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Sample records for epitaxial orthorhombic ymno3

  1. Strain tuned magnetoelectric coupling in orthorhombic YMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Marti, X.; Fina, I.; Skumryev, V.; Ferrater, C.; Varela, M.; Fábrega, L.; Sánchez, F.; Fontcuberta, J.

    2009-10-01

    Orthorhombic YMnO3 epitaxial thin films were grown on Nb(0.5%)-doped SrTiO3(001) substrates. Film's thickness was varied to tune the epitaxial strain. Structural and magnetic properties are well correlated, presenting a more pronounced ferromagnetic behavior as the unit cell becomes more distorted. Dielectric properties were investigated as a function of the temperature and magnetic field. The dielectric peak occurring at temperatures below the antiferromagnetic ordering is proved to be magnetoelectric and its amplitude is dependent on the unit cell distortion. These findings allow tailoring ferromagnetic and magnetoelectric properties via epitaxial strain.

  2. Origin of the photoinduced current of strongly correlated YMnO3 ferroelectric epitaxial films

    NASA Astrophysics Data System (ADS)

    Miura, Kohei; Zhang, Lejun; Kiriya, Daisuke; Ashida, Atsushi; Yoshimura, Takeshi; Fujimura, Norifumi

    2017-10-01

    We have studied the photoinduced carrier generation and the carrier emission resulting in a photoinduced current using strongly correlated YMnO3 ferroelectric thin films. The unipolar material YMnO3 is suitable for studying the effect of the ferroelectric polarization on the photoinduced current. A clear relationship between the direction of the polarization and the photoinduced current was recognized using (0001)YMnO3 epitaxial films. The current switching corresponding to the polarization switching is also observed under white light illumination. To study the origin of the photoinduced current that originated from the photoinduced carrier generation, the light energy dependence of the photoinduced current was investigated. A small peak at 1.75 eV and a broad peak at around 2.5 eV are observed at room temperature. The peak at 1.75 eV corresponds to the optical absorption at 1.7 eV generated by the electron transition between the Mn 3d (xy,x2 - y2) (e2g state)/O 2p hybridized band and upper Mn 3d (3z 2 ‑ r 2) (a1g state) orbital. The broad peak of the photoinduced current corresponds to the broad photoluminescence excitation spectrum at around 2.5 eV, which is never observed in absorption measurement but reported as the hidden optical channel. The origin of the photoinduced current of YMnO3 is discussed in relation to the carrier generation and the emission processes.

  3. Orbital Reconstruction Enhanced Exchange Bias in La0.6Sr0.4MnO3/Orthorhombic YMnO3 Heterostructures

    PubMed Central

    Zheng, Dongxing; Jin, Chao; Li, Peng; Wang, Liyan; Feng, Liefeng; Mi, Wenbo; Bai, Haili

    2016-01-01

    The exchange bias in ferromagnetic/multiferroic heterostructures is usually considered to originate from interfacial coupling. In this work, an orbital reconstruction enhanced exchange bias was discovered. As La0.6Sr0.4MnO3 (LSMO) grown on YMnO3 (YMO) suffers a tensile strain (a > c), the doubly degenerate eg orbital splits into high energy 3z2 − r2 and low energy x2 − y2 orbitals, which makes electrons occupy the localized x2 − y2 orbital and leads to the formation of antiferromagnetic phase in LSMO. The orbital reconstruction induced antiferromagnetic phase enhances the exchange bias in the LSMO/YMO heterostructures, lightening an effective way for electric-field modulated magnetic moments in multiferroic magnetoelectric devices. PMID:27090614

  4. Columnar epitaxy of hexagonal and orthorhombic silicides on Si(111)

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Nieh, C. W.; Xiao, Q. F.; Hashimoto, Shin

    1990-01-01

    Columnar grains of PtSi and CrSi2 surrounded by high-quality epitaxial silicon are obtained by ultrahigh vacuum codeposition of Si and metal in an approximately 10:1 ratio on Si(111) substrates heated to 610-840 C. This result is similar to that found previously for CoSi2 (a nearly-lattice-matched cubic-fluorite crystal) on Si(111), in spite of the respective orthorhombic and hexagonal structures of PtSi and CrSi2. The PtSi grains are epitaxial and have one of three variants of the relation defined by PtSi(010)/Si(111), with PtSi 001 line/Si 110 line type.

  5. Columnar epitaxy of hexagonal and orthorhombic silicides on Si(111)

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Nieh, C. W.; Xiao, Q. F.; Hashimoto, Shin

    1990-01-01

    Columnar grains of PtSi and CrSi2 surrounded by high-quality epitaxial silicon are obtained by ultrahigh vacuum codeposition of Si and metal in an approximately 10:1 ratio on Si(111) substrates heated to 610-840 C. This result is similar to that found previously for CoSi2 (a nearly-lattice-matched cubic-fluorite crystal) on Si(111), in spite of the respective orthorhombic and hexagonal structures of PtSi and CrSi2. The PtSi grains are epitaxial and have one of three variants of the relation defined by PtSi(010)/Si(111), with PtSi 001 line/Si 110 line type.

  6. Growth of epitaxial orthorhombic YO1.5-substituted HfO2 thin film

    NASA Astrophysics Data System (ADS)

    Shimizu, Takao; Katayama, Kiliha; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Funakubo, Hiroshi

    2015-07-01

    YO1.5-substituted HfO2 thin films with various substitution amounts were grown on (100) YSZ substrates by the pulsed laser deposition method directly from the vapor phase. The epitaxial growth of film with different YO1.5 amounts was confirmed by the X-ray diffraction method. Wide-area reciprocal lattice mapping measurements were performed to clarify the crystal symmetry of films. The formed phases changed from low-symmetry monoclinic baddeleyite to high-symmetry tetragonal/cubic fluorite phases through an orthorhombic phase as the YO1.5 amount increased from 0 to 0.15. The additional annular bright-field scanning transmission electron microscopy indicates that the orthorhombic phase has polar structure. This means that the direct growth by vapor is of polar orthorhombic HfO2-based film. Moreover, high-temperature X-ray diffraction measurements showed that the film with a YO1.5 amount of 0.07 with orthorhombic structure at room temperature only exhibited a structural phase transition to tetragonal phase above 450 °C. This temperature is much higher than the reported maximum temperature of 200 °C to obtain ferroelectricity as well as the expected temperature for real device application. The growth of epitaxial orthorhombic HfO2-based film helps clarify the nature of ferroelectricity in HfO2-based films (186 words/200 words).

  7. Ferromagnetic interactions in chromium (III) doped YMnO3

    NASA Astrophysics Data System (ADS)

    Thakur, Rajesh K.; Thakur, Rasna; Kaurav, N.; Okram, G. S.; Gaur, N. K.

    2016-05-01

    Both of the reported compounds with compositions YMn1-xCrxO3 (x = 0.1 and 0.2) are synthesized by using the conventional solid state reaction method and their magnetic properties are analyzed vigilantly. The XRD pattern reveals the hexagonal structure of the reported compounds with space group P63cm (25-1079). The in-depth analysis of the magnetic measurements reveals the enhancement in the ferromagnetic character with Cr doping in YMnO3 compounds. The observed enhancement in the ferromagnetism is found to be due to the increased double exchange interactions among the Cr3+ and Mn3+ ions with Cr doping.

  8. Unusual ferromagnetic YMnO3 phase in YMnO3/La2 / 3Sr1 / 3MnO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Autieri, Carmine; Sanyal, Biplab

    2014-11-01

    By means of first-principles density functional calculations, we study the structural, magnetic and electronic properties of YMnO3/L{{a}2/3}S{{r}1/3}MnO3 heterostructures. Although in the bulk the ground state of YMnO3 is an antiferromagnet, the YMnO3/L{{a}2/3}S{{r}1/3}MnO3 heterostructure stabilizes the ferromagnetic (FM) phase in YMnO3 in the interface region over a wide range of Coulomb repulsion parameters. The hypothetical FM phase of bulk YMnO3 is dielectric and due to substantial differences between the lattice constants in the ab plane, a strong magnetocrystalline anisotropy is present. This anisotropy produces a high coercivity of the unusual FM YMnO3 that can explain the large vertical shift in the hysteresis loops observed in recent experiments (Paul et al 2014 J. Appl. Crystallogr. 47 1054). The correlation between weak exchange bias and the vertical shift is proposed, which calls for reinvestigation of various systems showing vertical shifts.

  9. Low temperature magnetic and anomalous high temperature dielectric response of Dy-Ni co-doped hexagonal YMnO3 ceramics

    NASA Astrophysics Data System (ADS)

    Kumar, Virendra; Gaur, Anurag; Kumar Gaur, Umesh

    2015-06-01

    YMnO3 pristine and Dy-Ni co-doped Y1-xDyxMn1-xNixO3 compositions with x=0.01, 0.03 and 0.05 were synthesised by high temperature solid state route. In all synthesized samples with doping a minor phase of DyMnO3 is formed but no indication of phase transition from hexagonal to orthorhombic is observed. For 3 and 5% Dy-Ni co-doped YMnO3, a thin coercivity is observed at 10 K due to insertion of weak ferromagnetism in these compositions. For undoped YMnO3, crimps are observed in both FC and ZFC curves at exactly 75 K (Neel temperature), however crimps are shifted towards significantly lesser temperature after adding the dopants. For pristine and 1% Dy-Ni co-doped samples explicit bifurcation in FC-ZFC curves is observed, which is not pronounced for 3 and 5% Dy-Ni co-doped samples. Moreover, in these compositions cusps are observed only in ZFC curves at 25 and 19 K, respectively which can be considered as hallmark of weak spin glass behaviour in these compositions. Anomalous dielectric peaks are observed at 450 and 550 K for undoped YMnO3 while a distinct peak is observed at 450 K for 1% Dy-Ni co-doped sample along with the suppression of other peaks. It is proposed that relaxor behaviour of these peaks can be explained on the basis of the Maxwell-Wagner effect.

  10. Growth of epitaxial orthorhombic YO{sub 1.5}-substituted HfO{sub 2} thin film

    SciTech Connect

    Shimizu, Takao; Katayama, Kiliha; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Funakubo, Hiroshi

    2015-07-20

    YO{sub 1.5}-substituted HfO{sub 2} thin films with various substitution amounts were grown on (100) YSZ substrates by the pulsed laser deposition method directly from the vapor phase. The epitaxial growth of film with different YO{sub 1.5} amounts was confirmed by the X-ray diffraction method. Wide-area reciprocal lattice mapping measurements were performed to clarify the crystal symmetry of films. The formed phases changed from low-symmetry monoclinic baddeleyite to high-symmetry tetragonal/cubic fluorite phases through an orthorhombic phase as the YO{sub 1.5} amount increased from 0 to 0.15. The additional annular bright-field scanning transmission electron microscopy indicates that the orthorhombic phase has polar structure. This means that the direct growth by vapor is of polar orthorhombic HfO{sub 2}-based film. Moreover, high-temperature X-ray diffraction measurements showed that the film with a YO{sub 1.5} amount of 0.07 with orthorhombic structure at room temperature only exhibited a structural phase transition to tetragonal phase above 450 °C. This temperature is much higher than the reported maximum temperature of 200 °C to obtain ferroelectricity as well as the expected temperature for real device application. The growth of epitaxial orthorhombic HfO{sub 2}-based film helps clarify the nature of ferroelectricity in HfO{sub 2}-based films (186 words/200 words)

  11. Orientation control and domain structure analysis of {100}-oriented epitaxial ferroelectric orthorhombic HfO2-based thin films

    NASA Astrophysics Data System (ADS)

    Katayama, Kiliha; Shimizu, Takao; Sakata, Osami; Shiraishi, Takahisa; Nakamura, Shogo; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Uchida, Hiroshi; Funakubo, Hiroshi

    2016-04-01

    Orientation control of {100}-oriented epitaxial orthorhombic 0.07YO1.5-0.93HfO2 films grown by pulsed laser deposition was investigated. To achieve in-plane lattice matching, indium tin oxide (ITO) and yttria-stabilized zirconia (YSZ) were selected as underlying layers. We obtained (100)- and (001)/(010)-oriented films on ITO and YSZ, respectively. Ferroelastic domain formation was confirmed for both films by X-ray diffraction using the superlattice diffraction that appeared only for the orthorhombic symmetry. The formation of ferroelastic domains is believed to be induced by the tetragonal-orthorhombic phase transition upon cooling the films after deposition. The present results demonstrate that the orientation of HfO2-based ferroelectric films can be controlled in the same manner as that of ferroelectric films composed of conventional perovskite-type material such as Pb(Zr, Ti)O3 and BiFeO3.

  12. Orientation control and domain structure analysis of {100}-oriented epitaxial ferroelectric orthorhombic HfO{sub 2}-based thin films

    SciTech Connect

    Katayama, Kiliha; Shimizu, Takao; Sakata, Osami; Shiraishi, Takahisa; Nakamura, Shogo; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Uchida, Hiroshi; Funakubo, Hiroshi

    2016-04-07

    Orientation control of {100}-oriented epitaxial orthorhombic 0.07YO{sub 1.5}-0.93HfO{sub 2} films grown by pulsed laser deposition was investigated. To achieve in-plane lattice matching, indium tin oxide (ITO) and yttria-stabilized zirconia (YSZ) were selected as underlying layers. We obtained (100)- and (001)/(010)-oriented films on ITO and YSZ, respectively. Ferroelastic domain formation was confirmed for both films by X-ray diffraction using the superlattice diffraction that appeared only for the orthorhombic symmetry. The formation of ferroelastic domains is believed to be induced by the tetragonal–orthorhombic phase transition upon cooling the films after deposition. The present results demonstrate that the orientation of HfO{sub 2}-based ferroelectric films can be controlled in the same manner as that of ferroelectric films composed of conventional perovskite-type material such as Pb(Zr, Ti)O{sub 3} and BiFeO{sub 3}.

  13. Nonlinear Optical Spectroscopy of the Two-Order-Parameter Compound YMnO3

    NASA Astrophysics Data System (ADS)

    Fröhlich, D.; Leute, St.; Pavlov, V. V.; Pisarev, R. V.

    1998-10-01

    We have observed two types of optical second harmonic spectra of Mn3+ ions in hexagonal YMnO3, one of which is caused by the noncentrosymmetric ferroelectric ordering of charges, whereas the other is due to the centrosymmetric antiferromagnetic ordering of spins. Partial overlapping between the electronic transitions gives rise to a new kind of nonlinear optical polarization P\\(2ω\\) = PFE\\(2ω\\)+PAFM\\(2ω\\), which depends on two order parameters. The magnitude and phase of P\\(2ω\\) can be changed by varying the ratio between the two contributions, as demonstrated by changing the contrast between 180° antiferromagnetic domains, which are indistinguishable in linear optics.

  14. Analysis of the multiferroicity in the hexagonal manganite YMnO3.

    PubMed

    Singh, Kiran; Lepetit, Marie-Bernadette; Simon, Charles; Bellido, Natalia; Pailhès, Stéphane; Varignon, Julien; De Muer, Albin

    2013-10-16

    We performed magnetic and ferroelectric measurements, associated with Landau theory and symmetry analysis, in order to clarify the situation of the YMnO3 system, a classical example of type I multiferroics. We found that the only magnetic group compatible with all experimental data (neutron scattering, magnetization, polarization, dielectric constant, second harmonic generation) is the P6'(3) group. In this group a small ferromagnetic component along c is induced by the Dzyaloshinskii-Moriya interaction, and observed here in magnetization measurements. We found that the ferromagnetic and antiferromagnetic components can only be switched simultaneously, while the magnetic orders are functions of the polarization square and therefore insensitive to its sign.

  15. Bipolar resistive switching in YMnO3/Nb:SrTiO3 pn-heterojunctions

    NASA Astrophysics Data System (ADS)

    Bogusz, Agnieszka; Bürger, Danilo; Skorupa, Ilona; Schmidt, Oliver G.; Schmidt, Heidemarie

    2016-11-01

    Resistively switching oxides are promising materials for use in electronic applications such as nonvolatile memories, logic gates, and artificial synapses. This work presents the bipolar resistive switching (BRS) in YMnO3/Nb:SrTiO3 pn-heterojunctions. A thermally driven electroforming process is required prior to the observed BRS. Results indicate that the BRS in YMnO3/Nb:SrTiO3 originates from the combined effects of charge trapping and detrapping processes along with the electro-migration of charged point defects in the depletion layer of the pn-heterojunction. It is shown that the built-in voltage of the pn-heterojunctions can be tuned by the oxygen partial pressure during growth of the YMnO3 thin film and impacts the working parameters of the resistively switching cell. This study provides a guideline for material engineering of bipolar resistive switches based on pn-heterojunctions.

  16. A Generalizable Multigram Synthesis and Mechanistic Investigation of YMnO3 Nanoplates

    DOE PAGES

    McBean, Coray L.; Lewis, Crystal S.; Tiano, Amanda L.; ...

    2017-05-05

    We present that the reproducible gram-scale synthesis of crystalline nanoscale multiferroics is critical for the development of the next generation of commercially relevant electronic devices. Of the subset of multiferroic materials, yttrium manganese oxide (YMnO3) is highly attractive, because of its large magneto-electric coupling constants and the recent observation of giant polarization under pressure in these types of rare earth manganites. Utilizing a unique synthetic methodology that combines metal–oleate thermal degradation with the use of a molten salt protocol, we were able to reproducibly generate monodisperse distributions of morphologically distinctive yttrium manganese oxides. Specifically, using a molten NaCl flux, wemore » were able to synthesize phase-pure, single-crystalline hexagonal YMnO3 nanoplates, measuring 441 ± 241 nm in diameter and 46 ± 6 nm in height. Moreover, these nanoplates gave rise to multiferroic behavior, which was confirmed by the observation of a ferroelectric phase from a combination of high-resolution TEM (HRTEM) and selected-area electron diffraction (SAED) analysis. Magnetic measurements are consistent with the onset of a spin glass state below 5 K. To highlight the generalizability of the synthetic method we have developed herein, as a demonstration of principle, we have also successfully used the same protocol to produce nanocubes of lanthanum aluminum oxide (LaAlO3).« less

  17. Optical absorption spectrum and electronic structure of multiferroic hexagonal YMnO3 compound

    NASA Astrophysics Data System (ADS)

    Lima, A. F.; Lalic, M. V.

    2017-02-01

    Optical absorption (OA) spectrum and electronic structure of the hexagonal YMnO3 compound have been investigated by employment of the first-principles calculations based on density functional theory. The calculations were performed upon the ferroelectric structure of the YMnO3, by testing various approximations of the exchange-correlation effects between the Mn d-electrons and considering two types of magnetic ordering of the Mn sub-lattice: (1) collinear anti-ferromagnetic order of the G-type and (2) non-collinear antiferromagnetic order that correspond to magnetic space group P63. The results demonstrate that satisfactory agreement between the theoretical and the experimental OA spectrum can be achieved only if both non-collinear anti-ferromagnetic order of the Mn spins and strong correlations between the Mn d-electrons are taken into account. The latter is found to be best described by effective Hubbard parameter Ueff = 2.55 eV. The principal features of the OA spectrum are interpreted in terms of calculated electronic structure. It is found that the most important, threshold 1.6 eV OA peak is generated by electron transitions from strongly hybridized occupied Mn d- and its neighboring in-plane O p-states to unoccupied Mn d-states. It is also concluded that the electronic gap (calculated as ∼1.1 eV) should be smaller than the optical one (∼1.6 eV).

  18. Antiferromagnetic Resonance in Multiferroic YMnO3 and LuMnO3

    NASA Astrophysics Data System (ADS)

    Zvyagin, Sergei

    2009-03-01

    Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic orders. Combining conventional far-infrared Fourier-transform and THz-range free electron laser electron spin resonance (ESR) spectroscopy techniques, magnetic excitations in hexagonal multiferroic YMnO3 and LuMnO3 in the antiferromagnetically (AFM) ordered phase have been studied. The gap in the excitation spectrum (˜42 and ˜48 cm-1 for YMnO3 and LuMnO3, respectively) was observed directly. Similar slope of the frequency-field dependences of AFM resonance modes, ˜ 0.5 cm-1/T, was revealed for both compounds. A fine structure of AFM resonance absorption has been revealed by means of high-resolution ESR techniques, which can be explained taking into account a finite interaction between the neighboring Mn^3+ layers. The work was done in collaboration with M. Ozerov, D. Kamensky, E. Cizm'ar, J. Wosnitza, A.K. Kolezhuk, D. Smirnov, H.D. Zhou, and C.R. Wiebe.

  19. The effect of strontium doping on the structural and magnetic transition of YMnO3

    NASA Astrophysics Data System (ADS)

    Thakur, Rajesh K.; Thakur, Rasna; Awasthi, A. M.; Ganesan, V.; Gaur, N. K.

    2012-06-01

    A systematic study on the effect of strontium (Sr) doping in YMnO3 has been undertaken. Polycrystalline samples with composition Y1-xSrxMnO3 (x=0, 0.01) were synthesized by using high temperature solid state reaction method. The structural and thermal properties of the prepared samples have been carried out in the wide range of temperature. Our XRD reveals the single phase formation of the reported compounds in hexagonal structure with space group P63cm (JCPDS: 25-1079). The observed pointed kinks in the specific heat study are symptomatic of the probable coupling in between the electric and magnetic orders. Our specific heat curves show that the AFM transition temperature (TN) shifts to higher value with minute Sr doping to Y-site. Further, low temperature study shows independence of specific heat on magnetic field at 8T and 12T.

  20. Oxygen-storage behavior and local structure in Ti-substituted YMnO3

    NASA Astrophysics Data System (ADS)

    Levin, I.; Krayzman, V.; Vanderah, T. A.; Tomczyk, M.; Wu, H.; Tucker, M. G.; Playford, H. Y.; Woicik, J. C.; Dennis, C. L.; Vilarinho, P. M.

    2017-02-01

    Hexagonal manganates RMnO3 (R=Y, Ho, Dy) have been recently shown to exhibit oxygen-storage capacities promising for three-way catalysts, air-separation, and related technologies. Here, we demonstrate that Ti substitution for Mn can be used to chemically tune the oxygen-breathing properties of these materials towards practical applications. Specifically, Y(Mn1-xTix)O3 solid solutions exhibit facile oxygen absorption/desorption via reversible Ti3+↔Ti4+ and Mn3+↔Mn4+ reactions already in ambient air at ≈400 °C and ≈250 °C, respectively. On cooling, the oxidation of both cations is accompanied by oxygen uptake yielding a formula YMn3+1-x-yMn4+yTi4+xO3+δ. The presence of Ti promotes the oxidation of Mn3+ to Mn4+, which is almost negligible for YMnO3 in air, thereby increasing the uptake of oxygen beyond that required for a given Ti4+ concentration. The reversibility of the redox reactions is limited by sluggish kinetics; however, the oxidation process continues, if slowly, even at room temperature. The extra oxygen atoms are accommodated by the large interstices within a triangular lattice formed by the [MnO5] trigonal bipyramids. According to bond distances from Rietveld refinements using the neutron diffraction data, the YMnO3 structure features under-bonded Mn and even more severely under-bonded oxygen atoms that form the trigonal bases of the [MnO5] bipyramids. The tensile bond strain around the 5-fold coordinated Mn site and the strong preference of Ti4+(and Mn4+) for higher coordination numbers likely provide driving forces for the oxidation reaction. Reverse Monte Carlo refinements of the local atomic displacements using neutron total scattering revealed how the excess oxygen atoms are accommodated in the structure by correlated local displacements of the host atoms. Large displacements of the under-bonded host oxygen atoms play a key part in this lattice-relaxation process, facilitating reversible exchange of significant amounts of oxygen with atmosphere.

  1. Electronic and crystal structure changes induced by in-plane oxygen vacancies in multiferroic YMnO3

    DOE PAGES

    Cheng, Shaobo; Meng, Qingping; Li, Mengli; ...

    2016-02-08

    Here, the widely spread oxygen vacancies (VO) in multiferroic materials can strongly affect their physical properties. However, their exact influence has rarely been identified in hexagonal manganites. Here, with the combined use of transmission electron microscopy (TEM) and first-principles calculations, we have systematically studied the electronic and crystal structure modifications induced by VO located at the same Mn atomic plane (in-plane VO). Our TEM experiments reveal that the easily formed in-plane VO not only influence the electronic structure of YMnO3 but alter the in-plane Wyckoff positions of Mn ions, which may subsequently affect the intraplane and interplane exchange interaction ofmore » Mn ions. The ferroelectricity is also impaired due to the introduction of VO. Further calculations confirm these electronic and structural changes and modifications. Our results indicate that the electronic and crystal structure of YMnO3 can be manipulated by the creation of VO.« less

  2. Raman study of the antiferromagnetic phase transitions in hexagonal YMnO3 and LuMnO3.

    PubMed

    Vermette, J; Jandl, S; Mukhin, A A; Ivanov, V Yu; Balbashov, A; Gospodinov, M M; Pinsard-Gaudart, L

    2010-09-08

    The A(1), E(1) and E(2) Raman active modes in hexagonal YMnO(3) and LuMnO(3) single crystals are studied as a function of temperature and compared with previous measurements. In addition to anharmonicity, some phonon frequencies show below T(N) anomalous temperature dependences that reflect the atomic displacements while some other phonon frequencies are more sensitive to the spin-phonon coupling.

  3. Magnetic transition in Y-site doped multiferroic YMnO3

    NASA Astrophysics Data System (ADS)

    Thakur, Rajesh K.; Thakur, Rasna; Gaur, N. K.

    2016-05-01

    We have synthesized polycrystalline hexagonal Y1-xSrxMnO3 (x=0.02, 0.1) compounds by using conventional solid state reaction method. The detailed structural investigations are carried out by using XRD studies which reveals the single phase formation of the reported compounds with hexagonal structure and space group P63cm (JCPDS: 25-1079). Further the XRD data of reported compounds were analyzed by RIETVELD (FULLPROFF) method which shows the decrease in the lattice parameter with increasing concentration of divalent strontium to Y-site. The observed pointed kinks in the specific heat study are indicative of the probable coupling in between the electric and magnetic orders in this class of materials. The reported systematic specific heat studies shows that the antiferromagnetic (AFM) transition temperature (TN) shifts to higher value with increasing concentration of Sr2+ ion in the YMnO3 compound which is attributed to the enhanced lattice contribution to the specific heat in the this compound. The present compound shows the independence of specific heat and magnetic transition temperature with applied magnetic field of 8T and 12T.

  4. Grain size-dependent magnetic and electric properties in nanosized YMnO3 multiferroic ceramics

    PubMed Central

    2011-01-01

    Magnetic and electric properties are investigated for the nanosized YMnO3 samples with different grain sizes (25 nm to 200 nm) synthesized by a modified Pechini method. It shows that magnetic and electric properties are strongly dependent on the grain size. The magnetic characterization indicates that with increasing grain size, the antiferromagnetic (AFM) transition temperature increases from 52 to 74 K. A corresponding shift of the dielectric anomaly is observed, indicating a strong correlation between the electric polarization and the magnetic ordering. Further analysis suggests that the rising of AFM transition temperature with increasing grain size should be from the structural origin, in which the strength of AFM interaction as well as the electrical polarization is dependent on the in-plane lattice parameters. Furthermore, among all samples, the sample with grain size of 95 nm is found to have the smallest leakage current density (< 1 μA/cm2). PACS: 75.50.Tt, 75.50.Ee, 75.85.+t, 77.84.-s PMID:21711722

  5. Magnetic structure of hexagonal YMnO3 and LuMnO3 from a microscopic point of view

    NASA Astrophysics Data System (ADS)

    Solovyev, I. V.; Valentyuk, M. V.; Mazurenko, V. V.

    2012-08-01

    The aim of this work is to establish a basic microscopic picture, which stands behind complex magnetic properties of hexagonal manganites. For these purposes, we consider two characteristic compounds: YMnO3 and LuMnO3, which form different magnetic structures in the ground state (P6̲3cm̲ and P6̲3c̲m, respectively). First, we construct an electronic low-energy model for the Mn 3d bands of YMnO3 and LuMnO3, and derive parameters of this model from the first-principles calculations. From the solution of this model, we conclude that, despite strong frustration effects in the hexagonal lattice, the relativistic spin-orbit interaction lifts the degeneracy of the magnetic ground state. Furthermore, the experimentally observed magnetic structures are successfully reproduced by the low-energy model. Then, we analyze this result in terms of interatomic magnetic interactions, which were computed using different types of approximations (starting from the model Hamiltonian as well as directly from the first-principles electronic structure calculations in the local-spin-density approximation). We argue that the main reason why YMnO3 and LuMnO3 tend to form different magnetic structures is related to the behavior of the single-ion anisotropy, which reflects the directional dependence of the lattice distortion: namely, the expansion and contraction of the Mn-trimers, which take place in YMnO3 and LuMnO3, respectively. On the other hand, the magnetic coupling between the planes is controlled by the next-nearest-neighbor interactions, which are less sensitive to the direction of the trimerization. In the P6̲3cm̲ structure of YMnO3, the Dzyaloshinskii-Moriya interactions lead to the spin canting out of the hexagonal plane, which is additive to the effect of the single-ion anisotropy. Finally, using the Berry-phase formalism, we evaluate the magnetic-state dependence of the ferroelectric polarization, and discuss potential applications of the latter in magnetoelectric switching phenomena.

  6. Effect of gamma radiation on the structural, dielectric and magnetoelectric properties of nanostructured hexagonal YMnO3

    NASA Astrophysics Data System (ADS)

    Raneesh, B.; Saha, A.; Kalarikkal, Nandakumar

    2013-08-01

    Nanocrystalline YMnO3 ceramic powders have been synthesized by using the standard sol-gel method. The samples were irradiated with 60Co γ-radiation at a dose rate of 4.7 kGy/h for different time intervals. The effects of irradiation on surface morphology viz. grain size, porosity and also the existence of a few impurity phases have been studied by scanning electron microscopy, X-ray diffraction and far-infrared reflectivity spectroscopy. Irradiation in air produced changes in the dielectric spectrum in the frequency range between 100 Hz and 2 MHz. Subjection of γ-radiation brings about key change on the properties as a consequence of structural transformations. The attained data shows that the electrical conductivity and dielectric constant is actually so much dependent on radiation dose. A quantitative magnetoelectric coefficient measurement in YMnO3 nanosystem was performed by using the dynamic lock-in amplifier technique. The response of the magneto-electric coefficient shows perfect anisotropy in the irradiated samples.

  7. Epitaxial growth on silicon and characterization of MnF{sub 2} and ZnF{sub 2} layers with metastable orthorhombic structure

    SciTech Connect

    Kaveev, A.K.; Anisimov, O.V.; Banshchikov, A.G.; Kartenko, N.F.; Ulin, V.P.; Sokolov, N.S.

    2005-07-01

    The growth of MnF{sub 2} and ZnF{sub 2} layers on Si(001) and Si(111) substrates was studied by molecular-beam epitaxy. Calcium fluoride buffer layers with (001) (110), and (111) orientations were used to prevent chemical interaction of MnF{sub 2} and ZnF{sub 2} molecules with the Si substrate. The analysis of x-ray and reflection high-energy electron-diffraction (RHEED) patterns showed that MnF{sub 2} layers grow on all of these planes in the orthorhombic {alpha}-PbO{sub 2}-type crystal phase observed earlier only at high pressures and temperatures. Atomic force microscopy revealed a strong dependence of the surface morphology on the buffer orientation and growth temperature. The best-ordered MnF{sub 2} growth occurred at 500 deg. C on a CaF{sub 2} (110) buffer layer. The diffraction analysis enabled us to find the epitaxial relations at the MnF{sub 2}/CaF{sub 2} interface. A careful analysis of the RHEED patterns of the films grown on CaF{sub 2}(001) showed a similarity in the structure and growth modes between MnF{sub 2} and ZnF{sub 2} layers, with ZnF{sub 2} tending to form multiphase layers. These findings are in agreement with the x-ray diffraction measurements.

  8. Conductivity Contrast and Tunneling Charge Transport in the Vortexlike Ferroelectric Domain Patterns of Multiferroic Hexagonal YMnO3

    NASA Astrophysics Data System (ADS)

    Ruff, E.; Krohns, S.; Lilienblum, M.; Meier, D.; Fiebig, M.; Lunkenheimer, P.; Loidl, A.

    2017-01-01

    We deduce the intrinsic conductivity properties of the ferroelectric domain walls around the topologically protected domain vortex cores in multiferroic YMnO3 . This is achieved by performing a careful equivalent-circuit analysis of dielectric spectra measured in single-crystalline samples with different vortex densities. The conductivity contrast between the bulk domains and the less conducting domain boundaries is revealed to reach up to a factor of 500 at room temperature, depending on the sample preparation. Tunneling of localized defect charge carriers is the dominant charge-transport process in the domain walls that are depleted of mobile charge carriers. This work demonstrates that, via equivalent-circuit analysis, dielectric spectroscopy can provide valuable information on the intrinsic charge-transport properties of ferroelectric domain walls, which is of high relevance for the design of new domain-wall-based microelectronic devices.

  9. Enhanced Multiferroic Properties of YMnO3 Ceramics Fabricated by Spark Plasma Sintering Along with Low-Temperature Solid-State Reaction

    PubMed Central

    Wang, Meng; Wang, Ting; Song, Shenhua; Ravi, Muchakayala; Liu, Renchen; Ji, Shishan

    2017-01-01

    Based on precursor powders with a size of 200–300 nm prepared by the low-temperature solid-state reaction method, phase-pure YMnO3 ceramics are fabricated using spark plasma sintering (SPS). X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal that the high-purity YMnO3 ceramics can be prepared by SPS at 1000 °C for 5 minutes with annealing at 800 °C for 2 h. The relative density of the sample is as high as 97%, which is much higher than those of the samples sintered by other methods. The present dielectric and magnetic properties are much better than those of the samples fabricated by conventional methods and SPS with ball-milling precursors, and the ferroelectric loops at room temperature can be detected. These findings indicate that the YMnO3 ceramics prepared by the low temperature solid reaction method and SPS possess excellent dielectric lossy ferroelectric properties at room temperature, and magnetic properties at low temperature (10 K), making them suitable for potential multiferroic applications. PMID:28772832

  10. Change in crystal structure and physical properties of the Multiferroics YMnO3 single crystals by Strong gravitational field

    NASA Astrophysics Data System (ADS)

    Tokuda, M.; Weijian, M.; Hayami, S.; Yoshiasa, A.; Mashimo, T.

    2017-04-01

    Many researchers have studied the multiferroicity of the hexagonal RMnO3 (R: rare-earth element) for both applications and fundamental studies. To investigate the relationship between the structure and physical properties of materials, some people apply the chemical pressure effect. The procedure of chemical pressure effect involves substituting rare-earth elements for ones which have a different ionic radius. Mashimo et al. have developed a high-temperature ultracentrifuge apparatus that can generate extended duration strong gravitational field in excess of 106 G under a wide range of temperatures (up to 500°C). Strong gravitational fields directly act on each atom as a different body force. This can cause the change in crystal structure. Thus, we subjected YMnO3 single crystal to strong gravity experiments (0.78×106 G, 400°C, 2 h) and investigated the resulting changes in the crystal structure and physical properties of the gravity sample. The single crystal four-circle X-ray diffraction measurements revealed the change in the nearest neighboring Mn-Mn and M-O bond distances. The temperature dependence of magnetic susceptibility by SQUID showed the change in the magnetic anisotropy of gravity sample.

  11. Structural, magnetic, and dielectric properties of solid solutions between BiMnO3 and YMnO3

    NASA Astrophysics Data System (ADS)

    Belik, Alexei A.

    2017-02-01

    Bi1-xYxMnO3 (0.1≤x≤0.9) solid solutions were prepared by the high-pressure high-temperature method at 6 GPa and 1573 K. They crystallize in the GdFeO3-type perovskite structure with the Pnma symmetry. Crystal structures of Bi0.9Y0.1MnO3 and Bi0.5Y0.5MnO3 are studied by synchrotron X-ray powder diffraction at room temperature. Only one Néel temperature, TN, is found in samples with 0.1≤x≤0.9 in comparison with two Néel temperatures observed in YMnO3 (TN=29 and 39 K). Samples with 0.5≤x≤0.9 have almost constant TN=44 K, while TN starts to increase linearly for other compositions: TN=46 K for x=0.3, TN=58 K for x=0.2, and TN=68 K for x=0.1. Field-induced transitions from canted-antiferromagnetic states to antiferromagnetic states are detected at about 30 kOe for x=0.2 and 70 kOe for x=0.1. Dielectric constant increases below TN in samples with 0.5≤x≤1, while it decreases below TN in samples with 0.1≤x≤0.3. Our data suggest that a magnetic structure changes near x=0.4. By extrapolation, we could estimate lattice parameters (a=5.9221 Å, b=7.5738 Å, and c=5.4157 Å) and TN=79 K for a hypothetical Pnma modification of BiMnO3.

  12. The magnetic susceptibility, specific heat and dielectric constant of hexagonal YMnO3, LuMnO3 and ScMnO3

    NASA Astrophysics Data System (ADS)

    Tomuta, D. G.; Ramakrishnan, S.; Nieuwenhuys, G. J.; Mydosh, J. A.

    2001-05-01

    We report the magnetic susceptibility, specific heat and dielectric constant for high-purity polycrystalline samples of three hexagonal manganites: YMnO3, LuMnO3 and ScMnO3. These materials can exhibit a ferroelectric transition at very high temperatures (TFE>700 K). At lower temperatures there is magnetic ordering of the frustrated Mn3+ spins (S = 2) on a triangular Mn lattice (YMnO3: TN = 71 K LuMnO3: TN = 90 K and ScMnO3: TN = 130 K). The transition is characterized by a sharp kink in the magnetic susceptibility at TN below which it continues to increase due to the frustration on the triangular lattice. The specific heat shows one clear continuous phase transition at TN, which is independent of external magnetic field up to 9 T with an entropy content as expected for Mn3+ ions. The temperature-dependent dielectric constant displays a distinct anomaly at TN.

  13. Enhancing the orthorhombicity and antiferromagnetic-insulating state in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films by inserting a SmFeO3 buffer layer

    NASA Astrophysics Data System (ADS)

    Tan, Xuelian; Gao, Guanyin; Chen, Pingfan; Xu, Haoran; Zhi, Bowen; Jin, Feng; Chen, Feng; Wu, Wenbin

    2014-11-01

    Structural and magnetotransport properties of epitaxial La0.67Ca0.33MnO3(30 nm)/NdGaO3(001) [LCMO/NGO(001)] films are tuned by inserting an insulating SmFeO3 (SFO) buffer layer at various thicknesses (t). All the layers and the NGO substrates have the same Pbnm symmetry with the octahedra tilting about the b-axis, but different orthorhombicity (d). We found that as t increases, the fully strained (≤15 nm) or partially relaxed (30-60 nm) SFO layers can produce different d in the upper LCMO films. Correspondingly, the induced antiferromagnetic-insulating (AFI) state in LCMO is greatly enhanced with TAFI shifted from ˜250 K for t ≤ 15 nm to ˜263 K for t = 30-60 nm. We also show that the strain relaxation for t ≥ 30 nm is remarkably anisotropic, with a stable lattice constant a as that of the NGO substrates but increasing b of both SFO and LCMO layers. This indicates the octahedral coupling across the interfaces, leaving the strain along the a-axis accommodated by the octahedral tilts, while along the b-axis most probably by the octahedral deformations. The AFI state in the LCMO layer could be ascribed to the enhanced orthorhombicity with cooperatively increased Jahn-Teller-like distortions and tilting of the MnO6 octahedra. The results strongly suggest that the interfacial octahedral coupling plays a crucial role in epitaxial growth and in tuning functionalities of the perovskite oxide films.

  14. Concentration and temperature dependent double energy gap characteristic properties of hexagonal YMnO3-xBiFeO3 films

    NASA Astrophysics Data System (ADS)

    Xu, Z.; Deng, Q. L.; Zhang, P.; Zhang, J. Z.; Li, Y. W.; Hu, Z. G.; Chu, J. H.

    2016-11-01

    The study of hexagonal (1-x) YMnO3-xBiFeO3 (0≤slant x≤slant 2.5 % ) (YBMF x) films can realize the modulation of h-YMO films, especially for the significant modulation of crystal orientation and surface. The choice of the solvent and solution, and the co-doping of Fe and Bi are two important facts of realizing the modulation. The results of x-ray diffraction and atomic force microscopy measurements indicated that there are the internal relations of the lattice orientation and the surface morphology for highly c-axis-orientation (HCO) and no preferred orientation (NPO), respectively. X-ray photoelectron spectroscopy confirmed that manganese ions show a valence of  +3 in YMnO3 film. The peak positions of the Mn 2p level move to higher energy with increasing concentration. Furthermore, there is an optimal doping concentration of x=1.5 % for the YBMF x (0≤slant x≤slant 2.5 % ) films by taking the shapes of P-E loops, the values of 2P r and 2E c into consideration. The transmittance spectra at room temperature pointed out that the double energy gaps (˜1.25 eV and 3.3 eV) corresponded to significant absorption edges, the band gap (E g1) and subband gap (E g2), respectively. The different dependency of E g1 at the lower temperature can be explained by the ionized impurity scattering. A critical temperature (˜100 K) of E g2 can be attributed to the relaxation of antiferromagnetic phase transformation. The abnormal shrinkage of E g2 below 100 K can be explained by the pinning effect of composite domain walls and the accumulation of discrete oxygen vacancies at composite domain walls. The present study sheds light on the understanding of the electronic band structure, antiferromagnetic phase transformation and their relation in h-YMO. Moreover, it contributes to the verification and improvement of Katsufuji’s model (Katsufuji et al 2001 Phys. Rev. B 64 104419).

  15. Crystal-Orientation-Modulated Exchange Bias in Orthorhombic-YMnO3/La0.6Sr0.4MnO3 Multiferroic Heterostructures.

    PubMed

    Zheng, Dongxing; Gong, Junlu; Jin, Chao; Li, Peng; Bai, Haili

    2015-07-15

    The magnetic properties of the all-oxide multiferroic heterostructures composed of orthorhombic YMnO3 (YMO) with E-type antiferromagnetic and double-exchange ferromagnetic (FM) La0.6Sr0.4MnO3 (LSMO) were studied. An orientation-modulated exchange bias effect, which is related to the interfacial Mn-O-Mn bond angle, was discovered. Because of the large bond angle in YMO/LSMO(100) heterostructures, a strong exchange coupling at the interface is formed. This strong exchange coupling sustains an FM phase in YMO at the interface region. The FM phase with strong magnetocrystalline anisotropy contributes to the vertical shift and exchange bias effect in (100) orientation heterostructures. When LSMO (110) and (111) were layered with YMO, the Mn-O-Mn bond angle was reduced, leading to a weakened exchange coupling at the interface, and only a relatively small exchange bias at low temperatures was visible.

  16. Compression behavior of orthorhombic paracetamol.

    PubMed

    Joiris, E; Di Martino, P; Berneron, C; Guyot-Hermann, A M; Guyot, J C

    1998-07-01

    Orthorhombic crystals of paracetamol exhibit good technological properties during compression. The purpose of this study was to investigate the compression behavior of this substance and to compare it to that of monoclinic paracetamol. From the crystal structure, it could be hypothesized that sliding planes are present in the orthorhombic form, and could be responsible for an increase in crystal plasticity. Compression of pure orthorhombic or monoclinic paracetamol tablets was carried out on a fully instrumented single punch machine. Data was used to establish Heckel's profiles. Images of compressed crystals were obtained by scanning electron microscopy. Tabletability of the orthorhombic crystals was far better than that of the monoclinic ones, and capping was not observed even at high compression pressure. Compared to the monoclinic form, orthorhombic paracetamol exhibited greater fragmentation at low pressure, increased plastic deformation at higher pressure, and lower elastic recovery during decompression. Plastic behavior was confirmed by SEM - micrographs showing that crystals folded under pressure. A compactibility study showed that the nature of interparticle bonds was similar for both polymorphs, the number of bonds being greater for orthorhombic paracetamol. Unlike the monoclinic form, orthorhombic paracetamol is suitable for the direct compression process. The crystalline structure accounts for its better compression behavior, because of the presence of sliding planes.

  17. Antiferroelectric Topological Insulators in Orthorhombic A MgBi Compounds (A =Li , Na, K)

    NASA Astrophysics Data System (ADS)

    Monserrat, Bartomeu; Bennett, Joseph W.; Rabe, Karin M.; Vanderbilt, David

    2017-07-01

    We introduce antiferroelectric topological insulators as a new class of functional materials in which an electric field can be used to control topological order and induce topological phase transitions. Using first principles methods, we predict that several alkali-MgBi orthorhombic members of an A B C family of compounds are antiferroelectric topological insulators. We also show that epitaxial strain and hydrostatic pressure can be used to tune the topological order and the band gap of these A B C compounds. Antiferroelectric topological insulators could enable precise control of topology using electric fields, enhancing the applicability of topological materials in electronics and spintronics.

  18. Antiferroelectric Topological Insulators in Orthorhombic AMgBi Compounds (A=Li, Na, K).

    PubMed

    Monserrat, Bartomeu; Bennett, Joseph W; Rabe, Karin M; Vanderbilt, David

    2017-07-21

    We introduce antiferroelectric topological insulators as a new class of functional materials in which an electric field can be used to control topological order and induce topological phase transitions. Using first principles methods, we predict that several alkali-MgBi orthorhombic members of an ABC family of compounds are antiferroelectric topological insulators. We also show that epitaxial strain and hydrostatic pressure can be used to tune the topological order and the band gap of these ABC compounds. Antiferroelectric topological insulators could enable precise control of topology using electric fields, enhancing the applicability of topological materials in electronics and spintronics.

  19. Dispersion analysis of arbitrarily cut orthorhombic crystals.

    PubMed

    Höfer, Sonja; Ivanovski, Vladimir; Uecker, Reinhard; Kwasniewski, Albert; Popp, Jürgen; Mayerhöfer, Thomas G

    2017-06-05

    We developed a measurement and evaluation scheme to perform dispersion analysis on arbitrarily cut orthorhombic crystals based on the schemes developed for triclinic and uniaxial crystals. As byproduct of dispersion analysis the orientations of the crystal axes are found. In contrast to the spectra of arbitrarily cut uniaxial crystals, where the fit routine has to separate two independent principal spectra, the spectra of arbitrarily cut orthorhombic crystals are a combination of three independent spectra and the evaluation scheme gets more complex. Dispersion analysis is exemplary performed on two different crystals, which show different spectral features and different levels of difficulties to evaluate. Neodymium gallate (NdGaO3) has broad overlapping reflections bands while topaz (Al2SiO4 [F, OH]2) has a quite high total number of infrared active bands. Copyright © 2017 Elsevier B.V. All rights reserved.

  20. Observation of anomalous phonons in orthorhombic rare-earth manganites

    NASA Astrophysics Data System (ADS)

    Gao, P.; Chen, H. Y.; Tyson, T. A.; Liu, Z. X.; Bai, J. M.; Wang, L. P.; Choi, Y. J.; Cheong, S.-W.

    2010-12-01

    We observe the appearance of a phonon near the lock-in temperature in orthorhombic REMnO3 (RE denotes rare earth) (RE: Lu and Ho) and anomalous phonon hardening in orthorhombic LuMnO3. The anomalous phonon occurs at the onset of spontaneous polarization. No such changes were found in incommensurate orthorhombic DyMnO3. These observations directly reveal different electric polarization mechanisms in the E-type and incommensurate-type orthorhombic REMnO3.

  1. Stabilization of orthorhombic phase in single-crystal ZnSnN2 films

    NASA Astrophysics Data System (ADS)

    Senabulya, Nancy; Feldberg, Nathaniel; Makin, Robert. A.; Yang, Yongsoo; Shi, Guangsha; Jones, Christina M.; Kioupakis, Emmanouil; Mathis, James; Clarke, Roy; Durbin, Steven M.

    2016-07-01

    We report on the crystal structure of epitaxial ZnSnN2 films synthesized via plasma-assisted vapor deposition on (111) yttria stabilized zirconia (YSZ) and (001) lithium gallate (LiGaO2) substrates. X-ray diffraction measurements performed on ZnSnN2 films deposited on LiGaO2 substrates show evidence of single-crystal, phase-pure orthorhombic structure in the Pn21a symmetry [space group (33)], with lattice parameters in good agreement with theoretically predicted values. This Pn21a symmetry is imposed on the ZnSnN2 films by the LiGaO2 substrate, which also has orthorhombic symmetry. A structural change from the wurtzite phase to the orthorhombic phase in films grown at high substrate temperatures ˜550°C and low values of nitrogen flux ˜10-5 Torr is observed in ZnSnN2 films deposited on YSZ characterized by lattice contraction in the basal plane and a 5.7% expansion of the out-of-plane lattice parameter.

  2. Stabilization of orthorhombic phase in single-crystal ZnSnN{sub 2} films

    SciTech Connect

    Senabulya, Nancy; Jones, Christina M.; Mathis, James; Feldberg, Nathaniel; Makin, Robert A.; Durbin, Steven M.; Yang, Yongsoo; Shi, Guangsha; Kioupakis, Emmanouil; Clarke, Roy

    2016-07-15

    We report on the crystal structure of epitaxial ZnSnN{sub 2} films synthesized via plasma-assisted vapor deposition on (111) yttria stabilized zirconia (YSZ) and (001) lithium gallate (LiGaO{sub 2}) substrates. X-ray diffraction measurements performed on ZnSnN{sub 2} films deposited on LiGaO{sub 2} substrates show evidence of single-crystal, phase-pure orthorhombic structure in the Pn2{sub 1}a symmetry [space group (33)], with lattice parameters in good agreement with theoretically predicted values. This Pn2{sub 1}a symmetry is imposed on the ZnSnN{sub 2} films by the LiGaO{sub 2} substrate, which also has orthorhombic symmetry. A structural change from the wurtzite phase to the orthorhombic phase in films grown at high substrate temperatures ∼550°C and low values of nitrogen flux ∼10{sup −5} Torr is observed in ZnSnN{sub 2} films deposited on YSZ characterized by lattice contraction in the basal plane and a 5.7% expansion of the out-of-plane lattice parameter.

  3. Stabilization of orthorhombic phase in single-crystal ZnSnN2 films

    DOE PAGES

    Senabulya, Nancy; Feldberg, Nathaniel; Makin, Robert. A.; ...

    2016-09-22

    Here, we report on the crystal structure of epitaxial ZnSnN2 films synthesized via plasma-assisted vapor deposition on (111) yttria stabilized zirconia (YSZ) and (001) lithium gallate (LiGaO2) substrates. X-ray diffraction measurements performed on ZnSnN2 films deposited on LiGaO2 substrates show evidence of single-crystal, phase-pure orthorhombic structure in the Pn21a symmetry [space group (33)], with lattice parameters in good agreement with theoretically predicted values. This Pn21a symmetry is imposed on the ZnSnN2 films by the LiGaO2 substrate, which also has orthorhombic symmetry. A structural change from the wurtzite phase to the orthorhombic phase in films grown at high substrate temperatures ~550°Cmore » and low values of nitrogen flux ~10–5 Torr is observed in ZnSnN2 films deposited on YSZ characterized by lattice contraction in the basal plane and a 5.7% expansion of the out-of-plane lattice parameter.« less

  4. Malleability of uranium: Manipulating the charge-density wave in epitaxial films

    NASA Astrophysics Data System (ADS)

    Springell, R.; Ward, R. C. C.; Bouchet, J.; Chivall, J.; Wermeille, D.; Normile, P. S.; Langridge, S.; Zochowski, S. W.; Lander, G. H.

    2014-06-01

    We report x-ray synchrotron experiments on epitaxial films of uranium, deposited on niobium and tungsten seed layers. Despite similar lattice parameters for these refractory metals, the uranium epitaxial arrangements are different and the strains propagated along the orthorhombic a axis of the uranium layers are of opposite sign. At low temperatures these changes in epitaxy result in dramatic modifications to the behavior of the charge-density wave in uranium. The differences are explained with the current theory for the electron-phonon coupling in the uranium lattice. Our results emphasize the intriguing possibilities of producing epitaxial films of elements that have complex structures like the light actinides uranium to plutonium.

  5. An orthorhombic polymorph of mulinic acid.

    PubMed

    Brito, Iván; Bórquez, Jorge; Loyola, Luis Alberto; López-Rodríguez, Matías; Cárdenas, Alejandro

    2010-01-09

    THE TITLE COMPOUND [SYSTEMATIC NAME: (3S,3aS,10bR)-3-isopropyl-5a,8-dimethyl-2,3,4,5,5a,6,7,10,10a,10b-deca-hydro-endo-epidioxy-cyclo-hepta-[e]indene-3a(1H)-carboxylic acid], C(20)H(30)O(4), is a polymorphic form of a previously reported structure [Loyola et al. (1990 ▶). Tetra-hedron, 46, 5413-5420]. The newly found ortho-rhom-bic polymorph crystallizes in P2(1)2(1)2(1) with two mol-ecules in the asymmetric unit. The mol-ecules are linked into discrete D(2) chains by simple O-H⋯O inter-actions. There are only slight variations in the mol-ecular geometry and supra-molecular organization in the crystal structures of the two polymorphs. The densities are 1.145 (monoclinic, P2(1)) and 1.155 Mg m(-3) (ortho-rhom-bic, P2(1)2(1)2(1)).

  6. Epitaxial graphene

    NASA Astrophysics Data System (ADS)

    de Heer, Walt A.; Berger, Claire; Wu, Xiaosong; First, Phillip N.; Conrad, Edward H.; Li, Xuebin; Li, Tianbo; Sprinkle, Michael; Hass, Joanna; Sadowski, Marcin L.; Potemski, Marek; Martinez, Gérard

    2007-07-01

    Graphene multilayers are grown epitaxially on single crystal silicon carbide. This system is composed of several graphene layers of which the first layer is electron doped due to the built-in electric field and the other layers are essentially undoped. Unlike graphite the charge carriers show Dirac particle properties (i.e. an anomalous Berry's phase, weak anti-localization and square root field dependence of the Landau level energies). Epitaxial graphene shows quasi-ballistic transport and long coherence lengths; properties that may persist above cryogenic temperatures. Paradoxically, in contrast to exfoliated graphene, the quantum Hall effect is not observed in high-mobility epitaxial graphene. It appears that the effect is suppressed due to the absence of localized states in the bulk of the material. Epitaxial graphene can be patterned using standard lithography methods and characterized using a wide array of techniques. These favorable features indicate that interconnected room temperature ballistic devices may be feasible for low-dissipation high-speed nanoelectronics.

  7. Observation of Anomalous Phonons in Orthorhombic Rare-earth Manganites

    SciTech Connect

    P Gao; H Chen; T Tyson; Z Liu; J Bai; L Wang; Y Chio; S Cheong

    2011-12-31

    We observe the appearance of a phonon near the lock-in temperature in orthorhombic REMnO{sub 3} (RE denotes rare earth) (RE: Lu and Ho) and anomalous phonon hardening in orthorhombic LuMnO{sub 3}. The anomalous phonon occurs at the onset of spontaneous polarization. No such changes were found in incommensurate orthorhombic DyMnO{sub 3}. These observations directly reveal different electric polarization mechanisms in the E-type and incommensurate-type orthorhombic REMnO{sub 3}.

  8. Niobia and tantala codoped orthorhombic zirconia ceramics

    SciTech Connect

    Hoeftberger, M.; Gritzner, G.

    1995-04-15

    During recent studies it was found that codoping of zirconia with niobia and tantala yielded very corrosion resistant, orthorhombic zirconia ceramics. The powders for those novel ceramics were made via the sol-gel technique by hydrolysis of the respective metal propoxides; a method which required dry-box techniques during the preparation of the alkoxides. In these studies the authors investigated the fabrication of precursor material from aqueous solutions. The preparation of aqueous solutions of salts of zirconium, niobium and tantalum is hampered by rapid hydrolysis. Premature hydrolysis of the chlorides and oxichlorides of niobium, tantalum and zirconium can be, however, prevented in aqueous solutions of oxalic acid. Thus the authors investigated the coprecipitation of hydroxides as precursors by reacting oxalic acid solutions of the respective cations with aqueous ammonia. In addition they studied the effects of calcination and of hydrothermal conversion of the hydroxides to oxides on the powder characteristics and on the mechanical properties of the niobia and tantala codoped zirconia ceramics.

  9. Simulations of twisted bilayer orthorhombic black phosphorus

    NASA Astrophysics Data System (ADS)

    Pan, Douxing; Wang, Tzu-Chiang; Xiao, Wende; Hu, Dongmei; Yao, Yugui

    2017-07-01

    We identified, by means of coincidence site lattice theory, an evaluative stacking phase with a wavelike Moiré pattern, denoted as 2 O -t α P , from all potentially twisted bilayer orthorhombic black phosphorus. Such a twisted stacking comes with a low formation energy of -162.8 meV , very close to existing AB stacking, according to first-principles calculations. Particularly, classic molecular dynamic simulations verified that the stacking can be directly obtained in an in situ cleavage. The stability of 2 O -t α P stacking can be directly attributed to the corrugated configuration of black phosphorus leading to the van der Waals constraining forces, where the top layer can get stuck to the bottom when one layer rotates in plane relative to the other by ˜70 .5∘ . Tribological analysis further revealed that the interlayer friction of 2 O -t α P stacking reaches up to 1.3 nN, playing a key role in the origin of 2 O -t α P .

  10. Low Temperature Phonon Properties of Orthorhombic REMnO3

    NASA Astrophysics Data System (ADS)

    Liu, Zhenxian; Gao, Peng; Chen, Haiyan; Tyson, Trevor A.

    2010-03-01

    We present the temperature dependent phonon spectra of orthorhombic-LuMnO3 and DyMnO3. The temperature dependent phonon spectra results are compared with the XAFS measurement results to probe for structural changes in the low temperature region which may coincide with ferroelectric behavior.

  11. Formation of (111) orientation-controlled ferroelectric orthorhombic HfO2 thin films from solid phase via annealing

    NASA Astrophysics Data System (ADS)

    Mimura, Takanori; Katayama, Kiliha; Shimizu, Takao; Uchida, Hiroshi; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Sakata, Osami; Funakubo, Hiroshi

    2016-08-01

    0.07YO1.5-0.93HfO2 (YHO7) films were prepared on various substrates by pulse laser deposition at room temperature and subsequent heat treatment to enable a solid phase reaction. (111)-oriented 10 wt. % Sn-doped In2O3(ITO)//(111) yttria-stabilized zirconia, (111)Pt/TiOx/SiO2/(001)Si substrates, and (111)ITO/(111)Pt/TiOx/SiO2/(001)Si substrates were employed for film growth. In this study, X-ray diffraction measurements including θ-2θ measurements, reciprocal space mappings, and pole figure measurements were used to study the films. The film on (111)ITO//(111)yttria-stabilized zirconia was an (111)-orientated epitaxial film with ferroelectric orthorhombic phase; the film on (111)ITO/(111)Pt/TiOx/SiO2/(001)Si was an (111)-oriented uniaxial textured film with ferroelectric orthorhombic phase; and no preferred orientation was observed for the film on the (111)Pt/TiOx/SiO2/(001)Si substrate, which does not contain ITO. Polarization-hysteresis measurements confirmed that the films on ITO covered substrates had saturated ferroelectric hysteresis loops. A remanent polarization (Pr) of 9.6 and 10.8 μC/cm2 and coercive fields (Ec) of 1.9 and 2.0 MV/cm were obtained for the (111)-oriented epitaxial and uniaxial textured YHO7 films, respectively. These results demonstrate that the (111)-oriented ITO bottom electrodes play a key role in controlling the orientation and ferroelectricity of the phase formation of the solid films deposited at room temperature.

  12. Formation of (111) orientation-controlled ferroelectric orthorhombic HfO{sub 2} thin films from solid phase via annealing

    SciTech Connect

    Mimura, Takanori; Katayama, Kiliha; Shimizu, Takao; Uchida, Hiroshi; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Sakata, Osami; Funakubo, Hiroshi

    2016-08-01

    0.07YO{sub 1.5}-0.93HfO{sub 2} (YHO7) films were prepared on various substrates by pulse laser deposition at room temperature and subsequent heat treatment to enable a solid phase reaction. (111)-oriented 10 wt. % Sn-doped In{sub 2}O{sub 3}(ITO)//(111) yttria-stabilized zirconia, (111)Pt/TiO{sub x}/SiO{sub 2}/(001)Si substrates, and (111)ITO/(111)Pt/TiO{sub x}/SiO{sub 2}/(001)Si substrates were employed for film growth. In this study, X-ray diffraction measurements including θ–2θ measurements, reciprocal space mappings, and pole figure measurements were used to study the films. The film on (111)ITO//(111)yttria-stabilized zirconia was an (111)-orientated epitaxial film with ferroelectric orthorhombic phase; the film on (111)ITO/(111)Pt/TiO{sub x}/SiO{sub 2}/(001)Si was an (111)-oriented uniaxial textured film with ferroelectric orthorhombic phase; and no preferred orientation was observed for the film on the (111)Pt/TiO{sub x}/SiO{sub 2}/(001)Si substrate, which does not contain ITO. Polarization–hysteresis measurements confirmed that the films on ITO covered substrates had saturated ferroelectric hysteresis loops. A remanent polarization (P{sub r}) of 9.6 and 10.8 μC/cm{sup 2} and coercive fields (E{sub c}) of 1.9 and 2.0 MV/cm were obtained for the (111)-oriented epitaxial and uniaxial textured YHO7 films, respectively. These results demonstrate that the (111)-oriented ITO bottom electrodes play a key role in controlling the orientation and ferroelectricity of the phase formation of the solid films deposited at room temperature.

  13. Epitaxial stabilization of artificial hexagonal GdMnO3 thin films and their magnetic properties

    NASA Astrophysics Data System (ADS)

    Lee, D.; Lee, J.-H.; Murugavel, P.; Jang, S. Y.; Noh, T. W.; Jo, Y.; Jung, M.-H.; Ko, Y.-D.; Chung, J.-S.

    2007-04-01

    The authors investigated the role of oxygen partial pressure on the epitaxial growth of an artificial hexagonal GdMnO3 phase, which should exist in an orthorhombic structure in bulk. The hexagonal GdMnO3 film showed diverse, but obvious, magnetic phase transitions with highly enhanced ferromagnetic properties. Its remnant magnetization at 4.2K is higher than those of other hexagonal RMnO3 (R =Ho, Er, and Yb) compounds, and the Curie temperature increases by around 25K. The results demonstrate that the epitaxial stabilization technique is a promising method for fabricating an artificial material with enhanced magnetic properties.

  14. Specific features of nonvalent interactions in orthorhombic perovskites

    NASA Astrophysics Data System (ADS)

    Serezhkin, V. N.; Pushkin, D. V.; Serezhkina, L. B.

    2014-07-01

    It is established that isostructural orthorhombic perovskites ABO3 (sp. gr. Pnma in different systems, no. 62, Z = 4), depending on the specificity of nonvalent interactions (which determine the combinatorial-topological type of the Voronoi-Dirichlet polyhedra (VDPs) of four basis atoms), are divided into ten different stereotypes. It is shown by the example of 259 perovskites belonging to the DyCrO3 stereotype that VDP characteristics can be used to quantitatively estimate the distortion of BO6 octahedra, including that caused by the Jahn-Teller effect. It is found that one of the causes of the distortion of the coordination polyhedra of atoms in the structure of orthorhombic perovskites is heteroatomic metal-metal interactions, for which the interatomic distances are much shorter than the sum of the Slater radii of A and B atoms.

  15. Electronic and magnetic properties of orthorhombic iron selenide

    NASA Astrophysics Data System (ADS)

    Lovesey, S. W.

    2016-02-01

    Iron orbitals in orthorhombic iron selenide (FeSe) can produce chargelike multipoles that are polar (parity-odd). Orbitals in question include Fe (3 d ), Fe (4 p ), and p -type ligands that participate in transport properties and bonding. The polar multipoles may contribute weak, space-group forbidden Bragg spots to diffraction patterns collected with x rays tuned in energy to a Fe atomic resonance (Templeton & Templeton scattering). Ordering of conventional, axial magnetic dipoles does not accompany the tetragonal-orthorhombic structural phase transition in FeSe, unlike other known iron-based superconductors. We initiate a new line of inquiry for this puzzling property of orthorhombic FeSe, using a hidden magnetic order that belongs to the m'm'm' magnetic crystal class. It is epitomized by the absence of ferromagnetism and axial magnetic dipoles and the appearance of magnetic monopoles and magnetoelectric quadrupoles. A similar magnetic order occurs in cuprate superconductors, yttrium barium copper oxide and Hg1201, where it was unveiled with the Kerr effect and in Bragg diffraction patterns revealed by polarized neutrons.

  16. Van vleck paramagnetism in orthorhombic TiO2 (Brookite)

    USGS Publications Warehouse

    Senftle, F.E.; Thorpe, A.N.

    1968-01-01

    The magnetic susceptibility of the orthorhombic form of titanium dioxide has been measured from 5 to 300??K. After deducting the temperature-dependent component, which is probably due to defects or impurities, and the free-ion diamagnetic component, the Van Vleck paramagnetism was estimated to be 33??10-6 emu/mole. Comparison is made between this value and the Van Vleck paramagnetism of strontium titanate and the two tetragonal forms of titanium dioxide: rutile and anatase. ?? 1968 The American Physical Society.

  17. Universal Octahedral-Site Distortion in Orthorhombic Perovskite Oxides

    NASA Astrophysics Data System (ADS)

    Zhou, J.-S.; Goodenough, J. B.

    2005-02-01

    Lattice parameters of the orthorhombic perovskites RMO3 ( R=rare earth, M=Ti, V, …, Ni, and Ga) have been simulated based on the ionic M-O bond length and rigid MO6/2 octahedra. Comparison with experimental data shows that the long-standing lattice-parameter anomaly generally found for the larger R3+ ions in these families is caused by a structural feature that is not revealed by the geometric tolerance factor widely used for the perovskites.

  18. Epitaxial Graphene Quantum Electronics

    DTIC Science & Technology

    2014-05-19

    ferromagnetism with spintronics potential. * We have achieved the highest operational frequency in graphene transistors. Epitaxial graphene; quantum transport...important discovery with implications for spintronics . * We have found that ballistic transport most likely involves non-conventional charge carriers

  19. Study a compound orthorhombic lattice pattern in dielectric barrier discharge

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Dong, Lifang; Gao, Xing; Liu, Weibo; Wei, Lingyan; Pan, Yuyang

    2016-12-01

    The compound orthorhombic lattice pattern which is composed of the bright spot and the dim spot is observed for the first time in a dielectric barrier discharge system. It is found that the dim spot is located at the gravity center of the surrounding three bright spots. The discharge bifurcates from a square lattice, hexagon pattern to compound orthorhombic lattice pattern and finally changes to an irregular pattern. The phase diagram of the pattern types as a function of the applied voltage and the argon concentration is given. The spatio-temporal dynamics of the pattern is studied by the time correlation measurement and the high speed video camera images. Results show that the dim spot is formed by both volume discharge and surface discharge induced by the bright spot. The differences of plasma parameters between the bright spots and the dim spots obtained by optical emission spectroscopy verify that the dim spot is formed by both volume discharge and surface discharge. To better understand the mechanism of firing of the dim spots for the same conditions as in the first phase diagram, the phase diagram of the mechanism of firing of the dim spots as a function of the gas pressure and the argon concentration is given. The simulation of the electric fields of wall charges accumulated by bright spots further verifies that the bright spot has an effect on the formation of dim spot.

  20. Critical thickness of high structural quality SrTiO3 films grown on orthorhombic (101) DyScO3

    SciTech Connect

    Hawley, Marilyn E; Biegalski, Michael D; Schlom, Darrell G

    2008-01-01

    Strained epitaxial SrTiO{sub 3} films were grown on orthorhombic (101) DyScO{sub 3} substrates by reactive molecular-beam epitaxy. The epitaxy of this substrate/film combination is cube on cube with a pseudocubic out-of-plane (001) orientation. The strain state and structural perfection of films with thicknesses ranging from 50 to 1000 {angstrom} were examined using x-ray scattering. The critical thickness at which misfit dislocations was introduced was between 350 and 500 {angstrom}. These films have the narrowest rocking curves (full width at half maximum) ever reported for any heteroepitaxial oxide film (0.0018{sup o}). Only a modest amount of relaxation is seen in films exceeding the critical thicknesses even after postdeposition annealing at 700{sup o}C in 1 atm of oxygen. The dependence of strain relaxation on crystallographic direction is attributed to the anisotropy of the substrate. These SrTiO{sub 3} films show structural quality more typical of semiconductors such as GaAs and silicon than perovskite materials; their structural relaxation behavior also shows similarity to that of compound semiconductor films.

