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Sample records for epitaxial nbn films

  1. Characterization of NbN films for superconducting nanowire single photon detectors

    SciTech Connect

    Mcdonald, Ross D; Ayala - Valenzuela, Oscar E; Weisse - Bernstein, Nina R; Williamson, Todd L; Hoffbauer, M. A.; Graf, M. J.; Rabin, M. W.

    2011-01-14

    Nanoscopic superconducting meander patterns offer great promise as a new class of cryogenic radiation sensors capable of single photon detection. To realize this potential, control of the superconducting properties on the nanoscale is imperative. To this end, Superconducting Nanowire Single Photon Detectors (SNSPDs) are under development by means Energetic Neutral Atom Beam Lithography and Epitaxy, or ENABLE. ENABLE can growth highly-crystalline, epitaxial thin-film materials, like NbN, at low temperatures; such wide-ranging control of fabrication parameters is enabling the optimization of film properties for single photon detection. T{sub c}, H{sub c2}, {zeta}{sub GL} and J{sub c} of multiple thin films and devices have been studied as a function of growth conditions. The optimization of which has already produced devices with properties rivaling all reports in the existing literature.

  2. Room-Temperature Deposition of NbN Superconducting Films

    NASA Technical Reports Server (NTRS)

    Thakoor, S.; Lamb, J. L.; Thakoor, A. P.; Khanna, S. K.

    1986-01-01

    Films with high superconducting transition temperatures deposited by reactive magnetron sputtering. Since deposition process does not involve significantly high substrate temperatures, employed to deposit counter electrode in superconductor/insulator/superconductor junction without causing any thermal or mechanical degradation of underlying delicate tunneling barrier. Substrates for room-temperature deposition of NbN polymeric or coated with photoresist, making films accessible to conventional lithographic patterning techniques. Further refinements in deposition technique yield films with smaller transition widths, Tc of which might approach predicted value of 18 K.

  3. 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.

  4. Lower critical field measurements in NbN bulk and thin films.

    NASA Technical Reports Server (NTRS)

    Mathur, M. P.; Deis, D. W.; Gavaler, J. R.

    1972-01-01

    Low-field magnetization measurements were made at 4.2 K on thin-film and bulk NbN samples by using a vibrating-sample Foner magnetometer with a 50-kG superconducting solenoid. Values of the lower and upper critical fields are calculated, using magnetization curves as the basis. The significance of the Pauli spin paramagnetism and spin-orbit scattering in these materials is discussed.

  5. Study of phase transitions in NbN ultrathin films under composite ion beam irradiation

    NASA Astrophysics Data System (ADS)

    Prikhodko, K.; Gurovich, B.; Dement'eva, M.

    2016-04-01

    This work demonstrates implementation of Selective Displacement of Atoms (SDA) technique to change the crystal structure and atomic composition of thin superconductive film of NbN under low dose composite ion beam irradiation. All structure investigations were performed using High Resolution Transmission Electron Microscopy (HRTEM) technique by the analysis of Fourier transformation of bright field HRTEM images. It was found that composite ion beam irradiation induces the formation of niobium oxynitrides phases.

  6. Characteristics of an Indium Asenide-based nBn photodetectors grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Pedrazzani, Janet Renee

    The nBn photodetector design specifies an n-type absorption layer, a Barrier layer to majority carrier electrons, and an n-type contact layer. The absence of a depletion layer in the lattice-matched nBn photodetector results in substantially reduced levels of Shockley-Read-Hall (SRH) generation current as compared with the competing p-n junction photodiode. The nBn photodetector also suppresses surface leakage current, which is prevalent in cooled, narrow bandgap semiconductor p-n junction photodiodes. Barrier layers consisting of AlAsxSb1-x are used in these InAs-based nBn photodetectors. A zero valance band energy offset exists between the InAs and AlAsxSb1-x layers for a composition in the range 0.14 < x < 0.17, while a composition of x = 0.16 lattice matches InAs. Conduction band energy offsets much greater than kT exist between InAs and all compositions of AlAsxSb1-x, and barrier layers thicker than 100 Angstroms are predicted to attenuate current arising from electron tunnelling to negligible levels. A lattice-matched InAs-based nBn photodetector achieves background limited photodetection (BLIP) operation at 200 K, while surface leakage current prevents two examples of InAs-based photodiodes from achieving BLIP operation. At a temperature of 140 K, this InAs-based nBn photodetector has a measured dark current lower by over 6 orders of magnitude than that of the commercial InAs-based photodiode and 4 orders of magnitude lower than that of an InAs-based photodiode fabricated by the author. Measurements indicate InAs-based nBn photodetectors grown with lattice-mismatched absorption layers have higher dislocation densities and that SRH current is the primary contributor to the dark current. The BLIP temperatures of two nBn photodetectors with InAs absorption layers grown on GaAs substrates are 150 and 160 K. The BLIP temperature of an nBn photodetector with an InAs0.95Sb0.05 absorption layer grown on an InAs substrate is 185 K. Accurate calculation of the thermal

  7. High T(c) superconducting NbN films deposited at room temperature

    NASA Technical Reports Server (NTRS)

    Thakoor, S.; Lamb, J. L.; Thakoor, A. P.; Khanna, S. K.

    1985-01-01

    The dc reactive magnetron sputtering process yields stoichiometric NbN films with superconducting transition temperature T(c) as high as 15.7 K on substrates as varied as glass, glazed ceramic, fused quartz, and sapphire. These films posses fcc (B1) structure and (111) texture. The most dominant factors governing the formation of the transition metal nitrides are the relative metal and nitrogen fluxes incident on the substrate and the background argon pressure (which dictates the overall reactive sites and residence times for nitrogen).

  8. Berezinsky- Kosterlitz- Thouless transition in ultrathin NbN films near superconductor-insulator transition

    NASA Astrophysics Data System (ADS)

    Yong, Jie; Il'in, K.; Siegel, M.; Lemberger, Thomas

    2013-03-01

    We report temperature dependent superfluid densities λ -2(T) in ultrathin NbN films near thickness-tuned superconductor-insulator transition (SIT). Superfluid densities in these films are measured by two-coil mutual inductance apparatus. For thick films, dirty limit BCS theory fits experimental data well and this verifies the correctness of this technique. As films get thinner and closer to SIT, sharp downturns near transition temperatures (Tc), signature of Berezinsky-Kosterlitz-Thouless transition, are observed. This downturn occurs much earlier than what 2-D XY theory predicts. This might due to smaller vortex core energy than expected in 2-D XY model. The superconducting gap, deduced from fitting low temperature λ -2(T), is linear with Tc for most films but remain finite across SIT. This is consistent with the scenario that superconductivity is destroyed by phase fluctuations. Zero temperature sheet superfluid density also shows correlation with Tc, further proving the importance of fluctuations near SIT.

  9. Investigation of radiation-induced transformations in thin NbN films by analytical electron microscopy

    NASA Astrophysics Data System (ADS)

    Prikhodko, К; Gurovich, B.; Dement'eva, M.; Kutuzov, L.; Komarov, D.

    2016-04-01

    This work demonstrates implementation of low energy electron energy loss technique (EELS) in scanning transmission electron microscopy (STEM) to investigate the changes of free electron density at room temperature in ultra-thin NbN films under composite ion beam irradiation up to the deses of ∼3 d.p.a. for nitrogen atoms. It was found the constant value of the free electron density ∼1.6 ·1029 m-3 in this dose range while the irradiated material was characterized by metal type of electrical conductivity.

  10. Calorimetry of epitaxial thin films.

    PubMed

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

    2011-02-01

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

  11. Method of producing high T(subc) superconducting NBN films

    NASA Technical Reports Server (NTRS)

    Thakoor, Sarita (Inventor); Lamb, James L. (Inventor); Thakoor, Anilkumar P. (Inventor); Khanna, Satish K. (Inventor)

    1988-01-01

    Thin films of niobium nitride with high superconducting temperature (T sub c) of 15.7 K are deposited on substrates held at room temperature (approx 90 C) by heat sink throughout the sputtering process. Films deposited at P sub Ar 12.9 + or - 0.2 mTorr exhibit higher T sub c with increasing P sub N2,I with the highest T sub c achieved at P sub n2,I= 3.7 + or - 0.2 mTorr and total sputtering pressure P sub tot = 16.6 + or - 0.4. Further increase of N2 injection starts decreasing T sub c.

  12. Robustness of the Berezinskii-Kosterlitz-Thouless transition in ultrathin NbN films near the superconductor-insulator transition

    NASA Astrophysics Data System (ADS)

    Yong, Jie; Lemberger, T. R.; Benfatto, L.; Ilin, K.; Siegel, M.

    2013-05-01

    Occurrence of the Berezinskii-Kosterlitz-Thouless (BKT) transition is investigated by superfluid density measurements for two-dimensional (2D) disordered NbN films with disorder level very close to a superconductor-insulator transition (SIT). Our data show a robust BKT transition even near this 2D disorder-tuned quantum critical point. This observation is in direct contrast with previous data on deeply underdoped quasi-2D cuprates near the SIT. As our NbN films approach the quantum critical point, the vortex core energy, an important energy scale in the BKT transition, scales with the superconducting gap, not with the superfluid density, as expected within the standard 2D-XY model description of BKT physics.

  13. Unconventional superconductivity in ultrathin superconducting NbN films studied by scanning tunneling spectroscopy

    NASA Astrophysics Data System (ADS)

    Noat, Y.; Cherkez, V.; Brun, C.; Cren, T.; Carbillet, C.; Debontridder, F.; Ilin, K.; Siegel, M.; Semenov, A.; Hübers, H.-W.; Roditchev, D.

    2013-07-01

    Using scanning tunneling spectroscopy, we address the problem of the superconductor-insulator phase transition in homogeneously disordered ultrathin (2-15 nm) films of NbN. Samples thicker than 8 nm, for which the Ioffe-Regel parameter kFl≥5.6, manifest a conventional superconductivity: a spatially homogeneous BCS-like gap, vanishing at the critical temperature, and a disordered vortex lattice in magnetic field. Upon thickness reduction, however, while kFl lowers, the STS reveals striking deviations from the BCS scenario, among which a progressive decrease of the coherence peak height and small spatial inhomogeneities. In addition, the gap below TC develops on a spectral background, which becomes more and more “V-shaped” approaching the localization. The thinnest film (2.16 nm), while not being exactly at the superconductor-insulator transition (SIT) (TC≈0.4TCbulk), showed unconventional signatures such as the vanishing of the coherence peaks and the absence of vortices. This behavior suggests a weakening of long-range phase coherence, when approaching the SIT in this quasi-2D limit.

  14. Epitaxial thin film growth in outer space

    NASA Technical Reports Server (NTRS)

    Ignatiev, Alex; Chu, C. W.

    1988-01-01

    A new concept for materials processing in space exploits the ultravacuum component of space for thin-film epitaxial growth. The unique LEO space environment is expected to yield 10-ftorr or better pressures, semiinfinite pumping speeds, and large ultravacuum volume (about 100 cu m) without walls. These space ultravacuum properties promise major improvement in the quality, unique nature, and throughput of epitaxially grown materials, including semiconductors, magnetic materials, and thin-film high-temperature superconductors.

  15. Effects of substrate bias on the preferred orientation, phase transition and mechanical properties for NbN films grown by direct current reactive magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Wen, M.; Hu, C. Q.; Wang, C.; An, T.; Su, Y. D.; Meng, Q. N.; Zheng, W. T.

    2008-07-01

    NbN films are deposited using direct current reactive magnetron sputtering in discharge of a mixture of N2 and Ar gas, and the effects of substrate bias (Vb) on the preferred orientation, phase transition, and mechanical properties for NbN films are explored by x-ray diffraction, selective area electron diffraction, and nanoindentation measurements. It is found that Vb has a significant influence on the stress in NbN films, leading to a pronounced change in the preferred orientation, phase structure, and hardness. As the substrate is at voltage floating, the stress is tensile. In contrast, as negative Vb is applied, the stress becomes compressive, and increases with increasing the absolute value of negative Vb. It is observed that a phase transition from δ (face-centered cubic) to δ' (hexagonal) for NbN films occurs as Vb is in the range of -80to-120V, which can be attributed to a decrease in the strain energy for NbN films. In order to explore the relationship between the stress and phase transition as well as preferred orientation, density-functional theory based on first principles is used to calculate the elastic constants and shear modulus for NbN with a structure of δ or δ'. The calculated results show that the shear modulus for δ'-NbN is larger than that for δ-NbN, whereas the bulk modulus for δ'-NbN is almost equal to that for δ-NbN, resulting in a difference in hardness for δ- or δ'-NbN single crystal.

  16. Correlated conductance fluctuations close to the Berezinskii-Kosterlitz-Thouless transition in ultrathin NbN films.

    PubMed

    Koushik, R; Kumar, Siddhartha; Amin, Kazi Rafsanjani; Mondal, Mintu; Jesudasan, John; Bid, Aveek; Raychaudhuri, Pratap; Ghosh, Arindam

    2013-11-01

    We probe the presence of long-range correlations in phase fluctuations by analyzing the higher-order spectrum of resistance fluctuations in ultrathin NbN superconducting films. The non-Gaussian component of resistance fluctuations is found to be sensitive to film thickness close to the transition, which allows us to distinguish between mean field and Berezinskii-Kosterlitz-Thouless (BKT) type superconducting transitions. The extent of non-Gaussianity was found to be bounded by the BKT and mean field transition temperatures and depends strongly on the roughness and structural inhomogeneity of the superconducting films. Our experiment outlines a novel fluctuation-based kinetic probe in detecting the nature of superconductivity in disordered low-dimensional materials. PMID:24266483

  17. 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.

  18. Epitaxial piezoelectric thick film heterostructures on silicon

    NASA Astrophysics Data System (ADS)

    Kim, Dong Min

    The significantly higher dielectric permittivity, piezoelectric coefficients and electromechanical coupling coefficients of single crystal relaxor ferroelectrics make them very attractive for medical ultrasound transducers and microelectromechanical systems (MEMS) applications. The potential impact of thin-film relaxor ferroelectrics in integrated actuators and sensor on silicon has stimulated research on the growth and characterization of epitaxial piezoelectric thin films. We have fabricated heterostructures by (1) synthesizing optimally-oriented, epitaxial thin films of Pb(Mg1/3Nb2/3)O3-PbTiO 3 (PMN-PT) on miscut (001) Si wafers with epitaxial (001) SrTiO 3 template layers, where the single crystal form is known to have the giant piezoelectric response, and (2) nano-structuring to reduce the constraint imposed by the underlying silicon substrate. Up to now, the longitudinal piezoelectric coefficient (d33) values of PMN and PMN-PT thin films range from 50 to 200 pC/N have been reported, which are far inferior to the properties of bulk single crystals value (d33 ˜ 2000 pC/N). These might be attributed to substrate constraints, pyrochlore phases and other effects. Here, we have realized the giant d33 values by fabricating epitaxial PMN-PT thick films on silicon. When the PMN-PT film was subdivided into ˜1 mum2 capacitors by focused ion beam processing, a 4 mum thick film shows a low-field d33 of 800 pm/V that increases to over 1200 pm/V under bias, which is the highest d33 value ever realized on silicon substrates. These high piezo-reponse PMN-PT epitaxial heterostructures can be used for multilayered MEMS devices which function with low driving voltage, high frequency ultrasound transducer arrays for medical imaging, and capacitors for charge and energy storage. Since these PMN-PT films are epitaxially integrated with the silicon, they can make use of the well-developed fabrication process for patterning and micromachining of this large-area, cost

  19. Effect of Si addition on the structure and corrosion behavior of NbN thin films deposited by unbalanced magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Velasco, L.; Olaya, J. J.; Rodil, S. E.

    2016-02-01

    In this work, nanostructured NbxSiyNz thin films were deposited onto stainless steel AISI 304 substrates by co-sputtering a Nb target with Si additions while using unbalanced magnetron sputtering. The microstructure was analyzed by X-ray diffraction, and the chemical composition was identified by X-ray photoelectron spectroscopy. The hardness was measured by nanoindentation, and the corrosion resistance was studied by potentiodynamic polarization curves and electrochemical impedance spectroscopy using a 3 wt% NaCl solution. The addition of Si in the NbN thin films changed the microstructure from a crystalline to an amorphous phase. The chemical analysis showed the presence of both Si3N4 and NbN phases. The hardness decreased from 20 GPa (NbN) to 15 GPa for the film with the highest Si concentration (28.6 at.%). Nevertheless, the corrosion properties were significantly improved as the Si concentration increased; the polarization resistance after 168 h of immersion was two orders of magnitude larger in comparison with the substrate.

  20. Hydrothermal epitaxy of perovskite thin films

    NASA Astrophysics Data System (ADS)

    Chien, Allen T.

    1998-12-01

    This work details the discovery and study of a new process for the growth of epitaxial single crystal thin films which we call hydrothermal epitaxy. Hydrothermal epitaxy is a low temperature solution route for producing heteroepitaxial thin films through the use of solution chemistry and structurally similar substrates. The application of this synthesis route has led to the growth of a variety of epitaxial perovskite (BaTiOsb3, SrTiOsb3, and Pb(Zr,Ti)Osb3 (PZT)) thin films which provides a simple processing pathway for the formation of other materials of technological interest. BaTiOsb3 and PZT heteroepitaxial thin films and powders were produced by the hydrothermal method at 90-200sp°C using various alkali bases. XRD and TEM analysis shows that, in each case, the films and powders form epitaxially with a composition nearly identical to that of the starting precursors. Sequential growth experiments show that film formation initiates by the nucleation of submicron faceted islands at the step edges of the SrTiOsb3 substrates followed by coalescence after longer growth periods. A Ba-rich interfacial layer between the BaTiOsb3 islands and the SrTiOsb3 surface is seen by cross-section TEM during early growth periods. Electrophoretic and Basp{2+} adsorption data provide a chemical basis for the existence of the interfacial layer. Homoepitaxial growth of SrTiOsb3 on SrTiOsb3 also occurs by island growth, suggesting that the growth mode may be a consequence of the aqueous surface chemistry inherent in the process. Film formation is shown to be affected by any number of factors including type of base, pH, temperature, and substrate pretreatments. Different cation bases (Na-, K-, Rb-, Cs-, TMA-OH) demonstrated pronounced changes in powder and film morphology. For example, smaller cation bases (e.g., NaOH, KOH and RbOH) resulted the formation of 1.5 mum \\{100\\} faceted perovskite PbTiOsb3 blocks while larger cation bases (e.g., CsOH and TMA-OH) produced 500 nm sized

  1. 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.

  2. 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.

  3. Magnetic properties of novel epitaxial films

    SciTech Connect

    Bader, S.D.; Moog, E.R.

    1986-09-01

    The surface magneto-optic Kerr effect (SMOKE) is used to explore the magnetism of ultra-thin Fe Films extending into the monolayer regime. Both bcc ..cap alpha..-Fe and fcc ..gamma..-Fe single-crystalline, multilayer films are prepared on the bulk-terminated (1 x 1) structures of Au(100) and Cu(100), respectively. The characterizations of epitaxy and growth mode are performed using low energy electron diffraction and Auger electron spectroscopy. Monolayer-range Fe/Au(100) is ferromagnetic with a lower Curie temperature than bulk ..cap alpha..-Fe. The controversial ..gamma..-Fe/Cu(100) system exhibits a striking, metastable, surface magnetic phase at temperatures above room temperature, but does not exhibit bulk ferromagnetism.

  4. Growth of epitaxial thin films by pulsed laser ablation

    SciTech Connect

    Lowndes, D.H.

    1992-01-01

    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)

  5. 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)

  6. Magnetic anisotropy of strained epitaxial manganite films

    SciTech Connect

    Demidov, V. V. Borisenko, I. V.; Klimov, A. A.; Ovsyannikov, G. A.; Petrzhik, A. M.; Nikitov, S. A.

    2011-05-15

    The in-plane magnetic anisotropy of epitaxial La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO) films is studied at room temperature by the following three independent techniques: magnetooptical Kerr effect, ferromagnetic resonance at a frequency of 9.61 GHz, and recording of absorption spectra of electromagnetic radiation at a frequency of 290.6 MHz. The films are deposited onto NdGaO{sub 3} (NGO) substrates in which the (110)NGO plane is tilted at an angle of 0-25.7 Degree-Sign to the substrate plane. The uniaxial magnetic anisotropy induced by the strain of the film is found to increase with the tilt angle of the (110)NGO plane. A model is proposed to describe the change in the magnetic anisotropy energy with the tilt angle. A sharp increase in the radio-frequency absorption in a narrow angular range of a dc magnetic field near a hard magnetization axis is detected The anisotropy parameters of the LSMO films grown on (110)NGO, (001)SrTiO{sub 3}, and (001)[(LaAlO{sub 3}){sub 0.3} + (Sr{sub 2}AlTaO{sub 6}){sub 0.7}] substrates are compared.

  7. 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.

  8. A proposal for epitaxial thin film growth in outer space

    NASA Technical Reports Server (NTRS)

    Ignatiev, Alex; Chu, C. W.

    1988-01-01

    A new concept for materials processing in space exploits the ultravacuum component of space for thin film epitaxial growth. The unique low earth orbit space environment is expected to yield 10 to the -14th torr or better pressures, semiinfinite pumping speeds, and large ultravacuum volume without walls. These space ultravacuum properties promise major improvement in the quality, unique nature, and the throughput of epitaxially grown materials. Advanced thin film materials to be epitaxially grown in space include semiconductors, magnetic materials, and thin film high temperature superconductors.

