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Sample records for mgo thin filmsa

  1. Ion-induced grain growth and texturing in refractory thin films-A low temperature process

    SciTech Connect

    Seita, M.; Reiser, A.; Spolenak, R.

    2012-12-17

    Selective grain growth can be promoted in thin films independently of the materials intrinsic properties, such as the melting temperature, by ion-irradiation. This enables the previously impossible evolution of large grain-sized microstructures with controlled crystallographic textures even in refractory metals, such as {alpha}-tantalum. Experimental results from materials with different crystal structure are compared on the basis of a theoretical model, which reveals the differences in ion-induced grain-growth dynamics.

  2. Highly (100) oriented MgO growth on thin Mg layer in MTJ structure

    NASA Astrophysics Data System (ADS)

    Jimbo, K.; Nakagawa, S.

    2011-01-01

    In order to apply Stress Assisted Magnetization Reversal (SAMR) method to perpendicular magnetoresistive random access memory (p-MRAM) with magnetic tunnel junction (MTJ) using MgO (001) oriented barrier layer, multilayer of Ta/ Terfenol-D/ Mg/ MgO and Ta/ Terfenol-D/ MgO were prepared. While the MgO layer, deposited directly on the Terfenol-D layer, did not show (100) orientatin, very thin metallic Mg layer, deposited prior to the MgO deposition, was effective to attain MgO (100) orientation. The crystalline orientation was very weak without Mg, however, the multilayer with Mg showed very strong MgO(100) peak and the MgO orientation was shifted depending on the Mg thickness.

  3. When beauty is only skin deep; optimizing the sensitivity of specular neutron reflectivity for probing structure beneath the surface of thin filmsa)

    NASA Astrophysics Data System (ADS)

    Majkrzak, Charles F.; Carpenter, Elisabeth; Heinrich, Frank; Berk, Norman F.

    2011-11-01

    Specular neutron reflectometry has become an established probe of the nanometer scale structure of materials in thin film and multilayered form. It has contributed especially to our understanding of soft condensed matter of interest in polymer science, organic chemistry, and biology and of magnetic hard condensed matter systems. In this paper we examine a number of key factors which have emerged that can limit the sensitivity of neutron reflection as such a probe. Among these is loss of phase information, and we discuss how knowledge about material surrounding a film of interest can be applied to help resolve the problem. In this context we also consider what role the quantum phenomenon of interaction-free measurement might play in enhancing the statistical efficiency for obtaining reflectivity or transmission data.

  4. Giant intrinsic thermomagnetic effects in thin MgO magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Teixeira, J. M.; Costa, J. D.; Ventura, J.; Fernandez-Garcia, M. P.; Azevedo, J.; Araujo, J. P.; Sousa, J. B.; Wisniowski, P.; Cardoso, S.; Freitas, P. P.

    2013-05-01

    An intrinsic spin-dependent Seebeck effect in the linear tunneling transport regime of magnetic tunneling junctions (MTJs) was discovered recently. This effect leads to a nonlinear correction of Ohm's law in the dc response. We analyze this intrinsic magneto-thermoelectrical effect for MTJs with different MgO barrier (tb=0.7-1.35 nm) thicknesses. We report strong intrinsic effects in MTJs with thin MgO barriers (1189%), upon reversal of the magnetization of the two CoFeB layers. Such large effects are promising for useful spin caloritronic devices, integrating charge, heat, and spin tunnel transport.

  5. Defect structure of epitaxial CrxV1-x thin films on MgO(001)

    SciTech Connect

    Kaspar, Tiffany C.; Bowden, Mark E.; Wang, Chongmin; Shutthanandan, V.; Manandhar, Sandeep; van Ginhoven, Renee M.; Wirth, Brian D.; Kurtz, Richard J.

    2014-01-01

    Epitaxial thin films of CrxV1-x over the entire composition range were deposited on MgO(001) by molecular beam epitaxy. The films exhibited the expected 45° in-plane rotation with no evidence of phase segregation or spinodal decomposition. Pure Cr, with the largest lattice mismatch to MgO, exhibited full relaxation and cubic lattice parameters. As the lattice mismatch decreased with alloy composition, residual epitaxial strain was observed. For 0.2 ≤ x ≤ 0.4 the films were coherently strained to the substrate with associated tetragonal distortion; near the lattice-matched composition of x = 0.33, the films exhibited strain-free pseudomorphic matching to MgO. Unusually, films on the Cr-rich side of the lattice-matched composition exhibited more in-plane compression than expected from the bulk lattice parameters; this result was confirmed with both x-ray diffraction and Rutherford backscattering spectrometry channeling measurements. Although thermal expansion mismatch in the heterostructure may play a role, the dominant mechanism for this phenomenon is still unknown. High resolution transmission electron microscopy was utilized to characterize the misfit dislocation network present at the film/MgO interface. Dislocations were found to be present with a non-uniform distribution, which is attributed to the Volmer-Weber growth mode of the films. The CrxV1-x / MgO(001) system can serve as a model system to study both the fundamentals of defect formation in bcc films and the interplay between nanoscale defects such as dislocations and radiation damage.

  6. Competition between (001) and (111) MgO thin film growth on Al-doped ZnO by oxygen plasma assisted pulsed laser deposition

    SciTech Connect

    Xiao, Bo; Yang, Qiguang; Walker, Brandon; Gonder, Casey A.; Romain, Gari C.; Mundle, Rajeh; Bahoura, Messaoud; Pradhan, A. K.

    2013-06-07

    We report on the study of epitaxial MgO thin films on (0001) Al-doped ZnO (Al: ZnO) underlayers, grown by oxygen plasma assisted pulsed laser deposition technique. A systematic investigation of the MgO thin films was performed by X-ray diffraction and atomic force microscopy, along with the current-voltage characteristics. A distinguished behavior was observed that the preferred MgO orientation changes from (111) to (001) in the films as the growth temperature increases. Two completely different in-plane epitaxial relationships were also determined from X-ray diffraction as: [110]MgO//[1120]Al: ZnO and [110]MgO//[1100]Al: ZnO for (001) MgO with 60 Degree-Sign rotated triplet domains, and [110]MgO//[1120]Al: ZnO for (111) MgO with 180 Degree-Sign rotated twin. The pronounced temperature dependence indicates a reconciliation of the nucleation driving forces among surface, interfacial, and strain energy for heteroepitaxy of cubic MgO on hexagonal Al: ZnO. The related interfacial atomic registry is considered to be important to the formation of unusual (001) MgO on hexagonal crystals. In addition, the electrical characterization revealed a dramatic reduction of the leakage current in (001) MgO thin films, whereas the small grain size of (111) MgO is identified by atomic force microscopy as a main cause of large leakage current.

  7. Formation of Catalyst Model Dispersed of Pd on a thin MgO(100)

    NASA Astrophysics Data System (ADS)

    Baara, F.; Chemam, A.

    2016-04-01

    The nucleation kinetics or the formation of a catalyst model dispersed for the system Pd/thin MgO (100) are calculated by developing many programs using Fortran software. This simulation is based upon parameters studied in situ by transmission electron microscopy (TEM), related to the first quantitative study on the nucleation and the growth. Palladium nanoparticles deposited on thin MgO are tested in the temperature range 573-1073 K and deposition time of 1000 s. The nucleation kinetics are interpreted according to the theory of random nucleation. The general scheme is consisting of three stages namely, nucleation, growth and coalescence. The saturation density of clusters decreases when the substrate temperature increases following Arrhenius law. This behavior is in agreement with a recent AFM study for Ag/MgO and Au/MgO. The phenomenon of coalescence is explained via island migration process. It is shown that the coalescence occurs more rapidly when the substrate temperature is high.

  8. Microstructure and magnetic properties of FeCo epitaxial thin films grown on MgO single-crystal substrates

    SciTech Connect

    Shikada, Kouhei; Ohtake, Mitsuru; Futamoto, Masaaki; Kirino, Fumiyoshi

    2009-04-01

    FeCo epitaxial films were prepared on MgO(100), MgO(110), and MgO(111) substrates by ultrahigh vacuum molecular beam epitaxy. FeCo thin films with (100), (211), and (110) planes parallel to the substrate surface grow on respective MgO substrates. FeCo/MgO interface structures are studied by high-resolution cross-sectional transmission electron microscopy and the epitaxial growth mechanism is discussed. Atomically sharp boundaries are recognized between the FeCo thin films and the MgO substrates where misfit dislocations are introduced in the FeCo thin films presumably to decrease the lattice misfits. Misfit dislocations are observed approximately every 9 and 1.4 nm in FeCo thin film at the FeCo/MgO(100) and the FeCo/MgO(110) interfaces, respectively. X-ray diffraction analysis indicates that the lattice spacing measured parallel to the single-crystal substrate surfaces are in agreement within 0.1% with those of the respective bulk values of Fe{sub 50}Co{sub 50} alloy crystal, showing that the FeCo film strain is very small. The magnetic anisotropies of these epitaxial films basically reflect the magnetocrystalline anisotropy of bulk FeCo alloy crystal.

  9. Acetylene trimerization on Ag, Pd and Rh atoms deposited on MgO thin films.

    PubMed

    Judai, Ken; Wörz, Anke S; Abbet, Stéphane; Antonietti, Jean-Marie; Heiz, Ueli; Del Vitto, Annalisa; Giordano, Livia; Pacchioni, Gianfranco

    2005-03-01

    The acetylene trimerization on the group VIII transition metal atoms, Rh and Pd, as well as on Ag atoms supported on MgO thin films has been studied experimentally and theoretically. The three metal atoms with the atomic configurations 4d(8)5s1 (Rh), 4d10s0 (Pd) and 4d(10)5s1 (Ag) behave distinctly differently. The coinage metal atom silver is basically inert for this reaction, whereas Pd is active at 220 and 320 K, and Rh produces benzene in a rather broad temperature range from 350 to ca. 430 K. The origins of these differences are not only the different electronic configurations, leading to a weak interaction of acetylene with silver due to strong Pauli repulsion with the 5s electron but also the different stability and dynamics of the three atoms on the MgO surface. In particular, Rh and Pd atoms interact differently with surface defects like the oxygen vacancies (F centers) and the step edges. Pd atoms migrate already at low temperature exclusively to F centers where the cyclotrimerization is efficiently promoted. The Rh atoms on the other hand are not only trapped on F centers but also at step edges up to about 300 K. Interestingly, only Rh atoms on F centers catalyze the trimerization reaction whereas they are turned inert on the step edges due to strong steric effects. PMID:19791385

  10. Strain effects in epitaxial Mn{sub 2}O{sub 3} thin film grown on MgO(100)

    SciTech Connect

    Dang Duc Dung; Duong Van Thiet; Duong Anh Tuan; Cho, Sunglae

    2013-05-07

    We report on the epitaxial growth and magnetic properties of Mn{sub 2}O{sub 3} thin films grown on MgO(001) substrate by molecular beam epitaxy. We observed the reduction in binding energy of Mn valence states, the increase in satellite separation up to 12.7 eV, and the smaller band gap of 3.32 eV. In addition, the antiferromagnetic ordering below 90 K in bulk changed to ferrimagnetic up to 175 K. The results were possibly to be explained by a lattice mismatch strain on Mn{sub 2}O{sub 3} film on MgO(001) substrate.

  11. Surface Electronic Properties and Site-Specific Laser Desorption Processes of Highly Structured Nanoporous MgO Thin Films

    SciTech Connect

    Henyk, Matthias; Beck, Kenneth M.; Engelhard, Mark H.; Joly, Alan G.; Hess, Wayne P.; Dickinson, J T.

    2005-11-20

    The surface electronic properties of metal oxides critically depends on low-coordinated sites, such as kinks, corners and steps [1]. In order to characterize experimentally those surface states as well as their role for laser desorption processes, we prepare defect enriched surfaces by growing thin MgO films using reactive ballistic deposition [2] on crystalline dielectric substrates. With samples held at room temperature, the resulting MgO films are highly textured and consist of porous columns with column lengths ranging from tens of nanometers up to six micrometers. Measurements by x-ray photoelectron spectroscopy (XPS) are carried out in-situ for MgO films, vacuum-cleaved MgO crystals, and water vapor exposed samples. In the case of thin films, we observe O 1s spectra with a significant shoulder feature at 2.3 eV higher binding energy (HBE) than the corresponding peak at 530.0 eV representing regular lattice oxygen. We evaluate this feature in terms of non-stoichiometric oxygen and formation of an oxygen-rich layer at the topmost surface of the MgO columns. In contrast, no HBE-features are detectable from clean single crystal MgO surfaces, while the hydroxyl O 1s band peaks at 531.6 eV. Under excitation with 266-nm-laser-pulses, known to be resonant with low-coordinated surface anions [3], we observe preferential depletion of defective oxygen-states (HBE signal) and temporary restoration of ideal surface stoichiometry. Furthermore, auxiliary signals are observed on several micrometer thick films, acting like satellites to major photoelectron-peaks (O 1s, Mg 2s, and Mg 2p) but shifted by approximately 4 eV towards lower kinetic energy. These features are depleted by UV-light exposure, pointing to the occurrence of surface-charge imbalance, accompanied by photon stimulated charge-transfer reactions. These results are in line with desorption experiments of neutrals, stimulated by laser excitation at 266 nm. According to the low-coordination nature of nanoporous MgO

  12. Co2FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

    NASA Astrophysics Data System (ADS)

    Belmeguenai, M.; Tuzcuoglu, H.; Gabor, M. S.; Petrisor, T.; Tiusan, C.; Zighem, F.; Chérif, S. M.; Moch, P.

    2014-01-01

    10 nm and 50 nm Co2FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (Ta), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing Ta, while the uniaxial anisotropy field is nearly unaffected by Ta within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with Ta. Finally, the FMR linewidth decreases when increasing Ta, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10-3 and 1.3×10-3 for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively).

  13. Etching mechanism of MgO thin films in inductively coupled Cl{sub 2}/Ar plasma

    SciTech Connect

    Efremov, A.M.; Koo, Seong-Mo; Kim, Dong-Pyo; Kim, Kyoung-Tae; Kim, Chang-Il

    2004-09-01

    The etching mechanism of MgO thin films in Cl{sub 2}/Ar plasma was investigated. It was found that the increasing Ar in the mixing ratio of Cl{sub 2}/Ar plasma causes nonmonotonic MgO etch rate, which reaches a maximum value at 70%Ar+30%Cl{sub 2}. Langmuir probe measurement showed the noticeable influence of Cl{sub 2}/Ar mixing ratio on electron temperature and electron density. The zero-dimensional plasma model indicated monotonic changes of both densities and fluxes of active species. At the same time, analyses of surface kinetics showed the possibility of nonmonotonic etch rate behavior due to the concurrence of physical and chemical pathways in ion-assisted chemical reaction.

  14. Ion-induced secondary electron emission behavior of sol-gel-derived MgO thin films used for protective layers in alternating current plasma display panels

    NASA Astrophysics Data System (ADS)

    Jung, Hyun Suk; Lee, Jung-Kun; Hong, Kug Sun; Youn, Hyuk-Joon

    2002-09-01

    MgO thin films were prepared using two sols (hydrolyzed sol and stabilized sol) and the ion-induced secondary electron emission behavior of the resultant thin films was investigated. A severe fluctuation in the secondary electron emission current was found in MgO films from hydrolyzed sol. The instability of the ion-induced current was due to the nanosized pores, which were formed during the topotactic reaction of Mg(OH)2 to MgO. Nonhydrolyzed MgO films, however, showed a stable ion-induced current. The ion-induced secondary electron emission coefficients (gammai) of the MgO films had a maximum of 0.95plus-or-minus0.02 when the films were heat treated at 550 degC in O2. The change in gammai of nonhydrolyzed films was discussed from the viewpoint of crystallinity, residual organics, and surface roughness. The high gammai and low processing temperature of nonhydrolyzed MgO films revealed that the sol-gel process is suitable to prepare MgO films for use as a protective layer in ac plasma display panel cells.

  15. Preparation and characterization of thin films of MgO, Al2O3 and MgAl2O4 by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Huang, Ron; Kitai, Adrian H.

    1993-02-01

    MgO, Al2O3 and MgAl2O4 thin films were deposited on silicon substrates at various temperatures by the atomic layer deposition (ALD) method using bis(cyclopentadienyl)magnesium, triethylaluminum, and H2O and were characterized systematically. High-quality polycrystalline MgO films were deposited for a substrate temperature above 500°C, and amorphous thin films were deposited around 400°C. The deposited Al2O3 and MgAl2O4 thin films were characterized as amorphous in structure. Applicability of ALD to complex oxides is discussed.

  16. Application of ion scattering spectroscopy to measurement of surface potential of MgO thin film under ion irradiation

    SciTech Connect

    Nagatomi, T.; Kuwayama, T.; Takai, Y.; Yoshino, K.; Morita, Y.; Kitagawa, M.; Nishitani, M.

    2008-02-25

    An experimental approach was proposed for the measurement of the surface potential (SP) induced on an insulator surface during ion irradiation by ion scattering spectroscopy (ISS). The resultant ISS spectra obtained for a MgO thin film of 600 nm thickness on a Si substrate under 950 eV He{sup +} irradiation revealed that the surface is positively charged by approximately 230 V. In addition, the onset energy of a secondary ion peak indicated a SP of approximately 205 V. The present results confirmed that ISS is an effective technique for measuring the SP during ion irradiation.

  17. Interplay of uniaxial and cubic anisotropy in epitaxial Fe thin films on MgO (001) substrate

    NASA Astrophysics Data System (ADS)

    Mallik, Srijani; Chowdhury, Niru; Bedanta, Subhankar

    2014-09-01

    Epitaxial Fe thin films were grown on annealed MgO(001) substrates at oblique incidence by DC magnetron sputtering. Due to the oblique growth configuration, uniaxial anisotropy was found to be superimposed on the expected four-fold cubic anisotropy. A detailed study of in-plane magnetic hysteresis for Fe on MgO thin films has been performed by Magneto Optic Kerr Effect (MOKE) magnetometer. Both single step and double step loops have been observed depending on the angle between the applied field and easy axis i.e. along ⟨100⟩ direction. Domain images during magnetization reversal were captured by Kerr microscope. Domain images clearly evidence two successive and separate 90° domain wall (DW) nucleation and motion along cubic easy cum uniaxial easy axis and cubic easy cum uniaxial hard axis, respectively. However, along cubic hard axis two 180° domain wall motion dominate the magnetization reversal process. In spite of having four-fold anisotropy it is essential to explain magnetization reversal mechanism in 0°< ϕ < 90° span as uniaxial anisotropy plays a major role in this system. Also it is shown that substrate rotation can suppress the effect of uniaxial anisotropy superimposed on four-fold anisotropy.

  18. Real-time observation of the melting process of YBCO thin film on MgO substrate

    NASA Astrophysics Data System (ADS)

    J, Hu; X, Yao; L, Rao Q.

    2003-11-01

    In order to study the mechanism of the liquid phase hetero-epitaxial growth, the melting process of YBa2Cu3O7-dgr (YBCO) thin films was observed by high-temperature optical microscopy. During the heating from room temperature to a temperature above the YBCO peritectic temperature (Tp), we surprisingly find that the YBCO thin film with a MgO substrate can be substantially superheated above the Tp of the YBCO oxide (at least 50 °C) at a heating rate of 5 °C min-1. This is a novel superheating phenomenon involved in a peritectic reaction and an oxide material, which is different from one reported in systems of metals and their alloys. After the melting process, x-ray diffraction analysis was performed, which shows that Y2BaCuO5 (Y211) grains are in good alignment on the MgO substrate. The superheating mechanism of the YBCO oxide is discussed.

  19. Characterization of two different orientations of epitaxial niobium thin films grown on MgO(001) surfaces

    NASA Astrophysics Data System (ADS)

    Beringer, D. B.; Roach, W. M.; Clavero, C.; Reece, C. E.; Lukaszew, R. A.

    2013-12-01

    Epitaxial Nb thin films deposited onto the same crystalline insulating surface can evolve in very different fashions depending on specific deposition conditions, thereby affecting their microstructure, surface morphology and superconducting properties. Here, we examine and compare the microstructure and ensuing surface morphology from two distinct Nb/MgO series each with its own epitaxial registry—namely Nb(001)/MgO(001) and Nb(110)/MgO(001)—leading to distinct surface anisotropy and we closely examine the dynamical scaling of the surface features during growth. We compare our findings with those in other metal/MgO epitaxial systems and for the first time, general scaling formalism is applied to analyze anisotropic surfaces exhibiting biaxial symmetry. Further, Power Spectral Density is applied to the specific problem of thin film growth and surface evolution to qualify the set of deposition conditions leading to smoother surfaces. We find good correlation between the surface morphology and microstructure of the various Nb films with superconducting properties such as their residual resistance ratio and lower critical field.

  20. Characterization of two different orientations of epitaxial niobium thin films grown on MgO(001) surfaces

    SciTech Connect

    Beringer, Douglas B.; Roach, William M.; Clavero Perez, Cesar; Reece, Charles E.; Lukaszew, Rosa

    2013-12-01

    Epitaxial Nb thin films deposited onto the same crystalline insulating surface can evolve in very different fashions depending on specific deposition conditions, thereby affecting their microstructure, surface morphology and superconducting properties. Here, we examine and compare the microstructure and ensuing surface morphology from two distinct Nb/MgO series each with its own epitaxial registry?namely Nb(001)/MgO(001) and Nb(110)/MgO(001)?leading to distinct surface anisotropy and we closely examine the dynamical scaling of the surface features during growth. We compare our findings with those in other metal/MgO epitaxial systems and for the first time, general scaling formalism is applied to analyze anisotropic surfaces exhibiting biaxial symmetry. Further, Power Spectral Density is applied to the specific problem of thin film growth and surface evolution to qualify the set of deposition conditions leading to smoother surfaces. We find good correlation between the surface morphology and microstructure of the various Nb films with superconducting properties such as their residual resistance ratio and lower critical field.

  1. Superconducting YBa 2Cu 3O 7- δ thin film grown on metallic film evaporated on MgO

    NASA Astrophysics Data System (ADS)

    Verdyan, A.; Azoulay, J.; Lapsker, I.

    2001-03-01

    At present it is commonly accepted that thin film formation of YBa 2Cu 3O 7- δ (YBCO) on conducting substrate is one of the keys to further development of advanced devices in the microelectronic and other applications. We have grown YBCO thin films by resistive evaporation technique on MgO coated with metallic layers (Ni or Ag). A simple inexpensive vacuum system equipped with resistively heated boats for metal and precursor mixture of yttrium, copper and barium fluoride powders was used. X-ray diffraction (XRD) and scanning electron microscopy techniques were used for texture, morphology and surface analyses respectively. Electrical and magnetical properties were determined by a standard dc four-probe method. The way of heating process is shown to be critical parameter in the film quality. The physical and electrical properties of the YBCO films are discussed in light of the fact that XRD measurements done on the metallic buffer layers have revealed a multicrystalline structure.

  2. Unusual dissociative adsorption of H2 over stoichiometric MgO thin film supported on molybdenum

    NASA Astrophysics Data System (ADS)

    Song, Zhenjun; Xu, Hu

    2016-03-01

    The dissociation of a hydrogen molecule on perfect MgO(0 0 1) films deposited on Mo(0 0 1) surface is investigated systematically using periodic density-functional theory (DFT) method. The unusual adsorption behavior of heterolytic dissociative hydrogen molecule at neighboring surface oxygen and surface magnesium, is clarified here. To our knowledge, this heterolytic dissociative state has never been found before on bulk MgO(0 0 1) or metal supported perfect MgO(0 0 1) surfaces (without low coordination sites). The results confirm that, in all cases, the heterolytic dissociation is much more favorable that homolytic dissociation both energetically and kinetically. The energy differences between two dissociative states are very large, in the range of 1.1 eV-1.5 eV for Mo supported 1 ML-3 ML oxide films, which inhibits, to a great extent, the homolytic dissociation in the respect of reaction thermodynamics. The energy barriers of heterolytic dissociation are about 0.5 eV, much lower that the barrier of homolytic dissociation. The transformation reaction on thick films will be more endothermic. Passing through heterolytic dissociation state has significantly lowered the reaction heat and the energy barrier for obtaining homolytic dissociative structure, which makes the homolytic splitting of H2 easier on 2 ML oxide films. The results provide a useful strategy for enhancing the reactivity of the nonreducible metal oxide.

  3. Superconducting MgB2 thin films grown by pulsed laser deposition on Al2O3(0001) and MgO(100) substrates

    NASA Astrophysics Data System (ADS)

    Wang, S. F.; Dai, S. Y.; Zhou, Y. L.; Chen, Z. H.; Cui, D. F.; Xu, J. D.; He, M.; Lu, H. B.; Yang, G. Z.; Fu, G. S.; Han, L.

    2001-11-01

    Superconducting MgB2 thin films were fabricated on Al2O3(0001) and MgO(100) substrates by a two-step method. Boron thin films were deposited by pulsed laser deposition followed by an ex-situ annealing process. Resistance measurements of the deposited MgB2 films show a Tc of 38.6 K for MgB2/Al2O3 and 38.1 K for MgB2/MgO. Atomic force microscopy, scanning electron microscopy and x-ray diffraction were used to study the properties of the films. The results indicate that the MgB2/Al2O3 films consist of well-crystallized grains with a highly c-axis-oriented structure while the MgB2/MgO films have a dense uniform appearance with an unfixed orientation.

  4. Temperature dependence of reliability characteristics for magnetic tunnel junctions with a thin MgO dielectric film

    NASA Astrophysics Data System (ADS)

    Choi, Chul-Min; Oh, Young-Taek; Kim, Kyung-Jun; Park, Jin-Suk; Sukegawa, Hiroaki; Mitani, Seiji; Kim, Sung-Kyu; Lee, Jeong-Yong; Song, Yun-Heub

    2016-07-01

    Temperature dependence of the reliability characteristics of magnetic tunnel junctions (MTJs) with a thin (∼1 nm thick) MgO dielectric film were investigated by numerical analyses based on the E-model, 1/E-model, and power-law voltage V-model, as well as by measuring time-dependent dielectric breakdown (TDDB) degradation. Although the tunneling process giving rise to TDDB is still under debate, the temperature dependence of TDDB was much weaker using the 1/E model than the E-model or power-law model. The TDDB data measured experimentally in CoFeB/MgO/CoFeB MTJ devices also showed rather weak temperature dependence, in good agreement with the numerical results obtained from the 1/E-model considering the self-heating effect in MTJ devices. Moreover, we confirmed by interval voltage stress tests that some degradation in the MgO dielectric layer occurred. Based on our findings, we suggest that to characterize the reliability of MTJs, combined temperature measurements of TDDB and 1/E-model analyses taking the self-heating effect into account should be performed.

  5. Magnetic properties of Sm-Co thin films grown on MgO(100) deposited from a single alloy target

    SciTech Connect

    Verhagen, T. G. A.; Boltje, D. B.; Ruitenbeek, J. M. van; Aarts, J.

    2014-08-07

    We have grown epitaxial Sm-Co thin films by sputter deposition from a single alloy target with a nominal SmCo{sub 5} composition on Cr(100)-buffered MgO(100) single-crystal substrates. By varying the Ar gas pressure, we can change the composition of the film from a SmCo{sub 5}-like to a Sm{sub 2}Co{sub 7}-like phase. The composition, crystal structure, morphology, and magnetic properties of these films have been determined using Rutherford Backscattering, X-ray diffraction, and magnetization measurements. We find that we can grow films with, at room temperature, coercive fields as high as 3.3 T, but with a remanent magnetization which is lower than can be expected from the texturing. This appears to be due to the Sm content of the films, which is higher than expected from the content of the target, even at the lowest possible sputtering pressures. Moreover, we find relatively large variations of film properties using targets of nominally the same composition. At low temperatures, the coercive fields increase, as expected for these hard magnets, but in the magnetization, we observe a strong background signal from the paramagnetic impurities in the MgO substrates.

  6. Superconducting YBCO thin film on multicrystalline Ag film evaporated on MgO substrate

    NASA Astrophysics Data System (ADS)

    Azoulay, Jacob; Verdyan, Armen; Lapsker, Igor

    Superconducting YBa 2Cu 3O 7-δ films were grown by resistive evaporation on multicrystalline silver film which was evaporated on MgO substrate. A simple inexpensive vacuum system equipped with resistively heated boat was used for the whole process. Silver film was first evaporated on MgO substrate kept at 400°C during the evaporation after which with no further annealing a precursor mixture of yttrium small grains and Cu and BaF2 in powder form weighed in the atomic proportion to yield stoichiometric YBa 2Cu 3O 7 was evaporated. The films thus obtained were annealed at 740°C under low oxygen partial pressure of about 1Pa for 30 minutes to form the superconducting phase. X-ray diffraction and scanning electron microscopy techniques were used for texture and surface analysis. Electrical properties were determined using a standard dc four-probe for electrical measurements. The physical and electrical properties of the YBCO films are discussed in light of the fact that X-ray diffraction measurements done on the silver film have revealed a multicrystalline structure

  7. MgO platelets and high critical field in MgB2 thin films doped with carbon from methane

    NASA Astrophysics Data System (ADS)

    Zhu, Y.; Hunte, F.; Zhuang, C. G.; Feng, Q. R.; Gan, Z. Z.; Xi, X. X.; Larbalestier, D. C.; Voyles, P. M.

    2009-12-01

    We report that C-doped MgB2 thin films deposited by hybrid physical-chemical vapor deposition (HPCVD) using CH4 as the carbon source have Hc2(0 K)~60 T, similar to that of HPCVD films obtained using (MeCp)2Mg for the carbon. Using transmission electron microscopy, we show that in the films doped using CH4 there is a MgB2C2 layer on top of the MgB2 film, which does not degrade the MgB2 connectivity or Jc. We also find a high density of coherent MgO nanoplatelets in the MgB2 which create strain fields which may give rise to strong π-band scattering and the very high Hc2.

  8. Heteroepitaxial growth of Pt and Au thin films on MgO single crystals by bias-assisted sputtering

    PubMed Central

    Tolstova, Yulia; Omelchenko, Stefan T.; Shing, Amanda M.; Atwater, Harry A.

    2016-01-01

    The crystallographic orientation of a metal affects its surface energy and structure, and has profound implications for surface chemical reactions and interface engineering, which are important in areas ranging from optoelectronic device fabrication to catalysis. However, it can be very difficult and expensive to manufacture, orient, and cut single crystal metals along different crystallographic orientations, especially in the case of precious metals. One approach is to grow thin metal films epitaxially on dielectric substrates. In this work, we report on growth of Pt and Au films on MgO single crystal substrates of (100) and (110) surface orientation for use as epitaxial templates for thin film photovoltaic devices. We develop bias-assisted sputtering for deposition of oriented Pt and Au films with sub-nanometer roughness. We show that biasing the substrate decreases the substrate temperature necessary to achieve epitaxial orientation, with temperature reduction from 600 to 350 °C for Au, and from 750 to 550 °C for Pt, without use of transition metal seed layers. In addition, this temperature can be further reduced by reducing the growth rate. Biased deposition with varying substrate bias power and working pressure also enables control of the film morphology and surface roughness. PMID:26984041

  9. Heteroepitaxial growth of Pt and Au thin films on MgO single crystals by bias-assisted sputtering

    DOE PAGESBeta

    Tolstova, Yulia; Omelchenko, Stefan T.; Shing, Amanda M.; Atwater, Harry A.

    2016-03-17

    The crystallographic orientation of a metal affects its surface energy and structure, and has profound implications for surface chemical reactions and interface engineering, which are important in areas ranging from optoelectronic device fabrication to catalysis. However, it can be very difficult and expensive to manufacture, orient, and cut single crystal metals along different crystallographic orientations, especially in the case of precious metals. One approach is to grow thin metal films epitaxially on dielectric substrates. In this work, we report on growth of Pt and Au films on MgO single crystal substrates of (100) and (110) surface orientation for use asmore » epitaxial templates for thin film photovoltaic devices. We develop bias-assisted sputtering for deposition of oriented Pt and Au films with sub-nanometer roughness. We show that biasing the substrate decreases the substrate temperature necessary to achieve epitaxial orientation, with temperature reduction from 600 to 350 °C for Au, and from 750 to 550 °C for Pt, without use of transition metal seed layers. Additionally, this temperature can be further reduced by reducing the growth rate. Biased deposition with varying substrate bias power and working pressure also enables control of the film morphology and surface roughness.« less

  10. Heteroepitaxial growth of Pt and Au thin films on MgO single crystals by bias-assisted sputtering

    NASA Astrophysics Data System (ADS)

    Tolstova, Yulia; Omelchenko, Stefan T.; Shing, Amanda M.; Atwater, Harry A.

    2016-03-01

    The crystallographic orientation of a metal affects its surface energy and structure, and has profound implications for surface chemical reactions and interface engineering, which are important in areas ranging from optoelectronic device fabrication to catalysis. However, it can be very difficult and expensive to manufacture, orient, and cut single crystal metals along different crystallographic orientations, especially in the case of precious metals. One approach is to grow thin metal films epitaxially on dielectric substrates. In this work, we report on growth of Pt and Au films on MgO single crystal substrates of (100) and (110) surface orientation for use as epitaxial templates for thin film photovoltaic devices. We develop bias-assisted sputtering for deposition of oriented Pt and Au films with sub-nanometer roughness. We show that biasing the substrate decreases the substrate temperature necessary to achieve epitaxial orientation, with temperature reduction from 600 to 350 °C for Au, and from 750 to 550 °C for Pt, without use of transition metal seed layers. In addition, this temperature can be further reduced by reducing the growth rate. Biased deposition with varying substrate bias power and working pressure also enables control of the film morphology and surface roughness.

  11. The microstructure, electronic, and magnetic characterization of highly ordered Co{sub 2}MnSi thin films deposited on MgO substrate

    SciTech Connect

    Yang, F. J.; Chen, X. Q.

    2013-06-24

    Co{sub 2}MnSi thin films are usually deposited on Cr-buffered MgO substrate. In this work, Co{sub 2}MnSi thin films were deposited directly on MgO substrate and annealed at 350 Degree-Sign C to 650 Degree-Sign C to investigate the evolution of microstructure, electronic, and magnetic properties. Due to nearly perfect B2-ordering and very good L2{sub 1}-ordering, the M{sub s} increases to 1029 emu/cc and H{sub c} decreases to 27 Oe, respectively, after annealing at 650 Degree-Sign C. The large residual resistance ratio (RRR = 2.40) and small magnetic damping constant ({alpha} = 0.0039) further demonstrates that nearly perfect B2-ordering, good L2{sub 1} ordering, and nearly perfect film quality have been achieved.

  12. Co2FeAl thin films grown on MgO substrates: Correlation between static, dynamic, and structural properties

    NASA Astrophysics Data System (ADS)

    Belmeguenai, M.; Tuzcuoglu, H.; Gabor, M. S.; Petrisor, T., Jr.; Tiusan, C.; Berling, D.; Zighem, F.; Chauveau, T.; Chérif, S. M.; Moch, P.

    2013-05-01

    Co2FeAl (CFA) thin films with thickness varying from 10 to 115 nm have been deposited on MgO(001) substrates by magnetron sputtering and then capped by a Ta or Cr layer. X-ray diffraction (XRD) revealed that the cubic [001] CFA axis is normal to the substrate and that all the CFA films exhibit full epitaxial growth. The chemical order varies from the B2 phase to the A2 phase when decreasing the thickness. Magneto-optical Kerr effect (MOKE) and vibrating sample magnetometer (VSM) measurements show that, depending on the field orientation, one- or two-step switchings occur. Moreover, the films present a quadratic MOKE signal increasing with the CFA thickness, due to the increasing chemical order. Ferromagnetic resonance (FMR), MOKE transverse bias initial inverse susceptibility and torque (TBIIST) measurements reveal that the in-plane anisotropy results from the superposition of a uniaxial and of a fourfold symmetry term. The fourfold anisotropy is in accord with the crystal structure of the samples and is correlated to the biaxial strain and to the chemical order present in the films. In addition, a large negative perpendicular uniaxial anisotropy is observed. Frequency and angular dependencies of the ferromagnetic resonance linewidth show two magnon scattering and mosaicity contributions, which depend on the CFA thickness. A Gilbert damping coefficient as low as 0.0011 is found.

  13. Magneto-transport and thermoelectric properties of epitaxial FeSb2 thin film on MgO substrate

    NASA Astrophysics Data System (ADS)

    Duong, Anh Tuan; Rhim, S. H.; Shin, Yooleemi; Nguyen, Van Quang; Cho, Sunglae

    2015-01-01

    We report magneto-transport and thermoelectric properties of FeSb2 thin film epitaxially grown on the MgO substrate using molecular beam epitaxy. The film exhibits compressive strain of 1.74% owing to large lattice mismatch, whose physical consequences are nontrivial. Magnetic phase has been changed from diamagnetic in bulk, as evidenced by anomalous Hall effect (AHE) and negative magneto-resistance (MR). The FeSb2 film is semiconducting without any metallic transition unlike the bulk counterpart. In particular, hysteresis in MR with distinct feature of AHE is evident with coercive field of 500 and 110 Oe for T = 20 and 50 K, respectively. Furthermore, from the Seebeck coefficients and temperature dependence of the resistivity, it is evident that the film is semiconducting with small band gap: 3.76 meV for T < 40 K and 13.48 meV for T > 40 K, respectively, where maximum thermoelectric power factor of 12 μV/cm.K at T = 50 K.

  14. Magneto-transport and thermoelectric properties of epitaxial FeSb{sub 2} thin film on MgO substrate

    SciTech Connect

    Duong, Anh Tuan; Rhim, S. H. Shin, Yooleemi; Nguyen, Van Quang; Cho, Sunglae

    2015-01-19

    We report magneto-transport and thermoelectric properties of FeSb{sub 2} thin film epitaxially grown on the MgO substrate using molecular beam epitaxy. The film exhibits compressive strain of 1.74% owing to large lattice mismatch, whose physical consequences are nontrivial. Magnetic phase has been changed from diamagnetic in bulk, as evidenced by anomalous Hall effect (AHE) and negative magneto-resistance (MR). The FeSb{sub 2} film is semiconducting without any metallic transition unlike the bulk counterpart. In particular, hysteresis in MR with distinct feature of AHE is evident with coercive field of 500 and 110 Oe for T = 20 and 50 K, respectively. Furthermore, from the Seebeck coefficients and temperature dependence of the resistivity, it is evident that the film is semiconducting with small band gap: 3.76 meV for T < 40 K and 13.48 meV for T > 40 K, respectively, where maximum thermoelectric power factor of 12 μV/cm·K at T = 50 K.

  15. Band gap and defect states of MgO thin films investigated using reflection electron energy loss spectroscopy

    SciTech Connect

    Heo, Sung; Cho, Eunseog; Lee, Hyung-Ik; Park, Gyeong Su; Kang, Hee Jae; Nagatomi, T.; Choi, Pyungho; Choi, Byoung-Deog

    2015-07-15

    The band gap and defect states of MgO thin films were investigated by using reflection electron energy loss spectroscopy (REELS) and high-energy resolution REELS (HR-REELS). HR-REELS with a primary electron energy of 0.3 keV revealed that the surface F center (FS) energy was located at approximately 4.2 eV above the valence band maximum (VBM) and the surface band gap width (E{sub g}{sup S}) was approximately 6.3 eV. The bulk F center (F{sub B}) energy was located approximately 4.9 eV above the VBM and the bulk band gap width was about 7.8 eV, when measured by REELS with 3 keV primary electrons. From a first-principles calculation, we confirmed that the 4.2 eV and 4.9 eV peaks were F{sub S} and F{sub B}, induced by oxygen vacancies. We also experimentally demonstrated that the HR-REELS peak height increases with increasing number of oxygen vacancies. Finally, we calculated the secondary electron emission yields (γ) for various noble gases. He and Ne were not influenced by the defect states owing to their higher ionization energies, but Ar, Kr, and Xe exhibited a stronger dependence on the defect states owing to their small ionization energies.

  16. Low frequency noise in asymmetric double barrier magnetic tunnel junctions with a top thin MgO layer

    NASA Astrophysics Data System (ADS)

    Guo, Hui-Qiang; Tang, Wei-Yue; Liu, Liang; Wei, Jian; Li, Da-Lai; Feng, Jia-Feng; Han, Xiu-Feng

    2015-07-01

    Low frequency noise has been investigated at room temperature for asymmetric double barrier magnetic tunnel junctions (DBMTJs), where the coupling between the top and middle CoFeB layers is antiferromagnetic with a 0.8-nm thin top MgO barrier of the CoFeB/MgO/CoFe/CoFeB/MgO/CoFeB DBMTJ. At enough large bias, 1/f noise dominates the voltage noise power spectra in the low frequency region, and is conventionally characterized by the Hooge parameter αmag. With increasing external field, the top and bottom ferromagnetic layers are aligned by the field, and then the middle free layer rotates from antiparallel state (antiferromagnetic coupling between top and middle ferromagnetic layers) to parallel state. In this rotation process αmag and magnetoresistance-sensitivity-product show a linear dependence, consistent with the fluctuation dissipation relation. With the magnetic field applied at different angles (θ) to the easy axis of the free layer, the linear dependence persists while the intercept of the linear fit satisfies a cos(θ) dependence, similar to that for the magnetoresistance, suggesting intrinsic relation between magnetic losses and magnetoresistance. Project supported by the National Basic Research Program of China (Grant Nos. 2011CBA00106, 2012CB927400, 2010CB934401, and 2014AA032904), the National High Technology Research and Development Program of China (Grant No. 2014AA032904), and the National Natural Science Foundation of China (Grant Nos. 11434014 and 11104252).

  17. Giant perpendicular magnetocrystalline anisotropy of 3d transition-metal thin films on MgO

    SciTech Connect

    Nakamura, Kohji Ikeura, Yushi; Akiyama, Toru; Ito, Tomonori

    2015-05-07

    Magnetocrystalline anisotropy (MCA) of the Fe-based transition-metal thin films was investigated by means of first principles full-potential linearized augmented plane wave method. A giant perpendicular MCA (PMCA), up to 3 meV, was confirmed in a 7-layer Fe-Ni film/MgO(001), where an Fe{sub 2}/Ni/Fe/Ni/Fe{sub 2} atomic-layer alignment with a bcc-like-layer stacking and the Fe/MgO interfaces play key roles for leading to the large PMCA. Importantly, we find that the PMCA overcomes enough over the magnetic dipole-dipole anisotropy that favors the in-plane magnetization even when the film thickness increases.

  18. Co{sub 2}FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

    SciTech Connect

    Belmeguenai, M. Tuzcuoglu, H.; Zighem, F.; Chérif, S. M.; Moch, P.; Gabor, M. S. Petrisor, T.; Tiusan, C.

    2014-01-28

    10 nm and 50 nm Co{sub 2}FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (T{sub a}), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing T{sub a}, while the uniaxial anisotropy field is nearly unaffected by T{sub a} within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with T{sub a}. Finally, the FMR linewidth decreases when increasing T{sub a}, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10{sup −3} and 1.3×10{sup −3} for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively)

  19. A p-type Heusler compound: Growth, structure, and properties of epitaxial thin NiYBi films on MgO(100)

    SciTech Connect

    Shan Rong; Ouardi, Siham; Fecher, Gerhard H.; ViolBarbosa, Carlos E.; Felser, Claudia; Gao Li; Kellock, Andrew; Parkin, Stuart S. P.; Gloskovskii, Andrei; Ikenaga, Eiji

    2012-11-19

    Epitaxial semiconducting NiYBi thin films were directly prepared on MgO(100) substrates by magnetron sputtering. The intensity ratio of the (200) and (400) diffraction peaks, I(200)/I(400) = 2.93, was close to the theoretical value (3.03). The electronic structure of NiYBi was calculated using wien2k, and a narrow indirect band gap of width of 210 meV was found. The valence band spectra of the films obtained by linear dichroism in hard x-ray photoelectron spectroscopy exhibit clear structures that are in good agreement with the calculated band structure of NiYBi.

  20. Growth mode and properties of Mn-Co-Ni-O NTC thermistor thin films deposited on MgO (100) substrate by laser MBE

    NASA Astrophysics Data System (ADS)

    Xie, Yahong; Kong, Wenwen; Ji, Guang; Gao, Bo; Yao, Jincheng; Chang, Aimin

    2014-12-01

    Mn1.56Co0.96Ni0.48O4-δ thin films were deposited on MgO (100) substrate using laser molecular beam epitaxy (LMBE) technique at the temperature range of 300-600°C under oxygen partial pressure of 5 × 10-3 Pa. The effect of growth temperature on microstructure and electrical properties as well as the growth mode were studied using XRD, RHEED, AFM and resistance-temperature measurements. The results showed that all prepared thin films underwent epitaxial growth along the single-(100) orientation direction of the MgO substrate from 3D-island mode to 2D layer-by-layer mode, and exhibited good crystallinity and NTC thermistor behavior. Their resistance at room temperature can be in the range of 10-50 MΩ together with a B-value of about 3300 K, which are desirable for a wide range of practical applications of the NTC thermistors.

  1. Modifying magnetic properties of ultra-thin magnetite films by growth on Fe pre-covered MgO(001)

    SciTech Connect

    Schemme, T. Krampf, A.; Kuepper, K.; Wollschläger, J.; Bertram, F.; Kuschel, T.

    2015-09-21

    Iron oxide films were reactively grown on iron buffer films, which were deposited before on MgO(001) substrates to analyze the influence of the initial iron buffer layers on the magnetic properties of the magnetite films. X-ray photoelectron spectroscopy and low energy electron diffraction showed that magnetite films of high crystalline quality in the surface near region were formed by this two-step deposition procedure. The underlying iron film, however, was completely oxidized as proved by x-ray reflectometry and diffraction. The structural bulk quality of the iron oxide film is poor compared to magnetite films directly grown on MgO(001). Although the iron film was completely oxidized, we found drastically modified magnetic properties for these films using the magnetooptic Kerr effect. The magnetite films had strongly increased coercive fields, and their magnetic in-plane anisotropy is in-plane rotated by 45∘ compared to magnetite films formed directly by one step reactive growth on MgO(001)

  2. Effect of deposition pressure on the microstructure and thermoelectric properties of epitaxial ScN(001) thin films sputtered onto MgO(001) substrates

    SciTech Connect

    Burmistrova, Polina V.; Zakharov, Dmitri N.; Favaloro, Tela; Mohammed, Amr; Stach, Eric A.; Shakouri, Ali; Sands, Timothy D.

    2015-03-14

    Four epitaxial ScN(001) thin films were successfully deposited on MgO(001) substrates by dc reactive magnetron sputtering at 2, 5, 10, and 20 mTorr in an Ar/N2 ambient atmosphere at 650 °C. The microstructure of the resultant films was analyzed by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Electrical resistivity, electron mobility and concentration were measured using the room temperature Hall technique, and temperature dependent in-plain measurements of the thermoelectric properties of the ScN thin films were performed. The surface morphology and film crystallinity significantly degrade with increasing deposition pressure. The ScN thin film deposited at 20 mTorr exhibits the presence of <221> oriented secondary grains resulting in decreased electric properties and a low thermoelectric power factor of 0.5 W/m-K² at 800 K. ScN thin films grown at 5 and 10 mTorr are single crystalline, yielding the power factor of approximately 2.5 W/m-K² at 800 K. The deposition performed at 2 mTorr produces the highest quality ScN thin film with the electron mobility of 98 cm² V⁻¹ s⁻¹ and the power factor of 3.3 W/m-K² at 800 K.

  3. Effect of deposition pressure on the microstructure and thermoelectric properties of epitaxial ScN(001) thin films sputtered onto MgO(001) substrates

    DOE PAGESBeta

    Burmistrova, Polina V.; Zakharov, Dmitri N.; Favaloro, Tela; Mohammed, Amr; Stach, Eric A.; Shakouri, Ali; Sands, Timothy D.

    2015-03-14

    Four epitaxial ScN(001) thin films were successfully deposited on MgO(001) substrates by dc reactive magnetron sputtering at 2, 5, 10, and 20 mTorr in an Ar/N2 ambient atmosphere at 650 °C. The microstructure of the resultant films was analyzed by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Electrical resistivity, electron mobility and concentration were measured using the room temperature Hall technique, and temperature dependent in-plain measurements of the thermoelectric properties of the ScN thin films were performed. The surface morphology and film crystallinity significantly degrade with increasing deposition pressure. The ScN thin film deposited at 20 mTorr exhibitsmore » the presence of <221> oriented secondary grains resulting in decreased electric properties and a low thermoelectric power factor of 0.5 W/m-K² at 800 K. ScN thin films grown at 5 and 10 mTorr are single crystalline, yielding the power factor of approximately 2.5 W/m-K² at 800 K. The deposition performed at 2 mTorr produces the highest quality ScN thin film with the electron mobility of 98 cm² V⁻¹ s⁻¹ and the power factor of 3.3 W/m-K² at 800 K.« less

  4. Epitaxial growth of fcc-Co{sub x}Ni{sub 100-x} thin films on MgO(110) single-crystal substrates

    SciTech Connect

    Ohtake, Mitsuru; Nukaga, Yuri; Sato, Yoichi; Futamoto, Masaaki; Kirino, Fumiyoshi

    2009-12-15

    Co{sub x}Ni{sub 100-x} (x=100, 80, 20, 0 at. %) epitaxial thin films were prepared on MgO(110) single-crystal substrates heated at 300 deg. C by ultrahigh vacuum molecular beam epitaxy. The growth mechanism is discussed based on lattice strain and crystallographic defects. CoNi(110) single-crystal films with a fcc structure are obtained for all compositions. Co{sub x}Ni{sub 100-x} film growth follows the Volmer-Weber mode. X-ray diffraction analysis indicates that the out-of-plane and the in-plane lattice spacings of the Co{sub x}Ni{sub 100-x} films are in agreement within +-0.5% with the values of the respective bulk Co{sub x}Ni{sub 100-x} crystals, suggesting that the strain in the film is very small. High-resolution cross-sectional transmission microscopy shows that an atomically sharp boundary is formed between a Co(110){sub fcc} film and a MgO(110) substrate, where periodical misfit dislocations are preferentially introduced in the film at the Co/MgO interface. The presence of such periodical misfit dislocations relieves the strain caused by the lattice mismatch between the film and the substrate.

  5. Electronic and crystalline structures of zero band-gap LuPdBi thin films grown epitaxially on MgO(100)

    SciTech Connect

    Shan, Rong; Ouardi, Siham; Fecher, Gerhard H.; ViolBarbosa, Carlos E.; Felser, Claudia; Gao, Li; Kellock, Andrew; Roche, Kevin P.; Samant, Mahesh G.; Parkin, Stuart S. P.; Ikenaga, Eiji

    2013-04-29

    Thin films of the proposed topological insulator LuPdBi-a Heusler compound with the C1{sub b} structure-were prepared on Ta-Mo-buffered MgO(100) substrates by co-sputtering from PdBi{sub 2} and Lu targets. Epitaxial growth of LuPdBi films was confirmed by X-ray diffraction and reflection high-energy electron diffraction. The root-mean-square roughness of the films was as low as 1.45 nm, even though the films were deposited at high temperature. The film composition is close to the ideal stoichiometric ratio. The valence band spectra of the LuPdBi films, observed by hard X-ray photoelectron spectroscopy, correspond very well with the ab initio-calculated density of states.

  6. Growth of L10-ordered crystal in FePt and FePd thin films on MgO(001) substrate

    NASA Astrophysics Data System (ADS)

    Futamoto, Masaaki; Nakamura, Masahiro; Ohtake, Mitsuru; Inaba, Nobuyuki; Shimotsu, Teruho

    2016-08-01

    Formation of L10-oredered structure from disordered A1 phase has been investigated for FePt and FePd films on MgO(001) substrates employing a two-step method consisting of low temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. L10-(001) variant crystal with the c-axis perpendicular to the substrate grows preferentially in FePd films whereas L10-(100), (010) variants tend to be mixed with the L10-(001) variant in FePt films. The structure analysis by X-ray diffraction indicates that a difference in A1 lattice strain is the influential factor that determines the resulting L10-variant structure in ordered thin films. Misfit dislocations and anti-phase boundaries are observed in high-resolution transmission electron micrographs of 10 nm-thick Fe(Pt, Pd) film consisting of L10-(001) variants which are formed through atomic diffusion at 600 °C in a laterally strained FePt/PeFd epitaxial thin film. Based on the experimental results, a nucleation and growth model for explaining L10-variant formation is proposed, which suggests a possibility in tailoring the L10 variant structure in ordered magnetic thin films by controlling the alloy composition, the layer structure, and the substrate material.

  7. Domain wall pinning on strain relaxation defects (stacking faults) in nanoscale FePd (001)/MgO thin films

    NASA Astrophysics Data System (ADS)

    Hsiao, C. H.; Yao, Y. D.; Lo, S. C.; Chang, H. W.; Ouyang, Chuenhou Hao

    2015-10-01

    FePd (001) films, prepared by an electron beam deposition system on MgO(100), exhibit a perpendicular magnetic anisotropy (1.7 × 107 erg/cc) with a high order parameter (0.92). The relation between stacking faults induced by the strain relaxation, which act as strong domain wall pinning sites, and the perpendicular coercivity of (001) oriented L10 FePd films prepared at different temperatures have been investigated. Perpendicular coercivity can be apparently enhanced by raising the stacking fault densities, which can be elevated by climbing dissociation of total dislocation. The increased stacking fault densities (1.22 nm-2) with large perpendicular coercivity (6000 Oe) are obtained for samples prepared at 650 °C. This present work shows through controlling stacking fault density in FePd film, the coercivity can be manipulated, which can be applied in future magnetic devices.

  8. Relation between critical current densities and epitaxy of YBa2Cu3O7 thin films on MgO(100) and SrTiO3(100)

    NASA Astrophysics Data System (ADS)

    Kromann, R.; Bilde-Sorensen, J. B.; de Reus, R.; Andersen, N. H.; Vase, P.; Freltoft, T.

    1992-04-01

    Thin films of YBa2Cu3O7 with a thickness of about 250 nm were grown on single-crystal MgO(100) and SrTO3(100) substrates by laser ablation, under identical conditions, and their orientations were investigated using XRD and TEM techniques. The films were found to have ideal 1:2:3 composition, and no impurity phases were observed. All films were epitaxial with the c axis oriented perpendicular to the substrate, although minor traces of a-axis-oriented material were observed. Larger current densities were observed in films on SrTiO3 than on MgO. The difference is attributed to the larger in-plane mosaicity of the films deposited on MgO, which was found to be comparable to the orthorhombic splitting. The lattice mismatch between the film and the substrate caused no measurable strain in the films.

  9. Domain wall pinning on strain relaxation defects (stacking faults) in nanoscale FePd (001)/MgO thin films

    SciTech Connect

    Hsiao, C. H.; Ouyang, Chuenhou E-mail: houyang@mx.nthu.edu.tw; Yao, Y. D.; Lo, S. C.; Chang, H. W. E-mail: houyang@mx.nthu.edu.tw

    2015-10-05

    FePd (001) films, prepared by an electron beam deposition system on MgO(100), exhibit a perpendicular magnetic anisotropy (1.7 × 10{sup 7 }erg/cc) with a high order parameter (0.92). The relation between stacking faults induced by the strain relaxation, which act as strong domain wall pinning sites, and the perpendicular coercivity of (001) oriented L1{sub 0} FePd films prepared at different temperatures have been investigated. Perpendicular coercivity can be apparently enhanced by raising the stacking fault densities, which can be elevated by climbing dissociation of total dislocation. The increased stacking fault densities (1.22 nm{sup −2}) with large perpendicular coercivity (6000 Oe) are obtained for samples prepared at 650 °C. This present work shows through controlling stacking fault density in FePd film, the coercivity can be manipulated, which can be applied in future magnetic devices.

  10. Structure And Radiation Damage Behavior Of Epitaxial CrxMo1-x Alloy Thin Films On MgO

    SciTech Connect

    Wang, Chong M.; Kaspar, Tiffany C.; Shutthanandan, V.; Joly, Alan G.; Kovarik, Libor; Arey, Bruce W.; Gu, Meng; Devaraj, Arun; Wirth, Brian D.; Kurtz, Richard J.

    2013-06-01

    Phenomena related to the interaction of point defects and dopants with grain boundaries and interfaces have been very well documented. However, a quantitative understanding of such an interaction is still missing. In this paper we explore the correlation between radiation damage and interface structure. In doing so, CrxMo1-x(001) films of thickness ~100 nm were epitaxially grown on MgO (001) using molecular beam epitaxy. The interface dislocation density can be systematically varied by controlling the composition of the film. This system allows us to probe the response of the defects generated during the irradiation to the interface dislocation density. The microstructural features of these films before and after irradiation are carefully studied using high resolution scanning/transmission electron microscopy and electron diffraction. It has been found that the film/substrate system is very resistant to ion-induced irradiation damage. No visible point defect clusters, dislocation network or amorphization has been identified, which is contrasted with other materials of either metallic or ionic bonding. We conclude that the defects in the present system appear to be either sub-microscopic and highly dispersed or are annihilated during the irradiation process. Further detailed work is needed to identify the spatial distribution of the defects.

  11. The combined effect of thermal annealing of MgO substrate and Ca substitution on the surface resistance of YBa2Cu3Oz thin films

    NASA Astrophysics Data System (ADS)

    Murugesan, M.; Obara, H.; Yamasaki, H.

    2005-07-01

    Single-layer Y1-xCaxBa2Cu3Oz (YCBCO) thin films (x =0.00, 0.02, 0.05, and 0.10) grown on annealed as well as unannealed MgO substrates have been systematically investigated for their carrier concentration, critical current density Jc, and microwave surface resistance Rs. For x ⩽0.05, the grain growth follows a three-dimensional-spiral growth mechanism, while for x =0.10 we observed a mainly two-dimensional-like growth of grains. The results of Hall data reveal that the x =0.05 film is overdoped while films with x =0.02 and 0.10 are underdoped with respect to the x =0.00 film. However, the Hall mobility μH is highly enhanced for the x =0.02 film. Thermal annealing of MgO substrates prior to film deposition results to an improvement in the overall superconducting properties of the film such as suppression of normal-state resistivity, enhancement of Jc, and minimization of Rs both for pure as well as Ca-substituted films. Annealing of MgO substrates enhances the Jc value to a magnitude (i) nearly doubled for x =0.00 films and (ii) more than an order for x =0.02 films. Also it leads to a minimization of the Rs value to (i) more than half and (ii) nearly an order of magnitude higher, respectively, for x =0.00 and x =0.02 films. Furthermore, for the x =0.02 film, below 60K, we realized an enhanced Jc value in self- as well as in large-applied fields. For other than the Ca-2% substituted films, a suppression of Jc with a strong field dependency has been noticed. Furthermore, the Rs value of the x =0.02 film (0.1mΩ at 20K, 21.9GHz) was three times lower compared to that of the x =0.00 film (0.35mΩ at 20K, 21.9GHz). At 20K and 21.9GHz, the Rs value for the x =0.05 film is comparable to that of the x =0.00 film, whereas for the x =0.10 film it is twice that of x =0.00. The low normal-state resistivity, enhanced mobility, high Jc, and the minimized Rs observed for x =0.02 films firmly support the possible improvement of superconducting order parameters near the grain

  12. Magnetic and transport properties of epitaxial thin film MgFe2O4 grown on MgO (100) by molecular beam epitaxy

    PubMed Central

    Wu, Han-Chun; Mauit, Ozhet; Coileáin, Cormac Ó; Syrlybekov, Askar; Khalid, Abbas; Mouti, Anas; Abid, Mourad; Zhang, Hong-Zhou; Abid, Mohamed; Shvets, Igor V.

    2014-01-01

    Magnesium ferrite is a very important magnetic material due to its interesting magnetic and electrical properties and its chemical and thermal stability. Here we report on the magnetic and transport properties of epitaxial MgFe2O4 thin films grown on MgO (001) by molecular beam epitaxy. The structural properties and chemical composition of the MgFe2O4 films were characterized by X-Ray diffraction and X-Ray photoelectron spectroscopy, respectively. The nonsaturation of the magnetization in high magnetic fields observed for M (H) measurements and the linear negative magnetoresistance (MR) curves indicate the presence of anti-phase boundaries (APBs) in MgFe2O4. The presence of APBs was confirmed by transmission electron microscopy. Moreover, post annealing decreases the resistance and enhances the MR of the film, suggesting migration of the APBs. Our results may be valuable for the application of MgFe2O4 in spintronics. PMID:25388355

  13. Structural and magnetic properties of ferrimagnetic ε-phase Mn4N and antiferromagnetic ζ-phase Mn10N thin films on MgO(001)

    NASA Astrophysics Data System (ADS)

    Foley, Andrew; Corbett, Joseph; Richard, Andrea L.; Alam, Khan; Ingram, David C.; Smith, Arthur R.

    2016-07-01

    Single phase ε-Mn4N and ζ-Mn10N thin films are grown on MgO(001) using molecular beam epitaxy. The films are identified and characterized using reflection high-energy electron diffraction, x-ray diffraction, back scattered electron scanning electron microscopy, atomic/magnetic force microscopy and Rutherford backscattering spectrometry. These films are found to be highly smooth with root-mean-squared roughnesses 3.39 nm and below. The quality of ε-Mn4N grown is strongly dependent on substrate temperature during growth. Epitaxial growth of substantial grains composed of the antiferromagnetic η-phase Mn3N2 side by side with ferrimagnetic ε-phase grains is observed when growth temperature is below 480 °C. Ising domains isolated within areas roughly 0.5 μm across are observed in the ferrimagnetic ε-phase grains of samples consisting of a mix of η- and ε-phase grains. Magnetic domains following semi-continuous paths, which are 0.7-7.2 μm across, are observed in single phase ε-Mn4N. Measurements of the ζ-phase detail the structure and magnetism of the material as high Mn content γ-type ζ-phase with a regular surface corrugation along the [100]-direction and antiferromagnetic.

  14. Surface roughness of MgO thin film and its critical thickness for optimal biaxial texturing by ion-beam-assisted deposition

    SciTech Connect

    Miyata, S.; Ibi, A.; Izumi, T.; Shiohara, Y.

    2011-06-01

    We investigated the deposition time dependences of the in-plane grain alignment ({Delta}{phi}) and the surface roughness (w) of biaxially textured MgO thin films fabricated by ion-beam-assisted deposition (IBAD) and found a strong correlation between them. The time evolution of the surface roughness of IBAD-MgO showed an abrupt increase at the same time corresponding to the beginning of the deterioration in {Delta}{phi}. The roughness versus thickness profiles obtained under different deposition conditions with different assisting ion-beam currents collapsed to a single curve, even though the deposition rates were significantly different in each condition. This implies that the abrupt increase in roughness occurred at the same thickness--of about 4 nm--irrespective of the deposition rate. The result also indicated that the {Delta}{phi} deterioration began with the same thickness of about 4 nm. This ''critical'' thickness of about 4 nm might be related to the completion of the crystallization of the film. Further, deposition beyond the critical thickness, therefore, became merely a homoepitaxial deposition under the ''IBAD'' condition, which was far from optimal because of the ion bombardment and low temperature (no-heating), and thus {Delta}{phi} deteriorated. Based on these considerations, we propose an approach to attain a sharp texture in a IBAD-MgO-based biaxial substrate; moreover, we demonstrated this approach using a two-step deposition process.

  15. Measurement on electrical tunability of microstrip line resonators using YBa2Cu3O7-δ/SrTiO3/MgO multilayer thin films

    NASA Astrophysics Data System (ADS)

    Han, Seok K.; Kim, Jeha; Lee, Sang Yeol; Kang, Kwang-Yong

    1995-09-01

    We have fabricated YBa2Cu3O7-(delta ) (YBCO) superconducting line resonator and tunable line resonator on ferroelectric Sr0.5Ba0.5TiO3 (SBTO) buffered MgO(100) substrate and discussed the frequency shift mechanism of superconductor as a function of temperature and bias voltage, respectively. The resonators were designed using superconducting YBCO epitaxial thin films. Optimized resonator shown the resonant frequency of 10 GHz at 77 K. The YBCO films were grown in situ by pulsed laser deposition technique at 750 degree(s)C and oxygen partial pressure of 200 mTorr. The resonators have linear microstrip line separated by a gap of 5 micrometers and 0.5 mm, respectively. A gap is intentionally introduced to generate mainly a capacitive series reactance. The equivalence circuit of line resonator is a II network consisted of three capacitances. As the series capacitance C12 of SBTO ferroelectric thin films was changed by a bias voltage applied on the strip conductors including the gap, resonance frequency was shifted about 20 MHz from the unbiased center frequency of 10 GHz. The variation of resonance peak could be explained by a serial capacitance model. To find a central frequency mechanism depending on temperature, we fit the raw data using f(T)/f(10 K) and simple power law model. The shifting of the resonant frequencies due to temperature was fit to a two-fluid model, BCS theory and empirical formula. Also the surface impedance of superconducting YBCO films as a function of temperature at 10 GHz has been estimated by a transmission line method.

  16. Investigations of sol gel-derived highly (100)-oriented Ba0.5Sr0.5TiO3 : MgO composite thin films for phase-shifter applications

    NASA Astrophysics Data System (ADS)

    Jain, M.; Majumder, S. B.; Katiyar, R. S.; Bhalla, A. S.; Miranda, F. A.; van Keuls, F. W.

    2005-02-01

    Sol gel deposition of highly oriented Ba0.5Sr0.5TiO3 : MgO composite thin films has shown desirable dielectric constant reduction and higher figure of merit for phase-shifter applications. In this multilayer configuration, MgO distributed homogeneously through the Ba0.5Sr0.5TiO3 (BST50) matrix, and it helped in tailoring the dielectric constant and reducing the loss tangent significantly. In the present study, the high-frequency dielectric behavior of the films has been evaluated by fabricating an eight-element coupled microstrip phase shifter and measuring the degree of phase shift and insertion loss as a function of applied voltage at room temperature. An increase in phase-shifter figure of merit (degree of phase shift per dB insertion loss) from 28°/dB for pure BST50 to 71°/dB for a BST50 : MgO film (at 14 GHz and 333 kV/cm) has been observed.

  17. Magnetization behavior of L10-ordered FePt alloy thin films prepared on MgO(100), MgAl2O4(100), and KTaO3(100) single-crystal substrates

    NASA Astrophysics Data System (ADS)

    Iwama, Hiroki; Doi, Masaaki; Shima, Toshiyuki

    2016-07-01

    In order to investigate the effects of lattice mismatch between FePt thin films and single-crystal substrates on the tetragonality and magnetization process, FePt thin films were fabricated on several single-crystal substrates such as KTaO3 (KTO) (100), MgAl2O4 (MAO) (100), and MgO(100) at a substrate temperature of 700 °C. The Fe content of the FePt films was varied from 45.0 to 50.8 at. %. In addition to the fundamental (002) peak, the (001) and (003) superlattice peaks were clearly observed in the X-ray diffraction patterns of all the samples, indicating the formation of the L10-ordered structure. The magnetization measurements show that all the samples were perpendicularly magnetized. Coercivities (H c) of 57.8, 52.5, and 3.3 kOe were obtained for the films with Fe49.3Pt50.7 (at. %) deposited on the MgO, MAO, and KTO substrates. The marked reduction in H c is considered to arise from the morphology of FePt thin films.

  18. Ferroelectric properties of Pb(Mn{sub 1/3}Nb{sub 2/3})O{sub 3}-Pb(Zr,Ti)O{sub 3} thin films epitaxially grown on (001)MgO substrates

    SciTech Connect

    Zhang Tao; Wasa, Kiyotaka; Kanno, Isaku; Zhang Shuyi

    2008-07-15

    Ferroelectric ternary perovskite thin films of 0.06Pb(Mn{sub 1/3},Nb{sub 2/3})O{sub 3} (PMnN)-0.42PbZrO{sub 3} (PZ)-0.52PbTiO{sub 3} (PT)[0.06PMnN-0.94PZT(45/55)] have been grown on the (001)MgO substrates by radio frequency-magnetron sputtering with quenching processing. The deposition conditions, microstructures, piezoelectric, and ferroelectric properties of the ternary perovskite thin films are described in comparison with the binary compounds of PZ-PT (PZT). The out-plane x-ray diffraction (XRD) measurements for the ternary PMnN-PZT perovskite thin films of 1 to 1-3 {mu}m in film thickness show strong single (001) orientation. The in-plane {phi}-scan XRD curve verified the ternary thin films are single crystals of perovskite structure. Their lattice parameters are almost the same as bulk values and the ternary thin films are almost stress free. The PMnN-PZT thin films show high density without columnar structure. The PZT-based ternary perovskite thin films with the small addition of PMnN, i.e., 6 mole % PMnN, exhibit a strong hard ferroelectric response, i.e., P{sub s}=60 {mu}C/cm{sup 2} and 2E{sub c}=230 kV/cm. Their effective piezoelectric constants are typically e{sub 31,eff}=-7.7 C/m{sup 2}. These values are slightly higher than those of binary perovskite PZT thin 0011fil.

  19. Microstructure and transport properties of epitaxial topological insulator Bi2Se3 thin films grown on MgO (100), Cr2O3 (0001), and Al2O3 (0001) templates

    NASA Astrophysics Data System (ADS)

    Lee, Y. F.; Kumar, R.; Hunte, F.; Narayan, J.; Schwartz, J.

    2015-09-01

    We report the epitaxial integration of defect-induced room temperature ferromagnetic insulators, Cr2O3 and MgO, with topological insulators Bi2Se3 on c-sapphire substrate by pulsed laser deposition. The structural, magnetic, and magnetotransport properties of ˜15 nm Bi2Se3 thin films are investigated on each template. The lattice misfits of Cr2O3/Bi2Se3 and MgO/Bi2Se3 are ˜16% and ˜39%, respectively, where the critical thickness for pseudomorphic growth is less than one monolayer. The insulating behavior is more pronounced due to the additional scattering of the surface states of the Bi2Se3 layer by interfacing with MgO and Cr2O3. The weak antilocalization effect from the surface states is clearly suppressed, accounting for the presence of magnetic bottom layers. This work demonstrates an effective way to study the emergence of a ferromagnetic phase in topological insulators by the magnetic proximity effect in Bi2Se3, a step toward unveiling their exotic properties.

  20. In situ measurement of surface potential developed on MgO thin film surface under ion irradiation using ion scattering spectroscopy

    SciTech Connect

    Nagatomi, T.; Kuwayama, T.; Takai, Y.; Yoshino, K.; Morita, Y.; Kitagawa, M.; Nishitani, M.

    2009-11-15

    The application of ion scattering spectroscopy (ISS) to the in situ measurement of the surface potential developed on an insulator surface under positive ion irradiation was investigated. The ISS spectra measured for a MgO film of 600 nm thickness on a Si substrate by the irradiation of 950 eV He{sup +} ions revealed that the surface is positively charged by approximately 180 V. For accurate measurement of the surface potential, a correction to take into account the angular deflection of primary ions induced by the high surface potential is required. The dependence of the surface potential on the sample temperature revealed that no charging is induced above 700 deg. C, indicating that accumulated charges can be removed by heating to 700 deg. C. From the measurement of the ion-induced secondary electron yield using a collector electrode located in front of the sample surface, the surface potential and ion-induced secondary electron yield were found to be strongly affected by the experimental setup. Secondary electrons produced by the impact of slow positive secondary ions, the maximum energy of which corresponds to the surface potential, play an important role when the bias voltage applied to the collector electrode is positively high for the present experimental setup. The surface potential developed on the surface of MgO films of 600 and 200 nm thickness was measured in situ, revealing that the amount of accumulated charges and the time required to attain the steady state of charging are slightly dependent on the beam current of primary ions and strongly dependent on the thickness of the MgO film. The present results confirmed that the application of ISS has high potential for investigating charging phenomena and the secondary electron emission from insulator surfaces under positive ion irradiation.

  1. Enhancement of order degree and perpendicular magnetic anisotropy of L10 ordered Fe(Pt,Pd) alloy film by introducing a thin MgO cap-layer

    NASA Astrophysics Data System (ADS)

    Noguchi, Youhei; Ohtake, Mitsuru; Futamoto, Masaaki; Kirino, Fumiyoshi; Inaba, Nobuyuki

    2016-07-01

    Fe50PtxPd50-x (at%, x=0-50) alloy films of 10 nm thickness with and without 2-nm-thick MgO cap-layers are prepared on MgO(001) single-crystal substrates by employing a two-step method consisting of low-temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. The influences of MgO cap-layer on the structure and the magnetic properties are investigated. Fe50PtxPd50-x films epitaxially grow on the substrates at 200 °C. The Fe50Pd50 and the Fe50Pt12.5Pd37.5 films are respectively composed of (001) single-crystals with disordered fcc-based (A1) and bcc-based (A2) structures. The films with x>25 consist of mixtures of A1 and A2 crystals. The volume ratio of A2 to A1 crystal decreases with increasing the x value from 25 to 50. The in-plane and out-of-plane lattices are respectively expanded and shrunk due to accommodation of lattice mismatch between film and substrate. When the films are annealed at 600 °C, phase transformation to L10 ordered phase takes place. L10 phase transformation of Fe50PtxPd50-x film is promoted for a sample with MgO cap-layer and the order degree is higher than that without cap-layer. Furthermore, L10 ordering with the c-axis perpendicular to the substrate surface is enhanced for the film with cap-layer. The cap-layer is considered to be giving a tension stress to the magnetic film in lateral direction which promotes L10 ordering with the c-axis perpendicular to the substrate. Deposition of cap-layer is shown effective in achieving higher order degree and in enhancing perpendicular magnetic anisotropy with Fe(Pt,Pd) films.