  1. Epitaxial Garnets and Hexagonal Ferrites.

    DTIC Science & Technology

    1983-12-01

    Ferrites Lithium Ferrite Magnetostatic Wave Garnets Epitaxy Yttrium Iron Garnet Liquid Phase Epitaxy Hexagonal Ferrite Microwave Signal Processing...epitaxial ferrit ( materials for use in microwave and millirreter-wave signal processing devices. The major emphasis has been on multiple layer...overall objective of this research is to develop epitaxial single crystal ferrite films suitable for microwave and millimeter-wave signal processing at

  2. Orthorhombic C32: a novel superhard sp3 carbon allotrope.

    PubMed

    Zhang, Miao; Liu, Hanyu; Du, Yonghui; Zhang, Xinxin; Wang, Yanchao; Li, Quan

    2013-09-07

    Using a recently developed 'Crystal structure AnaLYsis by Particle Swarm Optimization' (CALYPSO) algorithm on a structural search, we predicted a novel sp(3) carbon allotrope possessing an orthorhombic lattice with the space group Cmmm (oC32). The calculated elastic constants and the simulated hardness revealed that oC32 simultaneously possesses ultra-incompressible and superhard properties with a high bulk modulus of 457 GPa and a high Vickers hardness of 96.2 GPa. This oC32 phase is dynamically stable and energetically more preferable than the experientially observed cold-compressed carbon, thus oC32 is expected to be experimentally synthesizable under extreme conditions. These results further expand the list of meta-stable carbon allotropes and superhard materials under atmospheric and extreme conditions.

  3. Novel superhard carbon: C-centered orthorhombic C8.

    PubMed

    Zhao, Zhisheng; Xu, Bo; Zhou, Xiang-Feng; Wang, Li-Min; Wen, Bin; He, Julong; Liu, Zhongyuan; Wang, Hui-Tian; Tian, Yongjun

    2011-11-18

    A novel carbon allotrope of C-centered orthorhombic C(8) (Cco-C(8)) is predicted by using a recently developed particle-swarm optimization method on structural search. Cco-C(8) adopts a sp(3) three-dimensional bonding network that can be viewed as interconnected (2,2) carbon nanotubes through 4- and 6-member rings and is energetically more favorable than earlier proposed carbon polymorphs (e.g., M carbon, bct-C(4), W carbon, and chiral C(6)) over a wide range of pressures studied (0-100 GPa). The simulated x-ray diffraction pattern, density, and bulk modulus of Cco-C(8) are in good accordance with the experimental data on structurally undetermined superhard carbon recovered from cold compression of carbon nanotube bundles. The simulated hardness of Cco-C(8) can reach a remarkably high value of 95.1 GPa, such that it is capable of cracking diamond.

  4. Nuclear quadrupole resonance studies of amorphous, orthorhombic, and rhombohedral arsenic

    SciTech Connect

    Jellison, G.E. Jr.; Petersen, G.L.; Taylor, P.C.

    1980-10-15

    Pulsed nuclear quadrupole resonance (NQR) experiments have been performed on three forms of elemental arsenic: amorphous (a), rhombohedral (rh), and orthorhombic (or). The temperature dependence of the spin-lattice relaxation time (T/sub 1/) provides evidence for the existence of disorder (tunneling) modes in a-As. It is found that the NQR line shape of a-As is highly asymmetric, and this asymmetry is attributed to a distribution of dihedral angles in a-As. The observed NQR frequencies indicate that the amount of bonding s admixture is different in each material (rh-As:3%, or-As:7%, a-As:10%). Simple calculations in comparison with x-ray results indicate that the bonding configurations in these three forms of arsenic do not necessarily correspond to maximum overlap of bonding orbitals on adjacent atoms.

  5. Electronically-driven orthorhombic distortion in FeSe

    NASA Astrophysics Data System (ADS)

    Watson, Matthew; Davies, Nathaniel; Haghighirad, Amir; Narayanan, Arjun; Kim, Timur; Hoersch, Moritz; Blake, Samuel; Coldea, Amalia

    2015-03-01

    FeSe is structurally the simplest of Fe-based superconductors, and exhibits a tetragonal-to-orthorhombic structural transition at ~ 90 K, but no long-range magnetism at any temperature. We report measurements of the resistivity anisotropy in FeSe above Ts finding a large and divergent response to an applied strain, with a comparable magnitude and temperature-dependence to measurements in Ba(Fe1-xCox)2As2, but opposite sign. We compare this data with literature reports on NMR and our own ARPES data, which taken together indicate that the structural transition is electronically-driven with orbital degrees of freedom playing a central role. This work was supported by EPSRC, UK (EP/I004475/1) and Diamond Light Source.

  6. Solute transport in orthorhombic lysozyme crystals: a molecular simulation study.

    PubMed

    Malek, Kourosh

    2007-12-01

    Long-time equilibrium molecular dynamics simulations were performed to study the passage of a substrate, L: -arabinose, through nanopores of orthorhombic hen egg white lysozyme crystals. Cross-linked protein crystals (CLPC), as novel biological nanoporous media, consist of an extensive regular matrix of chiral solvent-filled nanopores via which ions and solutes, e.g. sugars and amino acids, travel in and out. We studied the diffusive motion of arabinose inside protein channels. The computed diffusion coefficients within the crystal were orders of magnitudes lower relative to the diffusion coefficient of the solute in water. This study is valuable for understanding the nature of solute-protein interactions and transport phenomena in CLPCs and provides an understanding of biocatalytic and bioseparation processes using CLPC.

  7. Te vacancy-driven superconductivity in orthorhombic molybdenum ditelluride

    NASA Astrophysics Data System (ADS)

    Cho, Suyeon; Kang, Se Hwang; Yu, Ho Sung; Kim, Hyo Won; Ko, Wonhee; Hwang, Sung Woo; Han, Woo Hyun; Choe, Duk-Hyun; Jung, Young Hwa; Chang, Kee Joo; Lee, Young Hee; Yang, Heejun; Wng Kim, Sung

    2017-06-01

    Two-dimensional (2D) transition metal dichalcogenides (TMDs) have received great attentions because of diverse quantum electronic states such as topological insulating (TI), Weyl semimetallic (WSM) and superconducting states. Recently, the superconducting states emerged in pressurized semimetallic TMDs such as MoTe2 and WTe2 have become one of the central issues due to their predicted WSM states. However, the difficulty in synthetic control of chalcogen vacancies and the ambiguous magneto transport properties have hindered the rigorous study on superconducting and WSM states. Here, we report the emergence of superconductivity at 2.1 K in Te-deficient orthorhombic T d-MoTe2-x with an intrinsic electron-doping, while stoichiometric monoclinic 1T‧-MoTe2 shows no superconducting state down to 10 mK, but exhibits a large magnetoresistance of 32 000% at 2 K in a magnetic field of 14 T originating from nearly perfect compensation of electron and hole carriers. Scanning tunnelling spectroscopy and synchrotron x-ray diffraction combined with theoretical calculations clarify that Te vacancies trigger superconductivity via intrinsic electron doping and the evolution of the T d phase from the 1T‧ phase below 200 K. Unlike the pressure-induced superconducting state of monoclinic MoTe2, this Te vacancy-induced superconductivity is emerged in orthorhombic MoTe2, which is predicted as Weyl semimetal, via electron-doping. This chalcogen vacancy induced-superconductivity provides a new route for cultivating superconducting state together with WSM state in 2D van der Waals materials.

  8. Electrochemical Atomic Layer Epitaxy

    NASA Astrophysics Data System (ADS)

    Gregory, Brian Wayne

    1992-01-01

    Presented here are initial investigations into an electrochemical method whereby thin films of compound semiconductors are produced by epitaxial growth of the constituent elements. This method is the electrochemical analogue of atomic layer epitaxy (ALE) (a vacuum-based technique which relies on sequential formation of atomic layers of the constituent elements) and has been termed "Electrochemical atomic layer epitaxy" (ECALE). These preliminary studies are centered on the formation of CdTe, though in principle they could be extended to a number of other compound semiconductors. A background introduction on topics relevant to epitaxial growth in electrochemical systems will be presented. Predictions of underpotential behavior in the CdTe system will be made using potential -pH (Pourbaix) diagrams. Development of the method will proceed from our initial studies of Cd and Te underpotential deposition (UPD) on a number of metallic substrates, followed by results demonstrating the ECALE formation of two monolayers of CdTe on polycrystalline and single crystal gold substrates. The final chapter will present current attempts to design and construct an automated, computer-controlled thin-layer electrochemical flow cell, which is to be used for the deposition of thicker layers (up to 1 mu m) of compound semiconductors.

  9. Epitaxial thin films

    DOEpatents

    Hunt, Andrew Tye; Deshpande, Girish; Lin, Wen-Yi; Jan, Tzyy-Jiuan

    2006-04-25

    Epitatial thin films for use as buffer layers for high temperature superconductors, electrolytes in solid oxide fuel cells (SOFC), gas separation membranes or dielectric material in electronic devices, are disclosed. By using CCVD, CACVD or any other suitable deposition process, epitaxial films having pore-free, ideal grain boundaries, and dense structure can be formed. Several different types of materials are disclosed for use as buffer layers in high temperature superconductors. In addition, the use of epitaxial thin films for electrolytes and electrode formation in SOFCs results in densification for pore-free and ideal gain boundary/interface microstructure. Gas separation membranes for the production of oxygen and hydrogen are also disclosed. These semipermeable membranes are formed by high-quality, dense, gas-tight, pinhole free sub-micro scale layers of mixed-conducting oxides on porous ceramic substrates. Epitaxial thin films as dielectric material in capacitors are also taught herein. Capacitors are utilized according to their capacitance values which are dependent on their physical structure and dielectric permittivity. The epitaxial thin films of the current invention form low-loss dielectric layers with extremely high permittivity. This high permittivity allows for the formation of capacitors that can have their capacitance adjusted by applying a DC bias between their electrodes.

  10. Facile strategy and mechanism for orthorhombic SnO2 thin films

    NASA Astrophysics Data System (ADS)

    Chen, Zhiwen; Lai, Joseph K. L.; Shek, Chan-Hung

    2006-12-01

    Orthorhombic phase SnO2 is a material with unknown optical, electrical, and gas-sensing properties. It was found previously only at high pressures and temperatures. A facile strategy for the synthesis of orthorhombic SnO2 is of fundamental importance. Using pulsed-laser deposition, the authors report a kind of experimental realization of a pure orthorhombic SnO2 thin film under low pressure and temperature that are much lower than those of traditional methods. The optical properties of an orthorhombic SnO2 thin film were measured by spectrophotometric transmittance. The oxygen exchange reaction mechanism at the grain interfaces was proposed to explain the formation and optical properties of this orthorhombic phase.

  11. Two ortho-rhom-bic polymorphs of hydro-morphone.

    PubMed

    Mazurek, Jaroslaw; Hoffmann, Marcel; Fernandez Casares, Ana; Cox, D Phillip; Minardi, Mathew D; Sasine, Josh

    2016-05-01

    Conditions to obtain two polymorphic forms by crystallization from solution were determined for the analgesic drug hydro-morphone [C17H19NO3; systematic name: (4R,4aR,7aR,12bS)-9-hy-droxy-3-methyl-1,2,4,4a,5,6,7a,13-octa-hydro-4,12-methano-benzofuro[3,2-e]iso-quinolin-7-one]. These two crystalline forms, designated as I and II, belong to the P212121 ortho-rhom-bic space group. In both polymorphs, the hydro-morphone mol-ecules adopt very similar conformations with some small differences observed only in the N-methyl amine part of the mol-ecule. The crystal structures of both polymorphs feature chains of mol-ecules connected by hydrogen bonds; however, in form I this inter-action occurs between the hydroxyl group and the tertiary amine N atom whereas in form II the hydroxyl group acts as a donor of a hydrogen bond to the O atom from the cyclic ether part.

  12. Covalent dependence of octahedral rotations in orthorhombic perovskite oxides.

    PubMed

    Cammarata, Antonio; Rondinelli, James M

    2014-09-21

    The compositional dependence of metal-oxygen BO6 octahedral distortions, including bond elongations and rotations, is frequently discussed in the ABO3 perovskite literature; structural distortions alleviate internal stresses driven by under- or over-coordinated bond environments. Here we identify the dependence of octahedral rotations from changes in metal-oxygen bond covalency in orthorhombic perovskites. Using density functional theory we formulate a covalency metric, which captures both the real and k-space interactions between the magnitude and sense, i.e., in-phase or out-of-phase, octahedral rotations, to explore the link between the ionic-covalent Fe-O bond and the interoctahedral Fe-O-Fe bond angles in Pbnm ferrates. Our survey finds that the covalency of the metal-oxygen bond is correlated with the rotation amplitude: We find the more covalent the Fe-O bond, the less distorted is the structure and the more important the long-range inter-octahedral (Fe-O-Fe bond angle) interactions. Finally, we show how to indirectly tune the B-O bond covalency by A-cation induced BO6 rotations independent of ionic size, facilitating design of targeted bonding interactions in complex perovskites.

  13. Theoretical Study of Orthorhombic Distortions in High-Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Schnyder, Andreas; Manske, Dirk; Mudry, Christopher; Sigrist, Manfred

    2006-03-01

    Using a Fermi-liquid-based theory we calculate the response function for various spectroscopic probes in hole-doped high-TC superconductors, and determine the effects of orthorhombic distortions in the crystal lattice and asymmetry in the superconducting gap function. Employing the two-dimensional one-band Hubbard model and a generalized RPA-type theory we consider anisotropic hopping parameters (txty) and a mixing of d- and s-wave symmetry of the superconducting order parameter. Within this model, both the electronic Raman spectra and the dynamical magnetic susceptibility [1] are studied in detail. The relevance of these calculations to electronic Raman scattering measurements and inelastic neutron scattering experiments [2] on untwinned YBa2Cu3O6+x are discussed. [1] A. P. Schnyder, D. Manske, C. Mudry, and M. Sigrist, cond-mat/0510790. [2] V. Hinkov, S. Pailhes, P. Bourges, Y. Sidis, A. Ivanov, A. Kulakov, C. T. Lin, D. P. Chen, C. Bernhard, and B. Keimer, Nature 430, 650 (2004).

  14. Directed Growth of Orthorhombic Crystals in a Micropillar Array.

    PubMed

    Holzner, Gregor; Binder, Claudia; Kriel, Frederik H; Priest, Craig

    2017-02-14

    We report directed growth of orthorhombic crystals of potassium permanganate in spatial confinement of a micropillar array. The solution is introduced by spontaneous wicking to give a well-defined film (thickness 10-15 μm; volume ∼600 nL) and is connected to a reservoir (several microliters) that continuously "feeds" the evaporating film. When the film is supersaturated, crystals nucleate and preferentially grow in specific directions guided by one of several possible linear paths through the pillar lattice. Crystals that do not initially conform are stopped at an obstructing pillar, branch into another permitted direction, or spontaneously rotate to align with a path and continue to grow. Microspectroscopy is able to track the concentration of solute in a small region of interest (70 × 100 μm(2)) near to growing crystals, revealing that the solute concentration initially increases linearly beyond the solubility limit. Crystal growth near the region of interest resulted in a sharp decrease in the local solute concentration (which rapidly returns the concentration to the solubility limit), consistent with estimated diffusion time scales (<1 s for a 50 μm length scale). The ability to simultaneously track solute concentration and control crystal orientation in nanoliter samples will provide new insight into microscale dynamics of microscale crystallization.

  15. Orthorhombic Titanium Matrix Composite Subjected to Simulated Engine Mission Cycles

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.

    1997-01-01

    Titanium matrix composites (TMC's) are commonly made up of a titanium alloy matrix reinforced by silicon carbide fibers that are oriented parallel to the loading axis. These composites can provide high strength at lower densities than monolithic titanium alloys and superalloys in selected gas turbine engine applications. The use of TMC rings with unidirectional SiC fibers as reinforcing rings within compressor rotors could significantly reduce the weight of these components. In service, these TMC reinforcing rings would be subjected to complex service mission loading cycles, including fatigue and dwell excursions. Orthorhombic titanium aluminide alloys are of particular interest for such TMC applications because their tensile and creep strengths are high in comparison to those of other titanium alloys. The objective of this investigation was to assess, in simulated mission tests at the NASA Lewis Research Center, the durability of a SiC (SCS-6)/Ti-22Al-23Nb (at.%) TMC for compressor ring applications, in cooperation with the Allison Engine Company.

  16. Water in hydrated orthorhombic lysozyme crystal: Insight from atomistic simulations.

    PubMed

    Hu, Zhongqiao; Jiang, Jianwen; Sandler, Stanley I

    2008-08-21

    Biologically important water in orthorhombic lysozyme crystal is investigated using atomistic simulations. A distinct hydration shell surrounding lysozyme molecules is found from the number distribution of water molecules. While the number of water molecules in the hydration shell increases, the percentage decreases as the hydration level rises. Adsorption of water in the lysozyme crystal shows type-IV behavior. At low hydration levels, water molecules primarily intercalate the minor pores and cavity in the crystal due to the strong affinity between protein and water. At high hydration levels, the major pores are filled with liquidlike water as capillary condensation occurs. A type-H4 hysteresis loop is observed in the adsorption and desorption isotherms. The locations of the water molecules identified from simulation match fairly well with the experimentally determined crystallographic hydration sites. As observed in experiment, water exhibits anomalous subdiffusion because of the geometric restrictions and interactions of protein. With increasing hydration level, this anomaly is reduced and the diffusion of water tends to progressively approach normal Brownian diffusion. The flexibility of protein framework slightly enhances water mobility, but this enhancement decreases with increasing hydration level.

  17. Water in hydrated orthorhombic lysozyme crystal: Insight from atomistic simulations

    NASA Astrophysics Data System (ADS)

    Hu, Zhongqiao; Jiang, Jianwen; Sandler, Stanley I.

    2008-08-01

    Biologically important water in orthorhombic lysozyme crystal is investigated using atomistic simulations. A distinct hydration shell surrounding lysozyme molecules is found from the number distribution of water molecules. While the number of water molecules in the hydration shell increases, the percentage decreases as the hydration level rises. Adsorption of water in the lysozyme crystal shows type-IV behavior. At low hydration levels, water molecules primarily intercalate the minor pores and cavity in the crystal due to the strong affinity between protein and water. At high hydration levels, the major pores are filled with liquidlike water as capillary condensation occurs. A type-H4 hysteresis loop is observed in the adsorption and desorption isotherms. The locations of the water molecules identified from simulation match fairly well with the experimentally determined crystallographic hydration sites. As observed in experiment, water exhibits anomalous subdiffusion because of the geometric restrictions and interactions of protein. With increasing hydration level, this anomaly is reduced and the diffusion of water tends to progressively approach normal Brownian diffusion. The flexibility of protein framework slightly enhances water mobility, but this enhancement decreases with increasing hydration level.

  18. Thermal Decomposition Characteristics of Orthorhombic Ammonium Perchlorate (o-AP)

    SciTech Connect

    Behrens, R.; Minier, L.

    1999-03-01

    Preliminary STMBMS and SEM results of the thermal decomposition of AP in the orthorhombic phase are presented. The overall decomposition is shown to be complex and controlled by both physical and chemical processes. The data show that the physical and chemical processes can be probed and characterized utilizing SEM and STMBMS. The overall decomposition is characterized by three distinguishing features: an induction period, and accelerator period and a deceleratory period. The major decomposition event occurs in the subsurface of the AP particles and propagates towards the center of the particle with time. The amount of total decomposition is dependent upon particle size and increases from 23% for {approximately}50{micro}m-diameter AP to 33% for {approximately}200{micro}m-diameter AP. A conceptual model of the physical processes is presented. Insight into the chemical processes is provided by the gas formation rates that are measured for the gaseous products. To our knowledge, this is the first presentation of data showing that the chemical and physical decomposition processes can be identified from one another, probed and characterized at the level that is required to better understand the thermal decomposition behavior of AP. Future work is planned with the goal of obtaining data that can be used to develop a mathematical description for the thermal decomposition of o-AP.

  19. Germanium epitaxy on silicon

    PubMed Central

    Ye, Hui; Yu, Jinzhong

    2014-01-01

    With the rapid development of on-chip optical interconnects and optical computing in the past decade, silicon-based integrated devices for monolithic and hybrid optoelectronic integration have attracted wide attention. Due to its narrow pseudo-direct gap behavior and compatibility with Si technology, epitaxial Ge-on-Si has become a significant material for optoelectronic device applications. In this paper, we describe recent research progress on heteroepitaxy of Ge flat films and self-assembled Ge quantum dots on Si. For film growth, methods of strain modification and lattice mismatch relief are summarized, while for dot growth, key process parameters and their effects on the dot density, dot morphology and dot position are reviewed. The results indicate that epitaxial Ge-on-Si materials will play a bigger role in silicon photonics. PMID:27877657

  20. Vacancies in epitaxial graphene

    SciTech Connect

    Davydov, S. Yu.

    2015-08-15

    The coherent-potential method is used to consider the problem of the influence of a finite concentration of randomly arranged vacancies on the density of states of epitaxial graphene. To describe the density of states of the substrate, simple models (the Anderson model, Haldane-Anderson model, and parabolic model) are used. The electronic spectrum of free single-sheet graphene is considered in the low-energy approximation. Charge transfer in the graphene-substrate system is discussed. It is shown that, in all cases, the density of states of epitaxial graphene decreases proportionally to the vacancy concentration. At the same time, the average charge transferred from graphene to the substrate increases.

  1. Germanium epitaxy on silicon.

    PubMed

    Ye, Hui; Yu, Jinzhong

    2014-04-01

    With the rapid development of on-chip optical interconnects and optical computing in the past decade, silicon-based integrated devices for monolithic and hybrid optoelectronic integration have attracted wide attention. Due to its narrow pseudo-direct gap behavior and compatibility with Si technology, epitaxial Ge-on-Si has become a significant material for optoelectronic device applications. In this paper, we describe recent research progress on heteroepitaxy of Ge flat films and self-assembled Ge quantum dots on Si. For film growth, methods of strain modification and lattice mismatch relief are summarized, while for dot growth, key process parameters and their effects on the dot density, dot morphology and dot position are reviewed. The results indicate that epitaxial Ge-on-Si materials will play a bigger role in silicon photonics.

  2. Germanium epitaxy on silicon

    NASA Astrophysics Data System (ADS)

    Ye, Hui; Yu, Jinzhong

    2014-04-01

    With the rapid development of on-chip optical interconnects and optical computing in the past decade, silicon-based integrated devices for monolithic and hybrid optoelectronic integration have attracted wide attention. Due to its narrow pseudo-direct gap behavior and compatibility with Si technology, epitaxial Ge-on-Si has become a significant material for optoelectronic device applications. In this paper, we describe recent research progress on heteroepitaxy of Ge flat films and self-assembled Ge quantum dots on Si. For film growth, methods of strain modification and lattice mismatch relief are summarized, while for dot growth, key process parameters and their effects on the dot density, dot morphology and dot position are reviewed. The results indicate that epitaxial Ge-on-Si materials will play a bigger role in silicon photonics.

  3. Epitaxial thinning process

    NASA Technical Reports Server (NTRS)

    Siegel, C. M. (Inventor)

    1984-01-01

    A method is described for thinning an epitaxial layer of a wafer that is to be used in producing diodes having a specified breakdown voltage and which also facilitates the thinning process. Current is passed through the epitaxial layer, by connecting a current source between the substrate of the wafer and an electrolyte in which the wafer is immersed. When the wafer is initially immersed, the voltage across the wafer initially drops and then rises at a steep rate. When light is applied to the wafer the voltage drops, and when the light is interrupted the voltage rises again. These changes in voltage, each indicate the breakdown voltage of a Schottky diode that could be prepared from the wafer at that time. The epitaxial layer is thinned by continuing to apply current through the wafer while it is immersed and light is applied, to form an oxide film and when the oxide film is thick the wafer can then be cleaned of oxide and the testing and thinning continued. Uninterrupted thinning can be achieved by first forming an oxide film, and then using an electrolyte that dissolves the oxide about as fast as it is being formed, to limit the thickness of the oxide layer.

  4. Pressure-induced amorphization in orthorhombic Ta2O5: An intrinsic character of crystal

    NASA Astrophysics Data System (ADS)

    Li, Quanjun; Zhang, Huafang; Cheng, Benyuan; Liu, Ran; Liu, Bo; Liu, Jing; Chen, Zhiqiang; Zou, Bo; Cui, Tian; Liu, Bingbing

    2014-05-01

    The phase transition of orthorhombic Ta2O5 was investigated by in situ synchrotron X-ray diffraction and Raman spectroscopy. The orthorhombic phase transforms into an amorphous form completely at 24.7 GPa. A bulk modulus B0 = 139 (9) GPa for the orthorhombic Ta2O5 is derived from the P-V data. We suggest that the pressure-induced amorphization (PIA) in Ta2O5 can be attributed to the unstability of the a axis under high pressure leads to the connections of polyhedral breaking down and even triggers disorder of the whole crystal frame. These results demonstrate that the PIA is an intrinsic character of Ta2O5 which depends on its orthorhombic crystal structure rather than nanosize effects. This study provides a new kind of bulk material for investigating PIA in metal oxides.

  5. Structural and magnetic properties of epitaxially grown MnAs films on GaAs(110)

    NASA Astrophysics Data System (ADS)

    Kolovos-Vellianitis, D.; Herrmann, C.; Däweritz, L.; Ploog, K. H.

    2005-08-01

    MnAs films were grown by molecular beam epitaxy (MBE) on GaAs(110) substrates, since this orientation was recently identified as promising for the increase of spin lifetimes in semiconductor heterojunctions, which is of interest in spin injection experiments. A single epitaxial orientation was revealed for the MnAs films which consist of both the ferromagnetic, hexagonal α-MnAs and the paramagnetic, orthorhombic β-MnAs phase at room temperature. This phase coexistence could be imaged as a well ordered stripe pattern, whose periodicity depends on the film thickness. The study of the ferromagnetic properties shows a strong influence of the film thickness on the measured coercive fields and saturation magnetizations.

  6. Structural and magnetic properties of epitaxially grown MnAs films on GaAs(110)

    SciTech Connect

    Kolovos-Vellianitis, D.; Herrmann, C.; Daeweritz, L.; Ploog, K.H.

    2005-08-29

    MnAs films were grown by molecular beam epitaxy (MBE) on GaAs(110) substrates, since this orientation was recently identified as promising for the increase of spin lifetimes in semiconductor heterojunctions, which is of interest in spin injection experiments. A single epitaxial orientation was revealed for the MnAs films which consist of both the ferromagnetic, hexagonal {alpha}-MnAs and the paramagnetic, orthorhombic {beta}-MnAs phase at room temperature. This phase coexistence could be imaged as a well ordered stripe pattern, whose periodicity depends on the film thickness. The study of the ferromagnetic properties shows a strong influence of the film thickness on the measured coercive fields and saturation magnetizations.

  7. Misfit dislocations in epitaxy

    NASA Astrophysics Data System (ADS)

    van der Merwe, Jan H.

    2002-08-01

    This article on epitaxy highlights the following: the definition and some historical milestones; the introduction by Frenkel and Kontorowa (FK) of a truncated Fourier series to model the periodic interaction at crystalline interfaces; the invention by Frank and van der Merwe (FvdM)—using the FK model—of (interfacial) misfit dislocations as an important mechanism in accommodating misfit at epilayer-substrate interfaces; the generalization of the FvdM theory to multilayers; the application of the parabolic model by Jesser and van der Merwe to describe, for growing multilayers and superlattices, the impact of Fourier coefficients in the realization of epitaxial orientations and the stability of modes of misfit accommodation; the involvement of intralayer interaction in the latter—all features that impact on the attainment of perfection in crystallinity of thin films, a property that is so vital in the fabrication of useful uniformly thick epilayers (uniformity being another technological requirement), which also depends on misfit accommodation through the interfacial energy that function strongly in the criterion for growth modes, proposed by Bauer; and the ingenious application of the Volterra model by Matthews and others to describe misfit accommodation by dislocations in growing epilayers.

  8. Epitaxial Silicon Doped With Antimony

    NASA Technical Reports Server (NTRS)

    Huffman, James E.; Halleck, Bradley L.

    1996-01-01

    High-purity epitaxial silicon doped with antimony made by chemical vapor deposition, using antimony pentachloride (SbCI5) as source of dopant and SiH4, SiCI2H2, or another conventional source of silicon. High purity achieved in layers of arbitrary thickness. Epitaxial silicon doped with antimony needed to fabricate impurity-band-conduction photodetectors operating at wavelengths from 2.5 to 40 micrometers.

  9. Epitaxial Silicon Doped With Antimony

    NASA Technical Reports Server (NTRS)

    Huffman, James E.; Halleck, Bradley L.

    1996-01-01

    High-purity epitaxial silicon doped with antimony made by chemical vapor deposition, using antimony pentachloride (SbCI5) as source of dopant and SiH4, SiCI2H2, or another conventional source of silicon. High purity achieved in layers of arbitrary thickness. Epitaxial silicon doped with antimony needed to fabricate impurity-band-conduction photodetectors operating at wavelengths from 2.5 to 40 micrometers.

  10. Dipole-field sums and Lorentz factors for orthorhombic lattices, and implications for polarizable molecules

    NASA Technical Reports Server (NTRS)

    Purvis, C. K.; Taylor, P. L.

    1982-01-01

    A method for computing the Lorentz tensor components in single crystals via rapidly convergent sums of Bessels functions is developed using the relationship between dipole-field sums and the tensor components. The Lorentz factors for simple, body-centered, and base-centered orthorhombic lattices are computed using this method, and the derivative Lorentz factors for simple orthorhombic lattices are also determined. Both the Lorentz factors and their derivatives are shown to be very sensitive to a lattice structure. The equivalent of the Clausius-Mossotti relation for general orthorhombic lattices is derived using the Lorentz-factor formalism, and the permanent molecular dipole moment is related to crystal polarization for the case of a ferroelectric of polarizable point dipoles. It is concluded that the polarization enhancement due to self-polarization familiar from classical theory may actually be a reduction in consequences of negative Lorentz factors in one or two lattice directions for noncubic crystals.

  11. Theoretical research on general Hosford yield function of cubic orthorhombic sheets metals

    NASA Astrophysics Data System (ADS)

    Yang, Feng; Liu, Jun; Zhou, Hui

    2017-04-01

    Most of rolled sheet metals belong to orthorhombic aggregates of cubic crystallites. The texture coefficients, characterized by the preferred orientation of the crystallites, are important to set up the yield function. Although Hosford yield function is more suitable for describing both yield and plastic deformation of orthorhombic material than Hill, it suffers from the restriction that the three principal stresses have to be coaxial with the orthotropy of materials. Hence, this paper proposes a new Hosford yield function of cubic orthorhombic metal sheet at any stress states by introducing orientation-dependent functions. As well, the new yield function which covers 3 material parameters and 3 texture coefficients is more general than Hosford yield function. The plastic anisotropy of the q-value and yield stress under any stress states is obtained from the new yield function. This yield function lay a theoretical foundation for analyzing the mechanical properties of metal materials.

  12. Crystallization of the Focal Adhesion Kinase Targeting (FAT) Domain in a Primitive Orthorhombic Space Group

    SciTech Connect

    Magis,A.; Bailey, K.; Kurenova, E.; Hernandez Prada, J.; Cance, W.; Ostrov, D.

    2008-01-01

    X-ray diffraction data from the targeting (FAT) domain of focal adhesion kinase (FAK) were collected from a single crystal that diffracted to 1.99 Angstroms resolution and reduced to the primitive orthorhombic lattice. A single molecule was predicted to be present in the asymmetric unit based on the Matthews coefficient. The data were phased using molecular-replacement methods using an existing model of the FAK FAT domain. All structures of human focal adhesion kinase FAT domains solved to date have been solved in a C-centered orthorhombic space group.

  13. Structural and transport properties of orthorhombic GdMnO3

    NASA Astrophysics Data System (ADS)

    Modi, Anchit; Thakur, Rajesh K.; Thakur, Rasna; Gaur, N. K.; Kaurav, N.; Okram, G. S.

    2013-06-01

    We report structural and transport properties of the polycrystalline orthorhombic GdMnO3 compound synthesized by using conventional solid state reaction method. The XRD pattern reveals the single phase formation of the reported compound in orthorhombic crystal structure with space group Pbnm (JCPDS: 25-0337). The temperature dependent resistivity study indicates the highly resistive nature of the compound especially in the low temperature region. The effect of low temperature magnetic ordering can be clearly understood from the resistivity versus temperature plot. The calculated activation energy by using Arrhenius equation fitting are found slightly lesser than the reported value which indicates the lesser dense nature of the prepared compound.

  14. Submonolayer epitaxy with impurities

    NASA Astrophysics Data System (ADS)

    Kotrla, Miroslav; Krug, Joachim; Smilauer, Pavel

    2000-03-01

    The effect of impurities on epitaxial growth in the submonolayer regime is studied using kinetic Monte Carlo simulations of a two-species solid-on-solid growth model. Both species are mobile, and attractive interactions among adatoms and between adatoms and impurities are incorporated. Impurities can be codeposited with the growing material or predeposited prior to growth. The activated exchange of impurities and adatoms is identified as the key kinetic process in the formation a growth morphology in which the impurities decorate the island edges. The dependence of the island density N on flux F and coverage θ is studied in detail. The impurities strongly increase the island density without appreciably changing the exponent \\chi in the power law relation N ~ F^\\chi, apart from a saturation of the flux dependence at large F and small θ. Within the present model, even completely decorated island edges do not provide efficient barriers to the attachment of adatoms, and therefore the mechanism for the increase of \\chi proposed by D. Kandel [Phys. Rev. Lett. 78, 499 (1997)] is not operative. A simple analytic theory taking into account only the dependence of the adatom diffusion constant on impurity coverage is shown to provide semi-quantitative agreement with many features observed in the simulations.

  15. Method of epitaxially depositing cadmium sulfide

    NASA Technical Reports Server (NTRS)

    Hawrylo, Frank Z. (Inventor)

    1980-01-01

    A single crystal layer of either cadmium sulfide or an alloy of cadmium sulfide and indium phosphide is epitaxially deposited on a substrate of cadmium sulfide by liquid phase epitaxy using indium as the solvent.

  16. Is an orthorhombic lateral packing and a proper lamellar organization important for the skin barrier function?

    PubMed

    Groen, Daniël; Poole, Dana S; Gooris, Gert S; Bouwstra, Joke A

    2011-06-01

    The lipid organization in the stratum corneum (SC), plays an important role in the barrier function of the skin. SC lipids form two lamellar phases with a predominantly orthorhombic packing. In previous publications a lipid model was presented, referred to as the stratum corneum substitute (SCS), that closely mimics the SC lipid organization and barrier function. Therefore, the SCS serves as a unique tool to relate lipid organization with barrier function. In the present study we examined the effect of the orthorhombic to hexagonal phase transition on the barrier function of human SC and SCS. In addition, the SCS was modified by changing the free fatty acid composition, resulting in a hexagonal packing and perturbed lamellar organization. By measuring the permeability to benzoic acid as function of temperature, Arrhenius plots were constructed from which activation energies were calculated. The results suggest that the change from orthorhombic to hexagonal packing in human SC and SCS, does not have an effect on the permeability. However, the modified SCS revealed an increased permeability to benzoic acid, which we related to its perturbed lamellar organization. Thus, a proper lamellar organization is more crucial for a competent barrier function than the presence of an orthorhombic lateral packing. Copyright © 2010 Elsevier B.V. All rights reserved.

  17. High-efficient thermoelectric materials: The case of orthorhombic IV-VI compounds

    PubMed Central

    Ding, Guangqian; Gao, Guoying; Yao, Kailun

    2015-01-01

    Improving the thermoelectric efficiency is one of the greatest challenges in materials science. The recent discovery of excellent thermoelectric performance in simple orthorhombic SnSe crystal offers new promise in this prospect [Zhao et al. Nature 508, 373 (2014)]. By calculating the thermoelectric properties of orthorhombic IV-VI compounds GeS,GeSe,SnS, and SnSe based on the first-principles combined with the Boltzmann transport theory, we show that the Seebeck coefficient, electrical conductivity, and thermal conductivity of orthorhombic SnSe are in agreement with the recent experiment. Importantly, GeS, GeSe, and SnS exhibit comparative thermoelectric performance compared to SnSe. Especially, the Seebeck coefficients of GeS, GeSe, and SnS are even larger than that of SnSe under the studied carrier concentration and temperature region. We also use the Cahill's model to estimate the lattice thermal conductivities at the room temperature. The large Seebeck coefficients, high power factors, and low thermal conductivities make these four orthorhombic IV-VI compounds promising candidates for high-efficient thermoelectric materials. PMID:26045338

  18. Invariant elastic constants and eigentensors of orthorhombic, tetragonal, hexagonal and cubic crystalline media

    PubMed

    Theocaris; Sokolis

    2000-07-01

    The purpose of this paper is to present a simple and direct way of determining the eigenvalues and eigentensors, as well as their orientations, for all crystals of the orthorhombic, tetragonal, hexagonal and cubic symmetries, a procedure based on the spectral decomposition of the compliance and stiffness fourth-rank tensors. First, both the eigenvalues and the idempotent fourth-rank tensors are derived for the orthorhombic and tetragonal-7 symmetries. The latter decompose, respectively, the second-rank symmetric tensor spaces of orthorhombic and tetragonal-7 media into orthogonal subspaces, consisting of the stress and strain eigentensors, and split the elastic potential into distinct noninteracting strain-energy parts. Accordingly, the spectrum of the compliance tensor of the tetragonal-6 symmetry is evaluated, by reduction of the eigenvalues and eigentensors of either the orthorhombic or tetragonal-7 symmetry. These results are, then, applied in turn to each of the hexagonal and cubic crystal systems. In each case, the eigenvalues, the idempotent tensors and the stress and strain eigentensors are easily derived as particular cases of the results obtained for the tetragonal-6 symmetry. Furthermore, it is noted that the positivity of the eigenvalues for each symmetry is equivalent to the positive definiteness of the elastic potential and, thus, necessary and sufficient conditions are acquired, in terms of the compliance-tensor components, characteristic of each symmetry.

  19. Anisotropic electronic structure of orthorhombic RbC60: A high-field ESR investigation

    NASA Astrophysics Data System (ADS)

    Rahmer, J.; Grupp, A.; Mehring, M.; Hone, J.; Zettl, A.

    2001-02-01

    The full anisotropy of the electronic g tensor of a RbC60 single crystal was determined by applying high-field ESR. The principal values of the g tensor gxx=2.0014, gyy=2.0012, and gzz=2.0019 reflect the orthorhombic symmetry and 3D nature of this polymeric phase.

  20. Epitaxial technology for low cost solar cells

    NASA Technical Reports Server (NTRS)

    Kressel, H.; Raccah, P. M.

    1975-01-01

    Epitaxial solar cell structures on low cost silicon substrates are compared to direct diffusion substrates. Dislocation density in the epitaxial layers is found to be significantly lower than that of the substrate material. The saturation current density of diodes epitaxially formed on the substrate is commonly 2 to 3 orders of magnitude lower than for diodes formed by direct diffusion. Solar cells made epitaxially are substantially better than those made by direct diffusion into similar material.

  1. Polarization rotation associated critical phenomena in epitaxial PbTiO3 thin films near room temperature

    NASA Astrophysics Data System (ADS)

    Ma, Wenhui

    2016-04-01

    Strain-driven and temperature-driven monoclinic-orthorhombic phase transition in epitaxial PbTiO3 exhibit similar behavior under electric field, i.e., polarization discontinuity is reduced at the first-order ferroelectric-ferroelectric transition whose latent heat vanishes at a critical point. Due to critical phenomena the energy barrier for polarization rotation significantly diminishes, and hence thermodynamic response functions tend to diverge in the induced monoclinic states. Phenomenological calculations show that dielectric and piezoelectric properties are highly tunable by in-plane strain and electric field, and large electromechanical response may occur in epitaxial PbTiO3 thin films at room temperature. Phenomenological calculations show that large electrocaloric responsivity can also be expected at room temperature by manipulating the phase transition.

  2. Laser Induced Surface Chemical Epitaxy

    DTIC Science & Technology

    1990-03-01

    Laser-Induced Surface Chemical Epitaxy ( LSCE ). The essential features of LSCE as applied to CdTe epitaxy involve: coadsorption of DMCd and DMTe on a GaAs...DIAGRAM OF THE LSCE PROCESS UHV environment 1M substra1e 9 /X Adsorbed thin film produced CH 3 -Cd-GH 3 CH 3 -Te-CH, by molecular beam source hv ’ CH...with Anneal W/// substraIe %/"/,’ Figure 1.1. Schematic of the LSCE process. (1-2) t I 2. EXPERIMENTAL APPROACH 2.1 Experimental Apparatus The

  3. Orthorhombic faults system at the onset of the Late Mesozoic-Cenozoic Barents Sea rifting

    NASA Astrophysics Data System (ADS)

    Collanega, Luca; Breda, Anna; Massironi, Matteo

    2016-04-01

    The structures of the Late Mesozoic/Cenozoic Barents Sea rifting have been investigated with multichannel 3D seismics, covering an area of 7700 sqKm in the Hoop Fault Complex, a transitional area between the platform and the marginal basins. The main structural lineaments have been mapped in a time domain 3D surface and their activity ranges have been constrained through the sin-sedimentary thickness variations detected in time-thickness maps. Two main fault systems have been identified: an orthorhombic fault system consisting of two fault sets trending almost perpendicularly one to the other (WNW-ESE and NNE-SSW) and a graben/half-graben system, elongated approximately N-S in the central part of the study area. While the graben/half-graben system can be explained through the theory of Anderson, this landmark theory fails to explain the simultaneous activity of the two fault sets of the orthorhombic system. So far, the models that can better explain orthorhombic fault arrangements are the slip model by Reches (Reches, 1978; Reches, 1983; Reches and Dieterich, 1983) and the odd-axis model by Krantz (Krantz, 1988). However, these models are not definitive and a strong quest to better understand polymodal faulting is actual (Healy et al., 2015). In the study area, the presence of both a classical Andersonian and an orthorhombic system indicates that these models are not alternative but are both effective and necessary to explain faulting in different circumstances. Indeed, the Andersonian plain strain and the orthorhombic deformation have affected different part of the succession during different phases of the rifting. In particular, the orthorhombic system has affected only the Late Mesozoic-Cenozoic interval of the succession and it was the main active system during the initial phase of the rifting. On the other hand, the graben/half-graben system has affected the whole sedimentary succession, with an increasing activity during the development of the rifting. It has

  4. The Solubility of Orthorhombic Lysozyme Crystals Obtained at High pH

    SciTech Connect

    Aldabaibeh, Naser; Jones, Matthew J.; Myerson, Allan S.; Ulrich, Joachim

    2009-07-06

    The high pH region of the phase diagram of lysozyme with NaCl as a precipitant was determined. In this region of the phase diagram, lysozyme crystallizes in one of two different orthorhombic modifications, the low and high temperature orthorhombic modifications. The solubility of two modifications was measured at different temperatures, pH values, and NaCl concentrations. Both modifications show a similar dependence on the solution conditions where solubility increases with temperature and decreases with pH and NaCl concentration. The transition temperature between the two modifications was determined from the solubility curves and was shown to increase with pH and NaCl concentration. At pH values close to the isoelectric point (pH 11), the transition temperature becomes independent of NaCl concentration.

  5. Compressibility of orthorhombic perovskites. The effect of transition metal ions (TMI)

    NASA Astrophysics Data System (ADS)

    Ardit, Matteo

    2015-12-01

    Interest in perovskites evenly spans Materials Science and Geophysics. Due to their inimitably lattice flexibility enabling small as well as large ions to be accommodated, perovskites have become a base structure for new technological applications. Understanding the mechanisms governing their evolution at non-ambient conditions (such as high-pressure and high-temperature) is fundamentally important both for devising functional materials and in order to provide the most reliable possible deep-Earth model. With particular attention being paid to the chemical nature of the constituent ions, a suite of orthorhombic perovskites has been selected and contrasted using several parameterizations and models. A new perspective on the pressure-induced distortion of orthorhombic perovskite structures has enabled their compressional behaviour to be redefined.

  6. Ab initio structural, electronic and optical properties of orthorhombic CaGeO{sub 3}

    SciTech Connect

    Henriques, J.M.; Caetano, E.W.S. Freire, V.N.; Costa, J.A.P. da; Albuquerque, E.L.

    2007-03-15

    Orthorhombic CaGeO{sub 3} is studied using density-functional theory (DFT) considering both the local density and generalized gradient approximations, LDA and GGA, respectively. The electronic band structure, density of states, dielectric function and optical absorption are calculated. Two very close indirect (S->{gamma}) and direct ({gamma}->{gamma}) band gap energies of 1.68eV (2.31eV) and 1.75eV (2.41eV) were obtained within the GGA (LDA) approximation, as well as the effective masses for electrons and holes. Comparing with orthorhombic CaCO{sub 3} (aragonite), the substitution of carbon by germanium changes the localization of the valence band maximum of the indirect transition, and decreases by almost 2.0eV the Kohn-Sham band gap energies.

  7. Superconductivity in MgPtSi: An orthorhombic variant of MgB2

    NASA Astrophysics Data System (ADS)

    Kudo, Kazutaka; Fujimura, Kazunori; Onari, Seiichiro; Ota, Hiromi; Nohara, Minoru

    2015-05-01

    A ternary compound, MgPtSi, was synthesized by solid-state reaction. An examination of the compound by powder x-ray diffraction revealed that it crystallizes in the orthorhombic TiNiSi-type structure with the P n m a space group. The structure comprises alternately stacked layers of Mg and PtSi honeycomb network, which is reminiscent of MgB2, and the buckling of the honeycomb network causes orthorhombic distortion. Electrical and magnetic studies revealed that MgPtSi exhibited superconductivity with a transition temperature of 2.5 K. However, its isostructural compounds, namely, MgRhSi and MgIrSi, were not found to exhibit superconductivity.

  8. Liquid phase epitaxial growth of bismuth based superconductors

    NASA Astrophysics Data System (ADS)

    Takemoto, J.; Miyashita, S.; Inoue, T.; Komatsu, H.

    1996-05-01

    The liquid phase epitaxial growth of superconducting films of Bi 2Sr 2CaCu 2O y (2212 phase) and Bi 2Sr 2CuO z (2201 phase) were carried out on three types of substrates; SrTiO 3, LaAlO 3 and NdGaO 3. Twinning structures of the 2212 phase were observed in the films grown on the SrTiO 3 (100) and LaAlO 3 (100) substrates which belong to the cubic crystal system, while nearly twin-free structures were obtained when the film was grown on the NdGaO 3 (001) substrate (orthorhombic system). Atomic force microscopy revealed a 2201 phase film with a reasonably flat area (several μm 2) grown on the LaAlO 3 (100) substrate. It was observed that the 2212 phase nucleated on the substrate following the Volmer-Weber type mechanism (three-dimensional island growth mode). The enlarging processes of the island layers were discussed.

  9. Lattice dynamics of proton conductor SrZrO{sub 3} in orthorhombic phase

    SciTech Connect

    Sharma, Anupam Deep; Sinha, M. M.

    2014-04-24

    In the this paper, we are presenting the results of our theoretical investigation on the zone centre phonon frequencies and phonon dispersion relation of SrZrO{sub 3} in its orthorhombic phase by using lattice dynamical simulation method based on short range force constant model to understand the role of phonon in this system. The calculations involves interatomic force constants upto third neighbour. The calculated zone centre phonon frequencies in Raman mode, agrees well with available existing results.

  10. Angular dependences of spin-wave resonance spectra of inhomogeneous films with orthorhombic anisotropy

    NASA Astrophysics Data System (ADS)

    Zyuzin, A. M.; Bakulin, M. A.; Radaikin, V. V.; Yantsen, N. V.

    2017-02-01

    Zero spin-wave mode in inhomogeneous magnetic films with orthorhombic anisotropy has been found to exhibit a change of its localization region in two of three typical angular dependences of resonance fields of high-intensity modes. It has been shown that the anisotropy fields on both sides of the film can be determined from the resonance fields of the zero and uppermost high-intensity spin-wave modes of spin-wave resonance spectra.

  11. Finite-Difference Algorithm for 3D Orthorhombic Elastic Wave Propagation

    NASA Astrophysics Data System (ADS)

    Jensen, R.; Preston, L. A.; Aldridge, D. F.

    2016-12-01

    Many geophysicists concur that an orthorhombic elastic medium, characterized by three mutually orthogonal symmetry planes, constitutes a realistic representation of seismic anisotropy in shallow crustal rocks. This symmetry condition typically arises via a dense system of vertically-aligned microfractures superimposed on a finely-layered horizontal geology. Mathematically, the elastic stress-strain constitutive relations for an orthorhombic body contain nine independent moduli. In turn, these moduli can be determined by observing (or prescribing) nine independent P-wave and S-wave phase speeds along different propagation directions. We are developing an explicit time-domain finite-difference (FD) algorithm for simulating 3D elastic wave propagation in a heterogeneous orthorhombic medium. The components of the particle velocity vector and the stress tensor are governed by a set of nine, coupled, first-order, linear, partial differential equations (PDEs) called the velocity-stress system. All time and space derivatives are discretized with centered and staggered FD operators possessing second- and fourth-order numerical accuracy, respectively. Simplified FD updating formulae (with significantly reduced operation counts) for stress components are obtained by restricting the principle axes of the modulus tensor to be parallel to the global rectangular coordinate axes. Moreover, restriction to a piecewise homogeneous earth model reduces computational memory demand for storing the ten (including mass density) model parameters. These restrictions will be relaxed in the future. Novel perfectly matched layer (PML) absorbing boundary conditions, specifically designed for orthorhombic media, effectively suppress grid boundary reflections. Initial modeling results reveal the well-established anisotropic seismic phenomena of complex wavefront shapes, split (fast and slow) S-waves, and shear waves generated by a spherically-symmetric explosion in a homogeneous body.

  12. Molecular Beam Epitaxy of

    NASA Astrophysics Data System (ADS)

    Hsieh, Kuan Hsiung

    Ga(,0.48)In(,0.52)As recently emerges as a promising material for high speed applications. It also has a direct bandgap with gap energy suitable for optical applications. It is the purpose of this thesis to grow high quality Ga(,0.47)In(,0.53)As, lattice-matched Al(,0.48)In(,0.52)As and heterojunction structures by molecular beam epitaxy technique for applications in the areas of modulation-doped high mobility devices and internal photoemission Schottky diodes for infrared detection. Single crystal Al metal deposition on GaInAs by MBE is also studied for its electrical properties. Mobility enhancement has been demonstrated in modulation-doped structures at low temperatures. Very high mobilities were obtained: 10,900 cm('2)/Vs at room temperature, 55,500 cm('2)/Vs at 77K and 70,200 cm('2)/Vs at 10K with corresponding two-dimensional electron gas densities greater than 1 x 10('12) l/cm('2). The quality of Ga(,0.47)In(,0.53)As and the parallel conduction in this material are the limiting factors in its mobility. A new ohmic contact phenomenon has been observed in the MBE single crystal Al metal on Ga(,0.47)In(,0.53)AS samples. Its contact resistivity is measured to be as small as 1 x 10('-6) (OMEGA)-cm('2). The Fermi-level pinning near the conduction band edge might be caused by the interface defects. A planar doping technique has been employed to enhance the built-in barrier height to a value of about 0.5 eV in the single crystal Al on n-p('+)-n-Ga(,0.47)In(,0.52)As structures. This novel quasi-Schottky diode also shows a forward ideal factor of 1.03. As for optical detectors, four kinds of diodes were made for internal photoemission studies: Au Schottky on Ga(,0.47)In(,0.53)As in the wavelength range of 1.9 (mu)m to 2.5 (mu)m, Au Schottky on Al(,0.48)In(,0.52)As in 1.1 (mu)m to 2.0 (mu)m range, single crystal Al on (Al(,0.8)Ga(,0.2))(,0.48)In(,0.52)As with improved quantum yields and lastly a Ga(,0.47)In(,0.53)As/Al(,0.48)In(,0.52)As heterojunction with a measured

  13. Secondary cell with orthorhombic alkali metal/manganese oxide phase active cathode material

    DOEpatents

    Doeff, Marca M.; Peng, Marcus Y.; Ma, Yanping; Visco, Steven J.; DeJonghe, Lutgard C.

    1996-01-01

    An alkali metal manganese oxide secondary cell is disclosed which can provide a high rate of discharge, good cycling capabilities, good stability of the cathode material, high specific energy (energy per unit of weight) and high energy density (energy per unit volume). The active material in the anode is an alkali metal and the active material in the cathode comprises an orthorhombic alkali metal manganese oxide which undergoes intercalation and deintercalation without a change in phase, resulting in a substantially linear change in voltage with change in the state of charge of the cell. The active material in the cathode is an orthorhombic structure having the formula M.sub.x Z.sub.y Mn.sub.(1-y) O.sub.2, where M is an alkali metal; Z is a metal capable of substituting for manganese in the orthorhombic structure such as iron, cobalt or titanium; x ranges from about 0.2 in the fully charged state to about 0.75 in the fully discharged state, and y ranges from 0 to 60 atomic %. Preferably, the cell is constructed with a solid electrolyte, but a liquid or gelatinous electrolyte may also be used in the cell.

  14. Secondary cell with orthorhombic alkali metal/manganese oxide phase active cathode material

    DOEpatents

    Doeff, M.M.; Peng, M.Y.; Ma, Y.; Visco, S.J.; DeJonghe, L.C.

    1996-09-24

    An alkali metal manganese oxide secondary cell is disclosed which can provide a high rate of discharge, good cycling capabilities, good stability of the cathode material, high specific energy (energy per unit of weight) and high energy density (energy per unit volume). The active material in the anode is an alkali metal and the active material in the cathode comprises an orthorhombic alkali metal manganese oxide which undergoes intercalation and deintercalation without a change in phase, resulting in a substantially linear change in voltage with change in the state of charge of the cell. The active material in the cathode is an orthorhombic structure having the formula M{sub x}Z{sub y}Mn{sub (1{minus}y)}O{sub 2}, where M is an alkali metal; Z is a metal capable of substituting for manganese in the orthorhombic structure such as iron, cobalt or titanium; x ranges from about 0.2 in the fully charged state to about 0.75 in the fully discharged state, and y ranges from 0 to 60 atomic %. Preferably, the cell is constructed with a solid electrolyte, but a liquid or gelatinous electrolyte may also be used in the cell. 11 figs.

  15. High temperature far-infrared dynamics of orthorhombic NdMnO3: emissivity and reflectivity.

    PubMed

    Massa, Néstor E; del Campo, Leire; Meneses, Domingos De Sousa; Echegut, Patrick; Martínez-Lope, María Jesús; Alonso, José Antonio

    2013-06-12

    We report on near normal far- and mid-infrared emission and reflectivity of NdMnO3 perovskite from room temperature to sample decomposition above 1800 K. At 300 K the number of infrared active phonons is in close agreement with the 25 calculated for the orthorhombic D(2h)(16)-Pbnm (Z = 4) space group. Their number gradually decreases as we approach the temperature of orbital disorder at ~1023 K where the orthorhombic O' lower temperature cooperative phase coexists with the cubic orthorhombic O. At above ~1200 K, the three infrared active phonons coincide with that expected for cubic Pm-3m (Z = 1) in the high temperature insulating regime. Heating samples in dry air triggers double exchange conductivity by Mn(3+) and Mn(4+) ions and a small polaron mid-infrared band. Fits to the optical conductivity single out the octahedral antisymmetric and symmetric vibrational modes as the main phonons in the electron-phonon interactions at 875 K. For 1745 K, it is enough to consider the symmetric stretching internal mode. An overdamped defect induced Drude component is clearly outlined at the highest temperatures. We conclude that rare earth manganite eg electrons are prone to spin, charge, orbital, and lattice couplings in an intrinsic orbital distorted perovskite lattice, favoring embryonic low energy collective excitations.

  16. Comparative compressibility and equation of state of orthorhombic and tetragonal edingtonite

    NASA Astrophysics Data System (ADS)

    Gatta, G. D.; Ballaran, T. Boffa; Comodi, P.; Zanazzi, P. F.

    The high-pressure (HP) behaviour of a natural orthorhombic and tetragonal edingtonite from Ice River, Canada, has been investigated using in situ single-crystal X-ray diffraction. The two isothermal equations of state up to 6.74(5) GPa were determined. V0, KT0 and K' refined with a third-order Birch-Murnaghan equation of state (BM-EoS) are: V0 = 598.70(7) Å3, KT0 = 59(1) GPa and K'=3.9(4) for orthorhombic edingtonite and V0 = 600.9(2) Å3, KT0 = 59(1) GPa and K'=4.2(5) for tetragonal edingtonite. The experiments were conducted with nominally hydrous pressure penetrating transmitting medium. No overhydration effect was observed within the pressure range investigated. At high-pressures the main deformation mechanism is represented by cooperative rotation of the secondary building unit (SBU).Si/Al distribution slightly influences the elastic behaviour of the tetrahedral framework: the SBU bulk moduli are 125(8) GPa and 111(4) GPa for orthorhombic and tetragonal edingtonite, respectively. Extra-framework contents of both zeolites show an interesting behaviour under HP conditions: the split Ba2 site at P >2.85 GPa is completely empty; only the position Ba1 is occupied. Electronic Supplementary Material. Supplementary material to this paper (Observed and calculated structure factors) is available in electronic form at http://dx.doi.org/10.1007/s00269-004-0394-y.

  17. Oxidation protection of Ti-aluminide orthorhombic alloys: An engineered multilayer approach

    SciTech Connect

    Warrier, S.G.; Krishnamurthy, S.; Smith, P.R.

    1998-04-01

    The lack of high-temperature environmental resistance is a major issue in the application of orthorhombic-based titanium aluminide alloys (O alloys) and their composites. Improvement in environmental capability can be achieved by applying diffusion barrier coatings to the surface of the orthorhombic matrix alloy. However, since thin coatings are prone to foreign-object damage, an approach based on thicker multilayer materials may be more prudent for fracture-critical applications. In the present study, foils of the orthorhombic alloy were diffusion bonded on either side with a {gamma} alloy, the latter used in an attempt to provide environmental protection. Mechanical tests suggested that the {gamma} alloy was successful in preventing degradation of the O alloy due to oxidation and interstitial embrittlement under thermal cycling conditions. Processing below the {beta} transus of the O alloy provided an improvement in the stress and strain to failure of the joined material compared to materials processed above the transus. However, in either case, the strengths of the joined materials were significantly lower than that of the uncoated O alloy with similar microstructures. Results suggest that the low strength of the joined materials may be due to cracking of the {gamma} alloy, resulting in premature failure of the O alloy. Finite element analysis (FEA) was performed to understand the stress distribution in the joined material and to investigate approaches for reducing the residual stress. Several approaches for improving the stress and strain to failure of the joined material are presented.

  18. Tape cast second generation orthorhombic-based titanium aluminide alloys for MMC applications. [Metal Matrix Composites

    SciTech Connect

    Smith, P.R.; Rosenberger, A.H. . Materials and Mfg. Directorate); Shepard, M.J. )

    1999-06-18

    Titanium metal matrix composites (TMCs) utilizing continuous SiC fiber reinforcement are considered important, if not, enabling materials for advanced Air Force propulsion systems, wherein combinations of high specific strength and elevated temperature capability are prerequisites to obtain desired increases in thrust-to-weight ratios and decreased specific fuel consumption. One such class of TMCs being assessed for use in rotating engine components are those based upon the orthorhombic titanium aluminide phase, Ti[sub 2]AlNb. These orthorhombic titanium matrix composites (O TMCs) are being examined for sustained use at temperatures up to 700 C. Previous studies have primarily focused on O TMCs made using the foil-fiber-foil fabrication process. More recently the Materials and Manufacturing Directorate of the Air Force Research Laboratory has been focusing attention on an alternative powder metallurgy approach for fabrication of O TMCs via tape casting. This latter approach has the potential to produce significant cost reduction (<$70/lb) for the matrix input material (powder). Unfortunately, little work has been done to understand the effects of powder microstructures and the tape casting process itself on the mechanical performance of O TMCs. Therefore, the first objective of this study is to examine the microstructural evolution and mechanical performance (with and without heat treatment) of three unreinforced heat orthorhombic-based titanium aluminide matrices made via tape casting. A second objective is to assess the viability of powder metallurgy processing for the fabrication of O TMCs.

  19. Comparing hydrostatic-pressure- and epitaxial-strain-induced phase transitions in multiferroic PbNiO3 from first principles

    NASA Astrophysics Data System (ADS)

    Tian, Hao; Kuang, Xiao-Yu; Mao, Ai-Jie; Zhao, Hong-Jian; Li, Hui; Kuang, Fang-Guang

    2015-02-01

    First-principles calculations are performed to simulate hydrostatic pressure and misfit strain effect on PbNiO3 (PNO) material. Significant difference between hydrostatic pressure and misfit strain effect is discovered. That is (1) a hydrostatic-pressure-induced phase transition from a rhombohedral R3c phase to an orthorhombic Pnma phase emerges around 6 GPa; and (2) an epitaxial-strain-induced phase transition from a monoclinic Cc phase (the sequel to a monoclinic distortion from R3c) to an orthorhombic Pbnm phase occurs about -3.3% misfit strain. Besides, the behaviors of oxygen octahedra tilting, polarization and the magnetic ordering temperature TN have been found to be strikingly affected by the variation of hydrostatic pressure and misfit strain, respectively. Finally, origins of the induced phase transitions are revealed.

  20. Epitaxial silicon growth for solar cells

    NASA Technical Reports Server (NTRS)

    Daiello, R. V.; Robinson, P. H.; Richman, D.

    1979-01-01

    The epitaxial procedures, solar cell fabrication, and evaluation techniques are described. The development of baseline epitaxial solar cell structures grown on high quality conventional silicon substrates is discussed. Diagnostic layers and solar cells grown on four potentially low cost silicon substrates are considered. The crystallographic properties of such layers and the performance of epitaxially grown solar cells fabricated on these materials are described. An advanced epitaxial reactor, the rotary disc, is described along with the results of growing solar cell structures of the baseline type on low cost substrates. The add on cost for the epitaxial process is assessed and the economic advantages of the epitaxial process as they relate to silicon substrate selection are examined.

  1. Structural, electronic and optical properties of orthorhombic CdGeO{sub 3} from first principles calculations

    SciTech Connect

    Barboza, C.A.; Henriques, J.M.; Albuquerque, E.L.; Caetano, E.W.S.; Freire, V.N.; Costa, J.A.P. da

    2010-02-15

    Orthorhombic perovskite CdGeO{sub 3} was studied using the density-functional theory (DFT) formalism. The electronic band structure, density of states, effective masses, dielectric function and optical absorption were obtained. Comparing with orthorhombic CaGeO{sub 3}, which is an indirect S->GAMMA gap material, the substitution of calcium by cadmium changes the valence band maximum from the S point to the GAMMA point in reciprocal space, and decreases the Kohn-Sham band gap energy. Our results suggest that orthorhombic CdGeO{sub 3} has features of a semiconductor and is potentially useful for optoelectronic applications. - Abstract: Graphical Abstract Legend (TOC Figure): Different views of the unit cell of orthorhombic CdGeO{sub 3} (left, top). The electronic band structure near the main gap and the partial density of states (PDOS) are shown also (right), as well as the optical absorption for different polarizations of incident light (left, bottom).

  2. Chemical Vapor Deposition Epitaxy an Patternless and Patterned Substrates.

    ERIC Educational Resources Information Center

    Takoudis, Christos G.

    1990-01-01

    Discusses chemical vapor deposition epitaxy on patternless and patterned substrates for an electronic materials processing course. Describes the processs types and features of epitaxy. Presents some potential problems of epitaxy. Lists 38 references. (YP)

  3. Epitaxial Garnets and Hexagonal Ferrites.

    DTIC Science & Technology

    1982-04-20

    Iron Garnet Liquid Phase Epitaxy Hexagonal Ferrite microwave Signal Processing Millimeter-Wave 20. ABSTRACT (Continue ani revee arde if necoeermy and...le.’uIfy by block rns.) e objective of this research is to develop new and improved epitauial ferrite materials for use in microwave and millimeter... ferrite films suitable for microwave and millimeter-wave signal processing at frequencies above 1 GHz. The specific tasks are: a. Analyze and develop

  4. Recent developments in droplet epitaxy

    SciTech Connect

    Mano, Takaaki; Jo, Masafumi; Kuroda, Takashi; Abbarchi, Marco; Noda, Takeshi; Sakoda, Kazuaki

    2014-05-15

    The droplet epitaxy allows for self-assembly of lattice-matched GaAs quantum dots (QDs) with high quality and high uniformity. In this article, we show our efforts to realize the GaAs QDs with excellent optical properties. After the optimization of the several growth processes, we achieved current-injection lasing in the GaAs QDs. In addition, formation of further advanced nanostructure is presented.

  5. Epitaxial complex oxide tunnel barriers

    NASA Astrophysics Data System (ADS)

    Son, Junwoo; Moetakef, Pouya; Cagnon, Joël; Stemmer, Susanne

    2009-03-01

    Tunnel junctions with complex oxide thin film barriers are of interest for studies of the critical thickness of ferroelectricity, of phonon modes in ultrathin films and of traps by inelastic tunneling spectroscopy. We show that high-quality epitaxial SrTiO3 and BaTiO3 tunnel barriers can be grown on Pt bottom electrodes. Coherent, epitaxial Pt films with roughness of less than a unit cell were grown on (001) SrTiO3 to serve as bottom electrodes for epitaxial SrTiO3 and BaTiO3 tunnel barriers. All interfaces were atomically abrupt as confirmed by atomic resolution Z-contrast imaging. The IV characteristics were non-linear, demonstrating good insulating properties. For the SrTiO3 barriers and voltage sweeps up to ± 0.5 V, the measured tunnel current was independent of the sweep direction. At low biases, dynamic conductance curves showed a symmetrical parabolic shape around the origin in both resistance states. At high bias, deviation from the ideal tunnel behavior was observed. A large increase of the tunnel conductance occurred above a minimum positive bias. A dramatic decrease of tunnel conductance occurred for a large negative bias, indicating bipolar switching. We show the contributions to the resistive switching. Phonon modes and traps are determined using inelastic tunneling spectroscopy with both paraelectric and ferroelectric tunnel barriers.

  6. Surface relaxation and tilting in SrHfO 3 orthorhombic perovskite: Hybrid HF-DFT LCAO calculations

    NASA Astrophysics Data System (ADS)

    Evarestov, R. A.; Bandura, A. V.; Blokhin, E. N.

    2008-12-01

    HF-DFT LCAO hybrid simulations on (0 0 1) and (1 1 0) surfaces of orthorhombic and (0 0 1) surface of cubic SrHfO 3 perovskite are performed using a single slab model framework. PBE0 exchange-correlation functional is used for this study. The energy and crystal structure of bulk cubic and orthorhombic phases are calculated and compared. It is found that orthorhombic modification is more stable than cubic one by 24 kJ mol -1 per formula unit. Calculated average surface energies and relaxation energies proved to be similar for all orthorhombic surfaces. Atomic displacements along the direction normal to the surface are primarily determined by the type of termination and weakly depend on the surface indices. Without symmetry constraining, cubic surfaces are unstable with respect to reconstruction to corresponding orthorhombic surfaces at T = 0 K. While the upright displacements of the topmost atoms are mainly due to additional distortions of the surface octahedra, the lateral atomic displacements are closely related to changing in surface group tilting. The approach for the analysis of surface octahedron tilting is proposed and applied to the relaxed orthorhombic surfaces of SrHfO 3 perovskites. It is shown that the HfO 5 group on the HfO 2-termianted surfaces undergoes a considerable turn upon relaxation, resulting in alignment of Hf-O-Hf bonds to corresponding pseudo-cubic directions.

  7. Orthorhombic MoO3 nanobelts based NO2 gas sensor

    NASA Astrophysics Data System (ADS)

    Mane, A. A.; Moholkar, A. V.

    2017-05-01

    Molybdenum trioxide (MoO3) nanobelts have been deposited onto the glass substrates using chemical spray pyrolysis (CSP) deposition method. The XRD patterns reveal that films are polycrystalline having an orthorhombic crystal structure. Raman spectra confirm that the films are orthorhombic in phase. The XPS study shows the presence of two well resolved spectral lines of Mo-3d core levels appearing at the binding energy values of 232.82 eV and 235.95 eV corresponding to Mo-3d5/2 and Mo-3d3/2, respectively. These binding energy values are assigned to Mo6+ oxidation state of fully oxidized MoO3. The FE-SEM micrographs show the formation of nanobelts-like morphology. The AFM micrographs reveal that the RMS surface roughness increases from 16.5 nm to 17.5 nm with increase in film thickness from 470 nm to 612 nm and then decreases to 16 nm for 633 nm film thickness. The band gap energy is found to be decreased from 3.40 eV to 3.38 eV. To understand the electronic transport phenomenon in MoO3 thin films, dielectric properties are studied. For 612 nm film thickness, the highest NO2 gas response of 68% is obtained at an operating temperature of 200 °C for 100 ppm concentration with response and recovery times of 15 s and 150 s, respectively. The lower detection limit is found to be 10 ppm which is half of the immediately dangerous to life or health (IDLH) value of 20 ppm. Finally, NO2 gas sensing mechanism in an orthorhombic MoO3 crystal structure is discussed in detail.