  9. Optical properties of epitaxial YAG:Yb films

    NASA Astrophysics Data System (ADS)

    Ubizskii, S. B.; Matkovskii, A. O.; Melnyk, S. S.; Syvorotka, I. M.; Müller, V.; Peters, V.; Petermann, K.; Beyertt, A.; Giesen, A.

    2004-03-01

    This work deals with the investigation of the optical properties of epitaxial YAG:Yb films and their suitability as gain media for thin disk lasers. Epitaxial films of YAG:Yb were grown by the liquid phase epitaxy method in air on the (111)-oriented YAG substrates. The thickness of the grown layers was from 30 to 260 m. The melt composition was varied to obtain the desired doping level from 10 to 15% and to optimize the optical properties. The best epitaxial films were colourless and had an Yb3+ luminescence lifetime of more than 950 s, which is very close to the intrinsic lifetime of the Yb ions in the bulk YAG single crystals. These films were tested in a thin disk laser setup with 24 absorption passes of the 940 nm pumping beam. The maximum output power at 1.03 m wavelength in CW operation reached more than 60 W and the optical efficiency was close to 30%.

  10. Modulation of the penetration depth of Nb and NbN films by quasiparticle injection

    SciTech Connect

    Track, E.K.; Radparvar, M.; Faris, S.M.

    1989-03-01

    A novel approach to modulating the inductance of a superconducting microstrip is described. This approach could be the basis for numerous practical applications, such as phase shifters and high frequency tuning elements. The physical mechanisms involved are quasiparticle injection, gap suppression, and penetration depth modulation. In this current, the authors have investigated the modulation of the penetration depth of niobium and niobium nitride films by excess quasiparticle injection. To this effect, all-niobium and all-niobium-nitride SQUID circuits are designed and fabricated. These circuits allow quasiparticle injection into the inductive element of the SQUID. This injection is achieved by 1. optical irradiation through an opening in a Nb reflective layer which partially masks the rest of the circuit, and 2. electronic current injection through a tunnel junction overlaid on the microstrip inductance. Penetration depth modulation is achieved with both methods. The magnitude of the effect varies from 10% to over 200% change in inductance. These results and their dependence on temperature and on the parameters of the control mechanism (light intensity, amount of current injection, etc.) are presented and discussed.

  11. 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.

  12. 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.

  13. Epitaxial EuO thin films on GaAs

    SciTech Connect

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

    2010-09-13

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

  14. Commercial aspects of epitaxial thin film growth in outer space

    NASA Technical Reports Server (NTRS)

    Ignatiev, Alex; Chu, C. W.

    1988-01-01

    A new concept for materials processing in space exploits the ultra vacuum component of space for thin film epitaxial growth. The unique low earth orbit space environment is expected to yield 10 to the -14th torr or better pressures, semiinfinite pumping speeds and large ultra vacuum volume (about 100 cu m) without walls. These space ultra vacuum properties promise major improvement in the quality, unique nature, and the throughput of epitaxially grown materials especially in the area of semiconductors for microelectronics use. For such thin film materials there is expected a very large value added from space ultra vacuum processing, and as a result the application of the epitaxial thin film growth technology to space could lead to major commercial efforts in space.

  15. Growth and characterization of YAG:Cr4+epitaxial films

    NASA Astrophysics Data System (ADS)

    Ubizskii, Sergii B.; Syvorotka, Igor M.; Melnyk, Sergii S.; Matkovskii, Andrej O.; Kopczynski, Krzysztof; Mierczyk, Zygmunt; Frukacz, Zygmunt

    1999-03-01

    Epitaxial films with thickness of 10 - 250 micrometers of yttrium aluminum garnet (YAG) doped with Cr were grown by liquid phase epitaxy technique on YAG:Nd substrates. Co-doping with Mg2+ is used to force the Cr4+ valent state formation. Dependence of absorption spectra of obtained films on melt-solution composition, growth conditions and thermal treatment in reducing and oxidizing atmospheres is studied. A very intensive absorption band in UV region with maximum at 275 nm was found both in co-doped and YAG:Mg2+ epifilms caused probably by oxygen vacancies compensating the excess charge of Mg2+. Its intensity correlates with Cr4+ content in the film in that way: it decreases with Cr4+ entering in the film. The absorption being characteristic for YAG:Cr4+ crystals is found in co-doped films grown at higher temperatures (1000 - 1100 degree(s)C). The processes occurring during annealing are discussed.

  16. Epitaxy and fiber texture of Pb films on mica and glass.

    NASA Technical Reports Server (NTRS)

    Wyatt, P. W.; Yelon, A.

    1972-01-01

    We report the production of (111) epitaxial Pb films on mica and (111) textured Pb films on mica and glass. Film structure is studied by reflection electron diffraction and by etching and optical microscopy. Thin (about 1000 A) epitaxial films are found to be doubly positioned. Reorientation during growth of thicker films leads to single positioning in areas several tenths of a millimeter across.

  17. Investigation of optical properties of epitaxial yttrium iron garnet films

    NASA Astrophysics Data System (ADS)

    Paranin, V. D.

    2016-04-01

    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.

  18. Nanoscale electrical properties of epitaxial Cu3Ge film

    NASA Astrophysics Data System (ADS)

    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.

  19. Nanoscale electrical properties of epitaxial Cu3Ge film.

    PubMed

    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

  20. 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

  1. 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.

  2. Growth of Epitaxial Oxide Thin Films on Graphene

    PubMed Central

    Zou, Bin; Walker, Clementine; Wang, Kai; Tileli, Vasiliki; Shaforost, Olena; Harrison, Nicholas M.; Klein, Norbert; Alford, Neil M.; Petrov, Peter K.

    2016-01-01

    The transfer process of graphene onto the surface of oxide substrates is well known. However, for many devices, we require high quality oxide thin films on the surface of graphene. This step is not understood. It is not clear why the oxide should adopt the epitaxy of the underlying oxide layer when it is deposited on graphene where there is no lattice match. To date there has been no explanation or suggestion of mechanisms which clarify this step. Here we show a mechanism, supported by first principles simulation and structural characterisation results, for the growth of oxide thin films on graphene. We describe the growth of epitaxial SrTiO3 (STO) thin films on a graphene and show that local defects in the graphene layer (e.g. grain boundaries) act as bridge-pillar spots that enable the epitaxial growth of STO thin films on the surface of the graphene layer. This study, and in particular the suggestion of a mechanism for epitaxial growth of oxides on graphene, offers new directions to exploit the development of oxide/graphene multilayer structures and devices. PMID:27515496

  3. Growth of Epitaxial Oxide Thin Films on Graphene.

    PubMed

    Zou, Bin; Walker, Clementine; Wang, Kai; Tileli, Vasiliki; Shaforost, Olena; Harrison, Nicholas M; Klein, Norbert; Alford, Neil M; Petrov, Peter K

    2016-01-01

    The transfer process of graphene onto the surface of oxide substrates is well known. However, for many devices, we require high quality oxide thin films on the surface of graphene. This step is not understood. It is not clear why the oxide should adopt the epitaxy of the underlying oxide layer when it is deposited on graphene where there is no lattice match. To date there has been no explanation or suggestion of mechanisms which clarify this step. Here we show a mechanism, supported by first principles simulation and structural characterisation results, for the growth of oxide thin films on graphene. We describe the growth of epitaxial SrTiO3 (STO) thin films on a graphene and show that local defects in the graphene layer (e.g. grain boundaries) act as bridge-pillar spots that enable the epitaxial growth of STO thin films on the surface of the graphene layer. This study, and in particular the suggestion of a mechanism for epitaxial growth of oxides on graphene, offers new directions to exploit the development of oxide/graphene multilayer structures and devices. PMID:27515496

  4. Tailoring magnetic frustration in strained epitaxial FeRh films

    NASA Astrophysics Data System (ADS)

    Witte, Ralf; Kruk, Robert; Gruner, Markus E.; Brand, Richard A.; Wang, Di; Schlabach, Sabine; Beck, Andre; Provenzano, Virgil; Pentcheva, Rossitza; Wende, Heiko; Hahn, Horst

    2016-03-01

    We report on a strain-induced martensitic transformation, accompanied by a suppression of magnetic order in epitaxial films of chemically disordered FeRh. X-ray diffraction, transmission electron microscopy, and electronic structure calculations reveal that the lowering of symmetry (from cubic to tetragonal) imposed by the epitaxial relation leads to a further, unexpected, tetragonal-to-orthorhombic transition, triggered by a band-Jahn-Teller-type lattice instability. The collapse of magnetic order is a direct consequence of this structural change, which upsets the subtle balance between ferromagnetic nearest-neighbor interactions arising from Fe-Rh hybridization and frustrated antiferromagnetic coupling among localized Fe moments at larger distances.

  5. Epitaxial ternary nitride thin films prepared by a chemical solution method

    SciTech Connect

    Luo, Hongmei; Feldmann, David M; Wang, Haiyan; Bi, Zhenxing

    2008-01-01

    It is indispensable to use thin films for many technological applications. This is the first report of epitaxial growth of ternary nitride AMN2 films. Epitaxial tetragonal SrTiN2 films have been successfully prepared by a chemical solution approach, polymer-assisted deposition. The structural, electrical, and optical properties of the films are also investigated.

  6. Epitaxial growth of high quality WO3 thin films

    NASA Astrophysics Data System (ADS)

    Leng, X.; Pereiro, J.; Strle, J.; Bollinger, A. T.; Božović, I.

    2015-09-01

    We have grown epitaxial WO3 films on various single-crystal substrates using radio frequency magnetron sputtering. While pronounced surface roughness is observed in films grown on LaSrAlO4 substrates, films grown on Y AlO3 substrates show atomically flat surfaces, as demonstrated by atomic force microscopy and X-ray diffraction (XRD) measurements. The crystalline structure has been confirmed to be monoclinic by symmetric and skew-symmetric XRD. The dependence of the growth modes and the surface morphology on the lattice mismatch are discussed.

  7. Epitaxial growth of high quality WO3 thin films

    DOE PAGESBeta

    Leng, X.; Pereiro, J.; Strle, J.; Bollinger, A. T.; Bozovic, I.

    2015-09-09

    We have grown epitaxial WO3 films on various single-crystal substrates using radio-frequency (RF) magnetron sputtering. While pronounced surface roughness is observed in films grown on LaSrAlO4 substrates, films grown on YAlO3 substrates show atomically flat surfaces, as demonstrated by atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements. The crystalline structure has been confirmed to be monoclinic by symmetric and skew-symmetric XRD. Furthermore, the dependence of the growth modes and the surface morphology on the lattice mismatch is discussed.

  8. Microstructure and twinning in epitaxial NiMnGa films

    SciTech Connect

    Mahnke, Guido J.; Mayr, S. G.; Seibt, M.

    2008-07-01

    Although magnetic shape memory alloys have attracted large scientific interest, miniaturization as single-crystalline thin films is still a greatly unresolved issue. In the present work we investigate the microstructure of epitaxial NiMnGa thin films which are fabricated by sputter deposition on magnesium oxide substrates at elevated temperatures. Transmission and scanning electron microscopy as well as atomic force microscopy studies are employed to relate surface topography to twin formation in 7 M martensitic NiMnGa films. Additional findings include pore formation in substrate proximity as well as minor precipitation with reduced nickel and gallium contents.

  9. Substrate Preparations in Epitaxial ZnO Film Growth

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C.-H.; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; George, M. A.

    2000-01-01

    Epitaxial ZnO films were grown on the two polar surfaces (O-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. Annealing-temperature dependence of ZnO substrates was studied. ZnO films grown on sapphire substrates have also been investigated for comparison purposes and the annealing temperature of A1203 substrates is 1000 C. Substrates and films were characterized using photoluminescence (PL) spectrum, x-ray diffraction, atomic force microscope, energy dispersive spectrum, and electric transport measurements. It has been found that the ZnO film properties were different when films were grown on the two polarity surfaces of ZnO substrates and the A1203 substrates. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite surface. The measurements of homoepitaxial ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth.

  10. Epitaxial Cd3As2 Thin Films Synthesized by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Schumann, Timo; Goyal, Manik; Stemmer, Susanne

    Cd3As2 is a three-dimensional (3D) Dirac semimetal, i.e. it possesses Dirac cones in a 3D bulk state where the band dispersion relation is linear near the Fermi energy. Cd3As2 is has raised considerable interest due to its high electron mobilities in bulk crystals and for novel quantum phenomena, such as chiral anomalies. However, few studies have been performed using thin films of Cd3As2. In this presentation, we report on the synthesis of Cd3As2 thin films by molecular beam epitaxy (MBE). Single phase, epitaxial films were grown on undoped GaSb(111)B substrates with the (112) facet of Cd3As2 parallel to the GaSb(111) surface. We report on the structural quality and orientation variants in the films. Electrical transport properties indicate electron mobilities exceeding 6000 cm2V-1s-1. We discuss the impact of the MBE growth parameters and substrate preparation on the structural and electrical properties of the films.

  11. Probing orbital ordering in LaVO3 epitaxial films by Raman scattering

    NASA Astrophysics Data System (ADS)

    Vrejoiu, I.; Himcinschi, C.; Jin, L.; Jia, C.-L.; Raab, N.; Engelmayer, J.; Waser, R.; Dittmann, R.; van Loosdrecht, P. H. M.

    2016-04-01

    Single crystals of Mott-Hubbard insulator LaVO3 exhibit spin and orbital ordering along with a structural change below ≈140 K. The occurrence of orbital ordering in epitaxial LaVO3 films has, however, been little investigated. By temperature-dependent Raman scattering spectroscopy, we probed and evidenced the transition to orbital ordering in epitaxial LaVO3 film samples fabricated by pulsed-laser deposition. This opens up the possibility to explore the influence of different epitaxial strain (compressive vs. tensile) and of epitaxy-induced distortions of oxygen octahedra on the orbital ordering, in epitaxial perovskite vanadate films.

  12. Strain-induced properties of epitaxial VOx thin films

    NASA Astrophysics Data System (ADS)

    Rata, A. D.; Hibma, T.

    2005-01-01

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

  13. Electrocaloric properties of epitaxial strontium titanate films

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Misirlioglu, I. B.; Alpay, S. P.; Rossetti, G. A.

    2012-05-01

    The electrocaloric (EC) response of strontium titanate thin films is computed as a function of misfit strain, temperature, electric field strength, and electrode configuration using a nonlinear thermodynamic theory. For films in a capacitor configuration on compressive substrates, the transition between paraelectric and strain-induced ferroelectric tetragonal phases produces a large adiabatic temperature change, ΔT = 5 K, at room temperature for electric field changes ΔE = 1200 kV/cm. For films on tensile substrates, the transition between the paraelectric and strain-induced ferroelectric orthorhombic phases can also be accessed using inter-digitated electrodes (IDEs). The maximum EC response occurs for IDEs with a [110] orientation.

  14. Magnetic and magnetotransport properties of erbium silicide epitaxial films

    NASA Astrophysics Data System (ADS)

    Chroboczek, J. A.; Briggs, A.; Joss, W.; Auffret, S.; Pierre, J.

    1991-02-01

    Hexagonal Er3Si5 films epitaxially grown on Si show strong anisotropies in magnetization and magnetotransport below the ordering temperature. The magnetoresistance has a cusplike positive anomaly or is negative and featureless for a magnetic field applied, respectively, along or perpendicular to the [0001] axis. A noncollinear structure, composed of an antiferromagnetic and a ferromagnetic component accounts for the magnetization data. The latter used in conjunction with the Yamada-Takada theory of magnetotransport accounts for the magnetoresistance data.

  15. 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.

  16. Martensite transformation of epitaxial Ni-Ti films

    SciTech Connect

    Buschbeck, J.; Kozhanov, A.; Kawasaki, J. K.; James, R. D.; Palmstroem, C. J.

    2011-05-09

    The structure and phase transformations of thin Ni-Ti shape memory alloy films grown by molecular beam epitaxy are investigated for compositions from 43 to 56 at. % Ti. Despite the substrate constraint, temperature dependent x-ray diffraction and resistivity measurements reveal reversible, martensitic phase transformations. The results suggest that these occur by an in-plane shear which does not disturb the lattice coherence at interfaces.

  17. 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.

  18. Ultrafast transient reflectance of epitaxial semiconducting perovskite thin films

    SciTech Connect

    Smolin, S. Y.; Guglietta, G. W.; Baxter, J. B. E-mail: smay@coe.drexel.edu; Scafetta, M. D.; May, S. J. E-mail: smay@coe.drexel.edu

    2014-07-14

    Ultrafast pump-probe transient reflectance (TR) spectroscopy was used to study carrier dynamics in an epitaxial perovskite oxide thin film of LaFeO{sub 3} (LFO) with a thickness of 40 unit cells (16 nm) grown by molecular beam epitaxy on (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 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.

  19. Magnetism and deformation of epitaxial Pd and Rh thin films

    NASA Astrophysics Data System (ADS)

    KáÅa, Tomáš; Hüger, Erwin; Legut, Dominik; Čák, Miroslav; Šob, Mojmír

    2016-04-01

    By means of ab initio calculations, we investigated structural and magnetic properties of Pd and Rh thin films, determining their lattice parameters and epitaxial stresses when they are grown on various substrates, and provided a comparison with available experimental data. Further, we studied in detail the magnetic properties of Pd in the higher-energy hcp structure and of Rh in the higher-energy bcc structure. The results predict that the hcp (11 2 ¯0 ) Pd films [grown by epitaxy on the Nb(001) substrate] should not be ferromagnetically ordered. Concerning the hcp Pd, we mainly investigated the influence of the hcp c /a ratio on the hcp film stability and on the ferromagnetic order. It turns out that the c /a ratio has to be below 1.622 to induce the ferromagnetic order in hcp Pd. We proposed a technological route for obtaining ferromagnetic hcp (11 2 ¯0 ) Pd films and explained the experimentally observed ferromagnetism in twinned Pd nanoparticles induced by strain. We also found that bcc Rh is ferromagnetically ordered, but it cannot be stabilized in the form of thin films. Therefore, we investigated the dependence of ferromagnetic order in bct Rh on the tetragonal c /a ratio and compared our results with experiments performed on Rh/Fe(001) multilayers.

  20. Dewetting of Epitaxial Silver Film on Silicon by Thermal Annealing

    NASA Astrophysics Data System (ADS)

    Sanders, Charlotte E.; Kellogg, Gary L.; Shih, C.-K.

    2013-03-01

    It has been shown that noble metals can grow epitaxially on semiconducting and insulating substrates, despite being a non-wetting system: low temperature deposition followed by room temperature annealing leads to atomically flat film morphology. However, the resulting metastable films are vulnerable to dewetting, which has limited their utility for applications under ambient conditions. The physics of this dewetting is of great interest but little explored. We report on an investigation of the dewetting of epitaxial Ag(111) films on Si(111) and (100). Low energy electron microscopy (LEEM) shows intriguing evolution in film morphology and crystallinity, even at temperatures below 100oC. On the basis of these findings, we can begin to draw compelling inferences about film-substrate interaction and the kinetics of dewetting. Financial support is from NSF, DGE-0549417 and DMR-0906025. This work was performed, in part, at the Center for Integrated Nanotechnologies, User Facility operated for the U.S. DOE Office of Science. Sandia National Lab is managed and operated by Sandia Corp., a subsidiary of Lockheed Martin Corp., for the U.S. DOE's National Nuclear Security Administration under DE-AC04-94AL85000.

  1. 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.

  2. Growth of epitaxial ZnO films on sapphire substrates by plasma assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hyndman, Adam R.; Allen, Martin W.; Reeves, Roger J.

    2014-03-01

    Epitaxial layers of ZnO have been grown on c-plane, (0001) sapphire substrates by plasma assisted molecular beam epitaxy. The oxygen:zinc flux ratio was found to be crucial in obtaining a film with a smooth surface and good crystallinity. When increasing film thickness from ~80 to 220 nm we observed an increase in the streakiness of RHEED images, and XRD revealed a reduction in crystal strain and increase in crystal alignment. A film with surface roughness of 0.5 nm and a XRD rocking curve FWHM of 0.1 for the main ZnO peak (0002) was achieved by depositing a low temperature ZnO buffer layer at 450 °C and then growing for 120 minutes at 700 °C with a Zn-cell temperature of 320 °C and an oxygen partial pressure of 7e-7 Torr. We found novel structures on two samples grown outside of our ideal oxygen:zinc flux ratio. SEM images of a sample believed to have been grown in a Zn-rich environment showed flower like structures up to 150 um in diameter which appear to have formed during growth. Another sample believed to have been deposited in a Zn-deficient environment had rings approximately 1.5 um in diameter scattered on its surface.

  3. Epitaxial thin films for hyperbolic metamaterials

    NASA Astrophysics Data System (ADS)

    Fullager, D.; Alisafaee, H.; Tsu, R.; Fiddy, M. A.

