall measured copper level was 0.08± <0.01 at.% (fluence of 3.6 × 1023 n.m–3) and 0.09± <0.01 at.% Cu (fluence of 5.8 × 1023 n.m–3). Therefore, these slightly higher copper contents were above the solubility limit of Cu under these irradiation conditions. A best fit of all the composition data indicated that the size and number density of the Cu-enriched precipitates increased slightly in both size and number density by additional exposure to neutron irradiation. High number densities of Cu-enriched precipitates were observed in the higher Cu submerged arc weld for all irradiated conditions. The size and number density of the precipitates in the welds were higher than in the same fluence forgings. Some Cu-enriched precipitates were found to have Ni-, Mn- Si-, and P-enriched regions on their surfaces suggesting a preferential nucleation site. Furthermore, atom maps revealed P, Ni, and Mn

  18. Synthetic fluorescent probes for studying copper in biological systems

    PubMed Central

    Cotruvo, Joseph A.; Aron, Allegra T.; Ramos-Torres, Karla M.; Chang, Christopher J.

    2015-01-01

    The potent redox activity of copper is required for sustaining life. Mismanagement of its cellular pools, however, can result in oxidative stress and damage connected to aging, neurodegenerative diseases, and metabolic disorders. Therefore, copper homeostasis is tightly regulated by cells and tissues. Whereas copper and other transition metal ions are commonly thought of as static cofactors buried within protein active sites, emerging data points to the presence of additional loosely bound, labile pools that can participate in dynamic signalling pathways. Against this backdrop, we review advances in sensing labile copper pools and understanding their functions using synthetic fluorescent indicators. Following brief introductions to cellular copper homeostasis and considerations in sensor design, we survey available fluorescent copper probes and evaluate their properties in the context of their utility as effective biological screening tools. We emphasize the need for combined chemical and biological evaluation of these reagents, as well as the value of complementing probe data with other techniques for characterizing the different pools of metal ions in biological systems. This holistic approach will maximize the exciting opportunities for these and related chemical technologies in the study and discovery of novel biology of metals. PMID:25692243

  19. Atomic Force Microscopy Application in Biological Research: A Review Study

    PubMed Central

    Vahabi, Surena; Nazemi Salman, Bahareh; Javanmard, Anahita

    2013-01-01

    Atomic force microscopy (AFM) is a three-dimensional topographic technique with a high atomic resolution to measure surface roughness. AFM is a kind of scanning probe microscope, and its near-field technique is based on the interaction between a sharp tip and the atoms of the sample surface. There are several methods and many ways to modify the tip of the AFM to investigate surface properties, including measuring friction, adhesion forces and viscoelastic properties as well as determining the Young modulus and imaging magnetic or electrostatic properties. The AFM technique can analyze any kind of samples such as polymers, adsorbed molecules, films or fibers, and powders in the air whether in a controlled atmosphere or in a liquid medium. In the past decade, the AFM has emerged as a powerful tool to obtain the nanostructural details and biomechanical properties of biological samples, including biomolecules and cells. The AFM applications, techniques, and -in particular- its ability to measure forces, are not still familiar to most clinicians. This paper reviews the literature on the main principles of the AFM modality and highlights the advantages of this technique in biology, medicine, and- especially- dentistry. This literature review was performed through E-resources, including Science Direct, PubMed, Blackwell Synergy, Embase, Elsevier, and Scholar Google for the references published between 1985 and 2010. PMID:23825885

  20. Multi-component Cu-Strengthened Steel Welding Simulations: Atom Probe Tomography and Synchrotron X-ray Diffraction Analyses

    NASA Astrophysics Data System (ADS)

    Hunter, Allen H.; Farren, Jeffrey D.; DuPont, John N.; Seidman, David N.