  2. Pulsed Laser Deposition and Reflection High-Energy Electron Diffraction studies of epitaxial long range order, nano- and microstructured Ag thin films grown on MgO, Al2 O3 , STO and Si

    NASA Astrophysics Data System (ADS)

    Velazquez, Daniel; Seibert, Rachel; Man, Hamdi; Spentzouris, Linda; Terry, Jeff

    2015-03-01

    Pulsed Laser Deposition is a state-of-the-art technique that allows for the fine tunability of the deposition rate, highly uniform and epitaxial sample growth, the ability to introduce partial pressures of gases into the experimental chamber for growth of complex materials without interfering with the energy source (laser). An auxiliary in situ technique for growth monitoring, Reflection High-Energy Electron Diffraction, is a powerful characterization tool for predictability of the surface physical structure both, qualitatively and quantitatively. RHEED patterns during and post deposition of Ag thin films on MgO, Al2O3, Si and STO substrtates are presented and their interpretations are compared with surface imaging techniques (SEM, STM) to evidence the usefulness of the technique.

  3. Thin Film Ba(x)Sr(1-x)TiO3 Ku- and K-Band Phase Shifters Grown on MgO Substrates

    NASA Technical Reports Server (NTRS)

    VanKeuls, F. W.; Mueller, C. H.; Miranda, F. A.; Romanofsky, R. R.; Horwitz, J. S.; Chang, W.; Kim, W. J.

    1999-01-01

    We report measurements of gold circuits fabricated on four Ba(x)Sr(1-x)TiO3 films doped with 1% Mn grown on MgO substrates by laser ablation. Low frequency measurements of epsilon(sub r) and tan(delta) on interdigital capacitors are compared with high frequency measurements of phase shift and insertion loss on coupled microstrip phase shifters done on the same films. The variation in temperature of both high and low frequency device parameters is compared. Annealed and unannealed films are compared. Room temperature figures of merit of phase shift per insertion loss of up to 58.4 C/dB at 18 GHz and 400 V dc bias were measured.

  4. High photoelectron emission from Co-diffused MgO deposited using arc plasma gun

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shin-ichi; Kosuga, Hiroki

    2015-08-01

    MgO has several advantageous characteristics and has been applied in various fields. In this study, we deposited Co nanoparticles in an island pattern on a Si substrate using an arc plasma gun (APG). We subsequently formed a MgO thin film on this substrate by metal-organic decomposition (MOD), which enables the formation of films in the atmosphere, thereby yielding a double-layer structure. The MgO thin film formed on Co nanoparticles deposited using the APG with 500 pulses of arc discharge exhibited improved crystallinity and photoelectron emission at least threefold higher than that of a MgO thin film formed directly without depositing Co nanoparticles. Although the transmittance of the specimen formed by depositing Co nanoparticles was initially 30% or lower, it increased to greater than 90% after the formation of the MgO thin film and the dispersion of the Co nanoparticles in the MgO thin film during heat treatment at 900 °C. Our results clarify that the characteristics of MgO thin films are markedly improved by depositing Co nanoparticles before forming the films. The results of Kelvin probe force microscopy (KPFM) indicate that the outermost surface of the Co material had become CoO (cobalt oxide) with the dispersion of Co nanoparticles in the MgO thin film. The lattice parameter of CoO nanoparticles (an-axis lattice parameter of 4.2615 Å) after heating matches well with that of MgO (4.2126 Å). The MgO thin films that grew in conjunction with the CoO nanoparticles were highly crystallized. We successfully established a high-performance, cost-effective bottom-up process that requires no ion injection by dispersing Co nanoparticles in a MgO thin film through heat treatment.

  5. The MBE growth and optical quality of BaTiO{sub 3} and SrTiO{sub 3} thin films on MgO

    SciTech Connect

    McKee, R.A.; Specht, E.D.; Alexander, K.B.; Walker, F.J.

    1994-05-01

    High quality epitaxial BaTiO{sub 3} and SrTiO{sub 3} have been grown on MgO; stabilized at a one unit cell height; and grown to film thicknesses of 0.5--0.7 {mu}m. These relatively thick films remain adherent when thermally cycled between growth temperatures and room temperature, are crack free with high optical quality, and have both in-plane and out-of-plane X-ray rocking curves of 0.3--0.5{degree}. These films have been grown using molecular beam epitaxy (MBE) methods starting with the TiO{sub 2} layer of the perovskite structure. The TiO{sub 2}-layer/MgO interface uniquely satisfies electrostatic requirements for perovskite heteroepitaxy and provides the template structure that leads to the high quality films that are obtained. Wavelength dependence of optical loss has been characterized between 475 nm and 705 nm with loss coefficients < l dB/cm being obtained at the He-Ne wavelength.

  6. Growth of large single crystals of MgO

    SciTech Connect

    Boatner, L.A.; Urbanik, M.

    1997-06-12

    The progressive identification of new high-technology applications and requirements for MgO single crystals in the commercial realm, as well as in DOE and other government-agency project areas, has resulted in an increased demand and international market for this material. Specifically, the demand for MgO crystals in large sizes and quantities is presently increasing due to existing and developing applications that include: (a) MgO substrates for the formation of electro-optic thin films and devices, (b) epitaxial substrates for high-temperature thin-film superconducting devices MgO optical components - including high-temperature windows, lenses, and prisms, and (d) specialty MgO crucibles and evaporation sources for thin-film production. In the course of CRADA ORNL92-0091, carried out with Commercial Crystal Laboratories of Naples, Florida as the commercial participant, we have made major progress in increasing the size of single crystals of MgO produced by means of the submerged-arc-fusion technique-thereby increasing the commercial utility of this material. Prior to the accomplishments realized in the course of this CRADA, the only commercially available single crystals of MgO were produced in Japan, Israel, and Russia. The results achieved in the course of CRADA ORNL92-0091 have now led to the establishment of a domestic commercial source of MgO single-crystal substrates and components, and the U.S. is no longer totally dependent on foreign sources of this increasingly important material.

  7. L10 ordered phase formation in FePt, FePd, CoPt, and CoPd alloy thin films epitaxially grown on MgO(001) single-crystal substrates

    NASA Astrophysics Data System (ADS)

    Ohtake, Mitsuru; Ouchi, Shouhei; Kirino, Fumiyoshi; Futamoto, Masaaki

    2012-04-01

    The FePt, FePd, CoPt, and CoPd epitaxial thin films are prepared on MgO(001) single-crystal substrates by ultrahigh vacuum RF magnetron sputtering. The effects of the magnetic material and the substrate temperature on the film growth, the film structure, and the magnetic properties are investigated. The L10 ordered phase formation is observed for FePt, FePd, and CoPt films prepared at temperatures higher than 200, 400, and 600 °C, respectively, whereas that is not recognized for CoPd films. The L10-FePd(001) single-crystal films with the c-axis normal to the substrate surface are formed, whereas the FePt and CoPt epitaxial films include L10(100) crystals whose c-axis is parallel to the substrate surface, in addition to the L10(001) crystals. Upon increasing the substrate temperature, the ordering degree increases. A higher ordering parameter is observed in the order of FePd > FePt > CoPt. The magnetic properties are influenced by the crystal structure, the crystallographic orientation of the L10 crystal, and the ordering degree.

  8. Aging of magnetic properties in MgO films

    SciTech Connect

    Balcells, Ll.; Konstantinovic, Z.; Martinez, B.; Beltran, J. I.; Martinez-Boubeta, C.; Arbiol, J.

    2010-12-20

    In this work we report on the magnetic behavior of MgO thin films prepared by sputtering. A severe aging process of the ferromagnetic properties is detected in magnetic samples exposed to ambient atmosphere. However, ferromagnetism can be successively switched on again by annealing samples in vacuum. We suggest this behavior reflects the key role played by defects in stabilizing ferromagnetism in MgO films and is likely to be closely related to the hydrogen-driven instability of V-type centers in this material.

  9. Systematic study of magnetotransport properties and enhanced low-field magnetoresistance in thin films of La0.67Sr0.33MnO3 + Mg(O)

    NASA Astrophysics Data System (ADS)

    Staruch, M.; Cantoni, C.; Jain, M.

    2013-02-01

    La, Sr, Mn, and Mg precursors were mixed in stoichiometric ratio 0.67/0.33/1/x with solvent and were spin-coated onto (001) LaAlO3 substrates. X-ray diffraction and elemental mapping of these films indicate that for small addition of Mg precursor, Mg2+ acts as a dopant in La0.67Sr0.33MnO3 phase and for higher concentrations, MgO phase separates out. Curie temperature and metal-insulator transition temperature systematically decrease with increasing molar concentration of Mg(O). Low-field magnetoresistance of films significantly enhanced by Mg addition and for the highest amount of Mg at 10 K, values were -35.5% and -83.2% with 0.5 T and 3 T applied fields, respectively.

  10. Material Properties and Plasma Display Panel Discharging Characteristics Depending on MgO Evaporation Rate

    NASA Astrophysics Data System (ADS)

    Kwon, Sang Jik; Kim, Yong Jae; Lee, Seong Eui

    2006-11-01

    MgO thin film is most widely used as a protecting layer in ac Plasma Display Panel. The film is deposited using electron beam evaporation. The effects of the evaporation rate of MgO film deposited using an electron beam on the MgO properties and the discharge characteristics of the plasma display panel (PDP) were investigated. The evaporation rate was changed from 3 to 15 Å/s at a substrate temperature of 300 °C. MgO properties such as crystal orientation, surface roughness, contact angle, and film structure were inspected using X-ray diffraction (XRD), analysis atomic force microscopy (AFM), drop shape analysis, and secondary electron microscopy (SEM). The MgO properties were shown to be strongly dependent on the evaporation rate. We also studied the relation between MgO properties and PDP discharging characteristics. The minimum firing voltage and maximum luminous efficiency were obtained at an evaporation rate of 5 Å/s. In the MgO film deposited at 5 Å/s, the (200) orientation was most intensive and surface roughness was minimum.

  11. NO2-assisted molecular-beam epitaxy of Fe3O4, Fe3-δO4, and γ-Fe2O3 thin films on MgO(100)

    NASA Astrophysics Data System (ADS)

    Voogt, F. C.; Fujii, T.; Smulders, P. J. M.; Niesen, L.; James, M. A.; Hibma, T.

    1999-10-01

    We report on the molecular beam epitaxial growth of single-crystalline, stoichiometric Fe3O4 and γ-Fe2O3 films on MgO(100), using NO2 as the oxidizing agent. Mössbauer spectroscopy on 57Fe probe layers is used to determine accurately the stoichiometry of the films. It is found that also all intermediate nonstoichiometric Fe3-δO4 phases can be obtained. The formation of the metastable compound γ-Fe2O3 clearly demonstrates the large oxidizing power of NO2. Although the shape anisotropy dictates that the zero-field magnetization direction should lie entirely in the plane of the film, this is never observed. Stoichiometric Fe3O4 has large out-of-plane components and only in the case of highly oxidized Fe3-δO4 does the magnetization approach the film plane. Upon further oxidation to stoichiometric γ-Fe2O3, however, it rotates back, and finally becomes almost completely perpendicular to the plane of the film. Furthermore, in the case of (near-) stoichiometric Fe3O4, the magnetizations of the A and B sublattices are not completely coupled antiparallel. On average, the magnetization of the B site ions is 4° closer to the film plane than the magnetization of the A site ions. All the as-grown films exhibit a (2×2)R45° surface reconstruction, independent of the stoichiometry. Using simple electrostatic considerations, we propose three possible surface terminations: a half-filled A layer, a B layer with oxygen vacancies and a B layer with hydroxyl groups. Upon annealing, the (2×2)R45° reconstruction irreversibly transforms to a 3×1 reconstruction, caused by Mg outdiffusion from the substrate. Strong reflection high-energy electron diffraction intensity oscillations give direct, unambiguous evidence that Fe3O4 has a two-dimensional layer-by-layer growth mode over the entire temperature range studied, i.e., from 273 to 723 K, guaranteeing atomically flat surfaces and interfaces in multilayer structures. The largest oscillations are obtained on ex situ cleaved, UHV

  12. Microwave Absorption Studies on HIGH-Tc Superconductors and Related Materials VII — Esr of Dpph Coated on a Thin BiSrCaCuO Film Fabricated on MgO(100) Substrate

    NASA Astrophysics Data System (ADS)

    Sugawara, K.; Sugimoto, T.; Shiohara, Y.; Tanaka, S.

    ESR of DPPH coated on a Bi-Sr-Ca-Cu-O (BSCCO) film (350 Å thick) fabricated on MgO(100) substrate by MOCVD was studied. Temperature dependence of the ESR peak-to-peak linewidth, ΔHpp, and the effect of applied magnetic field on ΔHpp have been studied below about 100 K. The results were compared with those of ESR of DPPH coated on ceramic Y-Ba-Cu-O samples (powder and bulk) made by the MPMG method. The DPPH ESR for the BSCCO film revealed that ΔHpp was independent of applied magnetic field up to about 9 kG. In addition, no similarity between the temperature dependence of the excess ESR linewidth of the DPPH and that of critical current density was found for the BSCCO film. These results for the BSCCO film are different from those for the MPMG YBCO samples.

  13. In situ small-angle x-ray and nuclear resonant scattering study of the evolution of structural and magnetic properties of an Fe thin film on MgO (001)

    NASA Astrophysics Data System (ADS)

    Sharma, Gagan; Gupta, Ajay; Gupta, Mukul; Schlage, Kai; Wille, H.-C.

    2015-12-01

    Growth of magnetron sputtered Fe films on clean single crystalline MgO (001) substrate has been studied using in situ grazing incidence small angle x-ray scattering (GISAXS) and grazing incidence nuclear resonant scattering (GINRS) measurements. While GISAXS provides information about morphological changes, GINRS provides information about structural and magnetic properties, thus making it possible to correlate the evolution of magnetic properties with that of morphology and structure of the film. The film exhibits a Volmer-Weber type growth, with percolation transition occurring around 2 nm film thickness. Presence of a finite quadrupole splitting, as seen in GINRS measurements, suggests a significant distortion from cubic symmetry up to a film thickness of 3.5 nm, which can be attributed to hybridization between Fe 3 d and O 2 p orbitals at the interface as well as in-plane tensile strain induced as a result of coalescence of islands. Initially Fe islands exhibit superparamagnetic relaxation, while finite magnetic moment appears upon formation of macroscopic percolation islands. The film exhibits a weak perpendicular magnetic anisotropy (PMA), which vanishes concurrently with disappearance of structural distortion, suggesting that the observed PMA at least partly originates from inherent strain in the film. No presence of any known oxide of Fe was detected at the interface. More precise information about topological and magnetic structure of the interfaces between Fe and MgO layers is obtained using combined x-ray reflectivity and nuclear resonance reflectivity measurements on a 57Fe/MgO multilayer. Measurements show that about two monolayers of Fe at the interface have a reduced hyperfine field, providing evidence for hybridization with O atoms, as predicted by theory.

  14. Epitaxial Pb(Zr{sub x}Ti{sub 1{minus}x})O{sub 3}/SrRuO{sub 3} (x = 0, 0.35, 0.65) multilayer thin films on SrTiO{sub 3}(100) and MgO(100) prepared by MOCVD and RF sputtering

    SciTech Connect

    Foster, C.M.; Csencsits, R.; Baldo, P.M.; Bai, G.R.; Li, Z.; Rehn, L.E.; Wills, L.A.; Hiskes, R.

    1995-02-01

    Epitaxial SrRuO{sub 3} thin films were deposited on SrTiO{sub 3}(100) and MgO(100) substrates by RF sputtering for use as bottom electrodes and epitaxial buffer layers. On these conductive substrates, epitaxial Pb(Zr{sub x}Ti{sub 1{minus}x})O{sub 3} (PZT; x = 0.35,0.65) and PbTiO{sub 3} (PT; x = 0) thin films were deposited by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD), RBS channeling (RBS), transmission electron microscopy (TEM) and optical waveguiding were used to characterize the phase, microstructure, defect structure, refractive index, and film thickness of the deposited films. The PZT and PT films were epitaxial and c-axis oriented. 90{degree} domains, interfacial misfit dislocations and threading dislocations were the primary structural defects, and the films showed as high as a 70% RBS channeling reduction. Ferroelectric hysteresis and dielectric measurements of epitaxial PZT ferroelectric capacitor structures formed using evaporated Ag top electrode showed: a remanent polarization of 46.2 {mu}C/cm{sup 2}, a coercive field of 54.9 kV/cm, a dielectric constant of 410, a bipolar resistivity of {approximately}5.8 {times} 10{sup 9} {Omega}-cm at a field of 275 kV/cm, and a breakdown strength of >400 kV/cm. Cyclic fatigue measurements showed that the remanent polarization was maintained for >10{sup 9} cycles.

  15. High temperature and full-in-plane-direction workable high-frequency soft magnetic epitaxial FeSi thin films on MgO(0 0 1)

    NASA Astrophysics Data System (ADS)

    Guo, X. B.; Wu, K.; Cui, B. S.; Li, D.; Yun, J. J.; Zuo, Y. L.; Zuo, H. P.; Wang, T.; Xi, L.

    2016-02-01

    The epitaxial FeSi(0 0 1)[1 1 0]//MgO(0 0 1)[1 0 0] films were fabricated by sputtering and post annealing at 800 °C. A four-fold symmetric angular dependence of remanence ratios and coercivities of FeSi films were observed and well fitted by theoretical models considering the cubic anisotropy. The experimental ferromagnetic resonance frequency (f r) of epitaxial FeSi films reaches to 8.0 GHz, which is in agreement with the theoretical value derived from Landau-Lifshitz-Gilbert equation at room temperature. Moreover, the resonance phenomenon can be observed in any in-plane directions in contrast with the absence of resonance phenomenon in some specific directions for in-plane uniaxial soft magnetic Fe2Co films. Although the saturation magnetization, cubic anisotropy constant and f r all decrease with increasing temperature, f r still can keep as high as 3.2 GHz at 800 K, indicating that the epitaxial FeSi films with high Curie temperature have potential application in full angle workable microwave devices at relatively high temperature.

  16. Very high residual resistivity ratios of heteroepitaxial superconducting niobium films on MgO substrates

    SciTech Connect

    Krishnan, Mahadevan; Valderrama, E.; Bures, B.; Wilson-Elliott, K.; Zhao, Xin; Phillips, H. Larry; Valente, Anne-Marie; Spradlin, Joshua K.; Reece, Charles E.; Seo, Kang

    2011-11-01

    We report residual resistivity ratio (RRR) values (up to RRR-541) measured in thin film Nb grown on MgO crystal substrates, using a vacuum arc discharge, whose 60?160 eV Nb ions drive heteroepitaxial crystal growth. The RRR depends strongly upon substrate annealing and deposition temperatures. X-ray diffraction spectra and pole figures reveal that, as the crystal structure of the Nb film becomes more ordered, RRR increases, consistent with fewer defects or impurities in the lattice and hence longer electron mean free path. A transition from Nb(110) to purely Nb(100) crystal orientation on the MgO(100) lattice occurs at higher temperature.

  17. Investigating and engineering spin-orbit torques in heavy metal/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5}/MgO thin film structures

    SciTech Connect

    Loong, Li Ming; Deorani, Praveen; Qiu, Xuepeng; Yang, Hyunsoo

    2015-07-13

    Current-induced spin-orbit torques (SOTs) have the potential to revolutionize magnetization switching technology. Here, we investigate SOT in a heavy metal (HM)/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} (CFAS)/MgO thin film structure with perpendicular magnetic anisotropy (PMA), where the HM is either Pt or Ta. Our results suggest that both the spin Hall effect and the Rashba effect contribute significantly to the effective fields in the Pt underlayer samples. Moreover, after taking the PMA energies into account, current-induced SOT-based switching studies of both the Pt and Ta underlayer samples suggest that the two HM underlayers yield comparable switching efficiency in the HM/CFAS/MgO material system.

  18. Fabrication and characteristics of Zn2+ doped MgO films prepared by sol-gel method

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoju; Li, Peng; Lin, Zulun; Qi, Kangcheng; Chen, Zexiang; Cao, Guichuan

    2012-10-01

    One of the effective methods to improve the luminous efficiency and reduce power consumption of plasma display panel (PDP) is searching for new high secondary emission discharging materials. In this paper, doped MgO films with different Zn2+ dopant concentration are made on indium tin oxides glass substrates by sol-gel method. The effect of annealing atmosphere on the visible light transmittance is discussed, which indicates that the films annealed in the nitrogen have higher transmittance than that in the air. The discharge characteristics of the fabricated Zn2+ doped MgO thin films are studied in a tube filled with Ne-Xe gas mixtures imitating the real structure of alternating current plasma display panel (AC PDP). When the Zn2+ ratio is 10 %, the firing voltage of doped MgO thin film in Ne-Xe 5 % at the pressure of 10 torr is 378 V, in contrast to the pure MgO film of 390 V. In addition, burr sparks are also observed at the beginning of the test. As time go on, the gas discharge is more stable. The results show that Zn2+ doped MgO thin film, due to its lower firing voltage, can be a promising discharge layer for highly efficient AC PDP.

  19. Biaxial Texture Evolution in MgO Films Fabricated Using Ion Beam-Assisted Deposition

    NASA Astrophysics Data System (ADS)

    Xue, Yan; Zhang, Ya-Hui; Zhao, Rui-Peng; Zhang, Fei; Lu, Yu-Ming; Cai, Chuan-Bing; Xiong, Jie; Tao, Bo-Wan

    2016-04-01

    The growth of multifunctional thin films on flexible substrates is important technologically, because flexible electronics require such a platform. In this study, we examined the evolution of biaxial texture in MgO films prepared using ion beam-assisted deposition (IBAD) on a Hastelloy substrate. Texture and microstructure developments were characterized through in situ reflection high-energy electron diffraction monitoring, x-ray diffraction, and atomic force microscopy, which demonstrated that biaxial texture was developed during the nucleation stage (~2.2 nm). The best biaxial texture was obtained with a thickness of approximately 12 nm. As MgO continued to grow, the influence of surface energy was reduced, and film growth was driven by the attempt to minimize volume free-energy density. Thus the MgO grains were subsequently rotated at the (002) direction toward the ion beam. In addition, an approach was developed for accelerating in-plane texture evolution by pre-depositing an amorphous MgO layer before IBAD.

  20. Biaxial Texture Evolution in MgO Films Fabricated Using Ion Beam-Assisted Deposition

    NASA Astrophysics Data System (ADS)

    Xue, Yan; Zhang, Ya-Hui; Zhao, Rui-Peng; Zhang, Fei; Lu, Yu-Ming; Cai, Chuan-Bing; Xiong, Jie; Tao, Bo-Wan

    2016-07-01

    The growth of multifunctional thin films on flexible substrates is important technologically, because flexible electronics require such a platform. In this study, we examined the evolution of biaxial texture in MgO films prepared using ion beam-assisted deposition (IBAD) on a Hastelloy substrate. Texture and microstructure developments were characterized through in situ reflection high-energy electron diffraction monitoring, x-ray diffraction, and atomic force microscopy, which demonstrated that biaxial texture was developed during the nucleation stage (~2.2 nm). The best biaxial texture was obtained with a thickness of approximately 12 nm. As MgO continued to grow, the influence of surface energy was reduced, and film growth was driven by the attempt to minimize volume free-energy density. Thus the MgO grains were subsequently rotated at the (002) direction toward the ion beam. In addition, an approach was developed for accelerating in-plane texture evolution by pre-depositing an amorphous MgO layer before IBAD.

  1. Surfactant assisted growth of MgO films on GaN

    SciTech Connect

    Paisley, Elisibeth A.; Shelton, T C; Mita, S; Gaddy, Brian E.; Irving, D L; Christen, Hans M; Sitar, Z; Biegalski, Michael D; Maria, Jon Paul

    2012-01-01

    Thin epitaxial films of <111> oriented MgO on [0001]-oriented GaN were grown by molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) using the assistance of a vapor phase surfactant. In both cases, surfactant incorporation enabled layer-by-layer growth and a smooth terminal surface due to stabilizing the {111} rocksalt facet. MBE growth of MgO in water terminates after several monolayers, and is attributed to saturation of surface active sites needed to facilitate the Mg oxidation reaction. MgO films prepared by PLD grow continuously, this occurs due to the presence of excited oxidizing species in the laser plasma eliminate the need for catalytic surface sites. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly two order of magnitude reduction in leakage current density for the smoother surfactant-assisted samples. Collectively, these data verify numerous predictions and calculations regarding the role of H-termination in regulating the habit of MgO crystals.

  2. Autocatalytic Surface Hydroxylation of MgO(100) Terrace Sites Observed Under Ambient Conditions

    SciTech Connect

    Newberg, J.T.; Starr, D.; Yamamoto, S.; Kaya, S.; Kendelewicz, T.; Mysak E.R.; Porsgaard, S.; Salmeron, M.B.; Brown, Jr., G.E.; Nilsson, A.; Bluhm, H.

    2011-06-01

    We have investigated the reaction of water vapor with the MgO(100) surface using ambient pressure X-ray photoelectron spectroscopy (AP-XPS), which permits the study of the chemical composition of the MgO/water vapor interface at p(H{sub 2}O) in the Torr range. Water dissociation on thin MgO(100) films of 4-5.5 monolayers (ML) grown on Ag(100) was studied under isobaric conditions at p(H{sub 2}O) ranging from 0.005 to 0.5 Torr and temperatures from 380 to -10 C, up to a maximum relative humidity (RH) of 20%. At RH < 0.01% dissociative adsorption occurs only at defect sites (0.08 ML), while terrace sites remain unreactive toward water dissociation. In the range 0.01 < RH < 0.1% there is an abrupt onset of dissociative adsorption at terrace sites which saturates at 1 ML at 0.1% RH, and is accompanied by an increase in molecular water adsorption. At 20% RH there is 1 ML of molecularly adsorbed water interacting with a fully hydroxylated interface on MgO(100). The observed onset of hydroxylation near 0.01% RH is suggested to be due to water molecules aggregating at the surface, leading to an autocatalytic dissociation of water at MgO(100) terrace sites.

  3. Resputtering effect during MgO buffer layer deposition by magnetron sputtering for superconducting coated conductors

    SciTech Connect

    Xiao, Shaozhu; Shi, Kai; Deng, Shutong; Han, Zhenghe; Feng, Feng Lu, Hongyuan; Qu, Timing; Zhu, Yuping; Huang, Rongxia

    2015-07-15

    In this study, MgO thin films were deposited by radio-frequency magnetron sputtering. The film thickness in the deposition area directly facing the target center obviously decreased compared with that in other areas. This reduction in thickness could be attributed to the resputtering effect resulting from bombardment by energetic particles mainly comprising oxygen atoms and negative oxygen ions. The influences of deposition position and sputtering pressure on the deposition rate were investigated. Resputtering altered the orientation of the MgO film from (111) to (001) when the film was deposited on a single crystal yttria-stabilized zirconia substrate. The density distribution of energetic particles was calculated on the basis of the measured thicknesses of the MgO films deposited at different positions. The divergence angle of the energetic particle flux was estimated to be approximately 15°. The energetic particle flux might be similar to the assisting ion flux in the ion beam assisted deposition process and could affect the orientation of the MgO film growth.

  4. In Situ Fabrication of Reproducible YBCO/Au Planar Tunnel Junctions with an Artificial MgO Barrier

    NASA Astrophysics Data System (ADS)

    Furuyama, Masafumi; Iguchi, Ienari; Shirai, Koji; Kusumori, Takeshi; Ohtake, Hiroaki; Tomura, Shoji; Nasu, Masako

    1990-03-01

    The in situ fabrication of YBCO (YBa2Cu3Oy)/MgO/Au epitaxial planar tunnel junctions with a thin MgO barrier utilizing an electron-beam coevaporation technique is reported. The thickness of the MgO barrier is 3-12 nm and the tunnel resistance shows a strong dependence on barrier thickness. The fabricated tunnel junctions are highly reproducible and controllable. The observed tunnel characteristics contain the gap opening at about 20 mV and the anomaly around zero bias. The tunnel characteristics using the degraded films are also reported.

  5. MgO Solubility in Steelmaking Slags

    NASA Astrophysics Data System (ADS)

    Tayeb, Mohammed A.; Assis, Andre N.; Sridhar, Seetharaman; Fruehan, Richard J.

    2015-04-01

    A predominantly liquid and MgO-saturated slag is preferred in EAF and BOF steelmaking. Fully liquid slag provides a better environment for faster mass transfer due to lower bulk viscosities and larger liquid slag volume and these help dephosphorization and desulfurization. Also, an MgO-saturated slag would be preferable in order to increase the lifetime of furnace refractory lining by reducing the extent of dissolution. This article will demonstrate the factors that would influence MgO saturation, which includes FeO, CaO, P2O5, and Al2O3 contents and temperature. In addition, this paper comments on the applicability and accuracy of FactSage prediction, which are compared to laboratory experiments. The results indicate that FactSage may underestimate MgO solubility by up to 2.5 wt pct at higher basicities while there is reasonable agreement with current measurements at lower basicities.

  6. Report on the sintering and properties of MgO and MgO-5% TiC

    SciTech Connect

    Bengisu, M.; Inal, O.T.

    1992-07-01

    Sintering of technical grade MgO yields higher fractional densities compared to pure MgO. TiC reacts with MgO under sintering of MgO-TiC composites in air, yielding Mg{sub 2}TiO{sub 4} and CO or CO{sub 2}. This can be suppressed in vacuum by plasma sintering. Plasma sintering of MgO at 1300 C and short times does not produce satisfactory results. 5 vol% TiC increases the sinterability of MgO during conventional air sintering; larger additions (50 vol%) decrease sinterability due to macropores formed by gaseous reaction product. Microwave sintering of MgO is possible. Mechanical properties of MgO are improved by additions of small amounts of TiC to starting powders.

  7. Spray pyrolysis of MgO templates on Hastelloy C276 and 310-austenitic stainless steel substrates for Y Ba2Cu3O7 (YBCO) deposition by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Khateeb, Shadi Al; Button, T. W.; Abell, J. S.

    2010-09-01

    MgO thin films were deposited on Hastelloy C276 (HC) and 310 austenitic stainless steel by the spray pyrolysis technique, using magnesium nitrate and magnesium acetate as precursors. Thermogravimetrical analysis of the decomposition of the precursors was used to provide a guideline temperature for the thin film deposition. It was suggested that an amorphous MgO thin film was deposited on both 310-stainless steel and Hastelloy C-276 when using low concentration of the magnesium nitrate precursor. Higher concentrations were needed to obtain (200) oriented MgO films on C276. However, 310-stainless steel was found to not be a suitable substrate for MgO thin film deposition due to surface instability. A (200) oriented MgO thin film was grown on Hastelloy C276 using a magnesium acetate precursor at a much lower concentration compared to the nitrate precursor. The characterization of the thin films was done using scanning electron microscopy, x-ray photoelectron spectroscopy, atomic force microscopy, x-ray diffraction 2θ-scans, rocking curves (ω-scans), and pole figure measurements. MgO was found to have a very weak in-plane texture.

  8. Evidence for boron diffusion into sub-stoichiometric MgO (001) barriers in CoFeB/MgO-based magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Harnchana, V.; Hindmarch, A. T.; Sarahan, M. C.; Marrows, C. H.; Brown, A. P.; Brydson, R. M. D.

    2013-04-01

    Evidence of boron diffusion into the MgO barrier of a CoFeB/MgO based magnetic tunnel junction has been identified using analytical scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy. Structures were deposited by DC/RF-magnetron sputtering, where defective, sub-stoichiometric MgO barriers degrading device performance have been previously mitigated against by deposition of thin Mg layers prior to MgO deposition. We show that despite the protection offered by the Mg layer, disorder in the MgO barrier is still evident by STEM analysis and is a consequence of the oxidation of the Co40Fe40B20 surface during MgO deposition. Evidence of boron diffusion from CoFeB into the MgO barrier in the as-deposited and annealed structure is also presented, which in the as-deposited case we suggest results from the defective structures at the barrier interfaces. Annealing at 375 °C results in the presence of B in the trigonal coordination of [BO3]3- in the MgO barrier and partial crystallization of the top electrode (we presume there is also some boron diffusion into the Ta capping layer). The bottom electrode, however, fails to crystallize and much of the boron is retained in this thicker electrode. A higher annealing temperature or lower initial boron content is required to crystallize the bottom electrode.

  9. First stage of reaction of molten Al with MgO substrate

    SciTech Connect

    Morgiel, J.; Sobczak, N.; Pomorska, M.; Nowak, R.

    2015-05-15

    The Al/MgO couple was produced in vacuum (~ 5 × 10{sup −} {sup 4} Pa) by contact heating from RT up to 1000 °C and holding at that temperature for 1 h of a small 4 × 4 × 4 mm aluminium (5 N) sample placed on the [100] MgO single crystal substrate. TEM observations backed with electron diffraction analysis indicated that the interaction between liquid aluminium and MgO starts from a redox reaction producing a continuous layer of MgAl{sub 2}O{sub 4} spinel on the substrate surface. Its growth is controlled by solid state out-diffusion of magnesium and oxygen towards the surface being in contact with liquid metal. The thickening of spinel layer is accompanied by its cracking and infiltration with aluminium. The above process enables local dissolution of the MgO substrate and formation in it of a thin region of interpenetrating metallic channels walled with spinel. The removal of dissolved magnesium through open aluminium channels towards the drop and to vacuum locally produces areas of aluminium enriched with dissolved oxygen, which results in the nucleation of α-Al{sub 2}O{sub 3} at spinel clad walls. The growth of α-Al{sub 2}O{sub 3} is controlled only by the dissolution rate of MgO by aluminium, liquid state diffusion of Mg to drop/vacuum and oxygen to the front of the of α-Al{sub 2}O{sub 3} crystallites growing into MgO substrate. - Highlights: • New unique evidence of first stages of interaction of liquid Al with MgO substrates • Interaction of liquid Al with MgO starts with the formation of a layer MgAl{sub 2}O{sub 4}. • Growth of MgAl{sub 2}O{sub 4} is slow as controlled by solid state out-diffusion of Mg and O. • MgAl{sub 2}O{sub 4} serves as a nucleation site for Al{sub 2}O{sub 3} and consumed by it soon after. • Growth of Al{sub 2}O{sub 3} is fast as controlled by diffusion in liquid state.

  10. Origin of Perpendicular Magnetic Anisotropy and Large Orbital Moment in Fe Atoms on MgO.

    PubMed

    Baumann, S; Donati, F; Stepanow, S; Rusponi, S; Paul, W; Gangopadhyay, S; Rau, I G; Pacchioni, G E; Gragnaniello, L; Pivetta, M; Dreiser, J; Piamonteze, C; Lutz, C P; Macfarlane, R M; Jones, B A; Gambardella, P; Heinrich, A J; Brune, H

    2015-12-01

    We report on the magnetic properties of individual Fe atoms deposited on MgO(100) thin films probed by x-ray magnetic circular dichroism and scanning tunneling spectroscopy. We show that the Fe atoms have strong perpendicular magnetic anisotropy with a zero-field splitting of 14.0±0.3  meV/atom. This is a factor of 10 larger than the interface anisotropy of epitaxial Fe layers on MgO and the largest value reported for Fe atoms adsorbed on surfaces. The interplay between the ligand field at the O adsorption sites and spin-orbit coupling is analyzed by density functional theory and multiplet calculations, providing a comprehensive model of the magnetic properties of Fe atoms in a low-symmetry bonding environment. PMID:26684139

  11. Process for growing a film epitaxially upon a MgO surface

    DOEpatents

    McKee, Rodney Allen; Walker, Frederick Joseph

    1997-01-01

    A process and structure wherein optical quality perovskites, such as BaTiO.sub.3 or SrTiO.sub.3, are grown upon a single crystal MgO substrate involves the epitaxial build up of alternating planes of TiO.sub.2 and metal oxide wherein the first plane grown upon the MgO substrate is a plane of TiO.sub.2. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

  12. Process for growing a film epitaxially upon a MGO surface and structures formed with the process

    DOEpatents

    McKee, Rodney Allen; Walker, Frederick Joseph

    1998-01-01

    A process and structure wherein optical quality perovskites, such as BaTiO.sub.3 or SrTiO.sub.3, are grown upon a single crystal MgO substrate involves the epitaxial build up of alternating planes of TiO.sub.2 and metal oxide wherein the first plane grown upon the MgO substrate is a plane of TiO.sub.2. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

  13. Fabrication of decorated MgO crystalline fibers

    SciTech Connect

    Chen, Y.J.; Li, J.B.; Han, Y.S.; Yang, X.Z.; Dai, J.H

    2003-02-20

    By depositing Mg vapor generated via carbothermal reduction on boron powder in the presence of different additives, dumbbell-like MgO nanofibers, NaCl particle-decorated MgO nanofibers and camphor tree stalk-like MgO fibers were produced. SEM, TEM and EDS analysis showed that the additives of Si and NaCl deposited in the sites of stacking faults in fiber, which resulted in the growth of different morphologies of decorated fibers.

  14. Formation and stability of hollow MgO nanoshells.

    PubMed

    Krishnan, Gopi; Palasantzas, G; Kooi, B J

    2010-07-01

    High temperature annealing of gas phase synthesized Mg nanoparticles surrounded by an MgO shell leads to formation of hollow MgO nanoshells due to the evaporation assisted Kirkendall effect. Under electron beam exposure in TEM, the (220) MgO facets reduce their high surface energy by forming cube facets, which is followed by nanoshell size reduction and collapse within a few minutes. However, in ambient conditions the nanoshells remain stable for significant periods of time and further degrade by becoming filled with carbon while lossing any MgO identity. Finally, in moderate low vacuum they remained stable for months indicating promise for applications. PMID:21128428

  15. Interstitial Fe in MgO

    SciTech Connect

    Mølholt, T. E. Gislason, H. P.; Ólafsson, S.; Mantovan, R.; Gunnlaugsson, H. P.; Svane, A.; Weyer, G.; Masenda, H.; Naidoo, D.; Bharuth-Ram, K.; Fanciulli, M.; Johnston, K.; Sielemann, R.

    2014-01-14

    Isolated {sup 57}Fe atoms were studied in MgO single-crystals by emission Mössbauer spectroscopy following implantation of {sup 57}Mn decaying to {sup 57}Fe. Four Mössbauer spectral components were found corresponding to different Fe lattice positions and/or charge states. Two components represent Fe atoms substituting Mg as Fe{sup 2+} and Fe{sup 3+}, respectively; a third component is due to Fe in a strongly implantation-induced disturbed region. The fourth component, which is the focus of this paper, can be assigned to Fe at an interstitial site. Comparison of its measured isomer shift with ab initio calculations suggests that the interstitial Fe is located on, or close to, the face of the rock-salt MgO structure. To harmonize such an assignment with the measured near-zero quadrupole interaction a local motion process (cage motion) of the Fe has to be stipulated. The relation of such a local motion as a starting point for long range diffusion is discussed.

  16. Calcium adsorption on MgO(100): energetics, structure, and role of defects.

    PubMed

    Zhu, Junfa; Farmer, Jason A; Ruzycki, Nancy; Xu, Lijun; Campbell, Charles T; Henkelman, Graeme

    2008-02-20

    The adsorption of Ca on the MgO(100) surface at 300 K has been studied using microcalorimetry, in combination with LEED, AES, ISS, work function, sticking probability measurements, and density functional theory (DFT) calculations. The MgO(100) thin films (approximately 4 nm thick) were grown epitaxially on a 1 microm thick Mo(100) single-crystal. The sticking probability of Ca on MgO(100) at 300 K is unity. On the basis of AES and ISS measurements, it was determined that Ca grows mainly as 3D particles on the MgO(100) surface with a density of approximately 1 x 10(12) islands/cm2. Ca adsorbs initially at defect sites with a very high heat of adsorption (approximately 410 kJ/mol). DFT calculations attribute this high initial heat to Ca binding to kink sites (376 kJ/mol), step sites (205 kJ/mol), and lower concentrations of stronger binding sites. The heat of adsorption decreases rapidly with coverage, reaching a minimum of 162 kJ/mol at approximately 0.3 ML, where Ca is mainly adding to small 3D Ca clusters. Afterward, it increases to the value of bulk Ca heat of sublimation (178 kJ/mol) at approximately 1.2 ML, attributed to the increase in stability with increasing Ca particle size. A 1.0 eV decrease of the work function with Ca coverage from 0 to 0.3 ML indicates that Ca adsorbed at defects is cationic, in agreement with calculations showing that Ca donates electron density to the MgO. Light ion sputtering of the MgO(100) surface generates point defects, but these do not change the heat of adsorption versus coverage, implying that they do not nucleate Ca particles. Oxygen vacancies are a likely candidate; DFT calculations show that F and F+ center vacancies bind Ca more weakly than terrace sites. More extensive sputtering creates extended defects (such as steps and kinks) that adsorb Ca with heats of adsorption up to approximately 400 kJ/mol, similar to that at the intrinsic defect sites. PMID:18229925

  17. Fabrication of epitaxial CrO{sub 2} nanostructures directly on MgO(100) by pulsed laser deposition

    SciTech Connect

    Heinig, N. F.; Jalili, H.; Leung, K. T.

    2007-12-17

    Single-phase CrO{sub 2} nanostructured thin films have been grown directly on MgO(100) by pulsed laser ablation of a metallic Cr target in an O{sub 2} environment. X-ray diffraction shows that these films are strained and consist of CrO{sub 2} crystallites with two possible epitaxial relationships to the substrate; either CrO{sub 2}(110) or CrO{sub 2}(200) is parallel to MgO(100). Scanning electron microscopy and atomic force microscopy reveal orthogonally arranged nanoneedles and platelike structures (both 30-50 nm thick). X-ray photoemission confirms that the films are primarily CrO{sub 2} covered with a thin CrO{sub 3} overlayer and indicates its complete synthesis without any residual metallic Cr.

  18. Calorimetry of epitaxial thin films.

    PubMed

    Cooke, David W; Hellman, F; Groves, J R; Clemens, B M; Moyerman, S; Fullerton, E E

    2011-02-01

    Thin film growth allows for the manipulation of material on the nanoscale, making possible the creation of metastable phases not seen in the bulk. Heat capacity provides a direct way of measuring thermodynamic properties of these new materials, but traditional bulk calorimetric techniques are inappropriate for such a small amount of material. Microcalorimetry and nanocalorimetry techniques exist for the measurements of thin films but rely on an amorphous membrane platform, limiting the types of films which can be measured. In the current work, ion-beam-assisted deposition is used to provide a biaxially oriented MgO template on a suspended membrane microcalorimeter in order to measure the specific heat of epitaxial thin films. Synchrotron x-ray diffraction showed the biaxial order of the MgO template. X-ray diffraction was also used to prove the high quality of epitaxy of a film grown onto this MgO template. The contribution of the MgO layer to the total heat capacity was measured to be just 6.5% of the total addenda contribution. The heat capacity of a Fe(.49)Rh(.51) film grown epitaxially onto the device was measured, comparing favorably to literature data on bulk crystals. This shows the viability of the MgO∕SiN(x)-membrane-based microcalorimeter as a way of measuring the thermodynamic properties of epitaxial thin films. PMID:21361612

  19. TELEVISION, RADIO AND FILMS--A SURVEY.

    ERIC Educational Resources Information Center

    SKORNIA, HARRY J.

    THE AUTHOR BEMOANS THE LACK OF RIGOROUS RESEARCH IN EDUCATIONAL MEDIA, ATTRIBUTING IT TO POOR RESEARCH STANDARDS. HE IS CHEERED, HOWEVER, BY THE RECOGNITION OF RESEARCH AS A NEED. TV, RADIO, AND FILMS ARE EACH TREATED SEPARATELY, REFERRING TO HISTORICAL AND TECHNICAL MATTERS, AND THEN TOGETHER WITH REFERENCE TO COMMON PROBLEMS. THE AUTHOR URGES…

  20. Women's Films--A Critical Guide.

    ERIC Educational Resources Information Center

    Indiana Univ., Bloomington. Audio-Visual Center.

    Annotations of 192 recent films which address themselves to subjects of particular interest to women are presented in this reference guide. The guide is intended for use by women's film festivals, consciousness-raising groups, women's studies programs, and guidance programs. Issues considered by the feminists, professional television film crews,…

  1. Wurtzite ZnO (001) films grown on cubic MgO (001) with bulk-like opto-electronic properties

    SciTech Connect

    Zhou Hua; Wang Huiqiong; Chen Xiaohang; Zhan Huahan; Kang Junyong; Wu Lijun; Zhu Yimei; Zhang Lihua; Kisslinger, Kim

    2011-10-03

    We report the growth of ZnO (001) wurtzite thin films with bulk-like opto-electronic properties on MgO (001) cubic substrates using plasma-assisted molecular beam epitaxy. In situ reflection high-energy electron diffraction patterns and ex situ high resolution transmission electron microscopy images indicate that the structure transition from the cubic MgO substrates to the hexagonal films involves 6 ZnO variants that have the same structure but different orientations. This work demonstrates the possibility of integrating wurtzite ZnO films and functional cubic substrates while maintaining their bulk-like properties.

  2. On Interpreting the Photoelectron Spectra of MgO

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Partridge, Harry; Arnold, James (Technical Monitor)

    2001-01-01

    The (sup 2)Sigma(+) and (sup 2)Pi states of MgO(-) and the (sup 1)Sigma(+), (sup 1)Pi, and (sup 3)Pi states of MgO are studied using the averaged coupled-pair functional (ACPF) approach. The computed spectroscopic constants are in good agreement with the available experimental data. The computed Franck-Condon factors and photodetachment overlaps are compared with experiment.

  3. Secondary Ionization Coefficient of MgO and Accumulated Charge

    NASA Astrophysics Data System (ADS)

    Suzuki, Susumu; Sekizawa, Takashi; Kashiwagi, Yasuhide; Itoh, Haruo

    2011-10-01

    An experimental study on Townsend's secondary ionization coefficient γ of MgO is carried out in accordance with a previously reported sequential procedure. A sinusoidal voltage is applied between the MgO film electrode and a stainless-steel electrode in the frequency range of 0.1 Hz-2 kHz. The breakdown voltage is determined from the observed waveforms of applied voltage and accumulated charge on the MgO film electrode. The influence on the breakdown voltage of the voltage induced by the accumulated charge is investigated. We found that the accumulated charge does not affect the breakdown voltage at low frequency or the DC voltage, but it affects the breakdown voltage at high frequency. Using the breakdown voltage, we determine Townsend's secondary ionization coefficient γ of MgO. The obtained γ for MgO in the study is compared with other reported values. It is found that γ for MgO is larger than those of metallic electrodes.

  4. Growth, structural, and magnetic characterization of epitaxial Co2MnSi films deposited on MgO and Cr seed layers

    NASA Astrophysics Data System (ADS)

    Ortiz, G.; García-García, A.; Biziere, N.; Boust, F.; Bobo, J. F.; Snoeck, E.

    2013-01-01

    We report detailed structural characterization and magneto-optical Kerr magnetometry measurements at room temperature in epitaxial Co2MnSi thin films grown on MgO(001) and Cr(001) buffered MgO single crystals prepared by sputtering. While Co2MnSi/Cr//MgO(001) films display the expected cubic anisotropy, the magnetization curves obtained for Co2MnSi//MgO(001) samples exhibit a superimposed in-plane uniaxial magnetic anisotropy. The evolution of magnetization with film thickness points to a relevant interfacial Co2MnSi-buffer layer (Cr or MgO) contribution which competes with magnetic properties of bulk Co2MnSi, resulting in a drastic change in the magnetism of the whole sample. The origin of this interfacial magnetic anisotropy is discussed and correlated with our structural studies.

  5. Effect of MgO Cap Layer on Gilbert Damping of FeB Electrode Layer in MgO-Based Magnetic Tunnel Junctions

    NASA Astrophysics Data System (ADS)

    Konoto, Makoto; Imamura, Hiroshi; Taniguchi, Tomohiro; Yakushiji, Kay; Kubota, Hitoshi; Fukushima, Akio; Ando, Koji; Yuasa, Shinji

    2013-07-01

    We investigated the Gilbert damping of thin films with a MgO-barrier/Fe80B20/MgO-cap/Ta structure, in which the Fe80B20 layer corresponds to a free layer of a perpendicularly magnetized magnetic tunnel junction, by using ferromagnetic resonance (FMR). We systematically varied the thickness of the MgO cap layer and estimated the damping constant (α) by measuring the dependence of the FMR spectrum on the magnetic field angle. The MgO cap layer was found to reduce α to about 0.005, which is less than half the value without the cap. The significant reduction can be explained by the suppression of spin pumping by the dielectric MgO cap layer.

  6. Soft x-ray appearance potential spectroscopy study of MgO (100) and α-Al{sub 2}O{sub 3} (100) single crystals

    SciTech Connect

    Fukuda, Yasuo Sanada, Noriaki; Mochizuki, Sachie; Yatsuzuka, Ikuko

    2013-11-15

    Soft x-ray appearance potential spectroscopy (SXAPS) measurements was used to measure on MgO (100) and α-Al{sub 2}O{sub 3} (100) single crystals. Mg 1s, Al 1s, and O 1s SXAPS self-deconvoluted (SD) spectra were obtained. The features of the Mg 1s and O1s SD spectra are in fair agreement with those of the near-edge x-ray absorption fine structure spectra for an MgO thin film (3 ML) on Ag (100). This suggests that the SXAPS spectra reflect electronic states of the relaxed MgO (100) surface. The features of the Al 1s and O 1s SD spectra are in qualitative agreement with those of the electron energy-loss spectroscopy. The SXAPS SD spectra are discussed in terms of antibonding states and partial density of empty states obtained by theoretical calculations for MgO and α-Al{sub 2}O{sub 3,} respectively. The present result suggests that the “approximate dipole selection rule” is applicable to the SXAPS spectra of MgO and α-Al{sub 2}O{sub 3}, as well as 3d transition metal oxides.

  7. Multifunctional MgO Layer in Perovskite Solar Cells.

    PubMed

    Guo, Xudong; Dong, Haopeng; Li, Wenzhe; Li, Nan; Wang, Liduo

    2015-06-01

    A multifunctional magnesium oxide (MgO) layer was successfully introduced into perovskite solar cells (PSCs) to enhance their performance. MgO was coated onto the surface of mesoporous TiO(2) by the decomposition of magnesium acetate and, therefore, could block contact between the perovskite and TiO(2). X-ray photoelectron spectroscopy and infrared spectroscopy showed that the amount of H(2)O/hydroxyl absorbed on the TiO(2) decreased after MgO modification. The UV/Vis absorption spectra of the perovskite with MgO modification revealed an enhanced photoelectric performance compared with that of unmodified perovskite after UV illumination. In addition to the photocurrent, the photovoltage and fill factor also showed an enhancement after modification, which resulted in an increase in the overall efficiency of the cell from 9.6 to 13.9 %. Electrochemical impedance spectroscopy (EIS) confirmed that MgO acts as an insulating layer to reduce charge recombination. PMID:25851999

  8. Size effects in MgO cube dissolution.

    PubMed

    Baumann, Stefan O; Schneider, Johannes; Sternig, Andreas; Thomele, Daniel; Stankic, Slavica; Berger, Thomas; Grönbeck, Henrik; Diwald, Oliver

    2015-03-10

    Stability parameters and dissolution behavior of engineered nanomaterials in aqueous systems are critical to assess their functionality and fate under environmental conditions. Using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, we investigated the stability of cubic MgO particles in water. MgO dissolution proceeding via water dissociation at the oxide surface, disintegration of Mg(2+)-O(2-) surface elements, and their subsequent solvation ultimately leads to precipitation of Mg(OH)2 nanosheets. At a pH ≥ 10, MgO nanocubes with a size distribution below 10 nm quantitatively dissolve within few minutes and convert into Mg(OH)2 nanosheets. This effect is different from MgO cubes originating from magnesium combustion in air. With a size distribution in the range 10 nm ≤ d ≤ 1000 nm they dissolve with a significantly smaller dissolution rate in water. On these particles water induced etching generates (110) faces which, above a certain face area, dissolve at a rate equal to that of (100) planes.1 The delayed solubility of microcrystalline MgO is attributed to surface hydroxide induced self-inhibition effects occurring at the (100) and (110) microplanes. The present work underlines the importance of morphology evolution and surface faceting of engineered nanomaterials particles during their dissolution. PMID:25668706

  9. Surface exciton emission of MgO crystals

    NASA Astrophysics Data System (ADS)

    Kuang, Wen-Jian; Li, Qing; Chen, Yu-Xiang; Hu, Kai; Wang, Ning-Hui; Xing, Fang-Li; Yan, Qun; Sun, Shuai-Shuai; Huang, Yan; Tao, Ye; Tolner, Harm

    2013-09-01

    MgO crystals have been exposed to vacuum ultraviolet (VUV) radiation from a synchrotron, with energies up to 9 eV, and the emitted light, at wavelengths above 200 nm, was observed. It is concluded that bulk excitons, play an important role in the diffusion of energy inside MgO crystals, resulting in 5.85 eV (212 nm) emission from the MgO terraces of large (0.2-2 µm) MgO : F crystals. In the case of aliovalent impurity doping, then the bulk exciton energy is also transferred to the Vk centres and 5.3 eV (235 nm) light is emitted. Both fluorine and silicon doping appear to promote UV surface emission, acting similarly to an ns2 ion inside MgO, while strong scandium doping is killing the surface emission completely. The 212 nm surface UV emission and the 235 nm bulk UV emission can be excited only at the bandgap edge. Broadband visible light, centred around 400 nm, is also emitted. Contrary to the UV emission, this is not generated when excited at the bandgap edge; instead, we find that it is only excited at sub-bandgap energies, with a maximum at the 5C surface excitation energy of 5.71 eV (217 nm) for the MgO terraces.

  10. Atomically-Smooth MgO films grown on Epitaxial Graphene by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Stuart, Sean; Sandin, Andreas; Rowe, Jack; Dougherty, Dan; Ulrich, Marc

    2013-03-01

    The growth of high quality insulating films on graphene is a crucial materials science task for graphene electronic and spintronic applications. It has been demonstrated that direct spin injection from a magnetic electrode to graphene is possible using MgO tunnel barriers of sufficient quality. We have used pulsed laser deposition (PLD) to grow thin magnesium oxide films directly on epitaxial graphene on SiC(0001). We observe very smooth film morphologies (typical rms roughness of ~ 0.4 nm) that are nearly independent of film thickness and conform to the substrate surface which had ~ 0.2 nm rms roughness. Surface roughness of 0.04 nm have been recorded for ~ 1nm films with no pinholes seen by AFM. XPS and XRD data show non crystalline, hydroxylated MgO films with uniform coverage. This work shows that PLD is a good technique to produce graphene-oxide interfaces without pre-deposition of an adhesion layer or graphene functionalization. The details and kinetics of the deposition process will be described with comparisons being made to other dielectric-on-graphene deposition approaches. Funded by ARO Staff Research Contract # W911NF.

  11. Fabrication of Single Crystal MgO Capsules

    NASA Technical Reports Server (NTRS)

    Danielson, Lisa

    2012-01-01

    A method has been developed for machining MgO crystal blocks into forms for containing metallic and silicate liquids at temperatures up to 2,400 C, and pressures up to at least 320 kilobars. Possible custom shapes include tubes, rods, insulators, capsules, and guides. Key differences in this innovative method include drilling along the crystallographic zone axes, use of a vibration minimizing material to secure the workpiece, and constant flushing of material swarf with a cooling medium/lubricant (water). A single crystal MgO block is cut into a section .5 mm thick, 1 cm on a side, using a low-speed saw with a 0.004 blade. The cut is made parallel to the direction of cleavage. The block may be cut to any thickness to achieve the desired length of the piece. To minimize drilling vibrations, the MgO block is mounted on a piece of adhesive putty in a vise. The putty wad cradles the bottom half of the entire block. Diamond coring tools are used to drill the MgO to the desired custom shape, with water used to wet and wash the surface of swarf. Compressed air may also be used to remove swarf during breaks in drilling. The MgO workpiece must be kept cool at all times with water. After all the swarf is rinsed off, the piece is left to dry overnight. If the workpiece is still attached to the base of the MgO block after drilling, it may be cut off by using a diamond cutoff wheel on a rotary hand tool or by using a low-speed saw.

  12. 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.

  13. Properties of alkali metal atoms deposited on a MgO surface: a systematic experimental and theoretical study.

    PubMed

    Finazzi, Emanuele; Di Valentin, Cristiana; Pacchioni, Gianfranco; Chiesa, Mario; Giamello, Elio; Gao, Hongjun; Lian, Jichun; Risse, Thomas; Freund, Hans-Joachim

    2008-01-01

    The adsorption of small amounts of alkali metal atoms (Li, Na, K, Rb, and Cs) on the surface of MgO powders and thin films has been studied by means of EPR spectroscopy and DFT calculations. From a comparison of the measured and computed g values and hyperfine coupling constants (hfccs), a tentative assignment of the preferred adsorption sites is proposed. All atoms bind preferentially to surface oxide anions, but the location of these anions differs as a function of the deposition temperature and alkali metal. Lithium forms relatively strong bonds with MgO and can be stabilized at low temperatures on terrace sites. Potassium interacts very weakly with MgO and is stabilized only at specific sites, such as at reverse corners where it can interact simultaneously with three surface oxygen atoms (rubidium and cesium presumably behave in the same way). Sodium forms bonds of intermediate strength and could, in principle, populate more than a single site when deposited at room temperature. In all cases, large deviations of the hfccs from the gas-phase values are observed. These reductions in the hfccs are due to polarization effects and are not connected to ionization of the alkali metal, which would lead to the formation of an adsorbed cation and a trapped electron. In this respect, hydrogen atoms behave completely differently. Under similar conditions, they form (H(+))(e(-)) pairs. The reasons for this different behavior are discussed. PMID:18381711

  14. Strain-enhanced tunneling magnetoresistance in MgO magnetic tunnel junctions

    PubMed Central

    Loong, Li Ming; Qiu, Xuepeng; Neo, Zhi Peng; Deorani, Praveen; Wu, Yang; Bhatia, Charanjit S.; Saeys, Mark; Yang, Hyunsoo

    2014-01-01

    While the effects of lattice mismatch-induced strain, mechanical strain, as well as the intrinsic strain of thin films are sometimes detrimental, resulting in mechanical deformation and failure, strain can also be usefully harnessed for applications such as data storage, transistors, solar cells, and strain gauges, among other things. Here, we demonstrate that quantum transport across magnetic tunnel junctions (MTJs) can be significantly affected by the introduction of controllable mechanical strain, achieving an enhancement factor of ~2 in the experimental tunneling magnetoresistance (TMR) ratio. We further correlate this strain-enhanced TMR with coherent spin tunneling through the MgO barrier. Moreover, the strain-enhanced TMR is analyzed using non-equilibrium Green's function (NEGF) quantum transport calculations. Our results help elucidate the TMR mechanism at the atomic level and can provide a new way to enhance, as well as tune, the quantum properties in nanoscale materials and devices. PMID:25266219

  15. Surfactant assisted growth of MgO films on GaN

    SciTech Connect

    Paisley, E. A.; Shelton, T. C.; Collazo, R.; Sitar, Z.; Maria, J.-P.; Christen, H. M.; Biegalski, M. D.; Mita, S.

    2012-08-27

    Thin epitaxial films of <111> oriented MgO on [0001]-oriented GaN were grown by molecular beam epitaxy and pulsed laser deposition using the assistance of a vapor phase surfactant. In both cases, surfactant incorporation enabled layer-by-layer growth and a smooth terminal surface by stabilizing the {l_brace}111{r_brace} rocksalt facet. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100 Multiplication-Sign reduction in leakage current density for the surfactant-assisted samples. These data verify numerous predictions regarding the role of H-termination in regulating the habit of rocksalt crystals.

  16. Strain-enhanced tunneling magnetoresistance in MgO magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Loong, Li Ming; Qiu, Xuepeng; Neo, Zhi Peng; Deorani, Praveen; Wu, Yang; Bhatia, Charanjit S.; Saeys, Mark; Yang, Hyunsoo

    2014-09-01

    While the effects of lattice mismatch-induced strain, mechanical strain, as well as the intrinsic strain of thin films are sometimes detrimental, resulting in mechanical deformation and failure, strain can also be usefully harnessed for applications such as data storage, transistors, solar cells, and strain gauges, among other things. Here, we demonstrate that quantum transport across magnetic tunnel junctions (MTJs) can be significantly affected by the introduction of controllable mechanical strain, achieving an enhancement factor of ~2 in the experimental tunneling magnetoresistance (TMR) ratio. We further correlate this strain-enhanced TMR with coherent spin tunneling through the MgO barrier. Moreover, the strain-enhanced TMR is analyzed using non-equilibrium Green's function (NEGF) quantum transport calculations. Our results help elucidate the TMR mechanism at the atomic level and can provide a new way to enhance, as well as tune, the quantum properties in nanoscale materials and devices.

  17. Recovery of SO2 and MgO from By-Products of MgO Wet Flue Gas Desulfurization

    PubMed Central

    Yan, Liyun; Lu, Xiaofeng; Wang, Quanhai; Guo, Qiang

    2014-01-01

    Abstract An industrial demonstration unit using natural gas as a heat source was built to calcine the by-products of MgO wet flue gas desulfurization from power plants; influencing factors on the SO2 content in calciner gas were comprehensively analyzed; and an advantageous recycling condition of MgO and SO2 from by-products was summarized. Results showed that the SO2 content in the calciner gas was increased by more than 10 times under a lower excess air coefficient, a higher feed rate, a lower crystal water in by-products, and a higher feed port position. For the tests conducted under the excess air coefficient above and below one, the effect of the furnace temperature on the SO2 content in the calciner gas was reversed. Results of activity analysis indicate that particles of MgO generated under the calcination temperature of 900–1,000°C had a high activity. In contrast, due to the slight sintering, MgO generated under the calcination temperature of 1,100°C had a low activity. To recycle SO2 as well as MgO, a temperature range of 900–927°C for TE103 is proposed. These studies will prompt the desulfurization market diversification, reduce the sulfur's dependence on imports for making sulfuric acid, be meaningful to balance the usage of the natural resource in China, and be regarded as a reference for the development of this technology for other similar developing countries. PMID:25371652

  18. Recovery of SO2 and MgO from By-Products of MgO Wet Flue Gas Desulfurization.

    PubMed

    Yan, Liyun; Lu, Xiaofeng; Wang, Quanhai; Guo, Qiang

    2014-11-01

    An industrial demonstration unit using natural gas as a heat source was built to calcine the by-products of MgO wet flue gas desulfurization from power plants; influencing factors on the SO2 content in calciner gas were comprehensively analyzed; and an advantageous recycling condition of MgO and SO2 from by-products was summarized. Results showed that the SO2 content in the calciner gas was increased by more than 10 times under a lower excess air coefficient, a higher feed rate, a lower crystal water in by-products, and a higher feed port position. For the tests conducted under the excess air coefficient above and below one, the effect of the furnace temperature on the SO2 content in the calciner gas was reversed. Results of activity analysis indicate that particles of MgO generated under the calcination temperature of 900-1,000°C had a high activity. In contrast, due to the slight sintering, MgO generated under the calcination temperature of 1,100°C had a low activity. To recycle SO2 as well as MgO, a temperature range of 900-927°C for TE103 is proposed. These studies will prompt the desulfurization market diversification, reduce the sulfur's dependence on imports for making sulfuric acid, be meaningful to balance the usage of the natural resource in China, and be regarded as a reference for the development of this technology for other similar developing countries. PMID:25371652

  19. Adsorption of small Au clusters on MgO and MgO/Mo: the role of oxygen vacancies and the Mo-support

    NASA Astrophysics Data System (ADS)

    Frondelius, P.; Häkkinen, H.; Honkala, K.

    2007-09-01

    We report a systematic density functional theory investigation of adsorption of small Aun (n =1-6) clusters on ideal and defected MgO(100) single crystal surfaces and Mo(100) supported thin MgO(100) films. As a model defect, we consider a neutral surface oxygen vacancy (Fs). Optimal adsorption geometries and energies, cluster formation energies and cluster charges are discussed and compared in detail over four different substrates. For a given cluster size, the adsorption energy among these substrates increases in the order MgO, Fs/MgO, MgO/Mo and Fs/MgO/Mo. While cluster growth by association of atoms from gas phase is exothermic on all the substrates, cluster growth by diffusion and aggregation of pre-adsorbed Au atoms is an endothermic process for Au1→Au2, Au3→Au4 and Au5→Au6 on MgO/Mo and Au2→Au3 and Au5→Au6 on Fs/MgO/Mo. The adsorbed clusters are close to neutral on MgO, but adopt a significant anionic charge on other supports with the increasing order: MgO/Mo, Fs/MgO and Fs/MgO/Mo. The adsorption strength thus correlates with the amount of negative charge transferred from the substrate to gold.

  20. Interfacial effects on the tunneling magnetoresistance in L a0.7S r0.3Mn O3/MgO /Fe tunneling junctions

    NASA Astrophysics Data System (ADS)

    Galceran, R.; Balcells, Ll.; Martinez-Boubeta, C.; Bozzo, B.; Cisneros-Fernández, J.; de la Mata, M.; Magén, C.; Arbiol, J.; Tornos, J.; Cuellar, F. A.; Sefrioui, Z.; Cebollada, A.; Golmar, F.; Hueso, L. E.; Casanova, F.; Santamaría, J.; Martinez, B.

    2015-09-01

    We report on magnetotransport properties on L a0.7S r0.3Mn O3/MgO /Fe tunnel junctions grown epitaxially on top of (001)-oriented SrTi O3 substrates by sputtering. It is shown that the magnetoresistive response depends critically on the MgO /Fe interfacial properties. The appearance of an Fe OX layer by the interface destroys the Δ1 symmetry filtering effect of the MgO /Fe system and only a small negative tunneling magnetoresistance (TMR) (˜-3 %) is measured. However, in annealed samples a switchover from positive TMR (˜+25 % at 70 K) to negative TMR (˜-1 %) is observed around 120 K. This change is associated with the transition from semiconducting at high T to insulating at low T taking place at the Verwey transition (TV˜120 K ) in F e3O4, thus suggesting the formation of a very thin slab of magnetite at the MgO /Fe interface during annealing treatments. These results highlight the relevance of interfacial properties on the tunneling conduction process and how it can be substantially modified through appropriate interface engineering.

  1. NEXAFS Study of Air Oxidation for Mg Nanoparticle Thin Film

    NASA Astrophysics Data System (ADS)

    Ogawa, S.; Murakami, S.; Shirai, K.; Nakanishi, K.; Ohta, T.; Yagi, S.

    2013-03-01

    The air oxidation reaction of Mg nanoparticle thin film has been investigated by Mg K-edge NEXAFS technique. It is revealed that MgO is formed on the Mg nanoparticle surfaces at the early stage of the air oxidation for Mg nanoparticle thin film. The simulation of NEXAFS spectrum using standard spectra indicates the existence of complex magnesium carbonates (x(MgCO3).yMg(OH2).z(H2O)) in addition to MgO at the early stage of the air oxidation.

  2. Flexible MgO Barrier Magnetic Tunnel Junctions.

    PubMed

    Loong, Li Ming; Lee, Wonho; Qiu, Xuepeng; Yang, Ping; Kawai, Hiroyo; Saeys, Mark; Ahn, Jong-Hyun; Yang, Hyunsoo

    2016-07-01

    Flexible MgO barrier magnetic tunnel junction (MTJ) devices are fabricated using a transfer printing process. The flexible MTJ devices yield significantly enhanced tunneling magnetoresistance of ≈300% and improved abruptness of switching, as residual strain in the MTJ structure is released during the transfer process. This approach could be useful for flexible electronic systems that require high-performance memory components. PMID:27119207

  3. Phase Transitions of MgO Along the Hugoniot (Invited)

    NASA Astrophysics Data System (ADS)

    Root, S.; Shulenburger, L.; Lemke, R. W.; Cochrane, K. R.; Mattsson, T. R.

    2013-12-01

    The formation of terrestrial planets and planetary structure has become of great interest because of recent exoplanet discoveries of super earths. MgO is a major constituent of Earth's mantle, the rocky cores of gas giants such as Jupiter, and likely constitutes the interiors of many exoplanets. The high pressure - high temperature behavior of MgO directly affects equation of state models for planetary structure and formation. In this work, we examine single crystal MgO under shock compression utilizing experimental and density functional theory (DFT) methods to determine phase transformations along the Hugoniot. We perform plate impact experiments using Sandia's Z - facility on MgO up to 11.6 Mbar. The plate impact experiments generate highly accurate Hugoniot state data. The experimental results show the B1 - B2 solid - solid phase transition occurs near 4 Mbar on the Hugoniot. The solid - liquid transition is determined to be near 7 Mbar with a large region of B2-liquid coexistence. Using DFT methods, we also determine melt along the B1 and B2 solid phase boundaries as well as along the Hugoniot. The combined experimental and DFT results have determined the phase boundaries along the Hugoniot, which can be implemented into new planetary and EOS models. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Securities Administration under Contract No. DE-AC04-94AL85000.

  4. Helium diffraction from the MgO(001) surface

    NASA Astrophysics Data System (ADS)

    Jung, David R.; Mahgerefteh, Massoud; Frankl, Daniel R.

    1989-05-01

    Helium diffraction beam intensity measurements from an in situ cleaved, oxygen-treated, room-temperature surface of MgO(001) are reported. The in-plane spectra obtained at several angles in the main azimuthal planes at beam energies of 17.3 and 63 meV were analyzed using a hard corrugated surface model. A corrugation amplitude of about 0.17 Å gives a fair fit, in agreement with most previous work.

  5. Grain boundary mobility in anion doped MgO

    NASA Technical Reports Server (NTRS)

    Kapadia, C. M.; Leipold, M. H.

    1973-01-01

    Certain anions OH(-), F(-) and Gl(-) are shown to enhance grain growth in MgO. The magnitude of their effect decreases in the order in which the anions are listed and depends on their location (solid-solution, second phase) in the MgO lattice. As most anions exhibit relatively high vapor pressures at sintering temperatures, they retard densification and invariably promote residual porosity. The role of anions on grain growth rates was studied in relation to their effect on pore mobility and pore removal; the atomic process controlling the actual rates was determined from observed kinetics in conjunction with the microstructural features. With respect to controlling mechanisms, the effects of all anions are not the same. OH(-) and F(-) control behavior through creation of a defect structure and a grain boundary liquid phase while Cl(-) promotes matter transport within pores by evaporation-condensation. Studies on an additional anion, S to the minus 2nd power gave results which were no different from undoped MgO, possibly because of evaporative losses during hot pressing. Hence, the effect of sulphur is negligible or undetermined.

  6. Ab initio study of early stage Nb growth on MgO(001)

    NASA Astrophysics Data System (ADS)

    Shim, Yunsic; Amar, Jacques G.

    2016-03-01

    Using density functional theory calculations we have examined the effects of cluster shape and a neutral O vacancy on the energetics and stability of Nb monomers and clusters on the MgO(001) surface. The relative stability of different monolayer structures is also examined. As found in other cases of metal adsorbates on MgO(001), our results indicate that an O site is the preferred adsorption site for a Nb atom. In addition, O-vacancy sites tend to increase the binding energy of small clusters and thus act as nucleation sites, while the effect of a nearby O vacancy on the binding energy of a Nb cluster is much weaker. In particular, we find that the binding energy for a Nb monomer at an O site (O-vacancy site) is 1.5 eV (2.2 eV) while the corresponding activation barriers for Nb monomer diffusion are 0.58 eV (0.80 eV). We also find that, in the absence of O vacancies, the preferred planar structure for tetramers and pentamers is an isotropic (100)-like structure. In contrast, the presence of an O vacancy transforms the isotropic tetramer into an anisotropic (110)-like structure. In addition, due to strain effects as well as strong Nb-Nb interactions, for large clusters (e.g. a complete monolayer) the anisotropic (110) structure is favored over the (100) structure. These results appear to explain recent experimental observations for the dependence of thin-film orientation on deposition conditions. However, we also find that for small (100)-like and (110)-like clusters, three-dimensional (rather than planar) structures are energetically preferred due to the strong Nb-Nb interaction. These results suggest that the pathway to form a coherent (100) or (110) structure during the growth of Nb films on Mg(001) may be relatively complex.

  7. The effect of MgO(111) interlayer on the interface phase stability and structure of BaFe12O19/SiC(0001)

    NASA Astrophysics Data System (ADS)

    Lazarov, V. K.; Hasnip, P. J.; Cai, Z.; Yoshida, K.; Ziemer, K. S.