    2014-02-01

    Recent progress in the area of hyperbolic metamaterials (HMMs) has sparked interest in transparent conducting oxides (TCOs) that behave as plasmonic media in the near-IR and at optical frequencies for imaging and sensing applications. It has been shown that by depositing alternating layers of negative-epsilon/positive-epsilon materials, a medium can be created with unusual index values such as near zero. HMMs support high-k waves corresponding to a diverging photonic density of states (PDOS), the quantity determining phenomena such as spontaneous and thermal emission. Also, modeling such structures allows evanescent fields containing sub-wavelength information to be coupled to propagating radiation. We investigate the optical, electronic, and physical properties of radio frequency plasma-assisted molecular beam epitaxial (RF-MBE) growth of alternating layers of ZnO and TCO of uniform thickness for HMM applications. Preliminary work creating HMMs with ZnO and Al-doped ZnO (AZO) has shown a negative real part of the permittivity at near-IR whose modulus is proportional to the number density of Al dopant. However, increasing the Al content of the AZO increases the transmission losses to unacceptable levels for device applications at industry standard wavelengths. A TCO with conductivity and physical structure superior to that of AZO is gallium-doped ZnO (GZO). Uniformly grown GZO has been demonstrated to possess improved crystal quality over AZO due to the higher diffusivity of Al in the ZnO. AZO and GZO HMM structures grown by RF-MBE are characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Hall effect, four-point probing, deeplevel transient spectroscopy (DLTS), ellipsometry, visible and ultraviolet spectroscopy (UV-VIS) and in-situ reflection high energy electron diffraction (RHEED).

  4. Superconducting properties of epitaxial laser ablated thin films

    NASA Astrophysics Data System (ADS)

    Berling, D.; Del Vecchio, A.; Leggieri, G.; Loegel, B.; Luches, A.; Mehdaoui, A.; Tapfer, L.

    1996-02-01

    We present experimental results obtained for high quality epitaxial thin films (film thicknesses around 5000 Å; rocking curve FWHM down to 0.1°). These films are obtained by laser ablation of REBa 2Cu 3O 7-δ (RE = Y, Er) deposited on SrTio 3 and YSZ substrates. The superconducting properties have been studied by complex susceptibility in an extended AC field range ( hac ≤ 300 Oe) and show sharp magnetic transition width and high critical currents (10 7A cm -2 < jc(77K) < 10 8A cm -2). The loss peak is only weakly depressed by an increasing AC field and the observed shifts are up to an order of magnitude lower than those observed for intragranular contributions in bulk samples. The agreement with the behaviour expected from a critical state model is also discussed.

  5. Nonlinear optical properties of calcium barium niobate epitaxial thin films.

    PubMed

    Bancelin, Stéphane; Vigne, Sébastien; Hossain, Nadir; Chaker, Mohammed; Légaré, François

    2016-07-25

    We investigate the potential of epitaxial calcium barium niobate (CBN) thin film grown by pulsed laser deposition for optical frequency conversion. Using second harmonic generation (SHG), we analyze the polarization response of the generated signal to determine the ratios d15 / d32 and d33 / d32 of the three independent components of the second-order nonlinear susceptibility tensor in CBN thin film. In addition, a detailed comparison to the signal intensity obtained in a y-cut quartz allows us to measure the absolute value of these components in CBN thin film: d15 = 5 ± 2 pm / V, d32 = 3.1 ± 0.6 pm / V and d33 = 9 ± 2 pm / V. PMID:27464195

  6. Fluorination of epitaxial oxides: Creating ferrite and nickelate oxyfluoride films

    NASA Astrophysics Data System (ADS)

    May, Steven; Moon, Eun; Xie, Yujun; Keavney, David; Goebel, Justin; Laird, Eric; Li, Christopher

    2013-03-01

    In ABO3 perovskites, the physical properties are directly coupled to the nominal valence state of the B-site cation. In epitaxial thin films, the dominant strategy to control B-site valence is through the selection of a di- or trivalent cation on the A-site. However, this approach is limited, particularly when electron doping on the B-site is desired. Here we report a simple method for realizing oxyfluoride films, where the substitution of F for O is expected to reduce the B-site valence, providing a new means to tune electronic, optical and magnetic properties in thin films. Fluorination is achieved by spin coating an oxygen deficient film with poly(vinylidene fluoride). The film/polymer bilayer is then annealed, promoting the diffusion of F into the film. We have used this method to synthesize SrFeO3-δFδ and LaNiO3-δFδ (δ ? 0.5) films, as confirmed by x-ray photoemission spectroscopy and x-ray absorption spectroscopy. This work is supported by the U. S. Army Research Office under grant number W911NF-12-1-0132. Work at the Advanced Photon Source is supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences under contract DE-AC02-06CH11357.

  7. Epitaxial growth in dislocation-free strained asymmetric alloy films

    SciTech Connect

    Desai, Rashmi C.; Kim, Ho Kwon; Chatterji, Apratim; Ngai, Darryl; Chen Si; Yang Nan

    2010-06-15

    Epitaxial growth in strained asymmetric, dislocation-free, coherent, alloy films is explored. Linear-stability analysis is used to theoretically analyze the coupled instability arising jointly from the substrate-film lattice mismatch (morphological instability) and the spinodal decomposition mechanism. Both the static and growing films are considered. Role of various parameters in determining stability regions for a coherent growing alloy film is investigated. In addition to the usual parameters: lattice mismatch {epsilon}, solute-expansion coefficient {eta}, growth velocity V, and growth temperature T, we consider the alloy asymmetry arising from its mean composition. The dependence of elastic moduli on composition fluctuations and the coupling between top surface and underlying bulk of the film also play important roles. The theory is applied to group III-V films such as GaAsN, InGaN, and InGaP and to group IV Si-Ge films at temperatures below the bare critical temperature T{sub c} for strain-free spinodal decomposition. The dependences of various material parameters on mean concentration and temperature lead to significant qualitative changes.

  8. Structural study and ferroelectricity of epitaxial BaTiO3 films on silicon grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Mazet, L.; Bachelet, R.; Louahadj, L.; Albertini, D.; Gautier, B.; Cours, R.; Schamm-Chardon, S.; Saint-Girons, G.; Dubourdieu, C.

    2014-12-01

    Integration of epitaxial complex ferroelectric oxides such as BaTiO3 on semiconductor substrates depends on the ability to finely control their structure and properties, which are strongly correlated. The epitaxial growth of thin BaTiO3 films with high interfacial quality still remains scarcely investigated on semiconductors; a systematic investigation of processing conditions is missing although they determine the cationic composition, the oxygen content, and the microstructure, which, in turn, play a major role on the ferroelectric properties. We report here the study of various relevant deposition parameters in molecular beam epitaxy for the growth of epitaxial tetragonal BaTiO3 thin films on silicon substrates. The films were grown using a 4 nm-thick epitaxial SrTiO3 buffer layer. We show that the tetragonality of the BaTiO3 films, the crystalline domain orientations, and SiO2 interfacial layer regrowth strongly depend on the oxygen partial pressure and temperature during the growth and on the post-deposition anneal. The ferroelectricity of the films, probed using piezoresponse force microscopy, is obtained in controlled temperature and oxygen pressure conditions with a polarization perpendicular to the surface.

  9. Preparation and Characterization of Epitaxial VO2 Films on Sapphire Using Postepitaxial Topotaxy Route via Epitaxial V2O3 Films

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Iwao; Manabe, Takaaki; Tsuchiya, Tetsuo; Nakajima, Tomohiko; Sohma, Mitsugu; Kumagai, Toshiya

    2008-02-01

    Epitaxial VO2 films were prepared on the C-planes of α-Al2O3 substrates by a metal organic deposition (MOD) process. It was difficult to obtain the single phase of (010)M-oriented VO2 films, in which the subscript M refers to the monoclinic indices, by the heat treatment of amorphous precursor films in the VO2-stable region after the pyrolysis of the coating solution. The product films consisted of discontinuous circular grains of 1-2 µm size on the substrate surface. Therefore, we prepared the (010)M-oriented epitaxial VO2 films using postepitaxial topotaxy (PET), that is, topotactic oxidation of (0001)-oriented epitaxial V2O3 films. First, epitaxial V2O3(0001) films were obtained by MOD starting with a vanadium naphthenate solution. Second, the epitaxial V2O3(0001) films were topotactically oxidized at 500 °C in an Ar-O2 gas mixture with pO2 = 10-4 atm to obtain (010)M-oriented epitaxial VO2 films. The epitaxial relationships were VO2(010)M ∥ α-Al2O3(0001) and VO2[100]M ∥ α-Al2O3[0110], [1010], [1100]. The VO2(010)M films exhibited metal-semiconductor transitions with hysteresis loops at 60-80 °C. The resistivity change before and after the transition of the VO2(010)M film oxidized for 6 h was three orders of magnitude.

  10. Dynamic nonlinearity in epitaxial BaTi O3 films

    NASA Astrophysics Data System (ADS)

    Tyunina, M.; Savinov, M.

    2016-08-01

    Dynamic dielectric and piezoelectric constants of ferroelectrics increase proportionally to the amplitude of alternating electric field as a result of hysteretic Rayleigh-type motion of domain walls. Here a hysteresis-free quadratic field dependence of the dynamic dielectric response is experimentally demonstrated in the absence of domain walls in epitaxial BaTi O3 films. This extraordinary behavior is related to polar entities, whose presence is confirmed by the Vogel-Fulcher relaxation. The polar entities are ascribed to polarization fluctuations associated with lattice inhomogeneity.

  11. In situ growth of epitaxial cerium tungstate (100) thin films.

    PubMed

    Skála, Tomáš; Tsud, Nataliya; Orti, Miguel Ángel Niño; Menteş, Tevfik Onur; Locatelli, Andrea; Prince, Kevin Charles; Matolín, Vladimír

    2011-04-21

    The deposition of ceria on a preoxidized W(110) crystal at 870 K has been studied in situ by photoelectron spectroscopy and low-energy electron diffraction. Formation of an epitaxial layer of crystalline cerium tungstate Ce(6)WO(12)(100), with the metals in the Ce(3+) and W(6+) chemical states, has been observed. The interface between the tungsten substrate and the tungstate film consists of WO suboxide. At thicknesses above 0.89 nm, cerium dioxide grows on the surface of Ce(6)WO(12), favoured by the limited diffusion of tungsten from the substrate. PMID:21399780

  12. Stable Algorithms for Modeling Thin-Film Epitaxial Growth

    NASA Astrophysics Data System (ADS)

    Seyfarth, Greg; Vollmayr-Lee, Benjamin

    2013-03-01

    We search for stable time-stepping schemes for a phase-field model of thin film epitaxial growth. In particular, we consider a class of linear semi-implicit schemes which ensure the free energy decreases with time, a property called gradient stability. System dynamics slow at late times, so gradient stable schemes which allow adaptive time stepping are highly desirable. We perform a linear stability analysis and support it with numerical testing, revealing a region in parameter space of gradient stable semi-implicit schemes. Funded by NSF REU Grant #PHY-1156964.

  13. Single-domain epitaxial silicene on diboride thin films

    NASA Astrophysics Data System (ADS)

    Fleurence, A.; Gill, T. G.; Friedlein, R.; Sadowski, J. T.; Aoyagi, K.; Copel, M.; Tromp, R. M.; Hirjibehedin, C. F.; Yamada-Takamura, Y.

    2016-04-01

    Epitaxial silicene, which forms spontaneously on ZrB2(0001) thin films grown on Si(111) wafers, has a periodic stripe domain structure. By adsorbing additional Si atoms on this surface, we find that the domain boundaries vanish, and a single-domain silicene sheet can be prepared without altering its buckled honeycomb structure. The amount of Si required to induce this change suggests that the domain boundaries are made of a local distortion of the silicene honeycomb lattice. The realization of a single domain sheet with structural and electronic properties close to those of the original striped state demonstrates the high structural flexibility of silicene.

  14. Silicon Carbide Epitaxial Films Studied by Atomic Force Microscopy

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Silicon carbide (SiC) holds great potential as an electronic material because of its wide band gap energy, high breakdown electric field, thermal stability, and resistance to radiation damage. Possible aerospace applications of high-temperature, high-power, or high-radiation SiC electronic devices include sensors, control electronics, and power electronics that can operate at temperatures up to 600 C and beyond. Commercially available SiC devices now include blue light-emitting diodes (LED's) and high-voltage diodes for operation up to 350 C, with other devices under development. At present, morphological defects in epitaxially grown SiC films limit their use in device applications. Research geared toward reducing the number of structural inhomogeneities can benefit from an understanding of the type and nature of problems that cause defects. The Atomic Force Microscope (AFM) has proven to be a useful tool in characterizing defects present on the surface of SiC epitaxial films. The in-house High-Temperature Integrated Electronics and Sensors (HTIES) Program at the NASA Lewis Research Center not only extended the dopant concentration range achievable in epitaxial SiC films, but it reduced the concentration of some types of defects. Advanced structural characterization using the AFM was warranted to identify the type and structure of the remaining film defects and morphological inhomogeneities. The AFM can give quantitative information on surface topography down to molecular scales. Acquired, in part, in support of the Advanced High Temperature Engine Materials Technology Program (HITEMP), the AFM had been used previously to detect partial fiber debonding in composite material cross sections. Atomic force microscopy examination of epitaxial SiC film surfaces revealed molecular-scale details of some unwanted surface features. Growth pits propagating from defects in the substrate, and hillocks due, presumably, to existing screw dislocations in the substrates, were

  15. Hot Wall Epitaxy And Characterization Of Bismuth And Antimony Thin Films On Barium Fluoride Substrates

    NASA Astrophysics Data System (ADS)

    Collazo, Ramon; Dalmau, Rafael; Martinez, Antonio

    1998-03-01

    We have grown thin films of bismuth and antimony using hot wall epitaxy. The epitaxial films were grown on (111)-BaF2 substrates. The chemical integrity of the films was established using Auger electron spectroscopy and X ray Photoelectron Spectroscopy. The thickness of the films was measured using an atomic force microscope to establish their growth rate. The crystallographic properties of the films were assessed using x-ray diffraction techniques. Both bismuth and antimony thin films were found to be oriented with the [003] direction perpendicular to the plane of the films. Pole figures of both types of films indicate the epitaxial nature of the films. Bi/Sb multilayer structures were grown using the same growth technique. We will report on the results of the characterization of these films as well as on the growth apparatus and process. Work supported in part by EPSCoR-NSF Grant EHR-9108775 and NCRADA-NSWCDD-92-01.

  16. 5f band dispersion in epitaxial films of UO2

    SciTech Connect

    Durakiewicz, Tomasz; Jia, Quanxi; Roy, Lindsay E; Martin, Richard L; Joyce, John J

    2009-01-01

    Polymer-assisted deposition of epitaxial films utilizes lattice pinning to produce films of very high stability and properties identical with bulk crystal. Dispersion of the 5f band is shown for the first time in a actinide Mott insulator system, which suggestes hybridization as a leading process in establishing the electronic structure. Hybrid density functional is succesfully employed to calculate the electronic structure of UO{sub 2} in agreement with experiments. UO{sub 2} continues to be a mysterious and elusive compound in terms of understanding the physical properties of a material. Most actinide oxides, including UO{sub 2} are predicted to be metallic. However, UO{sub 2} is an antiferromagnetic insulator with a relatively large gap of about 2eV. The f orbital charater of the excitations across the gap places UO{sub 2} in a Mott insulator category, but no states at the gap center have ever been measured directly, in spite of intensive efforts. In this work we present the first results of the electronic structure investigation of a epitaxial film of UO{sub 2}, where we find even more unexpected properties, like the dispersive nature of 5f bands. We also demonstrate the unexpected, very high stability of the epitaxial film of UO{sub 2}. In the lattice-pinning scheme, the crystalline nature of the film is preserved all the way up to the topmost layers even after prolonged exposure to atmospheric conditions. Hybridized, dispersive bands are common in the itinerant uranium compounds. One usually finds hybridization of f-orbitals with conduction band to be quite common in f-electron systems at low temperatures. Such bands may reside in the vicinity of the Fermi level and participate in the construction of the Fermi surface. However, in the insulator like UO{sub 2}, one expects a more atomic band nature, where f-bands are relatively flat and shifted away from the Fermi level by the gap energy scale. Precise location of UO{sub 2} on the localization

  17. 90 K superconductivity of clean Pb1212 epitaxial films

    NASA Astrophysics Data System (ADS)

    Komori, S.; Kondo, A.; Kindo, K.; Kakeya, I.

    2016-08-01

    A single-phase {{Pb}}1-y{{Sr}}2{{{Y}}}1-x{{Ca}}x{{Cu}}2+y{{{O}}}7+δ (Pb1212) epitaxial film with {T}{{c,onset}}=90 {{K}} has been grown using a two-step technique, which allows lattice relaxation near the film/substrate interface and reduction of Pb vacancies. Using the upper critical field measurement, the coherence lengths are derived to be 20 and 4.3 Å, along the ab-plane and c-axis, respectively. The value of the irreversibility field is found to be close to that of YBa2Cu3O7. High magnetic field measurement has revealed normal state resistivity below {T}{{c}} and metallic behavior in the underdoped region.

  18. ASM stepper alignment through thick epitaxial silicon films

    NASA Astrophysics Data System (ADS)

    Black, Iain

    1999-04-01

    High voltage bipolar and BiCMOS processes often use thick epitaxially grown layers of silicon. These films 12-24 micrometers thick offer a considerable challenge to the alignment of subsequent process layers due to the 'wash out' and image distortion, caused to any underlying pattern, which render automatic alignment mark recognition difficult it not impossible. Historically using projection aligner technology these immediately post Epi layers have been manually aligned with future automatic alignment target defined at the first opportunity post Epi. This is not possible using ASM steppers, as these depend upon marks etched into the silicon, before first processing, to create marks, to which all subsequent layers are registered. To allow the stepper to run wafers with these Epi films a new approach was required.

  19. Magnetic x-ray dichroism in ultrathin epitaxial films

    SciTech Connect

    Tobin, J.G.; Goodman, K.W.; Cummins, T.R.

    1997-04-01

    The authors have used Magnetic X-ray Linear Dichroism (MXLD) and Magnetic X-ray Circular Dichroism (MXCD) to study the magnetic properties of epitaxial overlayers in an elementally specific fashion. Both MXLD and MXCD Photoelectron Spectroscopy were performed in a high resolution mode at the Spectromicroscopy Facility of the ALS. Circular Polarization was obtained via the utilization of a novel phase retarder (soft x-ray quarter wave plate) based upon transmission through a multilayer film. The samples were low temperature Fe overlayers, magnetic alloy films of NiFe and CoNi, and Gd grown on Y. The authors results include a direct comparison of high resolution angle resolved Photoelectron Spectroscopy performed in MXLD and MXCD modes as well as structural studies with photoelectron diffraction.

  20. Methodologies for measuring residual stress distributions in epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Liu, M.; Ruan, H. H.; Zhang, L. C.

    2013-01-01

    Residual stresses in a thin film deposited on a dissimilar substrate can bring about various interface or subsurface damages, such as delamination, dislocation, twinning and cracking. In high performance integrated circuits and MEMS, a too high residual stress can significantly alter their electronic properties. A proper residual stress characterization needs the description of full stress tensors and their variations with thickness. The problem is that film thickness measurement requires different means, and that direct measurement techniques to fulfill the tasks are not straightforward. This paper provides a simple method using X-ray diffraction (XRD) and Raman scattering for the measurement of residual stresses and their thickness dependence. Using the epitaxial silicon film on a sapphire substrate as an example, this paper demonstrates that the improved XRD technique can make use of multiple diffraction peaks to give rise to a highly accurate stress tensor. The co-existence of silicon and sapphire peaks in a Raman spectrum then allows a simultaneous measurement of film thickness from the peak intensity ratio and the residual stress from the peak shift. The paper also concludes the relation between film thickness and residual stresses.

  1. Surface-phonon dispersion in ultrathin epitaxial films of Ni on Cu(001)

    NASA Astrophysics Data System (ADS)

    Mohamed, Mohamed H.; Kim, Jae-Sung; Kesmodel, L. L.

    1989-07-01

    New measurements by high-resolution electron-energy-loss spectroscopy confirm the presence of localized film modes for ultrathin epitaxial films of nickel on a copper (001) substrate. These film modes, predicted recently in lattice-dynamical calculations by Chen, Wu, Yao, and Tong [Phys. Rev. B 39, 5617 (1989)] lie above the Cu-substrate bands and correspond to vibrational motion localized in the Ni overlayer. The Rayleigh-mode dispersion for the epitaxial overlayers is also reported.

  2. Structure and electron transport of strontium iridate epitaxial films

    NASA Astrophysics Data System (ADS)

    Kislinskii, Yu. V.; Ovsyannikov, G. A.; Petrzhik, A. M.; Constantinian, K. Y.; Andreev, N. V.; Sviridova, T. A.

    2015-12-01

    The crystallographic and electrophysical properties of epitaxial SrIrO3 films, in which the crystal lattice is deformed due to the mismatch between the lattice parameters of strontium iridate and the substrate, have been studied. Substrates (001) SrTiO3, (001) LaAlO3 + Sr2AlTaO6 (LSAT), (110) NdGaO3, and (001) LaAlO3 have been used. As a result of the deformation of the crystal lattice, the electrical resistivities of the films deposited on substrates with different lattice parameters differ by several times. The SrIrO3 films with thickness d = 90 nm, grown on SrTiO3 and LSAT substrates, have a nonmonotonic temperature dependence of the conductivity: type of the temperature dependence of the conductivity changes from metallic to dielectric at T L = 200-250 K. The electrical resistance of the films with thicknesses less than 20 nm on all the substrates decreases exponentially with increasing temperature.