    2015-07-01

    An experimental steel with the composition Fe-1.39Cu-2.70Ni-0.58Al-0.48Mn-0.48Si-0.065Nb-0.05C (wt pct) or alternatively Fe-1.43Cu-2.61Ni-1.21Al-0.48Mn-0.98Si-0.039Nb-0.23C (at. pct) has been developed at Northwestern University, which has both high toughness and high strength after quenching and aging treatments. Simulated heat-affected zone (HAZ) samples are utilized to analyze the microstructures typically obtained after gas metal arc welding (GMAW). Dissolution within the HAZ of cementite (Fe3C) and NbC (F.C.C.) is revealed using synchrotron X-ray diffraction, while dissolution of Cu precipitates is measured employing local electrode atom probe tomography. The results are compared to Thermo-Calc equilibrium calculations. Comparison of measured Cu precipitate radii, number density, and volume fraction with similar measurements from a GMAW sample suggests that the cooling rate in the simulations is faster than in the experimental GMAW sample, resulting in significantly less Cu precipitate nucleation and growth during the cooling part of the weld thermal cycle. The few Cu precipitates detected in the simulated samples are primarily located on grain boundaries resulting from heterogeneous nucleation. The dissolution of NbC precipitates and the resultant austenite coarsening in the highest-temperature sample, coupled with a rapid cooling rate, results in the growth of bainite, and an increase in the strength of the matrix in the absence of significant Cu precipitation.

  1. Probing interfacial electronic structures in atomic layer LaMnO{sub3} and SrTiO{sub 3} superlattices.

    SciTech Connect

    Shah, A. B.; Ramasse, Q. M.; Zhai, X.; Wen, J. G.; May, S. J.; Petrov, I.; Bhattacharya, A.; Abbamonte, P.; Eckstein, J. N.; Zuo, J.-M.; Univ. of Illinois; LBNL

    2010-01-01

    The interfacial electronic structure characterization of a m x (LaMnO{sub 3})/n x (SrTiO{sub 3}) superlattice based on scanning transmission electron microscopy and electron energy loss spectroscopy. Evidence of interfacial band alignment and electron transfer are presented based on the observation of O K edge of individual transition metal and oxygen atomic columns. Electron probe aberration correction was essential for the high spatial resolution mapping of interfacial electronic states.

  2. Effect of the interaction conditions of the probe of an atomic-force microscope with the n-GaAs surface on the triboelectrization phenomenon

    SciTech Connect

    Baklanov, A. V.; Gutkin, A. A.; Kalyuzhnyy, N. A.; Brunkov, P. N.

    2015-08-15

    Triboelectrization as a result of the scanning of an atomic-force-microscope probe over an n-GaAs surface in the contact mode is investigated. The dependences of the local potential variation on the scanning rate and the pressing force of the probe are obtained. The results are explained by point-defect formation in the surface layers of samples under the effect of deformation of these layers during probe scanning. The charge localized at these defects in the case of equilibrium changes the potential of surface, which is subject to triboelectrization. It is shown that, for qualitative explanation of the observed dependences, it is necessary to take into account both the generation and annihilation of defects in the region experiencing deformation.

  3. Advances in Structural Studies of Materials using Scattering Probes

    SciTech Connect

    Huq, Ashfia; Bozin, Emil; Welberry, Dr. Richard

    2010-01-01

    Study of contemporary materials and their remarkable properties is a challenging problem. To understand these complex properties and develop better materials it is essential to understand their structures, as the two are intimately linked. Great advances in materials scattering have been achieved due to the advent of synchrotron and neutron sources along with the availability of high-speed computational algorithms. Materials scientists can now collect data with high resolution, high throughput from very small amount of sample (both single crystal and powder), and analyze vast amount of data to unravel detailed structural description that was not possible before. This article presents some of these great advances in using scattering probes for materials characterization.

  4. Experimental study of linear magnetic dichroism in photoionization satellite transitions of atomic rubidium

    SciTech Connect

    Jaenkaelae, K.; Alagia, M.; Feyer, V.; Richter, R.; Prince, K. C.