  8. Stability of the ordered orthorhombic phase in Ti-24Al-11Nb

    NASA Technical Reports Server (NTRS)

    Hsiung, L. M.; Wadley, H. N. G.

    1992-01-01

    The ordered orthorhombic 'O' phase in the Ti-Al-Nb ordered alloy system emerges either through slow cooling from above 1200 C or through isothermal aging after quenching from that temperature regime. An experimental investigation is presently conducted of the structural relationship between the O and alpha(2) phases, in order to clarify the mechanism of transition between the two. The transition occurs with the formation of a platelike alpha(2) phase within the O matrix, and may be characterized as due to a shape-deformation mechanism associated with diffusion of excess Nb away from the O/alpha(2) interface.

  9. Temperature and Pressure Sensors Based on Spin-Allowed Broadband Luminescence of Doped Orthorhombic Perovskite Structures

    NASA Technical Reports Server (NTRS)

    Eldridge, Jeffrey I. (Inventor); Chambers, Matthew D. (Inventor)

    2014-01-01

    Systems and methods that are capable of measuring pressure or temperature based on luminescence are discussed herein. These systems and methods are based on spin-allowed broadband luminescence of sensors with orthorhombic perovskite structures of rare earth aluminates doped with chromium or similar transition metals, such as chromium-doped gadolinium aluminate. Luminescence from these sensors can be measured to determine at least one of temperature or pressure, based on either the intense luminescence of these sensors, even at high temperatures, or low temperature techniques discussed herein.

  10. Incommensurate magnetic structure in the orthorhombic perovskite ErMnO3

    NASA Astrophysics Data System (ADS)

    Ye, F.; Lorenz, B.; Huang, Q.; Wang, Y. Q.; Sun, Y. Y.; Chu, C. W.; Fernandez-Baca, J. A.; Dai, Pengcheng; Mook, H. A.

    2007-08-01

    By combining dielectric, specific heat, and magnetization measurements and high-resolution neutron powder diffraction, we have investigated the thermodynamic and magnetic and structural properties of the metastable orthorhombic perovskite ErMnO3 prepared by high-pressure synthesis. The system becomes antiferromagnetically correlated below 42K and undergoes a lock-in transition at 28K with propagation wave vector (0,kb,0) , which remains incommensurate at low temperature. The intercorrelation between the magnetic structure and electric properties and the role of the rare earth moment are discussed.

  11. On the orthorhombic phase in ZrO2-based alloys

    NASA Technical Reports Server (NTRS)

    Heuer, A. H.; Lanteri, V.; Chaim, R.; Lee, R.-R.; Farmer, S. C.

    1989-01-01

    During TEM observation, a tetragonal (t) to orthorhombic (o) phase transformation often occurs in thin portions of ZrO2-containing foils. This transformation is stress-induced and in some senses artifactual, in that the reaction product is actually a high-pressure phase, relative to monoclinic (m) ZrO2, that can form from metastable t-ZrO2 in the TEM because its density is intermediate between t- and m-ZrO2. Examples of the formation of o-ZrO2 in a number of different systems are given.

  12. [Effect of crystallization and branch on fine structure of orthorhombic in polyethylene].

    PubMed

    Kang, N; Xu, Y; Weng, S; Wu, J; Xu, D

    2001-02-01

    The CH2 rocking bands are used as a probe to monitor the crystalline behavior of polyethylene segments in a series of poly (ethylene-octene) copolymers. High resolution and cryogenic FTIR spectra reveal that different composition and/or crystalline condition of the copolymers result in significant variation on the CH2 rocking bands including the change in peak position, band width and A730/A720. We conclude that side chain in the copolymer can influence the structure of the orthorhombic polyethylene crystallite although they can not enter the crystal lattice.

  13. Structure of the welding zone between titanium and orthorhombic titanium aluminide for explosion welding: I. Interface

    NASA Astrophysics Data System (ADS)

    Rybin, V. V.; Grinberg, B. A.; Ivanov, M. A.; Kuz'min, S. V.; Lysak, V. I.; Elkina, O. A.; Patselov, A. M.; Inozemtsev, A. V.; Antonova, O. V.; Kozhevnikov, V. E.

    2011-10-01

    The structures of the interfaces and transition zones of bimetallic metal-intermetallide joints produced by explosion welding under various conditions have been studied. The welded materials were commercial-purity titanium and orthorhombic titanium aluminide of two alloying schemes. The specific features of the structure and substructure of the zones under study are discussed. Wave formation and formation of isolated vortex zones, as well as tracks of particles related to the transfer of particles of one metal into the other one, were observed. A possible scenario of formation of interfaces, depending on the composition of titanium aluminide and welding conditions, is proposed.

  14. Minimum strain rate and primary transient creep analysis of a fine structure orthorhombic titanium aluminide

    SciTech Connect

    Hayes, R.W.

    1996-03-15

    The purpose of the present paper is to present a preliminary analysis of the primary transient creep behavior of an orthorhombic titanium aluminide having a very fine microstructure. In order to analyze and understand the creep behavior within the primary transient regime it is necessary to understand the mechanisms controlling deformation within the minimum strain rate region. Therefore an analysis of the minimum strain rate behavior is also presented. It will be shown that the primary transient creep behavior is dependent upon whether creep in the minimum strain rate region is controlled by a viscous flow mechanism or a dislocation mechanism.

  15. Influence of a 60° domain structure on the orthorhombic niobate-based piezoelectric property

    NASA Astrophysics Data System (ADS)

    Tsuchida, Kohei; Kakimoto, Ken-ichi; Kagomiya, Isao

    2013-04-01

    The present work investigated the dependence of domain switching (90° and 60° domains) on the piezoelectric property due to an applied electric field in Mn-doped Na0.55K0.45NbO3 (Mn-NKN) ceramic samples. In addition, the electric-field-induced strain and temperature-dependent planar extensional electromechanical coupling factor k p were studied. The results indicate that the piezoelectric properties for the orthorhombic phase due to 60° domain switching are stable over a wide range of temperatures.

  16. 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.

  17. Epitaxial growth of CZT(S,Se) on silicon

    DOEpatents

    Bojarczuk, Nestor A.; Gershon, Talia S.; Guha, Supratik; Shin, Byungha; Zhu, Yu

    2016-03-15

    Techniques for epitaxial growth of CZT(S,Se) materials on Si are provided. In one aspect, a method of forming an epitaxial kesterite material is provided which includes the steps of: selecting a Si substrate based on a crystallographic orientation of the Si substrate; forming an epitaxial oxide interlayer on the Si substrate to enhance wettability of the epitaxial kesterite material on the Si substrate, wherein the epitaxial oxide interlayer is formed from a material that is lattice-matched to Si; and forming the epitaxial kesterite material on a side of the epitaxial oxide interlayer opposite the Si substrate, wherein the epitaxial kesterite material includes Cu, Zn, Sn, and at least one of S and Se, and wherein a crystallographic orientation of the epitaxial kesterite material is based on the crystallographic orientation of the Si substrate. A method of forming an epitaxial kesterite-based photovoltaic device and an epitaxial kesterite-based device are also provided.

  18. Epitaxial growth of europium monoxide on diamond

    SciTech Connect

    Melville, A.; Heeg, T.; Mairoser, T.; Schmehl, A.; Fischer, M.; Gsell, S.; Schreck, M.; Awschalom, D. D.; Holländer, B.; Schubert, J.; Schlom, D. G.

    2013-11-25

    We report the epitaxial integration of phase-pure EuO on both single-crystal diamond and on epitaxial diamond films grown on silicon utilizing reactive molecular-beam epitaxy. The epitaxial orientation relationship is (001) EuO ‖ (001) diamond and [110] EuO ‖[100] diamond. The EuO layer is nominally unstrained and ferromagnetic with a transition temperature of 68 ± 2 K and a saturation magnetization of 5.5 ± 0.1 Bohr magnetons per europium ion on the single-crystal diamond, and a transition temperature of 67 ± 2 K and a saturation magnetization of 2.1 ± 0.1 Bohr magnetons per europium ion on the epitaxial diamond film.

  19. The Facile Hydrothermal Preparation of Orthorhombic WO3 With (001) Facet and Its Photocatalytic Performance.

    PubMed

    Deng, Xiaoyan; Dou, Jinbiao; Li, Fenfen; Gao, Hongtao; Liu, Guangjun

    2015-12-01

    The orthorhombic WO3 nanoplates with (001) facet were fabricated via a facile hydrothermal process, using HBF4 as the acid source. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and UV-vis diffused reflectance spectroscopy (DRS), respectively. It indicated that the obtained product was orthorhombic WO3 (JCPDS No. 20-1324). And the energy gap was estimated to be 2.52 eV by the intersection point of the tangent of the absorption edge and the baseline. It was affirmed that WO3 crystalline grew along the (001) direction, indicating the product was exposed with (001) facet. The photocatalytic activity of (001) WO3 nanoplates was investigated on the degradation of Rhodamine B (RhB). It demonstrated that photocatalysts exhibited obvious photocatalytic performance under visible light irradiation. The degradation rate of RhB with the typical product reached 95% after being irradiated for 5 h. It indicated that the photocatalytic efficiency of WO3 could be improved by controlling the crystal growth and its morphology.

  20. Surface morphology of orthorhombic Mo2C catalyst and high coverage hydrogen adsorption

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Tian, Xinxin; Yang, Yong; Li, Yong-Wang; Wang, Jianguo; Beller, Matthias; Jiao, Haijun

    2016-09-01

    High coverage hydrogen adsorption on twenty two terminations of orthorhombic Mo2C has been systematically studied by using density functional theory and ab initio thermodynamics. Hydrogen stable coverage on the surfaces highly depends on temperatures and H2 partial pressure. The estimated hydrogen desorption temperatures under ultra-high vacuum condition on Mo2C are in reasonable agreement with the available temperature-programmed desorption data. Obviously, hydrogen adsorption can affect the surface stability and therefore modify the surface morphology of Mo2C. Upon increasing the chemical potential of hydrogen which can be achieved by increasing the H2 partial pressure and/or decreasing the temperature, the proportions of the (001), (010), (011) and (100) surfaces increase, while those of the (101), (110) and (111) surfaces decrease. Among these surfaces, the (100) surface is most sensitive upon hydrogen adsorption and the (111) surface is most exposed under a wide range of conditions. Our study clearly reveals the role of hydrogen on the morphology of orthorhombic Mo2C catalyst in conjugation with hydro-treating activity.

  1. Formation of vortices during explosion welding (titanium-orthorhombic titanium aluminide)

    NASA Astrophysics Data System (ADS)

    Rybin, V. V.; Greenberg, B. A.; Antonova, O. V.; Elkina, O. A.; Ivanov, M. A.; Inozemtsev, A. V.; Patselov, A. M.; Sidorov, I. I.

    2009-10-01

    The possibility of cladding commercially pure titanium by a plate of orthorhombic titanium aluminide has been investigated. The bimetallic joints of orthorhombic titanium aluminide (Ti-30Al-16Nb-1Zr-1Mo) with commercially pure titanium have been obtained by explosion welding. It has been found that the weld joint investigated had a multilayer structure consisting of a zone of continuous deformation observed in both materials, a zone of titanium recrystallization, and a transition zone near the interface. Wave formation and formation of isolated vortex zones have been observed. It has been found that upon explosion welding the bonding of the surfaces is effected via melting and subsequent mixing (in the zone of vortices) and the transfer of particles of one metal into another with the formation of particle tracks (outside the zone of vortices). A possible scenario of the formation of the vortex zone in the melt with a subsequent eutectic decomposition is proposed. The structure of the vortex zones was found to consist of an ultrafine mixture of α and β grains (both phases are disordered) with the grain size changing in the limits of 50-300 nm. The regions of transition from the vortex zone to the region of continuous deformation of the aluminide and to the recrystallized zone of titanium have been investigated.

  2. Molecular-Beam-Epitaxy Program

    NASA Technical Reports Server (NTRS)

    Sparks, Patricia D.

    1988-01-01

    Molecular Beam Epitaxy (MBE) computer program developed to aid in design of single- and double-junction cascade cells made of silicon. Cascade cell has efficiency 1 or 2 percent higher than single cell, with twice the open-circuit voltage. Input parameters include doping density, diffusion lengths, thicknesses of regions, solar spectrum, absorption coefficients of silicon (data included for 101 wavelengths), and surface recombination velocities. Results include maximum power, short-circuit current, and open-circuit voltage. Program written in FORTRAN IV.

  3. Growth of (111)-oriented epitaxial and textured ferroelectric Y-doped HfO2 films for downscaled devices

    NASA Astrophysics Data System (ADS)

    Katayama, Kiliha; Shimizu, Takao; Sakata, Osami; Shiraishi, Takahisa; Nakamura, Syogo; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Uchida, Hiroshi; Funakubo, Hiroshi

    2016-09-01

    In this study, the growth of (111)-oriented epitaxial and textured YO1.5-HfO2 (0.07:0.93 ratio) films using the pulsed laser deposition method is presented. Epitaxial films were prepared on ITO//(111)yttria-stabilized zirconia (YSZ) substrates (ITO: Sn-doped In2O3; YSZ: yttria-stabilized zirconia), while textured films were prepared on (111)Pt/TiOx/SiO2//Si substrates with and without an ITO buffer layer via the grain on grain coherent growth. Inserting an ITO layer increased the volume fraction of the ferroelectric orthorhombic phase. Both the epitaxial and uniaxially textured films exhibited similar ferroelectricity with a remanent polarization of around 10 μC/cm2 and a coercive field of 1.9 to 2.0 MV/cm. These results present us with a way of obtaining stable and uniform ferroelectric properties for each grain and device cells consisting of a small number of grains. This opens the door for ultimately miniaturized ferroelectric devices, such as ferroelectric field effect transistors with small gate length and resistive random access memory using ferroelectric tunnel junctions.

  4. Strain tuning of electronic structure in Bi4Ti3O12-LaCoO3 epitaxial thin films

    DOE PAGES

    Choi, Woo Seok; Lee, Ho Nyung

    2015-05-08

    In this study, we investigated the crystal and electronic structures of ferroelectric Bi4Ti3O12 single-crystalline thin films site-specifically substituted with LaCoO3 (LCO). The epitaxial films were grown by pulsed laser epitaxy on NdGaO3 and SrTiO3 substrates to vary the degree of strain. With increasing the LCO substitution, we observed a systematic increase in the c-axis lattice constant of the Aurivillius phase related with the modification of pseudo-orthorhombic unit cells. These compositional and structural changes resulted in a systematic decrease in the band gap, i.e., the optical transition energy between the oxygen 2p and transition-metal 3d states, based on a spectroscopic ellipsometrymore » study. In particular, the Co 3d state seems to largely overlap with the Ti t2g state, decreasing the band gap. Interestingly, the applied tensile strain facilitates the band-gap narrowing, demonstrating that epitaxial strain is a useful tool to tune the electronic structure of ferroelectric transition-metal oxides.« less

  5. Stripe Domain Structure in Epitaxial (001) BiFeO3 Thin Films on Orthorhombic TbScO3 Substrate

    DTIC Science & Technology

    2009-06-26

    nm were deposited by off- axis radio frequency magnetron sputtering at 690 °C.3 The fact the growth temperature is below the paraelectric to...Energy, Office of Basic Energy Science under Contract No. DMR -0820404, 0507146, and 0908718. Work at Pennsylvania State Univer- sity was supported by

  6. Artificial chemical and magnetic structure at the domain walls of an epitaxial oxide

    NASA Astrophysics Data System (ADS)

    Farokhipoor, S.; Magén, C.; Venkatesan, S.; Íñiguez, J.; Daumont, C. J. M.; Rubi, D.; Snoeck, E.; Mostovoy, M.; de Graaf, C.; Müller, A.; Döblinger, M.; Scheu, C.; Noheda, B.

    2014-11-01

    Progress in nanotechnology requires new approaches to materials synthesis that make it possible to control material functionality down to the smallest scales. An objective of materials research is to achieve enhanced control over the physical properties of materials such as ferromagnets, ferroelectrics and superconductors. In this context, complex oxides and inorganic perovskites are attractive because slight adjustments of their atomic structures can produce large physical responses and result in multiple functionalities. In addition, these materials often contain ferroelastic domains. The intrinsic symmetry breaking that takes place at the domain walls can induce properties absent from the domains themselves, such as magnetic or ferroelectric order and other functionalities, as well as coupling between them. Moreover, large domain wall densities create intense strain gradients, which can also affect the material's properties. Here we show that, owing to large local stresses, domain walls can promote the formation of unusual phases. In this sense, the domain walls can function as nanoscale chemical reactors. We synthesize a two-dimensional ferromagnetic phase at the domain walls of the orthorhombic perovskite terbium manganite (TbMnO3), which was grown in thin layers under epitaxial strain on strontium titanate (SrTiO3) substrates. This phase is yet to be created by standard chemical routes. The density of the two-dimensional sheets can be tuned by changing the film thickness or the substrate lattice parameter (that is, the epitaxial strain), and the distance between sheets can be made as small as 5 nanometres in ultrathin films, such that the new phase at domain walls represents up to 25 per cent of the film volume. The general concept of using domain walls of epitaxial oxides to promote the formation of unusual phases may be applicable to other materials systems, thus giving access to new classes of nanoscale materials for applications in nanoelectronics and

  7. Artificial chemical and magnetic structure at the domain walls of an epitaxial oxide.

    PubMed

    Farokhipoor, S; Magén, C; Venkatesan, S; Íñiguez, J; Daumont, C J M; Rubi, D; Snoeck, E; Mostovoy, M; de Graaf, C; Müller, A; Döblinger, M; Scheu, C; Noheda, B

    2014-11-20

    Progress in nanotechnology requires new approaches to materials synthesis that make it possible to control material functionality down to the smallest scales. An objective of materials research is to achieve enhanced control over the physical properties of materials such as ferromagnets, ferroelectrics and superconductors. In this context, complex oxides and inorganic perovskites are attractive because slight adjustments of their atomic structures can produce large physical responses and result in multiple functionalities. In addition, these materials often contain ferroelastic domains. The intrinsic symmetry breaking that takes place at the domain walls can induce properties absent from the domains themselves, such as magnetic or ferroelectric order and other functionalities, as well as coupling between them. Moreover, large domain wall densities create intense strain gradients, which can also affect the material's properties. Here we show that, owing to large local stresses, domain walls can promote the formation of unusual phases. In this sense, the domain walls can function as nanoscale chemical reactors. We synthesize a two-dimensional ferromagnetic phase at the domain walls of the orthorhombic perovskite terbium manganite (TbMnO3), which was grown in thin layers under epitaxial strain on strontium titanate (SrTiO3) substrates. This phase is yet to be created by standard chemical routes. The density of the two-dimensional sheets can be tuned by changing the film thickness or the substrate lattice parameter (that is, the epitaxial strain), and the distance between sheets can be made as small as 5 nanometres in ultrathin films, such that the new phase at domain walls represents up to 25 per cent of the film volume. The general concept of using domain walls of epitaxial oxides to promote the formation of unusual phases may be applicable to other materials systems, thus giving access to new classes of nanoscale materials for applications in nanoelectronics and

  8. Epitaxial Halide Perovskite Lateral Double Heterostructure.

    PubMed

    Wang, Yiping; Chen, Zhizhong; Deschler, Felix; Sun, Xin; Lu, Toh-Ming; Wertz, Esther A; Hu, Jia-Mian; Shi, Jian

    2017-03-28

    Epitaxial III-V semiconductor heterostructures are key components in modern microelectronics, electro-optics, and optoelectronics. With superior semiconducting properties, halide perovskite materials are rising as promising candidates for coherent heterostructure devices. In this report, spinodal decomposition is proposed and experimentally implemented to produce epitaxial double heterostructures in halide perovskite system. Pristine epitaxial mixed halide perovskites rods and films were synthesized via van der Waals epitaxy by chemical vapor deposition method. At room temperature, photon was applied as a knob to regulate the kinetics of spinodal decomposition and classic coarsening. By this approach, halide perovskite double heterostructures were created carrying epitaxial interfaces and outstanding optical properties. Reduced Fröhlich electron-phonon coupling was discovered in coherent halide double heterostructure, which is hypothetically attributed to the classic phonon confinement effect widely existing in III-V double heterostructures. As a proof-of-concept, our results suggest that halide perovskite-based epitaxial heterostructures may be promising for high-performance and low-cost optoelectronics, electro-optics, and microelectronics. Thus, ultimately, for practical device applications, it may be worthy to pursue these heterostructures via conventional vapor phase epitaxy approaches widely practised in III-V field.

  9. Electroless epitaxial etching for semiconductor applications

    DOEpatents

    McCarthy, Anthony M.

    2002-01-01

    A method for fabricating thin-film single-crystal silicon on insulator substrates using electroless etching for achieving efficient etch stopping on epitaxial silicon substrates. Microelectric circuits and devices are prepared on epitaxial silicon wafers in a standard fabrication facility. The wafers are bonded to a holding substrate. The silicon bulk is removed using electroless etching leaving the circuit contained within the epitaxial layer remaining on the holding substrate. A photolithographic operation is then performed to define streets and wire bond pad areas for electrical access to the circuit.

  10. Epitaxial silicon devices for dosimetry applications

    SciTech Connect

    Bruzzi, M.; Bucciolini, M.; Casati, M.; Menichelli, D.; Talamonti, C.; Piemonte, C.; Svensson, B. G.

    2007-04-23

    A straightforward improvement of the efficiency and long term stability of silicon dosimeters has been obtained with a n{sup +}-p junction surrounded by a guard-ring structure implanted on an epitaxial p-type Si layer grown on a Czochralski substrate. The sensitivity of devices made on 50-{mu}m-thick epitaxial Si degrades by only 7% after an irradiation with 6 MeV electrons up to 1.5 kGy, and shows no significant further decay up to 10 kGy. These results prove the enhanced radiation tolerance and stability of epitaxial diodes as compared to present state-of-the-art Si devices.

  11. Ion implanted epitaxially grown ZnSe

    NASA Technical Reports Server (NTRS)

    1974-01-01

    The epitaxial growth of ZnSe on (100) Ge using the close-spaced transport process is described. Substrate temperature of 575 C and source temperatures of 675 C yield 10 micron, single crystal layers in 10 hours. The Ge substrates provides a nonreplenishable chemical transport agent and the epitaxial layer thickness is limited to approximately 10 microns. Grown epitaxial layers show excellent photoluminescence structure at 77 K. Grown layers exhibit high resistivity, and annealing in Zn vapor at 575 C reduces the resistivity to 10-100 ohms-cm. Zinc vapor annealing quenches the visible photoluminescence.

  12. Failure development around a borehole in an orthorhombic thermo-elastoplastic rock medium

    NASA Astrophysics Data System (ADS)

    Piłacik, Alicja; Dąbrowski, Marcin

    2016-04-01

    The elastic anisotropy of a rock medium is one of the main factors affecting stress distribution around the borehole. It governs the initiation and propagation of the technologically induced compressive and tensile failure zones, and reopening of natural mechanical discontinuities. We conducted a two-dimensional analysis of failure around a pressurized horizontal borehole in an orthorhombic elastic rock medium subject to variable far-field loads. The analytical solution to the thermoelastic problem was derived. An elastoplastic finite element method code was developed using MILAMIN platform (milamin.org) and implemented in MATLAB. Various yield functions were used, including von Mises, Mohr-Coulomb, Drucker-Prager and Hoek-Brown failure criteria. The analysis was augmented by introducing rock heterogeneities and discrete mechanical discontinuities in the vicinity of the borehole.

  13. Quasi-one-dimensional electronic structure in orthorhombic RbC[sub 60

    SciTech Connect

    Chauvet, O.; Oszlanyi, G.; Forro, L. ); Stephens, P.W. ); Tegze, M.; Faigel, G.; Janossy, A. )

    1994-04-25

    X-ray diffraction studies show that the stable phase of the alkali fullerene RbC[sub 60] is orthorhombic ([ital o]-RbC[sub 60]) below 350 K. C[sub 60] molecules form chains along [bold a] with an unusually short spacing of 9.12 A and magnetic properties suggest that [ital o]-RbC[sub 60] is a quasi-1D metal with a transition to a spin density wave ground state at 50 K. The high temperature fcc phase of RbC[sub 60] may be stabilized below 300 K by quenching from 500 K; it is paramagnetic above 300 K and transforms into a nonmagnetic ground state beween 300 and 250 K.

  14. Solution-phase synthesis of rubidium lead iodide orthorhombic perovskite nanowires

    NASA Astrophysics Data System (ADS)

    Lim, Da-Hye; Ramasamy, Parthiban; Kwak, Do-Hyun; Lee, Jong-Soo

    2017-06-01

    Recently, metal halide perovskite nanocrystals have demonstrated outstanding properties in various optoelectronic applications. Cesium lead halides (CsPbX3) are the most studied perovskites in nanoscale dimensions. However, halide perovskite nanocrystals with other cations have rarely been reported. It is important to develop new perovskite compositions to further expand their application in various fields. In this paper, we first report the synthesis of colloidal rubidium lead iodide (RbPbI3) nanowires (NWs). RbPbI3 NWs have an orthorhombic crystal structure and are single-crystalline in nature. The diameter of the NWs is around 32 nm with lengths up to several tens of micrometers. RbPbI3 NWs absorb strongly below 450 nm. RbPbI3 devices exhibited good photoresponsive behavior, suggesting a potential use in optoelectronics.

  15. Locked octahedral tilting in orthorhombic perovskites: At the boundary of the general rule predicting phase transitions

    NASA Astrophysics Data System (ADS)

    Ardit, M.; Dondi, M.; Cruciani, G.

    2017-01-01

    Mainly ruled by oxygen octahedral rotations, perovskite oxides can exhibit zone boundary transitions (ZBTs) either with d Tc/d P >0 or d Tc/d P <0 . Synchrotron structural investigations at high pressure conditions place YA l0.25C r0.75O3 orthorhombic perovskite at the boundary of ZBTs. The absence of changes in the octahedral tilting and a volume reduction with pressure exclusively controlled by an isotropic polyhedral compression set YA l0.25C r0.75O3 as the first finding of a possible asymptote at the Clapeyron relation for predicting ZBTs in perovskites. Furthermore, the discovery of a "locked-tilt perovskite" can pave the way to a new class of functional materials.

  16. Structural transition of PETN-I to ferroelastic orthorhombic phase PETN-III at elevated pressures.

    PubMed

    Tschauner, O; Kiefer, B; Lee, Y; Pravica, M; Nicol, M; Kim, E

    2007-09-07

    Using powder x-ray diffraction and first-principles calculations, we provide evidence for a structural transition of PETN-I below 6 GPa to an orthorhombic phase of space group P2(1)2(1)2. The transition can be rationalized as shear-stress induced and ferroelastic, which involves a slight static displacement of the molecules that breaks the fourfold symmetry of PETN-I. Previously reported changes in the optical spectra reflect a lifting of the twofold degeneracy of modes in tetragonal PETN-I. The observed transition is expected to induce soft shear compliances along specific directions in PETN crystallites that may relate to the observed dependence of detonation pressure on crystal orientation.

  17. Structural Transition of PETN-I to Ferroelastic Orthorhombic Phase PETN-III at Elevated Pressures

    SciTech Connect

    Tschauner,O.; Kiefer, B.; Lee, Y.; Pravica, M.; Nicol, M.; Kim, E.

    2007-01-01

    Using powder x-ray diffraction and first-principles calculations, we provide evidence for a structural transition of PETN-I below 6 GPa to an orthorhombic phase of space group P2{sub 1}2{sub 1}2. The transition can be rationalized as shear-stress induced and ferroelastic, which involves a slight static displacement of the molecules that breaks the fourfold symmetry of PETN-I. Previously reported changes in the optical spectra reflect a lifting of the twofold degeneracy of modes in tetragonal PETN-I. The observed transition is expected to induce soft shear compliances along specific directions in PETN crystallites that may relate to the observed dependence of detonation pressure on crystal orientation.

  18. Determination of the resistivity anisotropy of orthorhombic materials via transverse resistivity measurements

    DOE PAGES

    Walmsley, P.; Fisher, I. R.

    2017-04-05

    Measurements of the resistivity anisotropy can provide crucial information about the electronic structure and scattering processes in anisotropic and low-dimensional materials, but quantitative measurements by conventional means often suffer very significant systematic errors. Here we describe a novel approach to measuring the resistivity anisotropy of orthorhombic materials, using a single crystal and a single measurement that is derived from a π/4 rotation of the measurement frame relative to the crystallographic axes. In this new basis, the transverse resistivity gives a direct measurement of the resistivity anisotropy, which combined with the longitudinal resistivity also gives the in-plane elements of the conventionalmore » resistivity tensor via a 5-point contact geometry. In conclusion, this is demonstrated through application to the charge-density wave compound ErTe3, and it is concluded that this method presents a significant improvement on existing techniques, particularly when measuring small anisotropies.« less

  19. Large magneto (thermo) dielectric effect in multiferroic orthorhombic LuMnO3

    NASA Astrophysics Data System (ADS)

    Wang, L. J.; Chai, Y. S.; Feng, S. M.; Zhu, J. L.; Manivannan, N.; Jin, C. Q.; Gong, Z. Z.; Wang, X. H.; Li, L. T.

    2012-06-01

    We have investigated the relation between ferroelectric and magnetic orders of orthorhombic (o-) LuMnO3 ceramics. The increase of dielectric constant ɛ exceeds 82% near incommensurate to commensurate E-type antiferromagnetic (AFM) spin ordering transition temperature TL, reflecting a large magneto (thermo) dielectric response. Meanwhile, distinct anomalies and thermal hysteresis behavior are observed near this temperature in both temperature dependence of ɛ and specific heat Cp, indicating a strong coupling between FE and magnetic orders in o-LuMnO3. Comparing to o-HoMnO3, TmMnO3, and YbMnO3 with similar E-type AFM ground state, o-LuMnO3 has the largest magneto (thermo) dielectric effect

  20. Anomalous Phonon Behavior in Orthorhombic LuMnO3 at Low Temperature

    NASA Astrophysics Data System (ADS)

    Gao, Peng; Chen, Haiyan; Tyson, Trevor A.; Liu, Zhenxian; Bai, Jianming; Wang, Liping; Choi, Youngjai; Cheong, Sang-Wook

    2011-03-01

    We present the pressure dependent phonon spectra of orthorhombic-LuMnO3 which are conducted in the low temperature region (below TN and TL) . A temperature dependent anomalous phonon coincides with the ferroelectric behavior at low pressure condition. At ~ 10 GPa, this anomalous phonon exhibits an unusual softening trend which will be suppressed at higher pressure. This work is supported by DOE Grant DE-FG02-07ER46402 (NJIT), by DE-FG02-07ER46402 (Rutgers), by COMPRES (U2A beam line at NSLS), the Consortium for Materials Properties Research in Earth Sciences under NSF Cooperative Agreement EAR01-35554, U.S. Department of Energy (DOE-BES and NNSA/CDAC) and by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886 (use of NSLS at Brookhaven National Laboratory).

  1. Body-centered orthorhombic C16: A novel topological node-line semimetal

    DOE PAGES

    Wang, Jian -Tao; Weng, Hongming; Nie, Simin; ...

    2016-05-11

    We identify by ab initio calculations a novel topological semimetal carbon phase in all-sp2 bonding networks with a 16-atom body-centered orthorhombic unit cell, termed bco-C16. Total-energy calculations show that bco-C16 is comparable to solid fcc-C60 in energetic stability, and phonon and molecular dynamics simulations confirm its dynamical stability. This all-sp2 carbon allotrope can be regarded as a three-dimensional modification of graphite, and its simulated x-ray diffraction (XRD) pattern matches well a previously unexplained diffraction peak in measured XRD spectra of detonation and chimney soot, indicating its presence in the specimen. Electronic band structure calculations reveal that bco-C16 is a topologicalmore » node-line semimetal with a single nodal ring. Lastly, these findings establish a novel carbon phase with intriguing structural and electronic properties of fundamental significance and practical interest.« less

  2. Electron-phonon scattering effects on electronic and optical properties of orthorhombic GeS

    NASA Astrophysics Data System (ADS)

    Villegas, Cesar E. P.; Rocha, A. R.; Marini, Andrea

    2016-10-01

    Group-VI monochalcogenides are attracting a great deal of attention due to their peculiar anisotropic properties. Very recently, it has been suggested that GeS could act as a promissory absorbing material with high input-output ratios, which are relevant features for designing prospective optoelectronic devices. In this work, we use the ab initio many-body perturbation theory to study the role of electron-phonon coupling on orthorhombic GeS. We identify the vibrational modes that efficiently couple with the electronic states responsible for giving rise to the first and second excitonic state. We also study finite-temperature optical absorption, and we show that even at T →0 K , the role of the electron-phonon interaction is crucial to properly describe the position and width of the main experimental excitation peaks. Our results suggest that the electron-phonon coupling is essential to properly describe the optical properties of the monochalcogenides family.

  3. Orthorhombic boron oxide under pressure: In situ study by X-ray diffraction and Raman scattering

    NASA Astrophysics Data System (ADS)

    Cherednichenko, Kirill A.; Le Godec, Yann; Kalinko, Aleksandr; Mezouar, Mohamed; Solozhenko, Vladimir L.

    2016-11-01

    High-pressure phase of boron oxide, orthorhombic β-B2O3, has been studied in situ by synchrotron X-ray diffraction to 22 GPa and Raman scattering to 46 GPa at room temperature. The bulk modulus of β-B2O3 has been found to be 169(3) GPa that is in good agreement with our ab initio calculations. Raman and IR spectra of β-B2O3 have been measured at ambient pressure; all experimentally observed bands have been attributed to the theoretically calculated ones, and the mode assignment has been performed. Based on the data on Raman shift as a function of pressure, combined with equation-of-state data, the Grüneisen parameters of all experimentally observed Raman bands have been calculated. β-B2O3 enriched by 10B isotope has been synthesized, and the effect of boron isotopic substitution on Raman spectra has been studied.

  4. High throughput vacuum chemical epitaxy

    NASA Astrophysics Data System (ADS)

    Fraas, L. M.; Malocsay, E.; Sundaram, V.; Baird, R. W.; Mao, B. Y.; Lee, G. Y.

    1990-10-01

    We have developed a vacuum chemical epitaxy (VCE) reactor which avoids the use of arsine and allows multiple wafers to be coated at one time. Our vacuum chemical epitaxy reactor closely resembles a molecular beam epitaxy system in that wafers are loaded into a stainless steel vacuum chamber through a load chamber. Also as in MBE, arsenic vapors are supplied as reactant by heating solid arsenic sources thereby avoiding the use of arsine. However, in our VCE reactor, a large number of wafers are coated at one time in a vacuum system by the substitution of Group III alkyl sources for the elemental metal sources traditionally used in MBE. Higher wafer throughput results because in VCE, the metal-alkyl sources for Ga, Al, and dopants can be mixed at room temperature and distributed uniformly though a large area injector to multiple substrates as a homogeneous array of mixed element molecular beams. The VCE reactor that we have built and that we shall describe here uniformly deposits films on 7 inch diameter substrate platters. Each platter contains seven two inch or three 3 inch diameter wafers. The load chamber contains up to nine platters. The vacuum chamber is equipped with two VCE growth zones and two arsenic ovens, one per growth zone. Finally, each oven has a 1 kg arsenic capacity. As of this writing, mirror smooth GaAs films have been grown at up to 4 μm/h growth rate on multiple wafers with good thickness uniformity. The background doping is p-type with a typical hole concentration and mobility of 1 × 10 16/cm 3 and 350 cm 2/V·s. This background doping level is low enough for the fabrication of MESFETs, solar cells, and photocathodes as well as other types of devices. We have fabricated MESFET devices using VCE-grown epi wafers with peak extrinsic transconductance as high as 210 mS/mm for a threshold voltage of - 3 V and a 0.6 μm gate length. We have also recently grown AlGaAs epi layers with up to 80% aluminum using TEAl as the aluminum alkyl source. The Al

  5. Thermoelectric properties of orthorhombic group IV-VI monolayers from the first-principles calculations

    NASA Astrophysics Data System (ADS)

    Guo, San-Dong; Wang, Yue-Hua

    2017-01-01

    Two-dimensional (2D) materials may have potential applications in thermoelectric devices. In this work, the thermoelectric properties of orthorhombic group IV-VI monolayers AB (A = Ge and Sn; B = S and Se) are systematically investigated by the first-principles calculations and semiclassical Boltzmann transport theory. The spin-orbit coupling (SOC) is considered for their electron part, which produces observable effects on the power factor, especially for n-type doping. According to the calculated ZT, the four monolayers exhibit diverse anisotropic thermoelectric properties although they have a similar hinge-like crystal structure. The GeS along zigzag and armchair directions shows the strongest anisotropy, while SnS and SnSe show mostly isotropic efficiency of thermoelectric conversion. This can be explained by the strength of anisotropy of their respective power factor and electronic and lattice thermal conductivities. The calculated results show that the ZT between n- and p-type doping has little difference for GeS, SnS, and SnSe. It is found that GeSe, SnS, and SnSe show better thermoelectric performance compared to GeS in n-type doping and that SnS and SnSe exhibit higher efficiency of thermoelectric conversion in p-type doping. Compared to other many 2D materials, orthorhombic group IV-VI monolayers AB (A = Ge and Sn; B = S and Se) may possess better thermoelectric performance due to lower lattice thermal conductivities. Our work would be beneficial to stimulate further theoretical and experimental works.

  6. The scattering potential of partial derivative wavefields in 3-D elastic orthorhombic media: an inversion prospective

    NASA Astrophysics Data System (ADS)

    Oh, Ju-Won; Alkhalifah, Tariq

    2016-09-01

    Multiparameter full waveform inversion (FWI) applied to an elastic orthorhombic model description of the subsurface requires in theory a nine-parameter representation of each pixel of the model. Even with optimal acquisition on the Earth surface that includes large offsets, full azimuth, and multicomponent sensors, the potential for trade-off between the elastic orthorhombic parameters are large. The first step to understanding such trade-off is analysing the scattering potential of each parameter, and specifically, its scattering radiation patterns. We investigate such radiation patterns for diffraction and for scattering from a horizontal reflector considering a background isotropic model. The radiation patterns show considerable potential for trade-off between the parameters and the potentially limited resolution in their recovery. The radiation patterns of C11, C22, and C33 are well separated so that we expect to recover these parameters with limited trade-offs. However, the resolution of their recovery represented by recovered range of model wavenumbers varies between these parameters. We can only invert for the short wavelength components (reflection) of C33 while we can mainly invert for the long wavelength components (transmission) of the elastic coefficients C11 and C22 if we have large enough offsets. The elastic coefficients C13, C23, and C12 suffer from strong trade-offs with C55, C44, and C66, respectively. The trade-offs between C13 and C55, as well as C23 and C44, can be partially mitigated if we acquire P-SV and SV-SV waves. However, to reduce the trade-offs between C12 and C66, we require credible SH-SH waves. The analytical radiation patterns of the elastic constants are supported by numerical gradients of these parameters.

  7. Epitaxial CuInSe2 thin films grown by molecular beam epitaxy and migration enhanced epitaxy

    NASA Astrophysics Data System (ADS)

    Abderrafi, K.; Ribeiro-Andrade, R.; Nicoara, N.; Cerqueira, M. F.; Gonzalez Debs, M.; Limborço, H.; Salomé, P. M. P.; Gonzalez, J. C.; Briones, F.; Garcia, J. M.; Sadewasser, S.

    2017-10-01

    While CuInSe2 chalcopyrite materials are mainly used in their polycrystalline form to prepare thin film solar cells, epitaxial layers have been used for the characterization of defects. Typically, epitaxial layers are grown by metal-organic vapor phase epitaxy or molecular beam epitaxy (MBE). Here we present epitaxial layers grown by migration enhanced epitaxy (MEE) and compare the materials quality to MBE grown layers. CuInSe2 layers were grown on GaAs (0 0 1) substrates by co-evaporation of Cu, In, and Se using substrate temperatures of 450 °C, 530 °C, and 620 °C. The layers were characterized by high resolution X-ray diffraction (HR-XRD), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and atomic force microscopy (AFM). HR-XRD and HR-TEM show a better crystalline quality of the MEE grown layers, and Raman scattering measurements confirm single phase CuInSe2. AFM shows the previously observed faceting of the (0 0 1) surface into {1 1 2} facets with trenches formed along the [1 1 0] direction. The surface of MEE-grown samples appears smoother compared to MBE-grown samples, a similar trend is observed with increasing growth temperature.

  8. Epitaxial growth of single crystal films

    NASA Technical Reports Server (NTRS)

    Lind, M. D.

    1980-01-01

    An experiment in gallium arsenide liquid phase epitaxy was performed successfully on the SPAR 6 flight October 17, 1979. The design, fabrication, and testing of the experimental apparatus, and the performance and results of the experiment are discussed.

  9. Epitaxial growth of silicon for layer transfer

    DOEpatents

    Teplin, Charles; Branz, Howard M

    2015-03-24

    Methods of preparing a thin crystalline silicon film for transfer and devices utilizing a transferred crystalline silicon film are disclosed. The methods include preparing a silicon growth substrate which has an interface defining substance associated with an exterior surface. The methods further include depositing an epitaxial layer of silicon on the silicon growth substrate at the surface and separating the epitaxial layer from the substrate substantially along the plane or other surface defined by the interface defining substance. The epitaxial layer may be utilized as a thin film of crystalline silicon in any type of semiconductor device which requires a crystalline silicon layer. In use, the epitaxial transfer layer may be associated with a secondary substrate.

  10. Amorphous/epitaxial superlattice for thermoelectric application

    NASA Astrophysics Data System (ADS)

    Ishida, Akihiro; Thao, Hoang Thi Xuan; Shibata, Mamoru; Nakashima, Seisuke; Tatsuoka, Hirokazu; Yamamoto, Hidenari; Kinoshita, Yohei; Ishikiriyama, Mamoru; Nakamura, Yoshiaki

    2016-08-01

    An amorphous/epitaxial superlattice system is proposed for application to thermoelectric devices, and the superlattice based on a PbGeTeS system was prepared by the alternate deposition of PbS and GeTe using a hot wall epitaxy technique. The structure was analyzed by high-resolution transmission electron microscopy (HRTEM) and X-ray analysis, and it was found that the superlattice consists of an epitaxial PbTe-based layer and a GeS-based amorphous layer by the reconstruction of the constituents. A reduction in thermal conductivity due to the amorphous/epitaxial system was confirmed by a 2ω method. Electrical and thermoelectric properties were measured for the samples.

  11. Silicon Holder For Molecular-Beam Epitaxy

    NASA Technical Reports Server (NTRS)

    Hoenk, Michael E.; Grunthaner, Paula J.; Grunthaner, Frank J.

    1993-01-01

    Simple assembly of silicon wafers holds silicon-based charge-coupled device (CCD) during postprocessing in which silicon deposited by molecular-beam epitaxy. Attains temperatures similar to CCD, so hotspots suppressed. Coefficients of thermal expansion of holder and CCD equal, so thermal stresses caused by differential thermal expansion and contraction do not develop. Holder readily fabricated, by standard silicon processing techniques, to accommodate various CCD geometries. Silicon does not contaminate CCD or molecular-beam-epitaxy vacuum chamber.

  12. Epitaxial Deposition Of Germanium Doped With Gallium

    NASA Technical Reports Server (NTRS)

    Huffman, James E.

    1994-01-01

    Epitaxial layers of germanium doped with gallium made by chemical vapor deposition. Method involves combination of techniques and materials used in chemical vapor deposition with GeH4 or GeCl4 as source of germanium and GaCl3 as source of gallium. Resulting epitaxial layers of germanium doped with gallium expected to be highly pure, with high crystalline quality. High-quality material useful in infrared sensors.

  13. Epitaxial Deposition Of Germanium Doped With Gallium

    NASA Technical Reports Server (NTRS)

    Huffman, James E.

    1994-01-01

    Epitaxial layers of germanium doped with gallium made by chemical vapor deposition. Method involves combination of techniques and materials used in chemical vapor deposition with GeH4 or GeCl4 as source of germanium and GaCl3 as source of gallium. Resulting epitaxial layers of germanium doped with gallium expected to be highly pure, with high crystalline quality. High-quality material useful in infrared sensors.

  14. Low-dimensional magnetic properties of orthorhombic MnV2O6 : A nonstandard structure stabilized at high pressure

    NASA Astrophysics Data System (ADS)

    Hneda, M. L.; da Cunha, J. B. M.; Gusmão, M. A.; Neto, S. R. Oliveira; Rodríguez-Carvajal, J.; Isnard, O.

    2017-01-01

    This paper presents the physical properties of a nonstandard orthorhombic form of MnV2O6 , including a comparison with the isostructural orthorhombic niobate MnNb2O6 , and with the usual MnV2O6 monoclinic polymorph. Orthorhombic (P b c n ) MnV2O6 is obtained under extreme conditions of high pressure (6.7 GPa) and high temperature (800 ∘C ). A negative Curie-Weiss temperature θCW is observed, implying dominant antiferromagnetic interactions at high temperatures, in contrast to the positive θCW of the monoclinic form. Specific-heat measurements are reported down to 1.8 K for all three compounds, and corroborate the magnetic-transition temperatures obtained from susceptibility data. Orthorhombic MnV2O6 presents a transition to an ordered antiferromagnetic state at TN=4.7 K. Its magnetic structure, determined by neutron diffraction, is unique among the columbite compounds, being characterized by a commensurate propagation vector k =(0 ,0 ,1/2 ) . It presents antiferromagnetic chains running along the c axis, but with a different spin pattern in comparison to the chains observed in MnNb2O6 . By a comparative discussion of our observations in this three compounds, we are able to highlight the interplay between competing interactions and dimensionality that yield their magnetic properties.

  15. Cubic and orthorhombic structures of aluminum hydride Al H3 predicted by a first-principles study

    NASA Astrophysics Data System (ADS)

    Ke, Xuezhi; Kuwabara, Akihide; Tanaka, Isao

    2005-05-01

    The most stable structure of aluminum hydride AlH3 is believed to be a hexagonal symmetry. However, using the density functional theory, we have identified two more stable structures for the AlH3 with the cubic and orthorhombic symmetries. Based on the quasiharmonic approximation, the cubic and orthorhombic AlH3 are almost degenerate when the zero-point energies are included. The geometric and electronic structures, the phonon, and the thermodynamic properties for the hexagonal, cubic, and orthorhombic AlH3 have been studied by means of density functional theory and direct ab initio force constant approach. The calculated electronic structures, phonon density of states, and thermodynamic functions [including S(T) and H(T)-H(0) ] for the three hydrides are similar. The results show that these three hydrides have negative enthalpies of formation, but positive free energies of formation. This conclusion is the same as that made by Wolverton for the hexagonal AlH3 [Phys. Rev. B 69, 144109 (2004)]. The thermodynamic properties indicate that the orthorhombic and cubic AlH3 should be more difficult to dissociate than the hexagonal AlH3 .

  16. Structural, optoelectronic, infrared and Raman spectra of orthorhombic SrSnO{sub 3} from DFT calculations

    SciTech Connect

    Moreira, E.; Henriques, J.M.; Azevedo, D.L.; Caetano, E.W.S.; Freire, V.N.; Albuquerque, E.L.

    2011-04-15

    Orthorhombic SrSnO{sub 3} was investigated using density functional theory (DFT) considering both the local density and generalized gradient approximations, LDA and GGA, respectively. The electronic band structure, density of states, complex dielectric function, optical absorption, and the infrared and Raman spectra were computed. Calculated lattice parameters are close to the experimental measurements, and an indirect band gap E(S{yields}{Gamma})=1.97eV (2.27 eV) was obtained within the GGA (LDA) level of calculation. Effective masses for holes and electrons were estimated, being very anisotropic in comparison with similar results for orthorhombic CaSnO{sub 3}. The complex dielectric function and the optical absorption of SrSnO{sub 3} were shown to be sensitive to the plane of polarization of the incident light. The infrared spectrum between 100 and 600 cm{sup -1} was obtained, with its main peaks being assigned, and a nice agreement between experimental and theoretical peaks of the Raman spectrum of orthorhombic SrSnO{sub 3} was achieved. -- Graphical abstract: Orthorhombic SrSnO{sub 3}: a view of the unit cell (left) and plots showing the calculated and experimental Raman spectra (right). Display Omitted Research highlights: {yields} We have performed DFT calculations on orthorhombic SrSnO{sub 3} crystals, obtaining their structural, electronical and optical properties. {yields} An indirect band gap was obtained, and anisotropic effective masses were found for both electrons and holes. {yields} The complex dielectric function and the optical absorption of SrSnO{sub 3} were shown to be very sensitive to the plane of polarization of the incident light. {yields} The infrared spectrum between 100 and 600 cm{sup -1} was obtained, with its main peaks being assigned, and a nice agreement between experimental and theoretical peaks of the Raman spectrum was achieved.

  17. Effects of Interfaces on the Structure and Novel Physical Properties in Epitaxial Multiferroic BiFeO₃ Ultrathin Films.

    PubMed

    Huang, Chuanwei; Chen, Lang

    2014-07-23

    In functional oxide films, different electrical/mechanical boundaries near film surfaces induce rich phase diagrams and exotic phenomena. In this paper, we review some key points which underpin structure, phase transition and related properties in BiFeO₃ ultrathin films. Compared with the bulk counterparts, we survey the recent results of epitaxial BiFeO₃ ultrathin films to illustrate how the atomic structure and phase are markedly influenced by the interface between the film and the substrate, and to emphasize the roles of misfit strain and depolarization field on determining the domain patterns, phase transformation and associated physical properties of BiFeO₃ ultrathin films, such as polarization, piezoelectricity, and magnetism. One of the obvious consequences of the misfit strain on BiFeO₃ ultrathin films is the emergence of a sequence of phase transition from tetragonal to mixed tetragonal & rhombohedral, the rhombohedral, mixed rhombohedral & orthorhombic, and finally orthorhombic phases. Other striking features of this system are the stable domain patterns and the crossover of 71° and 109° domains with different electrical boundary conditions on the film surface, which can be controlled and manipulated through the depolarization field. The external field-sensitive enhancements of properties for BiFeO₃ ultrathin films, including the polarization, magnetism and morphotropic phase boundary-relevant piezoelectric response, offer us deeper insights into the investigations of the emergent properties and phenomena of epitaxial ultrathin films under various mechanical/electrical constraints. Finally, we briefly summarize the recent progress and list open questions for future study on BiFeO₃ ultrathin films.

  18. Complexity of High-Pressure Orthorhombic Iron Oxides, the Characterization of Fe5O6

    NASA Astrophysics Data System (ADS)

    Lavina, B.; Meng, Y.

    2014-12-01

    Occurring as accessory minerals in most rocks and forming large deposits of considerable economical importance, iron oxides have a major petrological importance. Their role as oxygen buffers, in differentiation processes and as magnetic phases summarize the critical importance of iron oxides in most petrological contexts, independently of their abundance.The discovery of a new compound in the Fe-O system, Fe4O5[1], reshaped our assumptions on the behavior of iron oxides in the Earth's deep interior, where phases of FeO and Fe3O4 were considered the sole plausible players. Further studies found that Fe4O5 is stable in a wide compositional range[2] and can accept a wide extent of isomorphic substitutions[3].We used laser heating synthesis in diamond anvil cell and microdiffraction mapping with high brilliance synchrotron x-ray[4] to explore the complexity of the Fe-O system at high pressure and temperature. We found coexistence of two to three oxides in most of the samples we investigated. By means of a careful exploration of diffraction effects in the reciprocal space, we singled-out the diffraction peaks of a few grains in multiphase diffraction patterns. These allowed a reliable characterization of yet a new iron oxide, Fe5O6. This compound, synthesized between 10 and 20 GPa, is also orthorhombic and can be described with the same building blocks of the other known orthorhombic iron oxides. A comparison of compressibility and lattice parameters of the latest iron oxides will be presented. [1] Lavina, B. et al. Discovery of the recoverable high-pressure iron oxide Fe4O5. Proc Natl Acad Sci U S A 108, 17281-5 (2011).[2] Woodland, A. B., Frost, D. J., Trots, D. M., Klimm, K. & Mezouar, M. In situ observation of the breakdown of magnetite (Fe3O4) to Fe4O5 and hematite at high pressures and temperatures. Am Mineral 97, 1808-1811 (2012).[3] Woodland, A. B. et al. Fe4O5 and its solid solutions in several simple systems. Cotrib Mineral Petrol 166, 1677-1686 (2013

  19. Nanoscale monoclinic domains in epitaxial SrRuO{sub 3} thin films deposited by pulsed laser deposition

    SciTech Connect

    Ghica, C. Negrea, R. F.; Nistor, L. C.; Chirila, C. F.; Pintilie, L.

    2014-07-14

    In this paper, we analyze the structural distortions observed by transmission electron microscopy in thin epitaxial SrRuO{sub 3} layers used as bottom electrodes in multiferroic coatings onto SrTiO{sub 3} substrates for future multiferroic devices. Regardless of the nature and architecture of the multilayer oxides deposited on the top of the SrRuO{sub 3} thin films, selected area electron diffraction patterns systematically revealed the presence of faint diffraction spots appearing in forbidden positions for the SrRuO{sub 3} orthorhombic structure. High-resolution transmission electron microscopy (HRTEM) combined with Geometric Phase Analysis (GPA) evidenced the origin of these forbidden diffraction spots in the presence of structurally disordered nanometric domains in the SrRuO{sub 3} bottom layers, resulting from a strain-driven phase transformation. The local high compressive strain (−4% ÷ −5%) measured by GPA in the HRTEM images induces a local orthorhombic to monoclinic phase transition by a cooperative rotation of the RuO{sub 6} octahedra. A further confirmation of the origin of the forbidden diffraction spots comes from the simulated diffraction patterns obtained from a monoclinic disordered SrRuO{sub 3} structure.

  20. Effects of contamination on selective epitaxial growth

    NASA Astrophysics Data System (ADS)

    MacDonald, Brian J.; Paton, Eric; Adem, Ercan; En, Bill

    2004-06-01

    As MOSFET dimensions scale down in size, it has become increasingly difficult to maintain high drive current while suppressing the off-state leakage current. One method of avoiding short-channel effects is to scale the source/drain (S/D) junction depths proportionally with the gate length. Unfortunately, this increases the S/D resistance, which slows the circuit. To keep the S/D junction shallow without affecting the S/D resistance, a raised S/D (RSD) structure is required. Integrating RSD can be difficult. Selective epitaxial growth (SEG) is the process used to incorporate RSD. This process requires a relatively clean surface to initiate the growth. Insertion of SEG earlier in the process flow facilitates selective epitaxial growth. Insertion of SEG later in the process flow results in higher levels of contamination at the interface of the Si substrate and the RSD structure. In this paper, we identify some mechanisms that determine the quality of the selective epitaxial film. Results indicate that Si defects are not a dominant mechanism in SEG film quality. Instead, results suggest that higher levels of contamination increased the surface roughness of the epitaxial film. PMOS regions were found to have higher levels of contamination and rougher epitaxial films than NMOS regions. Hydrogen bake as high as 900 °C was required to lower the surface contamination and provide excellent epitaxial morphology. Unfortunately, this high temperature causes enhanced dopant diffusion and deactivation of the device. Previous work [H. van Meer, K. De Meyer, Symposium on VLSI Technology Digest of Technical Papers, 2002, p. 170.] identified an alternative integration that provides excellent quality selective epitaxy, without dopant diffusion and deactivation.

  1. Island morphologies in epitaxial growth.

    NASA Astrophysics Data System (ADS)

    Hessinger, Uwe; Leskovar, M.; Rumaner, Lee; Ohuchi, Fumio; Olmstead, Marjorie A.; Ueno, Keiji; Koma, Atsushi

    1996-03-01

    Growth of epitaxial films commonly occurs through the coalescence of individual islands. The morphology of islands has therefore a key importance for the film qualities desired. A uniform layer-by-layer growth of the film is achieved when islands in the first layer coalesce to form a uniform layer before a second layer nucleates; a non-uniform multi-layer growth results from multiple layers successively nucleating on top of each other before the first layer coalesces. We developed a kinetic model based on an analytic solution of the diffusion equation between nucleation events to calculate the evolving island morphology during growth. The morphologies depend on deposition rate, substrate temperature, and activation energies for surface diffusion on the substrate and deposited material. By applying this theory to atomic force microscopy data of GaSe multi-layer islands, we extract a value for the activation energy for Ga diffusion across steps of GaSe. Supported by NSF Grant No. ECS-9209652, DOE Grant No. DE-FG06-94ER45516, and the Japanese New Energy Development Organization.

  2. Engineering epitaxial graphene with oxygen

    NASA Astrophysics Data System (ADS)

    Kimouche, Amina; Martin, Sylvain; Winkelmann, Clemens; Fruchart, Olivier; Courtois, Hervé; Coraux, Johann; Hybrid system at low dimension Team

    2013-03-01

    Almost free-standing graphene can be obtained on metals by decoupling graphene from its substrate, for instance by intercalation of atoms beneath graphene, as it was shown with oxygen atoms. We show that the interaction of oxygen with epitaxial graphene on iridium leads to the formation of an ultrathin crystalline oxide extending between graphene and the metallic substrate via the graphene wrinkles. Graphene studied in this work was prepared under ultra-high vacuum by CVD. The samples were studied by combining scanning probe microscopy (STM, AFM) and spatially resolved spectroscopy (Raman, STS). The ultrathin oxide forms a decoupling barrier layer between graphene and Ir, yielding truly free-standing graphene whose hybridization and charge transfers with the substrate have been quenched. Our work presents novel types of graphene-based nanostructures, and opens the route to the transfer-free preparation of graphene directly onto an insulating support contacted to the metallic substrate which could serve as a gate electrode. Work supported by the EU-NMP GRENADA project

  3. Laser-synthesized epitaxial graphene.

    PubMed

    Lee, Sangwon; Toney, Michael F; Ko, Wonhee; Randel, Jason C; Jung, Hee Joon; Munakata, Ko; Lu, Jesse; Geballe, Theodore H; Beasley, Malcolm R; Sinclair, Robert; Manoharan, Hari C; Salleo, Alberto

    2010-12-28

    Owing to its unique electronic properties, graphene has recently attracted wide attention in both the condensed matter physics and microelectronic device communities. Despite intense interest in this material, an industrially scalable graphene synthesis process remains elusive. Here, we demonstrate a high-throughput, low-temperature, spatially controlled and scalable epitaxial graphene (EG) synthesis technique based on laser-induced surface decomposition of the Si-rich face of a SiC single-crystal. We confirm the formation of EG on SiC as a result of excimer laser irradiation by using reflection high-energy electron diffraction (RHEED), Raman spectroscopy, synchrotron-based X-ray diffraction, transmission electron microscopy (TEM), and scanning tunneling microscopy (STM). Laser fluence controls the thickness of the graphene film down to a single monolayer. Laser-synthesized graphene does not display some of the structural characteristics observed in EG grown by conventional thermal decomposition on SiC (0001), such as Bernal stacking and surface reconstruction of the underlying SiC surface.

  4. The nature of Mn4+ luminescence in the orthorhombic perovskite, GdAlO3

    NASA Astrophysics Data System (ADS)

    Srivastava, A. M.; Brik, M. G.

    2017-01-01

    In this paper we report on the spectroscopic properties of Mn4+ (3d3) ion in the orthorhombic perovskite, GdAlO3 and calculate the energy levels using the exchange charge model of crystal-field theory. The calculated Mn4+ energy levels are in good agreement with the experimental data. The results of our calculations yield the crystal-field splitting and Racah parameters of Dq = 2083 cm-1, B = 780 cm-1 and C = 2864 cm-1, with C/B = 3.67. The emission spectrum is composed of the zero phonon line (2Eg → 4A2g transition) with dominating intensity and its vibrational sidebands. We have also calculated Mulliken atomic charges and bond populations for three isostructural perovskites (GdAlO3, LaGaO3 and CaZrO3) to seek correlation between the energy position of the Mn4+2E level and the covalence of Mn4+sbnd O2- chemical bonding.

  5. Ferroelectric BaTiO3 phase of orthorhombic crystal structure contained in nanoparticles

    NASA Astrophysics Data System (ADS)

    Ram, S.; Jana, A.; Kundu, T. K.

    2007-09-01

    Ferroelectric BaTiO3 phase of a Pnma orthorhombic crystal structure is synthesized from a chemical method using a polymer complex of Ba2+ and Ti4+ with polyvinyl alcohol (PVA). After burning out the polymer at temperature as high as 550 °C in air for 2 h results in an average 15 nm crystallite BaTiO3 size, with lattice parameters a =0.6435 nm, b =0.5306 nm, c =0.8854 nm, and density 5.124 g/cm3. The relationship between dielectric constant ɛr and temperature showed a single Curie transition temperature TC=131 °C, with as large a ɛr value as 263 at TC. A low value of dissipation factor tan δ, as small as 0.033 at room temperature (frequency f =1 kHz), with good insulating properties made the sample promising for use in uncooled infrared detectors and thermal imaging applications. The ɛr value is nearly independent of f value up to 100 kHz. A spectrum of sharp EPR signals of g values 2.21 to 1.88 characterizes three major kinds of VBa-, VTi3-, and Ti3+-Vo2+ paramagnetic species present in the imperfections.

  6. High-pressure orthorhombic ferromagnesite as a potential deep-mantle carbon carrier

    DOE PAGES

    Liu, Jin; Lin, Jung -Fu; Prakapenka, Vitali B.

    2015-01-06

    In this study, knowledge of the physical and chemical properties of candidate deep-carbon carriers such as ferromagnesite [(Mg,Fe)CO3] at high pressure and temperature of the deep mantle is necessary for our understanding of deep-carbon storage as well as the global carbon cycle of the planet. Previous studies have reported very different scenarios for the (Mg,Fe)CO3 system at deep-mantle conditions including the chemical dissociation to (Mg,Fe)O+CO2, the occurrence of the tetrahedrally-coordinated carbonates based on CO4 structural units, and various high-pressure phase transitions. Here we have studied the phase stability and compressional behavior of (Mg,Fe)CO3 carbonates up to relevant lower-mantle conditions ofmore » approximately 120 GPa and 2400 K. Our experimental results show that the rhombohedral siderite (Phase I) transforms to an orthorhombic phase (Phase II with Pmm2 space group) at approximately 50 GPa and 1400 K. The structural transition is likely driven by the spin transition of iron accompanied by a volume collapse in the Fe-rich (Mg,Fe)CO3 phases; the spin transition stabilizes the high-pressure phase II at much lower pressure conditions than its Mg-rich counterpart. It is conceivable that the low-spin ferromagnesite phase II becomes a major deep-carbon carrier at the deeper parts of the lower mantle below 1900 km in depth.« less

  7. The compressibility of cubic white, orthorhombic black and rhombohedral black phosphorus

    SciTech Connect

    Clark, S; Zaug, J M

    2009-06-05

    The effect of pressure on the crystal structure of white phosphorus has been studied up to 22.4 GPa. The {alpha} phase was found to transform into the {alpha}' phase at 0.87 {+-} 0.04 GPa with a volume change of 0.1 {+-} 0.3 cc/mol. A fit of a second order Birch-Murghanan equation to the data gave Vo = 16.94 {+-} 0.08 cc/mol and K{sub o} = 6.7 {+-} 0.5 GPa for the {alpha} phase and Vo = 16.4 {+-} 0.1 cc/mol and K{sub o} = 9.1 {+-} 0.3 GPa for the {alpha}' phase. The {alpha}' phase was found to transform to the A17 phase of black phosphorus at 2.68 {+-} 0.34 GPa and then with increasing pressure to the A7 and then simple cubic phase of black phosphorus. A fit of a second order Birch-Murnaghan equation to our orthorhombic and rhombohedral black phosphorus data gave Vo = 11.43 {+-} 0.02 cc/mol and K{sub o} = 34.7 {+-} 0.5 GPa for the A17 phase and Vo = 9.62 {+-} 0.01 cc/mol and K{sub o} = 65.0 {+-} 0.6 GPa for the A7 phase.

  8. Molecular Structure and Dynamics in the Low Temperature (Orthorhombic) Phase of NH3BH3

    SciTech Connect

    Cho, Herman M.; Shaw, Wendy J.; Parvanov, Venci M.; Schenter, Gregory K.; Karkamkar, Abhijeet J.; Hess, Nancy J.; Mundy, Christopher J.; Kathmann, Shawn M.; Sears, Jesse A.; Lipton, Andrew S.; Ellis, Paul D.; Autrey, Thomas

    2008-05-08

    Variable temperature 2H NMR experiments on the orthorhombic phase of selectively deuterated NH3BH3 spanning the static to fast exchange limits of the borane and amine motions are reported. New values of the electric field gradient (EFG) tensor parameters have been obtained from the static 2H spectra of Vzz = 5.509(±0.275)×1014 statvolt/cm2 and ! = 0.00±0.05 for the borane hydrogens and Vzz = 9.615(±0.481)×1014 statvolt/cm2 and ! = 0.00±0.05 for the amine hydrogens. The molecular symmetry inferred from the observation of equal EFG tensors for both the boron and amine hydrogens is in sharp contrast with the Cs symmetry derived from diffraction studies. The origin of the apparent discrepancy has been investigated using molecular dynamics methods in combination with electronic structure calculations of NMR parameters, bond lengths, and bond angles. The computation of parameters from a statistical ensemble rather than from a single set of atomic Cartesian coordinates gives values that are in close quantitative agreement with the 2H NMR electric field gradient tensor measurements and are more consistent with the molecular symmetry revealed by the NMR spectra. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.

  9. Superconductivity at 3.1 K in the orthorhombic ternary silicide ScRuSi

    NASA Astrophysics Data System (ADS)

    Ruan, Bin-Bin; Wang, Xiao-Chuan; Yu, Jia; Pan, Bo-Jin; Mu, Qing-Ge; Liu, Tong; Chen, Gen-Fu; Ren, Zhi-An

    2017-02-01

    We report the synthesis, crystal structure, superconductivity and physical property characterizations of the ternary equiatomic compound ScRuSi. Polycrystalline samples of ScRuSi were prepared by an arc-melting method. The as-prepared samples were identified as the orthorhombic Co2P-type o-ScRuSi by powder x-ray diffraction analysis. Electrical resistivity measurements show o-ScRuSi to be a metal which superconducts below a T c of 3.1 K; the upper critical field μ 0 H c2(0) is estimated to be 0.87 T. The magnetization and specific heat measurements confirm the bulk type-II superconductivity in o-ScRuSi, with a specific heat jump within the BCS weak coupling limit. o-ScRuSi is the first Co2P-type superconductor to contain scandium. After annealing at 1273 K for a week, o-ScRuSi transforms into hexagonal Fe2P-type h-ScRuSi, which is a Pauli-paramagnetic metal with no superconductivity observed above 1.8 K.

  10. High-Pressure Orthorhombic Ferromagnesite as a Potential Deep-Mantle Carbon Carrier

    PubMed Central

    Liu, Jin; Lin, Jung-Fu; Prakapenka, Vitali B.

    2015-01-01

    Knowledge of the physical and chemical properties of candidate deep-carbon carriers such as ferromagnesite [(Mg,Fe)CO3] at high pressure and temperature of the deep mantle is necessary for our understanding of deep-carbon storage as well as the global carbon cycle of the planet. Previous studies have reported very different scenarios for the (Mg,Fe)CO3 system at deep-mantle conditions including the chemical dissociation to (Mg,Fe)O+CO2, the occurrence of the tetrahedrally-coordinated carbonates based on CO4 structural units, and various high-pressure phase transitions. Here we have studied the phase stability and compressional behavior of (Mg,Fe)CO3 carbonates up to relevant lower-mantle conditions of approximately 120 GPa and 2400 K. Our experimental results show that the rhombohedral siderite (Phase I) transforms to an orthorhombic phase (Phase II with Pmm2 space group) at approximately 50 GPa and 1400 K. The structural transition is likely driven by the spin transition of iron accompanied by a volume collapse in the Fe-rich (Mg,Fe)CO3 phases; the spin transition stabilizes the high-pressure phase II at much lower pressure conditions than its Mg-rich counterpart. It is conceivable that the low-spin ferromagnesite phase II becomes a major deep-carbon carrier at the deeper parts of the lower mantle below 1900 km in depth. PMID:25560542

  11. Enhancement of the antimicrobial properties of orthorhombic molybdenum trioxide by thermal induced fracturing of the hydrates.