  3. Epitaxial Brownmillerite Oxide Thin Films for Reliable Switching Memory.

    PubMed

    Acharya, Susant K; Nallagatla, Raveendra Venkata; Togibasa, Octolia; Lee, Bo W; Liu, Chunli; Jung, Chang U; Park, Bae Ho; Park, Ji-Yong; Cho, Yunae; Kim, Dong-Wook; Jo, Janghyun; Kwon, Deok-Hwang; Kim, Miyoung; Hwang, Cheol Seong; Chae, Seung C

    2016-03-01

    Resistive switching memory, which is mostly based on polycrystalline thin films, suffers from wide distributions in switching parameters-including set voltage, reset voltage, and resistance-in their low- and high-resistance states. One of the most commonly used methods to overcome this limitation is to introduce inhomogeneity. By contrast, in this paper, we obtained uniform resistive switching parameters and sufficiently low forming voltage by maximizing the uniformity of an epitaxial thin film. To achieve this result, we deposited an SrFeOx/SrRuO3 heteroepitaxial structure onto an SrTiO3 (001) substrate by pulsed laser deposition, and then we deposited an Au top electrode by electron-beam evaporation. This device exhibited excellent bipolar resistance switching characteristics, including a high on/off ratio, narrow distribution of key switching parameters, and long data retention time. We interpret these phenomena in terms of a local, reversible phase transformation in the SrFeOx film between brownmillerite and perovskite structures. Using the brownmillerite structure and atomically uniform thickness of the heteroepitaxial SrFeOx thin film, we overcame two major hurdles in the development of resistive random-access memory devices: high forming voltage and broad distributions of switching parameters. PMID:26955744

  4. Buffer-enhanced room-temperature growth and characterization of epitaxial ZnO thin films

    SciTech Connect

    Sasaki, Atsushi; Hara, Wakana; Matsuda, Akifumi; Tateda, Norihiro; Otaka, Sei; Akiba, Shusaku; Saito, Keisuke; Yodo, Tokuo; Yoshimoto, Mamoru

    2005-06-06

    The room-temperature epitaxial growth of ZnO thin films on NiO buffered sapphire (0001) substrate was achieved by using the laser molecular-beam-epitaxy method. The obtained ZnO films had the ultrasmooth surface reflecting the nanostepped structure of the sapphire substrate. The crystal structure at the surface was investigated in situ by means of coaxial impact-collision ion scattering spectroscopy. It was proved that the buffer-enhanced epitaxial ZnO thin films grown at room temperature had +c polarity, while the polarity of high-temperature grown ZnO thin films on the sapphire was -c. Photoluminescence spectra at room temperature were measured for the epitaxial ZnO films, showing only the strong ultraviolet emission near 380 nm.

  5. Room temperature epitaxy of Pd films on GaN under conventional vacuum conditions

    NASA Astrophysics Data System (ADS)

    Liu, Q. Z.; Lau, S. S.; Perkins, N. R.; Kuech, T. F.

    1996-09-01

    Pd films deposited at room temperature have been found to grow epitaxially on GaN grown by metalorganic vapor phase epitaxy (MOVPE). The Pd films were deposited on GaN substrates cleaned by chemicals only, and in a conventional e-beam evaporation system with a vacuum of ˜1×10-7 Torr. MeV 4He backscattering spectrometry and the Read x-ray camera were used to evaluate the Pd films. The effects of various chemical etchants—such as aqua regia, HCl:H2O, and HF:H2O—on the epitaxial quality of the Pd films have also been investigated. Ni and Pt films deposited on GaN in a similar manner were also found to be epitaxial.

  6. Conducting (Si-doped) aluminum nitride epitaxial films grown by molecular beam epitaxy

    SciTech Connect

    Kim, J.G.; Moorthy, M.; Park, R.M.

    1999-07-01

    As a member of the III-V nitride semiconductor family, AlN, which has a direct energy-gap of 6.2eV, has received much attention as a promising material for many applications. However, despite the promising attributes of AlN for various semiconductor devices, research on AlN has been limited and n-type conducting AlN has not been reported. The objective of this research was to understand the factors impacting the conductivity of AlN and to control the conductivity of this material through intentional doping. Prior to the intentional doping study, growth of undoped AlN epilayers was investigated. Through careful selection of substrate preparation methods and growth parameters, relatively low-temperature molecular beam epitaxial growth of AlN films was established which resulted in insulating material. Intentional Si doping during epilayer growth was found to result in conducting films under specific growth conditions. Above a growth temperature of 900 C, AlN films were insulating, however, below a growth temperature of 900 C, the AlN films were conducting. The magnitude of the conductivity and the growth temperature range over which conducting AlN films could be grown were strongly influenced by the presence of a Ga flux during growth. For instance, conducting, Si-doped, AlN films were grown at a growth temperature of 940 C in the presence of a Ga flux while the films were insulating when grown in the absence of a Ga flux at this particular growth temperature. Also, by appropriate selection of the growth parameters, epilayers with n-type conductivity values as large as 0.2 {Omega}{sup {minus}1} cm{sup {minus}1} for AlN and 17 {Omega}{sup {minus}1} cm{sup {minus}1} for Al{sub 0.75}Ga{sub 0.25}N were grown in this work for the first time.

  7. Method of fabricating low-dislocation-density epitaxially-grown films with textured surfaces

    DOEpatents

    Li, Qiming; Wang, George T

    2015-01-13

    A method for forming a surface-textured single-crystal film layer by growing the film atop a layer of microparticles on a substrate and subsequently selectively etching away the microparticles to release the surface-textured single-crystal film layer from the substrate. This method is applicable to a very wide variety of substrates and films. In some embodiments, the film is an epitaxial film that has been grown in crystallographic alignment with respect to a crystalline substrate.

  8. Quantum and thermal phase slips in superconducting niobium nitride (NbN) ultrathin crystalline nanowire: application to single photon detection.

    PubMed

    Delacour, Cécile; Pannetier, Bernard; Villegier, Jean-Claude; Bouchiat, Vincent

    2012-07-11

    We present low-temperature electronic transport properties of superconducting nanowires obtained by nanolithography of 4-nm-thick niobium nitride (NbN) films epitaxially grown on sapphire substrate. Below 6 K, clear evidence of phase slippages is observed in the transport measurements. Upon lowering the temperature, we observe the signatures of a crossover between a thermal and a quantum behavior in the phase slip regimes. We find that phase slips are stable even at the lowest temperatures and that no hotspot is formed. The photoresponse of these nanowires is measured as a function of the light irradiation wavelength and temperature and exhibits a behavior comparable with previous results obtained on thicker films. PMID:22694480

  9. Compensation in epitaxial cubic SiC films

    NASA Technical Reports Server (NTRS)

    Segall, B.; Alterovitz, S. A.; Haugland, E. J.; Matus, L. G.

    1986-01-01

    Hall measurements on four n-type cubic SiC films epitaxially grown by chemical vapor deposition on SiC substrates are reported. The temperature dependent carrier concentrations indicate that the samples are highly compensated. Donor ionization energies, E sub D, are less than one half the values previously reported. The values for E sub D and the donor concentration N sub D, combined with results for small bulk platelets with nitrogen donors, suggest the relation E sub D (N sub D) = E sub D(O) - alpha N sub N sup 1/3 for cubic SiC. A curve fit gives alpha is approx 2.6x10/5 meV cm and E sub D (O) approx 48 meV, which is the generally accepted value of E sub D(O) for nitrogen donors in cubic SiC.

  10. Ferroelastic twin structures in epitaxial WO3 thin films

    NASA Astrophysics Data System (ADS)

    Yun, Shinhee; Woo, Chang-Su; Kim, Gi-Yeop; Sharma, Pankaj; Lee, Jin Hong; Chu, Kanghyun; Song, Jong Hyun; Chung, Sung-Yoon; Seidel, Jan; Choi, Si-Young; Yang, Chan-Ho

    2015-12-01

    Tungsten trioxide is a binary oxide that has potential applications in electrochromic windows, gas sensors, photo-catalysts, and superconductivity. Here, we analyze the crystal structure of atomically flat epitaxial layers on YAlO3 single crystal substrates and perform nanoscale investigations of the ferroelastic twins revealing a hierarchical structure at multiple length scales. We have found that the finest stripe ferroelastic twin walls along pseudocubic <100> axes are associated with cooperative mosaic rotations of the monoclinic films and the larger stripe domains along pseudocubic <110> axes are created to reduce the misfit strain through a commensurate matching of an effective in-plane lattice parameter between film and substrate. The typical widths of the two fine and larger stripe domains increase with film thickness following a power law with scaling exponents of ˜0.6 and ˜0.4, respectively. We have also found that the twin structure can be readily influenced by illumination with an electron beam or a tip-based mechanical compression.

  11. Epitaxially grown strained pentacene thin film on graphene membrane.

    PubMed

    Kim, Kwanpyo; Santos, Elton J G; Lee, Tae Hoon; Nishi, Yoshio; Bao, Zhenan

    2015-05-01

    Organic-graphene system has emerged as a new platform for various applications such as flexible organic photovoltaics and organic light emitting diodes. Due to its important implication in charge transport, the study and reliable control of molecular packing structures at the graphene-molecule interface are of great importance for successful incorporation of graphene in related organic devices. Here, an ideal membrane of suspended graphene as a molecular assembly template is utilized to investigate thin-film epitaxial behaviors. Using transmission electron microscopy, two distinct molecular packing structures of pentacene on graphene are found. One observed packing structure is similar to the well-known bulk-phase, which adapts a face-on molecular orientation on graphene substrate. On the other hand, a rare polymorph of pentacene crystal, which shows significant strain along the c-axis, is identified. In particular, the strained film exhibits a specific molecular orientation and a strong azimuthal correlation with underlying graphene. Through ab initio electronic structure calculations, including van der Waals interactions, the unusual polymorph is attributed to the strong graphene-pentacene interaction. The observed strained organic film growth on graphene demonstrates the possibility to tune molecular packing via graphene-molecule interactions. PMID:25565340

  12. Structural investigation of magnetic FeRh epitaxial films

    NASA Astrophysics Data System (ADS)

    Castiella, M.; Gatel, C.; Bobo, J. F.; Ratel-Ramond, N.; Tan, R.; Respaud, M.; Casanove, M. J.

    2015-08-01

    We report on the structural investigation of FeRh thin films exhibiting a magnetic transition from an antiferromagnetic (AF) to a ferromagnetic (FM) state when heated above ≈350 K. The transition lying in a very narrow range of composition, close to the equiatomic one, and in a given chemically ordered phase (of B2-type), the composition and the growth conditions were carefully adjusted in the epitaxial growth process of the films on (001)MgO. Magnetic measurements confirmed the presence of the AF-FM transition. High-angle x-ray diffraction and electron microscopy experiments were used to characterize the FeRh structural details at different scales from statistical to highly localized information. Special attention was paid to the quality of the chemical order and the presence of defects, which condition the characteristics of the magnetic transition. Interestingly, the results reveal the presence of nanograins, displaying another structure in the equiatomic FeRh films, such grains having previously been observed in strained bulk specimens.

  13. Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films

    PubMed Central

    2014-01-01

    Since the discovery of graphene, the quest for two-dimensional (2D) materials has intensified greatly. Recently, a new family of 2D transition metal carbides and carbonitrides (MXenes) was discovered that is both conducting and hydrophilic, an uncommon combination. To date MXenes have been produced as powders, flakes, and colloidal solutions. Herein, we report on the fabrication of ∼1 × 1 cm2 Ti3C2 films by selective etching of Al, from sputter-deposited epitaxial Ti3AlC2 films, in aqueous HF or NH4HF2. Films that were about 19 nm thick, etched with NH4HF2, transmit ∼90% of the light in the visible-to-infrared range and exhibit metallic conductivity down to ∼100 K. Below 100 K, the films’ resistivity increases with decreasing temperature and they exhibit negative magnetoresistance—both observations consistent with a weak localization phenomenon characteristic of many 2D defective solids. This advance opens the door for the use of MXenes in electronic, photonic, and sensing applications. PMID:24741204

  14. 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.

  15. Epitaxial growth of intermetallic MnPt films on oxides and large exchange bias

    DOE PAGESBeta

    Liu, Zhiqi; Biegalski, Michael D.; Hsu, Shang-Lin; Shang, Shunli; Marker, Cassie; Liu, Jian; Li, Li; Fan, Lisha S.; Meyer, Tricia L.; Wong, Anthony T.; et al

    2015-11-05

    High-quality epitaxial growth of intermetallic MnPt films on oxides is achieved, with potential for multiferroic heterostructure applications. Antisite-stabilized spin-flipping induces ferromagnetism in MnPt films, although it is robustly antiferromagnetic in bulk. Thus, highly ordered antiferromagnetic MnPt films exhibit superiorly large exchange coupling with a ferromagnetic layer.

  16. Epitaxial Growth of Intermetallic MnPt Films on Oxides and Large Exchange Bias.

    PubMed

    Liu, Zhiqi; Biegalski, Michael D; Hsu, Shang-Lin; Shang, Shunli; Marker, Cassie; Liu, Jian; Li, Li; Fan, Lisha; Meyer, Tricia L; Wong, Anthony T; Nichols, John A; Chen, Deyang; You, Long; Chen, Zuhuang; Wang, Kai; Wang, Kevin; Ward, Thomas Z; Gai, Zheng; Lee, Ho Nyung; Sefat, Athena S; Lauter, Valeria; Liu, Zi-Kui; Christen, Hans M

    2016-01-01

    High-quality epitaxial growth of inter-metallic MnPt films on oxides is achieved, with potential for multiferroic heterostructure applications. Antisite-stabilized spin-flipping induces ferromagnetism in MnPt films, although it is robustly antiferromagnetic in bulk. Moreover, highly ordered antiferromagnetic MnPt films exhibit superiorly large exchange coupling with a ferromagnetic layer. PMID:26539758

  17. Properties of Epitaxial Films Made of Relaxor Ferroelectrics

    NASA Astrophysics Data System (ADS)

    Prosandeev, S.; Wang, Dawei; Bellaiche, L.

    2013-12-01

    Finite-temperature properties of epitaxial films made of Ba(Zr,Ti)O3 relaxor ferroelectrics are determined as a function of misfit strain, via the use of a first-principles-based effective Hamiltonian. These films are macroscopically paraelectric at any temperature, for any strain ranging between ≃-3% and ≃+3%. However, original temperature-versus-misfit strain phase diagrams are obtained for the Burns temperature (Tb) and for the critical temperatures (Tm,z and Tm,IP) at which the out-of-plane and in-plane dielectric response peak, respectively, which allow the identification of three different regions. These latter differ from their evolution of Tb, Tm,z, and/or Tm,IP with strain, which are the fingerprints of a remarkable strain-induced microscopic change: each of these regions is associated with its own characteristic behavior of polar nanoregions at low temperature, such as strain-induced rotation or strain-driven elongation of their dipoles or even increase in the average size of the polar nanoregions when the strength of the strain grows.

  18. Study of epitaxial multiferroic BiFeO{sub 3} films

    SciTech Connect

    Kothari, Deepti; Reddy, V. Raghavendra; Gupta, Ajay

    2010-12-01

    Multiferroic BiFeO{sub 3} epitaxial thin films are prepared using pulsed laser deposition method on single crystal SrTiO{sub 3}(001) substrates. The prepared films are characterized by [001] growth and the in-plane {phi}-scans haven shown that the films are characterized by ''cube-on-cube'' epitaxial growth. The photoelectron spectroscopy results confirm the presence of Fe{sup 3+} only. Better magnetic properties are observed in the case of less thickness BiFeO{sub 3} film as compared to higher thickness, which could be due to the in-plane strain effect.

  19. Epitaxial growth of SrTiO{sub 3} thin film on Si by laser molecular beam epitaxy

    SciTech Connect

    Zhou, X. Y.; Miao, J.; Dai, J. Y.; Chan, H. L. W.; Choy, C. L.; Wang, Y.; Li, Q.

    2007-01-01

    SrTiO{sub 3} thin films have been deposited on Si (001) wafers by laser molecular beam epitaxy using an ultrathin Sr layer as the template. X-ray diffraction measurements indicated that SrTiO{sub 3} was well crystallized and epitaxially aligned with Si. Cross-sectional observations in a transmission electron microscope revealed that the SrTiO{sub 3}/Si interface was sharp, smooth, and fully crystallized. The thickness of the Sr template was found to be a critical factor that influenced the quality of SrTiO{sub 3} and the interfacial structure. Electrical measurements revealed that the SrTiO{sub 3} film was highly resistive.

  20. Effect of growth temperature on defects in epitaxial GaN film grown by plasma assisted molecular beam epitaxy

    SciTech Connect

    Kushvaha, S. S. Pal, P.; Shukla, A. K.; Joshi, Amish G.; Gupta, Govind; Kumar, M.; Singh, S.; Gupta, Bipin K.; Haranath, D.

    2014-02-15

    We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 10{sup 8} cm{sup −2} at 750 °C) than that of the low temperature grown sample (1.1 × 10{sup 9} cm{sup −2} at 730 °C). A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

  1. Low-temperature plasma-deposited silicon epitaxial films: Growth and properties

    SciTech Connect

    Demaurex, Bénédicte Bartlome, Richard; Seif, Johannes P.; Geissbühler, Jonas; Ballif, Christophe; De Wolf, Stefaan; Alexander, Duncan T. L.; Jeangros, Quentin

    2014-08-07

    Low-temperature (≤200 °C) epitaxial growth yields precise thickness, doping, and thermal-budget control, which enables advanced-design semiconductor devices. In this paper, we use plasma-enhanced chemical vapor deposition to grow homo-epitaxial layers and study the different growth modes on crystalline silicon substrates. In particular, we determine the conditions leading to epitaxial growth in light of a model that depends only on the silane concentration in the plasma and the mean free path length of surface adatoms. For such growth, we show that the presence of a persistent defective interface layer between the crystalline silicon substrate and the epitaxial layer stems not only from the growth conditions but also from unintentional contamination of the reactor. Based on our findings, we determine the plasma conditions to grow high-quality bulk epitaxial films and propose a two-step growth process to obtain device-grade material.

  2. Low-temperature plasma-deposited silicon epitaxial films: Growth and properties

    SciTech Connect

    Demaurex, Bénédicte; Bartlome, Richard; Seif, Johannes P.; Geissbühler, Jonas; Alexander, Duncan T. L.; Jeangros, Quentin; Ballif, Christophe; De Wolf, Stefaan

    2014-08-05

    Low-temperature (≤ 180 °C) epitaxial growth yields precise thickness, doping, and thermal-budget control, which enables advanced-design semiconductor devices. In this paper, we use plasma-ehanced chemical vapor deposition to grow homo-epitaxial layers and study the different growth modes on crystalline silicon substrates. In particular, we determine the conditions leading to epitaxial growth in light of a model that depends only on the silane concentration in the plasma and the mean free path length of surface adatoms. For such growth, we show that the presence of a persistent defective interface layer between the crystalline silicon substrate and the epitaxial layer stems not only from the growth conditions but also from unintentional contamination of the reactor. As a result of our findings, we determine the plasma conditions to grow high-quality bulk epitaxial films and propose a two-step growth process to obtain device-grade material.

  3. Growth of epitaxial bismuth and gallium substituted lutetium iron garnet films by pulsed laser deposition

    SciTech Connect

    Leitenmeier, Stephan; Heinrich, Andreas; Lindner, Joerg K. N.; Stritzker, Bernd

    2006-04-15

    Epitaxial bismuth and gallium substituted lutetium iron garnet thin films have been grown on (100) oriented gadolinium gallium garnet Gd{sub 3}Ga{sub 5}O{sub 12} substrates by pulsed laser deposition. The films have been studied using x-ray diffraction, high resolution x-ray diffraction, Rutherford backscattering spectroscopy, transmission electron microscopy, and electron diffraction. We obtained smooth films with thicknesses between 0.3 and 1.0 {mu}m showing good crystalline quality and epitaxial growth.

  4. Ion-irradiation enhanced epitaxial growth of sol-gel TiO2 films

    NASA Astrophysics Data System (ADS)

    Lee, Jung-Kun; Jung, Hyun Suk; Wang, Yongqiang; Theodore, N. David; Alford, Terry L.; Nastasi, Michael

    2011-04-01

    We report the epitaxial growth of sol-gel TiO2 films by using ion-irradiation enhanced synthesis. Our present study shows that the ion-beam process can provide highly crystalline TiO2 even at 350°C. Nuclear energy deposition at amorphous/crystalline interface plays a dominant role in the epitaxial growth of the films at the reduced temperature via a defect-migration mechanism. In addition, the ion irradiation allows for increasing the film density by balancing the crystallization rate and the escape rate of organic components.

  5. Epitaxial niobium dioxide thin films by reactive-biased target ion beam deposition

    SciTech Connect

    Wang, Yuhan; Comes, Ryan B.; Kittiwatanakul, Salinporn; Wolf, Stuart A.; Lu, Jiwei

    2015-03-01

    Epitaxial NbO2 thin films were synthesized on Al2O3 (0001) substrates via reactive bias target ion beam deposition. X-ray diffraction and Raman spectra were used to confirm the tetragonal phase of pure NbO2. Through XPS, it was found that there was a ~ 1.3 nm thick Nb2O5 layer on the surface and the bulk of the thin film was NbO2. The epitaxial relationship between NbO2 film and substrate was determined. Electrical transport measurement as a function of temperature showed that the conduction mechanism could be described by variable range hopping mechanism.

  6. Process for forming epitaxial perovskite thin film layers using halide precursors

    DOEpatents

    Clem, Paul G.; Rodriguez, Mark A.; Voigt, James A.; Ashley, Carol S.