    2012-04-01

    We present a study on the effect of an interlayer of thin MgO(111) film on SiC(0001) on the interface phase stability and structure of the BaFe12O19 (BaM). The 10 nm MgO(111) interlayer followed by the BaM film were grown by molecular beam epitaxy on 6H-SiC. Cross-sectional transmission electron microscopy shows the formation of a magnesium ferrite spinel phase at the interface, and after 25 nm, a well structured BaM film was observed. In addition to the two main phases (Mg-ferrite and BaM), a thin layer of SiOx (2-3 nm) is formed at the SiC interface. In spite of the formation of this amorphous layer, the diffraction studies show that the BaM film is epitaxially grown and it has a single crystal structure. The energy dispersive x-ray analysis from the interface region shows that the MgO layer prevents significant outdiffusion of the Si into the film. Total energy calculations by density functional theory were used to investigate the stability of the various phases and to explain the observed interfacial phases in the studied system.

  8. Interface control by homoepitaxial growth in pulsed laser deposited iron chalcogenide thin films

    PubMed Central

    Molatta, Sebastian; Haindl, Silvia; Trommler, Sascha; Schulze, Michael; Wurmehl, Sabine; Hühne, Ruben

    2015-01-01

    Thin film growth of iron chalcogenides by pulsed laser deposition (PLD) is still a delicate issue in terms of simultaneous control of stoichiometry, texture, substrate/film interface properties, and superconducting properties. The high volatility of the constituents sharply limits optimal deposition temperatures to a narrow window and mainly challenges reproducibility for vacuum based methods. In this work we demonstrate the beneficial introduction of a semiconducting FeSe1−xTex seed layer for subsequent homoepitaxial growth of superconducting FeSe1−xTex thin film on MgO substrates. MgO is one of the most favorable substrates used in superconducting thin film applications, but the controlled growth of iron chalcogenide thin films on MgO has not yet been optimized and is the least understood. The large mismatch between the lattice constants of MgO and FeSe1−xTex of about 11% results in thin films with a mixed texture, that prevents further accurate investigations of a correlation between structural and electrical properties of FeSe1−xTex. Here we present an effective way to significantly improve epitaxial growth of superconducting FeSe1−xTex thin films with reproducible high critical temperatures (≥17 K) at reduced deposition temperatures (200 °C–320 °C) on MgO using PLD. This offers a broad scope of various applications. PMID:26548645

  9. Spectroscopic studies of refractory and dielectric thin films

    SciTech Connect

    Truong, C.M.

    1993-01-01

    This work demonstrated the application of the techniques and methodology of surface science to investigate the mechanisms of thin film deposition processes on solid surfaces. The synthesis of boron nitride (BN) thin films was studied using X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). In this model system, diborane (B[sub 2]H[sub 6]), ammonia (NH[sub 3]) and hydrazine (N[sub 2]H[sub 4]) were used as precursors to deposit BN thin films on a clean Ru(0001) surface. The result showed that ammonia reaction with diborane yielded only boron-rich boron nitride overlayers. However, stoichiometric BN films in excess of one monolayer could be produced when hydrazine was substituted for ammonia. The effects of oxygen on boron-rich and stoichiometric boron-nitrogen films were also examined. In the second part of this work, high resolution electron energy loss spectroscopy (HREELS) was used to characterize defect centers in MgO and in lithium-doped MgO thin films. The HREELS results showed that MgO thin films grown on Mo(100) were nearly defect-free at temperatures up to 1100 K. HREELS measurements indicated that annealings to higher temperatures induced F-type defect centers in the MgO films. The formation of [Li[sup +]O[sup [minus

  10. Location of Trapped Electron Centers in the Bulk of Epitaxial MgO(001) Films Grown on Mo(001) Using in situ W -band Electron Paramagnetic Resonance Spectroscopy

    NASA Astrophysics Data System (ADS)

    Cornu, Damien; Rocker, Jan; Gonchar, Anastasia; Risse, Thomas; Freund, Hans-Joachim

    2016-07-01

    We present the first in situ W -band (94-GHz) electron paramagnetic resonance (EPR) study of a trapped electron center in thin MgO(001) films. The improved resolution of the high-field EPR experiments proves that the signal originate from a well-defined species present in the bulk of the films, whose projection of the principal g -tensor components onto the (001) plane are oriented along the [110] direction of the MgO lattice. Based on a comparison between the structural properties of the films, knowledge of the ability of bulk defects to trap electrons, and the properties of the EPR signal, it is possible to propose that the paramagnetic species are located at the origin of a screw dislocation in the bulk of the film.

  11. High-rate deposition of MgO by reactive ac pulsed magnetron sputtering in the transition mode

    SciTech Connect

    Kupfer, H.; Kleinhempel, R.; Richter, F.; Peters, C.; Krause, U.; Kopte, T.; Cheng, Y.

    2006-01-15

    A reactive ac pulsed dual magnetron sputtering process for MgO thin-film deposition was equipped with a closed-loop control of the oxygen flow rate (F{sub O2}) using the 285 nm magnesium radiation as input. Owing to this control, most of the unstable part of the partial pressure versus flowrate curve became accessible. The process worked steadily and reproducible without arcing. A dynamic deposition rate of up to 35 nm m/min could be achieved, which was higher than in the oxide mode by about a factor of 18. Both process characteristics and film properties were investigated in this work in dependence on the oxygen flow, i.e., in dependence on the particular point within the transition region where the process is operated. The films had very low extinction coefficients (<5x10{sup -5}) and refractive indices close to the bulk value. They were nearly stoichiometric with a slight oxygen surplus (Mg/O=48/52) which was independent of the oxygen flow. X-ray diffraction revealed a prevailing (111) orientation. Provided that appropriate rf plasma etching was performed prior to deposition, no other than the (111) peak could be detected. The intensity of this peak increased with increasing F{sub O{sub 2}}, indicating an even more pronounced (111) texture. The ion-induced secondary electron emission coefficient (iSEEC) was distinctly correlated with the markedness of the (111) preferential orientation. Both refractive index and (111) preferred orientation (which determines the iSEEC) were found to be improved in comparison with the MgO growth in the fully oxide mode. Consequently, working in the transition mode is superior to the oxide mode not only with respect to the growth rate, but also to most important film properties.

  12. MgO Doped Tantalum Coating on Ti: Microstructural Study and Biocompatibility Evaluation

    PubMed Central

    Roy, Mangal; Balla, Vamsi Krishna; Bandyopadhyay, Amit; Bose, Susmita

    2012-01-01

    Pure and MgO incorporated Ta coatings were prepared on Cp-Ti substrate using laser engineered net shaping (LENS™) which resulted in diffuse coating-substrate interface. MgO was found along the Ta grain boundaries in the Ta matrix that increased the coating hardness from 185 ± 2.7 HV to 794 ± 93 HV. In vitro biocompatibility study showed excellent early cellular attachment and later stage proliferation in MgO incorporated coatings. The results indicated that although Ta coatings had higher biocompatibility than Ti, it could further be improved by incorporating MgO in the coating, while simultaneously increasing the mechanical properties. PMID:22248182

  13. Growth of atomically smooth MgO films on graphene by molecular beam epitaxy

    SciTech Connect

    Wang, W. H.; Han, W.; Pi, K.; McCreary, K. M.; Miao, F.; Bao, W.; Lau, C. N.; Kawakami, R. K.

    2008-11-03

    We investigate the growth of MgO films on graphene by molecular beam epitaxy and find that surface diffusion promotes a rough morphology. To reduce the mobility of surface atoms, the graphene surface is dressed by Ti atoms prior to MgO deposition. With as little as 0.5 ML (monolayer) of Ti, the MgO overlayer becomes atomically smooth. Furthermore, no aggregation of MgO is observed at the edges of the graphene sheet. These results are important for the fabrication of nanoscale electronic and spintronic devices.

  14. Measurement of Townsend's Secondary Ionization Coefficient of MgO Film in Argon

    NASA Astrophysics Data System (ADS)

    Suzuki, Susumu; Konno, Kazuya; Itoh, Haruo

    Townsend's secondary ionization coefficients γ of MgO in Ar are determined from the breakdown voltages and the Townsend's criterion. Breakdown voltages on MgO film are measured by the both wave forms, discharge current and applied voltage between the electrodes on the oscilloscope. According to the experimental procedure, γ of gold film and stainless steel electrodes are determined and compared with other experimental values. After the confirmation of the validity of those results, we have carried out the determination for γ of MgO. Furthermore, the influence of heating effect of MgO film to the value of γ is also discussed.

  15. Inversion of ferromagnetic proximity polarization by MgO interlayers.

    PubMed

    Li, Yan; Chye, Y; Chiang, Y F; Pi, K; Wang, W H; Stephens, J M; Mack, S; Awschalom, D D; Kawakami, R K

    2008-06-13

    We investigate the spin-dependent reflection properties in Fe/MgO/GaAs heterostructures by optical pump-probe measurement of the ferromagnetic proximity polarization (FPP). As a function of MgO thickness, the FPP is initially enhanced (<2.0 A) and then exhibits an unexpected sign reversal at approximately 5.0 A. The identification of two competing thresholds in the intensity dependence of FPP and the observation of FPP sign reversal in Fe/Mg/GaAs suggest that the inversion of FPP is related to an interfacial bonding effect. PMID:18643542

  16. Selective adsorption in 4MgO scattering

    NASA Astrophysics Data System (ADS)

    Mahgerefteh, Massoud; Jung, David R.; Frankl, Daniel R.

    1989-02-01

    Helium scattering data from an in situ cleaved, oxygen-treated, room-temperature surface of MgO(100) are reported. The sharpness of the selective adsorption line shapes as well as the strength of the scattered beams indicate an improvement over previous studies on air-cleaved surfaces. Selective adsorption line shapes in azimuthal scans of the specular intensity at many closely spaced angles of incidence are presented. Analysis of the resonances at several reciprocal lattice vectors yielded binding energies of 5.52, 2.57, 1.16, 0.54, and 0.26 meV.

  17. Structural and magnetic properties of epitaxial FeMn2O4 film on MgO (100)

    NASA Astrophysics Data System (ADS)

    Duong van, Thiet; Nguyen, Thi Minh Hai; Nguyen, Anh Phuong; Dang Duc, Dung; Duong, Anh Tuan; Nguyen van, Quang; Cho, Sunglae

    FeM2X4 spinel structures, where M is a transition metal and X is oxygen or sulfur, are candidate materials for spin filters, one of the key devices in spintronics. On the other hand, the electronic and magnetic properties of these spinel structures could be modified via the control of cation distribution. Among the spinel oxides, iron manganese oxide is one of promising materials for applications. FeMn2O4 shows inverse spinel structure above 390 K and ferrimagnetic properties below the temperature. In this work, we report on the structural and magnetic properties of epitaxial FeMn2O4 thin film on MgO(100) substrate. The reflection high energy electron diffraction (RHEED) and X-ray diffraction (XRD) results indicated that films were epitaxially grown on MgO(100) without the impurity phases. The valance states of Fe and Mn in the FeMn2O4film were carried out using x-ray photoelectron spectrometer (XPS). The magnetic properties were measured by vibrating sample magnetometer (VSM), indicating that the samples are ferromagnetic at room temperature. The structural detail and origin of magnetic ordering in FeMn2O4 will be discussed.

  18. Mangotoxin production of Pseudomonas syringae pv. syringae is regulated by MgoA

    PubMed Central

    2014-01-01

    Background The antimetabolite mangotoxin is a key factor in virulence of Pseudomonas syringae pv. syringae strains which cause apical necrosis of mango trees. Previous studies showed that mangotoxin biosynthesis is governed by the mbo operon. Random mutagenesis led to the identification of two other gene clusters that affect mangotoxin biosynthesis. These are the gacS/gacA genes and mgo operon which harbors the four genes mgoBCAD. Results The current study shows that disruption of the nonribosomal peptide synthetase (NRPS) gene mgoA resulted in loss of mangotoxin production and reduced virulence on tomato leaves. Transcriptional analyses by qPCR and promoter reporter fusions revealed that mbo expression is regulated by both gacS/gacA and mgo genes. Also, expression of the mgo operon was shown to be regulated by gacS/gacA. Heterologous expression under the native promoter of the mbo operon resulted in mangotoxin production in non-producing P. syringae strains, but not in other Pseudomonas species. Also introduction of the mbo and mgo operons in nonproducing P. protegens Pf-5 did not confer mangotoxin production but did enhance transcription of the mbo promoter. Conclusions From the data obtained in this study, we conclude that both mbo and mgo operons are under the control of the gacS/gacA two-component system and that the MgoA product acts as a positive regulator of mangotoxin biosynthesis. PMID:24555804

  19. Antibacterial activities of magnesium oxide (MgO) nanoparticles against foodborne pathogens

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The antibacterial activities of magnesium oxide nanoparticles (MgO NP) alone or in combination with other antimicrobials (nisin and ZnO NP) against E. coli O157:H7 and Salmonella Stanley were investigated. The results show that MgO NP have strong bactericidal activity against the pathogens, achievin...

  20. Nucleation and growth of MgO atomic layer deposition: A real-time spectroscopic ellipsometry study

    SciTech Connect

    Wang, Han; Fu, Kan

    2013-11-15

    The atomic layer deposition (ALD) of MgO thin films from bis(cyclopentadienyl) magnesium and H{sub 2}O was studied using in-situ real-time spectroscopic ellipsometry (SE), ex-situ x-ray photoelectron spectroscopy, and grazing-incidence x-ray diffraction. It is found that the initial growth is not linear during the first ten cycles, and magnesium silicate forms spontaneously on the SiO{sub 2}/Si substrates at 250 °C. Submonolayer sensitivity of SE is demonstrated by the analysis of each half-cycle and self-limiting adsorption, revealing characteristic features of hetero- and homo-MgO ALD processes.

  1. Growth of MgO on multi-layered graphene and Mg in PVA matrix

    NASA Astrophysics Data System (ADS)

    Marka, Sandeep K.; Mohiddon, Md. Ahamad; Prasad, Muvva D.; Srikanth, Vadali V. S. S.

    2015-07-01

    An easy and low temperature in-situ growth of MgO micro-rods on multi-layered graphene (MLG) in poly vinyl alcohol (PVA) matrix is elucidated. MLG decked with nanosized fragments of MgO and PVA are used as the starting materials to form MgO micro-rods (width = ∼1 μm and length = ∼4 μm) and MLG filled PVA composite film. Simple solution mixing, spin coating and simple drying processes are used to obtain the PVA composite. The growth mechanism of MgO micro-rods and the role of PVA in the growth of MgO micro-rods are explained on the basis of the observed morphological, structural and phase characteristics and a further controlled synthesis experiment, respectively.

  2. Grain Boundary Diffusion of Sulfur in MgO

    NASA Astrophysics Data System (ADS)

    Watson, H. C.; Watson, E. B.

    2013-12-01

    From being a candidate light element in the Earth's core to recording biosignatures on the surface, sulfur is a minor, but critical, element throughout the Earth. A deeper understanding the behaviour of sulfur under a wide scope of Earth relevant conditions will provide insight into geochemical cycles and reservoirs from the crust to the core. Sulfur isotope ratios in particular may be used to record specific geochemical processes such as ongoing core/mantle interaction, as well as shallower processes including cycling between the atmosphere/hydrosphere and lithosphere. The mobility of sulfur under these conditions will affect the reliability of using observed signatures to distinguish past processes and events. Grain boundary diffusion has often been shown to be orders of magnitude more rapid than diffusion through the crystal lattice of many materials. This effect is particularly important in cases where the diffusant is incompatible in the crystal lattice, and thus resides predominantly on grain boundaries. This is the case for sulfur and many of the minerals that comprise the interior of the Earth. If S diffusion is fast enough, the retention of some pristine signatures could be compromised. In other cases fast diffusion may allow for detection of signatures at large distances from their original source, as suggested by [1]. Experiments have been conducted in a piston-cylinder device at 1GPa and temperatures ranging from 1100°C to 1500°C to determine the rate of S grain boundary diffusion in an MgO matrix. A source-sink method similar to that used by [1] was employed using either FeS or FeS2 as a source and Mo foil as a sink separated by up to 3mm of pure MgO polycrystalline matrix. The foil sink was analyzed by electron microprobe and laser ablation ICP-MS for S content. Preliminary results show substantial diffusion of S through the MgO matrix. The results from these experiments, potential applications, and relevant numerical simulations will be presented

  3. Epitaxial growth of tungsten layers on MgO(001)

    SciTech Connect

    Zheng, Pengyuan; Ozsdolay, Brian D.; Gall, Daniel

    2015-11-15

    Smooth single crystal W(001) layers were grown on MgO(001) substrates by magnetron sputtering at 900 °C. X-ray diffraction ω–2θ scans, ω-rocking curves, pole figures, and reciprocal space maps indicate a 45°-rotated epitaxial relationship: (001){sub W}‖(001){sub MgO} and [010]{sub W}‖[110]{sub MgO}, and a relaxed lattice constant of 3.167 ± 0.001 nm. A residual in-plane biaxial compressive strain is primarily attributed to differential thermal contraction after growth and decreases from −0.012 ± 0.001 to −0.001 ± 0.001 with increasing layer thickness d = 4.8–390 nm, suggesting relaxation during cooling by misfit dislocation growth through threading dislocation glide. The in-plane x-ray coherence length increases from 3.4 to 33.6 nm for d = 4.8–390 nm, while the out-of-plane x-ray coherence length is identical to the layer thickness for d ≤ 20 nm, but is smaller than d for d ≥ 49.7 nm, indicating local strain variations along the film growth direction. X-ray reflectivity analyses indicate that the root-mean-square surface roughness increases from 0.50 ± 0.05 to 0.95 ± 0.05 nm for d = 4.8–19.9 nm, suggesting a roughness exponent of 0.38, but remains relatively constant for d > 20 nm with a roughness of 1.00 ± 0.05 nm at d = 47.9 nm.

  4. Epitaxial EuO thin films on GaAs

    SciTech Connect

    Swartz, A. G.; Ciraldo, J.; Wong, J. J. I.; Li Yan; Han Wei; Lin Tao; Shi, J.; Kawakami, R. K.; Mack, S.; Awschalom, D. D.

    2010-09-13

    We demonstrate the epitaxial growth of EuO on GaAs by reactive molecular beam epitaxy. Thin films are grown in an adsorption-controlled regime with the aid of an MgO diffusion barrier. Despite the large lattice mismatch, it is shown that EuO grows well on MgO(001) with excellent magnetic properties. Epitaxy on GaAs is cube-on-cube and longitudinal magneto-optic Kerr effect measurements demonstrate a large Kerr rotation of 0.57 deg., a significant remanent magnetization, and a Curie temperature of 69 K.

  5. MOCVD growth and structure of PbTiO{sub 3} thin films

    SciTech Connect

    Gao, Y.; Bai, G.; Merkle, K.L.; Chang, H.L.M.; Lam, D.J.

    1993-08-01

    PbTiO{sub 3} thin films grown on (001)MgO and (110)MgO by MOCVD have been characterized by x-ray diffraction and transmission electron microscopy. The PbTiO{sub 3} films deposited on (001)MgO under the optimum conditions always show a bi-layer structure. The top layer of the films near the free surface is c-axis oriented with the orientation relationship (001)[100]PbTiO{sub 3}{parallel}(001)[100]MgO. The bottom layer of the films near the substrate is a-axis oriented with (100)[001]PbTiO{sub 3}{parallel}(001)[100]MgO. 90{degrees} domains were observed, but only in the c-axis oriented layers. The thickness of the a-axis oriented layers near the substrate decreases with decreasing the cooling rate. PbTiO{sub 3} films deposited on (110) MgO, however, are single-layer, epitaxial films with (101)[001]PbTiO{sub 3}{parallel}(110)[001]MgO.

  6. A Redetermination of the Dissociation Energy of MgO(+)

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Partridge, Harry

    1994-01-01

    In 1986, we reported a dissociation energy (D(sub 0) of 2.31 eV for the X(sup 2)Pi ground state of MgO(+). This value was determined by computing the dissociation energy to the Mg(2+) + O(-) limit and adjusting the value to the Mg(+) + O limit using the experimental Ionization Potential (IP) of Mg(+) and the Electron Affinity (EA) of O. The success of this method relies on the assumption that there is little covalent contribution to the bonding. The very small (0.04 eV) correlation contribution to the binding energy was taken as corroboration for the validity of this approach. Our earlier theoretical value was estimated to be accurate to at least 0.2 eV. It is in excellent agreement with the subsequent value of 2.30 +/- 0.13 eV determined by Freiser and co-workers from photodissociation experiments. It is also consistent with the upper (less than 3.1 eV) and lower (greater than 1.1 eV) bounds determined by Rowe obtained by studying the reactions of Mg(+) with 03 and NO2. However, it is inconsistent with an upper bound of 1.7 eV reported by Kappes and Staley based on their failure to observe MgO(+) in the reaction of Mg(+) with N2O. The picture became somewhat clouded, however, by the recent guided-ion beam mass spectrometric studies of Dalleska and Armentrout. Their initial analysis of the reaction data for Mg(+) + O2 lead to a bond dissociation energy of 2.92 +/- 0.25 eV, which is considerably larger than the value of 2.47 +/- 0.06 eV deduced from their studies of the Mg(+)+NO2 reaction.

  7. Evidence of martensitic phase transitions in magnetic Ni-Mn-In thin films

    SciTech Connect

    Sokolov, A.; Zhang, Le; Dubenko, I.; Samanta, T.; Ali, N.; Stadler, S.

    2013-02-18

    Ni{sub 50}Mn{sub 35}In{sub 15} Heusler alloy thin films (with thicknesses of about 10 nm) have been grown on single crystal MgO and SrTiO{sub 3} (STO) (100) substrates using a laser-assisted molecular beam epitaxy method. Films of mixed austenitic and martensitic phases and of pure martensitic phase have been detected for those grown on MgO and STO substrates, respectively. Thermomagnetic curves were measured using a SQUID magnetometer and are consistent with those of off-stoichiometric In-based bulk Heusler alloys, including a martensitic transition at T = 315 K for films grown on MgO. The differences in the properties of the films grown on MgO and STO are discussed.

  8. Static and dynamic magnetic properties of epitaxial Co2FeAl Heusler alloy thin films

    NASA Astrophysics Data System (ADS)

    Ortiz, G.; Gabor, M. S.; Petrisor, T., Jr.; Boust, F.; Issac, F.; Tiusan, C.; Hehn, M.; Bobo, J. F.

    2011-04-01

    Structural and magnetic properties of epitaxial Co2FeAl Heusler alloy thin films were investigated. Films were deposited on single crystal MgO (001XS) substrates at room temperature, followed by an annealing process at 600 °C. MgO and Cr buffer layers were introduced in order to enhance crystalline quality, and improve magnetic properties. Structural analyses indicate that samples have grown in the B2 ordered epitaxial structure. VSM measures show that the MgO buffered sample displays a magnetization saturation of 1010 ± 30 emu/cm3, and Cr buffered sample displays a magnetization saturation of 1032 ± 40 emu/cm3. Damping factor was studied by strip-line ferromagnetic resonance measures. We observed a maximum value for the MgO buffered sample of about 8.5 × 10-3, and a minimum value of 3.8 × 10-3 for the Cr buffered one.

  9. Fe Spin Reorientation across the Metamagnetic Transition in Strained FeRh Thin Films

    NASA Astrophysics Data System (ADS)

    Bordel, C.; Juraszek, J.; Cooke, David W.; Baldasseroni, C.; Mankovsky, S.; Minár, J.; Ebert, H.; Moyerman, S.; Fullerton, E. E.; Hellman, F.

    2012-09-01

    A spin reorientation accompanying the temperature-induced antiferromagnetic (AFM) to ferromagnetic (FM) phase transition is reported in strained epitaxial FeRh thin films. Fe57 conversion electron Mössbauer spectrometry showed that the Fe moments have different orientations in FeRh grown on thick single-crystalline MgO and in FeRh grown on ion-beam-assist-deposited (IBAD) MgO. It was also observed, in both samples, that the Fe moments switch orientations at the AFM to FM phase transition. Perpendicular anisotropy was evidenced in the AFM phase of the film grown on IBAD MgO and in the FM phase of that grown on regular MgO. Density-functional theory calculations enabled this spin-reorientation transition to be accurately reproduced for both FeRh films across the AFM-FM phase transition and show that these results are due to differences in strain.

  10. Fe spin reorientation across the metamagnetic transition in strained FeRh thin films.

    PubMed

    Bordel, C; Juraszek, J; Cooke, David W; Baldasseroni, C; Mankovsky, S; Minár, J; Ebert, H; Moyerman, S; Fullerton, E E; Hellman, F

    2012-09-14

    A spin reorientation accompanying the temperature-induced antiferromagnetic (AFM) to ferromagnetic (FM) phase transition is reported in strained epitaxial FeRh thin films. (57)Fe conversion electron Mössbauer spectrometry showed that the Fe moments have different orientations in FeRh grown on thick single-crystalline MgO and in FeRh grown on ion-beam-assist-deposited (IBAD) MgO. It was also observed, in both samples, that the Fe moments switch orientations at the AFM to FM phase transition. Perpendicular anisotropy was evidenced in the AFM phase of the film grown on IBAD MgO and in the FM phase of that grown on regular MgO. Density-functional theory calculations enabled this spin-reorientation transition to be accurately reproduced for both FeRh films across the AFM-FM phase transition and show that these results are due to differences in strain. PMID:23005667

  11. Role of MgO impurity on the superconducting properties of MgB2

    NASA Astrophysics Data System (ADS)

    Singh, Dharmendra Kumar; Tiwari, Brajesh; Jha, Rajveer; Kishan, H.; Awana, V. P. S.

    2014-10-01

    We address the effect of MgO impurity on the superconducting properties of MgB2. The synthesis of MgB2 is very crucial because of sensitivity of Mg to oxidation which may lead to MgO as a secondary phase. Rietveld refinement was performed to determine the quantitative volume fraction of MgO in the samples synthesized by two different techniques. Both the samples were subjected to magnetization measurements under dc and a.c. applied magnetic fields and the observed results were compared as a function of temperature. Paramagnetic Meissner effect has been observed in a sample of MgB2 having more amount of MgO (with Tc = 37.1 K) whereas the pure sample MgB2 having minor quantity of MgO shows diamagnetic Meissner effect with Tc = 38.8 K. M-H measurements at 10 K reveal a slight difference in irreversibility field which is due to MgO impurity along with wide transition observed from ac magnetic susceptibility measurements. The magnetotransport measurements ρ(T) using ρN = 90%, 50% and 10% criterion on pure sample of MgB2 has been used to determine the upper critical field whereas the sample having large quantity of MgO does not allow these measurements due to its high resistance.

  12. Synthesis and characterization of mesoporous MgO by template-free hydrothermal method

    SciTech Connect

    Cui, Hongmei; Wu, Xiaofeng; Chen, Yunfa; Boughton, R.I.

    2014-02-01

    Highlights: • A simple synthesis of porous MgO with diameter size from 3 to 10 μm without any templates. • Effect of temperature and time were investigated. • Systematic characterization by TG/DTA, XRD, SEM, TEM, and nitrogen adsorption–desorption isotherm of MgO. • A possible formation and crystal growth mechanism of mesopores MgO is proposed. - Abstract: Mesoporous MgO particles have been synthesized through a novel template-free hydrothermal co-precipitation method using a Mg(NO{sub 3}){sub 2} solution as the magnesium source and NaCO{sub 3} as precipitant. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N{sub 2} adsorption–desorption analysis. The results indicate that the MgO samples have a disordered mesoporous structure, a large BET surface area, and a large pore volume. The effect of reaction temperature on the MgO product BET surface area was studied. A possible formation and crystal growth mechanism for mesoporous MgO is proposed.

  13. Characterization of MgO powders for use in thermal batteries

    SciTech Connect

    Guidotti, R.A.; Reinhardt, W.

    1996-09-01

    Ten commercial MgO powders were evaluated for their suitability to act as a binder in the separator of thermal batteries to immobilize the electrolyte when it is molten. One brand in particular, Maglite S from Calgon, outperformed all the others. This report describes the results of a characterization study of this MgO as well as similar materials from other commercial vendors. The study objective was to define the critical properties of Maglite S MgO that are responsible for its superior performance in thermal-battery separators. Separator mixes were prepared with the various MgO powders and the resulting powders and pellets were characterized, to correlate key physical properties of these materials to select physical and chemical properties of the MgO powders used in their preparation. The MgO pore-size distribution was the only parameter that could be related to the deformation and electrolyte-leakage behavior of separator pellets. A potential replacement for the Maglite S is currently being qualified, since Maglite S MgO is no longer available.

  14. Strengthening and toughening of poly(L-lactide) composites by surface modified MgO whiskers

    NASA Astrophysics Data System (ADS)

    Wen, Wei; Luo, Binghong; Qin, Xiaopeng; Li, Cairong; Liu, Mingxian; Ding, Shan; Zhou, Changren

    2015-03-01

    To improve both the strength and toughness of poly(L-lactide) (PLLA), fibrous-like MgO whiskers with diameters of 0.15-1 μm and lengths of 15-110 μm were prepared, and subsequently surface modified with L-lactide to obtain grafted MgO whiskers (g-MgO whiskers). The structures and properties of MgO whiskers and g-MgO whiskers were studied. Then, a series of MgO whiskers/PLLA and g-MgO whiskers/PLLA composites were prepared by solution casting method, for comparison, MgO particles/PLLA composite was prepared too. The resulting composites were evaluated in terms of hydrophilicity, crystallinity, dispersion of whiskers, interfacial adhesion and mechanical performance by means of polarized optical microscopy (POM), contact angle measurement, field emission scanning electron microscope (FSEM), transmission electron microscopy (TEM) and tensile testing. The results revealed that the crystallization rate and hydrophilicity of PLLA were improved by the introduction of MgO whiskers and g-MgO whiskers. The g-MgO whiskers can disperse more uniformly in and show stronger interfacial adhesion with the matrix than MgO whiskers as a result of the surface modification. Due to the bridge effect of the whiskers and the excellent interfacial adhesion between g-MgO whiskers and PLLA, g-MgO whiskers/PLLA composites exhibited remarkably higher strength, modulus and toughness compared to the pristine PLLA, MgO particles/PLLA and MgO whiskers/PLLA composites.

  15. Mesoporous MgO: Synthesis, physico-chemical, and catalytic properties

    NASA Astrophysics Data System (ADS)

    Maerle, A. A.; Kasyanov, I. A.; Moskovskaya, I. F.; Romanovsky, B. V.

    2016-06-01

    Mesoporous MgO was obtained via the hydrothermal synthesis using both ionogenic and non-ionogenic surfactants as structure-directing templates. The materials prepared were characterized by SEM, BET-N2, XRD, and TG-DTA techniques. MgO particles are spherical 20-μm aggregates of primary oxide particles well shaped as rectangular parallelepipeds. Magnesium oxide samples have the specific surface area of 290-400 m2/g and pore sizes of 3.3-4.1 nm. Their mesoporous structure remained unchanged after calcination up to 350°C. Catalytic activity of mesoporous MgO was studied in acetone condensation reaction.

  16. Volume stabilization of high MgO cement: Effect of curing conditions and fly ash addition

    SciTech Connect

    Ali, M.M.; Mullick, A.K.

    1998-11-01

    Hydration of high MgO cement paste under autoclave condition causes the rapid formation and crystallization of magnesium hydroxide and leads to the creation of larger pore sizes. This results in the loss of mechanical strength and higher expansion values. Under ambient water curing, precipitation and distribution of gelatinous calcium silicate hydrates into the finer network causes a homogeneous morphology and the development of smaller pores. The resultant higher mechanical strength associated with partial hydration of MgO yields reduced expansion. High MgO cement paste containing fly ash also showed considerable pore refinement and improved hydrate morphology favoring volume stability under both autoclave and ambient water curing.

  17. Dielectric properties and electrical conductivity of MgO synthesized by chemical precipitation and sol-gel method

    NASA Astrophysics Data System (ADS)

    Mbarki, Rabeh; Hichem Hamzaoui, Ahmed; Mnif, Adel

    2015-01-01

    MgO Powders were synthesized via simple chemical precipitation (SPC) and sol-gel process (SG). The electrical behavior of these powders was determined by complex impedance spectroscopy using an alternative current conductivity at various temperatures and frequencies. For MgO elaborated by SG, the activation energy is 1.49 eV while MgO prepared by SPC, this energy is equal to 0.39 and 4.13 eV. The structural properties of MgO powders were analyzed by X-ray diffraction and FT-IR spectroscopy. The results show that the cristallites size was 28.4 nm for MgO SPC and 42.5 nm for MgO SG. Others methods such DTA, TGA, BET and SEM were used to characterized MgO materials.

  18. Combustion synthesis of MgO nanoparticles using plant extract: Structural characterization and photoluminescence studies

    SciTech Connect

    Kumar, Danith; Chikkahanumantharayappa; Yadav, L. S. Reddy; Nagaraju, G.; Lingaraju, K.; Naika, H. Raja; Manjunath, K.; Suresh, D.; Prasad, Daruka; Nagabhushana, H.; Sharma, S. C.

    2015-06-24

    Magnesium oxide nanoparticles (MgO Nps) have been successfully synthesized via solution combustion method using Parthenium plant extract as fuel for the first time. Powder X-ray diffraction (PXRD) pattern reveal that product belongs to the cubic phase (Periclase). FTIR spectrum shows the band at 822 cm{sup −1} indicates the formation of cubic periclase MgO. The optical band gap of MgO Nps estimated from UV –Vis spectrum was found to be in the range 5.40–5.45 eV. SEM images showed that, the product is agglomerated and particle in nature. Photoluminescence (PL) studies shows violet emission at 390 nm, blue emission at 470 nm and green emission at 550 nm. MgO Nps shows good photocatalytic activity for the degradation of methylene blue (MB) dye under UV/Sun light irradiation.

  19. Discrete Layer-by-Layer Magnetic Switching in Fe /MgO (001 ) Superlattices

    NASA Astrophysics Data System (ADS)

    Moubah, R.; Magnus, F.; Warnatz, T.; Palsson, G. K.; Kapaklis, V.; Ukleev, V.; Devishvili, A.; Palisaitis, J.; Persson, P. O. Å.; Hjörvarsson, B.

    2016-04-01

    We report on a discrete layer-by-layer magnetic switching in Fe /MgO superlattices driven by an antiferromagnetic interlayer exchange coupling. The strong interlayer coupling is mediated by tunneling through MgO layers with thicknesses up to at least 1.8 nm, and the coupling strength varies with MgO thickness. Furthermore, the competition between the interlayer coupling and magnetocrystalline anisotropy stabilizes both 90° and 180° periodic alignment of adjacent layers throughout the entire superlattice. The tunable layer-by-layer switching, coupled with the giant tunneling magnetoresistance of Fe /MgO /Fe junctions, is an appealing combination for three-dimensional spintronic memories and logic devices.

  20. Regenerable MgO promoted metal oxide oxygen carriers for chemical looping combustion

    DOEpatents

    Siriwardane, Ranjani V.; Miller, Duane D.

    2014-08-19

    The disclosure provides an oxygen carrier comprised of a plurality of metal oxide particles in contact with a plurality of MgO promoter particles. The MgO promoter particles increase the reaction rate and oxygen utilization of the metal oxide when contacting with a gaseous hydrocarbon at a temperature greater than about 725.degree. C. The promoted oxide solid is generally comprised of less than about 25 wt. % MgO, and may be prepared by physical mixing, incipient wetness impregnation, or other methods known in the art. The oxygen carrier exhibits a crystalline structure of the metal oxide and a crystalline structure of MgO under XRD crystallography, and retains these crystalline structures over subsequent redox cycles. In an embodiment, the metal oxide is Fe.sub.2O.sub.3, and the gaseous hydrocarbon is comprised of methane.

  1. Combustion synthesis of MgO nanoparticles using plant extract: Structural characterization and photoluminescence studies

    NASA Astrophysics Data System (ADS)

    Kumar, Danith; Yadav, L. S. Reddy; Lingaraju, K.; Manjunath, K.; Suresh, D.; Prasad, Daruka; Nagabhushana, H.; Sharma, S. C.; Naika, H. Raja; Chikkahanumantharayappa, Nagaraju, G.

    2015-06-01

    Magnesium oxide nanoparticles (MgO Nps) have been successfully synthesized via solution combustion method using Parthenium plant extract as fuel for the first time. Powder X-ray diffraction (PXRD) pattern reveal that product belongs to the cubic phase (Periclase). FTIR spectrum shows the band at 822 cm-1 indicates the formation of cubic periclase MgO. The optical band gap of MgO Nps estimated from UV -Vis spectrum was found to be in the range 5.40-5.45 eV. SEM images showed that, the product is agglomerated and particle in nature. Photoluminescence (PL) studies shows violet emission at 390 nm, blue emission at 470 nm and green emission at 550 nm. MgO Nps shows good photocatalytic activity for the degradation of methylene blue (MB) dye under UV/Sun light irradiation.

  2. Process-Parameter-Dependent Optical and Structural Properties of ZrO2MgO Mixed-Composite Films Evaporated from the solid Solution

    NASA Technical Reports Server (NTRS)

    Sahoo, N. K.; Shapiro, A. P.

    1998-01-01

    The process-parameter-dependent optical and structural properties of ZrO2MgO mixed-composite material have been investigated. Optical properties were derived from spectrophotometric measurements. By use of atomic force microscopy, x-ray diffraction analysis, and energy-dispersive x-ray (EDX) analysis, the surface morphology, grain size distributions, crystallographic phases, and process-dependent material composition of films have been investigated. EDX analysis made evident the correlation between the oxygen enrichment in the films prepared at a high level of oxygen pressure and the very low refractive index. Since oxygen pressure can be dynamically varied during a deposition process, coatings constructed of suitable mixed-composite thin films can benefit from continuous modulation of the index of refraction. A step modulation approach is used to develop various multilayer-equivalent thin-film devices.

  3. Positron annihilation 2D-ACAR study of semi-coherent Li nanoclusters in MgO( 1 0 0 ) and MgO( 1 1 0 )

    NASA Astrophysics Data System (ADS)

    Falub, C. V.; Mijnarends, P. E.; Eijt, S. W. H.; van Huis, M. A.; van Veen, A.; Schut, H.

    2002-05-01

    Depth selective positron annihilation two-dimensional angular correlation of annihilation radiation (2D-ACAR) is used to determine the electronic structure of Li nanoclusters formed by implantation of 10 16 cm -26Li ions (with an energy of 30 keV) in MgO(1 0 0) and (1 1 0) crystals, and subsequently annealed at 950 K. The 2D-ACAR spectra of Li-implanted MgO obtained with 4 keV positrons reveal the semi-coherent ordering state of the embedded metallic Li nanoclusters. The results agree with ab initio Korringa-Kohn-Rostoker calculations.

  4. Studying some mechanical properties of MgO with used neon bulb glass

    SciTech Connect

    Issa, Tarik Talib; Khaleel, Saba Mahdi; Abdul Kareem, Noura Ammar

    2013-12-16

    Ceramic compact of MgO +WT% of UNBG were sintered at different sintering temperature (700, 900, 1100, 1300)°c, under static air for 3 hours. X-ray diffraction and some mechanical properties were conducted. The maximum sintered density, compression; fracture strength and hardness were indicated for the compilation of MgO −20 WT % UNBG, sintered at 1300 °c.

  5. Inelastic He-atom scattering from the MgO(001) surface

    NASA Astrophysics Data System (ADS)

    Cui, Jinhe; Jung, David R.; Frankl, Daniel R.

    1990-11-01

    Dispersion curves of Rayleigh phonons on an in situ cleaved, room-temperature surface of MgO(001) are determined by time-of-flight measurements of inelastically scattered He atoms. Along both the Γ¯ X¯ and Γ¯ M¯ directions, the measured phonon frequencies agree fairly well with a shell-model calculation for an unrelaxed MgO(001) surface.

  6. Surface Plasmons in Silver Films--A Novel Undergraduate Experiment

    ERIC Educational Resources Information Center

    Simon, H. J.; And Others

    1975-01-01

    Describes an experiment in which a 500-A-thick silver film is evaporated on the hypotenuse face of a right glass prism. The surface plasmon mode in the film is excited with a He-Ne laser. The dispersion relation for the surface plasmon and the reflectivity due to the excitation of this mode are calculated. (Author/MLH)

  7. Adsorption of nonmetallic elements on defect-free MgO(001) surface - DFT study

    NASA Astrophysics Data System (ADS)

    Pašti, Igor A.; Baljozović, Miloš; Skorodumova, Natalia V.

    2015-02-01

    Adsorption of 11 non-metals (H, B, C, N, O, F, Si, P, S, Cl and Br) on defect-free MgO(001) surface was investigate using DFT approach. Adsorption energies were found to be between - 0.56 eV (hydrogen adsorption) and - 2.63 eV (carbon adsorption). Charge transfer from substrate to adsorbate was observed to follow the periodicity in the Periodic Table of Elements, as increases from left to right and decreases from top to bottom. All investigated adsorbates prefer oxygen sites on MgO surface. The analysis of adsorbate-MgO(001) electronic structure suggested that the electronic structure of the O adsorption center and adsorbate atom is molecule-like and there is no strong interaction with MgO electronic bands. Based on the obtained dataset for adsorption energies of selected non-metallic adsorbates (X) the reactivity of MgO towards the bond cleavage in the cases of X-X, H-X and HO-X bonds was discussed. Obtained results point to weak reactivity of MgO(001) towards atomic adsorption and low activity for bond cleavage. However, these results can be used as a starting point for the functionalization of MgO, particularly in the cases where bond cleavage activity and surface-mediated stabilization of dissociation products are desired.

  8. Tailoring of polar and nonpolar ZnO planes on MgO (001) substrates through molecular beam epitaxy

    PubMed Central

    2012-01-01

    Polar and nonpolar ZnO thin films were deposited on MgO (001) substrates under different deposition parameters using oxygen plasma-assisted molecular beam epitaxy (MBE). The orientations of ZnO thin films were investigated by in situ reflection high-energy electron diffraction and ex situ X-ray diffraction (XRD). The film roughness measured by atomic force microscopy evolved as a function of substrate temperature and was correlated with the grain sizes determined by XRD. Synchrotron-based X-ray absorption spectroscopy (XAS) was performed to study the conduction band structures of the ZnO films. The fine structures of the XAS spectra, which were consistent with the results of density functional theory calculation, indicated that the polar and nonpolar ZnO films had different electronic structures. Our work suggests that it is possible to vary ZnO film structures from polar to nonpolar using the MBE growth technique and hence tailoring the electronic structures of the ZnO films. PACS: 81; 81.05.Dz; 81.15.Hi. PMID:22405056

  9. Epitaxial growth of ultrathin MgO layers on Fe3O4(0 0 1) films

    NASA Astrophysics Data System (ADS)

    Nordmann, T.; Kuschel, O.; Wollschläger, J.

    2016-09-01

    The initial growth stages of MgO on Fe3O4 films are studied by means of X-ray photoelectron spectroscopy and low energy electron diffraction to clarify stoichiometric and structural properties of these layered structures. This bilayer structure is important to fabricate high quality magnetic tunnel junctions based on Fe3O4 electrodes and MgO tunneling barriers. For this purpose, the deposition temperature of MgO has been varied between 100 °C and 250 °C. Initially, MgO grows layer-by-layer on Fe3O4/MgO(0 0 1) forming a wetting layer. Depending on the growth temperature, after growth of a 2-3 nm thick laminar wetting layer, the MgO films finally start to roughen during growth. Thus the growth of MgO on Fe3O4/MgO(0 0 1) is described by a Stranski-Krastanov growth mode. Diffraction experiments show that the magnetite (√{ 2} ×√{ 2})R45° superstructure is removed already during the initial stages of MgO deposition. Furthermore, these experiments show that MgO films are rougher for growth at low deposition temperatures.

  10. X-ray diffraction characterization of thin superconductive films

    SciTech Connect

    Kozaczek, K.J.; Watkins, T.R.; Book, G.W.; Carter, W.B.

    1995-12-31

    The physical and mechanical properties of thin films are often different from the properties of bulk material and are dictated by the film/substrate orientation relationship, crystal anisotropy and crystalgraphic texture of the film. X-ray diffraction texture analysis provides information about preferential film growth and can be used for optimization of deposition parameters and prediction of properties of thin films. An x-ray back reflection technique using the Braga-Brentano geometry with experimental corrections for absorption and defocusing was used to study thin ceramic films deposited by combustion chemical vapor deposition (CCVD). The film/substrate orientation relationships of YBa{sub 2}Cu{sub 3}O{sub x} (YBCO) superconducting thin films deposited via CCVD on single crystal MgO and polycrystalline silver substrates were studied. The as-deposited films on single crystal (100) MgO substrates showed strong preferential growth with the basal plane parallel to the substrate surface (c-axis up growth). Texture analysis showed two in-plane alignment orientations of the film with respect to the substrate, with YBCO [100] and [110] aligned with the [100] MgO substrate. YBCO films deposited on cold-rolled polycrystalline silver displayed c-axis up growth indicating that the orientation of the polycrystalline substrate (brass type texture) did not induce detectable in-plane preferential growth of the YBCO.

  11. Ab-initio modelling of defects in MgO

    NASA Astrophysics Data System (ADS)

    Gilbert, C. A.; Smith, R.; Kenny, S. D.

    2007-02-01

    The energetics of the key defects that are observed to occur during simulations of radiation damage in MgO are analysed using density functional theory. The results are compared with those from the empirical potentials used to carry out the radiation damage studies. The formation energies of vacancies, interstitials, Frenkel pairs, di-vacancies and di-interstitials are calculated as a function of the increasing supercell size in order to ensure good convergence. The supercell geometries were chosen to maximise the separation distance between periodic images. Their sizes ranged from cells containing 32 atoms up to cells containing 180 atoms. Results are presented for the formation energies of the first, second and third nearest neighbour defects. Results show that the di-vacancy formation energy is in the region of 4-6 eV and that formation energies for di-interstitials are more than double this, lying in the range 12-16 eV. Comparison of the results show that empirical potentials overestimate the formation energy of di-vacancies by 1-3 eV and underestimate the formation energies of di-interstitials by about 1-2 eV. The relative stability of the defects is, however, correctly predicted by the empirical potentials. The direction and the magnitude of the displacements of the atoms surrounding the defects are in good agreement for all the systems containing interstitials. For the systems containing vacancies the direction of the displacements are in agreement but the empirical potentials predict larger displacements in all cases.

  12. Micro and nano MgO particles for the improvement of fracture toughness of bone-cement interfaces

    PubMed Central

    Khandaker, Morshed; Li, Yanling; Morris, Tracy

    2013-01-01

    The objective of this study was to determine whether inclusion of magnesium oxide (MgO) in micro and nanoparticulate forms in poly Methyl MethAcrylate (PMMA) cement has any influence on the fracture toughness of bone-cement interfaces. An interfacial fracture mechanics technique was used to compare the values of fracture toughness (KIC) among bone-PMMA, bone-PMMA with micro MgO particles and bone-PMMA with nano MgO particles interfaces. This study found that the values of KIC of bone-PMMA with micro MgO particles and bone–PMMA with nano MgO particles interfaces were significantly higher when compared to the values of KIC of the bone-PMMA interface (p<0.0001). Results indicated that the addition of the micro and nano MgO particles to PMMA improved the quality of bone-cement union. PMID:23332232

  13. Effect of MgO Additive on Volumetric Expansion of Self-Degradable Cements

    SciTech Connect

    Sugama T.; Warren, J.; Butcher, T.

    2011-09-30

    We identified hard-burned magnesium oxide (MgO) as a suitable expansive additive for improving the plugging performance of self-degradable, temporary sodium silicate-activated slag/Class C fly ash (SSASC) blend cement sealers into rock fractures in Enhanced Geothermal Systems (EGSs). MgO extended the volumetric expansion of sealers during their exposure to a hydrothermal environment at 200 C under pressures, ranging from 300 to 1500 psi. A great expansion ratc of 19.3% was observed by adding 3.0 wt% MgO under 300 psi pressure, thus promising to plug thoroughly inner fracture. When the pressure was increased from 300 psi to 1500 psi, the expansion rate of cement markedly reduced, corresponding to the formaLion of crack-free specimens and the improvement of compressive strength. However, with 3.0 wt% MgO, the specimens still engendered the generation of numerous visual cracks, although they were prepared under a high pressure of 1500 psi. The effective content of MgO in minimizing and eliminating the generation of cracks was 2.0 wt%, which provided a moderate expansion of {ge} 0.5%. The compressive strength of 2.0 wt% MgO specimens made under a pressure of 300 psi rose {approx} 1.7-fold to 4816 psi with an increasing pressure to 1500 psi. The in-situ growth of brucite crystal formed by the hydrothermal hydration of MgO was responsive for such an expansion of the SSASC cement; meanwhile. two crystalline hydrothermal reaction products, 1.1 nm tobermorite and calcium silicate hydrated, contributed to the development of the sealer's compressive strength. Thus, the increasing pressure seems to suppress and control a growth rate of brucite crystal in response to a lower extension of expansion. Furthermore, all MgO-conlaining SSASC sealers possessed the water-catalyzed self-degradable properties.

  14. Cumulate Origins of the High MgO Eclogite Xenoliths from Koidu, West Africa

    NASA Astrophysics Data System (ADS)

    Barth, M. G.; Rudnick, R. L.; Horn, I.; McDonough, W. F.; Spicuzza, M. J.; Valley, J. W.; Haggerty, S. E.

    2001-05-01

    Xenolithic eclogites (bi-mineralic rocks composed of garnet and omphacite) from kimberlite pipes equilibrated at upper mantle pressures and temperatures, but the origin of the protoliths of these rocks and their subsequent metamorphic evolution are less certain. Xenolithic eclogites have been variously interpreted as crystallized high-pressure magmas or their cumulates, or as fragments of recycled oceanic crust. Eclogites from the Koidu kimberlite pipe, Sierra Leone, fall into two groups based on their major element chemistry. The low MgO group (6-13 wt% MgO) shows evidence for being derived from recycled oceanic crust that has been through a melting episode associated with subduction (Barth et al., 2001, GCA, in press). In contrast, the high MgO eclogites (>16 wt% MgO) have mantle-like δ 18O. Analyses of multiple mineral generations suggest that their variable light rare earth element (REE) patterns reflect variable degrees of metasomatic enrichment. High MgO and Al2O3 contents of these eclogites are suggestive of a cumulate origin, either as high-pressure (2-3 GPa) garnet-pyroxene cumulates or low-pressure (<1 GPa) plagioclase-pyroxene-olivine cumulates. The absence of modal olivine and orthopyroxene coupled with liquid lines of descent of mantle-derived magmas suggest that these eclogites formed at pressures lower than their current equilibrium pressures (>4 GPa). The high proportion of modal garnet (up to 65%) is difficult to explain as a cumulate phase in light of the relatively flat heavy to middle REE patterns. This, coupled with positive Sr anomalies, and low to moderate transition element contents is consistent with a low-pressure cumulate origin of the high MgO eclogites as metamorphosed olivine gabbros and troctolites. If this interpretation is correct, the high MgO eclogites could represent either the basal section of subducted oceanic crust or foundered mafic lower continental crust.

  15. Characterisation of the mgo operon in Pseudomonas syringae pv. syringae UMAF0158 that is required for mangotoxin production

    PubMed Central

    2012-01-01

    Background Mangotoxin is an antimetabolite toxin that is produced by strains of Pseudomonas syringae pv. syringae; mangotoxin-producing strains are primarily isolated from mango tissues with symptoms of bacterial apical necrosis. The toxin is an oligopeptide that inhibits ornithine N-acetyl transferase (OAT), a key enzyme in the biosynthetic pathway of the essential amino acids ornithine and arginine. The involvement of a putative nonribosomal peptide synthetase gene (mgoA) in mangotoxin production and virulence has been reported. Results In the present study, we performed a RT-PCR analysis, insertional inactivation mutagenesis, a promoter expression analysis and terminator localisation to study the gene cluster containing the mgoA gene. Additionally, we evaluated the importance of mgoC, mgoA and mgoD in mangotoxin production. A sequence analysis revealed an operon-like organisation. A promoter sequence was located upstream of the mgoB gene and was found to drive lacZ transcription. Two terminators were located downstream of the mgoD gene. RT-PCR experiments indicated that the four genes (mgoBCAD) constitute a transcriptional unit. This operon is similar in genetic organisation to those in the three other P. syringae pathovars for which complete genomes are available (P. syringae pv. syringae B728a, P. syringae pv. tomato DC3000 and P. syringae pv. phaseolicola 1448A). Interestingly, none of these three reference strains is capable of producing mangotoxin. Additionally, extract complementation resulted in a recovery of mangotoxin production when the defective mutant was complemented with wild-type extracts. Conclusions The results of this study confirm that mgoB, mgoC, mgoA and mgoD function as a transcriptional unit and operon. While this operon is composed of four genes, only the last three are directly involved in mangotoxin production. PMID:22251433

  16. Properties of two-dimensional insulators: A DFT study of bimetallic oxide CrW2O9 clusters adsorption on MgO ultrathin films

    NASA Astrophysics Data System (ADS)

    Zhu, Jia; Zhang, Hui; Zhao, Ling; Xiong, Wei; Huang, Xin; Wang, Bin; Zhang, Yongfan

    2016-08-01

    Periodic density functional theory calculations have been performed to study the electronic properties of bimetallic oxide CrW2O9 clusters adsorbed on MgO/Ag(001) ultrathin films (<1 nm). Our results show that after deposition completely different structures, electronic properties and chemical reactivity of dispersed CrW2O9 clusters on ultrathin films are observed compared with that on the thick MgO surface. On the thick MgO(001) surface, adsorbed CrW2O9 clusters are distorted significantly and just a little electron transfer occurs from oxide surface to clusters, which originates from the formation of adsorption dative bonds at interface. Whereas on the MgO/Ag(001) ultrathin films, the resulting CrW2O9 clusters keep the cyclic structures and the geometries are similar to that of gas-phase [CrW2O9]-. Interestingly, we predicted the occurrence of a net transfer of one electron by direct electron tunneling from the MgO/Ag(001) films to CrW2O9 clusters through the thin MgO dielectric barrier. Furthermore, our work reveals a progressive Lewis acid site where spin density preferentially localizes around the Cr atom not the W atoms for CrW2O9/MgO/Ag(001) system, indicating a potentially good bimetallic oxide for better catalytic activities with respect to that of pure W3O9 clusters. As a consequence, present results reveal that the adsorption of bimetallic oxide CrW2O9 clusters on the MgO/Ag(001) ultrathin films provide a new perspective to tune and modify the properties and chemical reactivity of bimetallic oxide adsorbates as a function of the thickness of the oxide films.

  17. Influence of ion beam assisted deposition parameters on the growth of MgO and CoFeB

    SciTech Connect

    Ferreira, Ricardo; Freitas, Paulo P.; Petrova, Rumyana; McVitie, Stephen

    2012-04-01

    The effect of the kinetic parameters of an assistance ion beam on the crystallization of ion beam deposited MgO was investigated. It is shown that the crystallization of MgO in the as-deposited state is strongly dependent on the assistance beam parameters. Furthermore, two deposition regimes corresponding to different ranges of the assistance beam energy are found. XRD and TEM studies of CoFeB/MgO/CoFeB with MgO deposited in the two regimes show that CoFeB crystallization is favored when low energy assist beams are used, despite no differences being found in the MgO.

  18. Experimental Work Conducted on MgO Inundated Hydration in WIPP-Relevant Brines

    NASA Astrophysics Data System (ADS)

    Deng, H.; Xiong, Y.; Nemer, M. B.; Johnsen, S.

    2009-12-01

    Magnesium oxide (MgO) is being emplaced in the Waste Isolation Pilot Plant (WIPP) as an engineered barrier to mitigate the effect of microbial CO2 generation on actinide mobility in a postclosure repository environment. MgO will sequester CO2 and consume water in brine or water vapor in the gaseous phase. Martin Marietta (MM) MgO is currently being emplaced in the WIPP. A fractional-factorial experiment has been performed to study the inundated-hydration of MM MgO as a function of its particle size, solid-to-liquid ratio, and brine type. MgO hydration experiments have been carried out with three MgO particle sizes and two solid-to-liquid ratios in three WIPP-related brines: ERDA-6, GWB and simplified GWB. ERDA-6 is a synthetic NaCl-rich brine typical of a Castile brine reservoir below the repository. GWB is a synthetic MgCl2- and NaCl-rich brine representative of intergranular brines from the Salado Formation at or near the stratigraphic horizon of the repository. Simplified GWB contains amounts of Mg, Na, and Cl similar to those in GWB without other minor constituents. The hydration products include brucite (Mg(OH)2) and phase 5 (Mg3(OH)5Cl4H2O). In addition to phase 5, MgO hydration in GWB or simplified GWB produces brucite, whereas MgO hydrated in ERDA-6 only produces brucite. The MgO particle size has had a significant effect on the formation of hydration products: small MgO particles have hydrated before the large particles. MgO has hydrated faster in simplified GWB than in the other two brines. In ERDA-6, the solid-to-liquid ratio has affected the brine pH due to the presence of CaO (~1 wt %) as an impurity in MM MgO. GWB has sufficient dissolved Mg to buffer pH despite small amounts of CaO. Both our results and thermodynamic modeling indicate that phase-5 is the stable Mg-OH-Cl phase in Mg-Na-Cl-dominated brines with ionic strengths and chemical compositions similar to that of GWB. In contrast, phase-3 (Mg2(OH)3Cl4H2O) is the stable phase in the MgCl2

  19. Growth of textured MgO through e-beam evaporation and inclined substrate deposition

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Lei, C. H.; Ma, B.; Evans, H.; Efstathiadis, H.; Manisha, R.; Massey, M.; Balachandran, U.; Bhattacharya, R.

    2006-08-01

    Long length textured MgO template on Hastelloy C276™ (HC) has been successfully deposited in a reel-to-reel (R2R) electron beam (e-beam) evaporation system by inclined substrate deposition (ISD). High deposition rate up to 10 nm s-1 with exposure length of 7 cm has been realized. The MgO template showed good in-plane texture of 9.5°-11.5° measured from the (002) phi scans. Experimental results reveal that MgO in-plane texture is formed by the preferred growth direction of [11n]\\parallel \\mathrm {substrate} normal and one of the MgO {200} planes rotates to the in-flux direction. A new expression, termed the 'two-thirds relationship', between the inclination angle α and the tilted angle of the (00l) plane from the substrate normal, β, has been summarized. YBa2Cu3O7-δ (YBCO) film deposited by pulsed laser deposition (PLD) on strontium ruthenate (SRO) buffered ISD MgO showed Tc of 91 K with transition width of 1 K. Critical current measurement indicated an Ic of 110 A cm-1 at 77 K in self-field for 0.68 µm YBCO film, corresponding to a Jc of 1.6 MA cm-2.

  20. Formation of Hydroxyl and Water Layers on MgO Films Studied with Ambient Pressure XPS

    SciTech Connect

    Newberg, J.T.; Starr, D.; Yamamoto, S.; Kaya, S.; Kendelewicz, T.; Mysak, E.R.; Porsgaard, S.; Salmeron, M.B.; Brown Jr., G.E.; Nilsson, A.; Bluhm, H.

    2011-01-01

    To understand the interaction of water with MgO(100), a detailed quantitative assessment of the interfacial chemistry is necessary. We have used ambient pressure X-ray photoelectron spectroscopy (XPS) to measure molecular (H{sub 2}O) and dissociative (OH) water adsorption on a 4 monolayer (ML) thick MgO(100)/Ag(100) film under ambient conditions. Since the entire 4 ML metal oxide (Ox) film is probed by XPS, the reaction of the MgO film with water can be quantitatively studied. Using a multilayer model (Model 1) that measures changes in Ox thickness from O 1s (film) and Ag 3d (substrate) spectra, it is shown that the oxide portion of the MgO film becomes thinner upon hydroxylation. A reaction mechanism is postulated in which the top-most layer of MgO converts to Mg(OH)2 upon dissociation of water. Based on this mechanism a second model (Model 2) is developed to calculate Ox and OH thickness changes based on OH/Ox intensity ratios from O 1s spectra measured in situ, with the known initial Ox thickness prior to hydroxylation. Models 1 and 2 are applied to a 0.15 Torr isobar experiment, yielding similar results for H{sub 2}O, OH and Ox thickness changes as a function of relative humidity.

  1. The effect of toxic malachite green on the bacterial community in Antarctic soil and the physiology of malachite green-degrading Pseudomonas sp. MGO.

    PubMed

    Jung, Jaejoon; Seo, Hyoju; Lee, Se Hee; Jeon, Che Ok; Park, Woojun

    2013-05-01

    The effects of malachite green (MG) on the bacterial community in Antarctic soil were assessed. Culture-independent community analysis using 16S rRNA gene pyrosequencing showed that, in the presence of MG, the relative abundance of Pseudomonas dramatically increased from 2.2 % to 36.6 % (16.6-fold), and Pseudomonas became the predominant genus. The reduction in bacterial biodiversity was demonstrated by diversity indices and rarefaction curves. MG-degrading Pseudomonas sp. MGO was isolated from Antarctic soil. MG tolerance and decolorization activity were confirmed by growth, spectrophotometric, high-performance liquid chromatography, and thin-layer chromatography analyses in high MG concentrations. Our data showed that the decolorization process occurred via biodegradation, while biosorption also occurred after some time during the fed-batch decolorization process. Significant inductions in laccase, nicotinamide adenine dinucleotide-2,6 dichlorophenol indophenol reductase, and MG reductase activities suggested their involvement in the decolorization process. We also showed that the high tolerance of strain MGO to toxic MG might be mediated by upregulation of oxidative stress defense systems such as superoxide dismutase and protease. Collectively, these results demonstrated the response of the Antarctic soil bacterial community to MG and provided insight into the molecular mechanism of MG-tolerant Pseudomonas strains isolated from Antarctic soil. PMID:23296502

  2. Electronic states of MgO: Spectroscopy, predissociation, and cold atomic Mg and O production

    SciTech Connect

    Maatouk, A.; Ben Houria, A.; Yazidi, O.; Jaidane, N.; Hochlaf, M.

    2010-10-14

    We used multiconfigurational methods and a large basis set to compute the potential energy curves of the valence and valence-Rydberg electronic states of MgO molecule. New bound electronic states are found. Using these highly correlated wave functions, we evaluated their mutual spin-orbit couplings and transition moment integrals. For the bound electronic states of MgO, we deduced an accurate set of spectroscopic constants that agree remarkably well with experimental results. Moreover, our potentials, transition moments, and spin-orbit coupling evolutions are incorporated into Fermi golden rule calculations to deduce the radiative lifetimes of MgO(B {sup 1}{Sigma}{sup +}) rovibrational levels and the natural lifetimes of MgO(A {sup 1}{Pi}) vibrational levels, where a good agreement is found with experimental values. Finally, we suggest new routes for the production of cold Mg and O atoms and cold MgO molecules.

  3. Surface Decoration of MgO Nanocubes with Sulfur Oxides: Experiment and Theory

    PubMed Central

    2013-01-01

    We investigated the effect of surface sulfate formation on the structure and spectroscopic properties of MgO nanocubes using X-ray diffraction, electron microscopy, several spectroscopic techniques, and ab initio calculations. After CS2 adsorption and oxidative treatment at elevated temperatures the MgO particles remain cubic and retain their average size of ∼6 nm. Their low coordinated surface elements (corners and edges) were found to bind sulfite and sulfate groups even after annealing up to 1173 K. The absence of MgO corner specific photoluminescence emission bands at 3.4 and 3.2 eV substantiates that sulfur modifies the electronic properties of characteristic surface structures, which we attribute to the formation of (SO3)2– and (SO4)2– groups at corners and edges. Ab initio calculations support these conclusions and provide insight into the local atomic structures and spectroscopic properties of these groups. PMID:23616910

  4. Structural and optical properties of MgO doped ZnO

    SciTech Connect

    Verma, Kavita; Shukla, S.; Varshney, Dinesh; Varshney, M.; Asthana, A.

    2014-04-24

    Samples of ZnO, Zn{sub 0.5}Mg{sub 0.5}O and MgO were prepared by co-precipitation method. X-ray diffraction (XRD) pattern infers that the sample of ZnO is in single-phase wurtzite structure (hexagonal phase, space group P6{sub 3}mc), MgO crystallizes in cubic Fd3m space group and Zn{sub 0.5}Mg{sub 0.5}O represents mixed nature of ZnO and MgO lattices. Similar features were observed from Raman spectroscopy. The energy band gaps estimated from UV-Vis spectroscopy are found to be 4.21 and 3.42 eV for ZnO and Zn{sub 0.5}Mg{sub 0.5}O samples respectively.

  5. Antibacterial effects of biosynthesized MgO nanoparticles using ethanolic fruit extract of Emblica officinalis.

    PubMed

    Ramanujam, Kalimuthan; Sundrarajan, Mahalingam

    2014-12-01

    Magnesium oxides nanoparticles were successfully synthesized from Mg(NO3)(2)·6H2O through a simple greener route using fruit extract (Emblica officinalis). The synthesized samples were characterized by different techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Scanning electron microscopy (SEM) with Energy dispersive X-ray spectroscopy (EDX) analysis. The XRD pattern shows the face centered cubic structure with 27 nm of crystalline size of MgO nanoparticles was confirmed by the Debye-Scherrer's Formula. The spherical in shape of MgO nanoparticles is confirmed by SEM analysis. MgO nanoparticles treated cotton fabric produced stronger antibacterial activity. These types of treated fabrics are used in medical application. PMID:25463681

  6. Structure and properties of ZrO2-MgO powders

    NASA Astrophysics Data System (ADS)

    Buyakova, S. P.; Kalatur, E. S.; Buyakov, A. S.; Kulkov, S. S.

    2016-04-01

    It have been studied magnesia stabilized zirconia (ZrO2-MgO) powders produced by high-frequency decomposition of water salt solutions. It have been shown that due to precursor dissociation powders consist of spherical particles with smooth surface and irregular hollow aggregates resembling foam. An increase in the magnesium concentration in the precursor has an effect on the powder properties, namely, the specific surface decreases significantly and the bulk density increases. Zirconia in the nanostructured state is present only in the powders with 8.6 and 13.9 mole% MgO, with the size of the c-ZrO2 crystallites in them no more than 100 nm. In powder with 43.3 mole% of MgO the magnesia content in c-ZrO2 solid solution corresponds to its solubility limit of 22.2 mole% at temperature 2100°C.

  7. Damage Processes In MgO Irradiated With Medium-energy Heavy Ions

    SciTech Connect

    Moll, Sandra J.; Zhang, Y.; Debelle, A.; Thome, Lionel; Crocombette, J.-P.; Zhu, Zihua; Jagielski, Jacek; Weber, William J.

    2015-04-01

    The micro-structural modifications produced in MgO single crystals exposed to medium-energy heavy ions (1.2-MeV Au) were investigated using Rutherford backscattering spectrometry in channeling geometry coupled to Monte-Carlo analyses, secondary ion mass spectrometry, X-ray diffraction and transmission electron microscopy. The damage accumulation and the elastic strain variation were interpreted in the framework of the multi-step damage accumulation (MSDA) model. Both build-ups follow a multi-step process similar to that recently observed for ion-irradiated yttria-stabilized zirconia (YSZ) single crystals. However, in MgO, an unexpectedly high disorder level occurs far beyond the theoretical damage distribution. These results strongly suggest that the migration of defects created in the near-surface layer is most likely at the origin of the broadening of the damage depth distribution in MgO.

  8. Study of phase transition and cohesive energy in MgO

    NASA Astrophysics Data System (ADS)

    Munjal, N.; Bhambhani, P.; Sharma, G.; Vyas, V.; Sharma, B. K.

    2012-07-01

    In this paper, we present first-principles study of phase transition and cohesive energy of MgO. The calculations are performed on the basis of density functional theory (DFT) based on linear combination of atomic orbitals (LCAO) method. In the present calculations, the generalized gradient approximation (GGA) proposed by Perdew-Burke- Ernzerhof (PBE) and Becke's scheme are considered to treat the correlation and exchange effects respectively. The study reveals that the stable phase of MgO is B1. The study also suggests B1 to B2 phase transition at 260.75 GPa and 10.98 eV cohesive energy of MgO in the stable phase. The calculated data are found in good agreement with the previous theoretical and experimental investigations.

  9. Geochemistry of xenolithic eclogites from West Africa, part 2: origins of the high MgO eclogites

    NASA Astrophysics Data System (ADS)

    Barth, Matthias G.; Rudnick, Roberta L.; Horn, Ingo; McDonough, William F.; Spicuzza, Michael J.; Valley, John W.; Haggerty, Stephen E.

    2002-12-01

    Oxygen isotope, mineral trace element, and measured and reconstructed whole-rock compositions are reported for the high MgO eclogite xenolith suite (16 to 20 wt% MgO in the whole rock) from the Koidu Kimberlite complex, Sierra Leone. In contrast to the previously published data for low MgO eclogites (6 to 13 wt% MgO) from this area, high MgO eclogites equilibrated at higher temperatures (1080 to 1130°C vs. 890 to 930°C) have only mantlelike δ 18O and show variable degrees of light rare earth element (REE) enrichment. Analyses of multiple mineral generations suggest that the heterogeneous REE patterns of the high MgO eclogites reflect variable degrees of metasomatic overprinting. High MgO and Al 2O 3 contents of the eclogites suggest a cumulate origin, either as high-pressure (2 to 3 GPa) garnet-pyroxene cumulates or low-pressure (<1 GPa) plagioclase-pyroxene-olivine cumulates. Trace element modeling suggests a low-P origin for eclogites with flat heavy REE patterns and a high-P origin for eclogites with fractionated heavy REE. Flat heavy REE patterns, the presence of Sr anomalies, and low to moderate transition element contents in the low-P group are consistent with a low-pressure origin as metamorphosed olivine gabbros and troctolites. These metagabbroic high MgO eclogites either could represent the basal section of subducted oceanic crust or foundered mafic lower continental crust. In the former case, the metagabbroic high MgO eclogites may be genetically related to the Koidu low MgO suite. Crystal fractionation trends suggest that the metapyroxenitic high MgO eclogites formed at lower pressures than their current estimated equilibrium pressures (>4 GPa).

  10. PLD growth of multilayered MgO/Ag(001)/MgO photocathode

    NASA Astrophysics Data System (ADS)

    Velazquez, Daniel; Yusof, Zikri; Spentzouris, Linda; Terry, Jeff

    2014-03-01

    Films of of Ag, MgO and multilayers of these were grown via pulsed laser deposition on clean Si(111) 7x7 substrates. The films were studied using reflection high-energy electron diffraction, Kelvin probe and ellipsometry. Information about crystalline and atomic structure as well as surface condition, work function and film thickness was obtained using these techniques. Deposition at various substrate temperatures and partial oxygen pressures was performed in order to understand the parameter settings that lead to higher quality crystalline films. Epitaxial films of Ag(111) were found to grow at an optimal substrate temperature of 256 °C (fig 1.). The superstructure Ag(111) √3 x √3 occurs when deposition takes place at a substrate temperature of 620 °C. In addition, MgO films were found to grow with small grain size on both, Si(111) 7x7 and Ag(111)/Si(111) at room temperature with a partial oxygen pressure of 5x10-5 Torr (fig. 2). Highly-oriented, polycrystalline growth of MgO films is evidenced by their RHEED pattern. In addition, the obliquely-shaped diffraction spots indicate the growth of secondary phase precipitates, most likely due to oxygen deficit. Measurements of the work function of these multilayers indicate that the Ag(111) work function (4.75 eV) is sharply suppressed with the first few MgO shots and has a quasi-linear increase for the first few monolayers (fig. 3). As the thickness of MgO increases (a few nanometers) the work function drops again and stabilizes at the level of MgO (~ 4.2 eV).

  11. First-principles study of Mg(0001)/MgO(1-11) interfaces

    NASA Astrophysics Data System (ADS)

    Song, Hong-Quan; Zhao, Ming; Li, Jian-Guo

    2016-06-01

    By means of first-principles density-functional calculations, we studied the surface energy of a nonstoichiometric MgO(1-11) slab, the interfacial energy and interfacial bonding characteristics of Mg-terminated and O-terminated Mg/MgO(1-11) interfaces with three stacking-site (TOP, HCP and FCC sites) models, and the effect of the thickness of Mg films on the O-terminated MgO(1-11) surface. The results indicate that the surface energies of the nonstoichiometric MgO(1-11) slab and interfacial energies of Mg/Mg(1-11) interface depend on Mg chemical potential. We found that the Mg-terminated MgO(1-11) surface is more stable than the O-terminated MgO(1-11) surface at high Mg chemical potential, and Mg/MgO(1-11) with FCC stacking-site model is the most stable configuration in the Mg/MgO(1-11) interfaces. The results of the electronic structure reveals that the interfacial bonding of Mg-terminated interface with FCC site model mainly consists of metallic bond and of the O-terminated interface with FCC site model is mainly ionic with a small degree of σ-type covalent bond. Although the interfacial energy of Mg-terminated Mg/MgO interface with FCC stacking-site model is slightly higher than that of O-terminated Mg/MgO interface, the molten Mg would epitaxially grow on the FCC sites of the Mg-terminated MgO(1-11) surface because of the high evaporation pressure of Mg at high temperature.