    PubMed

    Shafaei, Shahram; Van Opdenbosch, Daniel; Fey, Tobias; Koch, Marcus; Kraus, Tobias; Guggenbichler, Josef Peter; Zollfrank, Cordt

    2016-01-01

    The oxides of the transition metal molybdenum exhibit excellent antimicrobial properties. We present the preparation of molybdenum trioxide dihydrate (MoO3 × 2H2O) by an acidification method and demonstrate the thermal phase development and morphological evolution during and after calcination from 25 °C to 600 °C. The thermal dehydration of the material was found to proceed in two steps. Microbiological roll-on tests using Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa were performed and exceptional antimicrobial activities were determined for anhydrous samples with orthorhombic lattice symmetry and a large specific surface area. The increase in the specific surface area is due to crack formation and to the loss of the hydrate water after calcination at 300 °C. The results support the proposed antimicrobial mechanism for transition metal oxides, which based on a local acidity increase as a consequence of the augmented specific surface area. Copyright © 2015 Elsevier B.V. All rights reserved.

  12. Photo-thermoelectric properties of SnS nanocrystals with orthorhombic layered structure

    NASA Astrophysics Data System (ADS)

    Hyun, Cheol-Min; Choi, Jeong-Hun; Lee, Myoung-Jae; Ahn, Ji-Hoon

    2017-07-01

    The photo-thermoelectric properties of SnS nanocrystals, two-dimensional materials with an orthorhombic symmetry, were investigated using a focused laser scanning method. The SnS nanocrystals were synthesized by a vapor transport method, and their fundamental material and electrical properties were investigated. Upon shining a laser onto the SnS channel region under a positive source-drain bias, a positive photocurrent was observed due to photo-excited electron-hole pairs. On the other hand, when this external electric field was not applied, a strong photocurrent was observed within the metal electrode region rather than at the metal-semiconductor interface, which indicated that the major mechanism for the photocurrent under zero external bias was a photo-induced thermoelectric effect rather than a photovoltaic effect. Moreover, the Seebeck coefficient of the SnS nanocrystal device was approximately 1735 μV/K, which is 3.5 times larger than that of its bulk counterpart.

  13. Ferromagnetism in orthorhombic RAgAl3 (R = Ce and Pr) compounds

    NASA Astrophysics Data System (ADS)

    Nallamuthu, S.; Dzubinska, Andrea; Reiffers, Marian; Fernandez, Jesus Rodriguez; Nagalakshmi, R.

    2017-09-01

    We present a detailed study on magnetic, thermodynamic and transport properties of polycrystalline RAgAl3(R = Ce and Pr) compounds. Both compounds crystallize in orthorhombic structure, which is distorted from the tetragonal BaAl4 structure with the space group Cmcm. Heat capacity measurement indicates the bulk magnetic ordering of the compounds. CeAgAl3 and PrAgAl3 order ferromagnetically at TC=3.8 K and 5.8 K, respectively as it was confirmed from magnetic measurements. CeAgAl3 exhibits heavy fermion behaviour. The Schottky behaviour in heat capacity data was observed in both compounds. The crystalline electric field (CEF) analysis of the magnetic parts of heat capacity of CeAgAl3 and PrAgAl3 yielded to a CEF level scheme with three doublets and nine singlets and with an overall splitting of 51 K and 180 K, respectively. Fit yielded a magnetic doublet state for CeAgAl3, whereas for PrAgAl3 a pseudo-doublet ground-state with an energy difference of 15 K has been obtained. The resistivity measurements display a low temperature drop at the magnetic ordering temperature of the compounds. Negative magnetoresistance (MR) due to the ferromagnetic ordering has been observed for both Ce and Pr compounds.

  14. High-temperature deformation and failure of an orthorhombic titanium aluminide sheet material

    SciTech Connect

    Nicolaou, P.D.; Semiatin, S.L.

    1996-11-01

    The high-temperature deformation and failure behavior of an orthorhombic titanium aluminide sheet alloy (fabricated by diffusion bonding of six thin foils) was established by conducting uniaxial tension and plane-strain compression tests at 980 C and strain rates between 10{sup {minus}4} and 10{sup {minus}2} s{sup {minus}1}. The stress-strain response was characterized by a peak stress at low strains followed by moderate flow softening. Values of the strain-rate sensitivity index (m) were between 0.10 and 0.32, and the plastic anisotropy parameter (R) was of the order of 0.6 to 1.0. Cavity nucleation and growth were observed during tensile deformation at strain rates of 10{sup {minus}3} s{sup {minus}1} and higher. However, the combined effects of low m, low cavity growth rate {eta}, and flow softening were deduced to be the source of failure controlled by necking and flow localization rather than cavitation-induced fracture prior to necking.

  15. Magnetic performance of orthorhombic Mn35Ge35Te30 nanocrystals

    NASA Astrophysics Data System (ADS)

    Mahdy, Iman A.

    2017-01-01

    Nanocrystalline antiferromagnetic Mn35Ge35Te30 diluted magnetic semiconductors powder syntheses by the conventional direct reaction of pure metals. Nanocrystalline nature of the prepared sample confirmed using various techniques, where x-Ray diffraction (XRD) and atomic force microscope (AFM) measurements shows ~96 nm particle size, while transmission electron microscope (TEM) shows 92 nm particle size. XRD analysis show orthorhombic symmetry with lattice parameters a=7.386611±(0.0066) Å, b=8.962502±(0.0090) Å and c=7.027349±(0.0040) Å. Electron Spin resonance (ESR) show a broad asymmetric line whereas the remnant Mn2+ six-hyperfine lines are broadened within |+1/2>→|-1/2> line according to high anisotropy; calculated Landé g-factor is 2.047. Vibrating sample magnetometer (VSM) analysis, field-moment characteristics revealed a hysteresis loop with small coercive field indicating that Mn35Ge35Te30 is a soft magnetic material. Moreover, hysteresis measurements at different temperatures show increasing magnetization with increasing temperature up to 150 K followed by decreased with increasing temperature up to 300 K. This behavior indicated to the antiferromagnetic nature of the prepared nanocrystalline materials. Magnetic moment - temperature measurements show Néel temperature TN=172.6 K. Magnetic force microscope revealed magnetic domains as a result of interaction between magnetic dipole moments of magnetic cantilever and pressed powder.

  16. Thermal evolution of the crystal structure of the orthorhombic perovskite LaFeO{sub 3}

    SciTech Connect

    Dixon, Charlotte A.L.; Kavanagh, Christopher M.; Knight, Kevin S.; Kockelmann, Winfried; Morrison, Finlay D.; Lightfoot, Philip

    2015-10-15

    The thermal evolution of the crystal structure of the prototypical orthorhombic perovskite LaFeO{sub 3} has been studied in detail by powder neutron diffraction in the temperature range 25

  17. Electronic structure and thermoelectric properties of orthorhombic SrLiAs

    SciTech Connect

    Guo, Li Bin; Wang, Yuan Xu Yan, Yu Li; Yang, Gui; Yang, Jue Ming; Feng, Zhen Zhen

    2014-07-21

    The electronic structure and the transport properties of orthorhombic SrLiAs were investigated using first-principles calculations and the semiclassical Boltzmann theory. It is found that the electrical conductivity along the y-direction is higher than those along other two directions, which is most likely originated from the covalent ladder-like structure formed by the Li and As atoms. Moreover, the transport properties of n-type SrLiAs are better than those of p-type one, due to the large band dispersion along the y-direction near the Fermi level. Further, the value of power factor with respect to relaxation time achieves 9.2 × 10{sup 11} W K{sup −2} m{sup −1} s{sup −1} for n-type SrLiAs along the y-direction at 1000 K with an optimal carrier concentration of 6.5 × 10{sup 20 }cm{sup −3}. The obtained minimum lattice thermal conductivity is comparable to those of other Zintl phase compounds.

  18. Intrinsic ferroelectric polarization of orthorhombic manganites with E-type spin order

    NASA Astrophysics Data System (ADS)

    Chai, Y. S.; Oh, Y. S.; Wang, L. J.; Manivannan, N.; Feng, S. M.; Yang, Y. S.; Yan, L. Q.; Jin, C. Q.; Kim, Kee Hoon

    2012-05-01

    By directly measuring electrical hysteresis loops using the Positive-Up Negative-Down (PUND) method, we determined accurately the remanent ferroelectric polarization Pr of orthorhombic RMnO3 (R = Ho, Tm, Yb, and Lu) compounds below their E-type spin ordering temperatures. We found that LuMnO3 has the largest Pr of 0.17 μC/cm2 at 6 K in the series, the value of which allows us to predict that its single-crystal form can produce a Pr of at least 0.6 μC/cm2 at 0 K. Furthermore, at a fixed temperature, Pr decreases systematically with increasing rare earth ion radius from R = Lu to Ho, exhibiting a strong correlation with the variation of the in-plane Mn-O-Mn bond angle and Mn-O distances. Our experimental results suggest that the contribution of the Mn t2g orbitals may dominate the ferroelectric polarization.

  19. Thermal-expansion anisotropy of orthorhombic martensite in the two-phase (α + β) titanium alloy

    NASA Astrophysics Data System (ADS)

    Demakov, S. L.; Stepanov, S. I.; Illarionov, A. G.; Ryzhkov, M. A.

    2017-03-01

    Anisotropy of the thermal expansion coefficient (TEC) has been revealed along the axes of the crystal lattice of the α″ titanium martensite in the two-phase (α + β) titanium alloy of grade VT16 (Ti-3Al-5V-4.5Mo, wt %). It has been established by the method of in situ X-ray diffraction analysis that the lattice parameter b of the orthorhombic martensite obtained by quenching from different temperatures decreases upon heating. The TECs along the axes of the crystal lattice of the martensite obtained by quenching from different temperatures have been calculated. It has been shown that the uniaxial extension of bars of the VT16 alloy quenched for the metastable β phase with relative deformations of 0.7, 1, 2, 3, 4, 5, 6, and 8% leads to the formation of the deformation-induced martensite with an axial texture along the b direction of the martensite lattice. In the course of dilatometric studies of the deformed bars, it has been established that there are two temperature intervals (from-100 to +70°C and from 150 to 300°C) with a low TEC. In the first interval, the value of the TEC varies from-2 × 10-6 to +8 × 10-6 K-1 and is determined by the volume fraction of the oriented α″ martensite. This Invar effect is one-dimensional and is manifested along the b axis of the martensite.

  20. An unusual case of pseudo-merohedral twinning in orthorhombic crystals of Dicer.

    PubMed

    MacRae, Ian J; Doudna, Jennifer A

    2007-09-01

    The crystal structure of the enzyme Dicer from Giardia intestinalis was solved to 3.3 A resolution by MAD using crystals belonging to space group P2(1)2(1)2 [Macrae et al. (2006), Science, 311, 195-198]. These crystals were derived from crystals that diffracted X-rays to 3.0 A resolution but were refractory to structure determination because they were twinned. It is shown here that the original Dicer crystals represent an unusual case of perfect pseudo-merohedral twinning of orthorhombic crystals. Before the twinning problem was overcome, it was possible to calculate a low-resolution electron-density map in space group P4(1) that was used to build a partial molecular model. Experimental phases were sufficient to identify heavy-atom sites that indicated space-group inconsistency, leading to identification of the true space group. This information guided the search for different crystallization conditions that yielded untwinned crystals and ultimately a fully interpretable electron-density map.

  1. Silver-decorated orthorhombic nanotubes of lithium vanadium oxide: an impeder of bacterial growth and biofilm.

    PubMed

    Diggikar, Rahul S; Patil, Rajendra H; Kale, Sheetal B; Thombre, Dipalee K; Gade, Wasudeo N; Kulkarni, Milind V; Kale, Bharat B

    2013-09-01

    Reoccurrence of infectious diseases and ability of pathogens to resist antibacterial action has raised enormous challenges which may possibly be confronted by nanotechnology routes. In the present study, uniformly embedded silver nanoparticles in orthorhombic nanotubes of lithium vanadium oxide (LiV2O5/Ag) were explored as an impeder of bacterial growth and biofilm. The LiV2O5/Ag nanocomposites have impeded growth of Gram-positive Bacillus subtilis NCIM 2063 and Gram-negative Escherichia coli NCIM 2931 at 60 to 120 μg/mL. It also impeded the biofilm in Pseudomonas aeruginosa NCIM 2948 at 12.5 to 25 μg/mL. Impedance in the growth and biofilm occurs primarily by direct action of the nanocomposites on the cell surfaces of test organisms as revealed by surface perturbation in scanning electron microscopy. As the metabolic growth and biofilm formation phenomena of pathogens play a central role in progression of pathogenesis, LiV2O5/Ag nanocomposite-based approach is likely to curb the menace of reoccurrence of infectious diseases. Thus, LiV2O5/Ag nanocomposites can be viewed as a promising candidate in biofabrication of biomedical materials.

  2. Ambient stable tetragonal and orthorhombic phases in penta-twinned bipyramidal au microcrystals.

    PubMed

    Mettela, Gangaiah; Bhogra, Meha; Waghmare, Umesh V; Kulkarni, Giridhar U

    2015-03-04

    Face-centered cubic (fcc) lattice is the only known crystal structure of bulk gold. In the present work, we report the presence of body-centered tetragonal (bct) and body-centered orthorhombic (bco) phases in bipyramidal Au microcrystals with penta-twinned tips. These microcrystals have been obtained by thermolysis of (AuCl4)(-) stabilized with tetraoctylammonium bromide (ToABr) in air at about 220 °C for 30 min. Using a laboratory monochromatic X-ray source, the non-fcc phases could be readily detected. The remarkable occurrence of non-fcc phases of Au grown in the temperature window of 200-250 °C results from the geometrically induced strains in the bipyramids. Having derived first-principles theoretical support for the temperature-dependent stability of non-fcc Au structures under stress, we identify its origin in soft modes. Annealing at high temperatures relieves the stress, thus destabilizing the non-fcc phases.

  3. Determination of crystallographic orientation of lead-free piezoelectric (K,Na)NbO{sub 3} epitaxial thin films grown on SrTiO{sub 3} (100) surfaces

    SciTech Connect

    Yu, Qi; Zhu, Fang-Yuan; Cheng, Li-Qian; Wang, Ke; Li, Jing-Feng

    2014-03-10

    Crystallographic structure of sol-gel-processed lead-free (K,Na)NbO{sub 3} (KNN) epitaxial films on [100]-cut SrTiO{sub 3} single-crystalline substrates was investigated for a deeper understanding of its piezoelectric response. Lattice parameter measurement by high-resolution X-ray diffraction and transmission electron microscopy revealed that the orthorhombic KNN films on SrTiO{sub 3} (100) surfaces are [010] oriented (b-axis-oriented) rather than commonly identified c-axis orientation. Based on the crystallographic orientation and corresponding ferroelectric domain structure investigated by piezoresponse force microscopy, the superior piezoelectric property along b-axis of epitaxial KNN films than other orientations can be explained.

  4. Tunable bands in biased multilayer epitaxial graphene.

    PubMed

    Williams, Michael D; Samarakoon, Duminda K; Hess, Dennis W; Wang, Xiao-Qian

    2012-04-28

    We have studied the electronic characteristics of multilayer epitaxial graphene under a perpendicularly applied electric bias. Ultraviolet photoemission spectroscopy measurements reveal that there is notable variation of the electronic density-of-states in valence bands near the Fermi level. Evolution of the electronic structure of graphite and rotational-stacked multilayer epitaxial graphene as a function of the applied electric bias is investigated using first-principles density-functional theory including interlayer van der Waals interactions. The experimental and theoretical results demonstrate that the tailoring of electronic band structure correlates with the interlayer coupling tuned by the applied bias. The implications of controllable electronic structure of rotationally fault-stacked epitaxial graphene grown on the C-face of SiC for future device applications are discussed.

  5. Performance of epitaxial back surface field cells

    NASA Technical Reports Server (NTRS)

    Brandhorst, H. W., Jr.; Baraona, C. R.; Swartz, C. K.

    1974-01-01

    Epitaxial back surface field structures were formed by depositing a 10 micron thick 10 ohm-cm epitaxial silicon layer onto substrates with resistivities of 0.01, 0.1, 1.0 and 10 ohm-cm. A correlation between cell open-circuit voltage and substrate resistivity was observed and was compared to theory. The cells were also irradiated with 1-MeV electrons to a fluence of 5 times 10 to the 15th electrons per sq cm. The decrease of cell open-circuit voltage was in excellent agreement with theoretical predictions and the measured short-circuit currents were within 2% of the prediction. Calculations are presented for optimum cell performance as functions of epitaxial layer thickness, radiation fluence, and substrate diffusion length.

  6. Performance of epitaxial back surface field cells

    NASA Technical Reports Server (NTRS)

    Brandhorst, H. W., Jr.; Baraona, C. R.; Swartz, C. K.

    1973-01-01

    Epitaxial back surface field structures were formed by depositing a 10 micron thick 10 Omega-cm epitaxial silicon layer onto substrates with resistivities of 0.01, 0.1, 1.0 and 10 Omega-cm. A correlation between cell open-circuit voltage and substrate resistivity was observed and was compared to theory. The cells were also irradiated with 1 MeV electrons to a fluence of 5 X 10 to the 15th power e/cm2. The decrease of cell open-circuit voltage was in excellent agreement with theoretical predictions and the measured short circuit currents were within 2% of the prediction. Calculations are presented of optimum cell performance as functions of epitaxial layer thickness, radiation fluence and substrate diffusion length.

  7. Ultrafast structural dynamics of the orthorhombic distortion in the Fe-pnictide parent compound BaFe2As2

    PubMed Central

    Rettig, L.; Mariager, S. O.; Ferrer, A.; Grübel, S.; Johnson, J. A.; Rittmann, J.; Wolf, T.; Johnson, S. L.; Ingold, G.; Beaud, P.; Staub, U.

    2016-01-01

    Using femtosecond time-resolved hard x-ray diffraction, we investigate the structural dynamics of the orthorhombic distortion in the Fe-pnictide parent compound BaFe2As2. The orthorhombic distortion analyzed by the transient splitting of the (1 0 3) Bragg reflection is suppressed on an initial timescale of 35 ps, which is much slower than the suppression of magnetic and nematic order. This observation demonstrates a transient state with persistent structural distortion and suppressed magnetic/nematic order which are strongly linked in thermal equilibrium. We suggest a way of quantifying the coupling between structural and nematic degrees of freedom based on the dynamics of the respective order parameters. PMID:27158636

  8. Influence of downsizing of zeolite crystals on the orthorhombic ↔ monoclinic phase transition in pure silica MFI-type

    NASA Astrophysics Data System (ADS)

    Kabalan, Ihab; Michelin, Laure; Rigolet, Séverinne; Marichal, Claire; Daou, T. Jean; Lebeau, Bénédicte; Paillaud, Jean-Louis

    2016-08-01

    The impact of crystal size on the transition orthorhombic ↔ monoclinic phase in MFI-type purely silica zeolites is investigated between 293 and 473 K using 29Si MAS NMR and powder X-ray diffraction. Three silicalite-1 zeolites are synthesized: a material constituted of micron-sized crystals, pseudospherical nanometer-sized crystals and hierarchical porous zeolites with a mesoporous network created by the use of a gemini-type diquaternary ammonium surfactant giving nanosheet zeolites. Our results show for the first time that the orthorhombic ↔ monoclinic phase transition already known for micron-sized particles also occurs in nanometer-sized zeolite crystals whereas our data suggest that the extreme downsizing of the zeolite crystal to one unit cell in thickness leads to an extinction of the phase transition.

  9. Continuously controllable optical band gap in orthorhombic ferroelectric KNbO3-BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Pascual-Gonzalez, Cristina; Schileo, Giorgio; Murakami, Shunsuke; Khesro, Amir; Wang, Dawei; Reaney, Ian M.; Feteira, Antonio

    2017-04-01

    The optical bandgap of orthorhombic ferroelectric KNbO3 is shown to be continuously controllable via Bi and Fe co-substitution according to a K1-xBixNb1-xFexO3 doping mechanism. The room temperature X-ray diffraction data combined with Raman spectroscopy analysis show the polar orthorhombic crystal structure to persist up to x = 0.25, while the bandgap narrows monotonically by 1 eV (˜33%). In-situ Raman spectroscopy corroborates the polar nature of all compositions in the temperature range of -100 to 200 °C. The ability to control the bandgap while maintaining the spontaneous polarisation makes the K1-xBixNb1-xFexO3 system interesting for photoinduced processes in a wide temperature range.

  10. Epitaxial strain effect on the Jeff = 1/2 moment orientation in Sr2IrO4 thin films

    NASA Astrophysics Data System (ADS)

    Miao, Ludi; Xu, Hong; Mao, Z. Q.

    2014-01-01

    We have grown Sr2IrO4 (SIO) epitaxial thin films on SrTiO3 (STO) and NdGaO3 (NGO) substrates by a pulsed laser deposition method and characterized their structures and magnetic properties. We find that SIO films grown on STO substrates display tetragonal structure with a tensile strain of 0.13%, while SIO films grown on NGO substrates exhibit slightly orthorhombic structure with anisotropic biaxial tensile strains of 0.39% and 0.51% along the in-plane crystallographic axes. Although both films display insulating properties as bulk SIO does, their magnetic properties are distinct from that of bulk SIO. The ferromagnetic (FM) component of the Jeff = 1/2 canted antiferromagnetic order, which emerges below ˜240 K in bulk SIO, is significantly weakened in both films, with a greater weakening appearing in the SIO/NGO film. From structural and magnetoresistance anisotropy analyses for both films, we reveal that the weak FM component in SIO films is dependent on the epitaxial strain. The greater tensile strain leads to a smaller octahedral rotation: The rotation angle is ˜9.7(1)° for the SIO/NGO film and ˜10.7(2)° for the SIO/STO film. These findings indicate that the Jeff = 1/2 moment orientation in SIO follows the IrO6 octahedral rotation due to strong spin-orbit interaction.

  11. Growth and Structural Study of Epitaxial NaMnF3 Thin Films on SrTiO3

    NASA Astrophysics Data System (ADS)

    Kc, Amit; Johnson, Trent; Borisov, Pavel; Lederman, David

    2015-03-01

    Perovskite fluorides (ABF3) exhibit many interesting phenomena, e.g. dipolar and magnetic long-range order superconductivity, as well as magnetoelectric coupling. Recently, G. C. Garcia-Castro et al. predicted that orthorhombically distorted Pnma NaMnF3 perovskite should have a particularly soft ferroelectric mode, and is expected to demonstrate ferroelectric order regardless of elastic strain, despite the competing antiferrodistortive instability. Thus, in combination with weak ferromagnetic order, this material is expected to be multiferroic1. Here, we report the growth of epitaxial NaMnF3 thin films on SrTiO3(100) single crystal substrates via Molecular Beam Epitaxy (MBE). Structural qualities of the films were studied as a function of the substrate temperature and film thickness by the techniques of X-ray diffraction (XRD), in-situ reflection high-energy electron diffraction (RHEED), and atomic force microscopy (AFM). The best films were smooth single phase NaMnF3, grown with four in-plane and two out-of-plane twin domains.

  12. Domain Evolution and Piezoelectric Response across Thermotropic Phase Boundary in (K,Na)NbO3-Based Epitaxial Thin Films.

    PubMed

    Luo, Jin; Sun, Wei; Zhou, Zhen; Bai, Yu; Wang, Zhan Jie; Tian, Guo; Chen, Deyang; Gao, Xingsen; Zhu, Fangyuan; Li, Jing-Feng

    2017-04-19

    Recent research progress in (K,Na)NbO3 (KNN)-based lead-free piezoelectric ceramics has attracted increasing attention for their applications to microsystems or microelectromechanical systems (MEMS) in the form of thin films. This work demonstrates that high-quality KNN-based epitaxial films can be synthesized by a conventional sol-gel method, whose phase structure and domain characteristics have been investigated with emphasis on the temperature effect. A monoclinic MC structure is observed at room temperature in KNN-based epitaxial films, which is close to but different from the orthorhombic phase in bulk counterparts. Piezoresponse force microscopy (PFM) at elevated temperatures reveals continuous changes of ferroelectric domains in KNN films during heating and cooling cycles between room temperature and 190 °C. A distinct change in domain morphology is observed upon heating to 110 °C, accompanied by a clear variation of dielectric permittivity suggesting a thermotropic phase transition, which is revealed to belong to a MC-MA phase transition on the basis of structural and PFM analysis on local ferroelectric and piezoelectric behaviors. Enhanced piezoelectric response at the thermotropic phase boundary is observed, which is attributed to active domains and/or nanodomains formed across the boundary. Domain engineering by utilizing the phase transition should be important and effective in KNN-based films not only for property enhancement but also for its textured ceramics.

  13. Understanding the Rocksalt-to-Wurtzite phase transformation through microstructural analysis of (Al,Sc)N epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Saha, Bivas; Saber, Sammy; Stach, Eric A.; Kvam, Eric P.; Sands, Timothy D.

    2016-10-01

    Rocksalt-to-wurtzite structural phase transitions in semiconducting materials (such as III-V nitrides, ZnO, CdSe, and others) have been studied for several decades. Almost all experimental works related to this phase transition involve diamond anvil cells to apply hydrostatic pressure, and as a result, direct observation of the microstructural transformation during the phase transition has not been possible. In this article, we have addressed and uncovered the intimate microstructural details and epitaxial relationships between phases by capturing what is essentially a thin-film snapshot of the transformation after growth of AlxSc1-xN films with a composition chosen to be close to the equilibrium phase boundary between wurtzite and rocksalt. The results support the hypothesis that the transformation is triggered by defects at rs- {0 1 ¯ 1 } growth fronts that offer a nearly invariant plane with respect to the parallel w- {2 1 ¯ 1 ¯0 } planes. The intermediate crystal structures and their epitaxial relationships are consistent with theoretical models that predict a transformation pathway involving homogeneous orthorhombic shear strain.

  14. Chemical vapor deposition of epitaxial silicon

    DOEpatents

    Berkman, Samuel

    1984-01-01

    A single chamber continuous chemical vapor deposition (CVD) reactor is described for depositing continuously on flat substrates, for example, epitaxial layers of semiconductor materials. The single chamber reactor is formed into three separate zones by baffles or tubes carrying chemical source material and a carrier gas in one gas stream and hydrogen gas in the other stream without interaction while the wafers are heated to deposition temperature. Diffusion of the two gas streams on heated wafers effects the epitaxial deposition in the intermediate zone and the wafers are cooled in the final zone by coolant gases. A CVD reactor for batch processing is also described embodying the deposition principles of the continuous reactor.

  15. An affine transformation description of epitaxial heterostructures

    NASA Astrophysics Data System (ADS)

    Dakshinamurthy, S.; Rajan, K.

    1991-07-01

    The matching at the interface between the substrate and the film in an epitaxial deposit has been analyzed and explained very well in the literature for the various fcc-bcc metallic systems by the use of the energy minimization criteria such as invariant line criterion, the O-lattice approach etc. Though many orientation relationships have been reported for other crystal structures and non-metals, very little effort has been made to explain these relationships. Here, we attempt to rationalize the orientation relationships that we have obtained and which others have reported for epitaxial suicides using the above mentioned criteria.

  16. Crystal growth of calcium phosphates - epitaxial considerations

    NASA Astrophysics Data System (ADS)

    Koutsoukos, P. G.; Nancollas, G. H.

    1981-05-01

    The growth of one crystalline phase on the surface of another that offers a good crystal lattice match, may be important in environmental, physiological and pathological mineralization processes. The epitaxial relationships and kinetics of growth of hydroxyapatite on crystals of dicalcium phosphate dihydrate, calcium fluoride and calcite have been studied at sustained low supersaturation with respect to hydroxyapatite. At the very low supersaturations, the crystallization of hydroxyapatite takes place without the formation of precursor phases. The experimental results are in agreement with theoretical predictions for epitaxial growth, while the kinetics of hydroxyapatite crystallization on the foreign substrates is the same as that for the growth of hydroxyapatite on synthetic hydroxyapatite crystals.

  17. Phase transitions and rare-earth magnetism in hexagonal and orthorhombic DyMnO(3) single crystals.

    PubMed

    Harikrishnan, S; Rößler, S; Naveen Kumar, C M; Bhat, H L; Rößler, U K; Wirth, S; Steglich, F; Elizabeth, Suja

    2009-03-04

    The floating-zone method with different growth ambiences has been used to selectively obtain hexagonal or orthorhombic DyMnO(3) single crystals. The crystals were characterized by x-ray powder diffraction of ground specimens and a structure refinement as well as electron diffraction. We report magnetic susceptibility, magnetization and specific heat studies of this multiferroic compound in both the hexagonal and the orthorhombic structure. The hexagonal DyMnO(3) shows magnetic ordering of Mn(3+) (S = 2) spins on a triangular Mn lattice at T(N)(Mn) = 57 K characterized by a cusp in the specific heat. This transition is not apparent in the magnetic susceptibility due to the frustration on the Mn triangular lattice and the dominating paramagnetic susceptibility of the Dy(3+) (S = 9/2) spins. At T(N)(Dy) = 3 K, a partial antiferromagnetic order of Dy moments has been observed. In comparison, the magnetic data for orthorhombic DyMnO(3) display three transitions. The data broadly agree with results from earlier neutron diffraction experiments, which allows for the following assignment: a transition from an incommensurate antiferromagnetic ordering of Mn(3+) spins at T(N)(Mn) = 39 K, a lock-in transition at T(lock-in) = 16 K and a second antiferromagnetic transition at T(N)(Dy) = 5 K due to the ordering of Dy moments. Both the hexagonal and the orthorhombic crystals show magnetic anisotropy and complex magnetic properties due to 4f-4f and 4f-3d couplings.

  18. One-step hydrothermal synthesis, characterization and magnetic properties of orthorhombic PrCrO{sub 3} cubic particles

    SciTech Connect

    Zhang, Youjin Yao, Chengpeng; Fan, Yun; Zhou, Maozhong

    2014-11-15

    Highlights: • Orthorhombic PrCrO{sub 3} cubic particles were prepared by a simple and facile one-step hydrothermal method. • The possible formation mechanism of PrCrO{sub 3} cubic particles was proposed. • The as-synthesized PrCrO{sub 3} exhibited behaviors of magnetic transition and negative magnetization. - Abstract: Orthorhombic PrCrO{sub 3} cubic particles were synthesized by a simple and facile one-step hydrothermal method of processing temperature 280 °C for 7 days. The products prepared in this paper have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and field-emission scanning electron microscopy (FESEM). The magnetic properties of the final sample are also studied. The XRD pattern shows the pure orthorhombic phase for PrCrO{sub 3} particles, the XPS and FTIR results further demonstrate the purity and composition of the product. FESEM images show cubic morphology for the PrCrO{sub 3} particles. The possible growth mechanism for PrCrO{sub 3} cubic particles is proposed. Through the investigation of magnetic properties, it can be seen that the orthorhombic PrCrO{sub 3} cubic particles exhibit behaviors of magnetic transition and negative magnetization. The Néel temperature is about 232 K and the magnetic hysteresis loop under 4 K shows that the coercivity (H{sub C}) and remanence (M{sub r}) is about 1728 Oe and 4.88 emu/g, respectively.

  19. Anisotropic-strain-relaxation-induced crosshatch morphology in epitaxial SrTiO3/NdGaO3 thin films

    NASA Astrophysics Data System (ADS)

    Tan, X. L.; Chen, F.; Chen, P. F.; Xu, H. R.; Chen, B. B.; Jin, F.; Gao, G. Y.; Wu, W. B.

    2014-10-01

    We investigate the strain relaxation and surface morphology of epitaxial SrTiO3 (STO) films grown on (001)O and (110)O planes of orthorhombic NdGaO3 (NGO), and (001) plane of cubic (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) substrates. Although the average lattice mismatches are similar, strikingly regular crosshatched surface patterns can be found on STO/NGO(001)O[(110)O] films, contrary to the uniform surface of STO/LSAT(001). Based on the orientation and thickness dependent patterns and high-resolution x-ray diffractions, we ascribe the crosshatch morphology to the anisotropic strain relaxation with possibly the 60° misfit dislocation formation and lateral surface step flow in STO/NGO films, while an isotropic strain relaxation in STO/LSAT. Further, we show that the crosshatched STO/NGO(110)O surface could be utilized as a template to modify the magnetotransport properties of epitaxial La0.6Ca0.4MnO3 films. This study highlights the crucial role of symmetry mismatch in determining the surface morphology of the perovskite oxide films, in addition to their epitaxial strain states, and offers a different route for designing and fabricating functional perovskite-oxide devices.

  20. External and internal magnetic-field effects on ferroelectricity in orthorhombic rare-earth manganites

    NASA Astrophysics Data System (ADS)

    Kuwahara, H.; Noda, K.; Akaki, M.

    2006-03-01

    We report the dielectric and magnetic properties of the perovskite (Eu,Y)MnO3 crystal without the presence of the 4f magnetic moments of the rare earth ions. The subject compound, (Eu,Y)MnO3, was controlled the average ionic radius of the A site so that it was the same as that of TbMnO3 in which the intriguing magnetoelectric effect has been recently discovered. The (Eu,Y)MnO3 crystal was found to have two distinct ferroelectric phases with polarization along the a (Pa, T<=23K) and c (Pc, 23K<=T<=25K) axes in the orthorhombic Pbnm setting in a zero magnetic field. In addition, we have demonstrated a magnetic-field-induced switching between these ferroelectric phases: Pa changed to Pc by the application of magnetic fields parallel to the a axis (Ha). In analogy to the case of Pc in TbMnO3, this result is possibly interpreted as follows. In the case of (Eu,Y)MnO3, Mn 3d spins rotate in the ab plane and Pa would emerge in a zero field. In the Ha, the field will force the spins to rotate in the bc plane, in which Pc would be stabilized. Magnetization measurements supported this interpretation: We confirmed the change of the spin rotation axis of the helix from the c axis to the a axis induced by application of the Ha because there is no 4f moments acting as an internal magnetic field and interacting with the 3d spins. Results obtained with other rare-earth manganites such as (Gd,Tb)MnO3 and (Eu,Ho)MnO3 will be presented.

  1. New structure of high-pressure body-centered orthorhombic Fe2SiO4

    DOE PAGES

    Yamanaka, Takamitsu; Kyono, Atsushi; Nakamoto, Yuki; ...

    2015-08-01

    Here, a structural change in Fe2SiO4 spinel and the structure of a new high pressure phase are determined by Rietveld 26 profile fitting of x-ray diffraction data up to 64 GPa at ambient temperature. The compression curve of the spinel is discontinuous at approximately 20 GPa. Fe Kβ x-ray emission measurements at high pressure show that the transition from a high spin (HS) to an intermediate spin (IS) state begins at 17 GPa in the spinel phase. The IS electronic state is gradually enhanced with pressure, which results in an isostructural phase transition. A transition from the cubic spinel structure to a body centered orthorhombic phase (I-Fe2SiO4) with space group Imma and Z=4 was observed at approximately 34 GPa. The structure of I-Fe2SiO4 has two crystallographically distinct FeO6 octahedra, which are arranged in layers parallel to (101) and (011) and are very similar to the layers of FeO6 octahedra that constitute the spinel structure. Silicon also exists in six-fold coordination in I-Fe2SiO4. The transformation to the new high-pressure phase is reversible under decompression at ambient temperature. A Martensitic transformation of each slab of the spinel structure with translation vector [more » $$\\vec{1/8}$$ $$\\vec{1/8}$$ $$\\vec{1/8}$$] generates the I-Fe2SiO4 structure. Laser heating of I-Fe2SiO4 at 1500 K results in a decomposition of the material to rhombohedral FeO and SiO2 stishovite.« less

  2. Structural and ferromagnetic properties of an orthorhombic phase of MnBi stabilized with Rh additions

    SciTech Connect

    Taufour, Valentin; Thimmaiah, Srinivasa; March, Stephen; Saunders, Scott; Sun, Kewei; Lamichhane, Tej Nath; Kramer, Matthew J.; Bud’ko, Sergey L.; Canfield, Paul C.

    2015-07-28

    The article addresses the possibility of alloy elements in MnBi which may modify the thermodynamic stability of the NiAs-type structure without significantly degrading the magnetic properties. The addition of small amounts of Rh and Mn provides an improvement in the thermal stability with some degradation of the magnetic properties. The small amounts of Rh and Mn additions in MnBi stabilize an orthorhombic phase whose structural and magnetic properties are closely related to the ones of the previously reported high-temperature phase of MnBi (HT MnBi). The properties of the HT MnBi, which is stable between 613 and 719 K, have not been studied in detail because of its transformation to the stable low-temperature MnBi (LT MnBi), making measurements near and below its Curie temperature difficult. The Rh-stabilized MnBi with chemical formula Mn1.0625–xRhxBi [x=0.02(1)] adopts a new superstructure of the NiAs/Ni2In structure family. It is ferromagnetic below a Curie temperature of 416 K. The critical exponents of the ferromagnetic transition are not of the mean-field type but are closer to those associated with the Ising model in three dimensions. The magnetic anisotropy is uniaxial; the anisotropy energy is rather large, and it does not increase when raising the temperature, contrary to what happens in LT MnBi. The saturation magnetization is approximately 3μB/f.u. at low temperatures. Thus, while this exact composition may not be application ready, it does show that alloying is a viable route to modifying the stability of this class of rare-earth-free magnet alloys.

  3. Structural and ferromagnetic properties of an orthorhombic phase of MnBi stabilized with Rh additions

    DOE PAGES

    Taufour, Valentin; Thimmaiah, Srinivasa; March, Stephen; ...

    2015-07-28

    The article addresses the possibility of alloy elements in MnBi which may modify the thermodynamic stability of the NiAs-type structure without significantly degrading the magnetic properties. The addition of small amounts of Rh and Mn provides an improvement in the thermal stability with some degradation of the magnetic properties. The small amounts of Rh and Mn additions in MnBi stabilize an orthorhombic phase whose structural and magnetic properties are closely related to the ones of the previously reported high-temperature phase of MnBi (HT MnBi). The properties of the HT MnBi, which is stable between 613 and 719 K, have notmore » been studied in detail because of its transformation to the stable low-temperature MnBi (LT MnBi), making measurements near and below its Curie temperature difficult. The Rh-stabilized MnBi with chemical formula Mn1.0625–xRhxBi [x=0.02(1)] adopts a new superstructure of the NiAs/Ni2In structure family. It is ferromagnetic below a Curie temperature of 416 K. The critical exponents of the ferromagnetic transition are not of the mean-field type but are closer to those associated with the Ising model in three dimensions. The magnetic anisotropy is uniaxial; the anisotropy energy is rather large, and it does not increase when raising the temperature, contrary to what happens in LT MnBi. The saturation magnetization is approximately 3μB/f.u. at low temperatures. Thus, while this exact composition may not be application ready, it does show that alloying is a viable route to modifying the stability of this class of rare-earth-free magnet alloys.« less

  4. Structural and Ferromagnetic Properties of an Orthorhombic Phase of MnBi Stabilized with Rh Additions

    NASA Astrophysics Data System (ADS)

    Taufour, Valentin; Thimmaiah, Srinivasa; March, Stephen; Saunders, Scott; Sun, Kewei; Lamichhane, Tej Nath; Kramer, Matthew J.; Bud'ko, Sergey L.; Canfield, Paul C.

    2015-07-01

    The article addresses the possibility of alloy elements in MnBi which may modify the thermodynamic stability of the NiAs-type structure without significantly degrading the magnetic properties. The addition of small amounts of Rh and Mn provides an improvement in the thermal stability with some degradation of the magnetic properties. The small amounts of Rh and Mn additions in MnBi stabilize an orthorhombic phase whose structural and magnetic properties are closely related to the ones of the previously reported high-temperature phase of MnBi (HT MnBi). To date, the properties of the HT MnBi, which is stable between 613 and 719 K, have not been studied in detail because of its transformation to the stable low-temperature MnBi (LT MnBi), making measurements near and below its Curie temperature difficult. The Rh-stabilized MnBi with chemical formula Mn1.0625 -xRhx Bi [x =0.02 (1 ) ] adopts a new superstructure of the NiAs /Ni2In structure family. It is ferromagnetic below a Curie temperature of 416 K. The critical exponents of the ferromagnetic transition are not of the mean-field type but are closer to those associated with the Ising model in three dimensions. The magnetic anisotropy is uniaxial; the anisotropy energy is rather large, and it does not increase when raising the temperature, contrary to what happens in LT MnBi. The saturation magnetization is approximately 3 μB/f .u . at low temperatures. While this exact composition may not be application ready, it does show that alloying is a viable route to modifying the stability of this class of rare-earth-free magnet alloys.

  5. Crystallization kinetics of orthorhombic paracetamol from supercooled melts studied by non-isothermal DSC.

    PubMed

    Nikolakakis, Ioannis; Kachrimanis, Kyriakos

    2017-02-01

    A simple and highly reproducible procedure was established for the study of orthorhombic paracetamol crystallization kinetics, comprising melting, quench-cooling of the melt and scanning the formed glass by DSC at different heating rates. Results were analyzed on the basis of the mean as well as local values of the Avrami exponent, n, the energy of activation, as well as the Šesták-Berggren two-parameter autocatalytic kinetic model. The mean value of the Avrami kinetic exponent, n, ranged between 3 and 5, indicating deviation from the nucleation and growth mechanism underlying the Johnson-Mehl, Avrami-Kolmogorov (JMAK) model. To verify the extent of the deviation, local values of the Avrami exponent as a function of the volume fraction transformed were calculated. Inspection of the local exponent values indicates that the crystallization mechanism changes over time, possibly reflecting the uncertainty of crystallization onset, instability of nucleation due to an autocatalytic effect of the crystalline phase, and growth anisotropy due to impingement of spherulites in the last stages of crystallization. The apparent energy of activation, Ea, has a rather low mean value, close to 81 kJ/mol, which is in agreement with the observed instability of glassy-state paracetamol. Isoconversional methods revealed that Ea tends to decrease with the volume fraction transformed, possibly because of the different energy demands of nucleation and growth. The exponents of the Šesták-Berggren two-parameter model showed that the crystallized fraction influences the process, confirming the complexity of the crystallization mechanism.

  6. Microstructure and properties of a titanium alloy-orthorhombic titanium aluminide layered composite

    NASA Astrophysics Data System (ADS)

    Galeev, R. M.; Valiakhmetov, O. R.; Safiullin, R. V.; Imaev, V. M.; Imaev, R. M.

    2009-03-01

    The microstructure and tensile properties of a layered composite material fabricated by solid-state bonding of its components using pressure welding are studied at room and elevated temperatures. The components are made of a high-temperature VT25U titanium alloy and an intermetallic alloy ( O alloy) based on orthorhombic titanium aluminide of the composition Ti-23Al-22.7Nb-1.1V-0.6Zr-0.2Si-0.3C (at %). The study of the microstructure and chemical composition of the composite by scanning electron microscopy and energy dispersive X-ray analysis demonstrates that this method of producing a layered composite provides high-quality poreless bonding of materials of different types. The solid-state bonding zone has an intermediate chemical composition. Mechanical tests demonstrate that the room-temperature strength of the composite is comparable with that of the O alloy and is higher than that of the titanium alloy; as the fraction of the titanium alloy in the composite decreases, this strength increases. The relative elongation of the layered composite is found to be higher than that of the O alloy and lower than that of the titanium alloy. In the temperature range 500-700°C, the strength of the composite material is 25% higher than that of the titanium alloy, and its plasticity is lower than that of the titanium alloy. Our method is shown to be promising for producing layered composite materials that have high mechanical properties over a wide temperature range.

  7. High-pressure orthorhombic ferromagnesite as a potential deep-mantle carbon carrier

    SciTech Connect

    Liu, Jin; Lin, Jung -Fu; Prakapenka, Vitali B.

    2015-01-06

    In this study, knowledge of the physical and chemical properties of candidate deep-carbon carriers such as ferromagnesite [(Mg,Fe)CO3] at high pressure and temperature of the deep mantle is necessary for our understanding of deep-carbon storage as well as the global carbon cycle of the planet. Previous studies have reported very different scenarios for the (Mg,Fe)CO3 system at deep-mantle conditions including the chemical dissociation to (Mg,Fe)O+CO2, the occurrence of the tetrahedrally-coordinated carbonates based on CO4 structural units, and various high-pressure phase transitions. Here we have studied the phase stability and compressional behavior of (Mg,Fe)CO3 carbonates up to relevant lower-mantle conditions of approximately 120 GPa and 2400 K. Our experimental results show that the rhombohedral siderite (Phase I) transforms to an orthorhombic phase (Phase II with Pmm2 space group) at approximately 50 GPa and 1400 K. The structural transition is likely driven by the spin transition of iron accompanied by a volume collapse in the Fe-rich (Mg,Fe)CO3 phases; the spin transition stabilizes the high-pressure phase II at much lower pressure conditions than its Mg-rich counterpart. It is conceivable that the low-spin ferromagnesite phase II becomes a major deep-carbon carrier at the deeper parts of the lower mantle below 1900 km in depth.

  8. Bounds and self-consistent estimates for elastic constants of granular polycrystals composed of orthorhombics or crystal with higher symmetries

    SciTech Connect

    Berryman, J. G.

    2011-02-01

    Methods for computing Hashin-Shtrikman bounds and related self-consistent estimates of elastic constants for polycrystals composed of crystals having orthorhombic symmetry have been known for about three decades. However, these methods are underutilized, perhaps because of some perceived difficulties with implementing the necessary computational procedures. Several simplifications of these techniques are introduced, thereby reducing the overall computational burden, as well as the complications inherent in mapping out the Hashin-Shtrikman bounding curves. The self-consistent estimates of the effective elastic constants are very robust, involving a quickly converging iteration procedure. Once these self-consistent values are known, they may then be used to speed up the computations of the Hashin-Shtrikman bounds themselves. It is shown furthermore that the resulting orthorhombic polycrystal code can be used as well to compute both bounds and self-consistent estimates for polycrystals of higher-symmetry tetragonal, hexagonal, and cubic (but not trigonal) materials. The self-consistent results found this way are shown to be the same as those obtained using the earlier methods, specifically those methods designed specially for each individual symmetry type. But the Hashin-Shtrikman bounds found using the orthorhombic code are either the same or (more typically) tighter than those found previously for these special cases (i.e., tetragonal, hexagonal, and cubic). The improvement in the Hashin-Shtrikman bounds is presumably due to the additional degrees of freedom introduced into the available search space.

  9. Optical phonon characteristics of an orthorhombic-transformed polymorph of CaTa2O6 single crystal fibre

    NASA Astrophysics Data System (ADS)

    Almeida, R. M.; Andreeta, M. R. B.; Hernandes, A. C.; Dias, A.; Moreira, R. L.

    2014-03-01

    Infrared-reflectivity spectroscopy and micro-Raman scattering were used to determine the optical phonon features of orthorhombic calcium tantalite (CaTa2O6) single crystal fibres. The fibres, obtained by the Laser-Heated Pedestal Growth method, grew into an ordered cubic structure \\left( Pm\\bar{3} \\right). Long-time annealing was used to induce a polymorphic transformation to an aeschynite orthorhombic structure (Pnma space group). The phase transformation led to the appearance of structural domains and micro-cracks, responsible for diffuse scattering and depolarization of the scattered light in the visible range, but not in the infrared region. Thus, polarized infrared spectroscopy could be performed within oriented single domains, with an appropriate microscope, allowing us to determine all relevant polar phonons of the orthorhombic CaTa2O6. The obtained phononic dielectric response, {{\\epsilon }_{r}} = 22.4 and = 86 × 103 GHz, shows the appropriateness of the material for microwave applications. Totally symmetric Raman modes could be resolved by polarization, after re-polishing the cracked sample surface.

  10. Estimation of effective geostress parameters driven by anisotropic stress and rock-physics models with orthorhombic symmetry

    NASA Astrophysics Data System (ADS)

    Pan, Xinpeng; Zhang, Guangzhi; Yin, Xingyao

    2017-10-01

    Estimation of effective geostress parameters is fundamental to the trajectory design and hydraulic fracturing in shale-gas reservoirs. Considering the shale characteristics of excellent stratification, well-developed cracks or fractures and small-scale pores, an effective or suitable shale anisotropic rock-physics model contributes to achieving the accurate prediction of effective geostress parameters in shale-gas reservoirs. In this paper, we first built a shale anisotropic rock-physics model with orthorhombic symmetry, which helps to calculate the anisotropic and geomechanical parameters under the orthorhombic assumption. Then, we introduced an anisotropic stress model with orthorhombic symmetry compared with an isotropic stress model and a transversely isotropic stress model. Combining the effective estimation of the pore pressure and the vertical stress parameters, we finally obtained the effective geostress parameters including the minimum and maximum horizontal stress parameters, providing a useful guide for the exploration and development in shale-gas reservoirs. Of course, ultimately the optimal choice of the hydraulic-fracturing area may also take into consideration other multi-factors such as the rock brittleness, cracks or fractures, and hydrocarbon distribution.

  11. Effect of orthorhombic-tetragonal phase transition on structure and piezoelectric properties of KNN-based lead-free ceramics.

    PubMed

    Zhang, Yang; Li, Lingyu; Shen, Bo; Zhai, Jiwei

    2015-05-07

    (1 - x)(K0.5Na0.5)0.95Li0.05Nb0.93Sb0.07O3-xSrZrO3 ((1 - x)KNLNS-xSZ) lead free piezoelectric ceramics have been prepared by the conventional solid state reaction method, via adjusting the orthorhombic-tetragonal phase transition temperature to near room temperature with doping SrZrO3, and the effects of SrZrO3 content on polymorphic phase transition have been investigated. These results show that the phase structure of the ceramics was changed from orthorhombic to tetragonal at x ≥ 0.02 mol, and the orthorhombic-tetragonal phase transition temperature was modified to around room temperature with increasing SrZrO3. Remarkable piezoelectric and ferroelectric properties has been obtained in (1 - x)KNLNS-xSZ system with x = 0.02, which showed a piezoelectric parameter of d33 = 256 pC N(-1), Curie temperature Tc = 270 °C, strain levels of 0.16% at 50 kV cm(-1), remnant polarization Pr = 24.9 μC cm(-2) and coercive field Ec = 10.6 kV cm(-1).

  12. Photo-enhanced salt-water splitting using orthorhombic Ag8SnS6 photoelectrodes in photoelectrochemical cells

    NASA Astrophysics Data System (ADS)

    Cheng, Kong-Wei; Tsai, Wei-Tseng; Wu, Yu-Hsuan

    2016-06-01

    Orthorhombic Ag8SnS6 photoelectrodes are prepared on various substrates via reactive sulfurization using the radio-frequency magnetron sputtering of silver-tin metal precursors. Evaluations of the photoelectrochemical performances of Ag8SnS6 photoelectrodes with various levels of silver content are carried out in various aqueous solutions. X-ray diffraction patterns and Hall measurements of samples after a three-stage sulfurization process show that all samples are the pure orthorhombic Ag8SnS6 phase with n-type conductivity. The energy band gaps, carrier concentrations, and mobilities of samples on glass substrates are 1.31-1.33 eV, 7.07 × 1011-8.52 × 1012 cm-3, and 74.9-368 cm2 V-1 s-1, respectively, depending on the [Ag]/[Ag+Sn] molar ratio in samples. The highest photoelectrochemical performances of orthorhombic Ag8SnS6 photoelectrodes in aqueous 0.35 M Na2S + 0.25 M K2SO3 and 0.5 M NaCl solutions are respectively 2.09 and 2.5 mA cm-2 at an applied voltages of 0.9 and 1.23 V vs. a reversible hydrogen electrode under light irradiation with a light intensity of 100 mW cm-2 from a 300-W Xe lamp.

  13. Twinning induced by the rhombohedral to orthorhombic phase transition in lanthanum gallate (LaGaO3)

    NASA Astrophysics Data System (ADS)

    Wang, W. L.; Lu, H. Y.

    2006-10-01

    Phase-transformation-induced twins in pressureless-sintered lanthanum gallate (LaGaO3) ceramics have been analysed using the transmission electron microscopy (TEM). Twins are induced by solid state phase transformation upon cooling from the rhombohedral (r, Rbar{3}c) to orthorhombic ( o, Pnma) symmetry at ˜145°C. Three types of transformation twins {101} o , {121} o , and {123} o were found in grains containing multiple domains that represent orientation variants. Three orthorhombic orientation variants were distinguished from the transformation domains converged into a triple junction. These twins are the reflection type as confirmed by tilting experiment in the microscope. Although not related by group-subgroup relation, the transformation twins generated by phase transition from rhombohedral to orthorhombic are consistent with those derived from taking cubic Pm {bar {3}}m aristotype of the lowest common supergroup symmetry as an intermediate metastable structure. The r→ o phase transition of first order in nature may have occurred by a diffusionless, martensitic-type or discontinuous nucleation and growth mechanism.

  14. An orthorhombic representation of a heterogeneous medium for the finite-difference modelling of seismic wave propagation

    NASA Astrophysics Data System (ADS)

    Kristek, Jozef; Moczo, Peter; Chaljub, Emmanuel; Kristekova, Miriam

    2017-02-01

    The possibility of applying one explicit finite-difference (FD) scheme to all interior grid points (points not lying on a grid border) no matter what their positions are with respect to the material interface is one of the key factors of the computational efficiency of the FD modelling. Smooth or discontinuous heterogeneity of the medium is accounted for only by values of the effective grid moduli and densities. Accuracy of modelling thus very much depends on how these effective grid parameters are evaluated. We present an orthorhombic representation of a heterogeneous medium for the FD modelling. We numerically demonstrate its superior accuracy. Compared to the harmonic-averaging representation the orthorhombic representation is more accurate mainly in the case of strong surface waves that are especially important in local surface sedimentary basins. The orthorhombic representation is applicable to modelling seismic wave propagation and earthquake motion in isotropic models with material interfaces and smooth heterogeneities using velocity-stress, displacement-stress and displacement FD schemes on staggered, partly staggered, Lebedev and collocated grids.

  15. First-principles study of structural and elastic properties of monoclinic and orthorhombic BiMnO3.

    PubMed

    Mei, Zhi-Gang; Shang, Shun-Li; Wang, Yi; Liu, Zi-Kui

    2010-07-28

    The structural and elastic properties of BiMnO(3) with monoclinic (C 2/c) and orthorhombic (Pnma) ferromagnetic (FM) structures have been studied by first-principles calculations within LDA + U and GGA + U approaches. The equilibrium volumes and bulk moduli of BiMnO(3) phases are evaluated by equation of state (EOS) fittings, and the bulk properties predicted by LDA + U calculations are in better agreement with experiment. The orthorhombic phase is found to be more stable than the monoclinic phase at ambient pressure. A monoclinic to monoclinic phase transition is predicted to occur at a pressure of about 10 GPa, which is ascribed to magnetism versus volume instability of monoclinic BiMnO(3). The single-crystal elastic stiffness constants c(ij)s of the monoclinic and orthorhombic phases are investigated using the stress-strain method. The c(46) of the monoclinic phase is predicted to be negative. In addition, the polycrystalline elastic properties including bulk modulus, shear modulus, Young's modulus, bulk modulus-shear modulus ratio, Poisson's ratio, and elastic anisotropy ratio are determined based on the calculated elastic constants. The presently predicted phase transition and elastic properties open new directions for investigation of the phase transitions in BiMnO(3), and provide helpful guidance for the future elastic constant measurements.

  16. Morphology and Electrical Characterization of Reduced Epitaxial Graphene Oxide

    NASA Astrophysics Data System (ADS)

    Hu, Yike; Wu, Xiaosong; Sprinkle, Michael; Madiomanana, Nerasoa; Ruan, Ming; Berger, Claire; de Heer, Walter

    2009-03-01

    We present results for on-chip oxidation of epitaxial graphene and sequential reduction of the insulating graphene oxide layers. In our previous work , we have used the Hummer's method to oxidize epitaxial graphene and used electron beam exposure and heat treatment to reduce the epitaxial graphene oxide (EGO) band gap by changing the degree of oxidation. Here we further explore various oxidation and reduction methods on epitaxial graphene. EGO is characterized by atomic force microscopy, low-energy electron diffraction, ellipsometry, and Raman Spectrometry. Mobility measurements of patterned structures are presented where epitaxial graphene layers pads are seamlessly connected to EGO ribbons.

  17. Molecular Beam Epitaxy of GaN Nanowires on Epitaxial Graphene.

    PubMed

    Fernández-Garrido, Sergio; Ramsteiner, Manfred; Gao, Guanhui; Galves, Lauren A; Sharma, Bharat; Corfdir, Pierre; Calabrese, Gabriele; de Souza Schiaber, Ziani; Pfüller, Carsten; Trampert, Achim; Lopes, João Marcelo J; Brandt, Oliver; Geelhaar, Lutz

    2017-09-13

    We demonstrate an all-epitaxial and scalable growth approach to fabricate single-crystalline GaN nanowires on graphene by plasma-assisted molecular beam epitaxy. As substrate, we explore several types of epitaxial graphene layer structures synthesized on SiC. The different structures differ mainly in their total number of graphene layers. Because graphene is found to be etched under active N exposure, the direct growth of GaN nanowires on graphene is only achieved on multilayer graphene structures. The analysis of the nanowire ensembles prepared on multilayer graphene by Raman spectroscopy and transmission electron microscopy reveals the presence of graphene underneath as well as in between nanowires, as desired for the use of this material as contact layer in nanowire-based devices. The nanowires nucleate preferentially at step edges, are vertical, well aligned, epitaxial, and of comparable structural quality as similar structures fabricated on conventional substrates.

  18. Encapsulated solid phase epitaxy of a Ge quantum well embedded in an epitaxial rare earth oxide.

    PubMed

    Laha, Apurba; Bugiel, E; Jestremski, M; Ranjith, R; Fissel, A; Osten, H J

    2009-11-25

    An efficient method based on molecular beam epitaxy has been developed to integrate an epitaxial Ge quantum well buried into a single crystalline rare earth oxide. The monolithic heterostructure comprised of Gd2O3-Ge-Gd2O3 grown on an Si substrate exhibits excellent crystalline quality with atomically sharp interfaces. This heterostructure with unique structural quality could be used for novel nanoelectronic applications in quantum-effect devices such as nanoscale transistors with a high mobility channel, resonant tunneling diode/transistors, etc. A phenomenological model has been proposed to explain the epitaxial growth process of the Ge layer under oxide encapsulation using a solid source molecular beam epitaxy technique.

  19. Epitaxial growth of three dimensionally structured III-V photonic crystal via hydride vapor phase epitaxy

    SciTech Connect

    Zheng, Qiye; Kim, Honggyu; Zhang, Runyu; Zuo, Jianmin; Braun, Paul V.; Sardela, Mauro; Balaji, Manavaimaran; Lourdudoss, Sebastian; Sun, Yan-Ting

    2015-12-14

    Three-dimensional (3D) photonic crystals are one class of materials where epitaxy, and the resultant attractive electronic properties, would enable new functionalities for optoelectronic devices. Here we utilize self-assembled colloidal templates to fabricate epitaxially grown single crystal 3D mesostructured Ga{sub x}In{sub 1−x}P (GaInP) semiconductor photonic crystals using hydride vapor phase epitaxy (HVPE). The epitaxial relationship between the 3D GaInP and the substrate is preserved during the growth through the complex geometry of the template as confirmed by X-ray diffraction (XRD) and high resolution transmission electron microscopy. XRD reciprocal space mapping of the 3D epitaxial layer further demonstrates the film to be nearly fully relaxed with a negligible strain gradient. Fourier transform infrared spectroscopy reflection measurement indicates the optical properties of the photonic crystal which agree with finite difference time domain simulations. This work extends the scope of the very few known methods for the fabrication of epitaxial III-V 3D mesostructured materials to the well-developed HVPE technique.

  20. Electrostatic transfer of epitaxial graphene to glass.

    SciTech Connect

    Ohta, Taisuke; Pan, Wei; Howell, Stephen Wayne; Biedermann, Laura Butler; Beechem Iii, Thomas Edwin; Ross, Anthony Joseph, III

    2010-12-01

    We report on a scalable electrostatic process to transfer epitaxial graphene to arbitrary glass substrates, including Pyrex and Zerodur. This transfer process could enable wafer-level integration of graphene with structured and electronically-active substrates such as MEMS and CMOS. We will describe the electrostatic transfer method and will compare the properties of the transferred graphene with nominally-equivalent 'as-grown' epitaxial graphene on SiC. The electronic properties of the graphene will be measured using magnetoresistive, four-probe, and graphene field effect transistor geometries [1]. To begin, high-quality epitaxial graphene (mobility 14,000 cm2/Vs and domains >100 {micro}m2) is grown on SiC in an argon-mediated environment [2,3]. The electrostatic transfer then takes place through the application of a large electric field between the donor graphene sample (anode) and the heated acceptor glass substrate (cathode). Using this electrostatic technique, both patterned few-layer graphene from SiC(000-1) and chip-scale monolayer graphene from SiC(0001) are transferred to Pyrex and Zerodur substrates. Subsequent examination of the transferred graphene by Raman spectroscopy confirms that the graphene can be transferred without inducing defects. Furthermore, the strain inherent in epitaxial graphene on SiC(0001) is found to be partially relaxed after the transfer to the glass substrates.

  1. Improved Boat For Liquid-Phase Epitaxy

    NASA Technical Reports Server (NTRS)

    Connolly, John C.

    1991-01-01

    Liquid-phase epitaxial (LPE) growth boat redesigned. Still fabricated from ultra-high-purity graphite, but modified to permit easy disassembly and cleaning, along with improved wiping action for more complete removal of melt to reduce carry-over of gallium. Larger substrates and more uniform composition obtained.

  2. Epitaxial solar-cell fabrication, phase 2

    NASA Technical Reports Server (NTRS)

    Daiello, R. V.; Robinson, P. H.; Kressel, H.

    1977-01-01

    Dichlorosilane (SiH2Cl2) was used as the silicon source material in all of the epitaxial growths. Both n/p/p(+) and p/n/n(+) structures were studied. Correlations were made between the measured profiles and the solar cell parameters, especially cell open-circuit voltage. It was found that in order to obtain consistently high open-circuit voltage, the epitaxial techniques used to grow the surface layer must be altered to obtain very abrupt doping profiles in the vicinity of the junction. With these techniques, it was possible to grow reproducibly both p/n/n(+) and n/p/p(+) solar cell structures having open-circuit voltages in the 610- to 630-mV range, with fill-factors in excess of 0.80 and AM-1 efficiencies of about 13%. Combinations and comparisons of epitaxial and diffused surface layers were also made. Using such surface layers, we found that the blue response of epitaxial cells could be improved, resulting in AM-1 short-circuit current densities of about 30 mA/cm sq. The best cells fabricated in this manner had AM-1 efficiency of 14.1%.

  3. Epitaxial Graphene: A New Material for Electronics

    NASA Astrophysics Data System (ADS)

    de Heer, Walt A.

    2007-10-01

    Graphene multilayers are grown epitaxially on single crystal silicon carbide. This system is composed of several graphene layers of which the first layer is electron doped due to the built-in electric field and the other layers are essentially undoped. Unlike graphite the charge carriers show Dirac particle properties (i.e. an anomalous Berry's phase, weak anti-localization and square root field dependence of the Landau level energies). Epitaxial graphene shows quasi-ballistic transport and long coherence lengths; properties that may persists above cryogenic temperatures. Paradoxically, in contrast to exfoliated graphene, the quantum Hall effect is not observed in high mobility epitaxial graphene. It appears that the effect is suppressed due to absence of localized states in the bulk of the material. Epitaxial graphene can be patterned using standard lithography methods and characterized using a wide array of techniques. These favorable features indicate that interconnected room temperature ballistic devices may be feasible for low dissipation high-speed nano-electronics.

  4. Improved Boat For Liquid-Phase Epitaxy

    NASA Technical Reports Server (NTRS)

    Connolly, John C.

    1991-01-01

    Liquid-phase epitaxial (LPE) growth boat redesigned. Still fabricated from ultra-high-purity graphite, but modified to permit easy disassembly and cleaning, along with improved wiping action for more complete removal of melt to reduce carry-over of gallium. Larger substrates and more uniform composition obtained.

  5. New Sources for Chemical Beam Epitaxy.

    DTIC Science & Technology

    2007-11-02

    TBP, BPE , TDMAP, and TBBDMAP. This work has resulted in: (1) further development of safe and improved sources specifically for chemical beam epitaxy... BPE , TDMAP, and TBBDMAP was performed. The first reported growth of GaInP without precracking the phosphorous source, TDMAP, and the first reported

  6. Identification of the ferroelectric switching process and dopant-dependent switching properties in orthorhombic HfO2: A first principles insight

    NASA Astrophysics Data System (ADS)

    Clima, S.; Wouters, D. J.; Adelmann, C.; Schenk, T.; Schroeder, U.; Jurczak, M.; Pourtois, G.

    2014-03-01

    The origin of the ferroelectric polarization switching in orthorhombic HfO2 has been investigated by first principles calculations. The phenomenon can be regarded as being the coordinated displacement of four O ions in the orthorhombic unit cell, which can lead to a saturated polarization as high as 53 μC/cm2. We show the correlation between the computed polarization reversal barrier and the experimental coercive fields.

  7. Growth of ZnSnN2 by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Feldberg, N.; Aldous, J. D.; Stampe, P. A.; Kennedy, R. J.; Veal, T. D.; Durbin, S. M.

    2014-04-01

    The Zn-IV-N2 family of materials represents a potential earth abundant element alternative to conventional compound semiconductor materials that are based on gallium and indium. While both ZnSiN2 and ZnGeN2 have been studied to some degree, very little is known about the narrow-gap member ZnSnN2. Here, we investigate the growth dynamics of crystalline ZnSnN2 through plasma-assisted molecular beam epitaxy. All films exhibit some degree of crystalline order regardless of growth conditions, although significant tin coverage was observed for films grown with low Zn:Sn flux ratio; Zn flux in particular became increasingly problematic at increased substrate temperatures designed to improve crystallinity. Single-crystal material was achieved through careful optimization of growth parameters. Regardless of deposition conditions or substrate choice, however, all films exhibit a monoclinic structure as opposed to the predicted orthorhombic lattice; this can be directly attributed to sublattice disorder.

  8. Multiferroic fluoride BaCoF4 Thin Films Grown Via Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Borisov, Pavel; Johnson, Trent; García-Castro, Camilo; Kc, Amit; Schrecongost, Dustin; Cen, Cheng; Romero, Aldo; Lederman, David

    Multiferroic materials exhibit exciting physics related to the simultaneous presence of multiple long-range orders, in many cases consisting of antiferromagnetic (AF) and ferroelectric (FE) orderings. In order to provide a new, promising route for fluoride-based multiferroic material engineering, we grew multiferroic fluoride BaCoF4 in thin film form on Al2O3 (0001) substrates by molecular beam epitaxy. The films grow with the orthorhombic b-axis out-of-plane and with three in-plane structural twin domains along the polar c-axis directions. The FE ordering in thin films was verified by FE remanent hysteresis loops measurements at T = 14 K and by room temperature piezoresponse force microscopy (PFM). An AF behavior was found below Neel temperature TN ~ 80 K, which is in agreement with the bulk properties. At lower temperatures two additional magnetic phase transitions at 19 K and 41 K were found. First-principles calculations demonstrated that the growth strain applied to the bulk BaCoF4 indeed favors two canted spin orders, along the b- and a-axes, respectively, in addition to the main AF spin order along the c-axis. Supported by FAME (Contract 2013-MA-2382), WV Research Challenge Grant (HEPC.dsr.12.29), and DMREF-NSF 1434897.

  9. Interface control of a morphotropic phase boundary in epitaxial samarium modified bismuth ferrite superlattices

    NASA Astrophysics Data System (ADS)

    Maran, Ronald; Yasui, Shintaro; Eliseev, Eugene A.; Glinchuk, Maya D.; Morozovska, Anna N.; Funakubo, Hiroshi; Takeuchi, Ichiro; Nagarajan, Valanoor

    2014-12-01

    Interfacial control of a polar-(rhombohedral) to-non-polar (orthorhombic) phase transition in (001)-oriented epitaxial BiFe O3 / (B i1 -xS mx ) Fe O3 superlattices is presented. We demonstrate controlling the composition at which a polar phase transformation takes place by tuning the strength of the interlayer interactions while holding the average composition constant. It is shown that the thickness of the superlattice layers has a strong influence on the interlayer polar coupling, which in turn changes the phase transition. For the shortest periods studied (layers 5- and 10-nm thick) the onset of the phase transition is suppressed along with a significant broadening (as a function of S m3 + concentration) of an incommensurately modulated phase determined by two-dimensional x-ray diffraction mapping. Consequently, a ferroelectric character with robust polarization hysteresis and enhanced dielectric constant is observed even for substitution concentration of S m3 + which would otherwise lead to a leaky paraelectric in single-layer (B i1 -xS mx)Fe O3 films. The experimental results are fully consistent with a mean-field thermodynamic theory which reveals that the strength of the interlayer coupling is strongly affected by the polar-polar interaction across the interface.