    2011-11-15

    Laser orientation in the initial state has been used to study the properties of satellite transitions in inner-shell photoionization of rubidium atoms. The linear magnetic dichroism in the angular distribution (LMDAD) has been utilized to probe the continuum waves of orbital angular momentum conserving monopole, and angular momentum changing conjugate satellites, accompanying the 4p ionization of atomic Rb. We show experimentally that LMDAD of both types of satellite transitions is nonzero and that LMDAD of monopole satellites, measured as a function of photon energy, mimics the LMDAD of direct photoionization, whereas the LMDAD of conjugate transitions deviates drastically from that trend. The results indicate that conjugate transitions cannot be described theoretically without explicit inclusion of electron-electron interaction. The present data can thus be used as a very precise test of current models for photoionization.

  5. Quantifying adhesion of acidophilic bioleaching bacteria to silica and pyrite by atomic force microscopy with a bacterial probe.

    PubMed

    Diao, Mengxue; Taran, Elena; Mahler, Stephen; Nguyen, Tuan A H; Nguyen, Anh V

    2014-03-01

    The adhesion of acidophilic bacteria to mineral surfaces is an important phenomenon in bioleaching processes. In this study, functionalized colloidal probes covered by bioleaching bacterial cells (Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans) were developed and used to sense specific adhesion forces to a silica surface and a pyrite surface in various solutions. Experimentally, recorded retraction curves of A. thiooxidans revealed sawtooth features that were in good agreement with the wormlike chain model, while that of L. ferrooxidans exhibited stair-step separation. The magnitudes of adhesion forces and snap-off distances were strongly influenced by the ionic strength and pH. Macroscopic surface properties including hydrophobicity and surface potential for bacterial cells and substrata were measured by a sessile drop method and microelectrophoresis. The ATR-FTIR spectra indicated the presence of different types of biopolymers on two strains of bacteria. PMID:24355385

  6. Plasma-edge studies using carbon resistance probes

    SciTech Connect

    Wampler, W.R.

    1984-01-01

    Characterization of erosion and hydrogen-recycling processes occurring at the edge of magnetically confined plasmas requires knowledge of the energy and flux of hydrogen isotopes incident on the materials. A new plasma-edge probe technique, the carbon resistance probe, has been developed to obtain this information. This technique uti

  7. Microscopic techniques bridging between nanoscale and microscale with an atomically sharpened tip - field ion microscopy/scanning probe microscopy/ scanning electron microscopy.

    PubMed

    Tomitori, Masahiko; Sasahara, Akira

    2014-11-01

    Over a hundred years an atomistic point of view has been indispensable to explore fascinating properties of various materials and to develop novel functional materials. High-resolution microscopies, rapidly developed during the period, have taken central roles in promoting materials science and related techniques to observe and analyze the materials. As microscopies with the capability of atom-imaging, field ion microscopy (FIM), scanning tunneling microscopy (STM), atomic force microscopy (AFM) and transmission electron microscopy (TEM) can be cited, which have been highly evaluated as methods to ultimately bring forward the viewpoint of reductionism in materials science. On one hand, there have been difficulties to derive useful and practical information on large (micro) scale unique properties of materials using these excellent microscopies and to directly advance the engineering for practical materials. To make bridges over the gap between an atomic scale and an industrial engineering scale, we have to develop emergence science step-by-step as a discipline having hierarchical structures for future prospects by combining nanoscale and microscale techniques; as promising ways, the combined microscopic instruments covering the scale gap and the extremely sophisticated methods for sample preparation seem to be required. In addition, it is noted that spectroscopic and theoretical methods should implement the emergence science.Fundamentally, the function of microscope is to determine the spatial positions of a finite piece of material, that is, ultimately individual atoms, at an extremely high resolution with a high stability. To define and control the atomic positions, the STM and AFM as scanning probe microscopy (SPM) have successfully demonstrated their power; the technological heart of SPM lies in an atomically sharpened tip, which can be observed by FIM and TEM. For emergence science we would like to set sail using the tip as a base. Meanwhile, it is significant

  8. Study of Cold Potassium Atom - Calcium Ion Reactions

    NASA Astrophysics Data System (ADS)