    2001-01-01

    A process for forming an epitaxial perovskite-phase thin film on a substrate. This thin film can act as a buffer layer between a Ni substrate and a YBa.sub.2 Cu.sub.3 O.sub.7-x superconductor layer. The process utilizes alkali or alkaline metal acetates dissolved in halogenated organic acid along with titanium isopropoxide to dip or spin-coat the substrate which is then heated to about 700.degree. C. in an inert gas atmosphere to form the epitaxial film on the substrate. The YBCO superconductor can then be deposited on the layer formed by this invention.

  7. Suppression of inhomogeneous segregation in graphene growth on epitaxial metal films.

    PubMed

    Yoshii, Shigeo; Nozawa, Katsuya; Toyoda, Kenji; Matsukawa, Nozomu; Odagawa, Akihiro; Tsujimura, Ayumu

    2011-07-13

    Large-scale uniform graphene growth was achieved by suppressing inhomogeneous carbon segregation using a single domain Ru film epitaxially grown on a sapphire substrate. An investigation of how the metal thickness affected growth and a comparative study on metals with different crystal structures have revealed that locally enhanced carbon segregation at stacking domain boundaries of metal is the origin of inhomogeneous graphene growth. Single domain Ru film has no stacking domain boundary, and the graphene growth on it is mainly caused not by segregation but by a surface catalytic reaction. Suppression of local segregation is essential for uniform graphene growth on epitaxial metal films. PMID:21648391

  8. Epitaxial growth of iridate pyrochlore Nd2Ir2O7 films

    PubMed Central

    Gallagher, J. C.; Esser, B. D.; Morrow, R.; Dunsiger, S. R.; Williams, R. E. A.; Woodward, P. M.; McComb, D. W.; Yang, F. Y.

    2016-01-01

    Epitaxial films of the pyrochlore Nd2Ir2O7 have been grown on (111)-oriented yttria-stabilized zirconia (YSZ) substrates by off-axis sputtering followed by post-growth annealing. X-ray diffraction (XRD) results demonstrate phase-pure epitaxial growth of the pyrochlore films on YSZ. Scanning transmission electron microscopy (STEM) investigation of an Nd2Ir2O7 film with a short post-annealing provides insight into the mechanism for crystallization of Nd2Ir2O7 during the post-annealing process. STEM images reveal clear pyrochlore ordering of Nd and Ir in the films. The epitaxial relationship between the YSZ and Nd2Ir2O7 is observed clearly while some interfacial regions show a thin region with polycrystalline Ir nanocrystals. PMID:26923862

  9. Epitaxial growth of iridate pyrochlore Nd2Ir2O7 films

    DOE PAGESBeta

    Gallagher, J. C.; Esser, B. D.; Morrow, R.; Dunsiger, S. R.; Williams, R. E. A.; Woodward, P. M.; McComb, D. W.; Yang, F. Y.

    2016-02-29

    Epitaxial films of the pyrochlore Nd2Ir2O7 have been grown on (111)-oriented yttria-stabilized zirconia (YSZ) substrates by off-axis sputtering followed by post-growth annealing. X-ray diffraction (XRD) results demonstrate phase-pure epitaxial growth of the pyrochlore films on YSZ. Scanning transmission electron microscopy (STEM) investigation of an Nd2Ir2O7 film with a short post-annealing provides insight into the mechanism for crystallization of Nd2Ir2O7 during the post-annealing process. STEM images reveal clear pyrochlore ordering of Nd and Ir in the films. As a result, the epitaxial relationship between the YSZ and Nd2Ir2O7 is observed clearly while some interfacial regions show a thin region with polycrystallinemore » Ir nanocrystals.« less

  10. Epitaxial Cu2ZnSnS4 thin film on Si (111) 4° substrate

    NASA Astrophysics Data System (ADS)

    Song, Ning; Young, Matthew; Liu, Fangyang; Erslev, Pete; Wilson, Samual; Harvey, Steven P.; Teeter, Glenn; Huang, Yidan; Hao, Xiaojing; Green, Martin A.

    2015-06-01

    To explore the possibility of Cu2ZnSnS4 (CZTS)/Si based tandem solar cells, the heteroepitaxy of tetragonal Cu2ZnSnS4 thin films on single crystalline cubic Si (111) wafers with 4° miscut is obtained by molecular beam epitaxy. The X-ray θ-2θ scan and selected area diffraction patterns of the CZTS thin films and Si substrates, and the high resolution transmission electron microscopy image of the CZTS/Si interface region demonstrate that the CZTS thin films are epitaxially grown on the Si substrates. A CZTS/Si P-N junction is formed and shows photovoltaic responses, indicating the promising application of epitaxial CZTS thin films on Si.

  11. Epitaxial growth of iridate pyrochlore Nd2Ir2O7 films

    NASA Astrophysics Data System (ADS)

    Gallagher, J. C.; Esser, B. D.; Morrow, R.; Dunsiger, S. R.; Williams, R. E. A.; Woodward, P. M.; McComb, D. W.; Yang, F. Y.

    2016-02-01

    Epitaxial films of the pyrochlore Nd2Ir2O7 have been grown on (111)-oriented yttria-stabilized zirconia (YSZ) substrates by off-axis sputtering followed by post-growth annealing. X-ray diffraction (XRD) results demonstrate phase-pure epitaxial growth of the pyrochlore films on YSZ. Scanning transmission electron microscopy (STEM) investigation of an Nd2Ir2O7 film with a short post-annealing provides insight into the mechanism for crystallization of Nd2Ir2O7 during the post-annealing process. STEM images reveal clear pyrochlore ordering of Nd and Ir in the films. The epitaxial relationship between the YSZ and Nd2Ir2O7 is observed clearly while some interfacial regions show a thin region with polycrystalline Ir nanocrystals.

  12. Epitaxial growth and optical properties of Al- and N-polar AlN films by laser molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chen, X. W.; Jia, C. H.; Chen, Y. H.; Wang, H. T.; Zhang, W. F.

    2014-03-01

    Epitaxial aluminum nitride (AlN) films with c-axis orientation were grown on both (1 1 1) MgO and c-sapphire substrates by laser molecular beam epitaxy. The in-plane epitaxial relationships were determined to be [1 1 \\bar{{2}} 0]AlN‖[0 \\bar{{1}} 1]MgO and [1 \\bar{{1}} 0 0]AlN‖[1 1 \\bar{{2}} 0]sapphire, and the lattice mismatch was 4.2% and 13.2% for AlN films on MgO and sapphire, respectively. The AlN films were shown to be Al- and N-polar on MgO and sapphire, respectively. The former is assumed to be caused by the centre of inversion symmetry of (1 1 1) MgO substrate, while the latter is due to the O polarity of sapphire. The full-width at half-maximum of the ω-scanning spectrum for AlN film on (1 1 1) MgO substrate is smaller than that on the c-sapphire substrate. The optical band-gap energies for AlN films grown on MgO and sapphire were found to be 5.93 and 5.84 eV, close to the standard band gap of 6.2 eV, and the calculated Urbach energies were 0.27 eV and 0.53 eV, respectively. These results indicate a lower amorphous content and/or less defects/impurities in Al-polar than N-polar AlN.

  13. Pinhole-free growth of epitaxial CoSi.sub.2 film on Si(111)

    NASA Technical Reports Server (NTRS)

    Lin, True-Lon (Inventor); Fathauer, Robert W. (Inventor); Grunthaner, Paula J. (Inventor)

    1991-01-01

    Pinhole-free epitaxial CoSi.sub.2 films (14') are fabricated on (111)-oriented silicon substrates (10) with a modified solid phase epitaxy technique which utilizes (1) room temperature stoichiometric (1:2) codeposition of Co and Si followed by (2) room temperature deposition of an amorphous silicon capping layer (16), and (3) in situ annealing at a temperature ranging from about 500.degree. to 750.degree. C.

  14. Thin film epitaxy and structure property correlations for non-polar ZnO films

    SciTech Connect

    Pant, Punam; Budai, John D; Aggarwal, R; Narayan, Roger; Narayan, Jagdish

    2009-01-01

    Heteroepitaxial growth and strain relaxation were investigated in non-polar a-plane (11-20)ZnO films grown on r-plane (10-12)sapphire substrates in the temperature range 200-700 C by pulsed laser deposition. The lattice misfit in the plane of the film for this orientation varied from -1.26% in [0001] to ?18.52% in the [-1100] direction. The alignment of (11-20)ZnO planes parallel to (10-12)sapphire planes was confirmed by X-ray diffraction {theta}-2{theta} scans over the entire temperature range. X-ray {psi}-scans revealed the epitaxial relationship:[0001]ZnO[-1101]sap; [-1100]ZnO[-1-120]sap. Depending on the growth temperature, variations in the structural, optical and electrical properties were observed in the grown films. Room temperature photoluminescence for films grown at 700 C shows a strong band-edge emission. The ratio of the band-edge emission to green band emission is 135:1, indicating reduced defects and excellent optical quality of the films. The resistivity data for the films grown at 700 C shows semiconducting behavior with room temperature resistivity of 2.2 x 10{sup -3} {Omega}-cm.

  15. Polarity Effects of Substrate Surface in Epitaxial ZnO Film Growth

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C.-H.; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; George, M. A.; McCarty, P.

    1999-01-01

    Epitaxial ZnO films were grown on the two polar surfaces (0-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. As a comparison, films are also deposited on the (000 I) Al203 substrates. It is found that the two polar surfaces have different photoluminescence (PL) spectrum, surface structure and morphology, which are strongly inference the epitaxial film growth. The morphology and structure of epitaxial films on the ZnO substrates are different from the film on the Al203 substrates. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite Surface. The measurements of PL, low-angle incident x-ray diffraction, and atomic force microscopy of ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth using reactive sputtering deposition.

  16. Electrodeposition and electrochemical reduction of epitaxial metal oxide thin films and superlattices

    NASA Astrophysics Data System (ADS)

    He, Zhen

    The focus of this dissertation is the electrodeposition and electrochemical reduction of epitaxial metal oxide thin films and superlattices. The electrochemical reduction of metal oxides to metals has been studied for decades as an alternative to pyrometallurgical processes for the metallurgy industry. However, the previous work was conducted on bulk polycrystalline metal oxides. Paper I in this dissertation shows that epitaxial face-centered cubic magnetite (Fe3O4 ) thin films can be electrochemically reduced to epitaxial body-centered cubic iron (Fe) thin films in aqueous solution on single-crystalline Au substrates at room temperature. This technique opens new possibilities to produce special epitaxial metal/metal oxide heterojunctions and a wide range of epitaxial metallic alloy films from the corresponding mixed metal oxides. Electrodeposition, like biomineralization, is a soft solution processing method which can produce functional materials with special properties onto conducting or semiconducting solid surfaces. Paper II in this dissertation presents the electrodeposition of cobalt-substituted magnetite (CoxFe3-xO4, 0 of cobalt-substituted magnetite (CoxFe3-xO4, 0epitaxial thin films and superlattices on Au single-crystalline substrates, which can be potentially used in spintronics and memory devices. Paper III in this dissertation reports the electrodeposition of crystalline cobalt oxide (Co3O4) thin films on stainless steel and Au single-crystalline substrates. The crystalline Co3O4 thin films exhibit high catalytic activity towards the oxygen evolution reaction in an alkaline solution. A possible application of the electrodeposited Co 3O4 is the fabrication of highly active and low-cost photoanodes for photoelectrochemical water-splitting cells.

  17. Electrical properties of scandium nitride epitaxial films grown on (100) magnesium oxide substrates by molecular beam epitaxy

    SciTech Connect

    Ohgaki, Takeshi; Watanabe, Ken; Adachi, Yutaka; Sakaguchi, Isao; Hishita, Shunichi; Ohashi, Naoki; Haneda, Hajime

    2013-09-07

    Scandium nitride (ScN) films were grown on (100) MgO single crystals by a molecular beam epitaxy method. The effects of growth conditions, including [Sc]/[N] ratio, growth temperature, and nitrogen radical state, on the electrical properties of the ScN films were studied. The ScN films comprised many small columnar grains. Hall coefficient measurements confirmed that the ScN films were highly degenerate n-type semiconductors and that the carrier concentration of the ScN films was sensitive to the growth temperature and the nitrogen radical states during the film growth. The carrier concentrations of the ScN films ranged from 10{sup 19}–10{sup 21} cm{sup −3} while the Hall mobilities ranged from 50–130 cm{sup 2}·V{sup −1}·s{sup −1} for undoped films. The temperature-dependent Hall coefficient measurements showed that the carrier concentration is nearly independent of temperature, indicating that the change in resistivity with temperature is explained by a change in the Hall mobility. The temperature-dependence of the Hall mobility was strongly affected by the growth conditions.

  18. Layer matching epitaxy of NiO thin films on atomically stepped sapphire (0001) substrates

    PubMed Central

    Yamauchi, Ryosuke; Hamasaki, Yosuke; Shibuya, Takuto; Saito, Akira; Tsuchimine, Nobuo; Koyama, Koji; Matsuda, Akifumi; Yoshimoto, Mamoru

    2015-01-01

    Thin-film epitaxy is critical for investigating the original properties of materials. To obtain epitaxial films, careful consideration of the external conditions, i.e. single-crystal substrate, temperature, deposition pressure and fabrication method, is significantly important. In particular, selection of the single-crystal substrate is the first step towards fabrication of a high-quality film. Sapphire (single-crystalline α-Al2O3) is commonly used in industry as a thin-film crystal-growth substrate, and functional thin-film materials deposited on sapphire substrates have found industrial applications. However, while sapphire is a single crystal, two types of atomic planes exist in accordance with step height. Here we discuss the need to consider the lattice mismatch for each of the sapphire atomic layers. Furthermore, through cross-sectional transmission electron microscopy analysis, we demonstrate the uniepitaxial growth of cubic crystalline thin films on bistepped sapphire (0001) substrates. PMID:26402241

  19. Properties of epitaxial (210) iron garnet films exhibiting the magnetoelectric effect

    SciTech Connect

    Arzamastseva, G. V.; Balbashov, A. M.; Lisovskii, F. V. Mansvetova, E. G.; Temiryazev, A. G.; Temiryazeva, M. P.

    2015-04-15

    The properties of epitaxial magnetic (LuBi){sub 3}(FeGa){sub 5}O{sub 12} iron garnet films grown on (210) substrates, which exhibit the magnetoelectric effect, are experimentally studied. The induced anisotropy and the behavior of the domain structure in the films are investigated in uniform and nonuniform external fields. The existing hypotheses about the nature of the magnetoelectric coupling in such films are critically analyzed.

  20. Method for rapid, controllable growth and thickness, of epitaxial silicon films

    DOEpatents

    Wang, Qi; Stradins, Paul; Teplin, Charles; Branz, Howard M.

    2009-10-13

    A method of producing epitaxial silicon films on a c-Si wafer substrate using hot wire chemical vapor deposition by controlling the rate of silicon deposition in a temperature range that spans the transition from a monohydride to a hydrogen free silicon surface in a vacuum, to obtain phase-pure epitaxial silicon film of increased thickness is disclosed. The method includes placing a c-Si substrate in a HWCVD reactor chamber. The method also includes supplying a gas containing silicon at a sufficient rate into the reaction chamber to interact with the substrate to deposit a layer containing silicon thereon at a predefined growth rate to obtain phase-pure epitaxial silicon film of increased thickness.

  1. Strain-induced magneto-optical anisotropy in epitaxial hcp Co films

    NASA Astrophysics Data System (ADS)

    Arregi, J. A.; González-Díaz, J. B.; Idigoras, O.; Berger, A.

    2015-11-01

    We investigate the existence and origin of magneto-optical anisotropy in epitaxial hcp Co films. Our results show that a significant magneto-optical anisotropy exists in our samples and, more importantly, they reveal that its amplitude is directly correlated with epitaxial strain. We find a linear coefficient of 16.8 % magneto-optical anisotropy per every 1% epitaxial strain, which is in stark contrast to an isotropic magneto-optical coupling factor Q , a very frequent and common assumption in magneto-optics of metallic thin films and multilayers. In addition, the Co films exhibit a similar strain-induced increase of the magnetocrystalline anisotropy energy, evidencing the fact that both magneto-optical anisotropy and magnetocrystalline anisotropy are dependent on the modification of the spin-orbit coupling introduced by anisotropic lattice distortions.

  2. Van der Waals epitaxy of functional MoO2 film on mica for flexible electronics

    NASA Astrophysics Data System (ADS)

    Ma, Chun-Hao; Lin, Jheng-Cyuan; Liu, Heng-Jui; Do, Thi Hien; Zhu, Yuan-Min; Ha, Thai Duy; Zhan, Qian; Juang, Jenh-Yih; He, Qing; Arenholz, Elke; Chiu, Po-Wen; Chu, Ying-Hao

    2016-06-01

    Flexible electronics have a great potential to impact consumer electronics and with that our daily life. Currently, no direct growth of epitaxial functional oxides on commercially available flexible substrates is possible. In this study, in order to address this challenge, muscovite, a common layered oxide, is used as a flexible substrate that is chemically similar to typical functional oxides. We fabricated epitaxial MoO2 films on muscovite via pulsed laser deposition technique. A combination of X-ray diffraction and transmission electron microscopy confirms van der Waals epitaxy of the heterostructures. The electrical transport properties of MoO2 films are similar to those of the bulk. Flexible or free-standing MoO2 thin film can be obtained and serve as a template to integrate additional functional oxide layers. Our study demonstrates a remarkable concept to create flexible electronics based on functional oxides.

  3. Perpendicularly magnetized {tau}-MnAl (001) thin films epitaxied on GaAs

    SciTech Connect

    Nie, S. H.; Zhu, L. J.; Lu, J.; Pan, D.; Wang, H. L.; Yu, X. Z.; Xiao, J. X.; Zhao, J. H.

    2013-04-15

    Perpendicularly magnetized {tau}-MnAl films have been epitaxied on GaAs (001) by molecular-beam epitaxy. Crystalline quality and magnetic properties of the samples were strongly dependent on growth temperature. The highest coercivity of 10.7 kOe, saturation magnetization of 361.4 emu/cm{sup 3}, perpendicular magnetic anisotropy constant of 13.65 Merg/cm{sup 3}, and magnetic energy product of 4.44 MGOe were achieved. These tunable magnetic properties make MnAl films valuable as excellent and cost-effective alternative for not only high density perpendicular magnetic recording storage and spintronics devices but also permanent magnets.

  4. Formation and Characterization of Transversely Modulated Nanostructures in Metallic Thin Films using Epitaxial Control

    NASA Astrophysics Data System (ADS)

    Boyerinas, Brad Michael

    This thesis describes a fundamental investigation into the formation, characterization, and modeling of epitaxially-controlled self-assembly at the nanoscale. The presence of coherent nanophases and the clamping effect from an epitaxial substrate enables the formation of transversely modulated nanostructures (TMNS) resulting in improved functionality, which was previously observed through increased piezoelectric response in BiFeO3. The ability to fabricate high quality epitaxial films presents opportunity to investigate coherent phase decomposition in other material systems with multifunctional response. The research herein aims to extend the concept of nanoscale self assembly in metallic systems, including Ag-Si and Pd-PdH. First, the effect of annealing a Ag-Si couple was examined, and ordered, nanoscale Ag crystallites were observed along the interface with the epitaxial Si wafer. It is demonstrated that Ag foil can be used in place of doped Ag paste (commonly used in solar cell metallization) to achieve TMNS at the interface. It was proved that annealing the Ag-Si couple in air is necessary for the self-assembly reaction to take place, as doing so prevents bulk diffusion and eutectic melting. Electron backscatter diffraction was used to verify the epitaxial relation between the Ag nanostructures and Si crystal. A method to fabricate ordered, nanoscale PdH precipitates in epitaxial Pd thin films via high temperate gas phase hydrogenation was established. Epitaxial Pd films were deposited via e-beam deposition and a V buffer layer was necessary to induce epitaxy. This novel self-assembled nanostructure may enable hysteresis-less absorption and desorption, thus improving functionality with regard to hydrogen sensing and storage. The epitaxial Pd film was characterized before and after hydrogenation with x-ray diffraction and atomic force microscopy to determine composition and nanostructure of the film. A thermodynamic model was developed to demonstrate the

  5. Enhanced performance of room-temperature-grown epitaxial thin films of vanadium dioxide

    SciTech Connect

    Nag, Joyeeta; Payzant, E Andrew; More, Karren Leslie; HaglundJr., Richard F

    2011-01-01

    Stoichiometric vanadium dioxide in bulk, thin film and nanostructured forms exhibits an insulator-to-metal transition (IMT) accompanied by a structural phase transformation, induced by temperature, light, electric fields, doping or strain. We have grown epitaxial films of vanadium dioxide on c-plane (0001) of sapphire using two different procedures involving (1) room temperature growth followed by annealing and (2) direct high temperature growth. Strain at the film-substrate interface due to growth at different temperatures leads to interesting differences in morphologies and phase transition characteristics. Comparison of the morphologies and switching characteristics of the two films shows that contrary to conventional wisdom, the room-temperature grown films have smoother, more continuous morphologies and better switching performance, consistent with the behavior of epitaxially grown semiconductors.