  12. Preparation of nanocrystalline MgO by surfactant assisted precipitation method

    SciTech Connect

    Rezaei, Mehran; Khajenoori, Majid; Nematollahi, Behzad

    2011-10-15

    Highlights: {yields} Nanocrystalline magnesium oxide with high surface area. {yields} MgO prepared with surfactant showed different morphologies compared with the sample prepared without surfactant. {yields} MgO prepared with surfactant showed a plate-like shape. {yields} Refluxing temperature and time and the surfactant to metal molar ratio affect the textural properties of MgO. -- Abstract: Nanocrystalline magnesium oxide with high surface area was prepared by a simple precipitation method using pluronic P123 triblock copolymer (Poly (ethylene glycol)-block, Poly (propylene glycol)-block, Poly (ethylene glycol)) as surfactant and under refluxing conditions. The prepared samples were characterized by X-ray diffraction (XRD), N{sub 2} adsorption (BET) and scanning and transmission electron microscopies (SEM and TEM). The obtained results revealed that the refluxing time and temperature and the molar ratio of surfactant to metal affect the structural properties of MgO, because of the changes in the rate and extent of P123 adsorption on the prepared samples. The results showed that the addition of surfactant is effective to prepare magnesium oxide with high surface area and affects the morphology of the prepared samples. With increasing the P123/MgO molar ratio to 0.05 the pore size distribution was shifted to larger size. The sample prepared with addition of surfactant showed a plate-like shape which was completely different with the morphology of the sample prepared without surfactant. The formation of nanoplate-like MgO was related to higher surface density of Mg ions on the (0 0 1) plane than that on the other planes of the Mg(OH){sub 2} crystal. The (0 0 1) plane would be blocked preferentially by the adsorbed P123 molecules during the growing process of Mg(OH){sub 2} nanoentities and the growth on the (0 0 1) plane would be markedly restricted, and the consequence is the generation of nanoplate-like MgO. In addition, increase in refluxing temperature and time

  13. High-rate reel-to-reel continuous coating of biaxially textured magnesium oxide thin films for coated conductors

    SciTech Connect

    Chudzik, M. P.; Erck, R. A.; Balachandran, U.; Luo, Z. P.; Miller, D. J.; Kannewurf, C. R.

    2000-01-12

    Biaxially textured thin films of magnesium oxide (MgO) were deposited by electron beam evaporation at deposition rates of 0.6 {mu}m/min on moving Ni-based alloy tapes as oriented buffer layers for coated conductors. Moving substrates were inclined with respect to the atomic vapor and translated through collimated dual vapor sources. Growth anisotropy in the MgO and self-shadowing effects due to the inclined angle combine to create biaxial texture in the deposited thin films. MgO films grown to a thickness of 2.0 {mu}m with this inclined-substrate deposition technique have yielded in-plane textures of 10--12{degree} fill-width half-maximum (FWHM). Results of a parametric study on the in-plane texture in short-length static-mode samples are presented, along with preliminary results of long-length samples deposited under translating conditions.

  14. Magnetic anisotropy related to strain and thickness of ultrathin iron oxide films on MgO(001)

    NASA Astrophysics Data System (ADS)

    Schemme, T.; Pathé, N.; Niu, G.; Bertram, F.; Kuschel, T.; Kuepper, K.; Wollschläger, J.

    2015-01-01

    Iron oxide films with different thicknesses (7.6-30 nm) were grown on clean MgO(001) substrates using reactive molecular beam epitaxy at 250 °C depositing Fe in a 5 × 10-5 mbar oxygen atmosphere. X-ray photoelectron spectra and low energy electron diffraction experiments indicate the stoichiometry and the surface structure of magnetite (Fe3O4). Film thicknesses and the lattice constants were analyzed ex situ by x-ray reflectometry and x-ray diffraction, respectively. These experiments reveal the single crystalline and epitactic state of the iron oxide films. However, the obtained vertical layer distances are too small to be strained magnetite and would rather suit to maghemite. Although Raman spectroscopy carried out to analyze the present iron oxide phase showed that the films might have slightly been oxidized in ambient conditions, a posteriori performed XPS measurements exclude a strong oxidation of the surface. Therefore we consider the presence of anti phase boundaries to explain the low vertical layer distances of the magnetite films. Further magnetooptic Kerr measurements were performed to investigate the magnetic properties. While the thinnest film shows a magnetic isotropic behavior, the thicker films exhibit a fourfold magnetic in-plane anisotropy. The magnetic easy axes are in the Fe3O4 < 110> directions. We propose that the magnetocrystalline anisotropy is too weak for very thin iron oxide films to form fourfold anisotropy related to the cubic crystal structure.

  15. A Mechanism of Photo-Induced Desorption of Oxygen Atoms From MgO Nano-Crystals

    SciTech Connect

    Trevisanutto, P. E.; Sushko, Petr V.; Shluger, Alexander L.; Beck, Kenneth M.; Henyk, Matthias; Joly, Alan G.; Hess, Wayne P.

    2005-11-20

    In a series of recent experimental and theoretical papers we reported the results of our studies of photo-induced hyper-thermal halogen atom desorption from alkali halide surfaces. There we demonstrated that the yield, electronic state and velocity distributions of desorbed atoms can be controlled by carefully choosing parameters of photo-irradiation such as laser photon energy and pulse power [ ]. To achieve laser control over desorption process one must have clear understanding of possible desorption mechanisms and parameters responsible for their selective excitation. For alkali halides, as it has been shown through a combination of theory and experiment, such selectively is observed if the laser energy is tuned to preferentially excite surface excitons. If similar mechanisms could be demonstrated for a wider variety of materials, this approach could become a new method for controlling surface processes and hence modifying surface structures on an atomic scale. In this paper we report the first experimental observation of the hyper-thermal oxygen atom emission from an of MgO nano-clusters and thin films using frequency selected laser pulses oxide surface and investigate theoretically the mechanisms of this process. On this way we demonstrate a new concept that can be applied to studying surface reactions and desorption of binary oxides.

  16. Perpendicular magnetic anisotropy of Mn{sub 4}N films on MgO(001) and SrTiO{sub 3}(001) substrates

    SciTech Connect

    Yasutomi, Yoko; Ito, Keita; Sanai, Tatsunori; Toko, Kaoru; Suemasu, Takashi

    2014-05-07

    We grew Mn{sub 4}N epitaxial thin films capped with Au layers on MgO(001) and SrTiO{sub 3}(001) substrates by molecular beam epitaxy. Perpendicular magnetic anisotropy (PMA) was confirmed in all the samples at room temperature from the magnetization versus magnetic field curves using superconducting quantum interference device magnetometer. From the ω-2θ x-ray diffraction (XRD) and ϕ-2θ{sub χ} XRD patterns, the ratios of perpendicular lattice constant c to in-plane lattice constant a, c/a, were found to be about 0.99 for all the samples. These results imply that PMA is attributed to the in-plane tensile strain in the Mn{sub 4}N films.

  17. First-principles study of B, C, N and F doped graphene-like MgO monolayer

    NASA Astrophysics Data System (ADS)

    Wu, Ping; Huang, Min; Cheng, Wenjing; Tang, Fuling

    2016-07-01

    Based on the first-principles calculations, we have investigated the stable geometries, electronic and magnetic properties of the graphene-like MgO monolayer with O atom substituted by B, C, N, and F atoms. The formation energy decreases in the order of B>C>N>F, which may be influenced by the different electronegativities. The band gaps of p-type doped MgO monolayers are tunable due to the emergence of impurity states within the band gap, while F-doped MgO monolayer realizes the transition from semiconductor to metal. The results show that p-type doped MgO monolayer exhibit magnetic behaviors due to polarizations of dopants and surrounding Mg or O atoms near the dopants, while no magnetism is observed in the case of F doped MgO monolayer. These results are potentially useful for spintronic applications and the development of magnetic nanostructures.

  18. Electronic and magnetic structure of epitaxial Fe3O4(001 ) /NiO heterostructures grown on MgO(001) and Nb-doped SrTiO3(001 )

    NASA Astrophysics Data System (ADS)

    Kuepper, K.; Kuschel, O.; Pathé, N.; Schemme, T.; Schmalhorst, J.; Thomas, A.; Arenholz, E.; Gorgoi, M.; Ovsyannikov, R.; Bartkowski, S.; Reiss, G.; Wollschläger, J.

    2016-07-01

    We study the underlying chemical, electronic, and magnetic properties of a number of magnetite-based thin films. The main focus is placed onto Fe3O4 (001)/NiO bilayers grown on MgO(001) and Nb-SrTiO3(001) substrates. We compare the results with those obtained on pure Fe3O4 (001) thin films. It is found that the magnetite layers are oxidized and Fe3 + dominates at the surfaces due to maghemite (γ -Fe2O3 ) formation, which decreases with increasing magnetite layer thickness. For layer thicknesses of around 20 nm and above, the cationic distribution is close to that of stoichiometric Fe3O4 . At the interface between NiO and Fe3O4 we find the Ni to be in a divalent valence state, with unambiguous spectral features in the Ni 2 p core level x-ray photoelectron spectra typical for NiO. The formation of a significant NiFe2O4 interlayer can be excluded by means of x-ray magnetic circular dichroism. Magneto-optical Kerr effect measurements reveal significant higher coercive fields compared to magnetite thin films grown on MgO(001), and an altered in-plane easy axis pointing in the <100 > direction. We discuss the spin magnetic moments of the magnetite layers and find that a thickness of 20 nm or above leads to spin magnetic moments close to that of bulk magnetite.

  19. ME- μSR MgO study: search for O[-1] earthquake-like precursors

    NASA Astrophysics Data System (ADS)

    Boekema, C.; Welch, G.; Johnson, C. E.; Freund, F. T.

    2015-03-01

    We analyze O-1 earthquake-like precursor effects by studying the μSR signals of MgO using Muon-Spin Resonance and Maximum Entropy (ME). Due to its abundance in the earth crust, MgO is ideal for studying these features: O-1 (or positive hole) formation results from a break in an oxygen anion pair under elevated temperature or high pressure conditions. For a 3N-MgO single crystal above RT, a small percentage (<1%) is predicted to be in an O-1 state, instead of typical O-2 ions. ME analysis of transverse field (100 Oe) MgO data show asymmetrical μSR peaks at ~ 1.4 MHz. Small T-dependent deviations from a Lorentzian (Lor) signal could be effects of O-1 states in MgO. We have fitted ME transforms with three Lorentzians to obtain a reasonable description of the 1.4-MHz peak. The T dependences of this 3-Lor set and their B-field dependences at 17°C are reported and discussed, and their relation to precursor earthquake-like O-valency effects. Research supported by RSCA-SJSU, SETI, WiSE-SJSU and AFC San Jose.

  20. FeO and MgO in plagioclase of lunar anorthosites: Igneous or metamorphic?

    NASA Technical Reports Server (NTRS)

    Phinney, W. C.

    1994-01-01

    The combined evidence from terrestrial anorthosites and experimental laboratory studies strongly implies that lunar anorthosites have been subjected to high-grade metamorphic events that have erased the igneous signatures of FeO and MgO in their plagioclases. Arguments to the contrary have, to this point, been more hopeful than rigorous.

  1. Effect of gold nanorods in an MgO protective layer of AC plasma display panels.

    PubMed

    Cho, Seok Ho; Lee, Seong Min; Kim, Woo Hyun; Choi, Kyung Cheol

    2015-04-15

    We propose a modified MgO protective layer for alternating current plasma display panels. The modified MgO protective layer of the panel tested here has a structure that incorporates silica-coated Au nanorods (NRs), leading to localized surface plasmon resonance (LSPR) in the near-infrared (IR) region. The silica-coated Au NRs were synthesized by a simple chemical method and inserted into an MgO protective layer using an air-spray method. The operating voltage of the proposed structure was decreased by 10 V. The luminance and luminous efficacy of the test panel part with the silica-coated Au NRs both increased by about 15%. According to the measured results of the IR response time, the sustain discharge time lag was reduced. In addition, by inserting the silica-coated Au NRs into the MgO protective layer, a decrease of the IR emission proceeding from the plasma discharge was acquired. Finally, we investigated the LSPR effect of the silica-coated Au NRs in a simulation with a finite-difference time domain method. PMID:25793546

  2. Inter-diffusion study in MgO tunneling magneto-resistive (TMR) system by XPS

    NASA Astrophysics Data System (ADS)

    Yu, G. H.; Peng, Xilin

    2010-09-01

    In this paper, we investigated the elemental inter-diffusion in MgO TMR system, namely, between MgO barrier and free layer (CoFeB, NiFe or their combination) interface and the oxygen diffusion into the capping layers (Ta, Ru, TaN) at elevated temperatures using simple sheet film stack to simplify the results interpretation. Boron, cobalt, iron, and nickel show various diffusion tendencies into the MgO barrier after annealing the sheet film stack. Oxygen has different penetration depth into single CoFeB free layer upon annealing under N 2 + Ar protective atmosphere for different capping layers. Ru and TaN capping layer provide much better O 2 diffusion barrier, compared with Ta capping layer. This could potentially change the boron segregation tendency at free layer and capping layer interface and thus affect the interface crystallization process and lattice matching between the crystallized CoFeB free layer and the MgO(0 0 1) barrier layer. All these effects will impact the overall TMR performance.

  3. Nature of MgO and Al2O3 Dissolution in Metallurgical Slags

    NASA Astrophysics Data System (ADS)

    Yan, Pengcheng; Webler, Bryan A.; Pistorius, P. Chris; Fruehan, Richard J.

    2015-12-01

    The nature of MgO and Al2O3 dissolution in metallurgical slags may affect production cost, efficiency, and product quality. However, the rate-limiting dissolution mechanism, chemical reaction or boundary layer diffusion, is not well understood. In the present report, the dissolution mechanism of MgO and Al2O3 in metallurgical slag was evaluated based on available literature data. The mass balance between the dissolving particle and the flux equation through the boundary layer was applied to predict the dissolution curve. The influence of fluid flow was taken into account to calculate the mass transfer rate at the oxide/slag interface. It was found that the rate-limiting step of MgO and Al2O3 dissolution is the same: mass transfer through the boundary layer. Depending on the slag composition and experimental temperature, the effective diffusion coefficient for MgO and Al2O3 dissolution falls in the range of 10-12 to 10-9 m2/s.

  4. Influence of MgO on structure and optical properties of alumino-lithium-phosphate glasses

    NASA Astrophysics Data System (ADS)

    Jlassi, I.; Elhouichet, H.; Ferid, M.

    2016-07-01

    MgO doped lithium alumino phosphate glasses (PLA: P2O5+Li2O+Al2O3+MgO) were prepared by melt quenching technique. Raman spectra display three significant peaks at 698, 1164 and 1383 cm-1 attributed to: symmetric stretching vibrations of the bridging oxygen (BO) in the P-O-P chains, symmetric stretching vibrations of the PO2 groups, and the asymmetric vibrations vas(PO2) of the non-bridging oxygen (NBO) atoms, respectively. Also, the density, molar volumes and ion concentration have been discussed and correlated with the structural changes within the glassy matrix. Some optical constants such as refractive index and dispersion parameters (Eo: single-oscillator energy and Ed: dispersive energy) of the glasses were determined. Finally, the values of the optical band gap for direct and indirect allowed transitions have been determined from the absorption edge studies. It is deduced that the values of Eopt increase with increasing MgO content. It was assigned to structural changes induced from the formation of non-bridging oxygen. The Urbach energy (ΔE) was found to decrease from 0.578 to 0.339 eV with increasing MgO content from 0.5 to 2 mol.

  5. Nanocrystal Ghosting: Extensive radiation damage in MgO induced by low-energy electrons

    NASA Astrophysics Data System (ADS)

    Sawyer, William; Frankenfield, Zachery; Kane, Kenneth

    Radiation damage in magnesium oxide has been an ongoing source of investigation. Early work was motivated by its simple cubic structure and its excellent electrical insulating properties over a wide range of temperatures and mechanical conditions. The goal was to determine its suitability as an electrical insulator in radiation intense environments including nuclear reactors and proposed nuclear fusion devices. During this period experimental results for irradiation of MgO using electrons with energies less than 500 keV produced very limited damage. These results, supported by theoretical arguments, lead to the conclusion that MgO was relatively impervious to damage from electrons with energies below this threshold. More recently its excellent insulating properties and relative mechanical stability combined with an increased interest in nanomaterials applications have created renewed interest in MgO. In this paper direct evidence is presented for extensive radiation damage in MgO nanocrystals from intense irradiation by electrons (2 x 10 4electrons/nm2 sec) with beam energies between 120 keV and 60 keV.

  6. Efficient removal of fluoride by hierarchical MgO microspheres: Performance and mechanism study

    NASA Astrophysics Data System (ADS)

    Jin, Zhen; Jia, Yong; Luo, Tao; Kong, Ling-Tao; Sun, Bai; Shen, Wei; Meng, Fan-Li; Liu, Jin-Huai

    2015-12-01

    Hierarchical MgO microspheres assembled by numerous porous nanoplates were successfully obtained by annealing the precursors of magnesium carbonate hydroxide hydrate synthesized through a facile and cost-effective hydrothermal process at low temperature. The as-prepared products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller measurements. The fluoride removal performance of the hierarchical MgO microspheres was investigated. The adsorption isotherm could be well fitted in Freundlich model, and the adsorption capacity was over 115.5 mg/g at pH 7. The absorbent also showed high fluoride removal ability in a wide pH range of 2-10, which is favorable for practical application. The effect of co-existing anions on fluoride removal was also investigated. The result indicated that the fluoride adsorption capacity was influenced when carbonate, bicarbonate and phosphate existed above the concentration of 50 mg/g. In addition, the adsorption mechanism was investigated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. A novel hydroxyl and carbonate co-exchange mechanism has been proposed for the first time. It can be found that fluoride ions could replace the surface carbonates which formed by the reaction of MgO and the adsorbed CO2 molecules, and then anchored on the MgO surface.

  7. Transient Cataluminescence on Flowerlike MgO for Discrimination and Detection of Volatile Organic Compounds.

    PubMed

    Xu, Honglin; Li, Qiuyan; Zhang, Lichun; Zeng, Binrong; Deng, Dongyan; Lv, Yi

    2016-08-16

    Methodologies for simple and rapid identification of gas compounds are needed in the fields of environmental and security. Here, a new and simple method for the discrimination of gas compounds was designed through an interesting transient cataluminescence (TRCTL) phenomenon on the highly efficient MgO materials. The flowerlike MgO with high CTL activity was controllably synthesized via a facile and time-saving aqueous precipitation route and characterized by scanning electron microscopy, powder X-ray diffractometry, high-resolution transmission electron microscopy, and N2 adsorption measurements, etc. With flowerlike MgO working as the sensing material, the newly developed CTL gas sensor exhibited highly active, ultrafast, and characteristic responses toward many analytes; the TRCTL curves thus were obtained and 10 VOCs have been successfully identified. Parallel experimental results show that the controllable synthesis of flowerlike MgO can greatly enhance the discrimination capacities for VOCs. Further, the TRCTL of CHCl3 and C2H5OC2H5 were taken as typical examples to illustrate the possible sensing mechanism, which could contribute to explaining processes of catalytic oxidations. We expect this novel TRCTL concept will be of practical importance for applications including gas detection, gas discrimination, and research of chemical kinetics processes. PMID:27417505

  8. He atom near methane-plated MgO: Interaction and scattering

    NASA Astrophysics Data System (ADS)

    Jung, David R.; Cui, Jinhe; Frankl, Daniel R.; Ihm, G.; Kim, H.-Y.; Cole, M. W.

    1989-12-01

    Scattering experiments and potential-energy calculations are reported for the system consisting of a He atom near a MgO surface upon which is adsorbed a CH4 layer. Assuming either a fixed dipolar configuration or free rotation of the molecule, the theoretical potential yields bound-state-resonance (selective-adsorption) positions consistent with those measured experimentally.

  9. Subsurface Synthesis and Characterization of Ag Nanoparticles Embedded in MgO

    SciTech Connect

    Vilayur Ganapathy, Subramanian; Devaraj, Arun; Colby, Robert J.; Pandey, Archana; Varga, Tamas; Shutthanandan, V.; Manandhar, Sandeep; El-Khoury, Patrick Z.; Kayani, Asghar N.; Hess, Wayne P.; Thevuthasan, Suntharampillai

    2013-03-08

    Metal nanoparticles exhibit localized surface plasmon resonance (LSPR) which is very sensitive to the size and shape of the nanoparticle and the dielectric medium surrounding it. LSPR causes field enhancement near the surface of the nanoparticle making them interesting candidates for plasmonic applications. In particular, partially exposed metallic nanoparticles distributed in a dielectric matrix form hotspots which are prime locations for LSPR spectroscopy and sensing. This study involves synthesizing partially buried Ag nanoparticles in MgO and investigating the characteristics of this material system. Ag nanoparticles of different shapes and size distributions were synthesized below the surface of MgO by implanting 200 keV Ag+ ions followed by annealing at 10000C for 10 and 30 hours. A detailed optical and structural characterization was carried out to understand the evolution of Ag nanoparticle microstructure and size distribution inside the MgO matrix. Micro x-ray diffraction (MicroXRD) was employed to investigate the structural properties and estimate the crystallite size. The nanoparticles evolved from a spherical to faceted morphology with annealing time, assuming an octahedral shape truncated at the (001) planes as seen from aberration corrected transmission electron microscopy (TEM) images. The nanoparticles embedded in MgO were shown to be pure metallic Ag using atom probe tomography (APT). The nanoparticles were partially exposed to the surface employing plasma etch techniques to remove the overlaying MgO. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to study the surface morphology and obtain a height distribution for the partially exposed nanoparticles.

  10. Subsurface synthesis and characterization of Ag nanoparticles embedded in MgO.

    PubMed

    Vilayurganapathy, S; Devaraj, A; Colby, R; Pandey, A; Varga, T; Shutthanandan, V; Manandhar, S; El-Khoury, P Z; Kayani, Asghar; Hess, W P; Thevuthasan, S

    2013-03-01

    Metal nanoparticles exhibit a localized surface plasmon resonance (LSPR) which is very sensitive to the size and shape of the nanoparticle and the surrounding dielectric medium. The coupling between the electromagnetic radiation and the localized surface plasmon in metallic nanoparticles results in a sizable enhancement of the incident fields, making them possible candidates for plasmonic applications. In particular, partially exposed metallic nanoparticles distributed in a dielectric matrix can provide prime locations for LSPR spectroscopy and sensing. We report the synthesis and characterization of a plasmonic substrate consisting of Ag nanoparticles partially buried in MgO. Ag nanoparticles of different shapes and size distributions were synthesized below the surface of MgO by implanting 200 keV Ag(+) ions followed by annealing at 1000 °C for 10 and 30 h. A detailed optical and structural characterization was carried out to understand the evolution of the Ag nanoparticle and size distribution inside the MgO matrix. Micro x-ray diffraction (Micro-XRD) was employed to investigate the structural properties and estimate the crystallite size. The nanoparticles evolved from a spherical to a faceted morphology with annealing time, assuming an octahedral shape truncated at the (001) planes, as visualized from aberration-corrected transmission electron microscopy (TEM) images. The nanoparticles embedded in MgO were shown to be pure metallic Ag using atom probe tomography (APT). The nanoparticles were partially exposed to the surface by employing plasma etch techniques to remove the overlaying MgO. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to study the surface morphology and obtain a height distribution for the partially exposed nanoparticles. PMID:23403363

  11. Subsurface synthesis and characterization of Ag nanoparticles embedded in MgO

    NASA Astrophysics Data System (ADS)

    Vilayurganapathy, S.; Devaraj, A.; Colby, R.; Pandey, A.; Varga, T.; Shutthanandan, V.; Manandhar, S.; El-Khoury, P. Z.; Kayani, Asghar; Hess, W. P.; Thevuthasan, S.

    2013-03-01

    Metal nanoparticles exhibit a localized surface plasmon resonance (LSPR) which is very sensitive to the size and shape of the nanoparticle and the surrounding dielectric medium. The coupling between the electromagnetic radiation and the localized surface plasmon in metallic nanoparticles results in a sizable enhancement of the incident fields, making them possible candidates for plasmonic applications. In particular, partially exposed metallic nanoparticles distributed in a dielectric matrix can provide prime locations for LSPR spectroscopy and sensing. We report the synthesis and characterization of a plasmonic substrate consisting of Ag nanoparticles partially buried in MgO. Ag nanoparticles of different shapes and size distributions were synthesized below the surface of MgO by implanting 200 keV Ag+ ions followed by annealing at 1000 °C for 10 and 30 h. A detailed optical and structural characterization was carried out to understand the evolution of the Ag nanoparticle and size distribution inside the MgO matrix. Micro x-ray diffraction (Micro-XRD) was employed to investigate the structural properties and estimate the crystallite size. The nanoparticles evolved from a spherical to a faceted morphology with annealing time, assuming an octahedral shape truncated at the (001) planes, as visualized from aberration-corrected transmission electron microscopy (TEM) images. The nanoparticles embedded in MgO were shown to be pure metallic Ag using atom probe tomography (APT). The nanoparticles were partially exposed to the surface by employing plasma etch techniques to remove the overlaying MgO. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to study the surface morphology and obtain a height distribution for the partially exposed nanoparticles.

  12. Gallium-assisted growth of flute-like MgO nanotubes, Ga2O3-filled MgO nanotubes, and MgO/Ga2O3 co-axial nanotubes.

    PubMed

    Jie, Jiansheng; Wu, Chunyan; Yu, Yongqiang; Wang, Li; Hu, Zhizhong

    2009-02-18

    Flute-like MgO nanotubes were successfully synthesized via a simple thermal evaporation method by using Mg(3)N(2) and Ga(2)O(3) as the source materials. The nanotubes are single-crystal cubic MgO, and have [100] orientation. In contrast to conventional nanotubes with intact walls, the flute-like MgO nanotubes possess a unique porous structure. On the nanotubes there are series of holes aligned along the nanotube length with approximate equidistance. Ga(2)O(3)-filled MgO nanotubes and MgO/Ga(2)O(3) co-axial nanotubes were also found in the product. Further investigation confirms that the inner beta-Ga(2)O(3) has an epitaxial growth relation with the outer MgO nanotube due to their perfect lattice matching. A gallium-assisted growth mechanism was proposed to interpret the growth of the flute-like MgO nanotubes. The thermal expansion and evaporation of the filled liquid gallium in MgO nanotubes are likely responsible for the formation of the hole structures on the side walls. PMID:19417423

  13. X-ray diffraction study of the optimization of MgO growth conditions for magnetic tunnel junctions

    SciTech Connect

    O, Se Young; Lee, Chan-Gyu; Shapiro, Alexander J.; Egelhoff, William F. Jr.; Mallett, Jonathan; Pong, Philip W. T.; Vaudin, Mark D.; Ruglovsky, Jennifer L.

    2008-04-01

    We have carried out a systematic study optimizing the MgO growth via preparation and sputtering conditions and underlayer structures. It was found that to prevent water vapor which is detrimental to MgO (200) growth, the chamber pressure needs to be reduced below 10{sup -8} Torr. Simple underlayers such as 5 nm CoFeB tend to give better MgO, but we have also succeeded in growing MgO on more complicated underlayers such as 1 Ta/20 Au/5 Co{sub 40}Fe{sub 40}B{sub 20} and 1 Ta/20 conetic (Ni{sub 77}Fe{sub 14}Cu{sub 5}Mo{sub 4})/1.5 Co{sub 40}Fe{sub 40}B{sub 20} (units in nanometers). We accomplished this by extensive baking of the deposition chamber and use of Ti-getter films. Short sputtering distance and high sputtering power were found to optimize MgO deposition. We found that both preparation and sputtering conditions have important effects on the MgO growth. X-ray diffraction analysis was used as the characterization tool for optimizing the MgO growth conditions.

  14. Strain-induced properties of epitaxial VOx thin films

    NASA Astrophysics Data System (ADS)

    Rata, A. D.; Hibma, T.

    2005-01-01

    We have grown VOx thin films on different substrates in order to investigate the influence of epitaxial strain on the transport properties. We found that the electric conductivity is much larger for films grown under compressive strain on SrTiO3 substrates, as compared to bulk material and VOx films grown under tensile strain on MgO substrates. A clear crossover from metallic to semiconducting behavior is observed when increasing the oxygen content x. Apparently, the application of strain induces a Mott-Hubbard insulator-to-metal transition in VOx<1. The VOx/SrTiO3 films show an unexpected large positive magnetoresistance effect at low temperatures, which is not found in the VOx films grown under tensile strain on MgO or on a substrate with a similar lattice parameter.

  15. First-principles determination of elastic anisotropy and wave velocities of MgO at lower mantle conditions

    PubMed

    Karki; Wentzcovitch; de Gironcoli S; Baroni

    1999-11-26

    The individual elastic constants of magnesium oxide (MgO) have been determined throughout Earth's lower mantle (LM) pressure-temperature regime with density functional perturbation theory. It is shown that temperature effects on seismic observables (density, velocities, and anisotropy) are monotonically suppressed with increasing pressure. Therefore, at realistic LM conditions, the isotropic wave velocities of MgO remain comparable to seismic velocities, as previously noticed in athermal high-pressure calculations. Also, the predicted strong pressure-induced anisotropy is preserved toward the bottom of the LM, so lattice-preferred orientations in MgO may contribute substantially to the observed seismic anisotropy in the D" layer. PMID:10576730

  16. All magnesium diboride Josephson junctions with MgO and native oxide barriers

    NASA Astrophysics Data System (ADS)

    Costache, M. V.; Moodera, J. S.

    2010-02-01

    We present results on all-MgB2 tunnel junctions, where the tunnel barrier is deposited MgO or native-oxide of base electrode. For the junctions with MgO, the hysteretic I-V curve resembles a conventional underdamped Josephson junction characteristic with critical current-resistance product nearly independent of the junction area. The dependence of the critical current with temperature up to 20 K agrees with the [Ambegaokar and Baratoff, Phys. Rev. Lett. 10, 486 (1963)] expression. For the junctions with native-oxide, conductance at low bias exhibits subgap features while at high bias reveals thick barriers. As a result no supercurrent was observed in the latter, despite the presence of superconducting-gaps to over 30 K.

  17. Giant Magnetic Anisotropy of Co, Ru, and Os Adatoms on MgO (001) Surface.

    PubMed

    Ou, Xuedong; Wang, Hongbo; Fan, Fengren; Li, Zhengwei; Wu, Hua

    2015-12-18

    Large magnetic anisotropy energy (MAE) is desirable and critical for nanoscale magnetic devices. Here, using ligand-field level diagrams and density functional calculations, we well explain the very recent discovery [I. G. Rau et al., Science 344, 988 (2014)] that an individual Co adatom on a MgO (001) surface has a large MAE of more than 60 meV. More importantly, we predict that a giant MAE up to 110 meV could be realized for Ru adatoms on MgO (001), and even more for the Os adatoms (208 meV). This is a joint effect of the special ligand field, orbital multiplet, and significant spin-orbit interaction, in the intermediate-spin state of the Ru or Os adatoms on top of the surface oxygens. The giant MAE could provide a route to atomic scale memory. PMID:26722941

  18. Exploring long-time response to radiation damage in MgO

    NASA Astrophysics Data System (ADS)

    Uberuaga, B. P.; Smith, R.; Cleave, A. R.; Henkelman, G.; Grimes, R. W.; Voter, A. F.; Sickafus, K. E.

    2005-01-01

    Using a variety of computational modeling and simulation methods, we examine the production and long-time evolution of damage created in irradiated MgO. We find that the damage produced in low energy (order 1 keV) collision cascades typically consists of point defects and small defect clusters. Over long times, interstitials annihilate with vacancies and aggregate with other interstitials, forming larger clusters that exhibit surprising behavior. For example, a six-atom interstitial cluster is found to have extremely high mobility. The implications of highly-mobile large clusters are explored via a rate theory model and comparison to other materials. We conclude that successful modeling of radiation damage evolution in MgO requires explicit treatment of large interstitial clusters.

  19. Experimental Investigation of the Creep Behvior of MgO at High Pressures

    SciTech Connect

    Mei, S.; Kohlstedt, D; Durham, W; Wang, L

    2008-01-01

    The high-temperature rheological behavior of polycrystalline periclase, MgO, has been investigated using the deformation-DIA on a synchrotron beamline at pressures up to 10 GPa. Significant experimental scatter in stress measurement illustrates current limitations of this technique. Although temperature and stress sensitivities are not well constrained, there is a clear dependence of creep rate on pressure. Based on our results, the creep rate of MgO depends on confining pressure with an activation volume of V* e 2.4 x 10-6 m3/mol. The grain-scale view of deformation processes reveals, as other D-DIA studies have, that subpopulations of grains, grouped by orientation, obey slightly different flow laws. The measurements also reveal that stress heterogeneity in the sample, whether caused by external conditions or processes internal to the sample itself, contribute a significant portion of the overall uncertainty in stress measurement.

  20. Time-resolved high-resolution electron microscopy of structural stability in MgO clusters

    SciTech Connect

    Kizuka, T.; Tanaka, N.

    1996-12-31

    Structure and stability of atomic clusters have been studied by time-resolved high-resolution electron microscopy (TRHREM). Typical examples are observations of structural fluctuation in gold (Au) clusters supported on silicon oxide films, graphtized carbon films and magnesium oxide (MgO) films. All the observations have been performed on the clusters consisted of single metal element. Structural stability of ceramics clusters, such as metal-oxide, metal-nitride and metal-carbide clusters, has not been observed by TRHREM although the clusters show anomalous structural and functional properties concerning to solid state physics and materials science. In the present study, the behavior of ceramic, magnesium oxide (MgO) clusters is for the first time observed by TRHREM at 1/60 s time resolution and at atomic resolution down to 0.2 nm.

  1. Influence of adsorbed fluids on the rolling contact deformation of MgO single crystals

    NASA Technical Reports Server (NTRS)

    Dufrane, K. F.

    1977-01-01

    Basic phenomena associated with rolling contact deformation were studied using MgO as a model bearing material. A hardened steel ball was rolled on MgO single crystals in slow-speed reciprocating motion and in high-speed circular motion. The resulting deformation was studied by dislocation etch-pit techniques. The presence of adsorbed fluids, such as silicone oil, white mineral oil, and toluene, with slow-speed sliding caused a dramatic change in slip mode and premature surface spalling compared with similar experiments in air or under water. In contrast, dimethyl formamide inhibited these slip processes. The results are consistent with the dependence of dislocation mobility on adsorbed species. High-speed hydrodynamic rolling with mineral oil lubrication produced a different slip phenomena entirely from the slow-speed rolling. The slip bands resembled those produced in tensile tests, and all slip apparently initiated at subsurface sites.

  2. Giant Magnetic Anisotropy of Co, Ru, and Os Adatoms on MgO (001) Surface

    NASA Astrophysics Data System (ADS)

    Ou, Xuedong; Wang, Hongbo; Fan, Fengren; Li, Zhengwei; Wu, Hua

    2015-12-01

    Large magnetic anisotropy energy (MAE) is desirable and critical for nanoscale magnetic devices. Here, using ligand-field level diagrams and density functional calculations, we well explain the very recent discovery [I. G. Rau et al., Science 344, 988 (2014)] that an individual Co adatom on a MgO (001) surface has a large MAE of more than 60 meV. More importantly, we predict that a giant MAE up to 110 meV could be realized for Ru adatoms on MgO (001), and even more for the Os adatoms (208 meV). This is a joint effect of the special ligand field, orbital multiplet, and significant spin-orbit interaction, in the intermediate-spin state of the Ru or Os adatoms on top of the surface oxygens. The giant MAE could provide a route to atomic scale memory.

  3. A comparative study of the number and mass of fine particles emitted with diesel fuel and marine gas oil (MGO)

    NASA Astrophysics Data System (ADS)

    Nabi, Md. Nurun; Brown, Richard J.; Ristovski, Zoran; Hustad, Johan Einar

    2012-09-01

    The current investigation reports on diesel particulate matter emissions, with special interest in fine particles from the combustion of two base fuels. The base fuels selected were diesel fuel and marine gas oil (MGO). The experiments were conducted with a four-stroke, six-cylinder, direct injection diesel engine. The results showed that the fine particle number emissions measured by both SMPS and ELPI were higher with MGO compared to diesel fuel. It was observed that the fine particle number emissions with the two base fuels were quantitatively different but qualitatively similar. The gravimetric (mass basis) measurement also showed higher total particulate matter (TPM) emissions with the MGO. The smoke emissions, which were part of TPM, were also higher for the MGO. No significant changes in the mass flow rate of fuel and the brake-specific fuel consumption (BSFC) were observed between the two base fuels.

  4. Selectivity to olefins of Fe/SiO{sub 2}-MgO catalysts in the Fischer-Tropsch reaction

    SciTech Connect

    Gallegos, N.G.; Alvarez, A.M.; Cagnoli, M.V.; Bengoa, J.F.

    1996-06-01

    SiO{sub 2} covered with MgO has been used as support of iron catalysts in the Fischer-Tropsch reaction. Catalysts of 5% (w/w) iron concentration and 2, 4, and 8% (w/w) of MgO on SiO{sub 2} were prepared. Selective chemisorption of CO, volumetric oxidation, and Moessbauer spectroscopy were used to characterize the type of iron species and the metallic crystal sizes. MgO covers the SiO{sub 2} surface and modifies the metallic crystal size. The activity to total hydrocarbons increases with the amount of MgO added. An optimal concentration of about 4% (w/w) was found to have the highest selectivity to olefins. 45 refs., 13 figs., 3 tabs.

  5. High-index Cu2O (113) film on faceted MgO (110) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Huo, Wenxing; Shi, Jin'an; Mei, Zengxia; Liu, Lishu; Li, Junqiang; Gu, Lin; Du, Xiaolong; Xue, Qikun

    2015-06-01

    We report the growth of single-oriented Cu2O (113) film on faceted MgO (110) substrate by radio-frequency plasma assisted molecular beam epitaxy. A MgO {100} faceted homoepitaxial layer was introduced beforehand as a template for epitaxy of Cu2O film. The epitaxial relationship is determined to be Cu2O (113)//MgO (110) with a tilt angle of 4.76° and Cu2O [ 1 1 bar 0]//MgO [ 1 1 bar 0] by the combined study of in-situ reflection high-energy electron diffraction and ex-situ X-ray diffraction and transmission electron microscopy. The film demonstrates a good p-type conductivity and excellent optical properties, indicating that this unique approach is potentially applicable for high-index film preparation and device applications.

  6. O(minus 2) grain boundary diffusion and grain growth in pure dense MgO

    NASA Technical Reports Server (NTRS)

    Kapadia, C. M.; Leipold, M. H.

    1973-01-01

    Grain growth behavior in fully dense compacts of MgO of very high purity was studied, and the results compared with other similar behaving materials. The activation energy for the intrinsic self-diffusion of Mg(2minus) is discussed along with the grain boundary diffusion of O(2minus). Grain boundary diffusion of O(2minus) is proposed as the controlling mechanism for grain growth.

  7. NQRS Data for F6H12MgO6Si (Subst. No. 2195)

    NASA Astrophysics Data System (ADS)

    Chihara, H.; Nakamura, N.

    This document is part of Subvolume B 'Substances Containing C10H16 … Zn' of Volume 48 'Nuclear Quadrupole Resonance Spectroscopy Data' of Landolt-Börnstein - Group III 'Condensed Matter'. It contains an extract of Section '3.2 Data tables' of the Chapter '3 Nuclear quadrupole resonance data' providing the NQRS data for F6H12MgO6Si (Subst. No. 2195)

  8. Are Dispersive Forces Relevant for CO Adsorption on the MgO(001) Surface?

    SciTech Connect

    Ugliengo, Piero; Damin, A

    2002-12-20

    Periodic ab initio B3-LYP calculations on the MgO(001)/CO system underestimate the CO binding energy value with respect to experiment. The flaw is in the B3-LYP functional, unable to compute dispersive interactions. Here we show how to evaluate this contribution by adopting a two-layer ONIOM scheme in which the B3-LYP crystal energy is improved by the MP2 energy computed on the Mg9O9/CO cluster.

  9. The phase diagram and transport properties of MgO from theory and experiment

    NASA Astrophysics Data System (ADS)

    Shulenburger, Luke

    2013-06-01

    Planetary structure and the formation of terrestrial planets have received tremendous interest due to the discovery of so called super-earth exoplanets. MgO is a major constituent of Earth's mantle, the rocky cores of gas giants and is a likely component of the interiors of many of these exoplanets. The high pressure - high temperature behavior of MgO directly affects equation of state models for planetary structure and formation. In this work, we examine MgO under extreme conditions using experimental and theoretical methods to determine its phase diagram and transport properties. Using plate impact experiments on Sandia's Z facility the solid-solid phase transition from B1 to B2 is clearly determined. The melting transition, on the other hand, is subtle, involving little to no signal in us-up space. Theoretical work utilizing density functional theory (DFT) provides a complementary picture of the phase diagram. The solid-solid phase transition is identified through a series of quasi-harmonic phonon calculations and thermodynamic integration, while the melt boundary is found using phase coexistence calculations. One issue of particular import is the calculation of reflectivity along the Hugoniot and the influence of the ionic structure on the transport properties. Particular care is necessary because of the underestimation of the band gap and attendant overestimation of transport properties due to the use of semi-local density functional theory. We will explore the impact of this theoretical challenge and its potential solutions in this talk. The integrated use of DFT simulations and high-accuracy shock experiments together provide a comprehensive understanding of MgO under extreme conditions. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  10. Niobium Thin Film Characterization for Thin Film Technology Used in Superconducting Radiofrequency Cavities

    NASA Astrophysics Data System (ADS)

    Dai, Yishu; Valente-Feliciano, Anne-Marie

    2015-10-01

    Superconducting RadioFrequency (SRF) penetrates about 40-100 nm of the top surface, making thin film technology possible in producing superconducting cavities. Thin film is based on the deposition of a thin Nb layer on top of a good thermal conducting material such as Al or Cu. Thin film allows for better control of the surface and has negligible response to the Earth's magnetic field, eliminating the need for magnetic shielding of the cavities. Thin film superconductivity depends heavily on coating process conditions, involving controllable parameters such as crystal plane orientation, coating temperature, and ion energy. MgO and Al2O3 substrates are used because they offer very smooth surfaces, ideal for studying film growth. Atomic Force Microscopy is used to characterize surface's morphology. It is evident that a lower nucleation energy and a long coating time increases the film quality in the r-plane sapphire crystal orientation. The quality of the film increases with thickness. Nb films coated on r-plane, grow along the (001) plane and yield a much higher RRR compared to the films grown on a- and c-planes. This information allows for further improvement on the research process for thin film technology used in superconducting cavities for the particle accelerators. National Science Foundation, Department of Energy, Jefferson Lab, Old Dominion University.

  11. Low-temperature preparation of superconducting YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ films on Si, MgO, and SrTiO/sub 3/ by thermal coevaporation

    SciTech Connect

    Berberich, P.; Tate, J.; Dietsche, W.; Kinder, H.

    1988-09-05

    We used simple thermal coevaporation of yttrium, barium, and copper in an oxygen atmosphere to produce thin films of the 90 K superconductor, YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/, on silicon, magnesium oxide, and strontium titanate. The films were deposited on 650 /sup 0/C substrates and were superconducting when removed from the evaporator. A short post-anneal at 480 /sup 0/C produced films on bare Si with transition temperatures (R = 0) of 85 K. Films as thin as 0.13 ..mu..m, superconducting at 91 K (on MgO) and 89 K (on SrTiO/sub 3/), were obtained with no post-anneal.

  12. A comparative study on properties of synthesized MgO with different templates

    NASA Astrophysics Data System (ADS)

    Bagheri GH, A.; Sabbaghan, M.; Mirgani, Z.

    2015-02-01

    Magnesium oxide powders have been prepared by simple method using different templates as Hexamine (T1), alkylate-hexamine salt (T2) and alkylate-dihexamine salt (T3). The annealed products were systematically investigated by using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and UV-Visible absorption. It was found that the formation of nanoparticle could involved the role of performed "nucleus" and used template to control the growth rate of nucleuses. The results were shown that different templates affect on the size and species of particles. In this study, the crystallite size of the MgO products were in a range from 4 to 7 nm. The optical band gap of MgO nanoparticles was in the range 4.27-4.77 eV. The morphology of MgO was nanospheres or nanokongelemere-like. In this investigation photocatalytic degradation of Indigo carmine (IC) in water was studied. The effects of some parameters such as pH, amount of catalyst, initial concentration of dye were examined.

  13. A comparative study on properties of synthesized MgO with different templates.

    PubMed

    Bagheri GH, A; Sabbaghan, M; Mirgani, Z

    2015-02-25

    Magnesium oxide powders have been prepared by simple method using different templates as Hexamine (T1), alkylate-hexamine salt (T2) and alkylate-dihexamine salt (T3). The annealed products were systematically investigated by using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and UV-Visible absorption. It was found that the formation of nanoparticle could involved the role of performed "nucleus" and used template to control the growth rate of nucleuses. The results were shown that different templates affect on the size and species of particles. In this study, the crystallite size of the MgO products were in a range from 4 to 7 nm. The optical band gap of MgO nanoparticles was in the range 4.27-4.77 eV. The morphology of MgO was nanospheres or nanokongelemere-like. In this investigation photocatalytic degradation of Indigo carmine (IC) in water was studied. The effects of some parameters such as pH, amount of catalyst, initial concentration of dye were examined. PMID:25305623

  14. Two-band luminescence from an intrinsic defect in spherical and terraced MgO nanoparticles

    SciTech Connect

    Pikhitsa, Peter V. E-mail: mchoi@snu.ac.kr; Kim, Changhyuk; Chae, Sukbyung; Shin, Seungha; Jung, Sekwon; Choi, Mansoo E-mail: mchoi@snu.ac.kr; Kitaura, Mamoru; Kimura, Shin-ichi; Fukui, Kazutoshi

    2015-05-04

    Luminescent defect centers in wide bandgap materials such as MgO are of great interest for science and technology. Magnesium oxide nanocubes obtained by the self-combustion of Mg metal have long exhibited only a broad 2.9 eV cathodoluminescence band owing to oxygen vacancies (F centers). However, in this work, a room-temperature ultraviolet 4.8 eV cathodoluminescence band has been observed coincident with a 2.5 eV band of the same intensity from an unexplored intrinsic defect in MgO terraced nanocubes and nanospheres produced from Mg metal combustion in an H{sub 2}/O{sub 2} flame. Synchrotron radiation excitation spectra reveal that the excitation energy at the onset of both bands is just above the bandgap energy of 7.7 eV, where electrons and holes are generated. We determine that a defect, responsible for both emission bands, creates proximal anion-cation vacancy pairs named P centers that may appear instead of F centers because of changes in the MgO nanoparticle growth conditions.

  15. Lattice thermal conductivity of MgO at conditions of Earth’s interior

    PubMed Central

    Tang, Xiaoli; Dong, Jianjun

    2010-01-01

    Thermal conductivity of the Earth’s lower mantle greatly impacts the mantle convection style and affects the heat conduction from the core to the mantle. Direct laboratory measurement of thermal conductivity of mantle minerals remains a technical challenge at the pressure-temperature (P-T) conditions relevant to the lower mantle, and previously estimated values are extrapolated from low P-T data based on simple empirical thermal transport models. By using a numerical technique that combines first-principles electronic structure theory and Peierls–Boltzmann transport theory, we predict the lattice thermal conductivity of MgO, previously used to estimate the thermal conductivity in the Earth, at conditions from ambient to the core-mantle boundary (CMB). We show that our first-principles technique provides a realistic model for the P-T dependence of lattice thermal conductivity of MgO at conditions from ambient to the CMB, and we propose thermal conductivity profiles of MgO in the lower mantle based on geotherm models. The calculated conductivity increases from 15 –20 W/K-m at the 670 km seismic discontinuity to 40 –50 W/K-m at the CMB. This large depth variation in calculated thermal conductivity should be included in models of mantle convection, which has been traditionally studied based on the assumption of constant conductivity. PMID:20176973

  16. Modelling the rheology of MgO under Earth's mantle pressure, temperature and strain rates.

    PubMed

    Cordier, Patrick; Amodeo, Jonathan; Carrez, Philippe

    2012-01-12

    Plate tectonics, which shapes the surface of Earth, is the result of solid-state convection in Earth's mantle over billions of years. Simply driven by buoyancy forces, mantle convection is complicated by the nature of the convecting materials, which are not fluids but polycrystalline rocks. Crystalline materials can flow as the result of the motion of defects--point defects, dislocations, grain boundaries and so on. Reproducing in the laboratory the extreme deformation conditions of the mantle is extremely challenging. In particular, experimental strain rates are at least six orders of magnitude larger than in nature. Here we show that the rheology of MgO at the pressure, temperature and strain rates of the mantle is accessible by multiscale numerical modelling starting from first principles and with no adjustable parameters. Our results demonstrate that extremely low strain rates counteract the influence of pressure. In the mantle, MgO deforms in the athermal regime and this leads to a very weak phase. It is only in the lowermost lower mantle that the pressure effect could dominate and that, under the influence of lattice friction, a viscosity of the order of 10(21)-10(22) pascal seconds can be defined for MgO. PMID:22237109

  17. Theoretical evidence for unexpected O-rich phases at corners of MgO surfaces

    NASA Astrophysics Data System (ADS)

    Berger, Daniel; Levchenko, Sergey V.; Bhattacharya, Saswata; Reuter, Karsten; Ghiringhelli, Luca M.; Scheffler, Matthias

    2015-03-01

    Introducing charge carriers into MgO via p doping greatly reduces formation energy of an O-vacancy in the bulk and at the (100) surface. In this work, we use hybrid density functional theory to explore O-vacancy and O/O2-ad-species defects at corners of MgO surfaces. The defects are modelled using MgO clusters embedded into a field of norm-conserving pseudopotentials and point charges. The long-range response of the oxide to the charge carriers trapped at the defects is taken into account using a polarizable force field. The low-energy defect atomic structures are found using an ab initio genetic algorithm. Concentrations of O-vacancies and O-ad-species at realistic temperatures and pressures are obtained with ab initio atomistic thermodynamics. Unexpectedly, we find that O-ad-species rather than O-vacancies are dominating defects at realistic conditions. The stability of the O-ad-species over O-vacancies and pristine corners is explained by an interplay between bond-breaking, bond-making, and charge-carrier trapping. -

  18. Structural, compositional, mechanical characterization and biological assessment of bovine-derived hydroxyapatite coatings reinforced with MgF2 or MgO for implants functionalization.

    PubMed

    Mihailescu, Natalia; Stan, G E; Duta, L; Chifiriuc, Mariana Carmen; Bleotu, Coralia; Sopronyi, M; Luculescu, C; Oktar, F N; Mihailescu, I N

    2016-02-01

    Hydroxyapatite (HA) is a consecrated biomaterial for bone reconstruction. In the form of thin films deposited by pulsed laser technologies, it can be used to cover metallic implants aiming to increase biocompatibility and osseointegration rate. HA of animal origin (bovine, BHA) reinforced with MgF2 (2wt.%) or MgO (5wt.%) were used for deposition of thin coatings with improved adherence, biocompatibility and antimicrobial activity. For pulsed laser deposition experiments, a KrF* (λ=248nm, τFWHM≤25ns) excimer laser source was used. The deposited structures were characterized from a physical-chemical point of view by X-Ray Diffraction, Fourier Transform Infra-Red Spectroscopy, Scanning Electron Microscopy in top- and cross-view modes, Energy Dispersive X-Ray Spectroscopy and Pull-out adherence tests. The microbiological assay using the HEp-2 cell line revealed that all target materials and deposited thin films are non-cytotoxic. We conducted tests on three strains isolated from patients with dental implants failure, i.e. Microccocus sp., Enterobacter sp. and Candida albicans sp. The most significant anti-biofilm effect against Microcococcus sp. strain, at 72h, was obtained in the presence of BHA:MgO thin films. For Enterobacter sp. strain a superior antimicrobial activity at 72h was noticed, in respect with simple BHA or Ti control. The enhanced antimicrobial performances, correlated with good cytocompatibility and mechanical properties recommend these biomaterials as an alternative to synthetic HA for the fabrication of reliable implant coatings for dentistry and other applications. PMID:26652442

  19. Observation of radio frequency ring-shaped hollow cathode discharge plasma with MgO and Al electrodes for plasma processing

    SciTech Connect

    Ohtsu, Yasunori Matsumoto, Naoki

    2014-05-15

    Various high-density plasma sources have been proposed for plasma processing. Especially, the hollow cathode discharge is one of the powerful ones. In this work, radio-frequency (RF) driven ring-shaped hollow cathode discharges with high secondary-electron emission have been investigated, using an aluminum (Al) cathode, coated or not with magnesium oxide (MgO). The thickness of MgO thin film is approximately 200 nm. The RF discharge voltage for the coated cathode is almost the same as that for the uncoated one, in a wide range of Ar gas pressure, from 5.3 to 53.2 Pa. The results reveal that the plasma density has a peak at an Ar gas pressure of 10.6 Pa for both cathodes. The plasma density for the coated cathode is about 1.5–3 times higher than that for the uncoated one, at various gas pressures. To the contrary, the electron temperature for the coated cathode is lower than temperature obtained with the uncoated cathode, at various gas pressures. Radial profiles of electron saturation current, which is proportional to plasma flux, are also examined for a wide range of gas pressure. Radial profiles of electron temperature at various axial positions are almost uniform for both cathodes so that the diffusion process due to density gradient is dominant for plasma transport. The secondary electrons emitted from the coated cathode contribute to the improvement of the plasma flux radial profile obtained using the uncoated cathode.

  20. Reel-to-reel deposition of epitaxial double-sided MgO buffer layers for coated conductors

    NASA Astrophysics Data System (ADS)

    Xue, Yan; Xiong, Jie; Zhang, Yahui; Zhang, Fei; Zhao, Rui-Peng; Hui, Wang; Wang, Quiling; Cheng, Guo; Zhao, Xiao-Hui; Tao, Bo-Wan

    2016-06-01

    We have successfully employed a double-sided process to deposit MgO buffer layers on both sides of amorphous Y2O3 surface for double-sided YBa2Cu3O7-δ (YBCO) coated conductors (CCs) for the first time, the structure of which is of great prospect to improve the performance and cut the production cost. The biaxial textures of MgO buffer layer are noticeably affected by the ion energy and film thickness, which is demonstrated by X-ray diffraction. The best biaxial texture of double-sided MgO films shows ω-scan of (002) MgO and Φ-scan of (220) MgO yield full width at half maximum values of 4° and 7.8° for one side, respectively, as well as 3.5° and 6.7° for the other side. The subsequent double-sided YBCO films are deposited on the as-prepared MgO template with entire critical current of over 300 A/cm for both sides.

  1. Oxidation of Au by surface OH: nucleation and electronic structure of gold on hydroxylated MgO(001).

    PubMed

    Brown, Matthew A; Fujimori, Yuichi; Ringleb, Franziska; Shao, Xiang; Stavale, Fernando; Nilius, Niklas; Sterrer, Martin; Freund, Hans-Joachim

    2011-07-13

    The nucleation and electronic structure of vapor-deposited Au on hydroxylated MgO(001) surfaces has been investigated under ultrahigh vacuum conditions. Hydroxylated MgO(001) surfaces with two different hydroxyl coverages, 0.4 and 1 monolayer, respectively, were prepared by exposure to water (D(2)O) at room temperature. Scanning tunneling microscopy experiments show significantly higher gold particle densities and smaller particle sizes on the hydroxylated MgO surface as compared to gold deposited on clean MgO(001). Infrared spectroscopy and X-ray photoelectron spectroscopy experiments were performed to reveal details about the initial nucleation of gold. Gold atoms are found to chemically interact with a specific type of hydroxyl groups on the MgO surface, leading to the formation of oxidized gold particles. The enhanced adhesion of Au particles, which is due to the formation of strong Au-O interfacial bonds, is responsible for the observed higher stability of small Au clusters toward thermal sintering on hydroxylated MgO surfaces. The results are compared to similar studies on Au/TiO(2)(110) model systems and powder samples prepared by the deposition-precipitation route. PMID:21634792

  2. Assimilation Behavior of Calcium Ferrite and Calcium Diferrite with Sintered Al2O3 and MgO

    NASA Astrophysics Data System (ADS)

    Long, Hongming; Wu, Xuejian; Chun, Tiejun; Di, Zhanxia; Yu, Bin

    2016-06-01

    In this study, the assimilation behaviors between calcium ferrite (CF), calcium diferrite (CF2) and sintered Al2O3, and MgO were explored by an improved sessile drop technique, and the interfacial microstructure was discussed. The results indicated that the apparent contact angles of CF slag on Al2O3 and MgO substrate were 15.7 and 5.5 deg, and the apparent contact angles of CF2 slag on Al2O3 and MgO substrate were 17.9 and 7.2 deg, respectively. Namely, CF and CF2 slag were wetting well with Al2O3 and MgO substrate. The dissolution of Al2O3 substrate into the CF and CF2 slag was found to be the driving force of the wetting process. For the CF-MgO and CF2-MgO substrate systems, CaO contrarily distributed with MgO after wetting. For the CF-MgO system, after wetting, the slag was composed of CF and C2F, and most of the Fe2O3 permeated into substrate and formed two permeating layers.

  3. Characterization of Surface Chemical States of a Thick Insulator: Chemical State Imaging on MgO Surface

    NASA Astrophysics Data System (ADS)

    Yi, Yeonjin; Cho, Sangwan; Noh, Myungkeun; Whang, Chung-Nam; Jeong, Kwangho; Shin, Hyun-Joon

    2005-02-01

    We report a surface characterization tool that can be effectively used to investigate the chemical state and subtle radiation damage on a thick insulator surface. It has been used to examine the MgO surface of a plasma display panel (PDP) consisting of a stack of insulator layers of approximately 51 μm thickness on a 2-mm-thick glass plate. The scanning photoelectron microscopy (SPEM) image of the insulating MgO surface was obtained by using the difference in Au 4f peak shift due to the surface charging at each pixel, where a Au adlayer of approximately 15 {\\AA} thickness was formed on the surface to overcome the serious charging shift of the peak position and the spectral deterioration in the photoelectron spectra. The observed contrast in the SPEM image reveals the chemical modification of the underlying MgO surface induced by the plasma discharge damage. The chemical state analysis of the MgO surface was carried out by comparing the Mg 2p, C 1s and O 1s photoemission spectra collected at each pixel of the SPEM image. We assigned four suboxide phases, MgO, MgCO3, Mg(OH)2 and Mg1+, on the initial MgO surface, where the Mg(OH)2 and Mg1+ phases vanished rapidly as the discharge-induced surface damage began.

  4. The role of strain and structure on oxygen ion conduction in nanoscale zirconia and ceria thin films

    NASA Astrophysics Data System (ADS)

    Jiang, Jun

    Solid oxide fuel cells (SOFCs), an all solid-state energy conversion device, are promising for their high efficiency and materials stability. The solid oxide electrolytes are a key component that must provide high ionic conductivity, which is especially challenging for intermediate temperature SOFCs operating between 500 °C - 700 °C. Doped zirconia and ceria are the most common solid electrolyte materials. Recent reports have suggested that nanoscale ytrria stabilized zirconia (YSZ) thin films may provide better performance in this regard. However, the mechanism behind the increased conductivity of nanoscale thin films is still unclear and the reported experimental results are controversial. In the thesis presented here, the effects of mechanical strain and microstructure on the ionic conductivity have been investigated in ultrathin zirconia- and ceria-based thin films. Reactive RF co-sputtering with metal targets was used to prepare zirconia and ceria based thin films for high purity, modulated composition and thickness. The films were as thin as 10-20 atomic layers thick. X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy were the main tools to investigate the composition, crystal orientation and microstructure of these sputtered thin films. Microscale interdigitated Pt electrodes were prepared through a lift-off process using photolithography. The electrochemical properties of these sputtered doped zirconia and ceria thin films were investigated using impedance spectroscopy. YSZ thin films deposited on MgO (111) and, especially, MgO (100) showed highly variable crystal orientations, while MgO (110) offered much more stable growth. Regardless of whether the growth was epitaxial or highly disordered polycrystalline, 50 nm thick YSZ thin films on MgO (100), (110), and (111) substrates exhibited similar conductivity with YSZ single crystal. While decreasing the thickness further to 12 nm, the conductivities of YSZ thin films

  5. Optical Response in Amorphous GaAs Thin Films Prepared by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Kiwa, Toshihiko; Kawashima, Ichiro; Nashima, Shigeki; Hangyo, Masanori; Tonouchi, Masayoshi

    2000-11-01

    Femtosecond optical response in GaAs thin films has been studied. We prepared GaAs thin films on MgO substrates and on YBa2Cu3O7-δ (YBCO) thin films using pulsed laser deposition (PLD) at temperatures below 250^\\circC@. A photocarrier lifetime of less than 1 ps is measured for the prepared GaAs thin films using femtosecond time-domain reflectivity change measurements. Pulsed electromagnetic wave [terahertz (THz) radiaiton] containing a frequency component of up to 1 THz is emitted from fabricated photoconductive switches using the prepared thin films. We also evaluated the THz radiation properties emitted from the photoswitches on the YBCO thin films.

  6. The effects of substrate surface structure on yttria-stabilized zirconia thin films

    NASA Astrophysics Data System (ADS)

    Jiang, Jun; Clark, Daniel; Shen, Weida; Hertz, Joshua L.

    2014-02-01

    Thin film properties can be controlled to a large degree by the substrate upon which the film is grown. The substrate surface can affect the film's crystal phase and microstructure and, thereby, many other properties. In this study, yttria-stabilized zirconia films on single crystal MgO and Al2O3 substrates with polished, ion cleaned, or milled surfaces were studied. The different substrate surfaces influenced the thin films' microstructures and ionic conductivities. The increased roughness of the milled surfaces led to significant decreases in both the crystallinity and the ionic conductivity of the films. Ion cleaning of the substrate surface immediately before deposition did not affect the conductivity of films on MgO substrates but led to conductivity reductions by a factor of about 4 on sapphire substrates.

  7. Long-range phase coherence in YBCO ultra-thin films

    SciTech Connect

    Aprili, M.; Lesueur, J.; Quinton, W.A.; Dumoulin, L.

    1996-12-31

    The authors have investigated the resistive transition of YBCO ultra-thin films (thickness from 5 to 50 nm) grown on MgO(100). The amount of disorder increases as the thickness is reduced, leading to a broad transition that can be described using a 3D weakly-coupled Josephson array. Below a critical thickness, this regime seems to dominate even the fluctuating part of the transition (paraconductive region), when the system undergoes a 3D-0D transition.

  8. Nanoplough-constrictions on thin YBCO films made with atomic force microscopy.

    PubMed

    Elkaseh, A A O; Büttner, U; Meincken, M; Hardie, G L; Srinivasu, V V; Perold, W J

    2007-09-01

    Utilizing atomic force microscope (AFM) with a diamond tip, we were able to successfully plough nano-constrictions on epitaxially grown YBa2Cu3O(7-x) thin films deposited on MgO substrates. The thickness, width, and length of the obtained constrictions were in the range of a few 100 nm. Furthermore, we managed to produce a new S-type constriction, of which the dimensions are easier to control than for conventional constrictions. PMID:18019174

  9. YSZ thin films with minimized grain boundary resistivity.

    PubMed

    Mills, Edmund M; Kleine-Boymann, Matthias; Janek, Juergen; Yang, Hao; Browning, Nigel D; Takamura, Yayoi; Kim, Sangtae

    2016-04-21

    In recent years, interface engineering of solid electrolytes has been explored to increase their ionic conductivity and improve the performance of solid oxide fuel cells and other electrochemical power sources. It has been observed that the ionic conductivity of epitaxially grown thin films of some electrolytes is dramatically enhanced, which is often attributed to effects (e.g. strain-induced mobility changes) at the heterophase boundary with the substrate. Still largely unexplored is the possibility of manipulation of grain boundary resistivity in polycrystalline solid electrolyte films, clearly a limiting factor in their ionic conductivity. Here we report that the ionic conductivity of yttria stabilized zirconia thin films with nano-columnar grains grown on a MgO substrate nearly reaches that of the corresponding single crystal when the thickness of the films becomes less than roughly 8 nm (smaller by a factor of three at 500 °C). Using impedance spectroscopy, the grain boundary resistivity was probed as a function of film thickness. The resistivity of the grain boundaries near the film-substrate interface and film surface (within 4 nm of each) was almost entirely eliminated. This minimization of grain boundary resistivity is attributed to Mg(2+) diffusion from the MgO substrate into the YSZ grain boundaries, which is supported by time of flight secondary ion mass spectroscopy measurements. We suggest grain boundary "design" as an attractive method to obtain highly conductive solid electrolyte thin films. PMID:27030391

  10. X-Ray Diffraction Microstructural Analysis of Bimodal-Size-Distribution MgO Nanopowders

    NASA Astrophysics Data System (ADS)

    Pratapa, Suminar; Hartono, Budi

    2010-01-01

    Investigation on the characteristics of x-ray diffraction data for MgO powdered mixture of nano and sub-nano particles has been carried out to reveal the crystallite-size-related microstructural information. The MgO powders were prepared by co-precipitation method followed by heat treatment at 500, 800 and 1200° C for 1 hour, being the difference in the temperature was to obtain two powders with distinct crystallite size and size-distribution. The powders were then carefully blended in air to give the presumably strain-free, bimodal-size-distribution MgO nanopowder. High-quality laboratory X-ray diffraction data for the powders were collected and then analysed using Rietveld-based MAUD software using the lognormal size distribution. Results show that the single-mode powders exhibit spherical crystallite size (Dv) of 29(1) nm, 36(1) and 185(0) nm for the 500, 800 and 1200° C data respectively with the nanometric powder displays slightly narrower crystallite size distribution character, indicated by lognormal dispersion parameter (σ) of 0.22 as compared to 0.18 for the sub-nanometric 1200° C powder. The mixture exhibits relatively more asymmetric peak broadening. By analysing the x-ray diffraction data of the latter specimen by using the single phase approach the results obtained was not according to experimental finding. Introducing two phase models for the `double-phase' 500-1200 mixture to accommodate the bimodal-size-distribution characteristics give Dv = 34(2) and σ = 0.10 for the `nanometric phase' and Dv = 363(0) and σ = 1.38 for the `sub-nanometric phase'.

  11. Charge dynamics of MgO single crystals subjected to KeV electron irradiation

    NASA Astrophysics Data System (ADS)

    Boughariou, A.; Blaise, G.; Braga, D.; Kallel, A.

    2004-04-01

    A scanning electron microscope has been equipped to study the fundamental aspects of charge trapping in insulating materials, by measuring the secondary electron emission (SEE) yield σ with a high precision (a few percent), as a function of energy, electron current density, and dose. The intrinsic secondary electron emission yield σ0 of uncharged MgO single crystals annealed at 1000 °C, 2 h, has been studied at four energies 1.1, 5, 15, and 30 keV on three different crystal orientations (100), (110), and (111). At low energies (1.1 and 5 keV) σ0 depends on the crystalline orientation wheras at high energies (30 keV) no differentiation occurs. It is shown that the value of the second crossover energy E2, for which the intrinsic SEE yield σ0=1, is extremely delicate to measure with precision. It is about 15 keV±500 eV for the (100) orientation, 13.5 keV±500 eV for the (110), and 18.5 keV±500 eV for the (111) one. At low current density J⩽105 pA/cm2, the variation of σ with the injected dose makes possible the observation of a self-regulated regime characterized by a steady value of the SEE yield σst=1. At low energies 1.1 and 5 keV, there is no current density effects in MgO, but at high energies ≈30 keV, apparent current density effects come from a bad collect of secondary electrons, due to very high negative surface potential. At 30 keV energy, an intense erratic electron exoemission was observed on the MgO (110) orientation annealed at 1500 °C. This phenomenon is the result of a disruptive process similar to flashover, which takes place at the surface of the material.

  12. Properties of YBCO on LaMnO3-capped IBAD MgO-templates without Homo-epitaxial MgO layer.

    SciTech Connect

    Aytug, Tolga; Paranthaman, Mariappan Parans; Kim, Kyunghoon; Zhang, Yifei; Cantoni, Claudia; Zuev, Yuri L; Goyal, Amit; Thompson, James R; Christen, David K

    2009-01-01

    Previously, it has been well established that in an IBAD architecture for coated conductors, (1) LaMnO3 (LMO) buffer layers are structurally and chemically compatible with an underlying homo-epitaxial MgO layer and (2) high current density YBCO films can be grown on these LMO templates. In the present work, the homo-epi MgO layer has been successfully eliminated and a LMO cap layer was grown directly on the IBAD (MgO) template. The performance of the LMO/IBAD (MgO) samples has been qualified by depositing 1 m-thick YBCO coatings by pulsed laser deposition. Electrical transport measurements of YBCO films on the standard (with homo-epi MgO) and simplified (without homo-epi MgO) IBAD architectures were carried out. The angular dependencies of critical current density (Jc) are similar for both IBAD architectures. XRD measurements indicate good, c-axis aligned YBCO films. Transmission electron microscopy (TEM) images reveal that microstructures of YBCO/LMO/IBAD (MgO) and YBCO/LMO/homo-epi MgO/IBAD (MgO) templates are similar. These results demonstrate the strong potential of using LMO as a single cap layer directly on IBAD (MgO) for the development of a simplified IBAD architecture.

  13. Effect of MgO and MnO on Phosphorus Utilization in P-Bearing Steelmaking Slag

    NASA Astrophysics Data System (ADS)

    Lin, Lu; Bao, Yan-Ping; Wang, Min; Li, Xiang

    2016-04-01

    In order to recycle the phosphorus in P-bearing converter slag and make it used as slag phosphate fertilizer, the effect of MgO and MnO in P-bearing steelmaking slag on phosphorus existence form, P2O5 solubility and magnetic separation behavior were researched systematically. The results show that the phosphorus in slag is mainly in the form of n2CaO · SiO2-3CaO · P2O5 (for short nC2S-C3P) solid solution in the P-rich phase for CaO-SiO2-FetO-P2O5-X (X stands for MgO and MnO, respectively). And the increasing of MgO and MnO content has no influence on precipitation of nC2S-C3P solid solution in slag, MnO and MgO mainly enter into RO phase and base phase to form MnFe2O4 and MgFe2O4, which has little effect on the P2O5 content of P-rich phase, so which has little effect on the degree of phosphorus enrichment and phosphorus occurrence form of the P-bearing slag. And adding MgO and MnO into CaO-SiO2-P2O5-Fe2O3 slag system can break the complex net structure formed by Si-O on certain degree, and also hinder the precipitation of β-Ca3(PO4)2 crystal with low citric acid solubility during the melting-cooling process. Therefore, adding appropriate MgO and MnO content into slag can improve the slag P2O5 solubility, but the effect of different amounts of MgO and MnO on the P2O5 solubility has little difference. Meanwhile, adding MgO and MnO into slag can improve the metallization of slag and magnetism of iron-rich phase, make the magnetic substances content increase and separation of phosphorus and iron incomplete, so it is adverse to phosphorus resources recovery from P-bearing slag by magnetic separation method. In order to recycle the phosphorus in P-bearing converter slag, the MgO and MnO content in the P-bearing slag should be controlled in the steelmaking process.

  14. Lattice dynamics of MgO at high pressure: theory and experiment.

    PubMed

    Ghose, Subrata; Krisch, Michael; Oganov, Artem R; Beraud, Alexandre; Bosak, Alexey; Gulve, Revansidha; Seelaboyina, Raghunandan; Yang, Hexiong; Saxena, Surendra K

    2006-01-27

    The longitudinal acoustic and optical phonon branches along the Gamma-X direction of MgO at 35 GPa have been determined by inelastic x-ray scattering using synchrotron radiation and a diamond-anvil cell. The experimentally observed phonon branches are in remarkable agreement with ab initio lattice dynamics results. The derived thermodynamic properties, such as the specific heat CV and the entropy S are in very good accord with values obtained from a thermodynamically assessed data set involving measured data on molar volume, heat capacity at constant pressure, bulk modulus and thermal expansion. PMID:16486728

  15. The emission of atoms and molecules accompanying fracture of single-crystal MgO

    NASA Technical Reports Server (NTRS)

    Dickinson, J. T.; Jensen, L. C.; Mckay, M. R.; Freund, F.

    1986-01-01

    The emission of particles due to deformation and fracture of materials has been investigated. The emission of electrons (exoelectron emission), ions, neutral species, photons (triboluminescence), as well as long wavelength electromagnetic radiation was observed; collectively these emissions are referred to as fractoemission. This paper describes measurements of the neutral emission accompanying the fracture of single-crystal MgO. Masses detected are tentatively assigned to the emission of H2, CH4, H2O, CO, O2, CO2, and atomic Mg. Other hydrocarbons are also observed. The time dependencies of some of these emissions relative to fracture are presented for two different loading conditions.

  16. Structure and Mobility of Defects Formed from Collision Cascades in MgO

    NASA Astrophysics Data System (ADS)

    Uberuaga, B. P.; Smith, R.; Cleave, A. R.; Montalenti, F.; Henkelman, G.; Grimes, R. W.; Voter, A. F.; Sickafus, K. E.

    2004-03-01

    We study radiation-damage events in MgO on experimental time scales by augmenting molecular dynamics cascade simulations with temperature accelerated dynamics, molecular statics, and density functional theory. At 400eV, vacancies and mono- and di-interstitials form, but often annihilate within milliseconds. At 2 and 5keV, larger clusters can form and persist. While vacancies are immobile, interstitials aggregate into clusters (In) with surprising properties; e.g., an I4 is immobile, but an im­pinging I2 can create a metastable I6 that diffuses on the nanosecond time scale but is stable for years.