    Egodapitiya, Kisra; Gang, Shu; Clark, Robert; Brown, Kenneth

    2016-05-01

    We report on our progress towards constructing a hybrid system for studying reactions between cold Potassium (K) atoms and cold Calcium (Ca+) ions. Ca+ ions will be trapped and Doppler-cooled inside a linear quadrupole ion trap. Cold K atoms will be created inside a magneto optical trap, such that the ion and the atoms are in an overlapping volume. Trapping and re-pumping beams for the Potassium MOT are derived from the same laser with wavelength 766 nm using two acousto optic modulators. The reaction products will be detected using a time-of- flight mass spectrometer that is designed to detect radially ejected ions. The main objective of this experiment is to study the rate coefficients, and identification of reaction channels between cold K atoms and Ca+ ions. Subsequently this setup will be used to study reactions between cold K atoms and sympathetically cooled molecular ions such as CaO+, and to study internal state quenching of molecular ions.

  9. The influence of experimental parameters and specimen geometry on the mass spectra of copper during pulsed-laser atom-probe tomography.

    PubMed

    Kolli, R Prakash; Meisenkothen, Frederick

    2014-12-01

    We have studied the influence of experimental factors and specimen geometry on the quality of the mass spectra in copper (Cu) during pulsed-laser atom-probe tomography. We have evaluated the effects of laser pulse energy, laser pulse frequency, specimen base temperature, specimen tip radius, and specimen tip shank half-angle on the effects of mass resolving power, (m/Δm), at full-width at half-maximum and at full-width at tenth-maximum, the tail size after the major mass-to-charge state (m/n) ratio peaks, and the mass spectra. Our results indicate that mass resolving power improves with decreasing pulse energy between 40 and 80 pJ and decreasing base temperature between 20 and 80 K. The mass resolving power also improves with increasing tip radius and shank half-angle. A pulse frequency of 250 kHz slightly improves the mass resolving power relative to 100 or 500 kHz. The tail size decreases with increasing pulse energy. The mass resolving power improves when the cooling time is reduced, which is influenced by the thermal diffusivity of Cu and the specimen base temperature. PMID:25390364

  10. Probing the Atomic and Molecular Inventory of a Beta-Pic Analog, the Young, Edge-On Debris Disk of HD32297

    NASA Astrophysics Data System (ADS)

    Redfield, Seth

    2009-07-01

    Edge-on, optically thin, debris disks provide unique opportunities to probe physical properties of the disk itself. Using the host star as the background source, trace atomic and molecular disk species can be detected in absorption. Redfield {2007} found that the recently discovered edge-on system, HD32297, has the strongest NaI absorption feature of any known debris disk, 5 times the level observed toward beta Pic, the canonical edge-on debris disk. Roberge et al. {2006} compiled the only comprehensive chemical inventory of a debris disk, using beta Pic, and found that carbon was surprisingly overabundant, which has important implications for the physical structure and support of a stable gas disk. What is severely lacking are comparison observations to determine if such an abundance pattern is typical of debris disk systems. HD32297 represents the best opportunity to make such a comparative study and perform a comprehensive gas inventory of a debris disk, due to its high NaI column density. The UV is critical for this work due to the large number of strong transitions {almost 50 ions and molecules are accessible} that are located in, and often only in, the UV. These observations will provide a much needed comparison dataset for addressing the gas chemistry of debris disk systems that are at the critical stage, near the end of planet formation, and in the process of clearing their interplanetary environments.

  11. Direct imaging of thermally-activated grain-boundary diffusion in Cu/Co/IrMn/Pt exchange-bias structures using atom-probe tomography

    SciTech Connect

    Letellier, F.; Lardé, R.; Le Breton, J.-M.; Akmaldinov, K.; Auffret, S.; Dieny, B.; Baltz, V.

