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Sample records for mgo thin filmsa

  1. 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.

  2. Transparent Al+3 doped MgO thin films for functional applications

    NASA Astrophysics Data System (ADS)

    Maiti, Payel; Sekhar Das, Pradip; Bhattacharya, Manjima; Mukherjee, Smita; Saha, Biswajit; Mullick, Awadesh Kumar; Mukhopadhyay, Anoop Kumar

    2017-08-01

    The present work reports the utilization of a relatively simple, cost effective sol-gel technique based route to synthesize highly transparent, spin coated 4.1 at% Al+3 doped MgO thin films on quartz substrates. The films were characterized by XRD, XPS, Raman spectroscopy, and SIMS techniques. The microstructures were characterized by FESEM and TEM while the nanomechanical properties were assessed by the nanoindentation technique. Finally the optical transmittance was measured by UV-vis technique. The x-ray diffraction (XRD) study suggests the crystal facet (2 0 0) of MgO lattice to be distorted after incorporation of Al+3 into MgO lattice. From FESEM the doped films were found to have a dense microstructure with a crystallite size of about 20 nm as revealed by the TEM studies. Nanoindentation measurements indicated drastic increase of elastic modulus for the Al+3 doped MgO thin films by ~73% compared to that of the pristine MgO thin films along with retaining the nanohardness at ~8 GPa. The transmittance of Al+3 doped MgO thin films in the visible range was significantly higher (~99%) than that of pristine MgO (~90%) thin films. The films also had a relatively higher refractive index of about 1.45 as evaluated from the optical properties. The enhanced transmittance as well as the improved elastic modulus of Al+3 doped MgO thin films suggest its promising candidature in magnetic memory devices and as buffer layers of solar cells.

  3. YBCO thin film evaporation on as-deposited silver film on MgO

    NASA Astrophysics Data System (ADS)

    Azoulay, J.

    1999-11-01

    YBa 2Cu 3O 7- δ (YBCO) thin film was evaporated on as-deposited Ag buffer layer on MgO substrate. A simple, inexpensive vacuum system equipped with one resistively heated source was used. The subsequent heat treatment was carried out under low oxygen partial pressure at a relatively low temperature and short dwelling time. The films thus obtained were characterized for electrical properties using DC four-probe electrical measurements and inspected for structural properties and chemical composition by scanning electron microscopy (SEM). It is shown that YBCO thin film can grow on as-deposited thin silver layer on MgO substrate.

  4. Splitting methanol on ultra-thin MgO(100) films deposited on a Mo substrate.

    PubMed

    Song, Zhenjun; Xu, Hu

    2017-03-08

    The dissociation reaction of methanol on metal-supported MgO(100) films has been studied by employing density functional theory calculations. As far as we know, the dissociation of a single methanol molecule over inert oxide insulators such as MgO has not yet been successfully realized without the introduction of defects or low coordinated atoms. By depositing ultra-thin oxide films on a Mo substrate, we have successfully proposed the dissociative state of methanol. The dissociation reaction is energetically exothermic and nearly barrierless. The lattice mismatch between ultra-thin MgO(100) films and metal substrates plays a crucial role in the heterolytic dissociation of adsorbates, while the electronic effect of the Mo(100) substrate plays a non-ignorable role in the homolytic dissociation of methanol. The metal-supported ultra-thin oxide films studied herein provide a versatile approach to enhance the surface reaction activity and properties of oxides.

  5. A comparison study of Co and Cu doped MgO diluted magnetic thin films

    NASA Astrophysics Data System (ADS)

    Sarıtaş, S.; ćakıcı, T.; Muǧlu, G. Merhan; Kundakcı, M.; Yıldırım, M.

    2017-02-01

    Transition metal-doped MgO diluted magnetic thin films are appropriate candidates for spintronic applications and designing magnetic devices and sensors. Therefore, MgO:Co and MgO:Cu films were deposited on glass substrates by Chemical Spray Pyrolysis (CSP) method different thin film deposition parameters. Deposited different transition metal doped MgO thin films were compared in terms of optic and structural properties. Comparison optic analysis of the films was investigated spectral absorption and transmittance measurements by UV-Vis double beam spectrophotometer technique. Comparison structural analysis of the thin films was examined by using XRD, Raman Analysis, SEM, EDX and AFM techniques. The transition metal-doped; MgO:Co and MgO:Cu thin films maybe have potential applications in spintronics and magnetic data storage.

  6. Magnetism of Amorphous and Nano-Crystallized Dc-Sputter-Deposited MgO Thin Films

    PubMed Central

    Mahadeva, Sreekanth K.; Fan, Jincheng; Biswas, Anis; Sreelatha, K.S.; Belova, Lyubov; Rao, K.V.

    2013-01-01

    We report a systematic study of room-temperature ferromagnetism (RTFM) in pristine MgO thin films in their amorphous and nano-crystalline states. The as deposited dc-sputtered films of pristine MgO on Si substrates using a metallic Mg target in an O2 containing working gas atmosphere of (N2 + O2) are found to be X-ray amorphous. All these films obtained with oxygen partial pressure (PO2) ~10% to 80% while maintaining the same total pressure of the working gas are found to be ferromagnetic at room temperature. The room temperature saturation magnetization (MS) value of 2.68 emu/cm3 obtained for the MgO film deposited in PO2 of 10% increases to 9.62 emu/cm3 for film deposited at PO2 of 40%. However, the MS values decrease steadily for further increase of oxygen partial pressure during deposition. On thermal annealing at temperatures in the range 600 to 800 °C, the films become nanocrystalline and as the crystallite size grows with longer annealing times and higher temperature, MS decreases. Our study clearly points out that it is possible to tailor the magnetic properties of thin films of MgO. The room temperature ferromagnetism in MgO films is attributed to the presence of Mg cation vacancies.

  7. First-principles calculations of perpendicular magnetic anisotropy in Fe1-x Co x /MgO(001) thin films.

    PubMed

    Cai, Guanzhi; Wu, Zhiming; Guo, Fei; Wu, Yaping; Li, Heng; Liu, Qianwen; Fu, Mingming; Chen, Ting; Kang, Junyong

    2015-01-01

    The perpendicular magnetic anisotropy (PMA) of Fe1-x Co x thin films on MgO(001) was investigated via first-principles density-functional calculations. Four different configurations were considered based on their ground states: Fe/MgO, Fe12Co4/MgO, Fe10Co6/MgO, and Fe8Co8/MgO. As the Co composition increases, the amplitude of PMA increases first from Fe/MgO to Fe12Co4/MgO, and then decreases in Fe10Co6/MgO; finally, the magnetic anisotropy becomes horizontal in Fe8Co8/MgO. Analysis based on the second-order perturbation of the spin-orbit interaction was carried out to illustrate the contributions from Fe and Co atoms to PMA, and the differential charge density was calculated to give an intuitive comparison of 3d orbital occupancy. The enhanced PMA in Fe12Co4/MgO is ascribed to the optimized combination of occupied and unoccupied 3d states around the Fermi energy from both interface Fe and Co atoms, while the weaker PMA in Fe10Co6/MgO is mainly attributed to the modulation of the interface Co-d xy orbital around the Fermi energy. By adjusting the Co composition in Fe1-x Co x , the density of states of transitional metal atoms will be modulated to optimize PMA for future high-density memory application.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Investigation of AlN thin film growth on MgO(111) substrates using low temperature helicon sputtering system

    NASA Astrophysics Data System (ADS)

    Hsu, Wei-Fan; Kao, Hui-Ling; Lin, Zih-Ping

    2016-02-01

    An aluminum nitride (AlN) thin film has been grown on annealed magnesium oxide (MgO) (111)-plane substrate using low temperature helicon sputtering system. Both AlN films on as-received and annealed MgO(111) substrate are single crystalline with AlN[0001] || MgO[111]. X-ray rocking curve shows that AlN film on annealed MgO exhibits superior crystalline quality, which means more suitable for AlN crystal growth. Two different growths were found for the deposition of AlN on annealed MgO. It is believed that the partially recovered substrate surface caused by annealing process provides atomic smooth surface terraces with small lattice mismatch for AlN crystal to grow in 2D mode, enhance grain size, and thus reduce the dislocation density. This is the first time demonstrated for the growth mechanism of single crystal AlN thin film prepared on MgO(111) by sputtering system.

  13. 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

    2005-03-07

    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.

  14. Two-color Laser Desorption of Nanostructured MgO Thin Films

    SciTech Connect

    Beck, Kenneth M.; Joly, Alan G.; Hess, Wayne P.

    2009-09-30

    Neutral magnesium atom emission from nanostructured MgO thin films is induced using two-color nanosecond laser excitation. We find that combined visible/UV excitation, for single-color pulse energies below the desorption threshold, induces neutral Mg-atom emission with hyperthermal kinetic energies in the range of 0.1- 0.2 eV. The observed metal atom emission is consistent with a mechanism involving rapid electron transfer to 3-coordinated Mg surface sites. The two-color Mg-atom signal is significant only for parallel laser polarizations and temporally overlapped laser pulses indicating that intermediate excited states are short-lived compared to the 5 nanosecond laser pulse duration.

  15. Electron quantization in arbitrarily shaped gold islands on MgO thin films

    NASA Astrophysics Data System (ADS)

    Stiehler, Christian; Pan, Yi; Schneider, Wolf-Dieter; Koskinen, Pekka; Häkkinen, Hannu; Nilius, Niklas; Freund, Hans-Joachim

    2013-09-01

    Low-temperature scanning tunneling microscopy has been employed to analyze the formation of quantum well states (QWS) in two-dimensional gold islands, containing between 50 and 200 atoms, on MgO thin films. The energy position and symmetry of the eigenstates are revealed from conductance spectroscopy and imaging. The majority of the QWS originates from overlapping Au 6p orbitals in the individual atoms and is unoccupied. Their characteristic is already reproduced with simple particle-in-a-box models that account for the symmetry of the islands (rectangular, triangular, or linear). However, better agreement is achieved when considering the true atomic structure of the aggregates via a density functional tight-binding approach. Based on a statistically relevant number of single-island data, we have established a correlation between the island geometry and the gap between the highest-occupied and the lowest-unoccupied molecular orbital in the finite-sized islands. The linear eccentricity is identified as a suitable descriptor for this relationship, as it combines information on both island size and island shape. Finally, the depth of the confinement potential is determined from the spatial extension of QWS beyond the physical boundaries of the Au islands. Our paper demonstrates how electron quantization effects can be analyzed in detail in metal nanostructures. The results may help elucidating the interplay between electronic and chemical properties of oxide-supported clusters as used in heterogeneous catalysis.

  16. Effect of Si, Sc, Cr doping on the structural, optical and discharge characteristics of MgO thin films as protective layer for plasma display panels

    NASA Astrophysics Data System (ADS)

    Singh, Chandra Bhal; Barik, U. K.; Sarkar, Surajit; Singh, Vandana; Ram, Sanjay K.; Dwivedi, Harish K.; Kumar, Satyendra

    2012-10-01

    We report the effect of Si, Cr, Sc doping in the crystalline structure, optical and discharge characteristics of MgO thin films. Silicon and multiple (Si, Cr, Sc) doped MgO thin films demonstrate higher secondary electron emission (SEE). Si doping with Cr and Sc doping in MgO films shows much higher SEE as compared to pure and only Si doped MgO films. The importance of optimum amount of Sc doping is seen in our study where SEE reduced with further increase in Sc doping. The structural attributes of MgO films are correlated to the observed changes in discharge characteristics in the context of varying amount of Si, Sc, and Cr doping.

  17. Morphology of TiN thin films grown on MgO(001) by reactive dc magnetron sputtering

    SciTech Connect

    Ingason, A. S.; Magnus, F.; Olafsson, S.; Gudmundsson, J. T.

    2010-07-15

    Thin TiN films were grown by reactive dc magnetron sputtering on single-crystalline MgO(001) substrates at a range of temperatures from room temperature to 600 deg. C. Structural characterization was carried out using x-ray diffraction and reflection methods. TiN films grow epitaxially on the MgO substrates at growth temperatures of 200 deg. C and above. The crystal coherence length determined from Laue oscillations and the Scherrer method agrees with x-ray reflection thickness measurements to 6% and within 3% for growth temperatures of 200 and 600 deg. C, respectively. For lower growth temperatures the films are polycrystalline but highly textured and porous.

  18. Ultrathin magnetite in Fe3O4/MgO superlattices: Investigating the enhanced thin film magnetic moment

    NASA Astrophysics Data System (ADS)

    Mauit, Ozhet; Fleischer, Karsten; O'Coileáin, Cormac; Bulfin, Brendan; Fox, Daniel S.; Smith, Christopher M.; Mullarkey, Daragh; Sugurbekova, Gulnar; Zhang, Hongzhou; Shvets, Igor V.

    2017-03-01

    The electrical, crystallographic, and magnetic properties of ultrathin magnetite (Fe3O4 ) have been studied in detail, by employing superlattice structures of Fe3O4 /MgFe2O4 and Fe3O4 /MgO on a variety of substrates. By careful analysis of their properties, the influence of substrate stoichiometry, Fe3O4 thin film thickness, antiphase boundaries on the magnetic properties can be separated. In particular, the controversial enhanced magnetic moment in ultrathin films (<5 nm) was confirmed to be related to the substrate stoichiometry, specifically the migration of oxygen vacancies into the Fe3O4 thin films. The multilayer concept can be employed with many other such systems and offers methods of tuning the properties of thin magnetic oxides.

  19. 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.

  20. Orthorhombic polar Nd-doped BiFeO3 thin film on MgO substrate.

    PubMed

    Leontyev, I N; Yuzyuk, Yu I; Janolin, P-E; El-Marssi, M; Chernyshov, D; Dmitriev, V; Golovko, Yu I; Mukhortov, V M; Dkhil, B

    2011-08-24

    A Nd-doped BiFeO(3) thin film deposited on MgO substrate was studied by synchrotron diffraction. The ferroelectric nature of the film is proven by in-plane remanent polarization measurement. The highest possible symmetry of the film is determined to be orthorhombic, within the Fm2m space group. Such a structure is rotated by 45° with respect to the substrate and is consistent with tilts of oxygen octahedra doubling the unit cell. This polar structure presents a rather unusual strain-accommodation mechanism.

  1. Thermoelectric study of Y-Ba-Cu-O thin film on MgO substrate prepared by resistive evaporation

    NASA Astrophysics Data System (ADS)

    Pekala, M.; Pekala, K.; Lapsker, I.; Verdyan, A.; Azoulay, J.

    1993-04-01

    Thermoelectric measurements were carried out on Y-Ba-Cu-O thin film deposited on MgO substrate by resistive evaporation technique. A pulverized mixture of Y, BaF 2 and Cu weighed in the atomic proportion was evaporated from resistively heated source onto a MgO substrate kept at 400°C using a simple vacuum system. The substrate temperature was then raised to 700°C for insitu heat treatment. Oxygen was injected through a nozzle placed close to subtrate surface, thus raising the pressure to about 7 Pa during the heat treatment, which lasted for about 15 minutes. The film was then gradually cooled down to room temperature and the pressure raised to atmospheric pressure. The films thus obtained were measured and the values of thermoelectric power measurements in the plane of the film were found to be close to the typical thermoelectric power values of crystalline Y-Ba-Cu-O superconductors. As expected, vanishing values of the thermoelectric power have been observed below 80 K. If the relation observed for sintered Y-Ba-Cu-O is applied for thin films, it suggests an extremely low oxygen deficiency.

  2. 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.

  3. 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.

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

    SciTech Connect

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

    2013-12-14

    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.

  5. 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.

  6. Layer-by-layer epitaxial growth of polar FeO(111) thin films on MgO(111)

    NASA Astrophysics Data System (ADS)

    Gurgul, Jacek; Młyńczak, Ewa; Spiridis, Nika; Korecki, Józef

    2012-04-01

    We report on the structural properties of epitaxial FeO layers grown by molecular beam epitaxy on MgO(111). The successful stabilization of polar FeO films as thick as 16 monolayers (ML), obtained by deposition and subsequent oxidation of single Fe layers, is presented. FeO/MgO(111) thin films were chemically and structurally characterized using low-energy electron diffraction, Auger electron spectroscopy and conversion electron Mössbauer spectroscopy (CEMS). Detailed in situ CEMS measurements as a function of the film thickness demonstrated a size-effect-induced evolution of the hyperfine parameters, with the thickest film exhibiting the bulk-wüstite hyperfine pattern. Ex situ CEMS investigation confirmed existence of magnetic ordering of the wüstite thin film phase at liquid nitrogen temperature.

  7. 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.

  8. Large-area thin self-supporting carbon foils with MgO coatings

    NASA Astrophysics Data System (ADS)

    Stolarz, Anna; Maier-Komor, Peter

    2002-03-01

    Large area self-supporting carbon foils in the thickness of range of 8-22 μg/cm 2, coated with approximately 4 μg/cm 2 MgO have been prepared by e-gun evaporation. They were mounted on frames with apertures of 130 cm 2. Problems related to the parting agent preparation, floating procedure, and mounting onto frames are discussed. Special precautions necessary to avoid damage during foil drying, storage and transportation are suggested.

  9. Static and dynamic properties of Co2FeAl thin films: Effect of MgO and Ta as capping layers

    NASA Astrophysics Data System (ADS)

    Husain, Sajid; Barwal, Vineet; Kumar, Ankit; Behera, Nilamani; Akansel, Serkan; Goyat, Ekta; Svedlindh, Peter; Chaudhary, Sujeet

    2017-05-01

    The influence of MgO and Ta capping layers on the static and dynamic magnetic properties of Co2FeAl (CFA) Heusler alloy thin films has been investigated. It is observed that the CFA film deposited with MgO capping layer is preeminent compared to the uncapped or Ta capped CFA film. In particular, the magnetic inhomogeneity contribution to the ferromagnetic resonance line broadening and damping constant are found to be minimal for the MgO capped CFA thin film i.e., 0.12±0.01 Oe and 0.0074±0.00014, respectively. The saturation magnetization was found to be 960±25emu/cc.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. Island growth and surface topography of epitaxial Y-Ba-Cu-O thin films on MgO

    SciTech Connect

    Krebs, H.U.; Krauns, C. ); Yang, X.; Geyer, U. )

    1991-10-21

    High-quality epitaxial Y{sub 1}B{sub 2}Cu{sub 3}O{sub {ital x}} thin films ({ital T}{sub {ital c},{ital o}} {ge} ({ital R}18) 90 K, {ital j}{sub {ital c}} (77 K){ge} (R18)3 {times}10{sup 6}A/cm{sup 2}) were {ital in} {ital situ} grown on MgO by KrF excimer laser ablation. The combination of {ital in} {ital situ} resistance measurements, x-ray diffraction experiments, {ital T}{sub {ital c}} measurements, scanning electron microscopy and scanning tunneling microscopy gives clear indications for an island growth on these substrates and shows growth steps and spirals at the film surface.

  15. Skew scattering dominated anomalous Hall effect in Co x (MgO)100‑x granular thin films

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang; Wen, Yan; Zhao, Yuelei; Li, Peng; He, Xin; Zhang, Junli; He, Yao; Peng, Yong; Yu, Ronghai; Zhang, Xixiang

    2017-10-01

    We investigated the mechanism(s) of the anomalous Hall effect (AHE) in magnetic granular materials by fabricating 100 nm-thick thin films of Co x (MgO)100‑x with a Co volume fraction of 34  ⩽  x  ⩽  100 using co-sputtering at room temperature. We measured the temperature dependence of longitudinal resistivity ({{ρ }xx} ) and anomalous Hall resistivity ({{ρ }AHE} ) from 5 K to 300 K in all samples. We found that when x decreases from 100 to 34, the values of {{ρ }xx} and {{ρ }AHE} respectively increased by about four and three orders in magnitude. By linearly fitting the data, obtained at 5 K, of anomalous Hall coefficient ({{R}s} ) and of {{ρ }xx} to log({{R}s})∼ γ log({{ρ }xx}) , we found that our results perfectly fell on a straight line with a slope of γ = 0.97  ±  0.02. This fitting value of γ in {{R}s}\\propto ρ xxγ ~ clearly suggests that skew scattering dominated the AHE in this granular system. To explore the effect of the scattering on the AHE, we performed the same measurements on annealed samples. We found that although both {{ρ }xx} and {{ρ }AHE} significantly reduced after annealing, the correlation between them was almost the same, which was confirmed by the fitted value, γ   =  0.99  ±  0.03. These data strongly suggest that the AHE originates from the skew scattering in Co–MgO granular thin films no matter how strong the scattering of electrons by the interfaces and defects is. This observation may be of importance to the development of spintronic devices based on MgO.

  16. 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.

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

    DOE PAGES

    Tolstova, Yulia; Omelchenko, Stefan T.; Shing, Amanda M.; ...

    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

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

    SciTech Connect

    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 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. 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.

  19. Realization of Al2O3/MgO laminated structure at low temperature for thin film encapsulation in organic light-emitting diodes.

    PubMed

    Li, Min; Xu, Miao; Zou, Jianhua; Tao, Hong; Wang, Lei; Zhou, Zhongwei; Peng, Junbiao

    2016-12-09

    A laminated structure of Al2O3 and MgO deposited by atomic layer deposition (ALD) is used to realize a thin film encapsulation technology in organic light-emitting diodes (OLEDs). This film was targeted to achieve an excellent barrier performance. As the thickness of MgO layer increased from 0 nm to 20 nm, its physical properties transformed from the amorphous state into a crystalline state. The optimized cyclic ratio of ALD Al2O3 and MgO exhibited much lower water vapor transmission rate (WVTR) of 4.6 × 10(-6) gm(-2)/day evaluated by Calcium (Ca) corrosion at 60 °C&100% RH, owing to the formation of a terrific laminated structure. Top-emitting OLEDs encapsulated with laminated Al2O3/MgO show longer operating lifetime under rigorous environmental conditions. These improvements were attributed to the embedded MgO film that served as a modified layer to establish a laminated structure to obstruct gas permeation, as well as a scavenger to absorb water molecules, thus alleviating the hydrolysis of bulk Al2O3 material.

  20. Realization of Al2O3/MgO laminated structure at low temperature for thin film encapsulation in organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Li, Min; Xu, Miao; Zou, Jianhua; Tao, Hong; Wang, Lei; Zhou, Zhongwei; Peng, Junbiao

    2016-12-01

    A laminated structure of Al2O3 and MgO deposited by atomic layer deposition (ALD) is used to realize a thin film encapsulation technology in organic light-emitting diodes (OLEDs). This film was targeted to achieve an excellent barrier performance. As the thickness of MgO layer increased from 0 nm to 20 nm, its physical properties transformed from the amorphous state into a crystalline state. The optimized cyclic ratio of ALD Al2O3 and MgO exhibited much lower water vapor transmission rate (WVTR) of 4.6 × 10-6 gm-2/day evaluated by Calcium (Ca) corrosion at 60 °C&100% RH, owing to the formation of a terrific laminated structure. Top-emitting OLEDs encapsulated with laminated Al2O3/MgO show longer operating lifetime under rigorous environmental conditions. These improvements were attributed to the embedded MgO film that served as a modified layer to establish a laminated structure to obstruct gas permeation, as well as a scavenger to absorb water molecules, thus alleviating the hydrolysis of bulk Al2O3 material.

  1. 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.

  2. 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.

  3. 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.

  4. Effect of Cu buffer layer on magnetic anisotropy of cobalt thin films deposited on MgO(001) substrate

    NASA Astrophysics Data System (ADS)

    Ahmad, Syed Sheraz; He, Wei; Zhang, Yong-Sheng; Tang, Jin; Gul, Qeemat; Zhang, Xiang-Qun; Cheng, Zhao-Hua

    2016-11-01

    Cobalt thin films with 5 nm thickness were prepared on single-crystal MgO (001) substrates with different thickness Cu buffer (0 nm, 5 nm, 10 nm, 20 nm). The structure, magnetic properties and transport behaviors were investigated by employing low-energy-electron-diffraction (LEED), magneto-optical Kerr effect (MOKE) and anisotropic magnetoresistance (AMR). By comparing the magnetic properties of the sample as-deposited (without Cu buffer layer) one with those having the buffer Cu, we found that the magnetic anisotropy was extremely affected by the Cu buffer layer. The magnetic anisotropy of the as-deposited, without buffer layer, sample shows the uniaxial magnetic anisotropy (UMA). We found that the symmetry of the magnetic anisotropy is changed from UMA to four-fold when the thickness of the Cu buffer layer reaches to 20 nm. Meanwhile, the coercivity increased from 49 Oe (without buffer layer) to 300 Oe (with 20 nm Cu buffer), in the easy axis direction, as the thickness of the buffer layer increases. Moreover, the magnitudes of various magnetic anisotropy constants were determined from torque curves on the basis of AMR results. These results support the phenomenon shown in the MOKE.

  5. 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.

  6. Interface matching and intermixing of thin MgO barriers and ferromagnetic layers deposited on GaAs (001)

    NASA Astrophysics Data System (ADS)

    Tholapi, R.; Karateev, I. A.; Roshchin, B. S.; Asadchikov, V. E.; Slobodskyy, T.; Hansen, W.; Vasiliev, A. L.

    2017-05-01

    MgO tunneling barriers are extensively studied as a spin filtering and diffusion barrier for deposition of ferromagnetic layers on GaAs (001) surfaces. The relatively large lattice mismatch of the MgO and GaAs substrate and probable formation of interface states at the metal layer side require a careful barrier design. We present a study of deposition, microstructure, and strain relaxation in MgO barriers deposited on GaAs. The dependence of morphology of MgO layers on their thickness was characterized using a combination of X-Ray Reflectivity and High Resolution Transmission Electron Microscopy. The stress at the MgO/GaAs interface was observed to be released through the formation of misfit dislocations and partially by the formation of mis-oriented domains. The deposited MgO and Fe layers were found to be highly textured irrespective of the thickness of MgO layers. Energy dispersive X-ray microanalysis was used to observe intermixing at the interface of Fe and MgO layers.

  7. 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)

  8. ZnO-Based Transparent Thin-Film Transistors with MgO Gate Dielectric Grown by in-situ MOCVD

    NASA Astrophysics Data System (ADS)

    Zhao, Wang; Dong, Xin; Zhao, Long; Shi, Zhi-Feng; Wang, Jin; Wang, Hui; Xia, Xiao-Chuan; Chang, Yu-Chun; Zhang, Bao-Lin; Du, Guo-Tong

    2010-12-01

    ZnO transparent thin-film transistors with MgO gate dielectric were fabricated by in-situ metal organic chemical vapor deposition (MOCVD) technology. We used an uninterrupted growth method to simplify the fabrication steps and to avoid the unexpectable contaminating during epitaxy process. MgO layer is helpful to reduce the gate leakage current, as well as to achieve high transparency in visible light band, due to the wide band gap (7.7eV) and high dielectric constant (9.8). The XRD measurement indicates that the ZnO layer has high crystal quality. The field effect mobility and the on/off current ratio of the device is 2.69 cm2 V-1s-1 and ~ 1 × 104, respectively.

  9. Growth of Ni and Ni-Cr alloy thin films on MgO(001): Effect of alloy composition on surface morphology

    NASA Astrophysics Data System (ADS)

    Ramalingam, Gopalakrishnan; Reinke, Petra

    2016-12-01

    The effects of substrate treatment, growth temperature, and composition on the surface morphology of Ni-Cr thin films grown on MgO(001) are studied by scanning tunneling microscopy and atomic force microscopy. We demonstrate that a combination of acid-etched substrates and high temperature deposition (400 °C) will result in smooth films with well-defined terraces (up to 30 nm wide) that are suitable for the study of progression of chemical reactions on the surface. Two different treatments are used to prepare the MgO substrates for deposition and they introduce characteristic differences in film surface morphology. Thin films that are grown on the phosphoric acid-treated substrates present reduced nucleation density during the initial stages of film growth which results in long and wide terraces. Due to the ≈16% lattice mismatch in the Ni(001)/MgO(001) system, film growth at 400 °C yields discontinuous films and a two-step growth process is necessary to obtain a continuous layer. Ni films are deposited at 100 °C and subjected to a post-growth annealing at 300 °C for 2 h to obtain a smoother surface. The addition of just 5 wt. % Cr drastically changes the film growth processes and yields continuous films at 400 °C without de-wetting in contrast to pure Ni films. With increasing Cr content, the films become progressively smoother with wider terraces. Ni5Cr alloy thin films have an rms surface roughness of 3.63 ± 0.75 nm, while Ni33Cr thin film is smoother with an rms roughness of only 0.29 ± 0.13 nm. The changes in film growth initiated by alloying with Cr are due to changes in the interfacial chemistry which favorably alters the initial adsorption of the metal atoms on MgO surface and suggests a reduction of the Ehrlich-Schwoebel barrier. The growth of smooth Ni-Cr thin films with a well-defined surface structure opens up a new pathway for a wide range of surface science studies related to alloy performance.

  10. Annealing stability of magnetic tunnel junctions based on dual MgO free layers and [Co/Ni] based thin synthetic antiferromagnet fixed system

    NASA Astrophysics Data System (ADS)

    Devolder, T.; Couet, S.; Swerts, J.; Liu, E.; Lin, T.; Mertens, S.; Furnemont, A.; Kar, G.

    2017-03-01

    We study the annealing stability of bottom-pinned perpendicularly magnetized magnetic tunnel junctions based on dual MgO free layers and thin fixed systems comprising a hard [Co/Ni] multilayer antiferromagnetically coupled to thin a Co reference layer and a FeCoB polarizing layer. Using conventional magnetometry and advanced broadband ferromagnetic resonance, we identify the properties of each sub-unit of the magnetic tunnel junction and demonstrate that this material option can ensure a satisfactory resilience to the 400 °C thermal annealing needed in solid-state magnetic memory applications. The dual MgO free layer possesses an anneal-robust 0.4 T effective anisotropy and suffers only a minor increase of its Gilbert damping from 0.007 to 0.010 for the toughest annealing conditions. Within the fixed system, the ferro-coupler and texture-breaking TaFeCoB layer keeps an interlayer exchange above 0.8 mJ/m2, while the Ru antiferrocoupler layer within the synthetic antiferromagnet maintains a coupling above -0.5 mJ/m2. These two strong couplings maintain the overall functionality of the tunnel junction upon the toughest annealing despite the gradual degradation of the thin Co layer anisotropy that may reduce the operation margin in spin torque memory applications. Based on these findings, we propose further optimization routes for the next generation magnetic tunnel junctions.

  11. 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.

  12. Structure-Property Relationships in W Doped (Ba,Sr)TiO(3) Thin Films Deposited by Pulsed Laser Deposition on (001) MgO

    DTIC Science & Technology

    2003-04-03

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP013347 TITLE: Structure-Property Relationships in W Doped [Ba,Sr]TiO[3... Doped (Ba,Sr)TiO 3 Thin Films Deposited by Pulsed Laser Deposition on (001) MgO N. Navi1’*, J.S. Horwitz, H.-D. Wu2 and S.B. Qadri, Naval Research...oscillators, delay lines and phase shifters [1]. These devices will reduce the size and the operating power of the current semiconducting and ferrite based

  13. Enhancement of lower critical field in thin MgB2 films and MgB2/MgO multilayers

    NASA Astrophysics Data System (ADS)

    Tan, Teng; Johnson, Evan; Acharya, Narendra; Hambe, Michael; Chen, Ke; Krick, Alex; May, Steven; Xi, Xiaoxing

    2013-03-01

    Magnesium diboride is a conventional superconductor with a high Tc of 39 K, a low residual resistivity of < 0.1 μΩ cm (at 42 K), and higher thermodynamic critical field Hc values than Nb. These properties make MgB2 a promising superconductor as an alternative to Nb for future SRF cavities. However, the lower critical field Hc 1 of MgB2 is low, and vortex dissipation above Hc 1 can lead to degradation of the quality factor and low RF breakdown field. Here, we report an enhancement of Hc 1 in thin MgB2 films and MgB2/MgO multilayers. The value of Hc 1(5K) is increased from 40 mT in a 300 nm-thick MgB2 film to 180 mT when the MgB2 layer thickness is 100 nm either in a single-layer film or in a MgB2/MgO multilayer with a total MgB2 layer thickness of 300 nm. Superconducting MgB2 thin films have been coated in-situon the inner wall of a SRF cavity using the hybrid physical chemical vapor deposition (HPCVD) technique. The characterization of the coating will be presented.

  14. In situ oxygen conditioning of /001/ MgO thin film substrates for film growth studies by electron microscopy

    NASA Technical Reports Server (NTRS)

    Moorhead, R. D.; Poppa, H.

    1979-01-01

    It was found that the in situ treatment of 001-plane single-crystal films of MgO (prepared by epitaxial growth from the vapor phase) at high temperatures with a jet of oxygen will produce a surface that is almost equivalent, for epitaxial studies, to surfaces with the same orientation prepared by vacuum cleavage of bulk single crystals. The effectiveness of the process is demonstrated by its impact on the epitaxy of silver.

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

    DOE PAGES

    Burmistrova, Polina V.; Zakharov, Dmitri N.; Favaloro, Tela; ...

    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

  16. 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.

  17. 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)

  18. Enhancement of perpendicular magnetic anisotropy in FeB free layers using a thin MgO cap layer

    NASA Astrophysics Data System (ADS)

    Kubota, Hitoshi; Ishibashi, Shota; Saruya, Takeshi; Nozaki, Takayuki; Fukushima, Akio; Yakushiji, Kay; Ando, Koji; Suzuki, Yoshishige; Yuasa, Shinji

    2012-04-01

    We prepared magnetic tunnel junction films with PtMn/CoFe/Ru/CoFeB/MgO tunnel barrier/FeB free layer/MgO cap layer/Ta multilayers using sputtering and measured magnetic and magnetoresistive properties of the films at room temperature. The magnetization curves of the FeB plane film measured under perpendicular-to-plane magnetic fields showed much smaller saturation fields (Hs) than those expected from the demagnetizing field. Hs decreased from 4 to 0.4 kOe with increasing MgO cap layer thickness. The small Hs is due to the perpendicular magnetic anisotropy (PMA) induced at both MgO barrier-FeB and FeB-MgO cap interfaces. After microfabrication, the small free layer cells having a 1.6 nm thick MgO cap layer showed a magnetization easy axis in the perpendicular-to-plane direction. By inducing PMA from both upper and lower interfaces, we can stabilize the magnetization of the relatively thick (2 nm) FeB free layer in the perpendicular-to-plane direction.

  19. 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.

  20. Growth of InFeCoO 4 thin films on SrTiO 3 and MgO substrates

    NASA Astrophysics Data System (ADS)

    Matvejeff, M.; Lippmaa, M.

    2010-08-01

    We have studied the effect of deposition conditions and strain on the phase stability, grain structure, grain orientation, crystallinity, and magnetism of InFeCoO 4 spinel thin films grown on single-crystal (0 0 1) SrTiO 3 (STO) and (0 0 1) MgO substrates. The growth window for good-quality films exhibiting uniform orientation was observed to be very narrow with deviations from optimal conditions resulting in highly disordered growth characterized by mixed (0 0 1) and (1 1 1) type orientations, expanded out-of-plane lattice constants, and reduced symmetry for the (0 0 1) oriented grains. Bulk-like magnetic properties could be obtained in films grown on STO under optimal conditions, whereas significantly lower values for saturation magnetization and TC were observed for the disordered samples. The absence of frequency-dependent components in AC-magnetization measurements indicates the absence of a glassy state previously observed in bulk InFeCoO 4. The significantly smaller grain size of the samples grown on MgO at optimal conditions resulted in depressed TC in addition to a strong superparamagnetic effect below 20 K.

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

    PubMed

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

    2014-11-12

    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.

  2. Preparation and characterization of Bi2Sr2CaCu2O8+δ thin films on MgO single crystal substrates by chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Grivel, J.-C.; Kępa, K.; Hlásek, T.; Andersen, N. H.; Rubešová, K.

    2013-03-01

    Bi2Sr2CaCu2O8 thin films have been deposited on MgO single crystal substrates by spin-coating a solution based on 2-ethylhexanoate precursors. Pyrolysis takes place between 200 °C and 450 °C and is accompanied by the release of 2-ethylhexanoic acid, CO2 and H2O vapour. Highly c-axis oriented Bi2Sr2CaCu2O8 films were obtained after heat treatment at 840 °C in air. The highest Tc of 81 K was measured in a 10-layer film. Subsequent post-annealing in Ar and pure O2 did not improve the superconducting properties of the films and resulted in the appearance of Bi2CaCuO5 or Bi2(Sr, Ca)2CuO6 impurities.

  3. 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.

  4. 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.

  5. Growth of L1{sub 0}-ordered crystal in FePt and FePd thin films on MgO(001) substrate

    SciTech Connect

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

    2016-08-15

    Formation of L1{sub 0}-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. L1{sub 0}-(001) variant crystal with the c-axis perpendicular to the substrate grows preferentially in FePd films whereas L1{sub 0}-(100), (010) variants tend to be mixed with the L1{sub 0}-(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 L1{sub 0}-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 L1{sub 0}-(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 L1{sub 0}-variant formation is proposed, which suggests a possibility in tailoring the L1{sub 0} variant structure in ordered magnetic thin films by controlling the alloy composition, the layer structure, and the substrate material.

  6. Structural phase diagram for ultra-thin epitaxial Fe3O4 / MgO(0 01) films: thickness and oxygen pressure dependence

    DOE PAGES

    Alraddadi, S.; Hines, W.; Yilmaz, T.; ...

    2016-02-19

    A systematic investigation of the thickness and oxygen pressure dependence for the structural properties of ultra-thin epitaxial magnetite (Fe3O4) films has been carried out; for such films, the structural properties generally differ from those for the bulk when the thickness ≤10 nm. Iron oxide ultra-thin films with thicknesses varying from 3 nm to 20 nm were grown on MgO (001) substrates using molecular beam epitaxy under different oxygen pressures ranging from 1 × 10-7 torr to 1 × 10-5 torr. The crystallographic and electronic structures of the films were characterized using low energy electron diffraction (LEED) and x-ray photoemission spectroscopymore » (XPS), respectively. Moreover, the quality of the epitaxial Fe3O4 ultra-thin films was judged by magnetic measurements of the Verwey transition, along with complementary XPS spectra. We observed that under the same growth conditions the stoichiometry of ultra-thin films under 10 nm transforms from the Fe3O4 phase to the FeO phase. In this work, a phase diagram based on thickness and oxygen pressure has been constructed to explain the structural phase transformation. It was found that high-quality magnetite films with thicknesses ≤20 nm formed within a narrow range of oxygen pressure. An optimal and controlled growth process is a crucial requirement for the accurate study of the magnetic and electronic properties for ultra-thin Fe3O4 films. Furthermore, these results are significant because they may indicate a general trend in the growth of other oxide films, which has not been previously observed or considered.« less

  7. Thermal and irradiation induced interdiffusion in Fe 3O 4/MgO(0 0 1) thin film

    NASA Astrophysics Data System (ADS)

    Kim-Ngan, N.-T. H.; Balogh, A. G.; Meyer, J. D.; Brötz, J.; Hummelt, S.; Zając, M.; Ślęzak, T.; Korecki, J.

    2009-05-01

    The interface reactions in an epitaxial 10 nm-thick Fe3O4/MgO(0 0 1) film were investigated by using Rutherford Backscattering spectrometry (RBS), channeling (RBS-C) and X-ray reflectometry (XRR). The as-grown film had a good crystallinity indicated by the minimum yield and the half-angle value for Fe, respectively, χmin(Fe) = 22% and ψ1/2(Fe) = 0.62°. Annealing the films under partial argon pressure up to 600 °C led to a large enhancement of Mg out-diffusion into the film forming a wustite-type phase, but the total layer thickness did not change much. Ion irradiation of the film by 1 MeV Ar ion beam caused a strong Fe ion mixing resulting in a large interfacial zone with a thickness of 23 nm.

  8. Contribution from Ising domains overlapping out-of-plane to perpendicular magnetic anisotropy in Mn4N thin films on MgO(001)

    NASA Astrophysics Data System (ADS)

    Foley, Andrew; Corbett, Joseph; Khan, Alam; Richard, Andrea L.; Ingram, David C.; Smith, Arthur R.; Zhao, Lianshui; Gallagher, James C.; Yang, Fengyuan

    2017-10-01

    Single phase ε -Mn4N thin and ultrathin films are grown on MgO(001) using molecular beam epitaxy. Reflection high-energy electron diffraction and out-of-plane X-ray diffraction measurements are taken for each sample in order to determine the in- and out-of-plane strain for each sample. Vibrating sample magnetometry and superconducting quantum interference device measurements, which are performed on the thin and ultrathin films respectively, are used to plot the magnetization of each sample versus both in- and out-of-plane H → -fields and to determine the magnitude of perpendicular magnetic anisotropy in these films. Three significant components of perpendicular magnetic anisotropy are observed in these films and are attributed to sample strain (1 component) and shape (2 components). Among these components, the most significant component (0.8 - 4.9 Merg/cm3) is identified as a second term of shape anisotropy, which possesses a negative linear relationship with sample thickness over the range from 9 nm to 310 nm. Atomic (magnetic) force microscopy measurements show the presence of a surface localized magnetic polarization (22-82 %), which increases with decreasing thickness, when the net magnetizations of the films are zero. The second term of shape anisotropy as well as the surface localized polarization, which each depend on sample thickness, are each regarded as a consequence of Ising domains overlapping out-of-plane in these 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. Roughness analysis applied to niobium thin films grown on MgO(001) surfaces for superconducting radio frequency cavity applications

    SciTech Connect

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

    2013-02-05

    This paper describes surface studies to address roughness issues inherent to thin film coatings deposited onto superconducting radio frequency (SRF) cavities. This is particularly relevant for multilayered thin film coatings that are being considered as a possible scheme to overcome technical issues and to surpass the fundamental limit of ~500 MV/m accelerating gradient achievable with bulk niobium. In 2006, a model by Gurevich [ Appl. Phys. Lett. 88 012511 (2006)] was proposed to overcome this limit that involves coating superconducting layers separated by insulating ones onto the inner walls of the cavities. Thus, we have undertaken a systematic effort to understand the dynamic evolution of the Nb surface under specific deposition thin film conditions onto an insulating surface in order to explore the feasibility of the proposed model. We examine and compare the morphology from two distinct Nb/MgO series, each with its own epitaxial registry, at very low growth rates and closely examine the dynamical scaling of the surface features during growth. Further, we apply analysis techniques such as power spectral density to the specific problem of thin film growth and roughness evolution to qualify the set of deposition conditions that lead to successful SRF coatings.