  17. 8Li+ β-NMR in the Cubic Insulator MgO

    NASA Astrophysics Data System (ADS)

    MacFarlane, W. A.; Parolin, T. J.; Cortie, D. L.; Chow, K. H.; Hossain, M. D.; Kiefl, R. F.; Levy, C. D. P.; McFadden, R. M. L.; Morris, G. D.; Pearson, M. R.; Saadaoui, H.; Salman, Z.; Song, Q.; Wang, D.

    2014-12-01

    We present extensive high magnetic field β-NMR measurements of 8Li+ implanted in single crystals of MgO. The narrow resonance, consistent with a cubic 8Li+ site, likely the tetrahedral interstitital, is used routinely as a reference for shift measurements. We show the intrinsic linewidth is on the order of 200 Hz, allowing a frequency determination to an accuracy of a few Hz. We find no implantation energy dependence of the resonance within a few ppm, but there is evidence of slow spin dynamics in hole-burning measurements. The spin lattice relaxation is slow. The temperature dependence reveals interesting changes at low temperature whose origin remains uncertain.

  18. On nanoparticle surface growth: MgO nanoparticle formation during a Mg particle combustion

    NASA Astrophysics Data System (ADS)

    Altman, Igor S.; Agranovski, Igor E.; Choi, Mansoo

    2004-06-01

    It is demonstrated that formation of MgO nanoparticles during a Mg particle combustion occurs in the vapor adsorption regime and the particle coagulation and coalescence do not play any significant role in the process in question. Analysis of the particle size distributions shows that the rate of the nanoparticle condensation growth strongly depends on the actual particle size. The revealed dependence of the growth rate upon the size is consistent with the exponential law recently predicted. This finding can shed light on the long-standing general problem of gas-phase nanotechnology—the origin of lognormal size distribution behavior of generated nanoparticles.

  19. In situ investigation of the mobility of small gold clusters on cleaved MgO surfaces

    NASA Technical Reports Server (NTRS)

    Metois, J. J.; Heinemann, K.; Poppa, H.

    1976-01-01

    The mobility of small clusters of gold (about 10 A in diameter) on electron-beam-cleaved MgO surfaces was studied by in situ transmission electron microscopy under controlled vacuum and temperature conditions. During the first 10 min following a deposition at room temperature, over 10 per cent of the crystallites moved over short distances (about 20 A) discontinuously, with a velocity greater than 150 A/sec. Eighty per cent of the mobility events were characterized by the avoidance of proximity of other crystallites, and this was tentatively explained as the result of repulsive elastic forces between the interacting crystallites.

  20. Electric breakdown in ultrathin MgO tunnel barrier junctions for spin-transfer torque switching

    SciTech Connect

    Schaefers, M.; Drewello, V.; Reiss, G.; Thomas, A.; Thiel, K.; Eilers, G.; Muenzenberg, M.; Schuhmann, H.; Seibt, M.

    2009-12-07

    Magnetic tunnel junctions for spin-transfer torque (STT) switching are prepared to investigate the dielectric breakdown. Intact and broken tunnel junctions are characterized by transport measurements prior to transmission electron microscopy analysis. The comparison to our previous model for thicker MgO tunnel barriers reveals a different breakdown mechanism arising from the high current densities in a STT device: instead of local pinhole formation at a constant rate, massive electromigration and heating leads to displacement of the junction material and voids are appearing. This is determined by element resolved energy dispersive x-ray spectroscopy and three dimensional tomographic reconstruction.

  1. Atomically Resolved Site-Isolated Catalyst on MgO: Mononuclear Osmium Dicarbonyls formed from Os3(CO)12

    SciTech Connect

    Aydin, Ceren; kulkarni, Apoorva; Chi, Miaofang; Browning, Nigel D.; Gates, Bruce C.

    2012-01-01

    Supported triosmium clusters, formed from Os{sub 3}(CO){sub 12} on MgO, were treated in helium at 548 K for 2 h, causing fragmentation of the cluster frame and the formation of mononuclear osmium dicarbonyls. The cluster breakup and the resultant fragmented species were characterized by infrared and X-ray absorption spectroscopies, and the fragmented species were imaged by scanning transmission electron microscopy. The spectra identify the surface osmium complexes as Os(CO){sub 2}{l_brace}O{sub support}{r_brace}{sub n} (n = 3 or 4) (where the braces denote support surface atoms). The images show site-isolated Os atoms in mononuclear osmium species on MgO. The intensity analysis on the images of the MgO(110) face showed that the Os atoms were located atop Mg columns. This information led to a model of the Os(CO){sub 2} on MgO(110), with the distances approximated as those determined by EXAFS spectroscopy, which are an average over the whole MgO surface; the results imply that these complexes were located at Mg vacancies.

  2. Analysis of Waste Isolation Pilot Plan (WIPP) Underground and MGO Samples by the Savannah River National Laboratory (SRNL)

    SciTech Connect

    Young, J.; Ajo, H.; Brown, L.; Coleman, C.; Crump, S.; Diprete, C.; Diprete, D.; Ekechukwu, A.; Gregory, C.; Jones, M.; Missimer, D.; O'Rourke, P.; White, T.

    2014-12-31

    Analysis of the recent WIPP samples are summarized in this report; WIPP Cam Filters 4, 6, 9 (3, 7, 11 were analyzed with FAS-118 in a separate campaign); WIPP Drum Lip R16 C4; WIPP Standard Waste Box R15 C5; WIPP MgO R16 C2; WIPP MgO R16 C4; WIPP MgO R16 C6; LANL swipes of parent drum; LANL parent drum debris; LANL parent drum; IAEA Swipe; Unused “undeployed” Swheat; Unused “undeployed” MgO; and Masselin cloth “smears”. Analysis showed that the MgO samples were very pure with low carbonate and water content. Other samples showed the expected dominant presence of Mg, Na and Pb. Parent drum debris sample was mildly acidic. Interpretation of results is not provided in this document, but rather to present and preserve the analytical work that was performed. The WIPP Technical Analysis Team is responsible for result interpretation which will be written separately.

  3. Strain induced room temperature ferromagnetism in epitaxial magnesium oxide thin films

    SciTech Connect

    Jin, Zhenghe; Kim, Ki Wook; Nori, Sudhakar; Lee, Yi-Fang; Narayan, Jagdish; Kumar, D.; Wu, Fan; Prater, J. T.

    2015-10-28

    We report on the epitaxial growth and room-temperature ferromagnetic properties of MgO thin films deposited on hexagonal c-sapphire substrates by pulsed laser deposition. The epitaxial nature of the films has been confirmed by both θ-2θ and φ-scans of X-ray diffraction pattern. Even though bulk MgO is a nonmagnetic insulator, we have found that the MgO films exhibit ferromagnetism and hysteresis loops yielding a maximum saturation magnetization up to 17 emu/cc and large coercivity, H{sub c} = 1200 Oe. We have also found that the saturation magnetization gets enhanced and that the crystallization degraded with decreased growth temperature, suggesting that the origin of our magnetic coupling could be point defects manifested by the strain in the films. X-ray (θ-2θ) diffraction peak shift and strain analysis clearly support the presence of strain in films resulting from the presence of point defects. Based on careful investigations using secondary ion mass spectrometer and X-ray photoelectron spectroscopy studies, we have ruled out the possibility of the presence of any external magnetic impurities. We discuss the critical role of microstructural characteristics and associated strain on the physical properties of the MgO films and establish a correlation between defects and magnetic properties.

  4. Absence of low temperature phase transitions and enhancement of ferroelectric transition temperature in highly strained BaTiO{sub 3} epitaxial films grown on MgO Substrates

    SciTech Connect

    Kumar, Satish; Kumar, Dhirendra; Sathe, V. G.; Kumar, Ravi; Sharma, T. K.

    2015-04-07

    Recently, a large enhancement in the ferroelectric transition temperature of several oxides is reported by growing the respective thin films on appropriate substrates. This phenomenon is correlated with high residual strain in thin films often leading to large increase in the tetragonality of their crystal structure. However, such an enhancement of transition temperature is usually limited to very thin films of ∼10 nm thickness. Here, we report growth of fully strained epitaxial thin films of BaTiO{sub 3} of 400 nm thickness, which are coherently grown on MgO substrates by pulsed laser deposition technique. Conventional high resolution x-ray diffraction and also the reciprocal space map measurements confirm that the film is fully strained with in-plane tensile strain of 5.5% that dramatically increases the tetragonality to 1.05. Raman measurements reveal that the tetragonal to cubic structural phase transition is observed at 583 K, which results in an enhancement of ∼200 K. Furthermore, temperature dependent Raman studies on these films corroborate absence of all the low temperature phase transitions. Numerical calculations based on thermodynamical model predict a value of the transition temperature that is greater than 1500 °C. Our experimental results are therefore in clear deviation from the existing strain dependent phase diagrams.

  5. Magnetic Phase Formation in Self-Assembled Epitaxial BiFeO3-MgO and BiFeO3-MgAl2O4 Nanocomposite Films Grown by Combinatorial Pulsed Laser Deposition.

    PubMed

    Kim, Dong Hun; Sun, XueYin; Kim, Tae Cheol; Eun, Yun Jae; Lee, Taeho; Jeong, Sung Gyun; Ross, Caroline A

    2016-02-01

    Self-assembled epitaxial BiFeO3-MgO and BiFeO3-MgAl2O4 nanocomposite thin films were grown on SrTiO3 substrates by pulsed laser deposition. A two-phase columnar structure was observed for BiFeO3-MgO codeposition within a small window of growth parameters, in which the pillars consisted of a magnetic spinel phase (Mg,Fe)3O4 within a BiFeO3 matrix, similar to the growth of BiFeO3-MgFe2O4 nanocomposites reported elsewhere. Further, growth of a nanocomposite with BiFeO3-(CoFe2O4/MgO/MgFe2O4), in which the minority phase was grown from three different targets, gave spinel pillars with a uniform (Mg,Fe,Co)3O4 composition due to interdiffusion during growth, with a bifurcated shape from the merger of neighboring pillars. BiFeO3-MgAl2O4 did not form a well-defined vertical nanocomposite in spite of having lower lattice mismatch, but instead formed a two-phase film with in which the spinel phase contained Fe. These results illustrate the redistribution of Fe between the oxide phases during oxide codeposition to form a ferrimagnetic phase from antiferromagnetic or nonmagnetic targets. PMID:26750565

  6. Size-dependent structure of CdSe nanoclusters formed after ion implantation in MgO

    SciTech Connect

    Huis, M.A. van . E-mail: m.a.vanhuis@tnw.tudelft.nl; Veen, A. van; Schut, H.; Eijt, S.W.H.; Kooi, B.J.; Hosson, J.Th.M. de

    2005-03-01

    The band gap as well as the optical and structural properties of semiconductor CdSe nanoclusters change as a function of the nanocluster size. Embedded CdSe nanoclusters in MgO were created by means of sequential Cd and Se ion implantation followed by thermal annealing. Changes during annealing were monitored using optical absorption and positron annihilation spectroscopy. High-resolution TEM on cross-sections after annealing at a temperature of 1300 K showed that clusters with a size below 5 nm have the high-pressure rock-salt structure and are in a cube-on-cube orientation relation with MgO, whereas clusters larger than 5 nm adopt the stable wurtzite crystal structure and were observed in two different orientation relations with MgO.

  7. Damage accumulation in MgO irradiated with MeV Au ions at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Bachiller-Perea, Diana; Debelle, Aurélien; Thomé, Lionel; Behar, Moni

    2016-09-01

    The damage accumulation process in MgO single crystals under medium-energy heavy ion irradiation (1.2 MeV Au) at fluences up to 4 × 1014 cm-2 has been studied at three different temperatures: 573, 773, and 1073 K. Disorder depth profiles have been determined through the use of the Rutherford backscattering spectrometry in channeling configuration (RBS/C). The analysis of the RBS/C data reveals two steps in the MgO damage process, irrespective of the temperature. However, we find that for increasing irradiation temperature, the damage level decreases and the fluence at which the second step takes place increases. A shift of the damage peak at increasing fluence is observed for the three temperatures, although the position of the peak depends on the temperature. These results can be explained by an enhanced defect mobility which facilitates defect migration and may favor defect annealing. X-ray diffraction reciprocal space maps confirm the results obtained with the RBS/C technique.

  8. Annealing Effects on the Surface Plasmon of MgO Implanted with Gold

    NASA Technical Reports Server (NTRS)

    Ueda, A.; Mu, R.; Tung, Y. -S.; Henderson, D. O.; White, C. W.; Zuhr, R. A.; Zhu, Jane G.; Wang, P. W.

    1997-01-01

    Gold ion implantation was carried out with the energy of 1.1 MeV into (100) oriented MgO single crystal. Implanted doses are 1, 3, 6, 10 x 10(exp 16) ions/sq cm. The gold irradiation results in the formation of gold ion implanted layer with a thickness of 0.2 microns and defect formation. In order to form gold colloids from the as-implanted samples, we annealed the gold implanted MgO samples in three kinds of atmospheres: (1)Ar only, (2)H2 and Ar, and (3)O2 and Ar. The annealing over 1200 C enhanced the gold colloid formation which shows surface plasmon resonance band of gold. The surface plasmon bands of samples annealed in three kinds of atmospheres were found to be at 535 nm (Ar only), 524 nm(H2+Ar), and 560 nm (02+Ar), The band positions of surface plasmon can be reversibly changed by an additional annealing.

  9. Low-grade MgO used to stabilize heavy metals in highly contaminated soils.

    PubMed

    García, M A; Chimenos, J M; Fernández, A I; Miralles, L; Segarra, M; Espiell, F

    2004-08-01

    Low-grade MgO may be an economically feasible alternative in the stabilization of heavy metals from heavily contaminated soils. The use of MgO is described acting as a buffering agent within the pH 9-11 range, minimizing heavy metals solubility and avoiding the redissolution that occurs when lime is used. The effectiveness of LG-MgO has been studied as stabilizer agent of heavily polluted soils mainly contaminated by the flue-dust of the pyrite roasting. The use of LG-MgO as a reactive medium ensures that significant rates of metal fixation, greater than 80%, are achieved. The heavy metals leachate from the stabilized soil samples show a concentration lower than the limit set to classify the waste as non-special residue. Regardless of the quantity of stabilizer employed (greater than 10%), LG-MgO provides an alkali reservoir that allows guaranteeing long-term stabilization without varying the pH conditions. PMID:15212914

  10. Rhodium Complex with Ethylene Ligands Supported on Highly Dehydroxylated MgO: Synthesis, Characterization, and Reactivity

    SciTech Connect

    Bhirud,V.; Ehresmann, J.; Kletnieks, P.; Haw, J.; Gates, B.

    2006-01-01

    Mononuclear rhodium complexes with reactive olefin ligands, supported on MgO powder, were synthesized by chemisorption of Rh(C2H4)2(C5H7O2) and characterized by infrared (IR), {sup 13}C MAS NMR, and extended X-ray absorption fine structure (EXAFS) spectroscopies. IR spectra show that the precursor adsorbed on MgO with dissociation of acetylacetonate ligand from rhodium, with the ethylene ligands remaining bound to the rhodium, as confirmed by the NMR spectra. EXAFS spectra give no evidence of Rh-Rh contributions, indicating that site-isolated mononuclear rhodium species formed on the support. The EXAFS data also show that the mononuclear complex was bonded to the support by two Rh-O bonds, at a distance of 2.18 Angstroms, which is typical of group 8 metals bonded to oxide supports. This is the first simple and nearly uniform supported mononuclear rhodium-olefin complex, and it appears to be a close analogue of molecular catalysts for olefin hydrogenation in solution. Correspondingly, the ethylene ligands bonded to rhodium in the supported complex were observed to react with H{sub 2} to form ethane, and the supported complex was catalytically active for the ethylene hydrogenation at 298 K. The ethylene ligands also underwent facile exchange with C{sub 2}D{sub 4}, and exposure of the sample to carbon monoxide led to the formation of rhodium gem dicarbonyls.

  11. Dynamical simulations of radiation damage and defect mobility in MgO

    NASA Astrophysics Data System (ADS)

    Uberuaga, B. P.; Smith, R.; Cleave, A. R.; Henkelman, G.; Grimes, R. W.; Voter, A. F.; Sickafus, K. E.

    2005-03-01

    Collision cascades are investigated in MgO at energies ranging from 400eVto5keV . Initial energy is imparted to the principle knock-on atom in the lattice and the cascade development is tracked using classical molecular dynamics. Temperature accelerated dynamics is performed on representative defects to follow the behavior to experimental time scales. Molecular statics is used to calculate basic properties of these defects, while density functional theory calculations are used to verify the potential. In the cascades performed at the lowest energy, the lattice either reforms perfectly or, if residual defects remain, these consist of isolated interstitials and vacancies and charge-neutral Mg-O divacancies and di-interstitials. As the energy is increased to 5keV , isolated interstitials and di-interstitials remain the most common defects but more vacancy clustering can occur and interstitial defects consisting of up to seven atoms have been observed. Molecular statics calculations find that the binding energy per atom of the interstitial clusters increases from 3.5 to over 5eV as the size increases from 2 to 16 atoms. Long-time-scale dynamics reveal that vacancies essentially never move at room temperature but that some interstitial clusters can diffuse quickly. Although tetrainterstitial interstitial clusters are essentially immobile, there is a long-lived metastable state of the hexainterstitial that diffuses one dimensionally on the nanosecond time scale at room temperature.

  12. Tunneling Anisotropic Magnetoresistance in Fe Nanoparticles Embedded in MgO Matrix

    NASA Astrophysics Data System (ADS)

    Pham, T. V.; Miwa, S.; Suzuki, Y.

    2016-05-01

    The tunnel magnetoresistance (TMR) effect is related to the relative orientation of the magnetizations of the two ferromagnetic electrodes in magnetic tunnel junctions (MTJs). The tunnel anisotropic magnetoresistance (TAMR) effect is related to the orientation of the magnetization with respect to the current direction or the crystallographic axes. Beyond the TMR, the TAMR is not only present in MTJs in which both electrodes are ferromagnetic but may also appear in tunnel structures with a single magnetic electrode. We investigated the magnetotransport properties in an Au/MgO/Fe nanoparticles/MgO/Cu tunnel junction. We found that both the TMR and TAMR can appear in tunnel junctions with Fe nanoparticles embedded in an MgO matrix. The TMR is attributed to spin-dependent tunneling between Fe nanoparticles, so the device resistance depends on the magnetization directions of adjacent Fe nanoparticles. The TAMR is attributed to the interfacial spin-orbit interaction, so the device resistance depends on each magnetization direction of an Fe nanoparticle. This is the first observation of the TAMR in Fe nanoparticles embedded in an MgO matrix.

  13. Synthesis of MgO nanoparticle loaded mesoporous Al2O3 and its defluoridation study

    NASA Astrophysics Data System (ADS)

    Dayananda, Desagani; Sarva, Venkateswara R.; Prasad, Sivankutty V.; Arunachalam, Jayaraman; Parameswaran, Padmanabhan; Ghosh, Narendra N.

    2015-02-01

    MgO nanoparticle loaded mesoporous alumina has been synthesized using a simple aqueous solution based cost effective method for removal of fluoride from water. Wide angle powder X-ray diffraction, nitrogen adsorption desorption analysis, transmission electron microscopy techniques and energy dispersive X-ray spectroscopy were used to characterize the synthesized adsorbents. Synthesized adsorbents possess high surface area with mesoporous structure. The adsorbents have been thoroughly investigated for the adsorption of F- using batch adsorption method. MgO nanoparticle loading on mesoporous Al2O3 enhances the F- adsorption capacity of Al2O3 from 56% to 90% (initial F- concentration = 10 mg L-1). Kinetic study revealed that adsorption kinetics follows the pseudo-second order model, suggesting the chemisorption mechanism. The F- adsorption isotherm data was explained by both Langmuir and Freundlich model. The maximum adsorption capacity of 40MgO@Al2O3 was 37.35 mg g-1. It was also observed that, when the solutions having F- concentration of 5 mg L-1 and 10 mg L-1 was treated with 40MgO@Al2O3, the F- concentration in treated water became <1 mg L-1, which is well below the recommendation of WHO.

  14. Energy and Site Selectivity in O-Atom Photodesorption from Nanostructured MgO

    SciTech Connect

    Beck, Kenneth M.; Joly, Alan G.; Diwald, Oliver E.; Stankic, Slavica; Trevisanutto, P. E.; Sushko, Petr V.; Shluger, Alexander L.; Hess, Wayne P.

    2008-06-01

    Electronic excitation of wide gap ionic solids can induce desorption of neutral atoms with distinct hyperthermal and thermal kinetic energy distributions. Hyperthermal atomic desorption results from electronic surface excitation while thermal desorption is initiated primarily by bulk excitation. Calculations indicate that surface-localized transitions can be excited independently from bulk transitions using selected photon energies. The photon energy required to excite specific surface sites depends upon the site coordination with successively lower energies required to excite terrace, step, and corner sites. Here, we excite low-coordinated surface sites of nanostructured MgO samples using 4.7 eV UV laser pulses and observe dominant hyperthermal O-atom emission. We then selectively excite bulk sites of nanostructured MgO, using a 7.9 eV laser, and observe dominant thermal O-atom desorption. These results are analyzed in terms of laser desorption models developed previously for alkali halide crystals. We propose a multi-step mechanism for hyperthermal O-atom desorption, under surface selective excitation, based on hole trapping at 3C (corner) O-atom sites followed by exciton decomposition. The proposed “hole plus exciton” model has similarities to the surface exciton desorption model, established for alkali halides, but is more complex and requires more steps. Nonetheless, the principle of site-specific photoreaction, established for alkali halide crystals, is clearly extendable to a prototypical metal oxide.

  15. Theoretical characterization of divacancies at the surface and in bulk MgO

    NASA Astrophysics Data System (ADS)

    Ojamäe, Lars; Pisani, Cesare

    1998-12-01

    Two types of divacancy at the (001) surface of MgO are theoretically studied and compared with the corresponding defect in the bulk: the pit, where a surface magnesium and the oxygen ion underneath are removed, and the tub, where both removed ions are at the surface. All calculations have been performed by means of the EMBED program which adopts an embedded-cluster approach in the frame of the Hartree-Fock (HF) approximation [C. Pisani F. Corà, R. Nada, and R. Orlando, Comput. Phys. Commun. 82, 139 (1994); C. Pisani and U. Birkenheuer, ibid. 96, 152 (1996)]; the semi-infinite host crystal for the study of the surface defects has been simulated with a four-layer slab. The energy released on formation of the divacancy from the two charged isolated vacancies is very high, almost 300 kcal/mol. The tub divacancy is the most stable, both as a neutral and as a singly charged defect. For the paramagnetic center (one electron trapped in the cavity), spin density data are provided and discussed with reference to results from electron paramagnetic resonance experiments and molecular cluster calculations [E. Giamello M. C. Paganini, D. Murphy, A. M. Ferrari, and G. Pacchioni, J. Phys. Chem. 101, 971 (1997)]. It is suggested that the tub divacancy is a common defect, if not the most common, at the highly dehydrated MgO surface.

  16. Dynamical simulations of radiation damage and defect mobility in MgO

    SciTech Connect

    Uberuaga, B.P.; Smith, R.; Henkelman, G.; Voter, A.F.; Sickafus, K.E.; Cleave, A.R.; Grimes, R.W.

    2005-03-01

    Collision cascades are investigated in MgO at energies ranging from 400 eV to 5 keV. Initial energy is imparted to the principle knock-on atom in the lattice and the cascade development is tracked using classical molecular dynamics. Temperature accelerated dynamics is performed on representative defects to follow the behavior to experimental time scales. Molecular statics is used to calculate basic properties of these defects, while density functional theory calculations are used to verify the potential. In the cascades performed at the lowest energy, the lattice either reforms perfectly or, if residual defects remain, these consist of isolated interstitials and vacancies and charge-neutral Mg-O divacancies and di-interstitials. As the energy is increased to 5 keV, isolated interstitials and di-interstitials remain the most common defects but more vacancy clustering can occur and interstitial defects consisting of up to seven atoms have been observed. Molecular statics calculations find that the binding energy per atom of the interstitial clusters increases from 3.5 to over 5 eV as the size increases from 2 to 16 atoms. Long-time-scale dynamics reveal that vacancies essentially never move at room temperature but that some interstitial clusters can diffuse quickly. Although tetrainterstitial interstitial clusters are essentially immobile, there is a long-lived metastable state of the hexainterstitial that diffuses one dimensionally on the nanosecond time scale at room temperature.

  17. Ab Initio Modeling of Transition-Metal Impurities in MgO

    NASA Astrophysics Data System (ADS)

    Levchenko, Sergey V.; Alarcon Villaseca, Sebastian; Mazheika, Aliaksei; Scheffler, Matthias

    Fe- and Ni-doped MgO are promising materials for the catalytic conversion of methane and CO2. However, theoretical studies of these materials are scarce. The self-interaction error (SIE) in approximate DFT leads to an incorrect description of the electron localization and hybridization between d states of Ni or Fe and the oxide electronic bands. Replacing a fraction α of the (semi-)local exchange by the exact exchange reduces the SIE, but α remains a parameter depending on the target property. We explore the dependence of the formation energies of NiMg and FeMg substitutional defects in MgO on α in the Heyd-Scuseria-Ernzerhof hybrid functional (HSE), and compare the results to CCSD(T) embedded-cluster calculations. For NiMg defects HSE(α = 0.3) reproduces CCSD(T) formation energies and CO adsorption energies on NiMg. However, α = 0.48 is needed in the case of FeMg. For both NiMg and FeMg, α = 0.44-0.50 satisifies best the exact DFT condition that the HOMO does not depend on occupation. Contrary to PBE and HSE06, HSE(α ~ 0.5) reproduces the experimentally observed Oh -->D4 h (oblate) Jahn-Teller distortion for FeMg. We thank CoE UniCat for financial support.

  18. Measurement of FeO activity and solubility of MgO in smelting slags

    NASA Astrophysics Data System (ADS)

    Liu, Shih-Hsien; Fruehan, R. J.; Morales, A.; Ozturk, B.

    2001-02-01

    In bath smelting, the FeO activity of the slag must be known to predict the equilibrium of slag-metal reactions and for effective control of the rate of reduction in the system. Also, knowledge of the solubility of MgO in these slags is useful for reducing refractory consumption. A series of measurements of the FeO activity in simulated bath smelting slags (CaO-SiO2-Al2O3-MgOsat-FeO) were conducted by the electromotive force (EMF) technique. The influence of the slag composition on the relationship between the FeO activity coefficient and FeO content was studied. It has been found that the measured FeO activity coefficient decreases with increasing FeO content in the slag and increases slightly with increasing slag basicity, which is defined as (CaO + MgO)/(SiO2 + Al2O3) on a mole fraction basis. The measured values of the FeO activity coefficient are in reasonable agreement with previously published data. The solubility of MgO was also measured and found to rang from 16 to 30 pct and decrease with increasing basicity.

  19. Strong electric fields at a prototypical oxide/water interface probed by ab initio molecular dynamics: MgO(001).

    PubMed

    Laporte, Sara; Finocchi, Fabio; Paulatto, Lorenzo; Blanchard, Marc; Balan, Etienne; Guyot, François; Saitta, Antonino Marco

    2015-08-21

    We report a density-functional theory (DFT)-based study of the interface of bulk water with a prototypical oxide surface, MgO(001), and focus our study on the often-overlooked surface electric field. In particular, we observe that the bare MgO(001) surface, although charge-neutral and defectless, has an intense electric field on the Å scale. The MgO(001) surface covered with 1 water monolayer (1 ML) is investigated via a supercell accounting for the experimentally-observed (2 × 3) reconstruction, stable at ambient temperature, and in which two out of six water molecules are dissociated. This 1 ML-hydrated surface is also found to have a high, albeit short-ranged, normal component of the field. Finally, the oxide/water interface is studied via room-temperature ab initio molecular dynamics (AIMD) using 34 H2O molecules between two MgO(001) surfaces. To our best knowledge this is the first AIMD study of the MgO(001)/liquid water interface in which all atoms are treated using DFT and including several layers above the first adsorbed layer. We observe that the surface electric field, averaged over the AIMD trajectories, is still very strong on the fully-wet surface, peaking at about 3 V Å(-1). Even in the presence of bulk-like water, the structure of the first layer in contact with the surface remains similar to the (2 × 3)-reconstructed ice ad-layer on MgO(001). Moreover, we observe proton exchange within the first layer, and between the first and second layers - indeed, the O-O distances close to the surface are found to be distributed towards shorter distances, a property which has been shown to directly promote proton transfer. PMID:26193818

  20. Shape and size of crystalline MgO particles formed by the decomposition of Mg(OH)/sub 2/

    SciTech Connect

    Dahmen,; Kim, M.G.; Searcy, A.W.

    1988-08-01

    Decomposition of Mg(OH)/sub 2/ at 300/sup 0/ to 400/sup 0/C yields MgO crystals with often unequal edge lengths which, from counting of crystal planes in high-resolution transmission electron micrographs, range from 0.8 to 2.4 nm, in agreement with conclusions of Moodie and Warble. Optical diffractograms and electron diffraction patterns yield concordant results. An origin for discordant X-ray diffraction estimates of particle size for MgO produced from Mg(OH)/sub 2/ in the same temperature range is suggested.

  1. Preparation of anisotropic magnetic FeNiPt2 films on MgO(001): Atomistic mechanisms for the interdiffusion of two L10 phases

    NASA Astrophysics Data System (ADS)

    Montsouka, R. V. P.; Goyhenex, C.; Schmerber, G.; Ulhaq-Bouillet, C.; Derory, A.; Faerber, J.; Arabski, J.; Pierron-Bohnes, V.

    2006-10-01

    L10 -ordered FeNiPt2(001) thin films were prepared by the interdiffusion of FePt(001) and NiPt(001) layers codeposited on MgO(001) substrates by molecular beam epitaxy (MBE). A large uniaxial magnetic anisotropy (Ku=9.105J/m3) and a reduced magnetic transition temperature (Tc=400K) were obtained. Growth at 700K and a first annealing at 800K result in a large long-range order parameter reflecting the concentration modulation along the growth direction. This high long-range order parameter is conserved in the FeNiPt2 layers after interdiffusion at 900K , contrary to what is expected from a simple vacancy migration process. This experimental observation can be explained either by a 6-jump cycle mechanism or by the alternate diffusion of a double vacancy, which are both favored energetically over a second-nearest-neighbor jump mechanism or the simultaneous diffusion of a double vacancy as shown by quenched molecular dynamics simulations.

  2. Thin Clouds

    Atmospheric Science Data Center

    2013-04-18

    ... of this montage is a natural-color view of the Caribbean Sea east of the Yucatan Peninsula as seen by MISR's most steeply ... - Thin, feathery clouds of ice crystals over the Caribbean Sea. project:  MISR category:  gallery ...

  3. Evaluation of Heterogeneous Options: Effects of MgO versus UO2 Matrix Selection for Minor Actinide Targets in a Sodium Fast Reactor

    SciTech Connect

    M. Pope; S. Bays; R. Ferrer

    2008-03-01

    The primary focus of this work was to compare MgO with UO2 as target matrix material options for burning minor actinides in a transmutation target within a sodium fast reactor. This analysis compared the transmutation performance of target assemblies having UO2 matrix to those having specifically MgO inert matrix.

  4. Study on initial current leakage spots in CoFeB-capped MgO tunnel barrier by conductive atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Sato, Soshi; Honjo, Hiroaki; Ikeda, Shoji; Ohno, Hideo; Endoh, Tetsuo; Niwa, Masaaki

    2016-04-01

    Although a microscopic study on a MgO tunnel barrier by atomic force microscopy has been required to study the reliability of magnetic tunnel junctions, the deterioration of bare MgO due to the adsorption of H2O and CO2 has been a problem. For an accurate evaluation of the initial current leakage spots distributed in a MgO tunnel barrier, a CoFeB-capped MgO tunnel barrier structure is proposed for evaluation by means of conductive atomic force microscopy. The CoFeB capping layer thickness was optimized to be 2.0 nm to prevent H2O and CO2 adsorption on the MgO and to minimize the series resistance due to the capping layer. The initial current leakage spot density of the MgO tunnel barrier with the optimized CoFeB capping layer exponentially increased as the thickness of the MgO tunnel barrier decreased from 1.6 to 0.8 nm, and was 157 spots/µm2 at the MgO thickness of 1.2 nm and the bias voltage of 0.5 V.

  5. Microwave losses in MgO, LaAlO3, and (La0.3Sr0.7)(Al0.65Ta0.35)O3 dielectrics at low power and in the millikelvin temperature range

    NASA Astrophysics Data System (ADS)

    Arzeo, M.; Lombardi, F.; Bauch, T.

    2014-05-01

    We have investigated both the temperature and the power dependence of microwave losses for various dielectrics commonly used as substrates for the growth of high critical temperature superconductor thin films. We present measurement of niobium superconducting λ/2 coplanar waveguide resonators, fabricated on MgO, LaAlO3, and (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT), at the millikelvin temperature range and at low input power. By comparing our results with the two-level system model, we have discriminated among different dominant loss mechanisms. LSAT has shown the best results as regards the dielectric losses in the investigated regimes.

  6. Chemical Solution Derived Planarization Layers for Highly Aligned IBAD MgO Templates

    SciTech Connect

    Paranthaman, Mariappan Parans; Aytug, Tolga; Stan, Liliana; Jia, Quanxi; Cantoni, Claudia; Wee, Sung Hun

    2014-01-01

    The main goal of this research is to develop a chemical solution derived planarization layer to fabricate highly aligned IBAD-MgO templates for the development of high temperature superconductor (HTS) based coated conductors. The standard IBAD-MgO template needs an additional electrochemical polishing step of the mechanically polished 50- m-thick Hastelloy C-276 substrates to ensure a flat and smooth surface for subsequent growth of multi-layer buffer architectures, which include: sputtered 80-nm Al2O3; sputtered 7-nm Y2O3; IBAD 10-nm MgO; sputtered 30-nm homo-epi MgO; and sputtered 30-nm LaMnO3 (LMO) layers. We have successfully developed a solution planarization layer that removes the electrochemical polishing step and also acts as a barrier layer. Crack-free, smooth Al2O3 layers were prepared on mechanically polished Hastelloy substrates using a chemical solution process. A nearly 10-15-nm thick Al2O3 layer was formed with each coating and the coating was repeated several times to achieve the desired film thickness with intermediate heat-treatments after each coating. The Al2O3 planarization layer significantly reduced the surface roughness of the substrate. The average surface roughness value, Ra for a starting substrate was 9-10 nm. After 8 coatings of Al2O3 layer, the Ra was reduced to 2 nm. Highly aligned IBAD-MgO layers with out-of-plane and in-plane textures comparable to the standard IBAD-MgO layers were successfully deposited on top of the solution planarization Al2O3 layers with an Y2O3 nucleation layer using a reel-to-reel ion-beam sputtering system. Both homo-epi MgO and LMO layers were subsequently deposited on the IBAD-MgO layers using rf sputtering to complete the buffer stack required for the growth of HTS films. YBa2Cu3O7- (YBCO) films with a thickness of 0.8 m deposited on these IBAD-MgO templates by pulsed laser deposition showed a high self-field critical current density, Jc of 3.04 MA/cm2 at 77 K and 6.05 MA/cm2 at 65 K. These results

  7. Thin-film perovskites-ferroelectric materials for integrated optics

    SciTech Connect

    Walker, F.J. |; McKee, R.A.

    1995-12-31

    Optical guided wave (OGW) devices, based on LiNbO{sub 3} or GaAs. are commercially available products with established markets and applications. While LiNbO{sub 3} presently dominates the commercial applications, there are several drivers for the development of improved electro-optic (EO) materials. If the appropriate crystal quality could be obtained for thin-film BaTiO{sub 3} supported on MgO for example, or for an integrated BaTiO{sub 3}/Mg0 structure on silicon or GaAs, then the optimum OGW device structure might be realized. We report on our results for the growth of optical quality, epitaxial BaTiO{sub 3} and SrTiO{sub 3} on single-crystal MgO substrates using source shuttering molecular beam epitaxy (MBE) techniques. We also discuss how these materials can be integrated onto silicon. Our MBE studies show that, for this important class of perovskite oxides, heteroepitaxy between the perovskites and alkaline earth oxides is dominated by interfacial electrostatics at the first atomic layers. We have been able to demonstrate that a layer-by-layer energy minimization associated with interfacial electrostatics leads to the growth of high quality thin films of these materials. We have fabricated waveguides from these materials, and the optical clarity and loss coefficients have been characterized and found to be comparable to in-diffused waveguide structures typically represented by Ti drifted LiNbO{sub 3}.

  8. Substrate dependent structural and magnetic properties of pulsed laser deposited Fe3O4 thin films.

    PubMed

    Goyal, Rajendra N; Kaur, Davinder; Pandey, Ashish K

    2010-12-01

    Nanocrystalline iron oxide thin films have been deposited on various substrates such as quartz, MgO(100), and Si(100) by pulsed laser deposition technique using excimer KrF laser (248 nm). The orientations, crystallite size and lattice parameters were studied using X-ray diffraction. The XRD results show that the films deposited on MgO and Si substrates are highly oriented and show only (400) and (311) reflections respectively. On the other hand, the orientation of the films deposited on quarts substrate changed from (311) to (400) with an increase in the substrate temperature from 400 degrees C to 600 degrees C, indicating thereby that the film growth direction is highly affected with nature of substrate and substrate temperature. The surface morphology of the deposited films was studied using Atomic Force Microscopy (AFM) and spherical ball like regular features of nanometer size grains were obtained. The magnetic properties were studied by Superconducting Quantum Interference Device (SQUID) magnetometer in the magnetic field +/- 6 Tesla. The magnetic field dependent magnetization (M-H) curves of all the Fe3O4 thin films measured at 5 K and 300 K show the ferrimagnetic nature. The electrochemical sensing of dopamine studied for these films shows that the film deposited on MgO substrate can be used as a sensing electrode. PMID:21121292

  9. Self-healing of drying shrinkage cracks in cement-based materials incorporating reactive MgO

    NASA Astrophysics Data System (ADS)

    Qureshi, T. S.; Al-Tabbaa, A.

    2016-08-01

    Excessive drying shrinkage is one of the major issues of concern for longevity and reduced strength performance of concrete structures. It can cause the formation of cracks in the concrete. This research aims to improve the autogenous self-healing capacity of traditional Portland cement (PC) systems, adding expansive minerals such as reactive magnesium oxide (MgO) in terms of drying shrinkage crack healing. Two different reactive grades (high ‘N50’and moderately high ‘92–200’) of MgO were added with PC. Cracks were induced in the samples with restraining end prisms through natural drying shrinkage over 28 days after casting. Samples were then cured under water for 28 and 56 days, and self-healing capacity was investigated in terms of mechanical strength recovery, crack sealing efficiency and improvement in durability. Finally, microstructures of the healing materials were investigated using FT-IR, XRD, and SEM-EDX. Overall N50 mixes show higher expansion and drying shrinkage compared to 92–200 mixes. Autogenous self-healing performance of the MgO containing samples were much higher compared to control (only PC) mixes. Cracks up to 500 μm were sealed in most MgO containing samples after 28 days. In the microstructural investigations, highly expansive Mg-rich hydro-carbonate bridges were found along with traditional calcium-based, self-healing compounds (calcite, portlandite, calcium silicate hydrates and ettringite).

  10. ME μSR study of MgO: Search for O-1 Earthquake-like Precursors

    NASA Astrophysics Data System (ADS)

    Welch, G.; Lee, S. B.; Johnson, C. E.; Love, A.; Boekema, C.; Freund, F. T.

    2014-03-01

    While many precursory signals of earthquakes are known to exist, interpretation of these signals is inadequately understood. Earthquake-like precursor effects are detected by studying the signals generated by positive holes in MgO using Muon-Spin Resonance (μSR) and Maximum Entropy (ME). As an abundant earth-crust compound, MgO is an ideal model for studying eartquake-like signals. Positive hole formation results from a break in an oxygen anion pair under elevated temperature, or high stress conditions. For a 3N-MgO single crystal at elevated temperatures, a small percentage of oxygen is predicted to be in an O-1 state instead of normal O-2 ions. Preliminary ME analysis of transverse field (100 Oe) μSR MgO data show asymmetrical ME peaks at ~ 1.4 MHz. Small T-dependent deviations from a Lorentzian (Lor) signal seem to be effects of O-1 states in MgO. Tentatively, we have fitted ME transforms with three Lor's to obtain a reasonable description of the 1.4-MHz peak. The T dependences of this 3-Lor set are reported and discussed. Research is supported by RSCA-SJSU, SETI, WiSE@SJSU and AFC San Jose.

  11. Charge modulation of magnetization in X-doped MgO nanotube clusters (X=C, N)

    NASA Astrophysics Data System (ADS)

    Wang, Su-Fang; Chen, Li-Yong; Zhang, Tao; Xie, You

    2016-02-01

    First-principles calculations based on density functional theory are performed to study the magnetic and electronic properties of X-doped 8×7 MgO nanotube clusters (X=C, N). The N dopant easily occupies the O-site at the edge of MgO nanotube, embracing neutral or charged defect state, and induces notable magnetization in N-doped MgO tubular cluster. More important, this p-electron magnetization can be significantly modulated as the charged state of the defect changes. Regarding C doping, impurity atom readily substitute the Mg atom located at the edge of MgO nanotube to form neutral defect, and net magnetization is found to be zero. The calculated electron densities of states show that the O-site N doping at the edge greatly narrows or even destroys band-gap, while it enlarges somewhat for the Mg-site C doping at the edge. The results are likely to stimulate a promising class of materials for various applications ranging from spintronics to magneto-optics.

  12. Adsorption of NO on Au atoms and dimers supported on MgO(1 0 0): DFT studies

    NASA Astrophysics Data System (ADS)

    Fuente, Silvia A.; Belelli, Patricia G.; Ferullo, Ricardo M.; Castellani, Norberto J.

    2008-05-01

    The adsorption of NO on single gold atoms and Au 2 dimers deposited on regular O 2- sites and neutral oxygen vacancies (F s sites) of the MgO(1 0 0) surface have been studied by means of DFT calculations. For Au 1/MgO the adsorption of NO is stronger when the Au atom is supported on an anionic site than when it is on a F s site, with adsorption binding energies of 1.1 and 0.5 eV, respectively. In the first case the spin density is mainly concentrated on the metal atom and protruding from the surface. In such a way, an active site against radicals such as NO is generated. On the F s site, the presence of the vacancy delocalizes the spin into the substrate, weakening its coupling with NO. For Au 2/MgO, as this system has a closed-shell configuration, the NO molecules bonds weakly with Au 2. Regarding the N-O stretching frequencies, a very strong shift of ˜340-400 cm -1 to lower frequencies is observed for Au 1/MgO in comparison with free NO.

  13. Interaction of NO with Au nanoparticles supported on (100) terraces and topological defects of MgO

    NASA Astrophysics Data System (ADS)

    Fuente, Silvia A.; Ferullo, Ricardo M.; Domancich, Nicolás F.; Castellani, Norberto J.

    2011-01-01

    The adsorption of nitric oxide (NO) on Au n (n = 1-3) particles deposited on anionic (O 2-) sites of MgO has been studied using the DFT (Density Functional Theory) approach. The regular O 2- sites of MgO(100) and the sites in edge and corner topological defects with high symmetry of MgO were considered. The adhesion energy of Au n to MgO is larger for Au 2 and Au 3 due to higher polarization effects. On the other hand, the interaction strength of NO with supported Au n particles depends mainly on the electronic configuration (open or closed shell) of the particle; the Au particles with odd number of atoms show larger NO binding energies. A comparison was performed with the reactivity of free Au n particles. From this, it is possible to conclude that the support enhances the NO-Au n bonding strength for the monomer, weakens this interaction in the case of the dimer, and does not have an effect in the trimers. Besides, the NO-Au n bonding is essentially insensitive to the coordination of the anionic site where the Au n particle is linked. A large red-shift of the N-O stretching frequency was obtained, particularly for the Au particles with odd number of atoms, due to a negative charge transfer from Au to NO.

  14. Characterization of the MgO2+ dication in the gas phase: electronic states, spectroscopy and atmospheric implications.

    PubMed

    Linguerri, R; Hochlaf, M; Bacchus-Montabonel, M-C; Desouter-Lecomte, M

    2013-01-21

    Franzreb and Williams at Arizona State University detected recently the MgO(2+) molecular species in the gas phase. Here we report a very detailed theoretical investigation of the low-lying electronic states of this dication including their potentials, spin-orbit, rotational and radial couplings. Our results show that the potential energy curves of the dicationic electronic states have deep potential wells. This confirms that this dication does exist in the gas phase; it is a thermodynamically stable molecule in its ground state, and it has several excited long-lived metastable states. The potential energy curves are used then to predict a set of spectroscopic parameters for the bound states of MgO(2+). We have also incorporated these potentials, rotational and radial couplings in dynamical calculations to derive the cross sections for the charge transfer Mg(2+) + O → Mg(+) + O(+) reaction in the 1-10(3) eV collision energy domain via formation-decomposition of the MgO(2+) dication. Our work shows the role of MgO(2+) in the Earth ionosphere and more generally in atmospheric processes in solar planets, where this reaction efficiently participates in the predominance of Mg(+) cations in these media compared to Mg and Mg(2+). PMID:23202808

  15. MgO melting curve constraints from shock temperature and rarefaction overtake measurements in samples preheated to 2300 K

    NASA Astrophysics Data System (ADS)

    Fat'yanov, O. V.; Asimow, P. D.

    2014-05-01

    Continuing our effort to obtain experimental constraints on the melting curve of MgO at 100-200 GPa, we extended our target preheating capability to 2300 K. Our new Mo capsule design holds a long MgO crystal in a controlled thermal gradient until impact by a Ta flyer launched at up to 7.5 km/s on the Caltech two-stage light-gas gun. Radiative shock temperatures and rarefaction overtake times were measured simultaneously by a 6-channel VIS/NIR pyrometer with 3 ns time resolution. The majority of our experiments showed smooth monotonic increases in MgO sound speed and shock temperature with pressure from 197 to 243 GPa. The measured temperatures as well as the slopes of the pressure dependences for both temperature and sound speed were in good agreement with those calculated numerically for the solid phase at our peak shock compression conditions. Most observed sound speeds, however, were ~800 m/s higher than those predicted by the model. A single unconfirmed data point at 239 GPa showed anomalously low temperature and sound speed, which could both be explained by partial melting in this experiment and could suggest that the Hugoniot of MgO preheated to 2300 K crosses its melting line just slightly above 240 GPa.

  16. Relationship between characteristic length and average grain size in nanosize MgO added Bi-2212 superconductor ceramics

    NASA Astrophysics Data System (ADS)

    Hamid, N. A.; Asbullah, M. S. N.; Yahya, S. Y. S.; Hashim, A.

    2012-09-01

    In the present work, Bi2Sr2CaCu2O8 (Bi-2212)/MgO compound was prepared using the conventional solid-state reaction method. The powder of nanosize MgO particles was added to Bi-2212 superconductor with weight percentage of 3%, 5%, and 8%, respectively. The compound was sintered for 48 hours at 855°C in air. Besides the existence of a small amount of impurity phases, all the samples showed the Bi-2212 phase as the dominant phase. The temperature dependence of transport current density (Jc) in zero magnetic fields for each sample was measured from 40 K to transition temperature (Tc). It was found that the Jc value decreased with increasing temperature and this showed the consequence of thermal activated flux creep. Using the self-field approximation together with Jc dependence on temperature, we estimated that the characteristic length (Lc) associated with the pinning force is approximately the same as the average grain size (Rg) for the non-added sample and for sample with 8% nanosize MgO addition. In contrast, for samples with 3% and 5% addition, the results showed that Lc < Rg. This indicates that addition of 3% to 5% of nanosize MgO particles provides the optimum flux pinning centers for Bi-2212 superconductor ceramics.

  17. Elasticity of MgO to 11 GPa with an independent absolute pressure scale: Implications for pressure calibration

    SciTech Connect

    Li, B.; Woody, K; Kung, J

    2006-01-01

    P and S wave velocities and unit cell parameters (density) of MgO are measured simultaneously up to 11 GPa using combined ultrasonic interferometry and in situ X-ray diffraction techniques. The elastic bulk and shear moduli as well as their pressure derivatives are obtained by fitting the measured velocity and density data to the third-order finite strain equations, yielding K0S = 163.5(11) GPa, K'0S = 4.20(10), G0 = 129.8(6) GPa, and G'0 = 2.42(6), independent of pressure. These properties are subsequently used in a Birch-Murnaghan equation of state to determine the sample pressures at the observed strains. Comparison of the 300K isothermal compression of MgO indicates that current pressure scales from recent studies are in better than 1.5% agreement. We find that pressures derived from secondary pressure standards (NaCl, ruby fluorescence) at 300K are lower than those from current MgO scales by 5-8% ({approx}6% on average) in the entire pressure range of the current experiment. If this is taken into account, discrepancy in previous static compression studies on MgO at 300K can be reconciled, and a better agreement with the present study can be achieved.

  18. Site-isolated Iridium Complexes on MgO Powder: Individual Ir Atoms Imaged by Scanning Transmission Electron Microscopy

    SciTech Connect

    Uzun, A.; Ortalan, V; D. Browning, N; C. Gates , B

    2009-01-01

    Iridium complexes were synthesized on MgO powder by adsorption of Ir(C{sub 2}H{sub 4}){sub 2}(acac) [acac = acetonylacetonate]; images determined by aberration-corrected scanning transmission electron microscopy show individual Ir atoms, demonstrating that the supported complexes were site-isolated.

  19. Methylglyoxal (MGO) inhibits proliferation and induces cell death of human glioblastoma multiforme T98G and U87MG cells.

    PubMed

    Paul-Samojedny, Monika; Łasut, Barbara; Pudełko, Adam; Fila-Daniłow, Anna; Kowalczyk, Małgorzata; Suchanek-Raif, Renata; Zieliński, Michał; Borkowska, Paulina; Kowalski, Jan

    2016-05-01

    Glioblastoma multiforme (GBM) is the most malignant and invasive human brain tumor and it is characterized by a poor prognosis and short survival time. Current treatment strategies for GBM using surgery, chemotherapy and/or radiotherapy are ineffective. Thus new therapeutic strategies to target GBM are urgently needed. The effect of methylglyoxal (MGO) on the cell cycle, cell death and proliferation of human GBM cells was investigated. The T98G and U87MG cell lines were cultured in modified EMEM supplemented with 10% fetal bovine serum and maintained at 37°C in a humidified atmosphere of 5% CO2 in air. Cells were exposed to methylglyoxal (0.025mM) per 72h. The influence of MGO on T98G and U87MG cell cycle, proliferation and apoptosis was evaluated as well. Cell cycle phase distribution, proliferation, apoptosis were analyzed by flow cytometry. MGO causes changes in cell cycle and induces accumulation of G1/G0-phase cells and reduced fraction of cells in S and G2/M phases. We have also observed inhibition of cell proliferation and induction of apoptosis in cancer cells. We have also revealed that MGO induces senescence of U87MG but not T98G cells, but further studies are necessary in order to clarify and check mechanism of action of methylglyoxal and it Is a positive phenomenon for the treatment of GBM. PMID:27133062

  20. Using Variable Temperature Powder X-Ray Diffraction to Determine the Thermal Expansion Coefficient of Solid MgO

    ERIC Educational Resources Information Center

    Corsepius, Nicholas C.; DeVore, Thomas C.; Reisner, Barbara A.; Warnaar, Deborah L.

    2007-01-01

    A laboratory exercise was developed by using variable temperature powder X-ray diffraction (XRD) to determine [alpha] for MgO (periclase)and was tested in the Applied Physical Chemistry and Materials Characterization Laboratories at James Madison University. The experiment which was originally designed to provide undergraduate students with a…

  1. Polarization reversal induced by heating-cooling cycles in MgO doped lithium niobate crystals

    NASA Astrophysics Data System (ADS)

    Shur, V. Ya.; Mingaliev, E. A.; Lebedev, V. A.; Kuznetsov, D. K.; Fursov, D. V.

    2013-05-01

    Polarization reversal during heating-cooling cycles was investigated in MgO doped lithium niobate (MgO:LN) crystal using piezoresponse force microscopy. The essential dependence of the domain structure evolution scenario on the maximal temperature in the cycle has been revealed experimentally. It has been shown that the heating of the engineered domain matrix from room temperature to 85 °C leads to light size reduction of the isolated domains at the matrix edges, whereas the heating to 170 °C leads to essential reduction of the domain size. The opposite strong effect of the domain formation and growth during cooling after pulse heating have been revealed in single domain MgO:LN. The simulation of the time dependence of the pyroelectric field during heating-cooling cycle allowed to reveal the temperature hysteresis and to explain all observed effects taking into account the temperature dependence of the bulk conductivity.

  2. Optical, scintillation and dosimeter properties of MgO translucent ceramic doped with Cr3+

    NASA Astrophysics Data System (ADS)

    Kato, Takumi; Okada, Go; Yanagida, Takayuki

    2016-04-01

    We have investigated the photoluminescence (PL), scintillation and thermally-stimulated luminescence (TSL) dosimeter properties of MgO translucent ceramic doped with Cr3+ ion (0.001, 0.01 and 0.1%). The ceramic samples were synthesized by a Spark Plasma Sintering (SPS) technique. The broad and sharp emission peaks appeared around 600-850 nm in all the samples. The PL decay time constants of all the samples were a few ms which were on the typical order of Cr3+ doped phosphors. As with the PL, the peak resulted from Cr3+ ion was detected in the scintillation spectra. The TSL glow curves showed the main peak around 140 °C. The TSL response was confirmed to be linear to the irradiation dose over the dose range from 0.1 to 1000 mGy.

  3. Wavelength selective excitation of surface oxygen anions on highly dispersed MgO

    NASA Astrophysics Data System (ADS)

    Diwald, Oliver; Sterrer, Martin; Knözinger, Erich; Sushko, Peter V.; Shluger, Alexander L.

    2002-01-01

    Monochromatic UV light in the spectral interval between 4.0 and 5.5 eV is used in order to selectively excite 3- and 4-coordinated oxygen anion sites on the surface of MgO nanoparticles exposed to O2 gas. As a result, two different paramagnetic O- surface species and also ozonide anions O3- are observed by electron paramagnetic resonance (EPR) spectroscopy. The relative abundance of each of the O- species exhibits a specific dependence on the energy of the exciting photons. EPR data together with the results of theoretical modeling suggest that both O- species are located at 3-coordinated sites having different local environments. At sufficiently high O2 pressures molecular oxygen does not only act as an electron trap, favoring the O- formation, but it also contributes to UV induced O3- formation with a maximum efficiency at 4.2 eV.

  4. Dual anisotropic character in Fe/Pt multilayer grown on (001) MgO substrate

    SciTech Connect

    Pandey, Himanshu; Rakshit, R. K.; Gupta, Anurag; Maurya, K. K.; Dalai, M. K.; Budhani, R. C.

    2014-04-24

    The multilayers of [Fe(5Å)/Pt(25 Å)]{sub ×15} were prepared by dc magnetron sputtering on 50 Å Pt-buffered MgO substrates. The structural characterization of the multilayers was carried out using X-ray diffraction, X-ray reflectivity. The Secondary ion mass spectroscopy measurement reveals the depth profile and compositional modulations of the multilayer films as per our design specifications. Room temperature magnetic measurements were carried out by using SQUID both in-plane and out-of-plane sample geometry. Magnetization measurements show similar M-H loops for both in-plane and out-of-plane directions of external magnetic field with a coercivity of 190 Oe. These measurements indicate that our samples are magnetically soft and have multifunctional character which is important for making magnetic tunnel junctions.

  5. Adsorption of 2-propanol on MgO surface: A combined experimental and theoretical study

    NASA Astrophysics Data System (ADS)

    Fuente, Silvia A.; Ferretti, Cristián A.; Domancich, Nicolás F.; Díez, Verónica K.; Apesteguía, Carlos R.; Di Cosimo, J. Isabel; Ferullo, Ricardo M.; Castellani, Norberto J.

    2015-02-01

    The adsorption of 2-propanol (or isopropanol) on MgO was studied using infrared (IR) spectroscopy and density functional theory (DFT) simulations. The analysis of IR spectra indicates that the molecule can adsorb either molecularly or dissociatively. DFT calculations show that the adsorption mode depends on the active site of the catalyst. While on perfect terrace it adsorbs non-dissociatively, on edge and on threefold coordinated O anion (O-corner sites) the adsorption occurs dissociatively by breaking the Osbnd H bond without activation barrier giving 2-propoxide and a surface hydroxyl group. Calculations also suggest that vacant oxygen centers on terrace, edge and corner are also possible sites for non-dissociative adsorption. On Mg ions located at corners the adsorption is strong but non-dissociative, while on a Mg vacancy at the same position the molecule easily dissociates. Frequency modes are also calculated and compared in detail with experimental IR spectra.

  6. The mechanism of sputter-induced orientation change in YBCO films on MgO (001)

    SciTech Connect

    Huang, Y.; Vuchic, B.V.; Baldo, P.; Merkle, K.L.; Buchholz, D.B.; Mahajan, S.; Lei, J.S.; Markworth, P.R.; Chang, R.P.H.

    1996-12-01

    The mechanisms of the sputter-induced orientation change in YBa{sub 2}Cu{sub 3}O{sub 7{minus}x}(YBCO) films grown on MgO (001) substrates by pulsed organometallic beam epitaxy (POMBE) are investigated by x-ray diffraction. Rutherford backscatter spectroscopy (RBS), cross-section TEM (XTEM) and microanalysis. It is found that the W atom implantation concurring with the ion sputtering plays an important role in effecting the orientation change. This implantation changes the surface structure of the substrate and induces an intermediate layer in the initial growth of the YBCO film, which in turn acts as a template that induces the orientation change. It seems that the surface morphology change caused by ion sputtering has only a minor effect on the orientation change.

  7. First-principles study of the Fe | MgO(0 0 1) interface: magnetic anisotropy.

    PubMed

    Bose, Thomas; Cuadrado, Ramon; Evans, Richard F L; Chepulskii, Roman V; Apalkov, Dmytro; Chantrell, Roy W

    2016-04-20

    We present a systematic first-principles study of Fe | MgO bilayer systems emphasizing the influence of the iron layer thickness on the geometry, the electronic structure and the magnetic properties. Our calculations ensure the unconstrained structural relaxation at scalar relativistic level for various numbers of iron layers placed on the magnesium oxide substrate. Our results show that due to the formation of the interface the electronic structure of the interface iron atoms is significantly modified involving charge transfer within the iron subsystem. In addition, we find that the magnetic anisotropy energy increases from 1.9 mJ m(-2) for 3 Fe layers up to 3.0 mJ m(-2) for 11 Fe layers. PMID:26987845

  8. Charge localization on the hexa-interstitial cluster in MgO.

    PubMed

    Mulroue, J; Uberuaga, B P; Duffy, D M

    2013-02-13

    Density functional theory was used to study the effects of charge localization on the structure and mobility of the highly mobile hexa-interstitial cluster in MgO. It was found that the relative stability of the configurations changed as charge was localized, with the higher energy intermediate configuration of the neutral cluster becoming the lowest energy configuration for the doubly charged cluster. The singly charged cluster was found to have the lowest migration barrier, with a barrier of 0.18 eV. The high mobility of the singly charged hexa-interstitial cluster could have a significant effect on microstructure evolution following radiation damage, while the detailed properties will be sensitive to the level of doping in the material. PMID:23307696

  9. Surface core-level binding energy shifts for MgO(100).

    PubMed

    Nelin, Connie J; Uhl, Felix; Staemmler, Volker; Bagus, Paul S; Fujimori, Yuichi; Sterrer, Martin; Kuhlenbeck, Helmut; Freund, Hans-Joachim

    2014-10-28

    Theoretical and experimental results for the surface core-level binding energy, BE, shifts, SCLS, for MgO(100) are presented and the anomalous O(1s) SCLS is interpreted in terms of the surface electronic structure. While the Mg(2p) surface BE shifts to a higher value than bulk by ≈1 eV as expected from the different surface and bulk Madelung potentials, the O(1s) SCLS is almost 0 rather than ≈-1 eV, expected from the Madelung potentials. The distortion of the surface atoms from the spherical symmetry of the bulk Mg and O atoms is examined by a novel theoretical procedure. The anomalous O SCLS is shown to arise from the increase of the effective size of surface O anions. PMID:25212984

  10. Theoretical study of AuCu nanoalloys adsorbed on MgO(001)

    NASA Astrophysics Data System (ADS)

    Cerbelaud, M.; Barcaro, G.; Fortunelli, A.; Ferrando, R.

    2012-06-01

    The structures of AuCu clusters adsorbed on the (001) face of MgO are searched for by a two-step methodology. In a first step, the relevant structural motifs are singled out by global optimization searches within an atomistic model. In a second step, the lowest energy structures of each motif are relaxed by density-functional calculations. Three different sizes (30, 40 and 50 atoms) are considered. For each size, three compositions are analyzed. For size 30, a competition between fcc pyramids and a new motif (the daisy structure) is found. For 40 and 50 atoms, icosahedral fragments prevail. The results are discussed in connection with experimental data related to clusters of larger sizes.

  11. Ultraviolet stimulated emission from high-temperature-annealed MgO microcrystals at room temperature

    NASA Astrophysics Data System (ADS)

    Soma, Haruka; Uenaka, Yuki; Asahara, Akifumi; Suemoto, Tohru; Uchino, Takashi

    2015-01-01

    Research on semiconductor nanowires underlies the development of the miniaturization of laser devices with low cost and low energy consumption. In general, nanowire lasers are made of direct band gap semiconductors, e.g., GaN, ZnO and CdS, and their band-edge emissions are used to achieve optically pumped laser emission. In addition to the existing class of nanowire lasers, we here show that air-annealed micrometer-sized MgO cubic crystals with well-defined facets exhibit room-temperature stimulated emission at 394 nm under pulsed laser pumping at ˜350 nm. Surface midgap states are assumed to be responsible for the excitation and emission processes. The present findings will not only provide opportunities for the development of miniaturized lasers composed of insulating oxides, but will also open up functionality in various families of cubic crystalline materials.

  12. Plastic deformation of polycrystalline MgO up to 1250 K and 65 GPa

    NASA Astrophysics Data System (ADS)

    Merkel, S.; Liermann, H.; Miyagi, L. M.; Wenk, H.

    2009-12-01

    Understanding the development of lattice preferred orientations (LPO) in polycrystals is critical to constrain the anisotropy and dynamics of the Earth mantle. Until recently, it was not possible to study LPO under high pressure and high temperature. The introduction of the deformation-DIA (D-DIA) and radial diffraction experiments in the diamond anvil cell (DAC) have extended the range of pressures and temperatures that can be accessed. However, the pressure range accessible in the D-DIA remains limited (up to 19 GPa, 1) and LPO measurements in the DAC have been performed at 300 K (2). Recently, we have designed a new DAC that can be used to study LPO in polycrystalline samples up to temperatures of 1300 K and pressures of 65 GPa (3). In this study, we use this new device for the study of MgO up to 65 GPa and 1250 K. Four samples of polycrystalline MgO were deformed in the DAC at constant temperature: 300, 600, 900, and 1250 K. At each temperature, we study the development of stress and LPO as the sample is compressed between ambient and high pressures (up to 65 GPa). In all cases, we collect diffraction data in a radial geometry that can be used to extract lattice strains and LPO in the sample. A comparison of the LPO measured in the experiment and results of visco-plastic self-consistent models can be used to extract information about the active deformation mechanisms in the sample (2). Similarly, the measured lattice strains can be compared to results of an elasto-plastic self-consistent model to extract information on average stress, stress distribution among grains, and active deformation in the sample (4). Details of the measurements along with the LPO measured in the experiments will be presented. We will also discuss the implication of those results for our understanding of the behavior of MgO in the deep mantle. 1- N. Nishiyama, Y. Wang, M. L. Rivers, S. R. Sutton, D. Cookson, Rheology of e-iron up to 19 GPa and 600 K in the D-DIA, Geophys. Res. Lett., 34

  13. Shock Response and Phase Transitions of MgO at Planetary Impact Conditions

    NASA Astrophysics Data System (ADS)

    Root, Seth; Shulenburger, Luke; Lemke, Raymond W.; Dolan, Daniel H.; Mattsson, Thomas R.; Desjarlais, Michael P.

    2015-11-01

    The moon-forming impact and the subsequent evolution of the proto-Earth is strongly dependent on the properties of materials at the extreme conditions generated by this violent collision. We examine the high pressure behavior of MgO, one of the dominant constituents in Earth's mantle, using high-precision, plate impact shock compression experiments performed on Sandia National Laboratories' Z Machine and extensive quantum calculations using density functional theory (DFT) and quantum Monte Carlo (QMC) methods. The combined data span from ambient conditions to 1.2 TPa and 42 000 K, showing solid-solid and solid-liquid phase boundaries. Furthermore our results indicate that under impact the solid and liquid phases coexist for more than 100 GPa, pushing complete melting to pressures in excess of 600 GPa. The high pressure required for complete shock melting has implications for a broad range of planetary collision events.

  14. Electric field effect on a double MgO CoFeB-based free layer

    NASA Astrophysics Data System (ADS)

    Huang, Jiancheng; Sim, Cheow Hin; Naik, Vinayak Bharat; Tran, Michael; Lim, Sze Ter; Huang, Aihong; Yap, Qi Jia; Han, Guchang

    2016-03-01

    We study the electric field (EF) effect on MgO/CoFeB/Ta/CoFeB/MgO free layers by varying the thickness of the top MgO layer. The two CoFeB/MgO interfaces oppose the change in magnetic anisotropy from each other and this can be understood by considering the voltage drop as well as the efficiency of the anisotropy modulation from both interfaces. These results are proven by monitoring both coercivity and anisotropy field as a function of the applied EF. From the fit to the model, we show that the bottom CoFeB/MgO interface has a higher EF efficiency than the top interface.

  15. The compression study of MgO up to 3Mbar

    NASA Astrophysics Data System (ADS)

    Sakai, T.; Nishitani, N.; Ohtani, E.; Hirao, N.

    2011-12-01

    Periclase (MgO) is a most fundamental oxide in the terrestrial planets. It is also widely used as a pressure standard material for the high pressure experiment. Moreover, recently Super Earths which has a few times of Earth's mass were found in the extrasolar system. Theoretical study implied that MgSiO3 decompose to MgO and SiO2 in such huge planet's interior (Umemoto et al. 2006). Thus, the compression behavior of MgO at multi-megabar pressure is important to understand the Super Earth's interior. Here we report the compression study of MgO up to 3Mbar. Periclase powder (Wako Pure Chemical Industries, Ltd.) and platinum black (Wako Pure Chemical Industries, Ltd.) were used as the starting material. We used a symmetric-type diamond anvil cell for high pressure generation. The experimental pressure was determined by the Vinet equation of state of platinum as reported by Matsui et al. (2009). The sample was annealed by a double-sided laser-heating method using a fiber laser at the BL10XU beamline, Japanese SPring-8 synchrotron facility, in order to minimize the deviatoric stress in the sample. Experimental pressures were measured after laser annealing. A monochromatic incident X-ray beam with a wavelength of 0.41297(7) Å and 0.41298(8) Å at BL10XU was collimated to a diameter less than 10 μm (Ohishi et al., 2008). X-ray diffraction spectra were collected on an imaging plate (IP) with an exposure time of 5 min. The two-dimensional X-ray diffraction image was integrated as a function of 2θ to give a conventional one-dimensional X-ray diffraction pattern. The diffraction of cerium oxide (CeO2) was used to determine the wavelength and the distance between the sample and the IP. Periclase was successfully compressed up to 308 GPa. We estimated the uniaxial stress of platinum at 308 GPa. The uniaxial stress t is described as t = -3M1/(M0αS) (Singh and Takemura, 2001). Here, M0 and M1 are the intercept and slope of the gamma plot, respectively. The coefficient α is

  16. Shock response and phase transitions of MgO at planetary impact conditions

    DOE PAGESBeta

    Root, Seth; Shulenburger, Luke; Lemke, Raymond W.; Dolan, Daniel H.; Mattsson, Thomas R.; Desjarlais, Michael P.

    2015-11-04

    The moon-forming impact and the subsequent evolution of the proto-Earth is strongly dependent on the properties of materials at the extreme conditions generated by this violent collision. We examine the high pressure behavior of MgO, one of the dominant constituents in Earth’s mantle, using high-precision, plate impact shock compression experiments performed on Sandia National Laboratories’ Z Machine and extensive quantum calculations using density functional theory (DFT) and quantum Monte Carlo (QMC) methods. The combined data span from ambient conditions to 1.2 TPa and 42,000 K, showing solid-solid and solid-liquid phase boundaries. Furthermore our results indicate that under impact the solidmore » and liquid phases coexist for more than 100 GPa, pushing complete melting to pressures in excess of 600 GPa. Furthermore, the high pressure required for complete shock melting has implications for a broad range of planetary collision events.« less

  17. Shock response and phase transitions of MgO at planetary impact conditions

    SciTech Connect

    Root, Seth; Shulenburger, Luke; Lemke, Raymond W.; Dolan, Daniel H.; Mattsson, Thomas R.; Desjarlais, Michael P.

    2015-11-04

    The moon-forming impact and the subsequent evolution of the proto-Earth is strongly dependent on the properties of materials at the extreme conditions generated by this violent collision. We examine the high pressure behavior of MgO, one of the dominant constituents in Earth’s mantle, using high-precision, plate impact shock compression experiments performed on Sandia National Laboratories’ Z Machine and extensive quantum calculations using density functional theory (DFT) and quantum Monte Carlo (QMC) methods. The combined data span from ambient conditions to 1.2 TPa and 42,000 K, showing solid-solid and solid-liquid phase boundaries. Furthermore our results indicate that under impact the solid and liquid phases coexist for more than 100 GPa, pushing complete melting to pressures in excess of 600 GPa. Furthermore, the high pressure required for complete shock melting has implications for a broad range of planetary collision events.

  18. On the low-lying states of MgO. II

    NASA Technical Reports Server (NTRS)

    Bauschlicher, C. W., Jr.; Lengsfield, B. H., III; Silver, D. M.; Yarkony, D. R.

    1981-01-01

    Using a double zeta plus polarization basis set of Slater orbitals, full valence MCSCF (FVMCSCF) calculations were performed for the low-lying states of MgO. For each state the FVMCSCF calculations were used to identify the important configurations which are then used in the MCSCF calculation and subsequently as references in a single and double excitation CI calculation. This approach is found to treat all states equivalently, with the maximum error in the computed transition energies and equilibrium bond lengths of 800/cm and approximately 0.03 A, respectively. The b 3 Sigma + state which has yet to be characterized experimentally is predicted to have a transition energy of approximately 8300/cm and a bond length of 1.79 A. A spectroscopic analysis of the potential curves indicates that their shapes are in quite reasonable agreement with the range of experimental results.

  19. Mechanism of critical catalyst size effect on MgO nanowire growth by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Yanagida, Takeshi; Nagashima, Kazuki; Tanaka, Hidekazu; Kawai, Tomoji

    2008-07-01

    The size controllability of oxide nanowires formed via vapor-liquid-solid (VLS) mechanism is desired for the oxide nanowire-based device applications. However, the complex nature of oxide nanowire VLS growth has held back such size controllability. Here we demonstrate the critical size effect of a Au catalyst on MgO nanowire VLS growth by pulsed laser deposition. The presence of a critical catalyst size was found. Above such critical size, an oxide nanowire VLS growth is no longer feasible. Interestingly, such critical size increased with increasing growth temperature. The mechanism of the critical phenomenon is interpreted in terms of the catalyst size dependence on the amount of adatoms diffused from surroundings into the catalyst.