    2014-11-28

    Magnetic devices are often subject to thermal processing steps, such as field cooling to set exchange bias and annealing to crystallize amorphous magnetic electrodes. These processing steps may result in interdiffusion and the subsequent deterioration of magnetic properties. In this study, we investigated thermally-activated diffusion in Cu/Co/IrMn/Pt exchange biased polycrystalline thin-film structures using atom probe tomography. Images taken after annealing at 400 °C for 60 min revealed Mn diffusion into Co grains at the Co/IrMn interface and along Pt grain boundaries for the IrMn/Pt stack, i.e., a Harrison type C regime. Annealing at 500 °C showed further Mn diffusion into Co grains. At the IrMn/Pt interface, annealing at 500 °C led to a type B behavior since Mn diffusion was detected both along Pt grain boundaries and also into Pt grains. The deterioration of the films' exchange bias properties upon annealing was correlated to the observed diffusion. In particular, the topmost Pt capping layer thickness turned out to be crucial since a faster deterioration of the exchange bias properties for thicker caps was observed. This is consistent with the idea that Pt acts as a getter for Mn, drawing Mn out of the IrMn layer.

  12. Direct imaging of thermally-activated grain-boundary diffusion in Cu/Co/IrMn/Pt exchange-bias structures using atom-probe tomography

    NASA Astrophysics Data System (ADS)

    Letellier, F.; Lechevallier, L.; Lardé, R.; Le Breton, J.-M.; Akmaldinov, K.; Auffret, S.; Dieny, B.; Baltz, V.

    2014-11-01

    Magnetic devices are often subject to thermal processing steps, such as field cooling to set exchange bias and annealing to crystallize amorphous magnetic electrodes. These processing steps may result in interdiffusion and the subsequent deterioration of magnetic properties. In this study, we investigated thermally-activated diffusion in Cu/Co/IrMn/Pt exchange biased polycrystalline thin-film structures using atom probe tomography. Images taken after annealing at 400 °C for 60 min revealed Mn diffusion into Co grains at the Co/IrMn interface and along Pt grain boundaries for the IrMn/Pt stack, i.e., a Harrison type C regime. Annealing at 500 °C showed further Mn diffusion into Co grains. At the IrMn/Pt interface, annealing at 500 °C led to a type B behavior since Mn diffusion was detected both along Pt grain boundaries and also into Pt grains. The deterioration of the films' exchange bias properties upon annealing was correlated to the observed diffusion. In particular, the topmost Pt capping layer thickness turned out to be crucial since a faster deterioration of the exchange bias properties for thicker caps was observed. This is consistent with the idea that Pt acts as a getter for Mn, drawing Mn out of the IrMn layer.

  13. Model-independent measurement of the charge density distribution along an Fe atom probe needle using off-axis electron holography without mean inner potential effects

    SciTech Connect

    Migunov, V. Dunin-Borkowski, R. E.; London, A.; Farle, M.

    2015-04-07

    The one-dimensional charge density distribution along an electrically biased Fe atom probe needle is measured using a model-independent approach based on off-axis electron holography in the transmission electron microscope. Both the mean inner potential and the magnetic contribution to the phase shift are subtracted by taking differences between electron-optical phase images recorded with different voltages applied to the needle. The measured one-dimensional charge density distribution along the needle is compared with a similar result obtained using model-based fitting of the phase shift surrounding the needle. On the assumption of cylindrical symmetry, it is then used to infer the three-dimensional electric field and electrostatic potential around the needle with ∼10 nm spatial resolution, without needing to consider either the influence of the perturbed reference wave or the extension of the projected potential outside the field of view of the electron hologram. The present study illustrates how a model-independent approach can be used to measure local variations in charge density in a material using electron holography in the presence of additional contributions to the phase, such as those arising from changes in mean inner potential and specimen thickness.

  14. Analysis of a New High-Toughness Ultra-high-Strength Martensitic Steel by Transmission Electron Microscopy and Atom Probe Tomography

    NASA Astrophysics Data System (ADS)

    Hartshorne, Matthew I.; McCormick, Caroline; Schmidt, Michael; Novotny, Paul; Isheim, Dieter; Seidman, David N.; Taheri, Mitra L.