  11. 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

  12. 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.

  13. Post annealing induced magnetic anisotropy in CoFeSi thin films on MgO(0 0 1)

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    Co61Fe26Si13 (CoFeSi) thin films were deposited on MgO(0 0 1) substrates by magnetron sputtering and were annealed at different temperatures (T a). X-ray diffraction revealed that the crystal structure varies from the as-deposited amorphous phase to the cubic phase when T a  =  800 °C, indicating the re-crystallization process after annealing treatment. The static magnetic property measurements show a gradually four-fold cubic anisotropy dominating the magnetic anisotropy with the increasing T a. The ferromagnetic resonance technique based on vector network analyzer was utilized to analyze the dynamic magnetic properties. CoFeSi film annealed at 600 °C presents an obvious in-plane uniaxial magnetic anisotropy, and it presents a low effective damping constant of around 0.011 with a natural resonance frequency of around 3.4 GHz. However, the CoFeSi film annealed at 800 °C showed a strong cubic magnetocrystalline anisotropy and full-in-plane-direction workable natural resonance frequency at around 2.5 GHz.

  14. Enhancements of magnetic properties and planar magnetoresistance by electric fields in γ-Fe{sub 2}O{sub 3}/MgO thin films

    SciTech Connect

    Cheng, Bin; Qin, Hongwei; Pei, Jinliang; Liu, Liang; Ren, Shaoqing; Hu, Jifan E-mail: hu-jf@vip.163.com

    2016-05-23

    The treatment of perpendicular electric field upon γ-Fe{sub 2}O{sub 3}/MgO film at room temperature could adjust the magnetic properties (saturation magnetization, magnetic remanence, coercivity, and saturation magnetizing field) of the film. The enhancement of saturation magnetization after the treatment of electric field may be connected with the combined shift effects of Mg ions from MgO to γ-Fe{sub 2}O{sub 3} and O{sup 2−} ions from γ-Fe{sub 2}O{sub 3} to MgO. The negative magnetoresistance of the γ-Fe{sub 2}O{sub 3}/MgO film also enhances with the treatment of perpendicular electric field at room temperature, possibly due to the increasing of electron hopping rate between Fe{sup 2+} and Fe{sup 3+}.

  15. Crystallinity of YBCO thin films on an MgO substrate using an amorphous buffer layer deposited at a low temperature

    NASA Astrophysics Data System (ADS)

    Nakamura, Y.; Kudo, S.; Mukaida, M.; Ohshima, S.

    2002-10-01

    We have investigated crystallinity of YBCO films on an MgO substrate using an amorphous buffer layer. The evaluated films are obtained as follows: an amorphous YBCO buffer layer is deposited on the MgO substrate at a low temperature (200 °C); and then, an amorphous buffer layer is crystallized by the thermal annealing at a high temperature from 910 to 1030 °C; finally, main YBCO film is grown on the crystalline YBCO buffer layer over the MgO substrate. A significant improvement in the crystalline quality of the YBCO films was achieved, when amorphous buffer layers of 100 nm in thickness were crystallized by annealing temperature 950 °C and then annealing is continued for 1 h in air atmosphere. We confirmed that YBCO films grown on a well-crystallized buffer layer had better crystallinity than ones on bare MgO substrate, which has substantially large lattice mismatch.

  16. Room temperature ferromagnetic properties of epitaxial (111) Y0.225Sr0.775CoO3-δ thin film grown on single crystalline (111) MgO substrate

    NASA Astrophysics Data System (ADS)

    Seo, Jeongdae; Ahn, Yoonho; Yeog Son, Jong

    2015-08-01

    Epitaxial (111) Y0.225Sr0.775CoO3-δ (YSCO) thin films were deposited on single crystalline (111) MgO substrates by a pulsed laser deposition method. The YSCO thin film exhibited room temperature ferromagnetism with a remanent magnetization of 1.5×10-5 emu. The magnetic force microscopy (MFM) study revealed that the YSCO thin film had a mosaic MFM domain structure. The comparison of domain wall energy for the YSCO and PZT indicates that the large domain wall energy induce the large domain size, though the large magnetization value reduce the magnetic domain size in the case of Co. According to the optical conductivity analysis by spectroscopic ellipsometry, it is inferred that the transition from the intermediate spin state to the high spin state of the YSCO thin film is attributed to the ferromagnetism of the Co4+ ion.

  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. 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.

  19. 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.

  20. Structural phase diagram for ultra-thin epitaxial Fe3O4 / MgO(0 01) films: thickness and oxygen pressure dependence

    SciTech Connect

    Alraddadi, S.; Hines, W.; Yilmaz, T.; Gu, G. D.; Sinkovic, B.

    2016-02-19

    A systematic investigation of the thickness and oxygen pressure dependence for the structural properties of ultra-thin epitaxial magnetite (Fe3O4) films has been carried out; for such films, the structural properties generally differ from those for the bulk when the thickness ≤10 nm. Iron oxide ultra-thin films with thicknesses varying from 3 nm to 20 nm were grown on MgO (001) substrates using molecular beam epitaxy under different oxygen pressures ranging from 1 × 10-7 torr to 1 × 10-5 torr. The crystallographic and electronic structures of the films were characterized using low energy electron diffraction (LEED) and x-ray photoemission spectroscopy (XPS), respectively. Moreover, the quality of the epitaxial Fe3O4 ultra-thin films was judged by magnetic measurements of the Verwey transition, along with complementary XPS spectra. We observed that under the same growth conditions the stoichiometry of ultra-thin films under 10 nm transforms from the Fe3O4 phase to the FeO phase. In this work, a phase diagram based on thickness and oxygen pressure has been constructed to explain the structural phase transformation. It was found that high-quality magnetite films with thicknesses ≤20 nm formed within a narrow range of oxygen pressure. An optimal and controlled growth process is a crucial requirement for the accurate study of the magnetic and electronic properties for ultra-thin Fe3O4 films. Furthermore, these results are significant because they may indicate a general trend in the growth of other oxide films, which has not been previously observed or considered.

  1. 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.

  2. Growth and characterization of thin Cu-phthalocyanine films on MgO(001) layer for organic light-emitting diodes

    PubMed Central

    2012-01-01

    Surface morphology and thermal stability of Cu-phthalocyanine (CuPc) films grown on an epitaxially grown MgO(001) layer were investigated by using atomic force microscope and X-ray diffractometer. The (002) textured β phase of CuPc films were prepared at room temperature beyond the epitaxial MgO/Fe/MgO(001) buffer layer by the vacuum deposition technique. The CuPc structure remained stable even after post-annealing at 350°C for 1 h under vacuum, which is an important advantage of device fabrication. In order to improve the device performance, we investigated also current-voltage-luminescence characteristics for the new top-emitting organic light-emitting diodes with different thicknesses of CuPc layer. PMID:23181826

  3. Growth and characterization of thin Cu-phthalocyanine films on MgO(001) layer for organic light-emitting diodes.

    PubMed

    Bae, Yu Jeong; Lee, Nyun Jong; Kim, Tae Hee; Cho, Hyunduck; Lee, Changhee; Fleet, Luke; Hirohata, Atsufumi

    2012-11-26

    Surface morphology and thermal stability of Cu-phthalocyanine (CuPc) films grown on an epitaxially grown MgO(001) layer were investigated by using atomic force microscope and X-ray diffractometer. The (002) textured β phase of CuPc films were prepared at room temperature beyond the epitaxial MgO/Fe/MgO(001) buffer layer by the vacuum deposition technique. The CuPc structure remained stable even after post-annealing at 350°C for 1 h under vacuum, which is an important advantage of device fabrication. In order to improve the device performance, we investigated also current-voltage-luminescence characteristics for the new top-emitting organic light-emitting diodes with different thicknesses of CuPc layer.

  4. 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.

  5. 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.

  6. 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.

  7. Optical properties of epitaxial CaxBa1-xNb2O6 thin film based rib-waveguide structure on (001) MgO for electro-optic applications.

    PubMed

    Vigne, Sébastien; Hossain, Nadir; Fesharaki, Faezeh; Kabir, S M Humayun; Margot, Joëlle; Wu, Ke; Chaker, Mohamed

    2016-12-12

    In this work, optical properties of epitaxial CaxBa1-xNb2O6, CBN (x = 0.28) thin film based waveguides are studied at 1550 nm optical communications wavelength. CBN thin films are deposited epitaxially on MgO substrates using Pulsed Laser Deposition and characterized by prism coupling to extract the refractive index and propagation loss. It is shown that the 2 µm-thick epitaxial CBN thin films have a refractive index close to the bulk form and the CBN planar waveguides have a propagation loss of 4.3 ± 0.5 dB/cm. 1 cm-long rib waveguide structures were fabricated using a high density plasma etching. Their propagation losses were measured by the cutback method at 8.4 ± 0.6 dB/cm.

  8. Ultrathin MgO diffusion barriers for ferromagnetic electrodes on GaAs(001).

    PubMed

    Sarkar, Anirban; Wang, Shibo; Grafeneder, Wolfgang; Arndt, Martin; Koch, Reinhold

    2015-04-24

    Ultrathin MgO(100) films serving as a diffusion barrier between ferromagnetic electrodes and GaAs(001) semiconductor templates have been investigated. Using Fe as an exemplary ferromagnetic material, heterostructures of Fe/MgO/GaAs(001) were prepared at 200 °C with the MgO thickness ranging from 1.5 to 3 nm. Structural characterization reveals very good crystalline ordering in all layers of the heterostructure. Auger electron spectroscopy depth-profiling and cross-sectional high-resolution transmission electron microscopy evidence diffusion of Fe into MgO and-for too thin MgO barriers-further into GaAs(001). Our results recommend a MgO barrier thickness larger than or equal to 2.6 nm for its application as a reliable diffusion barrier on GaAs(001) in spintronics devices.

  9. Epitaxial growth and dielectric properties of Pb0.4Sr0.6TiO3 thin films on (00l)-oriented metallic Li0.3Ni0.7O2 coated MgO substrates

    NASA Astrophysics Data System (ADS)

    Li, X. T.; Du, P. Y.; Mak, C. L.; Wong, K. H.

    2007-06-01

    Highly (00l)-oriented Li0.3Ni0.7O2 thin films have been fabricated on (001) MgO substrates by pulsed laser deposition. The Pb0.4Sr0.6TiO3 (PST40) thin film deposited subsequently also shows a significant (00l)-oriented texture. Both the PST40 and Li0.3Ni0.7O2 have good epitaxial behavior. The epitaxial growth of the PST40 thin film is more perfect with the Li0.3Ni0.7O2 buffer layer due to the less distortion in the film. The dielectric tunability of the PST40 thin film with Li0.3Ni0.7O2 buffer layer therefore reaches 70%, which is 75% higher than that without Li0.3Ni0.7O2 buffer layer, and the dielectric loss of the PST40 thin film is 0.06.

  10. Microwave absorption studies on high-T sub c superconductors and related materials 7--ESR of DPPH coated on a thin BiSrCaCuO film fabricated on MgO(100) substrate

    SciTech Connect

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

    1992-05-10

    In this paper, ESR of DPPH coated on a Bi-Sr-Ca-Cu-O (BSCCO) film (350 {Angstrom} thick) fabricated on MgO(100) substrate by MOCVD is studied. Temperature dependence of the ESR peak-to-peak linewidth, {Delta}H{sub pp}, and the effect of applied magnetic field on {Delta}H{sub pp} are below about 100 K. The results are 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 reveals that {Delta}H{sub pp} 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.

  11. 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.

  12. 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.

  13. Rapid Gel Cast Prototyping of Complex Paraelectric (Ba,Sr)TiO(3)/MgO Composites

    DTIC Science & Technology

    2003-04-03

    40 wt% BaO. 55Sro.45TiO 3 / 60 wt% MgO (see ref. 1) MgCO 3 (Alfa Aesar, MA) + 3 wt% oxalic acid (Fisher Scientific, NY) MgO (Alfa Aesar, MA...the particles with oxalic acid to produce a thin surface layer of magnesium oxalate (cf. Figure 3b). Figure 3. Green body interior a) 40wt% Ba

  14. Heteroepitaxial growth of TiN film on MgO (100) by reactive magnetron sputtering

    PubMed Central

    2014-01-01

    TiN thin films were deposited on MgO (100) substrates at different substrate temperatures using rf sputtering with Ar/N2 ratio of about 10. At 700°C, the growth rate of TiN was approximately 0.05 μm/h. The structural and electrical properties of TiN thin films were characterized with x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Hall measurements. For all deposition conditions, XRD results show that the TiN films can be in an epitaxy with MgO with cube-on-cube orientation relationship of (001)TiN // (001)MgO and [100]TiN // [100]MgO. TEM with selected-area electron diffraction pattern verifies the epitaxial growth of the TiN films on MgO. SEM and AFM show that the surface of the TiN film is very smooth with roughness approximately 0.26 nm. The minimum resistivity of the films can be as low as 45 μΩ cm. PMID:25324706

  15. Heteroepitaxial growth of TiN film on MgO (100) by reactive magnetron sputtering.

    PubMed

    Chen, Wei-Chun; Peng, Chun-Yen; Chang, Li

    2014-01-01

    TiN thin films were deposited on MgO (100) substrates at different substrate temperatures using rf sputtering with Ar/N2 ratio of about 10. At 700°C, the growth rate of TiN was approximately 0.05 μm/h. The structural and electrical properties of TiN thin films were characterized with x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Hall measurements. For all deposition conditions, XRD results show that the TiN films can be in an epitaxy with MgO with cube-on-cube orientation relationship of (001)TiN // (001)MgO and [100]TiN // [100]MgO. TEM with selected-area electron diffraction pattern verifies the epitaxial growth of the TiN films on MgO. SEM and AFM show that the surface of the TiN film is very smooth with roughness approximately 0.26 nm. The minimum resistivity of the films can be as low as 45 μΩ cm.

  16. The study of origin of interfacial perpendicular magnetic anisotropy in ultra-thin CoFeB layer on the top of MgO based magnetic tunnel junction

    NASA Astrophysics Data System (ADS)

    Li, Zhi-Peng; Li, Shaoping; Zheng, Yuankai; Fang, Jason; Chen, Lifan; Hong, Liang; Wang, Haifeng

    2016-10-01

    A comprehensive microstructure study has been conducted experimentally for identifying the origin or mechanism of perpendicular magnetic anisotropy (PMA) in the ultra-thin (10 Å) CoFeB layer on the top of magnetic tunnel junction (MTJ). The high resolution transmission electron microscopy reveals that the feature of crystal structure in 10 Å-CoFeB layer is localized in nature at the CoFeB-MgO interface. On the other hand, the strain-relaxed crystalline structure is observed in the thick CoFeB (20 Å) layer at the CoFeB-MgO interface, associated with a series of dislocation formations. The electron energy loss spectroscopy further suggests that the local chemical stoichiometry of the ultra-thin 10 Å-CoFeB layer is notably changed at the CoFeB-MgO interface, compared with an atomic stoichiometry in a thick 20 Å-CoFeB layer. The origin of PMA mechanism is therefore identified experimentally as an interface effect, which can be attributed to a change of local atom bonding or lattice constant of the transition metal at the CoFeB-MgO based MTJ interface. Furthermore, such a local interfacial atom bonding change is seemly induced by the localized anisotropic strain and consistent with previous theoretical speculations and calculations. The observed experimental findings provide some perspective on microstructure and chemistry on PMA in ultra-thin CoFeB film at the MTJ interface, then deepening our understanding of the mechanism of PMA within MTJ stack and thus facilitating advancement for emerging spintronics technology.

  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. Effect of MgO spacer and annealing on interface and magnetic properties of ion beam sputtered NiFe/Mg/MgO/CoFe layer structures

    SciTech Connect

    Bhusan Singh, Braj; Chaudhary, Sujeet

    2012-09-15

    The effect of variation in the thickness of ion assisted ion beam sputtered MgO spacer layer deposited at oxygen ion assisted energy of 50 eV on the extent of magnetic coupling of NiFe and CoFe layers in Si/NiFe(10 nm)/Mg(1 nm)/MgO(2,4,6 nm)/CoFe(10 nm) sandwich structure is investigated. At MgO spacer layer thickness of 4 nm, the separate reversal of magnetizations of the two ferromagnetic layers is observed in the hystresis loop recorded along easy direction. This results in a 3.5 Oe wide plateau like region during magnetization reversal, which became 4.5 Oe at 6 nm thin MgO. At 2 nm thin MgO, the absence of plateau during magnetization reversal region revealed ferromagnetic coupling between the two ferromagnetic layers, which is understood to arise due to the growth of very thin and low density (1.22 gm/cc) MgO spacer layer, indicating the presence of pinholes as revealed by x-ray reflectometry. After vaccum annealing (200 Degree-Sign C/1 h), the plateau region for 4 and 6 nm thin MgO case decreased to 1.5 Oe and 2.0 Oe, respectively, due to enhanced interface roughness/mixing. In addition, an enhancement of the in-plane magnetic anisotropy is also observed.

  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

    2016-07-01

    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.

  20. Preparation and characterization of MgO nanorods coated with SnO2.

    PubMed

    Kim, Hyunsu; Jin, Changhyun; Kim, Hyoun Woo; Lee, Chongmu

    2012-05-01

    MgO nanorods have been grown by thermal evaporation of Mg3N2 powders on Si (100) substrates coated with gold (Au) thin films. The MgO nanorods grown on Al2O3 (0001) were 0.1-0.2 microm in diameter and up to a few tens of micrometers in length. MgO/SnO2 coaxial nanorods have also been prepared by atomic layer deposition (ALD) of SnO2 onto the nanorods. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis results indicate that the MgO-cores and the SnO2 shells of the annealed coaxial nanorods are of a single crystalline nature with cubic and orthorhombic structures, respectively. The photoluminescence (PL) spectroscopy analysis results show that SnO2 coating slightly increases the PL emission intensity of MgO nanorods. The PL emission of the SnO2-coated MgO nanorods is found to be considerably enhanced by thermal annealing and to strongly depend on the annealing atmosphere. The PL emission intensity of the MgO/SnO2 coaxial nanorods has been significantly increased by annealing in a reducing atmosphere. The origin of the PL enhancement by annealing in a reducing atmosphere is discussed on the basis of energy-dispersive X-ray spectroscopy analyses.

  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. 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.

  3. 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.

  4. Formation mechanism, degradation behavior, and cytocompatibility of a nanorod-shaped HA and pore-sealed MgO bilayer coating on magnesium.

    PubMed

    Li, Bo; Han, Yong; Qi, Kai

    2014-10-22

    A novel bilayer coating (HT24h) was fabricated on magnesium using microarc oxidation (MAO) and hydrothermal treatment (HT). The coating comprises an outer layer of narrow interrod spaced hydroxyapatite (HA) nanorods and an inner layer of MgO containing Mg(OH)2/HA-sealing-pores. The hydrothermal formation mechanism of HA nanorods on MAO-formed MgO was explored. Also, evolution of structure and bonding integrity of HT24h coating with immersion in physiological saline (PS) for 0-90 days, corrosion resistance and cytocompatibility of the coating were investigated, together with MgO containing Mg(OH)2-sealing-pores (HT2h) and porous MgO (MAO) coatings. Corrosion resistance was identified by three-point bending and electrochemical tests in PS, while cytocompatibility was determined by MTT, live/dead staining, and vinculin-actin-nucleus tricolor staining assays of hFOB1.19 cells. Immersion tests indicate that cracking rather than delamination is a common feature in most areas of the coatings up to day 90 and degradation is the reason for thinning in thickness of the coatings. MAO and HT2h coatings exhibit a significant thinning due to fast degradation of MgO. However, HT24h coating shows a quite small thinning, owing to the fact that the HA nanorods underwent quite slow degradation while the underlying MgO only underwent conversion to Mg(OH)2 without dissolution of the Mg(OH)2. Scratch tests reveal that HT24h coating still retains relatively high bonding integrity, although the failure position changes from the MgO interior to a point between the HA and MgO layers after 90 days of immersion. HT24h coating appears far more effective than MAO and HT2h coatings in reducing degradation and maintaining the mechanical integrity of Mg, as well as enhancing the mitochondrial activity, adhesion, and proliferation of osteoblasts.

  5. 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.

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

    SciTech Connect

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

    2013-04-28

    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 Co{sub 40}Fe{sub 40}B{sub 20} 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 Degree-Sign C results in the presence of B in the trigonal coordination of [BO{sub 3}]{sup 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.

  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. Probing specific oxides as potential supports for metal/oxide model catalysts: MgO(111) polar film

    NASA Astrophysics Data System (ADS)

    Grigorkina, G. S.; Ramonova, A. G.; Kibizov, D. D.; Kozyrev, E. N.; Zaalishvili, V. B.; Fukutani, K.; Magkoev, T. T.

    2017-05-01

    The growth of thermally evaporated magnesium oxide thin film on Mo(110) substrate in ultra-high vacuum was studied by means of Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and work function (WF) measurements. It is shown that at a growth rate of c.a. 0.1 monolayer per minute and the substrate temperature of 600 K the film acquires the MgO(111) structure. This structure begins to form at two monolayers and holds up to six monolayers. At higher thickness the film disorders due to weakening of the ordering effect of the isosymmetric Mo(110) support. Adsorption of CO and H2 on the formed MgO(111) film cooled down to 90 K was studied by means of ultraviolet photoelectron spectroscopy (UPS) and reflection absorption infrared spectroscopy (RAIRS) and compared with in-situ obtained results for CO on Pt(111). Comparison of UPS data of CO on MgO(111) and Pt(111) in combination with RAIRS results reveals quite different bonding mechanisms on the metal and the oxide supports. The main feature of CO on MgO(111) is quite high intensity of CO stretch vibration, considerably exceeding that on amorphous MgO, and comparable to that of CO on Pt(111). This is presumably due to the electrostatic effect of the uncompensated microscopic dipole moment of ultrathin MgO(111) film on the enhancing of CO dynamical dipole moment. Adsorption of H2 dramatically reduces the CO stretch intensity as a possible result of removing of dipole moment of MgO(111) surface by hydrogen and (CO+H2) interaction.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

    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.

  12. 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

    2015-12-04

    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.

  13. 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.

  14. 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.

  15. -MgO Melt by Super Gravity

    NASA Astrophysics Data System (ADS)

    Li, Juncheng; Guo, Zhancheng; Gao, Jintao; Li, Jingwei

    2014-08-01

    Perovskite phase was successfully separated from CaO-TiO2-SiO2-Al2O3-MgO melt by super gravity. Under the hypothesis that the titanium exists in the slag in terms of TiO2, with the gravity coefficient G = 600, time t = 5 minutes, and temperature T = 1563 K (1290 °C), the mass fraction of TiO2 in the concentrate is up to 52.94 pct, while that of the tailing is just 5.88 pct. The recovery ratio of Ti in the concentrate is up to 81.28 pct by centrifugal separation.

  16. 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.

  17. WIPP Magnesium Oxide (MgO) - Planned Change Request

    EPA Pesticide Factsheets

    On April 10, 2006, the DOE submitted a planned change request pertaining to the amount of MgO emplaced in the WIPP repository. MgO is an engineered barrier that DOE included as part of the original WIPP Certification Decision.

  18. 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.

  19. Amorphisation of MgO single crystal specimens prepared by ion milling for transmission electron microscopy studies.

    PubMed

    Khan, M Y; Brown, L M; Chaudhri, M M

    1990-08-01

    Single crystal MgO specimens having low load Vickers indentations were thinned in an ion milling machine employing a single ion gun, and their characteristics were investigated with optical microscopy and high voltage electron microscopy (HVEM). It was found that the state of cleanliness of the specimen chamber of the ion milling machine had a very marked influence on the quality of the thinned specimens. If the specimen chamber was not well cleaned before ion milling a fresh specimen, the latter tended to show amorphisation due to the deposition on the specimen of the debris left in the chamber from the previously ion-milled specimens. Such observations were made from MgO specimens ion milled in several different types of commercial ion milling machine employing a single gun. It is proposed that to obtain good-quality ion milled TEM specimens, it is important to clean the specimen chamber thoroughly prior to milling.

  20. Antioxidant status in MgO nanoparticle-exposed rats.

    PubMed

    Kiranmai, G; Reddy, A Rama Narsimha

    2013-11-01

    In this present study, antioxidant status was evaluated in rat serum following exposure to magnesium oxide (MgO) nanoparticles. The lungs of rats were intratracheally instilled with (single dose) phosphate-buffered saline (PBS) + 1% of Tween 80 (solvent control) or MgO or carbonyl iron (negative control) or quartz particles (positive control) at a dose of 1 and 5 mg/kg of body weight. The blood samples were collected at 1, 7, and 30 days of postinstillation of nanoparticles after their exposure, and different parameters were estimated to assess the oxidative stress induced by the instillation of MgO. Exposure of rats to MgO produced a significant (p < 0.05) dose-dependent reduction in blood total antioxidant capacity, superoxide dismutase, and catalase activity levels than PBS + 1% Tween 80 control group. This reduction in the antioxidant capacity in MgO nanoparticle-exposed rats indicates the reduction in antioxidant defense mechanisms due to the instillation of MgO. These results indicate that exposure to MgO nanoparticles induces oxidative stress by reducing the total antioxidant capacity in rats. The findings suggest possible occupational health hazard in chronic exposures.

  1. Interaction of free-base tetraphenylporphyrin with magnesium oxide: Influence of MgO morphology on metalation.

    PubMed

    Di Filippo, Gianluca; Classen, Andrej; Pöschel, Rebecca; Fauster, Thomas

    2017-02-14

    Using x-ray photoemission spectroscopy, we investigated the self-metalation of free-base tetraphenylporphyrin (2HTPP) on thin MgO(100) films on Ag(100). The deposition of one monolayer 2HTPP on MgO results in the formation of magnesium(ii) tetraphenylporphyrin (MgTPP) at room temperature. We demonstrate that the efficiency of the reaction drastically depends on the morphology of the oxide layers. The latter is changed by varying the substrate temperature during the oxide growth. We observe the complete metalation of the 2HTPP monolayer when the MgO films are grown at 393 K. The increase of the growth temperature to 573 K leads to the reduction of the percentage of metalated molecules to ∼50%. We ascribe these results to the fact that MgTPP formation takes place through the hydroxilation of steps and defects on the MgO surface, which leads to an increase of the OH component in the O 1s line.

  2. Interaction of free-base tetraphenylporphyrin with magnesium oxide: Influence of MgO morphology on metalation

    NASA Astrophysics Data System (ADS)

    Di Filippo, Gianluca; Classen, Andrej; Pöschel, Rebecca; Fauster, Thomas

    2017-02-01

    Using x-ray photoemission spectroscopy, we investigated the self-metalation of free-base tetraphenylporphyrin (2HTPP) on thin MgO(100) films on Ag(100). The deposition of one monolayer 2HTPP on MgO results in the formation of magnesium(ii) tetraphenylporphyrin (MgTPP) at room temperature. We demonstrate that the efficiency of the reaction drastically depends on the morphology of the oxide layers. The latter is changed by varying the substrate temperature during the oxide growth. We observe the complete metalation of the 2HTPP monolayer when the MgO films are grown at 393 K. The increase of the growth temperature to 573 K leads to the reduction of the percentage of metalated molecules to ˜50 % . We ascribe these results to the fact that MgTPP formation takes place through the hydroxilation of steps and defects on the MgO surface, which leads to an increase of the OH component in the O 1s line.

  3. 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…

  4. 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,…

  5. Magnetic behavior of Co and Ni implanted MgO

    NASA Astrophysics Data System (ADS)

    Cruz, M. M.; da Silva, R. C.; Pinto, J. V.; González, R. Gonzalez; Alves, E.; Godinho, M.

    2004-05-01

    Single crystals of MgO were implanted with high doses of Co and Ni ions, aiming at the possibility of producing colloidal dispersions of metallic precipitates. Post-implantation annealing in vacuum is used to promote the diffusion of the implanted ions and the recovery of the MgO lattice. Results of magnetization measurements as a function of temperature and magnetic field are presented and correlated with information obtained by Rutherford backscattering measurements in the same samples.

  6. 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.

  7. 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.

  8. Interlayer exchange coupling, dipolar coupling and magnetoresistance in Fe/MgO/Fe trilayers with a subnanometer MgO barrier

    NASA Astrophysics Data System (ADS)

    Kozioł-Rachwał, A.; Skowroński, W.; Frankowski, M.; Chęciński, J.; Ziętek, S.; Rzeszut, P.; Ślęzak, M.; Matlak, K.; Ślęzak, T.; Stobiecki, T.; Korecki, J.

    2017-02-01

    Fe/MgO/Fe trilayers with a subnanometer MgO tunnel barrier were grown by molecular beam epitaxy. Longitudinal magnetooptic Kerr effect measurements confirmed the existence of the antiferromagnetic interlayer exchange coupling (IEC) between the Fe layers for 2 ÅMgO buffer layer, and its IEC constant was estimated to be -3.3 erg/cm2 at a MgO thickness of 2.7 Å. After magnetic characterization, the sample was patterned into circular-shaped pillars with diameters ranging from 200 nm to 520 nm. We showed that the dipolar coupling that appeared after the nanofabrication process modified the effective coupling between layers, and we determined dependence of the dipolar coupling on the pillar diameter. Finally, magnetoresistance (MR) was measured as a function of MgO thickness (dMgO), and a non-zero MR was found for the MgO as thin as 3.4 Å. Extrapolation of the MR (dMgO) dependence to MR=0 allowed us to determine the length of the pinholes in our sample, which was estimated to be (3.2±0.5) Å.

  9. 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.

  10. Multifunctional MgO Layer in Perovskite Solar Cells.

    PubMed

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

    2015-06-08

    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.

  11. 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.

  12. Use of porous MgO in pyrochemical applications

    SciTech Connect

    Maiya, P.S.; Sweeney, S.M.; Carroll, L.A.; Dusek, J.T.

    1994-11-01

    Pyrochemical methods for the extraction of transuranic elements from light water reactor spent fuel require a reduction step in which the oxide fuel is reduced to metals by Li in molten LiCl. The Li{sub 2}O formed is electrolytically reduced to metal in a cell that uses a carbon (or inert) anode and a Li cathode to recycle the salt and minimize the waste. Use of a carbon anode causes carbon dust that interferes with the process. Moreover, current efficiency is reduced as a result of oxidation of Li to Li{sub 2}O by CO{sub 2}. A porous MgO shroud around the anode was found to obviate these problems. Porous MgO crucibles and rectangular bar specimens were fabricated from MgO powders (electrically fused MgO, reagent grade MgO were mixed in appropriate combinations with a binder and lubricant). Particle size, force applied to the powders during cold pressing, and sintering temperature were varied to achieve a total porosity of >45% (mostly open porosity) and to control pore size and pore distribution. Mercury intrusion porosimetry was used to determine the pore size and pore size distribution. Flexural strength is observed to be proportional to the square root of pore size, which is consistent with fracture mechanics.

  13. Molecular dynamics simulation of Pd clusters colliding onto MgO(0 0 1) surface

    NASA Astrophysics Data System (ADS)

    Long, Y.; Chen, N. X.

    2008-11-01

    The atomistic simulation of metal clusters colliding onto oxide surface is a challenge in surface science and technology. It requires a reasonable way to get the interatomic potentials for the metal-oxide system. In this work, we use a Chen-Möbius inversion method to extract the atom-atom, atom-ion and ion-ion potentials from ab initio cohesive and adhesive energies. Based on these potentials, the dynamic process of Pd cluster colliding onto MgO(0 0 1) surface is studied by molecular dynamics. The simulation result shows that there are three kinds of collision processes say “adsorption”, “reflection” and “penetration” correspond to low, middle and high incident energies, respectively. In addition, in the case of “adsorption”, the resultant cluster structure is strongly dependent on the incident energy. In summary, our work gives a good qualitative understanding of Pd cluster colliding onto MgO(0 0 1) surface with some interesting predictions. These results might be helpful to the techniques of thin film growth and surface cleaning as well as the related physics.

  14. Electronic structure of Gd-doped MgO

    NASA Astrophysics Data System (ADS)

    Lukoyanov, A. V.; Anisimov, V. I.

    2016-02-01

    The electronic structure of Gd-doped MgO is investigated using the LSDA+U (local spin density approximation with U-correction) method and compared with the MgO structure. The total density of states obtained accounting for the correlation effects in the 4 f shell of gadolinium is found to be formed by the oxygen 2 p states at the valence band and the 4 f gadolinium occupied states, while the conduction band is represented by a mixture of empty electronic states. Magnetic properties of the calculated Gd-doped MgO are found to be formed solely by the Gd-4 f-magnetic moment of about 7μB, in good agreement with recent experimental results suggesting a ferromagnetic coupling of the local magnetic moments induced by Gd.

  15. CVD synthesis of graphene nanoplates on MgO support

    NASA Astrophysics Data System (ADS)

    Jugade, Ravin M.; Sharma, Shalini; Gokhale, Suresh

    2014-06-01

    Synthesis of graphene directly on MgO has been carried out and the structural properties of the obtained material have been investigated. Few-layered graphene was produced by simple thermal decomposition of methane over MgO powder at 950 °C in a CVD reactor. The samples were purified by 10 N HNO3 treatment, and studied by TEM, Raman spectroscopy, EDAX and SEM. TEM clearly indicated the formation of graphene. EDAX showed that the purified sample contained only carbon and no traces of MgO. The characteristic Raman features of graphene were also seen as D-band at 1316 cm-1, G-band at 1602 cm-1, and a small 2D-band at 2700 cm-1 in the Raman spectra. The strong D-band suggests that the graphene possess large number of boundary defects. The small 2D-band indicates the formation of few-layered graphene.

  16. 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.

  17. 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.

  18. Enhanced moments in bcc Co1-xMnx on MgO(001)

    NASA Astrophysics Data System (ADS)

    Snow, R. J.; Bhatkar, H.; N'Diaye, A. T.; Arenholz, E.; Idzerda, Y. U.

    2016-12-01

    A 40% enhancement of the Co magnetic moment has been found for thin films of bcc Co1-xMnx grown by molecular beam epitaxy on a 2 nm bcc Fe buffer layer on MgO(001). Although the bcc phase cannot be stabilized in the bulk, we confirm that it is stable as an epitaxial film in the composition range x=0-0.7. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism, we show that the Co moment is a maximum of 2.38 μB at x=0.24, while the net Mn moment remains roughly constant until x=0.24, then drops steadily. Mn is found to align parallel with Co for all ferromagnetic concentrations, up to x=0.7, where the total moment of the film abruptly collapses to zero, most likely due to the onset of the observed structural instability.

  19. 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

  20. Electrical conductivity of MgO crystals implanted with lithium ions

    NASA Astrophysics Data System (ADS)

    Tardío, M.; Ramírez, R.; González, R.; Chen, Y.; Alves, E.

    2002-05-01

    MgO single crystals were implanted with a fluence of 1×10 17 Li +/cm 2 with 175 keV. Using ac and dc techniques, the electrical conductivity of these crystals was investigated in the temperature range 296-440 K. The electrical conductivity of the implanted region was 14 orders of magnitude higher than the unimplanted area. Measurements at different temperatures suggest a thermally activated process with an activation energy of about 0.33 eV. In the implanted area, electrical contacts are found to be ohmic whereas contacts are blocking in unimplanted crystals. Removal of thin layers of the implanted region by immersing the crystal in hot phosphoric acid suggests that the enhancement in conductivity in the implanted region is associated with the intrinsic defects created by the implantation, rather than with the Li ions.

  1. Lectin coated MgO nanoparticle: its toxicity, antileishmanial activity, and macrophage activation.

    PubMed

    Jebali, Ali; Hekmatimoghaddam, Seyedhossein; Kazemi, Bahram; Allaveisie, Azra; Masoudi, Alireza; Daliri, Karim; Sedighi, Najme; Ranjbari, Javad

    2014-10-01

    The purpose of this research was to evaluate toxicity of uncoated magnesium oxide nanoparticles (MgO NPs), MgO NPs coated with Peanut agglutinin (PNA) lectin, and PNA alone on the promastigotes of Leishmania major (L. major) and macrophages of BALB/c mice. On the other hand, antileishmanial property of uncoated MgO NPs, lectin coated MgO NPs, and PNA lectin alone was evaluated, and also macrophage activation was investigated after treatment with these materials by measurement of nitrite, H2O2, and some interleukins. This study showed that PNA lectin and lectin coated MgO NPs had approximately no toxicity on L. major and macrophages, but some toxic effects were observed for uncoated MgO NPs, especially at concentration of 500 µg/mL. Interestingly, lectin coated MgO NPs had the highest antileishmanial activity and macrophage activation, compared with uncoated MgO NPs and PNA lectin.

  2. Enhanced boron adsorption onto synthesized MgO nanosheets by ultrasonic method.

    PubMed

    Li, Ping; Liu, Chuang; Zhang, Li; Zheng, Shili; Zhang, Yi

    2017-01-01

    MgO nanosheets with high adsorption performance were fabricated by an ultrasonic method. It was revealed that, nest-like MgO was formed from the magnesium salt solution precipitation and further calcination. Then the nest-like MgO was exfoliated by ultrasonic waves to obtain MgO nanosheets with approximately a lateral of 200-600nm and a thickness of 10nm. Adjusting the ultrasonic time and power, the specific surface areas of MgO nanosheets could be tuned in a range of 79-168m(2)/g. The synthesized MgO nanosheets were used as adsorbents to remove boron from aqueous solution, and the maximum boron adsorption capacity of these MgO nanosheets reached 87mgg(-1). The high uptake capability of the MgO nanosheets makes it potentially adsorbent for the removal of boron from wastewaters.

  3. Origin of steps in magnetization loops of martensitic Ni-Mn-Ga films on MgO(001)

    NASA Astrophysics Data System (ADS)

    Laptev, Aleksej; Lebecki, Kristof; Welker, Gesa; Luo, Yuansu; Samwer, Konrad; Fonin, Mikhail

    2016-09-01

    We study the temperature dependent magnetization properties of (010)-oriented Ni-Mn-Ga epitaxial films on MgO(001) substrates. In the martensitic phase, we observe pronounced abrupt slope changes in the magnetization loops for all studied samples. Our experimental findings are discussed in conjunction with the micromagnetic simulations, revealing that the characteristic magnetization behavior is governed solely by the magnetization switching within the specific martensitic variant pattern, and no reorientation of twin variants is involved in the process. Our study emphasizes the important role of the magnetostatic interactions in the magnetization behavior of magnetic shape memory alloy thin films.

  4. Structure of Ultrathin MgO Films on Mo(001)

    SciTech Connect

    Gallagher, Marc C.; Fyfield, Margaret S.; Bumm, Lloyd A.; Cowin, James P.; Joyce , Stephen A.

    2003-11-24

    We have studied the structure of ultrathin MgO films grown on a single crystal Mo(001) surface. Scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) were used to investigate the effect of substrate temperature and oxygen partial pressure on the growth and morphology of these films.

  5. Nano-cube MgO formed on silicon substrate using pulsed laser deposition.

    PubMed

    Kaneko, Satoru; Ito, Takeshi; Akiyama, Kensuke; Yasui, Manabu; Hirabayashi, Yasuo; Soga, Masayasu; Miyake, Yumiko; Yoshimoto, Mamoru

    2012-03-01

    Nano-cube MgO particles were formed on Si substrates by deposition of an MgO target using pulsed laser deposition method. An epitaxial film grows on Si(001) substrate with its contraction of lattice constants. In this study, expecting high quality MgO film, the MgO film prepared in the oxygen pressure ranging from 75-400 mTorr at the high temperature of -750 degrees C. The deposited MgO showed the growth of (001) preferred orientation on the Si(001) substrate. However, X-ray Photoelectron Spectroscopy (XPS) indicated the MgO film did not form a continuous film on the Si surface. Interestingly, the surface morphology observed by an Atomic Force Microscopy (AFM) showed nano-cube MgO particles scattered on the smooth surface of Si substrate. After annealing the nano-cube MgO, the shape of MgO particles were changed from nano-cube to round shaped particles. The AFM image of the surface showed round shaped MgO nanoparticles scattered on rough surface. X-ray Diffraction (XRD) revealed the epitaxial growth of MgO(001) with cubic on cubic arrangement on the Si(001) substrate (MgO[100] parallel to Si[100]).

  6. Influence of an MgO interfacial layer on the properties of Pb(Zr,Ti)O3/ZnO ferroelectric-semiconductor heterostructures

    NASA Astrophysics Data System (ADS)

    Xiao, Bo; Walker, Brandon; Pradhan, Aswini K.

    2014-05-01

    We report on the study of high quality Pb(Zr,Ti)O3 thin films grown by radio-frequency magnetron sputtering on (0 0 0 1) ZnO with an MgO interfacial seed layer. A systematic investigation of the heterostructures has been performed by x-ray diffraction, atomic force microscopy (AFM) and ultraviolet-visible spectroscopy for the structural and optical properties, along with the electrical characterization and simulation. (0 1 1)-oriented perovskite phase was observed in Pb(Zr,Ti)O3 thin films which used the MgO seed layer, whereas the pyrochlore phase was dominant in the films deposited directly on ZnO. The surface morphology measured by AFM indicated that the introduction of the MgO interfacial seed layer promoted formation of a smooth surface and uniform grain structures in the thin films. The transmission spectra also showed an increase of the optical transmittance measured by ultraviolet-visible spectroscopy. The capacitance-voltage measurements exhibited butterfly-shaped capacitance curves which bear a resemblance to those of the typical metal-ferroelectric-metal structures. The characteristics of the polarization versus electric field were investigated by a simulation to understand the behaviour of the hysteresis loops in this metal-ferroelectric-insulator-semiconductor structure.

  7. Carbon monoxide MgO from dispersed solids to single crystals: a review and new advances

    NASA Astrophysics Data System (ADS)

    Spoto, G.; Gribov, E. N.; Ricchiardi, G.; Damin, A.; Scarano, D.; Bordiga, S.; Lamberti, C.; Zecchina, A.