  20. Sonocatalyzed decolorization of synthetic textile wastewater using sonochemically synthesized MgO nanostructures.

    PubMed

    Darvishi Cheshmeh Soltani, Reza; Safari, Mahdi; Mashayekhi, Masumeh

    2016-05-01

    The present study focused on the synthesis of nanostructured MgO via sonochemical method and its application as sonocatalyst for the decolorization of Basic Red 46 (BR46) dye under ultrasonic irradiation. The sonocatalyst was characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray microanalysis (EDX). In the following, the sonocatalytic removal of the dye under different operational conditions was evaluated kinetically on the basis of pseudo first-order kinetic model. The reaction rate of sonocatalyzed decolorization using MgO nanostructures (12.7 × 10(-3) min(-1)) was more efficient than that of ultrasound alone (2.0 × 10(-3) min(-1)). The increased sonocatalyst dosage showed better sonocatalytic activity but the application of excessive dosage should be avoided. The presence of periodate ions substantially increased the decolorization rate from 14.76 × 10(-3) to 33.4 × 10(-3) min(-1). Although the application of aeration favored the decolorization rate (17.8 × 10(-3) min(-1)), the addition of hydrogen peroxide resulted in a considerable decrease in the decolorization rate (9.5 × 10(-3) min(-1)) due to its scavenging effects at specific concentrations. Unlike alcoholic compounds, the addition of phenol had an insignificant scavenging effect on the sonocatalysis. A mineralization rate of 7.4 × 10(-3) min(-1) was obtained within 120 min. The intermediate byproducts were also detected using GC-MS analysis. PMID:26615797

  1. Moment Mapping of bcc Fe1-xMnx Alloy Films on MgO(001)

    NASA Astrophysics Data System (ADS)

    Idzerda, Yves; Bhatkar, Harsh; Arenholz, Elke

    2015-03-01

    The magnetic moments of ~ 20 nm single crystal films of compositionally graded Fe1-xMnx films (0.1 <= x <= 0.2) grown on MgO(001) are determined by spatially resolved moment mapping using X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (MCD). RHEED measurements confirmed that the growth of Fe1-xMnx films remained epitaxial and in the bcc phase up to x =0.35 but, like Fe growth, is rotated 45 degree with respect to the MgO(001) surface net. This is beyond the bulk bcc stability limit of x =0.12. Both magnetometry and XMCD measurements show that the net magnetic moment of these alloy films behave similarly to the bulk behavior, with a gradual moment reduction at low Mn concentrations followed by an abrupt departure from the Slater-Pauling curve and disappearance of the moment at x =0.15. By generating a compositional variation around this critical concentration and subsequently using spatially resolved mapping of the X-ray absorption at the Fe and Mn L3-edge using linear and circular polarized soft X-rays, the local composition and elemental moments can be simultaneously mapped across the surface of the sample. The Fe moment is found to gradually reduce with increasing Mn content with a very abrupt decline at x =0.15. Surprisingly, the Mn moment shows a very small net moment (<0.1 muB) at all compositions, suggesting a complicated Mn spin structure.

  2. Thin Film?

    NASA Astrophysics Data System (ADS)

    Kariper, İ. Afşin

    2014-09-01

    This study focuses on the critical surface tension of lead sulfite (PbSO3) crystalline thin film produced with chemical bath deposition on substrates (commercial glass).The PbSO3 thin films were deposited at room temperature at different deposition times. The structural properties of the films were defined and examined according to X-ray diffraction (XRD) and the XRD results such as dislocation density, average grain size, and no. of crystallites per unit area. Atomic force microscopy was used to measure the film thickness and the surface properties. The critical surface tension of the PbSO3 thin films was measured with an optical tensiometer instrument and calculated using the Zisman method. The results indicated that the critical surface tension of films changed in accordance with the average grain size and film thickness. The film thickness increased with deposition time and was inversely correlated with surface tension. The average grain size increased according to deposition time and was inversely correlated with surface tension.

  3. Interfacial electronic transport phenomena in single crystalline Fe-MgO-Fe thin barrier junctions

    SciTech Connect

    Gangineni, R. B.; Negulescu, B.; Baraduc, C.; Gaudin, G.

    2014-05-05

    Spin filtering effects in nano-pillars of Fe-MgO-Fe single crystalline magnetic tunnel junctions are explored with two different sample architectures and thin MgO barriers (thickness: 3–8 monolayers). The two architectures, with different growth and annealing conditions of the bottom electrode, allow tuning the quality of the bottom Fe/MgO interface. As a result, an interfacial resonance states (IRS) is observed or not depending on this interface quality. The IRS contribution, observed by spin polarized tunnel spectroscopy, is analyzed as a function of the MgO barrier thickness. Our experimental findings agree with theoretical predictions concerning the symmetry of the low energy (0.2 eV) interfacial resonance states: a mixture of Δ{sub 1}-like and Δ{sub 5}-like symmetries.

  4. Polyethylene Nanocomposites for the Next Generation of Ultralow-Transmission-Loss HVDC Cables: Insulation Containing Moisture-Resistant MgO Nanoparticles.

    PubMed

    Pourrahimi, Amir Masoud; Pallon, Love K H; Liu, Dongming; Hoang, Tuan Anh; Gubanski, Stanislaw; Hedenqvist, Mikael S; Olsson, Richard T; Gedde, Ulf W

    2016-06-15

    The use of MgO nanoparticles in polyethylene for cable insulation has attracted considerable interest, although in humid media the surface regions of the nanoparticles undergo a conversion to a hydroxide phase. A facile method to obtain MgO nanoparticles with a large surface area and remarkable inertness to humidity is presented. The method involves (a) low temperature (400 °C) thermal decomposition of Mg(OH)2, (b) a silicone oxide coating to conceal the nanoparticles and prevent interparticle sintering upon exposure to high temperatures, and (c) heat treatment at 1000 °C. The formation of the hydroxide phase on these silicone oxide-coated MgO nanoparticles after extended exposure to humid air was assessed by thermogravimetry, infrared spectroscopy, and X-ray diffraction. The nanoparticles showed essentially no sign of any hydroxide phase compared to particles prepared by the conventional single-step thermal decomposition of Mg(OH)2. The moisture-resistant MgO nanoparticles showed improved dispersion and interfacial adhesion in the LDPE matrix with smaller nanosized particle clusters compared with conventionally prepared MgO. The addition of 1 wt % moisture-resistant MgO nanoparticles was sufficient to decrease the conductivity of polyethylene 30 times. The reduction in conductivity is discussed in terms of defect concentration on the surface of the moisture-resistant MgO nanoparticles at the polymer/nanoparticle interface. PMID:27203860

  5. X-ray absorption spectroscopy and magnetic circular dichroism studies of L10-Mn-Ga thin films

    NASA Astrophysics Data System (ADS)

    Glas, M.; Sterwerf, C.; Schmalhorst, J. M.; Ebke, D.; Jenkins, C.; Arenholz, E.; Reiss, G.

    2013-11-01

    Tetragonally distorted Mn3-xGax thin films with 0.1MgO is problematic due to oxide formation, we examined the influence of a CoFeB interlayer and of two different deposition methods for the MgO barrier on the formation of interfacial Mn-O for Mn62Ga38 by element specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD). A highly textured L10 crystal structure of the Mn-Ga films was verified by X-ray diffraction measurements. For samples with e-beam evaporated MgO barrier no evidence for Mn-O was found whereas in samples with magnetron sputtered MgO, Mn-O was detected, even for the thickest interlayer thickness. Both XAS and XMCD measurements showed an increasing interfacial Mn-O amount with decreasing CoFeB interlayer thickness. Additional element specific full hysteresis loops determined an out-of-plane magnetization axis for the Mn and Co, respectively.

  6. X-ray absorption spectroscopy and magnetic circular dichroism studies of L1{sub 0}-Mn-Ga thin films

    SciTech Connect

    Glas, M. Sterwerf, C.; Schmalhorst, J. M.; Reiss, G.; Ebke, D.; Jenkins, C.; Arenholz, E.

    2013-11-14

    Tetragonally distorted Mn{sub 3−x}Ga{sub x} thin films with 0.1MgO is problematic due to oxide formation, we examined the influence of a CoFeB interlayer and of two different deposition methods for the MgO barrier on the formation of interfacial Mn-O for Mn{sub 62}Ga{sub 38} by element specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD). A highly textured L1{sub 0} crystal structure of the Mn-Ga films was verified by X-ray diffraction measurements. For samples with e-beam evaporated MgO barrier no evidence for Mn-O was found whereas in samples with magnetron sputtered MgO, Mn-O was detected, even for the thickest interlayer thickness. Both XAS and XMCD measurements showed an increasing interfacial Mn-O amount with decreasing CoFeB interlayer thickness. Additional element specific full hysteresis loops determined an out-of-plane magnetization axis for the Mn and Co, respectively.

  7. Beta (β) tungsten thin films: Structure, electron transport, and giant spin Hall effect

    SciTech Connect

    Hao, Qiang; Chen, Wenzhe; Xiao, Gang

    2015-05-04

    We use a simple magnetron sputtering process to fabricate beta (β) tungsten thin films, which are capable of generating giant spin Hall effect. As-deposited thin films are always in the metastable β-W phase from 3.0 to 26.7 nm. The β-W phase remains intact below a critical thickness of 22.1 nm even after magnetic thermal annealing at 280 °C, which is required to induce perpendicular magnetic anisotropy (PMA) in a layered structure of β-W/Co{sub 40}Fe{sub 40}B{sub 20}/MgO. Intensive annealing transforms the thicker films (>22.1 nm) into the stable α-W phase. We analyze the structure and grain size of both β- and α-W thin films. Electron transport in terms of resistivity and normal Hall effect is studied over a broad temperature range of 10 K to at least 300 K on all samples. Very low switching current densities are achieved in β-W/Co{sub 40}Fe{sub 40}B{sub 20}/MgO with PMA. These basic properties reveal useful behaviors in β-W thin films, making them technologically promising for spintronic magnetic random access memories and spin-logic devices.

  8. Fabrication of stable, wide-bandgap thin films of Mg, Zn and O

    DOEpatents

    Katiyar, Ram S.; Bhattacharya, Pijush; Das, Rasmi R.

    2006-07-25

    A stable, wide-bandgap (approximately 6 eV) ZnO/MgO multilayer thin film is fabricated using pulsed-laser deposition on c-plane Al2O3 substrates. Layers of ZnO alternate with layers of MgO. The thickness of MgO is a constant of approximately 1 nm; the thicknesses of ZnO layers vary from approximately 0.75 to 2.5 nm. Abrupt structural transitions from hexagonal to cubic phase follow a decrease in the thickness of ZnO sublayers within this range. The band gap of the thin films is also influenced by the crystalline structure of multilayer stacks. Thin films with hexagonal and cubic structure have band-gap values of 3.5 and 6 eV, respectively. In the hexagonal phase, Mg content of the films is approximately 40%; in the cubic phase Mg content is approximately 60%. The thin films are stable and their structural and optical properties are unaffected by annealing at 750.degree. C.

  9. The influence of incorporating MgO into Ni-based cermets by plasma spraying on anode microstructural and chemical stability in dry methane

    NASA Astrophysics Data System (ADS)

    Lay, E.; Metcalfe, C.; Kesler, O.

    2012-11-01

    The Solution Precursor Plasma Spray (SPPS) process was successfully used to deposit cermet coatings that exhibit fine microstructures with high surface area. MgO addition in Ni-YSZ and Ni-SDC cermets results in (Ni,Mg)O solid solution formation, and nickel particles after reduction are finer than in coatings without magnesia. The influence of MgO on the chemical stability of cermets in anodic operating conditions is discussed. It was found that a sufficient amount of magnesia addition (Ni0.9(MgO)0.1) helps to reduce carbon deposition in dry methane.

  10. High- Tc thin-film magnetometer

    SciTech Connect

    Miklich, A.H.; Wellstood, F.C.; Kingston, J.J.; Clarke, J. ); Colclough, M.S. ); Cardona, A.H.; Bourne, L.C.; Olson, W.L.; Eddy, M.M. )

    1990-09-01

    We have constructed and tested high-{Tc} magnetometers by coupling a high-{Tc} thin-film Superconducting QUantum Interference Device (SQUID) to two different high-{Tc} thin-film flux transformers. The SQUID was made from Tl{sub 2}CaBa{sub 2}Cu{sub 2}O{sub 8+y} films grown on MgO, with junctions consisting of native grain boundaries. The flux transformers were made from YBa{sub 2}Cu{sub 3}O{sub 7-x}, and each had 10-turn input coils and a single-turn pickup loop. The first transformer, which was patterned with a combination of shadow masks and photolithography, yielded a magnetic field gain of about {minus}7.5, functioned up to 79 K, and gave a magnetic field sensitivity B{sub N} (10 Hz) {approx} 3.1 pT Hz{sup {minus}1/2}at 38 K. The second transformer, which was patterned entirely by photolithography, yielded a gain of about {minus}8.7, functioned up to 25 K, and had a sensitivity B{sub N} (10 Hz) {approx} 3.5 pT Hz{sup {minus}1/2} at 4.2 K. In both cases, the limiting noise arose in the SQUID. 10 refs., 5 figs., 1 tab.

  11. Thin Films

    NASA Astrophysics Data System (ADS)

    Khorshidi, Zahra; Bahari, Ali; Gholipur, Reza

    2014-11-01

    Effect of annealing temperature on the characteristics of sol-gel-driven Ta ax La(1- a) x O y thin film spin-coated on Si substrate as a high- k gate dielectric was studied. Ta ax La(1- a) x O y thin films with different amounts of a were prepared (as-prepared samples). X-ray diffraction measurements of the as-prepared samples indicated that Ta0.3 x La0.7 x Oy film had an amorphous structure. Therefore, Ta0.3 x La0.7 x O y film was chosen to continue the present studies. The morphology of Ta0.3 x La0.7 x O y films was studied using scanning electron microscopy and atomic force microscopy techniques. The obtained results showed that the size of grain boundaries on Ta0.3 x La0.7 x O y film surfaces was increased with increasing annealing temperature. Electrical and optical characterizations of the as-prepared and annealed films were investigated as a function of annealing temperature using capacitance-voltage ( C- V) and current density-voltage ( J- V) measurements and the Tauc method. The obtained results demonstrated that Ta0.3 x La0.7 x O y films had high dielectric constant (≈27), wide band gap (≈4.5 eV), and low leakage current density (≈10-6 A/cm2 at 1 V).

  12. Thin Films

    NASA Astrophysics Data System (ADS)

    Naffouti, Wafa; Nasr, Tarek Ben; Mehdi, Ahmed; Kamoun-Turki, Najoua

    2014-11-01

    Titanium dioxide (TiO2) thin films were synthesized on glass substrates by spray pyrolysis. The effect of solution flow rate on the physical properties of the films was investigated by use of x-ray diffraction (XRD), scanning electron microscopy, atomic force microscopy (AFM), and spectrophotometry techniques. XRD analysis revealed the tetragonal anatase phase of TiO2 with highly preferred (101) orientation. AFM images showed that grain size on top of TiO2 thin films depended on solution flow rate. An indirect band gap energy of 3.46 eV was determined by means of transmission and reflection measurements. The envelope method, based on the optical transmission spectrum, was used to determine film thickness and optical constants, for example real and imaginary parts of the dielectric constant, refractive index, and extinction coefficient. Ultraviolet and visible photoluminescence emission peaks were observed at room temperature. These peaks were attributed to the intrinsic emission and to the surface defect states, respectively.

  13. Phenomenological in-situ TEM gas exposure studies of palladium particles on MgO at room temperature

    NASA Technical Reports Server (NTRS)

    Heinemann, K.; Poppa, H.; Osaka, T.

    1983-01-01

    It has been found that very small vapor-deposited catalytically active metal particles in the 1-2 nm size range on metal oxide substrates can undergo significant changes when they are exposed to gases such as oxygen or air, or even when allowed to 'anneal' at room temperature (RT) under vacuum conditions. The present investigation is concerned with continued in-situ gas exposures of as-deposited, 1 to 2 nm size palladium particles on MgO to air, oxygen, nitrogen, hydrogen, CO, and water vapor at RT. It is found that the low-pressure exposure to various gases at RT can significantly affect small palladium particles supported on MgO surfaces. Exposure to oxygen for 3 min at 0.0002 m bar produces a considerable amount of coalescence, flattening of the particles, and some distinct crystallographic particle shapes.

  14. Effect of Relative Humidity and CO2 Concentration on the Properties of Carbonated Reactive MgO Cement Based Materials

    NASA Astrophysics Data System (ADS)

    Bilan, Yaroslav

    Sustainability of modern concrete industry recently has become an important topic of scientific discussion, and consequently there is an effort to study the potential of the emerging new supplementary cementitious materials. This study has a purpose to investigate the effect of reactive magnesia (reactive MgO) as a replacement for general use (GU) Portland Cements and the effect of environmental factors (CO2 concentrations and relative humidity) on accelerated carbonation curing results. The findings of this study revealed that improvement of physical properties is related directly to the increase in CO2 concentrations and inversely to the increase in relative humidity and also depends much on %MgO in the mixture. The conclusions of this study helped to clarify the effect of variable environmental factors and the material replacement range on carbonation of reactive magnesia concrete materials, as well as providing an assessment of the optimal conditions for the effective usage of the material.

  15. Possibility of a 2D SiC monolayer formation on Mg(0001) and MgO(111) substrates

    NASA Astrophysics Data System (ADS)

    Kuzubov, A. A.; Eliseeva, N. S.; Krasnov, P. O.; Tomilin, F. N.; Fedorov, A. S.; Tolstaya, A. V.

    2013-08-01

    The geometrical characteristics of a 2D SiC monolayer on Mg(0001) and MgO(111) plates regarded as potential materials for growing two-dimensional silicon carbide were studied. The most favorable positions of the atoms of 2D SiC on the substrates were determined. In the 2D SiC/Mg(0001) system, unlike in 2D SiC/MgO(111), the deviation of the carbon atom from the silicon carbide monolayer was insignificant (0.08 Å). Consequently, magnesium can be used as a substrate for growing two-dimensional silicon carbide. The use of MgO(111) is not recommended because of a significant distortion of the 2D SiC surface.

  16. Tunnel magnetoresistance in epitaxially grown magnetic tunnel junctions using Heusler alloy electrode and MgO barrier

    SciTech Connect

    Tsunegi, S.; Sakuraba, Y.; Oogane, M.; Telling, N. D.; Shelford, L. R.; Arenholz, E.; van der Laan, G.; Hicken, R. J.; Takanashi, K.; Ando, Y.

    2009-07-01

    Epitaxially grown magnetic tunnel junctions (MTJs) with a stacking structure of Co{sub 2}MnSi/MgO/CoFe were fabricated. Their tunnel magnetoresistance (TMR) effects were investigated. The TMR ratio and tunnelling conductance characteristics of MTJs were considerably different between those with an MgO barrier prepared using sputtering (SP-MTJ) and those prepared using EB evaporation (EB-MTJ). The EB-MTJ exhibited a very large TMR ratio of 217% at room temperature and 753% at 2 K. The bias voltage dependence of the tunnelling conductance in the parallel magnetic configuration for the EB-MTJ suggests that the observed large TMR ratio at RT results from the coherent tunnelling process through the crystalline MgO barrier. The tunnelling conductance in the anti-parallel magnetic configuration suggests that the large temperature dependence of the TMR ratio results from the inelastic spin-flip tunnelling process.

  17. Effects of MgO Doping on DC Bias Aging Behavior of Mn-Doped BaTiO3

    NASA Astrophysics Data System (ADS)

    Hahn, Dong Woo; Hong, Jeong Oh; Han, Young Ho

    2008-07-01

    The capacitance aging of multilayer ceramic capacitors (MLCCs) based on BaTiO3 dielectrics under DC electric fields has been studied. At a DC field of 1 V/µm, the capacitance of MLCC specimens decreased immediately in a very short period (<10 s, the first stage) and then decreased continuously with time (the second stage). Substitution of Mn ions markedly increased the slope of aging curves in the second stage. MgO doping significantly decreased the second stage aging rate of Mn-doped specimens. This aging rate decreased in the second stage with increasing MgO content. This may be due to the existence of a stable defect complex (MgTi''-VO••) inhibiting domain wall motion. MgO-doped specimens showed a small decrease in capacitance in the first stage, which may be due to small grain size and low dielectric permittivity.

  18. Boron diffusion in magnetic tunnel junctions with MgO (001) barriers and CoFeB electrodes

    SciTech Connect

    Kurt, H.; Rode, K.; Oguz, K.; Coey, J. M. D.; Boese, M.; Faulkner, C. C.

    2010-06-28

    Boron diffusion out of the CoFeB layers in model systems with thick CoFeB and MgO layers grown by radiofrequency sputtering or electron-beam evaporation and in MgO-based magnetic tunnel junctions (MTJs) is probed after annealing by x-ray photoemission spectroscopy (XPS) and electron energy loss spectroscopy. Successive interfaces are exposed by ion milling the stacks, layer by layer, in the XPS system. Despite the presence of thick CoFeB and a high annealing temperature of 400 deg. C, we found no boron in the MgO or at the MgO/CoFe interfaces. Similar results are also obtained in the MTJs.

  19. Contact induced spin relaxation in graphene spin valves with Al2O3 and MgO tunnel barriers

    NASA Astrophysics Data System (ADS)

    Amamou, Walid; Lin, Zhisheng; van Baren, Jeremiah; Turkyilmaz, Serol; Shi, Jing; Kawakami, Roland K.

    2016-03-01

    We investigate spin relaxation in graphene by systematically comparing the roles of spin absorption, other contact-induced effects (e.g., fringe fields), and bulk spin relaxation for graphene spin valves with MgO barriers, Al2O3 barriers, and transparent contacts. We obtain effective spin lifetimes by fitting the Hanle spin precession data with two models that include or exclude the effect of spin absorption. Results indicate that additional contact-induced spin relaxation other than spin absorption dominates the contact effect. For tunneling contacts, we find reasonable agreement between the two models with median discrepancy of ˜20% for MgO and ˜10% for Al2O3.

  20. Effects of MgO Nano Particles on Microstructural and Mechanical Properties of Aluminum Matrix Composite prepared via Powder Metallurgy Route

    NASA Astrophysics Data System (ADS)

    Baghchesara, Mohammad Amin; Abdizadeh, Hossein; Baharvandi, Hamid Reza

    The objective of the present investigation was to evaluate the microstructural and mechanical properties of Al/nano MgO composite prepared via powder metallurgy method. Pure atomized aluminum powder with an average particle size of 1μm and MgO particulate with an average particle size between 60 to 80 nm were used. Composites containing 1.5, 2.5 and 5 percent of volume fraction of MgO were prepared by powder metallurgy method. The specimens were pressed by Cold Isostatic Press machine (CIP), subsequently were sintered at 575, 600 and 625°C. After sintering and preparing the samples, mechanical properties were measured. The results of microstructure, compression and hardness tests indicated that addition of MgO particulates to aluminum matrix composites improves the mechanical properties.

  1. Rutherford Backscattering and Channeling Studies of Mg and Fe Diffusion at the Interface of gamma-Fe₂O₃(001)/MgO(001)

    SciTech Connect

    Thevuthasan, Suntharampillai; Jiang, Weilin; McCready, David E.; Chambers, Scott A.

    1999-12-01

    Investigates the crystalline quality of an epitaxially grown gamma-FeO(001) film on Mg/O(001) substrate along with the Mg and Fe inter-diffusion using Rutherford Backscattering and channeling experiments.

  2. Depth-selective electronic and magnetic properties of a Co2MnSi tunnel magneto-resistance electrode at a MgO tunnel barrier

    NASA Astrophysics Data System (ADS)

    Krumme, B.; Ebke, D.; Weis, C.; Makarov, S. I.; Warland, A.; Hütten, A.; Wende, H.

    2012-12-01

    We investigated the electronic structure as well as the magnetic properties of a Co2MnSi film on MgO(100) element-specifically at the interface to a MgO tunnel barrier by means of X-ray absorption spectroscopy and X-ray magnetic circular dichroism. The electronic structure of the Co atoms as a function of the capping layer thickness remained unchanged, whereas the XA spectra of Mn indicate an increase of the unoccupied d states. The experimental findings are consistent with the interfacial structure proposed in the work by B. Hülsen et al. [Phys. Rev. Lett. 103, 046802 (2009)], where a MnSi layer is present at the interface to the MgO with oxygen atoms at top positions in the first MgO layer.

  3. Structural Properties of Alternate Monatomic Layered [Fe/Co]n Epitaxial Films on MgO Substrate

    NASA Astrophysics Data System (ADS)

    Chu, In Chang; Saki, Yoshinobu; Kawasaki, Shohei; Doi, Masaaki; Sahashi, Masashi

    2008-06-01

    Body-centered-cubic (bcc) Fe50Co50 material is reported to show a high bulk spin scattering coefficient on current perpendicular to plane-giant magneto-resistance (CPP-GMR) system. But the origin of that phenomenon does not make sure yet. We prepared artificially alternate monatomic layered (AML) [Fe/Co] 41 MLs epitaxial films (Ts: 75, 250 °C) by monatomic deposition method and investigated the topology of AML [Fe/Co]n epitaxial films on MgO substrate with different orientation (001), (011) by the scanning tunnel microscopy (STM) and reflection high energy electron diffraction (RHEED), which we could confirm Frank-van der Merwe (FM) growth mode for AML [Fe/Co]n on MgO(001) and Volmer-Weber (VW) growth mode for that on Mg(011). The roughness of surface, Ra (0.20 nm) of AML [Fe/Co] 41 MLs epitaxial film grown at 75 °C on MgO(001) is smaller than that (0.46 nm) of AML [Fe/Co] grown at 250 °C on MgO(001), which has the large terraces of over 50 nm (Ra: 0.17 nm), even though there are some valleys between large terraces. Moreover we confirmed the structural properties of trilayered epitaxial films with AML [Fe/Co]n (Ra: 0.18 nm) and Fe50Co50 alloy epitaxial film on Au electrode by RHEED before confirming the characteristics of CPP-GMR devices.

  4. Shock-Induced Melting and Vaporization of MgO by Multi-Mbar Shock and Release Experiments

    NASA Astrophysics Data System (ADS)

    Kraus, R. G.; Root, S.; Desjarlais, M. P.; Stewart, S. T.; Shulenburger, L.; Knudson, M. D.; Lemke, R.; Dolan, D. H.; Seagle, C. T.; Jacobsen, S. B.; Flicker, D. G.; Mattsson, T.

    2012-12-01

    The thermal state of the Earth after the final giant impact event is uncertain due to the lack of accurate wide-ranging equations of state for mantle minerals. In particular, current models for shock-induced melting and vaporization of the refractory phases within the Earth's mantle are poorly constrained due to the difficulty in reaching and measuring states in the relevant regions of the phase diagram. Using the Z-machine at Sandia National Laboratory, we performed high velocity (15-25 km/s) planar impact experiments onto MgO. We use a novel shock, release, and stagnation technique to determine the density of MgO along the liquid branch of the liquid-vapor dome. This region of the phase diagram is inaccessible to most static techniques and these experiments represent the first measurements of their kind. We will present our measurements of the temperature and density along the liquid-vapor dome of MgO and discuss the utility of these measurements in developing wide-ranging multi-phase equation of state models. We will also present a new model for the entropy along the principal Hugoniot of MgO, which we use to derive the criteria for shock-induced melting and vaporization and to address the commonly made assumption that the Moon-forming impact event melted Earth's entire mantle. We acknowledge support from NNSA SSGF, NNSA HEDLP, and the Z Fundamental Science User Program. We also thank the Z facility staff and technicians. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.

  5. First principles investigation of magnetocrystalline anisotropy at Full Heusler / MgO interfaces

    NASA Astrophysics Data System (ADS)

    Vadapoo, Rajasekarakumar; Hallal, Ali; Chshiev, Mairbek

    2014-03-01

    Magnetic tunnel junctions with perpendicular magnetic anisotropy (PMA) have the potential for realizing next generation high density nonvolatile memories and logic devices. The origin of high PMA in these interfaces has been explained by orbital hybridizations at interface along with spin-orbit interactions. Here we present a systematic study of PMA in Heusler alloy [X2YZ]/ MgO interfaces using first principle methods with X =Co, YZ =FeAl, MnGe and MnSi. Among the interfaces studied, we found that Co terminated interface of Co2FeAl/MgO gives rise to PMA value of 1.2erg/cm2 in agreement with recent experimental observations. On the contrary, FeAl terminated interfaces of the same structure shows in-plane magnetic anisotropy (IMA). We also found that the most of PMA contribution originates from dyz and dz2 orbitals of Co atoms at the interface. Finally, Co2MnGe and Co2MnSi structures tend to favor IMA for any termination.

  6. Selective radiative cooling with MgO and/or LiF layers

    DOEpatents

    Berdahl, P.H.

    1984-09-14

    A selective radiation cooling material which is absorptive only in the 8 to 13 microns wavelength range is accomplished by placing ceramic magnesium oxide and/or polycrystalline lithium fluoride on an infrared-reflective substrate. The reflecting substrate may be a metallic coating, foil or sheet, such as aluminum, which reflects all atmospheric radiation from 0.3 to 8 microns, the magnesium oxide and lithium fluoride being nonabsorptive at those wavelengths. <10% of submicron voids in the material is permissible in which case the MgO and/or LiF layer is diffusely scattering, but still nonabsorbing, in the wavelength range of 0.3 to 8 microns. At wavelengths from 8 to 13 microns, the magnesium oxide and lithium fluoride radiate power through the ''window'' in the atmosphere, and thus remove heat from the reflecting sheet of material and the attached object to be cooled. At wavelengths longer than 13 microns, the magnesium oxide and lithium fluoride reflects the atmospheric radiation back into the atmosphere. This high reflectance is only obtained if the surface is sufficiently smooth: roughness on a scale of 1 micron is permissible but roughness on a scale of 10 microns is not. An infrared-transmitting cover or shield is mounted in spaced relationship to the material to reduce convective heat transfer. If this is utilized in direct sunlight, the infrared transmitting cover or shield should be opaque in the solar spectrum of 0.3 to 3 microns.

  7. First-principles calculations of the indigo encapsulation and adsorption by MgO nanotubes

    SciTech Connect

    Sánchez-Ochoa, F. Cocoletzi, Gregorio H.; Canto, Gabriel I.; Takeuchi, Noboru

    2014-06-07

    We have performed ab-initio calculations to investigate the structural and electronic properties of (m,m) chiral magnesium oxide nanotubes, (m,m)MgONTs, to explore the encapsulation, inclusion, and adsorption of dyes (organic molecules) such as Indigo (IND). Studies start by determining the structural parameters of the MgO nanotubes with different diameters and the IND. The indigo encapsulation into the MgONT is studied considering four (m,m) chiralities which yield 4 different NT diameters. In the endohedral functionalization, the indigo is within the NT at a tilt angle as in previous theoretical studies of organic molecules inside carbon and boron-nitride nanotubes. Results show that the encapsulation is a strong exothermic process with the m = 6 case exhibiting the largest encapsulation energy. It is also explored the indigo adsorption on the NT surface in the parallel and perpendicular configurations. The perpendicular configuration of the IND adsorption on the (8,8)MgONT exhibits the largest energy. The indigo inclusion within the NTs meets a potential barrier when m < 6, however this barrier diminishes as the index increases. Additionally, we have determined the total density of states (DOS), partial DOS, electron charge redistributions, and the highest occupied molecular orbital–lowest unoccupied molecular orbital levels for the NTs with m = 6. Very strong binding energies and electron charge transfer from the IND to NTs is present in the atomic structures.

  8. First-principles calculations of the indigo encapsulation and adsorption by MgO nanotubes

    NASA Astrophysics Data System (ADS)

    Sánchez-Ochoa, F.; Cocoletzi, Gregorio H.; Canto, Gabriel I.; Takeuchi, Noboru

    2014-06-01

    We have performed ab-initio calculations to investigate the structural and electronic properties of (m,m) chiral magnesium oxide nanotubes, (m,m)MgONTs, to explore the encapsulation, inclusion, and adsorption of dyes (organic molecules) such as Indigo (IND). Studies start by determining the structural parameters of the MgO nanotubes with different diameters and the IND. The indigo encapsulation into the MgONT is studied considering four (m,m) chiralities which yield 4 different NT diameters. In the endohedral functionalization, the indigo is within the NT at a tilt angle as in previous theoretical studies of organic molecules inside carbon and boron-nitride nanotubes. Results show that the encapsulation is a strong exothermic process with the m = 6 case exhibiting the largest encapsulation energy. It is also explored the indigo adsorption on the NT surface in the parallel and perpendicular configurations. The perpendicular configuration of the IND adsorption on the (8,8)MgONT exhibits the largest energy. The indigo inclusion within the NTs meets a potential barrier when m < 6, however this barrier diminishes as the index increases. Additionally, we have determined the total density of states (DOS), partial DOS, electron charge redistributions, and the highest occupied molecular orbital-lowest unoccupied molecular orbital levels for the NTs with m = 6. Very strong binding energies and electron charge transfer from the IND to NTs is present in the atomic structures.

  9. Pure and Zn-doped Pt Clusters go Flat and Upright on MgO(100)

    SciTech Connect

    Shen, Lu; Dadras, Mostafa J.; Alexandrova, Anastassia N.

    2014-12-28

    Pure and doped sub-nanoclusters can exhibit superb catalytic activity, which, however, strongly depends on their size, shape, composition, and the nature of the support. This work is about surface-deposited sub-nano Pt-based clusters, which are promising catalysts for the reactions of dehydrogenation. Using density functional theory and ab initio calculations, and an ab initio genetic algorithm for finding the global minima of clusters, we found a peculiar effect that Pt₅ and Pt₄Zn clusters exhibit upon deposition on MgO(100). Both of them change shapes from the gas phase 3-D form to a planar form, and they stand upright on the support. Several reasons are responsible for this behaviour. In part, clusters go flat due to the electron transfer from the support. Indeed, the anionic Pt₅- and Pt₄Zn- species are flat also in the gas phase. Charging induces the second-order Jahn–Teller effect (or partial covalency) facilitated by the recruitment of the higher-energy 6p atomic orbitals on Pt into the valence manifold, and that is the reason for the planarization of the anions. Secondly, clusters maximize interactions with the surface O atoms (resulting in further favouring of 2-D structures over 3-D), and avoid contacts with surface Mg atoms (resulting in upright morphologies).

  10. Improved virus removal in ceramic depth filters modified with MgO.

    PubMed

    Michen, Benjamin; Fritsch, Johannes; Aneziris, Christos; Graule, Thomas

    2013-02-01

    Ceramic filters, working on the depth filtration principle, are known to improve drinking water quality by removing human pathogenic microorganisms from contaminated water. However, these microfilters show no sufficient barrier for viruses having diameters down to 20 nm. Recently, it was shown that the addition of positively charged materials, for example, iron oxyhydroxide, can improve virus removal by adsorption mechanisms. In this work, we modified a common ceramic filter based on diatomaceous earth by introducing a novel virus adsorbent material, magnesium oxyhydroxide, into the filter matrix. Such filters showed an improved removal of about 4-log in regard to bacteriophages MS2 and PhiX174. This is explained with the electrostatic enhanced adsorption approach that is the favorable adsorption of negatively charged viruses onto positively charged patches in an otherwise negatively charged filter matrix. Furthermore, we provide theoretical evidence applying calculations according to Derjaguin-Landau-Verwey-Overbeek theory to strengthen our experimental results. However, modified filters showed a significant variance in virus removal efficiency over the course of long-term filtration experiments with virus removal increasing with filter operation time (or filter aging). This is explained by transformational changes of MgO in the filter upon contact with water. It also demonstrates that filter history is of great concern when filters working on the adsorption principles are evaluated in regard to their retention performance as their surface characteristics may alter with use. PMID:23286835

  11. Adsorption of Ponceau S from aqueous solution by MgO nanoparticles

    NASA Astrophysics Data System (ADS)

    Venkatesha, T. G.; Nayaka, Y. Arthoba; Chethana, B. K.

    2013-07-01

    Ponceau S or Acid Red 112 is a widely used dye with versatile applications whose biotransformation products are toxic and is a suspected carcinogen. In the present work, magnesium oxide (MgO) nanoparticles were synthesized by precipitation method and used for the sorption of Ponceau S from aqueous solution. The effects of parameters like contact time, pH and temperature on the adsorption capacity were studied. The adsorption isotherm studies were carried out using Langmuir, Freundlich and Temkin models, of which Langmuir model was found more suitable. Pseudo-second-order model fitted well with good agreement with the experimental values of qe (equilibrium adsorption capacity). The values of thermodynamic parameters like enthalpy (ΔH°) and entropy (ΔS°) were found to be 35.71 kJ/mol and 0.127 J/K/mol, respectively. The negative values of standard free energy (ΔG°) suggested that the adsorption process is spontaneous with the energy of activation equal to 28.58 kJ/mol.

  12. Shock Response and Phase Transitions of MgO at Planetary Impact Conditions.

    PubMed

    Root, Seth; Shulenburger, Luke; Lemke, Raymond W; Dolan, Daniel H; Mattsson, Thomas R; Desjarlais, Michael P

    2015-11-01

    The moon-forming impact and the subsequent evolution of the proto-Earth is strongly dependent on the properties of materials at the extreme conditions generated by this violent collision. We examine the high pressure behavior of MgO, one of the dominant constituents in Earth's mantle, using high-precision, plate impact shock compression experiments performed on Sandia National Laboratories' Z Machine and extensive quantum calculations using density functional theory (DFT) and quantum Monte Carlo (QMC) methods. The combined data span from ambient conditions to 1.2 TPa and 42 000 K, showing solid-solid and solid-liquid phase boundaries. Furthermore our results indicate that under impact the solid and liquid phases coexist for more than 100 GPa, pushing complete melting to pressures in excess of 600 GPa. The high pressure required for complete shock melting has implications for a broad range of planetary collision events. PMID:26588422

  13. Structure of helicoptering H2 molecules on MgO(001)

    NASA Astrophysics Data System (ADS)

    Jack, David B.; Sadeghifar, Alireza; Livingston, Christina F.; Kootnekoff, Brandon A.; Makins, Caitlyn; Hawrylo, Jennifer; Creelman, J. Brianna; McTaggart, Julie L.

    2015-11-01

    Monte Carlo (MC) simulations of helicoptering (J = 1; mj = ± 1) H2 molecules on the MgO(001) surface using rotationally averaged interaction potentials are reported and show that at the coverage Ө = 0.5 the film forms a structure with c(2 × 2) symmetry in agreement with experiment. This structure is stable up to 6 K. The unit cell is arranged in a quincunx pattern and has a density of two H2 molecules per unit cell. Each molecule sits above the cation sites with its axis of quantization pointing perpendicular to the surface on average. The unit cell symmetry is "c" type in agreement with helium atom scattering experiment and in contrast with the "p" type structures observed in previous simulations which did not include quantum mechanically averaged potentials from the start. The occurrence of defects was also observed with increasing frequency as the temperature rose. An increase in the number of defects was accompanied by greater aggregation at the expense of the c(2 × 2) structure.

  14. Chemistry at corners and edges: Generation and adsorption of H atoms on the surface of MgO nanocubes

    SciTech Connect

    Sterrer, Martin; Berger, Thomas; Diwald, Oliver; Knoezinger, Erich; Sushko, Peter V.; Shluger, Alexander L.

    2005-08-08

    We used UV light to generate site-selective O{sup -} hole centers at three-coordinated corner oxygen sites on MgO nanocubes. These highly reactive O{sup -} radicals split H{sub 2} homolytically and, in the course of this reaction, become hydroxylated and produce hydrogen atoms. The hydrogen atoms adsorb predominantly at cube edges and dissociate into surface-trapped electrons and protons. We propose that the experimentally observed (H{sup +})(e{sup -}) centers are formed adjacent to the hydroxyl groups generated in the homolytic splitting process and can be defined as (H{sup +}){sub 3C}{center_dot}{center_dot}{center_dot}(e{sup -})(H{sup +}){sub NC} centers where 3C and NC refer to the coordination numbers of the corresponding hydroxylated oxygen sites. Our ab initio embedded cluster calculations reveal that the electronic properties of (H{sup +}){sub 3C}{center_dot}{center_dot}{center_dot}(e{sup -})(H{sup +}){sub 4C} centers situated along MgO nanocube edges are consistent with both the electron-paramagnetic-resonance signal parameters and the reported optical-absorption properties. The transformation of corner O{sup -} centers into the (H{sup +}){sub 3C}{center_dot}{center_dot}{center_dot}(e{sup -})(H{sup +}){sub NC}-type centers prevents their recombination with electronic surface centers and, hence, significantly alters the electronic structure of MgO nanocubes by introducing shallow electron traps.

  15. Visible Color Tunable Emission in Three-Dimensional Light Emitting Diodes by MgO Passivation of Pyramid Tip.

    PubMed

    Kim, Ji-Hyun; Ye, Byeong Uk; Park, Joonmo; Yoo, Chul Jong; Kim, Buem Joon; Jeong, Hu Young; Hur, Jin-Hoe; Kim, Jong Kyu; Lee, Jong-Lam; Baik, Jeong Min

    2015-12-23

    We demonstrated visible color tunable three-dimensional (3D) pyramidal light emitting diodes by depositing the MgO on and near the tip of the pyramid as an insulating layer. Here, we show that the degradation of the materials (i.e., p-GaN) crystallinity and the built-in electric field due to the nanoscale geometry of the tip region is responsible for the large leakage current observed in LEDs. Confocal scanning electroluminescence microscopy images clearly showed that the intensity of the light emitted out of the side facet of the pyramid is much higher than that of the light extracted out of the tip surface, indicating that the MgO layer prohibited the carrier injection to the MQWs layer, suppressing the leakage occurring at or near the tip region of the pyramids. The color range of the LEDs can be also tuned by using the MgO layer, a blue-shift by 10.3 nm in the wavelength. This technique is simple and scalable, providing a promising solution for developing 3D pyramidal LEDs with low leakage current and controllable light emission. PMID:26575093

  16. Addition of MgO Nanoparticles to Carbon Structural Steel and the Effect on Inclusion Characteristics and Microstructure

    NASA Astrophysics Data System (ADS)

    Gao, Xiangzhou; Yang, Shufeng; Li, Jingshe; Liao, Hang; Gao, Wei; Wu, Tuo

    2016-04-01

    An innovative approach for pre-dispersing MgO nanoparticles with AlSi alloy nanoparticles was established, and the nanoparticles were dispersed well in carbon structural steel. After adding different mass fractions of MgO nanoparticles in steel, the majority of inclusions contained MgO·Al2O3 spinel and MgO-Al2O3-bearing hybrid inclusion, and these inclusions promoted acicular ferrite (AF) formation. With increasing amount of added nanoparticles, the average inclusion size increased from 0.90 to 1.50 μm and the inclusion size was considerably refined, but the ability of inclusions to induce AF was greatly declined. It was revealed that the inclusion size was the decisive factor influencing the inducing ability of inclusions for AF, which also got a solid support from the nucleation thermomechanical and dynamic analyses. When the mass fraction of MgO nanoparticles reached 0.05 pct, the proportion of AF in microstructure is relatively larger and the degree of interlocking of the AF within the microstructure was optimized. The ferrite grains also got refined and the average grain size decreased by more than 94 pct compared with that of the original steel.

  17. Evaluation of novel reactive MgO activated slag binder for the immobilisation of lead and zinc.

    PubMed

    Jin, Fei; Al-Tabbaa, Abir

    2014-12-01

    Although Portland cement is the most widely used binder in the stabilisation/solidification (S/S) processes, slag-based binders have gained significant attention recently due to their economic and environmental merits. In the present study, a novel binder, reactive MgO activated slag, is compared with hydrated lime activated slag in the immobilisation of lead and zinc. A series of lead or zinc-doped pastes and mortars were prepared with metal to binder ratio from 0.25% to 1%. The hydration products and microstructure were studied by X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The major hydration products were calcium silicate hydrate and hydrotalcite-like phases. The unconfined compressive strength was measured up to 160 d. Findings show that lead had a slight influence on the strength of MgO-slag paste while zinc reduced the strength significantly as its concentration increased. Leachate results using the TCLP tests revealed that the immobilisation degree was dependent on the pH and reactive MgO activated slag showed an increased pH buffering capacity, and thus improved the immobilisation efficiency compared to lime activated slag. It was proposed that zinc was mainly immobilised within the structure of the hydrotalcite-like phases or in the form of calcium zincate, while lead was primarily precipitated as the hydroxide. It is concluded, therefore, that reactive MgO activated slag can serve as clinker-free alternative binder in the S/S process. PMID:25123653

  18. The influence of an MgO nanolayer on the planar Hall effect in NiFe films

    SciTech Connect

    Li, Minghua; Zhao, Zhiduo; Ma, Lin; Lu, Xiangan; Teng, Jiao; Yu, Guanghua; Yu, Guoqiang; Amiri, Pedram Khalili; Wang, Kang L.; Zhou, Wenping

    2015-03-28

    The Planar Hall Effect (PHE) in NiFe films was studied using MgO as the buffer and capping layer to reduce the shunt effect. The thermal annealing was found to be effective in increasing the sensitivity. The sensitivity of the magnetic field reached as high as 865 V/AT in a MgO (3 nm)/NiFe (5 nm)/MgO(3 nm)/Ta(3 nm) structure after annealing at 500 °C for 2 h, which is close to the sensitivity of semiconductor Hall Effect (HE) sensors. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were used to study the sample. The results show that the top crystallization of MgO and NiFe (111) texture were improved by proper annealing. The smooth and clear bottom MgO/NiFe and top NiFe/MgO interface is evident from our data. In addition, the shunt current of Ta was decreased. These combined factors facilitate the improvement of the sensitivity of the magnetic field.

  19. Nano SiO2 and MgO Improve the Properties of Porous β-TCP Scaffolds via Advanced Manufacturing Technology

    PubMed Central

    Gao, Chengde; Wei, Pingpin; Feng, Pei; Xiao, Tao; Shuai, Cijun; Peng, Shuping

    2015-01-01

    Nano SiO2 and MgO particles were incorporated into β-tricalcium phosphate (β-TCP) scaffolds to improve the mechanical and biological properties. The porous cylindrical β-TCP scaffolds doped with 0.5 wt % SiO2, 1.0 wt % MgO, 0.5 wt % SiO2 + 1.0 wt % MgO were fabricated via selective laser sintering respectively and undoped β-TCP scaffold was also prepared as control. The phase composition and mechanical strength of the scaffolds were evaluated. X-ray diffraction analysis indicated that the phase transformation from β-TCP to α-TCP was inhibited after the addition of MgO. The compressive strength of scaffold was improved from 3.12 ± 0.36 MPa (β-TCP) to 5.74 ± 0.62 MPa (β-TCP/SiO2), 9.02 ± 0.55 MPa (β-TCP/MgO) and 10.43 ± 0.28 MPa (β-TCP/SiO2/MgO), respectively. The weight loss and apatite-forming ability of the scaffolds were evaluated by soaking them in simulated body fluid. The results demonstrated that both SiO2 and MgO dopings slowed down the degradation rate and improved the bioactivity of β-TCP scaffolds. In vitro cell culture studies indicated that SiO2 and MgO dopings facilitated cell attachment and proliferation. Combined addition of SiO2 and MgO were found optimal in enhancing both the mechanical and biological properties of β-TCP scaffold. PMID:25815597

  20. Microstructure and dielectric tunable properties of Ba0.6Sr0.4TiO3-Mg2SiO4-MgO composite.

    PubMed

    He, Yanyan; Xu, Yebin; Liu, Ting; Zeng, Chunlian; Chen, Wanping

    2010-07-01

    Ba(0.6)Sr(0.4)TiO(3)-Mg(2)SiO(4)-MgO composite ceramics were prepared by a solid-state reaction method and their dielectric tunable characteristics were investigated for the potential application as microwave tunable materials. The addition of Mg(2)SiO(4)-MgO into Ba(0.6)Sr(0.4)TiO(3) forms ferroelectric (Ba(0.6)Sr(0.4)TiO(3))-dielectric (Mg(2)SiO(4)-MgO) composites and shifts the Curie temperature to a lower temperature. The dielectric constant and loss tangent of Ba(0.6)Sr(0.4)TiO(3)-Mg(2)Si(O4)- MgO composites have been decreased and the overall tunability is maintained at a sufficiently high level. The microwave dielectric properties of Ba(0.6)Sr(0.4)TiO(3)-Mg(2)Si(O4)-MgO composites were evaluated. Ba(0.6)Sr(0.4)TiO(3)-Mg(2)SiO(4)-MgO composites have tunability of 9.2 to 10.5% at 100 kHz under 2 kV/mm, indicating that it is a promising candidate material for tunable microwave applications requiring a low dielectric constant. PMID:20639146

  1. Effect of MgO content in sinter on the softening-melting behavior of mixed burden made from chromium-bearing vanadium-titanium magnetite

    NASA Astrophysics Data System (ADS)

    Liu, Zheng-gen; Chu, Man-sheng; Wang, Hong-tao; Zhao, Wei; Xue, Xiang-xin

    2016-01-01

    The effect of sinter with different MgO contents on the softening-melting behavior of mixed burden made from chromium- bearing vanadium-titanium magnetite was investigated. The results show that with increasing MgO content in the sinter, the softening interval and melting interval increased and the location of the cohesive zone shifted downward slightly and became moderately thicker. The softening-melting characteristic value was less pronounced when the MgO content in the sinter was 2.98wt%-3.40wt%. Increasing MgO content in the sinter reduced the content and recovery of V and Cr in the dripped iron. In addition, greater MgO contents in the sinter resulted in the generation of greater amounts of high-melting-point components, which adversely affected the permeability of the mixed burden. When the softening-melting behavior of the mixed burden and the recovery of valuable elements were taken into account, proper MgO contents in the sinter and slag ranged from 2.98wt% to 3.40wt% and from 11.46wt% to 12.72wt%, respectively, for the smelting of burden made from chromium-bearing vanadium-titanium magnetite in a blast furnace.

  2. Improvement of Resistance to Slag Penetration in Magnesia-Based Refractory with Colloidal Alumina Addition II by Means of a Proper Particle Size Distribution of MgO

    NASA Astrophysics Data System (ADS)

    Wang, Huijun; Sichen, Du

    2016-06-01

    By addition of colloidal alumina, three different particle sizes of dead burnt MgO were employed as raw materials to prepare MgO-based spinel substrates at 1773 K (1500 °C). It was found that the particle size of MgO, as well as its size distribution, had substantial impact on the resistance of the refractory to the slag penetration at 1873 K (1600 °C). Using relatively small particles of MgO (<0.5 mm) can efficiently limit the slag penetration, due to the formation of solid phases (CaO·Al2O3 and CaO-MgO-Al2O3) at the grain boundaries. A particularly significant improvement against the slag penetration was found on MgO substrates with a proper particle size distribution in a size range of 0-1 mm. The improvement could be mainly related to the higher density and distribution of spinel phase in the MgO matrix, which is mostly located at the borders of large MgO particles.

  3. Ferroelectric thin film microstructure development and related property enhancement

    SciTech Connect

    Tuttle, B.; Voigt, J.A.; Headley, T.J.; Potter, B.G.; Dimos, D.; Schwartz, R.W.; Dugger, M.T.; Michael, J.; Nasby, R.D.; Garino, T.J.; Goodnow, D.C.

    1993-11-01

    Factors that control phase evolution, microstructural development and ferroelectric domain assemblage are evaluated for chemically prepared lead zirconate titanate (PZT) thin films. Zirconium to titanium stoichiometry is shown to strongly influence microstructure. As Ti content increases, there is an apparent enhancement of the perovskite phase nucleation rate, grain size becomes smaller, and the amount of pyrochlore phase, if present, decreases. While the pyrochlore matrix microstructure for near morphotropic phase boundary composition thin films consists of two interpenetrating nanophases (pyrochlore and an amorphous phase), the pyrochlore microstructure for PZT 20/80 films deposited on MgO substrates is single phase and consists of 10nm grains. Zirconium to titanium stoichiometry also has a substantial influence on process integration. Near morphotropic phase boundary films exhibit extensive reaction with underlying TiO{sub 2} diffusion barriers; conversely, there is no chemical reaction for identically processed PZT 20/80 thin films. The authors have attempted to directly correlate the optical quality of PZT thin films to the following microstructural features: (1) presence of a second phase, (2) domain orientation, and (3) nanometer surface morphology.

  4. Oriented lead zirconate titanate thin films: Characterization of film crystallization

    SciTech Connect

    Voigt, J.A.; Tuttle, B.A.; Headley, T.J.; Eatough, M.O.; Lamppa, D.L.; Goodnow, D.

    1993-11-01

    Film processing temperature and time was varied to characterize the pyrochlore-to-perovskite crystallization of solution-derived PZT 20/80 thin films. 3000 {Angstrom} thick films were prepared by spin deposition using <100> single crystal MgO as substrate. By controlled rapid thermal processing, films at different stages in the perovskite crystallization process were prepared with the tetragonal PZT 20/80 phase being <100>/<001> oriented relative to the MgO surface. An activation energy for the conversion process of 326 kJ/mole was determined by use of an Arrhenius expression using rate constants found by application of the method of Avrami. Activation energy for formation of the PZT 20/80 perovskite phase of the solution-derived films compared favorably with that calculated from data by Kwok and Desu for sputter-deposited 3500 {Angstrom} thick PZT 55/45 films. Similarity in activation energies indicates that the energetics of the conversion process are not strongly dependent on the method used for film deposition.

  5. Electrooptic modulation up to 40 GHz in a barium titanate thin film waveguide modulator

    NASA Astrophysics Data System (ADS)

    Tang, Pingsheng; Towner, D. J.; Hamano, T.; Meier, A. L.; Wessels, B. W.

    2004-11-01

    The high frequency operation of a low-voltage electrooptic modulator based on a strip-loaded BaTiO3 thin film waveguide structure has been demonstrated. The epitaxial BaTiO3 thin film on an MgO substrate forms a composite structure with a low effective dielectric constant of 20.8 at 40 GHz. A 3.9 V half-wave voltage with a 3.7 GHz 3-dB bandwidth and a 150 pm/V effective electrooptic coefficient is obtained for the 3.2mm-long modulator at 1.55 μm. Broadband modulation up to 40 GHz is measured with a calibrated detection system. Numerical simulations indicate that the BaTiO3 thin film modulator has the potential for a 3-dB operational bandwidth in excess of 40 GHz through optimized design.

  6. Proton Transport and Microstructure Properties in Superlattice Thin Films Fabricated by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Kuwata, Naoaki; Sata, Noriko; Tsurui, Takao; Yugami, Hiroo

    2005-12-01

    Superlattice thin films of the perovskite-type oxide proton conductor SrZr0.95Y0.05O3/SrTiO3 was fabricated by pulsed laser deposition. Their structural and proton transport properties were reported. X-ray diffraction analysis and selected area electron diffraction revealed that the thin films were epitaxially grown on MgO(001) substrate. High-density edge dislocations and a columnar structure were observed in the films by high-resolution electron microscopy. The in-plane electrical conductivity of the thin films was determined by impedance spectroscopy. The contribution of proton transport to the total conductivity of the films was confirmed by H2O/D2O exchange measurement. The conductivity of superlattice films was increased by introducing heterointerfaces. The high activation energy (Ea=1.0 eV) was explained by the grain-boundary effect of the columnar structure in the films.

  7. Growth of thin Fe(0 0 1) films for terahertz emission experiments

    NASA Astrophysics Data System (ADS)

    Meserole, C. A.; Fisher, G. L.; Hilton, D. J.; Averitt, R. D.; Funk, D. J.; Taylor, A. J.

    2007-06-01

    The electrical and magnetic properties of thin iron (Fe) films have sparked significant scientific interest. Our interest, however, is in the fundamental interactions between light and matter. We have discovered a novel application for thin Fe films. These films are sources of terahertz (THz) radiation when stimulated by an incident laser pulse. After intense femtosecond pulse excitation by a Ti:sapphire laser, these films emit picosecond, broadband THz frequencies. The terahertz emission provides a direct measure of the induced ultrafast change in magnetization within the Fe film. The THz generation experiments and the growth of appropriate thin Fe films for these experiments are discussed. Several criteria are used to select the substrate and film growth conditions, including that the substrate must permit the epitaxial growth of a continuous, monocrystalline or single crystal film, yet must also be transparent to the emitted THz radiation. An Fe(0 0 1) film grown on the (0 0 1) surface of a magnesium oxide (MgO) substrate makes an ideal sample. The Fe films are grown by physical vapor deposition (PVD) in an ultrahigh vacuum (UHV) system. Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) are used to characterize the Fe(0 0 1) films. Two substrate surface preparation methods are investigated. Fe(0 0 1) films grown on MgO(0 0 1) substrates that are used as-received and films grown on MgO(0 0 1) substrates that have been UV/ozone-cleaned ex vacuo and annealed in vacuo produce the same results in the THz generation experiments. Either substrate preparation method permits the growth of samples suitable for the THz emission experiments.

  8. Magnesium Vacancy Segregation and Fast Pipe Diffusion for the ½<110>{110} Edge Dislocation in MgO

    NASA Astrophysics Data System (ADS)

    Walker, A. M.; Zhang, F.; Wright, K.; Gale, J. D.

    2009-12-01

    The movement of point defects in minerals plays a key role in determining their rheological properties, both by permitting diffusional creep and by allowing recovery by dislocation climb. Point defect diffusion can also control the kinetics of phase transitions and grain growth, and can determine the rate of chemical equilibration between phases. Because of this, and the difficulties associated with experimental studies of diffusion, the simulation of point defect formation and migration has been a subject of considerable interest in computational mineral physics. So far, studies have concentrated on point defects moving through otherwise perfect crystals. In this work we examine the behavior of magnesium vacancies close to the core of an edge dislocation in MgO and find that the dislocation dramatically changes the behavior of the point defect. An atomic scale model of the ½<110>{110} edge dislocation in MgO was constructed by applying the anisotropic linear elastic displacement field to the crystal structure and subsequently minimizing the energy of the crystal close to the dislocation core using a parameterized potential model. This process yielded the structure of an isolated edge dislocation in an otherwise perfect crystal. The energy cost associated with introducing magnesium vacancies around the dislocation was then mapped and compared to the formation energy of an isolated magnesium vacancy in bulk MgO. We find that the formation energy of magnesium vacancies around the dislocation mirrors the elastic strain field. Above the dislocation line σxx and σyy are negative and the strain field is compressional. Atoms are squeezed together to make room for the extra half plane effectively increasing the pressure in this region. Below the dislocation line σxx and σyy are positive and the strain field is dilatational. Planes of atoms are pulled apart to avoid a discontinuity across the glide plane and the effective pressure is decreased. In the region with a

  9. PZT thin films for piezoelectric MEMS mechanical energy harvesting

    NASA Astrophysics Data System (ADS)

    Yeager, Charles

    This thesis describes the optimization of piezoelectric Pb(ZrxTi 1-x)O3 (PZT) thin films for energy generation by mechanical energy harvesting, and self-powered micro-electro-mechanical systems (MEMS). For this purpose, optimization of the material was studied, as was the incorporation of piezoelectric films into low frequency mechanical harvesters. A systematic analysis of the energy harvesting figure of merit was made. As a figure of merit (e31,ƒ)2/epsilon r (transverse piezoelectric coefficient squared over relative permittivity) was utilized. PZT films of several tetragonal compositions were grown on CaF2, MgO, SrTiO3, and Si substrates, thereby separating the dependence of composition on domain orientation. To minimize artifacts associated with composition gradients, and to extend the temperature growth window, PZT films were grown by metal organic chemical vapor deposition (MOCVD). Using this method, epitaxial {001} films achieved c-domain textures above 90% on single crystal MgO and CaF2 substrates. This could be tailored via the thermal stresses established by the differences in thermal expansion coefficients of the film and the substrate. The single-domain e31,ƒ for PZT thin films was determined to exceed -12 C/m2 in the tetragonal phase field for x ≥ 0.19, nearly twice the phenomenologically modeled value. The utilization of c-domain PZT films is motivated by a figure of merit above 0.8 C2/m4 for (001) PZT thin films. Increases to the FoM via doping and hot poling were also quantified; a 1% Mn doping reduced epsilonr by 20% without decreasing the piezoelectric coefficient. Hot poling a device for one hour above 120°C also resulted in a 20% reduction in epsilonr ; furthermore, 1% Mn doping reduced epsilonr by another 12% upon hot poling. Two methods for fabricating thin film mechanical energy harvesting devices were investigated. It was found that phosphoric acid solutions could be used to pattern MgO crystals, but this was typically accompanied by

  10. Electrodynamic properties of lead Zirconate-Titanate thin films in the terahertz frequency range

    NASA Astrophysics Data System (ADS)

    Komandin, G. A.; Porodinkov, O. E.; Iskhakova, L. D.; Spektor, I. E.; Volkov, A. A.; Vorotilov, K. A.; Seregin, D. S.; Sigov, A. S.

    2014-11-01

    The transmission/reflection spectra of bilayer structures consisting of thin amorphous and polycrystalline Pb(Zr0.52Ti0.48)O3 ferroelectric films deposited on dielectric substrates of magnesium oxide MgO and sapphire α-Al2O3 were measured in the frequency range of 5-4000 cm-1. Based on these spectra and using the dispersion analysis method, the spectra of complex dielectric permittivity ɛ*(ν) and dynamic conductivity σ'(ν) of the films were simulated, the electrodynamic parameters of the films were determined, and the dielectric dispersion responsible for the formation of static permittivity was found.

  11. Electric field modulation of thermopower for transparent amorphous oxide thin film transistors

    NASA Astrophysics Data System (ADS)

    Koide, Hirotaka; Nagao, Yuki; Koumoto, Kunihito; Takasaki, Yuka; Umemura, Tomonari; Kato, Takeharu; Ikuhara, Yuichi; Ohta, Hiromichi

    2010-11-01

    To clarify the electronic density of states (DOS) around the conduction band bottom for state of the art transparent amorphous oxide semiconductors (TAOSs), InGaZnO4 and In2MgO4, we fabricated TAOS-based transparent thin film transistors (TTFTs) and measured their gate voltage dependence of thermopower (S). TAOS-based TTFTs exhibit an unusual S behavior. The |S|-value abruptly increases but then gradually decreases as Vg increases, clearly suggesting the antiparabolic shaped DOS is hybridized with the original parabolic shaped DOS around the conduction band bottom.

  12. Ligand-free osmium clusters supported on MgO. A density functional study

    SciTech Connect

    Goellner, J.F.; Neyman, K.M.; Mayer, M.; Noertemann, F.; Gates, B.C.; Roesch, N.

    2000-03-21

    The interactions of Os{sub 4}, Os{sub 5}, and Os{sub 5}C clusters with various sites of a MgO(001) support were investigated theoretically with the aid of a scalar-relativistic density functional cluster model method. Adsorption geometries of C{sub 4{upsilon}} clusters centered above a magnesium cation and the Os atoms oriented either to the nearest surface oxygen anions (A) or between them (B) were considered. The influence of surface V{sub s} and V{sub s}{sup 2{minus}} defects on the adsorption of the clusters was also investigated. The calculated base Os-Os distances in supported Os{sub 5} and Os{sub 5}C square-pyramidal clusters are at most 0.1 {angstrom} longer (2.5--2.6{angstrom}) than the values calculated for the corresponding free osmium cluster but about 0.4{angstrom} (or more) shorter than the values determined by EXAFS spectroscopy for MgO-powder-supported clusters formed by decarbonylation of [Os{sub 5}C(CO){sub 14}]{sup 2{minus}} and shown to retains the Os{sub 5}C frame. The experimental Os-Os distances characterizing the supported clusters are close to the experimental and calculated bond lengths for coordinatively saturated osmium carbonyl clusters; the result favors the suggestion that the supported clusters characterized by EXAFS spectroscopy were not entirely ligand-free. The models reported here are inferred to be too simplified to capture all the pertinent structural details of MgO-powder-supported osmium clusters, but they are sufficient to indicate a significant role of defect sites in the adsorption of supported osmium clusters and, the authors infer, other transition metal clusters.

  13. Overcoming the polarization catastrophe in the rocksalt oxides MgO and CaO

    NASA Astrophysics Data System (ADS)

    Gaddy, Benjamin E.; Paisley, Elizabeth A.; Maria, Jon-Paul; Irving, Douglas L.

    2014-09-01

    Interfaces between dissimilar polar materials may provide a pathway to new device functionality, including high carrier mobility layers at the interface. The development of these materials has proven challenging, in part because of the high energy cost of forming polar surfaces. Our density functional theory calculations explore the mechanisms by which a real material satisfies the electrostatic criteria for stability imposed by a polar surface. The consequences of polarity are studied by comparing the formation energies, charge distribution, and electronic structure of a number of low-index surfaces of rocksalt MgO and CaO. These surfaces are explored both in their bare, undecorated form as well as with surface reconstructions and adsorbed foreign species. Our ground-state surface energies are extended to relevant environmental conditions by use of ab initio thermodynamics. We find that the high energy of bare polar surfaces is the result of the significant charge redistribution that arises to compensate the polarity and pushes electronic states into the forbidden band gap. Other mechanisms of polarity compensation (reconstruction or foreign species adsorption) are therefore seen more frequently. We explain the experimental observations of surface roughness during growth in the [111] direction. In typical epitaxial growth conditions, there is preferential formation of an octopolar reconstruction of the {111} surface, which exposes {001}-type nanofacets. The low energy of the {001} surface likely causes these facets to grow, leading to a rough surface morphology. Our results indicate that when water vapor is present during growth, a smooth, polar surface can be stabilized by the formation of a hydroxyl layer.

  14. Structural and magnetic properties of SmCo5/Co exchange coupled nanocomposite thin films

    NASA Astrophysics Data System (ADS)

    Chowdhury, P.; Krishnan, M.; Barshilia, Harish C.; Sridhara Rao, D. V.; Kumar, Deepak; Shivakumara, C.

    2013-09-01

    We investigated the structural and magnetic properties of SmCo5/Co exchange coupled nanocomposite thin films grown by magnetron sputtering from Sm and Co multitargets successively. The growth of the films was carried out at elevated substrate temperature followed by in situ annealing. On Si (100) substrate, X-ray diffraction confirms the formation of textured (110) SmCo5 hard phase, whereas on MgO(110) substrate, the diffraction pattern shows the epitaxial growth of SmCo5 phase with crystalline orientation along [100] direction. Secondary Ion Mass Spectroscopy reveals the structural transformation from multilayered (Sm/Co) to SmCo5/Co nano-composite films due to high reactivity of Sm at elevated temperature. Transmission electron microscopy indicates the existence of nanocrystalline phase of SmCo5 along with unreacted Co. Observed single phase behavior in magnetic hysteresis measurements indicates well exchange coupling between the soft and the hard phases in these nano-composite films. For samples with samarium layer thickness, tSm=3.2 nm and cobalt layer thickness, tCo=11.4 nm, the values of (BH)max were obtained as 20.1 MGOe and 12.38 MGOe with Hc value ∼3.0 kOe grown on MgO and Si substrates, respectively. Formation of SmCo5/Co exchange spring nanocomposite films with successive deposition of Sm and Co layers at 450 °C. This technique gives the textured growth of the film on Si and epitaxial growth on crystalline MgO Substrate. High (BH)max on MgO substrate and large anisotropy.

  15. FeO2/MgO(1 0 0) supported cluster: Computational pursual for a low-cost and low-temperature CO nanocatalyst

    NASA Astrophysics Data System (ADS)

    Zamora, A. Y.; Reveles, J. U.; Mejia-Olvera, R.; Baruah, T.; Zope, R. R.

    2014-09-01

    CO oxidation of only 0.23 eV.Regarding the CO catalytic activity of iron oxide species at low-temperatures, it has been experimentally observed that thin oxide films on metals may indeed exhibit greatly enhanced catalytic activity compared to the underlying metal substrate under the same conditions [24]. In addition to the above studies, low temperature CO oxidation over Ag supported ultrathin MgO films was recently reported [17]. In this case, the activation barrier (0.7 eV) resulted lower than the corresponding barrier of CO oxidation on Pt(1 1 1) of 0.9 eV. The gas phase reaction (½O2 + CO → CO2) was calculated to present an overall exothermicity of 3.2 eV. Importantly, this study showed the possibility to generate a catalyst in which the CO adsorption energy of only 0.4 eV is low enough to prevent CO poisoning, therefore enabling a low temperature CO oxidation route, and addressing the cold start problem [25].Despite the above mentioned studies, the development of active and stable catalysts, without noble metals, for low-temperature CO oxidation under an ambient atmosphere remains a significant challenge. Earlier reports, as mentioned above, indicate that the Fe2O3 is the most active iron oxide surface toward CO oxidation at high temperatures (∼300 °C) [8]. Furthermore, a number of theoretical and experimental cluster studies have also shown that selected iron oxide compositions and charge states are the most reactive toward CO oxidation, i.e. FeO2, Fe2O3, FeO2- Fe2O3- FeO+, FeO2+, Fe2O+, Fe2O2+ and Fe2O3+[26,27].The aim of the proposed work is to carry out a detailed investigation that will provide information about the electronic, geometrical, and catalytic properties of the iron oxide FeO2 cluster adsorbed on defect-free MgO(1 0 0) surfaces on the quest for a low-cost and low-temperature CO nano-catalysts. Note that thin oxide films have been found more active at low temperature [24] as compared to the iron oxide surfaces [14]. Our objective is to show

  16. FeO2/MgO(1 0 0) supported cluster: Computational pursual for a low-cost and low-temperature CO nanocatalyst

    NASA Astrophysics Data System (ADS)

    Zamora, A. Y.; Reveles, J. U.; Mejia-Olvera, R.; Baruah, T.; Zope, R. R.

    2014-09-01

    CO oxidation of only 0.23 eV.Regarding the CO catalytic activity of iron oxide species at low-temperatures, it has been experimentally observed that thin oxide films on metals may indeed exhibit greatly enhanced catalytic activity compared to the underlying metal substrate under the same conditions [24]. In addition to the above studies, low temperature CO oxidation over Ag supported ultrathin MgO films was recently reported [17]. In this case, the activation barrier (0.7 eV) resulted lower than the corresponding barrier of CO oxidation on Pt(1 1 1) of 0.9 eV. The gas phase reaction (½O2 + CO → CO2) was calculated to present an overall exothermicity of 3.2 eV. Importantly, this study showed the possibility to generate a catalyst in which the CO adsorption energy of only 0.4 eV is low enough to prevent CO poisoning, therefore enabling a low temperature CO oxidation route, and addressing the cold start problem [25].Despite the above mentioned studies, the development of active and stable catalysts, without noble metals, for low-temperature CO oxidation under an ambient atmosphere remains a significant challenge. Earlier reports, as mentioned above, indicate that the Fe2O3 is the most active iron oxide surface toward CO oxidation at high temperatures (∼300 °C) [8]. Furthermore, a number of theoretical and experimental cluster studies have also shown that selected iron oxide compositions and charge states are the most reactive toward CO oxidation, i.e. FeO2, Fe2O3, FeO2- Fe2O3- FeO+, FeO2+, Fe2O+, Fe2O2+ and Fe2O3+[26,27].The aim of the proposed work is to carry out a detailed investigation that will provide information about the electronic, geometrical, and catalytic properties of the iron oxide FeO2 cluster adsorbed on defect-free MgO(1 0 0) surfaces on the quest for a low-cost and low-temperature CO nano-catalysts. Note that thin oxide films have been found more active at low temperature [24] as compared to the iron oxide surfaces [14]. Our objective is to show

  17. The power of in situ pulsed laser deposition synchrotron characterization for the detection of domain formation during growth of Ba0.5Sr0.5TiO3 on MgO.

    PubMed

    Bauer, Sondes; Lazarev, Sergey; Molinari, Alan; Breitenstein, Andreas; Leufke, Philipp; Kruk, Robert; Hahn, Horst; Baumbach, Tilo

    2014-03-01

    A highly sophisticated pulsed laser deposition (PLD) chamber has recently been installed at the NANO beamline at the synchrotron facility ANKA (Karlsruhe, Germany), which allows for comprehensive studies on the PLD growth process of dielectric, ferroelectric and ferromagnetic thin films in epitaxial oxide heterostructures or even multilayer systems by combining in situ reflective high-energy diffraction with the in situ synchrotron high-resolution X-ray diffraction and surface diffraction methods. The modularity of the in situ PLD chamber offers the opportunity to explore the microstructure of the grown thin films as a function of the substrate temperature, gas pressure, laser fluence and target-substrate separation distance. Ba0.5Sr0.5TiO3 grown on MgO represents the first system that is grown in this in situ PLD chamber and studied by in situ X-ray reflectivity, in situ two-dimensional reciprocal space mapping of symmetric X-ray diffraction and acquisition of time-resolved diffraction profiles during the ablation process. In situ PLD synchrotron investigation has revealed the occurrence of structural distortion as well as domain formation and misfit dislocation which all depend strongly on the film thickness. The microstructure transformation has been accurately detected with a time resolution of 1 s. The acquisition of two-dimensional reciprocal space maps during the PLD growth has the advantage of simultaneously monitoring the changes of the crystalline structure as well as the formation of defects. The stability of the morphology during the PLD growth is demonstrated to be remarkably affected by the film thickness. A critical thickness for the domain formation in Ba0.5Sr0.5TiO3 grown on MgO could be determined from the acquisition of time-resolved diffraction profiles during the PLD growth. A splitting of the diffraction peak into two distinguishable peaks has revealed a morphology change due to modification of the internal strain during growth

  18. The effect of MgO on the optical properties of lithium sodium borate doped with Cu+ ions

    NASA Astrophysics Data System (ADS)

    Alajerami, Yasser Saleh Mustafa; Hashim, Suhairul; Hassan, Wan Muhamad Saridan Wan; Ramli, Ahmad Termizi; Saleh, Muneer Aziz

    2013-04-01

    The current work presented the photoluminescence (PL) properties of a new glass system, which are reported for the first time. Based on the attractive properties of borate glass, a mixture of boric acid (70-x mol %) modified with lithium (20 mol %) and sodium carbonate (10 mol %) was prepared. The current study illustrated the effect of dopant and co-dopant techniques on the lithium sodium borate (LNB). Firstly, 0.1 mol % of copper ions doped with LNB was excited at 610 nm. The emission spectrum showed two prominent peaks in the violet region (403 and 440 nm). Then, we remarked the effect of adding different concentration of MgO on the optical properties of LNB. The results showed the great effect of magnesium oxide on the PL intensities (enhanced more than two times). Moreover, an obvious shifting has been defined toward the blue region (440 → 475 nm). The up-conversion optical properties were observed in all emission spectra. This enhancement is contributed to the energy transfer from MgO ions to monovalent Cu+ ion. It is well known that magnesium oxide alone generates weak emission intensity, but during this increment the MgO act as an activator (co-doped) for Cu+ ions. Finally, energy band gap, density, ion concentration, molar volume, Polaron radius and inter-nuclear distance all were measured for the current samples. The current samples were subjected to XRD for amorphous confirmation and IR for glass characterization before and after dopants addition. Finally, some of significant physical and optical parameters were also calculated.