  10. An orthorhombic crystal form of cyclohexaicosaose, CA26.32.59 H(2)O: comparison with the triclinic form.

    PubMed

    Nimz, O; Gessler, K; Usón, I; Saenger, W

    2001-11-08

    Cycloamylose containing 26 glucose residues (cyclohexaicosaose, CA26) crystallized from water and 30% (v/v) polyethyleneglycol 400 in the orthorhombic space group P2(1)2(1)2(1) in the highly hydrated form CA26.32.59 H(2)O. X-ray analysis of the crystals at 0.85 A resolution shows that the macrocycle of CA26 is folded into two short left-handed V-amylose helices in antiparallel arrangement and related by a twofold rotational pseudosymmetry as reported recently for the (CA26)(2).76.75 H(2)O triclinic crystal form [Gessler, K. et al. Proc. Natl. Acad. Sci. USA 1999, 96, 4246-4251]. In the orthorhombic crystal form, CA26 molecules are packed in motifs reminiscent of V-amylose in hydrated and anhydrous forms. The intramolecular interface between the V-helices in CA26 is dictated by formation of an extended network of interhelical C-H...O hydrogen bonds; a comparable molecular arrangement is also evident for the intermolecular packing, suggesting that it is a characteristic feature of V-amylose interaction. The hydrophobic channels of CA26 are filled with disordered water molecules arranged in chains and held in position by multiple C-H...O hydrogen bonds. In the orthorhombic and triclinic crystal forms, the structures of CA26 molecules are equivalent but the positions of the individual water molecules are different, suggesting that the patterns of water chains are perturbed even by small structural changes associated with differences in packing arrangements in the two crystal lattices rather than with differences in the CA26 geometry.

  11. Tetragonal-to-Orthorhombic Structural Phase Transition at 90Kin the Superconductor Fe1:01Se

    SciTech Connect

    McQueen, T.M.; Tao, J.; Williams, A.J.; Stephens, P.W.; Zhu, Y.; Ksenofontov, V.; Casper, F.; 4 C.; Cava, R.J.

    2009-07-30

    In this Letter we show that superconducting Fe{sub 1.01}Se undergoes a structural transition at 90 K from a tetragonal to an orthorhombic phase but that nonsuperconducting Fe{sub 1.03}Se does not. High resolution electron microscopy at low temperatures further reveals an unexpected additional modulation of the crystal structure of the superconducting phase that involves displacements of the Fe atoms, and that the nonsuperconducting composition shows a different, complex nanometer-scale structural modulation. Finally, we show that magnetism is not the driving force for the phase transition in the superconducting phase.

  12. 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.

  13. Strain effect on electronic structure and thermoelectric properties of orthorhombic SnSe: A first principles study

    SciTech Connect

    Cuong, Do Duc; Rhim, S. H. Hong, Soon Cheol; Lee, Joo-Hyong

    2015-11-15

    Strain effect on thermoelectricity of orthorhombic SnSe is studied using density function theory. The Seebeck coefficients are obtained by solving Boltzmann Transport equation (BTE) with interpolated band energies. As expected from the crystal structure, calculated Seebeck coefficients are highly anisotropic, and agree well with experiment. Changes in the Seebeck coefficients are presented, when strain is applied along b and c direction with strength from -3% to +3%, where influence by band gaps and band dispersions are significant. Moreover, for compressive strains, the sign change of Seebeck coefficients at particular direction suggests that the bipolar transport is possible for SnSe.

  14. Effect of hydrogen on the structure of quenched orthorhombic titanium aluminide-based alloy and phase transformations during subsequent heating

    NASA Astrophysics Data System (ADS)

    Khadzhieva, O. G.; Illarionov, A. G.; Popov, A. A.; Grib, S. V.

    2013-06-01

    The effect of hydrogen on structure formation and changes in the volume fractions of phases in an alloy based on orthorhombic titanium aluminide ( O phase) alloy upon its quenching is studied. X-ray diffraction analysis is used to determine the lattice parameters of phases. It has been shown that hydrogen is dissolved mainly in the β0 phase. Differential thermal analysis is used to determine stages and temperature ranges of phase transformations during heating; it was found that introduced hydrogen shifts the β0 → O and reverse O → β0 transformations into the low-temperature range; the enthalpies of transformation are calculated.

  15. Magnetic transition anisotropies in orthorhombic LuMnO3 and HoMnO3 multiferroic thin films

    NASA Astrophysics Data System (ADS)

    Tsai, T. Y.; Lin, T. H.; Slowry, S.; Luo, C. W.; Wu, K. H.; Lin, J.-Y.; Uen, T. M.; Juang, J. Y.

    2010-01-01

    We have successfully prepared the b-axis-oriented orthorhombic LuMnO3 (LuMO) and HoMnO3 (HMO) thin films by pulsed laser deposition on (110)-LaAlO3 substrates. The nearly perfect alignment between the film growth orientation and the substrate allows us to study the magnetic transitions along the respective crystal orientation, which has displayed marked anisotropic behaviours. In particular, with the largest ionic size difference between Lu and Ho for the family of RMnO3 displaying the E-type AFM, the effects of lattice distortion on the magnetic transition are compared.

  16. Ground state of orthorhombic RbC60: A high-field electron-spin-resonance investigation

    NASA Astrophysics Data System (ADS)

    Bennati, M.; Griffin, R. G.; Knorr, S.; Grupp, A.; Mehring, M.

    1998-12-01

    We report on electron paramagnetic resonance in the low-temperature phase of orthorhombic RbC60 at 94 and 140 GHz microwave frequencies. Below about 25-30 K characteristic features that could be related to antiferromagnetic resonance (AFMR) or alternatively to spin clusters are clearly distinguished from the conduction-electron spin resonance signal above 50 K. The different scenarios, AFMR vs spin glass or spin clusters, are discussed. If the experimental data are interpreted within the AFMR scenario the corresponding spin-flop field can be estimated to be about 0.34 T.

  17. Wafer bonded epitaxial templates for silicon heterostructures

    DOEpatents

    Atwater, Jr., Harry A.; Zahler, James M.; Morral, Anna Fontcubera I

    2008-03-11

    A heterostructure device layer is epitaxially grown on a virtual substrate, such as an InP/InGaAs/InP double heterostructure. A device substrate and a handle substrate form the virtual substrate. The device substrate is bonded to the handle substrate and is composed of a material suitable for fabrication of optoelectronic devices. The handle substrate is composed of a material suitable for providing mechanical support. The mechanical strength of the device and handle substrates is improved and the device substrate is thinned to leave a single-crystal film on the virtual substrate such as by exfoliation of a device film from the device substrate. An upper portion of the device film exfoliated from the device substrate is removed to provide a smoother and less defect prone surface for an optoelectronic device. A heterostructure is epitaxially grown on the smoothed surface in which an optoelectronic device may be fabricated.

  18. Wafer bonded epitaxial templates for silicon heterostructures

    NASA Technical Reports Server (NTRS)

    Atwater, Harry A., Jr. (Inventor); Zahler, James M. (Inventor); Morral, Anna Fontcubera I (Inventor)

    2008-01-01

    A heterostructure device layer is epitaxially grown on a virtual substrate, such as an InP/InGaAs/InP double heterostructure. A device substrate and a handle substrate form the virtual substrate. The device substrate is bonded to the handle substrate and is composed of a material suitable for fabrication of optoelectronic devices. The handle substrate is composed of a material suitable for providing mechanical support. The mechanical strength of the device and handle substrates is improved and the device substrate is thinned to leave a single-crystal film on the virtual substrate such as by exfoliation of a device film from the device substrate. An upper portion of the device film exfoliated from the device substrate is removed to provide a smoother and less defect prone surface for an optoelectronic device. A heterostructure is epitaxially grown on the smoothed surface in which an optoelectronic device may be fabricated.

  19. Ultrahigh efficiencies in vertical epitaxial heterostructure architectures

    SciTech Connect

    Fafard, S. E-mail: simon.fafard@azastra.com; Proulx, F.; York, M. C. A.; Arès, R.; Aimez, V.; Valdivia, C. E.; Wilkins, M. M.; Hinzer, K.; Masson, D. P.

    2016-02-15

    Optical to electrical power converting semiconductor devices were achieved with breakthrough performance by designing a Vertical Epitaxial Heterostructure Architecture. The devices are featuring modeled and measured conversion efficiencies greater than 65%. The ultrahigh conversion efficiencies were obtained by monolithically integrating several thin GaAs photovoltaic junctions tailored with submicron absorption thicknesses and grown in a single crystal by epitaxy. The heterostructures that were engineered with a number N of such ultrathin junctions yielded an optimal external quantum efficiencies approaching 100%/N. The heterostructures are capable of output voltages that are multiple times larger than the corresponding photovoltage of the input light. The individual nanoscale junctions are each generating up to ∼1.2 V of output voltage when illuminated in the infrared. We compare the optoelectronic properties of phototransducers prepared with designs having 5 to 12 junctions and that are exhibiting voltage outputs between >5 V and >14 V.

  20. Domain epitaxy for thin film growth

    DOEpatents

    Narayan, Jagdish

    2005-10-18

    A method of forming an epitaxial film on a substrate includes growing an initial layer of a film on a substrate at a temperature T.sub.growth, said initial layer having a thickness h and annealing the initial layer of the film at a temperature T.sub.anneal, thereby relaxing the initial layer, wherein said thickness h of the initial layer of the film is greater than a critical thickness h.sub.c. The method further includes growing additional layers of the epitaxial film on the initial layer subsequent to annealing. In some embodiments, the method further includes growing a layer of the film that includes at least one amorphous island.

  1. Photoluminescence studies in epitaxial CZTSe thin films

    NASA Astrophysics Data System (ADS)

    Sendler, Jan; Thevenin, Maxime; Werner, Florian; Redinger, Alex; Li, Shuyi; Hägglund, Carl; Platzer-Björkman, Charlotte; Siebentritt, Susanne

    2016-09-01

    Epitaxial Cu 2 ZnSnSe 4 (CZTSe) thin films were grown by molecular beam epitaxy on GaAs(001) using two different growth processes, one containing an in-situ annealing stage as used for solar cell absorbers and one for which this step was omitted. Photoluminescences (PL) measurements carried out on these samples show no dependence of the emission shape on the excitation intensity at different temperatures ranging from 4 K to 300 K . To describe the PL measurements, we employ a model with fluctuating band edges in which the density of states of the resulting tail states does not seem to depend on the excited charge carrier density. In this interpretation, the PL measurements show that the annealing stage removes a defect level, which is present in the samples without this annealing.

  2. Epitaxy: Programmable Atom Equivalents versus Atoms

    SciTech Connect

    Wang, Mary X.; Seo, Soyoung E.; Gabrys, Paul A.; Fleischman, Dagny; Lee, Byeongdu; Kim, Youngeun; Atwater, Harry A.; MacFarlane, Robert J.; Mirkin, Chad A.

    2017-01-01

    The programmability of DNA makes it an attractive structure-directing ligand for the assembly of nanoparticle superlattices in a manner that mimics many aspects of atomic crystallization. However, the synthesis of multilayer single crystals of defined size remains a challenge. Though previous studies considered lattice mismatch as the major limiting factor for multilayer assembly, thin film growth depends on many interlinked variables. Here, a more comprehensive approach is taken to study fundamental elements, such as the growth temperature and the thermodynamics of interfacial energetics, to achieve epitaxial growth of nanoparticle thin films. Under optimized equilibrium conditions, single crystal, multilayer thin films can be synthesized over 500 × 500 μm2 areas on lithographically patterned templates. Importantly, these superlattices follow the same patterns of crystal growth demonstrated in thin film atomic deposition, allowing for these processes to be understood in the context of well-studied atomic epitaxy, and potentially enabling a nanoscale model to study fundamental crystallization processes.

  3. Ultrahigh efficiencies in vertical epitaxial heterostructure architectures

    NASA Astrophysics Data System (ADS)

    Fafard, S.; York, M. C. A.; Proulx, F.; Valdivia, C. E.; Wilkins, M. M.; Arès, R.; Aimez, V.; Hinzer, K.; Masson, D. P.

    2016-02-01

    Optical to electrical power converting semiconductor devices were achieved with breakthrough performance by designing a Vertical Epitaxial Heterostructure Architecture. The devices are featuring modeled and measured conversion efficiencies greater than 65%. The ultrahigh conversion efficiencies were obtained by monolithically integrating several thin GaAs photovoltaic junctions tailored with submicron absorption thicknesses and grown in a single crystal by epitaxy. The heterostructures that were engineered with a number N of such ultrathin junctions yielded an optimal external quantum efficiencies approaching 100%/N. The heterostructures are capable of output voltages that are multiple times larger than the corresponding photovoltage of the input light. The individual nanoscale junctions are each generating up to ˜1.2 V of output voltage when illuminated in the infrared. We compare the optoelectronic properties of phototransducers prepared with designs having 5 to 12 junctions and that are exhibiting voltage outputs between >5 V and >14 V.

  4. Chemical Beam Epitaxy of ZnSe

    DTIC Science & Technology

    1990-10-17

    is curren:ly underway in Japan and Europe with major investment in funds and manpower. However, the problems which remain are largely still an issue...of availability of suitable materials, specifically availability of p-type ZnSe with sufficient useable hole carrier concentrations. The problem ...contract provided essential seed funding necessary to accumulate sufficient funds to build and equip a state-or-the-art chemical beam epitaxy facility at

  5. Hetero epitaxial graphene on various substrates

    NASA Astrophysics Data System (ADS)

    Harris, Gary; Kaut, Gurpreet; Taylor, Crawford

    2015-03-01

    Large-scale production of graphene is pivotal for the development of graphene-based electronics. These results focus on the synthesis and characterization of graphene layers. Two methods were used to grow graphene films. First, graphene films were epitaxially grown on silicon carbide substrates by thermal decomposition of SiC at high temperature and low pressure. In-house built reactor consisting of induction furnace was used to form epitaxial films for electronic applications. Second, chemical vapor deposition method was used for direct graphene synthesis on 3C-SiC with the use of copper as a catalyst. In thermal CVD process, hydrogen and methane gases were used as precursors. Methane acts as a carbon source and annealing and cooling were done hydrogen environment. Different polytypes of silicon carbide (6H-SiC and 3C-SiC) and their crystal orientations were exploited as substrates to form epitaxial graphene. Hetero epitaxial 3C-SiC epilayer was first deposited on Si substrate using chemical vapor deposition technique in cold wall, low pressure, and horizontal CVD reactor. The reactor temperature, argon pressure, flow rates and concentration of different gases (propane, silane, hydrogen and argon) was investigated to control the growth of 3C-SiC and silicon sublimation rate. The resulting graphene films were confirmed using Raman spectroscopy. Further, graphene films have been characterized with the tools of atomic force microscopy (AFM) and scanning electron microscopy (SEM). Mobility, electrical resistivity and carrier density measurements were taken using hall measurements. NSF_PRDM

  6. Method of deposition by molecular beam epitaxy

    DOEpatents

    Chalmers, Scott A.; Killeen, Kevin P.; Lear, Kevin L.

    1995-01-01

    A method is described for reproducibly controlling layer thickness and varying layer composition in an MBE deposition process. In particular, the present invention includes epitaxially depositing a plurality of layers of material on a substrate with a plurality of growth cycles whereby the average of the instantaneous growth rates for each growth cycle and from one growth cycle to the next remains substantially constant as a function of time.

  7. Method of deposition by molecular beam epitaxy

    DOEpatents

    Chalmers, S.A.; Killeen, K.P.; Lear, K.L.

    1995-01-10

    A method is described for reproducibly controlling layer thickness and varying layer composition in an MBE deposition process. In particular, the present invention includes epitaxially depositing a plurality of layers of material on a substrate with a plurality of growth cycles whereby the average of the instantaneous growth rates for each growth cycle and from one growth cycle to the next remains substantially constant as a function of time. 9 figures.

  8. Optical Epitaxial Growth of Gold Nanoparticle Arrays.

    PubMed

    Huang, Ningfeng; Martínez, Luis Javier; Jaquay, Eric; Nakano, Aiichiro; Povinelli, Michelle L

    2015-09-09

    We use an optical analogue of epitaxial growth to assemble gold nanoparticles into 2D arrays. Particles are attracted to a growth template via optical forces and interact through optical binding. Competition between effects determines the final particle arrangements. We use a Monte Carlo model to design a template that favors growth of hexagonal particle arrays. We experimentally demonstrate growth of a highly stable array of 50 gold particles with 200 nm diameter, spaced by 1.1 μm.

  9. Junction Transport in Epitaxial Film Silicon Heterojunction Solar Cells: Preprint

    SciTech Connect

    Young, D. L.; Li, J. V.; Teplin, C. W.; Stradins, P.; Branz, H. M.

    2011-07-01

    We report our progress toward low-temperature HWCVD epitaxial film silicon solar cells on inexpensive seed layers, with a focus on the junction transport physics exhibited by our devices. Heterojunctions of i/p hydrogenated amorphous Si (a-Si) on our n-type epitaxial crystal Si on n++ Si wafers show space-charge-region recombination, tunneling or diffusive transport depending on both epitaxial Si quality and the applied forward voltage.

  10. Epitaxial nucleation and growth of molecular films

    NASA Astrophysics Data System (ADS)

    Hooks, Daniel Edwin

    2000-10-01

    The last decade has witnessed an increased emphasis on the design and use of molecular-based materials, commonly in thin film form, as components in electronic devices, sensors, displays, and logic elements. The growing interest in films based on molecular components, rather than their more traditional inorganic counterparts, stems largely from the premise that collective optical and electronic properties can be systematically manipulated through molecular design. Many of these properties depend strongly upon film structure and orientation with respect to the substrate upon which they are deposited. This relationship mandates careful attention to the interface between the primary molecular overlayer and the substrate. Further advances in molecular films and multilayer composites based on molecular films require improved understanding of the role of epitaxy in molecular organization as well as the nucleation events that precede film formation. Determination of critical nucleus dimensions and elucidation of the factors that govern critical size are particularly important for fabricating nanoscale molecular features and controlling domain defects in contiguous molecular films. This thesis describes an examination of the role of epitaxy in the growth of molecular films, including a hierarchical classification and grammar of molecular epitaxy, an atomic force microscopy (AFM) investigation of the intercalation of molecular components into multilayer organic-inorganic composites, and an AFM investigation of the nucleation of molecular films.

  11. Epitaxial Crystal Growth: Methods and Materials

    NASA Astrophysics Data System (ADS)

    Capper, Peter; Irvine, Stuart; Joyce, Tim

    The epitaxial growth of thin films of material for a wide range of applications in electronics and optoelectronics is a critical activity in many industries. The original growth technique used, in most instances, was liquid-phase epitaxy (LPE), as this was the simplest and often the cheapest route to producing device-quality layers. These days, while some production processes are still based on LPE, most research into and (increasingly) much of the production of electronic and optoelectronic devices now centers on metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). These techniques are more versatile than LPE (although the equipment is more expensive), and they can readily produce multilayer structures with atomic-layer control, which has become more and more important in the type of nanoscale engineering used to produce device structures in as-grown multilayers. This chapter covers these three basic techniques, including some of their more common variants, and outlines the relative advantages and disadvantages of each. Some examples of growth in various important systems are also outlined for each of the three techniques.

  12. Electron holography of devices with epitaxial layers

    SciTech Connect

    Gribelyuk, M. A. Ontalus, V.; Baumann, F. H.; Zhu, Z.; Holt, J. R.

    2014-11-07

    Applicability of electron holography to deep submicron Si devices with epitaxial layers is limited due to lack of the mean inner potential data and effects of the sample tilt. The mean inner potential V{sub 0} = 12.75 V of the intrinsic epitaxial SiGe was measured by electron holography in devices with Ge content C{sub Ge} = 18%. Nanobeam electron diffraction analysis performed on the same device structure showed that SiGe is strain-free in [220] direction. Our results showed good correlation with simulations of the mean inner potential of the strain-free SiGe using density function theory. A new method is proposed in this paper to correct electron holography data for the overlap of potentials of Si and the epitaxial layer, which is caused by the sample tilt. The method was applied to the analysis of the dopant diffusion in p-Field-effect Transistor devices with the identical gate length L = 30 nm, which had alternative SiGe geometry in the source and drain regions and was subjected to different thermal processing. Results have helped to understand electrical data acquired from the same devices in terms of dopant diffusion.

  13. Epitaxy: Programmable Atom Equivalents Versus Atoms.

    PubMed

    Wang, Mary X; Seo, Soyoung E; Gabrys, Paul A; Fleischman, Dagny; Lee, Byeongdu; Kim, Youngeun; Atwater, Harry A; Macfarlane, Robert J; Mirkin, Chad A

    2017-01-24

    The programmability of DNA makes it an attractive structure-directing ligand for the assembly of nanoparticle (NP) superlattices in a manner that mimics many aspects of atomic crystallization. However, the synthesis of multilayer single crystals of defined size remains a challenge. Though previous studies considered lattice mismatch as the major limiting factor for multilayer assembly, thin film growth depends on many interlinked variables. Here, a more comprehensive approach is taken to study fundamental elements, such as the growth temperature and the thermodynamics of interfacial energetics, to achieve epitaxial growth of NP thin films. Both surface morphology and internal thin film structure are examined to provide an understanding of particle attachment and reorganization during growth. Under equilibrium conditions, single crystalline, multilayer thin films can be synthesized over 500 × 500 μm(2) areas on lithographically patterned templates, whereas deposition under kinetic conditions leads to the rapid growth of glassy films. Importantly, these superlattices follow the same patterns of crystal growth demonstrated in atomic thin film deposition, allowing these processes to be understood in the context of well-studied atomic epitaxy and enabling a nanoscale model to study fundamental crystallization processes. Through understanding the role of epitaxy as a driving force for NP assembly, we are able to realize 3D architectures of arbitrary domain geometry and size.

  14. Selective epitaxy using the gild process

    DOEpatents

    Weiner, Kurt H.

    1992-01-01

    The present invention comprises a method of selective epitaxy on a semiconductor substrate. The present invention provides a method of selectively forming high quality, thin GeSi layers in a silicon circuit, and a method for fabricating smaller semiconductor chips with a greater yield (more error free chips) at a lower cost. The method comprises forming an upper layer over a substrate, and depositing a reflectivity mask which is then removed over selected sections. Using a laser to melt the unmasked sections of the upper layer, the semiconductor material in the upper layer is heated and diffused into the substrate semiconductor material. By varying the amount of laser radiation, the epitaxial layer is formed to a controlled depth which may be very thin. When cooled, a single crystal epitaxial layer is formed over the patterned substrate. The present invention provides the ability to selectively grow layers of mixed semiconductors over patterned substrates such as a layer of Ge.sub.x Si.sub.1-x grown over silicon. Such a process may be used to manufacture small transistors that have a narrow base, heavy doping, and high gain. The narrowness allows a faster transistor, and the heavy doping reduces the resistance of the narrow layer. The process does not require high temperature annealing; therefore materials such as aluminum can be used. Furthermore, the process may be used to fabricate diodes that have a high reverse breakdown voltage and a low reverse leakage current.

  15. Growth of pseudomorphic structures through organic epitaxy

    SciTech Connect

    Kaviyil, Sreejith Embekkat; Sassella, Adele; Borghesi, Alessandro; Campione, Marcello; Su Genbo; He Youping; Chen Chenjia

    2012-12-14

    The control of molecular orientation in thin solid film phases of organic semiconductors is a basic factor for the exploitation of their physical properties for optoelectronic devices. We compare structural and optical properties of thin films of the organic semiconductor {alpha}-quarterthiophene grown by molecular beam epitaxy on different organic substrates. We show how epitactic interactions, characteristic of the surface of organic crystals, can drive the orientation of the crystalline overlayer and the selection of specific polymorphs and new pseudomorphic phases. We identify a key role in this phenomenon played by the marked groove-like corrugations present in some organic crystal surfaces. Since different polymorphs possess rather different performance in terms of, e.g., charge carrier mobility, this strategy is demonstrated to allow for the growth of oriented phases with enhanced physical properties, while keeping the substrate at room temperature. These results provide useful guidelines for the design of technological substrates for organic epitaxy and they substantiate the adoption of an organic epitaxy approach for the fabrication of optoelectronic devices based on thin films of organic semiconductors.

  16. Low temperature laser molecular beam epitaxy and characterization of AlGaN epitaxial layers

    NASA Astrophysics Data System (ADS)

    Tyagi, Prashant; Ch., Ramesh; Kushvaha, S. S.; Kumar, M. Senthil

    2017-05-01

    We have grown AlGaN (0001) epitaxial layers on sapphire (0001) by using laser molecular beam epitaxy (LMBE) technique. The growth was carried out using laser ablation of AlxGa1-x liquid metal alloy under r.f. nitrogen plasma ambient. Before epilayer growth, the sapphire nitradation was performed at 700 °C using r.f nitrogen plasma followed by AlGaN layer growth. The in-situ reflection high energy electron diffraction (RHEED) was employed to monitor the substrate nitridation and AlGaN epitaxial growth. High resolution x-ray diffraction showed wurtzite hexagonal growth of AlGaN layer along c-axis. An absorption bandgap of 3.97 eV is obtained for the grown AlGaN layer indicating an Al composition of more than 20 %. Using ellipsometry, a refractive index (n) value of about 2.19 is obtained in the visible region.

  17. Silicon epitaxy process recipe and tool configuration optimization

    NASA Astrophysics Data System (ADS)

    Moy, W. H.; Cheong, K. Y.

    2017-07-01

    Silicon epitaxy is widely used in semiconductor fabrication due to its ability to produce high quality and low cost thin film. Epitaxy optimized process condition with respect to the process recipe and tool for the maximization of n-type epitaxial production has been investigated. For standard recipe of an epitaxy process, there are seven main steps, namely purge, ramp, bake, stab, deposition, post and cooling. This project focuses on the recipe optimization on ramp, bake and stab steps. For the tool configuration, cool-down step has been optimized. Impact on slip, haze, wafers warpage and crystal originated particles have been investigated.

  18. Orthorhombic phases with large unit cells coexisting with the decagonal quasicrystal in an AlCoNiTb alloy

    SciTech Connect

    Yu, R.C. . Beijing Lab. of Electron Microscopy Jilin Univ., Changchun . Dept. of Physics); Li, X.Z.; Zhang, Z.; Kuo, K.H. . Beijing Lab. of Electron Microscopy); Xu, D.P.; Su, W.H. . Dept. of Physics)

    1994-11-15

    Elser and Henley suggested that if the irrational golden number [tau] = (1 + [radical]5)/2 associated with the three mutually orthogonal, equivalent twofold axes in an IQC (icosahedral quasicrystal) is approximated by a rational ratio of two consecutive Fibonacci numbers (0, 1, 1, 2, 3, 5, 8, [hor ellipsis], F[sub 0] = 0, F[sub 1] = 1, and F[sub n+1] = F[sub n] + F[sub n[minus]1]), such as F[sub n+1]/F[sub n] = 1/0, 1/1, 2/1, 3/2, 5/3, 8/5, [hor ellipsis], then a cubic crystalline phase generally called an approximant will result. Such an analysis has been extended later to 2-dimensional decagonal quasicrystals (DQCs). If the irradiation [tau] along two mutually orthogonal, non-equivalent, quasiperiodic twofold directions perpendicular to the periodic tenfold axis of a DQC is replaced by rational ratios F[sub n+1]/F[sub n], an orthorhombic approximant with a large unit cell will form. This not only explains the existing orthorhombic Al-TM (transitional metals) phases with large unit cells, such as Al[sub 60]Mn[sub 11]Ni[sub 4] and Al[sub 3]Mn, but also predicts many new approximants with even larger unit cells some of which have been found experimentally afterwards.

  19. Phase stability, mechanical and thermodynamic properties of orthorhombic and trigonal MgSiN2: an ab initio study

    NASA Astrophysics Data System (ADS)

    Arab, Fahima; Sahraoui, F. Ali; Haddadi, Khelifa; Bouhemadou, Abdelmadjid; Louail, Layachi

    2016-05-01

    Structural stability and mechanical and thermodynamic properties of the orthorhombic and trigonal MgSiN2 polymorphs (or-MgSiN2 and tr-MgSiN2) were investigated through density functional theory and quasi-harmonic Debye model (QHDM). Our calculations show that or-MgSiN2 is energetically the stable polymorph at low pressure, in agreement with previous experimental and theoretical study. Under pressure, a crystallographic transition from the orthorhombic structure to the trigonal one occurs around 25, 17.45 and 19.05 GPa as obtained from the generalized gradient approximation of Perdew-Wang (GGA-PW91), the generalized gradient approximation parameterized recently by Perdew et al (GGA-PBEsol) and the local density approximation developed by Ceperley and Alder and parameterized by Perdew and Zunger (LDA-CAPZ), respectively. Single-crystalline and polycrystalline elastic constants and related properties, namely Vickers hardness, acoustic Grüneisen parameter, minimum thermal conductivity, isotropic sound velocities and Debye temperature, were numerically estimated for both or-MgSiN2 and tr-MgSiN2. We have showed that the hardness of tr-MgSiN2 is comparable to that of the harder materials like c-BN and B6O. Temperature and pressure dependencies of volume, bulk modulus, thermal expansion, Grüneisen parameter, heat capacities and Debye temperature were investigated using QHDM.

  20. Luminescence of Bi3+ in the orthorhombic perovskites, SrB4+O3 (B4+=Zr, Sn)

    NASA Astrophysics Data System (ADS)

    Srivastava, Alok M.

    2017-10-01

    This paper examines the optical properties of Bi3+ in the orthorhombic perovskites SrB4+O3 [B4+=Sn, Zr]. The luminescence of SrZrO3 is associated with emission from the D-state that corresponds with the Bi3+ (6s2) -Zr4+ (4d0) charge transfer transition. The emission spectrum as a function of temperature was monitored for SrSnO3:Bi3+. At low temperatures, the localized 3P0,1 → 1S0 transition dominates the emission spectrum. With increasing temperature, the localized emission quenches in favor of emission from the D-state. A comparative study of the Bi3+ luminescence in the orthorhombic perovskites CaZrO3, CaSnO3, SrZrO3 and SrSnO3 shows that D-state emission occurs when the fundamental absorption band of the perovskite host lattice is less than about 6 eV.

  1. Field Induced Phase Transition with Quadrupole Fluctuation in HoFe2Al10 with Orthorhombic Symmetry

    NASA Astrophysics Data System (ADS)

    Kamikawa, Shuhei; Ishii, Isao; Takezawa, Kohki; Sakami, Tatsuhiro; Nakagawa, Fumiya; Tanida, Hiroshi; Sera, Masafumi; Suzuki, Takashi

    2017-04-01

    To explore phase transitions in HoFe2Al10 with an orthorhombic structure, we performed ultrasonic measurements on transverse elastic moduli C55 and C66 under magnetic fields H. At zero magnetic field, C55 and C66 show an elastic softening down to 0.5 K without a clear anomaly, suggesting that no phase transition exists at zero magnetic field. However, in H along the a- and c-axes, the softening of C55 under 0.6 (0.4) T stops at TQ = 0.8 (0.75) K for H || a (c). Below TQ, C55 shows an elastic hardening. With further increasing H, we observed a remarkable softening of C55 toward TQ. C66 also shows a kink anomaly at TQ in H || a and c. From the results, we clarified the field induced phase transition for H || a and c in HoFe2Al10. The minimum point of C55 at TQ suggests that the field induced phase transition results from a quadrupolar ordering with the order parameter of quadrupole Ozx despite a singlet ground state under an orthorhombic crystal electric field in HoFe2Al10.

  2. Orthorhombic fulleride (CH3NH2)K3C60 close to Mott-Hubbard instability: Ab initio study

    NASA Astrophysics Data System (ADS)

    Potočnik, Anton; Manini, Nicola; Komelj, Matej; Tosatti, Erio; Arčon, Denis

    2012-08-01

    We study the electronic structure and magnetic interactions in methylamine-intercalated orthorhombic alkali-doped fullerene (CH3NH2)K3C60 within the density functional theory. As in the simpler ammonia intercalated compound (NH3)K3C60, the orthorhombic crystal-field anisotropy Δ lifts the t1u triple degeneracy at the Γ point and drives the system deep into the Mott-insulating phase. However, the computed Δ and conduction electron bandwidth W cannot alone account for the abnormally low experimental Néel temperature, TN=11 K, of the methylamine compound, compared to the much higher value TN=40 K of the ammonia one. Significant interactions between CH3NH2 and C603- are responsible for the stabilization of particular fullerene-cage distortions and the ensuing low-spin S=1/2 state. These interactions also seem to affect the magnetic properties, as interfullerene exchange interactions depend on the relative orientation of deformations of neighboring C603- molecules. For the ferro-orientational order of CH3NH2-K+ groups we find an apparent reduced dimensionality in magnetic exchange interactions, which may explain the suppressed Néel temperature. The disorder in exchange interactions caused by orientational disorder of CH3NH2-K+ groups could further contribute to this suppression.

  3. Electrochemical characterization of orthorhombic Na{sub x}MnO{sub 2} for alkali metal polymer batteries

    SciTech Connect

    Doeff, M.M.; Ding, Lie; DeJonghe, L.C.

    1995-04-01

    Electrochemical potential spectroscopy (ECPS) has been used successfully to observe and explain ordering transitions in orthorhombic Na{sub x}MnO{sub 2} as it is discharged in a sodium/polymer cell. Features can be assigned on the basis of sequential filling of sites in the small and then the large tunnels of the structure as the reduction progresses. Intercalation of lithium into Na{sub x}MnO{sub 2} may be less straightforward than that of sodium, and is worthy of investigation by ECPS. Li/Na{sub x}MnO{sub 2} cells have a greater discharge capacity than Na/Na{sub x}MnO{sub 2} cells, suggesting that more than four lithiums per large tunnel can be inserted. (It is also possible, but less likely that more than one lithium can be placed inside the small tunnels.) This implies that the sites for lithium occupancy might be somewhat different than that for sodium. Further investigation into the properties of orthorhombic Na{sub x}MnO{sub 2} and its utility as a positive electrode for rechargeable sodium and lithium cells is presently underway in this laboratory.

  4. Composition and temperature-induced structural evolution in La, Sm, and Dy substituted BiFeO3 epitaxial thin films at morphotropic phase boundaries

    NASA Astrophysics Data System (ADS)

    Kan, Daisuke; Cheng, Ching-Jung; Nagarajan, Valanoor; Takeuchi, Ichiro

    2011-07-01

    Detailed structural investigations on the substitution-induced structural phase transition from the rhombohedral phase to an orthorhombic phase in (Bi,RE)FeO3 epitaxial thin films (RE = La, Sm, and Dy) grown on (100) SrTiO3 substrates are presented. X ray diffraction reveals that the unit cell dimensions of the orthorhombic phase are strongly dependent on the type of the RE dopant. For RE = La3+ ion, which has an ionic size comparable to the Bi3+ ion, the unit cell is found to be a0 × a0 × 2a0, where a0 is the pseudo-cubic lattice parameter. This is in contrast with the √2a0 × √2a0 × 2a0 unit cell for the case of smaller ionic radius RE (= Sm and Dy) elements. While clear double-hysteresis loops in the polarization versus electric-field curves due to field-induced transitions are observed for smaller ionic radius RE (= Sm and Dy), no signature of the double hysteresis loops is observed for the RE = La case across the structural boundary. We have also performed systematic tracking of the structural phases as functions of the RE composition and temperature, based on which we propose a phase diagram. This work reveals that the ionic size of the RE element plays a critical role in the evolution of the structural and functional properties of RE-substituted BiFeO3 thin film materials systems.

  5. Defect-free epitaxial lateral overgrowth of oxidized (111) Si by liquid phase epitaxy

    NASA Astrophysics Data System (ADS)

    Bergmann, R.; Bauser, E.; Werner, J. H.

    1990-07-01

    We report on epitaxial lateral overgrowth of Si on oxidized (111) Si wafers by liquid phase epitaxy. The growth starts in oxide-free seeding windows and proceeds laterally over the SiO2. Growth effectively ceases when (111) sidewalls form. This observation allows the development of a geometrical model that, for the first time, explains the observed dependence of the overgrowth width on the orientation of the seeding windows. We obtain a maximum overgrowth width of 120-130 μm and a maximum aspect ratio of 40:1. Transmission electron microscopy reveals no crystallographic defects in the overgrown lamellae.

  6. Epitaxial Approaches to Carbon Nanotube Organization

    NASA Astrophysics Data System (ADS)

    Ismach, Ariel

    Carbon nanotubes have unique electronic, mechanical, optical and thermal properties, which make them ideal candidates as building blocks in nano-electronic and electromechanical systems. However, their organization into well-defined geometries and arrays on surfaces remains a critical challenge for their integration into functional nanosystems. In my PhD, we developed a new approach for the organization of carbon nanotubes directed by crystal surfaces. The principle relies on the guided growth of single-wall carbon nanotubes (SWNTs) by atomic features presented on anisotropic substrates. We identified three different modes of surface-directed growth (or 'nanotube epitaxy'), in which the growth of carbon nanotubes is directed by crystal substrates: We first observed the nanotube unidirectional growth along atomic steps ('ledge-directed epitaxy') and nanofacets ('graphoepitaxy') on the surface of miscut C-plane sapphire and quartz. The orientation along crystallographic directions ('lattice-directed epitaxy') was subsequently observed by other groups on different crystals. We have proposed a "wake growth" mechanism for the nanotube alignment along atomic steps and nanofacets. In this mechanism, the catalyst nanoparticle slides along the step or facet, leaving the nanotube behind as a wake. In addition, we showed that the combination of surface-directed growth with external forces, such as electric-field and gas flow, can lead to the simultaneous formation of complex nanotube structures, such as grids and serpentines. The "wake growth" model, which explained the growth of aligned nanotubes, could not explain the formation of nanotube serpentines. For the latter, we proposed a "falling spaghetti" mechanism, in which the nanotube first grows by a free-standing process, aligned in the direction of the gas flow, then followed by absorption on the stepped surface in an oscillatory manner, due to the competition between the drag force caused by the gas flow on the suspended

  7. Metalorganic vapor phase epitaxy of ternary rhombohedral (Bi1-xSbx) 2 Se3 solid solutions

    NASA Astrophysics Data System (ADS)

    Kuznetsov, P. I.; Yakushcheva, G. G.; Shchamkhalova, B. S.; Luzanov, V. A.; Temiryazev, A. G.; Jitov, V. A.

    2016-01-01

    We studied the metalorganic vapor phase epitaxy (MOVPE) of (Bi1-xSbx) 2Se3 solid solution films with a different Sb content on (001) Al2O3 substrates with thin ZnSe buffer layer in the range of temperatures 250-480 °C. As-grown films were studied by atom force and scanning electron microscopy (AFM and SEM), Raman spectroscopy and X-ray diffractometry (XRD) techniques. To determine the elemental composition of the grown films, we used an energy dispersive spectrometer (EDS). The dependencies of the crystal structure of films on the growth temperature and Sb content (0 ≤ x ≤ 1) were explored. At different growth temperatures we obtained the following bismuth compounds: the films grown at the temperature of 370 °C or lower consist of the pure Bi phase, whereas we got the Bi4Se3 phase at 380 °C, the phase BiSe at 430 °C and Bi2Se3 at the temperature of 460 °C or above. We found out that at the temperature of 480 °C the single-phase films of (Bi1-xSbx) 2Se3 with rhombohedral and orthorhombic lattices are realized when x is less than 0.25 and greater than 0.935, respectively. For 0.25 < x < 0.935 the grown films are composites of rhombohedral and orthorhombic phases. At the temperature of 440 °C we obtained films consisting of three rhombohedral phases (Bi1-xSbx) 4Se3, (Bi1-xSbx) Se and Bi. The room temperature transport properties of rhombohedral samples were characterized using the Van der Pauw technique.

  8. First-principles study of the photovoltaic properties of orthorhombic Ca2Si1-xPx (0

    NASA Astrophysics Data System (ADS)

    Cen, Weifu; Yang, Yinye; Fan, Menghui

    2017-06-01

    Electronic structure and optical properties of simple orthorhombic Ca2Si1-xPx have been calcu-lated by the first-principles methods. The result shown that the band gap of the simple ortho-rhombic Ca2Si1-xPx was still a direct semiconductor and the band gap was increased with the concentration of P impurity increased. The dielectric constant and refractive index were in-creased with the concentration of P impurity increased. The extinction coefficient, the reflectivi-ty, the absorption and the conductivity have significant changed in the energy range of 0eV∼1eV. Therefore, Transmission property of energy band structure and optical properties of simple or- thorhombic Ca2Si1-xPx were changed by changing the impurity concentration. It is a useful method for modulating photoelectric transmission property of the simple orthorhombic Ca2Si1-xPx.

  9. Hot-Dipped Metal Films as Epitaxial Substrates

    NASA Technical Reports Server (NTRS)

    Shlichta, P. J.

    1985-01-01

    Multistep process forms semiconductor devices on macrocrystalline films of cadmium or zinc. Solar-cell fabrication processes use hot-dipped macrocrystalline films on low-cost sheet-metal base as substrates for epitaxy. Epitaxial layers formed by variety of methods of alternative sequence paths. Solar cells made economically by forming desired surface substance directly on metal film by chemical reactions.

  10. High quality thick epitaxial films for power semiconductor devices

    NASA Astrophysics Data System (ADS)

    Chang, Hsueh-Rong; Temple, V. A. K.

    1986-01-01

    High quality epitaxial layers with low defect levels are the key to fabrication of high voltage power devices. Growth of 100 μm thick epitaxial layers has been performed using a thermally driven chemical vapor deposition process. Three important parameters that have significant influence on epitaxy quality have been identified: substrate surface condition, reactor system cleanliness, and deposition process. The prerequisite p- n- p structure of a 6 kV thyristor was fabricated using 100 μm thick epitaxial layers to form the p-base. Defect density (hillocks and dislocations) in epitaxial layers has been correlated with the breakdown voltage of the p- n- p structure. It was found that an order of magnitude improvement of the defect level was obtained using well polished substrates instead of poorly polished substrates. Further improvement was achieved with the use of an etched reactor system before epitaxial growth, resulting in the reduction of defect density by another order of magnitude. A new cycled process, consisting of successive H 2 purges and deposition steps, is proposed that effectively reduces the defect level by an additional factor of 4, as compared with the conventional continuous deposition process. Specular epitaxial layers without spikes were obtained. Experimental results showed that for thick epitaxial films (100 μm), a susceptor with round-bottomed depressions provides higher dislocation density than one with flat-bottomed depressions, leading to a lower breakdown voltage of test devices.

  11. Sequential imposed layer epitaxy of cuprate films

    SciTech Connect

    Laguees, M.; Tebbji, H.; Mairet, V.; Hatterer, C.; Beuran, C.F.; Hass, N.; Xu, X.Z. ); Cavellin, C.D. )

    1994-02-01

    Layer-by-layer epitaxy has been used to grow cuprate films since the discovery of high-Tc compounds. This deposition technique is in principle suitable for the growth of layered crystalline structures. However, the sequential deposition of atomic layer by atomic layer of cuprate compounds has presently not been optimized. Nevertheless, this deposition process is the only one which allows one to build artificial cell structures such as Bi[sub 2]Sr[sub 2]Ca[sub (n[minus]1)]Cu[sub n]O[sub y] with n as large as 10. This process will also be the best one to grow films of the so-called infinite layer phase compounds belonging to the Sr[sub 1[minus]x]Ca[sub x]CuO[sub 2] family, in order to improve the transport properties and the morphological properties of the cuprate films. When performed at high substrate temperature (typically more than 600[degree]C), the layer-by-layer epitaxy of cuprates exhibits usually 3D aggregate nucleation. Then the growth of the film no longer obeys the layer-by-layer sequence imposed during the deposition. We present here two experimental situations of true 2D sequential imposed layer epitaxy; the growth at 500[degree]C under atomic oxygen pressure of Bi[sub 2]Sr[sub 2]CuO[sub 6] and of Sr[sub 1[minus]x]Ca[sub y]CuO[sub 2] phases. 20 refs., 2 figs.

  12. Microstructure and Mechanics of Superconductor Epitaxy via the Chemical Solution Deposition Method

    SciTech Connect

    Frederick F. Lange

    2006-11-30

    funding was intermittent to say the least, and funding to support the student and the research expenses has to be supplemented by Lange’s gift funds. During the first part of the second year, strontium zirconate was identified as an alternative to lanthanum manganite as a buffer layer for use on the IBAD MgO superconducting wire. A lattice parameter of 4.101 Angstroms offers a reduced lattice mismatch between the MgO and SrZrO3. Studies were focused on investigating hybrid precursor routes, combining Sr acetate with a number of different Zr alkoxides. Initial results from heat treating precursors to form powders are positive with the formation of orthorhombic SrZrO3 at temperatures between 800°C and 1100°C under a reducing atmosphere of Ar – 5% H2. Buffer layer research on RABiTS substrates were centered on GdAlO3 (3.71 Å) and YAlO3 (3.68 Å) buffer layer materials. Powder experiments in YAlO3 have shown the perovskite phase to be metastable at processing temperatures below 1500 °C. Experiments involving spin coating of YAlO3 precursors have found significant problems involved with wettability of the YAlO3 precursor (Yttrium acetate, Aluminum tri-sec butoxide, DI water and Formic Acid) on RABiTS substrates; this, and the demise of the funds precluded further research using YAlO3. The diminished funds for the second year, and the small, tricked funds during the third year lead to a redirection of the student to another research area., and a stop to any experimental achievements that were much too ambition relative to the available funds. The only positive results obtained during this latter period was the understanding why two dissimilar structures could result in an epitaxial relation. It was shown that two rules of crystal chemistry, cation/anion coordination and charge balance, could be applied to understand the epitaxy of SrTiO3 on Ni c(2 X 2)S, TiO2 (anatase) on LaAlO3, TiO2 (rutile) on r-plane Al2O3, and Zr1-x(Yx)O2 on (0001) Al2O3. This new understanding of

  13. Epitaxial Growth of GeGaAs.

    DTIC Science & Technology

    1981-06-01

    liquid solvent for epitaxial growth of Ge. Because of the finite solubility of GaAs in Pb (7 x 10-4 atomic fraction at 500°C) relatively fast initial...mixture of Pb and Sn was used as a melt. The solubility of Ge in a PbSn eutetic mixture is significantly higher than the solubility of Ge in pure Pb...shallow donor acceptor levels. Addition of a deep level to the crystal lat- tice at this point would further pin the fermi level near mid-gap

  14. Epitaxy of layered semiconductor thin films

    NASA Astrophysics Data System (ADS)

    Brahim Otsmane, L.; Emery, J. Y.; Jouanne, M.; Balkanski, M.

    1993-03-01

    Epilayers of InSe on InSe(00.1) and GaSe(00.1) have been grown by the molecular beam epitaxy (MBE) technique. Raman spectroscopy was used for a characterization of the structure and crystallinity in InSe/InSe(00.1) (homoepitaxy) and InSe/GaSe(00.1) (heteroepitaxy). The Raman spectra of the InSe thin films are identical to those of polytype γ-InSe. An activation of the E(LO) mode at 211 cm -1 is observed in these films here. Scanning electron microscopy (SEM) is also used to investigate surfaces of these films.

  15. Perspective: Oxide molecular-beam epitaxy rocks!

    SciTech Connect

    Schlom, Darrell G.

    2015-06-01

    Molecular-beam epitaxy (MBE) is the “gold standard” synthesis technique for preparing semiconductor heterostructures with high purity, high mobility, and exquisite control of layer thickness at the atomic-layer level. Its use for the growth of multicomponent oxides got off to a rocky start 30 yr ago, but in the ensuing decades, it has become the definitive method for the preparation of oxide heterostructures too, particularly when it is desired to explore their intrinsic properties. Examples illustrating the unparalleled achievements of oxide MBE are given; these motivate its expanding use for exploring the potentially revolutionary states of matter possessed by oxide systems.

  16. Epitaxial superlattices of ionic conductor oxides

    NASA Astrophysics Data System (ADS)

    Orsini, A.; Medaglia, P. G.; Sanna, S.; Traversa, E.; Licoccia, S.; Tebano, A.; Balestrino, G.

    2009-07-01

    Pulsed Laser Deposition technique was used to engineer heterostructures of Yttrium-stabilized Zirconia (YSZ) and Gadolinium-doped Ceria (GDC) on perovskite substrates like Neodymium Gallate (NGO) and Strontium Titanate (STO). Epitaxial superlattices of the same number of layers of both materials were deposited with each block thickness as thin as 2 unit cells up to 30 unit cells. X-ray diffraction (XRD) investigation of the (002) symmetrical reflection allowed to evaluate the amount of material deposited in each layer constituting the superlattices. (113) asymmetrical reflections were analyzed to investigate strain effects on YSZ and GDC lattice parameters, evidencing the cube on cube growth of these films.

  17. Large area epitaxial germanane for electronic devices

    NASA Astrophysics Data System (ADS)

    Amamou, Walid; Odenthal, Patrick M.; Bushong, Elizabeth J.; O'Hara, Dante J.; Luo, Yunqiu Kelly; van Baren, Jeremiah; Pinchuk, Igor; Wu, Yi; Ahmed, Adam S.; Katoch, Jyoti; Bockrath, Marc W.; Tom, Harry W. K.; Goldberger, Joshua E.; Kawakami, Roland K.

    2015-09-01

    We report the synthesis and transfer of epitaxial germanane (GeH) onto arbitrary substrates by electrochemical delamination and investigate its optoelectronic properties. GeH films with thickness ranging from 1 to 600 nm (2-1000 layers) and areas up to ˜1 cm2 have been reliably transferred and characterized by photoluminescence, x-ray diffraction, and energy-dispersive x-ray spectroscopy. Wavelength dependent photoconductivity measurements on few-layer GeH exhibit an absorption edge and provide a sensitive characterization tool for ultrathin germanane materials. The transfer process also enables the possibility of integrating germanane into vertically stacked heterostructures.

  18. Interfacing epitaxial oxides to gallium nitride

    NASA Astrophysics Data System (ADS)

    Losego, Mark Daniel

    Molecular beam epitaxy (MBE) is lauded for its ability to control thin film material structures at the atomic level. This precision of control can improve performance of microelectronic devices and cultivate the development of novel device structures. This thesis explores the utility of MBE for designing interfaces between oxide epilayers and the wide band gap semiconductor gallium nitride (GaN). The allure of wide gap semiconductor microelectronics (like GaN, 3.4 eV) is their ability to operate at higher frequencies, higher powers, and higher temperatures than current semiconductor platforms. Heterostructures between ferroelectric oxides and GaN are also of interest for studying the interaction between GaN's fixed polarization and the ferroelectric's switchable polarization. Two major obstacles to successful integration of oxides with GaN are: (1) interfacial trap states; and (2) small electronic band offsets across the oxide/nitride interface due to the semiconductor's large band gap. For this thesis, epitaxial rocksalt oxide interfacial layers (˜8 eV band gap) are investigated as possible solutions to overcoming the challenges facing oxide integration with GaN. The cubic close-packed structure of rocksalt oxides forms a suitable epitaxial interface with the hexagonal close-packed wurtzite lattice of GaN. Three rocksalt oxide compounds are investigated in this thesis: MgO, CaO, and YbO. All are found to have a (111) MO || (0001) GaN; <1 10> MO || <11 20> GaN epitaxial relationship. Development of the epilayer microstructure is dominated by the high-energy polar growth surface (drives 3D nucleation) and the interfacial symmetry, which permits the formation of twin boundaries. Using STEM, strain relief for these ionicly bonded epilayers is observed to occur through disorder within the initial monolayer of growth. All rocksalt oxides demonstrate chemical stability with GaN to >1000°C. Concurrent MBE deposition of MgO and CaO is known to form complete solid

  19. AFM observation of the surface morphology and impurity effects on orthorhombic hen egg-white lysozyme crystals

    NASA Astrophysics Data System (ADS)

    Matsuzuki, Y.; Kubota, T.; Liu, X. Y.; Ataka, M.; Takano, K. J.

    2002-07-01

    Cation-exchange high performance liquid chromatography at pH 6, developed originally to purify human lysozyme, was applied to hen egg-white lysozyme. We could remove at least three kinds of impurities from the commercial product. The impurities were considered to be modified lysozyme molecules, mostly based on N-terminal amino acid analyses. Atomic force microscopic observation was made on the crystals both from the purified and non-purified solutions. The (1 1 0) faces of the orthorhombic crystals grown at 40°C from the purified solution contained linear steps, while most of the linear edges became round and rugged on the crystals from non-purified solutions. A similar change in step morphology is known to occur on insulin crystals when two amino acids were mutated from the wild type. On the (0 1 0) face, elongated, round steps became rugged when crystals grew from non-purified solutions.

  20. Ferroelectricity and competing interactions in Ho-deficient non-stoichiometric orthorhombic HoMnO{sub 3}

    SciTech Connect

    Wang, J. X.; Yan, Z. B.; Xie, Y. L.; Zhou, X. H.; Liu, J.-M.

    2015-05-07

    We investigate the consequences of the Ho-deficient non-stoichiometry in orthorhombic HoMnO{sub 3} in terms of microscopic mechanisms for ferroelectricity modulation. It is suggested that the Ho-deficiency (then Mn excess) results in Ho-vacancies and then Mn occupation of the Ho-site with increasing non-stoichiometry. The Ho-deficiency enhances the Mn-Mn symmetric exchange striction by suppressing the independent Ho-Ho interaction, and thus benefits to the induced Ho spin ordering against the independent Ho spin ordering. The symmetric Ho-Mn exchange striction is thus enhanced by this induced Ho spin ordering, leading to remarkably enhanced ferroelectric polarization as observed. This work presents an alternative scheme to modulate the multiferroicity in rare-earth manganites of strong 4f-3d coupling.

  1. Spectacular switching from ferrimagnetism to antiferromagnetism by zinc doping in "114" orthorhombic CaBaCo4O7

    NASA Astrophysics Data System (ADS)

    Sarkar, Tapati; Motin Seikh, Md.; Pralong, V.; Caignaert, V.; Raveau, B.

    2012-06-01

    We report a spectacular switching from ferrimagnetism to antiferromagnetism in orthorhombic "114" CaBaCo4O7 by doping with a diamagnetic cation, Zn2+. Magnetic hysteresis loops, together with M(T) and χ'(T) curves at various frequencies, show that ferrimagnetism is abruptly converted to antiferromagnetism below T ˜ 80 K for less than 3% Zn doping, with the simultaneous appearance of local magnetic frustration. A model is proposed based on the ordered doping of Zn2+ at Co2+ sites in the ferromagnetic zig-zag chains of CaBaCo4O7, leading, by domino effect, to ferrimagnetic domains distributed at random and ordered at 180°. The boundaries of the junction of these domains contain Zn2+ and are magnetically frustrated. The crucial role of such ferromagnetic zig-zag chains for designing and tuning magnetic properties in oxides with a triangular metallic lattice is emphasized.

  2. Mapping of second-nearest-neighbor fluoride ions of orthorhombic Gd 3+-Ag + complexes in CaF 2

    NASA Astrophysics Data System (ADS)

    Nakata, R.; Den Hartog, H. W.

    The ENDOR technique is applied to determine the positions of 24 second-nearest-neighbor F - ions around an orthorhombic Gd 3+-Ag + complex in CaF 2 crystals. Experimental ENDOR data of the second-nearest-neighbor F - ions are analyzed by using the usual spin Hamiltonian and a least-squares fitting method. The best fits of the experimental results give superhyperfine (shf) constants and the F - directions ( K, L, M) with respect to the Gd 3+ ion, from which the distance between the second-nearest-neighbor F - ion and the Gd 3+ ion is determined by assuming that the hyperfine interaction is due to the classical dipole-dipole interaction. The displacements of the F - ions are estimated and compared with the theoretical values calculated by Bijvank and den Hartog on the basis of a polarizable point charge model.

  3. The ultraviolet and visible luminescence of Bi3+ in the orthorhombic perovskite, GdAlO3

    NASA Astrophysics Data System (ADS)

    Srivastava, A. M.; Comanzo, H. A.

    2017-01-01

    The spectroscopic properties of the Bi3+ ion as a function of its concentration is examined to clarify the nature of optical transitions that are responsible for the ultraviolet (333 nm) and visible emission of GdAlO3:Bi3+. The UV band which is characterized by small Stokes shift (0.52 eV) is ascribed to emission from isolated Bi3+ ions (3P0,1 → 1S0 transition). The peak emission wavelength and the width of the visible band depend on the Bi3+ concentration. This emission is ascribed to pairs or cluster of Bi3+ ions in the perovskite lattice. The spectroscopic properties of the pair emission in GdAlO3 are contrasted with the impurity trapped excitonic emission in CaSnO3. A comparative study of the behavior of Bi3+ luminescence in a series of materials with the orthorhombic perovskite structure is presented.

  4. Magnetic structure and properties of orthorhombic Li2Ni(SO4)2: A possible magnetoelectric material

    NASA Astrophysics Data System (ADS)

    Reynaud, Marine; Rodríguez-Carvajal, Juan; Chotard, Jean-Noël; Tarascon, Jean-Marie; Rousse, Gwenaëlle

    2014-03-01

    In this paper, we report on the structural and magnetic properties, as deduced from susceptibility measurements and neutron powder diffraction experiments, of an orthorhombic nickel disulfate, Li2Ni(SO4)2. This phase presents NiO6 octahedra linked via SO4 groups only, leading to an antiferromagnetic behavior resulting from super-super-exchange interactions. Magnetic moments order below TN = 28 K and the observed magnetic structure can be explained using two antiferromagnetic and one ferromagnetic exchange interactions, which are discussed in relation with the Goodenough-Kanamori-Anderson rules. The magnetic structure, with k = (0, 0, 0), has the symmetry Pb' c'a' that has the inversion center associated with time inversion, so the compound should be a linear magnetoelectric.

  5. Ferroelectricity and competing interactions in Ho-deficient non-stoichiometric orthorhombic HoMnO3

    NASA Astrophysics Data System (ADS)

    Wang, J. X.; Yan, Z. B.; Xie, Y. L.; Zhou, X. H.; Liu, J.-M.

    2015-05-01

    We investigate the consequences of the Ho-deficient non-stoichiometry in orthorhombic HoMnO3 in terms of microscopic mechanisms for ferroelectricity modulation. It is suggested that the Ho-deficiency (then Mn excess) results in Ho-vacancies and then Mn occupation of the Ho-site with increasing non-stoichiometry. The Ho-deficiency enhances the Mn-Mn symmetric exchange striction by suppressing the independent Ho-Ho interaction, and thus benefits to the induced Ho spin ordering against the independent Ho spin ordering. The symmetric Ho-Mn exchange striction is thus enhanced by this induced Ho spin ordering, leading to remarkably enhanced ferroelectric polarization as observed. This work presents an alternative scheme to modulate the multiferroicity in rare-earth manganites of strong 4f-3d coupling.

  6. Synthesis, photoluminescence and Judd-Ofelt parameters of LiNa3P2O7:Eu3+ orthorhombic microstructures

    NASA Astrophysics Data System (ADS)

    Munirathnam, K.; Dillip, G. R.; Raju, B. Deva Prasad; Joo, S. W.; Dhoble, S. J.; Nagabhushana, B. M.; Hari Krishna, R.; Ramesh, K. P.; Varadharaj Perumal, S.; Prakashbabu, D.

    2015-09-01

    We report, for the first time, the photoluminescence properties of Eu3+-doped LiNa3P2O7 phosphor, synthesized by a facile solid-state reaction method in air atmosphere. The crystal structure and phase purity of the phosphors were analyzed by X-ray diffraction analysis. Orthorhombic structural morphology was identified by scanning electron microscopy. The phosphate groups in the phosphor were confirmed by Fourier transform infrared analysis. Bandgap of the phosphor was calculated from the diffuse reflectance spectra data using Kubelka-Munk function. Under 395-nm UV excitation, the phosphors show signs of emitting red color due to the 5D0 → 7F2 transition. In accordance with Judd-Ofelt theory, spectroscopic parameters such as oscillator intensity parameter Ω t ( t = 2), spontaneous emission probabilities, fluorescence branching ratios and radiative lifetimes were calculated and analyzed for the first time in this system.

  7. Interface-controlled fatigue cracking of SCS-6/Ti-22Al-23Nb orthorhombic titanium aluminide composite

    SciTech Connect

    Her, Y.C.; Wang, P.C.; Yang, J.M.

    1998-11-01

    The effect of aging at elevated temperature on interfacial stability and fatigue behavior of a SCS-6/Ti-22Al-23Nb orthorhombic (O) titanium aluminide composite is investigated. The composite was heat treated in vacuum at 900 C for up to 250 hours to change the microstructural characteristics. The stability of the matrix alloy and interfacial reaction zone after extended thermal exposure was analyzed. The effect of interface on fatigue behavior, including stiffness degradation, evolution of fatigue damage, and crack growth rates, was characterized. Finally, a modified shear-lag model was used to predict the saturated matrix crack spacing in the composite under fatigue loading. The results demonstrate that aging at elevated temperature affects the stability of the interfacial reaction zone, which, in turn, degrades the fatigue properties of the composite. However, fatigue crack will not developed from the ruptured interfacial reaction layer until the thickness of the reaction zone or the maximum applied stress exceeds a critical value.

  8. Structure of the welding zone between titanium and orthorhombic titanium aluminide for explosion welding: II. Local melting zones

    NASA Astrophysics Data System (ADS)

    Grinberg, B. A.; Ivanov, M. A.; Rybin, V. V.; Kuz'min, S. V.; Lysak, V. I.; Elkina, O. A.; Patselov, A. M.; Antonova, O. V.; Inozemtsev, A. V.

    2011-10-01

    The structure and chemical composition of the local melting zones that form during explosion welding of orthorhombic titanium aluminide with commercial-purity titanium near a wavy interface between them are studied. The Rayleigh number is estimated to propose a possible mechanism for the formation of a concentric structure in these zones. Titanium aluminide fragments are detected near the zone boundaries. It is assumed that the fragmentation in the transition zone is caused by the division of a material into loosely coupled microvolumes under the action of a strong external action in a time comparable with the explosion time. Outside the transition zone, fragmentation occurs via a traditional way beginning from dislocation accumulation. Both processes occur in titanium aluminide and only one process (banded structure formation) takes place in titanium.

  9. The electrocaloric effect around the orthorhombic- tetragonal first-order phase transition in BaTiO3

    NASA Astrophysics Data System (ADS)

    Bai, Yang; Ding, Kai; Zheng, Guang-Ping; Shi, San-Qiang; Cao, Jiang-Li; Qiao, Lijie

    2012-06-01

    This paper demonstrates the electrocaloric effect (ECE) around BaTiO3's orthorhombic-tetragonal first-order phase transition. By manipulating a field-induced transition of a metastable phase in the thermal hysteresis zone, a huge exothermic or endothermic peak appears after first applying or removing electric fields because of the energy change of lattice structure. A large ECE of ΔT/E = 1.4K.m/MV, equaling to latent heat, is achieved under 10kV/cm at 10°C. The entropy change for polarization ordering alone induces an ECE two orders of magnitude lower under the same condition. It confirms the dominant factor to ECE of the energy flow due to the structural phase transition.

  10. Non-planar Dzyaloshinskii spirals and magnetic domain walls in non-centrosymmetric systems with orthorhombic anisotropy.

    PubMed

    Heide, Marcus; Bihlmayer, Gustav; Blügel, Stefan

    2011-04-01

    The basic micromagnetic models of Landau, Lifshitz, and Dzyaloshinskii, are extended by an anisotropy term with two independent parameters. The resulting ground states of the magnetic domains and the domain-wall profiles are discussed for crystal lattices with orthorhombic unit cells. In these simple geometries, the magnetization is not confined to a single plane. Depending on the relations between the spin-stiffness, anisotropy, and Dzyaloshinskii-Moriya interaction several different zero-temperature phases of the magnetic structure are found. The corresponding phase diagrams are obtained numerically. Analytical results are given for some special cases. The studied model is of particular relevance for magnetic wires, nanostripes and ultrathin magnetic films deposited on non-magnetic surfaces.

  11. The effect of lattice mismatch on epitaxial La{sub 0.67}Ca{sub 0.33}MnO{sub 3} films.

    SciTech Connect

    Eastell, C. J.; Lin, Y.-K.; Miller, D. J.

    1999-05-06

    We present a study of the effect of lattice mismatch on the structure and magneto-transport properties of La{sub 0.67}Ca{sub 0.33}MnO{sub 3} (LCMO) epitaxial films. Pulsed laser deposition was used to synthesize epitaxial LCMO thin films on LaAlO{sub 3} (LAO), NdGaO{sub 3} (NGO), SrTiO{sub 3} (STO), and MgO substrates. Our results show that the nature of the lattice mismatch and the structure of the substrate governs the microstructure of the film. The microstructure consists of domains of two crystal structures, a pseudo-cubic phase and a monoclinic phase. The monoclinic phase forms as the film relaxes away from the interface, with an orientation dependent on whether the film is under a tensile or compressive in-plane strain. A special case is observed on NGO where the orthorhombic nature of the substrate results in the alignment of the monoclinic phase so that its long axis is in the plane. The observation of an in-plane anisotropy in the magnetoresistance data for LCMO on NGO suggests that the monoclinic phase is important in explaining the magneto-transport properties.

  12. Studies of the EPR g factors and the local structures for the orthorhombic Er 3+ centers in garnets

    NASA Astrophysics Data System (ADS)

    Wu, Shao-Yi; Dong, Hui-Ning

    2005-05-01

    The perturbation formulas of the EPR g factors gx, gy and gz for a 4f11 ion in orthorhombic symmetry are established. In these formulas, the contributions to the g factors arising from the second-order perturbation terms and the admixture of various states are taken into account. The above formulas are applied to the orthorhombic Er3+ centers in YAG, YGG and LuGG garnets. By analyzing their g factors, we find that the polar angles θj‧ of the impurity-ligand bonds related to the Z axis of the crystals in these Er3+ centers are smaller than the host angles θj in pure crystals, whereas the azimuthal angles ϕj ‧ related to the X axis in the impurity centers are larger than the corresponding ϕj in the hosts. The g factors and their anisotropies Δg [= gz - (gx + gy)/2] and δg (= gx - gy) for Er3+ in the garnets based on the above local structural parameters are in good agreement with the observed values. In addition, the angular distortions Δθ (=θj‧ -θj) or Δϕ (=ϕj‧ -ϕj) obtained by analyzing the EPR data in this work are different from Δθ2 or Δϕ2 (for only the second set of ligands, i.e., j = 2) based on the superposition model crystal-field analysis in the previous work. The validity of the results is discussed.

  13. Structure, bonding and physical properties of tetragonal and orthorhombic SiS{sub 2} from (hybrid) DFT calculations

    SciTech Connect

    Zwijnenburg, Martijn A. Bell, Robert G.; Cora, Furio

    2008-09-15

    The energetics, structure and physical properties of tetragonal and orthorhombic SiS{sub 2} were calculated by periodic density functional theory (DFT) calculations, using both localized orbital and projected augmented wave basis-sets. All methods applied agree upon the relative energies of the different polymorphs but show differences in the predicted geometries, which are minimized upon improving the basis-set quality. The hybrid PBE0 functional was found to give the best match between experimental and calculated structures. When comparing SiS{sub 2} with its much better studied oxide analog silica, we observe that upon substituting sulphur for oxygen, the energy landscape changes dramatically. Other effects of changing S for O are found to be smaller Si-X-Si angles, a broader distribution of X-Si-X angles, a more flexible framework and a significantly reduced band gap. The latter is in line with the experimental observation of photoluminescence in related GaGeS{sub 2} compounds and suggests that SiS{sub 2} might find application in UV light emitting diodes. Finally, a comparison of the maximally localized Wannier functions demonstrates that the Si-S bonds in SiS{sub 2} have a considerably more covalent character than the Si-O bonds in silica. - Graphical abstract: Periodic DFT calculations were employed to study the (physical) properties of tetragonal and orthorhombic SiS{sub 2}. The results obtained were compared with those for SiS{sub 2} better studied oxide analog silica and demonstrate large changes in the materials' energy landscape, nature of bonding, flexibility and band gap, upon substitution of sulphur for oxygen.