    2004-10-01

    In this review we describe 30 years of research on the surface properties of magnesium oxide, considered as the model prototype oxide of cubic structure. The surface properties of single crystals, thin films and powdered samples (sintered at progressive higher temperatures) are considered and compared, with the aim of demonstrating that the gap between “believed perfect” single crystal surfaces, typical of “pure” Surface Science, and high surface area samples, typical of Catalysis Science, can be progressively reduced. The surface features considered in this review are the structural (morphological), optical, absorptive and reactive properties. As the carbon monoxide molecule is able to probe the surface properties of both anions and cations, it can give a complete information of the surface structure of MgO samples. For this reason the adsorption and spectroscopy of this molecule is preferentially considered in this review. Particular emphasis is given in reviewing results obtained by high resolution transmission microscopy and in situ IR spectroscopy of adsorbed species (in both reflection and transmission modes), but also UV-Vis diffuse reflectance, photoluminescence, TDS, EPR, electron based techniques are mentioned. Reviewed experimental results are also commented in view of the important theoretical literature available on this topic and are complemented by new transmission IR data concerning CO adsorbed, down to 60 K, on powdered MgO samples with increasing surface area. These innovative experiments allow us to perform, on powdered samples, the adsorption experiments typical of single crystals (or films) Surface Science, with an increase of the S/N of the vibrational features higher than two order of magnitude. As far the new results (never published before) are concerned, we report IR spectra of CO dosed at 60 K on polycrystalline MgO samples with different surface area obtained by Mg(OH) 2 decomposition and progressive sintering at high temperature

  8. 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.

  9. 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

  10. Sustain and address discharge characteristics of AC-PDP with MgO surface coated by MgO nano crystal powders.

    PubMed

    Kim, J H; Park, C S; Park, H D; Tae, H S; Lee, S H

    2013-05-01

    This paper examined the sustain and address discharge characteristics of ac-PDPs with MgO surface coated by MgO nano crystal powders. The MgO nano crystal powder was deposited by about 5% on the MgO surface by using the spray method. To investigate the effects of the partial addition of MgO nano crystal powders on the sustain discharge as well as the address discharge, the luminance, IR spectra of 823, 828 nm, cathodoluminance, and firing voltage were measured with the measurement of the address delay times and wall voltage variation in the 42-inch ac-PDP module with a high Xe content of 17%. As a result, the statistical delay characteristics were improved considerably especially under the low panel temperature of -5 degrees C for the MgO surface with MgO nano crystal powder. However, both MgO surfaces with and without the MgO nano crystal powder showed almost similar sustain and address discharge characteristics except the statistical delay characteristics.

  11. Ultraintense short-wavelength emission from ZnO-sheathed MgO nanorods induced by subwavelength optical resonance cavity formation: verification of previous hypothesis.

    PubMed

    Jin, Changhyun; Kim, Hyunsu; Lee, Chongmu

    2012-03-01

    A recent paper reported that intense emissions with a range of wavelengths over a wide spectral range, from ultraviolet to infrared light, might be possible by sheathing MgO nanorods with a semiconducting material with an optimal sheath thickness. In addition, the paper hypothesized that an ultraintense short-wavelength emission could be obtained by sheathing MgO nanorods with a ~17 nm ZnO thin film in the paper. In this study, we found that the intensity ratio of the near-band edge emission to the deep level emission (I(NBE)/I(DL)) of the MgO-core/ZnO-shell nanorods with a mean shell layer thickness of 17 nm was as high as ~30, whereas the I(NBE)/I(DL) ratio of the bare-MgO nanorods was 0. This near-band edge emission intensity enhancement by sheathing the MgO nanorods with ZnO is by far more significant than that by sheathing the ZnO nanorods with other materials including MgO. This is because subwavelength optical resonance cavities form in the MgO-core/ZnO-shell nanorods with faceted surfaces, whereas they do not form in the ZnO-core/MgO (or other material)-shell nanorods with no faceted surfaces.

  12. Bulk and surface properties of magnesium peroxide MgO2

    NASA Astrophysics Data System (ADS)

    Esch, Tobit R.; Bredow, Thomas

    2016-12-01

    Magnesium peroxide has been identified in Mg/air batteries as an intermediate in the oxygen reduction reaction (ORR) [1]. It is assumed that MgO2 is involved in the solid-electrolyte interphase on the cathode surface. Therefore its structure and stability play a crucial role in the performance of Mg/air batteries. In this work we present a theoretical study of the bulk and low-index surface properties of MgO2. All methods give a good account of the experimental lattice parameters for MgO2 and MgO bulk. The reaction energies, enthalpies and free energies for MgO2 formation from MgO are compared among the different DFT methods and with the local MP2 method. A pronounced dependence from the applied functional is found. At variance with a previous theoretical study but in agreement with recent experiments we find that the MgO2 formation reaction is endothermic (HSE06-D3BJ: ΔH = 51.9 kJ/mol). The stability of low-index surfaces MgO2 (001) (Es = 0.96 J/m2) and (011) (Es = 1.98 J/m2) is calculated and compared to the surface energy of MgO (001). The formation energy of neutral oxygen vacancies in the topmost layer of the MgO2 (001) surface is calculated and compared with defect formation energies for MgO (001).

  13. Annealing behaviour of defects in helium implanted MgO

    NASA Astrophysics Data System (ADS)

    Schut, H.; Van Veen, A.; Labohm, F.; Fedorov, A. V.; Neeft, E. A. C.; Konings, R. J. M.

    1999-01-01

    Virgin MgO (1 1 0) single crystals have been implanted with 30 keV 3He + ions to a dose of 5 × 10 15 cm -2. After implantation the samples have been annealed under air for 30 min in a tube oven. The annealing behaviour of the defects and 3He has been monitored by three experimental techniques: positron beam Doppler broadening, neutron depth profiling (NDP) and optical absorption in the UV to near-IR region. The observations in MgO lead to the conclusion that below 1000 oC the vacancy like defects are stabilised by the implanted He atoms. Above this temperature He may dissociate from these small defects, allowing the formation of larger vacancy clusters.

  14. Defective non-planar surfaces of MgO

    NASA Astrophysics Data System (ADS)

    Colbourn, E. A.; Kendrick, J.; Mackrodt, W. C.

    1983-03-01

    Defect lattice and ab initio SCF calculations are reported for defective non-planar surfaces of MgO. It is suggested that the concentration of free vacancies and Ca 2+ will be much lower at non-planar irregularities than at planar surfaces and in the bulk, whereas the level of Li + and trapped holes will be higher. The binding of H atoms and CO to three-coordinated comer sites is found to be appreciably higher than to the five-coordinated {001} surface. Thus it is concluded that calcium doping of MgO will affect neither CO chemisorption nor the dissociative chemisorption of hydrogen whereas lithium doping will influence both.

  15. Collisional excitation of MgO by He

    NASA Astrophysics Data System (ADS)

    Mogren Al Mogren, M.; Ajili, Y.; Almania, S.; Ben Abdallah, D.; Hochlaf, M.

    2015-09-01

    Using a well-established ab initio methodology to generate the potential energy surface of the MgO-He interacting system and a quantum close-coupling treatment of nuclear motion, we give the rotational (de-)excitation cross-sections and the collision rate coefficients for the first 16 rotational levels of the MgO molecule and He for temperatures ranging from 10 up to 300 K. A clear propensity rule in favour of Δj = 1 rotational transitions is observed. These data are compared with previous works on astrophysical oxygen-bearing diatomic species. This work should be useful for the eventual detection of the key metal-oxide MgO molecule in the circumstellar and interstellar media with current and future high-resolution telescopes.

  16. 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.

  17. 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. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Enhancement of proton transport in an oriented polypeptide thin film.

    PubMed

    Nagao, Yuki; Matsui, Jun; Abe, Takashi; Hiramatsu, Hirotsugu; Yamamoto, Hitoshi; Miyashita, Tokuji; Sata, Noriko; Yugami, Hiroo

    2013-06-11

    Proton transport properties of a partially protonated poly(aspartic acid)/sodium polyaspartate (P-Asp) were investigated. A remarkable enhancement of proton conductivity has been achieved in the thin film. Proton conductivity of 60-nm-thick thin film prepared on MgO(100) substrate was 3.4 × 10(-3) S cm(-1) at 298 K. The electrical conductivity of the oriented thin film was 1 order of magnitude higher than the bulk specimen, and the activation energies for the proton conductivity were 0.34 eV for the oriented thin film and 0.65 eV for the pelletized sample, respectively. This enhancement of the proton transport is attributable to the highly oriented structure on MgO(100) substrate. This result proposes great potential for a new strategy to produce a highly proton-conductive material using the concept of an oriented thin film structure without strong acid groups.

  19. Oxygen-vacancy driven tunnelling spintronics across MgO

    NASA Astrophysics Data System (ADS)

    Halisdemir, U.; Schleicher, F.; Kim, D. J.; Taudul, B.; Lacour, D.; Choi, W. S.; Gallart, M.; Boukari, S.; Schmerber, G.; Davesne, V.; Panissod, P.; Halley, D.; Majjad, H.; Henry, Y.; Leconte, B.; Boulard, A.; Spor, D.; Beyer, N.; Kieber, C.; Sternitzky, E.; Cregut, O.; Ziegler, M.; Montaigne, F.; Arabski, J.; Beaurepaire, E.; Jo, W.; Alouani, M.; Gilliot, P.; Hehn, M.; Bowen, M.

    2016-10-01

    The conservation of an electron's spin and symmetry as it undergoes solid-state tunnelling within magnetic tunnel junctions (MTJs) is thought to be best understood using MgO-based MTJs1. Yet the very large experimental values of tunnelling magnetoresistance (TMR) that justify this perception are often associated with tunnelling barrier heights well below those suggested by the MgO optical band gap. This combination of high TMR and low RA-product, while spawning spin-transfer/spin-orbit torque experiments and considerable industrial interest, cannot be explained by standard theory. Noting the impact of a tunnel barrier's altered stoichiometry on TMR2, we reconcile this 10+year-old contradiction between theory and experiment by considering the impact of the MgO barrier's structural defects3-5. We find that the ground and excited states of oxygen vacancies can promote localized states within the band gap with differing electronic character. By setting symmetry- and temperature-dependent tunnelling barrier heights, they alter symmetry-polarized tunnelling and thus TMR. We will examine how annealing, depending on MgO growth conditions, can alter the nature of these localized states. This oxygen vacancy paradigm of inorganic tunnelling spintronics opens interesting perspectives into endowing the MTJ with additional functionalities, such as optically manipulating the MTJ's spintronic response.

  20. 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.

  1. Cytotoxic effects of MgO nanoparticles on human umbilical vein endothelial cells in vitro.

    PubMed

    Ge, S; Wang, G; Shen, Y; Zhang, Q; Jia, D; Wang, H; Dong, Q; Yin, T

    2011-06-01

    The MgO nanoparticles are widely used in many fields. However, the toxicity of these nanoparticles to cells and organs remains fairly undiscovered. In this study, the cytotoxicity of MgO nanoparticles on human umbilical vein endothelial cells (HUVECs) in vitro was examined. The morphology and size of MgO nanoparticles were analysed by the transmission electron microscope (TEM) and nanoparticle size analyser. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2 h-tetrazolium bromide) assay, 4',6-diamidino-2-phenylindole (DAPI) staining analysis, NO release and total antioxidation competence (T-AOC) assay were used to evaluate the cytotoxicity of MgO nanoparticles. The results showed that most MgO nanoparticles were spherical with agglomerated state and the diameter of single particle was about 100 nm. Meanwhile, low concentration (below 200 [micro sign]g/ml) of MgO nanoparticles suspension showed no cytotoxicity by MTT assay. However, once the concentration of MgO nanoparticles was higher than 500 [micro sign]g/ml, the relative growth rate was lower than the control. The DAPI staining analysis results showed no significant difference of the cells morphology between the groups with or without MgO nanoparticles. In addition, the MgO nanoparticles significantly enhanced the NO release and T-AOC content of the HUVECs. The testing results indicated that low concentration of MgO nanoparticles exhibited non-cytotoxicity.

  2. Integration of Ferroelectric/Semiconductor Thin Films for SLM and Photorefractive Applications

    DTIC Science & Technology

    1993-08-09

    multilayer devices is excellent. In another approach, doped grain oriented PLZT and BaTiO3 thin films have been fabricated on SBN substrates. Because of the...films on (a) SrTiO3 and (b) MgO substrates with an intervening LSC layer ................................... 12 3.7 Temperature dependence of the...Films ........................................... 10 3.4 Properties of PZT Films Grown on SBN, SrTiO3 and MgO Substrates... 15 Oil% Rockwell Intemational

  3. 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.

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

    NASA Astrophysics Data System (ADS)

    Jin, Tony; He, Yiping

    2011-12-01

    The antibacterial activities of magnesium oxide nanoparticles (MgO NP) alone or in combination with other antimicrobials (nisin and ZnO NP) against Escherichia coli O157:H7 and Salmonella Stanley were investigated. The results show that MgO NP have strong bactericidal activity against the pathogens, achieving more than 7 log reductions in bacterial counts. The antibacterial activity of MgO NP increased as the concentrations of MgO increased. A synergistic effect of MgO in combination with nisin was observed as well. However, the addition of ZnO NP to MgO NP did not enhance the antibacterial activity of MgO against both pathogens. Scanning electron microscopy was used to characterize the morphological changes of E. coli O157:H7 before and after antimicrobial treatments. It was revealed that MgO NP treatments distort and damage the cell membrane, resulting in a leakage of intracellular contents and eventually the death of bacterial cells. These results suggest that MgO NP alone or in combination with nisin could potentially be used as an effective antibacterial agent to enhance food safety.

  5. Crystal structure of MgO along the shock Hugoniot

    NASA Astrophysics Data System (ADS)

    Smith, R.; Wicks, J. K.; Kraus, R. G.; Eggert, J.; Coppari, F.; Newman, M.; Millot, M. A.; Duffy, T. S.

    2016-12-01

    As many as 30% of main sequence stars are estimated to have planetary companions. Of the more than 6000 confirmed and candidate extrasolar planets discovered to date those that are 1-4 times the radius of the Earth are now known to be the most abundant. Determining the interior structure and composition of exoplanets is challenging but is key to understanding the diversity and evolution of planetary systems. The silicate compounds that dominate the Earth's mantle likely dissociate into component oxides at the extreme pressures (200-2000 GPa) and temperatures (5000-10000 K) existing in super-Earth mantles. Magnesium oxide (periclase), an end-member of the ferropericlase solid solution (Mg,Fe)O and an important component the Earth's mantle, has been thoroughly studied under static compression in the pressure and temperature range found within the Earth ( 135 GPa, 2500-4000K). However, as static compression techniques are typically limited to peak pressures of < 200 GPa, much less is known about its behavior under high-pressure and -temperature conditions. In our experiments, the structure of MgO upon shock compression over the 200-700 GPa pressure range was interrogated at the Omega-EP Laser facility at the Laboratory for Laser Energetics, University of Rochester. Laser drives of up to 2 kJ over 10 ns focused onto a polyimide ablator were used to shock compress 50-um thick polycrystalline or single-crystal MgO. Scattered He-α X-rays from an Cu backlighter timed with maximum compression were collected using the PXRDiP diagnostic, in which image plates line the inner walls of a box attached to the target package. Along the shock Hugoniot MgO transforms from a B1-B2 phase transformation at 400 GPa and B2-liquid at 700 GPa. For each pressure we measure pressure (velocity interferometry), density (x-ray diffraction) and shock temperature (pyrometry).

  6. Adsorption of Ar on a nonuniform MgO surface

    NASA Technical Reports Server (NTRS)

    Hinman, D. C.; Halsey, G. D.

    1976-01-01

    Data are presented for the adsorption of Ar and N2 on a strongly heterogeneous MgO surface at 84 K and for Ar at a range of temperatures between 130 and 250 K. The high-temperature data are analyzed according to a model which separates the contributions to the potential into bulk and surface terms, providing a method for the determination of the surface area from parameters characteristic of the bulk material. A solid-gas energy parameter and parameters indicating the strength of the impurity sites are also evaluated.

  7. The low-lying electronic states of MgO

    NASA Astrophysics Data System (ADS)

    Bauschlicher, Charles W.; Schwenke, David W.

    2017-09-01

    The low-lying singlet and triplet states of MgO have been studied using a SA-CASCF/IC-MRCI approach using the aug-cc-pV5Z basis set. The spectroscopic constants (re,ωe , and Te) are in good agreement with the available experimental data. The computed lifetime for the B state is in excellent agreement with two of the three experimental results. The d state lifetime is in good agreement with experiment, while the computed D state lifetime is about twice as long as experiment.

  8. Solution-processed high-k magnesium oxide dielectrics for low-voltage oxide thin-film transistors

    NASA Astrophysics Data System (ADS)

    Jiang, Guixia; Liu, Ao; Liu, Guoxia; Zhu, Chundan; Meng, You; Shin, Byoungchul; Fortunato, Elvira; Martins, Rodrigo; Shan, Fukai

    2016-10-01

    Solution-processed metal-oxide thin films with high dielectric constants (k) have been extensively studied for low-cost and high-performance thin-film transistors (TFTs). In this report, MgO dielectric films were fabricated using the spin-coating method. The MgO dielectric films annealed at various temperatures (300, 400, 500, and 600 °C) were characterized by using thermogravimetric analysis, optical spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and atomic-force microscopy. The electrical measurements indicate that the insulating properties of MgO thin films are improved with an increase in annealing temperature. In order to clarify the potential application of MgO thin films as gate dielectrics in TFTs, solution-derived In2O3 channel layers were separately fabricated on various MgO dielectric layers. The optimized In2O3/MgO TFT exhibited an electron mobility of 5.48 cm2/V s, an on/off current ratio of 107, and a subthreshold swing of 0.33 V/dec at a low operation voltage of 6 V. This work represents a great step toward the development of portable and low-power consumption electronics.

  9. Monolayer alkali and transition-metal monoxides: MgO, CaO, MnO, and NiO

    NASA Astrophysics Data System (ADS)

    Shayeganfar, F.; Vasu, K. S.; Nair, R. R.; Peeters, F. M.; Neek-Amal, M.

    2017-04-01

    Two-dimensional crystals with strong interactions between layers has attracted increasing attention in recent years in a variety of fields. In particular, the growth of a single layer of oxide materials (e.g., MgO, CaO, NiO, and MnO) over metallic substrates were found to display different physical properties than their bulk. In this study, we report on the physical properties of a single layer of metallic oxide materials and compare their properties with their bulk and other two-dimensional (2D) crystals. We found that the planar structure of metallic monoxides are unstable whereas the buckled structures are thermodynamically stable. Also, the 2D-MnO and NiO exhibit different magnetic (ferromagnetic) and optical properties than their bulk, whereas band-gap energy and linear stiffness are found to be decreasing from NiO to MgO. Our findings provide insight into oxide thin-film technology applications.

  10. Mechanisms of antibacterial activity of MgO: non-ROS mediated toxicity of MgO nanoparticles towards Escherichia coli.

    PubMed

    Leung, Yu Hang; Ng, Alan M C; Xu, Xiaoying; Shen, Zhiyong; Gethings, Lee A; Wong, Mabel Ting; Chan, Charis M N; Guo, Mu Yao; Ng, Yip Hang; Djurišić, Aleksandra B; Lee, Patrick K H; Chan, Wai Kin; Yu, Li Hong; Phillips, David Lee; Ma, Angel P Y; Leung, Frederick C C

    2014-03-26

    The toxicity of metal oxide nanomaterials and their antimicrobial activity is attracting increasing attention. Among these materials, MgO is particularly interesting as a low cost, environmentally-friendly material. The toxicity of MgO, similar to other metal oxide nanomaterials, is commonly attributed to the production of reactive oxygen species (ROS). We investigated the toxicity of three different MgO nanoparticle samples, and clearly demonstrated robust toxicity towards Escherichia coli bacterial cells in the absence of ROS production for two MgO nanoparticle samples. Proteomics data also clearly demonstrate the absence of oxidative stress and indicate that the primary mechanism of cell death is related to the cell membrane damage, which does not appear to be due to lipid peroxidation.

  11. Enhanced Luminescence in Epitaxial Oxide Thin-Film Phosphors

    SciTech Connect

    Lee, Y.E.; Norton, D.P.; Budai, J.D.; Park, C.; Kim, M.; Pennycook, S.J.; Rack, P.D.; Potter, M.D.

    1999-11-08

    Undoped and Mn-doped ZnGa{sub 2}O{sub 4} thin-film phosphors were grown using pulsed laser ablation on (100) MgO single crystal and glass substrates. X-ray results showed the films on (100) MgO are well aligned both out-of plane and in-plane. Epitaxial films show superior photoluminescent intensity as compared to randomly oriented polycrystalline films, indicating that intragranular crystallinity strongIy influences luminescent properties. Li-doped ZnGa{sub 2}O{sub 4} exhibited significantly enhanced photoluminescence intensity.

  12. 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

  13. Influence of oxygen content on the crystallinity of MgO layers in magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Yongle, Lou; Yuming, Zhang; Daqing, Xu; Hui, Guo; Yimen, Zhang; Yuchen, Li

    2014-08-01

    With RF sputtering process, Si/SiO2/Ta/Ru/Ta/CoFeB/MgO/CoFeB/Ta/Ru structure has been grown on Si (100) substrate. Attempting different targets and adjusting the oxygen dose, the crystallization quality of the MgO layer is studied. The X-ray diffraction measurements demonstrate that crystal structure and crystallization quality of MgO layers are related to the type of target and concentration of oxygen in sputtering process. With the method sputtering Mg in an ambient flow of oxygen, not only the crystallization quality of a normal MgO layer with lattice constant of 0.421 nm is improved, but also a new MgO crystal with lattice constant of 0.812 nm is formed and the perpendicular magnetic anisotropy of CoFeB is enhanced. Also it is found that crystallization quality for both the normal MgO and new MgO is more improved with MgO target and same oxygen dose, which means that this new method is helpful to form a new structure of MgO with lattice constant of 0.812 nm. All of the samples were annealed at 400 °C in vacuum.

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

    USDA-ARS?s Scientific Manuscript database

    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...

  15. Ultrathin hexagonal MgO nanoflakes coated medical textiles and their enhanced antibacterial activity

    NASA Astrophysics Data System (ADS)

    Veeran Ponnuvelu, Dinesh; Selvaraj, Aravind; Prema Suriyaraj, Shanmugam; Selvakumar, Rajendran; Pulithadathail, Biji

    2016-10-01

    A facile hydrothermal method for development of ultrathin MgO nanoplates from different precursors and their enhanced antibacterial activity after coating onto medical textiles is reported. Ultrathin MgO nanoplates having hexagonal structure were characterized using UV-visible spectroscopy, atomic force microscopy, field emission scanning electron microscopy, x-ray diffraction and high resolution transmission electron microscopy. The formation of MgO nanoplates was found to exhibit profound anionic effect leading to ultrathin, planar structures with exposed MgO [111] facets, which may be responsible for enhanced antimicrobial activity. Medical fabrics (bleached 100% cotton) were coated with MgO nanoplates using pad-dry-cure method. The antibacterial activity of these fabrics was tested against Bacillus subtilis and Escherichia coli. The MgO nanoplates coated onto the fabric were found to have good adherence properties owing to their two-dimensional structure and were durable even after repeated washings without substantial reduction in the antimicrobial activity. The enhanced antibacterial activity may be attributed to the presence of oxygen vacancies, surface oxygen anions and hydroxyl groups on the surface of MgO nanoplates. This cost-effective functional finish (anti-microbial) to cotton fabric using MgO nanoplates may be suitable for many prospective medical applications and can serve as an alternative to the costlier silver based antimicrobial textiles.

  16. Pulsed laser deposition of novel nitride solid solution films Ni xTi 1- xN y on MgO(0 0 1)

    NASA Astrophysics Data System (ADS)

    Sakamoto, Koyo; Inumaru, Kei; Yamanaka, Shoji

    2002-10-01

    A novel nitride solid solution, Ni xTi 1- xN y (0≤ x≤0.31, 0.59≤ y≤1) was grown on MgO(0 0 1) using a pulsed laser deposition (PLD) method combined with RF nitrogen radical irradiation. Compressed disks made of mixtures of titanium hydride and nickel metal were used as the PLD targets. Simple Ti-Ni alloyed targets gave no crystalline nitride. High-resolution X-ray diffraction reciprocal space mapping revealed that the deposited films were epitaxially grown on MgO(0 0 1) and that the lattice of the films shrunk to fit the lattice of MgO(0 0 1) in the plane. The lattice constant perpendicular to the plane decreased linearly as the Ni content increased up to x=0.31, demonstrating the incorporation of Ni atoms into the crystal structure. These thin films were metallic conductors. X-ray photoelectron spectra showed that the substitution of Ti for Ni brought about the formation of large amounts of nitrogen vacancies.

  17. Growth and Characterization of Pulsed-Laser-Deposited Ilmenite Hematite Thin Films

    NASA Astrophysics Data System (ADS)

    Kale, P.; Padmini, P.; Dou, J.; Navarrete, L.; Shamsuzzoha, M.; Schad, R.; Pandey, R. K.

    2007-09-01

    The ilmenite hematite (1 - x) FeTiO3 · xFe2O3 solid solution system is considered to be a novel material for spin-electronics, microelectronics, high-temperature electronics, and radhard electronics. This paper focuses on thin films of composition x = 0.33 grown on (100) MgO single-crystal substrates using pulsed-laser deposition (PLD) under different argon oxygen mixtures. The surface of the MgO was found to possess MgO2 crystals, yielding an orientation relationship, [001] MgO ∥ [011] MgO2 and ( overline{1} 00)MgO ∥ ( overline{1} 10) MgO2. The structural characterizations show that the films are crystalline and homogeneous without any secondary phase. The films show a weak and inclined (11 overline{2} 0) growth epitaxy. A bandgap of 3.4 3.7 eV was obtained for these films from optical measurements carried out in the UV visible region. Electrical measurements confirmed the semiconducting behavior. However, the resistivity was found to increase substantially on the slightest addition of oxygen into the chamber.

  18. Growth of YBCO Thin Films on TiN(001) and CeO2-Coated TiN Surfaces

    DTIC Science & Technology

    2012-02-01

    substrates. Thin CeO2 (~200 nm thick) and YBCO (~300 nm thick) layers were grown on TiN-coated MgO substrates, using pulsed laser deposition. While YBCO ...and YBCO (300 nm thick) layers were grown on TiN-coated MgO substrates, using pulsed laser deposition. While YBCO grown directly on TiN was of poor...grown on the TiN-coated MgO and then an 300 nm thick YBCO layers was subsequently depos- ited. For other samples, YBCO deposition directly on the

  19. Pure ultraviolet emission from ZnO quantum dots-based/GaN heterojunction diodes by MgO interlayer

    NASA Astrophysics Data System (ADS)

    Chen, Cheng; Liang, Renli; Chen, Jingwen; Zhang, Jun; Wang, Shuai; Zhao, Chong; Zhang, Wei; Dai, Jiangnan; Chen, Changqing

    2017-07-01

    We demonstrate the fabrication and characterization of ZnO/GaN-based heterojunction light-emitting diodes (LEDs) by using air-stable and solution-processable ZnO quantum dots (QDs) with a thin MgO interlayer acting as an electron blocking layer (EBL). The ZnO QDs/MgO/ p-GaN heterojunction can only display electroluminescence (EL) characteristic in reverse bias regime. Under sufficient reverse bias, a fairly pure ultraviolet EL emission located at 370 nm deriving from near band edge of ZnO with a full width at half maximum (FWHM) of 8.3 nm had been obtained, while the deep-level emission had been almost totally suppressed. The EL origination and corresponding carrier transport mechanisms were investigated qualitatively in terms of photoluminescence (PL) results and energy band diagram.[Figure not available: see fulltext.

  20. Formation and destruction of cube texture in MgO films using ion beam assisted pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Hühne, Ruben; Beyer, Christoph; Holzapfel, Bernhard; Oertel, Carl-Georg; Schultz, Ludwig; Skrotzki, Werner

    2001-07-01

    Biaxially textured MgO thin films were deposited on amorphous substrates using ion beam assisted pulsed laser deposition. The development of the texture and microstructure was investigated with electron diffraction and atomic force microscopy. After the first few nanometers of growth, a sharp nucleation texture is observed. During further growth a texture change takes place, leading to two texture components, one in the <220> direction and the other in the <111> direction parallel to the substrate normal. In both cases the <200> direction is parallel to the ion beam. This texture change can be explained in terms of the highly anisotropic sputter rate observed in experiments on single crystals, leading to grains having a <200> direction parallel to the ion beam during growth being preferred. Without ion beam assistance during further growth, one of the two texture components dominates.

  1. 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.

  2. Cellulose extraction from Zoysia japonica pretreated by alumina-doped MgO in AMIMCl.

    PubMed

    Liu, Le; Ju, Meiting; Li, Weizun; Jiang, Yang

    2014-11-26

    In this study, alumina-doped MgO was produced as a solid alkali for lignocellulose pretreatment. Pretreatment with alumina-doped MgO disrupted the lignocellulose structure and significantly reduced the lignin content of the Z. japonica. After pretreatment, Z. japonica showed significant solubility in 1-allyl-3-methylimidazolium chloride (AMIMCl). The similar high solubility of pretreated Z. japonica samples by original alumina-doped MgO and used alumina-doped MgO also proved that alumina-doped MgO had strong stability, which can be recycled and used repeatedly. The regenerated cellulose was similar to microcrystalline cellulose according to FTIR and NMR analyses. Compared to microcrystalline cellulose, only the crystallinity of the regenerated cellulose decreased.

  3. Point defects and magnetic properties of neutron irradiated MgO single crystal

    NASA Astrophysics Data System (ADS)

    Cao, Mengxiong; Ma, Yaru; Wang, Xingyu; Ma, Chunlin; Zhou, Weiping; Wang, Xiaoxiong; Tan, Weishi; Du, Jun

    2017-05-01

    (100)-oriented MgO single crystals were irradiated to introduce point defects with different neutron doses ranging from 1.0×1016 to 1.0×1020 cm-2. The point defect configurations were studied with X-ray diffuse scattering and UV-Vis absorption spectra. The isointensity profiles of X-ray diffuse scattering caused by the cubic and double-force point defects in MgO were theoretically calculated based on the Huang scattering theory. The magnetic properties at different temperature were measured with superconducting quantum interference device (SQUID). The reciprocal space mappings (RSMs) of irradiated MgO revealed notable diffuse scattering. The UV-Vis spectra indicated the presence of O Frenkel defects in irradiated MgO. Neutron-irradiated MgO was diamagnetic at room temperature and became ferromagnetic at low temperature due to O Frenkel defects induced by neutron-irradiation.

  4. Adsorption sites of individual metal atoms on ultrathin MgO(100) films

    NASA Astrophysics Data System (ADS)

    Fernandes, Edgar; Donati, Fabio; Patthey, François; Stavrić, Srdjan; Šljivančanin, Željko; Brune, Harald

    2017-07-01

    We use Ca doping during growth of one- and two-monolayer-thick MgO films on Ag(100) to identify the adsorption sites of individual adatoms with scanning tunneling microscopy. For this we combine atomic resolution images of the bare MgO layer with images of the adsorbates and the substitutional Ca atoms taken at larger tip-sample distance. For Ho atoms, the adsorption sites depend on MgO thickness. On the monolayer, they are distributed on the O and bridge sites according to the abundance of those sites, 1 /3 and 2 /3 , respectively. On the MgO bilayer, Ho atoms populate almost exclusively the O site. A third species adsorbed on Mg is predicted by density functional theory and can be created by atomic manipulation. Au atoms adsorb on the bridge sites for both MgO thicknesses, while Co and Fe atoms prefer the O sites, again for both thicknesses.

  5. Effect of MgO and Basicity on Microstructure and Metallurgical Properties of Iron Ore Sinter

    NASA Astrophysics Data System (ADS)

    Zhang, Mingming; Andrade, Marcelo W.

    The metallurgical properties of iron ore sinter mainly depends on sinter mineralogy and microstructure, which in turn depends on the chemical composition of the sinter mix. In order to meet blast furnace requirement on sinter quality, it is essential to optimize the MgO in sinter mix and sinter basicity to get desired properties. Laboratory pot grate sintering experiments and quantitative analysis of sinter mineralogical phases have been carried out to investigate the influence of MgO addition on microstructure and properties of low basicity and high basicity sinter. MgO addition has been varied from 2. 2 to 4. 5% for low basicity (2. 1), and high basicity (3. 5) sinter mixes. Mineralogical examination indicated that Magnetite-Mg phases increases when MgO content in sinter increases. To achieve balanced sinter quality to meet blast furnace specifications, high basicity with medium range of MgO sinter was recommended to sinter plant.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. Interatomic forces and bonding mechanisms in MgO clusters

    SciTech Connect

    Wright, N.F.; Painter, G.S.

    1990-01-01

    We report results from a first-principles local spin density quantum mechanical study of the energetics and elastic properties of a series of magnesium-oxygen clusters of various morphologies. The role of quantum effects, e.g. covalency, in the bonding character of diatomic MgO is determined by comparison of classical and quantum restoring force curves. The dependence of binding properties on geometry and metal to oxygen ratio is determined by comparison of binding energy curves for a series of clusters. Results show that while gross features of the binding curves may be represented by simple interatomic potentials, details require the many body corrections of a full quantum treatment. 6 refs., 5 figs.

  11. Stabilities and structures of gas phase MgO clusters

    SciTech Connect

    Ziemann, P.J.; Castleman, A.W. Jr. )

    1991-01-01

    Gas phase (MgO){sup +}{sub {ital n}} and (MgO){sub {ital n}}Mg{sup +} clusters ({ital n}{le}90) were produced in a gas aggregation source and studied by using laser-ionization time-of-flight mass spectrometry. The abundance maxima observed in the mass spectra indicate that the clusters form compact cubic structures similar to pieces of the MgO crystal lattice. The abundance maxima of the metal-rich clusters show an interesting dependence on the ionization wavelength that appears to be due to different fragmentation pathways for the cluster ions and neutrals, and may be indicative of excess electron behavior analogous to that observed in solid state color centers. Calculations of cluster structures and stabilities made with an ionic model were useful in obtaining qualitative information about the primary fragmentation channels and cluster electronic properties, but also indicate that covalent bonding interactions must be included to obtain quantitatively accurate results.

  12. 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.

  13. 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.

  14. Electron-Induced Secondary Electron Emission Properties of MgO/Au Composite Thin Film Prepared by Magnetron Sputtering

    NASA Astrophysics Data System (ADS)

    Li, Jie; Hu, Wenbo; Wei, Qiang; Wu, Shengli; Hua, Xing; Zhang, Jintao

    2017-03-01

    As a type of electron-induced secondary electron emitter, MgO/Au composite thin film was prepared by reactive magnetron sputtering of individual Mg target and Au target, and the effects of key process parameters on its surface morphology and secondary electron emission (SEE) properties were investigated. It is found that to deposit a NiO buffer layer on the substrate is conducive to the subsequent growth of MgO grains owing to the lattice matching. The gold addition can raise the electrical conductivity of MgO film and further suppress the surface charging. However, the gold deposition would interfere with the MgO crystallization and increase the surface roughness of MgO/Au film. Therefore, MgO/Au composite thin film with a NiO buffer layer and proper deposition times of MgO and Au can achieve superior SEE properties due to good MgO crystallization, low surface roughness and reasonable electrical conductivity. The optimized MgO/Au composite thin film has a higher SEE coefficient and a lower 1-h SEE degradation rate under electron beam bombardment in comparison with MgO film.

  15. 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.

  16. 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.

  17. Influence of different ions doping on the antibacterial properties of MgO nanopowders

    NASA Astrophysics Data System (ADS)

    Rao, Yuanyuan; Wang, Wei; Tan, Fatang; Cai, Yuncheng; Lu, Junwen; Qiao, Xueliang

    2013-11-01

    Compared with other inorganic antibacterial agents, magnesium oxide (MgO) nanopowders exhibit a unique antibacterial mechanism and various advantages in applications, having attracted extensive attention. In this study, MgO nanopowders doped with different ions (Li+, Zn2+ and Ti4+) were synthesized by a sol-gel method, respectively. The structures and morphologies of the as-obtained precursors and nanopowders were characterized and confirmed by X-ray diffraction (XRD), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) analysis. The influence of three metal ions doping on the antibacterial properties of MgO nanopowders was also investigated by their bactericidal activity against Escherichia coli (E. coli, ATCC 25922) using the broth microdilution method and the agar method. The results show that Li-doped MgO exhibits better antibacterial activity, Zn-doped and Ti-doped MgO display poorer antibacterial activity than pure MgO. It can be concluded that the influence of different ions doping on the antibacterial properties of MgO mainly lies on oxygen vacancies and basicity of nanopowders.

  18. Microstructural, optical and magnetic properties study of nanocrystalline MgO

    NASA Astrophysics Data System (ADS)

    Choudhury, Biswajit; Choudhury, Amarjyoti

    2014-04-01

    Nanocrystalline MgO is prepared by precipitation method. It has a crystallite size of 13 nm. The particles are agglomerated with varied size ranges. N2 adsorption-desorption isotherm confirms the mesoporous structure of MgO nanoparticles with a surface area of 145 m2 g-1. MgO contains hydride related impurities as evidenced from the Fourier transform infrared (FTIR) spectroscopy results. The UV-vis absorption spectrum of MgO contains several visible absorption peaks mostly associated with oxygen vacancies. These oxygen vacancies trap electrons and form color centers such as F, F +, F 2+, F 2 2+, etc. Photoluminescence (PL) and photoluminescence excitation (PLE) results have revealed that the UV and visible emission peaks of MgO result from these color centers. MgO also exhibits room temperature ferromagnetism. Vacuum annealing, however, reduces the magnetization. Thus, the observed magnetism may not be associated with oxygen vacancies. It is the Mg vacancy which is most likely promoting ferromagnetism in nanoscale MgO.

  19. Temperature-Dependent Morphology, Magnetic and Optical Properties of Li-Doped MgO

    SciTech Connect

    Myrach, Philipp; Niklas, Nilius; Levchenko, Sergey; Gonchar, Anastasia; Risse, Thomas; Klaus-Peter, Dinse; Boatner, Lynn A; Frandsen, Wiebke; Horn, Raimund; Hans-Joachim, Freund; Schlçgl, Robert; Scheffler, Matthias

    2010-01-01

    Li-doped MgO is a potential catalyst for the oxidative coupling of methane, whereby surface Li+ O centers are suggested to be the chemically active species. To elucidate the role of Li in the MgO matrix, two model systems are prepared and their morphological, optical and magnetic properties as a function of Li doping are investigated. The first is an MgO film deposited on Mo(001) and doped with various amounts of Li, whereas the second is a powder sample fabricated by calcination of Li and Mg precursors in an oxygen atmosphere. Scanning tunneling and transmission electron microscopy are performed to characterize the morphology of both samples. At temperatures above 700 K, Li starts segregating towards the surface and forms irregular Li-rich oxide patches. Above 1050 K, Li desorbs from the MgO surface, leaving behind a characteristic defect pattern. Traces of Li also dissolve into the MgO, as concluded from a distinct optical signature that is absent in the pristine oxide. No electron paramagnetic resonance signal that would be compatible with Li+O centers is detected in the two Li/ MgO samples. Density-functional theory calculations are used to determine the thermodynamic stability of various Li-induced defects in the MgO. The calculations clarify the driving forces for Li segregation towards the MgO surface, but also rationalize the absence of Li+O centers. From the combination of experimental and theoretical results, a detailed picture arises on the role of Li for the MgO properties, which can be used as a starting point to analyze the chemical behavior of the doped oxide in future.

  20. 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.

  1. 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.

  2. Catalytic Cycle Employing a TEMPO-Anion Complex to Obtain a Secondary Mg-O2 Battery.

    PubMed

    Shiga, Tohru; Hase, Yoko; Yagi, Yusuke; Takahashi, Naoko; Takechi, Kensuke

    2014-05-15

    Nonaqueous Mg-O2 batteries are suitable only as primary cells because MgO precipitates formed during discharging are not decomposed electrochemically at ambient temperatures. To address this problem, the present study examined the ability of the 2,2,6,6-tetramethylpiperidine-oxyl (TEMPO)-anion complex to catalyze the decomposition of MgO. It was determined that this complex was capable of chemically decomposing MgO at 60 °C. A catalytic cycle for the realization of a rechargeable Mg-O2 electrode was designed by combining the decomposition of MgO via the TEMPO-anion complex and the TEMPO-redox couple. This work also demonstrates that a nonaqueous Mg-O2 battery incorporating acrylate polymer having TEMPO side units in the cathode shows evidence of being rechargeable.

  3. Preparation of (001)-oriented Pb(Zr,Ti)O3 thin films and their piezoelectric applications.

    PubMed

    Fujii, Eiji; Takayama, Ryoichi; Nomura, Kouji; Murata, Akiko; Hirasawa, Taku; Tomozawa, Atsushi; Fujii, Satoru; Kamada, Takeshi; Torii, Hideo

    2007-12-01

    Preparation of (001)-oriented Pb(Zr,Ti)O(3) (PZT) thin films and their applications to a sensor and actuators were investigated. These thin films, which have a composition close to the morphotropic phase boundary, were epitaxially grown on (100)MgO single-crystal substrates by RF magnetron sputtering. These (001)-oriented PZT thin films could be obtained on various kinds of substrates, such as glass and Si, by introducing (100)-oriented MgO buffer layers. In addition, the (001) oriented PZT thin films could be obtained on Si substrates without buffer layers by optimizing the sputtering conditions. All of these thin films showed excellent piezoelectric properties without the need for poling treatment. The PZT thin films on the MgO substrates had a high piezoelectric coefficient, d(31), of -100 pm/V, and an extremely low relative dielectric constant, epsilon(r), of 240. The PZT thin films on Si substrate had a very high d(31) of -150 pm/V and an epsilon(r) = 700. These PZT thin films were applied to an angular rate sensor with a tuning fork in a car navigation system, to a dual-stage actuator for positioning the magnetic head of a high-density hard disk drive, and to an actuator for an inkjet printer head for industrial on-demand printers.

  4. 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.

  5. 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.

  6. An Arc Origin for Archean High MgO "Eclogite" Xenoliths?

    NASA Astrophysics Data System (ADS)

    Horodyskyj, U. N.; Lee, C. A.