  19. Effects of MgO buffer annealing on optical and electrical quality of P-MBE grown ZnO films on c-sapphire

    NASA Astrophysics Data System (ADS)

    Setiawan, A.; Yao, T.

    2016-04-01

    Zinc oxide (ZnO) has been attracting much attention because of its potential applications in photonic and optoelectronic devices. In this present study, we investigated the effect of MgO buffer annealing on the optical and electrical quality of P-MBE grown ZnO films on c-sapphire with MgO buffer layer. The optical quality was observed by low-temperature PL (photoluminescence) measurement in the near band edge emission region measured at 10K and at 77K. The emission line located at 3.368eV dominates the spectrum in both samples (ZnO with and without MgO buffer annealing) at 10K and 77K. This emission can be divided into two peaks, 3.367eV and 3.363eV and assigned as I2 (ionized donor bound excitons emission) and I4 (Hydrogen donor related emission), respectively. The relative intensity of these donor bound exactions to free exaction emission of the sample without MgO buffer annealing is greater than that of the sample with MgO buffer annealing. Comparison of the PL spectra of ZnO with and without annealing revealed that the intensity of free exciton emission from the sample with MgO buffer annealing is twice of that from the sample without annealing. We also found that the intensity of deep-level broad emission is reduced by about 1/3 by MgO-buffer annealing. Hence, the decrease of deep level emission intensity and the increase of free exciton emission intensity by annealing of MgO buffer corresponds to the reduction of defects of the ZnO film. The PL properties also suggest that there are fewer nonradiative recombination centers in ZnO layers with MgO buffer annealing than those in ZnO layers grown without MgO buffer annealing. The electrical quality was measured by room temperature Hall measurements. We found that the samples have a background n-type carrier concentration. The ZnO samples with MgO buffer annealing has a carrier concentration of 1.17×1017 cm-3 and Hall mobility of 120 cm2/V.s, while the ZnO sample without MgO buffer annealing has a carrier

  20. Single-crystal elasticity of pyrope and MgO to 20 GPa by Brillouin scattering in the diamond cell

    NASA Astrophysics Data System (ADS)

    Sinogeikin, Stanislav V.; Bass, Jay D.

    2000-06-01

    The single-crystal elastic properties of synthetic pyrope (Mg 3Al 2Si 3O 12) and periclase (MgO) have been measured by Brillouin scattering in a diamond anvil cell (DAC) up to 20 GPa. A 16:3:1 mixture of methanol-ethanol-water was used as a pressure-transmitting medium. Above the freezing pressure of this medium (˜14 GPa), heat treatment and accompanying stress relaxation produces quasi-hydrostatic conditions. An analysis of geometric errors associated with the DAC indicates that the DAC introduces an additional uncertainty in velocity of ≤0.5% (as compared to measurements in air), if there is no vignetting of the incident and scattered beams. The nonhydrostaticity caused by freezing of the pressure-transmitting medium results in lower velocities and elastic moduli than are obtained under hydrostatic conditions, and this leads to an overestimation of the second pressure derivatives of the elastic moduli. Fitting our hydrostatic data to finite-strain equations of state yields the following adiabatic bulk ( KS) and shear ( μ) moduli and their pressure derivatives: KS=163.2(10), K'=3.96(10), Kʺ=-0.044(20), μ=130.2(10), μ'=2.35(10), μʺ=-0.040(20) for MgO and KS=171.2(20), K'=4.1(3), μ=93.7 (20), μ'=1.3(2) for pyrope, where primes indicate pressure derivatives of moduli. Our results for MgO are in excellent agreement with previous ultrasonic measurements performed at lower pressures, and in particular the values of K' agree to within a few percent. Our data are in good agreement with recent compression measurements on pyrope to pressures exceeding 20 GPa, suggesting that Brillouin scattering is an accurate method for high-pressure density and elastic moduli measurements. Pyrope is nearly elastically isotropic at ambient conditions and remains isotropic over the pressure range studied here. In contrast, the elastic anisotropy of MgO is observed to decrease dramatically with increasing pressure, becoming elastically isotropic at ˜21.5 GPa.

  1. Electrical Properties of Sol-Gel MgO - ZrO2 Insulation Coatings under Compression for Magnet Technology

    NASA Astrophysics Data System (ADS)

    Cakiroglu, O.; Arda, L.; Aslanoglu, Z.; Akin, Y.; Dur, O.; Kaplan, A.; Hascicek, Y. S.

    2004-06-01

    The high temperature compatible MgO - ZrO2 insulation coatings were applied on Stainless-Steel-304 (SS) ribbons by sol-gel process for magnet technologies. SS ribbons did not considerably oxidize, even though the coating process occurs in an oxidation atmosphere. Electrical properties of the samples such as high voltage breakdown (HVbd), electrical strength and dielectric constant under varying stress, at Room Temperature (RT) and 77 K were investigated. The measurements were carried out with and without epoxy impregnation. Surface morphologies of insulated samples were examined by using Environmental Scanning Electron Microscope (ESEM), after high voltage breakdown test.

  2. Electrical Properties of Sol-Gel MgO - ZrO2 Insulation Coatings under Compression for Magnet Technology

    SciTech Connect

    Cakiroglu, O.; Arda, L.; Aslanoglu, Z.; Dur, O.; Hascicek, Y.S.; Akin, Y.; Kaplan, A.

    2004-06-28

    The high temperature compatible MgO - ZrO2 insulation coatings were applied on Stainless-Steel-304 (SS) ribbons by sol-gel process for magnet technologies. SS ribbons did not considerably oxidize, even though the coating process occurs in an oxidation atmosphere. Electrical properties of the samples such as high voltage breakdown (HVbd), electrical strength and dielectric constant under varying stress, at Room Temperature (RT) and 77 K were investigated. The measurements were carried out with and without epoxy impregnation. Surface morphologies of insulated samples were examined by using Environmental Scanning Electron Microscope (ESEM), after high voltage breakdown test.

  3. Degradation Characteristics of MgO Based Magnetic Tunnel Junction Caused by Surface Roughness of Ta/Ru Buffer Layers.

    PubMed

    Lee, Jung Min; Choi, Chul Min; Sukegawa, Hiroaki; Lee, Jeong Yong; Mitani, Seiji; Song, Yun-Heub

    2016-01-01

    We investigated how surface roughness of a Ta/Ru buffer layer affects the degradation characteristics on MgO-based magnetic tunnel junctions (MTJs). MTJs with worse surface roughness on the buffer layer showed increased resistance drift and degraded time-dependent dielectric breakdown (TDDB) characteristics. We suggest that this resulted from reduced MgO thickness on the MTJ with worse surface roughness on the buffer layer, which was estimated by the TDDB and analytic approach. As a result, surface roughness of the buffer layer is a critical factors that impacts the reliability of MTJs, and it should be controlled to have the smallest roughness value as possible. PMID:27398503

  4. Growth of monocrystalline Cu(1 1 1) films on MgO(1 1 1) by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Aweke, F.; Antoni, F.; Hulik, J.; Morvan, G.; Speisser, C.; Veis, P.; Le Normand, F.

    2015-05-01

    Copper (Cu) films with a minimal thickness of 300 nm were grown on MgO(1 1 1) substrates in high vacuum by pulsed laser deposition (PLD) at various temperatures to achieve a single crystal Cu film with flat terraces without grain boundaries. We investigated the effect of the substrate temperature, the pulse repetition rate, the deposition time and the laser fluence. A temperature threshold is observed above which the growth mode is changed from a uniform flat mode to a three dimensional mode. A combined process involving a germination step at moderate temperature followed by a growth step at higher temperature yields a 450 nm almost continuous film.

  5. Y2O3-MgO Nano-Composite Synthesized by Plasma Spraying and Thermal Decomposition of Solution Precursors

    NASA Astrophysics Data System (ADS)

    Muoto, Chigozie Kenechukwu

    This research aims to identify the key feedstock characteristics and processing conditions to produce Y2O3-MgO composite coatings with high density and hardness using solution precursor plasma spray (SPPS) and suspension plasma spray (SPS) processes, and also, to explore the phenomena involved in the production of homogenized nano-composite powders of this material system by thermal decomposition of solution precursor mixtures. The material system would find potential application in the fabrication of components for optical applications such as transparent windows. It was shown that a lack of major endothermic events during precursor decomposition and the resultant formation of highly dense particles upon pyrolysis are critical precursor characteristics for the deposition of dense and hard Y2O3-MgO coatings by SPPS. Using these principles, a new Y2O3-MgO precursor solution was developed, which yielded a coating with Vickers hardness of 560 Hv. This was a considerable improvement over the hardness of the coatings obtained using conventional solution precursors, which was as low as 110 Hv. In the thermal decomposition synthesis process, binary solution precursor mixtures of: yttrium nitrate (Y[n]) or yttrium acetate (Y[a]), with magnesium nitrate (Mg[n]) or magnesium acetate (Mg[a]) were used in order to study the effects of precursor chemistry on the structural characteristics of the resultant Y2O3-MgO powders. The phase domains were coarse and distributed rather inhomogeneously in the materials obtained from the Y[n]Mg[n] and Y[a]Mg[a] mixtures; finer and more homogeneously-distributed phase domains were obtained for ceramics produced from the Y[a]Mg[n] and Y[n]Mg[a] mixtures. It was established that these phenomena were related to the thermal characteristics for the decomposition of the precursors and their effect on phase separation during oxide crystallization. Addition of ammonium acetate to the Y[n[Mg[n] mixture changed the endothermic process to exothermic

  6. Geochemistry of xenolithic eclogites from West Africa, part I: A link between low MgO eclogites and archean crust formation

    NASA Astrophysics Data System (ADS)

    Barth, Matthias G.; Rudnick, Roberta L.; Horn, Ingo; McDonough, William F.; Spicuzza, Michael J.; Valley, John W.; Haggerty, Stephen E.

    2001-05-01

    - Oxygen isotope, mineral trace element, and measured and reconstructed whole rock compositions are reported for low MgO (6-13 wt.% MgO in the whole rock) eclogite xenoliths from the Koidu kimberlite complex, Sierra Leone. The δ 18O values of garnet (4.7-6.8‰), determined by laser fluorination on clean mineral separates, extend beyond the range for mantle peridotites. All low MgO eclogites have reconstructed trace element patterns that are depleted in Ba, Th, U, and light rare earth element (LREE), with jadeite-rich samples having more variable trace element patterns than jadeite-poor samples. These observations, coupled with low SiO 2 contents, and Nb-rich but LREE-depleted reconstructed whole rock compositions, suggest the low MgO eclogites are remnants of altered oceanic crust that was partially melted during subduction. Partial melting of a mafic protolith at high pressure (leaving a garnet-bearing residue) is the preferred model to explain the origin of Archean tonalite-trondhjemite-granodiorite (TTG) suites, which make up large portions of the crust in Archean cratons. We therefore suggest that the Koidu low MgO eclogites may be residues from Archean continental crust formation.

  7. High rate buffer layer for IBAD MgO coated conductors

    DOEpatents

    Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.

    2007-08-21

    Articles are provided including a base substrate having a layer of an oriented material thereon, and, a layer of hafnium oxide upon the layer of an oriented material. The layer of hafnium oxide can further include a secondary oxide such as cerium oxide, yttrium oxide, lanthanum oxide, scandium oxide, calcium oxide and magnesium oxide. Such articles can further include thin films of high temperature superconductive oxides such as YBCO upon the layer of hafnium oxide or layer of hafnium oxide and secondary oxide.

  8. Thin Film Substrates from the Raman spectroscopy point of view

    NASA Astrophysics Data System (ADS)

    Gasparov, Lev; Jegorel, Theo; Loetgering, Lars; Middey, Srimanta; Chakhalian, Jak

    2014-03-01

    We have investigated ten standard single crystal substrates of complex oxides on the account of their applicability in the Raman spectroscopy based thin film research. In this study we suggest a spectra normalization procedure that utilises a comparison of the substrate's Raman spectra to those of well-established Raman reference materials. We demonstrate that MgO, LaGaO3, (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT), DyScO3, YAlO3, and LaAlO3 can be of potential use for a Raman based thin film research. At the same time TiO2 (rutile), NdGaO3, SrLaAlO4, and SrTiO3 single crystals exhibit multiple phonon modes accompanied by strong Raman background that substantially hinder the Raman based thin film experiments. L.G. acknowledges the support from the National Science Foundation (NSF) Grants DMR-0805073, DMR-0958349, Office of Naval Research award N00014-06-1-0133 and the UNF Terry Presidential Professorship. J. C. was supported by DOD-ARO under Grant No. 0402-172.

  9. Transesterification of Nannochloropsis oculata microalga's lipid to biodiesel on Al2O3 supported CaO and MgO catalysts.

    PubMed

    Umdu, Emin Selahattin; Tuncer, Mert; Seker, Erol

    2009-06-01

    In this study, we present the activities of Al(2)O(3) supported CaO and MgO catalysts in the transesterification of lipid of yellow green microalgae, Nannochloropsis oculata, as a function of methanol amount and the CaO and MgO loadings at 50 degrees C. We found that pure CaO and MgO were not active and CaO/Al(2)O(3) catalyst among all the mixed oxide catalysts showed the highest activity. Not only the basic site density but also the basic strength is important to achieve the high biodiesel yield. Biodiesel yield over 80 wt.% CaO/Al(2)O(3) catalyst increased to 97.5% from 23% when methanol/lipid molar ratio was 30. PMID:19201601

  10. Efficient one-pot synthesis of pyrido[2,3-d]pyrimidines catalyzed by nanocrystalline MgO in water

    NASA Astrophysics Data System (ADS)

    Rad, Amaneh Mossafaii; Mokhtary, Masoud

    2015-04-01

    The direct three-component condensation of 6-aminouracil, 6-amino-2-thiouracil or 6-amino-1,3-dimethyluracil, with arylaldehydes and malononitrile to generate a series of pyrido[2,3-d]pyrimidine derivatives has been carried out over nanocrystalline MgO with high efficiency in water as a green solvent at 80 °C. The morphology and structure of the nanocrystalline MgO were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results confirmed the nanocrystalline MgO particle size is approximately 50 nm. This methodology offers significant improvements for the synthesis of pyrido[2,3-d]pyrimidine derivatives with regard to the yield of products, simplicity in operation, and green aspects by avoiding toxic catalysts and solvents.

  11. Graphitic encapsulation of MgO and Fe{sub 3}C nanoparticles in the reaction of iron pentacarbonyl with magnesium

    SciTech Connect

    Dyjak, Sławomir; Cudziło, Stanisław; Polański, Marek; Budner, Bogusław; Bystrzycki, Jerzy

    2013-07-15

    A simple method to produce highly ordered carbon nanostructures by combustion synthesis is presented. Graphite-encapsulated magnesium oxide, iron carbide nanoparticles and carbon nanobelts were synthesized by the one-step reduction of iron pentacarbonyl with magnesium. High-resolution transmission electron microscopy analysis of the products revealed nanocrystalline MgO and Fe{sub 3}C particles surrounded by a well-crystallized, tight graphite film. The possible formation mechanism is presented and discussed. - Highlights: • We present a simple method to produce highly ordered carbon nanostructures by combustion synthesis. • The cubic MgO particles are completely coated by tight graphitic shells. • The mechanism of formation a distant carbon film on MgO surface has been discussed. • The presented method can be applied to synthesis of other core-shell structures.

  12. The role of hydroxylation in the step stability and in the interaction between steps: a first-principles study of vicinal MgO surfaces.

    PubMed

    Finocchi, Fabio; Geysermans, Pascale; Bourgeois, Antonin

    2012-10-21

    Atomic structure and thermodynamic stability of vicinal MgO surfaces showing monoatomic steps are studied using density functional theory. We extend the general definition of step energy to the case of ledges that are covered by adsorbates. Using this definition, we consider the effect of hydroxylation on the thermodynamic stability of steps, either polar or non-polar, on (001) or (011) terraces. Clean non-polar steps along [100] on MgO(001) are the most stable ones. Upon water adsorption, the free energy of all hydroxylated ledges, almost independently of their orientation, is significantly reduced and approaches thermal energies for increasing water pressure, favoring the formation of hydroxylated steps on MgO surfaces. Furthermore, we show that interaction between polar steps can be either repulsive or attractive. This quite unusual behavior is described in terms of electrostatic interactions between ledges. PMID:22968346

  13. Effects of interactions between NiM (M = Mn, Fe, Co and Cu) bimetals with MgO (1 0 0) on the adsorption of CO2

    NASA Astrophysics Data System (ADS)

    Wang, Baojun; Yan, Ruixia; Liu, Hongyan

    2012-09-01

    A density-functional theory method has been conducted to investigate the interactions of NiM (M = Mn, Fe, Co and Cu) with MgO (1 0 0) as well as the effects of interactions on the adsorption of CO2. The binding energies of NiM on MgO and the adsorption energies of CO2 on NiM/MgO have been calculated, and the results show that the defective NiM/MgO catalysts exhibit stronger metal-support interaction (MSI) than the perfect NiM/MgO catalysts do, leading to weaker adsorption ability to CO2, except NiMn/MgO system. However, for the catalysts with the same MgO surface and different bimetals, the stronger the MSI is, the stronger adsorption ability of the substrate to CO2 is, except NiCu/MgO system.

  14. X-ray magnetic circular dichroism study of epitaxial magnetite ultrathin film on MgO(100)

    SciTech Connect

    Liu, W. Q.; Xu, Y. B. E-mail: rzhang@nju.edu.cn; Song, M. Y.; Lin, J. G.; Maltby, N. J.; Li, S. P.; Samant, M. G.; Parkin, S. S. P.; Bencok, P.; Steadman, Paul; Dobrynin, Alexey; Zhang, R. E-mail: rzhang@nju.edu.cn

    2015-05-07

    The spin and orbital magnetic moments of the Fe{sub 3}O{sub 4} epitaxial ultrathin film synthesized by plasma assisted simultaneous oxidization on MgO(100) have been studied with X-ray magnetic circular dichroism. The ultrathin film retains a rather large total magnetic moment, i.e., (2.73 ± 0.15) μ{sub B}/f.u., which is ∼70% of that for the bulk-like Fe{sub 3}O{sub 4}. A significant unquenched orbital moment up to 0.54 ± 0.05 μ{sub B}/f.u. was observed, which could come from the symmetry breaking at the Fe{sub 3}O{sub 4}/MgO interface. Such sizable orbital moment will add capacities to the Fe{sub 3}O{sub 4}-based spintronics devices in the magnetization reversal by the electric field.

  15. Magnesite formation from MgO and CO2 at the pressures and temperatures of Earth's mantle

    SciTech Connect

    Scott, Henry P.; Doczy, Vincent M.; Frank, Mark R.; Hasan, Maggie; Lin, Jung-Fu; Yang, Jing

    2013-08-02

    Magnesite (MgCO3) is an important phase for the carbon cycle in and out of the Earth’s mantle. Its comparably large P-T stability has been inferred for several years based on the absence of its decomposition in experiments. Here we report the first experimental evidence for synthesis of magnesite out of its oxide components (MgO and CO2) at P-T conditions relevant to the Earth’s mantle. Magnesite formation was observed in situ using synchrotron X-ray diffraction, coupled with laser-heated diamond-anvil cells (DACs), at pressures and temperatures of Earth’s mantle. Despite the existence of multiple high-pressure CO2 polymorphs, the magnesite-forming reaction was observed to proceed at pressures ranging from 5 to 40 GPa and temperatures between 1400 and 1800 K. No other pressure-quenchable materials were observed to form via the MgO + CO2 = MgCO3 reaction. This work further strengthens the notion that magnesite may indeed be the primary host phase for oxidized carbon in the deep Earth.

  16. Molecular-dynamics simulation of methane adsorbed on MgO: Evidence for a Kosterlitz-Thouless transition

    NASA Astrophysics Data System (ADS)

    Alavi, Ali

    A realistic model of a monolayer molecular crystal of methane adsorbed on the (100) surface of MgO has been studied by means of molecular dynamics. The model treates the atomicity of the MgO substrate explicitly. Large corrugations in energy are found for both the translational and rotational motion of methane across the substrate. The preferred configurations of adsorption is over an Mg2+ ion in a tripod-down orientation. The orientationally ordered low-energy states of the monolayer have been found. Finite-size-scaling calculations on systems of different sizes indicate, however, that the ordered state exhibits only quasi-long-range order. The disclinations in the ordered phase exist in low concentrations and in bound pairs. Evidence is presented for a Kosterlitz-Thouless-type unbinding transition occurring at Tc ≈ 27 K. No evidence is found for a first-order transition. The specific heat exhibits an anomaly at T ≈ 32 K. The disclination density in the region of the transition is reported; below Tc, this density can be fitted to an Arrhenius-type law, yielding an estimate of the core enegy for a bound vortex-antivortex pair.

  17. Molecular Beam Epitaxial Growth and Properties of CoFe2O4 on MgO(001)

    SciTech Connect

    Chambers, Scott A.; Farrow, Robin F.; Maat, S.; Toney, M.; Folks, L.; Catalano, J.G.; Trainor, T.P.; Brown, G.E. Jr.

    2002-04-01

    We have grown single-crystal Co ferrite (CoFe2O4) on MgO(001) by oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE), and have characterized the composition, structure, surface morphology, and magnetic properties by a number of methods The as-grown OPA-MBE material forms a perfect inverse spinel, in which all Co is in the? formal oxidation state, and occupies octahedral sites within the cation sublattice. The OPA-MBE film surfaces are very flat, with mean roughnesses of only a few A, and exhibit large, stable magnetic domains. The measured moment per unit volume is 250 emu/cm3, and the saturation magnetization for films in the 1000A film thickness range is {approx}60% of that of bulk Co ferrite. The material also exhibits strain-dependent magnetic anisotropy that can be understood by considering the various contributions to the total magnetic energy. The overall quality of epitaxial Co ferrite grown on MgO by OPA-MBE is superior in every respect to that obtained using pulsed laser deposition as the growth method.

  18. Swelling under irradiation of MgO pellets containing americium oxide: The ECRIX-H irradiation experiment

    NASA Astrophysics Data System (ADS)

    Lamontagne, J.; Béjaoui, S.; Hanifi, K.; Valot, Ch.; Loubet, L.

    2011-06-01

    The ECRIX-H irradiation experiment studied the behaviour of pellets containing americium dispersed in MgO. The purpose of the irradiation was to demonstrate the capacity of magnesia to provide an efficient support matrix. After fabrication, the sintered pellets contained 16.65 wt.% of Am microdispersed in the inert matrix. The ECRIX-H pellets were irradiated under a locally moderated neutron flux in the Phénix sodium-cooled fast reactor (SFR) for 318 Effective Full Power Days (EFPD). Post-test calculations indicated that the fission and transmutation rates of americium at the maximum flux plane reached 33.9% and 92.6% respectively at the end of the irradiation phase. The results of the post-irradiation examinations - both non-destructive and destructive - are discussed in this paper. These results indicate a satisfactory behaviour of the MgO matrix. Particularly, a moderate swelling occurs in the pellets under irradiation even with significant quantities of helium generated and at high transmutation rate.

  19. Banyan latex: a facile fuel for the multifunctional properties of MgO nanoparticles prepared via auto ignited combustion route

    NASA Astrophysics Data System (ADS)

    Kumar, M. R. Anil; Nagaswarupa, H. P.; Anantharaju, K. S.; Gurushantha, K.; Pratapkumar, C.; Prashantha, S. C.; Shashishekar, T. R.; Nagabhushana, H.; Sharma, S. C.; Vidya, Y. S.; Daruka Prasad, B.; Vivek Babu, C. S.; Vishnu Mahesh, K. R.

    2015-09-01

    MgO nanoparticles (MNPs) were prepared by a solution combustion route using banyan tree (BT) latex and glycine as fuels. The powder x-ray diffraction results indicate the formation of a single cubic phase and the crystallite size obtained from transmission electron microscopy was found to be ˜10-15 nm. Scanning electron microscopy result reveals spherical-shaped particles obtained with BT latex. However, in a chemical route, porous and agglomerated particles were obtained. The energy band gap of MNPs obtained using BT latex and a chemical route were found to be in the range 4.85-5.0 eV. Photoluminescence peaks observed at 473, 514, and 588 nm when excited at 433 nm, which were attributed to surface defects. The enhanced photocatalytic activities of spherical MgO were due to smaller crystallite size, higher surface defects, dye sensitization, and capability to reduce the electron-hole pair recombination. Further, green-synthesized MNPs exhibit superior antifungal activity against various plant pathogens. The present studies demonstrated a green engineering route for the synthesis of multifunctional MNPs using BT latex.

  20. Thermodynamic Analysis of V-concentrating Phase Formation in V-bearing Steelmaking Slag Modified by MgO

    NASA Astrophysics Data System (ADS)

    Wu, Liushun; Gao, Wei; Xie, Dawei; Li, Liaosha; Dong, Yuanchi

    2015-10-01

    In the study, magnesium oxide acting as modifier was added to V-bearing steelmaking slag to concentrate vanadium, and then the effect of magnesium oxide on the formation of V-concentrating phase during cooling was investigated. Experimental results show that, in the case of the original slag, di-calcium silicate along with most of vanadate and phosphate in the slag forms solid solution, calcium ferrite which contains small part of vanadium in the slag and matrix without vanadium in turn precipitate during slowly cooling; For the sample with 8% MgO addition, two new phases (merwinite and V-concentrating phase) generate during slowly cooling, and the amount of di-calcium silicate decreases. Merwinite phase doesn't contain vanadium, and V-concentrating phase (Ca3(V,P)2O8·nCa2SiO4) contains 17-19% V2O5 by mass; For the sample with 16% MgO addition, another new phase (monticellite) precipitates from liquid slag, the phase of di-calcium silicate disappears, and most of vanadium concentrates in V-concentrating phase-Ca3(V,P)2O8·nCa2SiO4 (18-21%V2O5).

  1. Adsorption of a water molecule on the MgO(100) surface as described by cluster and slab models.

    PubMed

    Karalti, Ozan; Alfè, Dario; Gillan, Michael J; Jordan, Kenneth D

    2012-06-01

    The interaction of a water molecule with the (100) surface of MgO as described by cluster models is studied using MP2, coupled MP2 (MP2C) and symmetry-adapted perturbation theory (SAPT) methods. In addition, diffusion Monte Carlo (DMC) results are presented for several slab models as well as for the smallest, 2X2 cluster model. For the 2X2 model it is found that the MP2C, DMC, and CCSD(T) methods give nearly the same potential energy curve for the water-cluster interaction, whereas the potential energy curve from the SAPT calculations differs slightly from those of the other methods. The interaction of the water molecule with the cluster models of the MgO(100) surface is weakened upon expanding the number of layers from one to two and also upon expanding the description of the layers from 2X2 to 4X4 to 6X6. The SAPT calculations reveal that both these expansions of the cluster model are accompanied by reductions in the magnitudes of the induction and dispersion constributions. The best estimate of the energy for binding an isolated water molecule to the surface obtained from the cluster model calculations is in good agreement with that obtained from the DMC calculations using a 2-layer slab model with periodic boundary conditions. PMID:22535216

  2. Influence of the MgO barrier thickness on the lifetime characteristics of magnetic tunnelling junctions for sensors

    NASA Astrophysics Data System (ADS)

    Conca, A.; Casper, F.; Paul, J.; Lehndorff, R.; Jakob, G.; Kläui, M.; Hillebrands, B.; Leven, B.

    2016-06-01

    Magnetic tunnelling junctions increasingly enter the market for magnetic sensor applications. Thus, technological parameters such as the lifetime characteristics become more and more important. Here, an analysis of the lifetime characteristics of magnetic tunnelling junctions using the Weibull statistical distribution for CoFeB/MgO/CoFeB junctions is presented. The Weibull distribution is governed by two parameters, the characteristic lifetime η of the population and the shape parameter β, which gives information about the presence of an infant mortality. The suitability of the Weibull distribution is demonstrated for the description of dielectric breakdown processes in MgO-based tunnelling junctions at different voltages. A study of the dependence of the characteristic lifetime extrapolated to the low voltage regime, and the β parameter on the nominal barrier thickness and the resistance  ×  area product of the MgO barrier is shown. The influence of the RF deposition power for the MgO barrier and an annealing step on the Weibull parameters is also discussed.

  3. Microstructural Characteristics of Y2O3-MgO Composite Coatings Deposited by Suspension Plasma Spray

    NASA Astrophysics Data System (ADS)

    Muoto, Chigozie K.; Jordan, Eric H.; Gell, Maurice; Aindow, Mark

    2012-12-01

    Dense composite Y2O3-MgO coatings have been deposited by suspension plasma spray. Ethanol-based suspensions of powders synthesized by thermal decomposition of precursor solutions containing yttrium nitrate (Y[n]) and magnesium nitrate (Mg[n]) or magnesium acetate (Mg[a]) were selected as the feedstock; this gave powders with both phases in each particle, to inhibit phase segregation during solvent evaporation. The influence of powder characteristics on the microstructures of the coatings was investigated. The Y[n]Mg[a] suspension was more stable, with a better dispersion of the component phases than the Y[n]Mg[n] suspension. The coatings deposited using each suspension type exhibited lamellar structures comprising Y2O3 and MgO phases in wavy alternating streaks, with unmelted/semi-melted particles entrapped in the lamellae; this indicates that phase segregation still occurred in the molten state. Eutectic structures were formed in the coating generated using the Y[n]Mg[a] suspension, resulting from improved mixing of the component phases in the suspension powder.

  4. Biodiesel production from waste cooking oil catalyzed by TiO2-MgO mixed oxides.

    PubMed

    Wen, Zhenzhong; Yu, Xinhai; Tu, Shan-Tung; Yan, Jinyue; Dahlquist, Erik

    2010-12-01

    Mixed oxides of TiO(2)-MgO obtained by the sol-gel method were used to convert waste cooking oil into biodiesel. Titanium improved the stability of the catalyst because of the defects induced by the substitution of Ti ions for Mg ions in the magnesia lattice. The best catalyst was determined to be MT-1-923, which is comprised of an Mg/Ti molar ratio of 1 and calcined at 923 K, based on an assessment of the activity and stability of the catalyst. The main reaction parameters, including methanol/oil molar ratio, catalyst amount, and temperature, were investigated. The catalytic activity of MT-1-923 decreased slowly in the reuse process. After regeneration, the activity of MT-1-923 slightly increased compared with that of the fresh catalyst due to an increase in the specific surface area and average pore diameter. The mixed oxides catalyst, TiO(2)-MgO, showed good potential in large-scale biodiesel production from waste cooking oil. PMID:20696572

  5. A density functional study of NO2 adsorption on perfect and defective MgO (1 0 0) and Li/MgO (1 0 0) surfaces

    NASA Astrophysics Data System (ADS)

    Eid, Kh. M.; Ammar, H. Y.

    2012-07-01

    The density functional theory (DFT) in combination with embedded cluster model have been used to study the adsorption of nitrogen dioxide molecule (NO2) on Li atom deposited on the surfaces of metal oxide MgO (1 0 0) on both anionic (O2-) and defect (Fs and Fs+-centers) sites. The adsorption energy (Eads) of NO2 molecule (N-down as well as O-down) in different positions on O-2, Fs and Fs+-sites is considered. The geometrical optimizations have been done for the additive materials and MgO substrate surfaces. The formation energies have been evaluated for Fs and Fs+ of MgO substrate surfaces. The ionization potential (IP) and electron affinity (eA) for defect free and defect containing surfaces have been calculated. The adsorption properties of NO2 are analyzed in terms of the adsorption energy, the electron donation (basicity), the elongation of Nsbnd O bond length and the atomic charges on adsorbed materials. The densities of states (DOS) have been calculated and used for examining the adsorption properties. The NO2 molecule is dissociated due to the interaction with the defective substrate surface (Fs-site) producing an oxygen atom strongly chemisorbed to the vacancy of the substrate and gaseous NO far away from the surface. The presence of the Li atom increases the surface chemistry of the anionic O2--site of MgO substrate surfaces (converted from physisorption to chemisorption). On the other hand, the presence of the Li atom decreases the surface chemistry of the Fs and Fs+-sites of MgO substrate surfaces. Generally, the NO2 molecule is strongly adsorbed (chemisorption) on the MgO substrate surfaces containing Fs and Fs+-centers.

  6. Epitaxial thin films of the superconducting spinel oxide LiTi2O4

    NASA Astrophysics Data System (ADS)

    Chopdekar, Rajesh; Suzuki, Yuri

    2006-03-01

    Lithium titanate is the only superconducting spinel oxide documented in literature. Related oxide spinels[1] such as the heavy fermion system LiV2O4 and charge-ordered LiMn2O4 indicate that electron correlations are strong in these systems. We have fabricated epitaxial films of LiTi2O4 on MgAl2O4 and MgO single crystalline substrates to explore such behavior in thin film form. Atomic force microscopy indicates <1nm RMS surface roughness, and 2- and 4-circle x-ray diffraction confirms film epitaxy. Films on MgAl2O4 have a critical temperature Tc of up to 11.3K with a resistivity transition width of 0.25K, while films on MgO have lower Tc with broader transitions. Magnetization vs. magnetic field of a zero-field cooled sample shows Meissner shielding consistent with Type II superconductors. Such films can be used in spin-polarization measurements of complex oxide half-metallic thin films, as well as fundamental studies of the effect of epitaxial strain, microstructure, and cation disorder/substitution on the superconducting properties of LiTi2O4. [1] M. Lauer et al, Phys Rev B 69, 075117 (2004).

  7. Optical and thermodynamic properties of MgO from radiative shock temperature and sound speed measurements on samples preheated to 2300 K

    NASA Astrophysics Data System (ADS)

    Fatýanov, O. V.; Asimow, P. D.

    2013-12-01

    Thermodynamic properties of MgO, one of the major end-members of deep planetary interiors, play a significant role in the processes inside the Earth's lower mantle. Of particular importance in geophysics and geochemistry is the MgO melting behavior at high pressure. Despite considerable theoretical and experimental efforts over decades, it remains essentially unknown. The melting temperature predictions for MgO at 135 GPa, the Earth's core-mantle boundary pressure, range from 5 to 9 kK. In a continuous effort to resolve this inconsistency and to probe the P-T region previously unexplored, we developed a technique for radiative shock temperature measurements in single-crystal MgO preheated to 2300 K. Large ventilated Mo capsules were employed to hold ~20 mm long MgO crystals with controlled longitudinal thermal gradients. These hot targets were impacted by 0.8 mm thick Ta flyers launched at 6.5 to 7.5 km/s on the Caltech two-stage light-gas gun. Six spectral radiance histories from MgO shock front were recorded in every shot with 3 ns time resolution over 440-750 nm or 500-830 nm spectral range. The majority of our experiments showed smooth pressure dependence of MgO shock temperature and sound speed consistent with the solid phase at 197-243 GPa. Although most observed temperatures are ~700 K lower and sound speeds ~1 km/s higher than the model predictions, the pressure slopes for both parameters are in close agreement with those calculated for the solid phase. Unconfirmed data from a single experiment at 239 GPa and 8.3 kK showed correlated temperature and sound speed anomalies (both values lower than expected) that may be explained by partial melting. Our past and recent data on shock-compressed preheated MgO suggest its melting curve above 200 GPa is higher than the extrapolation of the experiments of Zerr & Boehler or the theoretical calculation by Strachan et. al. These results, features of shock experiments with 2300 K pre-heat temperatures, data analysis

  8. Influence of MgO doping on spontaneous polarization and second-order susceptibility in LiNbO 3 crystals

    NASA Astrophysics Data System (ADS)

    Sen, Pratima; Sisodia, Namita; Bartwal, K. S.

    2006-11-01

    On the basis of 'average effective electronegativity' of A and B site in LiNbO 3 crystal, the influence of MgO doping on structural and optical properties are theoretically analyzed. An empirical formula is also suggested to determine the Mg ion occupancy at A site. Present analysis suggests that the spontaneous polarization and second-order susceptibility decreases rapidly up to 4.5 mol% MgO doping while a sluggish decrease in its values is expected above this doping concentration.

  9. Thermodynamics and Kinetics of the Formation of Al2O3/ MgAl2O4/MgO in Al-Silica Metal Matrix Composite

    NASA Astrophysics Data System (ADS)

    Sreekumar, V. M.; Ravi, K. R.; Pillai, R. M.; Pai, B. C.; Chakraborty, M.

    2008-04-01

    The formation of Al2O3, MgAl2O4, and MgO has been widely studied in different Al base metal matrix composites, but the studies on thermodynamic aspects of the Al2O3/ MgAl2O4/MgO phase equilibria have been limited to few systems such as Al/Al2O3 and Al/SiC. The present study analyzes the Al2O3/MgAl2O4 and MgAl2O4/MgO equilibria with respect to the temperature and the Mg content in Al/SiO2 system using an extended Miedema model. There is a linear and parabolic variation in Mg with respect to the temperature for MgAl2O4/MgO and Al2O3/MgAl2O4 equilibria, respectively, and the influence of Si and Cu in the two equilibria is not appreciable. The experimental verification has been limited to MgAl2O4/MgO equilibria due to the high Mg content (≥0.5 wt pct) required for composite processing. The study has been carried out on two varieties of Al/SiO2 composites, i.e., Al/Silica gel and Al/Micro silica processed by liquid metallurgy route (stir casting route). MgO is found to be more stable compared to MgAl2O4 at Mg levels ≥5 and 1 wt pct in Al/Silica gel and Al/Micro silica composites, respectively, at 1073 K. MgO is also found to be more stable at lower Mg content (3 wt pct) in Al/Silica gel composite with decreasing particle size of silica gel from 180 micron to submicron and nanolevels. The MgO to MgAl2O4 transformation has taken place through a series of transition phases influenced by the different thermodynamic and kinetic parameters such as holding temperature, Mg concentration in the alloy, holding time, and silica particle size.

  10. Pyrolyzed thin film carbon

    NASA Technical Reports Server (NTRS)

    Tai, Yu-Chong (Inventor); Liger, Matthieu (Inventor); Harder, Theodore (Inventor); Konishi, Satoshi (Inventor); Miserendino, Scott (Inventor)

    2010-01-01

    A method of making carbon thin films comprises depositing a catalyst on a substrate, depositing a hydrocarbon in contact with the catalyst and pyrolyzing the hydrocarbon. A method of controlling a carbon thin film density comprises etching a cavity into a substrate, depositing a hydrocarbon into the cavity, and pyrolyzing the hydrocarbon while in the cavity to form a carbon thin film. Controlling a carbon thin film density is achieved by changing the volume of the cavity. Methods of making carbon containing patterned structures are also provided. Carbon thin films and carbon containing patterned structures can be used in NEMS, MEMS, liquid chromatography, and sensor devices.

  11. Metallic transport and large anomalous Hall effect at room temperature in ferrimagnetic Mn{sub 4}N epitaxial thin film

    SciTech Connect

    Shen, Xi; Shigematsu, Kei; Chikamatsu, Akira Fukumura, Tomoteru; Hirose, Yasushi; Hasegawa, Tetsuya

    2014-08-18

    We report the electrical transport properties of ferrimagnetic Mn{sub 4}N (001) epitaxial thin films grown by pulsed laser deposition on MgO (001) substrates. The Mn{sub 4}N thin films were tetragonally distorted with a ratio of out-of-plane to in-plane lattice constants of 0.987 and showed perpendicular magnetic anisotropy with an effective magnetic anisotropy constant of 0.16 MJ/m{sup 3}, which is comparable with that of a recently reported molecular-beam-epitaxy-grown film. The thin films exhibited metallic transport with a room temperature resistivity of 125 μΩ cm in addition to a large anomalous Hall effect with a Hall angle tangent of 0.023.

  12. Nanowires of Fe/multi-walled carbon nanotubes and nanometric thin films of Fe/MgO

    SciTech Connect

    Newman, Alexander; Khatiwada, Suman; Neupane, Suman; Seifu, Dereje

    2015-04-14

    We observed that nanowires of Fe grown in the lumens of multi-walled carbon nanotubes required four times higher magnetic field strength to reach saturation compared to planar nanometric thin films of Fe on MgO(100). Nanowires of Fe and nanometric thin films of Fe both exhibited two fold magnetic symmetries. Structural and magnetic properties of 1-dimensional nanowires and 2-dimensional nanometric films were studied by several magnetometery techniques. The θ-2θ x-ray diffraction measurements showed that a (200) peak of Fe appeared on thin film samples deposited at higher substrate temperatures. In these samples prepared at higher temperatures, lower coercive field and highly pronounced two-fold magnetic symmetry were observed. Our results show that maximum magnetocrystalline anisotropy occurred for sample deposited at 100 °C and it decreased at higher deposition temperatures.

  13. High-RRR thin-films of NB produced using energetic condensation from a coaxial, rotating vacuum ARC plasma (CEDTM)

    NASA Astrophysics Data System (ADS)

    Valderrama, Enrique Francisco; James, Colt; Krishnan, Mahadevan; Zhao, Xin; Phillips, Larry; Reece, Charles; Seo, Kang

    2012-06-01

    We have recently demonstrated unprecedentedly high values of RRR (up to 542) in thin-films of pure Nb deposited on a-plane sapphire and MgO crystal substrates. The Nb films were grown using a vacuum arc discharge struck between a reactor grade Nb cathode rod (RRR 30) and a coaxial, semi-transparent Mo mesh anode, with a heated substrate placed just outside it. The substrates were pre-heated for several hours prior to deposition at different temperatures. Low pre-heat temperatures (<300°C) and deposition temperatures (<300°C) give low RRR (<50) films, whereas higher pre-heat (700°C) and coating temperatures (500°C) give RRR=214 on a-sapphire and RRR=542 on MgO. XRD (Bragg-Brentano scans and Pole Figures), EBSD and SIMS data reveal several features: (1) on asapphire, higher temperatures show better 3D registry for epitaxial growth of Nb; the crystal structure evolves from textured, polycrystalline (with twins) to single-crystal; (2) on MgO, there is a transition from {110} planes to {100} as the temperature is increased beyond 500°C. The dramatic increase in RRR (from 10 at <300°C to 500 at >600°C) is correlated with better epitaxial crystal structure in both a-sapphire and MgO substrate grown films. However, the SIMS data reveal that the most important requirement for high-RRR Nb films on either substrate is the reduction of impurities in the film, especially hydrogen. The hydrogen content in the MgO grown films is 1000 times lower than in bulk Nb tested as a reference from SRF cavity grade Nb. This result has potential implications for SRF accelerators. Coating bulk Nb cavities with an MgO layer followed by our CEDTM deposited Nb films, might create superior SRF cavities that would avoid Q-slope and operate at higher peak fields. This research was supported by Department of Energy grants DE-SC0004994 and DE-FG02-08ER85162.

  14. Growth of highly oriented γ- and α-Al2O3 thin films by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Balakrishnan, G.; Babu, R. Venkatesh; Shin, K. S.; Song, J. I.

    2014-03-01

    Highly oriented aluminum oxide (Al2O3) thin films were grown on SrTiO3 (100), α-Al2O3 (11¯02), α-Al2O3 (0001) and MgO (100) single crystal substrates at an optimized oxygen partial pressure of 3.5×10-3 mbar and 700 °C by pulsed laser deposition. The films were characterized by X-ray diffraction and atomic force microscopy. The X-ray diffraction studies indicated the highly oriented growth of γ-Al2O3 (400) ǁ SrTiO3 (100), α-Al2O3 (024) ǁ α-Al2O3 (11¯02), α-Al2O3 (006) ǁ α-Al2O3 (0001) and α-Al2O3 (006) ǁ MgO (100). Formation of nanostructures with dense and smooth surface morphology was observed using atomic force microscopy. The root mean square surface roughness of the films were 0.2 nm, 0.5 nm, 0.7 nm and 0.3 nm on SrTiO3 (100), α-Al2O3 (11¯02), α-Al2O3 (0001) and MgO (100) substrates, respectively.

  15. The field induced e{sub 31,f} piezoelectric and Rayleigh response in barium strontium titanate thin films

    SciTech Connect

    Garten, L. M. Trolier-McKinstry, S.

    2014-09-29

    The electric field induced e{sub 31,f} piezoelectric response and tunability of Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} (70:30) and Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} (60:40) thin films on MgO and silicon was measured. The relative dielectric tunabilities for the 70:30 and 60:40 compositions on MgO were 83% and 70%, respectively, with a dielectric loss of less than 0.011 and 0.004 at 100 kHz. A linear increase in induced piezoelectricity to −3.0 C/m{sup 2} and −1.5 C/m{sup 2} at 110 kV/cm was observed in Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} on MgO and Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} on Si. Hysteresis in the piezoelectric and dielectric response of the 70:30 composition films was consistent with the positive irreversible dielectric Rayleigh coefficient. Both indicate a ferroelectric contribution to the piezoelectric and dielectric response over 40–80 °C above the global paraelectric transition temperature.

  16. Pulsed laser deposition of air-sensitive hydride epitaxial thin films: LiH

    SciTech Connect

    Oguchi, Hiroyuki; Isobe, Shigehito; Kuwano, Hiroki; Shiraki, Susumu; Hitosugi, Taro; Orimo, Shin-ichi

    2015-09-01

    We report on the epitaxial thin film growth of an air-sensitive hydride, lithium hydride (LiH), using pulsed laser deposition (PLD). We first synthesized a dense LiH target, which is key for PLD growth of high-quality hydride films. Then, we obtained epitaxial thin films of [100]-oriented LiH on a MgO(100) substrate at 250 °C under a hydrogen pressure of 1.3 × 10{sup −2} Pa. Atomic force microscopy revealed that the film demonstrates a Stranski-Krastanov growth mode and that the film with a thickness of ∼10 nm has a good surface flatness, with root-mean-square roughness R{sub RMS} of ∼0.4 nm.

  17. Epitaxial thin film deposition of magnetostrictive materials and its effect on magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    McClure, Adam Marc

    Magnetostriction means that the dimensions of a material depend on its magnetization. The primary goal of this dissertation was to understand the effect of magnetostriction on the magnetic anisotropy of single crystal magnetostrictive thin films, where the epitaxial pinning of the material to a substrate could inhibit its conversion to new dimensions. In order to address this goal, several Fe-based binary alloys were deposited onto various substrates by molecular beam epitaxy. The samples were characterized by an array of techniques including electron diffraction, Rutherford backscattering, vibrating sample magnetometry, ferromagnetic resonance, and x-ray absorption spectroscopies. The attempted growths of crystalline magnetostrictive thin films resulted in successful depositions of Fe1-xGax and Fe1-x Znx. Depositions onto MgO(001) substrates result in an in-plane cubic magnetic anisotropy, as expected from the cubic symmetry of the Fe-based thin films, and a strong out-of-plane uniaxial anisotropy that forces the magnetization to lie in the plane of the films. Depositions onto ZnSe/GaAs(001) substrates feature an additional in-plane uniaxial anisotropy. The magnitudes and signs of the in-plane anisotropies depend on the Ga content. Furthermore, the cubic anisotropy constant of Fe1-xGax samples deposited onto MgO substrates switches sign at a lower Ga concentration than is seen in bulk Fe1-xGax. The effect on the magnetic anisotropy of depositing a magnetostrictive material as an epitaxial thin film is influenced by the material's magnetostrictive properties and the substrate upon which it is deposited. In particular, pinning a magnetoelastic material to a substrate will modify its cubic anisotropy, and depositions on substrates compliant to an anisotropic strain relaxation may result in a strong in-plane uniaxial anisotropy.

  18. Microwave losses in MgO, LaAlO{sub 3}, and (La{sub 0.3}Sr{sub 0.7})(Al{sub 0.65}Ta{sub 0.35})O{sub 3} dielectrics at low power and in the millikelvin temperature range

    SciTech Connect

    Arzeo, M.; Lombardi, F.; Bauch, T.

    2014-05-26

    We have investigated both the temperature and the power dependence of microwave losses for various dielectrics commonly used as substrates for the growth of high critical temperature superconductor thin films. We present measurement of niobium superconducting λ∕2 coplanar waveguide resonators, fabricated on MgO, LaAlO{sub 3}, and (La{sub 0.3}Sr{sub 0.7})(Al{sub 0.65}Ta{sub 0.35})O{sub 3} (LSAT), at the millikelvin temperature range and at low input power. By comparing our results with the two-level system model, we have discriminated among different dominant loss mechanisms. LSAT has shown the best results as regards the dielectric losses in the investigated regimes.

  19. Large anisotropic Fe orbital moments in perpendicularly magnetized Co2FeAl Heusler alloy thin films revealed by angular-dependent x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Okabayashi, Jun; Sukegawa, Hiroaki; Wen, Zhenchao; Inomata, Koichiro; Mitani, Seiji

    2013-09-01

    Perpendicular magnetic anisotropy (PMA) in Heusler alloy Co2FeAl thin films sharing an interface with a MgO layer is investigated by angular-dependent x-ray magnetic circular dichroism. Orbital and spin magnetic moments are deduced separately for Fe and Co 3d electrons. In addition, the PMA energies are estimated using the orbital magnetic moments parallel and perpendicular to the film surfaces. We found that PMA in Co2FeAl is determined mainly by the contribution of Fe atoms with large orbital magnetic moments, which are enhanced at the interface between Co2FeAl and MgO. Furthermore, element specific magnetization curves of Fe and Co are found to be similar, suggesting the existence of ferromagnetic coupling between Fe and Co PMA directions.

  20. Optical properties and surface morphology of Li-doped ZnO thin films deposited on different substrates by DC magnetron sputtering method

    NASA Astrophysics Data System (ADS)

    Mohamed, Galal A.; Mohamed, El-Maghraby; Abu El-Fadl, A.

    2001-12-01

    Thin films of zinc oxide doped with Zn 1- xLi xO with x=0.2 (ZnO : Li), have been prepared on sapphire, MgO and quartz substrates by DC magnetron sputtering method at 5 mTorr. The substrate temperatures were fixed to about 573 K. We have measured the transmission and reflection spectra and determined the absorption coefficient, optical band-gap ( Egdopt), the high frequency dielectric constant ε‧ ∞ and the carrier concentration N for the as-prepared films at room temperature. The films show direct allowed optical transitions with Egdopt values of 3.38, 3.43 and 3.29 eV for films deposited on sapphire, MgO and quartz substrates, respectively. The dependence of the obtained results on the substrate type are discussed.

  1. DIELECTRIC PROPERTIES OF BA(0.6)SR(0.4)TiO(3) THIN FILMS WITH VARIOUS STRAIN STATES

    SciTech Connect

    B. PARK; E. PETERSON; ET AL

    2001-04-01

    We could systematically control the strain states of a Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} film by depositing a very thin Ba{sub 1{minus}x}Sr{sub x}TiO{sub 3} interlayer between the main layer of the Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} and a MgO(001) substrate. Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} films showed very strong dependence of dielectric properties on the strain states. The strain induced by the MgO substrate was relaxed faster than that induced by an interlayer.

  2. Reducing spin-torque switching current by incorporating an ultra-thin Ta layer with CoFeB free layer in magnetic tunnel junctions

    SciTech Connect

    Liu, R. S. Meng, H.; Naik, V. B.; Sim, C. H.; Yap, S.; Luo, P.

    2014-12-15

    We studied the spin torque switching in dual MgO layer based magnetic tunnel junctions (MTJs) by incorporating an ultra-thin (0.5 nm) Ta layer at the CoFeB free layer/top MgO layer interface. The Ta incorporated MTJ showed a significant reduction (∼30%) in critical switching current density (J{sub C0} ) as compared to that of the control MTJ whilst maintaining the same tunneling magnetoresistance as well as thermal stability. The reduction of J{sub C0} can be attributed to the perpendicular magnetic anisotropy arising from the incorporation of an ultrathin Ta layer with the MgO|CoFeB structure. This scheme of reducing J{sub C0} without degrading other properties may contribute to the development of spin-transfer-torque magnetic random access memory for low power applications.

  3. Strain enhanced charge order melting in Pr0.5Ca0.5MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Baisnab, Dipak Kumar; Kumary, T. Geetha; Satya, A. T.; Mani, Awadhesh; Janaki, J.; Nithya, R.; Vaidhyanathan, L. S.; Janawadkar, M. P.; Bharathi, A.

    2011-06-01

    The effect of strain on charge order melting in half doped manganite Pr0.5Ca0.5MnO3 thin films of different thicknesses has been investigated. The films were deposited on (100) oriented MgO substrates by pulsed laser deposition technique and were characterized by x-ray diffraction, electrical resistivity and magnetoresistance measurements. A field induced charge order melting is observed for films with very small thickness. The charge order transition temperature and the magnetic field induced charge order melting appears to be governed by the nature of strain that is experienced by the film.

  4. Magnetic and electrical characterization of YBa 2Cu 3O 7 thin films made by laser ablation

    NASA Astrophysics Data System (ADS)

    Vase, Per; Shen, Yue Quang; Freltoft, Torsten

    1991-09-01

    High quality epitaxial thin films of YBa 2Cu 3O 7 have been deposited on single crystal MgO (100), SrTiO 3 (100), and LaAlO 3 (100) by laser ablation. The transport critical current density at 77 K is in the range of 10 6 - 10 7 A/cm 2 depending on the type of substrate. An alternative way to measure the critical current density based on high probe field ac-susceptibility measurements, avoiding the needs of patterning, is described, and the results are compared to transport measurement.

  5. Microstructural, Magnetic Anisotropy, and Magnetic Domain Structure Correlations in Epitaxial FePd Thin Films with Perpendicular Magnetic Anisotropy

    NASA Technical Reports Server (NTRS)

    Skuza, J. R.; Clavero, C.; Yang, K.; Wincheski, B.; Lukaszew, R. A.

    2009-01-01

    L1(sub 0)-ordered FePd epitaxial thin films were prepared using dc magnetron sputter deposition on MgO (001) substrates. The films were grown with varying thickness and degree of chemical order to investigate the interplay between the microstructure, magnetic anisotropy, and magnetic domain structure. The experimentally measured domain size/period and magnetic anisotropy in this high perpendicular anisotropy system were found to be correlated following the analytical energy model proposed by Kooy and Enz that considers a delicate balance between the domain wall energy and the demagnetizing stray field energy.

  6. Net sputtering rate due to hot ions in a Ne-Xe discharge gas bombarding an MgO layer

    SciTech Connect

    Ho, S.; Tamakoshi, T.; Ikeda, M.; Mikami, Y.; Suzuki, K.

    2011-04-15

    An analytical method is developed for determining net sputtering rate for an MgO layer under hot ions with low energy (<100 eV) in a neon-xenon discharge gas at near-atmospheric pressure. The primary sputtering rate is analyzed according to spatial and energy distributions of the hot ions with average energy, E{sup h}{sub i}, above a threshold energy of sputtering, E{sub th,i}, multiplied by a yield coefficient. The threshold energy of sputtering is determined from dissociation energy required to remove an atom from MgO surface multiplied by an energy-transfer coefficient. The re-deposition rate of the sputtered atoms is calculated by a diffusion simulation using a hybridized probabilistic and analytical method. These calculation methods are combined to analyze the net sputtering rate. Maximum net sputtering rate due to the hot neon ions increases above the partial pressure of 4% xenon as E{sup h}{sub Ne} becomes higher and decreases near the partial pressure of 20% xenon as ion flux of neon decreases. The dependence due to the hot neon ions on partial pressure and applied voltage agrees well with experimental results, but the dependence due to the hot xenon ions deviates considerably. This result shows that the net sputtering rate is dominated by the hot neon ions. Maximum E{sup h}{sub Ne} (E{sup h}{sub Ne,max} = 5.3 - 10.3 eV) is lower than E{sub th,Ne} (19.5 eV) for the MgO layer; therefore, weak sputtering due to the hot neon ions takes place. One hot neon ion sputters each magnesium and each oxygen atom on the surface and distorts around a vacancy. The ratio of the maximum net sputtering rate is approximately determined by number of the ions at E{sup h}{sub i,max} multiplied by an exponential factor of -E{sub th,i}/E{sup h}{sub i,max}.

  7. Crystal Structure Transformations of a Magnetoresistive La 0.8MnO 3- δ Thin Film

    NASA Astrophysics Data System (ADS)

    Vincent, H.; Audier, M.; Pignard, S.; Dezanneau, G.; Sénateur, J. P.

    2002-03-01

    Structural transformations of an epitaxial La0.8MnO3-δ thin film deposited on MgO (100) substrate by metal-organic chemical vapor deposition were conjointly studied by X-ray diffraction using a conventional 4-circles-diffractometer and by transmission electron microscopy. As reported in a previous work [Pignard et al., J. Appl. Phys., 82(9), 4445 (1997)] changes of physical properties of this material have been observed through annealing treatments: Films deposited at 650°C exhibit temperatures of semiconductor-metal and para-ferromagnetic transitions at 130 and 200 K while after successive annealings between 600 and 800°C in air, these transition temperatures increase up to 310 and 330 K, respectively. Two different film structures related to the evolution of these properties were determined at room temperature in their paramagnetic state. As a result, the film structures were found to be monoclinic and arranged in twinned microdomains. Several structural transformations resulting of annealing treatments were deduced: (i) The as-deposited film is almost single-phased with a I2/b space group structure and transforms into a mixing of two phases of I2/b and P21/a space groups in a 82/18% ratio, respectively; (ii) Mn octahedra become more regular, with significant increases of Mn-O-Mn bond angles, close to 180°. These structural changes are interpreted in a discussion related to an increase of the Mn4+/Mn3+ ratio. Besides, as a surprising feature, observations by transmission electron microscopy on La0.8MnO3-δ/MgO interfaces showed that MgO exhibits domains of Fdoverline3 cubic lattice and a cell parameter twice this of normal MgO. This seems to be the result of a strain occurring between the film and the MgO substrate rather than a chemical diffusion.

  8. Growth of Tl 2Ba 2CaCu 2O 8 superconducting thin films on curved substrates for metamaterials applications

    NASA Astrophysics Data System (ADS)

    Speller, S. C.; Dinner, R. B.; Grovenor, C. R. M.

    2008-08-01

    Recent developments in the field of magnetic metamaterials have shown that coupled resonator structures can manipulate magnetic fields on a scale shorter than the wavelength of the electromagnetic radiation [E. Shamonina, V.A. Kalinin, K.H. Ringhofer, L. Solymar, J. Appl. Phys. 92 (10) (2002) 6252]. Major improvements in the sensitivity of such devices could be achieved by fabricating the resonating elements from high temperature superconducting (HTS) films on appropriate dielectric substrates. In order to produce a stack of superconducting/dielectric resonator structures, the ideal method involves patterning them into an HTS film grown on the curved surface of a dielectric cylinder. We report here our initial attempts at the growth of Tl 2Ba 2CaCu 2O 8 (Tl-2212) thin films on the surface of LaAlO 3 and MgO single-crystal cylinders. We have found that Tl-2212 thin films grow epitaxially on LaAlO 3 cylinders with Tl-2212 [0 0 1] aligned with the closest LaAlO 3 pseudocubic <1 0 0> direction, resulting in abrupt changes in Tl-2212 plate orientation at four positions around the cylinder. In contrast, Tl-2212 films grow smoothly on MgO cylinders, with Tl-2212 [0 0 1] aligned roughly parallel to the surface normal at all positions around the cylinder. This smooth growth on MgO leads to higher critical current values than epitaxial growth, making HTS on MgO a promising candidate for metamaterial device applications.

  9. Orientation of FePt nanoparticles on top of a-SiO2/Si(001), MgO(001) and sapphire(0001): effect of thermal treatments and influence of substrate and particle size.

    PubMed

    Schilling, Martin; Ziemann, Paul; Zhang, Zaoli; Biskupek, Johannes; Kaiser, Ute; Wiedwald, Ulf

    2016-01-01

    Texture formation and epitaxy of thin metal films and oriented growth of nanoparticles (NPs) on single crystal supports are of general interest for improved physical and chemical properties especially of anisotropic materials. In the case of FePt, the main focus lies on its highly anisotropic magnetic behavior and its catalytic activity, both due to the chemically ordered face-centered tetragonal (fct) L10 phase. If the c-axis of the tetragonal system can be aligned normal to the substrate plane, perpendicular magnetic recording could be achieved. Here, we study the orientation of FePt NPs and films on a-SiO2/Si(001), i.e., Si(001) with an amorphous (a-) native oxide layer on top, on MgO(001), and on sapphire(0001) substrates. For the NPs of an approximately equiatomic composition, two different sizes were chosen: "small" NPs with diameters in the range of 2-3 nm and "large" ones in the range of 5-8 nm. The 3 nm thick FePt films, deposited by pulsed laser deposition (PLD), served as reference samples. The structural properties were probed in situ, particularly texture formation and epitaxy of the specimens by reflection high-energy electron diffraction (RHEED) and, in case of 3 nm nanoparticles, additionally by high-resolution transmission electron microscopy (HRTEM) after different annealing steps between 200 and 650 °C. The L10 phase is obtained at annealing temperatures above 550 °C for films and 600 °C for nanoparticles in accordance with previous reports. On the amorphous surface of a-SiO2/Si substrates we find no preferential orientation neither for FePt films nor nanoparticles even after annealing at 630 °C. On sapphire(0001) supports, however, FePt nanoparticles exhibit a clearly preferred (111) orientation even in the as-prepared state, which can be slightly improved by annealing at 600-650 °C. This improvement depends on the size of NPs: Only the smaller NPs approach a fully developed (111) orientation. On top of MgO(001) the effect of annealing on

  10. Synthesis of Dimethyl Carbonate from Ethylene Carbonate and Methanol Over Nano-Catalysts Supported on CeO2-MgO.

    PubMed

    Jun, Jin Oh; Lee, Joongwon; Kang, Ki Hyuk; Song, In Kyu

    2015-10-01

    A series of CeO2(X)-MgO(1-X) (X = 0, 0.25, 0.5, 0.75, and 1.0) nano-catalysts were prepared by a co-precipitation method for use in the synthesis of dimethyl carbonate from ethylene carbonate and methanol. Among the CeO2(X)-MgO(1-X) catalysts, CeO2(0.25)-MgO(0.75) nano-catalyst showed the best catalytic performance. Alkali and alkaline earth metal oxides (MO = Li2O, K2O, Cs2O, SrO, and BaO) were then supported on CeO2(0.25)-MgO(0.75) by an incipient wetness impregnation method with an aim of improving the catalytic performance of CeO2(0.25)-MgO(0.75). Basicity of the catalysts was determined by CO2-TPD experiments in order to elucidate the effect of basicity on the catalytic performance. The correlation between catalytic performance and basicity showed that basicity played an important role in the reaction. Yield for dimethyl carbonate increased with increasing basicity of the catalysts. Among the catalysts tested, Li2O/CeO2(0.25)-MgO(0.75) nano-catalyst with the largest basicity showed the best catalytic performance in the synthesis of dimethyl carbonate. PMID:26726512

  11. Effect of MgO(100) support on structure and properties of Pd and Pt nanoparticles with 49-155 atoms

    NASA Astrophysics Data System (ADS)

    Kozlov, Sergey M.; Aleksandrov, Hristiyan A.; Goniakowski, Jacek; Neyman, Konstantin M.

    2013-08-01

    Presently, density functional computational studies of nanostructures in heterogeneous catalysts consider either sufficiently big ("scalable with size") unsupported metal nanoparticles (NPs) or small supported metal clusters. Both models may not be sufficiently representative of a few nm in size supported transition metal NPs dealt with in experiment. As a first step in closing the gap between theoretical models and prepared systems, we investigate the effect of a rather chemically inert oxide support, MgO(100), on relative energies and various properties of Pd and Pt NPs that consist of 49-155 atoms (1.2-1.6 nm in size) and exhibit bulk-like fcc structural arrangements. Shapes and interface configurations of metal NPs on MgO were obtained as a result of thorough optimization within the fcc motif using interatomic potentials. Then the stability and properties of the NPs were studied with a density functional method. We comprehensively characterize interaction between the NPs and MgO(100) support, their interface and effect of the support on NP properties. While the effect of MgO on relative stabilities of NPs with different shapes is found to be significant, other properties of the NPs such as electronic structure and interatomic distances within NP do not notably change upon deposition. This work paves the way to large-scale first-principles computational studies of more realistic models of oxide-supported metal catalysts.

  12. Effects of MgO and TiO2 on the viscous behaviors and phase compositions of titanium-bearing slag

    NASA Astrophysics Data System (ADS)

    Feng, Cong; Chu, Man-sheng; Tang, Jue; Qin, Jin; Li, Feng; Liu, Zheng-gen

    2016-08-01

    The effects of MgO and TiO2 on the viscosity, activation energy for viscous flow, and break-point temperature of titanium-bearing slag were studied. The correlation between viscosity and slag structure was analyzed by Fourier transform infrared (FTIR) spectroscopy. Subsequently, main phases in the slag and their content changes were investigated by X-ray diffraction and Factsage 6.4 software package. The results show that the viscosity decreases when the MgO content increases from 10.00wt% to 14.00wt%. Moreover, the break-point temperature increases, and the activation energy for viscous flow initially increases and subsequently decreases. In addition, with increasing TiO2 content from 5.00wt% to 9.00wt%, the viscosity decreases, and the break-point temperature and activation energy for viscous flow initially decrease and subsequently increase. FTIR analyses reveal that the polymerization degree of complex viscous units in titanium-bearing slag decreases with increasing MgO and TiO2 contents. The mechanism of viscosity variation was elucidated. The basic phase in experimental slags is melilite. Besides, as the MgO content increases, the amount of magnesia-alumina spinel in the slag increases. Similarly, the sum of pyroxene and perovskite phases in the slag increases with increasing TiO2 content.

  13. Charge separation and covalent bonding in metal oxide surfaces: A local density functional study on the MgO(001) surface

    SciTech Connect

    Birkenheuer, U. ); Boettger, J.C. ); Roesch, N. )

    1994-05-01

    A first principles local density functional investigation on extended, two-dimensional periodic slab models of the MgO(001) surface is performed, using the linear combination of Gaussian-type orbitals (LCGTO) technique as implemented in the FILMS program package. Stimulated by recent theoretical evidence for a reduced charge separation in MgO(001), a detailed analysis of the charge distribution and its influence on the electrical field above the surface is carried out. Two different methods to quantify the charge separation in the ionic substrate are employed, a local one based on the topological atom approach and a global one derived from the Madelung field of the surface near potential adsorbates. Both procedures lead to a charge separation significantly (10%--20%) below the nominal ionic value of [plus minus]2 a.u. A variational atomic orbital analysis is utilized to discuss the origin of the Mg 3[ital s] and 3[ital p] structures discernible in the crystal orbitals of the MgO slab systems. They are identified as covalent magnesium valence orbital admixtures to the oxygen dominated valence bands in consistence with the reduced charge separation. Their influence on the cohesive energy of crystalline MgO, however, is found to be only 5% ([similar to]0.5 eV).

  14. Magnetic anisotropy of [Co{sub 2}MnSi/Pd]{sub n} superlattice films prepared on MgO(001), (110), and (111) substrates

    SciTech Connect

    Matsushita, Naoki; Takamura, Yota; Fujino, Yorinobu; Nakagawa, Shigeki; Sonobe, Yoshiaki

    2015-02-09

    Superlattice films with full-Heusler Co{sub 2}MnSi (CMS) alloy and Pd layers prepared on Pd-buffered MgO(001), (110), and (111) substrates were investigated. Crystal orientation and epitaxial relationship of Pd and CMS layers were analyzed from x-ray diffraction, pole figure measurements, and transmission electron microscope observation. Formation of the L2{sub 1}-ordered structure in the CMS layers was confirmed by observation of CMS(111) diffraction. Perpendicular magnetic anisotropy (PMA) was obtained in the [CMS (0.6 nm)/Pd (2 nm)]{sub 6} superlattice film formed using MgO(111) substrates although other superlattice films prepared using MgO(001) and (110) substrates showed in-plane and isotropic magnetic anisotropy, respectively. The perpendicular magnetic anisotropy energy constant K for the superlattice films prepared using MgO(111) substrate was estimated to be 2.3 Mergs/cm{sup 3}, and an interfacial anisotropy constant K{sub i} per one CMS-Pd interface in the superlattice films was estimated to be 0.16 ergs/cm{sup 2}. K{sub i} in superlattice films with various crystal orientations showed positive values, indicating that Pd/CMS interfaces had an ability to induce PMA regardless of their crystal orientation.

  15. Preparation of bi-axially aligned YBa 2Cu 3O 7- δ film on CeO 2-buffered MgO by chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Yamagiwa, K.; Hiei, H.; Takahashi, Y.; Kim, S. B.; Matsumoto, K.; Ikuta, H.; Mizutani, U.; Hirabayashi, I.

    2000-06-01

    We have succeeded in preparing in-plane aligned YBa 2Cu 3O 7- δ (Y123) film by chemical solution deposition (CSD) processing on CeO 2 (100)-buffered MgO (100) substrates. The CeO 2 buffer film was deposited on MgO (100) single crystalline substrate by pulsed laser deposition (PLD). For CSD coating, a homogeneous coating solution having a molar ratio of Y:Ba:Cu=1:2:3, was prepared by dissolving metal naphthenates in toluene. This solution was spin-coated both on the YSZ (100) and on the CeO 2-buffered MgO (100) single crystalline substrates. The precursor films were calcined at 425°C and fired at various temperatures under low oxygen partial pressure ( pO 2). All Y123 films showed strong (00 n) peaks, which correspond to c-axis orientation perpendicular to the substrates and their a/ b-axes were in-plane aligned. We confirmed that CeO 2 buffer is usable for CSD processing. While the Y123 films on the YSZ reacted with the substrate forming BaZrO 3 phase and did not show sufficient superconducting properties. The Tc,zero value of the Y123 film prepared on CeO 2-buffered MgO substrate was 91.5 K and Jc was 1.2×10 5 A/cm 2 at 77 K, 0 T.

  16. Effect of SnO, MgO and Ag2O Mix-doping on the Formation and Superconducting Properties of Bi-2223 Ag/tapes

    NASA Astrophysics Data System (ADS)

    Lu, X. Y.; Yi, D.; Chen, H.; Nagata, A.

    The Ag/tapes with the composition Bi1.8Pb0.4Sr1.9Ca2.1Cu3.5Oy + x wt% SnO + y wt% MgO + z wt% Ag2O (x = 0, 0.2, 0.4; y = 0, 0.2; z = 0, 0.2) were prepared by sintering at 835°C for 120 h after partial-melting at 845°C for 1 h. The individual SnO doping, SnO and Ag2O mix-doping, and SnO and MgO mix-doping all decrease the conversion of Bi-2212 phase to Bi-2223 phase. The tape with individual 0.4 wt% SnO doping shows the lowest conversion and the lowest critical current density. However, the SnO, MgO and Ag2O mix-doping increase the conversion of Bi-2212 phase to Bi-2223 phase. The tape with 0.2 wt% SnO, 0.2 wt% MgO and 0.2 wt%Ag2O mix-doping shows the highest proportion of Bi-2223 phase and the highest critical current density.

  17. Perpendicular magnetization of Co2FeAl full-Heusler alloy films induced by MgO interface

    NASA Astrophysics Data System (ADS)

    Wen, Zhenchao; Sukegawa, Hiroaki; Mitani, Seiji; Inomata, Koichiro

    2011-06-01

    The perpendicular magnetization of Co2FeAl (CFA) full-Heusler alloy films was achieved in the structures of CFA/MgO and MgO/CFA with the perpendicular magnetic anisotropy energy density (KU) of 2-3×106 erg/cm3, which can be used as the perpendicular ferromagnetic electrodes of MgO-based magnetic tunnel junctions (MTJs) with high thermal stability at sub-50-nm dimension. The CFA thickness dependence of KU was investigated at different annealing temperatures, indicating that the perpendicular anisotropy of CFA is contributed by the interfacial anisotropy between CFA and MgO. This letter will open up a way for obtaining perpendicular magnetization of Co-based full-Heusler alloys, which is promising for further reduction in the critical current of current induced magnetization switching in MgO-based MTJ nanopillars with perpendicular full-Heusler alloy electrodes.

  18. Use of MgO doped with a divalent or trivalent metal cation for removing arsenic from water

    DOEpatents

    Moore, Robert C; Holt-Larese, Kathleen C; Bontchev, Ranko

    2013-08-13

    Systems and methods for use of magnesium hydroxide, either directly or through one or more precursors, doped with a divalent or trivalent metal cation, for removing arsenic from drinking water, including water distribution systems. In one embodiment, magnesium hydroxide, Mg(OH).sub.2 (a strong adsorbent for arsenic) doped with a divalent or trivalent metal cation is used to adsorb arsenic. The complex consisting of arsenic adsorbed on Mg(OH).sub.2 doped with a divalent or trivalent metal cation is subsequently removed from the water by conventional means, including filtration, settling, skimming, vortexing, centrifugation, magnetic separation, or other well-known separation systems. In another embodiment, magnesium oxide, MgO, is employed, which reacts with water to form Mg(OH).sub.2. The resulting Mg(OH).sub.2 doped with a divalent or trivalent metal cation, then adsorbs arsenic, as set forth above. The method can also be used to treat human or animal poisoning with arsenic.