  6. Pulsed laser deposition of air-sensitive hydride epitaxial thin films: LiH

    SciTech Connect

    Oguchi, Hiroyuki; Isobe, Shigehito; Kuwano, Hiroki; Shiraki, Susumu; Hitosugi, Taro; Orimo, Shin-ichi

    2015-09-01

    We report on the epitaxial thin film growth of an air-sensitive hydride, lithium hydride (LiH), using pulsed laser deposition (PLD). We first synthesized a dense LiH target, which is key for PLD growth of high-quality hydride films. Then, we obtained epitaxial thin films of [100]-oriented LiH on a MgO(100) substrate at 250 °C under a hydrogen pressure of 1.3 × 10{sup −2} Pa. Atomic force microscopy revealed that the film demonstrates a Stranski-Krastanov growth mode and that the film with a thickness of ∼10 nm has a good surface flatness, with root-mean-square roughness R{sub RMS} of ∼0.4 nm.

  7. Perpendicular magnetic anisotropy in epitaxially strained cobalt-ferrite (001) thin films

    SciTech Connect

    Yanagihara, H. Utsumi, Y.; Niizeki, T. Inoue, J.; Kita, Eiji

    2014-05-07

    We investigated the dependencies of both the magnetization characteristics and the perpendicular magnetic anisotropy of Co{sub x}Fe{sub 3–x}O{sub 4}(001) epitaxial films (x = 0.5 and 0.75) on the growth conditions of the reactive magnetron sputtering process. Both saturation magnetization and the magnetic uniaxial anisotropy constant K{sub u} are strongly dependent on the reactive gas (O{sub 2}) flow rate, although there is little difference in the surface structures for all samples observed by reflection high-energy electron diffraction. In addition, certain dead-layer-like regions were observed in the initial stage of the film growth for all films. Our results suggest that the magnetic properties of Co{sub x}Fe{sub 3–x}O{sub 4} epitaxial films are governed by the oxidation state and the film structure at the vicinity of the interface.

  8. Surface acoustic wave devices fabricated on epitaxial AlN film

    NASA Astrophysics Data System (ADS)

    Gao, Junning; Hao, Zhibiao; Yanxiong E.; Niu, Lang; Wang, Lai; Sun, Changzheng; Xiong, Bin; Han, Yanjun; Wang, Jian; Li, Hongtao; Luo, Yi; Li, Guoqiang

    2016-04-01

    This paper reports surface acoustic wave (SAW) devices fabricated on AlN epitaxial film grown on sapphire, aiming to avoid the detrimental polarization axis inconsistency and refrained crystalline quality of the normally used polycrystalline AlN films. Devices with center frequency of 357 MHz and 714 MHz have been fabricated. The stop band rejection ratio of the as-obtained device reaches 24.5 dB and the pass band ripple is profoundly smaller compared to most of the reported AlN SAW devices with the similar configuration. Judging from the rather high edge dislocation level of the film used in this study, the properties of the SAW devices have great potential to be improved by further improving the crystalline quality of the film. It is then concluded that the AlN epitaxial film is favorable for high quality SAW devices to meet the high frequency and low power consumption challenges facing the signal processing components.

  9. Highly Crystalline Films of Organic Small Molecules with Alkyl Chains Fabricated by Weak Epitaxy Growth.

    PubMed

    Zhu, Yangjie; Chen, Weiping; Wang, Tong; Wang, Haibo; Wang, Yue; Yan, Donghang

    2016-05-12

    Because side-chain engineering of organic conjugated molecules has been widely utilized to tune organic solid-state optoelectronic properties, the achievement of their high-quality films is important for realizing high-performance devices. Here, highly crystalline films of an organic molecule with short alkyl chains, 5,8,15,18-tetrabutyl-5,8,15,18-tetrahydroindolo[3,2-a]indole[30,20:5,6]quinacridone (C4-IDQA), are fabricated by weak epitaxy growth, and highly oriented, large-area, and continuous films are obtained. Because of the soft matter properties, the C4-IDQA molecules can adjust themselves to realize commensurate epitaxy growth on the inducing layers and exhibited good lattice matching in the thin film phase. The crystalline phase is also observed in thicker C4-IDQA films. The growth behavior of C4-IDQA on the inducing layer is further investigated, including the strong dependence of film morphologies on substrate temperatures and deposition rates due to the poor diffusion ability of C4-IDQA molecules. Moreover, highly crystalline films and high electron field-effect mobility are also obtained for the small molecule N,N'-dioctyl-3,4:9,10-perylene tetracarboxylic diimide (C8-PTCDI), which demonstrate that the weak epitaxy growth method could be an effective way to fabricate highly crystalline films of organic small molecules with flexible side chains. PMID:27116036

  10. Electrochemical properties and applications of nanocrystalline, microcrystalline, and epitaxial cubic silicon carbide films.

    PubMed

    Zhuang, Hao; Yang, Nianjun; Zhang, Lei; Fuchs, Regina; Jiang, Xin

    2015-05-27

    Microstructures of the materials (e.g., crystallinitiy, defects, and composition, etc.) determine their properties, which eventually lead to their diverse applications. In this contribution, the properties, especially the electrochemical properties, of cubic silicon carbide (3C-SiC) films have been engineered by controlling their microstructures. By manipulating the deposition conditions, nanocrystalline, microcrystalline and epitaxial (001) 3C-SiC films are obtained with varied properties. The epitaxial 3C-SiC film presents the lowest double-layer capacitance and the highest reversibility of redox probes, because of its perfect (001) orientation and high phase purity. The highest double-layer capacitance and the lowest reversibility of redox probes have been realized on the nanocrystalline 3C-SiC film. Those are ascribed to its high amount of grain boundaries, amorphous phases and large diversity in its crystal size. Based on their diverse properties, the electrochemical performances of 3C-SiC films are evaluated in two kinds of potential applications, namely an electrochemical capacitor using a nanocrystalline film and an electrochemical dopamine sensor using the epitaxial 3C-SiC film. The nanocrystalline 3C-SiC film shows not only a high double layer capacitance (43-70 μF/cm(2)) but also a long-term stability of its capacitance. The epitaxial 3C-SiC film shows a low detection limit toward dopamine, which is one to 2 orders of magnitude lower than its normal concentration in tissue. Therefore, 3C-SiC film is a novel but designable material for different emerging electrochemical applications such as energy storage, biomedical/chemical sensors, environmental pollutant detectors, and so on. PMID:25939808

  11. Structure-property correlation in epitaxial (2 0 0) rutile films on sapphire substrates

    NASA Astrophysics Data System (ADS)

    Bayati, M. R.; Joshi, Sh.; Molaei, R.; Narayan, R. J.; Narayan, J.

    2012-03-01

    We have investigated the influence of the deposition variables on photocatalytic properties of epitaxial rutile films. Despite a large lattice misfit of rutile with sapphire substrate, (2 0 0) epitaxial layers were grown on (0 0 0 1)sapphire by domain matching epitaxy paradigm. Using φ-scan XRD and cross section TEM, the epitaxial relationship was determined to be rutile(1 0 0)||sapphire(0 0 0 1), rutile(0 0 1)||sapphire(1 0 -1 0), and rutile(0 1 0)||sapphire(1 -2 1 0). Based on the XRD patterns, increasing the repetition rate introduced tensile stress along the film normal direction, which may arise as a result of trapped defects. Formation of such defects was studied by UV-VIS, PL, and XPS techniques. AFM studies showed that the film roughness increases with the repetition rate. Finally, photocatalytic performance of the layers was investigated through measuring decomposition rate of 4-chlorophenol on the films surface. The films grown at higher frequencies revealed higher photocatalytic efficiency. This behavior was mainly related to formation of point defects which enhance the charge separation.

  12. Growth of CdTe films on GaAs by ionized cluster beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tang, H. P.; Feng, J. Y.; Fan, Y. D.; Li, H. D.

    1991-06-01

    Stoichiometric epitaxial films of CdTe were grown on (100)GaAs substrates by ionized cluster beam (ICB) epitaxy. Streaky RHEED patterns indicated good crystallinity and surface flatness of the epitaxial CdTe films. CdTe(100) orientation was obtained when the substrate preheating temperature was 480°C, while CdTe growth inboth (100) and (111) orientations occured when the substrate preheating temperature was above 550°C. The characteristics of the ICB growth process were investigated and the cluster-involving growth behavior has been evidenced. When sufficient clusters were generated in the deposition beam under adequate source vapor pressures, the crystalline quality of the resulting CdTe epilayers improved significantly with the increase of kinetic energy of the CdTe clusters. The best CdTe epilayer obtained exhibited a CdTe(400) double crystal rocking curve (DCRC) having a FWHM of 630 arc sec.

  13. The in-plane anisotropic magnetic damping of ultrathin epitaxial Co2FeAl film

    NASA Astrophysics Data System (ADS)

    Qiao, Shuang; Yan, Wei; Nie, Shuaihua; Zhao, Jianhua; Zhang, Xinhui

    2015-08-01

    The in-plane orientation-dependent effective damping of ultrathin Co2FeAl film epitaxially grown on GaAs(001) substrate by molecular beam epitaxy (MBE) has been investigated by employing the time-resolved magneto-optical Kerr effect (TR-MOKE) measurements. It is found that the interface-induced uniaxial anisotropy is favorable for precession response and the anisotropy of precession frequency is mainly determined by this uniaxial anisotropy, while the magnetic relaxation time and damping factor exhibit the fourfold anisotropy at high-field regime. The field-independent anisotropic damping factor obtained at high fields indicates that the effective damping shows an intrinsic fourfold anisotropy for the epitaxial Co2FeAl thin films.

  14. Epitaxial thin films of the superconducting spinel oxide LiTi2O4

    NASA Astrophysics Data System (ADS)

    Chopdekar, Rajesh; Suzuki, Yuri

    2006-03-01

    Lithium titanate is the only superconducting spinel oxide documented in literature. Related oxide spinels[1] such as the heavy fermion system LiV2O4 and charge-ordered LiMn2O4 indicate that electron correlations are strong in these systems. We have fabricated epitaxial films of LiTi2O4 on MgAl2O4 and MgO single crystalline substrates to explore such behavior in thin film form. Atomic force microscopy indicates <1nm RMS surface roughness, and 2- and 4-circle x-ray diffraction confirms film epitaxy. Films on MgAl2O4 have a critical temperature Tc of up to 11.3K with a resistivity transition width of 0.25K, while films on MgO have lower Tc with broader transitions. Magnetization vs. magnetic field of a zero-field cooled sample shows Meissner shielding consistent with Type II superconductors. Such films can be used in spin-polarization measurements of complex oxide half-metallic thin films, as well as fundamental studies of the effect of epitaxial strain, microstructure, and cation disorder/substitution on the superconducting properties of LiTi2O4. [1] M. Lauer et al, Phys Rev B 69, 075117 (2004).

  15. Magneto-capacitance effects in epitaxial TbMn2O5 thin films

    NASA Astrophysics Data System (ADS)

    Song, Jong Hyun; Kang, Sun Hee; Kim, Ill Won; Jeong, Yoon Hee; Koo, Tae Yeong

    2012-11-01

    Thin films of TbMn2O5 (TMO) were grown on Nb-doped TiO2 (110) substrates by using pulsed laser deposition to investigate the effects of substrate-induced strains on the multiferroic properties observed in the bulk phase. The epitaxial qualities of the films were confirmed by using X-ray azimuthal angle scans of the TMO (201) and the TiO2 (111) reflections. TMO films were magnetically ordered at temperatures below T N ≈ 43 K, consistent with the value observed in the bulk. A maximum negative magneto-capacitance effect of about 10% at 8 T was detected near 16 K, where the dielectric constant changed rapidly with a step-like anomaly. Magnetization-induced ferroelectric phases in the epitaxial thin films appear to become destabilized at temperatures below T N due to substrate-induced tensile strains causing a weakening of the magnetic exchange interactions.

  16. Method for forming single phase, single crystalline 2122 BCSCO superconductor thin films by liquid phase epitaxy

    NASA Technical Reports Server (NTRS)

    Pandey, Raghvendra K. (Inventor); Raina, Kanwal (Inventor); Solayappan, Narayanan (Inventor)

    1994-01-01

    A substantially single phase, single crystalline, highly epitaxial film of Bi.sub.2 CaSr.sub.2 Cu.sub.2 O.sub.8 superconductor which has a T.sub.c (zero resistance) of 83 K is provided on a lattice-matched substrate with no intergrowth. This film is produced by a Liquid Phase Epitaxy method which includes the steps of forming a dilute supercooled molten solution of a single phase superconducting mixture of oxides of Bi, Ca, Sr, and Cu having an atomic ratio of about 2:1:2:2 in a nonreactive flux such as KCl, introducing the substrate, e.g., NdGaO.sub.3, into the molten solution at 850.degree. C., cooling the solution from 850.degree. C. to 830.degree. C. to grow the film and rapidly cooling the substrate to room temperature to maintain the desired single phase, single crystalline film structure.

  17. Epitaxial layers of 2122 BCSCO superconductor thin films having single crystalline structure

    NASA Technical Reports Server (NTRS)

    Pandey, Raghvendra K. (Inventor); Raina, Kanwal K. (Inventor); Solayappan, Narayanan (Inventor)

    1995-01-01

    A substantially single phase, single crystalline, highly epitaxial film of Bi.sub.2 CaSr.sub.2 Cu.sub.2 O.sub.8 superconductor which has a T.sub.c (zero resistance) of 83K is provided on a lattice-matched substrate with no intergrowth. This film is produced by a Liquid Phase Epitaxy method which includes the steps of forming a dilute supercooled molten solution of a single phase superconducting mixture of oxides of Bi, Ca, Sr, and Cu having an atomic ratio of about 2:1:2:2 in a nonreactive flux such as KCl, introducing the substrate, e.g., NdGaO.sub.3, into the molten solution at 850.degree. C., cooling the solution from 850.degree. C. to 830.degree. C. to grow the film and rapidly cooling the substrate to room temperature to maintain the desired single phase, single crystalline film structure.

  18. Epitaxial growth and electronic properties of mixed valence YbAl3 thin films

    NASA Astrophysics Data System (ADS)

    Chatterjee, Shouvik; Sung, Suk Hyun; Baek, David J.; Kourkoutis, Lena F.; Schlom, Darrell G.; Shen, Kyle M.

    2016-07-01

    We report the growth of thin films of the mixed valence compound YbAl3 on MgO using molecular-beam epitaxy. Employing an aluminum buffer layer, epitaxial (001) films can be grown with sub-nm surface roughness. Using x-ray diffraction, in situ low-energy electron diffraction, and aberration-corrected scanning transmission electron microscopy, we establish that the films are ordered in the bulk as well as at the surface. Our films show a coherence temperature of 37 K, comparable to that reported for bulk single crystals. Photoelectron spectroscopy reveals contributions from both f13 and f12 final states establishing that YbAl3 is a mixed valence compound and shows the presence of a Kondo Resonance peak near the Fermi-level.

  19. Formation of Organic Thin Films of Nonlinear Optical Materials by Molecular Layer Epitaxy

    NASA Astrophysics Data System (ADS)

    Burtman, V.; Kopylova, T. N.; Van Der Boom, M.; Gadirov, R. M.; Tel'minov, E. N.; Nikonov, S. Yu.; Nikonova, E. N.

    2016-03-01

    Conditions are described under which films of [(aminophenyl)azo]pyridine are formed by molecular layer epitaxy, and their optical absorption and x-ray photoelectron spectra are investigated. The nonlinear properties of such structures are described with the help of measurements of the intensity of second harmonic generation as a function of the angle of incidence.

  20. Epitaxial growth and stress relaxation of vapor-deposited Fe-Pd magnetic shape memory films

    NASA Astrophysics Data System (ADS)

    Kühnemund, L.; Edler, T.; Kock, I.; Seibt, M.; Mayr, S. G.

    2009-11-01

    To achieve maximum performance in microscale magnetic shape memory actuation devices epitaxial films several hundred nanometers thick are needed. Epitaxial films were grown on hot MgO substrates (500 °C and above) by e-beam evaporation. Structural properties and stress relaxation mechanisms were investigated by high-resolution transmission electron microscopy, in situ substrate curvature measurements and classical molecular dynamics (MD) simulations. The high misfit stress incorporated during Vollmer-Weber growth at the beginning was relaxed by partial or perfect dislocations depending on the substrate temperature. This relaxation allowed the avoidance of a stress-induced breakdown of epitaxy and no thickness limit for epitaxy was found. For substrate temperatures of 690 °C or above, the films grew in the fcc austenite phase. Below this temperature, iron precipitates were formed. MD simulations showed how these precipitates influence the movements of partial dislocations, and can thereby explain the higher stress level observed in the experiments in the initial stage of growth for these films.

  1. Epitaxial Growth of Pure 28Si Thin Films Using Isotopically Purified Ion Beams

    NASA Astrophysics Data System (ADS)

    Tsubouchi, Nobuteru; Chayahara, Akiyoshi; Mokuno, Yoshiaki; Kinomura, Atsushi; Horino, Yuji

    2001-12-01

    Isotopically purified 28Si homoepitaxial films were grown by means of an ion-beam deposition (IBD) method with isotopically mass-selected negative 28Si- ion beams. The surface structural evolution during the film growth and the film structure after the growth were investigated using reflection high-energy electron diffraction (RHEED), cross-sectional transmission electron microscopy (TEM) and transmission electron diffraction (TED). The Si isotopic composition (28Si : 29Si : 30Si = 99.9982 : 0.0016 : 0.0002 at.%) of the resulting Si epitaxial film was determined by secondary-ion-mass spectrometry (SIMS).

  2. Computer simulation of ferroelectric domain structures in epitaxial BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Zhang, J. X.; Li, Y. L.; Choudhury, S.; Chen, L. Q.; Chu, Y. H.; Zavaliche, F.; Cruz, M. P.; Ramesh, R.; Jia, Q. X.

    2008-05-01

    Ferroelectric domain structures of (001)c, (101)c, and (111)c oriented epitaxial BiFeO3 thin films were studied by using the phase-field approach. Long-range elastic and electrostatic interactions were taken into account. The effects of various types of substrate constraint on the domain morphologies were systematically analyzed. It is demonstrated that domain structures of BiFeO3 thin films could be controlled by selecting proper film orientations and substrate constraint. The dependence of the {110}c-type domain wall orientation on substrate constraint for the (001)c oriented BiFeO3 thin film was also discussed.

  3. Optical absorption of Ni2+ and Ni3+ ions in gadolinium gallium garnet epitaxial films

    NASA Astrophysics Data System (ADS)

    Vasileva, N. V.; Gerus, P. A.; Sokolov, V. O.; Plotnichenko, V. G.

    2012-12-01

    Single-crystal Ni-doped gadolinium gallium garnet films were grown for the first time from supercooled Bi2O3-B2O3-based melt solutions by liquid-phase epitaxy. Optical absorption bands due to Ni2+, Ni3+ and Bi3+ ions were observed in those films. Interpretation and tabulation of all absorption bands of nickel ions occupying octahedral and tetrahedral sites in the garnet lattice are presented.

  4. Epitaxial Structure of (001)- and (111)-Oriented Perovskite Ferrate Films Grown by Pulsed-Laser Deposition.

    PubMed

    Chakraverty, Suvankar; Ohtomo, Akira; Okude, Masaki; Ueno, Kazunori; Kawasaki, Masashi

    2010-04-01

    The epitaxial structures of SrFeO(2.5) films grown on SrTiO(3) (001) and (111) substrates by PLD are reported. A layer-by-layer growth mode was achieved in the initial stage on both substrates. The films were stabilized with a monoclinic structure, where we identified the in-plane domain structures and orientation relationship. Our study presents a guide to control the heteroepitaxy of (111)-oriented noncubic perovskites. PMID:20383295

  5. Structural characterization of metastable hcp-Ni thin films epitaxially grown on Au(100) single-crystal underlayers

    SciTech Connect

    Ohtake, Mitsuru; Tanaka, Takahiro; Futamoto, Masaaki; Kirino, Fumiyoshi

    2010-05-15

    Ni(1120) epitaxial thin films with hcp structure were prepared on Au(100) single-crystal underlayers at 100 deg. C by ultra high vacuum molecular beam epitaxy. The detailed film structure is studied by in situ reflection high energy electron diffraction, x-ray diffraction, and transmission electron microscopy. The hcp-Ni film consists of two types of variants whose c-axes are rotated around the film normal by 90 deg. each other. An atomically sharp boundary is recognized between the film and the underlayer, where misfit dislocations are introduced. Presence of such dislocations seems to relieve the strain caused by the lattice mismatch between the film and the underlayer.

  6. Lateral solid-phase epitaxy of oxide thin films on glass substrate seeded with oxide nanosheets.

    PubMed

    Taira, Kenji; Hirose, Yasushi; Nakao, Shoichiro; Yamada, Naoomi; Kogure, Toshihiro; Shibata, Tatsuo; Sasaki, Takayoshi; Hasegawa, Tetsuya

    2014-06-24

    We developed a technique to fabricate oxide thin films with uniaxially controlled crystallographic orientation and lateral size of more than micrometers on amorphous substrates. This technique is lateral solid-phase epitaxy, where epitaxial crystallization of amorphous precursor is seeded with ultrathin oxide nanosheets sparsely (≈10% coverage) deposited on the substrate. Transparent conducting Nb-doped anatase TiO2 thin films were fabricated on glass substrates by this technique. Perfect (001) orientation and large grains with lateral sizes up to 10 μm were confirmed by X-ray diffraction, atomic force microscopy, and electron beam backscattering diffraction measurements. As a consequence of these features, the obtained film exhibited excellent electrical transport properties comparable to those of epitaxial thin films on single-crystalline substrates. This technique is a versatile method for fabricating high-quality oxide thin films other than anatase TiO2 and would increase the possible applications of oxide-based thin film devices. PMID:24867286

  7. Epitaxial growth of (001)-oriented and (110)-oriented SrBi2Ta2O9 thin films

    NASA Astrophysics Data System (ADS)

    Lettieri, J.; Jia, Y.; Urbanik, M.; Weber, C. I.; Maria, J.-P.; Schlom, D. G.; Li, H.; Ramesh, R.; Uecker, R.; Reiche, P.