    2005-12-01

    The origin and evolution of Archean continental crust is an important topic in the Earth sciences. By understanding how Archean crust forms, we are better able to track how chemical differentiation and geodynamic processes have evolved on the Earth over billion-year timescales. Suggested mechanisms responsible for Archean crust formation include melting of subducted slabs, melting of orogenically thickened basaltic crust, and generation of large oceanic plateaus (proto-continents). In all these scenarios, high temperatures are required. Since it is reasonable to assume that the mantle in the Archean was probably hotter, these mechanisms may have been dominant at that time. The likely colder temperatures in the Phanerozoic, however, would prevent these mechanisms from operating extensively today. Instead, most continental crust formation in the Phanerozoic tends to be associated with arc magmas formed not by slab melting but by hydrous melting of the peridotitic mantle wedge. The question we wish to address is the extent to which Phanerozoic-like arc processes might also have operated in the mid- to late-Archean. Answering this question may help us better understand Earth's secular thermal evolution. Towards these ends, we have been focusing on understanding the origins of high MgO "eclogite" xenoliths found in Archean cratons. While the origin of low MgO "eclogites" is understood to be partially melted subducted oceanic crust, the origin of the high MgO "eclogites" is still debated. Here we show that high MgO Archean "eclogite" xenoliths have major element systematics remarkably similar to high MgO garnet pyroxenite ("eclogite") xenoliths originating from the lithospheric root underlying the Phanerozoic Sierra Nevada batholith in California, the remnant of a Mesozoic continental arc. Both groups have similarly high MgO contents, high Mg/(Mg+Fe) ratios, and relatively high SiO2 contents. Such compositions are not represented by typical frozen melts. In the case of

  7. Synthesis of MgO powder from magnesium nitrate using spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Pradita, T.; Shih, S. J.; Aji, B. B.; Sudibyo

    2017-03-01

    A variety of advantages such as catalyst, paints, flame retardants, semiconductors, additives in refractory and solid adsorbent can be obtained from Magnesium Oxide (MgO) based material. Ultrasonic spray pyrolysis (SP) process was conducted to synthesize MgO from Mg(NO3)2.6H2O (MgN) precursor. The MgO particles were characterized using Thermogravimetric Analysis (TGA), X-Ray Diffraction analysis (XRD) and Field Emission-Secondary Electron Microscopy (FE-SEM). In this study, Hollow spherical and irregular MgO particles were successfully obtained. It suggests that the particle size will decrease along with the increasing of the SP temperature, the smallest particle size obtained is in the range of 354±104 nm at 900°C SP temperature.

  8. Sol-gel synthesis and dilute magnetism of nano MgO powder doped with Fe

    NASA Astrophysics Data System (ADS)

    Nomura, Kiyoshi; Taya, Souichirou; Okazawa, Atsushi; Kojima, Norimichi

    2014-04-01

    Mg oxides doped with 1 % 57Fe were prepared by a sol-gel method, and annealed at various temperatures. Nano-size Mg oxides were characterized by Mössbauer spectrometry, magnetization and XRD measurements. The crystalline size of MgO increases with increase of annealing temperature. Samples annealed at 600 °C and 800 °C gave only doublet peaks of paramagnetic Fe3+ in Mössbauer spectra although Fe3+ doping into MgO induced a distorted structure and showed weak ferromagnetism. It is considered that the magnetic property is due to defect induced magnetism by doping Fe3+ into MgO. For a sample heated at 1000 °C, it is found from low temperature Mössbauer spectra that Fe3+ species are located at the core and shell of fine MgFe2O4 grains and diluted in MgO matrix.

  9. 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.

  10. 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.

  11. Grain Boundary Transport of Siderophile Elements in MgO at High Pressure

    NASA Astrophysics Data System (ADS)

    Watson, H. C.; Siebert, J.; Ryerson, F. J.; Roberts, J. J.; Hayden, L.; Watson, E. B.

    2007-12-01

    The extent of interaction between the Earth's core and mantle remains an actively debated question. Siderophile element signatures in rocks that can be observed at the surface indicate that the mantle and core may have exchanged material over the history of the Earth. Here, a potential physical mechanism to facilitate this communication is considered. It has recently been shown that grain boundaries in lower mantle analog materials at 2.5 GPa act as reservoirs and fast transport pathways for incompatible elements, specifically siderophile elements [1]. In the present study, we conducted multi-anvil experiments held at 10 GPa and 1600°C for 5 hours to examine the persistence of fast grain boundary transport at higher pressures. Thin layers of Os and Au powders were loaded in a standard 10/5 multi-anvil assembly and separated from a Pt foil by a cylindrical MgO plug approximately 1mm long. These two elements were expected to be among the slowest and fastest diffusers respectively. The final composition of the Pt foil was measured by electron microprobe. The presence of measurable siderophile element "blebs" in the Pt foil indicates substantial grain boundary diffusion. Our preliminary results suggest that siderophile element mobility and presence on grain boundaries may be affected slightly with increased pressure, but could remain a viable mechanism for transport on length scales applicable to communication within the deeper Earth over it's history. The effect of pressure and grain size on grain boundary diffusion, and potential reasons for a large variation between diffusivities of different siderophile elements will be discussed. [1] Hayden, L., and Watson, E.B., 2006. GCA Supp., v. 70, iss. 18, p. 238

  12. Stability and optical activity of Er implanted MgO

    NASA Astrophysics Data System (ADS)

    Pinto, J. V.; da Silva, R. C.; Alves, E.; Soares, M. J.; Monteiro, T.; González, R.

    2004-06-01

    MgO single crystals were implanted with Er ions to a fluence of 5 × 10 15 ions/cm 2. The implantations were carried out at room temperature with an energy of 150 keV. Despite the large amount of damage produced during the implantation the Er ions are incorporated in optically active sites. Photoluminescence measurements at 77 K reveal the presence of the fingerprint Er 3+ emission at 1.54 μm due to 4I 13/2 → 4I 15/2 transition. Angular scans performed through the main axes show complete overlap between Er and magnesium curves. Subsequent annealing in a reducing atmosphere at 1000 °C for 1 h leads to the recovery of the implantation damage. During the annealing the fraction of Er in Mg sites decreases from 100% to 53%. This movement of the Er ions is accompanied by changes in the optical spectra. Further annealing for 2 h at the same temperature leads to more precipitation of Er into random sites, whereby the fraction of Er in Mg lattice sites decreases to 20% while there is an enhancement of optical activity.

  13. Pumping laser excited spins through MgO barriers

    NASA Astrophysics Data System (ADS)

    Martens, Ulrike; Walowski, Jakob; Schumann, Thomas; Mansurova, Maria; Boehnke, Alexander; Huebner, Torsten; Reiss, Günter; Thomas, Andy; Münzenberg, Markus

    2017-04-01

    We present a study of the tunnel magneto-Seebeck (TMS)4 effect in MgO based magnetic tunnel junctions (MTJs). The electrodes consist of CoFeB with in-plane magnetic anisotropy. The temperature gradients which generate a voltage across the MTJs layer stack are created using laser heating. Using this method, the temperature can be controlled on the micrometer length scale: here, we investigate, how both, the TMS voltage and the TMS effect, depend on the size, position and intensity of the applied laser spot. For this study, a large variety of different temperature distributions was created across the junction. We recorded 2D maps of voltages generated by heating in dependence of the laser spot position and the corresponding calculated TMS values. The voltages change in value and sign, from large positive values when heating the MTJ directly in the centre to small values when heating the junction on the edges and even small negative values when heating the sample away from the junction. Those zero crossings lead to very high calculated TMS ratios. Our systematic analysis shows, that the distribution of the temperature gradient is essential, to achieve high voltage signals and reasonable resulting TMS ratios. Furthermore, artefacts on the edges produce misleading results, but also open up further possibilities of more complex heating scenarios for spincaloritronics in spintronic devices.

  14. Reliability enhancement due to in-situ post-oxidation of sputtered MgO barrier in double MgO barrier magnetic tunnel junction

    NASA Astrophysics Data System (ADS)

    Yoshida, Chikako; Noshiro, Hideyuki; Yamazaki, Yuichi; Sugii, Toshihiro

    2017-06-01

    We have investigated the effects of in-situ post-oxidation (PO) of a sputtered MgO barrier in a double-MgO-barrier magnetic tunnel junction (MTJ) and found that the short error rate was significantly reduced, the magnetoresistance (MR) ratio was increased approximately 18%, and the endurance lifetime was extend. In addition, we found that the distribution of breakdown number (a measure of endurance) exhibits trimodal characteristics, which indicates competition between extrinsic and intrinsic failures. This improvement in reliability might be related to the suppression of Fe and Co diffusion to the MgO barrier, as revealed by electron energy-loss spectroscopy (EELS) analysis.

  15. 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.

  16. Effect of MgO nanofillers on burst release reduction from hydrogel nanocomposites.

    PubMed

    Hezaveh, Hadi; Muhamad, Ida Idayu

    2013-06-01

    In this study, MgO nanoparticles are applied to control the initial burst release by modification of matrix structure, thereby affecting the release mechanism. The effects of MgO nanofiller loading on the in vitro release of a model drug are investigated. Surface topography and release kinetics of hydrogel nanocomposites are also studied in order to have better insight into the release mechanism. It was found that the incorporation of MgO nanofillers can significantly decrease the initial burst release. The effect of genipin (GN) on burst release was also compared with MgO nanoparticles, and it was found that the impact of MgO on burst release reduction is more obvious than GN; however, GN cross-linking caused greater final release compared to blanks and nanocomposites. To confirm the capability of nanocomposite hydrogels to reduce burst release, the release of β-carotene in Simulated Gastric Fluid and Simulated Intestinal Fluid was also carried out. Thus, the application of MgO nanoparticles seems to be a promising strategy to control burst release.

  17. Porphyrin Metalation at the MgO Nanocube/Toluene Interface.

    PubMed

    Schneider, Johannes; Kollhoff, Fabian; Bernardi, Johannes; Kaftan, Andre; Libuda, Jörg; Berger, Thomas; Laurin, Mathias; Diwald, Oliver

    2015-10-21

    Molecular insights into porphyrin adsorption on nanostructured metal oxide surfaces and associated ion exchange reactions are key to the development of functional hybrids for energy conversion, sensing, and light emission devices. Here we investigated the adsorption of tetraphenyl-porphyrin (2HTPP) from toluene solution on two types of MgO powder. We compare MgO nanocubes with an average size d < 10 nm and MgO cubes with 10 nm ≤ d ≤ 1000 nm. Using molecular spectroscopy techniques such as UV/vis transmission and diffuse reflectance (DR), photoluminescence (PL), and diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy in combination with structural characterization techniques (powder X-ray diffraction and transmission electron microscopy, TEM), we identified a new room temperature metalation reaction that converts 2HTPP into magnesium tetraphenyl-porphyrin (MgTPP). Mg(2+) uptake from the MgO nanocube surfaces and the concomitant protonation of the oxide surface level off at a concentration that corresponds to roughly one monolayer equivalent adsorbed on the MgO nanocubes. Larger MgO cubes, in contrast, show suppressed exchange, and only traces of MgTPP can be detected by photoluminescence.

  18. 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.

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

    PubMed

    Zhou, Hua; Wang, Hui-Qiong; Liao, Xia-Xia; Zhang, Yufeng; Zheng, Jin-Cheng; Wang, Jia-Ou; Muhemmed, Emin; Qian, Hai-Jie; Ibrahim, Kurash; Chen, Xiaohang; Zhan, Huahan; Kang, Junyong

    2012-03-09

    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.

  20. Continuous modeling of a grain boundary in MgO and its disclination induced grain-boundary migration mechanism

    NASA Astrophysics Data System (ADS)

    Cordier, P.; Sun, X.; Taupin, V.; Fressengeas, C.

    2016-12-01

    Grain boundaries (GBs) are thin material layers where the lattice rotates from one orientation to the next one within a few nanometers. Because they treat these layers as infinitely thin interfaces, large-scale polycrystalline representations fail to describe their structure. Conversely, atomistic representations provide a detailed description of the GBs, but their character remains discrete and not prone to coarse-graining procedures. Continuum descriptions based on kinematic and crystal defect fields defined at interatomic scale are appealing because they can provide smooth and thorough descriptions of GBs, recovering in some sense the atomistic description and potentially serving as a basis for coarse-grained polycrystalline representations. In this work, a crossover between atomistic description and continuous representation of a MgO tilt boundary in polycrystals is set-up to model the periodic arrays of structural units by using dislocation and disclination dipole arrays along GBs. The strain, rotation, curvature, disclination and dislocation density fields are determined in the boundary area by using the discrete atomic positions generated by molecular dynamics simulations. Then, this continuous disclination/dislocation model is used as part of the initial conditions in elasto-plastic continuum mechanics simulations to investigate the shear-coupled boundary migration of tilt boundaries. The present study leads to better understanding of the structure and mechanical architecture of grain boundaries.

  1. The effect of MgO(111) interlayer on the interface phase stability and structure of BaFe{sub 12}O{sub 19}/SiC(0001)

    SciTech Connect

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

    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 BaFe{sub 12}O{sub 19} (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.

  2. 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.

  3. Static and dynamic magnetic properties of epitaxial Co{sub 2}FeAl Heusler alloy thin films

    SciTech Connect

    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 Co{sub 2}FeAl 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 deg. 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/cm{sup 3}, and Cr buffered sample displays a magnetization saturation of 1032 {+-} 40 emu/cm{sup 3}. Damping factor was studied by strip-line ferromagnetic resonance measures. We observed a maximum value for the MgO buffered sample of about 8.5 x 10{sup -3}, and a minimum value of 3.8 x 10{sup -3} for the Cr buffered one.

  4. 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)

  5. 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)

  6. The perpendicular anisotropy of Co40Fe40B20 sandwiched between Ta and MgO layers and its application in CoFeB/MgO/CoFeB tunnel junction

    NASA Astrophysics Data System (ADS)

    Wang, W. X.; Yang, Y.; Naganuma, H.; Ando, Y.; Yu, R. C.; Han, X. F.

    2011-07-01

    Magnetic anisotropy of Co40Fe40B20 thin films sandwiched between Ta and MgO layers was investigated. Magnetic properties of CoFeB layers deposited on top and bottom of MgO layer are different. The thickness of the CoFeB layer and annealing temperature are the critical parameters to achieve and keep the perpendicular magnetic anisotropy. The phase diagram of perpendicular anisotropic strength of CoFeB layers on annealing temperatures and thicknesses of CoFeB layers is observed. According to phase diagrams, perpendicular CoFeB/MgO/CoFeB tunnel junctions were fabricated, and tunneling magnetoresistance (TMR) ratio was higher than 30% at low temperatures.

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

    PubMed

    Khandaker, Morshed; Li, Yanling; Morris, Tracy

    2013-03-15

    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.

  8. Functionalization of mesoporous carbon with superbasic MgO nanoparticles for the efficient synthesis of sulfinamides.

    PubMed

    Chakravarti, Rajashree; Mano, Ajayan; Iwai, Hideo; Aldeyab, Salem S; Kumar, R Pradeep; Kantam, M Lakshmi; Vinu, Ajayan

    2011-06-06

    Highly basic MgO nanoparticles with different sizes have been successfully immobilized over mesoporous carbon with different pore diameters by a simple wet-impregnation method. The prepared catalysts have been characterized by various sophisticated techniques, such as XRD, nitrogen adsorption, electron energy loss spectroscopy, high-resolution TEM, X-ray photoelectron spectroscopy, and the temperature-programmed desorption of CO(2). XRD results reveal that the mesostructure of the support is retained even after the huge loading of MgO nanoparticles inside the mesochannels of the support. It is also demonstrated that the particle size and dispersion of the MgO nanoparticles on the support can be finely controlled by the simple adjustment of the textural parameters of the supports. Among the support materials studied, mesoporous carbon with the largest pore diameter and large pore volume offered highly crystalline small-size cubic-phase MgO nanoparticles with a high dispersion. The basicity of the MgO-supported mesoporous carbons can also be controlled by simply changing the loading of the MgO and the pore diameter of the support. These materials have been employed as heterogeneous catalysts for the first time in the selective synthesis of sulfinamides. Among the catalysts investigated, the support with the large pore diameter and high loading of MgO showed the highest activity with an excellent yield of sulfinamides. The catalyst also showed much higher activity than the pristine MgO nanoparticles. The effects of the reaction parameters, including the solvents and reaction temperature, and textural parameters of the supports in the activity of the catalyst have also been demonstrated. Most importantly, the catalyst was found to be highly stable, showing excellent activity even after the third cycle of reaction.

  9. In SituObservation of MgO Inclusions in Liquid Iron-Aluminum Alloys

    NASA Astrophysics Data System (ADS)

    Mu, Haoyuan; Zhang, Tongsheng; Yang, Liang; Xavier, Rodrigo R.; Fruehan, Richard J.; Webler, Bryan A.

    2016-12-01

    This study showed that MgO inclusions can be stable in liquid iron with elevated Al and it illustrated an important role of vaporization in the evolution of inclusions. Previous studies have shown that dissolved Al reduces MgO from slags and refractories, leading to spinel (MgAl2O4) inclusions. The elevated Al content of newer steels raises the possibility that MgO inclusions can be stable. In this work, MgO inclusions were produced and observed in an Fe-Al alloy. The inclusions in the liquid alloy at 1873 K (1600 °C) were observed in situ with a Confocal Laser Scanning Microscope (CLSM). Two types of experiments were performed: one where only a metal sample was melted and the other where the sample was in contact with a liquid, MgO-saturated slag. When no slag was present, the MgO inclusions shrank and disappeared at 1873 K (1600 °C). No inclusions were observed in situ during cooling or in post-CLSM analysis. When the MgO-saturated slag was present, the inclusion sizes were essentially constant and MgO was observed on the surface of post-CLSM samples. Analysis of the results showed that MgO can be stable in 1873 K (1600 °C), but that its presence depends on the rate of removal of Mg due to vaporization and the supply of Mg due to slag/metal or refractory/metal reactions.

  10. 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.

  11. 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.

  12. 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.

  13. First-principles study of the adsorption of MgO molecules on a clean Fe(001) surface

    NASA Astrophysics Data System (ADS)

    Wiśnios, Damian; Kiejna, Adam; Korecki, Józef

    2015-10-01

    The adsorption of MgO molecules on a Fe(001) surface was studied using density functional theory and projector augmented-wave methods. The energetically most favored configurations for different adsorption sites considered were identified. The most preferable adsorption geometry is when the MgO molecules are parallel to the surface, with Mg in the interstitial site and O in the on-top site of the Fe atom. During the adsorption of subsequent MgO molecules in this geometry, a sharp, nonoxidized interface is formed between the MgO adlayer and the Fe(001) surface. The adsorption of MgO perpendicular to the surface, with oxygen incorporated in the topmost Fe layer, is less probable, but it may lead to the formation of the FeO layer when stabilized with an excess of oxygen atoms. Structural, electronic, and magnetic properties of both interface types were examined for the MgO coverage from 1/9 to 1 monolayer (ML). Electronic and magnetic properties are sensitive to the MgO coverage. For lower coverage of MgO, clear hybridization between the Fe 3 d and O 2 p states is shown. The average magnetic moment of the surface Fe atoms is reduced with coverage, achieving 2.78 μB for 1 ML of MgO.

  14. 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

  15. Ion beam assisted deposition of MgO barriers for magnetic tunnel junctions

    SciTech Connect

    Cardoso, S.; Macedo, R. J.; Ferreira, R.; Augusto, A.; Wisniowski, P.; Freitas, P. P.

    2008-04-01

    This work reports for the first time results on MgO tunnel junctions prepared by ion beam. The MgO barrier was deposited from a ceramic MgO target using an assisted beam, following the deposition and assisted beam phase diagram which relate the beam profile with the current and energy. The deposition rate for MgO is calculated with and without assisted beam, and compared with the experimental values. The MgO film growth on Ta/CoFeB/MgO simple stacks was optimized aiming at a (002) preferred orientation for the MgO growth, measured by x-ray diffraction. The optimum assist beam energy was tuned for each deposition beam condition (+800,+1000,+1200 V), using assist beams of 40 mA ({approx}130 {mu}A/cm{sup 2}) with 0 to +600 V. Without assist beam, no texture is observed for the MgO, while the (002) orientation appears for assisted deposition. The optimum range of assist voltages is large, being limited by the onset of etching at high voltages, reducing the deposition rate. Magnetic tunnel junctions were deposited with the structure Ta 50 A/Ru 200 A/Ta 50 A/Mn{sub 78}Ir{sub 22} 150 A/Co{sub 90}Fe{sub 10} 30 A/Ru 8 A/Co{sub 56}Fe{sub 24}B{sub 20} 40 A/MgO t/Co{sub 56}Fe{sub 24}B{sub 20} 30 A/Ru 30 A/Ta 50 A, with the MgO barrier deposited with the conditions optimized by x rays. The effect of the assist beam energy on the junction properties (magnetoresistance and magnetization) are discussed. Tunnel magnetoresistance values up to 110%, with RA products of 100-400 {omega} {mu}m{sup 2}, for 11 A thick MgO barriers are obtained using assisted deposition with a +100 V assist beam, which is a major improvement of the {approx}30% of TMR, if no beam is used.

  16. A novel approach for arsenic adsorbents regeneration using MgO.

    PubMed

    Tresintsi, Sofia; Simeonidis, Konstantinos; Katsikini, Maria; Paloura, Eleni C; Bantsis, Georgios; Mitrakas, Manassis

    2014-01-30

    An integrated procedure for the regeneration of iron oxy-hydroxide arsenic adsorbents by granulated MgO is proposed in this study. A continuous recirculation configuration, with a NaOH solution flowing sequentially through the saturated adsorbent (leaching step) and the MgO (adsorption step) column beds, was optimized by utilizing the high arsenic adsorption efficiency of MgO at strong alkaline environments. Experimental results indicated that the total amount of leached arsenic was captured by MgO whereas the regenerated iron oxy-hydroxide recovered around 80% of its removal capacity upon reuse. The improved adsorption capacity of MgO for As(V), which is maximized at pH 10, is explained by the intermediate hydration to Mg(OH)2 and the following As(V) oxy-anions adsorption on its surface through the formation of monodentate inner sphere complexes, as it is deduced from the AsK-edge X-ray absorption fine structure (EXAFS) analysis. In addition to the economical-benefits, corresponding tests proved that the solid wastes of this process, namely spent MgO/Mg(OH)2, can be environmentally safely disposed as stable additives in cement products, while the alkaline solution is completely detoxified and can be recycled to the regeneration task.

  17. Synthesis and characterization of isolated iron oxide nanoparticle dispersed in MgO matrix

    NASA Astrophysics Data System (ADS)

    Choa, Yong-Ho; Yang, Jae-Kyo; Yang, Won-Jae; Auh, Keun-Ho

    2003-10-01

    γ-Fe 2O 3/MgO nanocomposite powders, which can be used for biomedical, magnetic and the catalytic applications, were fabricated by means of spray pyrolysis using an ultrasonic atomizer. The liquid source was prepared using Fe and Mg nitrates dissolved in pure water. The liquid was atomized using an ultrasonic atomizer and carried into a pre-heated chamber (500-800°C) by air carrier gas. The mist was then decomposed into γ-Fe 2O 3 and MgO nanopowders. The entire operation was performed at 1 atm. The γ-Fe 2O 3/MgO powder was found to be perfectly crystallized at 800°C. The particle size of γ-Fe 2O 3/MgO nanocomposite powders prepared at 800°C was about 10 nm for γ-Fe 2O 3 and MgO, which were calculated by XRD using Scherrer's formula and measured by TEM observation. The samples indicate the presence of superparamagnetic properties and a blocking temperature ( TB) of 125 K.

  18. 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.

  19. Formation of hydroxyl and water layers on MgO films studied with ambient pressure XPS

    NASA Astrophysics Data System (ADS)

    Newberg, John T.; Starr, David E.; Yamamoto, Susumu; Kaya, Sarp; Kendelewicz, Tom; Mysak, Erin R.; Porsgaard, Soeren; Salmeron, Miquel B.; Brown, Gordon E., Jr.; Nilsson, Anders; Bluhm, Hendrik

    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 2O) 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 2O, OH and Ox thickness changes as a function of relative humidity.

  20. Near UV excitable yellow light emitting Zn doped MgO for WLED application

    NASA Astrophysics Data System (ADS)

    Vasanthi, V.; Kottaisamy, M.; Anitha, K.; Ramakrishnan, V.

    2017-06-01

    Nanoparticles of Mg1-xZnxO (x = 0, 0.05, 0.1, 0.15) were synthesized by sol-gel assisted combustion method and their optical properties has been investigated. Crystal structure, phase purity and doping of Zn2+ ions in MgO are confirmed from Powder X-ray diffraction method. Spherical shape porous particles are found with increasing particle density as a function of doping concentration. Doping of Zn ions in MgO has altered the optical band gap of MgO and reduced the band gap from 4.6 eV to 3.9 eV as the concentration of Zn increases. The optical absorption bands are observed in the visible region exhibited the presence of various defects such as F, F+, F2+ in MgO and these defects concentration increases with Zn doping. The photoluminescence emission spectra of Zn doped MgO shows a bright bluish green emission which starts from 450 nm to 570 nm and this light can be obtained at the excitation of near UV light from 330 to 380 nm. However, the same defective structure has led to a highly intense broad band emission which starts from 450 nm to 750 nm at the excitation of near UV LED (at 375 nm). This material can be used as a yellow emitting phosphor for phosphor converted white LEDs (PCWLEDs) at the excitation of near UV LEDs.

  1. Evolution of magnetic properties in the vicinity of the Verwey transition in Fe3O4 thin films

    NASA Astrophysics Data System (ADS)

    Liu, X. H.; Liu, W.; Zhang, Z. D.

    2017-09-01

    We have systematically studied the evolution of magnetic properties, especially the coercivity and the remanence ratio in the vicinity of the Verwey transition temperature (TV), of high-quality epitaxial Fe3O4 thin films grown on MgO (001), MgAl2O4 (MAO) (001), and SrTiO3 (STO) (001) substrates. We observed rapid change of magnetization, coercivity, and remanence ratio at TV, which are consistent with the behaviors of resistivity versus temperature [ρ (T )] curves for the different thin films. In particular, we found quite different magnetic behaviors for the thin films on MgO from those on MAO and STO, in which the domain size and the strain state play very important roles. The coercivity is mainly determined by the domain size but the demagnetization process is mainly dependent on the strain state. Furthermore, we observed a reversal of remanence ratio at TV with thickness for the thin films grown on MgO: from a rapid enhancement for 40-nm- to a sharp drop for 200-nm-thick film, and the critical thickness is about 80 nm. Finally, we found an obvious hysteretic loop of coercivity (or remanence ratio) with temperature around TV, corresponding to the hysteretic loop of the ρ (T ) curve, in Fe3O4 thin film grown on MgO.

  2. Modeling the thickness dependence of the magnetic phase transition temperature in thin FeRh films

    NASA Astrophysics Data System (ADS)

    Ostler, Thomas Andrew; Barton, Craig; Thomson, Thomas; Hrkac, Gino

    2017-02-01

    FeRh and its first-order phase transition can open new routes for magnetic hybrid materials and devices under the assumption that it can be exploited in ultra-thin-film structures. Motivated by experimental measurements showing an unexpected increase in the phase transition temperature with decreasing thickness of FeRh on top of MgO, we develop a computational model to investigate strain effects of FeRh in such magnetic structures. Our theoretical results show that the presence of the MgO interface results in a strain that changes the magnetic configuration which drives the anomalous behavior.

  3. Preparation of [100] oriented SrTiO3 thin films on flexible polymer sheets

    NASA Astrophysics Data System (ADS)

    Nishikawa, Hiroaki; Morita, Yusuke; Kusunoki, Masanobu; Hontsu, Shigeki; Tanaka, Hidekazu; Endo, Tamio

    2014-01-01

    In this study, we prepared a uniaxially oriented oxide on a flexible polymer substrate. We first grew [100] oriented SrTiO3 (STO) on a MgO(100) substrate. After bonding the STO film to a poly(ethylene naphthalete) (PEN) sheet with a photoresist, we etched the MgO substrate with a phosphoric acid solution to transfer the oxide film to the PEN sheet. The thin (300 nm) STO films did not crack after release, even after bending the sheet around a rod with a 1 cm radius, while the thicker (800 nm) films did. Ultimately, this process could be adapted to prepare a flexible epitaxial oxide.

  4. Texture improvement of sputtered YBa 2Cu 3O 7- x films on MgO (100) with a SrTiO 3 buffer layer

    NASA Astrophysics Data System (ADS)

    Lucía, M. L.; Santamaría, J.; Iborra, E.; Hernández-Rojas, J. L.; Sánchez-Quesada, F.

    1993-12-01

    SrTiO 3 buffer layers have been grown on MgO (100) substrates to provide a better match to RF sputtered YBa 2Cu 3O 7- x films. This heterostructure allows a highly textured growth to be achieved over thickness as high as 1 μm. The granularity of films grown without buffer layer on MgO (100) and YSZ (100) has been shown to be thickness dependent affecting the critical current density: Jc at 77 K is typically 3 × 10 5 A/cm 2 in 1000 Å thin films while it reduces to 10 3 A/cm 2 in μm films. A of how the improvement of lattice matching makes the critical current density increase from 10 3 A/cm 2 for 1 μm films grown on YSZ to 4 × 10 5 A/cm 2 for films grown with a SrTiO 3 buffer layer.

  5. 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.

  6. Preparation of MgO Films by Atmospheric Metal-Organic Chemical Vapor Deposition as a Protective Layer in AC Plasma Display Panels

    NASA Astrophysics Data System (ADS)

    Okada, Takeru; Komaki, Toshihiro

    2008-03-01

    MgO thin films were fabricated by atmospheric metal-organic chemical vapor deposition as a protective layer of AC plasma display panels. The deposition conditions and the discharge properties of the films were evaluated. Among four Mg precursors tested, Mg(C11H19O2)2 [Mg(DPM)2] was the most suitable source material in film growth properties and discharge characteristics. The deposition rate increased with increasing vaporizing temperature and substrate temperature, and the maximum deposition rate reached 3.3 nm/s (5.1 min/µm). The films had (200) main orientations, and highly crystalline square-pyramid structures were observed in high deposition-rate films. Under the high-rate deposition condition, the firing voltage and the discharge delay of the film were comparable to those of conventional vacuum-evaporated MgO film. The discharge delay was shorter when the crystal size was larger, the work function was smaller, and the concentrations of impurities were lower.

  7. 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.

  8. 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.

  9. Molecular dynamics study on low-energy sputtering properties of MgO surfaces

    SciTech Connect

    Ahn, Hyo-Shin; Kim, Tae-Eun; Cho, Eunae; Ji, Miran; Lee, Choong-Ki; Han, Seungwu; Cho, Youngmi; Kim, Changwook

    2008-04-01

    In an effort to understand microscopic processes occurring between MgO protective layers and impinging plasma ions in a discharge cell of plasma-display panel, sputtering properties of MgO(100) surface by He, Ne, and Xe atoms are studied with molecular dynamics simulations. Interatomic potentials between constituent atoms are fitted to first-principles data sets for representative configurations. Various incident directions of ions are considered with kinetic energies under 100 eV. It is found that sputtering yields for the Ne atom are largest among tested noble gases. The angle dependence of sputtering yields indicates that (111)-oriented MgO films are much more vulnerable to ion attacks than (100)-oriented layers. A surface model including the monolayer step is also studied and it is found that the yields increase substantially for grazing-angle incidence.

  10. 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.

  11. 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.

  12. Multi-particle assembled porous nanostructured MgO: its application in fluoride removal

    NASA Astrophysics Data System (ADS)

    Gangaiah, Vijayakumar; Siddaramanna, Ashoka; Thimanna Chandrappa, Gujjarahalli

    2014-12-01

    In this article, a simple and economical route based on ethylene glycol mediated process was developed to synthesize one-dimensional (1D) multiparticle assembled nanostructured MgO using magnesium acetate and urea as reactants. Porous multiparticle chain-like MgO has been synthesized by the calcination of a solvothermally derived single nanostructured precursor. The prepared products were characterized by an x-ray diffraction (XRD) pattern, thermogravimetry, scanning/transmission electron microscopy (SEM/TEM) and N2 adsorption (BET). As a proof of concept, the porous multiparticle chain-like MgO has been applied in a water treatment for isolated and rural communities, and it has exhibited an excellent adsorption capability to remove fluoride in waste water. In addition, this method could be generalized to prepare other 1D nanostructures with great potential for various attractive applications.

  13. Tunnel magnetoresistance properties and film structures of double MgO barrier magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Gan, H. D.; Ikeda, S.; Shiga, W.; Hayakawa, J.; Miura, K.; Yamamoto, H.; Hasegawa, H.; Matsukura, F.; Ohkubo, T.; Hono, K.; Ohno, H.

    2010-05-01

    The authors fabricated double MgO barrier magnetic tunnel junctions (MTJs) with 3-nm-thick Co40Fe40B20 free layer. When annealed at 350 °C, tunnel magnetoresistance (TMR) ratio at room temperature was 130%, much lower than that (297%) of single MgO barrier MTJs processed and annealed under the same condition. The middle CoFeB free layer sandwiched between the two MgO barriers was found to be mostly amorphous. Replacement of the Co40Fe40B20 free layer by a highly oriented Co50Fe50 layer and a composite Co50Fe50/Co40Fe40B20 layer led to the enhanced TMR ratios up to 165% and 212% at annealing temperature of 350 °C, respectively.

  14. 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

  15. Fabrication of a New Pyroelectric Infrared Sensor Using MgO Surface Micromachining

    NASA Astrophysics Data System (ADS)

    Kotani, Tokumi; Nakanishi, Tsutomu; Nomura, Koji

    1993-12-01

    A new La-modified PbTiO3 (PLT) pyroelectric infrared sensor with a microcavity has been successfully fabricated by MgO surface micromachining. A microcavity under the sensing element is formed by etching the front surface of the substrate in order to improve the thermal properties. To precisely control the fabrication of a microcavity, process conditions were investigated in detail. As the concentration in phosphoric acid decreased and Pt diffusion into MgO substrate increased, the side etch rate of the MgO substrate increased from 1.9 to 3.4 μm/min at 80°C. The sizes of the fabricated sensor, sensing area, and etching holes were 1× 2 mm2, 200× 240 μm2, and 60× 120 μm2, respectively. Pyroelectric coefficients of 4.0× 10-8C/cm2 K were obtained.

  16. Damage processes in MgO irradiated with medium-energy heavy ions

    SciTech Connect

    Moll, Sandra; Zhang, Yanwen; Debelle, Aurelien; Thomé, Lionel; Crocombette, Jean-Paul; Zihua, Z.; Jagielski, Jacek; Weber, William J.

    2015-01-01

    In this research, 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. In conclusion, 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 t he damage depth distribution in MgO.

  17. The reactivity of CO2 with K atoms adsorbed on MgO powders.

    PubMed

    Preda, Gloria; Pacchioni, Gianfranco; Chiesa, Mario; Giamello, Elio

    2009-10-01

    In this combined quantum chemical and EPR study we have investigated the formation of CO(2)(-) radicals by contact of CO(2) molecules with a K precovered MgO surface. K atoms have been deposited on polycrystalline MgO samples, and then exposed to CO(2). The typical EPR signal of the isolated K atoms disappears when the reaction with CO(2) takes place and a new paramagnetic species attributed to CO(2)(-) is observed. DFT cluster model calculations show that there is a spontaneous electron transfer from the adsorbed K atom to the CO(2) molecule, with formation of K(+)CO(2)(-) surface complexes. These species have the same electronic characteristics and spin distribution of gas-phase M(+)CO(2)(-) (M = Li, Na, K) molecules, but are stabilized by the presence of the ionic surface. The most stable MgO sites where the adsorption of CO(2) occurs and the computed EPR properties are discussed.

  18. Synthesis of MgO granule and its precursors via common ion effect.

    PubMed

    Choi, Se-Bum; Lee, Dong-Kyu; Yu, Hyunung

    2012-07-01

    It is well known that the shape and size of inorganic nanostructures have much influence on their optical, electrical and physical properties. MgO is a promising material with potential applications in a variety of fields such as catalyst support, reinforcing reagent and good component in superconductors. In this study, flower-like Mg(OH)2 and cubic MgCO3 have been successfully prepared via hydrolysis control of magnesium salt and alkaline solution with common ions under hydrothermal condition by the formation of nano-platelets assembly. Subsequent calcination converts both Mg(OH)2 and MgCO3 into the corresponding MgO granules of similar flower-like and cubic morphology and size to each precursor. The physical and chemical properties of MgO and its precursors of Mg(OH)2 and MgCO3 are investigated by SEM, XRD, FT-IR, and TGA analysis.

  19. Preparation of MgO supported platinum nanoparticle catalyst using toluene dispersed platinum sol

    NASA Astrophysics Data System (ADS)

    Seth, Jhumur; Nepak, Devadutta; Chaudhari, Vijay R.; Prasad, Bhagavatula L. V.

    2017-10-01

    An effective way of anchoring Pt nanoparticles on MgO using toluene dispersed platinum nanoparticles (Pt-NPs) as one of the ingredient is demonstrated. The usage of particles dispersed in toluene allows the retention of size and size distribution of preformed Pt-NPs even after deposition on MgO support with high active surface area, which is crucial for heterogeneous catalysis. The catalyst thus prepared, displayed selective hydrogenation of cinnamaldehyde to cinnamyl alcohol with high turn on frequency (TOF - 105 h-1) with respect to the total Pt content. We attribute this efficient catalytic performance to the uniform distribution and deposition of Pt on the active MgO support and its better accessible surface as evidenced by the cyclic-voltammetry results.

  20. Grain boundaries at the surface of consolidated MgO nanocrystals and acid-base functionality.

    PubMed

    Vingurt, Dima; Fuks, David; Landau, Miron V; Vidruk, Roxana; Herskowitz, Moti

    2013-09-21

    The increase of the surface basicity-acidity of MgO material by factors of 1.8-3.0 due to consolidation of its nanocrystals was demonstrated by the indicator titration. It was shown that the parallel increase of surface acidity and basicity is attributed to the formation of grain boundaries (GB) after MgO aerogel densification. A simple model predicting the increase of surface acidity-basicity of MgO that correlates with the results of direct measurements was proposed. The model is based on the study of the fine atomic structure at GB surface areas in consolidated MgO nanocrystals in the framework of Density Functional Theory. It is found that the displacements of coordinatively unsaturated surface ions near the GB are significant at the distances ~3-4 atomic layers from the geometrical contact plane between nanocrystals. The detailed analysis of atomic positions inside GB demonstrated the coordination deficiency of surface atoms at the GB areas leading to the formation of stretched bonds and to creation of low coordinated surface ions due to splitting of coordination numbers of surface atoms belonging to GB areas. Density of states for electrons shows the existence of additional states in the band gap close to the bottom of the conduction band. The adsorption energy of CO2 molecules atop oxygen atoms exposed at surface GB areas is of the same order of magnitude as that reported for oxygen atoms at crystallographic edges and corners of MgO crystals. It provides additional options for bonding of molecules at the surface of nanocrystalline MgO increasing the adsorption capacity and catalytic activity.

  1. New optical properties of MgO after MeV metal ion implantation

    NASA Astrophysics Data System (ADS)

    Zimmerman, R. L.; Ila, D.; Williams, E. K.; Sarkisov, S. S.; Poker, D. B.; Hensley, D. K.

    1999-06-01

    The implantation of metal ions into single crystals of MgO(100) followed by thermal annealing leads to an increase in absorption of ultra violet and visible light. Metal ions of Au, Sn, Ag, Cu and Ti were implanted at a depth of a few thousand Angstroms followed by thermal annealing. MgO samples implanted with He and Si ions at greater depths were used to study the optical effects and thermal annealing of radiation damage. The influence of bombardment fluence and heat treatment on the size of the metal clusters and on the fraction of atoms in clusters were measured using absorption photospectrometry.

  2. Preparation and characterization of MgO surfaces by reflection electron microscopy.

    PubMed

    Crozier, P A; Gajdardziska-Josifovska, M; Cowley, J M

    1992-02-15

    We have employed several different methods to prepare (100) and (111) surfaces of MgO crystals. (100) surfaces prepared by simple cleaving give good reflection high energy electron diffraction (RHEED) patterns and surfaces with a high density of coarse steps. Chemical polishing of this surface results in a roughening of the topography whilst annealing in oxygen considerably smoothens the surfaces although they appear to be contaminated. Under certain conditions we find that the MgO crystals will cleave along the (111) plane. Both cleaved and mechanically polished (111) surfaces are atomically flat and reconstructed after oxygen annealing.

  3. Noncatalytic dissociation of MgO by laser pulses towards sustainable energy cycle

    NASA Astrophysics Data System (ADS)

    Yabe, T.; Mohamed, M. S.; Uchida, S.; Baasandash, C.; Sato, Y.; Tsuji, M.; Mori, Y.

    2007-06-01

    We succeeded in dissociating MgO using laser pulses without a reducing agent. The energy efficiency from laser to magnesium reaction energy exceeded 42.5%. Although 1kW CO2 cw laser and Nd-YAG pulse laser are used in this experiment, the laser can be pumped by natural resources such as solar light or wind power. Thus natural resources are stored in the form of magnesium, which can be used through the reaction with water whenever we need the energy, and thus a renewable energy system will be established. This paper reports the preliminary experiments of MgO reduction toward a sustainable energy cycle.

  4. 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

  5. Improved transport properties of polycrystalline YBCO thin-films

    NASA Astrophysics Data System (ADS)

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

    1994-12-01

    Resistive evaporation technique was used to fabricate polycrystalline YBaCuO and YBaNaCuO thin films on MgO substrates. Heat treatment was carried out in a low oxygen partial pressure. Polycrystalline YBCO and Na doped YBCO thin films samples were thus obtained using the same technique and conditions. The critical current density of Na doped YBCO sample was measured to be significantly higher than that of the undoped YBCO one. The results are discussed in terms of the Na contribution to the intragrain conductivity.

  6. Enhancement of the Co magnetic moment in bcc Co1-xMnx on MgO

    NASA Astrophysics Data System (ADS)

    Snow, Ryan; Bhatkar, Harsh; N'diaye, Alpha; Arenholz, Elke; Idzerda, Yves; Montana State University Team; Lawrence Berkeley National Laboratries Team

    Using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (MCD), we show that the elemental Co moment for MBE grown thin films of bcc Co1-xMnx grown on MgO(001) is enhanced by 40% to a maximum value of 2.1 μB at x =0.24. The net Mn moment is found to align parallel with Co for all concentrations and remains roughly constant until x =0.3, then drops steadily, up to x =0.7, where the total moment of the film abruptly collapses to zero. Using a low-concentration Mn moment of 3.0 μB, the average magnetization lies directly on the Slater-Pauling (SP) curve for concentrations up to about x =.25, where it reaches a maximum moment of 2.3 μB /atom. This peak is slightly shifted and the slope is steeper on the high-Mn concentration side of the peak relative to the standard SP curve. This is in stark contrast to the fcc CoMn and hcp CoCr bulk behavior which shows only a rapid total moment reduction with Mn concentration. This material is based upon work supported by the National Science Foundation under Grant ECCS-1542210. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Con.