  14. A new phase in the system lithium-aluminum: Characterization of orthorhombic Li{sub 2}Al

    SciTech Connect

    Puhakainen, Kati; Bostroem, Magnus; Groy, Thomas L.; Haeussermann, Ulrich

    2010-11-15

    Investigation of the Li rich part of the binary Li-Al system revealed the existence of a new phase, orthorhombic Li{sub 2}Al, which is isostructural to Li{sub 2}Ga and Li{sub 2}In. The crystal structure was determined from single crystal X-ray diffraction data (Cmcm, a=4.658(2) A, b=9.767(4) A, c=4.490(2) A, Z=4). Refinement of atomic position site occupancies yielded a composition Li{sub 1.92}Al{sub 1.08} (64 at% Li) indicating a small homogeneity range, Li{sub 2-x}Al{sub 1+x}. Li{sub 2}Al is the peritectic decomposition product of the stoichiometric compound Li{sub 9}Al{sub 4}, which is stable below 270{+-}2 {sup o}C. Li{sub 2}Al itself decomposes peritectically to Li{sub 3}Al{sub 2} and Li rich melt at 335{+-}2 {sup o}C. The discovery of Li{sub 2}Al (Li{sub 2-x}Al{sub 1+x}) settles a long standing inconsistency in the Li-Al phase diagram which was based on the assumption that Li{sub 9}Al{sub 4} possesses a high temperature modification. - Graphical abstract: A new phase, Li{sub 2}Al, has been discovered in the binary Li-Al system. The structure of orthorhombic Li{sub 2}Al is closely related to that of the established monoclinic phase Li{sub 9}Al{sub 4}.

  15. Strain tuning of electronic structure in Bi4Ti3O12-LaCoO3 epitaxial thin films

    SciTech Connect

    Choi, Woo Seok; Lee, Ho Nyung

    2015-05-08

    In this study, we investigated the crystal and electronic structures of ferroelectric Bi4Ti3O12 single-crystalline thin films site-specifically substituted with LaCoO3 (LCO). The epitaxial films were grown by pulsed laser epitaxy on NdGaO3 and SrTiO3 substrates to vary the degree of strain. With increasing the LCO substitution, we observed a systematic increase in the c-axis lattice constant of the Aurivillius phase related with the modification of pseudo-orthorhombic unit cells. These compositional and structural changes resulted in a systematic decrease in the band gap, i.e., the optical transition energy between the oxygen 2p and transition-metal 3d states, based on a spectroscopic ellipsometry study. In particular, the Co 3d state seems to largely overlap with the Ti t2g state, decreasing the band gap. Interestingly, the applied tensile strain facilitates the band-gap narrowing, demonstrating that epitaxial strain is a useful tool to tune the electronic structure of ferroelectric transition-metal oxides.

  16. High quality epitaxial CoSi{sub 2} using plasma nitridation-mediated epitaxy: The effects of the capping layer

    SciTech Connect

    Lee, Han-Bo-Ram; Gu, Gil Ho; Son, J. Y.; Park, C. G.; Kim, Hyungjun

    2007-11-01

    The epitaxial growth of CoSi{sub 2} from Co with a Ti capping layer using plasma nitridation-mediated epitaxy (PNME) was demonstrated. By exposing the Si substrate to the NH{sub 3} plasma, an a-SiN{sub x} layer was formed with atomic scale thickness controllability. After Co and Ti deposition followed by annealing, high quality epitaxial CoSi{sub 2} was formed on Si(001) with a perfectly flat interface. However, the epitaxial growth was observed for Co with a Ti capping layer prepared only by ex situ deposition, not by in situ deposition. The epitaxial CoSi{sub 2} was analyzed by x-ray diffraction and a scanning transmission electron microscope. Based on these results, the mechanism of PNME and the effects of the Ti capping layer process on silicidation were discussed.

  17. Epitaxial thick film high-Tc SQUIDs

    NASA Astrophysics Data System (ADS)

    Faley, M. I.; Mi, S. B.; Jia, C. L.; Poppe, U.; Urban, K.; Fagaly, R. L.

    2008-02-01

    Low-noise operation of superconducting quantum interference devices (SQUIDs) in magnetic fields requires high critical current and strong pinning of vortices in the superconducting electrodes and in the flux transformer. Crack-free epitaxial high-Tc dc-SQUID structures with a total thickness ?5 μm and a surface roughness determined by 30 nm high growth spirals were prepared with YBa2Cu3O7-x (YBCO) films on MgO substrates buffered by a SrTiO3/BaZrO3-bilayer. HRTEM demonstrated a high quality epitaxial growth of the films. The YBCO films and SQUID structures deposited on the buffered MgO substrates had a superconducting transition temperature Tc exceeding 91 K and critical current densities Jc > 3 MA/cm2 at 77 K up to a thickness ~5 μm. The application of thicker superconducting and insulator films helped us to increase the critical current and dynamic range of the multilayer high-Tc flux transformer and improve the insulation between the superconducting layers. An optimization of SQUID inductance allowed us to fabricate 8 mm SQUID magnetometers with SQUID voltage swings of ~60 μV and a field resolution of ~30 fT/√Hz at 77 K.

  18. Epitaxy of advanced nanowire quantum devices

    NASA Astrophysics Data System (ADS)

    Gazibegovic, Sasa; Car, Diana; Zhang, Hao; Balk, Stijn C.; Logan, John A.; de Moor, Michiel W. A.; Cassidy, Maja C.; Schmits, Rudi; Xu, Di; Wang, Guanzhong; Krogstrup, Peter; Op Het Veld, Roy L. M.; Zuo, Kun; Vos, Yoram; Shen, Jie; Bouman, Daniël; Shojaei, Borzoyeh; Pennachio, Daniel; Lee, Joon Sue; van Veldhoven, Petrus J.; Koelling, Sebastian; Verheijen, Marcel A.; Kouwenhoven, Leo P.; Palmstrøm, Chris J.; Bakkers, Erik P. A. M.

    2017-08-01

    Semiconductor nanowires are ideal for realizing various low-dimensional quantum devices. In particular, topological phases of matter hosting non-Abelian quasiparticles (such as anyons) can emerge when a semiconductor nanowire with strong spin-orbit coupling is brought into contact with a superconductor. To exploit the potential of non-Abelian anyons—which are key elements of topological quantum computing—fully, they need to be exchanged in a well-controlled braiding operation. Essential hardware for braiding is a network of crystalline nanowires coupled to superconducting islands. Here we demonstrate a technique for generic bottom-up synthesis of complex quantum devices with a special focus on nanowire networks with a predefined number of superconducting islands. Structural analysis confirms the high crystalline quality of the nanowire junctions, as well as an epitaxial superconductor-semiconductor interface. Quantum transport measurements of nanowire ‘hashtags’ reveal Aharonov-Bohm and weak-antilocalization effects, indicating a phase-coherent system with strong spin-orbit coupling. In addition, a proximity-induced hard superconducting gap (with vanishing sub-gap conductance) is demonstrated in these hybrid superconductor-semiconductor nanowires, highlighting the successful materials development necessary for a first braiding experiment. Our approach opens up new avenues for the realization of epitaxial three-dimensional quantum architectures which have the potential to become key components of various quantum devices.

  19. Graphene nanoribbons epitaxy on boron nitride

    NASA Astrophysics Data System (ADS)

    Lu, Xiaobo; Yang, Wei; Wang, Shuopei; Wu, Shuang; Chen, Peng; Zhang, Jing; Zhao, Jing; Meng, Jianling; Xie, Guibai; Wang, Duoming; Wang, Guole; Zhang, Ting Ting; Watanabe, Kenji; Taniguchi, Takashi; Yang, Rong; Shi, Dongxia; Zhang, Guangyu

    2016-03-01

    In this letter, we report a pilot study on epitaxy of monolayer graphene nanoribbons (GNRs) on hexagonal boron nitride (h-BN). We found that GNRs grow preferentially from the atomic steps of h-BN, forming in-plane heterostructures. GNRs with well-defined widths ranging from ˜15 nm to ˜150 nm can be obtained reliably. As-grown GNRs on h-BN have high quality with a carrier mobility of ˜20 000 cm2 V-1 s-1 for ˜100-nm-wide GNRs at a temperature of 1.7 K. Besides, a moiré pattern induced quasi-one-dimensional superlattice with a periodicity of ˜15 nm for GNR/h-BN was also observed, indicating zero crystallographic twisting angle between GNRs and h-BN substrate. The superlattice induced band structure modification is confirmed by our transport results. These epitaxial GNRs/h-BN with clean surfaces/interfaces and tailored widths provide an ideal platform for high-performance GNR devices.

  20. Epitaxy of advanced nanowire quantum devices.

    PubMed

    Gazibegovic, Sasa; Car, Diana; Zhang, Hao; Balk, Stijn C; Logan, John A; de Moor, Michiel W A; Cassidy, Maja C; Schmits, Rudi; Xu, Di; Wang, Guanzhong; Krogstrup, Peter; Op Het Veld, Roy L M; Zuo, Kun; Vos, Yoram; Shen, Jie; Bouman, Daniël; Shojaei, Borzoyeh; Pennachio, Daniel; Lee, Joon Sue; van Veldhoven, Petrus J; Koelling, Sebastian; Verheijen, Marcel A; Kouwenhoven, Leo P; Palmstrøm, Chris J; Bakkers, Erik P A M

    2017-08-23

    Semiconductor nanowires are ideal for realizing various low-dimensional quantum devices. In particular, topological phases of matter hosting non-Abelian quasiparticles (such as anyons) can emerge when a semiconductor nanowire with strong spin-orbit coupling is brought into contact with a superconductor. To exploit the potential of non-Abelian anyons-which are key elements of topological quantum computing-fully, they need to be exchanged in a well-controlled braiding operation. Essential hardware for braiding is a network of crystalline nanowires coupled to superconducting islands. Here we demonstrate a technique for generic bottom-up synthesis of complex quantum devices with a special focus on nanowire networks with a predefined number of superconducting islands. Structural analysis confirms the high crystalline quality of the nanowire junctions, as well as an epitaxial superconductor-semiconductor interface. Quantum transport measurements of nanowire 'hashtags' reveal Aharonov-Bohm and weak-antilocalization effects, indicating a phase-coherent system with strong spin-orbit coupling. In addition, a proximity-induced hard superconducting gap (with vanishing sub-gap conductance) is demonstrated in these hybrid superconductor-semiconductor nanowires, highlighting the successful materials development necessary for a first braiding experiment. Our approach opens up new avenues for the realization of epitaxial three-dimensional quantum architectures which have the potential to become key components of various quantum devices.

  1. Exceptional ballistic transport in epitaxial graphene nanoribbons.

    PubMed

    Baringhaus, Jens; Ruan, Ming; Edler, Frederik; Tejeda, Antonio; Sicot, Muriel; Taleb-Ibrahimi, Amina; Li, An-Ping; Jiang, Zhigang; Conrad, Edward H; Berger, Claire; Tegenkamp, Christoph; de Heer, Walt A

    2014-02-20

    Graphene nanoribbons will be essential components in future graphene nanoelectronics. However, in typical nanoribbons produced from lithographically patterned exfoliated graphene, the charge carriers travel only about ten nanometres between scattering events, resulting in minimum sheet resistances of about one kilohm per square. Here we show that 40-nanometre-wide graphene nanoribbons epitaxially grown on silicon carbide are single-channel room-temperature ballistic conductors on a length scale greater than ten micrometres, which is similar to the performance of metallic carbon nanotubes. This is equivalent to sheet resistances below 1 ohm per square, surpassing theoretical predictions for perfect graphene by at least an order of magnitude. In neutral graphene ribbons, we show that transport is dominated by two modes. One is ballistic and temperature independent; the other is thermally activated. Transport is protected from back-scattering, possibly reflecting ground-state properties of neutral graphene. At room temperature, the resistance of both modes is found to increase abruptly at a particular length--the ballistic mode at 16 micrometres and the other at 160 nanometres. Our epitaxial graphene nanoribbons will be important not only in fundamental science, but also--because they can be readily produced in thousands--in advanced nanoelectronics, which can make use of their room-temperature ballistic transport properties.

  2. Graphene nanoribbons epitaxy on boron nitride

    SciTech Connect

    Lu, Xiaobo; Wang, Shuopei; Wu, Shuang; Chen, Peng; Zhang, Jing; Zhao, Jing; Meng, Jianling; Xie, Guibai; Wang, Duoming; Wang, Guole; Zhang, Ting Ting; Yang, Rong; Shi, Dongxia; Yang, Wei; Watanabe, Kenji; Taniguchi, Takashi; Zhang, Guangyu

    2016-03-14

    In this letter, we report a pilot study on epitaxy of monolayer graphene nanoribbons (GNRs) on hexagonal boron nitride (h-BN). We found that GNRs grow preferentially from the atomic steps of h-BN, forming in-plane heterostructures. GNRs with well-defined widths ranging from ∼15 nm to ∼150 nm can be obtained reliably. As-grown GNRs on h-BN have high quality with a carrier mobility of ∼20 000 cm{sup 2} V{sup −1} s{sup −1} for ∼100-nm-wide GNRs at a temperature of 1.7 K. Besides, a moiré pattern induced quasi-one-dimensional superlattice with a periodicity of ∼15 nm for GNR/h-BN was also observed, indicating zero crystallographic twisting angle between GNRs and h-BN substrate. The superlattice induced band structure modification is confirmed by our transport results. These epitaxial GNRs/h-BN with clean surfaces/interfaces and tailored widths provide an ideal platform for high-performance GNR devices.

  3. Optical Properties of Epitaxially Grown Silver Films

    NASA Astrophysics Data System (ADS)

    Wu, Yanwen; Zhang, Chendong; Zhang, Matt; Shih, Chih-Kang; Li, Xiaoqin

    2013-03-01

    One major obstacle in the advancing field of plasmonics is the loss in metals. A sizable contribution of this loss comes from grain boundaries and surface roughness introduced during thin film growth using conventional deposition methods. A novel epitaxial growth technique is used to produce silver (Ag) thin films free of such flaws. We investigate the optical properties-namely the dielectric optical constants-of these new epitaxial films in the bulk region and in the ultrathin film limit where quantum mechanical behaviors emerge due to energy quantization in the growth direction. The values for the dielectric optical constants are extracted from the spectral ellipsometry (SE) measurements over a wide range of optical frequencies. By using an adequate model of the sample structure and initial values of the fitting parameters (i.e. the real and imaginary parts of the optical constants), we can extract these measured values for the new Ag films. We have confirmed that in the bulk region, the optical constants converge with the well-known Johnson and Christy measurements. In the ultrathin film limit, however, we observed significant changes near the D-band transition likely due to a quantum well-like density of states. Equal contribution. Also affiliated with Department of Physics, The University of South Carolina, Columbia, SC 29208

  4. 2D vibrational properties of epitaxial silicene on Ag(111)

    NASA Astrophysics Data System (ADS)

    Solonenko, Dmytro; Gordan, Ovidiu D.; Le Lay, Guy; Sahin, Hasan; Cahangirov, Seymur; Zahn, Dietrich R. T.; Vogt, Patrick

    2017-03-01

    The two-dimensional silicon allotrope, silicene, could spur the development of new and original concepts in Si-based nanotechnology. Up to now silicene can only be epitaxially synthesized on a supporting substrate such as Ag(111). Even though the structural and electronic properties of these epitaxial silicene layers have been intensively studied, very little is known about its vibrational characteristics. Here, we present a detailed study of epitaxial silicene on Ag(111) using in situ Raman spectroscopy, which is one of the most extensively employed experimental techniques to characterize 2D materials, such as graphene, transition metal dichalcogenides, and black phosphorous. The vibrational fingerprint of epitaxial silicene, in contrast to all previous interpretations, is characterized by three distinct phonon modes with A and E symmetries. Both, energies and symmetries of theses modes are confirmed by ab initio theory calculations. The temperature dependent spectral evolution of these modes demonstrates unique thermal properties of epitaxial silicene and a significant electron-phonon coupling. These results unambiguously support the purely two-dimensional character of epitaxial silicene up to about 300 °C, whereupon a 2D-to-3D phase transition takes place. The detailed fingerprint of epitaxial silicene will allow us to identify it in different environments or to study its modifications.

  5. Comparison of Epitaxial Growth Techniques for III-V Layer Structures

    DTIC Science & Technology

    1992-05-22

    FOR Ill-V LAYER STRUCTURES DTIC byS ELECTE G. B. STRINGFELLOW MAY 2 819S2 A Prepared for Publication in the Proceedings of croissance de cristaux et de...epitaxial growth techniques have been used for semiconductors, including liquid phase epitaxy (LPE), chloride vapor phase epitaxy (CIVPE) using...MBE (GSMBE), organometallic MBE (OMMBE or MOMBE), and chemical beam epitaxy (CBE). II. LIQUID PHASE EPITAXY The first technique listed, LPE, was one of

  6. Layered-structural monoclinic–orthorhombic perovskite La{sub 2}Ti{sub 2}O{sub 7} to orthorhombic LaTiO{sub 3} phase transition and their microstructure characterization

    SciTech Connect

    Herrera, G.; Jiménez-Mier, J.; Chavira, E.

    2014-03-01

    The layered-structural ceramics, such as lanthanum titanate (La{sub 2}Ti{sub 2}O{sub 7}), have been known for their good temperature and low dielectric loss at microwave frequencies that make them good candidate materials for high frequency applications. However, few studies have been conducted on the synthesis optimization by sol gel reaction, in particular by acrylamide polymerization route. The interest in La{sub 2}Ti{sub 2}O{sub 7} ceramic has been greatly increased recently due to the effect of oriented grains. This anisotropy of the microstructure leads to anisotropy in dielectric, electrical and mechanical properties. In this study, grain oriented lanthanum titanate was produced by the sol–gel acrylamide polymerization route. The characterizations of the samples were achieved by thermal analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). X-ray diffraction indicates that the formation of monoclinic perovskite La{sub 2}Ti{sub 2}O{sub 7} nanocrystals is a necessary first step to obtain orthorhombic LaTiO{sub 3} nanocomposites (with space group Pbnm). In this work we identified that the monoclinic perovskite La{sub 2}Ti{sub 2}O{sub 7} with space group P2{sub 1} transforms its structure into one with the orthorhombic space group Cmc2{sub 1} at approximately 1073 K. The microstructure associated consisted of flaky monoclinic La{sub 2}Ti{sub 2}O{sub 7} nanocomposites in comparison with round-shaped LaTiO{sub 3} nanocomposites. - Highlights: • The flaky-like La{sub 2}Ti{sub 2}O{sub 7} compound was synthesized by sol–gel acrylamide route. • Simultaneous monitoring of the DTA and XRD with temperature was performed. • Phase transformation characterization of La{sub 2}Ti{sub 2}O{sub 7} has been carried out. • The variation of the La{sub 2}Ti{sub 2}O{sub 7} and LaTiO{sub 3} grain morphology has been compared.

  7. Reclamation of a molecular beam epitaxy system and conversion for oxide epitaxy

    SciTech Connect

    Carver, Alexander G.; Henderson, Walter; Doolittle, W. Alan

    2008-11-15

    An early 1980s vintage molecular beam epitaxy system, a Varian Gen II system, originally used for HgCdTe epitaxy, was converted into a system capable of growing thin-film complex metal oxides. The nature of some of the alternative oxides requires a thorough cleaning and, in some cases, complete replacement of system components. Details are provided regarding the chemistry of the etchants used, safety requirements for properly handling, and disposal of large quantities of etchants and etch by-products, and components that can be reused versus components that require replacement are given. Following the given procedures, an ultimate base pressure of 2x10{sup -10} Torr was obtained. Films grown in the system after reclamation contained no evidence of previously present materials down to the detection limit of secondary ion mass spectrometry.

  8. Substrate heater for the growth of epitaxial silicon films

    NASA Astrophysics Data System (ADS)

    Deming, Matthew; Varhue, Walter; Adams, Edward; Lavoie, Mark

    1999-03-01

    The single wafer processing of epitaxial Si films requires that special attention be paid to the design of the substrate heater assembly. This document describes the evolution and testing of an in situ heater used to deposit epitaxial Si films at temperatures as high as 700 °C. One problem encountered was the production of excessive levels of ultraviolet radiation which contributed to the desorption of water vapor from the vacuum chamber walls during the in situ cleaning process. A second problem involved the formation of a molybdenum containing film that poisoned epitaxial growth. A final proven in situ heater design is presented which avoids these problems.

  9. Experimental Evidence for Epitaxial Silicene on Diboride Thin Films

    NASA Astrophysics Data System (ADS)

    Fleurence, Antoine; Friedlein, Rainer; Ozaki, Taisuke; Kawai, Hiroyuki; Wang, Ying; Yamada-Takamura, Yukiko

    2012-06-01

    As the Si counterpart of graphene, silicene may be defined as an at least partially sp2-hybridized, atom-thick honeycomb layer of Si that possesses π-electronic bands. Here we show that two-dimensional, epitaxial silicene forms through surface segregation on zirconium diboride thin films grown on Si wafers. A particular buckling of silicene induced by the epitaxial relationship with the diboride surface leads to a direct π-electronic band gap at the Γ point. These results demonstrate that the buckling and thus the electronic properties of silicene are modified by epitaxial strain.

  10. Droplet Epitaxy Image Contrast in Mirror Electron Microscopy

    NASA Astrophysics Data System (ADS)

    Kennedy, S. M.; Zheng, C. X.; Jesson, D. E.

    2017-01-01

    Image simulation methods are applied to interpret mirror electron microscopy (MEM) images obtained from a movie of GaAs droplet epitaxy. Cylindrical symmetry of structures grown by droplet epitaxy is assumed in the simulations which reproduce the main features of the experimental MEM image contrast, demonstrating that droplet epitaxy can be studied in real-time. It is therefore confirmed that an inner ring forms at the droplet contact line and an outer ring (or skirt) occurs outside the droplet periphery. We believe that MEM combined with image simulations will be increasingly used to study the formation and growth of quantum structures.

  11. Point defect balance in epitaxial GaSb

    SciTech Connect

    Segercrantz, N. Slotte, J.; Makkonen, I.; Kujala, J.; Tuomisto, F.; Song, Y.; Wang, S.

    2014-08-25

    Positron annihilation spectroscopy in both conventional and coincidence Doppler broadening mode is used for studying the effect of growth conditions on the point defect balance in GaSb:Bi epitaxial layers grown by molecular beam epitaxy. Positron annihilation characteristics in GaSb are also calculated using density functional theory and compared to experimental results. We conclude that while the main positron trapping defect in bulk samples is the Ga antisite, the Ga vacancy is the most prominent trap in the samples grown by molecular beam epitaxy. The results suggest that the p–type conductivity is caused by different defects in GaSb grown with different methods.

  12. Multifunctional epitaxial systems on silicon substrates

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Prater, John Thomas; Narayan, Jagdish

    2016-09-01

    Multifunctional heterostructures can exhibit a wide range of functional properties, including colossal magneto-resistance, magnetocaloric, and multiferroic behavior, and can display interesting physical phenomena including spin and charge ordering and strong spin-orbit coupling. However, putting this functionality to work remains a challenge. To date, most of the work reported in the literature has dealt with heterostructures deposited onto closely lattice matched insulating substrates such as DyScO3, SrTiO3 (STO), or STO buffered Si(100) using concepts of lattice matching epitaxy (LME). However, strain in heterostructures grown by LME is typically not fully relaxed and the layers contain detrimental defects such as threading dislocations that can significantly degrade the physical properties of the films and adversely affect the device characteristics. In addition, most of the substrates are incompatible with existing CMOS-based technology, where Si (100) substrates dominate. This review discusses recent advances in the integration of multifunctional oxide and non-oxide materials onto silicon substrates. An alternative thin film growth approach, called "domain matching epitaxy," is presented which identifies approaches for minimizing lattice strain and unwanted defects in large misfit systems (7%-25% and higher). This approach broadly allows for the integration of multifunctional materials onto silicon substrates, such that sensing, computation, and response functions can be combined to produce next generation "smart" devices. In general, pulsed laser deposition has been used to epitaxially grow these materials, although the concepts developed here can be extended to other deposition techniques, as well. It will be shown that TiN and yttria-stabilized zirconia template layers provide promising platforms for the integration of new functionality into silicon-based computer chips. This review paper reports on a number of thin-film heterostructure systems that span a

  13. Multifunctional epitaxial systems on silicon substrates

    SciTech Connect

    Singamaneni, Srinivasa Rao; Prater, John Thomas; Narayan, Jagdish

    2016-09-15

    Multifunctional heterostructures can exhibit a wide range of functional properties, including colossal magneto-resistance, magnetocaloric, and multiferroic behavior, and can display interesting physical phenomena including spin and charge ordering and strong spin-orbit coupling. However, putting this functionality to work remains a challenge. To date, most of the work reported in the literature has dealt with heterostructures deposited onto closely lattice matched insulating substrates such as DyScO{sub 3}, SrTiO{sub 3} (STO), or STO buffered Si(100) using concepts of lattice matching epitaxy (LME). However, strain in heterostructures grown by LME is typically not fully relaxed and the layers contain detrimental defects such as threading dislocations that can significantly degrade the physical properties of the films and adversely affect the device characteristics. In addition, most of the substrates are incompatible with existing CMOS-based technology, where Si (100) substrates dominate. This review discusses recent advances in the integration of multifunctional oxide and non-oxide materials onto silicon substrates. An alternative thin film growth approach, called “domain matching epitaxy,” is presented which identifies approaches for minimizing lattice strain and unwanted defects in large misfit systems (7%–25% and higher). This approach broadly allows for the integration of multifunctional materials onto silicon substrates, such that sensing, computation, and response functions can be combined to produce next generation “smart” devices. In general, pulsed laser deposition has been used to epitaxially grow these materials, although the concepts developed here can be extended to other deposition techniques, as well. It will be shown that TiN and yttria-stabilized zirconia template layers provide promising platforms for the integration of new functionality into silicon-based computer chips. This review paper reports on a number of thin

  14. Epitaxial integration of nanowires in microsystems by local micrometer-scale vapor-phase epitaxy.

    PubMed

    Mølhave, Kristian; Wacaser, Brent A; Petersen, Dirch Hjorth; Wagner, Jakob B; Samuelson, Lars; Bøggild, Peter

    2008-10-01

    Free-standing epitaxially grown nanowires provide a controlled growth system and an optimal interface to the underlying substrate for advanced optical, electrical, and mechanical nanowire device connections. Nanowires can be grown by vapor-phase epitaxy (VPE) methods such as chemical vapor deposition (CVD) or metal organic VPE (MOVPE). However, VPE of semiconducting nanowires is not compatible with several microfabrication processes due to the high synthesis temperatures and issues such as cross-contamination interfering with the intended microsystem or the VPE process. By selectively heating a small microfabricated heater, growth of nanowires can be achieved locally without heating the entire microsystem, thereby reducing the compatibility problems. The first demonstration of epitaxial growth of silicon nanowires by this method is presented and shows that the microsystem can be used for rapid optimization of VPE conditions. The important issue of the cross-contamination of other parts of the microsystem caused by the local growth of nanowires is also investigated by growth of GaN near previously grown silicon nanowires. The design of the cantilever heaters makes it possible to study the grown nanowires with a transmission electron microscope without sample preparation.

  15. Metamorphic Epitaxy for Multijunction Solar Cells

    SciTech Connect

    France, Ryan M.; Dimroth, Frank; Grassman, Tyler J.; King, Richard R.

    2016-03-01

    Multijunction solar cells have proven to be capable of extremely high efficiencies by combining multiple semiconductor materials with bandgaps tuned to the solar spectrum. Reaching the optimum set of semiconductors often requires combining high-quality materials with different lattice constants into a single device, a challenge particularly suited for metamorphic epitaxy. In this article, we describe different approaches to metamorphic multijunction solar cells, including traditional upright metamorphic, state-of-the-art inverted metamorphic, and forward-looking multijunction designs on silicon. We also describe the underlying materials science of graded buffers that enables metamorphic subcells with low dislocation densities. Following nearly two decades of research, recent efforts have demonstrated high-quality lattice-mismatched multijunction solar cells with very little performance loss related to the mismatch, enabling solar-to-electric conversion efficiencies over 45%.

  16. Friction boosted by spontaneous epitaxial rotations

    NASA Astrophysics Data System (ADS)

    Mandelli, Davide; Vanossi, Andrea; Manini, Nicola; Tosatti, Erio

    2015-03-01

    It is well known in surface science that incommensurate adsorbed monolayers undergo a spontaneous, energy-lowering epitaxial rotation from aligned to misaligned relative to a periodic substrate. We show first of all that a model 2D colloidal monolayer in an optical lattice, of recent importance as a frictional model, also develops in full equilibrium a small rotation angle, easy to detect in the Moiré pattern. The colloidal monolayer misalignment is then shown by extensive sliding simulations to increase the dynamic friction by a considerable factor over the aligned case. More generally, this example suggests that spontaneous rotations are rather ubiquitous and should not be ignored in all tribological phenomena between mismatched lattices. This work was mainly supported by the ERC Advanced Grant No. 320796-MODPHYSFRICT, and partly by SINERGIA contract CRSII2 136287, by PRIN/COFIN Contract 2010LLKJBX 004, by COST Action MP1303.

  17. Epitaxial oxide bilayer on Pt (001) nanofacets

    NASA Astrophysics Data System (ADS)

    Hennessy, Daniel; Komanicky, Vladimir; Iddir, Hakim; Pierce, Michael S.; Menzel, Andreas; Chang, Kee-Chul; Barbour, Andi; Zapol, Peter; You, Hoydoo

    2012-01-01

    We observed an epitaxial, air-stable, partially registered (2 × 1) oxide bilayer on Pt (001) nanofacets [V. Komanicky, A. Menzel, K.-C. Chang, and H. You, J. Phys. Chem. 109, 23543 (2005)]. The bilayer is made of two half Pt layers; the top layer has four oxygen bonds and the second layer two. The positions and oxidation states of the Pt atoms are determined by analyzing crystal truncation rods and resonance scattering data. The positions of oxygen atoms are determined by density functional theory (DFT) calculations. Partial registry on the nanofacets and the absence of such registry on the extended Pt (001) surface prepared similarly are explained in DFT calculations by strain relief that can be accommodated only by nanoscale facets.

  18. Shaping metal nanocrystals through epitaxial seeded growth

    SciTech Connect

    Habas, Susan E.; Lee, Hyunjoo; Radmilovic, Velimir; Somorjai,Gabor A.; Yang, Peidong

    2008-02-17

    Morphological control of nanocrystals has becomeincreasingly important, as many of their physical and chemical propertiesare highly shape-dependent. Nanocrystal shape control for both single andmultiple material systems, however, remains fairly empirical andchallenging. New methods need to be explored for the rational syntheticdesign of heterostructures with controlled morphology. Overgrowth of adifferent material on well-faceted seeds, for example, allows for the useof the defined seed morphology to control nucleation and growth of thesecondary structure. Here, we have used highly faceted cubic Pt seeds todirect the epitaxial overgrowth of a secondary metal. We demonstrate thisconcept with lattice matched Pd to produce conformal shape-controlledcore-shell particles, and then extend it to lattice mismatched Au to giveanisotropic growth. Seeding with faceted nanocrystals may havesignificant potential towards the development of shape-controlledheterostructures with defined interfaces.

  19. Low energy dislocation structures in epitaxy

    NASA Technical Reports Server (NTRS)

    Van Der Merwe, Jan H.; Woltersdorf, J.; Jesser, W. A.

    1986-01-01

    The principle of minimum energy was applied to epitaxial interfaces to show the interrelationship beteen misfit, overgrowth thickness and misfit dislocation spacing. The low energy dislocation configurations were presented for selected interfacial geometries. A review of the interfacial energy calculations was made and a critical assessment of the agreement between theory and experiment was presented. Modes of misfit accommodation were presented with emphasis on the distinction between kinetic effects and equilibrium conditions. Two-dimensional and three-dimensional overgrowths were treated together with interdiffusion-modified interfaces, and several models of interfacial structure were treated including the classical and the current models. The paper is concluded by indicating areas of needed investigation into interfacial structure.

  20. Infrared Rugates by Molecular Beam Epitaxy

    NASA Technical Reports Server (NTRS)

    Rona, M.

    1993-01-01

    Rugates are optical structures that have a sinusoidal index of refraction (harmonic gradient-index field). As their discrete high/ low index filter counterparts, they can be used as narrow rejection band filters. However, since rugates do not have abrupt interfaces, they tend to have a smaller absorption, hence deliver a higher in band reflectivity. The absence of sharp interfaces makes rugates even more desirable for high-energy narrow band reflectors. In this application, the lack of a sharp interface at the maximum internal standing wave electric field results in higher breakdown strengths. Our method involves fabricating rugates, with molecular beam epitaxy, on GaAs wafers as an Al(x)Ga(1-x)As single-crystal film.

  1. Epitaxial oxide bilayer on Pt(001) nanofacts.

    SciTech Connect

    Hennessy, D.; Komanicky, V.; Iddir, H.; Pierce, M. S.; Menzel, A.; Chang, K-C.; Barbour, A.; Zapol, P.; You, H.

    2012-01-01

    We observed an epitaxial, air-stable, partially registered (2 x 1) oxide bilayer on Pt (001) nanofacets [V. Komanicky, A. Menzel, K.-C. Chang, and H. You, J. Phys. Chem. 109, 23543 (2005)]. The bilayer is made of two half Pt layers; the top layer has four oxygen bonds and the second layer two. The positions and oxidation states of the Pt atoms are determined by analyzing crystal truncation rods and resonance scattering data. The positions of oxygen atoms are determined by density functional theory (DFT) calculations. Partial registry on the nanofacets and the absence of such registry on the extended Pt (001) surface prepared similarly are explained in DFT calculations by strain relief that can be accommodated only by nanoscale facets.

  2. Transport properties of epitaxial lift off films

    NASA Technical Reports Server (NTRS)

    Mena, R. A.; Schacham, S. E.; Young, P. G.; Haugland, E. J.; Alterovitz, S. A.

    1993-01-01

    Transport properties of epitaxially lifted-off (ELO) films were characterized using conductivity, Hall, and Shubnikov-de Haas measurements. A 10-15 percent increase in the 2D electron gas concentration was observed in these films as compared with adjacent conventional samples. We believe this result to be caused by a backgating effect produced by a charge build up at the interface of the ELO film and the quartz substrate. This increase results in a substantial decrease in the quantum lifetime in the ELO samples, by 17-30 percent, but without a degradation in carrier mobility. Under persistent photoconductivity, only one subband was populated in the conventional structure, while in the ELO films the population of the second subband was clearly visible. However, the increase of the second subband concentration with increasing excitation is substantially smaller than anticipated due to screening of the backgating effect.

  3. Mechanistic study of organometallic vapor phase epitaxy

    SciTech Connect

    Stringfellow, G.B.

    1990-12-31

    Only AsH{sub 3} and PH{sub 3} have been used as the group V source molecules for organometallic vapor phase epitaxy (OMVPE) of III/V semiconductors until recently, since they have been the only precursors yielding device quality materials. This paper reviews recent work on the pyrolysis of individual organometallic molecules, with emphasis on the group V sources, including: (1) the methylarsines, di- and tri-methylarsine, (2) the ethylarsines, mono-, di-, and tri-ethylarsine, and (3) the singly substituted tertiarybutyl arsine and phosphine molecules. The pyrolysis and growth reactions occurring when both group III and group V precursors are present simultaneously, i.e., the reactions occuring during OMVPE growth of several III/V semiconductors, are also briefly reviewed.

  4. Mechanistic study of organometallic vapor phase epitaxy

    SciTech Connect

    Stringfellow, G.B.

    1990-01-01

    Only AsH{sub 3} and PH{sub 3} have been used as the group V source molecules for organometallic vapor phase epitaxy (OMVPE) of III/V semiconductors until recently, since they have been the only precursors yielding device quality materials. This paper reviews recent work on the pyrolysis of individual organometallic molecules, with emphasis on the group V sources, including: (1) the methylarsines, di- and tri-methylarsine, (2) the ethylarsines, mono-, di-, and tri-ethylarsine, and (3) the singly substituted tertiarybutyl arsine and phosphine molecules. The pyrolysis and growth reactions occurring when both group III and group V precursors are present simultaneously, i.e., the reactions occuring during OMVPE growth of several III/V semiconductors, are also briefly reviewed.

  5. Nanoscale selective area epitaxy for optoelectronic devices

    NASA Astrophysics Data System (ADS)

    Elarde, V. C.; Coleman, J. J.

    Self-assembled quantum dots have been heavily researched in recent years because of the potential applications to quantum electronic and optoelectronic devices they present. The non-uniformity and random ordering resulting from the self-assembly processes, however, are detrimental to potential applications, prohibiting the type of engineering control necessary for complex systems. The work presented in this document has sought to overcome the limitations of self-assembly by combining selective area epitaxy via MOCVD with high-resolution electron beam lithography to achieve lateral control over semiconductor structures at the nanometer scale. Two different structures are presented. The first is patterned quantum dots which improve on the uniformity and order of similar self-assembled quantum dots. The second is an entirely novel structure, the nanopore active layer, which demonstrates the potential for this process to extend beyond the constraints of self-assembly. Experimental and theoretical results for both structures are presented.

  6. Epitaxy on Substrates with Hexagonal Lattice Symmetry.

    NASA Astrophysics Data System (ADS)

    Braun, Max Willi Hermann

    A general description of epitaxy between thin films and substrates of general symmetry was developed from a model with rigid substrate and overgrowth and extended to include strain of the overgrowth. The overgrowth-substrate interaction was described by Fourier series, usually truncated, defined on the reciprocal lattice of the interface surfaces of the crystals. Energy considerations lead directly to a criterion that epitaxial configurations occur when a pair of surface reciprocal lattice vectors of the substrate and overgrowth coincide, equivalent to atomic row matching. This is analogous to the von Laue criterion and Bragg equations of diffraction theory, with a geometrical realization related to the Ewald construction. When generalized, misfit strain, the spacing, line sense and Burgers vectors of misfit dislocations and misfit verniers are obtained from the reciprocal lattices of crystals with any symmetry and misfit. The most general structures can be described with convenient unit cells by using structure factors. Homogeneous misfit strain, the interfacial atom positions after local relaxation and misfit and elastic (harmonic approximation) strain energies were obtained by direct minimization of the total interfacial energy of a large (1105 atoms), but finite, system. The local relaxation was calculated with a Finite Element formulation. Systems with fcc {111 } or bcc{ 110} overgrowths on fcc {111} or hcp{0001} substrates were studied with respect to substrate symmetry, overgrowth size and anisotropy of the overgrowth elastic constants. Configurations such as Kurdjumov-Sachs (KS), Nishiyama-Wassermann (NW) and a pseudomorphic phase (2DC) were explained, while several other higher order configurations were predicted. The inherent difference in nature between the KS and NW and their relationship to the 2DC were emphasized. Deviations from the ideal orientation of KS linked to anisotropy for systems undergoing misfit strain were discovered. Deviations were also

  7. STM Properties and Manipulation of Epitaxial Graphene

    NASA Astrophysics Data System (ADS)

    Thibado, Paul

    2014-03-01

    Epitaxial graphene grown on SiC has been identified as one of the most likely avenues to graphene-based electronics. Understanding how morphology affects electronic properties is therefore important. In our work, epitaxial graphene was grown on the polar and non-polar a-, m-, and r-crystallographic oriented surfaces of SiC, and was investigated using scanning tunneling microscopy (STM). Bunched nano-ridges ten times smaller than previously recorded were observed throughout the surface. A new STM technique called electrostatic-manipulation scanning tunneling microscopy (EM-STM) was performed to modify the morphology of the nano-ridges. By modeling the electrostatics involved in the EM-STM measurement, we estimate that a force of 5 nN and energy of 10 eV was required to alter the local interfacial bonding. At the atomic scale, STM images of Moire patterns reveal low-angle, twisted bi-layer graphene, grain boundaries, and an apparent lattice constant dilation. We will show that this dilation is due to the STM tip electrostatically dragging the graphene surface. Collaborators: P. Xu, D. Qi, M.L. Ackerman, S.D. Barber, J.K. Schoelz, and J. Thompson, Department of Physics, University of Arkansas, Fayetteville, AR, 72701, USA; V.D. Wheelr, R.L. Myers-Ward, C.R. Eddy, Jr., and D.K. Gaskill, U.S. Naval Research Laboratory, Washington, DC 20375, USA; and L.O. Nyakiti, Texas A&M University. Department of Physics, University of Arkansas, Fayetteville, AR, 72701, USA.

  8. Epitaxial growth of Si deposited on (100) Si

    NASA Astrophysics Data System (ADS)

    Hung, L. S.; Lau, S. S.; von Allmen, M.; Mayer, J. W.; Ullrich, B. M.; Baker, J. E.; Williams, P.; Tseng, W. F.

    1980-11-01

    Epitaxial growth of deposited amorphous Si on chemically cleaned (100) Si has been found and layer-by-layer growth occurred at rates comparable to those in self-ion-implanted-amorphous Si. There is no evidence for appreciable oxygen penetration into the deposited layer during storage in air. The critical factors in achieving epitaxial growth are fast (˜50 Å/sec) deposition of Si onto a surface cleaned with a HF dip as a last rinse before loading into the vacuum system. Channeling and transmission electron microscopy measurements indicated that the epitaxial layers are essentially defect free. Secondary-ion mass spectroscopic analysis showed about 1014 oxygen/cm2 at the amorphous/crystal interface. With either higher interfacial oxygen coverage or slow (˜2 Å/sec) deposition, epitaxial growth rates are significantly slower.

  9. Growth of strontium ruthenate films by hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Marshall, Patrick B.; Kim, Honggyu; Ahadi, Kaveh; Stemmer, Susanne

    2017-09-01

    We report on the growth of epitaxial Sr2RuO4 films using a hybrid molecular beam epitaxy approach in which a volatile precursor containing RuO4 is used to supply ruthenium and oxygen. The use of the precursor overcomes a number of issues encountered in traditional molecular beam epitaxy that uses elemental metal sources. Phase-pure, epitaxial thin films of Sr2RuO4 are obtained. At high substrate temperatures, growth proceeds in a layer-by-layer mode with intensity oscillations observed in reflection high-energy electron diffraction. Films are of high structural quality, as documented by x-ray diffraction, atomic force microscopy, and transmission electron microscopy. The method should be suitable for the growth of other complex oxides containing ruthenium, opening up opportunities to investigate thin films that host rich exotic ground states.

  10. Coincident-site lattice matching during van der Waals epitaxy

    PubMed Central

    Boschker, Jos E.; Galves, Lauren A.; Flissikowski, Timur; Lopes, Joao Marcelo J.; Riechert, Henning; Calarco, Raffaella

    2015-01-01

    Van der Waals (vdW) epitaxy is an attractive method for the fabrication of vdW heterostructures. Here Sb2Te3 films grown on three different kind of graphene substrates (monolayer epitaxial graphene, quasi freestanding bilayer graphene and the SiC (6√3 × 6√3)R30° buffer layer) are used to study the vdW epitaxy between two 2-dimensionally (2D) bonded materials. It is shown that the Sb2Te3 /graphene interface is stable and that coincidence lattices are formed between the epilayers and substrate that depend on the size of the surface unit cell. This demonstrates that there is a significant, although relatively weak, interfacial interaction between the two materials. Lattice matching is thus relevant for vdW epitaxy with two 2D bonded materials and a fundamental design parameter for vdW heterostructures. PMID:26658715

  11. Epitaxial CoSi2 on MOS devices

    DOEpatents

    Lim, Chong Wee; Shin, Chan Soo; Petrov, Ivan Georgiev; Greene, Joseph E.

    2005-01-25

    An Si.sub.x N.sub.y or SiO.sub.x N.sub.y liner is formed on a MOS device. Cobalt is then deposited and reacts to form an epitaxial CoSi.sub.2 layer underneath the liner. The CoSi.sub.2 layer may be formed through a solid phase epitaxy or reactive deposition epitaxy salicide process. In addition to high quality epitaxial CoSi.sub.2 layers, the liner formed during the invention can protect device portions during etching processes used to form device contacts. The liner can act as an etch stop layer to prevent excessive removal of the shallow trench isolation, and protect against excessive loss of the CoSi.sub.2 layer.

  12. Improved process for epitaxial deposition of silicon on prediffused substrates

    NASA Technical Reports Server (NTRS)

    Clarke, M. G.; Halsor, J. L.; Word, J. C.

    1968-01-01

    Process for fabricating integrated circuits uniformly deposits silicon epitaxially on prediffused substrates without affecting the sublayer diffusion pattern. Two silicon deposits from different sources, and deposited at different temperatures, protect the sublayer pattern from the silicon tetrachloride reaction.

  13. Formation Of Ohmic Gold Contacts On Epitaxial GaAs

    NASA Technical Reports Server (NTRS)

    Hecht, Michael H.; Bell, L. Doug; Kaiser, William J.

    1991-01-01

    New low-temperature procedure used to deposit ohmic gold contacts on gallium arsenide epitaxial films, forming ohmic electrical contacts. Keeping wafer in vacuum until metallization prevents formation of rectifying contacts.

  14. 100-GHz Transistors from Wafer-Scale Epitaxial Graphene

    NASA Astrophysics Data System (ADS)

    Lin, Y.-M.; Dimitrakopoulos, C.; Jenkins, K. A.; Farmer, D. B.; Chiu, H.-Y.; Grill, A.; Avouris, Ph.

    2010-02-01

    The high carrier mobility of graphene has been exploited in field-effect transistors that operate at high frequencies. Transistors were fabricated on epitaxial graphene synthesized on the silicon face of a silicon carbide wafer, achieving a cutoff frequency of 100 gigahertz for a gate length of 240 nanometers. The high-frequency performance of these epitaxial graphene transistors exceeds that of state-of-the-art silicon transistors of the same gate length.

  15. Growth of epitaxial thin films by pulsed laser ablation

    SciTech Connect

    Lowndes, D.H.

    1992-10-01

    High-quality, high-temperature superconductor (HTSc) films can be grown by the pulsed laser ablation (PLA) process. This article provides a detailed introduction to the advantages and curent limitations of PLA for epitaxial film growth. Emphasis is placed on experimental methods and on exploitation of PLA to control epitaxial growth at either the unit cell or the atomic-layer level. Examples are taken from recent HTSc film growth. 33 figs, 127 refs. (DLC)

  16. Flux monitoring and control in epitaxy by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Pearsall, T. P.; Brown, N.; Ricker, N. L.; Johnson, M.

    1998-06-01

    Atomic fluorescence spectroscopy is a promising technique to detect individual chemical species at typical growth pressures in chemical beam and metal-organic epitaxy. We report results of initial experiments to measure triethyl gallium and dimethylethylamine-alane. We have successfully detected both species, but further development is needed to adapt this measurement to the needs of real-time sensing and control in chemical beam epitaxy.

  17. Investigation of antimicrobial physiology of orthorhombic and monoclinic nanoallotropes of sulfur at the interface of transcriptome and metabolome.

    PubMed

    Roy Choudhury, Samrat; Mandal, Amrita; Ghosh, Mahua; Basu, Sulagna; Chakravorty, Dipankar; Goswami, Arunava

    2013-07-01

    Nanosized elemental sulfur (ES) is already reported to exert superior antimicrobial efficacy than micron-sized ES, which encourages their use in drugs and therapeutics. The aim of the present study is to explore the possible route and mode of antimicrobial action of orthorhombic (α-SNPs) and monoclinic (β-SNPs) allotropes of sulfur, respectively, at their nano-dimensions. The antimicrobial efficacy of α- and β-SNPs was determined against both the conventionally ES-resistant and ES-susceptible fungi and bacteria. Both the SNPs inhibited the microbial growth, irrespective of their resistance profile to ES and caused significant deformities on the microbial cell surfaces. However, the extent of antimicrobial efficacy was found to be optimum for α-SNPs, which can be attributed to their size, shape, and surface modification. Subsequent transcript profiling, metabolite profiling, and enzymatic analyses revealed that α- and β-SNPs impaired a cluster of mitochondrial enzymes involved in cellular respiration and oxidative phosphorylation. ES and SNPs stress were found to elicit the NADPH-dependent glutathione reductase mediated ES-detoxification response in fungi and caused them to undertake the glyoxylate shunt in favor of energy conservation. A simultaneous study was also undertaken to assess the biocompatible or bio-adverse properties of SNPs in terms of their cytotoxic and genotoxic effects against the human derived lung fibroblast cell line (MRC-5). The present study hence explores the antimicrobial physiology of two novel functional materials and demonstrates their compatibility as a future putative antimicrobial drug.

  18. Crystal Field Splitting is Limiting the Stability and Strength of Ultra-incompressible Orthorhombic Transition Metal Tetraborides

    PubMed Central

    Zhang, R. F.; Wen, X. D.; Legut, D.; Fu, Z. H.; Veprek, S.; Zurek, E.; Mao, H. K.

    2016-01-01

    The lattice stability and mechanical strengths of the supposedly superhard transition metal tetraborides (TmB4, Tm = Cr, Mn and Fe) evoked recently much attention from the scientific community due to the potential applications of these materials, as well as because of general scientific interests. In the present study, we show that the surprising stabilization of these compounds from a high symmetry to a low symmetry structure is accomplished by an in-plane rotation of the boron network, which maximizes the in-plane hybridization by crystal field splitting between d orbitals of Tm and p orbitals of B. Studies of mechanical and electronic properties of TmB4 suggest that these tetraborides cannot be intrinsically superhard. The mechanical instability is facilitated by a unique in-plane or out-of-plane weakening of the three-dimensional covalent bond network of boron along different shear deformation paths. These results shed a novel view on the origin of the stability and strength of orthorhombic TmB4, highlighting the importance of combinational analysis of a variety of parameters related to plastic deformation of the crystalline materials when attempting to design new ultra-incompressible, and potentially strong and hard solids. PMID:26976479

  19. Density Functional Studies of Stoichiometric Surfaces of Orthorhombic Hybrid Perovskite CH3NH3PbI3

    SciTech Connect

    Wang, Yun; Huang, Jingsong; Sumpter, Bobby G.; Zhang, Haimin; Liu, Porun; Yang, Huagui; Zhao, Huijun

    2014-12-19

    Organic/inorganic hybrid perovskite materials are highly attractive for dye-sensitized solar cells as demonstrated by their rapid advances in energy conversion efficiency. In this work, the structures, energetics, and electronic properties for a range of stoichiometric surfaces of the orthorhombic perovskite CH3NH3PbI3 are theoretically studied using density functional theory. Various possible spatially and constitutionally isomeric surfaces are considered by diversifying the spatial orientations and connectivities of surface Pb-I bonds. The comparison of the surface energies for the most stable configurations identified for various surfaces shows that the stabilities of stoichiometric surfaces are mainly dictated by the coordination numbers of surface atoms, which are directly correlated with the numbers of broken bonds. Additionally, Coulombic interactions between I anions and organic countercations on the surface also contribute to the stabilization. Electronic properties are compared between the most stable (100) surface and the bulk phase, showing generally similar features except for the lifted band degeneracy and the enhanced bandgap energy for the surface. These studies on the stoichiometric surfaces serve as the first step toward gaining a fundamental understanding of the interfacial properties in the current structural design of perovskite based solar cells, in order to achieve further breakthroughs in solar conversion efficiencies.

  20. Analytical study of body waves in orthorhombic media and comparison with SKS-phase observations from selected stations

    NASA Astrophysics Data System (ADS)

    Löberich, Eric; Bokelmann, Götz

    2016-04-01

    Anisotropic effects of wave propagation, observed in the Earth, provide interesting applications in basic research and practice, e.g., in reservoir geophysics and other fields. Teleseismic waves often evidence upper mantle anisotropy, as created by aligned olivine grains. While each grain is associated with orthorhombic symmetry, the preferred alignment may lead to a transversely isotropic characteristic. Considering body waves passing through an anisotropic medium, a splitting of shear waves can usually be observed, since their transverse polarization leads to a separation of the two quasi-shear waves. The associated splitting-delay is generated if the related fast and slow seismic velocities differ. Most of the previous shear-wave splitting investigations were based on the common assumption of near-vertical incidence. However, the influence of increasing incidence angles, which may lead to angular dependent splitting-delay and fast polarization orientation, has been pointed out by Davis (2003). Our study investigates the occurrence of these postulated dependences on azimuth and incidence angle (distance), examining splitting observations in SKS-recordings at selected broadband stations (e.g., Djibouti and Red Lake, Ontario).

  1. Crystal structure and partial Ising-like magnetic ordering of orthorhombic Dy2TiO5

    DOE PAGES

    Shamblin, Jacob; Calder, Stuart; Dun, Zhiling; ...

    2016-07-12

    The structure and magnetic properties of orthorhombic Dy2TiO5 have been investigated using x-ray diffraction, neutron diffraction, and alternating current (ac)/direct current (dc) magnetic susceptibility measurements. In this paper, we report a continuous structural distortion below 100 K characterized by negative thermal expansion in the [0 1 0] direction. Neutron diffraction and magnetic susceptibility measurements revealed that two-dimensional (2D) magnetic ordering begins at 3.1 K, which is followed by a three-dimensional magnetic transition at 1.7 K. The magnetic structure has been solved through a representational analysis approach and can be indexed with the propagation vector k = [0 1/2 0]. Themore » spin structure corresponds to a coplanar model of interwoven 2D “sheets” extending in the [0 1 0] direction. The local crystal field is different for each Dy3+ ion (Dy1 and Dy2), one of which possesses strong uniaxial symmetry indicative of Ising-like magnetic ordering. In conclusion, consequently, two succeeding transitions under magnetic field are observed in the ac susceptibility, which are associated with flipping each Dy3+ spin independently.« less

  2. Effect of film thickness on NO2 gas sensing properties of sprayed orthorhombic nanocrystalline V2O5 thin films

    NASA Astrophysics Data System (ADS)

    Mane, A. A.; Moholkar, A. V.

    2017-09-01

    The nanocrystalline V2O5 thin films with different thicknesses have been grown onto the glass substrates using chemical spray pyrolysis (CSP) deposition method. The XRD study shows that the films exhibit an orthorhombic crystal structure. The narrow scan X-ray photoelectron spectrum of V-2p core level doublet gives the binding energy difference of 7.3 eV, indicating that the V5+ oxidation state of vanadium. The FE-SEM micrographs show the formation of nanorods-like morphology. The AFM micrographs show the high surface area to volume ratio of nanocrystalline V2O5 thin films. The optical study gives the band gap energy values of 2.41 eV, 2.44 eV, 2.47 eV and 2.38 eV for V2O5 thin films deposited with the thicknesses of 423 nm, 559 nm, 694 nm and 730 nm, respectively. The V2O5 film of thickness 559 nm shows the NO2 gas response of 41% for 100 ppm concentration at operating temperature of 200 °C with response and recovery times of 20 s and 150 s, respectively. Further, it shows the rapid response and reproducibility towards 10 ppm NO2 gas concentration at 200 °C. Finally, NO2 gas sensing mechanism based on chemisorption process is discussed.

  3. Density Functional Studies of Stoichiometric Surfaces of Orthorhombic Hybrid Perovskite CH3NH3PbI3

    DOE PAGES

    Wang, Yun; Huang, Jingsong; Sumpter, Bobby G.; ...

    2014-12-19

    Organic/inorganic hybrid perovskite materials are highly attractive for dye-sensitized solar cells as demonstrated by their rapid advances in energy conversion efficiency. In this work, the structures, energetics, and electronic properties for a range of stoichiometric surfaces of the orthorhombic perovskite CH3NH3PbI3 are theoretically studied using density functional theory. Various possible spatially and constitutionally isomeric surfaces are considered by diversifying the spatial orientations and connectivities of surface Pb-I bonds. The comparison of the surface energies for the most stable configurations identified for various surfaces shows that the stabilities of stoichiometric surfaces are mainly dictated by the coordination numbers of surface atoms,more » which are directly correlated with the numbers of broken bonds. Additionally, Coulombic interactions between I anions and organic countercations on the surface also contribute to the stabilization. Electronic properties are compared between the most stable (100) surface and the bulk phase, showing generally similar features except for the lifted band degeneracy and the enhanced bandgap energy for the surface. These studies on the stoichiometric surfaces serve as the first step toward gaining a fundamental understanding of the interfacial properties in the current structural design of perovskite based solar cells, in order to achieve further breakthroughs in solar conversion efficiencies.« less

  4. Direct Formation of Large-Area 2D Nanosheets from Fluorescent Semiconducting Homopolymer with Orthorhombic Crystalline Orientation.

    PubMed

    Yang, Sanghee; Shin, Suyong; Choi, Inho; Lee, Jaeho; Choi, Tae-Lim

    2017-03-01

    Semiconducting polymers have been widely investigated due to their intriguing optoelectronic properties and their high crystallinity that provides a strong driving force for self-assembly. Although there are various reports of successful self-assembly of nanostructures using semiconducting polymers, direct in situ self-assembly of these polymers into two-dimensional (2D) nanostructures has proven difficult, despite their importance for optoelectronics applications. Here, we report the synthesis of a simple conjugated homopolymer by living cyclopolymerization of a 1,6-heptadiyne (having a fluorene moiety) and its efficient in situ formation of large-area 2D fluorescent semiconducting nanostructures. Using high-resolution imaging tools such as atomic force microscopy and transmission electron microscopy, we observed the solvent-dependent self-assembly behaviors of this homopolymer; the identical starting polymer formed 2D nanosheets with different shapes, such as rectangle, raft, and leaf, when dissolved in different solvents. Furthermore, super-resolution optical microscopy enabled the real-time imaging of the fluorescent 2D nanosheets, revealing their stable and uniform shapes, fluorescence, and solution dynamics. Notably, we propose an orthorhombic crystalline packing model to explain the direct formation of 2D nanostructures based on various diffraction patterns, providing important insight for their shape modulation during the self-assembly.

  5. Polymorphic CoSe2 with mixed orthorhombic and cubic phases for highly efficient hydrogen evolution reaction.

    PubMed

    Zhang, Hongxiu; Yang, Bin; Wu, Xiaolin; Li, Zhongjian; Lei, Lecheng; Zhang, Xingwang

    2015-01-28

    We report polymorphic CoSe2 (p-CoSe2) with mixed orthorhombic and cubic phases as a highly active electrocatalyst toward hydrogen evolution reaction (HER). The p-CoSe2 is obtained by calcining CoSex via electrodeposition at 300 °C. The results of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) demonstrated the crystal structure of p-CoSe2. The p-CoSe2 exhibits excellent electrocatalytic activity for HER with a low onset overpotential of -70 mV and a small Tafel slope of ∼30 mV/decade, which are basically state-of-the-art performance of earth-abundant electrocatalysts. The HER performance of p-CoSe2 was much higher than that of amorphous CoSex, cubic CoSe2, and CoSe. This study offers a competitive electrocatalyst for HER and opens up a new strategy to the synthesis of catalysts for energy conversion.

  6. Stimulated Raman scattering spectroscopy and χ(3)-nonlinear lasing effects in single crystals of aragonite (orthorhombic CaCO3)

    NASA Astrophysics Data System (ADS)

    Kaminskii, A. A.; Rhee, H.; Lux, O.; Eichler, H. J.; Koltashev, V. V.; Kleinschrodt, R.; Bohatý, L.; Becker, P.

    2012-04-01

    The present work gives a brief review of the nonlinear χ(2)- and χ(3)-lasing properties of SRS-active natural crystals (minerals) known so far. This compilation complements new results of a detailed investigation of Raman induced χ(3)-effects in aragonite single crystals (orthorhombic CaCO3) under single- and dual-wavelength picosecond excitation in the UV, visible and near-IR spectral ranges. The studied effects at room and cryogenic temperatures comprise Stokes and anti-Stokes combs of almost two octaves bandwidth, THG, SFG, as well as cascaded and cross-cascaded χ(3) leftrightarrow χ(3) interactions. All recorded lasing χ(3)-components were identified and attributed to three observed SRS-promoting vibration modes ωSRS1 ≈ 1087 cm-1, ωSRS2 ≈ 152 cm-1, and ωSRS3 ≈ 205 cm-1 (at room temperature) of aragonite. Stimulated Raman scattering (SRS) investigations of minerals so far enrich the arsenal of SRS-active crystals, which can be applied to solve fundamental and applied tasks of modern laser physics and nonlinear optics.

  7. Onset of N-Atlantic rifting in the Hoop Fault Complex (SW Barents Sea): An orthorhombic dominated faulting?

    NASA Astrophysics Data System (ADS)

    Collanega, Luca; Massironi, Matteo; Breda, Anna; Kjølhamar, Bent Erlend

    2017-06-01

    The Hoop Fault Complex is one of the main fault systems in the south-western Barents Sea. This platform underwent a long extensional history under the influence of both the Atlantic and the Arctic rifts, which culminated in the Atlantic break-up in the Cenozoic. The object of this paper is the structural analysis of the late Mesozoic rifting in the Hoop Fault Complex area, based on a 10,000 km2 3D seismic volume. We constrained the intervals of activity of the main fault systems during the late Mesozoic rifting through the synsedimentary thickness variations, reconstructing the evolution of the strain field. In order to clarify the relationship between the strain field and the rheological layering, we compared the structures at different depths, highlighting a decoupling of shallow and deep deformations along the Triassic ductile clay-rich layers. A transition from an orthorhombic faulting, corresponding to a 3D strain field, to an Andersonian faulting, related to a planar strain field, was observed. The change of the strain field could be driven by the evolution of the regional stress field or, alternatively, by the reactivation of deep structures. In this latter case, the structural evolution of the Hoop Fault Complex could potentially represent a general process to be extended to other rifting settings with a similar mechanical stratigraphy.

  8. Fatigue damage evolution and property degradation of a SCS-6/Ti-22Al-23Nb orthorhombic titanium aluminide composite

    SciTech Connect

    Wang, P.C.; Jeng, S.M.; Yang, J.M.; Russ, S.M.

    1996-08-01

    The fatigue damage evolution and property degradation of a SCS-6/Ti-22Al-23Nb orthorhombic titanium aluminide composite under low cycle fatigue loading at room temperature was investigated. The fatigue test was conducted under a load-controlled mode with a load ratio (R) of 0.1, a frequency of 10 Hz, and a maximum applied stress ranging from 600 to 945 MPa. The stiffness reduction as well as the evolution of microstructural damage which includes matrix crack length, matrix crack density and interfacial debonding length as a function of fatigue cycles, and applied stresses were measured. An analytical model and a computer simulation were also developed to predict the residual stiffness and the post-fatigued tensile strength as a function of microstructural damage. Finally, a steady-state crack growth model proposed by Marshall et al. was used to predict the interfacial frictional stress and the critical crack length. Correlation between the theoretical predictions and experimental results were also discussed.

  9. Native defects and Pr impurities in orthorhombic CaTiO3 by first-principles calculations

    NASA Astrophysics Data System (ADS)

    Zhu, Ailing; Wang, Jianchuan; Zhao, Dongdong; Du, Yong

    2011-07-01

    Formation energies of native defects and Pr impurities in orthorhombic CaTiO3 are explored using the first-principles calculations. The Ca vacancy (VCa), Ti vacancy (VTi) and Ca antisite (CaTi) are found to be energetically preferable. The Ti antisite (TiCa) and O vacancy (VO) are not energetically favorable in the wide range of Fermi level. In Pr-doped CaTiO3, Pr substituting for Ca (PrCa) is likely to form under condition A in which CaTiO3 is in equilibrium with CaO and O2. Under condition B (TiO2, CaTiO3 and O2 are in equilibrium), PrTi defect is energetically preferable depending on the Fermi levels. Several native defects and the two sites of Pr impurities in CaTiO3 are coincided with several different defects in Pr-doped CaTiO3 reported in the literature. Based on the present calculations, we can elucidate that the Ca deficiency design of the traditional formula Ca1-xVCa(x/2)PrxTiO3 is not the best for efficient red photoluminescence, which is realized via the experimental measurements.

  10. Epitaxial patterning of thin-films: conventional lithographies and beyond

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Krishnan, Kannan M.

    2014-09-01

    Thin-film based novel magnetic and electronic devices have entered a new era in which the film crystallography, structural coherence, and epitaxy play important roles in determining their functional properties. The capabilities of controlling such structural and functional properties are being continuously developed by various physical deposition technologies. Epitaxial patterning strategies further allow the miniaturization of such novel devices, which incorporates thin-film components into nanoscale architectures while keeping their functional properties unmodified from their ideal single-crystal values. In the past decade, epitaxial patterning methods on the laboratory scale have been reported to meet distinct scientific inquires, in which the techniques and processes used differ from one to the other. In this review we summarize many of these pioneering endeavors in epitaxial patterning of thin-film devices that use both conventional and novel lithography techniques. These methods demonstrate epitaxial patterning for a broad range of materials (metals, oxides, and semiconductors) and cover common device length scales from micrometer to sub-hundred nanometer. Whilst we have been motivated by magnetic materials and devices, we present our outlook on developing systematic-strategies for epitaxial patterning of functional materials which will pave the road for the design, discovery and industrialization of next-generation advanced magnetic and electronic nano-devices.

  11. The Controller Synthesis of Metastable Oxides Utilizing Epitaxy and Epitaxial Stabilization

    SciTech Connect

    Schlom, Darrell

    2003-12-02

    Molecular beam epitaxy (MBE) has achieved unparalleled control in the integration of semiconductors at the nanometer. These advances were made through the use of epitaxy, epitaxial stabilization, and a combination of composition-control techniques including adsorption-controlled growth and RHEED-based composition control that we have developed, understood, and utilized for the growth of oxides. Also key was extensive characterization (utilizing RHEED, four-circle x-ray diffraction, AFM, TEM, and electrical characterization techniques) in order to study growth modes, optimize growth conditions, and probe the structural, dielectric, and ferroelectric properties of the materials grown. The materials that we have successfully engineered include titanates (PbTiO3, Bi4Ti3O12), tantalates (SrBi2Ta2O9), and niobates (SrBi2Nb2O9); layered combinations of these perovskite-related materials (Bi4Ti3O12-SrTiO3 and Bi4Ti3O12-PbTiO3 Aurivillius phases and metastable PbTiO3/SrTiO3 and BaTiO3/SrTiO3 superlattices), and new metastable phases (Srn+1TinO3n+1 Ruddlesden-Popper phases). The films were grown by reactive MBE and pulsed laser deposition (PLD). Many of these materials are either new or have been synthesized with the highest perfection ever reported. The controlled synthesis of such layered oxide heterostructures offers great potential for tailoring the superconducting, ferroelectric, and dielectric properties of these materials. These properties are important for energy technologies.

  12. Hydride vapor phase epitaxy of aluminum nitride

    NASA Astrophysics Data System (ADS)

    Kamber, Derrick Shane

    AlN is a promising substrate material for AlGaN-based UV optoelectronic devices and high-power, high-frequency electronic devices. Since large-area bulk AlN crystals are not readily available, one approach to prepare AlN substrates is to heteroepitaxially deposit thick (e.g., 10-300+ mum) AlN layers by hydride vapor phase epitaxy. Initial efforts focused on growing AlN layers on sapphire substrates with growth rates up to 75 mum/hr. The resulting layers were colorless, smooth, and specular. Subsurface cracking, attributed to the plastic relief of tensile strain from island coalescence, was observed but did not adversely affect the surface morphology of the AlN layers. The surfaces possessed rms roughnesses as low as 0.316 nm over 5 x 5 mum2 sampling areas, but hexagonal hillock formation was observed for thick films grown at high growth rates. TEM revealed that the threading dislocation (TD) density of the films was 2 x 109 cm-2. The high TD densities for direct growth of AlN films on foreign substrates motivated the development of lateral epitaxial overgrowth approaches for defect reduction. Growth of AlN layers on patterned SiC substrates produced coalesced AlN films possessing TD densities below 8.3 x 106 cm -2 in the laterally grown wing regions, as compared to 1.8 x 109 cm-2 in the seed regions. These films, however, cracked on cooldown due to the difference in thermal expansion coefficients for AlN and SiC. To avoid this cracking, AlN layers were grown on patterned sapphire substrates. Although the films were able to be coalesced and contained few or no cracks, the TDs in these films were not confined to the seed regions. This produced a relatively uniform distribution of TDs over the surfaces of the films, with only a modest reduction in the TD density of 1 x 10 8 cm-2. Selective area growth of AlN was also pursued using Si3N4, SiO2, and Ti masks. Growth selectivity and film coalescence was observed for films grown on each masking material, but none of the

  13. Quality of epitaxial InAs nanowires controlled by catalyst size in molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zhang, Zhi; Lu, Zhen-Yu; Chen, Ping-Ping; Xu, Hong-Yi; Guo, Ya-Nan; Liao, Zhi-Ming; Shi, Sui-Xing; Lu, Wei; Zou, Jin

    2013-08-01

    In this study, the structural quality of Au-catalyzed InAs nanowires grown by molecular beam epitaxy is investigated. Through detailed electron microscopy characterizations and analysis of binary Au-In phase diagram, it is found that defect-free InAs nanowires can be induced by smaller catalysts with a high In concentration, while comparatively larger catalysts containing less In induce defected InAs nanowires. This study indicates that the structural quality of InAs nanowires can be controlled by the size of Au catalysts when other growth conditions remain as constants.