    1998-11-01

    Epitaxial SrBi2Ta2O9 thin films have been grown with (001) and (110) orientations by pulsed laser deposition on (001) LaAlO3-Sr2AlTaO6 and (100) LaSrAlO4 substrates, respectively. Four-circle x-ray diffraction and transmission electron microscopy reveal nearly phase pure epitaxial films. Minimization of surface mesh mismatch between the film and substrate (i.e., choice of appropriate substrate material and orientation) was used to stabilize the desired orientations and achieve epitaxial growth.

  8. Lutetium-doped EuO films grown by molecular-beam epitaxy

    SciTech Connect

    Melville, A.; Heeg, T.; Mairoser, T.; Schmehl, A.; Shai, D. E.; Monkman, E. J.; Harter, J. W.; Hollaender, B.; Schubert, J.; Shen, K. M.; Mannhart, J.; Schlom, D. G.

    2012-05-28

    The effect of lutetium doping on the structural, electronic, and magnetic properties of epitaxial EuO thin films grown by reactive molecular-beam epitaxy is experimentally investigated. The behavior of Lu-doped EuO is contrasted with doping by lanthanum and gadolinium. All three dopants are found to behave similarly despite differences in electronic configuration and ionic size. Andreev reflection measurements on Lu-doped EuO reveal a spin-polarization of 96% in the conduction band, despite non-magnetic carriers introduced by 5% lutetium doping.

  9. Magnetism and transport properties of epitaxial Fe-Ga thin films on GaAs(001)

    SciTech Connect

    Duong Anh Tuan; Shin, Yooleemi; Cho, Sunglae; Dang Duc Dung; Vo Thanh Son

    2012-04-01

    Epitaxial Fe-Ga thin films in disordered bcc {alpha}-Fe crystal structure (A2) have been grown on GaAs(001) by molecular beam epitaxy. The saturated magnetization (M{sub S}) decreased from 1371 to 1105 kA/m with increasing Ga concentration from 10.5 to 24.3 % at room temperature. The lattice parameter increased with the increase in Ga content because of the larger atomic radius of Ga atom than that of Fe. The increase in carrier density with Ga content caused in lower resistivity.

  10. Epitaxial neodymium-doped sapphire films, a new active medium for waveguide lasers.

    PubMed

    Kumaran, Raveen; Webster, Scott E; Penson, Shawn; Li, Wei; Tiedje, Thomas; Wei, Peng; Schiettekatte, Francois

    2009-11-01

    Epitaxial films of neodymium-doped sapphire have been grown by molecular beam epitaxy on R-, A-, and M-plane sapphire substrates. The emission spectrum features sharp lines consistent with single-site doping of the Nd(3+) ion into the host crystal. This material is believed to be a nonequilibrium phase, inaccessible by conventional high-temperature growth methods. Neodymium-doped sapphire has a promising lasing line at 1096 nm with an emission cross section of 11.9x10(-19) cm(2), similar to the 1064 nm line of Nd:YVO(4). PMID:19881593

  11. Laser induced chemical vapor phase epitaxial growth of III-V semiconductor films

    NASA Astrophysics Data System (ADS)

    Chu, Shirley S.; Chu, Ting L.

    1991-05-01

    The objective of this project is to investigate the homo- and hetero-epitaxial growth of device quality III-V semiconductor films by the free electron laser (FEL) induced growth at lower temperatures. An ArF excimer laser was used in this investigation. Metalorganic vapor phase epitaxy (MOVPE) is the commonly used technique in the growth of III-V compounds and alloys. The major concern to the use of MOVPE is the hazard involved in using highly toxic arsine and phosphine gases as the group V source materials. Efforts during this period have been focused to the homoepitaxial growth of GaAs and heteroepitaxial growth of InP on GaAs using alternate sources to eliminate the use of arsine and phosphine. Good quality epitaxial GaAs films have been prepared from elemental arsenic for the first time by either conventional substrate heating or laser enhanced processes. The epitaxial GaAs films grown from elemental arsenic are suitable for many GaAs based devices, particularly for large area devices such as solar cells. Significant cost reduction and less stringent safety requirements are major advantages.

  12. Composition measurement of epitaxial Sc x Ga1‑x N films

    NASA Astrophysics Data System (ADS)

    Tsui, H. C. L.; Goff, L. E.; Barradas, N. P.; Alves, E.; Pereira, S.; Palgrave, R. G.; Davies, R. J.; Beere, H. E.; Farrer, I.; Ritchie, D. A.; Moram, M. A.

    2016-06-01

    Four different methods for measuring the compositions of epitaxial Sc x Ga1‑x N films were assessed and compared to determine which was the most reliable and accurate. The compositions of epitaxial Sc x Ga1‑x N films with 0 ≤ x ≤ 0.26 were measured directly using Rutherford backscattering (RBS) and x-ray photoelectron spectroscopy (XPS), and indirectly using c lattice parameter measurements from x-ray diffraction and c/a ratio measurements from electron diffraction patterns. RBS measurements were taken as a standard reference. XPS was found to underestimate the Sc content, whereas c lattice parameter and c/a ratio were not reliable for composition determination due to the unknown degree of strain relaxation in the film. However, the Sc flux used during growth was found to relate linearly with x and could be used to estimate the Sc content.

  13. Field-effect modulation of anomalous Hall effect in diluted ferromagnetic topological insulator epitaxial films

    NASA Astrophysics Data System (ADS)

    Chang, CuiZu; Liu, MinHao; Zhang, ZuoCheng; Wang, YaYu; He, Ke; Xue, QiKun

    2016-03-01

    High quality chromium (Cr) doped three-dimensional topological insulator (TI) Sb2Te3 films are grown via molecular beam epitaxy on heat-treated insulating SrTiO3 (111) substrates. We report that the Dirac surface states are insensitive to Cr doping, and a perfect robust long-range ferromagnetic order is unveiled in epitaxial Sb2- x Cr x Te3 films. The anomalous Hall effect is modulated by applying a bottom gate, contrary to the ferromagnetism in conventional diluted magnetic semiconductors (DMSs), here the coercivity field is not significantly changed with decreasing carrier density. Carrier-independent ferromagnetism heralds Sb2- x Cr x Te3 films as the base candidate TI material to realize the quantum anomalous Hall (QAH) effect. These results also indicate the potential of controlling anomalous Hall voltage in future TI-based magneto-electronics and spintronics.

  14. Tunable band gap in epitaxial ferroelectric Ho(Mn,Ga)O3 films

    NASA Astrophysics Data System (ADS)

    Lee, Daesu; Choi, Woo Seok; Noh, Tae Won

    2016-05-01

    Ferroelectrics have recently attracted attention as a new class of materials for use in optical and photovoltaic devices. We studied the electronic properties in epitaxially stabilized ferroelectric hexagonal Ho(Mn1-xGax)O3 (x = 0, 0.33, 0.67, and 1) thin films. Our films exhibited systematic changes in electronic structures, such as bandgap and optical transitions, according to the Ga concentration. In particular, the bandgap increased systematically from 1.4 to 3.2 eV, including the visible light region, with increasing Ga concentration from x = 0 to 1. These systematic changes, attributed to lattice parameter variations in epitaxial Ho(Mn1-xGax)O3 films, should prove useful for the design of optoelectronic devices based on ferroelectrics.

  15. Red photoluminescence in praseodymium-doped titanate perovskite films epitaxially grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Takashima, Hiroshi; Ueda, Kazushige; Itoh, Mitsuru

    2006-12-01

    Intense red photoluminescence (PL) under ultraviolet (UV) excitation was observed in epitaxially grown Pr-doped Ca0.6Sr0.4TiO3 perovskite films. The films were grown on SrTiO3 (100) substrates by pulsed laser deposition, and their epitaxial growth was confirmed by x-ray diffraction and reflected high-energy electron diffraction. The observed sharp PL peak centered at 610nm was assigned to the transition of Pr3+ ions from the D21 state to the H43 state. The PL intensity was markedly enhanced by postannealing treatments at 1000°C, above the film-growth temperature of 600 or 800°C. Because the excitation and absorption spectra are similar to each other, it was suggested that the UV energy absorbed by the host lattice was transferred to the Pr ions, resulting in the red luminescence.

  16. Epitaxially stabilized iron thin films via effective strain relief from steps

    NASA Astrophysics Data System (ADS)

    Miyamachi, T.; Nakashima, S.; Kim, S.; Kawamura, N.; Tatetsu, Y.; Gohda, Y.; Tsuneyuki, S.; Komori, F.

    2016-07-01

    The growth and electronic structures of about 7 monolayer-thick Fe thin films on a vicinal Cu(001) surface have been investigated by scanning tunneling microscopy. We find from atomically resolved observations that the Fe epitaxial fcc(001) lattice is stabilized near the step edges, while several kinds of reconstructed surfaces exist on the regions relatively far from the step edges. Statistical analyses of the surface lattices reveal the importance of high-density Cu steps serving as strain relievers to preserve epitaxially stabilized Fe fcc(001) lattice against transforming bulk stable bcc(110) lattice. Spectroscopic measurements further clarify the intrinsic electronic structures of the fcc Fe thin film in real space, implying the electronic differences between the topmost layers in 6 and 7 monolayer-thick films induced by the expansion of the lateral lattice constant.

  17. Epitaxial growth and characterization of CaVO3 thin films

    SciTech Connect

    Liberati, Marco; Chopdekar, R.V.; Mehta, V.; Arenholz, E.; Suzuki, Y.

    2009-01-09

    Epitaxial thin films of CaVO{sub 3} were synthesized on SrTiO{sub 3}, LaAlO{sub 3} and (La{sub 0.27}Sr{sub 0.73})(Al{sub 0.65}Ta{sub 0.35})O{sub 3} substrates by pulsed laser deposition. All CaVO{sub 3} films, independent of epitaxial strain, exhibit metallic and Pauli paramagnetic behavior as CaVO{sub 3} single crystals. X-ray absorption measurements confirmed the 4+ valence state for Vanadium ions. With prolonged air exposure, an increasing amount of V{sup 3+} is detected and is attributed to oxygen loss in the near surface region of the films.

  18. Soft-chemistry-based routes to epitaxial α-quartz thin films with tunable textures.

    PubMed

    Carretero-Genevrier, A; Gich, M; Picas, L; Gazquez, J; Drisko, G L; Boissiere, C; Grosso, D; Rodriguez-Carvajal, J; Sanchez, C

    2013-05-17

    Piezoelectric nanostructured quartz films of high resonance frequencies are needed for microelectronic devices; however, synthesis methods have been frustrated by the inhomogeneous crystal growth, crystal twinning, and loss of nanofeatures upon crystallization. We report the epitaxial growth of nanostructured polycrystalline quartz films on silicon [Si(100)] substrates via the solution deposition and gelation of amorphous silica thin films, followed by thermal treatment. Key to the process is the combined use of either a strontium (Sr(2+)) or barium (Ba(2+)) catalyst with an amphiphilic molecular template. The silica nanostructure constructed by cooperative self-assembly permits homogeneous distribution of the cations, which are responsible for the crystallization of quartz. The low mismatch between the silicon and α-quartz cell parameters selects this particular polymorph, inducing epitaxial growth. PMID:23687040

  19. Epitaxial niobium dioxide thin films by reactive-biased target ion beam deposition

    SciTech Connect

    Wang, Yuhan Kittiwatanakul, Salinporn; Lu, Jiwei; Comes, Ryan B.; Wolf, Stuart A.

    2015-03-15

    Epitaxial NbO{sub 2} thin films were synthesized on Al{sub 2}O{sub 3} (0001) substrates via reactive bias target ion beam deposition. X-ray diffraction and Raman spectra were used to confirm the tetragonal phase of pure NbO{sub 2}. Through XPS, it was found that there was a ∼1.3 nm thick Nb{sub 2}O{sub 5} layer on the surface and the bulk of the thin film was NbO{sub 2}. The epitaxial relationship between the NbO{sub 2} film and the substrate was determined. Electrical transport measurement was measured up to 400 K, and the conduction mechanism was discussed.

  20. Role of thermal processes in dewetting of epitaxial Ag(111) film on Si(111)

    SciTech Connect

    Sanders, Charlotte E.; Zhang, Chendong D.; Kellogg, Gary L.; Shih, Chih-Kang

    2014-08-01

    Epitaxially grown silver (Ag) film on silicon (Si) is an optimal plasmonic device platform, but its technological utility has been limited by its tendency to dewet rapidly under ambient conditions (standard temperature and pressure). The mechanisms driving this dewetting have not heretofore been determined. In our study, scanning probe microscopy and low-energy electron microscopy are used to compare the morphological evolution of epitaxial Ag(111)/Si(111) under ambient conditions with that of similarly prepared films heated under ultra-high vacuum (UHV) conditions. Furthermore, dewetting is seen to be initiated with the formation of pinholes, which might function to relieve strain in the film. We find that in the UHV environment, dewetting is determined by thermal processes, and while under ambient conditions, thermal processes are not required. Finally, we conclude that dewetting in ambient conditions is triggered by some chemical process, most likely oxidation.

  1. Phase-Controlled Electrochemical Activity of Epitaxial Mg-Spinel Thin Films.

    PubMed

    Feng, Zhenxing; Chen, Xiao; Qiao, Liang; Lipson, Albert L; Fister, Timothy T; Zeng, Li; Kim, Chunjoong; Yi, Tanghong; Sa, Niya; Proffit, Danielle L; Burrell, Anthony K; Cabana, Jordi; Ingram, Brian J; Biegalski, Michael D; Bedzyk, Michael J; Fenter, Paul

    2015-12-30

    We report an approach to control the reversible electrochemical activity (i.e., extraction/insertion) of Mg(2+) in a cathode host through the use of phase-pure epitaxially stabilized thin film structures. The epitaxially stabilized MgMn2O4 (MMO) thin films in the distinct tetragonal and cubic phases are shown to exhibit dramatically different properties (in a nonaqueous electrolyte, Mg(TFSI)2 in propylene carbonate): tetragonal MMO shows negligible activity while the cubic MMO (normally found as polymorph at high temperature or high pressure) exhibits reversible Mg(2+) activity with associated changes in film structure and Mn oxidation state. These results demonstrate a novel strategy for identifying the factors that control multivalent cation mobility in next-generation battery materials. PMID:26641524

  2. Role of thermal processes in dewetting of epitaxial Ag(111) film on Si(111)

    NASA Astrophysics Data System (ADS)

    Sanders, Charlotte E.; Zhang, Chendong; Kellogg, Gary L.; Shih, Chih-Kang

    2014-12-01

    Epitaxially grown silver (Ag) film on silicon (Si) is an optimal plasmonic device platform, but its technological utility has been limited by its tendency to dewet rapidly under ambient conditions (standard temperature and pressure). The mechanisms driving this dewetting have not heretofore been determined. In this study, scanning probe microscopy and low-energy electron microscopy are used to compare the morphological evolution of epitaxial Ag(111)/Si(111) under ambient conditions with that of similarly prepared films heated under ultra-high vacuum (UHV) conditions. Dewetting in both cases is seen to be initiated with the formation of pinholes, which might function to relieve strain in the film. We find that in the UHV environment, dewetting is determined by thermal processes, while under ambient conditions, thermal processes are not required. We conclude that dewetting in ambient conditions is triggered by some chemical process, most likely oxidation.

  3. Thermal generation of spin current in epitaxial CoFe2O4 thin films

    DOE PAGESBeta

    Guo, Er -Jia; Herklotz, Andreas; Kehlberger, Andreas; Cramer, Joel; Jakob, Gerhard; Klaeui, Mathias

    2016-01-12

    The longitudinal spin Seebeck effect (LSSE) has been investigated in high-quality epitaxial CoFe2O4 (CFO) thin films. The thermally excited spin currents in the CFO films are electrically detected in adjacent Pt layers due to the inverse spin Hall effect (ISHE). The LSSE signal exhibits a linear increase with increasing temperature gradient, yielding a LSSE coefficient of –100 nV/K at room temperature. The temperature dependence of the LSSE is investigated from room temperature down to 30 K, showing a significant reduction at low temperatures, revealing that the total amount of thermally generated magnons decreases. Moreover, we demonstrate that the spin Seebeckmore » effect is an effective tool to study the magnetic anisotropy induced by epitaxial strain, especially in ultrathin films with low magnetic moments.« less

  4. Process for growing a film epitaxially upon an oxide surface and structures formed with the process

    DOEpatents

    McKee, Rodney Allen; Walker, Frederick Joseph

    1998-01-01

    A process and structure wherein a film comprised of a perovskite or a spinel is built epitaxially upon a surface, such as an alkaline earth oxide surface, involves the epitaxial build up of alternating constituent metal oxide planes of the perovskite or spinel. The first layer of metal oxide built upon the surface includes a metal element which provides a small cation in the crystalline structure of the perovskite or spinel, and the second layer of metal oxide built upon the surface includes a metal element which provides a large cation in the crystalline structure of the perovskite or spinel. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

  5. Process for growing a film epitaxially upon an oxide surface and structures formed with the process

    DOEpatents

    McKee, Rodney A.; Walker, Frederick J.

    1995-01-01

    A process and structure wherein a film comprised of a perovskite or a spinel is built epitaxially upon a surface, such as an alkaline earth oxide surface, involves the epitaxial build up of alternating constituent metal oxide planes of the perovskite or spinel. The first layer of metal oxide built upon the surface includes a metal element which provides a small cation in the crystalline structure of the perovskite or spinel, and the second layer of metal oxide built upon the surface includes a metal element which provides a large cation in the crystalline structure of the perovskite or spinel. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

  6. Role of thermal processes in dewetting of epitaxial Ag(111) film on Si(111)

    DOE PAGESBeta

    Sanders, Charlotte E.; Zhang, Chendong D.; Kellogg, Gary L.; Shih, Chih-Kang

    2014-08-01

    Epitaxially grown silver (Ag) film on silicon (Si) is an optimal plasmonic device platform, but its technological utility has been limited by its tendency to dewet rapidly under ambient conditions (standard temperature and pressure). The mechanisms driving this dewetting have not heretofore been determined. In our study, scanning probe microscopy and low-energy electron microscopy are used to compare the morphological evolution of epitaxial Ag(111)/Si(111) under ambient conditions with that of similarly prepared films heated under ultra-high vacuum (UHV) conditions. Furthermore, dewetting is seen to be initiated with the formation of pinholes, which might function to relieve strain in the film.more » We find that in the UHV environment, dewetting is determined by thermal processes, and while under ambient conditions, thermal processes are not required. Finally, we conclude that dewetting in ambient conditions is triggered by some chemical process, most likely oxidation.« less

  7. Epitaxially-Grown Europium-Doped Barium Titanate Films on Various Substrates for Red Emission.

    PubMed

    Hwang, Kyu-Seog; Jeon, Young-Sun; Lee, Young-Hwan; Hwangbo, Seung; Kim, Jin-Tae

    2015-10-01

    Intense red photoluminescence under ultraviolet excitation was observed in epitaxially-grown europium-doped perovskite BaTiO3 thin films deposited on the SrTiO3 (100), MgO (100) and sapphire (0001) substrates using metal carboxylate complexes. Precursor films prepared by spin coating were pyrolyzed at 250 °C for 120 min in argon, followed by final annealing at 850 °C for 60 min in argon. Crystallinity and epitaxy of the films were analyzed by X-ray diffraction θ-2θ scan and pole-figure analysis. Photoluminescence of the thin films at room temperature under 254 nm was confirmed by a fluorescent spectrophotometer. The obtained epitaxial BaTiO3 thin films on the SrTiO3 (100) and MgO (100) substrates show an intense red-emission lines at 615 nm corresponding to the (5)D0 --> (7)F2 transitions on Eu(3+) with broad bands at 595 and 650 nm. PMID:26726427

  8. Preparation of Macroporous Epitaxial Quartz Films on Silicon by Chemical Solution Deposition.

    PubMed

    Carretero-Genevrier, Adrián; Gich, Martí

    2015-01-01

    This work describes the detailed protocol for preparing piezoelectric macroporous epitaxial quartz films on silicon(100) substrates. This is a three-step process based on the preparation of a sol in a one-pot synthesis which is followed by the deposition of a gel film on Si(100) substrates by evaporation induced self-assembly using the dip-coating technique and ends with a thermal treatment of the material to induce the gel crystallization and the growth of the quartz film. The formation of a silica gel is based on the reaction of a tetraethyl orthosilicate and water, catalyzed by HCl, in ethanol. However, the solution contains two additional components that are essential for preparing mesoporous epitaxial quartz films from these silica gels dip-coated on Si. Alkaline earth ions, like Sr(2+) act as glass melting agents that facilitate the crystallization of silica and in combination with cetyl trimethylammonium bromide (CTAB) amphiphilic template form a phase separation responsible of the macroporosity of the films. The good matching between the quartz and silicon cell parameters is also essential in the stabilization of quartz over other SiO2 polymorphs and is at the origin of the epitaxial growth. PMID:26710210

  9. Large refractive index in BiFeO3-BiCoO3 epitaxial films

    NASA Astrophysics Data System (ADS)

    Shima, Hiromi; Nishida, Ken; Yamamoto, Takashi; Tadokoro, Toshiyasu; Tsutsumi, Koichi; Suzuki, Michio; Naganuma, Hiroshi

    2013-05-01

    Rhombohedral (R-) and tetragonal (T-) Bi(Fe,Co)O3 (BFCO) films were epitaxially grown on the SrTiO3 (100) substrates, and the optical properties of the BFCO films were evaluated by spectroscopic ellipsometry. It was revealed that the refractive indexes of R- and T-BFCO epitaxial films were 2.93 and 2.86 at wavelength of 600 nm, and 2.65 and 2.59 at 1550 nm, respectively, which are comparable to the pure BiFeO3. The refractive index of the R-BFCO film was totally larger than that of the T-BFCO film; it might be caused by structural strain and local symmetry breaking. It was confirmed that the extinction coefficients of both films were almost zero at wavelengths larger than 600 nm. In addition, the optical band gaps of the R- and T-BFCO films were estimated to be 2.78 and 2.75 eV, respectively. It can expect that the BFCO film has a possibility to use optical-magnetic field sensor working at room temperature.