  7. The effect of annealing temperature on the magnetic anisotropy in Co ultrathin film on MgO(001) substrate

    NASA Astrophysics Data System (ADS)

    Zhang, Yong-Sheng; He, Wei; Tang, Jin; Ahmad, Syed Sheraz; Zhang, Wei; Li, Yan; Zhang, Xiang-Qun; Cheng, Zhao-Hua

    2017-05-01

    Co epitaxial thin films with 2.5nm thickness were prepared on single-crystal MgO(001) substrates and annealed at different temperatures. The contribution of each interface of the MgO/Co/Cu trilayer to the in-plane magnetic anisotropy (IMA) was studied by changing interfacial coupling through annealing. The structure was measured by low energy electron diffraction (LEED), and the magnetic properties were measured using the anisotropic magnetoresistance (AMR) measurements and the longitudinal Magneto-optical Kerr effect magnetometer (MOKE). We found that the magnetic anisotropy of the as-deposited one shows superposition of a two-fold symmetry with a weak four-fold contribution caused by the stress of the interface between Co/Cu, which is along the easy axis [-110]. After annealing at 200°C, the symmetry of magnetic anisotropy was changed from uniaxial magnetic anisotropy (UMA) into four-fold symmetry due to the significant increasing of four-fold magnetocrystalline anisotropy. When the films were annealed above 300°C, the damage of the MgO/Co interface additionally decreased the IMA to isotropy. Meanwhile, the coercivity raised from 45Oe (without annealing) to 1200Oe (annealed at 400°C) along the easy axis direction. Our experimental results prove that the Co/Cu interface and the MgO/Co interface play an essential role in manipulating the four-fold and the UMA in the system.

  8. Growth, structure, and magnetic properties of γ-Fe2O3 epitaxial films on MgO

    NASA Astrophysics Data System (ADS)

    Gao, Y.; Kim, Y. J.; Thevuthasan, S.; Chambers, S. A.; Lubitz, P.

    1997-04-01

    Single-crystal epitaxial thin films of γ-Fe2O3(001) have been grown on MgO(001) using oxygen-plasma-assisted molecular beam epitaxy. The structure and magnetic properties of these films have been characterized by a variety of techniques, including reflection high-energy electron diffraction (RHEED), low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy and x-ray photoelectron/Auger electron diffraction (XPD/AED), vibrating sample magnetometry, and ferromagnetic resonance. Real-time RHEED reveals that the film growth occurs in a layer-by-layer fashion. The γ-Fe2O3(001) film surface exhibits a (1×1) LEED pattern. The growth of γ-Fe2Ooverflow="scroll">3 films at 450 °C is accompanied by significant Mg outdiffusion. AED of Mg KLL Auger emission reveals that Mg substitutionally incorporates in the γ-Fe2O3 lattice, occupying the octahedral sites. Magnetic moments are ˜2300 G and ˜4500 G for γ-Fe2O3 films grown at 250 °C and 450 °C, respectively. The high magnetic moment for the films grown at 450 °C could be attributed to the high degree of structural order of the films and Mg substitution at octahedral sites.

  9. Nanodomain induced anomalous magnetic and electronic transport properties of LaBaCo{sub 2}O{sub 5.5+δ} highly epitaxial thin films

    SciTech Connect

    Ruiz-Zepeda, F.; Ma, C.; Bahena Uribe, D.; Cantu-Valle, J.; Wang, H.; Xu, Xing; Yacaman, M. J.; Ponce, A.; Chen, C.; Lorenz, B.; Jacobson, A. J.; Chu, P. C. W.

    2014-01-14

    A giant magnetoresistance effect (∼46% at 20 K under 7 T) and anomalous magnetic properties were found in a highly epitaxial double perovskite LaBaCo{sub 2}O{sub 5.5+δ} (LBCO) thin film on (001) MgO. Aberration-corrected Electron Microscopy and related analytical techniques were employed to understand the nature of these unusual physical properties. The as-grown film is epitaxial with the c-axis of the LBCO structure lying in the film plane and with an interface relationship given by (100){sub LBCO} || (001){sub MgO} and [001]{sub LBCO} || [100]{sub MgO} or [010]{sub MgO}. Orderly oxygen vacancies were observed by line profile electron energy loss spectroscopy and by atomic resolution imaging. Especially, oxygen vacancy and nanodomain structures were found to have a crucial effect on the electronic transport and magnetic properties.

  10. Nanodomain induced anomalous magnetic and electronic transport properties of LaBaCo2O5.5+δ highly epitaxial thin films

    PubMed Central

    Ruiz-Zepeda, F.; Ma, C.; Bahena Uribe, D.; Cantu-Valle, J.; Wang, H.; Xu, Xing; Yacaman, M. J.; Chen, C.; Lorenz, B.; Jacobson, A. J.; Chu, P. C. W.; Ponce, A.

    2014-01-01

    A giant magnetoresistance effect (∼46% at 20 K under 7 T) and anomalous magnetic properties were found in a highly epitaxial double perovskite LaBaCo2O5.5+δ (LBCO) thin film on (001) MgO. Aberration-corrected Electron Microscopy and related analytical techniques were employed to understand the nature of these unusual physical properties. The as-grown film is epitaxial with the c-axis of the LBCO structure lying in the film plane and with an interface relationship given by (100)LBCO || (001)MgO and [001]LBCO || [100]MgO or [010]MgO. Orderly oxygen vacancies were observed by line profile electron energy loss spectroscopy and by atomic resolution imaging. Especially, oxygen vacancy and nanodomain structures were found to have a crucial effect on the electronic transport and magnetic properties. PMID:24453381

  11. Study of the Verwey transition of Fe{sub 3}O{sub 4} films and Fe{sub 3}O{sub 4}/MgO multilayers grown by MBE

    SciTech Connect

    Veerdonk, R.J.M. van de; Heijden, P.A.A. van der |; Gijs, M.A.M.; Wolf, R.M.; Jonge, W.J.M. de

    1996-11-01

    Thin magnetite (Fe{sub 3}O{sub 4}) films and Fe{sub 3}O{sub 4}/MgO multilayers have been epitaxially grown by Molecular Beam Epitaxy (MBE) on MgO(100) and MgAl{sub 2}O{sub 4}(100) substrates. The epitaxial growth on MgO(100) substrates, with a slightly larger bulk lattice parameter than that of magnetite, resulted in an in-plane expansion of the magnetite lattice, accompanied by a perpendicular compression. For films grown on MgAl{sub 2}O{sub 4}(100), with a smaller lattice parameter, the substrate misfit is relaxed by the incorporation of misfit dislocations at the interface. It is shown that the substrates have a large effect on the magnetic and electronic properties of the films. The characteristic Verwey transition is shifted towards lower temperatures, broadened, and reduced in amplitude, more so for thinner films. This can not be quantitatively explained by substrate induced stress alone, but is more likely due to a rigid structural coupling between the magnetite film and the cubic lattice of the substrate. Hereby the orthorhombic deformation accompanying the Verwey transition may be suppressed. When growing at reduced oxygen pressure, the length scale for the rigid coupling will be reduced by the introduction of vacancies. This leads to more bulk-like resistivity and Verwey transition characteristics, but also to deviations from stoichiometry, as suggested by magnetization and Ferromagnetic Resonance (FMR) experiments.

  12. 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.

  13. Y1Ba2Cu3O7-δ thin films grown by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Takano, Satoshi; Hayashi, Noriki; Okuda, Shigeru; Hitosuyanagi, Hajime

    1989-12-01

    Y1Ba2Cu3O7-δ thin films were grown on (100)MgO and polycrystalline YSZ substrates by RF magnetron sputtering. We measured the magnetic field dependence of Jc of these films. The films grown on MgO with Jc of 4.0x106, 2.9 x106 and 1.5x104 A/cm2 at OT showed 7.1x105 A/cm2 at 8T, 1x104 A/cm2 at 20T and 1.1x103 A/cm2 at 5 T, respectively . We could attain a c-axis oriented film with a Jc of 1.2x104 A/cm2 on YSZ polycrystalline substrate, however, it showed greater degradation than the films grown on MgO in Jc with magnetic field.

  14. Y 1Ba 2Cu 3O 7-δ thin films grown by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Takano, Satoshi; Hayashi, Noriki; Okuda, Shigeru; Hitosuyanagi, Hajime

    1989-12-01

    Y 1Ba 2Cu 3O 7-δ thin films were grown on (100)MgO and polycrystalline YSZ substrates by RF magnetron sputtering. We measured the magnetic field dependence of Jc of these films. The films grown on MgO with Jc of 4.0x10 6, 2.9 x10 6 and 1.5x10 4 A/cm 2 at OT showed 7.1x10 5 A/cm 2 at 8T, 1x10 4 A/cm 2 at 20T and 1.1x10 3 A/cm 2 at 5 T, respectively . We could attain a c-axis oriented film with a Jc of 1.2x10 4 A/cm 2 on YSZ polycrystalline substrate, however, it showed greater degradation than the films grown on MgO in Jc with magnetic field.

  15. 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.

  16. Synergistic effect of MgO nanoparticles for electrochemical sensing, photocatalytic-dye degradation and antibacterial activity

    NASA Astrophysics Data System (ADS)

    Reddy Yadav, L. S.; Lingaraju, K.; Manjunath, K.; Raghu, G. K.; Sudheer Kumar, K. H.; Nagaraju, G.

    2017-02-01

    MgO nanoparticles (NPs) have been synthesized by a simple and eco-friendly route using watermelon juice as a novel fuel. The synthesized MgO NPs have been subjected to detailed characterization using various analytical techniques. The XRD pattern confirms the crystal structure of MgO which is composed of cubic phase of periclase. The FTIR spectrum gave another manifest for the presence of Mg–O bonding at 552 cm‑1. The surface structure, morphology and particle size have been studied using SEM and TEM which show the MgO NPs are in agglomerated form, almost spherical in shape and average size is about 30–50 nm. Finally, the multidimensional studies have been examined by subjecting MgO NPs as a catalyst for the photodegradation of methylene blue dye (one of the most commonly encountered environmental pollutants), antibacterial activities and electrochemical sensing for the detection of hydrazine at trace level concentration.

  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. Optical properties of MgO doped near-stoichiometric LiTaO 3 single crystals

    NASA Astrophysics Data System (ADS)

    Hu, Pengchao; Zhang, Lianhan; Xiong, Jing; Yin, Jigang; Zhao, Chengchun; He, Xiaoming; Hang, Yin

    2011-09-01

    Comparative study of the optical properties of undoped and 1-3 mol% MgO doped near-stoichiometric LiTaO 3 (SLT) crystals were undertaken. It was observed that the red shift in the absorption edge occurred with the increasing MgO doping concentration. The infrared absorption spectrum of the OH-stretch-mode in SLT was measured for crystals of undoped and 1-3 mol% MgO doped compositions. The coercive field for the crystals was measured to be 0.913, 0.610 and 0.735 kV/mm for 1-3 mol% MgO doped SLT, respectively. Photorefractive damage of SLT single crystals with 1-3 mol% MgO doping levels was measured to be 136.29, 180.25 and 222.54 MW/cm 2.

  19. Ultrathin IBAD MgO films for epitaxial growth on amorphous substrates and sub-50 nm membranes

    DOE PAGES

    Wang, Siming; Antonakos, C.; Bordel, C.; ...

    2016-11-07

    Here, a fabrication process has been developed for high energy ion beam assisted deposition (IBAD) biaxial texturing of ultrathin (~1 nm) MgO films, using a high ion-to-atom ratio and post-deposition annealing instead of a homoepitaxial MgO layer. These films serve as the seed layer for epitaxial growth of materials on amorphous substrates such as electron/X-ray transparent membranes or nanocalorimetry devices. Stress measurements and atomic force microscopy of the MgO films reveal decreased stress and surface roughness, while X-ray diffraction of epitaxial overlayers demonstrates the improved crystal quality of films grown epitaxially on IBAD MgO. The process simplifies the synthesis ofmore » IBAD MgO, fundamentally solves the “wrinkle” issue induced by the homoepitaxial layer on sub-50 nm membranes, and enables studies of epitaxial materials in electron/X-ray transmission and nanocalorimetry.« less

  20. 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.

  1. Efficient activation of peroxymonosulfate by magnetic Mn-MGO for degradation of bisphenol A.

    PubMed

    Du, Jiangkun; Bao, Jianguo; Liu, Ying; Ling, Haibo; Zheng, Han; Kim, Sang Hoon; Dionysiou, Dionysios D

    2016-12-15

    A heterogeneous manganese/magnetite/graphene oxide (Mn-MGO) hybrid catalyst was fabricated through the reduction of KMnO4 by ethylene glycol in the presence of magnetite/GO (MGO) particles. The Mn-MGO catalyst exhibited high efficacy and long-term stability in activating peroxymonosulfate (PMS) to generate sulfate radicals for the removal of bisphenol A (BPA) from water. The results of the batch experiments indicated that an increase in the catalyst dose and solution pH could enhance BPA degradation in the coupled Mn-MGO/PMS system. Regardless of the initial pH, the solution pH significantly dropped after the reaction, which was caused by catalytic PMS activation. The production of sulfate radicals and hydroxyl radicals was validated through radical quenching and electron paramagnetic resonances (EPR) tests. BPA degradation pathways were proposed on the basis of LC-MS and GC-MS analyses. Finally, a possible mechanism of catalytic PMS activation was proposed that involved electron transfer from MnO or Mn2O3 to PMS with the generation of sulfate radicals, protons and MnO2, as well as the simultaneous reduction of MnO2 by PMS.

  2. Assessment of pulmonary toxicity of MgO nanoparticles in rats.

    PubMed

    Gelli, Kiranmai; Porika, Mahendar; Anreddy, Rama Narsimha Reddy

    2015-03-01

    In this study, we have evaluated the pulmonary toxicity of MgO nanoparticles (MgO NPs) in rats following their exposure. NPs in phosphate buffered saline + 1% Tween 80 were exposed via intratracheal instillation at a doses of 1 mg/kg or 5 mg/kg into rat lungs and evaluated for various tissue damage markers like alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) in bronchoalveolar lavage (BAL) fluid and histopathology of lungs at 1, 7, and 30 days of post-exposure intervals. A dose-dependant increase in ALP and LDH activity was observed in BAL fluids of rat lungs than sham control at all post-exposure periods (P <0.05), and a dose-dependant infiltration of interstitial lymphocytes, peribronchiolar lymphocytic infiltration, and dilated and/or congested vessels at 1 day post-exposure period, worsened at 1 week period, and were reduced at 1 month at histology, indicating the pulmonary toxicity of MgO NPs. In conclusion, MgO NPs exposure produced a dose-dependent pulmonary toxicity in rats and was comparable with that of Quartz particles.

  3. 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.

  4. 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.

  5. Melting temperatures of MgO under high pressure by micro-texture analysis

    NASA Astrophysics Data System (ADS)

    Kimura, T.; Ohfuji, H.; Nishi, M.; Irifune, T.

    2017-06-01

    Periclase (MgO) is the second most abundant mineral after bridgmanite in the Earth's lower mantle, and its melting behaviour under pressure is important to constrain rheological properties and melting behaviours of the lower mantle materials. Significant discrepancies exist between the melting temperatures of MgO determined by laser-heated diamond anvil cell (LHDAC) and those based on dynamic compressions and theoretical predictions. Here we show the melting temperatures in earlier LHDAC experiments are underestimated due to misjudgment of melting, based on micro-texture observations of the quenched samples. The high melting temperatures of MgO suggest that the subducted cold slabs should have higher viscosities than previously thought, suggesting that the inter-connecting textural feature of MgO would not play important roles for the slab stagnation in the lower mantle. The present results also predict that the ultra-deep magmas produced in the lower mantle are peridotitic, which are stabilized near the core-mantle boundary.

  6. Melting temperatures of MgO under high pressure by micro-texture analysis

    PubMed Central

    Kimura, T.; Ohfuji, H.; Nishi, M.; Irifune, T.

    2017-01-01

    Periclase (MgO) is the second most abundant mineral after bridgmanite in the Earth's lower mantle, and its melting behaviour under pressure is important to constrain rheological properties and melting behaviours of the lower mantle materials. Significant discrepancies exist between the melting temperatures of MgO determined by laser-heated diamond anvil cell (LHDAC) and those based on dynamic compressions and theoretical predictions. Here we show the melting temperatures in earlier LHDAC experiments are underestimated due to misjudgment of melting, based on micro-texture observations of the quenched samples. The high melting temperatures of MgO suggest that the subducted cold slabs should have higher viscosities than previously thought, suggesting that the inter-connecting textural feature of MgO would not play important roles for the slab stagnation in the lower mantle. The present results also predict that the ultra-deep magmas produced in the lower mantle are peridotitic, which are stabilized near the core–mantle boundary. PMID:28580945

  7. Removal of azo and anthraquinone reactive dyes from industrial wastewaters using MgO nanoparticles.

    PubMed

    Moussavi, Gholamreza; Mahmoudi, Maryam

    2009-09-15

    In the present investigation, a porous MgO powder was synthesized and tested for the removal of dyes from aqueous solution. The size of the MgO particles was in the range of 38-44 nm, with an average specific surface area of 153.7 m(2)/g. Adsorption of reactive blue 19 and reactive red 198 was conducted to model azo and anthraquinone dyes at various MgO dosages, dye concentrations, solution pHs and contact times in a batch reactor. Experimental results indicate that the prepared MgO powder can remove more than 98% of both dyes under optimum operational conditions of a dosage of 0.2g, pH 8 and a contact time of 5 min for initial dye concentrations of 50-300 mg/L. The isotherm evaluations revealed that the Langmuir model attained better fits to the experimental equilibrium data than the Freundlich model. The maximum predicted adsorption capacities were 166.7 and 123.5mg of dye per gram of adsorbent for RB 19 and RR 198, respectively. In addition, adsorption kinetic data followed a pseudo-second-order rate for both tested dyes.

  8. 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.

  9. 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.

  10. SO2 Initiates the Efficient Conversion of NO2 to HONO on MgO Surface.

    PubMed

    Ma, Qingxin; Wang, Tao; Liu, Chang; He, Hong; Wang, Zhe; Wang, Weihao; Liang, Yutong

    2017-04-04

    Nitrous acid (HONO) is an important source of hydroxyl radical (OH) that determines the fate of many chemically active and climate relevant trace gases. However, the sources and the formation mechanisms of HONO remain poorly understood. In this study, the effect of SO2 on the heterogeneous reactions of NO2 on MgO as a mineral dust surrogate was investigated. The reactivity of MgO to NO2 is weak, while coexisting SO2 can increase the uptake coefficients of NO2 on MgO by 2-3 orders of magnitude. The uptake coefficients of NO2 on SO2-aged MgO are independent of NO2 concentrations in the range of 20-160 ppbv and relative humidity (0-70%RH). The reaction mechanism was demonstrated to be a redox reaction between NO2 and surface sulfite. In the presence of SO2, NO2 was reduced to nitrite under dry conditions, which could be further converted to gas-phase HONO in humid conditions. These results suggest that the reductive effect of SO2 on the heterogeneous conversion of NO2 to HONO may have a significant contribution to the unknown sources of HONO observed in polluted areas (for example, in China).

  11. 1/f noise in linearized low resistance MgO magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Almeida, J. M.; Ferreira, R.; Freitas, P. P.; Langer, J.; Ocker, B.; Maass, W.

    2006-04-01

    Low RA MgO magnetic tunnel junctions prepared at Singulus (Ta 3/CuN 30/Ta 5/PtMn 20/CoFe 2.5/Ru 0.7/CoFeB 3/MgO 1.2/CoFeB 3/Ta 5 (thickness in nanometers) were microfabricated at INESC-MN. The junctions were patterned into micron-sized sensors (5-20 μm2) with controlled shape anisotropy (aspect ratio ranging from 2 to 20). A small external longitudinal bias field (15-30 Oe) was further used to improve sensor linearity. The MgO junctions have a resistance-area product of 150 Ω μm2 and a maximum tunnel magnetoresistance of 130%. Noise measurements were done in linearized sensors, from dc to 500 kHz. The magnetic and nonmagnetic contributions to the 1/f noise were determined. From the data fitting, Hooge parameters of ~2.20×10-9 μm2 were obtained for the nonmagnetic 1/f noise. Analysis of direct experimental data revealed the possibility to detect variations of magnetic fields in the order of 10-10 T/Hz0.5 with these MgO junctions, demonstrating their potential for ultralow-field detection.

  12. 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.

  13. Nanocrystal ghosting: Extensive radiation damage in MgO induced by low-energy electrons

    NASA Astrophysics Data System (ADS)

    Frankenfield, Zackery; Kane, Kenneth; Sawyer, William H.

    2017-03-01

    We report direct evidence of extensive radiation damage in MgO nanocrystals due to intense bombardment (2 × 10 electrons/nm sec) by electrons with beam energies between 60 keV and 120 keV. Based upon a minimum intensity necessary to produce the observed damage, we present an explanation based on the Knotek-Feibelman process.

  14. 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.

  15. Hydrogen production from steam reforming of ethylene glycol over iron loaded on MgO

    NASA Astrophysics Data System (ADS)

    Chen, Mingqiang; Wang, Yishuang; Liang, Tian; Yang, Jie; Yang, Zhonglian

    2017-01-01

    In this study, a series of Fe-based catalysts loaded on MgO were prepared by a precipitation technique. And they were tested in hydrogen production from steam reforming of ethylene glycol (SRE), which was a representative model compound of fast bio-oil. The catalysts were characterized by XRD, SEM and H2-TPR analysis. The results showed that the crystalline phases of catalysts contained Fe2O3 (Hematite), Fe3O4 (Magnetite), Fe2MgO4 (iron magnesium oxide) and MgO, and morphology of MgO was changed from the rugby-ball like particles to spherical particles with the addition of Fe. In addition, the catalytic test results indicated that the 18%Fe/MgO catalyst exhibited the highest ethylene glycol conversion (˜99.8%) and H2 molar percent (˜77%) during at the following conditions: H2O/C molar ratio is 5˜7, the feeding rate is 14 mL/h and the reaction temperature at 600˜650°C. Furthermore, the 18%Fe/MgO catalyst can keep outstanding stability during SRE for 12 h.

  16. Preparation of highly dispersed MgO and its bactericidal properties

    NASA Astrophysics Data System (ADS)

    Huang, L.; Li, D.-Q.; Evans, D. G.; Duan, X.

    2005-07-01

    Samples of layered double hydroxides (LDHs) were prepared by a method involving separate nucleation and aging steps recently developed in our laboratory, using varying [ Mg2+] /[ Al3+] ratios and different aging conditions. The samples were characterized by X-ray diffraction (XRD), FT-IR spectroscopy and laser granulometry. The results showed that LDHs with different particle sizes could be obtained by controlling the reaction temperature and degree of supersaturation. Calcination of these materials affords mixtures of highly dispersed MgO and mixed metal oxides. Bactericidal experiments against Bacillus subtilis var. niger and Staphylococcus aureus were carried out using materials formed by calcination of the LDHs at 500 circC. The mechanism of bactericidal activity was also investigated. It is known that MgO is very readily hydrated and that reaction with dissolved oxygen affords superoxide anions O{2}-, which attack the secondary amide structure of proteins leading to destruction of the bacteria. The bactericidal activity of the MgO increases with specific surface area because this leads to an increased number of surface hydroxyl groups and higher concentrations of O{2}- in solution. The bactericidal ability of MgO therefore increases with decreasing particle size.

  17. 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.

  18. 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.

  19. Synthesis and Characterization of Magnesium-Alloyed Hematite Thin Films

    NASA Astrophysics Data System (ADS)

    Tang, Houwen; Matin, M. A.; Wang, Heli; Al-Jassim, Mowafak; Turner, John; Yan, Yanfa

    2012-11-01

    We have synthesized pure and Mg-alloyed hematite thin films on F-doped, SnO2-coated glass substrates by radiofrequency magnetron cosputtering of iron oxide with and without MgO sources in mixed Ar/O2 and mixed N2/O2 ambient. We found that hematite films deposited in N2/O2 ambient exhibited much poorer crystallinity than those deposited in Ar/O2 ambient. We determined that Mg alloying led to increased crystallinity and bandgap. Furthermore, we found that Mg alloying inverted the type of conductivity of the thin films: pure hematite thin films exhibited n-type conductivity, whereas Mg-alloyed hematite thin films exhibited p-type conductivity.

  20. Stability and capping of magnetite ultra-thin films

    NASA Astrophysics Data System (ADS)

    Fleischer, K.; Mauit, O.; Shvets, I. V.

    2014-05-01

    Ultrathin films of Fe3O4 have been grown epitaxially on nearly lattice matched MgO(001). The stability of 4 nm thick films in ambient air and under annealing in an oxygen atmosphere at 200 °C has been studied. By magneto optical and Raman measurements, we can confirm the presence of the Fe3O4 phase and the formation of a maghemite top layer passivating the Fe3O4 thin film. In a second step, we are able to demonstrate that this top layer oxidation in ambient air can be prevented by a 2 nm thick magnesium ferrite passivation layer, while a thicker 20 nm MgO layer prevents oxidation even at elevated temperatures.

  1. Theoretical study of oxidation-reduction reaction of Fe2O3 supported on MgO during chemical looping combustion

    NASA Astrophysics Data System (ADS)

    Qin, Wu; Chen, Qiuluan; Wang, Yang; Dong, Changqing; Zhang, Junjiao; Li, Wenyan; Yang, Yongping

    2013-02-01

    We applied density-functional theory (DFT) in periodic system to investigate the two reactions (CO + Fe2O3/MgO → CO2 + Fe2O2/MgO, O2 + Fe2O2/MgO → O + Fe2O3/MgO) in chemical looping combustion system. While Fe2O3 was supported on MgO(1 0 0) surface Fe2O3 gathered together to form a cluster shape on MgO(1 0 0), denoted as Fe2O3/MgO, where the Fe2O3 was activated by MgO(1 0 0). Then CO interacted with Fe2O3/MgO and carbonate generated during a stepwise reaction with the calculated maximum barrier energy of 0.95 eV, far less than that of the reaction between CO and the pure Fe2O3 cluster (2.59 eV). CO was oxidized by Fe2O3/MgO and then Fe2O3/MgO transformed into the reduced state Fe2O2/MgO, corresponding to the reaction in the fuel reactor in the CLC system. Then the breaking of the adsorbed O2 molecule on Fe2O2/MgO made an O atom bind to a Fe site with the barrier energy of 0. 20 eV, which played as the key step for the oxidizing of Fe2O2/MgO by O2 into Fe2O3/MgO, corresponding to the reaction in the air reactor in the CLC system.

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

    NASA Astrophysics Data System (ADS)

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

    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 10-8Torr. Simple underlayers such as 5nm 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 Co40Fe40B20 and 1 Ta/20 conetic (Ni77Fe14Cu5Mo4)/1.5 Co40Fe40B20 (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.

  3. 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.

  4. Enhanced dielectric and piezoelectric responses in Zn1-xMgxO thin films near the phase separation boundary

    DOE PAGES

    Kang, Xiaoyu; Shetty, Smitha; Garten, Lauren; ...

    2017-01-23

    Dielectric and piezoelectric properties for Zn1-xMgxO (ZMO) thin films are reported as a function of MgO composition up to and including the phase separation region. Zn1-xMgxO (0.25 ≤ x ≤ 0.5) thin films with c-axis textures were deposited by pulsed laser deposition on platinized sapphire substrates. The films were phase pure wurtzite for MgO concentrations up to 40%; above that limit, a second phase with rocksalt structure evolves with strong {100} texture. With increasing MgO concentration, the out-of-plane (d33,f) and in-plane (e31,f) piezoelectric coefficients increase by 360% and 290%, respectively. The increase in piezoelectric coefficients is accompanied by a 35%more » increase in relative permittivity. Loss tangent values fall monotonically with increasing MgO concentration, reaching a minimum of 0.001 for x ≥ 0.30, at which point the band gap is reported to be 4 eV. As a result, the enhanced piezoelectric response, the large band gap, and the low dielectric loss make Zn1-xMgxO an interesting candidate for thin film piezoelectric devices, and demonstrate that compositional phase transformations provide opportunities for property engineering.« less

  5. Enhanced dielectric and piezoelectric responses in Zn1-xMgxO thin films near the phase separation boundary

    NASA Astrophysics Data System (ADS)

    Kang, Xiaoyu; Shetty, Smitha; Garten, Lauren; Ihlefeld, Jon F.; Trolier-McKinstry, Susan; Maria, Jon-Paul

    2017-01-01

    Dielectric and piezoelectric properties for Zn1-xMgxO (ZMO) thin films are reported as a function of MgO composition up to and including the phase separation region. Zn1-xMgxO (0.25 ≤ x ≤ 0.5) thin films with c-axis textures were deposited by pulsed laser deposition on platinized sapphire substrates. The films were phase pure wurtzite for MgO concentrations up to 40%; above that limit, a second phase with rocksalt structure evolves with strong {100} texture. With increasing MgO concentration, the out-of-plane (d33,f) and in-plane (e31,f) piezoelectric coefficients increase by 360% and 290%, respectively. The increase in piezoelectric coefficients is accompanied by a 35% increase in relative permittivity. Loss tangent values fall monotonically with increasing MgO concentration, reaching a minimum of 0.001 for x ≥ 0.30, at which point the band gap is reported to be 4 eV. The enhanced piezoelectric response, the large band gap, and the low dielectric loss make Zn1-xMgxO an interesting candidate for thin film piezoelectric devices, and demonstrate that compositional phase transformations provide opportunities for property engineering.

  6. 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.

  7. Ion beam mixing effects in Ag precipitates embedded in MgO crystals

    NASA Astrophysics Data System (ADS)

    Fuchs, G.; Abouchacra, G.; Treilleux, M.; Thevenard, P.; Serughetti, J.

    1988-05-01

    MgO single crystals have been implanted at room temperature with 8 × 10 16 Ag cm -2 of 180 keV energy. After 973 K thermal annealing, Ag atoms precipitate in the MgO matrix. The MgOAg samples were then irradiated at 77 K with 800 keV xenon up to 1.7 × 10 16 ions cm -2. The modification of the metallic precipitated phase induced by such ionic bombardment, has been characterized by optical absorption spectroscopy (OAS) and transmission electron microscopy (TEM). The evolution of the optical spectra with xenon bombardment has been interpreted in terms of silver precipitate dispersion induced by ion beam mixing effects. The inhibition of atomic diffusion or radiation induced diffusion, due the low sample temperature during irradiation, increases the efficiency of atomic mixing effects. TEM observations confirm this assumption.

  8. Dynamics of Photocarriers in Crystalline α-Al_2O3 and MgO

    NASA Astrophysics Data System (ADS)

    Shan, Jie; Wang, Feng; Bonn, Mishca; Heinz, Tony F.

    2003-03-01

    The lifetime of mobile carriers in crystalline insulators is often very short because of the presence of traps, as well as exciton localization effects. Consequently direct measurement of the lifetime are challenging. Here we report application of terahertz time-domain spectroscopy together with ultrafast optical excitation [1] to probe photo-generated carriers in crystalline α-Al_2O3 (sapphire) and MgO. In high purity samples, carrier lifetimes ˜ 100 ps are observed. Sapphire shows a single exponential behavior, while bi-exponential decay is seen in MgO. We analyze these results, and their temperature dependence, in terms of a model based on trap states. 1. E Knoesel, M. Bonn, J. Shan, and T.F. Heinz, Phys. Rev. Lett. 86, 340 (2001)

  9. Photodestruction of CCl{sub 4} on MgO films with/without water

    SciTech Connect

    Zhou, X.L.; Cowin, J.P.

    1996-01-18

    Ultrahigh-vacuum (UHV) studies shows that UV irradiation (193 nm) of carbon tetrachloride adsorbed on a MgO surface produces phosgene both with/without coadsorbed water. Isotope studies show the oxygen required for the phosgene formation comes from the MgO lattice in the absence of water and from the water when coadsorbed. The reaction kinetics differ strongly between the wet and dry conditions. The observations suggest that UHV studies can reproduce important features seen in bulk studies of oxides for destruction of environmental hydrocarbons and that surface reactions may play a more important role in air or aqueous photocatalytic destruction of hydrocarbons than typically assumed. 50 refs., 17 figs.

  10. Influence of MgO doping in hot-pressing tricalcium phosphate

    NASA Astrophysics Data System (ADS)

    Acchar, W.; Costa, A. C. S.; Cairo, C. A. A.

    2011-10-01

    Tricalcium phosphate ceramics (TCP) has been widely investigated. The main advantage of this bioceramic is its bioresorbable behavior. The factor that still limits the application of these materials as temporary implants is the low strength resistance of the TCP sintered material. The tricalcium phosphate presents an allotropic transformation β to α phase around 1250 °C that degrades its resistance, limiting the sintering temperature of the compacted samples. The objective of this work is to study the physical and mechanical properties of hot-pressed tricalcium phosphate with MgO additions. The results obtained have shown that the hot-pressed process increases significantly the mechanical properties of TCP materials. The addition of MgO has not improved the sintering process and the properties of hot-pressed tricalcium phosphate.

  11. Martensitic transformation thermodynamic calculation of ZrO2-MgO system

    NASA Astrophysics Data System (ADS)

    Li, Jing; Peng, Jinhui; Guo, Shenghui; Qv, Wenwen; Chen, Guo; Li, Wei; Zhang, Libo

    2012-11-01

    The phase transformation of different polymorphs in zirconia is very important for the processing and mechanical properties of zirconia ceramics. In this work, thermodynamic description of ZrO2-MgO system is investigated using the related thermodynamic parameters. Special attention is paid to the calculation of the Gibbs free energy change between tetragonal and monoclinic phases in ZrO2-MgO, namely t → m phase transformation driving force, as a function of composition and temperature. Furthermore, in 8.7 mol% MgO-ZrO2, the equilibrium temperature between tetragonal and monoclinic phases, T0, was obtained as 1107.8 K and martensitic transformation start temperature (Ms) for t → m of this ceramic with a mean grain size of 1.15 mm was also calculated to be as 737.7 K, which is in good agreement with experiment one of 689.5 K with 7.0% residual.

  12. Processing-thermal conductivity relationships in MGO-pyrochlore composite inert matrix materials

    NASA Astrophysics Data System (ADS)

    Yates, Samantha J.

    2009-12-01

    Inert matrix (IM) materials are proposed to act as non-fertile matrices to burn excess plutonium and minor actinides in nuclear reactors. MgO is a good IM candidate because of its high thermal conductivity, good radiation resistance, and high temperature stability, but its hot water corrosion resistance is poor limiting its use in light water reactors. A composite approach has been suggested to improve the hydration resistance of the MgO by adding a pyrochlore phase to act as a hydration barrier while maximizing the effective thermal conductivity of the composite. In this work, MgO-Nd 2Zr2O7 composites are fabricated using four different processing methods to deliberately vary the microstructure thus enabling the investigation of processing-microstructure-thermal conductivity relationships in the composites. The first processing-microstructure-property relationship that is developed is the effect of the composite processing method on the sample-to-sample variation in the thermal diffusivity. The processing method affects the formation of agglomerates in the mixed composite powders, and these agglomerates are the source of MgO and Nd2Zr2O7 heterogeneities in the sintered composites. Differential sintering occurs in some of the agglomerates, resulting in the formation of circumferential cracks between the heterogeneity and the matrix. The presence of the circumferential cracks cause sample-to-sample variations of up to +/- 2 Wm-1K-1 in the thermal conductivity between composites fabricated from the same batch of mixed composite powder. This variation makes it more difficult to accurately and reliably predict the thermal conductivity of the composites. The second processing-microstructure-property relationship developed describes the effect of the contiguity of the MgO on the average thermal conductivity of the composites. The processing method is found to affect the contiguity of the MgO in the composites. Lower MgO contiguity values cause the average thermal

  13. Epitaxy of MgO magnetic tunnel barriers on epitaxial graphene.

    PubMed

    Godel, Florian; Pichonat, Emmanuelle; Vignaud, Dominique; Majjad, Hicham; Metten, Dominik; Henry, Yves; Berciaud, Stéphane; Dayen, Jean-Francois; Halley, David

    2013-11-29

    Epitaxial growth of electrodes and tunnel barriers on graphene is one of the main technological bottlenecks for graphene spintronics. In this paper, we demonstrate that MgO(111) epitaxial tunnel barriers, one of the prime candidates for spintronic application, can be grown by molecular beam epitaxy on epitaxial graphene on SiC(0001). Ferromagnetic metals (Fe, Co, Fe20Ni80) were epitaxially grown on top of the MgO barrier, thus leading to monocrystalline electrodes on graphene. Structural and magnetic characterizations were performed on these ferromagnetic metals after annealing and dewetting: they form clusters with a 100 nm typical lateral width, which are mostly magnetic monodomains in the case of Fe. This epitaxial stack opens the way to graphene spintronic devices taking benefits from a coherent tunnelling current through the epitaxial MgO/graphene stack.

  14. 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.

  15. Kinetic Modeling for the Dissolution of MgO Lining Refractory in Al-Killed Steels

    NASA Astrophysics Data System (ADS)

    Huang, Fuxiang; Zhang, Lifeng; Zhang, Ying; Ren, Ying

    2017-08-01

    A kinetic model for the dissolution of the magnesia refractory in Al-killed steels was developed to predict the change of chemical compositions in the molten steel. Coupled reaction model and empirical equations were employed to calculate reactions between the refractory and the molten steel. The calculated result showed good agreement with the experimental value from the literature. The relationship between the mass transfer coefficient and the stirring energy dissipation in the molten steel was obtained as k = ( {5.6 - 4.7 × e^{-96.6\\dot{ɛ } ) × 10^{ - 4} m/s. The formation of spinels is dependent on the chemical composition of the molten steel. The MgO refractory may react with Al and O in the liquid steel. Meanwhile, the decomposing of the MgO refractory also plays an important role in the dissolution of the magnesia refractory in Al-killed steels.

  16. Products of hydratation in fine grained mixtures MgO - SiO2

    NASA Astrophysics Data System (ADS)

    Szczerba, J.; Prorok, R.; Madej, D.; Sniezek, E.

    2013-12-01

    The aim of this study was to evaluate the influence of time of ageing on phase evolution of paste from MgO-SiO2-H2O phase system. The paste was composed of fine grained sintered magnesia and microsilica in 1:2 molar ratio and water, with water to solid ratio equal 0,5. After preparation the paste was ageing during specified time up to 180 days in temperature 20° C. Phase composition of mixture of MgO and SiO2 with water was studied by XRD, DTA-TGA. The analysis revealed that product of reaction in mixture of MgO, SiO2 and water was a probably poorly crystalline magnesium silicate.

  17. Calculated elastic and thermal properties of MGO at high pressures and temperatures

    NASA Astrophysics Data System (ADS)

    Isaak, Donald G.; Cohen, Ronald E.; Mehl, Michael J.

    1990-05-01

    Using the potential-induced breathing model, we calculate the pressure and temperature dependence of the thermoelastic properties of MgO. These calculations represent the first attempt to obtain a consistent set of thermodynamic elastic moduli for an oxide from an ab initio model over a wide range of pressure and temperature. By assuming the quasi-harmonic approximation for the free energies, we find excellent agreement between the temperature dependence of calculated elastic moduli and those obtained from experiments. Comparison of the calculated athermal and isothermal elastic moduli shows approximations using athermal values to be unreliable at high temperature. The elastic moduli for MgO are presented for pressures and temperatures appropriate for the lower mantle, a regime in which elastic moduli cannot be obtained by direct measurement.

  18. A comparative study of equations of state for MgO

    NASA Astrophysics Data System (ADS)

    Kushwah, S. S.; Shanker, J.

    1998-10-01

    The pressure-volume-temperature relationship, isothermal bulk modulus KT and pressure derivative of KT have been evaluated for MgO in the temperature range 300-2000 K and down to a compression of V/ V0=0.60 using six different phenomenological forms for the isothermal equation of state (EOS). The results are discussed and compared with the values for MgO obtained by Isaak et al. using the potential induced breathing electron gas model based on the first principles approach. It is found that phenomenological isothermal equations are applicable even at a high temperature if the input parameters ( K0 and K0‧) corresponding to that temperature are used. The results obtained from the Vinet EOS and the Shanker EOS are very similar and also close to the ab initio values determined by Isaak et al.

  19. Influence of Basicity and MgO on Fluidity and Desulfurization Ability of High Aluminum Slag

    NASA Astrophysics Data System (ADS)

    Wang, Ping; Meng, Qing-min; Long, Hong-ming; Li, Jia-xin

    2016-08-01

    The viscosity of experimental slag, which was mixed based on the composition of a practical blast furnace slag, was measured in this paper. The influence of Al2O3 and MgO content, basicity R2 = w(CaO)/w(SiO2) on the fluidity of slag was studied. The stepwise regression analysis in SPSS was used to reveal the relationship between sulfur distribution coefficient LS and slag composition as well as furnace temperature. The results show that increasing of MgO up to 12% can decrease the slag viscosity. The w(MgO) should be controlled below 8% when there is 20% Al2O3 in the slag. Temperature of hot metal and content of CaO in slag are the two dominant factors on the desulfurization capacity of slag.

  20. 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

  1. First-principles investigation of magnetocrystalline anisotropy at the L 21 full Heusler |MgO interfaces and tunnel junctions

    NASA Astrophysics Data System (ADS)

    Vadapoo, Rajasekarakumar; Hallal, Ali; Yang, Hongxin; Chshiev, Mairbek

    2016-09-01

    Magnetocrystalline anisotropy at Heusler alloy |MgO interfaces has been studied using first-principles calculations. It has been found that Co-terminated Co2FeAl |MgO interfaces show perpendicular magnetic anisotropy up to 1.31 mJ/m2, while those with FeAl termination exhibit in-plane magnetic anisotropy. Atomic layer-resolved analysis indicates that the origin of perpendicular magnetic anisotropy in Co2FeAl |MgO interfaces can be attributed to the out-of-plane orbital contributions of interfacial Co atoms. At the same time, Co2MnGe and Co2MnSi interfaced with MgO tend to favor in-plane magnetic anisotropy for all terminations.

  2. Valence band offset of MgO /InN heterojunction measured by x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, P. F.; Liu, X. L.; Zhang, R. Q.; Fan, H. B.; Song, H. P.; Wei, H. Y.; Jiao, C. M.; Yang, S. Y.; Zhu, Q. S.; Wang, Z. G.