  14. Uniaxial strain-induced magnetic order transition from E-type to A-type in orthorhombic YMnO{sub 3} from first-principles

    SciTech Connect

    Lin, S. X.; Fang, X. G.; Zhang, A. H.; Lu, X. B.; Gao, J. W.; Gao, X. S.; Zeng, M.; Liu, J.-M.

    2014-10-28

    The spin ordering magnetic structures of orthorhombic YMnO{sub 3} subjected to uniaxial strain have been investigated using first-principles calculations based on density functional theory. On applying compressive uniaxial strain of −0.8% along the b orientation, the spin ordering magnetic structure is predicted to change from E-type to A-type antiferromagnetic orderings. The structure analysis also reveals that the uniaxial strain has a dramatic influence on the Mn-O bond lengths and Mn-O-Mn bond angles, allowing the gradual suppression of the alternation of the long and short Mn-O-Mn bonds in the ab plane. These changes present very interesting possibilities for engineering the spin ordering along with ferroelectric property in orthorhombic YMnO{sub 3}.

  15. Experimental and ab initio investigations of the x-ray absorption near edge structure of orthorhombic LuMnO3

    NASA Astrophysics Data System (ADS)

    Hu, Y.; Borca, C. N.; Kleymenov, E.; Nachtegaal, M.; Delley, B.; Janousch, M.; Dönni, A.; Tachibana, M.; Kitazawa, H.; Takayama-Muromachi, E.; Kenzelmann, M.; Niedermayer, C.; Lippert, T.; Wokaun, A.; Schneider, C. W.

    2012-06-01

    X-ray near edge absorption spectroscopy was used to probe the electronic structure of multiferroic orthorhombic LuMnO3 polycrystalline samples and strained, twin-free orthorhombic (1-10) LuMnO3 films grown by pulsed laser deposition on (1-10) YAlO3 substrates. For all o-LuMnO3 samples x-ray near edge absorption spectroscopy spectra reveal that the pre-edge structure is influenced by the increase in MnO6 distortion as a result of the smaller Re-ion or film strain. Furthermore there is clear evidence of anisotropic Mn-O bonding and Mn orbital ordering along the c- and [110] direction. The experimental film and bulk data are in agreement with ab initio simulations.

  16. Epitaxial oxidation of Ni-V biaxially textured tapes

    NASA Astrophysics Data System (ADS)

    Petrisor, T.; Boffa, V.; Celentano, G.; Ciontea, L.; Fabbri, F.; Galluzzi, V.; Gambardella, U.; Mancini, A.; Rufoloni, A.; Varesi, E.

    2002-08-01

    The epitaxial oxidation of the (0 0 1)[1 0 0] textured Ni 100- xV x tapes was studied because of the practical interest of NiO as a first buffer layer for the YBCO based coated conductors. The study revealed that the oxidation of the Ni-V alloy is rather complex, the less noble V being internally oxidized, while Ni undergoes an external oxidation. Moreover, the formation of the NiVO 3 and of Ni 7V 5O 17 compounds have negative effects on the epitaxial oxidation and on the surface morphology, as well. The role of vanadium on the epitaxial oxidation of Ni-V alloy has not been fully understood yet. The optimum conditions for the epitaxial oxidation have been found to be: 700epitaxial NiO films obtained under these conditions have a good out-of-plane and in-plane orientation, with a full-width-half-maximum of about 6.5° and 9.5°, respectively. The in-plane epitaxial relationship is [1 0 0]NiO∥[1 1 0]Ni-V. The as-obtained films have a compact and crack-free morphology, with grain sizes ranging from 30 to 300 nm. Nevertheless, the NiO films grown on (1 1 3) oriented grains or on twins are polycrystalline with a bright aspect, exhibiting a spongeous morphology. Epitaxial YBCO/CeO 2/NiO/Ni-V structures grown on the NiO template have a critical current density of about 0.6 MA/cm 2 at 77 K and zero magnetic field.

  17. The structure of an orthorhombic crystal form of a ‘forced reduced’ thiol peroxidase reveals lattice formation aided by the presence of the affinity tag

    PubMed Central

    Beckham, Katherine S. H.; Byron, Olwyn; Roe, Andrew J.; Gabrielsen, Mads

    2012-01-01

    Thiol peroxidase (Tpx) is an atypical 2-Cys peroxiredoxin, which has been suggested to be important for cell survival and virulence in Gram-negative pathogens. The structure of a catalytically inactive version of this protein in an orthorhombic crystal form has been determined by molecular replacement. Structural alignments revealed that Tpx is conserved. Analysis of the crystal packing shows that the linker region of the affinity tag is important for formation of the crystal lattice. PMID:22691780

  18. The structure of an orthorhombic crystal form of a 'forced reduced' thiol peroxidase reveals lattice formation aided by the presence of the affinity tag.

    PubMed

    Beckham, Katherine S H; Byron, Olwyn; Roe, Andrew J; Gabrielsen, Mads

    2012-05-01

    Thiol peroxidase (Tpx) is an atypical 2-Cys peroxiredoxin, which has been suggested to be important for cell survival and virulence in Gram-negative pathogens. The structure of a catalytically inactive version of this protein in an orthorhombic crystal form has been determined by molecular replacement. Structural alignments revealed that Tpx is conserved. Analysis of the crystal packing shows that the linker region of the affinity tag is important for formation of the crystal lattice.

  19. Implementing Room-Temperature Multiferroism by Exploiting Hexagonal-Orthorhombic Morphotropic Phase Coexistence in LuFeO3 Thin Films.

    PubMed

    Song, Seungwoo; Han, Hyeon; Jang, Hyun Myung; Kim, Young Tae; Lee, Nam-Suk; Park, Chan Gyung; Kim, Jeong Rae; Noh, Tae Won; Scott, James F

    2016-09-01

    Room-temperature multiferroism in LuFeO3 (LFO) films is demonstrated by exploiting the orthorhombic-hexagonal (o-h) morphotrophic phase coexistence. The LFO film further reveals a magnetoelectric coupling effect that is not shown in single-phase (h- or o-) LFO. The observed multiferroism is attributed to the combination of sufficient polarization from h-LFO and net magnetization from o-LFO.

  20. Mesoporous orthorhombic Nb2O5 nanofibers as pseudocapacitive electrodes with ultra-stable Li storage characteristics

    NASA Astrophysics Data System (ADS)

    Cheong, Jun Young; Jung, Ji-Won; Youn, Doo-Young; Kim, Chanhoon; Yu, Sunmoon; Cho, Su-Ho; Yoon, Ki Ro; Kim, Il-Doo

    2017-08-01

    Ultra-stable pseudocapacitive electrodes for lithium-ion batteries (LIBs) are increasing in demand as highly sustainable energy storage system with excellent charge transport is important. The establishment of facile, controllable, and scalable synthesis of pseudocapacitive electrode materials is an attractive solution to realize such objectives. Here, we have successfully fabricated mesoporous orthorhombic Nb2O5 nanofibers (m-T-Nb2O5 NFs) by simple single-spinneret electrospinning followed by calcination at 600 °C. As-formed m-T-Nb2O5 NFs exhibit high surface area (23.7 m2 g-1) and a number of mesopores in the vacant sites where organic polymer was once decomposed. Such rationally designed m-T-Nb2O5-NFs allow facile Li ion and electron transport, with pseudocapacitive behavior. Arising from the high surface area coupled with mesopores in-between the Nb2O5 nanograins, it exhibits ultra-long cycle retention (a capacity of ∼160 mAh g-1 at 500 mA g-1 after 2000 cycles and ∼88 mAh g-1 at 3000 mA g-1 after 5000 cycles) and higher rate capability (∼70 mAh g-1 at 5000 mA g-1). Such cycle retention characteristics of m-T-Nb2O5-NFs are at least 100-fold slower capacity decay compared with previously reported one-dimensional (1D) Nb2O5 nanostructures and even superior or comparable to recently reported Nb2O5-graphene composite materials.

  1. Cd4Cu7As, the first representative of a fully ordered, orthorhombically distorted MgCu2 Laves phase.

    PubMed

    Osters, Oliver; Nilges, Tom; Schöneich, Michael; Schmidt, Peer; Rothballer, Jan; Pielnhofer, Florian; Weihrich, Richard

    2012-08-06

    The ternary Laves phase Cd(4)Cu(7)As is the first intermetallic compound in the system Cu-Cd-As and a representative of a new substitution variant for Laves phases. It crystallizes orthorhombically in the space group Pnnm (No. 58) with lattice parameters a = 9.8833(7) Å; b = 7.1251(3) Å; c = 5.0895(4) Å. All sites are fully occupied within the standard deviations. The structure can be described as typical Laves phase, where Cu and As are forming vertex-linked tetrahedra and Cd adopts the structure motive of a distorted diamond network. Cd(4)Cu(7)As was prepared from stoichiometric mixtures of the elements in a solid state reaction at 1000 °C. Magnetic measurements are showing a Pauli paramagnetic behavior. During our systematical investigations within the ternary phase triangle Cd-Cu-As the cubic C15-type Laves phase Cd(4)Cu(6.9(1))As(1.1(1)) was structurally characterized. It crystallizes cubic in the space group Fd3m with lattice parameter a = 7.0779(8) Å. Typically for quasi-binary Laves phases Cu and As are both occupying the 16c site. Chemical bonding, charge transfer and atomic properties of Cd(4)Cu(7)As were analyzed by band structure, ELF, and AIM calculations. On the basis of the general formula for Laves phases AB(2), Cd is slightly positively charged forming the A substructure, whereas Cu and As represent the negatively charged B substructure in both cases. The crystal structure distortion is thus related to local effects caused by Arsenic that exhibits a larger atomic volume (18 Å(3) compared to 13 Å(3) for Cu) and higher ionicity in bonding.

  2. Thermally and optically stimulated luminescence in long persistent orthorhombic strontium aluminates doped with Eu, Dy and Eu, Nd

    NASA Astrophysics Data System (ADS)

    Zúñiga-Rivera, N. J.; Salas-Castillo, P.; Chernov, V.; Díaz-Torres, L. A.; Meléndrez, R.; García-Gutierrez, R.; Carrillo-Torres, R. C.; Barboza-Flores, M.

    2017-05-01

    The long persistent luminescence, thermoluminescence (TL) and IR stimulated luminescence properties of two orthorhombic strontium aluminates (Sr4Al14O25) co-doped with Eu2+, Dy3+ and Eu2+, Nd3+ exposed to beta radiation is reported. The phosphors were synthesized by the combustion method followed by a post-annealing treatment under a reductive carbon atmosphere. Photoluminescence emission spectra of both phosphors are typical for emission of Eu2+ ions with 7-fold and 10-fold coordination in Sr4Al14025 and consist of the main band at 480 nm and a weak band between 390 and 440 nm. After exposure to beta radiation the Sr4Al14025:Eu2+,Dy3+ phosphor exhibits two strongly overlapped TL peaks at about 70 and 100 °C while the low temperature TL of the Sr4Al14025:Eu2+,Nd3+ phosphor consist of two well separated peaks with maxima at about 60 and 130 °C. Additionally, both phosphors exhibit a weak TL between 180 and 400 °C. The traps responsible for the low temperature TL peaks are the Dy3+ and Nd3+ centers situated in two different Sr sites with 7-fold and 10-fold coordination. The thermal emptying of the Dy and Nd filled traps creates ultra-long intense afterglow, which gradually decays with time and remains detectable after 220 h storage in dark. IR stimulation of beta irradiated phosphors creates intense IR stimulated luminescence, which is related to the release of electrons from the filled Dy and Nd traps.

  3. Environmental effects on orthorhombic alloy Ti-22Al-25Nb in air between 650 and 1,000 C

    SciTech Connect

    Leyens, C. |

    1999-12-01

    The environmental behavior of an orthorhombic titanium-aluminide alloy, Ti-22Al-25Nb, was studied in dry and humid air between 650 and 1,000 C by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Microhardness measurements were performed after exposure to gage hardening due to nitrogen and oxygen ingress. The parabolic rate constant of Ti-22Al-25Nb was of the same order as conventional titanium alloys and Ti{sub 3}Al-based titanium aluminides at and below 750 C. Between 800 and 1,000 C, the oxidation resistance of Ti-22Al-25Nb was as good as {gamma}-TiAl base aluminides; however, the growth rate changed from parabolic to linear after several tens of hours at 900 and 1,000 C. The mixed oxide scale consisted of TiO{sub 2}, AlNbO{sub 4}, and Al{sub 2}O{sub 3} with TiO{sub 2} being the dominant oxide phase. Underneath the oxide scale, a nitride layer formed in the temperature range investigated and, at 1,000 C, internal oxidation was observed below this layer. In all cases, oxygen diffused deeply into the subsurface zone and caused severe embrittlement. Microhardness measurements revealed that Ti-22Al-25Nb was hardened in a zone as far as 300 {micro}m below the oxide scale when exposed to air at 900 C for 500 hr. The peak hardness depended on exposure time and reached five times the average hardness of the bulk material under the above conditions.

  4. Modelling Orthorhombic Anisotropic Effects for Reservoir Fracture Characterization of a Naturally Fractured Tight Carbonate Reservoir, Onshore Texas, USA

    NASA Astrophysics Data System (ADS)

    Osinowo, Olawale Olakunle; Chapman, Mark; Bell, Rebecca; Lynn, Heloise B.

    2017-09-01

    In this study we present a step-by-step theoretical modelling approach, using established seismic wave propagation theories in anisotropic media, to generate unique anisotropic reflection patterns observed from three-dimensional pure-mode pressure (3D-PP), full-azimuth and full-offset seismic reflection data acquired over a naturally fractured tight carbonate field, onshore Texas, USA. Our aim is to gain an insight into the internal structures of the carbonate reservoir responsible for the observed anisotropic reflection patterns. From the generated model we were able to establish that the observed field seismic reflection patterns indicate azimuthal anisotropy in the form of crack induced shear-wave splitting and variation in P-wave velocity with offset and azimuth. Amplitude variation with azimuth (AVAZ) analysis also confirmed multi-crack sets induced anisotropy which is characteristic of orthorhombic symmetry, evident as multiple bright and dim-amplitude azimuth directions as well as complete reversal of bright-amplitude to dim-amplitude azimuth direction as the angle of incidence increases from near (≤15°) to mid (≥30°) offsets. Finally, we fitted the generated P-wave velocity into an ellipse to determine the intensity and orientation (N26E) of the open crack set as well as the direction of the minimum in situ stress axis (N116E) within the reservoir. The derived information served as an aid for the design of horizontal well paths that would intercept open fractures and ensure production optimization of the carbonate reservoir, which was on production decline despite reservoir studies that indicate un-depleted reserves.

  5. with Orthorhombic Structure

    NASA Astrophysics Data System (ADS)

    Kawamoto, Yusuke; Iwasaki, Hideo

    2014-06-01

    Thermoelectric properties of the substitution system (Bi1- x Sb x )2S3 have been investigated, where binary Bi2S3 and Sb2S3 are narrow-gap semiconductors. It is confirmed that metallic conduction, originating from mobile electrons due to production of sulfur vacancies, is observed in Bi2S3 over a wide temperature range below room temperature. In Sb2S3, mobile carriers are not created and insulating behavior is observed because of the considerably wide bandgap. Change of the carrier number by substitution of antimony contributes strongly to the thermoelectric properties (resistivity and Seebeck coefficient). As a result, the nondimensional figure of merit, ZT, decreases monotonically with increasing antimony content. The maximum value of ZT is obtained in Bi2S3 as ZT ≈ 0.1 at room temperature. It is pointed out that control of the carrier number, which is achieved by production of sulfur vacancies, is important to achieve high thermoelectric performance in the (Bi1- x Sb x )2S3 system. It is possible that the thermoelectric efficiency could be improved by control of the carrier concentration in the bismuth-rich region, including pure binary Bi2S3.

  6. Asymmetric shape transitions of epitaxial quantum dots

    NASA Astrophysics Data System (ADS)

    Wei, Chaozhen; Spencer, Brian J.

    2016-06-01

    We construct a two-dimensional continuum model to describe the energetics of shape transitions in fully faceted epitaxial quantum dots (strained islands) via minimization of elastic energy and surface energy at fixed volume. The elastic energy of the island is based on a third-order approximation, enabling us to consider shape transitions between pyramids, domes, multifaceted domes and asymmetric intermediate states. The energetics of the shape transitions are determined by numerically calculating the facet lengths that minimize the energy of a given island type of prescribed island volume. By comparing the energy of different island types with the same volume and analysing the energy surface as a function of the island shape parameters, we determine the bifurcation diagram of equilibrium solutions and their stability, as well as the lowest barrier transition pathway for the island shape as a function of increasing volume. The main result is that the shape transition from pyramid to dome to multifaceted dome occurs through sequential nucleation of facets and involves asymmetric metastable transition shapes. We also explicitly determine the effect of corner energy (facet edge energy) on shape transitions and interpret the results in terms of the relative stability of asymmetric island shapes as observed in experiment.

  7. Epitaxial overgrowth of platinum on palladium nanocrystals

    NASA Astrophysics Data System (ADS)

    Jiang, Majiong; Lim, Byungkwon; Tao, Jing; Camargo, Pedro H. C.; Ma, Chao; Zhu, Yimei; Xia, Younan

    2010-11-01

    This paper describes a systematic study on the epitaxial overgrowth of Pt on well-defined Pd nanocrystals with different shapes (and exposed facets), including regular octahedrons, truncated octahedrons, and cubes. Two different reducing agents, i.e., citric acid and L-ascorbic acid, were evaluated and compared for the reduction of K2PtCl4 in an aqueous solution in the presence of Pd nanocrystal seeds. When citric acid was used as a reducing agent, conformal overgrowth of octahedral Pt shells on regular and truncated octahedrons of Pd led to the formation of Pd-Pt core-shell octahedrons, while non-conformal overgrowth of Pt on cubic Pd seeds resulted in the formation of an incomplete octahedral Pt shell. On the contrary, localized overgrowth of Pt branches was observed when L-ascorbic acid was used as a reducing agent regardless of the facets expressed on the surface of Pd nanocrystal seeds. This work shows that both the binding affinity of a reducing agent to the Pt surface and the reduction kinetics for a Pt precursor play important roles in determining the mode of Pt overgrowth on Pd nanocrystal surface.

  8. Epitaxial Growth of Two-Dimensional Stanene

    NASA Astrophysics Data System (ADS)

    Jia, Jinfeng

    Ultrathin semiconductors present various novel electronic properties. The first experimental realized two-dimensional (2D) material is graphene. Searching 2D materials with heavy elements bring the attention to Si, Ge and Sn. 2D buckled Si-based silicene was realized by molecular beam epitaxy (MBE) growth. Ge-based germanene was realized by mechanical exfoliation. Sn-based stanene has its unique properties. Stanene and its derivatives can be 2D topological insulators (TI) with a very large band gap as proposed by first-principles calculations, or can support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall (QAH) effect. For the first time, in this work, we report a successful fabrication of 2D stanene by MBE. The atomic and electronic structures were determined by scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) in combination with first-principles calculations. This work will stimulate the experimental study and exploring the future application of stanene. In cooperation with Fengfeng Zhu, Wei-jiong Chen, Yong Xu, Chun-lei Gao, Dan-dan Guan, Canhua Liu, Dong Qian, Shou-Cheng Zhang.

  9. Growth of very large InN microcrystals by molecular beam epitaxy using epitaxial lateral overgrowth

    SciTech Connect

    Kamimura, J.; Kishino, K.; Kikuchi, A.

    2015-02-28

    Very thick InN (∼40 μm) was grown by molecular beam epitaxy using the epitaxial lateral overgrowth (ELO) technique. In some regions, the ELO of InN was observed as expected, indicating an important step toward fabricating quasi-bulk InN substrates. Interestingly, most parts of the sample consist of large flat-topped microcrystals and well-faceted microstructures. This is likely due to local growth condition variations during ELO, which is supported by an experiment where ELO of InN was performed on a substrate with various stripe mask patterns. TEM characterization of a flat top InN microcrystal revealed few stacking faults and only related threading dislocations. Defect-free small faceted microcrystals were also observed. The thick InN crystals show a narrow photoluminescence spectrum with a peak at 0.679 eV and linewidth of 16.8 meV at 4 K.

  10. Layer-by-Layer Epitaxial Growth of Scalable WSe2 on Sapphire by Molecular Beam Epitaxy.

    PubMed

    Nakano, Masaki; Wang, Yue; Kashiwabara, Yuta; Matsuoka, Hideki; Iwasa, Yoshihiro

    2017-09-13

    Molecular beam epitaxy (MBE) provides a simple but powerful way to synthesize large-area high-quality thin films and heterostructures of a wide variety of materials including accomplished group III-V and II-VI semiconductors as well as newly developing oxides and chalcogenides, leading to major discoveries in condensed-matter physics. For two-dimensional (2D) materials, however, main fabrication routes have been mechanical exfoliation and chemical vapor deposition by making good use of weak van der Waals bonding nature between neighboring layers, and MBE growth of 2D materials, in particular on insulating substrates for transport measurements, has been limited despite its fundamental importance for future advanced research. Here, we report layer-by-layer epitaxial growth of scalable transition-metal dichalocogenide (TMDC) thin films on insulating substrates by MBE and demonstrate ambipolar transistor operation. The proposed growth protocol is broadly applicable to other TMDCs, providing a key milestone toward fabrication of van der Waals heterostructures with various 2D materials for novel properties and functionalities.

  11. Applying CLIPS to control of molecular beam epitaxy processing

    NASA Technical Reports Server (NTRS)

    Rabeau, Arthur A.; Bensaoula, Abdelhak; Jamison, Keith D.; Horton, Charles; Ignatiev, Alex; Glover, John R.

    1990-01-01

    A key element of U.S. industrial competitiveness in the 1990's will be the exploitation of advanced technologies which involve low-volume, high-profit manufacturing. The demands of such manufacture limit participation to a few major entities in the U.S. and elsewhere, and offset the lower manufacturing costs of other countries which have, for example, captured much of the consumer electronics market. One such technology is thin-film epitaxy, a technology which encompasses several techniques such as Molecular Beam Epitaxy (MBE), Chemical Beam Epitaxy (CBE), and Vapor-Phase Epitaxy (VPE). Molecular Beam Epitaxy (MBE) is a technology for creating a variety of electronic and electro-optical materials. Compared to standard microelectronic production techniques (including gaseous diffusion, ion implantation, and chemical vapor deposition), MBE is much more exact, though much slower. Although newer than the standard technologies, MBE is the technology of choice for fabrication of ultraprecise materials for cutting-edge microelectronic devices and for research into the properties of new materials.

  12. Continuum model of surface roughening and epitaxial breakdown during low-temperature Ge(001) molecular beam epitaxy

    SciTech Connect

    Bratland, K. A.; Spila, T.; Cahill, D. G.; Greene, J. E.; Desjardins, P.

    2011-03-15

    Numerical simulations based on a discrete model describing step edge motion are used to compute the surface morphological evolution of Ge(001) layers deposited by low-temperature (T{sub s} = 45-230 deg. C) molecular beam epitaxy and to probe the relationship between surface roughening and the onset of epitaxial breakdown - the abrupt growth mode transition from epitaxial to amorphous - at temperature-dependent critical film thicknesses h{sub 1}(T{sub s}). Computed surface widths w and in-plane coherence lengths d as a function of layer thickness h exhibit good agreement with experimental values. Inspired by experimental results indicating that epitaxial breakdown is initiated at facetted interisland trenches as the surface roughness reaches a T{sub s}-independent overall aspect ratio, we show that simulated data for w/d = 0.03 correspond to thicknesses h{sub 1{proportional_to}} exp (-E{sub 1}/kT{sub s}) with E{sub 1} = 0.63 eV, a value equal to the Ge adatom diffusion activation energy on Ge(001). Simulated h{sub 1} values agree well with experimental data. Above a critical growth temperature of 170 deg. C, computed w/d values saturate at large film thicknesses, never reaching the critical aspect ratio w/d = 0.03. Thus, the model also predicts that epitaxial breakdown does not occur for T{sub s} > 170 deg. C as observed experimentally.

  13. Manipulation of Dirac cones in intercalated epitaxial graphene

    DOE PAGES

    Kim, Minsung; Tringides, Michael C.; Hershberger, Matthew T.; ...

    2017-07-12

    Graphene is an intriguing material in view of its unique Dirac quasi-particles, and the manipulation of its electronic structure is important in material design and applications. Here, we theoretically investigate the electronic band structure of epitaxial graphene on SiC with intercalation of rare earth metal ions (e.g., Yb and Dy) using first-principles calculations. We can use the intercalation to control the coupling of the constituent components (buffer layer, graphene, and substrate), resulting in strong modification of the graphene band structure. We also demonstrate that the metal-intercalated epitaxial graphene has tunable band structures by controlling the energies of Dirac cones asmore » well as the linear and quadratic band dispersion depending on the intercalation layer and density. Thus, the metal intercalation is a viable method to manipulate the electronic band structure of the epitaxial graphene, which can enhance the functional utility and controllability of the material.« less

  14. Electric circuit model for strained-layer epitaxy

    NASA Astrophysics Data System (ADS)

    Kujofsa, Tedi; Ayers, John E.

    2016-11-01

    For the design and analysis of a strained-layer semiconductor device structure, the equilibrium strain profile may be determined numerically by energy minimization but this method is computationally intense and non-intuitive. Here we present an electric circuit model approach for the equilibrium analysis of an epitaxial stack, in which each sublayer may be represented by an analogous configuration involving a current source, a resistor, a voltage source, and an ideal diode. The resulting node voltages in the analogous electric circuit correspond to the equilibrium strains in the original epitaxial structure. This new approach enables analysis using widely accessible circuit simulators, and an intuitive understanding of electric circuits may be translated to the relaxation of strained-layer structures. In this paper, we describe the mathematical foundation of the electrical circuit model and demonstrate its application to epitaxial layers of Si1-x Ge x grown on a Si (001) substrate.

  15. Thermodynamic considerations for epitaxial growth of III/V alloys

    NASA Astrophysics Data System (ADS)

    Stringfellow, G. B.

    2017-06-01

    III/V semiconductor alloys have been extensively studied because of their usefulness for electronic and photonic devices. Nevertheless, the search for new alloys for specific applications continues. Often, thermodynamic factors restrict the compositional range accessible by epitaxial growth processes, particularly when the size difference between atoms mixing on a particular sublattice is large. This causes solid phase immiscibility, leading to important effects on the epitaxial growth, the resultant alloy properties, and, consequently, device performance. Stringent thermodynamic limits exist for a number of alloys being considered for advanced LED, laser, and solar cell applications where the atomic sizes are very dissimilar, such as GaInN, GaAsN and GaAsBi. This paper will review the basic thermodynamics of the epitaxial growth processes and mixing in semiconductor alloys, as well as the causes and consequences of the resultant complex microstructures.

  16. Localized States Influence Spin Transport in Epitaxial Graphene

    NASA Astrophysics Data System (ADS)

    Maassen, T.; van den Berg, J. J.; Huisman, E. H.; Dijkstra, H.; Fromm, F.; Seyller, T.; van Wees, B. J.

    2013-02-01

    We developed a spin transport model for a diffusive channel with coupled localized states that result in an effective increase of spin precession frequencies and a reduction of spin relaxation times in the system. We apply this model to Hanle spin precession measurements obtained on monolayer epitaxial graphene on SiC(0001). Combined with newly performed measurements on quasi-free-standing monolayer epitaxial graphene on SiC(0001) our analysis shows that the different values for the diffusion coefficient measured in charge and spin transport measurements on monolayer epitaxial graphene on SiC(0001) and the high values for the spin relaxation time can be explained by the influence of localized states arising from the buffer layer at the interface between the graphene and the SiC surface.

  17. Solid phase epitaxial regrowth of (001) anatase titanium dioxide

    SciTech Connect

    Barlaz, David Eitan; Seebauer, Edmund G.

    2016-03-15

    The growing interest in metal oxide based semiconductor technologies has driven the need to produce high quality epitaxial films of one metal oxide upon another. Largely unrecognized in synthetic efforts is that some metal oxides offer strongly polar surfaces and interfaces that require electrostatic stabilization to avoid a physically implausible divergence in the potential. The present work examines these issues for epitaxial growth of anatase TiO{sub 2} on strontium titanate (001). Solid phase epitaxial regrowth yields only the (001) facet, while direct crystalline growth by atomic layer deposition yields both the (112) and (001). The presence of amorphous TiO{sub 2} during regrowth may provide preferential stabilization for formation of the (001) facet.

  18. Epitaxial Atomic Layer Deposition of Sn-Doped Indium Oxide

    SciTech Connect

    Emery, Jonathan D.; Schlepütz, Christian M.; Guo, Peijun; Chang, Robert P. H.; Martinson, Alex B. F.

    2016-02-03

    Coherently strained, epitaxial Sn-doped In2O3 (ITO) thin films were fabricated at temperatures as low as 250 degrees C using atomic layer deposition (ALD) on (001)-, (011)-, and (111)-oriented single-crystal Y-stabilized ZrO2 (YSZ) substrates. Resultant films possess cube-on-cube epitaxial relationships with the underlying YSZ substrates and are smooth, highly conductive, and optically transparent. This epitaxial ALD approach is favorable compared to many conventional growth techniques as it is a large-scale synthesis method that does not necessitate the use of high temperatures or ultrahigh vacuum. These films may prove valuable as a conductive growth template in areas where high-quality crystalline thin film substrates are important, such as solar energy materials, light-emitting diodes, or wide bandgap semiconductors. Furthermore, we discuss the applicability of this ALD system as an excellent model system for the study of ALD surface chemistry, nucleation, and film growth.

  19. Fluoride waveguide lasers grown by liquid phase epitaxy

    NASA Astrophysics Data System (ADS)

    Starecki, Florent; Bolaños, Western; Brasse, Gurvan; Benayad, Abdelmjid; Doualan, Jean-Louis; Braud, Alain; Moncorgé, Richard; Camy, Patrice

    2013-03-01

    High optical quality rare-earth-doped LiYF4 (YLF) epitaxial layers were grown on pure YLF substrates by liquid phase epitaxy (LPE). Thulium, praseodymium and ytterbium YLF crystalline waveguides co-doped with gadolinium and/or lutetium were obtained. Spectroscopic and optical characterization of these rare-earth doped waveguides are reported. Internal propagation losses as low as 0.11 dB/cm were measured on the Tm:YLF waveguide and the overall spectroscopic characteristics of the epitaxial layers were found to be comparable to bulk crystals. Laser operation was achieved at 1.87 μm in the Tm3+ doped YLF planar waveguide with a very good efficiency of 76% with respect to the pump power. Lasing was also demonstrated in a Pr3+ doped YLF waveguide in the red and orange regions and in a Yb3+:YLF planar waveguide at 1020 nm and 994 nm.

  20. New structure of high-pressure body-centered orthorhombic Fe 2 SiO 4

    SciTech Connect

    Yamanaka, Takamitsu; Kyono, Atsushi; Nakamoto, Yuki; Kharlamova, Svetlana; Struzhkin, Viktor V.; Gramsch, Stephen A.; Mao, Ho-kwang; Hemley, Russell J.

    2015-08-01

    A structural change in Fe2SiO4 spinel (ringwoodite) has been found by synchrotron powder diffraction study and the structure of a new high-pressure phase was determined by Monte-Carlo simulation method and Rietveld profile fitting of X-ray diffraction data up to 64 GPa at ambient temperature. A transition from the cubic spinel structure to a body centered orthorhombic phase (I-Fe2SiO4) with space group Imma and Z = 4 was observed at approximately 34 GPa. The structure of I-Fe2SiO4 has two crystallographically independent FeO6 octahedra. Iron resides in two different sites of sixfold coordination: Fe1 and Fe2, which are arranged in layers parallel to (101) and (011) and are very similar to the layers of FeO6 octahedra in the spinel structure. Silicon is located in the sixfold coordination in I-Fe2SiO4. The transformation to the new high-pressure phase is reversible under decompression at ambient temperature. A martensitic transformation of each slab of the spinel structure with translation vector Embedded Image generates the I-Fe2SiO4 structure. Laser heating of I-Fe2SiO4 at 1500 K results in a decomposition of the material to rhombohedral FeO and SiO2 stishovite. FeKβ X-ray emission measurements at high pressure up to 65 GPa show that the transition from a high spin (HS) to an intermediate spin (IS) state begins at 17 GPa in the spinel phase. The IS electron spin state is gradually enhanced with pressure. The Fe2+ ion at the octahedral site changes the ion radius under compression at the low spin, which results in the changes of the lattice parameter and the deformation of the octahedra of the spinel structure. The compression curve of the lattice parameter of the spinel is discontinuous at ~20 GPa. The spin transition induces an isostructural change.

  1. On the polarity of GaN micro- and nanowires epitaxially grown on sapphire (0001) and Si(111) substrates by metal organic vapor phase epitaxy and ammonia-molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Alloing, B.; Vézian, S.; Tottereau, O.; Vennéguès, P.; Beraudo, E.; Zuniga-Pérez, J.

    2011-01-01

    The polarity of GaN micro- and nanowires grown epitaxially by metal organic vapor phase epitaxy on sapphire substrates and by molecular-beam epitaxy, using ammonia as a nitrogen source, on sapphire and silicon substrates has been investigated. On Al2O3(0001), whatever the growth technique employed, the GaN wires show a mixture of Ga and N polarities. On Si(111), the wires grown by ammonia-molecular beam epitaxy are almost entirely Ga-polar (around 90%) and do not show inversion domains. These results can be understood in terms of the growth conditions employed during the nucleation stage.

  2. On the polarity of GaN micro- and nanowires epitaxially grown on sapphire (0001) and Si(111) substrates by metal organic vapor phase epitaxy and ammonia-molecular beam epitaxy

    SciTech Connect

    Alloing, B.; Vezian, S.; Tottereau, O.; Vennegues, P.; Beraudo, E.; Zuniga-Perez, J.

    2011-01-03

    The polarity of GaN micro- and nanowires grown epitaxially by metal organic vapor phase epitaxy on sapphire substrates and by molecular-beam epitaxy, using ammonia as a nitrogen source, on sapphire and silicon substrates has been investigated. On Al{sub 2}O{sub 3}(0001), whatever the growth technique employed, the GaN wires show a mixture of Ga and N polarities. On Si(111), the wires grown by ammonia-molecular beam epitaxy are almost entirely Ga-polar (around 90%) and do not show inversion domains. These results can be understood in terms of the growth conditions employed during the nucleation stage.

  3. Scanning X-ray nanodiffraction from ferroelectric domains in strained K0.75Na0.25NbO3 epitaxial films grown on (110) TbScO3 1

    PubMed Central

    Schmidbauer, Martin; Kwasniewski, Albert; Braun, Dorothee; von Helden, Leonard; Feldt, Christoph; Leake, Steven John

    2017-01-01

    Scanning X-ray nanodiffraction on a highly periodic ferroelectric domain pattern of a strained K0.75Na0.25NbO3 epitaxial layer has been performed by using a focused X-ray beam of about 100 nm probe size. A 90°-rotated domain variant which is aligned along [12]TSO has been found in addition to the predominant domain variant where the domains are aligned along the [12]TSO direction of the underlying (110) TbScO3 (TSO) orthorhombic substrate. Owing to the larger elastic strain energy density, the 90°-rotated domains appear with significantly reduced probability. Furthermore, the 90°-rotated variant shows a larger vertical lattice spacing than the 0°-rotated domain variant. Calculations based on linear elasticity theory substantiate that this difference is caused by the elastic anisotropy of the K0.75Na0.25NbO3 epitaxial layer. PMID:28381975

  4. Scanning X-ray nanodiffraction from ferroelectric domains in strained K0.75Na0.25NbO3 epitaxial films grown on (110) TbScO3.

    PubMed

    Schmidbauer, Martin; Hanke, Michael; Kwasniewski, Albert; Braun, Dorothee; von Helden, Leonard; Feldt, Christoph; Leake, Steven John; Schwarzkopf, Jutta

    2017-04-01

    Scanning X-ray nanodiffraction on a highly periodic ferroelectric domain pattern of a strained K0.75Na0.25NbO3 epitaxial layer has been performed by using a focused X-ray beam of about 100 nm probe size. A 90°-rotated domain variant which is aligned along [1[Formula: see text]2]TSO has been found in addition to the predominant domain variant where the domains are aligned along the [[Formula: see text]12]TSO direction of the underlying (110) TbScO3 (TSO) orthorhombic substrate. Owing to the larger elastic strain energy density, the 90°-rotated domains appear with significantly reduced probability. Furthermore, the 90°-rotated variant shows a larger vertical lattice spacing than the 0°-rotated domain variant. Calculations based on linear elasticity theory substantiate that this difference is caused by the elastic anisotropy of the K0.75Na0.25NbO3 epitaxial layer.

  5. Process for growing epitaxial gallium nitride and composite wafers

    DOEpatents

    Weber, Eicke R.; Subramanya, Sudhir G.; Kim, Yihwan; Kruger, Joachim

    2003-05-13

    A novel growth procedure to grow epitaxial Group III metal nitride thin films on lattice-mismatched substrates is proposed. Demonstrated are the quality improvement of epitaxial GaN layers using a pure metallic Ga buffer layer on c-plane sapphire substrate. X-ray rocking curve results indicate that the layers had excellent structural properties. The electron Hall mobility increases to an outstandingly high value of .mu.>400 cm.sup.2 /Vs for an electron background concentration of 4.times.10.sup.17 cm.sup.-3.

  6. Optical Probing of metamagnetic phases in epitaxial EuSe

    SciTech Connect

    Galgano, G. D.; Henriques, A. B.; Bauer, G.; Springholz, G.

    2011-12-23

    EuSe is a wide gap magnetic semiconductors with a potential for applications in proof-of-concept spintronic devices. When the temperature is lowered, EuSe goes through sharp transitions between a variety of magnetic phases and is thus described as metamagnetic. The purpose of the present investigation is to correlate the magnetic order to the sharp dichroic doublet, discovered recently in high quality thin epitaxial layers of EuSe, grown by molecular beam epitaxy. We report detailed measurements of the doublet positions and intensities as a function of magnetic field in low temperatures, covering several magnetic phases.

  7. Fundamental Study of Antimonide Nanostructures by Molecular Beam Epitaxy

    DTIC Science & Technology

    2016-02-04

    to conduct experimental work in molecular beam epitaxial growth of GaSb/GaAs and InSb/GaAs quantum dots (QDs) are conducted and compared with...September 2014 to July 2015 being conducted at Chulalongkorn University in Thailand. Following the research work on InAs quantum dots (QDs) and quantum ... dot molecules (QDMs) grown by molecular beam epitaxy (MBE), the research target is extended to GaSb QDs and InSb QDs which are type II quantum

  8. Seed layer technique for high quality epitaxial manganite films.

    PubMed

    Graziosi, P; Gambardella, A; Calbucci, M; O'Shea, K; MacLaren, D A; Riminucci, A; Bergenti, I; Fugattini, S; Prezioso, M; Homonnay, N; Schmidt, G; Pullini, D; Busquets-Mataix, D; Dediu, V

    2016-08-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  9. Seed layer technique for high quality epitaxial manganite films

    NASA Astrophysics Data System (ADS)

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O'Shea, K.; MacLaren, D. A.; Riminucci, A.; Bergenti, I.; Fugattini, S.; Prezioso, M.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-08-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  10. Concept of epitaxial silicon structures for edge illuminated solar cells

    NASA Astrophysics Data System (ADS)

    Sarnecki, J.; Gawlik, G.; Teodorczyk, M.; Jeremiasz, O.; Kozłowski, R.; Lipiński, D.; Krzyżak, K.; Brzozowski, A.

    2011-12-01

    A new concept of edge illuminated solar cells (EISC) based on silicon epitaxial technique has been proposed. In this kind of photovoltaic (PV) devices, sun-light illuminates directly a p-n junction through the edge of the structure which is perpendicular to junction surface. The main motivation of the presented work is preparation of a working model of an edge-illuminated silicon epitaxial solar cell sufficient to cooperation with a luminescent solar concentrator (LSC) consisted of a polymer foil doped with a luminescent material. The technological processes affecting the cell I-V characteristic and PV parameters are considered.

  11. Tunable interfacial properties of epitaxial graphene on metal substrates

    NASA Astrophysics Data System (ADS)

    Gao, Min; Pan, Yi; Zhang, Chendong; Hu, Hao; Yang, Rong; Lu, Hongliang; Cai, Jinming; Du, Shixuan; Liu, Feng; Gao, H.-J.

    2010-02-01

    We report on tuning interfacial properties of epitaxially-grown graphenes with different kinds of metal substrates based on scanning tunneling microscopy experiments and density functional theory calculations. Three kinds of metal substrates, Ni(111), Pt(111), and Ru(0001), show different interactions with the epitaxially grown graphene at the interfaces. The different interfacial interaction making graphene n-type and p-type doped, leads to the polarity change of the thermoelectric property of the graphene/metal systems. These findings may give further insights to the interfacial interactions in the graphene/metal systems and promote the use of graphene-based heterostructures in devices.

  12. Seed layer technique for high quality epitaxial manganite films

    PubMed Central

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O’Shea, K.; MacLaren, D. A.; Bergenti, I.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-01-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived. PMID:27648371

  13. Nanocluster dynamics in fast rate epitaxy under mesoplasma condition

    NASA Astrophysics Data System (ADS)

    Chen, L. W.; Shibuta, Y.; Kambara, M.; Yoshida, T.

    2013-03-01

    The dynamics of Si nano-clusters during epitaxial growth has been investigated with molecular dynamics simulation using the Tersoff potential. Several nm sized Si cluster formed during rapid cooling was found to deform instantaneously upon impingement on a Si(1 0 0) substrate at the same time with the spontaneous ordering of the atomic structure to that of the substrate. Due to the increased fraction of high-energy atoms at the surface, smaller clusters (˜1 nm) are favorable for such a deformation even at lower temperatures. This is the advantage of loosely-bound cluster as growth precursor to attain epitaxy with reduced impact energies.

  14. Magnetic Nanostructures by Adaptive Twinning in Strained Epitaxial Films

    NASA Astrophysics Data System (ADS)

    Kauffmann-Weiss, Sandra; Gruner, Markus E.; Backen, Anja; Schultz, Ludwig; Entel, Peter; Fähler, Sebastian

    2011-11-01

    We exploit the intrinsic structural instability of the Fe70Pd30 magnetic shape memory alloy to obtain functional epitaxial films exhibiting a self-organized nanostructure. We demonstrate that coherent epitaxial straining by 54% is possible. The combination of thin film experiments and large-scale first-principles calculations enables us to establish a lattice relaxation mechanism, which is not expected for stable materials. We identify a low twin boundary energy compared to a high elastic energy as key prerequisite for the adaptive nanotwinning. Our approach is versatile as it allows to control both, nanostructure and intrinsic properties for ferromagnetic, ferroelastic, and ferroelectric materials.

  15. Fully planar method for creating adjacent ``self-isolating'' silicon-on-insulator and epitaxial layers by epitaxial lateral overgrowth

    NASA Astrophysics Data System (ADS)

    Glenn, J. L., Jr.; Neudeck, G. W.; Subramanian, C. K.; Denton, J. P.

    1992-01-01

    A novel and simple process is demonstrated for creating isolated silicon-on-insulator (SOI) tubs adjacent to selective epitaxial substrate layers. The process results in a fully planar wafer surface which is uniquely suited for mixed bipolar/complementary metal-oxide-semiconductor device fabrication. Low-temperature epitaxial lateral overgrowth (ELO) using SiH2Cl2/HCl/H2 is carried out in a reduced-pressure chemical vapor deposition reactor to create SOI islands in thermally grown SiO2 valleys. SOI islands and epitaxial seed regions are ``self-isolated'' by chemical-mechanical planarization. The as-grown ELO is single-crystal material with well-defined facets. Planarized SOI and epilayer regions have planar, featureless surfaces. Defect etching for the nonoptimized SOI layers indicates about 5×104 stacking faults/cm2.

  16. A study on the epitaxial Bi2Se3 thin film grown by vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Lin, Yen-Cheng; Chen, Yu-Sung; Lee, Chao-Chun; Wu, Jen-Kai; Lee, Hsin-Yen; Liang, Chi-Te; Chang, Yuan Huei

    2016-06-01

    We report the growth of high quality Bi2Se3 thin films on Al2O3 substrates by using chemical vapor deposition. From the atomic force microscope, x-ray diffraction and transmission electron microscope measurements we found that the films are of good crystalline quality, have two distinct domains and can be grown epitaxially on the Al2O3 substrate. Carrier concentration in the sample is found to be 1.1 × 1019 cm-3 between T = 2 K to T = 300 K, and electron mobility can reach 954 cm2/V s at T = 2 K. Weak anti-localization effect is observed in the low temperature magneto-transport measurement for the sample which indicates that the thin film has topological surface state.

  17. Epitaxial growth of AlN films via plasma-assisted atomic layer epitaxy

    SciTech Connect

    Nepal, N.; Qadri, S. B.; Hite, J. K.; Mahadik, N. A.; Mastro, M. A.; Eddy, C. R. Jr.

    2013-08-19

    Thin AlN layers were grown at 200–650 °C by plasma assisted atomic layer epitaxy (PA-ALE) simultaneously on Si(111), sapphire (1120), and GaN/sapphire substrates. The AlN growth on Si(111) is self-limited for trimethyaluminum (TMA) pulse of length > 0.04 s, using a 10 s purge. However, the AlN nucleation on GaN/sapphire is non-uniform and has a bimodal island size distribution for TMA pulse of ≤0.03 s. The growth rate (GR) remains almost constant for T{sub g} between 300 and 400 °C indicating ALE mode at those temperatures. The GR is increased by 20% at T{sub g} = 500 °C. Spectroscopic ellipsometry (SE) measurement shows that the ALE AlN layers grown at T{sub g} ≤ 400 °C have no clear band edge related features, however, the theoretically estimated band gap of 6.2 eV was measured for AlN grown at T{sub g} ≥ 500 °C. X-ray diffraction measurements on 37 nm thick AlN films grown at optimized growth conditions (T{sub g} = 500 °C, 10 s purge, 0.06 s TMA pulse) reveal that the ALE AlN on GaN/sapphire is (0002) oriented with rocking curve full width at the half maximum (FWHM) of 670 arc sec. Epitaxial growth of crystalline AlN layers by PA-ALE at low temperatures broadens application of the material in the technologies that require large area conformal growth at low temperatures with thickness control at the atomic scale.

  18. Angle-resolved photoemission spectroscopy of strontium lanthanum copper oxide thin films grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Harter, John Wallace

    Among the multitude of known cuprate material families and associated structures, the archetype is "infinite-layer" ACuO2, where perfectly square and flat CuO2 planes are separated by layers of alkaline earth atoms. The infinite-layer structure is free of magnetic rare earth ions, oxygen chains, orthorhombic distortions, incommensurate superstructures, ordered vacancies, and other complications that abound among the other material families. Furthermore, it is the only cuprate that can be made superconducting by both electron and hole doping, making it a potential platform for decoding the complex many-body interactions responsible for high-temperature superconductivity. Research on the infinite-layer compound has been severely hindered by the inability to synthesize bulk single crystals, but recent progress has led to high-quality superconducting thin film samples. Here we report in situ angle-resolved photoemission spectroscopy measurements of epitaxially-stabilized Sr1-chiLa chiCuO2 thin films grown by molecular-beam epitaxy. At low doping, the material exhibits a dispersive lower Hubbard band typical of other cuprate parent compounds. As carriers are added to the system, a continuous evolution from Mott insulator to superconducting metal is observed as a coherent low-energy band develops on top of a concomitant remnant lower Hubbard band, gradually filling in the Mott gap. For chi = 0.10, our results reveal a strong coupling between electrons and (pi,pi) anti-ferromagnetism, inducing a Fermi surface reconstruction that pushes the nodal states below the Fermi level and realizing nodeless superconductivity. Electron diffraction measurements indicate the presence of a surface reconstruction that is consistent with the polar nature of Sr1-chiLachiCuO2. Most knowledge about the electron-doped side of the cuprate phase diagram has been deduced by generalizing from a single material family, Re2-chi CechiCuO4, where robust antiferromagnetism has been observed past chi

  19. Classification of epitaxy in reciprocal and real space: rigid versus flexible lattices.

    PubMed

    Forker, Roman; Meissner, Matthias; Fritz, Torsten

    2017-03-01

    Early investigations of epitaxy focused on inorganic adsorbates consisting of atoms or few-atom molecules, where commensurate registries are predominantly encountered. Expanding such studies to larger (organic) molecules has revealed hitherto unknown types of epitaxy with coherence between adlayer and substrate lattices in just one direction. Here we review recent contributions to the fundamental understanding and modeling of epitaxy. By sorting the ideas brought forward in the literature and amending some basic algebraic considerations a universal scheme for the classification of lattice epitaxy is presented. Ultimately, the occurrence of the different types of epitaxy is made plausible by easy-to-grasp energetic arguments.

  20. Au impact on GaAs epitaxial growth on GaAs (111)B substrates in molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Liao, Zhi-Ming; Chen, Zhi-Gang; Lu, Zhen-Yu; Xu, Hong-Yi; Guo, Ya-Nan; Sun, Wen; Zhang, Zhi; Yang, Lei; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2013-02-01

    GaAs growth behaviour under the presence of Au nanoparticles on GaAs {111}B substrate is investigated using electron microscopy. It has been found that, during annealing, enhanced Ga surface diffusion towards Au nanoparticles leads to the GaAs epitaxial growth into {113}B faceted triangular pyramids under Au nanoparticles, governed by the thermodynamic growth, while during conventional GaAs growth, growth kinetics dominates, resulting in the flatted triangular pyramids at high temperature and the epitaxial nanowires growth at relatively low temperature. This study provides an insight of Au nanoparticle impact on GaAs growth, which is critical for understanding the formation mechanisms of semiconductor nanowires.

  1. In-situ epitaxial growth of graphene/h-BN van der Waals heterostructures by molecular beam epitaxy.

    PubMed

    Zuo, Zheng; Xu, Zhongguang; Zheng, Renjing; Khanaki, Alireza; Zheng, Jian-Guo; Liu, Jianlin

    2015-10-07

    Van der Waals materials have received a great deal of attention for their exceptional layered structures and exotic properties, which can open up various device applications in nanoelectronics. However, in situ epitaxial growth of dissimilar van der Waals materials remains challenging. Here we demonstrate a solution for fabricating van der Waals heterostructures. Graphene/hexagonal boron nitride (h-BN) heterostructures were synthesized on cobalt substrates by using molecular beam epitaxy. Various characterizations were carried out to evaluate the heterostructures. Wafer-scale heterostructures consisting of single-layer/bilayer graphene and multilayer h-BN were achieved. The mismatch angle between graphene and h-BN is below 1°.

  2. In-situ epitaxial growth of graphene/h-BN van der Waals heterostructures by molecular beam epitaxy

    PubMed Central

    Zuo, Zheng; Xu, Zhongguang; Zheng, Renjing; Khanaki, Alireza; Zheng, Jian-Guo; Liu, Jianlin

    2015-01-01

    Van der Waals materials have received a great deal of attention for their exceptional layered structures and exotic properties, which can open up various device applications in nanoelectronics. However, in situ epitaxial growth of dissimilar van der Waals materials remains challenging. Here we demonstrate a solution for fabricating van der Waals heterostructures. Graphene/hexagonal boron nitride (h-BN) heterostructures were synthesized on cobalt substrates by using molecular beam epitaxy. Various characterizations were carried out to evaluate the heterostructures. Wafer-scale heterostructures consisting of single-layer/bilayer graphene and multilayer h-BN were achieved. The mismatch angle between graphene and h-BN is below 1°. PMID:26442629

  3. A Simple Process for Synthesis of Transparent Thin Films of Molybdenum Trioxide in the Orthorhombic Phase ( α-MoO3)

    NASA Astrophysics Data System (ADS)

    Chibane, Loundja; Belkaid, Mohamed Said; Zirmi, Rachid; Moussi, Abderrahmane

    2017-04-01

    Transparent orthorhombic molybdenum trioxide (α-MoO3) thin films were prepared on glass substrates by sol-gel dip coating technique of a quality comparable to those prepared by more sophisticated techniques regarded as very costly and difficult to carry out. The prepared films were annealed in air at different temperatures in the range of 150-350°C. X-ray diffraction analysis of the films prepared at 250°C and 350°C confirmed the formation of a single-phase of MoO3 in an orthorhombic crystal system (α-MoO3). Scanning electron microscopy of the films annealed at 350°C indicated a stack of nano-layers with thickness of approximately 30 nm-40 nm. Fourier transform infrared transmittance analysis revealed the Mo=O stretching vibration, which is an indicator of the layered orthorhombic MoO3 phase. Energy dispersive x-ray analysis confirmed the existence of Mo and O in the deposited films. A maximum optical transmittance of 82% in the visible range was obtained from the films annealed at 350°C. The band gap value of the films was evaluated and it was in the range of 3.28 eV-3.40 eV. The obtained results showed that the α-MoO3 thin films prepared at 350°C exhibit good structural, chemical, and optical properties, which might be of interest to the photovoltaic and optoelectronic devices.

  4. A Simple Process for Synthesis of Transparent Thin Films of Molybdenum Trioxide in the Orthorhombic Phase (α-MoO3)

    NASA Astrophysics Data System (ADS)

    Chibane, Loundja; Belkaid, Mohamed Said; Zirmi, Rachid; Moussi, Abderrahmane

    2017-01-01

    Transparent orthorhombic molybdenum trioxide (α-MoO3) thin films were prepared on glass substrates by sol-gel dip coating technique of a quality comparable to those prepared by more sophisticated techniques regarded as very costly and difficult to carry out. The prepared films were annealed in air at different temperatures in the range of 150-350°C. X-ray diffraction analysis of the films prepared at 250°C and 350°C confirmed the formation of a single-phase of MoO3 in an orthorhombic crystal system (α-MoO3). Scanning electron microscopy of the films annealed at 350°C indicated a stack of nano-layers with thickness of approximately 30 nm-40 nm. Fourier transform infrared transmittance analysis revealed the Mo=O stretching vibration, which is an indicator of the layered orthorhombic MoO3 phase. Energy dispersive x-ray analysis confirmed the existence of Mo and O in the deposited films. A maximum optical transmittance of 82% in the visible range was obtained from the films annealed at 350°C. The band gap value of the films was evaluated and it was in the range of 3.28 eV-3.40 eV. The obtained results showed that the α-MoO3 thin films prepared at 350°C exhibit good structural, chemical, and optical properties, which might be of interest to the photovoltaic and optoelectronic devices.

  5. Multiperiod quantum-cascade nanoheterostructures: Epitaxy and diagnostics

    SciTech Connect

    Egorov, A. Yu. Brunkov, P. N.; Nikitina, E. V.; Pirogov, E. V.; Sobolev, M. S.; Lazarenko, A. A.; Baidakova, M. V.; Kirilenko, D. A.; Konnikov, S. G.

    2014-12-15

    Advances in the production technology of multiperiod nanoheterostructures of quantum-cascade lasers with 60 cascades by molecular-beam epitaxy (MBE) on an industrial multiple-substrate MBE machine are discussed. The results obtained in studying the nanoheterostructures of quantum-cascade lasers by transmission electron microscopy, high-resolution X-ray diffraction analysis, and photoluminescence mapping are presented.

  6. Novel Epitaxy Between Oxides and Semiconductors - Growth and Interfacial Structures

    DTIC Science & Technology

    2007-05-16

    applications in high-temperature, high- power electronics because of their wide band gaps, high breakdown fields and high saturation velocity in high...semiconductor field-effect-transistors ( MOSFETs ) because of their relatively low leakage currents, power consumption and capability of greater voltage swings...Novel epitaxy between oxides and semiconductors – Growth and Interfacial Structures Professor Minghwei HONG Department of Materials Science

  7. Depositing spacing layers on magnetic film with liquid phase epitaxy

    NASA Technical Reports Server (NTRS)

    Moody, J. W.; Shaw, R. W.; Sanfort, R. M.

    1975-01-01

    Liquid phase epitaxy spacing layer is compatible with systems which are hard-bubble proofed by use of second magnetic garnet film as capping layer. Composite is superior in that: circuit fabrication time is reduced; adherence is superior; visibility is better; and, good match of thermal expansion coefficients is provided.

  8. Multi Bandgap Photodetectors with Buried Epitaxial Metallic Contacts

    DTIC Science & Technology

    2014-01-09

    of bulk diffusion or bulk segregation. These highly tuneable nanocomposites show promise for direct integration into epitaxial semiconductor device...0119 Surface Mediated Tunable Self-Assembly of Single Crystal Semimetallic Rare- earth-group-V/III-V Semiconductor Nanocomposite Structures C.J... nanostructures embedded within a semiconducting matrix are of great interest for applications in plasmonics, photonic crystals, and nanoscale ohmic contacts

  9. Disordered Fermi liquid in epitaxial graphene from quantum transport measurements.

    PubMed

    Lara-Avila, Samuel; Tzalenchuk, Alexander; Kubatkin, Sergey; Yakimova, Rositza; Janssen, T J B M; Cedergren, Karin; Bergsten, Tobias; Fal'ko, Vladimir

    2011-10-14

    We have performed magnetotransport measurements on monolayer epitaxial graphene and analyzed them in the framework of the disordered Fermi liquid theory. We have separated the electron-electron and weak-localization contributions to resistivity and demonstrated the phase coherence over a micrometer length scale, setting the limit of at least 50 ps on the spin relaxation time in this material.

  10. Epitaxial silicide formation on recoil-implanted substrates

    SciTech Connect

    Hashimoto, Shin; Egashira, Kyoko; Tanaka, Tomoya; Etoh, Ryuji; Hata, Yoshifumi; Tung, R. T.

    2005-01-15

    An epitaxy-on-recoil-implanted-substrate (ERIS) technique is presented. A disordered surface layer, generated by forward recoil implantation of {approx}0.7-3x10{sup 15} cm{sup -2} of oxygen during Ar plasma etching of surface oxide, is shown to facilitate the subsequent epitaxial growth of {approx}25-35-nm-thick CoSi{sub 2} layers on Si(100). The dependence of the epitaxial fraction of the silicide on the recoil-implantation parameters is studied in detail. A reduction in the silicide reaction rate due to recoil-implanted oxygen is shown to be responsible for the observed epitaxial formation, similar to mechanisms previously observed for interlayer-mediated growth techniques. Oxygen is found to remain inside the fully reacted CoSi{sub 2} layer, likely in the form of oxide precipitates. The presence of these oxide precipitates, with only a minor effect on the sheet resistance of the silicide layer, has a surprisingly beneficial effect on the thermal stability of the silicide layers. The agglomeration of ERIS-grown silicide layers on polycrystalline Si is significantly suppressed, likely from a reduced diffusivity due to oxygen in the grain boundaries. The implications of the present technique for the processing of deep submicron devices are discussed.

  11. Epitaxial gallium oxide on a SiC/Si substrate

    NASA Astrophysics Data System (ADS)

    Kukushkin, S. A.; Nikolaev, V. I.; Osipov, A. V.; Osipova, E. V.; Pechnikov, A. I.; Feoktistov, N. A.

    2016-09-01

    Well-textured gallium oxide β-Ga2O3 layers with a thickness of 1 μm and a close to epitaxial layer structure were grown by the method of chloride vapor phase epitaxy on Si(111) wafers with a nano-SiC buffer layer. In order to improve the growth, a high-quality silicon carbide buffer layer 100 nm thick was preliminarily synthesized by the substitution of atoms on the silicon surface. The β-Ga2O3 films were thoroughly investigated using reflection high-energy electron diffraction, ellipsometry, X-ray diffraction, scanning electron microscopy, and micro-Raman spectroscopy. The investigations revealed that the films are textured with a close to epitaxial structure and consist of a pure β-phase Ga2O3 with the (overline 2 01) orientation. The dependence of the dielectric constant of epitaxial β-Ga2O3 on the photon energy ranging from 0.7 to 6.5 eV in the isotropic approximation was measured.

  12. Thermodynamic and Kinetic Aspects of III/V Epitaxy

    DTIC Science & Technology

    1992-05-22

    a applications electroniques et optiques University of Utah Dept. of Materials Science & Engineering Salt Lake City, UT 84112 May 22, 1992... microscopic strain energy. The kinetic aspects of epitaxy are by far the most complex and, consequently, the least understood. We are beginning to understand

  13. Crystallization engineering as a route to epitaxial strain control

    SciTech Connect

    Akbashev, Andrew R.; Plokhikh, Aleksandr V.; Barbash, Dmitri; Lofland, Samuel E.; Spanier, Jonathan E.

    2015-10-01

    The controlled synthesis of epitaxial thin films offers opportunities for tuning their functional properties via enabling or suppressing strain relaxation. Examining differences in the epitaxial crystallization of amorphous oxide films, we report on an alternate, low-temperature route for strain engineering. Thin films of amorphous Bi–Fe–O were grown on (001)SrTiO{sub 3} and (001)LaAlO{sub 3} substrates via atomic layer deposition. In situ X-ray diffraction and X-ray photoelectron spectroscopy studies of the crystallization of the amorphous films into the epitaxial (001)BiFeO{sub 3} phase reveal distinct evolution profiles of crystallinity with temperature. While growth on (001)SrTiO{sub 3} results in a coherently strained film, the same films obtained on (001)LaAlO{sub 3} showed an unstrained, dislocation-rich interface, with an even lower temperature onset of the perovskite phase crystallization than in the case of (001)SrTiO{sub 3}. Our results demonstrate how the strain control in an epitaxial film can be accomplished via its crystallization from the amorphous state.

  14. A neutron diffraction study of oxygen and nitrogen ordering in a kinetically stable orthorhombic iron doped titanium oxynitride

    SciTech Connect

    Wu, On Ying; Parkin, Ivan P; Hyett, Geoffrey

    2012-06-15

    The synthesis of a polycrystalline powder sample of iron doped orthorhombic titanium oxynitride, Ti{sub 2.92}Fe{sub 0.01}O{sub 4.02}N{sub 0.98}, on the scale of 0.7 g has been achieved. This was conducted by the unusual route of delamination from a steel substrate of a thin film deposited using atmospheric pressure chemical vapour deposition. The structure of the titanium oxynitride is presented, determined from a combined analysis of X-ray and neutron powder diffraction data. The use of neutron diffraction allows the position of the oxygen and nitrogen ions in the material to be reported unambiguously for the first time. In this study Ti{sub 2.92}Fe{sub 0.01}O{sub 4.02}N{sub 0.98} is found to crystallise in the Cmcm space group, iso-structural pseudobrookite, with lattice parameters a=3.81080(6) A, b=9.6253(2) A, and c=9.8859(2) A, and contains partial oxygen-nitrogen ordering. Of the three anion sites in this structure one is exclusively occupied by oxygen, while the remaining two sites are occupied by oxygen and nitrogen in a disordered manner. Testing indicates that this iron doped titanium oxynitride is a metastable phase that decomposes above 700 Degree-Sign C into TiN and TiO{sub 2}, the thermodynamic products. - Graphical abstract: We report the synthesis of Ti{sub 2.92}Fe{sub 0.01}O{sub 4.02}N{sub 0.98} deposited as a thin film using atmospheric pressure chemical vapour deposition onto stainless steel, which is then delaminated to produce a polycrystalline powder sample. This powder sample was used in a neutron diffraction experiment, and analysis of this data has allowed the position of the oxygen and nitrogen ions in the material to be reported unambiguously for the first time. Ti{sub 2.92}Fe{sub 0.01}O{sub 4.02}N{sub 0.98} is found to crystallise in the Cmcm space group iso-structural pseudobrookite and contains partial oxygen-nitrogen ordering. Highlights: Black-Right-Pointing-Pointer Partial oxygen and nitrogen ordering has been observed using neutron

  15. Epitaxial metal-gallium arsenide contacts via electrodeposition

    NASA Astrophysics Data System (ADS)

    Bao, Zhi Liang

    The fabrication of epitaxial metal-GaAs contacts via electrodeposition and the electrical properties of the Schottky diodes are reported in this dissertation. Epitaxial electrodeposition of copper, iron, cobalt, iron-nickel, and bismuth on GaAs was discovered to rely on three major factors: the preparation of the GaAs surface by (NH4)OH etching, the addition of (NH 4)2SO4 to the electrolytes, and the control of deposition current density. The surface preparation by (NH4)OH provides a hydrophilic surface likely due to passivation via a layer of hydroxide bonds. Ammonium sulphate inhibits oxidation of the metal cations and likely acts as a surfactant both on the metal and GaAs surfaces. Control of adatom flux, similar to vacuum deposition techniques such as molecular beam epitaxy, determined the crystallinity, varying from polycrystalline to epitaxial to dendritic for current densities from 0.01 to 1 mA/mm2. The effects of other electrodeposition conditions including pH and electrolyte temperature were also investigated. Neutral electrolytes are needed for copper, iron, nickel-iron alloy, and cobalt epitaxial deposition, while acidic solution works for bismuth deposition indicating that the control of hydrogen evolution may be important. Cobalt nanodisc formation was obtained for lower temperatures (2 - 22°C) while optimal copper, iron, and bismuth epitaxy required higher deposition temperatures, 53, 56, and 70°C, respectively. The growth is via island nucleation and coalescence. The iron films develop a small decrease in lattice constant with residual compressive stress, which is a function of temperature. This is likely due to an impurity such as oxygen. Copper and cobalt formed nanometer scale reacted interfaces with GaAs, while iron and bismuth/GaAs formed abrupt interfaces. The electrical properties of these Schottky diodes were, nevertheless, found to be close to ideal and comparable to vacuum deposited diodes. Fe and Co/GaAs diodes showed identical

  16. On the density of states of disordered epitaxial graphene

    SciTech Connect

    Davydov, S. Yu.

    2015-05-15

    The study is concerned with two types of disordered epitaxial graphene: (i) graphene with randomly located carbon vacancies and (ii) structurally amorphous graphene. The former type is considered in the coherent potential approximation, and for the latter type, a model of the density of states is proposed. The effects of two types of substrates, specifically, metal and semiconductor substrates are taken into account. The specific features of the density of states of epitaxial graphene at the Dirac point and the edges of the continuous spectrum are analyzed. It is shown that vacancies in epitaxial graphene formed on the metal substrate bring about logarithmic nulling of the density of states of graphene at the Dirac point and the edges of the continuous spectrum. If the Dirac point corresponds to the middle of the band gap of the semiconductor substrate, the linear trend of the density of states to zero in the vicinity of the Dirac point in defect-free graphene transforms into a logarithmic decrease in the presence of vacancies. In both cases, the graphene-substrate interaction is assumed to be weak (quasi-free graphene). In the study of amorphous epitaxial graphene, a simple model of free amorphous graphene is proposed as the initial model, in which account is taken of the nonzero density of states at the Dirac point, and then the interaction of the graphene sheet with the substrate is taken into consideration. It is shown that, near the Dirac point, the quadratic behavior of the density of states of free amorphous graphene transforms into a linear dependence for amorphous epitaxial graphene. In the study, the density of states of free graphene corresponds to the low-energy approximation of the electron spectrum.

  17. SiGe channel deposition by batch epitaxy

    NASA Astrophysics Data System (ADS)

    Reichel, Carsten; Schoenekess, Joerg; Dietel, Andreas; Wasyluk, Joanna; Chow, Yew Tuck; Kammler, Thorsten

    2015-08-01

    Batch epitaxy has been introduced for high volume manufacturing of SiGe channels in order to reduce the cost for this epitaxial process by a factor of 3. Beside cost, SiGe channel deposition by batch epitaxy offers many benefits for manufacturing. The stability of the process and the reduced variability of the SiGe thickness greatly improve the variation of VT. The batch epitaxy process does not show a pattern loading effect for SiGe thickness reducing the complexity for manufacturing significantly. However, since the tool concept is very different to that of the widely used single wafer tools, there are some tool specific issues that need to be managed. The wafer backside is critical for batch epitaxy. A nitride backside facing the front side of the wafer results in a clear degradation of the uniformity and a change of the morphology of the SiGe channel compared to that facing a Si backside. The thermal rounding is more pronounced for the channels deposited in a batch tool for both large and narrow width devices. The device parameters of the large width device are not affected by thermal rounding but the performance of the narrow width device is clearly degraded. The thin SiGe layer at the edge of the channel driven by thermal rounding affects the VT and thus the effective device width. An in-situ etching before SiGe deposition to avoid thermal rounding was not feasible due to defects issues which were induced by the wafer backside. Finally a thermal rounding of the Si by an aggressive H2 bake before SiGe deposition improves the SiGe channel uniformity and recovers the performance degradation of the narrow width device partly.