    2016-04-01

    The microstructure of a new martensitic high-strength steel (Fe-0.40C-3.81Ni-1.31Cr-1.50Si-0.75Mn-0.52Mo-0.51Cu-0.30V) with high fracture toughness is characterized by transmission electron microscopy and atom probe tomography (APT). MC, M6C, and M23C6 precipitates form inside the martensitic lath matrix. The fracture toughness is insensitive to the dissolution of M23C6 precipitates at austenitizing temperatures above 1164 K (891 °C). APT reveals that solute segregation at the prior austenite grain boundaries (PAGB) is not uniform, with C, Mo, Si, Ni, and/or P enrichment varying at different areas of the PAGB. Si depletion is detected in the same area as the highest C enrichment. Carbon also segregates at lath boundaries. Segregation of C indicates the presence of retained austenite films at both PAGB and lath boundaries. Regions enriched in C up to 10 pct were found within the laths; however, no regions were enriched to the level expected of cementite or ɛ-carbide. The observed C distribution and high fracture toughness indicates that the tempering behavior is significantly different than that observed in 300M steel. The effect of Si, Ni, and Cu on the formation and stabilization of the regions of C enrichment and retained austenite require further study, as it may be key to the increased toughness.

  15. Titan probe technology assessment and technology development plan study

    NASA Technical Reports Server (NTRS)

    Castro, A. J.

    1980-01-01

    The need for technology advances to accomplish the Titan probe mission was determined by defining mission conditions and requirements and evaluating the technology impact on the baseline probe configuration. Mission characteristics found to be technology drivers include (1) ten years dormant life in space vacuum; (2) unknown surface conditions, various sample materials, and a surface temperature; and (3) mission constraints of the Saturn Orbiter Dual Probe mission regarding weight allocation. The following areas were identified for further development: surface sample acquisition system; battery powered system; nonmetallic materials; magnetic bubble memory devices, and the landing system. Preentry science, reliability, and weight reduction and redundancy must also be considered.

  16. Titan Lake Probe: The Ongoing NASA Decadal Study Preliminary Report

    NASA Astrophysics Data System (ADS)

    Waite, J. Hunter; Brockwell, Tim; Elliot, John; Reh, Kim; Spencer, John; Outer Planets Satellites Decadal Subpanel, The

    2010-05-01

    This talk provides an update on the scientific requirements and preliminary design of a Titan Lake Probe for a future NASA Flagship mission. The starting point for this study is the joint NASA ESA TSSM mission. Using this as a starting point we have revisited the scientific requirements and expanded them to include the possibility of a lake floater and a submersible. The preliminary results of this ongoing study will be presented. The scientific objectives of a Titan Lake Probe mission are: 1) to understand the formation and evolution of Titan and its atmosphere through measurement of the composition of the target lake (e.g., Kraken Mare), with particular emphasis on the isotopic composition of dissolved minor species and on dissolved noble gases, 2) to study the lake-atmosphere interaction in order to determine the role of Titan's lakes in the methane cycle, 3) to investigate the target lake as a laboratory for both pre-biotic organic chemistry in both water (or ammonia-enriched water) solutions and non-water solvents, and 4) to determine if Titan has an interior ocean by measuring tidal changes in the level of the lake over the course of Titan's sixteen-day orbit. The driving requirements for the mission are: 1) the need to land on and explore the lake at depth while adequately communicating the data back to Earth via either direct to Earth or relay communications, 2) thermal design that allows sustained (>32 days) sampling of the 94K lake environment, and 3) a mass spectrometer inlet system that allows sampling of gas, liquid, and solids from the 94K environment. The primary payload is an analytical chemistry laboratory that includes an inlet system for sampling gas, liquid, and solids in and above the lake feeding two capable mass spectrometers that determine the organic and isotopic composition of the sampled materials. The instrumentation also includes a meteorological package that can measure the rate of gas exchange between the lake and the atmosphere, and

  17. Atom interferometric studies of light scattering - A new technique for measuring atomic recoil

    NASA Astrophysics Data System (ADS)