    2008-01-01

    MgO may be a promising gate dielectric and surface passivation film for InN based devices and the valence band offset of MgO /InN heterojunction has been measured by x-ray photoelectron spectroscopy. The valence band offset is determined to be 1.59±0.23eV. Given the experimental band gap of 7.83 for the MgO, a type-I heterojunction with a conduction band offset of 5.54±0.23eV is found. The accurate determination of the valence and conduction band offsets is important for use of MgO /InN electronic devices.

  3. Very low 1/f barrier noise in sputtered MgO magnetic tunnel junctions with high tunneling magnetoresistance

    SciTech Connect

    Feng, J. F.; Chen, J. Y.; Kurt, H.; Coey, J. M. D.

    2012-12-15

    Low frequency 1/f barrier noise has been investigated in sputtered MgO magnetic tunnel junctions (MTJs) with a tunneling magnetoresistance ratio of up to 330% at room temperature. The lowest normalized noise parameter {alpha} of the tunnel barrier reaches 2.5 Multiplication-Sign 10{sup -12}-2.1 Multiplication-Sign 10{sup -11} {mu}m{sup 2}, which is comparable to that found in MTJs with the MgO barrier grown by MBE or electron-beam evaporation. This normalized barrier noise is almost bias independent in the voltage range of up to {+-}1.2 V. The low noise level and high voltage stability may reflect the high quality of the sputtered MgO with a uniform distribution of defects in the MgO layer.

  4. 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.

  5. Crystalline Structure of MgO Prepared by the Sol-Gel Technique with Different Hydrolysis Catalysts

    NASA Astrophysics Data System (ADS)

    Bokhimi; Morales, A.; Lopez, T.; Gomez, R.

    1995-03-01

    We have prepared MgO by the sol-gel technique using different hydrolysis catalysts that control the size of the particle and its evolution with temperature. The phases in the sample were identified by X-ray diffraction. The evolution in the temperature range between 150 and 900°C of the MgO crystalline structure was studied by Rietveld refinement technique. As a profile for the diffraction peaks we used a modified pseudo-Voigt function with the average particle size as one of its fitting parameters. This allowed us to follow the evolution of particle size with temperature for the different hydrolysis catalysts. From the Mg deficiency in the MgO lattice we find Mg:O molar ratios between 3.56(2):4.00 and 3.85(3):4.00 depending on the average particle size.

  6. Modelling the chemistry of Mn-doped MgO for bulk and (100) surfaces.

    PubMed

    Logsdail, Andrew J; Downing, Christopher A; Keal, Thomas W; Sherwood, Paul; Sokol, Alexey A; Catlow, C Richard A

    2016-10-19

    We have investigated the energetic properties of Mn-doped MgO bulk and (100) surfaces using a QM/MM embedding computational method, calculating the formation energy for doped systems, as well as for surface defects, and the subsequent effect on chemical reactivity. Low-concentration Mn doping is endothermic for isovalent species in the bulk but exothermic for higher oxidation states under p-type conditions, and compensated by electrons going to the Fermi level rather than cation vacancies. The highest occupied dopant Mn 3d states are positioned in the MgO band gap, about 4.2 eV below the vacuum level. Surface Mn-doping is more favourable than subsurface doping, and marginally exothermic on a (100) surface at high O2 pressures. For both types of isovalent Mn-doped (100) surfaces, the formation energy for catalytically important oxygen defects is less than for pristine MgO, with F(0) and F(2+)-centres favoured in n- and p-type conditions, respectively. In addition, F(+)-centres are stabilised by favourable exchange coupling between the Mn 3d states and the vacancy-localised electrons, as verified through calculation of the vertical ionisation potential. The adsorption of CO2 on to the pristine and defective (100) surface is used as a probe of chemical reactivity, with isovalent subsurface Mn dopants mildly affecting reactivity, whereas isovalent surface-positioned Mn strongly alters the chemical interactions between the substrate and adsorbate. The differing chemical reactivity, when compared to pristine MgO, justifies further detailed investigations for more varied oxidation states and dopant species.

  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. 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.

  9. A One-Phase Approach for Predicting the Melting Curve of MgO

    NASA Astrophysics Data System (ADS)

    Okamoto, Kazuma; Fuchizaki, Kazuhiro

    2017-06-01

    The melting curve of MgO, an important compound dissociated from the component of the Earth's lower mantle, was predicted in this work by using a one-phase approach. The existing data for the melting points under pressures were used as input. The necessary thermodynamic information was supplemented by constructing the equation of state. The melting point near the core-mantle boundary was estimated to be approximately 6000 K.

  10. Thermal and irradiation induced interdiffusion in magnetite thin films grown on magnesium oxide (0 0 1) substrates

    NASA Astrophysics Data System (ADS)

    Kim-Ngan, N.-T. H.; Balogh, A. G.; Meyer, J. D.; Brötz, J.; Zając, M.; Ślęzak, T.; Korecki, J.

    2009-05-01

    Epitaxial Fe 3O 4(0 0 1) thin films (with a thickness in the range of 10-20 nm) grown on MgO substrates were characterized using low-energy electron diffraction (LEED), conversion electron Mössbauer spectroscopy (CEMS) and investigated using Rutherford backscattering spectrometry (RBS), channeling (RBS-C) experiments and X-ray reflectometry (XRR). The Mg out-diffusion from the MgO substrate into the film was observed for the directly-deposited Fe 3O 4/MgO(0 0 1) films. For the Fe 3O 4/Fe/MgO(0 0 1) films, the Mg diffusion was prevented by the Fe layer and the surface layer is always a pure Fe 3O 4 layer. Annealing and ion beam mixing induced a very large interface zone having a spinel and/or wustite formula in the Fe 3O 4-on-Fe film system.

  11. Elasticity of Single Crystal MgO to 8 Gigapascals and 1600 Kelvin

    SciTech Connect

    Chen,G.; Liebermann, R.; Weidner, D.

    1998-01-01

    The cross pressure (P) and temperature (T) dependence of the elastic moduli (C{sub ij}) of single-crystal samples of periclase (MgO) from acoustic wave travel times was measured with ultrasonic interferometry: {partial_derivative}{sup 2}C{sub 11}/{partial_derivative}P{partial_derivative}T = (-1.3 {+-} 0.4) x 10{sup -3} per kelvin; {partial_derivative}{sup 2}C{sub 110}/{partial_derivative}P{partial_derivative}T = (1.7 {+-} 0.7) x 10{sup -3} per kelvin; and {partial_derivative}{sup 2}C{sub 44}/{partial_derivative}P{partial_derivative}T = (-0.2 {+-} 0.3) x 10{sup -3} per kelvin. The elastic anisotropy of MgO decreases with increasing pressure at ambient temperature, but then increases as temperature is increased at high pressure. An assumption of zero cross pressure and temperature derivatives for the elastic moduli underestimates the elastic anisotropy and overestimates the acoustic velocities of MgO at the extrapolated high-pressure and high-temperature conditions of Earth's mantle.

  12. Derivation of the spin Hamiltonians for Fe in MgO

    NASA Astrophysics Data System (ADS)

    Ferrón, A.; Delgado, F.; Fernández-Rossier, J.

    2015-03-01

    A method to calculate the effective spin Hamiltonian for a transition metal impurity in a non-magnetic insulating host is presented and applied to the paradigmatic case of Fe in MgO. In the first step we calculate the electronic structure employing standard density functional theory (DFT), based on generalized gradient approximation (GGA), using plane waves as a basis set. The corresponding basis of atomic-like maximally localized Wannier functions is derived and used to represent the DFT Hamiltonian, resulting in a tight-binding model for the atomic orbitals of the magnetic impurity. The third step is to solve, by exact numerical diagonalization, the N electron problem in the open shell of the magnetic atom, including both effects of spin-orbit and Coulomb repulsion. Finally, the low energy sector of this multi-electron Hamiltonian is mapped into effective spin models that, in addition to the spin matrices S, can also include the orbital angular momentum L when appropriate. We successfully apply the method to Fe in MgO, considering both the undistorted and Jahn-Teller (JT) distorted cases. Implications for the influence of Fe impurities on the performance of magnetic tunnel junctions based on MgO are discussed.

  13. Structural properties of Au and Ag nanoclusters embedded in MgO

    NASA Astrophysics Data System (ADS)

    van Huis, M. A.; Fedorov, A. V.; van Veen, A.; Falub, C. V.; Eijt, S. W. H.; Kooi, B. J.; De Hosson, J. Th. M.; Hibma, T.; Zimmerman, R. L.

    2002-05-01

    Gold and silver nanoclusters embedded in MgO were created by means of ion implantation of 1.0 MeV Au or 600 keV Ag ions to a dose of 10 16 cm -2 into single crystals of MgO(1 0 0) and subsequent annealing at 1473 K for a period of 22 h. The structural properties of the nanoclusters were characterised by optical absorption spectroscopy (OAS), high-resolution X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). Nanocluster sizes are estimated using three different methods: using the Doyle formula for the broadening of the optical absorption peak associated with Mie plasmon resonance; using the Scherrer formula for the broadening of the Au and Ag XRD peaks, and from direct observation of TEM images. For the Au clusters, the methods are in excellent agreement with mean cluster sizes of 4-5 nm. For the Ag clusters, the optical Doyle method yields a mean nanocluster size of 5 nm while the XRD and XTEM methods yield 10-11 nm. The XRD and XTEM results reveal a cube-on-cube orientation relationship of the Au and Ag nanoclusters with respect to the MgO matrix.

  14. Lattice thermal conductivity of MgO at conditions of Earth's interior.

    PubMed

    Tang, Xiaoli; Dong, Jianjun

    2010-03-09

    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.

  15. Spin pumping in magnetic trilayer structures with an MgO barrier

    PubMed Central

    Baker, A. A.; Figueroa, A. I.; Pingstone, D.; Lazarov, V. K.; van der Laan, G.; Hesjedal, T.

    2016-01-01

    We present a study of the interaction mechanisms in magnetic trilayer structures with an MgO barrier grown by molecular beam epitaxy. The interlayer exchange coupling, Aex, is determined using SQUID magnetometry and ferromagnetic resonance (FMR), displaying an unexpected oscillatory behaviour as the thickness, tMgO, is increased from 1 to 4 nm. Transmission electron microscopy confirms the continuity and quality of the tunnelling barrier, eliminating the prospect of exchange arising from direct contact between the two ferromagnetic layers. The Gilbert damping is found to be almost independent of the MgO thickness, suggesting the suppression of spin pumping. The element-specific technique of x-ray detected FMR reveals a small dynamic exchange interaction, acting in concert with the static interaction to induce coupled precession across the multilayer stack. These results highlight the potential of spin pumping and spin transfer torque for device applications in magnetic tunnel junctions relying on commonly used MgO barriers. PMID:27752117

  16. Effects of MgO on the Reduction of Vanadium Titanomagnetite Concentrates with Char

    NASA Astrophysics Data System (ADS)

    Chen, Chao; Sun, TiChang; Wang, XiaoPing; Hu, TianYang

    2017-10-01

    The effects of MgO on the carbothermic reduction behavior of vanadium titanomagnetite concentrates (VTC) from Chengde, China, were investigated via temperature-programmed heating under nitrogen atmosphere in a sealed furnace. Gaseous product content was measured by using an infrared gas analyzer, and it was found that the addition of MgO to VTC with char decreased the reduction rate and reduction degree, and the utilization of CO in VTC reduction was also reduced. X-ray diffraction results showed that magnesium titanate (Mg2TiO4) was formed but FeTi2O5 was not observed in the VTC reduction process by adding 6 wt.% MgO, which can be explained by thermodynamic analysis. Scanning electron microscopy revealed that the enrichment of Mg in the unreacted core was the main reason that the further reduction of VTC was restricted. However, comparatively pure particles of Mg2TiO4 were generated, and the titanium and iron were separated well due to the combination of magnesium and titanium.

  17. Spin pumping in magnetic trilayer structures with an MgO barrier

    NASA Astrophysics Data System (ADS)

    Baker, A. A.; Figueroa, A. I.; Pingstone, D.; Lazarov, V. K.; van der Laan, G.; Hesjedal, T.

    2016-10-01

    We present a study of the interaction mechanisms in magnetic trilayer structures with an MgO barrier grown by molecular beam epitaxy. The interlayer exchange coupling, Aex, is determined using SQUID magnetometry and ferromagnetic resonance (FMR), displaying an unexpected oscillatory behaviour as the thickness, tMgO, is increased from 1 to 4 nm. Transmission electron microscopy confirms the continuity and quality of the tunnelling barrier, eliminating the prospect of exchange arising from direct contact between the two ferromagnetic layers. The Gilbert damping is found to be almost independent of the MgO thickness, suggesting the suppression of spin pumping. The element-specific technique of x-ray detected FMR reveals a small dynamic exchange interaction, acting in concert with the static interaction to induce coupled precession across the multilayer stack. These results highlight the potential of spin pumping and spin transfer torque for device applications in magnetic tunnel junctions relying on commonly used MgO barriers.

  18. Spin pumping in magnetic trilayer structures with an MgO barrier.

    PubMed

    Baker, A A; Figueroa, A I; Pingstone, D; Lazarov, V K; van der Laan, G; Hesjedal, T

    2016-10-18

    We present a study of the interaction mechanisms in magnetic trilayer structures with an MgO barrier grown by molecular beam epitaxy. The interlayer exchange coupling, Aex, is determined using SQUID magnetometry and ferromagnetic resonance (FMR), displaying an unexpected oscillatory behaviour as the thickness, tMgO, is increased from 1 to 4 nm. Transmission electron microscopy confirms the continuity and quality of the tunnelling barrier, eliminating the prospect of exchange arising from direct contact between the two ferromagnetic layers. The Gilbert damping is found to be almost independent of the MgO thickness, suggesting the suppression of spin pumping. The element-specific technique of x-ray detected FMR reveals a small dynamic exchange interaction, acting in concert with the static interaction to induce coupled precession across the multilayer stack. These results highlight the potential of spin pumping and spin transfer torque for device applications in magnetic tunnel junctions relying on commonly used MgO barriers.

  19. 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

  20. 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.

  1. 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. Copyright © 2014. Published by Elsevier B.V.

  2. 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.

  3. Structural, electronic, magnetic and chemical properties of B-, C- and N-doped MgO(001) surfaces.

    PubMed

    Pašti, Igor A; Skorodumova, Natalia V

    2016-01-07

    Doping of simple oxide materials can give rise to new exciting physical and chemical properties and open new perspectives for a variety of possible applications. Here we use density functional theory calculations to investigate the B-, C- and N-doped MgO(001) surfaces. We have found that the investigated dopants induce magnetization of the system amounting to 3, 2 and 1 μB for B, C and N, respectively. The dopants are found to be in the X(2-) state and tend to segregate to the surface. These impurity sites also present the centers of altered chemical reactivity. We probe the chemisorption properties of the doped MgO(001) surfaces with the CO molecule and atomic O. The adsorption of CO is much stronger on B- and C-doped MgO(001) compared to pure MgO(001) as the impurity sites serve as potent electron donors. The situation is similar to the case of atomic oxygen, for which we find the adsorption energy of -8.78 eV on B-doped MgO(001). The surface reactivity changes locally around the dopant atom, which is mainly restricted to its first coordination shell. The presented results suggest doped MgO as a versatile multifunctional material with possible use as an adsorbent or a catalyst.

  4. 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.

  5. 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

    2016-10-01

    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.

  6. Enhancement of electric-field-induced change of magnetic anisotropy by interface engineering of MgO magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Bonaedy, Taufik; Choi, Jun Woo; Jang, Chaun; Min, Byoung-Chul; Chang, Joonyeon

    2015-06-01

    Electric-field-induced modification of magnetic anisotropy is studied using tunnel magnetoresistance of the Co40Fe40B20/ MgO/ Co40Fe40B20 and Co40Fe40B20/ Hf (0.08 nm)/ MgO/ Co40Fe40B20 magnetic tunnel junctions. In both systems, the interfacial perpendicular magnetic anisotropy is increased with increasing electron density at the MgO interface. A quantitative comparison between the two systems reveals that the change of magnetic anisotropy energy with electric field is significantly enhanced in Co40Fe40B20/ Hf/ MgO/ Co40Fe40B20 compared to Co40Fe40B20/ MgO/ Co40Fe40B20. The sub-monolayer Hf insertion at the Co40Fe40B20/MgO interface turns out to be critical to the enhanced electric field control of the magnetic anisotropy, indicating the interface sensitive nature of the effect.

  7. Effects of high temperature and e-beam irradiation on the stability of refractory thin films

    NASA Technical Reports Server (NTRS)

    Lee, E. H.; Poppa, H.

    1977-01-01

    Refractory thin films of Al2O3, ZrO2, MgO, ThO2, and BN have been investigated in situ in an UHV transmission electron microscope. The electron transparent refractory films were prepared by electron-beam evaporation, anodization, RF sputtering, and thinning of bulk crystal materials. The study concentrates on monitoring the thermal and mechanical stability of the films, phase and structural changes, and electron irradiation effects as a function of film-preparation conditions. With increasing temperatures, five different crystallographic phases were observed for both anodized and electron-beam-evaporated alumina films. Zirconia films exhibited two phase transitions upon heating to 1200 C and electron-irradiation-induced crystallization of ZrO2 even at room temperature. MgO, ThO2, and BN films did not undergo any noticeable phase transformation but ruptured due to sintering below 1200 C.

  8. Investigations of LBMO thin films deposited on different substrates by electron beam evaporation

    NASA Astrophysics Data System (ADS)

    Seshendra Reddy, Ch.; Ashoka Reddy, Ch.; Sivasankar Reddy, A.; Sreedhara Reddy, P.

    2016-04-01

    La0.7Ba0.3MnO3 (LBMO) thin films were prepared on different substrates such as Si, MgO, and c-ZrO2 substrates at substrate temperature 1023 K using electron beam evaporation technique for first time. Through optimizing the preparation condition, the better film uniformity of thickness, composition, and temperature was achieved. To find the influence of substrates, we studied the structural, compositional, morphological, and electrical properties of LBMO thin films. All the LBMO films exhibited a single phase and good crystallinity with no impurity phases. Films deposited on MgO have high temperature coefficient of resistance (TCR) value with low transition temperature (245 K). Better TCR (4.09 %/K) value at room temperature is observed in LBMO films deposited on Si substrate.

  9. High Quality Transferable AlN Thin Film by PLD

    NASA Astrophysics Data System (ADS)

    Li, Heng; Lu, Xiaoli; Li, Xin; Zhang, JinCheng; Hao, Yue

    2017-06-01

    AlN thin film was epitaxial grown on c-plane sapphire substrate by pulsed laser deposition. To reduce structural defects from largely lattice mismatched substrate, MgO or ZnO buffer layer was inserted between AlN and sapphire. Crystal structure and surface morphology of as prepared AlN were characterized by XRD, AFM, and SEM. It was found that buffer layers significantly improve crystalline quality of AlN, especially using ZnO. Furthermore, a general and steady wet chemical process was developed to selectively etch away ZnO layer, so that high quality free-standing AlN thin film was obtained. This film could be transferred onto any other host substrates such as Si, quartz, etc. Moreover, with no clamping effect from the substrate, the as-prepared free-standing AlN thin films may find potential applications in high sensitivity piezoelectric devices, flexible wearable detectors and so on.

  10. 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.

  11. YSZ thin films with minimized grain boundary resistivity

    SciTech Connect

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

    2016-03-31

    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 Mg2+ 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.

  12. 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.

  13. Origin of the giant magnetic moment in epitaxial Fe3O4 thin films

    NASA Astrophysics Data System (ADS)

    Orna, J.; Algarabel, P. A.; Morellón, L.; Pardo, J. A.; de Teresa, J. M.; López Antón, R.; Bartolomé, F.; García, L. M.; Bartolomé, J.; Cezar, J. C.; Wildes, A.

    2010-04-01

    We study the enhanced magnetic moment observed in epitaxial magnetite (Fe3O4) ultrathin films (t<15nm) grown on MgO (001) substrates by means of pulsed laser deposition. The Fe3O4 (001) thin films exhibit high crystallinity, low roughness, and sharp interfaces with the substrate, and the existence of the Verwey transition at thicknesses down to 4 nm. The evolution of the Verwey transition temperature with film thickness shows a dependence with the antiphase boundaries density. Superconducting quantum interference device (SQUID) and vibrating sample magnetometry measurements in ultrathin films show a magnetic moment much higher than the bulk magnetite value. In order to study the origin of this anomalous magnetic moment, polarized neutron reflectivity (PNR), and x-ray magnetic circular dichroism (XMCD) experiments have been performed, indicating a decrease in the magnetization with decreasing sample thickness. X-ray photoemission spectroscopy measurements show no metallic Fe clusters present in the magnetite thin films. Through inductively coupled plasma mass spectroscopy and SQUID magnetometry measurements performed in commercial MgO (001) substrates, the presence of Fe impurities embedded within the substrates has been observed. Once the substrate contribution has been corrected, a decrease in the magnetic moment of magnetite thin films with decreasing thickness is found, in good agreement with the PNR and XMCD measurements. Our experiments suggest that the origin of the enhanced magnetic moment is not intrinsic to magnetite but due to the presence of Fe impurities in the MgO substrates.

  14. Multifunctional ferrimagnetic-ferroelectric thin films for microwave applications

    NASA Astrophysics Data System (ADS)

    Heindl, R.; Srikanth, H.; Witanachchi, S.; Mukherjee, P.; Heim, A.; Matthews, G.; Balachandran, S.; Natarajan, S.; Weller, T.

    2007-06-01

    Ferrimagnetic and ferroelectric structures based on barium strontium titanate and barium hexaferrite are investigated for potential applications in tunable microwave devices. Thin film bilayers were grown on MgO and sapphire, and their underlying crystallographic, microstructural, and magnetic properties were analyzed and compared. Microcircuits were fabricated using optical lithography, and microwave properties and electrical tunability were measured in the range of 1-50GHz. Overall, the studies demonstrate the possibility of realizing high quality multifunctional microwave materials that combine tunable magnetic and dielectric properties.

  15. Detecting properties of YBaCuO thin film bridges

    SciTech Connect

    Tavkhelidze, A.N.; Kuzmin, L.S.; Soldatov, E.S. ); OkhrimenKo, V.N.; Kovalev, A.S.; Seleznev, B.V.; Pirogov, V.G. )

    1991-03-01

    The paper studies the properties of YBaCuO superconducting microbridges. They were fabricated by both direct photolithographic techniques and focused laser beam patterning. The YBaCuO thin films were deposited onto ZrO{sub 2}, MgO, and SrTiO{sub 3} substrates by laser ablation of a massive YBaCuO target. Josephson effect was observed in the bridges by detecting Shapiro steps and selective response under irradiation with the signal frequency of 27-36 GHz.

  16. Experimental and DFT studies of gold nanoparticles supported on MgO(111) nano-sheets and their catalytic activity.

    PubMed

    Li, Zhi; Ciobanu, Cristian V; Hu, Juncheng; Palomares-Báez, Juan-Pedro; Rodríguez-López, José-Luis; Richards, Ryan

    2011-02-21

    A wet chemical preparation of MgO with the (111) facet as the primary surface has recently been reported and with alternating layers of oxygen anions and magnesium cations, this material shows unique chemical and physical properties. The potential to utilize the MgO(111) surface for the immobilization of metal particles is intriguing because the surface itself offers a very different environment for the metal particle with an all oxygen interface, as opposed to the typical (100) facet that possesses alternating oxygen anion and magnesium cation sites on the surface. Gold nanoparticles have demonstrated a broad range of interesting catalytic properties, but are often susceptible to aggregation at high temperatures and are very sensitive to substrate effects. Here, we investigate gold-supported on MgO(111) nanosheets as a catalyst system for the aerobic oxidation of benzyl alcohol. Gold nanoparticles deposited on MgO(111) show an increased level of activity in the solvent-free benzyl alcohol aerobic oxidation as compared to gold nanoparticles deposited on a typical MgO aerogel. TEM studies reveal that the gold nanoparticles have a hemispherical shape while sitting on the main surface of MgO(111) nanosheets, with a large Au-MgO interface. Given that the gold nanoparticles deposited on the two types of MgO have similar size, and that the two types of unmodified MgO show almost the same activities in the blank reaction, we infer that the high activity of Au/MgO(111) is due to the properties of the (111) support and/or those of the gold-support interface. To understand the binding of Au on low-index MgO surfaces and the charge distribution at the surface of the support, we have performed density functional theory (DFT) calculations on all low-index MgO substrates (with and without gold), using a model Au(10) cluster. Due to similar lattice constants of Au(111) and MgO(111) planes, the Au cluster retains its structural integrity and binds strongly on MgO(111) with either

  17. Ion-beam-induced texturing in oxide thin films and its applications

    NASA Astrophysics Data System (ADS)

    Wang, Pin-Chin Connie

    1999-11-01

    Ion-beam-assisted deposition (IBAD) has been demonstrated to be one of the most promising methods to artificially control thin films' texture. Recent years, much research has been conducted to try to control the in-plane alignment in oxide films for the high Tc superconductor YBa 2Cu3O7-x (HTS YBCO) power applications. The IBAD films deposited on engineering substrate can potentially replace the single crystal substrates, enabling large area and economical applications of the YBCO film. Thus far, the focus has been on IBAD YSZ and CeO2. However, both need to be thick to achieve good in-plane alignment. This requirement makes the IBAD process too costly for production. The IBAD MgO work started at Stanford several years ago. In contrast to YSZ, we demonstrated that the MgO texture started from the nucleation stage and we were able to obtain 7° in-plane alignment in a 100A IBAD MgO film. This reduces the processing cost by orders of magnitude as compared with IBAD YSZ. We studied the MgO texture development process using in-situ RHEED and ex-situ TEM and XRD. The results showed that the IBAD MgO film formed small rectangular islands, which coalesced to form a continuous film. We discussed the MgO texture as functions of key parameters, such as ion energy, ion angle, ion beam divergence, ion-to-molecule ratio, deposition temperature, etc. The ion angle study supported the differential sputtering yield/ion channeling type of ion-selecting-texture mechanism. The results of IBAD MgO were compared with that of the IBAD YSZ, suggesting that the different crystalline structures between the two materials can be used to explain the differences. This thesis also discusses our attempt to substitute single crystal substrates with the IBAD MgO in practical systems. In the HTS YBCO application, we obtained YBCO films on alpha-SiN coated poly-Alumina with in-plane misalignment less than 4° and Jc of 2.5MA/cm2. In the magnetic spin valve device applications, we obtained Ni

  18. Dynamical Interplay Between Intrinsic Defects and Impurity Ions in Very Dilute Fe-doped MgO Thin Films

    NASA Astrophysics Data System (ADS)

    Wang, Yung Jui; Kapilashrami, Mukes; Li, Xin; Glans, Per-Anders; Fang, Mei; Riazanova, Anastasia V.; Belova, Lyubov M.; Rao, K. V.; Luo, Yi; Barbiellini, B.; Lin, Hsin; Markiewicz, R. S.; Hussain, Zahid; Guo, Jinghua; Bansil, A.

    2015-03-01

    The nature of intrinsic defects and impurities in the dielectric layer of a typical magneto tunneling junction is of great interest to understand tunneling of spin-polarized currents. In this connection, we have carried out studies of the electronic and magnetic properties of Mg1-xFexO. In particular, we have compared results from first principles calculations based on Density Functional Theory with highly accurate experiments. The measurements were performed with a Quantum Interference Device and by using soft x-ray absorption spectroscopy. Our study reveals basic defect units composed a Fe impurity coupled to one or two Mg vacancies. The trimer unit (i.e. Fe with two Mg vacancies) produces a magnetic net spin opposed to the dilute magnetism present in the oxide matrix. These findings could pave a way for engineering dielectric layers with high endurance and optimal tunneling properties by controlling the concentration of impurities and defects in the oxide matrix. Work supported by the US DOE.

  19. Mechanism and electric field induced modification of magnetic exchange stiffness in transition metal thin films on MgO(001)

    NASA Astrophysics Data System (ADS)

    Pradipto, Abdul-Muizz; Akiyama, Toru; Ito, Tomonori; Nakamura, Kohji

    2017-07-01

    Magnetic exchange stiffness in TM/MgO(001) [transition metal (TM) = Fe, Co, and Ni] is investigated by means of the first-principles full-potential linearized augmented plane wave method. We find that while the exchange stiffness constants are positive (ferromagnetic) in all considered systems, there are negative energy orbital contributions to the exchange stiffness preferring antiferromagnetic alignment. The different contributions can be explained simply in terms of bandwidth narrowing of the dx z band arising from an introduction of spin canting on neighboring TM atoms along the x direction. This scenario reflects well the stability of the d bands, especially in the cases of Fe/MgO and Co/MgO, on going from the ferromagnetic state towards the spin spiral states, and the exchange stiffness constant may be determined by the position of the Fermi level. As for the Ni/MgO system, we find that the exchange stiffness constant is much smaller than in the other two cases due to the almost full occupation of the relevant d orbitals. When this mechanism which is associated with the bandwidth narrowing is applied to investigate the effect of external field on the exchange stiffness, we find that in both Fe/MgO and Co/MgO, the application of positive field increases the exchange stiffness due to the modification of the TM-O atomic distance.

  20. Effects of MgO Content on Dielectric Properties of Ba0.94Bi0.04Sn0.06Ti0.94O3/MgO Composite Ceramics

    NASA Astrophysics Data System (ADS)

    Zhou, Peng; Zhang, Qingmeng; Zhou, Hao; Tan, Feihu; Chen, Junyou

    2017-08-01

    The composite ceramics of Ba0.94Bi0.04Sn0.06Ti0.94O3 (BBST) with x wt.% MgO (0 ≤ x ≤ 30) were prepared by solid-state sintering. The effects of MgO content on the microstructure and dielectric properties of the composite ceramics have been investigated. The results show that MgO is uniformly distributed in BBST matrix and enhances the relative density of composite ceramics remarkably, which effectively optimizes the performances of dielectric loss, alternating current (AC) breakdown strength (BDS) and insulation. With the content of MgO increasing from 0 wt.% to 30 wt.%, the dielectric constant decreases from 2900 to 920, dielectric loss decreases from 0.011 to 0.0065, BDS is improved from 26 kV/cm to 53.6 kV/cm and leakage current density decreases from 2.96 × 10-7 A/cm2 to 9.55 × 10-8 A/cm2. The ceramic added with 30 wt.% MgO exhibits the best comprehensive dielectric properties, which is a superior dielectric used in high-voltage ceramic capacitors.

  1. 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.

  2. Effect of Mould Coating on Skin Formation and Nodule Characteristics of Thin Wall Ductile Iron Casting

    NASA Astrophysics Data System (ADS)

    Dhaneswara, D.; Suharno, B.; Aprilio, A.; Ariobimo, R. D. S.; Sofyan, N.

    2017-05-01

    Thin wall ductile iron (TWDI) has the potential alternative for lightweight aluminium use in automotive parts. The main problem in TWDI, however, is the formation of skin during the casting, which may reduce its mechanical properties. This casting skin is formed by the decomposition of nodular graphite at the mould interface during the casting process. One of the ways to work around this problem is by using mould coating to control the cooling process. In this work, three variables of mould coatings were used, i.e. graphite, MgO, and MgO/graphite double layers. The results showed that the average casting skin thickness in double layer coating was the lowest (30.41 μm), 57% lower than that of in MgO (71.46 μm) and 60% lower than that of graphite (74.44 μm). The reduction of casting skin thickness increased the mechanical properties of TWDI (346 MPa), 69% higher than that of MgO (223 MPa) and 26% higher than that of graphite (297 MPa). The same is true for ductility (2.7%), which was higher than that of MgO (1.43%) and that of graphite (1.43%).

  3. Interaction between bimetal cluster Ni2Co2 and MgO and its effect on H adsorption and H2 dissociation: A DFT study

    NASA Astrophysics Data System (ADS)

    Li, Kai; Liu, Hongyan; Zhang, Riguang; Ling, Lixia; Wang, Baojun

    2016-12-01

    It is investigated for the interactions of bimetal NiCo with MgO as well as its effects on the H adsorption and H2 dissociation using a density functional theory method. Two models, Ni2Co2 cluster supported on perfect MgO(001) and oxygen-vacancy MgO(001) are used to represent bimetal NiCo deposited on MgO catalysts. The results show that the Ni2Co2/MgO catalyst with oxygen-vacancy exhibits stronger metal-support interaction compared to the perfect Ni2Co2/MgO, however, it has the weaker H adsorption ability as well as the better H2 dissociation activity. Compared with Ni4/MgO, the interaction between metal and support is weaker on the corresponding Ni2Co2/MgO, and H adsorption is stronger as well as the H2 dissociation is accelerated. The results indicate that both addition of a second metal Co and modification the support MgO can tune the metal-support interaction, further to change the H adsorption ability, meanwhile improve the activity of H2 dissociation. This work finely identifies the experimental result that tune the metal-support interaction can improve the catalyst's performance.

  4. 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.

  5. Effect of TiO2 on Sintering and Grain Growth Kinetics of MgO from MgCl2·6H2O

    NASA Astrophysics Data System (ADS)

    Huang, Qiong-Zhu; Lu, Gui-Min; Sun, Ze; Song, Xing-Fu; Yu, Jian-Guo

    2013-04-01

    The effect of TiO2 on the grain growth kinetics of MgO prepared from MgCl2·6H2O was studied by the tradition phenomenological rate equation. The results showed that the addition of TiO2 decreased the activation energy of MgO grain growth, accelerated the growth rate of MgO grain, and markedly promoted the sintering of MgO. Without TiO2 addition, the MgO grain growth exponent n was 3, the grain growth activation energy Q was 556.9 kJ·mol-1, and the process was considered as volume diffusion controlled. With 0.2 wt pct TiO2 addition, the MgO grain growth exponent n was 2, the grain growth activation energy Q was 272.8 kJ·mol-1, and the process was considered as interface diffusion controlled. The apparent and closed porosities of MgO-0.2 wt pct TiO2 sample were decreased significantly, and the bulk density increased to 3.49 g·cm-3 (relative density is 97.5 pct). The main mechanism of TiO2 promoting the sintering of MgO was that TiO2 solubilized in MgO to form unequivalence substitutional solid solutions and cation vacancies that were favorable to cation diffusion.

  6. Mechanisms of absorption and desorption of CO2 by molten NaNO3-promoted MgO.

    PubMed

    Jo, Seung-Ik; An, Young-In; Kim, Kang-Yeong; Choi, Seo-Yeong; Kwak, Jin-Su; Oh, Kyung-Ryul; Kwon, Young-Uk

    2017-02-22

    In order to realize carbon capture and sequestration (CCS), a technology proposed to circumvent the global warming problem while maintaining the present level of economic activity, the development of efficient carbon-capturing agents is of prime importance. In addition to the prevailing amine-based agents that operate at temperatures lower than 200 °C, agents that can operate at higher temperatures are being considered to reduce the cost of CCS. For the mid-temperature (200-500 °C) operation, alkali nitrate-promoted MgO is a promising candidate; whose detailed reaction mechanisms are not yet fully understood, however. In the present study, we have performed a comprehensive investigation on the mechanisms of CO2 absorption and desorption of NaNO3-promoted MgO. Highly efficient CO2 absorbents were obtained by decomposing Mg5(CO3)4(OH)2·4H2O with NaNO3 intimately mixed with it. Our collective data, including isothermal CO2 uptake curves, MgO solubility in molten NaNO3, and observations on the reaction of MgO wafers with CO2, indicate that the absorption takes place in the molten NaNO3 medium in which both CO2 and MgO are dissolved. MgCO3 is formed inside the molten promoter through the nucleation and growth steps. The decomposition of MgCO3 back to MgO, that is desorption of CO2, is also facilitated by molten NaNO3, which we attribute to the decreased relative stability of MgCO3 with respect to MgO when in contact with molten NaNO3. The relative affinity of molten nitrate to MgO and MgCO3 was estimated by measuring the 'contact angles' of nitrate on them. Implications of our findings for the real applications of alkali nitrate-promoted MgO absorbents with numerous repeated cycles of absorption and desorption of CO2 are discussed.

  7. 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.

  8. 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.

  9. 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.

  10. Band structure and thermodynamic properties of He atoms near a MgO surface

    NASA Astrophysics Data System (ADS)

    Schwartz, Carey; Karimi, Majid; Vidali, Gianfranco

    1989-06-01

    The energy-band structure and thermodynamic properties of a single He atom adsorbed upon MgO are computed numerically. The bound-state energy eigenvalues, wave functions, and matrix elements were obtained by solving the single-particle Schrödinger equation using the recently developed semi-empirical potential of Karimi and Vidali as input. We find at the center of the Brillouin zone an effective mass enhancement {m ∗}/{m} =1.081 that agrees well with the predictions of a perturbation theory. The heat capacity and isosteric heat of adsorption are calculated and compared to the data of Sullivan et al. [Surface Sci. 162 (1985) 461].

  11. Band structure and thermodynamic properties of He atoms near a MgO surface

    NASA Astrophysics Data System (ADS)

    Schwartz, Carey; Karimi, Majid; Vidali, Gianfranco

    The energy-band structure and thermodynamic properties of a single He atom adsorbed upon MgO are computed numerically. The bound-state energy eigenvalues, wave functions, and matrix elements were obtained by solving the single-particle Schrödinger equation using the recently developed semi-empirical potential of Karimi and Vidali as input. We find at the center of the Brillouin zone an effective mass enhancement m ∗/m = 1.081 that agrees well with the predictions of a perturbation theory. The heat capacity and isosteric heat of adsorption are calculated and compared to the data of Sullivan et al. [Surface Sci. 162 (1985) 461].

  12. Rectangular nanovoids in helium-implanted and thermally annealed MgO(100)

    NASA Astrophysics Data System (ADS)

    Kooi, B. J.; van Veen, A.; De Hosson, J. Th. M.; Schut, H.; Fedorov, A. V.; Labohm, F.

    2000-02-01

    Cleaved MgO(100) single crystals were implanted with 30 keV 3He ions with doses varying from 1×1019 to 1×1020m-2 and subsequently thermally annealed from 100 to 1100 °C. Transmission electron microscopy observations revealed the existence of sharply rectangular nanosize voids at a depth slightly shallower than the helium-implantation range. Monitoring of the defect depth profile and the retained amount of helium was performed by positron-beam analysis and neutron depth profiling, respectively.

  13. Melting temperatures of MgO under high pressure determined by micro-texture observation

    NASA Astrophysics Data System (ADS)

    Kimura, T.; Ohfuji, H.; Nishi, M.; Irifune, T.

    2016-12-01

    Periclase (MgO) is the second abundant mineral after bridgmanite in the Earth's lower mantle, and its melting temperature (Tm) under pressure is important to constrain the chemical composition of ultra-deep magma formed near the mantle-core boundary. However, the melting behavior is highly controversial among previous studies: a laser-heated diamond anvil cell (LHDAC) study reported a melting curve with a dTm/dP of 30 K/GPa at zero pressure [1], while several theoretical computations gave substantially higher dTm/dP of 90 100 K/GPa [2,3]. We performed a series of LHDAC experiments for measurements of Tm of MgO under high pressure, using single crystal MgO as the starting material. The melting was detected by using micro-texture observations of the quenched samples. We found that the laser-heated area of the sample quenched from the Tm in previous LHDAC experiments [1] showed randomly aggregated granular crystals, which was not caused by melting, but by plastic deformation of the sample. This suggests that the Tms of their study were substantially underestimated. On the other hand, the sample recovered from the temperature higher by 1500-1700 K than the Tms in previous LHDAC experiments showed a characteristic internal texture comparable to the solidification texture typically shown in metal casting. We determined the Tms based on the observation of this texture up to 32 GPa. Fitting our Tms to the Simon equation yields dTm/dP of 82 K/GPa at zero pressure, which is consistent with those of the theoretical predictions (90 100 K/GPa) [2,3]. Extrapolation of the present melting curve of MgO to the pressure of the CMB (135 GPa) gives a melting temperature of 8900 K. The present steep melting slope offers the eutectic composition close to peridotite (in terms of Mg/Si ratio) throughout the lower mantle conditions. According to the model for sink/float relationship between the solid mantle and the magma [4], a considerable amount of iron (Fe/(Mg+Fe) > 0.24) is expected

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    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.

  15. Preparation and properties of amorphous MgB2/MgO superstructures: Model disordered superconductor

    NASA Astrophysics Data System (ADS)

    Siemons, W.; Steiner, M. A.; Koster, G.; Blank, D. H. A.; Beasley, M. R.; Kapitulnik, A.

    2008-05-01

    In this paper, we introduce a unique method for fabricating MgB2/MgO multilayers and demonstrate the potential for using them as a new model for disordered superconductors. In this approach, we control the annealing of the MgB2 to yield an interesting new class of disordered (amorphous) superconductors with relatively high transition temperatures. The multilayers appear to exhibit quasi-two-dimensional superconductivity with controlled anisotropy. We discuss the properties of the multilayers as the thickness of the components of the bilayers vary.

  16. Peculiarities of post-irradiation annealing of MgO crystals

    NASA Astrophysics Data System (ADS)

    Kvatchadze, V. G.; Kalabegishvili, T. L.; Abramishvili, M. G.; Akhvlediani, Z. G.; Galustashvili, M. V.; Garibashvili, K. I.

    The influence of high-temperature annealing on absorption spectra of nominally pure and impure MgO crystals irradiated in a nuclear reactor has been investigated. In nominally pure crystals, as a whole, the accumulation of defect aggregates of non-monotonous character takes place during the whole cycle of the action of radiation plus post-irradiation annealing: the creation of defects in the process of irradiation, their destruction by annealing at 700 °C and repeated creation at higher annealing temperature. In irradiated impure crystals, where the mentioned defects exist in larger quantities, their thermal reanimation is not observed after the decay at 700 °C.

  17. 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.

  18. MgO Nanoparticle Modified Anode for Highly Efficient SnO2-Based Planar Perovskite Solar Cells.

    PubMed

    Ma, Junjie; Yang, Guang; Qin, Minchao; Zheng, Xiaolu; Lei, Hongwei; Chen, Cong; Chen, Zhiliang; Guo, Yaxiong; Han, Hongwei; Zhao, Xingzhong; Fang, Guojia

    2017-09-01

    Reducing the energy loss and retarding the carrier recombination at the interface are crucial to improve the performance of the perovskite solar cell (PSCs). However, little is known about the recombination mechanism at the interface of anode and SnO2 electron transfer layer (ETL). In this work, an ultrathin wide bandgap dielectric MgO nanolayer is incorporated between SnO2:F (FTO) electrode and SnO2 ETL of planar PSCs, realizing enhanced electron transporting and hole blocking properties. With the use of this electrode modifier, a power conversion efficiency of 18.23% is demonstrated, an 11% increment compared with that without MgO modifier. These improvements are attributed to the better properties of MgO-modified FTO/SnO2 as compared to FTO/SnO2, such as smoother surface, less FTO surface defects due to MgO passivation, and suppressed electron-hole recombinations. Also, MgO nanolayer with lower valance band minimum level played a better role in hole blocking. When FTO is replaced with Sn-doped In2O3 (ITO), a higher power conversion efficiency of 18.82% is demonstrated. As a result, the device with the MgO hole-blocking layer exhibits a remarkable improvement of all J-V parameters. This work presents a new direction to improve the performance of the PSCs based on SnO2 ETL by transparent conductive electrode surface modification.