  18. Effects of external mechanical loading on phase diagrams and dielectric properties in epitaxial ferroelectric thin films with anisotropic in-plane misfit strains

    NASA Astrophysics Data System (ADS)

    Qiu, J. H.; Jiang, Q.

    2007-02-01

    A phenomenological Landau-Devonshine theory is used to describe the effects of external mechanical loading on equilibrium polarization states and dielectric properties in epitaxial ferroelectric thin films grown on dissimilar orthorhombic substrates which induce anisotropic misfit strains in the film plane. The calculation focuses on single-domain perovskite BaTiO3 and PbTiO3 thin films on the assumption that um1=-um2. Compared with the phase diagrams without external loading, the characteristic features of "misfit strain-misfit strain" phase diagrams at room temperature are the presence of paraelectric phase and the strain-induced ferroelectric to paraelectric phase transition. Due to the external loading, the "misfit strain-stress" and "stress-temperature" phase diagrams also have drastic changes, especially for the vanishing of paraelectric phase in "misfit strain-stress" phase map and the appearance of possible ferroelectric phases. We also investigate the dielectric properties and the tunability of both BaTiO3 and PbTiO3 thin films. We find that the external stress dependence of phase diagrams and dielectric properties largely depends on strain anisotropy as well.

  19. Growth and crystallographic characterization of molecular beam epitaxial WO3 and MoO3/WO3 thin films on sapphire substrates

    NASA Astrophysics Data System (ADS)

    Yano, Mitsuaki; Koike, Kazuto; Matsuo, Masayuki; Murayama, Takayuki; Harada, Yoshiyuki; Inaba, Katsuhiko

    2016-09-01

    Molecular beam epitaxy of tungsten trioxide (WO3) on (01 1 bar 2)-oriented (r-plane) sapphire substrates and molybdenum trioxide (MoO3) on the WO3 was studied by focusing on their crystallogrhaphic properties. Although polycrystalline monoclinic (γ-phase) WO3 films were grown at 500 °C and they became single-crystalline (0 0 1)-oriented γ-phase at 700 °C, the latter films were oxygen-deficient from stoichiometry and contained dense and deep thermal etchpits. By using a two-step growth method where only the initial 15 nm was grown at 700 °C and the rest part was grown at 500 °C, (0 0 1)-oriented γ-phase single-crystalline WO3 films with stoichiometric composition and smooth surface were obtained. On top of the 15-nm-thick WO3 initiation layer, (1 1 0)-oriented orthorhombic (α-phase) MoO3 films with smooth surface were obtained.

  20. Cosine (Cobalt Silicide Growth Through Nitrogen-Induced Epitaxy) Process For Epitaxial Cobalt Silicide Formation For High Performance Sha

    DOEpatents

    Lim, Chong Wee; Shin, Chan Soo; Gall, Daniel; Petrov, Ivan Georgiev; Greene, Joseph E.

    2004-09-28

    A method for forming an epitaxial cobalt silicide layer on a MOS device includes sputter depositing cobalt in an ambient to form a first layer of cobalt suicide on a gate and source/drain regions of the MOS device. Subsequently, cobalt is sputter deposited again in an ambient of argon to increase the thickness of the cobalt silicide layer to a second thickness.

  1. Efficient Interlayer Relaxation and Transition of Excitons in Epitaxial and Non-epitaxial MoS2/WS2 Heterostructures

    SciTech Connect

    Yu, Yifei; Hu, Shi; Su, Liqin; Huang, Lujun; Liu, Yi; Jin, Zhenghe; Puretzky, Alexander A.; Geohegan, David B.; Kim, Ki Wook; Zhang, Yong; Cao, Linyou

    2014-12-03

    Semiconductor heterostructurs provide a powerful platform for the engineering of excitons. Here we report on the excitonic properties of two-dimensional (2D) heterostructures that consist of monolayer MoS2 and WS2 stacked epitaxially or non-epitaxially in the vertical direction. We find similarly efficient interlayer relaxation and transition of excitons in both the epitaxial and non-epitaxial heterostructures. This is manifested by a two orders of magnitude decrease in the photoluminescence and an extra absorption peak at low energy region of both heterostructures. The MoS2/WS2 heterostructures show weak interlayer coupling and essentially act as an atomic-scale heterojunction with the intrinsic band structures of the two monolayers largely preserved. They are particularly promising for the applications that request efficient dissociation of excitons and strong light absorption, including photovoltaics, solar fuels, photodetectors, and optical modulators. Our results also indicate that 2D heterostructures promise to provide capabilities to engineer excitons from the atomic level without concerns of interfacial imperfection.

  2. Methods of preparing flexible photovoltaic devices using epitaxial liftoff, and preserving the integrity of growth substrates used in epitaxial growth

    DOEpatents

    Forrest, Stephen R; Zimmerman, Jeramy; Lee, Kyusang; Shiu, Kuen-Ting

    2015-01-06

    There is disclosed methods of making photosensitive devices, such as flexible photovoltaic (PV) devices, through the use of epitaxial liftoff. Also described herein are methods of preparing flexible PV devices comprising a structure having a growth substrate, wherein the selective etching of protective layers yields a smooth growth substrate that us suitable for reuse.

  3. Efficient Interlayer Relaxation and Transition of Excitons in Epitaxial and Non-epitaxial MoS2/WS2 Heterostructures

    DOE PAGES

    Yu, Yifei; Hu, Shi; Su, Liqin; ...

    2014-12-03

    Semiconductor heterostructurs provide a powerful platform for the engineering of excitons. Here we report on the excitonic properties of two-dimensional (2D) heterostructures that consist of monolayer MoS2 and WS2 stacked epitaxially or non-epitaxially in the vertical direction. We find similarly efficient interlayer relaxation and transition of excitons in both the epitaxial and non-epitaxial heterostructures. This is manifested by a two orders of magnitude decrease in the photoluminescence and an extra absorption peak at low energy region of both heterostructures. The MoS2/WS2 heterostructures show weak interlayer coupling and essentially act as an atomic-scale heterojunction with the intrinsic band structures of themore » two monolayers largely preserved. They are particularly promising for the applications that request efficient dissociation of excitons and strong light absorption, including photovoltaics, solar fuels, photodetectors, and optical modulators. Our results also indicate that 2D heterostructures promise to provide capabilities to engineer excitons from the atomic level without concerns of interfacial imperfection.« less

  4. Methods of preparing flexible photovoltaic devices using epitaxial liftoff, and preserving the integrity of growth substrates used in epitaxial growth

    DOEpatents

    Forrest, Stephen R; Zimmerman, Jeramy; Lee, Kyusang; Shiu, Kuen-Ting

    2013-02-19

    There is disclosed methods of making photosensitive devices, such as flexible photovoltaic (PV) devices, through the use of epitaxial liftoff. Also described herein are methods of preparing flexible PV devices comprising a structure having a growth substrate, wherein the selective etching of protective layers yields a smooth growth substrate that us suitable for reuse.

  5. Difference in the luminescence properties of orthorhombic and monoclinic forms of Y{sub 2}GeO{sub 5}:Ln (Ln = Tb{sup 3+} and Dy{sup 3+})

    SciTech Connect

    Tyagi, Adish; Shah, Alpa; Sudarsan, V. Vatsa, R.K.; Jain, V.K.

    2015-04-15

    Highlights: • Improved emission colour purity with orthorhombic form of Y{sub 2}GeO{sub 5}. • Non-stationary quenching exists in orthorhombic and monoclinic forms of Y{sub 2}GeO{sub 5}:Tb. • Ion pair formation and cross relaxation quenching operating for Y{sub 2}GeO{sub 5}:Dy samples. - Abstract: The luminescence properties of Tb{sup 3+} and Dy{sup 3+} doped orthorhombic and monoclinic forms of Y{sub 2}GeO{sub 5} are significantly different. Orthorhombic Y{sub 2}GeO{sub 5} doped with Tb{sup 3+} and Dy{sup 3+} ions gives bright green and blue emission upon UV light excitation with CIE coordinates (0.25, 0.46) and (0.25, 0.24), respectively. The monoclinic Y{sub 2}GeO{sub 5} doped with these ions exhibits light green and yellowish white emissions, respectively. This has been attributed to the differences in crystallographic environments around Y{sup 3+} ions in orthorhombic and monoclinic forms of Y{sub 2}GeO{sub 5}. Quantum yield of emission for orthorhombic Y{sub 2}GeO{sub 5}:Tb (∼29%) is significantly higher than that of the monoclinic Y{sub 2}GeO{sub 5}:Tb (∼14%). Lifetime values corresponding to {sup 4}F{sub 9/2} level of Dy{sup 3+} ions in both monoclinic and orthorhombic forms of Y{sub 2}GeO{sub 5} follow an opposite trend with respect to {sup 5}D{sub 4} level of Tb{sup 3+} ions. This is attributed to difference in the concentration quenching mechanism operating for Tb{sup 3+} and Dy{sup 3+} ions.

  6. A DFT+U study of the structural, electronic, magnetic, and mechanical properties of cubic and orthorhombic SmCoO3

    NASA Astrophysics Data System (ADS)

    Olsson, Emilia; Aparicio-Anglès, Xavier; de Leeuw, Nora H.

    2016-12-01

    SmCoO3 is a perovskite material that has gained attention as a potential substitute for La1-xSrxMnO3-d as a solid oxide fuel cell cathode. However, a number of properties have remained unknown due to the complexity of the material. For example, we know from experimental evidence that this perovskite exists in two different crystal structures, cubic and orthorhombic, and that the cobalt ion changes its spin state at high temperatures, leading to a semiconductor-to-metal transition. However, little is known about the precise magnetic structure that causes the metallic behavior or the spin state of the Co centers at high temperature. Here, we therefore present a systematic DFT+U study of the magnetic properties of SmCoO3 in order to determine what magnetic ordering is the one exhibited by the metallic phase at different temperatures. Similarly, mechanical properties are difficult to measure experimentally, which is why there is a lack of data for the two different phases of SmCoO3. Taking advantage of our DFT calculations, we have determined the mechanical properties from our calculated elastic constants, finding that both polymorphs exhibit similar ductility and brittleness, but that the cubic structure is harder than the orthorhombic phase.

  7. Coupled orthorhombic distortion, antiferromagnetism, and superconductivity in a single twin domain of Ba(Fe1-xCox)2 As2 (x =0.047)

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang; Wang, Wenjie; Hansen, B.; Ni, N.; Bud'Ko, S. L.; Canfield, P. C.; McQueeney, R. L.; Vaknin, D.; Kim, J. W.

    2013-03-01

    The interplay between structure, magnetism, and superconductivity in single crystal Ba(Fe1-xCox)2 As2 (x =0.047) has been studied using high-resolution X-ray diffraction by monitoring charge Bragg peaks in each twin domain separately. The emergence of superconducting state is correlated with the suppression of theorthorhombic distortion around TC, exhibiting the competition between orthorhombicity and superconductivity. Above TS, the Bragg peak widths gradually broaden, possibly induced by orthorhombic (nematic) fluctuations in the paramagnetic tetragonal phase. Upon cooling, anomalies in the peak width are observed at TS and also TN indicative of strong magnetoelastic coupling. Using the capability to study individual twin domains, the peak widths in the ab-plane are found to exhibit anisotropic behavior along and perpendicular to the stripe-type AFM wave vector. In contrast, the temperature dependencies of the out-of-plane peak width showan anomaly at TN, reflecting the connection between Fe-As distance and Fe local moment. Supported by DOE Basic Energy Sciences contract no. DE-AC02-07CH11358.

  8. Orthorhombic YBaCo4O8.4 crystals as a result of saturation of hexagonal YBaCo4O7 crystals with oxygen

    NASA Astrophysics Data System (ADS)

    Podberezskaya, N. V.; Bolotina, N. B.; Komarov, V. Yu.; Kameneva, M. Yu.; Kozeeva, L. P.; Lavrov, A. N.; Smolentsev, A. I.

    2015-07-01

    Hexagonal YBaCo4O7 crystals (sp. gr. P63 mc, a h = 6.3058(4) Å, c h = 10.2442(7) Å, Z = 2) are saturated with oxygen to the YBaCo4O8.4 composition and studied by X-ray diffraction (XRD) analysis. The saturation is completed by a structural first-order phase transition to orthorhombic crystals (sp. gr. Pbc21, a o = 31.8419(2) Å, b o = 10.9239(5) Å, c o = 10.0960(5) Å, Z = 20). The connection of two lattices is expressed in terms of the action of matrix (500/120/001) on the hexagonal basis. Five structural fragments of the same type but with different degrees of order alternate along the long axis of the oxygen-saturated orthorhombic structure. The XRD data on single crystals differ from the results obtained by other researchers on ceramic samples; possible causes of these differences are discussed.

  9. Bond-stretching phonon mode in stripe ordered orthorhombic Nd1.67Sr0.33NiO4.

    NASA Astrophysics Data System (ADS)

    Hücker, M.; Fukuda, T.; Gu, G. D.; Tranquada, J. M.; Baron, A. Q. R.; Hill, J. P.

    2007-03-01

    Inelastic x-ray scattering (IXS) experiments on Nd1.67Sr0.33NiO4 have been performed to study electron-phonon interactions in this charge stripe ordered nickelate. Resurgent interest in such phenomena has been triggered by recent results on the high temperature superconductors, where a kink in the electron dispersion as well as striking anomalies in high- energy optical phonon modes have been observed. A significant softening of the bond-stretching-phonon mode for Q||[100] was also observed in the tetragonal nickelate La1.69Sr0.31NiO4 with inelastic neutron scattering. Moreover, this compound shows an apparent splitting of the bond-stretching mode along the [110] direction. Here we present first IXS results for Q||[110] on the orthorhombic compound Nd1.67Sr0.33NiO4, which is characterized by domains with unidirectional stripe order. By probing different spots on the sample with different domain distribution, a weak contrast between the phonon spectra has been observed. We discuss these differences in terms of phonons propagating parallel and perpendicular to the stripe direction, as well as the anisotropic, i.e. orthorhombic, lattice structure.

  10. A Scanning Transmission X-ray Microscopy Study of Cubic and Orthorhombic C3A and Their Hydration Products in the Presence of Gypsum

    PubMed Central

    Rheinheimer, Vanessa; Chae, Sejung Rosie; Rodríguez, Erich D.; Geng, Guoqing; Kirchheim, Ana Paula; Monteiro, Paulo J. M.

    2016-01-01

    This paper shows the microstructural differences and phase characterization of pure phases and hydrated products of the cubic and orthorhombic (Na-doped) polymorphs of tricalcium aluminate (C3A), which are commonly found in traditional Portland cements. Pure, anhydrous samples were characterized using scanning transmission X-ray microscopy (STXM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and demonstrated differences in the chemical and mineralogical composition as well as the morphology on a micro/nano-scale. C3A/gypsum blends with mass ratios of 0.2 and 1.9 were hydrated using a water/C3A ratio of 1.2, and the products obtained after three days were assessed using STXM. The hydration process and subsequent formation of calcium sulfate in the C3A/gypsum systems were identified through the changes in the LIII edge fine structure for Calcium. The results also show greater Ca LII binding energies between hydrated samples with different gypsum contents. Conversely, the hydrated samples from the cubic and orthorhombic C3A at the same amount of gypsum exhibited strong morphological differences but similar chemical environments. PMID:28773865

  11. A DFT+U study of the structural, electronic, magnetic, and mechanical properties of cubic and orthorhombic SmCoO3.

    PubMed

    Olsson, Emilia; Aparicio-Anglès, Xavier; de Leeuw, Nora H

    2016-12-14

    SmCoO3 is a perovskite material that has gained attention as a potential substitute for La1-xSrxMnO3-d as a solid oxide fuel cell cathode. However, a number of properties have remained unknown due to the complexity of the material. For example, we know from experimental evidence that this perovskite exists in two different crystal structures, cubic and orthorhombic, and that the cobalt ion changes its spin state at high temperatures, leading to a semiconductor-to-metal transition. However, little is known about the precise magnetic structure that causes the metallic behavior or the spin state of the Co centers at high temperature. Here, we therefore present a systematic DFT+U study of the magnetic properties of SmCoO3 in order to determine what magnetic ordering is the one exhibited by the metallic phase at different temperatures. Similarly, mechanical properties are difficult to measure experimentally, which is why there is a lack of data for the two different phases of SmCoO3. Taking advantage of our DFT calculations, we have determined the mechanical properties from our calculated elastic constants, finding that both polymorphs exhibit similar ductility and brittleness, but that the cubic structure is harder than the orthorhombic phase.

  12. Effects of high source flow and high pumping speed on gas source molecular beam epitaxy / chemical beam epitaxy

    NASA Astrophysics Data System (ADS)

    McCollum, M. J.; Jackson, S. L.; Szafranek, I.; Stillman, G. E.

    1990-10-01

    We report the growth of GaAs by molecular beam epitaxy (MBE), gas source molecular beam epitaxy (GSMBE), and chemical beam epitaxy (CBE) in an epitaxial III-V reactor which features high pumping speed. The system is comprised of a modified Perkin-Elmer 430P molecular beam epitaxy system and a custom gas source panel from Emcore. The growth chamber is pumped with a 7000 1/s (He) diffusion pump (Varian VHS-10 with Monsanto Santovac 5 oil). The gas source panel includes pressure based flow controllers (MKS 1150) allowing triethylaluminum (TEA), triethylgallium (TEG), and trimethylindium (TMI) to be supplied without the use of hydrogen. All source lines, including arsine and phosphine, are maintained below atmospheric pressure. The high pumping speed allows total system flow rates as high as 100 SCCM and V/III ratios as high as 100. The purity of GaAs grown by MBE in this system increases with pumping speed. GaAs layers grown by GSMBE with arsine flows of 10 and 20 SCCM have electron concentrations of 1 × 10 15 cm -3 (μ 77=48,000 cm 2/V·) and 2 × 10 14 cm -3 (μ 77=78,000 cm 2/V·s) respectively. El ectron concentration varies with hydride injector temperature such that the minimum in electron concentration occurs for less than complete cracking. The effect of V/III ratio and the use of a metal eutectic bubbler on residual carrier concentration in GaAs grown by CBE is presented. Intentional Si and Be doping of CBE grown GaAs is demonstrated at a high growth rate of 5.4 μm/h.

  13. Cyclotron resonance in epitaxial Bi1-xSbx films grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Heremans, J.; Partin, D. L.; Thrush, C. M.; Karczewski, G.; Richardson, M. S.; Furdyna, J. K.

    1993-10-01

    The far-infrared magnetotransmission of thin films of semiconducting and semimetallic Bi1-xSbx alloys grown by molecular-beam epitaxy has been measured at fixed photon energies between 2.5 and 21.4 meV in magnetic fields up to 6 T, at T=1.8 K. The samples, grown on BaF2 substrates with composition 0<=x<=22.5%, were monocrystalline, with the trigonal axis perpendicular to the surface plane. The measurements were carried out in Faraday and Voigt geometries, with the magnetic field oriented parallel to binary, bisectrix, and trigonal axes of the films. Cyclotron-resonance lines of both electrons and holes were observed. From them, we establish the composition dependence of the effective-mass tensor, of the direct L-point band gap, and of the energy overlap in the semimetallic samples. We conclude that all band-structure parameters are the same in the films as in bulk Bi1-xSbx alloys, except for the energy overlap, which is increased by 16 meV independently of composition, possibly because of the strain induced by the substrate.

  14. The effect of anharmonicity in epitaxial interfaces. I. Substrate-induced dissociation of finite epitaxial islands

    NASA Astrophysics Data System (ADS)

    Milchev, Andrey; Markov, Ivan

    1984-01-01

    The behaviour of finite epitaxial islands in the periodic field of the substrate is theoretically investigated whereby the role of anharmonicity in the interatomic forces of the deposit is examined. The harmonic potential, traditionally adopted in the model of Frank and van der Merwe, is replaced by Toda and Morse potentials and sets of difference recursion equations, governing the static properties of such a system, are derived and solved numerically. Thus a new effect of substrate-induced rupture of anharmonic chains migrating on the surface, is found. It is shown that dissociation of migrating clusters is enhanced, if: (i) The substrate potential becomes increasingly modulated, (ii) the natural misfit between deposit and substrate is decreased (in absolute value), (iii) the misfit is negative, rather than positive (with the same absolute value) and (iv) the size of the cluster increases. A relation between dislocations in the chain and rupture appears to exist, suggesting dilatons (enormously stretched interatomic bonds) as the origin for destruction. The influence of anharmonicity on the equilibrium structure of the overgrowth is considered in Part II.

  15. Surface morphological evolution of epitaxial CrN(001) layers

    SciTech Connect

    Frederick, J.R.; Gall, D.

    2005-09-01

    CrN layers, 57 and 230 nm thick, were grown on MgO(001) at T{sub s}=600-800 deg. C by ultrahigh-vacuum magnetron sputter deposition in pure N{sub 2} discharges from an oblique deposition angle {alpha}=80 deg. . Layers grown at 600 deg. C nucleate as single crystals with a cube-on-cube epitaxial relationship with the substrate. However, rough surfaces with cauliflower-type morphologies cause the nucleation of misoriented CrN grains that develop into cone-shaped grains that protrude out of the epitaxial matrix to form triangular faceted surface mounds. The surface morphology of epitaxial CrN(001) grown at 700 deg. C is characterized by dendritic ridge patterns extending along the orthogonal <110> directions superposed by square-shaped super mounds with <100> edges. The ridge patterns are attributed to a Bales-Zangwill instability while the supermounds form due to atomic shadowing which leads to the formation of epitaxial inverted pyramids that are separated from the surrounding layer by tilted nanovoids. Growth at 800 deg. C yields complete single crystals with smooth surfaces. The root-mean-square surface roughness for 230-nm-thick layers decreases from 18.8 to 9.3 to 1.1 nm as T{sub s} is raised from 600 to 700 to 800 deg. C. This steep decrease is due to a transition in the roughening mechanism from atomic shadowing to kinetic roughening. Atomic shadowing is dominant at 600 and 700 deg. C, where misoriented grains and supermounds, respectively, capture a larger fraction of the oblique deposition flux in comparison to the surrounding epitaxial matrix, resulting in a high roughening rate that is described by a power law with an exponent {beta}>0.5. In contrast, kinetic roughening controls the surface morphology for T{sub s}=800 deg. C, as well as the epitaxial fraction of the layers grown at 600 and 700 deg. C, yielding relatively smooth surfaces and {beta}{<=}0.27.

  16. 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

  17. Epitaxy of Polar Oxides and Semiconductors

    NASA Astrophysics Data System (ADS)

    Shelton, Christopher Tyrel

    Integrating polar oxide materials with wide-bandgap nitride semiconductors offers the possibility of a tunable 2D carrier gas (2DCG) - provided defect densities are low and interfaces are abrupt. This dissertation investigates a portion of the synthesis science necessary to produce a "semiconductor-grade" interface between these highly dissimilar materials. A significant portion of this work is aligned with efforts to engineer a step-free GaN substrate to produce single in-plane oriented rocksalt oxide films. Initially, we explore the homoepitaxial MOCVD growth conditions necessary to produce highquality GaN films on ammonothermally grown substrates. Ammono substrates are only recently available for purchase and are the market leader in low-dislocation density material. Their novelty requires development of an understanding of morphology trade-offs in processing space. This includes preservation of the epi-polished surface in aggressive MOCVD environments and an understanding of the kinetic barriers affecting growth morphologies. Based on several factors, it was determined that GaN exhibits an 'uphill' diffusion bias that may likely be ascribed to a positive Ehrlich-Schwoebel (ES) barrier. This barrier should have a stabilizing effect against step-bunching but, for many growth conditions, regular step bunching was observed. One possible explanation for the step-bunching instability is the presence of impurities. Experimentally, conditions which incorporate more carbon into GaN homoepitaxial layers are correlated with step-bunching while conditions that suppress carbon produce bilayer stepped morphologies. These observations lead us to the conclusion that GaN homoepitaxial morphology is a competition between impurity induced step-bunching and a stabilizing diffusion bias due to a positive ES barrier. Application of the aforementioned homoepitaxial growth techniques to discrete substrate regions using selected- and confined area epitaxy (SAE,CAE) produces some

  18. Characteristics of strong ferromagnetic Josephson junctions with epitaxial barriers

    NASA Astrophysics Data System (ADS)

    Bell, C.; Loloee, R.; Burnell, G.; Blamire, M. G.

    2005-05-01

    We present the measurement of superconductor/ferromagnetic Josephson junctions, based on an epitaxial Nb bottom electrode and epitaxial Fe20Ni80 barrier. Uniform junctions have been fabricated with a barrier thicknesses in the range 2-12nm . The maximum critical current density ˜2.4±0.2×109Am-2 was found for a device with a 3-nm -thick barrier at 4.2K , corresponding to an average characteristic voltage ICRN˜16μV . The ICRN showed a nonmonotonic behavior with Fe20Ni80 thickness. The variation of the resistance of a unit area ARN , of the junctions with barrier thickness gave a Nb/Py specific interface resistance of 6.0±0.5fΩm2 and Fe20Ni80 resistivity of 174±50nΩm , consistent with other studies in polycrystalline samples.

  19. Oxidized Monolayers of Epitaxial Silicene on Ag(111)

    PubMed Central

    Johnson, Neil W.; Muir, David I.; Moewes, Alexander

    2016-01-01

    The properties of epitaxial silicene monolayers on Ag(111) at various levels of oxidation are determined through complementary density functional theory calculations and soft X-ray spectroscopy experiments. Our calculations indicate that moderate levels of oxidation do not cause a significant bandgap opening in the epitaxial silicene monolayer, suggesting that oxygen functionalization is not a viable mechanism for bandgap tuning while the silicene monolayer remains on its metallic substrate. In addition, moderate oxidation is calculated to strongly distort the hexagonal Si lattice, causing it to cluster in regions of highest oxygen adatom concentration but retain its 2D sheet structure. However, our experiments reveal that beam-induced oxidation is consistent with the formation of islands of bulk-like SiO2. Complete exposure of the monolayer to ambient conditions results in a fully oxidized sample that closely resembles bulk SiO2, of which a significant portion is completely detached from the substrate. PMID:26936144

  20. Study of zinc oxide epitaxial film growth and UV photodetectors

    NASA Astrophysics Data System (ADS)

    Nahhas, Ahmed Mohammed

    ZnO is a versatile material, and has been extensively studied for various applications such as varistors, transducers, transparent conducting electrodes, sensors, and catalysts. While polycrystalline ZnO is commonly used in these conventional applications, there has been a growing interest in obtaining single-crystalline ZnO films on various substrates. ZnO is a II-VI wide bandgap semiconductor with a relatively large exciton binding energy, and holds a potential for light emitting/detecting or nonlinear optical devices in the UV range. ZnO is isomorphic to wurtzite GaN with good lattice match, and therefore there has been a great deal of interest in using ZnO as a buffer layer or a substrate in growing high quality GaN films (or vice versa ZnO growth on GaN). In this study, we have investigated epitaxial growth of ZnO films on sapphire and silicon substrates. High quality epitaxial ZnO films were grown on sapphire (0001) single crystal substrates using a rf magnetron sputtering technique. X-ray diffraction analysis shows that the ZnO films are of a monocrystalline wurtzite structure with their epitaxial relationship of ZnO[0001]//sapphire[0001] along the growth direction and ZnO[112&barbelow;0]//sapphire[11&barbelow;00] along the in-plane direction. ZnO on Si also offers an interesting opportunity that the various functional properties of ZnO can be combined with the advanced Si electronics on the same substrate. Direct growth of epitaxial ZnO on Si, however, is known to be an extremely difficult task due to the oxidation problem during the nucleation stage of a ZnO growth process. We have overcome this problem by introducing an epitaxial GaN buffer layer, and have successfully grown epitaxial ZnO films on Si(111) substrates. X-ray diffraction analysis confirms an epitaxial relationship of ZnO[0001]//GaN[0001]//Si[111] along the growth direction and ZnO[112&barbelow;0]//GaN[112&barbelow;0]//Si[11&barbelow;0] along the in-plane direction. As an application of the

  1. Epitaxial Nanoflag Photonics: Semiconductor Nanoemitters Grown with Their Nanoantennas.

    PubMed

    Sorias, Ofir; Kelrich, Alexander; Gladstone, Ran; Ritter, Dan; Orenstein, Meir

    2017-09-06

    Semiconductor nanostructures are desirable for electronics, photonics, quantum circuitry, and energy conversion applications as well as for fundamental science. In photonics, optical nanoantennas mediate the large size difference between photons and semiconductor nanoemitters or detectors and hence are instrumental for exhibiting high efficiency. In this work we present epitaxially grown InP nanoflags as optically active nanostructures encapsulating the desired characteristics of a photonic emitter and an efficient epitaxial nanoantenna. We experimentally characterize the polarized and directional emission of the nanoflag-antenna and show the control of these properties by means of structure, dimensions, and constituents. We analyze field enhancement and light extraction by the semiconductor nanoflag antenna, which yield comparable values to enhancement factors of metallic plasmonic antennas. We incorporated quantum emitters within the nanoflag structure and characterized their emission properties. Merging of active nanoemitters with nanoantennas at a single growth process enables a new class of devices to be used in nanophotonics applications.

  2. Quantum Hall effect in epitaxial graphene with permanent magnets

    NASA Astrophysics Data System (ADS)

    Parmentier, F. D.; Cazimajou, T.; Sekine, Y.; Hibino, H.; Irie, H.; Glattli, D. C.; Kumada, N.; Roulleau, P.

    2016-12-01

    We have observed the well-kown quantum Hall effect (QHE) in epitaxial graphene grown on silicon carbide (SiC) by using, for the first time, only commercial NdFeB permanent magnets at low temperature. The relatively large and homogeneous magnetic field generated by the magnets, together with the high quality of the epitaxial graphene films, enables the formation of well-developed quantum Hall states at Landau level filling factors v = ±2, commonly observed with superconducting electro-magnets. Furthermore, the chirality of the QHE edge channels can be changed by a top gate. These results demonstrate that basic QHE physics are experimentally accessible in graphene for a fraction of the price of conventional setups using superconducting magnets, which greatly increases the potential of the QHE in graphene for research and applications.

  3. Epitaxial growth of VO{sub 2} by periodic annealing

    SciTech Connect

    Tashman, J. W.; Paik, H.; Merz, T. A.; Lee, J. H.; Moyer, J. A.; Schiffer, P.; Misra, R.; Mundy, J. A.; Spila, T.; Schubert, J.; Muller, D. A.; Schlom, D. G.

    2014-02-10

    We report the growth of ultrathin VO{sub 2} films on rutile TiO{sub 2} (001) substrates via reactive molecular-beam epitaxy. The films were formed by the cyclical deposition of amorphous vanadium and its subsequent oxidation and transformation to VO{sub 2} via solid-phase epitaxy. Significant metal-insulator transitions were observed in films as thin as 2.3 nm, where a resistance change ΔR/R of 25 was measured. Low angle annular dark field scanning transmission electron microscopy was used in conjunction with electron energy loss spectroscopy to study the film/substrate interface and revealed the vanadium to be tetravalent and the titanium interdiffusion to be limited to 1.6 nm.

  4. Nanoscale electrical properties of epitaxial Cu3Ge film.

    PubMed

    Wu, Fan; Cai, Wei; Gao, Jia; Loo, Yueh-Lin; Yao, Nan

    2016-07-01

    Cu3Ge has been pursued as next-generation interconnection/contact material due to its high thermal stability, low bulk resistivity and diffusion barrier property. Improvements in electrical performance and structure of Cu3Ge have attracted great attention in the past decades. Despite the remarkable progress in Cu3Ge fabrication on various substrates by different deposition methods, polycrystalline films with excess Ge were frequently obtained. Moreover, the characterization of nanoscale electrical properties remains challenging. Here we show the fabrication of epitaxial Cu3Ge thin film and its nanoscale electrical properties, which are directly correlated with localized film microstructures and supported by HRTEM observations. The average resistivity and work function of epitaxial Cu3Ge thin film are measured to be 6 ± 1 μΩ cm and ~4.47 ± 0.02 eV respectively, qualifying it as a good alternative to Cu.

  5. Investigation of optical properties of epitaxial yttrium iron garnet films

    SciTech Connect

    Paranin, V. D.

    2016-04-13

    In work we investigated yttrium iron garnet epitaxial films with a thickness of 10 µm and 55 µm which were grown on the surface of garnet substrate. Using the polarizing microscopy method the branching domain structure of films was shown with the period of domains 21.5 µm and 42.5 µm. Disappearance of domains at presence of an external magnetic field up to 100 Oe was noted. The optical transmission of films for the polarized beam of HeNe laser is investigated and zero diffraction order and odd diffraction rings orders were shown. Interconnection of the period of chaotically oriented domains with angles of axially symmetric diffraction rings orders was shown. Diffraction patterns at various longitudinal magnetic fields are investigated. Disappearance of odd diffraction orders and increasing in intensity of zero diffraction order were fixed. Optical transmission of epitaxial films was measured in range of 500 - 900 nm.

  6. Nanoscale electrical properties of epitaxial Cu3Ge film

    PubMed Central

    Wu, Fan; Cai, Wei; Gao, Jia; Loo, Yueh-Lin; Yao, Nan

    2016-01-01

    Cu3Ge has been pursued as next-generation interconnection/contact material due to its high thermal stability, low bulk resistivity and diffusion barrier property. Improvements in electrical performance and structure of Cu3Ge have attracted great attention in the past decades. Despite the remarkable progress in Cu3Ge fabrication on various substrates by different deposition methods, polycrystalline films with excess Ge were frequently obtained. Moreover, the characterization of nanoscale electrical properties remains challenging. Here we show the fabrication of epitaxial Cu3Ge thin film and its nanoscale electrical properties, which are directly correlated with localized film microstructures and supported by HRTEM observations. The average resistivity and work function of epitaxial Cu3Ge thin film are measured to be 6 ± 1 μΩ cm and ~4.47 ± 0.02 eV respectively, qualifying it as a good alternative to Cu. PMID:27363582

  7. Carbon molecular beam epitaxy on various semiconductor substrates

    SciTech Connect

    Jerng, S.K.; Yu, D.S.; Lee, J.H.; Kim, Y.S.; Kim, C.; Yoon, S.; Chun, S.H.

    2012-10-15

    Direct graphene growth on semiconductor substrates is an important goal for successful integration of graphene with the existing semiconductor technology. We test the feasibility of this goal by using molecular beam epitaxy on various semiconductor substrates: group IV (Si, SiC), group III–V (GaAs, GaN, InP), and group II–VI (ZnSe, ZnO). Graphitic carbon has been formed on most substrates except Si. In general, the crystallinities of carbon layers are better on substrates of hexagonal symmetry than those on cubic substrates. The flatness of graphitic carbon grown by molecular beam epitaxy is noticeable, which may help the integration with semiconductor structures.

  8. Quantum Hall effect in epitaxial graphene with permanent magnets

    PubMed Central

    Parmentier, F. D.; Cazimajou, T.; Sekine, Y.; Hibino, H.; Irie, H.; Glattli, D. C.; Kumada, N.; Roulleau, P.

    2016-01-01

    We have observed the well-kown quantum Hall effect (QHE) in epitaxial graphene grown on silicon carbide (SiC) by using, for the first time, only commercial NdFeB permanent magnets at low temperature. The relatively large and homogeneous magnetic field generated by the magnets, together with the high quality of the epitaxial graphene films, enables the formation of well-developed quantum Hall states at Landau level filling factors v = ±2, commonly observed with superconducting electro-magnets. Furthermore, the chirality of the QHE edge channels can be changed by a top gate. These results demonstrate that basic QHE physics are experimentally accessible in graphene for a fraction of the price of conventional setups using superconducting magnets, which greatly increases the potential of the QHE in graphene for research and applications. PMID:27922114

  9. Anti-damping spin transfer torque through epitaxial nickel oxide

    SciTech Connect

    Moriyama, Takahiro; Nagata, Masaki; Yoshimura, Yoko; Matsuzaki, Noriko; Ono, Teruo; Takei, So; Tserkovnyak, Yaroslav; Terashima, Takahito

    2015-04-20

    We prepare the high quality epitaxial MgO(001)[100]/Pt(001)[100]/NiO(001)[100]/FeNi/SiO{sub 2} films to investigate the spin transport in the NiO antiferromagnetic insulator. The ferromagnetic resonance measurements of the FeNi under a spin current injection from the Pt by the spin Hall effect revealed the change of the ferromagnetic resonance linewidth depending on the amount of the spin current injection. The results can be interpreted that there is an angular momentum transfer through the NiO. A high efficient angular momentum transfer we observed in the epitaxial NiO can be attributed to the well-defined orientation of the antiferromagnetic moments and the spin quantization axis of the injected spin current.

  10. Silicon surface preparation for III-V molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Madiomanana, K.; Bahri, M.; Rodriguez, J. B.; Largeau, L.; Cerutti, L.; Mauguin, O.; Castellano, A.; Patriarche, G.; Tournié, E.

    2015-03-01

    We report on a silicon substrate preparation for III-V molecular-beam epitaxy (MBE). It combines sequences of ex situ and in situ treatments. The ex situ process is composed of cycles of HF dip and O2 plasma treatments. Ellipsometry and atomic force microscopy performed after each step during the substrate preparation reveal surface cleaning and de-oxidation. The in situ treatment consists in flash annealing the substrate in the MBE chamber prior to epitaxial growth. GaSb-based multiple quantum well heterostructures emitting at 1.55 μm were grown by MBE on Si substrates prepared by different methods. Structural characterizations using XRD and TEM coupled with photoluminescence spectroscopy demonstrates the efficiency of our preparation process. This study thus unravels a simple and reproducible protocol to prepare the Si surface prior to III-V MBE.

  11. Quantum Hall effect in epitaxial graphene with permanent magnets.

    PubMed

    Parmentier, F D; Cazimajou, T; Sekine, Y; Hibino, H; Irie, H; Glattli, D C; Kumada, N; Roulleau, P

    2016-12-06

    We have observed the well-kown quantum Hall effect (QHE) in epitaxial graphene grown on silicon carbide (SiC) by using, for the first time, only commercial NdFeB permanent magnets at low temperature. The relatively large and homogeneous magnetic field generated by the magnets, together with the high quality of the epitaxial graphene films, enables the formation of well-developed quantum Hall states at Landau level filling factors v = ±2, commonly observed with superconducting electro-magnets. Furthermore, the chirality of the QHE edge channels can be changed by a top gate. These results demonstrate that basic QHE physics are experimentally accessible in graphene for a fraction of the price of conventional setups using superconducting magnets, which greatly increases the potential of the QHE in graphene for research and applications.

  12. a Study of Epitaxial Growth of Calcium Fluoride on Silicon

    NASA Astrophysics Data System (ADS)

    Howard, L. K.

    Available from UMI in association with The British Library. The alkaline earth fluorides are good insulators at room temperature and have received significant attention as epitaxial dielectrics on semiconductors, their crystal structure and lattice parameters resembling those of common semiconductors. Such dielectrics enable passivation of semiconductors lacking stable oxides, isolation of devices on one substrate, and fabrication of 3-dimensional epitaxial heterostructures. The CaF_2/Si system was the structure investigated since the room temperature lattice mismatch is only 0.6%. A vacuum system was therefore developed for the deposition of CaF_2 onto silicon, and an RBS system, incorporating detector cooling, developed to establish the dependence of epitaxy on substrate temperature using channeling of 340 keV protons (giving an enhanced depth resolution and improved sensitivity to light elements compared to 2 MeV He^{+ } analysis). Epitaxial growth was obtained on n-type Si(111) and Si(100) substrates at 400-750 ^circC and 575-675^ circC respectively. A reaction between the CaF_2 and silicon occurred at higher temperatures producing non-uniform films. The epitaxy was also dependent on film thickness, the optimum de-channelled fractions obtained in the film of 8.25% and 15.2% for Si(111) and Si(100) substrates respectively were unobtainable for films under 1200 A. The insulator surface morphology was examined using Scanning Electron Microscopy. Epitaxial films on Si(111) were generally smooth, while preferential growth along <110> directions was observed for epitaxial insulators on Si(100), possibly due to slip along the (111) fluorite cleavage planes resulting from differences in the thermal expansion coefficients of CaF_2 and silicon and an increase in lattice mismatch with substrate temperature, although no cracking of the insulator was observed. The insulation and electrical properties of the films were investigated. Film resistivities upto 5E8 Omegacm and

  13. On the kinetic barriers of graphene homo-epitaxy

    SciTech Connect

    Zhang, Wei; Yu, Xinke; Xie, Ya-Hong; Cahyadi, Erica; Ratsch, Christian

    2014-12-01

    The diffusion processes and kinetic barriers of individual carbon adatoms and clusters on graphene surfaces are investigated to provide fundamental understanding of the physics governing epitaxial growth of multilayer graphene. It is found that individual carbon adatoms form bonds with the underlying graphene whereas the interaction between graphene and carbon clusters, consisting of 6 atoms or more, is very weak being van der Waals in nature. Therefore, small carbon clusters are quite mobile on the graphene surfaces and the diffusion barrier is negligibly small (∼6 meV). This suggests the feasibility of high-quality graphene epitaxial growth at very low growth temperatures with small carbon clusters (e.g., hexagons) as carbon source. We propose that the growth mode is totally different from 3-dimensional bulk materials with the surface mobility of carbon hexagons being the highest over graphene surfaces that gradually decreases with further increase in cluster size.

  14. Growth of high-quality p-type GaAs epitaxial layers using carbon tetrabromide by gas source molecular-beam epitaxy and molecular-beam epitaxy

    SciTech Connect

    Houng, Y.M.; Lester, S.D.; Mars, D.E.

    1993-05-01

    Heavily C-doped p-type GaAs epitaxial films have been grown using carbon tetrabromide (CBr{sub 4}) as a dopant source in both gas source molecular-beam epitaxy (GSMBE) and molecular-beam epitaxy (MBE). It was found that CBr;{sub 4} has a great potential as a p-type dopant source for use in a conventional MBE chamber without any major modification of its pumping system because of its high-doping efficiency and low gas load. Hole concentrations in excess of 1x10{sup 20} cm{sup {minus}3} have been measured in CBr{sub 4}-doped GaAs grown from both the MBE or GSMBE techniques, using As{sub 4} or AsH{sub 3}, respectively. A Hall mobility of > 80 cm{sup 2}/V s was measured in layers with doping level of 5x10{sup 19} cm{sup {minus}3}, which is comparable to that from chemical beam exitaxially (CBE) grown TMGa-doped GaAs. Under GSMBE and MBE modes, the doping memory effect in AlGaAs was greatly reduced using CBr{sub 4} as compared to TMGa doping source. GSMBE grown heterojunction bipolar transistors with a CBr{sub 4} as compared to TMGa doping source. GSMBE grown heterojunction bipolar transistors with a CBr{sub 4}-doped base layer have a current gain as high as 79 and a base sheet resistance as low as 225 {Omega}/{open_square}. 15 refs., 4 figs., 1 tab.

  15. Faceted ceramic fibers, tapes or ribbons and epitaxial devices therefrom

    SciTech Connect

    Goyal, Amit

    2013-07-09

    A crystalline article includes a single-crystal ceramic fiber, tape or ribbon. The fiber, tape or ribbon has at least one crystallographic facet along its length, which is generally at least one meter long. In the case of sapphire, the facets are R-plane, M-plane, C-plane or A-plane facets. Epitaxial articles, including superconducting articles, can be formed on the fiber, tape or ribbon.

  16. Three-dimensional lattice matching of epitaxially embedded nanoparticles

    NASA Astrophysics Data System (ADS)

    May, Brelon J.; Anderson, Peter M.; Myers, Roberto C.

    2017-02-01

    For a given degree of in-plane lattice mismatch between a two-dimensional (2D) epitaxial layer and a substrate (εIP*), there is a critical thickness above which interfacial defects form to relax the elastic strain energy. Here, we extend the 2D lattice-matching conditions to three-dimensions in order to predict the critical size beyond which epitaxially encased nanoparticles, characterized by both εIP* and out-of-plane lattice mismatch (εOP*), relax by dislocation formation. The critical particle length (Lc) at which defect formation proceeds is determined by balancing the reduction in elastic energy associated with dislocation introduction with the corresponding increase in defect energy. Our results, which use a modified Eshelby inclusion technique for an embedded, arbitrarily-faceted nanoparticle, provide new insight to the nanoepitaxy of low dimensional structures, especially quantum dots and nanoprecipitates. By engineering εIP* and εOP*, the predicted Lc for nanoparticles can be increased to well beyond the case of encapsulation in a homogenous matrix. For the case of truncated pyramidal shaped InAs, Lc 10.8 nm when fully embedded in GaAs (εIP* = εOP* = - 0.072); 16.4 nm when the particle is grown on GaAs, but capped with InSb (εIP* = - 0.072 and εOP* =+0.065); and a maximum of 18.4 nm if capped with an alloy corresponding to εOP* =+0.037. The effect, which we term "3D Poisson-stabilization" provides a means to increase the epitaxial strain tolerance in epitaxial heterostructures by tailoring εOP*.

  17. Characterization of epitaxially grown films of vanadium oxides

    SciTech Connect

    Rogers, K.D.; Coath, J.A.; Lovell, M.C. , Shrivenham, Swindon, Wiltshire, SN6 8LA, England )

    1991-08-01

    The growth of VO{sub 2} and V{sub 2}O{sub 3} thin films by reactive sputtering has been investigated. Previously reported studies of such thin films have often presented ambiguous results concerning the precise nature of the layers produced. A thorough and comprehensive characterization program including x-ray diffraction, scanning electron microscopy, Rutherford-backscattering spectroscopy, and electrical conductivity measurements has been undertaken to ensure that the films produced were of a true epitaxial nature.

  18. Preferentially Etched Epitaxial Liftoff of InP Material

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G. (Inventor); Wilt, David M. (Inventor); DeAngelo, Frank L. (Inventor)

    1997-01-01

    The present invention is directed toward a method of removing epitaxial substrates from host substrates. A sacrificial release layer of ternary material is placed on the substrate. A layer of InP is then placed on the ternary material. Afterward a layer of wax is applied to the InP layer to apply compressive force and an etchant material is used to remove the sacrificial release layer.

  19. Preferentially etched epitaxial liftoff of InP material

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G. (Inventor); Wilt, David M. (Inventor); Deangelo, Frank L. (Inventor)

    1995-01-01

    The present invention is directed toward a method of removing epitaxial substrates from host substrates. A sacrificial release layer of ternary material is placed on the substrate. A layer of InP is then placed on the ternary material. Afterward a layer of wax is applied to the InP layer to apply compressive force and an etchant material is used to remove the sacrificial release layer.

  20. Thermoreversible, epitaxial fcc<-->bcc transitions in block copolymer solutions.

    PubMed

    Bang, Joona; Lodge, Timothy P; Wang, Xiaohui; Brinker, Kristin L; Burghardt, Wesley R

    2002-11-18

    Uncharged block copolymer micelles display thermoreversible transitions between close-packed and bcc lattices for a range of concentration, solvent selectivity, and copolymer composition. Using small-angle x-ray scattering on shear-oriented solutions, highly aligned fcc crystals are seen to transform epitaxially to bcc crystals, with fcc/bcc orientational relationships that are well established in martensitic transformations in metals. The transition is driven by decreasing solvent selectivity with increasing temperature, inducing solvent penetration of the micellar core.

  1. Gradient bounds for a thin film epitaxy equation

    NASA Astrophysics Data System (ADS)

    Li, Dong; Qiao, Zhonghua; Tang, Tao

    2017-02-01

    We consider a gradient flow modeling the epitaxial growth of thin films with slope selection. The surface height profile satisfies a nonlinear diffusion equation with biharmonic dissipation. We establish optimal local and global wellposedness for initial data with critical regularity. To understand the mechanism of slope selection and the dependence on the dissipation coefficient, we exhibit several lower and upper bounds for the gradient of the solution in physical dimensions d ≤ 3.

  2. Faceted ceramic fibers, tapes or ribbons and epitaxial devices therefrom

    DOEpatents

    Goyal, Amit [Knoxville, TN

    2012-07-24

    A crystalline article includes a single-crystal ceramic fiber, tape or ribbon. The fiber, tape or ribbon has at least one crystallographic facet along its length, which is generally at least one meter long. In the case of sapphire, the facets are R-plane, M-plane, C-plane or A-plane facets. Epitaxial articles, including superconducting articles, can be formed on the fiber, tape or ribbon.

  3. Ferromagnetic elements by epitaxial growth: A density functional prediction

    NASA Astrophysics Data System (ADS)

    Schönecker, Stephan; Richter, Manuel; Koepernik, Klaus; Eschrig, Helmut

    2012-01-01

    The periodic table contains only six natural elements with a ferromagnetic ground state. For example, the metal uranium, which is magnetically ordered in many compounds, is paramagnetic in all its known elemental bulk phases. Also, the iron-group elements ruthenium and osmium are known to be bulk paramagnets. We predict by means of density functional calculations that epitaxial growth of uranium, ruthenium, or osmium on suitable substrates may allow stabilization of bulklike films with tetragonal structures showing ferromagnetic order.

  4. Measurement of magnetostriction coefficients of epitaxial garnet films.

    PubMed

    Vella-Coleiro, G P

    1979-09-01

    A technique for measuring the magnetostriction coefficients of epitaxial garnet films on 50-mm-diam wafers is described. The measurement is based on the shift of the microwave ferrimagnetic resonance produced by stressing the film, which is achieved by supporting the wafer around its circumference and reducing the atmospheric pressure on one side. A simple, nonresonant transmission microwave spectrometer which is well suited for measurements on large wafers is also described.

  5. Heterogeneous integration of epitaxial nanostructures: strategies and application drivers

    NASA Astrophysics Data System (ADS)

    Chui, Chi On; Shin, Kyeong-Sik; Kina, Jorge; Shih, Kun-Huan; Narayanan, Pritish; Moritz, C. Andras

    2012-10-01

    In order to sustain the historic progress in information processing, transmission, and storage, concurrent integration of heterogeneous functionality and materials with fine granularity is clearly imperative for the best connectivity, system performance, and density metrics. In this paper, we review recent developments in heterogeneous integration of epitaxial nanostructures for their applications toward our envisioned device-level heterogeneity using computing nanofabrics. We first identify the unmet need for heterogeneous integration in modern nanoelectronics and review state-of-the-art assembly approaches for nanoscale computing fabrics. We also discuss the novel circuit application driver, known as Nanoscale Application Specific Integrated Circuits (NASICs), which promises an overall performance-power-density advantage over CMOS and embeds built-in defect and parameter variation resilience. At the device-level, we propose an innovative cross-nanowire field-effect transistor (xnwFET) structure that simultaneously offers high performance, low parasitics, good electrostatic control, ease-of-manufacturability, and resilience to process variation. In addition, we specify technology requirements for heterogeneous integration and present two wafer-scale strategies. The first strategy is based on ex situ assembly and stamping transfer of pre-synthesized epitaxial nanostructures that allows tight control over key nanofabric parameters. The second strategy is based on lithographic definition of epitaxial nanostructures on native substrates followed by their stamping transfer using VLSI foundry processes. Finally, we demonstrate the successful concurrent heterogeneous co-integration of silicon and III-V compound semiconductor epitaxial nanowire arrays onto the same hosting substrate over large area, at multiple locations, with fine granularity, close proximity and high yield.

  6. Microwave studies of weak localization and antilocalization in epitaxial graphene

    SciTech Connect

    Drabińska, Aneta; Kamińska, Maria; Wołoś, Agnieszka; Baranowski, J. M.

    2013-12-04

    A microwave detection method was applied to study weak localization and antilocalization in epitaxial graphene sheets grown on both polarities of SiC substrates. Both coherence and scattering length values were obtained. The scattering lengths were found to be smaller for graphene grown on C-face of SiC. The decoherence rate was found to depend linearly on temperature, showing the electron-electron scattering mechanism.

  7. Robust surface states in epitaxial Bi(111) thin films

    NASA Astrophysics Data System (ADS)

    Zhu, Kai; Jin, Xiaofeng

    Bulk Bi a prototype semimetal with trivial electronic band topology. Unanticipatedly, we show the Altshuler-Aronov-Spivak and Aharonov-Bohm effects in epitaxial Bi(111) thin films. Meanwhile, we clearly identify the interaction of the top and bottom surface states via quantum tunneling by the electrical conductance and weak anti-localization measurements. These results have significantly enriched our understanding about the electronic structure of Bi, which might be helpful for clearing up some of its longstanding subtle issues.

  8. Intrinsically incompatible crystal (ligand) field parameter sets for transition ions at orthorhombic and lower symmetry sites in crystals and their implications

    NASA Astrophysics Data System (ADS)

    Rudowicz, C.; Gnutek, P.

    2010-01-01

    Central quantities in spectroscopy and magnetism of transition ions in crystals are crystal (ligand) field parameters (CFPs). For orthorhombic, monoclinic, and triclinic site symmetry CF analysis is prone to misinterpretations due to large number of CFPs and existence of correlated sets of alternative CFPs. In this review, we elucidate the intrinsic features of orthorhombic and lower symmetry CFPs and their implications. The alternative CFP sets, which yield identical energy levels, belong to different regions of CF parameter space and hence are intrinsically incompatible. Only their ‘images’ representing CFP sets expressed in the same region of CF parameter space may be directly compared. Implications of these features for fitting procedures and meaning of fitted CFPs are categorized into negative: pitfalls and positive: blessings. As a case study, the CFP sets for Tm 3+ ions in KLu(WO 4) 2 are analysed and shown to be intrinsically incompatible. Inadvertent, so meaningless, comparisons of incompatible CFP sets result in various pitfalls, e.g., controversial claims about the values of CFPs obtained by other researchers as well as incorrect structural conclusions or faulty systematics of CF parameters across rare-earth ion series based on relative magnitudes of incompatible CFPs. Such pitfalls bear on interpretation of, e.g., optical spectroscopy, inelastic neutron scattering, and magnetic susceptibility data. An extensive survey of pertinent literature was carried out to assess recognition of compatibility problems. Great portion of available orthorhombic and lower symmetry CFP sets are found intrinsically incompatible, yet these problems and their implications appear barely recognized. The considerable extent and consequences of pitfalls revealed by our survey call for concerted remedial actions of researchers. A general approach based on the rhombicity ratio standardization may solve compatibility problems. Wider utilization of alternative CFP sets in the

  9. Numerical adiabatic potentials of orthorhombic Jahn-Teller effects retrieved from ultrasound attenuation experiments. Application to the SrF2:Cr crystal

    NASA Astrophysics Data System (ADS)

    Zhevstovskikh, I. V.; Bersuker, I. B.; Gudkov, V. V.; Averkiev, N. S.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Shakurov, G. S.; Ulanov, V. A.; Surikov, V. T.

    2016-06-01

    A methodology is worked out to retrieve the numerical values of all the main parameters of the six-dimensional adiabatic potential energy surface (APES) of a polyatomic system with a quadratic T-term Jahn-Teller effect (JTE) from the ultrasound experiments. The method is based on a verified assumption that ultrasound attenuation and speed encounter anomalies when the direction of propagation and polarization of its wave of strain coincides with the characteristic directions of symmetry breaking in the JTE. For the SrF2:Cr crystal, employed as a basic example, we observed anomaly peaks in the temperature dependence of attenuation of ultrasound at frequencies of 50-160 MHz in the temperature interval of 40-60 K for the wave propagating along the [110] direction, for both the longitudinal and the shear modes, the latter with two polarizations along the [001] and [1 1 ¯ 0 ] axes, respectively. We show that these anomalies are due to the ultrasound relaxation by the system of non-interacting Cr2+ JT centers with orthorhombic local distortions. The interpretation of the experimental findings is based on the T2 g⊗(eg+t2 g) JTE problem including the linear and the quadratic terms of vibronic interactions in the Hamiltonian and the same-symmetry modes reduced to one interaction mode. Combining the experimental results with a theoretical analysis, we show that on the complicated six-dimensional APES of this system with three tetragonal, four trigonal, and six orthorhombic extrema points, the latter are global minima, while the former are saddle points, and we estimate numerically all the main parameters of this surface, including the linear and quadratic vibronic coupling constants, the primary force constants, the coordinates of all the extrema points and their energies, the energy barrier between the orthorhombic minima, and the tunneling splitting of the ground vibrational states. To our knowledge, such a based-on-experimental-data numerical reconstruction of the APES

  10. Graphene Substrate for van der Waals Epitaxy of Layer-Structured Bismuth Antimony Telluride Thermoelectric Film.

    PubMed

    Kim, Eun Sung; Hwang, Jae-Yeol; Lee, Kyu Hyoung; Ohta, Hiromichi; Lee, Young Hee; Kim, Sung Wng

    2017-02-01

    Graphene as a substrate for the van der Waals epitaxy of 2D layered materials is utilized for the epitaxial growth of a layer-structured thermoelectric film. Van der Waals epitaxial Bi0.5 Sb1.5 Te3 film on graphene synthesized via a simple and scalable fabrication method exhibits good crystallinity and high thermoelectric transport properties comparable to single crystals.

  11. Identifying potential BO2 oxide polymorphs for epitaxial growth candidates.

    PubMed

    Mehta, Prateek; Salvador, Paul A; Kitchin, John R

    2014-03-12

    Transition metal dioxides (BO2) exhibit a number of polymorphic structures with distinct properties, but the isolation of different polymorphs for a given composition is carried out using trial and error experimentation. We present computational studies of the relative stabilities and equations of state for six polymorphs (anatase, brookite, rutile, columbite, pyrite, and fluorite) of five different BO2 dioxides (B = Ti, V, Ru, Ir, and Sn). These properties were computed in a consistent fashion using several exchange correlation functionals within the density functional theory formalism, and the effects of the different functionals are discussed relative to their impact on predictive synthesis. We compare the computational results to prior observations of high-pressure synthesis and epitaxial film growth and then use this discussion to predict new accessible polymorphs in the context of epitaxial stabilization using isostructural substrates. For example, the relative stabilities of the columbite polymorph for VO2 and RuO2 are similar to those of TiO2 and SnO2, the latter two of which have been previously stabilized as epitaxial films.

  12. Epitaxial nucleation of CVD bilayer graphene on copper.

    PubMed

    Song, Yenan; Zhuang, Jianing; Song, Meng; Yin, Shaoqian; Cheng, Yu; Zhang, Xuewei; Wang, Miao; Xiang, Rong; Xia, Yang; Maruyama, Shigeo; Zhao, Pei; Ding, Feng; Wang, Hongtao

    2016-12-08

    Bilayer graphene (BLG) has emerged as a promising candidate for next-generation electronic applications, especially when it exists in the Bernal-stacked form, but its large-scale production remains a challenge. Here we present an experimental and first-principles calculation study of the epitaxial chemical vapor deposition (CVD) nucleation process for Bernal-stacked BLG growth on Cu using ethanol as a precursor. Results show that a carefully adjusted flow rate of ethanol can yield a uniform BLG film with a surface coverage of nearly 90% and a Bernal-stacking ratio of nearly 100% on ordinary flat Cu substrates, and its epitaxial nucleation of the second layer is mainly due to the active CH3 radicals with the presence of a monolayer-graphene-covered Cu surface. We believe that this nucleation mechanism will help clarify the formation of BLG by the epitaxial CVD process, and lead to many new strategies for scalable synthesis of graphene with more controllable structures and numbers of layers.

  13. Compliant substrate epitaxy: Au on MoS2

    NASA Astrophysics Data System (ADS)

    Zhou, Yuzhi; Kiriya, Daisuke; Haller, E. E.; Ager, Joel W.; Javey, Ali; Chrzan, D. C.

    2016-02-01

    A theory for the epitaxial growth of Au on MoS2 is developed and analyzed. The theory combines continuum linear elasticity theory with density functional theory to analyze epitaxial growth in this system. It is demonstrated that if one accounts for interfacial energies and strains, the presence of misfit dislocations, and the compliance of the MoS2 substrate, the experimentally observed growth orientation is favored despite the fact that it represents a larger elastic mismatch than two competing structures. The stability of the experimentally preferred orientation is attributed to the formation of a large number of strong Au-S bonds, and it is noted that this strong bond may serve as a means to exfoliate and transfer large single layers sheets of MoS2, as well as to engineer strain within single layers of MoS2. The potential for using a van der Waals-bonded layered material as a compliant substrate for applications in 2D electronic devices and epitaxial thin film growth is discussed.

  14. Terahertz and mid-infrared reflectance of epitaxial graphene

    PubMed Central

    Santos, Cristiane N.; Joucken, Frédéric; De Sousa Meneses, Domingos; Echegut, Patrick; Campos-Delgado, Jessica; Louette, Pierre; Raskin, Jean-Pierre; Hackens, Benoit

    2016-01-01

    Graphene has emerged as a promising material for infrared (IR) photodetectors and plasmonics. In this context, wafer scale epitaxial graphene on SiC is of great interest in a variety of applications in optics and nanoelectronics. Here we present IR reflectance spectroscopy of graphene grown epitaxially on the C-face of 6H-SiC over a broad optical range, from terahertz (THz) to mid-infrared (MIR). Contrary to the transmittance, reflectance measurements are not hampered by the transmission window of the substrate, and in particular by the SiC Reststrahlen band in the MIR. This allows us to present IR reflectance data exhibiting a continuous evolution from the regime of intraband to interband charge carrier transitions. A consistent and simultaneous analysis of the contributions from both transitions to the optical response yields precise information on the carrier dynamics and the number of layers. The properties of the graphene layers derived from IR reflection spectroscopy are corroborated by other techniques (micro-Raman and X-ray photoelectron spectroscopies, transport measurements). Moreover, we also present MIR microscopy mapping, showing that spatially-resolved information can be gathered, giving indications on the sample homogeneity. Our work paves the way for a still scarcely explored field of epitaxial graphene-based THz and MIR optical devices. PMID:27102827

  15. Ultrafast transient reflectance of epitaxial semiconducting perovskite thin films

    NASA Astrophysics Data System (ADS)

    Smolin, S. Y.; Scafetta, M. D.; Guglietta, G. W.; Baxter, J. B.; May, S. J.

    2014-07-01

    Ultrafast pump-probe transient reflectance (TR) spectroscopy was used to study carrier dynamics in an epitaxial perovskite oxide thin film of LaFeO3 (LFO) with a thickness of 40 unit cells (16 nm) grown by molecular beam epitaxy on (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT). TR spectroscopy shows two negative transients in reflectance with local maxima at ˜2.5 eV and ˜3.5 eV which correspond to two optical transitions in LFO as determined by ellipsometry. The kinetics at these transients were best fit with an exponential decay model with fast (5-40 ps), medium (˜200 ps), and slow (˜ 3 ns) components that we attribute mainly to recombination of photoexcited carriers. Moreover, these reflectance transients did not completely decay within the observable time window, indicating that ˜10% of photoexcited carriers exist for at least 3 ns. This work illustrates that TR spectroscopy can be performed on thin (<20 nm) epitaxial oxide films to provide a quantitative understanding of recombination lifetimes, which are important parameters for the potential utilization of perovskite films in photovoltaic and photocatalytic applications.

  16. Polydomain structures in ferroelectric and ferroelastic epitaxial films

    NASA Astrophysics Data System (ADS)

    Roytburd, Alexander L.; Ouyang, Jun; Artemev, Andrei

    2017-04-01

    A review of theoretical models, phase field modeling and experimental studies of domain structures in epitaxial films is presented. The thermodynamic theory of such domain structures is presented within the macroscopic thermo-mechanical framework. The theory allows for the evaluation of the main parameters of the domain structure using the energy minimization approach applied to the energy of elastic interactions. For homophase (polytwin) films, the thermodynamic theory provides a quantitative tool that can be used to estimate domain fractions in the film and the type of domain structure architecture. For heterophase films, the theory describes (a) the conditions under which two-phase structures can be obtained in epitaxial films, and (b) the phase and domain fractions in these films. The thermodynamic theory can also be used to describe the extrinsic contributions from domain structures to the functional properties of epitaxial ferroelectric films. The review of phase field modeling demonstrates that computational results reproduce the predictions of the thermodynamic theory. It is also shown that the phase field modeling that utilizes the energy minimization procedure for elastic and interfacial energies can be used to predict domain morphology for the films with two-phase structures produced either by phase transformation or through the co-deposition of immiscible phases. The experimental data presented in the review validate predictions of the thermodynamic model and the results of phase field modeling.

  17. Epitaxial growth of three-dimensionally architectured optoelectronic devices.

    PubMed

    Nelson, Erik C; Dias, Neville L; Bassett, Kevin P; Dunham, Simon N; Verma, Varun; Miyake, Masao; Wiltzius, Pierre; Rogers, John A; Coleman, James J; Li, Xiuling; Braun, Paul V

    2011-07-24

    Optoelectronic devices have long benefited from structuring in multiple dimensions on microscopic length scales. However, preserving crystal epitaxy, a general necessity for good optoelectronic properties, while imparting a complex three-dimensional structure remains a significant challenge. Three-dimensional (3D) photonic crystals are one class of materials where epitaxy of 3D structures would enable new functionalities. Many 3D photonic crystal devices have been proposed, including zero-threshold lasers, low-loss waveguides, high-efficiency light-emitting diodes (LEDs) and solar cells, but have generally not been realized because of material limitations. Exciting concepts in metamaterials, including negative refraction and cloaking, could be made practical using 3D structures that incorporate electrically pumped gain elements to balance the inherent optical loss of such devices. Here we demonstrate the 3D-template-directed epitaxy of group III-V materials, which enables formation of 3D structured optoelectronic devices. We illustrate the power of this technique by fabricating an electrically driven 3D photonic crystal LED.

  18. Process for depositing an oxide epitaxially onto a silicon substrate and structures prepared with the process

    DOEpatents

    McKee, Rodney A.; Walker, Frederick J.

    1993-01-01

    A process and structure involving a silicon substrate utilizes an ultra high vacuum and molecular beam epitaxy (MBE) methods to grow an epitaxial oxide film upon a surface of the substrate. As the film is grown, the lattice of the compound formed at the silicon interface becomes stabilized, and a base layer comprised of an oxide having a sodium chloride-type lattice structure grows epitaxially upon the compound so as to cover the substrate surface. A perovskite may then be grown epitaxially upon the base layer to render a product which incorporates silicon, with its electronic capabilities, with a perovskite having technologically-significant properties of its own.

  19. Au impact on GaAs epitaxial growth on GaAs (111){sub B} substrates in molecular beam epitaxy

    SciTech Connect

    Liao, Zhi-Ming; Chen, Zhi-Gang; Xu, Hong-Yi; Guo, Ya-Nan; Sun, Wen; Zhang, Zhi; Yang, Lei; Lu, Zhen-Yu; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2013-02-11

    GaAs growth behaviour under the presence of Au nanoparticles on GaAs {l_brace}111{r_brace}{sub B} substrate is investigated using electron microscopy. It has been found that, during annealing, enhanced Ga surface diffusion towards Au nanoparticles leads to the GaAs epitaxial growth into {l_brace}113{r_brace}{sub B} faceted triangular pyramids under Au nanoparticles, governed by the thermodynamic growth, while during conventional GaAs growth, growth kinetics dominates, resulting in the flatted triangular pyramids at high temperature and the epitaxial nanowires growth at relatively low temperature. This study provides an insight of Au nanoparticle impact on GaAs growth, which is critical for understanding the formation mechanisms of semiconductor nanowires.

  20. Epitaxial Growth of Aluminum on Silicon Substrates by Metalorganic Molecular Beam Epitaxy using Dimethyl-Ethylamine Alane

    NASA Astrophysics Data System (ADS)

    Neo, Yoichiro; Otoda, Toshihiro; Sagae, Katumi; Mimura, Hidenori; Yokoo, Kuniyoshi

    1998-05-01

    In this paper, the growth process of aluminum on a silicon substrate by metalorganic molecular beam epitaxy using dimethyl-ethylamine alane has been described. The crystallographic orientation of the aluminum grains strongly depends on the substrate temperature. The epitaxial single crystalline (111) Al grains grow on a (111) Si substrate at a substrate temperature between 450 and 500°C. The bi-crystalline (110) Al grains grow on a (100) Si substrate at the substrate temperature between 350 and 450°C. For a (100) Si substrate, the orientation of Al is related to the reconstruction of the Si substrate. Furthermore, the selective growth of Al into 1.5-µm-diameter via-holes is shown to be possible.