    Beattie, Scott

    the technique is both simple and robust. We also show that coherence functions can be used to make a direct measurement of the probabilities of momentum states associated with the ground state. This measurement is interesting as it is performed under the conditions where the velocity distribution of the sample is much larger than the recoil velocity upsilon r = ℏkm . These measurements are consistent with Monte Carlo wave function simulations. The signal shape obtained in the second technique is also described by a much simpler analytical function than the fitting function used in the first technique. We present an analytical calculation of this signal shape using the theory of echo formation. This theory enables us to understand the effects of spontaneous emission and spatial profile of the laser beam on the signal shape. We show that the results for the signal shape match the predictions obtained using coherence functions. The theory of echo formation also predicts scaling laws for the grating contrast as a function of pulse area and number of additional standing wave pulses that are investigated experimentally. These studies are important for realizing improvements in precision measurements of oq. If the additional pulse at t = 2T -- delta T is a traveling wave, we observe an overall loss in contrast due to decoherence associated with spontaneous emission. The signal exhibits quasi-periodic revivals in contrast as a function of deltaT and this shape can be described by a suitable coherence function. This aspect of our work resembles previous studies in atomic beams. From the data, we accurately measure the probabilities of single and multiple photon scattering events and investigate the dependence of the photon scattering rate on detuning. The grating contrast is studied as a function of the intensity of continuous wave light and this data is used to extract the photon scattering rate as a function of detuning and light intensity as well as to infer the photon

  18. Analytical study of ultrasound influence on the molten metals atomization

    NASA Astrophysics Data System (ADS)

    Antonnikova, A.; Arkhipov, V.; Boiko, V.; Basalaev, S.; Konovalenko, A.; Zolotorev, N.

    2016-04-01

    This paper focuses on the study of influence of ultrasound on liquid atomization using ejection nozzles. Two principles of influence of ultrasound on the atomization process such as a change of conditions on gas-liquid boundary during the generation of ultrasound oscillation in the gas and liquid jet (film) disintegration under the action of capillary forces in cases of generation of ultrasound oscillation in the liquid are considered. The optimal values of the ultrasound oscillation frequencies are calculated. Two constructions of the nozzles patented are proposed.

  19. Atomic softness-based QSAR study of testosterone

    NASA Astrophysics Data System (ADS)

    Srivastava, H. K.; Pasha, F. A.; Singh, P. P.

    Ionization potential of an atom in a molecule, electron affinity of an atom in a molecule, and quantum chemical descriptor atomic softness values En‡-based quantitative structure-activity relationship (QSAR) study of testosterone derivatives have been done with the help of PM3 calculations on WinMOPAC 7.21 software. The 3D modeling and geometry optimization of all the compounds have been done with the help of PCMODEL software. The biological activities of testosterone derivatives have been taken from literature. The predicted values of biological activity with the help of multiple linear regression (MLR) analysis is very close to observed biological activity. The cross-validation coefficient and correlation coefficient also indicate that the QSAR model is valuable. Regression analysis shows a very good relationship with biological activity and En‡ values. With the help of these values, prediction of the biological activity of any unknown compound is possible.

  20. Study the friction behaviour of poly[2-(dimethylamino)ethyl methacrylate] brush with AFM probes in contact mechanics

    NASA Astrophysics Data System (ADS)

    Raftari, Maryam; Zhang, Zhenyu; Leggett, Graham J.; Geoghegan, Mark

    2011-10-01

    We have studied the frictional behaviour of grafted poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) films using friction force microscopy (FFM). The films were prepared on native oxide-terminated silicon substrates using the technique of atom transfer radical polymerization (ATRP). We show that single asperity contact mechanics (Johnson-Kendall-Roberts(JKR) and Derjaguin-Muller-Toporov(DMT)) as well as a linear (Amontons) relation between applied load and frictional load depending on the pH of the FFM probe. Measurements were made using functionalized and unfunctionalized silicon nitride triangular probes. Functionalized probes included gold-coated probes, and ones coated with a self-assembled monolayer of dodecanethiol (DDT). The frictional behaviour between PDMAEMA and all tips immersed in pH from 3 to 11 are corresponded to the DMT or JKR model and are linear in pH=1, 2, and 12. These results show that contact mechanics of polyelectrolytes in water is complex and strongly dependent on the environmental pH.