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

    PubMed

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

    2012-07-19

    Supported triosmium clusters, formed from Os3(CO)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)2{Osupport}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)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.

  20. Superconducting tunnel junctions on MgB2 using MgO and CaF2 as a barrier

    NASA Astrophysics Data System (ADS)

    Sakoda, Masahito; Aibara, Masato; Mede, Kazuya; Kikuchi, Motoyuki; Naito, Michio

    2016-11-01

    We report the fabrication of superconducting tunnel junctions, both of superconductor-insulator-normal metal (SIN) and superconductor-insulator-superconductor (SIS), on MgB2 using MgO and CaF2 as a barrier. The SIN junctions fabricated using an MgO barrier showed excellent quasi-particle characteristics, including a large superconducting gap (Δ) of 2.5-3 meV and a low zero-bias conductance. We have also fabricated SIS junctions with an MgO barrier, but the quasi-particle characteristics of the SIS junctions are not as good as those of the SIN junctions, namely a reduced superconducting gap and a high zero-bias conductance. It appears that top MgB2 electrodes do not grow well on an MgO barrier, which is also suggested from in-situ RHEED observation. The SIN junctions fabricated using a CaF2 barrier showed less sharp quasi-particle characteristics than using an MgO barrier. However, the SIS junctions using a CaF2 barrier showed a fairly large IcRN value at 4.2 K over 1 mV and also exhibited finite Josephson current up to almost the film's Tc (∼30 K). The RHEED observation revealed that top MgB2 electrodes grow well on a CaF2 barrier.

  1. Structural and optical characterization of Er-alkali-metals codoped MgO nanoparticles synthesized by solution combustion route

    NASA Astrophysics Data System (ADS)

    Sivasankari, J.; Selvakumar Sellaiyan, S.; Sankar, S.; Devi, L. Vimala; Sivaji, K.

    2017-01-01

    Pure MgO, rare-earth (Er) doped MgO (MgO:Er), and alkali metal ions (Li, Na and K) co-doped MgO:Er [i.e. MgO: Er+X (X=Li, Na, and K)] nanopowders were synthesized by solution combustion method and characterized. The XRD analysis reveals the cubic structure and the substitution of dopants and co-dopants in MgO. Annealing at 800 °C, increases the sizes of nano-crystallites of all samples appreciably, indicating the grain growth and the improvement in crystallinity of all the samples. Increase in lattice parameter, d spacing and band gap were observed after annealing. Structural and morphological analysis using scanning electron microscope (SEM) and transmission electron microscope (TEM) studies has shown that the samples contain structures like agglomerated clusters. FT-IR spectra confirm the stretching mode of hydroxyl groups, carbonate and presence of MgO bonding. The characteristic wavelength ranging from 2600 cm-1 to 3000 cm-1 were assigned to transition of 4S3/2→4I13/2 and 4I11/2→4I15/2 of Er3+.

  2. Fourier Transform Infrared Spectroscopy of the A1Π- X1Σ + System of MgO

    NASA Astrophysics Data System (ADS)

    Kagi, E.; Hirano, T.; Takano, S.; Kawaguchi, K.

    1994-11-01

    The gas-phase infrared absorption spectrum of the A1Π- X1Σ + system of MgO was observed in the 2700-5400 cm -1 region with a high-resolution Fourier transform infrared spectrometer. The MgO molecule was produced in a reaction of Mg vapor with N 2O. The observed 501 spectral lines were assigned to five vibrational bands, vA- vX = 1-0 2-0, 3-0, 2-1, and 0-1 of 24MgO. These lines were analyzed to determine the band origins, the rotational, centrifugal distortion, and Λ-type doubling constants in the A1Π state. The term value Te of the A1Π state was derived to be 3563.8377 (74) cm -1, with one standard deviation in parentheses. The rotational levels in the A1Π state were found to be perturbed by those of the vibrational levels of the X1Σ + state through rotational-electronic interaction, and the analysis of the perturbation was carried out to determine the interaction constants. The spectra of the vA- vX = 1-0 bands of the isotopic species, 25MgO and 26MgO, wer also observed and analyzed.

  3. 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.

  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. Thin Clouds

    Atmospheric Science Data Center

    2013-04-18

    ... their delicate appearance, thin, feathery clouds of ice crystals called cirrus may contribute to global warming. Some scientists ... minutes after MISR imaged the cloud from space. At the same time, another NASA high-altitude jet, the WB-57, flew right through the ...

  6. 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

    2016-02-03

    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.

  7. Growth and investigation of the Slater-Pauling behavior by X-ray characterization of single crystal bcc FexMn1-x on MgO(001)

    NASA Astrophysics Data System (ADS)

    Bhatkar, Harshawardhan Ramesh

    Magnetic memory storage industry is always searching for materials that can store, read, and write data ever so faster, with lower power, with accuracy and on denser packaging. The material research was spurred with discovery and successful implementation of Giant Magnetoresistance phenomena into critical components of devices. GMR devices essentially were multilayered thin films of a set of magnetically ordered metals. Fe-Mn thin films were used to create one of its moment pinning layers. Fcc Fe-Mn thin films were studied enthusiastically for their AFM properties but very little was known about the rare bcc structured single crystals. Bcc Fe-Mn was found to be ferromagnetic in parts of phase diagram of Fe-Mn. The magnetic moment of alloys usually follows a regular linear trend based upon electronic configuration of constituent elements, known as Slater-Pauling curve. While most alloys follow the trend, bcc Fe-Mn binary alloys show a dramatic collapse in the bulk magnetic moment, as concentration of Mn is varied. In this work, we successfully fabricate bcc single crystal thin film of Fe-Mn on MgO(001) substrate by Molecular Beam Epitaxy method. We confirm using Reflection High Energy Electron Diffraction that, the bcc phase of Fe-Mn thin film is achieved, albeit being a forced structure, stable up to 35% of Mn concentration. X-ray absorption spectra of individual elements were used to confirm the compositions of Fe-Mn films and x-ray magnetic circular dichroism was used to track the elemental magnetic moment as the composition was varied. We found that the magnetic moment of Fe drops faster than expected and Mn has very small identical moment in all compositions. We also successfully created a compositionally graded Fe-Mn sample in MBE and spatially mapped its Fe moment by around the critical composition. The mechanism for collapse of magnetic moment over a spread of composition of Mn is a very complex problem yet we provide our experimental findings of

  8. Al embedded MgO barrier MTJ: A first principle study for application in fast and compact STT-MRAMs

    NASA Astrophysics Data System (ADS)

    Yadav, Manoj Kumar; Gupta, Santosh Kumar; Rai, Sanjeev; Pandey, Avinash C.

    2017-03-01

    The first principle comparative study of a novel single Al sheet embedded MgO and pure MgO barrier having Fe electrodes magnetic tunnel junction has been presented. Al embedded MgO is reported to provide enhanced spin polarised tunnelling current due to increase of spin-polarized density of states at Fermi energy in the barrier region. This novel MTJ provides a current density and resistance area (RA) product of 94.497 ×107 A / cm2 and 0.105  Ω - μm2 respectively. With such a low RA product; it allows higher deriving current due to which switching time of magnetization reversal reduces without inducing barrier related breakdowns in non-volatile magnetic random access memories. The low RA product and high current density of the proposed MTJ may have possible applications in integration with existing MOS circuits.

  9. Measurements of Sound Velocity and Grüneisen Parameter in CH and MgO Shocked to Mbar Pressures

    NASA Astrophysics Data System (ADS)

    McCoy, C. A.; Gregor, M. C.; Polsin, D. N.; Boehly, T. R.; Meyerhofer, D. D.; Fratanduono, D. E.; Celliers, P. M.

    2015-11-01

    We present sound velocity measurements using an unsteady wave analysis to relate acoustic perturbations in a sample to those in a standard with known sound velocity and Grüneisen parameter. The contraction and dilation of perturbations in the shock velocities in each material provide information on the sound velocity. Experiments measured the sound velocity and Grüneisen parameter in shocked CH and MgO (periclase) relative to a quartz standard. Hugoniot measurements were also made for MgO shocked to the fluid state; a modified Us -up relation is presented. The results are compared to SESAME and LEOS tables for CH and MgO. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

  10. Dielectric Properties of BaTiO3 Codoped with Er2O3 and MgO

    NASA Astrophysics Data System (ADS)

    Hwang, Jin Hyun; Choi, Sang Keun; Han, Young Ho

    2001-08-01

    The effect of Er2O3 and MgO addition on the dielectric properties of BaTiO3 ceramics was studied in a reduced atmosphere. MgO effectively prevented the material from being reduced and suppressed grain growth. An X7R material with moderate temperature dependence was developed by the addition of MgO with higher than 2.0 mol% Er2O3 to BaTiO3, which is ascribed to the decrease in grain size and the grain core-grain shell structure. In the presence of equimolar amount of B-site metal ions, there was no evidence to support the incorporation of Er ions into the octahedral and dodecahedral cation sites.

  11. Removal of scratch on the surface of MgO single crystal substrate in chemical mechanical polishing process

    NASA Astrophysics Data System (ADS)

    Kang, R. K.; Wang, K.; Wang, J.; Guo, D. M.

    2008-05-01

    Etching and chemical mechanical polishing (CMP) experiments of the MgO single crystal substrate with an artificial scratch on its surface are respectively performed with the developed polishing slurry mainly containing 2 vol.% phosphoric acid (H 3PO 4) and 10-20 nm colloidal silica particles, through observing the variations of the scratch topography on the substrate surface in experiments process, the mechanism and effect of removing scratch during etching and polishing are studied, some evaluating indexes for effect of removing scratch are presented. Finally, chemical mechanical polishing experiments of the MgO substrates after lapped are conducted by using different kinds of polishing pads, and influences of the polishing pad hardness on removal of the scratches on the MgO substrate surface are discussed.

  12. In Vitro Cytotoxic Evaluation of MgO Nanoparticles and Their Effect on the Expression of ROS Genes

    PubMed Central

    Kumaran, Rangarajulu Senthil; Choi, Yong-Keun; Singh, Vijay; Song, Hak-Jin; Song, Kyung-Guen; Kim, Kwang Jin; Kim, Hyung Joo

    2015-01-01

    Water-dispersible MgO nanoparticles were tested to investigate their cytotoxic effects on oxidative stress gene expression. In this in vitro study, genes related to reactive oxygen species (ROS), glutathione S-transferase (GST) and catalase, were quantified using real-time polymerase chain reactions (molecular level) and molecular beacon technologies (cellular level). The monodispersed MgO nanoparticles, 20 nm in size, were used to treat human cancer cell lines (liver cancer epithelial cells) at different concentrations (25, 75 and 150 µg/mL) and incubation times (24, 48 and 72 h). Both the genetic and cellular cytotoxic screening methods produced consistent results, showing that GST and catalase ROS gene expression was maximized at 150 µg/mL nanoparticle treatment with 48 h incubation. However, the genotoxic effect of MgO nanoparticles was not significant compared with control experiments, which indicates its significant potential applications in nanomedicine as a diagnostic and therapeutic tool. PMID:25854426

  13. In vitro cytotoxic evaluation of MgO nanoparticles and their effect on the expression of ROS genes.

    PubMed

    Kumaran, Rangarajulu Senthil; Choi, Yong-Keun; Singh, Vijay; Song, Hak-Jin; Song, Kyung-Guen; Kim, Kwang Jin; Kim, Hyung Joo

    2015-04-03

    Water-dispersible MgO nanoparticles were tested to investigate their cytotoxic effects on oxidative stress gene expression. In this in vitro study, genes related to reactive oxygen species (ROS), glutathione S-transferase (GST) and catalase, were quantified using real-time polymerase chain reactions (molecular level) and molecular beacon technologies (cellular level). The monodispersed MgO nanoparticles, 20 nm in size, were used to treat human cancer cell lines (liver cancer epithelial cells) at different concentrations (25, 75 and 150 µg/mL) and incubation times (24, 48 and 72 h). Both the genetic and cellular cytotoxic screening methods produced consistent results, showing that GST and catalase ROS gene expression was maximized at 150 µg/mL nanoparticle treatment with 48 h incubation. However, the genotoxic effect of MgO nanoparticles was not significant compared with control experiments, which indicates its significant potential applications in nanomedicine as a diagnostic and therapeutic tool.

  14. 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.

  15. Ab initio molecular dynamics simulations of low energy recoil events in MgO

    NASA Astrophysics Data System (ADS)

    Petersen, B. A.; Liu, B.; Weber, W. J.; Zhang, Y.

    2017-04-01

    Low-energy recoil events in MgO are studied using ab intio molecular dynamics simulations to reveal the dynamic displacement processes and final defect configurations. Threshold displacement energies, Ed, are obtained for Mg and O along three low-index crystallographic directions, [100], [110], and [111]. The minimum values for Ed are found along the [110] direction consisting of the same element, either Mg or O atoms. Minimum threshold values of 29.5 eV for Mg and 25.5 eV for O, respectively, are suggested from the calculations. For other directions, the threshold energies are considerably higher, 65.5 and 150.0 eV for O along [111] and [100], and 122.5 eV for Mg along both [111] and [100] directions, respectively. These results show that the recoil events in MgO are partial-charge transfer assisted processes where the charge transfer plays an important role. There is a similar trend found in other oxide materials, where the threshold displacement energy correlates linearly with the peak partial-charge transfer, suggesting this behavior might be universal in ceramic oxides.

  16. Ab initio molecular dynamics simulations of low energy recoil events in MgO

    DOE PAGES

    Petersen, B. A.; Liu, B.; Weber, W. J.; ...

    2017-01-11

    In this paper, low-energy recoil events in MgO are studied using ab initio molecular dynamics simulations to reveal the dynamic displacement processes and final defect configurations. Threshold displacement energies, Ed, are obtained for Mg and O along three low-index crystallographic directions, [100], [110], and [111]. The minimum values for Ed are found along the [110] direction consisting of the same element, either Mg or O atoms. Minimum threshold values of 29.5 eV for Mg and 25.5 eV for O, respectively, are suggested from the calculations. For other directions, the threshold energies are considerably higher, 65.5 and 150.0 eV for Omore » along [111] and [100], and 122.5 eV for Mg along both [111] and [100] directions, respectively. These results show that the recoil events in MgO are partial-charge transfer assisted processes where the charge transfer plays an important role. Finally, there is a similar trend found in other oxide materials, where the threshold displacement energy correlates linearly with the peak partial-charge transfer, suggesting this behavior might be universal in ceramic oxides.« less

  17. A vinyl acetate sensor based on cataluminescence on MgO nanoparticles.

    PubMed

    Wu, Chen Chou; Cao, Xiaoan; Wen, Qiang; Wang, Zehua; Gao, Qianqian; Zhu, Huichang

    2009-10-15

    A novel cataluminescence (CTL) sensor using nanosized MgO as the sensing material for determination of the trace of vinyl acetate in air was proposed in the present study. Eight catalysts were examined and the results showed that the CTL intensity on MgO nanoparticles was the strongest. Under the optimized conditions, the linear range of the CTL intensity versus the concentration of vinyl acetate vapor was 2-2000 ppm with a detection limit of 1.0 ppm (3sigma) and a relative standard deviation (R.S.D.) of 1.18% for five times determination of 1000 ppm vinyl acetate. There were no CTL emissions when foreign substances, including ammonia, benzene, acetic acid, formaldehyde and ethyl acetate, passed through the sensor. CTL emissions were detected for methanol, ethanol and acetaldehyde at levels around 5.5%, 10.1% and 13.4% compared with the responsed vinyl acetate. The sensor had a long lifetime more than 100 h.

  18. Spin relaxation mechanism in silver nanowires covered with MgO protection layer

    NASA Astrophysics Data System (ADS)

    Idzuchi, H.; Fukuma, Y.; Wang, L.; Otani, Y.

    2012-07-01

    Spin-flip mechanism in Ag nanowires with MgO surface protection layers has been investigated by nonlocal spin injection using permalloy/Ag lateral spin valves. The spin flip events mediated by surface scattering are effectively suppressed by the MgO capping layer. The spin relaxation process was found to be well described in the framework of Elliott-Yafet mechanism (R. J. Elliott, Phys. Rev. 96, 266 (1954); Y. Yafet, in Solid State Physics, edited by F. Seitz and D. Turnbull (Academic, New York, 1963), pp. 1-98) and then the probabilities of spin-filp scattering for phonon or impurity mediated momentum scattering is precisely determined in the nanowires. The temperature dependent spin-lattice relaxation follows the Bloch-Grüneisen theory (V. F. Bloch, Z. Phys. 59, 208 (1930); V. E. Grüneisen, Ann. Phys. 5, 530 (1933)) and falls on to a universal curve of Ag as in the conduction-electron-spin resonance data for bulk.

  19. 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.

  20. High temperature annealing of MgO based perpendicular MTJ with Co/Pd multilayers

    NASA Astrophysics Data System (ADS)

    Tofizur Rahman, M.; Lyle, Andrew; Zhao, Hui; Wang, Jian-Ping

    2010-03-01

    MgO based perpendicular MTJ (pMTJ) are becoming increasing demanded due to their thermal stability and unlimited cell aspect ratio [1]. Promising results are reported for pMTJs with TbFeCo or Co/Pt (Pd,Ni) MLs but these materials could not withstand high temperature annealing above 250^oC. However, annealing at or above 300^oC is required to fully crystallize the MgO. We fabricated Sub/Pd/(Co/Pd)n/CoFeB/MgO/CoFeB/Pd/(Co/Pd)n/Pd pMTJ structure by engineering the exchange coupling between CoFeB and (Co/Pd)n and the interface morphology of Co and Pd in (Co/Pd)n layers and annealed at different temperatures up to 350^oC. To clarify the thermal effects on free layer completely, we also studied the annealing of free layer only. The perpendicular squareness of the free layer and the full stack after annealing at 350^oC are 0.90 and 1, respectively. The existence of good perpendicular anisotropy at high temperature is ascribed to the sharp and defect free interfaces. Field and spin torque switching results will also be presented.[4pt] [1] H.Meng, APL, 88, 172506 (2006),]M. Nakayama, JAP, 103, 07A710.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. X-ray diffraction residual stress calculation on textured La 2/3Sr 1/3MnO 3 thin film

    NASA Astrophysics Data System (ADS)

    Meda, Lamartine; Dahmen, Klaus H.; Hayek, Saleh; Garmestani, Hamid

    2004-03-01

    Residual stresses and texture in La2/3Sr1/3MnO3 (LSMO) thin films have been investigated. The films were deposited on (1 0 0) LaAlO3 (LAO) and (1 0 0) MgO single crystals by liquid delivery-metal organic chemical vapor deposition (LD-MOCVD). X-ray diffraction (XRD) pole figures showed (0 0 1)LSMO//(0 0 1)LAO and (0 0 1)LSMO//(0 0 1)MgO preferred orientation. Residual stresses were calculated using a modified sin2 ψ method, crystallite group method (CGM), assuming a biaxial stress state. Compressive stresses on the order of 224 and 1150 MPa were obtained for LSMO films deposited on LAO (LSMO/LAO) and MgO (LSMO/MgO), respectively.

  6. Ligand/cluster/support catalytic complexes in heterogeneous ultrananocatalysis: NO oxidation on Ag3/MgO(100).

    PubMed

    Sementa, Luca; Barcaro, Giovanni; Negreiros, Fabio R; Fortunelli, Alessandro

    2014-12-28

    In the present work we explore via first-principles simulations whether the ligand/cluster/support catalytic complex generated by CO oxidation over silver trimers deposited on the regular MgO(100) surface - i.e. a Ag3/carbonate or Ag3(CO3)/MgO(100) species - can be used as a catalyst in a different reaction: the selective oxidation of NO to NO2 (or NOox). The Ag3(CO3)/MgO(100) complex is first shown to be reasonably stable at room temperature in terms of both disaggregation and sintering, and that it can be generated from Ag3 adsorbed onto an oxygen vacancy defect of the regular MgO(100) surface under oxidation conditions. It is then found that the Ag3(CO3)/MgO(100) species transforms under NOox conditions into an even more complex aggregate, a mixed carbonate/double-nitrite Ag3(CO3)(NO2)2/MgO(100) species, which can then act as an efficient catalyst of NOox. It is noteworthy that under NOox reaction conditions a different ligand/cluster/support catalytic complex is formed with respect to the original COox one. These findings prove the diversity of the catalytic chemistry of subnanometer (or ultranano) metal clusters deposited on oxide substrates, associated with the formation of many different ligand/cluster/support aggregates, the vast amount of combinatorial possibilities thus opening, and the need for computational approaches to perform systematic structural and stoichiometric searches in order to cope with such a multiform diversity.

  7. 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.

  8. NO2 interaction with Au atom adsorbed on perfect and defective MgO(100) surfaces: density functional theory calculations.

    PubMed

    Ammar, H Y; Eid, Kh M

    2013-10-01

    The interactions of nitrogen dioxide molecule (NO2) on Au atom adsorbed on the surfaces of metal oxide MgO (100) on both anionic (O2-) and defect (F(s) and F(s)(+)-centers) sites have been studied using the Density Functional Theory (DFT) in combination with embedded cluster model. The adsorption energies of NO2 molecule (N-down as well as O-down) on O(-2), F(s) and F(s)(+)-sites were considered. Full optimization for the additive materials and partial optimization for MgO substrate surfaces have been done. The formation energies were evaluated for F(s) and F(s)(+) of MgO substrate surfaces. Some parameters, the Ionization Potential (IP) and electron Affinity (eA), for defect free and defect containing surfaces have been calculated. The interaction properties of NO2 have been analyzed in terms of the adsorption energy, the electron donation (basicity), the elongation of N-O bond length and the charge distribution by using Natural Bond Orbital (NBO) analysis. The adsorption properties were examined by calculation of the Density of State (DOS). The presence of the Au atom increases the surface chemistry of the anionic O(2-)-site of MgO substrate surfaces. On the other hand, the presence of the Au atom decreases the surface chemistry of the F(s) and F(s)(+)-sites of MgO substrate surfaces. Generally, the NO2 molecule is strongly adsorbed (chemisorption) on the MgO substrate surfaces containing F(s) and F(s)(+)-centers.

  9. Epitaxial CeO 2/MgO buffer layers on cubic textured Ni substrates for superconducting tapes

    NASA Astrophysics Data System (ADS)

    Yang, Jian; Gu, Hongwei; Hu, Guangyong; Shi, Kai; Yuan, Guansen

    Reported here is a novel epitaxial buffer layer configuration combined with MgO and CeO 2 on biaxially texture Ni substrates for high temperature superconducting (HTS) tapes. The hetero-epitaxial CeO 2/MgO/Ni structure was grown by magnetron sputtering method. After formation of the buffer layers, θ-2θ and Φ scans of x-ray diffraction were used to measure the film in-plane and out-plane orientation, respectively. The deposited CeO 2 and MgO buffer layers showed good in-plane alignment.

  10. Using polarity for engineering oxide nanostructures: structural phase diagram in free and supported MgO(111) ultrathin films.

    PubMed

    Goniakowski, Jacek; Noguera, Claudine; Giordano, Livia

    2004-11-19

    Using an ab initio total energy approach, we study the stability of free and Ag(111)-supported MgO(111) ultrathin films. We unravel a novel microscopic mechanism of stabilization of polar oxide orientations, based on a strong modification of the MgO structural phase diagram with respect to the bulk material. We predict that, at low thickness, films which are either unsupported or deposited on Ag(111) display a graphitelike Bk structure rather than the expected rocksalt one. Our results provide a consistent interpretation of recent experimental findings, exemplify the efficiency of this novel stabilization mechanism, and suggest new methods to engineer oxide nanostructures.

  11. Comparison of interface structure of BCC metallic (Fe, V and Nb) films on MgO (100) substrate

    NASA Astrophysics Data System (ADS)

    Du, J. L.; Zhang, L. Y.; Fu, E. G.; Ding, X.; Yu, K. Y.; Wang, Y. G.; Wang, Y. Q.; Baldwin, J. K.; Wang, X. J.; Xu, P.

    2017-07-01

    This study systematically investigates the interface structure of three body-centered-cubic (BCC) metallic (Fe, V and Nb) films grown on MgO(100) substrates through experiments and simulations. Orientation relationships of their interfaces with the different lattice mismatches exhibit cube-on-cube configurations. The misfit dislocations at these three interfaces exhibit different characteristics. High resolution TEM (HRTEM), combined with first principle calculations, demonstrates the O-atop match type between metal atoms and MgO substrates for the first time. The fundamental mechanism in determining the interface configuration is discussed in terms of the work of separation and delocalization of atomic charge density.

  12. Room-Temperature Magnetic and Magneto-Optical Properties of Sr2FeMoO6 Thin Films

    NASA Astrophysics Data System (ADS)

    Asano, Hidefumi; Osugi, Masahiro; Kohara, Yasuhiro; Higashida, Daisuke; Matsui, Masaaki

    2001-08-01

    Epitaxial thin films of a half-metallic ferromagnet Sr2FeMoO6 have been grown on (001) SrTiO3, and MgO substrates by magnetron sputtering in Ar+H2 mixture gas. Their structural, magnetic, magneto-optical and transport properties at room temperature were investigated and compared. Large difference has been observed especially in the magnetic and magneto-optical properties between thin films on SrTiO3 and MgO@. The films on SrTiO3 exhibited stronger out-of-plane magnetic anisotropy and larger complex polar Kerr effect with a rotation θk up to -0.32\\circ at 1.6 eV and RT@. The observed difference in the properties of the films on the two substrates can be interpreted in terms of the structural disorder.

  13. Investigation of reaction mechanisms of NO with CO on Pd1/MgO and Pd4/MgO catalysts

    NASA Astrophysics Data System (ADS)

    Yin, Zhenfen; Li, Chaoqun; Su, Yanwei; Liu, Yongfei; Wang, Yan; Chen, Guangju

    2012-02-01

    The stepwise and concerted reaction mechanisms of NO with CO on Pd1 atom and Pd4 cluster adsorbed on the MgO surface have been studied by using the DFT/B3LYP method with the embedded cluster model. The reaction barriers have been calculated by using the IMOMO method at the CCSD level. The results suggest that the rate-controlling step barrier of the NO dissociation on the supported Pd4 cluster for the stepwise reaction mechanism is about 57 kcal/mol and lower by about 33 kcal/mol than that on the single supported Pd atom. However, the concerted reaction pathways on the single supported Pd atom and four supported Pd atoms are energetically unfavorable with the barriers of about 98 kcal/mol and 71 kcal/mol, respectively. Compared to the concerted reaction mechanism, the stepwise reaction mechanism of NO + CO is a possible pathway of CO2 molecule formation on the supported Pd catalysts.

  14. Deposition of epitaxial Cu 2O films on (100) MgO by laser ablation and their processing using ion beams

    NASA Astrophysics Data System (ADS)

    Ogale, S. B.; Bilurkar, P. G.; Mate, Nitant; Parikh, Nalin; Patnaik, B.

    1993-03-01

    Epitaxial thin films of Cu2O have been deposited on (100) MgO substrates by pulsed excimer laser ablation technique. Chemical polishing of the substrates by etching them in hot phosphoric acid prior to film deposition is found to be a critical step in realizing epitaxy. A KrF excimer laser operating at 248 nm wavelengths was used for ablation. The depositions were carried out at the laser energy density of 2 J/cm2 and the pulse repetition rate of 5 Hz. The substrate temperature was held at 700°C and the oxygen partial pressure during deposition and cooling was 10-3 Torr. The epitaxial nature of the deposited films was established via X-ray diffraction (XRD) and Rutherford back-scattering (RBS) channelling measurements. The epitaxial films thus obtained were then subjected to ion bombardment for studies of damage formation. Implantations were carried out using 110 keV Ar+ ions over a dose range between 5 x 1014 and 1.5 x 1016 ions/cmz. The as-grown and implanted samples were subjected to resistivity versus temperature measurements in view of the importance of the Cu-O system in the context of the phenomenon of high temperature superconductivity.

  15. Growth, structure, and magnetic properties of {gamma}-Fe{sub 2}O{sub 3} epitaxial films on MgO

    SciTech Connect

    Gao, Y.; Kim, Y.J.; Thevuthasan, S.; Chambers, S.A.; Lubitz, P.

    1997-04-01

    Single-crystal epitaxial thin films of {gamma}-Fe{sub 2}O{sub 3}(001) have been grown on MgO(001) using oxygen-plasma-assisted molecular beam epitaxy. The structure and magnetic properties of these films have been characterized by a variety of techniques, including reflection high-energy electron diffraction (RHEED), low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy and x-ray photoelectron/Auger electron diffraction (XPD/AED), vibrating sample magnetometry, and ferromagnetic resonance. Real-time RHEED reveals that the film growth occurs in a layer-by-layer fashion. The {gamma}-Fe{sub 2}O{sub 3}(001) film surface exhibits a (1{times}1) LEED pattern. The growth of {gamma}-Fe{sub 2}O{sub 3} films at 450 {degree}C is accompanied by significant Mg outdiffusion. AED of Mg KLL Auger emission reveals that Mg substitutionally incorporates in the {gamma}-Fe{sub 2}O{sub 3} lattice, occupying the octahedral sites. Magnetic moments are {approximately}2300 G and {approximately}4500 G for {gamma}-Fe{sub 2}O{sub 3} films grown at 250{degree}C and 450{degree}C, respectively. The high magnetic moment for the films grown at 450{degree}C could be attributed to the high degree of structural order of the films and Mg substitution at octahedral sites. {copyright} {ital 1997 American Institute of Physics.}

  16. 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.

  17. Growth of oriented diamond on nickel wafers and thin films

    NASA Astrophysics Data System (ADS)

    Liu, Wei

    2000-10-01

    Growth of highly oriented diamond thin films on nickel was achieved by a multi-step process involving seeding, high temperature carbon dissolution, and growth. This process is very sensitive to the substrate temperature and requires accurate timing of both the nucleation and growth steps. It was observed that the surface morphology changed dramatically during the nucleation process and that in-situ monitoring of the surface morphology could provide valuable feedback for process control. An optical monitoring system developed under this study has significantly improved both the reproducibility and overall quality of the oriented diamond films grown on Ni substrates. However, since a significant fraction of carbon diffused into the bulk, as confirmed by Auger carbon depth profiling, the highest nucleation density on the bulk Ni substrate was 107 cm-2. To prevent carbon diffusion away from the surface and to maintain a supersaturated surface region, epitaxial nickel and iridium thin films were deposited by electron-beam evaporation on MgO which acted as a carbon diffusion barrier. A multi-layer structure with 100 A iridium and 1 mum nickel grown epitaxially on an MgO (100) wafer by electron-beam evaporation was used as a substrate. The 100 A thick Ir interlayer was used to overcome the delamination of Ni from the MgO substrate during processing. Oriented diamond was successfully deposited on these substrates and yielded nucleation densities of 3 x 108 cm-2, that resulted in faster coalescence of diamond particles. Coalesced diamond thin films on Ni/Ir/MgO substrates were grown in about six hours of growth, as compared to about 25 hours for the bulk Ni substrates. However, a much narrower process widow on Ni thin films made reproducible growth of oriented diamond more challenging. Cross-sectional high-resolution transmission electron microscopy (XHRTEM) was used to investigate the interfacial microstructure formed during hot filament chemical vapor deposition (HFCVD

  18. 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.

  19. 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.

  20. Characterization of the Order-Annealing Response of Nanostructured Iron-Palladium Based Ferromagnetic Thin-Films

    DTIC Science & Technology

    2001-11-01

    techniques have been used to characterize the response of room temperature magnetron sputtered Fe-Pd thin films on Si-susbtrates to post-deposition order...beam epitaxy (MBE) [3] and by magnetron sputtering on Pt-underlayers on MgO substrates [4]. The latter method allows more rapid deposition and is...currently popularly employed in most industrial operations. Unlike MBE, magnetron sputtering without substrate heating usually produces intermetallic

  1. TiO2 as an electrostatic template for epitaxial growth of EuO on MgO(001) by reactive molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Swartz, Adrian; Wong, Jared; Pinchuk, Igor; Kawakami, Roland

    2012-02-01

    Interfacial electrostatics play a key role in determining epitaxial quality in the heteroepitaxy of ionic rock salt materials. We investigate the initial growth modes and the role of interfacial electrostatic interactions of EuO epitaxy on MgO(001) by reactive molecular beam epitaxy. A TiO2 interfacial monolayer is employed to alleviate electrostatic interactions between the ions of the EuO and MgO to produce high quality epitaxial growth of EuO on MgO(001) with a 45 degree in plane rotation. For comparison, direct deposition of EuO on MgO, without the TiO2 layer, is discussed. A key difference of EuO epitaxy on TiO2/MgO is the ability to form EuO by substrate assisted oxidation and without the introduction of external oxygen to the interface. Such ultrathin films are shown to have bulk like magnetic properties

  2. High coercivity Sm-Co thin films from elemental Sm/Co multilayer deposition and their microstructural aspects

    NASA Astrophysics Data System (ADS)

    Krishnan, M.; Predeep, P.; Sridhara Rao, D. V.; Prajapat, C. L.; Singh, M. R.; Barshilia, Harish C.; Chowdhury, P.

    2017-05-01

    Hard magnetic thin films with high coercivity were fabricated by magnetron sputtering on MgO(100) and quartz substrates. The films were grown by depositing sequentially Sm and Co layers at an elevated substrate temperature of 500 °C. Subsequent post-annealing was carried out at various temperatures in range of 500-700 °C to form Sm-Co hard magnetic thin films. X-ray diffraction studies revealed the formation of randomly oriented SmCo5 crystallites on quartz substrate, whereas, a textured growth of Sm2Co7 with strong (110) crystalline phases was observed on MgO substrate. Microstructural analyses were carried out using Transmission Electron Microscopy (TEM) for samples grown on MgO substrate at 650 °C and inferred the presence of high density planar defects along with large grain boundaries. Further microdiffraction studies confirmed the presence of SmCo3 as an impurity phase in the films. Magnetic hysteresis measurements indicate the square hysteresis behaviors with high coercivity value of 3.1 T and 2.7 T for 650 °C annealed samples on both MgO and quartz substrates, respectively. The origin of such high coercivity value was then correlated with pinning type of spin reversal mechanism as confirmed through the analyses of demagnetization curves. The magnetic force microscopy images for films on MgO substrate, annealed at 650 °C, revealed the presence of magnetic domains with size higher than 1 μm. The formed magnetic domains lacked well defined boundaries indicating an enhanced exchange coupling between the grain clusters.

  3. 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

  4. Synchrotron Radial X-ray Diffraction Studies of Deformation of Polycrystalline MgO

    NASA Astrophysics Data System (ADS)

    Girard, J.; Tsujino, N.; Mohiuddin, A.; Karato, S. I.

    2016-12-01

    X-ray diffraction analyses have been used for decades to study mechanical properties of polycrystalline samples during in-situ high-pressure deformation. When polycrystalline materials are deformed, stresses develop in grains and lead to lattice distortion. Using X-ray diffraction we can estimate the lattice strain for each (hkl) diffraction plans and calculate the applied stress for each (hkl), using [Singh, 1993] relation. However, this method doesn't take into account plastic anisotropy. As a results of plastic anisotropy present in the material, stress estimated from this method can be largely differ depending on (hkl) diffraction planes [Karato, 2009]. Studying the stress estimate for each (hkl) plane, might help us distinguish dominant deformation mechanisms activated during deformation such as diffusion (we will observe small stress variation as a function of (hkl) diffraction planes) or dislocation creep (we will observe a stress variation as a function of (hkl) diffraction planes that could also give us clues on potential slip system activity). In this study we observed stress evolution in MgO polycrystalline samples deformed under mantle pressure and temperature for (200) and (220) diffraction planes. Using a range MgO grain sizes we were able to control the active deformation mechanism (for e.g. diffusion creep or dislocation creep). For coarse-grained specimens, we observed strong (hkl) dependence of radial strain indicating the operation of dislocation creep. The observed (hkl) dependence changes with pressure suggesting a change in the slip system: at pressures higher than 27 GPa, (200) shows larger stress estimate than (220). In contrast, at lower pressures, (220) shows larger stress estimate than (200). This might indicate a slip system transition in MgO occurring under lower mantle conditions. From {110} plane to {100} plane. This is in good agreement with theoretical predictions and numerical calculation [Amodeo et al., 2012] and has an important

  5. Interfacial phases in epitaxial growth of Y{sub 2}O{sub 3} on MgO studied via combining electron energy-loss spectroscopy and real-space self-consistent full multiple scattering calculations

    SciTech Connect

    Pailloux, F.; Jublot, M.; Gaboriaud, R.J.; Jaouen, M.; Paumier, F.; Imhoff, D.

    2005-09-15

    Electron energy loss spectroscopy (EELS), high resolution transmission electron microscopy (HRTEM), and electron diffraction were used to investigate Y{sub 2}O{sub 3} thin films epitaxially grown on (001) MgO substrate. In the vicinity of the film/substrate interface, HRTEM experiments evidenced the presence of grains with various crystallographic structures most of them crystallizing in the well-known Ia3 cubic phase. Some other grains, nanometric in size, and only observed in the vicinity of the film/substrate interface, have a different and unknown crystallographic structure. EELS spectra have been acquired close to the Y{sub 2}O{sub 3}/MgO interface, to get a better knowledge of the phases nucleated close to the substrate surface. Spectra exhibiting different fine structures have been recorded and compared to multiple scattering calculations. The Ia3 phase has been detected as constituting the main component of the Y{sub 2}O{sub 3} thin film in agreement with previous observations. It is found that calculations performed in a real space self-consistent full multiple scattering scheme (SC-FMS) and experiments are in pretty good agreement even for small cluster sizes. The second family of spectra has also been compared to calculations performed for monoclinic C2/m yttrium oxide, with a little success. Another approach considering a local oxygen neighboring close to a distorted rock-salt-like structure led to a good match between experimental and calculated spectra. Our results emphasize how powerful is the combination of spectroscopic measurements at nanometer scale, as feasible with EELS and modern microscopes, with ab initio calculations for structure determination at such small scale lengths.

  6. The electronic and magnetic properties of La{sub 0.85}Zr{sub 0.15}MnO{sub 3} deposited on SrTiO{sub 3} and MgO substrates

    SciTech Connect

    Deshpande, N. G.; Weng, C. H.; Wang, Y. F.; Shao, Y. C.; Cheng, C. Q.; Ling, D. C. E-mail: wfpong@mail.tku.edu.tw; Hsueh, H. C.; Du, C. H.; Pong, W. F. E-mail: wfpong@mail.tku.edu.tw; Tsai, H. M.; Pao, C. W.; Lin, H. J.; Lee, J. F.; Chiou, J. W.; Tsai, M. H.

    2014-06-21

    The electronic and magnetic properties of tetravalent-ion-doped La{sub 0.85}Zr{sub 0.15}MnO{sub 3} (LZMO) thin films that were epitaxially grown on SrTiO{sub 3} (STO) and MgO substrates were studied using temperature-dependent x-ray diffraction (XRD), x-ray absorption near-edge structure, x-ray linear dichroism, and x-ray magnetic circular dichroism at the Mn L{sub 3,2}- and K-edge. XRD studies reveal that the LZMO thin films have compressive and tensile strains (along the c-axis) on the STO and MgO substrates, respectively. As the temperature is reduced from room temperature to below magnetic transition temperature, the preferentially occupied Mn majority-spin e{sub g} orbital changes from the in-plane d{sub x}{sup 2}{sub -y}{sup 2} to the out-of-plane d{sub 3z}{sup 2}{sub -r}{sup 2} orbital for LZMO/STO, and vice versa for LZMO/MgO. Experimental results suggest that the new hopping path that is mediated by the Mn{sup 2+} ions triggers a stronger d{sub 3z}{sup 2}{sub -r}{sup 2} orbital ordering of Mn{sup 3+} ions and enhances the ferromagnetic coupling between the Mn spin moments of t{sub 2g} electrons in LZMO/STO, whereas the strong tensile strain stabilizes the d{sub x}{sup 2}{sub -y}{sup 2} orbital by inducing lattice distortions of the MnO{sub 6} octahedra in LZMO/MgO.

  7. Roles of MgO release from polyethylene glycol 6000-based solid dispersions on microenvironmental pH, enhanced dissolution and reduced gastrointestinal damage of telmisartan.

    PubMed

    Tran, Phuong Ha-Lien; Tran, Thao Truong-Dinh; Lee, Seung Aeon; Nho, Vo Hong; Chi, Sang-Cheol; Lee, Beom-Jin

    2011-05-01

    The roles of magnesium oxide (MgO) release from solid dispersions (SDs) in simulated gastric fluid (SGF), simulated intestinal fluid (SIF) and water were investigated to elucidate the enhanced dissolution and reduced intestinal damages of telmisartan as a model drug. The polyethylene glycol 6000 (PEG 6000) was used to prepare the SDs. Three SDs were prepared: SD1 (PEG, MgO, TEL), SD2 (PEG 6000, TEL), SD3 (MgO, TEL). The physical mixture (PM) consisting of SD2 and MgO was also prepared. A binary SD without MgO (SD2) was also prepared for comparison in microenvironmental pH (pH(M)) modulation. The faster MgO released, the less control of pH(M) and the less enhanced dissolution of TEL were in consequences. SD3 increased dissolution in SIF and water (about 67%). Interestingly, ternary SD1 showed almost complete dissolution in all three media but dissolution of PM was the lowest due to the fast release of MgO and poor modulation of pH(M). MgO did not change the drug crystallinity but did have a strong molecular interaction with the drug. Additionally, the SD3-bearing tablet quickly increased pH(M) but then gradually decreased due to faster release of MgO while the SD1-bearing tablet gradually increased pH(M) at all fractional dimensions of the tablet by the MgO slowly released. The pH(M) of PM-bearing tablets was not varied as a function of time. Thus, the MgO-bearing SD1 also minimized gastrointestinal tissue damage caused by the model drug.

  8. 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.