  19. Efficient Explicitly Correlated Many-Electron Perturbation Theory for Solids: Application to the Schottky Defect in MgO

    NASA Astrophysics Data System (ADS)

    Grüneis, Andreas

    2015-08-01

    We introduce a novel and efficient explicitly correlated implementation of second-order perturbation theory for solids. The required three-electron integrals are computed directly using a plane wave basis set. We parametrize the employed correlation factors using results previously obtained for a finite uniform electron gas simulation cell. We demonstrate for a range of solids that basis set converged correlation energies, equilibrium volumes, and bulk moduli can be obtained efficiently in this theory using a few ten orbitals per atom. To stretch the capabilities of this novel method we compute the Schottky defect formation energy in MgO, studying systems with 54 atoms in the supercell. We verify the accuracy of the calculated formation energies using the more accurate coupled cluster singles and doubles theory. Furthermore, we discuss other potential applications for the derived and implemented expressions such as an occupied orbital only correlation energy functional.

  20. Morphology of Monolayer MgO Films on Ag(100): Switching from Corrugated Islands to Extended Flat Terraces

    NASA Astrophysics Data System (ADS)

    Pal, Jagriti; Smerieri, Marco; Celasco, Edvige; Savio, Letizia; Vattuone, Luca; Rocca, Mario

    2014-03-01

    The ability to engineer nearly perfect ultrathin oxide layers, up to the limit of monolayer thickness, is a key issue for nanotechnological applications. Here we face the difficult and important case of ultrathin MgO films on Ag(100), for which no extended and well-ordered layers could thus far be produced in the monolayer limit. We demonstrate that their final morphology depends not only on the usual growth parameters (crystal temperature, metal flux, and oxygen partial pressure), but also on aftergrowth treatments controlling so far neglected thermodynamics constraints. We thus succeed in tuning the shape of the oxide films from irregular, nanometer-sized, monolayer-thick islands to slightly larger, perfectly squared, bilayer islands, to extended monolayers limited apparently only by substrate steps.

  1. Morphology of monolayer MgO films on Ag(100): switching from corrugated islands to extended flat terraces.

    PubMed

    Pal, Jagriti; Smerieri, Marco; Celasco, Edvige; Savio, Letizia; Vattuone, Luca; Rocca, Mario

    2014-03-28

    The ability to engineer nearly perfect ultrathin oxide layers, up to the limit of monolayer thickness, is a key issue for nanotechnological applications. Here we face the difficult and important case of ultrathin MgO films on Ag(100), for which no extended and well-ordered layers could thus far be produced in the monolayer limit. We demonstrate that their final morphology depends not only on the usual growth parameters (crystal temperature, metal flux, and oxygen partial pressure), but also on aftergrowth treatments controlling so far neglected thermodynamics constraints. We thus succeed in tuning the shape of the oxide films from irregular, nanometer-sized, monolayer-thick islands to slightly larger, perfectly squared, bilayer islands, to extended monolayers limited apparently only by substrate steps. PMID:24724662

  2. Large perpendicular magnetic anisotropy of single Co atom on MgO monolayer: A first-principles study

    SciTech Connect

    Shao, Bin; Shi, Wu-Jun; Feng, Min; Zuo, Xu

    2015-05-07

    Realizing the magnetic bit with a single atom is the ultimate goal for magnetic storage. Based on density functional theory, the magnetic anisotropy (MA) of single Co atom on MgO monolayer has been investigated. Results show that this two dimensional system possesses a large perpendicular MA, about 5.8 meV per Co atom. Besides, there exists remarkable unquenched orbital moments for different magnetization directions, which can be attributed to the reduction of coordination number in two dimensional system and is responsible for the enhanced MA. The Bloch pseudo-wavefunction and band structure of Co d-orbitals have been calculated to elucidate the origin of the perpendicular MA.

  3. Development and characterization of Mn{sup 2+}-doped MgO nanoparticles by solution combustion synthesis

    SciTech Connect

    Basha, Md. Hussain; Gopal, N. O.; Rao, J. L.; Nagabhushana, H.; Nagabhushana, B. M.; Chakradhar, R. P. S.

    2015-06-24

    Mn doped MgO Nanoparticles have been prepared by Solution Combustion Synthesis. The synthesized sample is characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Electron Paramagnetic Resonance (EPR). The prepared MgO:Mn (1 mol%) nano crystals appear to be of simple cubic crystalline phase with lattice parameters a = 4.218(2) Å and cell volume = 74.98 (7) Å{sup 3}. SEM micrograph of powders show highly porous, many agglomerates with irregular morphology, large voids, cracks and pores. EPR spectrum of the sample at room temperature exhibit an isotropic sextet hyperfine pattern, centered at g=1.99, characteristic if Mn{sup 2+} ions with S=I=5/2.The observed g value and the hyperfine value reveal the ionic bonding between Mn{sup 2+} and its surroundings.

  4. Dynamics and kinetics of monolayer CH4 on MgO(001) studied by helium-atom scattering

    NASA Astrophysics Data System (ADS)

    Jung, David R.; Cui, Jinhe; Frankl, Daniel R.

    1991-05-01

    The structure, vibrational excitations, and adsorption and desorption kinetics of monolayer CH4 on MgO have been investigated using several techniques of helium scattering. Structural information is presented in the form of high-order diffraction-peak intensities. A vibrational excitation of 7.5 meV measured by time-of-flight methods shows no dispersion. This excitation energy is used in an analysis of the Debye-Waller effect for the [00] and [1¯0] beams. Studies of adsorption and desorption rates exploiting the He-methane diffuse-scattering cross section indicate an island-growth mode and allow determination of the desorption activation energy. Differences between the low-coverage adsorption rates for adsorption on fresh versus previously exposed surfaces suggest that higher-binding-energy sites are present after the desorption of a methane monolayer.

  5. Defect states at organic-inorganic interfaces: Insight from first principles calculations for pentaerythritol tetranitrate on MgO surface

    NASA Astrophysics Data System (ADS)

    Tsyshevsky, Roman V.; Rashkeev, Sergey N.; Kuklja, Maija M.

    2015-07-01

    Light-responsive organic-inorganic interfaces offer experimental opportunities that are otherwise difficult to achieve. Since laser light can be manipulated very precisely, it becomes possible to engineer selective, predictive, and highly controlled interface properties. Photochemistry of organic-inorganic energetic interfaces is a rapidly emerging research field in which energy absorption and interface stability mechanisms have yet to be established. To explore the interaction of the laser irradiation with molecular materials, we performed first principle calculations of a prototype organic-inorganic interface between a nitroester (pentaerythritol tetranitrate, PETN, C5H8N4O12) and a magnesium oxide (MgO) surface. We found that the light absorption is defined by the band alignment between interface components and interfacial charge transfer coupled with electronic states in the band gap, generated by oxide surface defects. Hence the choice of an oxide substrate and its morphology makes the optical absorption tunable and governs both the energy accumulation and energy release at the interface. The obtained results offer a possible consistent interpretation of experiments on selective laser initiation of energetic materials, which reported that the presence of metal oxide additives triggered the photoinitiation by excitation energy much lower than the band gap. We suggest that PETN photodecomposition is catalyzed by oxygen vacancies (F0 centers) at the MgO surface. Our conclusions predict ways for a complete separation of thermo- and photo-stimulated interface chemistry of molecular materials, which is imperative for highly controllable fast decomposition and was not attainable before. The methodology described here can be applied to any type of molecular material/wide band gap dielectric interfaces. It provides a solid basis for novel design and targeted improvements of organic-inorganic interfaces with desired properties that promise to enable vastly new concepts

  6. Calculated polarizations and piezoelectric constants of wurtzite ZnO, CdO and MgO

    NASA Astrophysics Data System (ADS)

    Gopal, Priya

    2006-03-01

    The macroscopic polarization in wurtzite crystal structures such as GaN and ZnO has a strong influence on the electrical and optical properties. This property has been exploited in GaN/AlGaN heterostructures, where the difference in the polarizations between layers induces an electric field at the interface forming a high mobility two-dimensional electron gas (2DEG) [1]. Here we calculate the polarization and the piezoelectric properties of the corresponding wurtzite-structure binary oxides ZnO, MgO and CdO. The knowledge of these properties is essential to explore the possibility of creating similar high mobility polarization induced 2DEGs in the ZnO-based material system. However, since wurtzite-structure MgO and CdO are not experimentally accessible, the values can be obtained computationally. We use the recently developed self-interaction corrected pseudopotential (pseudo-SIC) implementation [2] of the density functional theory and the widely used Berry phase method [3] for obtaining the polarization and piezoelectric constants. We find that the polarization gradients between the end-point compounds in the MgO-ZnO-CdO are larger than in the GaN analogues. [1]U. K. Mishra,Y. Wu, B.P. Keller, S. Keller and S.P. Denbaars IEEE Transactions on Microwave theory and Techniques, 46, 6 (1998). [2] A. Filippetti and N.A. Spaldin Phys. Rev. B 67, 125109 (2003). [3]R. D. Kingsmith and D. Vanderbilt Phys. Rev. B 49, 5828 (1994). [4]P. Gopal and N.A. Spaldin submitted analogues.

  7. Structural and optical properties of ZnMgO thin films grown by pulsed laser deposition using ZnO-MgO multiple targets

    NASA Astrophysics Data System (ADS)

    Maemoto, Toshihiko; Ichiba, Nobuyasu; Ishii, Hiroaki; Sasa, Shigehiko; Inoue, Masataka

    2007-04-01

    We report on structural and optical properties for Zn1-xMgxO (ZMO) thin films produced by pulsed laser ablation. ZMO thin films were grown on a-plane Al2O3 substrates at 400°C. In order to efficiently incorporate Mg into ZnO thin films, we used multiple ZnO-MgO ablation targets. Pulses from a Nd:YAG laser (4th harmonic generation: 266 nm) were directed on the ZnO-MgO ablation targets, which consisted of MgO single crystals mounted on ZnO ceramic targets. The ZMO films were characterized by x-ray diffraction, optical transmittance and cathodeluminescence (CL) measurements. Highly c-axis oriented ZMO(0002) reflections corresponding to the wurtzite-phase were observed. The c-axis lattice constants of the films were determined from the ZnMgO(0002) peak. The c-axis length of the ZMO films decreased linearly with Mg content. From the optical transmittance spectra of ZMO films, we observed a blue shift in the absorption edge with increasing Mg content. Band gap energies of ZMO thin films were determined from the optical transmittance and CL spectra. We found that the band gap energy changed from 3.27 eV to 3.95 eV. The Mg content of ZMO films increased monotonically with the number of laser pulses which struck the MgO target. These results show that laser ablation using multiple targets of ZnO and MgO is effective for band engineering of ZMO.

  8. Investigation of optical loss mechanisms in oxide thin films

    SciTech Connect

    Chow, A.F.; Kingon, A.I.; Auciello, O.; Poker, D.B.

    1995-05-01

    KNbO{sub 3}, K(Ta,Nb)O{sub 3}, KTaO{sub 3}, and Ta{sub 2}O{sub 5} thin films have been grown by ion-beam sputter deposition. KNbO{sub 3} has excellent nonlinear properties for second harmonic generation; however, high optical losses are still characteristic of these films. Several loss mechanisms, such as, high angle grain boundaries, twin domains, interface and surface scattering, and oxygen vacancies can all contribute to the high losses. In order to isolate the various mechanisms, amorphous Ta{sub 2}O{sub 5} films, epitaxial cubic KTaO{sub 3} and tetragonal K(Ta,Nb)O{sub 3} films were grown on MgO and Al{sub 2}O{sub 3} substrates subjected to post-deposition annealing treatments and various oxygen pressure conditions. The optical losses and refractive indices were observed to differ depending on the substrate surface and annealing treatments. Resonant scattering experiments were performed to analyze the oxygen composition. The optical properties of these oxide thin film systems are reported and the breakdown of the loss mechanisms is addressed.

  9. Domain structure sequence in ferroelectric Pb(Zr0.2Ti0.8)O3 thin film on MgO

    NASA Astrophysics Data System (ADS)

    Janolin, Pierre-Eymeric; Fraisse, Bernard; Dkhil, Brahim; Le Marrec, Françoise; Ringgaard, Erling

    2007-04-01

    The structural evolution of a polydomain ferroelectric Pb(Zr0.2Ti0.8)O3 film was studied by temperature-dependent x-ray diffraction. Two critical temperatures were evidenced: T*=740K, corresponding to a change in the domain structure (a /c/a/c to a1/a2/a1/a2), and TCfilm=825K, where the film undergoes a ferroelectric-paraelectric phase transition. The film remains tetragonal on the whole range of temperature investigated. The evolutions of the domain structure and lattice parameters were found to be in very good agreement with the calculated domain stability map and theoretical temperature-misfit strain phase diagram, respectively.

  10. Domain formation in epitaxial Pb(Zr, Ti)O3 thin films

    NASA Astrophysics Data System (ADS)

    Lee, K. S.; Choi, J. H.; Lee, J. Y.; Baik, S.

    2001-10-01

    Ferroelectric twin-domain structures in epitaxial Pb(Zr, Ti)O3 (PZT) thin films grown on various single-crystal substrates such as MgO(001), KTaO3(001), and SrTiO3(001) were investigated by two-dimensional reciprocal space mapping using synchrotron x-ray diffraction. Each system showed a characteristic domain structure. PbTiO3 thin films grown on MgO(001) showed highly c-axis oriented domain structures consisting of a periodic array of 90° twinlike domains. Perfectly c-axis oriented films were obtained on SrTiO3(001), while the films grown on KTaO3(001) showed a-domain dominant structures with a small amount of c domains embedded in matrix a domains. Contributions of net elastic strain stored in each heteroepitaxial layer and its relaxation to the final domain structures were evaluated considering thermodynamic equilibrium relief of coherency strain by misfit dislocation generation at the film growth temperature. A comparison between theoretical consideration and experimental results clearly demonstrates that the nature of effective misfit strain and its relaxation during film growth play a critical role in the formation of domain structures in epitaxial PZT thin films. Moreover, it was verified that the control of such critical strain factors by changing film composition could modify dominant domain structures in a drastic way. In addition, it was found that the crystalline quality of the films is closely correlated to the tilting nature of the domain structure in each system and coherency strain across the 90° domain boundary is accommodated mainly by the domain tilt of the minor domain.

  11. Tilt grain boundaries in YBa sub 2 Cu sub 3 O sub 7-x thin films

    SciTech Connect

    Gao, Y.; Bai, G.; Chang, H.L.M.; Merkle, K.L.; Lam, D.J.

    1990-07-01

    Grain boundaries in YBa{sub 2}Cu{sub 3}O{sub 7-x} superconductor thin films grown on (001) MgO by metal-organic chemical vapor deposition (MOCVD) have been characterized using transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). It was found that the YBa{sub 2}Cu{sub 3}O{sub 7-x} thin films were highly textured with the c axes, or (001) orientation, nearly parallel between grains and perpendicular to the MgO substrate. A majority of the grain boundaries are low-angle boundaries with a tilt angle, {theta}, less than 15{degree}. The low-angle boundaries appear to be strongly faceted on an atomic scale in such a way that the boundary planes tend to be parallel to the (100), (010), or (110) lattice planes in one of the adjacent grains. Almost all of the lattice planes, except for a number of distorted regions along the boundaries, are continuous across the boundaries from one grain to another, accommodating the misorientation with a slight bending of the lattice planes. The small-angle boundaries are shown to consist of arrays of dislocations. A domain structure, formed by the interchange of a and b axes has been observed in large grains. The domain boundaries are strongly faceted with the (100) and (010) lattice planes parallel to the boundaries. These observations on the atomic structure of boundaries, are used to discuss the effect of grain boundaries on superconductor properties in YBa{sub 2}Cu{sub 3}O{sub 7-x} thin films. 15 refs., 9 figs.

  12. Electrical surface-resistivity, dielectric resonance, polarization and magnetic properties of Bi0.5Sr0.5FeO3-δ thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Balamurugan, K.; Ramachandran, B.; Krishna Surendra, M.; Kumar, N. Harish; Ramachandra Rao, M. S.; Santhosh, P. N.

    2014-09-01

    Polycrystalline and highly preferred (1\\,0\\,\\bar{{2}}) orientated Bi0.5Sr0.5FeO3-δ thin films were grown by pulsed laser deposition (PLD) on n-Si (2 0 0) and MgO (2 0 0) single crystalline substrates respectively. The thin films were inspected using x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy and atomic force microscopy techniques. The electrical surface-resistivity, dielectric resonance, electric polarization, and magnetic properties of the thin films were studied. At room temperature, depending on deposition conditions, the polycrystalline thin films grown on n-Si substrates were found to exhibit an electrical surface-resistivity of the order of 103-106 Ω, a piezoelectric resonance in the frequency range of about 25-26 MHz, a relaxor-type ferroelectric hysteresis with a maximum polarization of 0.015-0.055 µC cm-2 and magnetic hysteresis. Similarly, the thin films grown on MgO substrates exhibited an electrical surface-resistivity of the order of 109 Ω, multiple piezoelectric resonances in the frequency range of about 8-45 MHz, a linear variation of polarization with applied electric field and either a linearly varying magnetization or magnetic hysteresis which depends on the deposition conditions.

  13. Thermodynamic simulation on mineralogical composition of CaO-SiO2-Al2O3-MgO quaternary slag system.

    PubMed

    Liu, Chao; Zhang, Yu-Zhu; Li, Jie; Li, Jun-Guo; Kang, Yue

    2016-01-01

    It is necessary to elucidate the crystallization thermodynamic of mineralogical phases during the cooling process of the molten BFS with different chemical composition, because the high-melting point mineral phase maybe crystallized during the fiber forming and thereafter cooling process. Thermodynamic calculation software FactSage6.4 and the hot remelting experiments were performed to explore the influence of basicity, Al2O3 content and MgO content on the crystallization of mineralogical components and their transformation. The results showed that the main mineralography of the CaO-SiO2-Al2O3-MgO quaternary slag system was melilite, and a certain amount of anorthite and calcium metasilicate. The crystallographic temperature of melilite is increased with the increasing of basicity, MgO and Al2O3 content, which has a significant impact on the utilization performance of the mineral wool prepared with the hot blast furnace slag directly. With the increasing of basicity, there was a tendency that crystallographic amount of melilite increased to the summit and then declined, while the amount of anorthite and calcium metasilicate decreased consistently. Finally, these two mineralogical components could be replaced by magnesium rhodonite and spinel with the increasing of basicity. When the basicity and MgO content were 1.0 and 9 %, the crystallographic mass ratio of melilite and anorthite increased, while that of calcium silicate declined, and replaced by spinel finally with the increasing of Al2O3 content. When the basicity and Al2O3 content were 1.0 and 13 %, the crystallographic mass ratio of melilite increased, while that of anorthite and calcium silicate declined, and replaced by pyroxene and spinel with the increasing of MgO content. To decline fiberization temperature of the melt BFS, the basicity, MgO and Al2O3 content should be decreased during the modification process of chemical composition, because the crystallization temperature of the primary crystalline

  14. Properties of MgO to 1.2 TPa from high-precision experiments on Sandia's Z machine and first-principles simulations using QMC and DFT

    NASA Astrophysics Data System (ADS)

    Shulenburger, Luke

    2015-11-01

    MgO is a major constituent of Earth's mantle, the rocky cores of gas giants and is a likely component of the interiors of many exoplanets. The high pressure - high temperature behavior of MgO directly affects equation of state models for planetary structure and formation. In this work, we examine MgO under extreme conditions using experimental and theoretical methods to determine the phase diagram and transport properties. Using plate impact experiments on Sandia's Z facility a low entropy solid-solid phase transition from B1 to B2 is clearly determined. The melting transition, on the other hand, is subtle, involving little to no signal in us-up space. Theoretical work utilizing density functional theory (DFT) provides a complementary picture of the phase diagram. The solid-solid phase transition is identified through a series of quasi-harmonic phonon calculations and thermodynamic integration, while the melt boundary is found using phase coexistence calculations. The calculation of reflectivity along the Hugoniot and the influence of the ionic structure on the transport properties requires particular care because of the underestimation of the band gap and attendant overestimation of transport properties due to the use of semi-local density functional theory. We will explore the impact of this theoretical challenge and its potential solutions in this talk. Finally, understanding the behavior of MgO as the pressure releases from the Hugoniot state is a key ingredient to modeling giant impact events. We explore this regime both through additional DFT calculations and by observing the release state of the MgO into lower impedance materials. The integrated use of DFT simulations and high-accuracy shock experiments together provide a comprehensive understanding of MgO under extreme conditions. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U

  15. Creation of nanopores on graphene planes with MgO template for preparing high-performance supercapacitor electrodes

    NASA Astrophysics Data System (ADS)

    Wang, Huanjing; Sun, Xiuxia; Liu, Zonghuai; Lei, Zhibin

    2014-05-01

    Creation of nanopores on graphene planar sheets is of great significance in promoting the kinetic diffusion of electrolyte and enhancing the utilization efficiency of graphene planar sheets. Herein, we developed a facile chemical vapor deposition strategy to prepare highly porous graphene with flake-like MgO as template and ferrocene as the carbon precursor. The graphene layers show a highly porous structure with small mesopores of 4-8 nm, large mesopores of 10-20 nm and additional macropores of 100-200 nm. These nanopores on graphene sheets provide numerous channels for fast ion transport perpendicular to the 2D basal plane, while the good powder conductivity ensures an effective electron propagation within the 2D graphene plane. As a result, a specific capacitance of 303 F g-1, an areal capacitance up to 17.3 μF cm-2 and a nearly tenfold shorter time constant were achieved when compared with those of nonporous and stacked graphene electrodes. The method demonstrated herein would open up an opportunity to prepare porous graphene for a wide applications in energy storage, biosensors, nanoelectronics and catalysis.Creation of nanopores on graphene planar sheets is of great significance in promoting the kinetic diffusion of electrolyte and enhancing the utilization efficiency of graphene planar sheets. Herein, we developed a facile chemical vapor deposition strategy to prepare highly porous graphene with flake-like MgO as template and ferrocene as the carbon precursor. The graphene layers show a highly porous structure with small mesopores of 4-8 nm, large mesopores of 10-20 nm and additional macropores of 100-200 nm. These nanopores on graphene sheets provide numerous channels for fast ion transport perpendicular to the 2D basal plane, while the good powder conductivity ensures an effective electron propagation within the 2D graphene plane. As a result, a specific capacitance of 303 F g-1, an areal capacitance up to 17.3 μF cm-2 and a nearly tenfold shorter time

  16. Rheology and texture evolution of the lower mantle analogue CaGeO3+MgO

    NASA Astrophysics Data System (ADS)

    Gasc, J.; Wang, Y.; Hilairet, N.

    2013-12-01

    Even using available state of the art techniques, getting insights into the lower mantle physical properties remains challenging because of the high pressures involved (>22 GPa). The use of CaGeO3 perovskite (GePv) as an analog material, stable at much lower pressure than the natural (Mg, Fe)SiO3 perovskite, allows us to study the rheology of the lower mantle. In a previous study on a two-phase composite GePv + MgO, Wang et al. (2013) showed that up to 15% total bulk strain, the samples remain a Load Bearing Framework (LBF) texture, with the GePv phase supporting the applied stress. In another analogue, FeNiS + dunite, the initial LBF texture was shown to undergo a drastic transition to an interconnected weak layer (IWL) texture under a shear strain of about 1 (Wang et al., 2011). In order to determine if such a behavior occurs in GePv + MgO, we deformed this lower-mantle analog material to larger strains, using the Deformation-DIA (DDIA) apparatus at sector 13 of the Advanced Photon Source. These experiments were carried out at pressures of ~10 GPa (using anvils with a truncated edge length of 3 mm) and temperatures of 1000 K. The samples were deformed at strain rates of 10-5 - 10-4 s-1, up to finite bulk strains of ~50%. Using a monochromatic incident beam, angle dispersive X-ray diffraction patterns were collected upon deformation. The full Debye diffraction rings were interpreted in terms of lattice d-spacing. In this manner, the strain of six lattice planes for GePv and two for MgO could be resolved and were used to determine the micro-stress evolution of each phase. The samples show a dramatic weakening above 20% of strain. The diffraction patterns also evidence significant lattice preferred orientation (i.e., texture) development in both phases upon deformation. Textural quantification is in progress and a microscopy study of the recovered samples will be conducted to determine whether the samples have experienced a transition from the initial LBF texture to

  17. Fabrication of air-stable n-type carbon nanotube thin-film transistors on flexible substrates using bilayer dielectrics.

    PubMed

    Li, Guanhong; Li, Qunqing; Jin, Yuanhao; Zhao, Yudan; Xiao, Xiaoyang; Jiang, Kaili; Wang, Jiaping; Fan, Shoushan

    2015-11-14

    Single-walled carbon nanotube (SWNT) thin-film transistors hold great potential for flexible electronics. However, fabrication of air-stable n-type devices by methods compatible with standard photolithography on flexible substrates is challenging. Here, we demonstrated that by using a bilayer dielectric structure of MgO and atomic layer deposited (ALD) Al2O3 or HfO2, air-stable n-type devices can be obtained. The mechanism for conduction type conversion was elucidated and attributed to the hole depletion in SWNT, the decrease of the trap state density by MgO assimilating adsorbed water molecules in the vicinity of SWNT, and the energy band bending because of the positive fixed charges in the ALD layer. The key advantage of the method is the relatively low temperature (120 or 90 °C) required here for the ALD process because we need not employ this step to totally remove the absorbates on the SWNTs. This advantage facilitates the integration of both p-type and n-type transistors through a simple lift off process and compact CMOS inverters were demonstrated. We also demonstrated that the doping of SWNTs in the channel plays a more important role than the Schottky barriers at the metal contacts in carbon nanotube thin-film transistors, unlike the situation in individual SWNT-based transistors. PMID:26451806

  18. Thin film hydrogen sensor

    DOEpatents

    Cheng, Y.T.; Poli, A.A.; Meltser, M.A.

    1999-03-23

    A thin film hydrogen sensor includes a substantially flat ceramic substrate with first and second planar sides and a first substrate end opposite a second substrate end; a thin film temperature responsive resistor on the first planar side of the substrate proximate to the first substrate end; a thin film hydrogen responsive metal resistor on the first planar side of the substrate proximate to the fist substrate end and proximate to the temperature responsive resistor; and a heater on the second planar side of the substrate proximate to the first end. 5 figs.

  19. Electrochemical thinning of silicon

    SciTech Connect

    Medernach, J.W.

    1994-01-11

    Porous semiconducting material, e.g. silicon, is formed by electrochemical treatment of a specimen in hydrofluoric acid, using the specimen as anode. Before the treatment, the specimen can be masked. The porous material is then etched with a caustic solution or is oxidized, depending of the kind of structure desired, e.g. a thinned specimen, a specimen, a patterned thinned specimen, a specimen with insulated electrical conduits, and so on. Thinned silicon specimen can be subjected to tests, such as measurement of interstitial oxygen by Fourier transform infra-red spectroscopy (FTIR). 14 figures.

  20. Electrochemical thinning of silicon

    DOEpatents

    Medernach, John W.

    1994-01-01

    Porous semiconducting material, e.g. silicon, is formed by electrochemical treatment of a specimen in hydrofluoric acid, using the specimen as anode. Before the treatment, the specimen can be masked. The porous material is then etched with a caustic solution or is oxidized, depending of the kind of structure desired, e.g. a thinned specimen, a specimen, a patterned thinned specimen, a specimen with insulated electrical conduits, and so on. Thinned silicon specimen can be subjected to tests, such as measurement of interstitial oxygen by Fourier transform infra-red spectroscopy (FTIR).

  1. Biomimetic thin film synthesis

    SciTech Connect

    Graff, G.L.; Campbell, A.A.; Gordon, N.R.

    1995-05-01

    The purpose of this program is to develop a new process for forming thin film coatings and to demonstrate that the biomimetic thin film technology developed at PNL is useful for industrial applications. In the biomimetic process, mineral deposition from aqueous solution is controlled by organic functional groups attached to the underlying substrate surface. The coatings process is simple, benign, inexpensive, energy efficient, and particularly suited for temperature sensitive substrate materials (such as polymers). In addition, biomimetic thin films can be deposited uniformly on complex shaped and porous substrates providing a unique capability over more traditional line-of-sight methods.

  2. Thin film hydrogen sensor

    DOEpatents

    Cheng, Yang-Tse; Poli, Andrea A.; Meltser, Mark Alexander

    1999-01-01

    A thin film hydrogen sensor, includes: a substantially flat ceramic substrate with first and second planar sides and a first substrate end opposite a second substrate end; a thin film temperature responsive resistor on the first planar side of the substrate proximate to the first substrate end; a thin film hydrogen responsive metal resistor on the first planar side of the substrate proximate to the fist substrate end and proximate to the temperature responsive resistor; and a heater on the second planar side of the substrate proximate to the first end.

  3. Microstructure and Magnetic Properties of PrMnO3 Bulk and Thin Film

    NASA Astrophysics Data System (ADS)

    Lim, K. P.; Halim, S. A.; Chen, S. K.; Ng, S. W.; Wong, J. K.; Gan, H. M. Albert; Woon, H. S.

    2011-03-01

    Perovskite PrMnO3 (PMO) had been prepared in bulk by solid state reaction and thin films on corning glass, fused silica and MgO (100) glass substrate by pulsed laser deposition technique. SEM micrographs show that grains with size 2˜3 μm is observed in bulk PMO while thin films PMO show strongly connected grain structure with particle size that not larger than 100 nm. X-ray diffraction analysis shows that all samples are in single phase with orthorhombic crystal structure. Bulk PMO sample had lattice strain of 0.134% which is the lowest value among others. However, larger lattice strain was observed in thin film samples due to lattice mismatch between film-substrate and caused the MnO6 to deform. All samples shown paramagnetic or antiferromagnetic behavior, enhancement in magnetization value occurred for all PMO grew as film. We believe that larger lattice strain favor the grain growth of PMO towards more order phase. In summary, formation of structure and microstructure of thin film PMO depends on type of substrate used and it affect the magnetic property.

  4. Experimental evidence of tunable space-charge-layer-induced electrical properties of nanocrystalline ceria thin films.

    PubMed

    Lee, Kyung-Ryul; Lee, Jong-Ho; Yoo, Han-Ill

    2013-10-01

    Fully dense nanocrystalline ceria films were successfully deposited on a MgO single crystal by pulsed laser deposition (PLD). The electrical conductivity of the nanocrystalline thin film was 20 times higher than that of the bulk sample. The activation energy of bulk ceria was 2.3 eV, whereas the activation energy of the nanocrystalline sample was only 1.2 eV. After post-annealing at 1273 K in which the grain size of the nanocrystalline thin film increased to ~400 nm, the electrical conductivity and activation energy of the film were changed similar to those of bulk. These unique electrical properties of the nano-crystalline thin-film can be attributed to the grain size effect, or more specifically, to the space charge layer (SCL) effect. Furthermore, the electrical conductivity of the nanocrystalline thin film became similar to that of the bulk in an extremely reducing atmosphere because of the unusual dependence of the SCL effect on the oxygen partial pressure. PMID:23942424

  5. Microstructure and Magnetic Properties of PrMnO{sub 3} Bulk and Thin Film

    SciTech Connect

    Lim, K. P.; Halim, S. A.; Chen, S. K.; Ng, S. W.; Wong, J. K.; Gan, H. M. Albert; Woon, H. S.

    2011-03-30

    Perovskite PrMnO{sub 3}(PMO) had been prepared in bulk by solid state reaction and thin films on corning glass, fused silica and MgO (100) glass substrate by pulsed laser deposition technique. SEM micrographs show that grains with size 2{approx}3 {mu}m is observed in bulk PMO while thin films PMO show strongly connected grain structure with particle size that not larger than 100 nm. X-ray diffraction analysis shows that all samples are in single phase with orthorhombic crystal structure. Bulk PMO sample had lattice strain of 0.134% which is the lowest value among others. However, larger lattice strain was observed in thin film samples due to lattice mismatch between film-substrate and caused the MnO{sub 6} to deform. All samples shown paramagnetic or antiferromagnetic behavior, enhancement in magnetization value occurred for all PMO grew as film. We believe that larger lattice strain favor the grain growth of PMO towards more order phase. In summary, formation of structure and microstructure of thin film PMO depends on type of substrate used and it affect the magnetic property.

  6. Thermal stability of NdBCO/YBCO/MgO thin film seeds

    NASA Astrophysics Data System (ADS)

    Volochová, D.; Kavečanský, V.; Antal, V.; Diko, P.; Yao, X.

    2016-04-01

    Thermal stability of the Nd1+x Ba2-x Cu3O7-δ (Nd-123 or NdBCO) thin films deposited on MgO substrate, with YBa2Cu3O7-δ (Y-123 or YBCO) buffer layer (NdBCO/YBCO/MgO thin film), has been experimentally studied in order to determine the optimal film thickness acting as seed for bulk YBCO growth. YBCO bulk superconductors with Y2BaCuO5 (Y-211) and CeO2 addition were prepared by the top seeded melt growth process in a chamber furnace using NdBCO/YBCO/MgO thin film seeds of different thicknesses (200-700 nm with 20 nm YBCO buffer layer) and different maximum temperatures, T max. The maximum temperatures varied in the range of 1040 °C-1125 °C. The highest thermal stability 1118 °C was observed in the case of NdBCO/YBCO/MgO thin film of 300 nm thickness. These results are corroborated with differential scanning calorimetry and high temperature x-ray diffraction measurements, as well as microstructure observations.

  7. Homo- and hetero-epitaxial growth of hexagonal and cubic MgxZn1-x O alloy thin films by pulsed laser deposition technique

    NASA Astrophysics Data System (ADS)

    Hullavarad, S. S.; Hullavarad, N. V.; Pugel, D. E.; Dhar, S.; Takeuchi, I.; Venkatesan, T.; Vispute, R. D.

    2007-08-01

    In this work, we describe the homo- and hetero-epitaxial growth of hexagonal and cubic MgxZn1-xO thin films on lattice matched substrates of c-Al2O3, ZnO, MgO and SrTiO3. The crystalline quality, composition and epitaxial nature of the alloy films are obtained by x-ray diffraction and Rutherford backscattering spectroscopy (RBS) techniques. The RBS channeling yields are in the range 3-8% for homoepitaxial and hetero-epitaxial thin films. The metal-semiconductor-metal and ultraviolet detectors were fabricated on hexagonal and cubic MgxZn1-xO thin films and the leakage current and UV-visible rejection ratio are correlated with the epitaxial relationship between the film and substrates.

  8. Atomization characteristics and direct determination of manganese and magnesium in biological samples using a magnetically altered thin-film plasma

    SciTech Connect

    Brewer, S.W. Jr.; Sacks, R.D.

    1988-09-01

    A magnetic field with peak value of 3.7 kG is used to improve the atomization characteristics of an electrically vaporized thin-film plasma for the direct determination of Mg and Mn in solid biological materials. Plasmas are generated by high-current capacitive discharges through 350-..mu..g Ag or Au thin films formed on polypropylene substrates. Radiation intensity vs time plots are compared with and without the magnetic field for the NBS materials bovine liver, oyster tissue, orchard leaves, citrus leaves, tomato leaves, and pine needles. Analytical standard for Mg are prepared from suspensions of MgO powder, and standards for Mn are prepared from aqueous solutions of Mn(NO/sub 3/)/sub 2/ or MnSO/sub 4/. Analytical accuracy usually is improved with the presence of the magnetic field.

  9. Fabrication and magnetic properties of single-crystalline La0.33Pr0.34Ca0.33MnO3/MgO nanowires

    NASA Astrophysics Data System (ADS)

    Li, Lin; Li, Hui; Zhai, Xiaofang; Zeng, Changgan

    2013-09-01

    Single crystalline La0.33Pr0.34Ca0.33MnO3/MgO core-shell nanowires with diameters about tens of nanometers are synthesized by a two-step process. Structure and morphology characterizations confirm the epitaxial growth of La0.33Pr0.34Ca0.33MnO3 shell layers on MgO core layers. Clear interfaces are observed between the core and shell layers. Magnetic measurements suggest the existence of electronic phase separation in the one dimensional nanowires similar to the bulk. However, the nanowires exhibit significantly increased amount of magnetically frozen phase and increased coercivity, which are attributed to the strongly modulated magnetic structure in the one dimensional structure.

  10. Quantitative evaluation of antibacterial activities of metallic oxide powders (ZnO, MgO and CaO) by conductimetric assay.

    PubMed

    Sawai, J

    2003-08-01

    Antibacterial activities of metallic oxide (ZnO, MgO and CaO) powders against Staphylococcus aureus and Escherichia coli were quantitatively evaluated by measuring the change in electrical conductivity of the growth medium caused by bacterial metabolism (conductimetric assay). The obtained conductivity curves were analyzed using the growth inhibition kinetic model proposed by Takahashi for calorimetric evaluation, and the metallic oxides were determined for the antibacterial efficacy and kinetic parameters. The parameters provide some useful indicators for antimicrobial agents, such as the dependence of antibacterial activity on agent concentration, and the affinity between the agent and the bacterial cells. CaO was the most effective, followed by MgO and ZnO, against E. coli. On the other hand, ZnO was the most effective for S. aureus and was suggested to have a strong affinity to the cells of S. aureus. PMID:12782373

  11. Electron Capture and Loss Processes in the Interaction of Hydrogen, Oxygen, and Fluorine Atoms and Negative Ions with a MgO(100) Surface

    SciTech Connect

    Ustaze, S.; Verucchi, R.; Lacombe, S.; Guillemot, L.; Esaulov, V.A.

    1997-11-01

    A study of electron capture and loss processes during the scattering of H, O, and F atoms and anions on a MgO(100) surface is described. Large fractions of anions in the scattering of atoms are observed, indicating the existence of an efficient electron capture process. This is ascribed to a nonresonant, localized charge exchange mechanism between an atom and a MgO lattice oxygen anion. This charge transfer becomes possible because of anion level shifts in the Madelung field. The existence of an electron loss channel is demonstrated using incident anions and is ascribed to loss to the conduction band or Mg cations. {copyright} {ital 1997} {ital The American Physical Society}

  12. Growth and Characterization of Epitaxial FexPt100-xFilms on MgO(111)

    SciTech Connect

    Mani, P.; Krishnamurthy, V. V.; Maat, S.; Kellock, A. J.; Robertson, Lee; Mankey, G. J.

    2005-01-01

    Fe{sub x}Pt{sub 100-x} films were grown on MgO(111) by co-sputtering Fe and Pt. Composition of the films was determined by Rutherford backscattering spectrometry with an accuracy of 1%. Epitaxy and alloy ordering were quantified by x-ray diffraction and the order parameter was determined to be 0.97 for a film with x = 30 and 0.99 for a film with x = 25. Neutron diffraction measurements established the presence of an antiferromagnetic phase at T = 100 K in 500 nm FePt{sub 3} samples grown on MgO(111). Since FePt{sub 3} can be grown as an ordered antiferromagnet and a disordered ferromagnet, these films provide a pathway to grow lattice matched interfaces for exchange bias studies.

  13. EFFECT OF MgO ON STRUCTURE AND DIELECTRIC PROPERTIES OF CaO-Al2O3-B2O3-SiO2 GLASSES

    NASA Astrophysics Data System (ADS)

    Du, Zhao; Zhang, Xuehong; Yue, Yunlong; Wu, Haitao

    2012-12-01

    The effect of MgO on structure and dielectric properties of aluminoborosilicate glasses was investigated. FTIR data indicated that glass network was mainly built by tetrahedral [SiO4], [BO4], [AlO4] and trigonal [BO3]. A small amount of AlO5 or AlO6 units also existed. The glass system was characterized with lower dielectric constant (4.17 4.6) and dielectric loss (12.3 × 10-4 14.77 × 10-4) at 1 MHz. With the increase of MgO content, the quantity of AlO5 or AlO6 units decreased. The variation of density showed a decreasing tendency. The dielectric constant and loss were all found to decrease.

  14. Role of Y{sub 2}O{sub 3}, CaO, MgO additives on structural and microstructural behavior of zirconia/mullite aggregates

    SciTech Connect

    Mishra, D. K.; Prusty, Sasmita; Mohapatra, B. K.; Singh, S. K.; Behera, S. N.

    2012-07-23

    Zirconia mullite (MUZ), Y{sub 2}O{sub 3}-MUZ, CaO-MUZ and MgO-MUZ composites, synthesized through plasma fusion technique, are becoming important due to their commercial scale of production within five minutes of plasma treatment from sillimanite, zircon and alumina mixture. The X-ray diffraction studies reveal the monoclinic zirconia phase in MUZ composite whereas mixed monoclinic, tetragonal and cubic phases of zirconia have been observed in Y{sub 2}O{sub 3}, CaO, MgO added MUZ composites. The Y{sub 2}O{sub 3}, CaO and MgO additives act as sintering aids to favour the transformation and stabilisation of tetragonal and cubic zirconia phases at room temperature. These additives also play a key role in the development of various forms of microstructure to achieve dense MUZ composites.

  15. Accumulation and Decay Characteristics of Exoelectron Sources at MgO Protective Layer Surface in Alternating-Current Plasma Display Panels

    NASA Astrophysics Data System (ADS)

    Yoshino, Kyohei; Nagatomi, Takaharu; Morita, Yukihiro; Oue, Toshiyasu; Kosugi, Naoki; Nishitani, Mikihiko; Kitagawa, Masatoshi; Takai, Yoshizo

    2010-08-01

    The accumulation and decay characteristics of exoelectron sources at a MgO protective layer surface in alternating-current plasma display panels (AC-PDPs) were investigated. The positively charged MgO surface provides a larger number of exoelectrons than the negatively charged surface, indicating that electrons trapped in shallow carrier traps coexist with trapped holes, and exoelectrons are emitted through Auger and/or photoionization processes after their recombination. The exoelectron sources are accumulated by sustain discharges and always decay. The half-life of the decay of the exoelectron sources is relatively long, of the order of a few tens of ms, confirming that the exoelectron emission property at the address discharge in a certain television (TV) field is strongly affected by sustain firings in the previous two TV fields or more. The effects of such a long-term decay of the exoelectron sources should be taken into consideration when designing the driving waveforms of AC-PDPs.

  16. The effect of Al2O3, CaO, Cr2O3 and MgO on devitrification of silica

    NASA Technical Reports Server (NTRS)

    Zaplatynsky, Isidor

    1988-01-01

    The effect of doping on devitrification of vitreous silica was studied at 1100, 1200, and 1300 C. Dispersion of dopants on a molecular scale was accomplished via a sol-gel technique. All dopants accelerated the devitrification of silica but to different degrees. The most active was CaO followed by MgO, Al2O3, and Cr2O3. Pure silica and silica containing Cr2O3 and Al2O3 devitrified to alpha-cristobalite only, whereas silica doped with CaO and MgO produced alpha-quartz and alpha-cristobalite. It appears that prolonged heat treatment would cause alpha-quartz to transform to alpha-cristobalite.

  17. Relationship between bond stiffness and electrical energy storage capacity in oxides: density functional calculations for h-La2O3, MgO and BeO

    SciTech Connect

    Xu, Bo; Cooper, Valentino R; Singh, David J; Feng, Yuan Ping

    2011-01-01

    We report finite electric field calculations for three representative oxide dielectrics: MgO, La{sub 2}O{sub 3}, and BeO. These materials have very different dielectric constants and bond stiffness. Good accord with experimental low field data is obtained. We discuss the results from the point of view of dielectric energy storage and suggest that the low dielectric constant, high bond stiffness material BeO is best from the viewpoint of energy density.

  18. 3D printed tricalcium phosphate scaffolds: Effect of SrO and MgO doping on in vivo osteogenesis in a rat distal femoral defect model

    PubMed Central

    Tarafder, Solaiman; Davies, Neal M.; Bandyopadhyay, Amit; Bose, Susmita

    2013-01-01

    The presence of interconnected macro pores is important in tissue engineering scaffolds for guided tissue regeneration. This study reports in vivo biological performance of interconnected macro porous tricalcium phosphate (TCP) scaffolds due to the addition of SrO and MgO as dopants in TCP. We have used direct three dimensional printing (3DP) technology for scaffold fabrication followed by microwave sintering. Mechanical strength was evaluated by scaffolds with 500 µm, 750 µm, and 1000 µm interconnected designed pore sizes. Maximum compressive strength of 12.01 ± 1.56 MPa was achieved for 500 µm interconnected designed pore size Sr-Mg doped scaffold. In vivo biological performance of the microwave sintered pure TCP and Sr-Mg doped TCP scaffolds was assessed by implanting 350 µm designed interconnected macro porous scaffolds in rat distal femoral defect. Sintered pore size of these 3D printed scaffolds were 311 ± 5.9 µm and 245 ± 7.5 µm for pure and SrO-MgO doped TCP scaffolds, respectively. These 3D printed scaffolds possessed multiscale porosity, i.e., 3D interconnected designed macro pores along with intrinsic micro pores. Histomorphology and histomorphometric analysis revealed a significant increase in osteoid like new bone formation, and accelerated mineralization inside SrO and MgO doped 3D printed TCP scaffolds as compared to pure TCP scaffolds. An increase in osteocalcin and type I collagen level was also observed in rat blood serum with SrO and MgO doped TCP scaffolds compared to pure TCP scaffolds. Our results show that these 3D printed SrO and MgO doped TCP scaffolds with multiscale porosity contributed to early healing through accelerated osteogenesis. PMID:24729867

  19. Study on the water durability of zinc boro-phosphate glasses doped with MgO, Fe2O3, and TiO2

    NASA Astrophysics Data System (ADS)

    Hwang, Moon Kyung; Ryu, Bong Ki

    2016-07-01

    The water durability of zinc boro-phosphate (PZB) glasses with the composition 60P2O5-20ZnO-20B2O3- xMeO ( x = 0, 2, 4, 6 and MeO = MgO, Fe2O3, or TiO2) (mol%) was measured, and PZB glass was studied in terms of its thermal properties, density, and FTIR characteristics. The surface conditions and corrosion byproducts were analyzed using scanning electron microscopy. When MgO, Fe2O3, and TiO2 were doped into the PZB glass, Q2 was decreased and Q1 was increased in the phosphate structure, while the number of BO4 structures increased with increasing MeO content. The density of the PZB glass was increased by the addition of Fe2O3 and TiO2, while the glass transition temperature ( T g ) and dilatometric softening temperature ( T d ) were increased when additional MgO, Fe2O3, and TiO2 were added. From the weight loss analysis (95 ◦ C, 96 h), TiO2 doped glass showed the lowest weight loss (1.70 × 10 -3 g/cm2) while MgO doped glass showed the highest value (2.44 × 10 -3 g/cm2), compared with PZB glass (3.07 × 10 -3 g/cm2). These results were discussed in terms of the Me n+ ions in the glass structure, and their different coordination numbers and bonding strengths.

  20. Biological and mechanical properties of an experimental glass-ionomer cement modified by partial replacement of CaO with MgO or ZnO.

    PubMed

    Kim, Dong-Ae; Abo-Mosallam, Hany; Lee, Hye-Young; Lee, Jung-Hwan; Kim, Hae-Won; Lee, Hae-Hyoung

    2015-01-01

    Some weaknesses of conventional glass ionomer cement (GIC) as dental materials, for instance the lack of bioactive potential and poor mechanical properties, remain unsolved.Objective The purpose of this study was to investigate the effects of the partial replacement of CaO with MgO or ZnO on the mechanical and biological properties of the experimental glass ionomer cements.Material and Methods Calcium fluoro-alumino-silicate glass was prepared for an experimental glass ionomer cement by melt quenching technique. The glass composition was modified by partial replacement (10 mol%) of CaO with MgO or ZnO. Net setting time, compressive and flexural properties, and in vitrorat dental pulp stem cells (rDPSCs) viability were examined for the prepared GICs and compared to a commercial GIC.Results The experimental GICs set more slowly than the commercial product, but their extended setting times are still within the maximum limit (8 min) specified in ISO 9917-1. Compressive strength of the experimental GIC was not increased by the partial substitution of CaO with either MgO or ZnO, but was comparable to the commercial control. For flexural properties, although there was no significance between the base and the modified glass, all prepared GICs marked a statistically higher flexural strength (p<0.05) and comparable modulus to control. The modified cements showed increased cell viability for rDPSCs.Conclusions The experimental GICs modified with MgO or ZnO can be considered bioactive dental materials. PMID:26398508

  1. Biological and mechanical properties of an experimental glass-ionomer cement modified by partial replacement of CaO with MgO or ZnO

    PubMed Central

    Dong-Ae, KIM; Hany, ABO-MOSALLAM; Hye-Young, LEE; Jung-Hwan, LEE; Hae-Won, KIM; Hae-Hyoung, LEE

    2015-01-01

    Some weaknesses of conventional glass ionomer cement (GIC) as dental materials, for instance the lack of bioactive potential and poor mechanical properties, remain unsolved. Objective The purpose of this study was to investigate the effects of the partial replacement of CaO with MgO or ZnO on the mechanical and biological properties of the experimental glass ionomer cements. Material and Methods Calcium fluoro-alumino-silicate glass was prepared for an experimental glass ionomer cement by melt quenching technique. The glass composition was modified by partial replacement (10 mol%) of CaO with MgO or ZnO. Net setting time, compressive and flexural properties, and in vitro rat dental pulp stem cells (rDPSCs) viability were examined for the prepared GICs and compared to a commercial GIC. Results The experimental GICs set more slowly than the commercial product, but their extended setting times are still within the maximum limit (8 min) specified in ISO 9917-1. Compressive strength of the experimental GIC was not increased by the partial substitution of CaO with either MgO or ZnO, but was comparable to the commercial control. For flexural properties, although there was no significance between the base and the modified glass, all prepared GICs marked a statistically higher flexural strength (p<0.05) and comparable modulus to control. The modified cements showed increased cell viability for rDPSCs. Conclusions The experimental GICs modified with MgO or ZnO can be considered bioactive dental materials. PMID:26398508

  2. A Site-isolated Mononuclear Iridium Complex Catalyst Supported on MgO: Characterization by Spectroscopy and Aberration-corrected Scanning Transmission Electron Microscopy

    SciTech Connect

    Uzun, A.; Ortalan, V; Browning, N; Gates , B

    2010-01-01

    Supported mononuclear iridium complexes with ethene ligands were prepared by the reaction of Ir(C{sub 2}H{sub 4}){sub 2}(acac) (acac is CH{sub 3}COCHCOCH{sub 3}) with highly dehydroxylated MgO. Characterization of the supported species by extended X-ray absorption fine structure (EXAFS) and infrared (IR) spectroscopies showed that the resultant supported organometallic species were Ir(C{sub 2}H{sub 4}){sub 2}, formed by the dissociation of the acac ligand from Ir(C{sub 2}H{sub 4}){sub 2}(acac) and bonding of the Ir(C{sub 2}H{sub 4}){sub 2} species to the MgO surface. Direct evidence of the site-isolation of these mononuclear complexes was obtained by aberration-corrected scanning transmission electron microscopy (STEM); the images demonstrate the presence of the iridium complexes in the absence of any clusters. When the iridium complexes were probed with CO, the resulting IR spectra demonstrated the formation of Ir(CO){sub 2} complexes on the MgO surface. The breadth of the {nu}{sub CO} bands demonstrates a substantial variation in the metal-support bonding, consistent with the heterogeneity of the MgO surface; the STEM images are not sufficient to characterize this heterogeneity. The supported iridium complexes catalyzed ethene hydrogenation at room temperature and atmospheric pressure in a flow reactor, and EXAFS spectra indicated that the mononuclear iridium species remained intact. STEM images of the used catalyst confirmed that almost all of the iridium complexes remained intact, but this method was sensitive enough to detect a small degree of aggregation of the iridium on the support.

  3. Desulfurization behavior of iron-based sorbent with MgO and TiO{sub 2} additive in hot coal gas

    SciTech Connect

    Weiren Bao; Zong-you Zhang; Xiu-rong Ren; Fan Li; Li-ping Chang

    2009-07-15

    The sulfidation behaviors of iron-based sorbent with MgO and MgO-TiO{sub 2} are studied under different isothermal conditions from 623 to 873 K in a fixed bed reactor. The results of sorbents sulfidation experiments indicate that the sorbents with MgO and TiO{sub 2} additives are more attractive than those without additives for desulfurization of hot coal gas. The sulfur capacity (16.17, 18.45, and 19.68 g S/100 g sorbent) of M1F, M3F, and M5F sorbent containing 1, 3, and 5% MgO, respectively, is obviously bigger than that (15.02 g S/100 g sorbent) of M0F without additive. The feasible sulfidation temperature range for M3F sorbent is 773-873 K. The M3F sorbent is optimally regenerated at the temperature of 873 K, under the gas containing 2% oxygen, 15% steam and N{sub 2}, in the space velocity of 2500 h{sup -1}. The sorbent regenerated is also well performed in the second sulfidation (the effective sulfur capacities of 17.98 g S/100 g sorbents and the efficiency of removal sulfur of 99%). The capacity to remove sulfur decreases with steam content increasing in feeding gas from 0 to 10%, but it can restrain the formation of carbon and iron carbide. The addition of TiO{sub 2} in sorbent can shift the optimal sulfidation temperature lower. The iron-based sorbent with 3% MgO and 10% TiO{sub 2} (MFT) is active to the deep removal of H{sub 2}S and COS, especially in the temperature range of 673-723 K. The sulfur removal capacity of MFT sorbent is 21.60 g S/100 g sorbent. 16 refs., 12 figs., 8 tabs.

  4. Growth and microstructure of columnar Y-doped SrZrO{sub 3} films deposited on Pt-coated MgO by pulsed laser deposition

    SciTech Connect

    Luo, Sijun Riggs, Brian C.; Shipman, Joshua T.; Adireddy, Shiva; Sklare, Samuel C.; Chrisey, Douglas B.; Zhang, Xiaodong; Koplitz, Brent

    2015-07-21

    Direct integration of proton conductor films on Pt-coated substrates opens the way to film-based proton transport devices. Columnar SrZr{sub 0.95}Y{sub 0.05}O{sub 3−δ} (SZY) films with dense microstructure were deposited on Pt-coated MgO(100) substrates at 830 °C by pulsed laser deposition. The optimal window of ambient O{sub 2} pressure for good crystallinity of SZY films is from 400 to 600 mTorr. The ambient O{sub 2} compresses the plasma plume of SZY and increases the deposition rate. The 10 nm thick Ti adhesion layer on MgO(100) greatly affects the orientation of the sputtered Pt layers. Pt deposited directly on MgO shows a highly (111)-preferred orientation and leads to preferentially oriented SZY films while the addition of a Ti adhesion layer makes Pt show a less preferential orientation that leads to randomly oriented SZY films. The RMS surface roughness of preferentially oriented SZY films is larger than that of randomly oriented SZY films deposited under the same ambient O{sub 2} pressure. As the O{sub 2} pressure increased, the RMS surface roughness of preferentially oriented SZY films increased, reaching 45.7 nm (2.61% of film thickness) at 600 mTorr. This study revealed the ambient O{sub 2} pressure and orientation dependent surface roughness of SZY films grown on Pt-coated MgO substrates, which provides the potential to control the surface microstructure of SZY films for electrochemical applications in film-based hydrogen devices.

  5. Production of carbon nanotubes: Chemical vapor deposition synthesis from liquefied petroleum gas over Fe-Co-Mo tri-metallic catalyst supported on MgO

    NASA Astrophysics Data System (ADS)

    Setyopratomo, P.; Wulan, Praswasti P. D. K.; Sudibandriyo, M.

    2016-06-01

    Carbon nanotubes were produced by chemical vapor deposition method to meet the specifications for hydrogen storage. So far, the various catalyst had been studied outlining their activities, performances, and efficiencies. In this work, tri-metallic catalyst consist of Fe-Co-Mo supported on MgO was used. The catalyst was prepared by wet-impregnation method. Liquefied Petroleum Gas (LPG) was used as carbon source. The synthesis was conducted in atmospheric fixed bed reactor at reaction temperature range 750 - 850 °C for 30 minutes. The impregnation method applied in this study successfully deposed metal component on the MgO support surface. It found that the deposited metal components might partially replace Mg(OH)2 or MgO molecules in their crystal lattice. Compare to the original MgO powder; it was significant increases in pore volume and surface area has occurred during catalyst preparation stages. The size of obtained carbon nanotubes is ranging from about 10.83 nm OD/4.09 nm ID up to 21.84 nm OD/6.51 nm ID, which means that multiwall carbon nanotubes were formed during the synthesis. Yield as much as 2.35 g.CNT/g.catalyst was obtained during 30 minutes synthesis and correspond to carbon nanotubes growth rate of 0.2 μm/min. The BET surface area of the obtained carbon nanotubes is 181.13 m2/g and around 50 % of which is contributed by mesopores. Micropore with half pore width less than 1 nm contribute about 10% volume of total micro and mesopores volume of the carbon nanotubes. The existence of these micropores is very important to increase the hydrogen storage capacity of the carbon nanotubes.

  6. Ceramic Composite Thin Films

    NASA Technical Reports Server (NTRS)

    Ruoff, Rodney S. (Inventor); Stankovich, Sasha (Inventor); Dikin, Dmitriy A. (Inventor); Nguyen, SonBinh T. (Inventor)

    2013-01-01

    A ceramic composite thin film or layer includes individual graphene oxide and/or electrically conductive graphene sheets dispersed in a ceramic (e.g. silica) matrix. The thin film or layer can be electrically conductive film or layer depending the amount of graphene sheets present. The composite films or layers are transparent, chemically inert and compatible with both glass and hydrophilic SiOx/silicon substrates. The composite film or layer can be produced by making a suspension of graphene oxide sheet fragments, introducing a silica-precursor or silica to the suspension to form a sol, depositing the sol on a substrate as thin film or layer, at least partially reducing the graphene oxide sheets to conductive graphene sheets, and thermally consolidating the thin film or layer to form a silica matrix in which the graphene oxide and/or graphene sheets are dispersed.

  7. Super Thin Ceramic Coatings

    NASA Video Gallery

    New technology being developed at NASA's Glenn Research Center creates super thin ceramic coatings on engine components. The Plasma Spray – Physical Vapor Deposition (PS-PVD) rig uses a powerful ...

  8. Thin film metrology.

    PubMed

    Nitsch, Gerald; Flinn, Gregory

    2007-10-01

    Thin film metrology is suitable for characterising and performing quality control of a variety of coatings and films used in medical applications. The capabilities of today's systems are described. PMID:18078184

  9. Line Thinning Algorithm

    NASA Astrophysics Data System (ADS)

    Feigin, G.; Ben-Yosef, N.

    1983-10-01

    A thinning algorithm, of the banana-peel type, is presented. In each iteration pixels are attacked from all directions (there are no sub-iterations), and the deletion criteria depend on the 24 nearest neighbours.

  10. Thermodynamic, Modeling and Neutron Investigations of Cycloalkanes Adsorbed on MgO (100) and Graphite Basal Plane

    NASA Astrophysics Data System (ADS)

    Wahida, Fatema; Strange, Nicholas; Larese, John Z.

    Understanding the adsorption of molecules on solid surfaces is central to many scientific and technological challenges. Solid surfaces such as metal oxides, carbonaceous archetypes, porous silica, and metal organic frameworks currently represent significant components of nanomaterial research because of their widespread use in optoelectronics, separation chemistry, and catalysis. Understanding the interaction between adsorbed molecules and surfaces is a necessity for developing synthetic methods to produce materials with specific functional properties. An investigation of the effects of molecular and adsorbate symmetry is proposed in this study. The principal aim of this work is to identify the role of surface and molecular symmetry on the physicochemical properties of 2D layers of cyclic molecules adsorbed on metal oxide and semiconductor substrates. Initially our characterization will focus on the thermodynamic and microscopic structure and dynamics of cyclopentane and cyclohexane on the MgO (100) surface and graphite basal plane. In order to realize this goal adsorption isotherms, inelastic neutron scattering (INS) and molecular dynamics (MD) simulation studies will be performed to investigate the structure, dynamics and wetting properties.

  11. Structural and magnetic properties of MnPd/Fe grown on MgO(100) substrate: Ab initio studies

    NASA Astrophysics Data System (ADS)

    Malonda-Boungou, B. R.; Magnoungou, J. H. J.; M'Passi-Mabiala, B.; Demangeat, C.

    2016-07-01

    Structural and magnetic properties of ultrathin films MnPd/Fe grown on MgO(001) are investigated using a self-consistent pseudopotential plane waves method based on density functional theory in the Perdew-Burke-Ernzerhof generalized gradient approximation. The results obtained reveal the presence of an antiferromagnetic coupling between successive Mn [100] rows, combined with a ripple where Mn outward atoms exhibit a positive magnetic moment, in the case of Mn overlayer on Fe/MgO(001). In the case of MnPd monolayer ordered alloy, the c(2 × 2) structure formation is more favorable than the p(1 × 2) one, exhibiting a ferromagnetic coupling between Mn neighbor atoms with a positive induced ferromagnetic moment on Pd atoms. Pd atoms are pushed outward. For 1-ML MnxPd1 - x on Fe/MgO, the Mn absolute mean magnetization per atom increases as x coverage increases, whereas the Pd mean induced magnetic moment decreases. For systems alternating Mn and Pd monolayers on Fe/MgO(001), a complex magnetic structure is shown on Mn monolayers: changing from Mn neighboring antiferromagnetic coupling to Mn [010] rows antiferromagnetic behavior. The correlation is made between the electronic structure and the magnetic properties, by comparing filled with partially filled components (Pd, Mn and Fe) d-bands. The magnetization easy-axis changes between the in-plane and the out-of-plane orientations from Fe/MgO to MnPd/Fe/MgO systems.

  12. Itacolumite like High Damping Ceramics in the System Al2O3-TiO2-MgO

    SciTech Connect

    Shimazu, T.; Miura, M.; Isu, N.; Ogawa, T.; Ichikawa, A.; Ishida, E. H.

    2006-05-15

    Ceramics is rigid and brittle originally. If the weakness could be overcome, the application will be widely expanded. Itacolumite known as high flexibility rock is the group of sand stone which consist of quartz and slight amount of muscovite. The microstructure of itacolumite has a lot of narrow gaps between the grains, the gap was thought to be formed by the dissolution of minerals in between quartz grains into the groundwater. This narrow space enables a little displacement of the particles, and the rock can bend with stress like plastic deformation. These characters of itacolumite showed the new ceramic functions such as stress relaxation properties and high damping capacity (internal friction Q-1=0.03). The authors tried to develop high damping ceramics by the mimic of itacolumite, and found the Al2O3-TiO2-MgO ceramics. The ceramics had stress relaxation properties and high damping capacity (Q-1=0.01) since microcracks were formed during sintering by the discontinuous grain growth and the anisotropic thermal expansion in the cooling process.

  13. Organic linkers on oxide surfaces: Adsorption and chemical bonding of phthalic anhydride on MgO(100)

    NASA Astrophysics Data System (ADS)

    Mohr, Susanne; Doepper, Tibor; Xu, Tao; Tariq, Quratulain; Lytken, Ole; Laurin, Mathias; Steinrueck, Hans-Peter; Goerling, Andreas; Libuda, Joerg

    2016-04-01

    To elucidate the adsorption behavior and interaction mechanisms of organic linker units on oxide surfaces, we have performed a model study under ultrahigh vacuum (UHV) conditions. We apply infrared reflection absorption spectroscopy (IRAS) in combination with density-functional theory (DFT), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). Phthalic anhydride (PAA) was deposited at temperatures between 100 and 300 K by physical vapor deposition (PVD) onto an ordered MgO(100) film grown on Ag(100). At 100 K, the first monolayer adsorbs molecularly with the molecular plane aligned parallel to the surface. Subsequent growth of a multilayer film at low temperature also occurs with preferential molecular alignment parallel to the surface. At 240 K, the multilayer desorbs without decomposition. At 300 K, a mixed monolayer of chemically modified ring-opened and intact phthalic anhydride exists on the surface. The chemically modified species binds in a strongly tilted geometry via opening of the anhydride ring to form a bis-carboxylate species. This species additionally stabilizes the coadsorbed molecular PAA via intermolecular interactions. Finally, surface defects and hydroxyl groups are found to increase the amount of surface bis-carboxylate at 300 K, whereas the relative amount of coadsorbed molecular PAA decreases.

  14. Adsorption energy and spin state of first-row transition metals adsorbed on MgO(100)

    NASA Astrophysics Data System (ADS)

    Markovits, A.; Paniagua, J. C.; López, N.; Minot, C.; Illas, F.

    2003-03-01

    Slab and cluster model spin-polarized calculations have been carried out to study various properties of isolated first-row transition metal atoms adsorbed on the anionic sites of the regular MgO(100) surface. The calculated adsorption energies follow the trend of the metal cohesive energies, indicating that the changes in the metal-support and metal-metal interactions along the series are dominated by atomic properties. In all cases, except for Ni at the generalized gradient approximation level, the number of unpaired electron is maintained as in the isolated metal atom. The energy required to change the atomic state from high to low spin has been computed using the PW91 and B3LYP density-functional-theory-based methods. PW91 fails to predict the proper ground state of V and Ni, but the results for the isolated and adsorbed atom are consistent within the method. B3LYP properly predicts the ground state of all first-row transition atom the high- to low-spin transition considered is comparable to experiment. In all cases, the interaction with the surface results in a reduced high- to low-spin transition energy.

  15. NO2-assisted molecular-beam epitaxy of wustitelike and magnetitelike Fe oxynitride films on MgO(100)

    NASA Astrophysics Data System (ADS)

    Voogt, F. C.; Smulders, P. J.; Wijnja, G. H.; Niesen, L.; Fujii, T.; James, M. A.; Hibma, T.

    2001-03-01

    In an attempt to obtain wustite Fe1-xO as epitaxial films on MgO(100), NO2-assisted molecular-beam epitaxy was applied. At low NO2 fluxes, the low-energy electron diffraction and reflection high-energy electron diffraction images indeed indicate the formation of a rocksaltlike structure. In addition, Mössbauer spectroscopy provides evidence for the formation of a phase that is paramagnetic at room temperature. However, the layers are not pure oxides but are well-ordered oxynitrides with composition Fe1-xO1-yNy. The nitrogen atoms occupy substitutional sites on the oxygen-anion sublattice. Similarly, at slightly higher NO2 fluxes, magnetitelike oxynitride films with composition Fe3+δO4-yNy are obtained. By correlating x-ray photoelectron spectroscopy spectra with the intensity oscillation periods observed during reflection high-energy electron diffraction, it is possible to derive the complete stoichiometry of the films. We propose that the abrupt incorporation of nitrogen atoms only occurs if the atomic oxygen provided by the NO2 flux is insufficient to form a stoichiometric Fe3O4.

  16. Mononuclear, trinuclear, and metallic rhenium catalysts supported on MgO: Effects of structure on catalyst performance

    SciTech Connect

    Kirlin, P.S.; Gates, B.C. ); Knoezinger, H. )

    1990-11-01

    MgO-supported Re catalysts were prepared from (HRe(CO){sub 5}) and (H{sub 3}Re{sub 3}(CO){sub 12}) to give isolated Re subcarbonyls and ensembles of three Re subcarbonyls, respectively. The latter sample was reduced in H{sub 2} to give Re metal crystallites on the support. The reactivities of the various surface species were characterized by temperature-programmed reduction, temperature-programmed desorption, and wet chemical experiments. The samples were probed as catalysts for the structure-insensitive propene hydrogenation and the structure-sensitive cyclopropane isomerization/hydrogenolysis. The supported Re complexes formed from (HRe(CO){sub 5}) and MgO catalyze the alkene hydrogenation but not the C-C bond rupture. The ensembles of these complexes formed from (H{sub 3}Re{sub 3}(CO){sub 12}) catalyze both, in this respect resembling supported crystallites of Re metal partially poisoned with CO. It is inferred that neighboring metal centers are required for the C-C bond rupture, whereas isolated metal centers are active for the hydrogenation. The catalyst containing Re metal is also active for both of these conversions and is the only one of these samples that is active for the isomerization of cyclopropane to give propene.

  17. Global optimization study of small (10 < or = N < or = 120) Pd clusters supported on MgO(100).

    PubMed

    Rossi, G; Mottet, C; Nita, F; Ferrando, R

    2006-04-13

    Experimental evidence suggests that Pd clusters on MgO, known to be good reaction catalysts, have face centered cubic (fcc) epitaxial structures. The structure of such clusters is the result of the interplay of Pd-Pd and Pd-substrate bonds, the former inclined to favor icosahedral (Ih) and decahedral (Dh)-like structures, the latter leading to place Pd atoms on top of oxygen sites, according to an epitaxial stacking. This paper shows the results of a basin-hopping global optimization procedure applied to free and MgO-supported Pd clusters in the size range 10 < or = N < or = 120. Pd-MgO interactions are modeled by an analytical function fitted to ab initio results, while Pd-Pd interactions are modeled by a semiempirical potential. Besides the tight-binding Rosato-Guillopé-Legrand (RGL) potential, we have adopted a modified version of RGL that better reproduces the experimental surface energy of palladium, modifying the attractive part of Pd atoms potential energy. We have compared the two potential models, and as a result, the RGL potential favors clusters with epitaxial arrangements, so that cluster structures are epitaxial fcc in almost all the size ranges considered. On the contrary, the alternative potential model preserves some Ih-like characteristics typical of the free Pd clusters, and it suggests that a transition size from Ih-like to epitaxial structures can take place at about 100 atoms. PMID:16599522

  18. Underlayer Effect on Perpendicular Magnetic Anisotropy in Co20Fe60B20\\MgO Films

    PubMed Central

    Chen, P.J.; Iunin, Y.L.; Cheng, S.F.; Shull, R.D.

    2016-01-01

    Perpendicular Magnetic Tunneling Junctions (pMTJs) with Ta\\CoFeB\\MgO have been extensively studied in recent years. However, the effects of the underlayer on the formation of the CoFeB perpendicular magnetic anisotropy (PMA) are still not well understood. Here we report the results of our systematic use of a wide range of elements (Ti, V, Cr, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt and Au) encompassed by columns IVA, VA, VIA, VIIA and VIIIA of the periodic table as the underlayer in a underlayer\\Co20Fe60B20\\MgO stack. Our goals were to survey more elements which could conceivably create a PMA in CoFeB and thereby to explore the mechanisms enabling these underlayers to enhance or create the PMA. We found underlayer elements having both an outer shell of 4d electrons (Zr, Nb Mo, and Pd) and 5d electrons (Hf, Ta, W, Re, Ir, and Pt) resulted in the development of a PMA in the MgO-capped Co20Fe60B20. Hybridization between the 3d electrons of the Fe or Co (in the Co20Fe60B20) at the interface with the 4d or 5d electrons of the underlayer is thought to be the cause of the PMA development. PMID:27499549

  19. Spincaloric properties of epitaxial Co2MnSi /MgO /Co2MnSi magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Geisler, Benjamin; Kratzer, Peter

    2015-10-01

    The electronic transport and spincaloric properties of epitaxial magnetic tunnel junctions with half-metallic Co2MnSi Heusler electrodes, MgO tunneling barriers, and different interface terminations are investigated by using first-principles calculations. An approach to spincaloric properties is presented that circumvents the linear response approximation inherent in the Seebeck coefficient and compared to the method of Sivan and Imry. This approach supports two different temperatures in the two electrodes and provides the exact current and/or voltage response of the system. Moreover, it accounts for temperature-dependent chemical potentials in the electrodes and finite-bias effects. We find that especially the former are important for obtaining qualitatively correct results, even if the variations of the chemical potentials are small. It is shown how the spincaloric properties can be tailored by the choice of the growth conditions. We find a large effective and spin-dependent Seebeck coefficient of -65 μ V /K at room temperature for the purely Co-terminated interface. We suggest to use such interfaces in thermally operated magnetoresistive random access memory modules, which exploit the magneto-Seebeck effect, to maximize the thermally induced readout voltage.

  20. Growth mechanisms of MgO nanocrystals via a sol-gel synthesis using different complexing agents

    PubMed Central

    2014-01-01

    In the preparation of nanostructured materials, it is important to optimize synthesis parameters in order to obtain the desired material. This work investigates the role of complexing agents, oxalic acid and tartaric acid, in the production of MgO nanocrystals. Results from simultaneous thermogravimetric analysis (STA) show that the two different synthesis routes yield precursors with different thermal profiles. It is found that the thermal profiles of the precursors can reveal the effects of crystal growth during thermal annealing. X-ray diffraction confirms that the final products are pure, single phase and of cubic shape. It is also found that complexing agents can affect the rate of crystal growth. The structures of the oxalic acid and tartaric acid as well as the complexation sites play very important roles in the formation of the nanocrystals. The complexing agents influence the rate of growth which affects the final crystallite size of the materials. Surprisingly, it is also found that oxalic acid and tartaric acid act as surfactants inhibiting crystal growth even at a high temperature of 950°C and a long annealing time of 36 h. The crystallite formation routes are proposed to be via linear and branched polymer networks due to the different structures of the complexing agents. PMID:24650322