  9. Epitaxial TiN(001) wetting layer for growth of thin single-crystal Cu(001)

    SciTech Connect

    Chawla, J. S.; Zhang, X. Y.; Gall, D.

    2011-08-15

    Single-crystal Cu(001) layers, 4-1400 nm thick, were deposited on MgO(001) with and without a 2.5-nm-thick TiN(001) buffer layer. X-ray diffraction and reflection indicate that the TiN(001) surface suppresses Cu-dewetting, yielding a 4 x lower defect density and a 9 x smaller surface roughness than if grown on MgO(001) at 25 deg. C. In situ and low temperature electron transport measurements indicate that ultra-thin (4 nm) Cu(001) remains continuous and exhibits partial specular scattering at the Cu-vacuum boundary with a Fuchs-Sondheimer specularity parameter p = 0.6 {+-} 0.2, suggesting that the use of epitaxial wetting layers is a promising approach to create low-resistivity single-crystal Cu nanoelectronic interconnects.

  10. 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…

  11. Facile synthesis of MgO and Ni-MgO nanostructures with enhanced adsorption of methyl blue dye

    NASA Astrophysics Data System (ADS)

    Mohamed, R. M.; Shawky, Ahmed; Mkhalid, I. A.

    2017-02-01

    Nanostructured Magnesium oxide (MgO) was prepared by a simple method using a non-ionic block copolymer as surfactant. Ni was introduced to MgO to improve surface properties. The effect of Ni loading on the MgO crystalline structure, surface morphology and magnetic properties was observed by powder X-ray diffraction, field-emission scanning electron microscopy and a vibrating sample magnetometer, respectively. Textural properties of produced samples were investigated by nitrogen adsorption-desorption isotherms and the Brunauer-Emmett-Teller method. The as-prepared samples were employed as an adsorbent for the removal of Methyl blue (MeB) dye. The adsorption isotherms were studied using the Langmuir model. The results show a high adsorptive behavior for relatively high concentrated MeB with a maximum adsorption capacity of 367 mg g-1 indicating the enhanced adsorption performance of our produced structures. A mechanism for adsorption of MeB molecules on the prepared MgO is proposed.

  12. The determination of step heights on the non-uhv heat-treated MgO (100) surface by CBED

    SciTech Connect

    King, S.; McKernan, S.; Carter, C.B.

    1992-12-31

    Conditions are established whereby step heights may be measured in the acid-washed and air-annealed MgO single-crystals currently employed as substrates for pulsed-laser-deposition. Preliminary data indicates that the steps are typically a few nanometers in height.

  13. 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…

  14. 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.

  15. Simulation Study on Understanding the Spin Transport in MgO Adsorbed Graphene Based Magnetic Tunnel Junction

    NASA Astrophysics Data System (ADS)

    Raturi, Ashish; Choudhary, Sudhanshu

    2016-11-01

    First principles calculations of spin-dependent electronic transport properties of magnetic tunnel junction (MTJ) consisting of MgO adsorbed graphene nanosheet sandwiched between two CrO2 half-metallic ferromagnetic (HMF) electrodes is reported. MgO adsorption on graphene opens bandgap in graphene nanosheet which makes it more suitable for use as a tunnel barrier in MTJs. It was found that MgO adsorption suppresses transmission probabilities for spin-down channel in case of parallel configuration (PC) and also suppresses transmission in antiparallel configuration (APC) for both spin-up and spin-down channel. Tunnel magneto-resistance (TMR) of 100% is obtained at all bias voltages in MgO adsorbed graphene-based MTJ which is higher than that reported in pristine graphene-based MTJ. HMF electrodes were found suitable to achieve perfect spin filtration effect and high TMR. I-V characteristics for both parallel and antiparallel magnetization states of junction are calculated. High TMR suggests its usefulness in spin valves and other spintronics-based applications.

  16. 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.

  17. 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.

  18. Effect of hot extrusion, other constituents, and temperature on the strength and fracture of polycrystalline MgO

    SciTech Connect

    Rice, R.W. )

    1993-12-01

    Improved agreement was confirmed between the Petch intercept and single-crystal yield stresses at 22 C. Hot-extruded MgO crystal specimens stressed parallel with the resultant axial texture (1) gave the highest and least-scattered strength-grain size results at 22 C, (2) showed direct fractographic evidence of microplastic initiated fracture at 22 C and showed macroscopic yield at 1,315 and especially 1,540 C, and (3) fractured entirely via transgranular cleavage, except for intergranular failure initiation from one or a few grain boundary surfaces exposed on the subsequent fracture surface, mainly at 1,540 C. Hot-extruded, hot-pressed MgO billets gave comparable strength when fracture initiated transgranularly, but lower strength when fracture initiated from one or especially a few grain boundary surfaces exposed on the fracture. The extent and frequency of such boundary fracture increased with test temperature. While oxide additions of [<=] 5% or impurities in hot-pressed or hot-extruded MgO can make limited strength increases at larger grain sizes, those having limited solubility can limit strength at finer grain sizes, as can coarser surface finish. Overall, MgO strength is seen as a balance between flaw and microplastic controlled failure, with several parameters shifting the balance.

  19. 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).

  20. The Dissolution Kinetics of MgO into CaO-MgO-Fe2O3 Slag

    NASA Astrophysics Data System (ADS)

    Wei, Ruirui; Lv, Xuewei; Yue, Zhiwen; Xiang, Shenglin

    2017-02-01

    Calcium ferrite is the main binding phase for high-basicity sinter. The production and structure of calcium ferrite greatly influence the quality of the sinter. With the change in gangue composition, MgO becomes an important factor in the generation of calcium ferrite. In this study, the rotating cylinder method was used to study the dissolution kinetics of MgO into CaO-MgO-Fe2O3 melt. The experimental variables included the temperature, the initial composition of the melt, the Fe2O3/CaO mass ratio, the rotation time, and the rotation speed. The results indicate that the dissolution rate increases with increasing dissolution time, temperature, and rotation speed but decreases with increasing MgO content and Fe2O3/CaO mass ratio in the initial slag. The dissolution rate was observed to increase and then decrease with the addition of SiO2 in the initial slag. The activation energy and diffusion coefficient for MgO dissolution were found to range from 117.31 to 234.24 kJ mol-1 and from 1.03 × 10-6 to 1.18 × 10-5 cm2 s-1, respectively. The concentration difference between the solid and liquid phases is the main driving force for dissolution, but the viscosity and magnesium ion diffusivity of the melt also affect the process.

  1. Site-isolated iridium complexes on MgO powder: individual Ir atoms imaged by scanning transmission electron microscopy.

    PubMed

    Uzun, Alper; Ortalan, Volkan; Browning, Nigel D; Gates, Bruce C

    2009-08-21

    Iridium complexes were synthesized on MgO powder by adsorption of Ir(C(2)H(4))(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.

  2. High switching efficiency in FePt exchange coupled composite media mediated by MgO exchange control layers

    NASA Astrophysics Data System (ADS)

    Dutta, Tanmay; Piramanayagam, S. N.; Saifullah, M. S. M.; Bhatia, C. S.

    2017-07-01

    Satisfying the mutually conflicting requirements of easy switchability and high thermal stability still remains a hindrance to achieving ultra-high areal densities in hard disk drives. Exchange coupled composite media used with proper exchange control layers (ECLs) presents a potential solution to circumvent this hindrance. In this work, we have studied the role of MgO and Ta ECLs of different thicknesses in reducing the switching field of FePt media. MgO ECL was found to be more effective than a Ta ECL. For a 2 nm MgO ECL, the switching field could be reduced by 41% and at the cost of only a limited loss in thermal stability. Furthermore, a very high switching efficiency of 1.9 was obtained using 2 nm MgO ECL. So, with a proper choice of ECL material and thickness, the switching field of FePt media can be substantially reduced while ensuring high thermal stability and a better signal-to-noise ratio, thus potentially paving the way for very high areal density media.

  3. Novel Approach for the Reduction of ZnO and MgO Using a Direct Diode-Laser

    NASA Astrophysics Data System (ADS)

    Mahmoud, M. S.; Yabe, T.; Iida, E.

    2017-02-01

    In this work, we present the results of using the diode laser with an energy density of 6.6 × 1011 W/m3 for reducing ZnO to Zn in vacuum as a first step. Subsequently, we use the diode laser for the reduction of MgO using Zn as the reducing agent. Although Zn is one of the candidates proposed for the renewable energy cycle, it is more auspicious to use it as a recyclable reducing agent. Herein, the reduction efficiency was measured in terms of moles of Zn or Mg obtained per moles of ZnO or MgO ablated. The energy efficiency is measured in terms of mass of Zn or Mg produced per energy consumed by diode laser. For the first part, the largest reduction rate was 15.8 mg/s, corresponding to reduction and energy efficiencies of 76.6 pct and 16.14 mg/kJ, respectively. The yield for the process was 8.8 pct of the theoretically calculated one, which is only better than the solar ZnO reduction process. For the second part, the reduction of MgO with Zn was attainable by diode laser, the resultant Mg was associated with Zn traces, and the electron probe micro analysis results showed that the MgO reduction efficiency fluctuates between 14.4 and 26.6 pct. Different scenarios were suggested for the mechanism of the reaction.

  4. 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.

  5. The interaction of Fe on MgO(1 0 0) surfaces

    NASA Astrophysics Data System (ADS)

    Fetzer, Cs.; Dézsi, I.; Szűcs, I.; Tanczikó, F.; Balogh, A. G.

    2009-10-01

    The atomic interaction and magnetic properties of ultrathin Fe films grown on cleaved and polished MgO(1 0 0) surfaces were studied by conversion electron Mössbauer spectroscopy (CEMS). 57Fe layers were deposited as probe atoms in different layer positions in 10 ML thick Fe films. Fe layers of different thicknesses were formed on polished and cleaved substrate surfaces at RT deposition. The analysis of the spectra showed no Fe-O interaction in MgO/Fe interface. FeO phase formation was excluded. The Mössbauer spectrum of 5 ML 57Fe sample showed enhanced internal magnetic field at 80 K. No interdiffusion of 57Fe and 56Fe atoms was observed between the layers at room temperature.

  6. Atomic structure and electronic properties of MgO grain boundaries in tunnelling magnetoresistive devices

    PubMed Central

    Bean, Jonathan J.; Saito, Mitsuhiro; Fukami, Shunsuke; Sato, Hideo; Ikeda, Shoji; Ohno, Hideo; Ikuhara, Yuichi; McKenna, Keith P.

    2017-01-01

    Polycrystalline metal oxides find diverse applications in areas such as nanoelectronics, photovoltaics and catalysis. Although grain boundary defects are ubiquitous their structure and electronic properties are very poorly understood since it is extremely challenging to probe the structure of buried interfaces directly. In this paper we combine novel plan-view high-resolution transmission electron microscopy and first principles calculations to provide atomic level understanding of the structure and properties of grain boundaries in the barrier layer of a magnetic tunnel junction. We show that the highly [001] textured MgO films contain numerous tilt grain boundaries. First principles calculations reveal how these grain boundaries are associated with locally reduced band gaps (by up to 3 eV). Using a simple model we show how shunting a proportion of the tunnelling current through grain boundaries imposes limits on the maximum magnetoresistance that can be achieved in devices. PMID:28374755

  7. Shock response and phase transitions of MgO at planetary impact conditions

    DOE PAGES

    Root, Seth; Shulenburger, Luke; Lemke, Raymond W.; ...

    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

  8. 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.

  9. Elemental moment variation of bcc FexMn1-x on MgO(001)

    NASA Astrophysics Data System (ADS)

    Bhatkar, H.; Snow, R. J.; Arenholz, E.; Idzerda, Y. U.

    2017-02-01

    We report the growth, structural characterization, and electronic structure evolution of epitaxially grown bcc FexMn1-x on MgO(001). It is observed that the 20 nm thick FexMn1-x alloy films remained bcc from 0.65≤x≤1, much beyond the bulk stability range of 0.88≤x≤1. X-ray absorption spectroscopy and X-ray magnetic circular dichroism show that both the Fe and Mn L3 binding energies slightly increase with Mn incorporation and that the elemental moment of Fe in the 20 nm crystalline bcc alloy film remain nearly constant, then shows a dramatic collapse near x 0.84. The Mn MCD intensity is found to be small at all compositions that exhibit ferromagnetism

  10. Structure and electromagnetic properties of FeSiAl particles coated by MgO

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Zhou, Ting-dong

    2017-03-01

    FeSiAl particles with a layer of MgO surface coating have excellent soft magnetic and electromagnetic properties. In order to obtain the FeSiAl/MgO composites, Mg(OH)2 sol prepared by sol-gel process was well-mixed with FeSiAl flake particles, and then treated by calcination at 823 K in vacuum. The microstructural, morphological and electromagnetic parameters of FeSiAl/MgO particles were tested. Accordingly, the electromagnetic wave reflection loss in the frequency range of 0.5-18 GHz was calculated. The results show that the surface coating increases coercivity Hc and decreases complex permittivity, leading to a good impedance matching. When the coating amount was 7.5%, reflection loss of the composite particles can reach to -33 dB.

  11. Atomic structure and electronic properties of MgO grain boundaries in tunnelling magnetoresistive devices.

    PubMed

    Bean, Jonathan J; Saito, Mitsuhiro; Fukami, Shunsuke; Sato, Hideo; Ikeda, Shoji; Ohno, Hideo; Ikuhara, Yuichi; McKenna, Keith P

    2017-04-04

    Polycrystalline metal oxides find diverse applications in areas such as nanoelectronics, photovoltaics and catalysis. Although grain boundary defects are ubiquitous their structure and electronic properties are very poorly understood since it is extremely challenging to probe the structure of buried interfaces directly. In this paper we combine novel plan-view high-resolution transmission electron microscopy and first principles calculations to provide atomic level understanding of the structure and properties of grain boundaries in the barrier layer of a magnetic tunnel junction. We show that the highly [001] textured MgO films contain numerous tilt grain boundaries. First principles calculations reveal how these grain boundaries are associated with locally reduced band gaps (by up to 3 eV). Using a simple model we show how shunting a proportion of the tunnelling current through grain boundaries imposes limits on the maximum magnetoresistance that can be achieved in devices.

  12. Copper nanocolloids in MgO crystals implanted with Cu ions

    NASA Astrophysics Data System (ADS)

    Savoini, B.; Cáceres, D.; González, R.; Chen, Y.; Pinto, J. V.; da Silva, R. C.; Alves, E.

    2004-06-01

    Rutherford backscattering and optical absorption measurements were used to characterize both intrinsic and extrinsic defects produced in MgO single crystals by implantation with 250 keV Cu 2+ ions at a fluence of 1 × 10 17 ions/cm 2. Several absorption bands identical to those found in neutron irradiated crystals were observed and have been previously associated with oxygen vacancies and higher-order defects involving oxygen vacancies. In addition, a broad extinction band centered at ≈3.0 eV is observed and is attributed to copper precipitates. The maximum concentration of the implanted Cu ions occurs at a penetration depth of ≈130 nm. The copper colloids start to dissolve at temperatures above 1100 K and by 1500 K most of the copper ions have diffused into substitutional sites. Hardening induced by implantation was characterized by nanoindentation measurements.

  13. Atomic structure and electronic properties of MgO grain boundaries in tunnelling magnetoresistive devices

    NASA Astrophysics Data System (ADS)

    Bean, Jonathan J.; Saito, Mitsuhiro; Fukami, Shunsuke; Sato, Hideo; Ikeda, Shoji; Ohno, Hideo; Ikuhara, Yuichi; McKenna, Keith P.

    2017-04-01

    Polycrystalline metal oxides find diverse applications in areas such as nanoelectronics, photovoltaics and catalysis. Although grain boundary defects are ubiquitous their structure and electronic properties are very poorly understood since it is extremely challenging to probe the structure of buried interfaces directly. In this paper we combine novel plan-view high-resolution transmission electron microscopy and first principles calculations to provide atomic level understanding of the structure and properties of grain boundaries in the barrier layer of a magnetic tunnel junction. We show that the highly [001] textured MgO films contain numerous tilt grain boundaries. First principles calculations reveal how these grain boundaries are associated with locally reduced band gaps (by up to 3 eV). Using a simple model we show how shunting a proportion of the tunnelling current through grain boundaries imposes limits on the maximum magnetoresistance that can be achieved in devices.

  14. Time-dependent dielectric breakdown of MgO magnetic tunnel junctions and novel test method

    NASA Astrophysics Data System (ADS)

    Kim, Kyungjun; Choi, Chulmin; Oh, Youngtaek; Sukegawa, Hiroaki; Mitani, Seiji; Song, Yunheub

    2017-04-01

    Time-dependent dielectric breakdown (TDDB), which is used to measure reliability, depends on both the thickness of the tunnel barrier and bias voltage. In addition, the heat generated by self-heating in a magnetic tunneling junction (MTJ) affects TDDB. Therefore, we investigated TDDB with the self-heating effect for a MgO tunnel barrier with thicknesses of 1.1 and 1.2 nm by the constant voltage stress (CVS) method. Using the results of this experiment, we predicted a TDDB of 1.0 nm for the tunnel barrier. Also, we suggested the use of not only the CVS method, which is a common way of determining TDDB, but also the constant current stress (CCS) method, which compensates for the disadvantages of the CVS method.

  15. MgO Deoxidization by Focused Laser Pulse for a New Energy Cycle

    NASA Astrophysics Data System (ADS)

    Yabe, Takashi; Ikuta, Kazunari; Baasandash, Choijil; Katano, Ryoichi; Uchida, Shigeaki; Tsuji, Minoru; Mori, Yuichi; Maehara, Jun; Mahmoud, Mohamed Salah; Toya, Tomohiro

    2006-05-01

    In order to resolve the environmental problem, we proposed a new energy cycle that uses the reaction of magnesium with water. In order to realize the sustainable society, we need to deoxidize MgO to obtain Mg again. Such deoxidization will be achieved with a high-power laser. Actually the preliminary experiments implie that 70% of pure magnesium among ablated materials can be separated. Candidates for such lasers will be solar-energy-pumped laser or diode-pumped solid-state laser powered by wind power generator. Thus Mg acts as a reservoir of energy for such unsteady energy sources like solar and wind power. This paper reports the preliminary experiments toward this goal by using Nd-YAG laser.

  16. In vitro reactivity of Na2O MgO SiO2 glasses

    NASA Astrophysics Data System (ADS)

    Roy, Debdas

    2007-12-01

    A variety of bioactive glasses have been investigated over the last two decades as substitute material for diseased or damaged tissues in a human body. In this investigation, three different melt derived bioactive glasses, each having 55% by mole SiO2 and ratio of MgO to Na2O varying from 1:8 to 8:1, were prepared by melting various oxides at temperature >1250 °C. After microstructure evolution, vitro reactivity of these glasses was examined by keeping them in simulated body fluid (trans buffered pH 7.25 at 25 cc). The surface reactivity of these glasses gradually increased with increasing Na2O/MgO ratio.

  17. 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

    2015-11-06

    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.

  18. 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.

  19. Vibrational infrared spectrum of NH 3 adsorbed on MgO(100). I. Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Allouche, A.; Corà, F.; Girardet, C.

    1995-12-01

    The perturbed cluster approach, previously devoted to the calculation of the stable adsorption site and energy for ammonia adsorbed on MgO(100), is used to determine the frequency and the intensity of the main peaks associated with the normal vibrational modes of the admolecule. The ab initio model based on a cluster embedded in an array of point charges is then compared to the perturbed cluster approach and used to investigate different molecular orientations and associations on the surface in order to give an interpretation to the occurrence of the infrared signals. Six normal modes for each admolecule are calculated due to the removing of internal degeneracy by adsorption. The characteristics of the calculated spectrum are compared to the experimental infrared data and it is shown that the set of selected situations is able to explain almost every band in the spectrum without implication of NH 3 dissociation on the surface.

  20. Effects of superparamagnetism in MgO based magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Shen, Weifeng; Schrag, Benaiah D.; Girdhar, Anuj; Carter, Matthew J.; Sang, Hai; Xiao, Gang

    2009-01-01

    We have investigated the magnetic and transport behavior of MgO based magnetic tunnel junctions incorporating Co40Fe40B20 free layers with thicknesses in the vicinity of 15Å . The magnetic response of the free layer changes rapidly as its thickness decreases. Linear and hysteresis-free switching is obtained when the CoFeB free layer thickness is thinner than a critical thickness of ˜15Å . The tunneling magnetoresistance and hysteresis properties of the free layer change abruptly around the critical thickness. We have analyzed the transfer curves of junctions below the critical thickness and show that they agree well with the Langevin equation describing superparamagnetism. At even lower thicknesses, the total magnetic moment of the magnetic clusters decreases rapidly, possibly due to the reduction in the magnetic ordering temperature to below room temperature.

  1. 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.

  2. Amplified spontaneous and stimulated Mg L emissions from MgO pumped by FEL pulses

    NASA Astrophysics Data System (ADS)

    Jonnard, Philippe; André, Jean-Michel; Le Guen, Karine; Wu, Meiyi; Principi, Emiliano; Simoncig, Alberto; Gessini, Alessandro; Mincigrucci, Riccardo; Masciovecchio, Claudio; Peyrusse, Olivier

    2017-05-01

    Stimulated emission is a fundamental process in nature that deserves to be investigated and understood in the EUV and X-ray regimes. Today this is definitely possible through high energy density FEL beams. In this context, we show evidence for soft x-ray stimulated emission from a MgO solid target pumped by extreme ultraviolet FEL pulses formed in the regime of travelling-wave amplified spontaneous emission in backward geometry. Our results combine two effects separately reported in previous works: emission in a privileged direction and existence of a material-dependent threshold, for the stimulated emission. We have developed a theoretical framework, based on coupled rate and transport equations taking into account the solid density plasma state of the target. Our model, accounts for both observed mechanisms that are the privileged direction for the stimulated emission of the Mg L2,3 characteristic emission and the pumping threshold.

  3. First-principles optical spectra for F centers in MgO.

    PubMed

    Rinke, Patrick; Schleife, André; Kioupakis, Emmanouil; Janotti, Anderson; Rödl, Claudia; Bechstedt, Friedhelm; Scheffler, Matthias; Van de Walle, Chris G

    2012-03-23

    The study of the oxygen vacancy (F center) in MgO has been aggravated by the fact that the positively charged and the neutral vacancy (F+ and F0, respectively) absorb at practically identical energies. Here we apply many-body perturbation theory in the G0W0 approximation and the Bethe-Salpeter approach to calculate the optical absorption and emission spectrum of the oxygen vacancy in all three charge states. We observe unprecedented agreement between the calculated and the experimental optical absorption spectra for the F0 and F+ center. Our calculations reveal that not only the absorption but also the emission spectra of different charge states peak at nearly the same energy, which leads to a reinterpretation of the F center's optical properties.

  4. 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.

  5. Transmission electron microscopy of epitaxial Au on (001) MgO

    NASA Astrophysics Data System (ADS)

    Hoel, R. H.

    1986-04-01

    Au islands have been grown epitaxially on MgO in a cube-cube orientation. Although misfit dislocations are not directly observed, the moiré fringes are distorted, and this distortion can be associated with the creation of such dislocations, in agreement with a model described by Vincent and Matthews. The phase boundary is found to consist of coherent domains bounded by incoherent bands running in the <110> directions. Such a structure is consistent with the "lock-in" model recently suggested by Fecht and Gleiter. Applying the geometrical O-lattice model and the coherency strain energy model suggested by Matthews, it is shown that the theoretical dislocation spacings may differ by up to several percent.

  6. Atomic force microscopy and scanning electron microscopy study of MgO(110) surface faceting

    NASA Astrophysics Data System (ADS)

    Giese, D. R.; Lamelas, F. J.; Owen, H. A.; Plass, R.; Gajdardziska-Josifovska, M.

    2000-06-01

    Phosphoric- and nitric-acid etching of the MgO(110) surface generates vicinal faceting in both the <001> and <110> directions. Vacuum annealing (to 1000°C) does not introduce thermal faceting, and does not alter the chemical-etch morphology. Three types of acid-induced faceting (early-stage pits, later-stage grooves, and inverted trapezoidal pyramids) are seen as a function of etching time. Facet-angle analysis by atomic force microscopy (AFM) and scanning electron microscopy (SEM) shows the etch morphology to be vicinal, with angles in the range of 9° to 23°, not the low-energy {100} planes expected from minimization of surface energy.

  7. A compact and high efficiency diode pumped green laser based on MgO doped PPLN

    NASA Astrophysics Data System (ADS)

    Zheng, X. S.; Ji, B.; Jia, F. Q.; Cai, Z. P.; Xu, H. Y.; Xu, C. Q.

    2011-11-01

    In this work, an efficient intra-cavity second harmonic generation of green laser in a periodically poled MgO doped LiNbO3 (MgO:PPLN) bulk crystal using a compact Nd:YVO4 laser as a fundamental laser source is reported. Different length, different working temperature MgO:PPLN crystals are tested and investigated in the SHG experiments. The maximum output power at 532 nm is 6.2 W at the absorbed pump power at 808 nm of 14 W, the optical to optical conversion efficiencies from 808 to 532 nm and 1064 to 532 nm are 43 and 77%, respectively, the instability in 2 hours is less than 5%.

  8. 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.

  9. 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.

  10. 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.

  11. Thermoelectric properties of Bi2Te2.7Se0.3 nanocomposites embedded with MgO nanoparticles

    NASA Astrophysics Data System (ADS)

    Joo, Sung-Jae; Son, Ji-Hee; Min, Bok-Ki; Lee, Ji-Eun; Kim, Bong-Seo; Ryu, Byungki; Park, Su-Dong; Lee, Hee-Woong

    2016-10-01

    Bi2Te2.7Se0.3 bulk materials containing x vol% MgO nanoparticles (average particle size ≈ 100 nm, x = 0, 0.5, 1.0, 1.5) were synthesized by using high-energy ball milling and plasma- activated sintering (PAS) without any special process for nanoparticle dispersion. A microstructure investigation using a scanning electron microscope (SEM) confirmed that MgO nanoparticles were properly dispersed in the Bi2Te2.7Se0.3 matrix and that the grain size was smaller in MgO-containing samples due to suppressed grain growth. The resistivity and the maximum Seebeck coefficient of Bi2Te2.7Se0.3 increased with increasing MgO content whereas the thermal conductivity decreased in the measurement temperature range of 298 K - 573 K. As a result, the maximum dimensionless figure of merit, ZT max, increased about 8.5% in this study, from 0.806 for pristine Bi2Te2.7Se0.3 to 0.875 when x = 1.5. The ZT max was observed to shift to lower temperature, the electron concentration to decrease, and the electron mobility to increase with increasing x, which were explained using a hypothesis that the Te Bi antisite defect concentration decreased as the MgO content increased. In summary, the addition of MgO nanoparticles has been shown to be a simple and effective method to improve the low-temperature thermoelectric properties of n-type Bi2Te3 materials.

  12. 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).

  13. 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.

  14. 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.

  15. 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.

  16. Growth mechanism of single-crystalline NiO thin films grown by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Roffi, Teuku Muhammad; Nozaki, Shinji; Uchida, Kazuo

    2016-10-01

    Nickel oxide (NiO) thin films were grown by atmospheric-pressure metal organic chemical vapor deposition (APMOCVD). Growth was carried out using various growth parameters, including the growth temperature, the input precursor (O2/Ni) ratio, and the type of substrate material. Effects of the growth parameters on the structural and electrical properties of the films were investigated. X-ray diffraction analysis revealed that the crystal structure and quality were strongly affected by the growth temperature and the type of substrate material. At an optimized growth temperature, single-crystalline NiO films were grown on MgO(100) and MgO(111) substrates in a cube-on-cube orientation relationship, while on an Al2O3(001) substrate, the film was grown in the NiO[111] direction. The use of MgO substrates successfully suppressed the formation of twin defects, which have been frequently reported in the growth of NiO. The difference in the formation of the twin defects on MgO and Al2O3 substrates was discussed. It was observed that the resistivity dependence on crystal quality was affected by the choice of substrate material. The effects of the precursor ratio on the transmittance and resistivity of the films were also investigated. Improved transparency in the visible wavelength region and higher conductivity were found in films grown with higher O2/Ni ratios.

  17. Beta (β) tungsten thin films: Structure, electron transport, and giant spin Hall effect

    NASA Astrophysics Data System (ADS)

    Hao, Qiang; Chen, Wenzhe; Xiao, Gang

    2015-05-01

    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/Co40Fe40B20/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/Co40Fe40B20/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.

  18. 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.

  19. 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.

  20. Investigating and comparison of electronic and optical properties of MgO nanosheet in (100) and (111) structural directions based on the density functional theory

    NASA Astrophysics Data System (ADS)

    Akhtar, A.; Pilevarshahri, R.; Benam, Mohammad Reza

    2016-12-01

    In this paper, we investigate the electronic and optical properties of MgO nanosheet in (100) and (111) directions. Our calculations carried out under the framework of density functional theory (DFT) exploiting WIEN2K code with Full potential, periodic boundary conditions, augmented plane-wave basis sets and GGA approximation. Electronic results indicate that MgO(111) nanosheet has an indirect band gap of 3.67 eV and MgO(100) nanosheet has a direct band gap of 3.14 eV. MgO(100) nanosheet exhibit more ionic bonding than MgO(111) and MgO(111) has more covalent bonding than MgO(100) nanosheet. Moreover, the optical results indicate that variation of dielectric function in x direction is more than the z direction. DOS and imaginary part of the dielectric function survey confirm semiconductor properties with different bang gap for structures. Comparing the imaginary part of dielectric functions in x and z directions for two structures, blue and red shift have been observed respectively. Our results indicate that these two nanostructures are transparent in a wide range of energy spectra and have low reflectivity.

  1. Characterization of the MgO nano powder synthesized by using a liquid phase precursor method for plasma display panels protecting layer.

    PubMed

    Jungo, C H; Lee, J Y; Yoon, D H

    2012-02-01

    The characterization of MgO nano powders that were synthesized using a conventional firing liquid phase precursor, rapid firing liquid phase precursor and rapid cooling firing liquid phase precursor were investigated as a function of the heating and cooling rates and the concentration of the impregnated Mg(NO3)2 x 6H2O solution from 1 to 20%. The relative intensity of diffraction peak in the MgO nano powder increased with increasing firing temperature from 800 to 1200 degrees C, indicating a higher crystalline MgO nano powder. In addition, the relative intensities of the MgO nano powder synthesized at the designated temperature showed similar behavior regardless of the impregnated Mg(NO3)2 x 6H2O solution concentration from the XRD analysis. The field emission scanning electron microscope and high resolution transmission electron microscope analysis showed that the size and shape of the MgO nano powder can be controlled by the temperature, the firing and cooling processes, and the impregnated Mg(NO3)2 x 6H2O solution concentration. Moreover, the CL spectra of the synthesized MgO nano powders showed a higher luminance efficiency than commercial MgO nano powder.

  2. 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.

  3. Periodic DFT study of acidic trace atmospheric gas molecule adsorption on Ca- and Fe-doped MgO(001) surface basic sites.

    PubMed

    Baltrusaitis, Jonas; Hatch, Courtney; Orlando, Roberto

    2012-08-02

    The electronic properties of undoped and Ca- or Fe-doped MgO(001) surfaces, as well as their propensity toward atmospheric acidic gas (CO2, SO2, and NO2) uptake was investigated with an emphasis on gas adsorption on the basic MgO oxygen surface sites, O(surf), using periodic density functional theory (DFT) calculations. Adsorption energy calculations show that MgO doping will provide stronger interactions of the adsorbate with the O(surf) sites than the undoped MgO for a given adsorbate molecule. Charge transfer from the iron atom in Fe-doped MgO(001) to NO2 was shown to increase the binding interaction between adsorbate by an order of magnitude, when compared to that of undoped and Ca-doped MgO(001) surfaces. Secondary binding interactions of adsorbate oxygen atoms were observed with surface magnesium sites at distances close to those of the Mg-O bond within the crystal. These interactions may serve as a preliminary step for adsorption and facilitate further adsorbate transformations into other binding configurations. Impacts on global atmospheric chemistry are discussed as these adsorption phenomena can affect atmospheric gas budgets via altered partitioning and retention on mineral aerosol surfaces.

  4. Diffusion and solubility of argon in forsterite, enstatite, quartz, corundum and MgO

    NASA Astrophysics Data System (ADS)

    Thomas, J. B.; Cherniak, D. J.; Watson, E. B.

    2006-12-01

    The geochemistry of argon has proven important in geochronology and for the development of models for terrestrial accretion, mantle structure, outgassing and atmosphere formation. In order to develop models of geochemical processes using noble gases, their diffusivities and solubilities must be known. Many studies during the last several decades have increased our understanding of noble gas diffusion and solubility in glasses and melts. Fewer studies have measured these properties in minerals, and existing noble gas solubility measurements in minerals are highly variable and inconclusive. We determined argon diffusivities and solubilities in forsterite, enstatite, quartz, corundum and MgO from experiments conducted at 1230 to 1550 bars Ar pressure and temperatures from 400°C to 1020°C. Single, gem-quality crystals of each mineral were cut into ~3 mm2 wafers and polished prior to loading them into unsealed ceramic containers, which were then inserted into cold-seal reaction vessels for pressurization with Ar. Rutherford backscattering spectroscopy was used to measure diffusive uptake concentration gradients that developed in the crystals, from which solubilities and diffusivities were extracted. The temperature dependence of argon diffusion is described by Arrhenius relationships. The D0 values range from 1.45x10^{-20} to 8.05x10^{-20} for forsterite, enstatite, corundum and quartz. Activation energies (Ea) range from 30 to 47 kJ/mol for all the minerals except MgO, which preliminary results suggest has a significantly higher D0 and Ea for diffusion of argon. The results for quartz are in agreement with a previously determined Arrhenius relation (Watson and Cherniak, 2003). Our results indicate that argon is retained in these minerals (except perhaps MgO) through protracted, high temperature thermal events. Fractional loss calculations show that a forsterite crystal with a 1 mm radius would retain ~20% of its argon for >106 years at 1300°C. The solubility of

  5. Pd Diffusion on MgO(100): The Role of Defects and Small Cluster Mobilit.

    SciTech Connect

    Xu, Lijun; Henkelman, Graeme A.; Campbell, Charles T.; Jonsson, Hannes

    2006-02-09

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Density functional theory is used to explore the energy landscape of Pd atoms adsorbed on the terrace of MgO(10 0) and at oxygen vacancy sites. Saddle point finding methods reveal that small Pd clusters diffuse on the terrace in interesting ways. The monomer and dimer diffuse via single atom hops between oxygen sites with barriers of 0.34 eV and 0.43 eV respectively. The trimer and tetramer, however, form 3D clusters by overcoming a 2D–3D transition barrier of less than 60 meV. The trimer diffuses along the surface either by a walking or flipping motion, with comparable barriers of ca. 0.5 eV. The tetramer rolls along the terrace with a lower barrier of 0.42 eV. Soft rotational modes at the saddle point lead to an anomalously high prefactor of 1.3 · 1014 s!1 for tetramer diffusion. This prefactor is two order of magnitude higher than for monomer diffusion, making the tetramer the fastest diffusing species on the terrace at all temperatures for which diffusion is active (above 200 K). Neutral oxygen vacancy sites are found to bind Pd monomers with a 2.63 eV stronger binding energy than the terrace. A second Pd atom, however, binds to this trapped monomer with a smaller energy of 0.56 eV, so that dimers at defects dissociate on a time scale of milliseconds at room temperature. Larger clusters bind more strongly at defects. Trimers and tetramers dissociate from monomer-bound-defects at elevated temperatures of ca. 600 K. These species are also mobile on the terrace, suggesting they are important for the ripening observed at P600 K during Pd vapor deposition on MgO(100) by Haas et al. [G. Haas, A. Menck, H. Brune, J.V. Barth, J.A. Venables, K. Kern, Phys. Rev. B 61 (2000) 11105].

  6. Modeling plasticity of MgO at the mesoscale using 2.5D Dislocation Dynamics.

    NASA Astrophysics Data System (ADS)

    Reali, R.; Boioli, F.; Gouriet, K.; Carrez, P.; Cordier, P.

    2016-12-01

    In the lower mantle, viscosity results from the rheological behavior of its two main constituent minerals, namely (Mg,Fe)SiO3 bridgmanite and (Mg,Fe)O ferropericlase. Understanding how these phases deform is thus of primary importance in geophysics. This is also a very challenging task, since the extreme conditions to which the lower mantle aggregate is subjected are barely reachable in laboratory experiments.In this study, the contribution of dislocations to the deformation of periclase at the mesoscale is investigated by Dislocation Dynamics (DD) simulations, a modeling tool which considers the collective motion and interactions of dislocations. To model their behavior a so-called 2.5D DD approach is employed. Within this method, dislocations are considered as straight segments perpendicular to a 2D reference plane and local rules are added to mimic 3D behavior [1]. In this framework, both the glide and climb mechanisms can be taken into account [2].Before simulating the deformation of MgO under P, T and strain rate conditions of the lower mantle, it is necessary to benchmark the model at ambient pressure, in order to compare the simulated behavior with experiments performed in the same conditions.At high temperatures (1500-1800 K) the observed creep strain rates are controlled by the competition between dislocation glide and climb mechanisms, the former being responsible for strain production and the latter being the rate-limiting factor.Results are found in agreement with previous experimental data, confirming that the underlying physical processes are well described and permitting further investigations of MgO plasticity in the Earth's interior environment. We present the results obtained from simulations run at different temperatures and pressures within the lower mantle range of conditions. The possibility to constrain deformation with respect to time allows a characterization of the relationship between stresses and strain rates, a feature that wasn

  7. 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.

  8. 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.

  9. Surface reactivity enhancement by O2 dissociation on a single-layer MgO film deposited on metal substrate

    NASA Astrophysics Data System (ADS)

    Li, Cequn; Fan, Jing; Xu, Bin; Xu, Hu

    2016-10-01

    Improving reactivity on an insulating surface is crucial due to its important applications in surface catalytic reactions. In this work, we carried out first-principles calculations to investigate the adsorption of O2 on a single-layer MgO(100) film deposited on a metal substrate. The adsorption configurations, reaction pathways, molecular dynamics simulations, and electronic properties are reported. We reveal that O2 can completely dissociate on the surface, which is in sharp contrast to that on MgO(100) films thicker than one monolayer. The dissociated O2 tends to penetrate into the interfacial region, behaving like a switch to trigger subsequent chemical reactions. As an example, the interplay between water and the interfacial oxygen results in the formation of hydroxyl radicals. This study paves an avenue to accomplish the desired surface catalytic reactions, especially those involving oxygen.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. UHV and Ambient Pressure XPS: Potentials for Mg, MgO, and Mg(OH)2 Surface Analysis

    NASA Astrophysics Data System (ADS)

    Head, Ashley R.; Schnadt, Joachim

    2016-12-01

    The surface sensitivity of x-ray photoelectron spectroscopy (XPS) has positioned the technique as a routine analysis tool for chemical and electronic structure information. Samples ranging from ideal model systems to industrial materials can be analyzed. Instrumentational developments in the past two decades have popularized ambient pressure XPS, with pressures in the tens of mbar now commonplace. Here, we briefly review the technique, including a discussion of developments that allow data collection at higher pressures. We illustrate the information XPS can provide by using examples from the literature, including MgO studies. We hope to illustrate the possibilities of ambient pressure XPS to Mg, MgO, and Mg(OH)2 systems, both in fundamental and applied studies.

  16. Fast and accurate approximate quasiparticle band structure calculations of ZnO, CdO, and MgO polymorphs

    NASA Astrophysics Data System (ADS)

    Ataide, C. A.; Pelá, R. R.; Marques, M.; Teles, L. K.; Furthmüller, J.; Bechstedt, F.

    2017-01-01

    We investigate ZnO, CdO, and MgO oxides crystallizing in rocksalt, wurtzite, and zincblende structures. Whereas in MgO calculations, the conventional LDA-1/2 method is employed through a self-energy potential (VS), the shallow d bands in ZnO and CdO are treated through an increased amplitude (A ) of VS to modulate the self-energy of the d states to place them in the quasiparticle position. The LDA+A -1/2 scheme is applied to calculate band structures and electronic density of states of ZnO and CdO. We compare the results with those of more sophisticated quasiparticle calculations and experiments. We demonstrate that this new LDA+A -1/2 method reaches accuracy comparable to state-of-the-art methods, opening a door to study more complex systems containing shallow core electrons to the prize of LDA studies.

  17. 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.

  18. Dependency of Tunneling-Magnetoresistance Ratio on Nanoscale Spacer Thickness and Material for Double MgO Based Perpendicular-Magnetic-Tunneling-Junction.

    PubMed

    Lee, Du-Yeong; Hong, Song-Hwa; Lee, Seung-Eun; Park, Jea-Gun

    2016-12-08

    It was found that in double MgO based perpendicular magnetic tunneling junction spin-valves ex-situ annealed at 400 °C, the tunneling magnetoresistance ratio was extremely sensitive to the material and thickness of the nanoscale spacer: it peaked at a specific thickness (0.40~0.53 nm), and the TMR ratio for W spacers (~134%) was higher than that for Ta spacers (~98%). This dependency on the spacer material and thickness was associated with the (100) body-centered-cubic crystallinity of the MgO layers: the strain enhanced diffusion length in the MgO layers of W atoms (~1.40 nm) was much shorter than that of Ta atoms (~2.85 nm) and the shorter diffusion length led to the MgO layers having better (100) body-centered-cubic crystallinity.

  19. 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.

  20. Dependency of Tunneling-Magnetoresistance Ratio on Nanoscale Spacer Thickness and Material for Double MgO Based Perpendicular-Magnetic-Tunneling-Junction

    NASA Astrophysics Data System (ADS)

    Lee, Du-Yeong; Hong, Song-Hwa; Lee, Seung-Eun; Park, Jea-Gun

    2016-12-01

    It was found that in double MgO based perpendicular magnetic tunneling junction spin-valves ex-situ annealed at 400 °C, the tunneling magnetoresistance ratio was extremely sensitive to the material and thickness of the nanoscale spacer: it peaked at a specific thickness (0.40~0.53 nm), and the TMR ratio for W spacers (~134%) was higher than that for Ta spacers (~98%). This dependency on the spacer material and thickness was associated with the (100) body-centered-cubic crystallinity of the MgO layers: the strain enhanced diffusion length in the MgO layers of W atoms (~1.40 nm) was much shorter than that of Ta atoms (~2.85 nm) and the shorter diffusion length led to the MgO layers having better (100) body-centered-cubic crystallinity.