  10. Epitaxial growth of high quality WO{sub 3} thin films

    SciTech Connect

    Leng, X.; Pereiro, J.; Bollinger, A. T.; Strle, J.; Božović, I.

    2015-09-01

    We have grown epitaxial WO{sub 3} films on various single-crystal substrates using radio frequency magnetron sputtering. While pronounced surface roughness is observed in films grown on LaSrAlO{sub 4} substrates, films grown on Y AlO{sub 3} substrates show atomically flat surfaces, as demonstrated by atomic force microscopy and X-ray diffraction (XRD) measurements. The crystalline structure has been confirmed to be monoclinic by symmetric and skew-symmetric XRD. The dependence of the growth modes and the surface morphology on the lattice mismatch are discussed.

  11. Evidence of enhanced electron-phonon coupling in ultrathin epitaxial copper films

    SciTech Connect

    Timalsina, Yukta P. Shen, Xiaohan; Boruchowitz, Grant; Fu, Zhengping; Qian, Guoguang; Yamaguchi, Masashi; Wang, Gwo-Ching; Lewis, Kim M.; Lu, Toh-Ming

    2013-11-04

    Electron phonon (el-ph) coupling is a fundamental quantity that controls the electron transport through a conductor. We experimentally determined the el-ph coupling strength of epitaxial copper (Cu) films ranging from 5 to 1000 nm thick using both ultra-fast, optical pump-probe reflectivity and temperature-dependent resistivity measurements. An enhancement of the el-ph coupling strength was observed when the thickness of the films was reduced to below 50 nm. We suggest that this unexpected enhancement of the el-ph coupling strength is partially responsible for the observed increase of resistivity in the films below 50 nm thick.

  12. Strain effect on coercive field of epitaxial barium titanate thin films

    NASA Astrophysics Data System (ADS)

    Choudhury, S.; Li, Y. L.; Chen, L. Q.; Jia, Q. X.

    2008-04-01

    Strain is generally known to increase the coercive field of a ferroelectric thin film as compared to a stress-free single crystal or a strain-relaxed film. We studied the coercive fields and remanent polarizations of (001)-oriented epitaxial barium titanate thin films using the phase-field approach. It is demonstrated, while the remanent polarization decreases as in-plane strain changes from being compressive to tensile, the variation of coercive field with strain is complicated. We noted more than two times drop in coercive field with a reduction of compressive strain of only ˜0.05%, which we attribute to the existence of multiple ferroelectric phases.

  13. Phase-field model for epitaxial ferroelectric and magnetic nanocomposite thin films

    NASA Astrophysics Data System (ADS)

    Zhang, J. X.; Li, Y. L.; Schlom, D. G.; Chen, L. Q.; Zavaliche, F.; Ramesh, R.; Jia, Q. X.

    2007-01-01

    A phase-field model was developed for studying the magnetoelectric coupling effect in epitaxial ferroelectric and magnetic nanocomposite thin films. The model can simultaneously take into account the ferroelectric and magnetic domain structures, the electrostrictive and magnetostrictive effects, substrate constraint, as well as the long-range interactions such as magnetic, electric, and elastic interactions. As an example, the magnetic-field-induced electric polarization in BaTiO3-CoFe2O4 nanocomposite film was analyzed. The effects of the film thickness, morphology of the nanocomposite, and substrate constraint on the degree of magnetoelectric coupling were discussed.

  14. Epitaxial growth of high quality WO3 thin films

    SciTech Connect

    Leng, X.; Pereiro, J.; Strle, J.; Bollinger, A. T.; Bozovic, I.

    2015-09-09

    We have grown epitaxial WO3 films on various single-crystal substrates using radio-frequency (RF) magnetron sputtering. While pronounced surface roughness is observed in films grown on LaSrAlO4 substrates, films grown on YAlO3 substrates show atomically flat surfaces, as demonstrated by atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements. The crystalline structure has been confirmed to be monoclinic by symmetric and skew-symmetric XRD. Furthermore, the dependence of the growth modes and the surface morphology on the lattice mismatch is discussed.

  15. Amorphization and recrystallization of epitaxial ReSi2 films grown on Si(100)

    NASA Technical Reports Server (NTRS)

    Kim, Kun HO; Bai, G.; Nicolet, MARC-A.; Mahan, John E.; Geib, Kent M.

    1991-01-01

    The effects of implantation damage and the chemical species of the implant on structural and electrical properties of epitaxial ReSi2 films on Si(100) implanted with Si-28 or Ar-40 ions, at doses ranging from 10 to the 13th/sq cm to 10 to the 15th/sq cm, were investigated using the backscattering spectrometry, XRD, and the van der Pauw techniques. Results showed that ion implantation produces damage in the film, which increases monotonically with dose; the resistivity of the film decreases monotonically with dose.

  16. Realizing Half Metallicity in Sr2FeMoO6 Epitaxial Films: Roadblocks and Successes

    NASA Astrophysics Data System (ADS)

    Yang, Fengyuan

    2010-03-01

    Half-metallic Sr2FeMoO6 has attracted much attention due to its high Tc of 420 K for magnetoelectronic applications. However, the potential of its half metallicity is far from being realized due to the unusual challenges in the fabrication of Sr2FeMoO6 films. In this talk, I will discuss a number of hurdles that troubled the deposition of Sr2FeMoO6 films, some of which have been largely ignored to date. We have succeeded in overcoming some of the dominant problems in the epitaxial film growth and obtained phase-pure, fully epitaxial, and stoichiometric Sr2FeMoO6 films on SrTiO3 with high structural and magnetic ordering using off-axis ultrahigh vacuum sputtering. First, by precisely controlling the growth environment, we achieved pure double perovskite phase and complete epitaxy in Sr2FeMoO6 films without any detectable secondary phases (such as SrMoO4) as confirmed by Bragg-Brentano and triple-axis X-ray diffraction (XRD) and aberration-corrected TEM. Secondly, we discovered using Rutherford backscattering (RBS) that the films have much more Mo than Fe under typical growth conditions (high sputter pressure) for complex oxides. The optimal pressure for obtaining stoichiometric films is around 10 mTorr at certain off-axis geometry. Next, we focused on improving the Fe/Mo ordering by tuning growth rate, substrate temperature and sputtering pressure. To date, the highest Fe/Mo ordering parameter we have is around 90% obtained by Rietveld refinements on epitaxial Sr2FeMoO6 (111) films with ordered double perovskite XRD peaks. More importantly, the Sr2FeMoO6 films exhibit strong magnetic shape anisotropy, i.e. the in-plane hysteresis loops are fairly square and the out-of-plane loops are perfectly slanted lines with a saturation filed of ˜3800 Oe. The clear shape anisotropy, which has never been seen before in Sr2FeMoO6 films, indicates strong magnetic coupling across the films. We are pursuing further improvement of the Sr2FeMoO6 film quality and incorporating it into

  17. Vibrational properties of epitaxial Bi4Te3 films as studied by Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Hao; Song, Yuxin; Pan, Wenwu; Chen, Qimiao; Wu, Xiaoyan; Lu, Pengfei; Gong, Qian; Wang, Shumin

    2015-08-01

    Bi4Te3, as one of the phases of the binary Bi-Te system, shares many similarities with Bi2Te3, which is known as a topological insulator and thermoelectric material. We report the micro-Raman spectroscopy study of 50 nm Bi4Te3 films on Si substrates prepared by molecular beam epitaxy. Raman spectra of Bi4Te3 films completely resolve the six predicted Raman-active phonon modes for the first time. Structural features and Raman tensors of Bi4Te3 films are introduced. According to the wavenumbers and assignments of the six eigenpeaks in the Raman spectra of Bi4Te3 films, it is found that the Raman-active phonon oscillations in Bi4Te3 films exhibit the vibrational properties of those in both Bi and Bi2Te3 films.

  18. Defect Characterization in Ge/(001)Si Epitaxial Films Grown by Reduced-Pressure Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Bharathan, Jayesh; Narayan, Jagdish; Rozgonyi, George; Bulman, Gary E.

    2013-10-01

    We studied the microstructural characteristics and electrical properties of epitaxial Ge films grown on Si(001) substrates by x-ray diffraction, atomic force microscopy, and transmission electron microscopy. The films were grown using a two-step technique by reduced-pressure chemical vapor deposition, where the first step promotes two-dimensional growth at a lower substrate temperature. We observed a decrease in defect density with increasing film thickness. Ge films with thickness of 3.5 μm exhibited threading dislocation densities of 5 × 106 cm-2, which yielded devices with dark current density of 5 mA cm-2 (1 V reverse bias). We also noted the presence of stacking faults in the form of lines in the films and establish that this is an important defect for Ge films grown by this deposition technique.

  19. Morphological instability in epitaxially strained dislocation-free solid films - Linear stability theory

    NASA Technical Reports Server (NTRS)

    Spencer, B. J.; Voorhees, P. W.; Davis, S. H.

    1993-01-01

    The morphological instability of a growing epitaxially strained dislocation-free solid film is analyzed. An evolution equation for the film surface is derived in the dilute limit of vacancies based on surface diffusion driven by a stress-dependent chemical potential. From the time-dependent linear stability problem the conditions for which a growing film is unstable are determined. It is found that the instability is driven by the lattice mismatch between the film and the substrate; however, low temperatures as well as elastically stiff substrates are stabilizing influences. The results also reveal that the critical film thickness for instability depends on the growth rate of the film itself. Detailed comparison with experimental observations indicates that the instability described exhibits many of the observed features of the onset of the 'island instability'.

  20. Growth and properties of amorphous silicon films grown using pulsed-flow reactive plasma beam epitaxy

    NASA Technical Reports Server (NTRS)

    Dalal, Vikram L.; Knox, Ralph; Kandalaft, Nabeeh; Baldwin, Greg

    1991-01-01

    The growth and properties of a-Si:H films grown using a novel deposition technique, reactive plasma beam epitaxy, are discussed. In this technique, a remote H plasma produced in a microwave-ECR reactor is used to grow a-Si:H films at low pressures. The H ions react with SiH4 introduced near the substrate to produce the film. The flow of SiH4 is pulsed on or off, thereby achieving in-situ annealing of the film during growth by H ions and radicals. The films produced by this technique appear to have good electronic quality, and are more stable than the standard glow discharge films.

  1. Strain Induced Magnetism in SrRuO3 Epitaxial Thin Films

    SciTech Connect

    Grutter, A.; Wong, F.; Arenholz, E.; Liberati, M.; Suzuki, Y.

    2010-01-10

    Epitaxial SrRuO{sub 3} thin films were grown on SrTiO{sub 3}, (LaAlO{sub 3}){sub 0.3}(SrAlO{sub 3}){sub 0.7} and LaAlO{sub 3} substrates inducing different biaxial compressive strains. Coherently strained SrRuO{sub 3} films exhibit enhanced magnetization compared to previously reported bulk and thin film values of 1.1-1.6 {micro}{sub B} per formula unit. A comparison of (001) and (110) SrRuO{sub 3} films on each substrate indicates that films on (110) oriented have consistently higher saturated moments than corresponding (001) films. These observations indicate the importance of lattice distortions in controlling the magnetic ground state in this transitional metal oxide.

  2. Strain effect on ferroelectric polarization of epitaxial LuFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Ahn, Yoonho; Jang, Joonkyung; Son, Jong Yeog

    2016-05-01

    Epitaxial LuFeO3(LFO) thin films were deposited on La0.5Sr0.5MnO3(LSMO)/LaAlO3(LAO) substrates by pulsed laser deposition method. The LFO thin film with a thickness of 100 nm exhibited tetragonally strained structure on the LSMO/LAO substrate, in which the film showed c/ a ratio of 1.045 based on X-ray diffraction experiment. The LFO thin film had a remnant polarization of about 15.2 μC/cm2, which was higher than the previously reported values. By using piezoresponse force microscopy study, it was confirmed that the LFO thin films had mosaic ferroelectric domain structure and that their domain wall energy was estimated to be lower than that of PbTiO3 thin films.

  3. Physical vapour deposition growth and transmission electron microscopy characterization of epitaxial thin metal films on single-crystal Si and Ge substrates

    NASA Astrophysics Data System (ADS)

    Westmacott, K. H.; Hinderberger, S.; Dahmen, U.

    2001-06-01

    Epitaxial fcc, bcc and hcp metal and alloy films were grown in high vacuum by physical vapour deposition at high rate ('flash' deposition) on the (111), (110) and (100) surfaces of Si and Ge at different deposition temperatures. The resulting epitaxial relationships and morphological features of these films were characterized by transmission electron microscopy and diffraction. Simple epitaxial relationships were found mainly for the fcc metals that form binary eutectic systems with Si and G e. Of these, Ag exhibited exceptional behaviour by forming in a single crystal cube-cube relationship on all six semiconductor surfaces. Al and Au both formed bicrystal films on (100) substrates but differed in their behaviours on (111) substrates. Silicide formers such as the fcc metals Cu and Ni, as well as all bcc and hcp metals investigated, did not adopt epitaxial relationships on most semiconductor substrates. However, epitaxial single-crystal, bicrystal and tricrystal films of several metals and alloys could be grown by using a Ag buffer layer. The factors controlling the epitaxial growth of metal films are discussed in the light of the observations and compared with the predictions of established models for epitaxial relationships. It is concluded that epitaxial films can be grown easily if the film forms a simple eutectic or monotectic system with the substrate. The epitaxial relationships of those films depend on crystallographic factors for metal-metal epitaxy and on the substrate surface structure for metal-semiconductor epitaxy.

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

    SciTech Connect

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

    2014-01-01

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

  5. Low-temperature plasma-deposited silicon epitaxial films: Growth and properties

    DOE PAGESBeta

    Demaurex, Bénédicte; Bartlome, Richard; Seif, Johannes P.; Geissbühler, Jonas; Alexander, Duncan T. L.; Jeangros, Quentin; Ballif, Christophe; De Wolf, Stefaan

    2014-08-05

    Low-temperature (≤ 180 °C) epitaxial growth yields precise thickness, doping, and thermal-budget control, which enables advanced-design semiconductor devices. In this paper, we use plasma-ehanced chemical vapor deposition to grow homo-epitaxial layers and study the different growth modes on crystalline silicon substrates. In particular, we determine the conditions leading to epitaxial growth in light of a model that depends only on the silane concentration in the plasma and the mean free path length of surface adatoms. For such growth, we show that the presence of a persistent defective interface layer between the crystalline silicon substrate and the epitaxial layer stems notmore » only from the growth conditions but also from unintentional contamination of the reactor. As a result of our findings, we determine the plasma conditions to grow high-quality bulk epitaxial films and propose a two-step growth process to obtain device-grade material.« less

  6. Single-Nucleus Polycrystallization in Thin Film Epitaxial Growth

    SciTech Connect

    Sadowski, J. T.; Nishikata, S.; Al-Mahboob, A.; Fujikawa, Y.; Nakajima, K.; Sakurai, T.; Sazaki, G.; Tromp, R. M.

    2007-01-26

    We have observed, by use of low-energy electron microscopy, the first direct evidence of self-driven polycrystallization evolved from a single nucleus in the case of epitaxial pentacene growth on the Si(111)-H terminated surface. In this Letter we demonstrate that such polycrystallization can develop in anisotropic systems (in terms of crystal structure and/or the intermolecular interactions) when kinetic growth conditions force the alignment of the intrinsic preferential growth directions along the density gradient of diffusing molecules. This finding gives new insight into the crystallization of complex molecular systems, elucidating the importance of nanoscale control of the growth conditions.

  7. Synthesis of LiCoO2 epitaxial thin films using a sol-gel method

    NASA Astrophysics Data System (ADS)

    Kwon, Taeri; Ohnishi, Tsuyoshi; Mitsuishi, Kazutaka; Ozawa, Tadashi C.; Takada, Kazunori

    2015-01-01

    Epitaxial LiCoO2 films are synthesized using a sol-gel method. The precursors are aqueous solutions of acetates or nitrates of Li and Co with polyvinylpyrrolidone as a thickener. The LiCoO2 films prepared from the solutions by spin coating are epitaxially grown on sapphire (0001) substrates with c-axis orientation and in-plane alignment of LiCoO2 [ 1 1 bar 0 ] ‖sapphire [100]. A two-step heat treatment of the spin-coated films consisting of preheating on a hotplate at the crystallization temperature followed by a high-temperature treatment notably promotes the c-axis orientation. In addition, the crystal orientation is controllable on different planes of the SrTiO3 substrates; the LiCoO2 films are grown with epitaxial relationships of LiCoO2 (001)‖SrTiO3 (111), LiCoO2 (018)‖SrTiO3 (110), and LiCoO2 (104)‖SrTiO3 (100).

  8. Thermal stability of MBE-grown epitaxial MoSe2 and WSe2 thin films

    NASA Astrophysics Data System (ADS)

    Chang, Young Jun; Choy, Byoung Ki; Phark, Soo-Hyon; Kim, Minu

    Layered transition metal dichalcogenides (TMDs) draw much attention, because of its unique optical properties and band structures depending on the layer thicknesses. However, MBE growth of epitaxial films demands information about thermal stability of stoichiometry and related electronic structure for high temperature range. We grow epitaxial MoSe2 and WSe2 ultrathin films by using molecular beam epitaxy (MBE). We characterize stoichiometry of films grown at various growth temperature by using various methods, XPS, EDX, and TOF-MEIS. We further test high temperature stability of electronic structure for those films by utilizing in-situ ellipsometry attached to UHV chamber. We discuss threshold temperatures up to 700~1000oC, at which electronic phases changes from semiconductor to metal due to selenium deficiency. This information can be useful for potential application of TMDs for fabrication of Van der Waals multilayers and related devices. This research was supported by Nano.Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning. (2009-0082580), NRF-2014R1A1A1002868.

  9. Crack healing during molecular-beam-epitaxy growth of GaP/GaAs thin films

    SciTech Connect

    Li, Y.; Weatherly, G.C.; Niewczas, M.

    2005-07-01

    A crack-healing phenomenon occurring during epitaxial growth of GaP films on a GaAs substrate was studied by transmission electron microscopy. The process is driven by a decrease in the surface energy of the cracked film. The results indicate that the fundamental mechanism operating during healing is the deposition and diffusion of Ga and P atoms onto the crack surface in the GaP lattice, combined with self-diffusion of GaAs within the crack tip in the GaAs substrate. This process is not fully completed in the GaP/GaAs system; unhealed crack tips located in the GaAs substrate always remain in the structure. Development of cracks and subsequent crack healing during film growth lead to a decrease in residual stress in the film. New cracks are formed at an equilibrium spacing which increases with increasing film thickness. A modified expression for predicting the relation between crack spacing and film thickness in epitaxial films is proposed.

  10. Fabrication and characterization of Bismuth-Cerium composite iron garnet epitaxial films for magneto optical applications

    SciTech Connect

    Chandra Sekhar, M.; Singh, Mahi R.

    2012-10-15

    The Bi{sub x}Ce{sub 3-x}Fe{sub 5}O{sub 12} (x = 0.8) epitaxial films of high quality were grown by means of pulsed laser deposition on paramagnetic substrates of Gadolinium Gallium Garnet. We study the modifications of substitutions in the parent garnet Y{sub 3}Fe{sub 5}O{sub 12} that produces a higher magneto-optical response at communication wavelengths. These films displayed a strong in plane textures which are treated in argon as well as reduced atmosphere conditions. The elemental constituents of these films were confirmed by energy dispersive-X ray analysis, elastic recoil detection system, Rutherford backscattering spectroscopy, and X-ray photoelectron spectroscopy measurements. The transmittance spectra were measured and found these films exhibit good transmittance values. The transmittance-spectra were fitted with the theoretical model and the optical constants such as refractive index and absorption edge were evaluated. The highest (negative) Faraday rotation was found for these films treated in the environment of Ar + H{sub 2}. A density matrix theory has been developed for the Faraday rotation and a good agreement between the theory and experiment is found. These epitaxial garnet films can be used in a wide range of frequencies from visible to infrared spectra making them ideal for many magneto optical applications. Therefore, these films may overcome many issues in fabricating all optical isolators which is the viable solution for integrated photonics.

  11. Coherent piezoelectric strain transfer to thick epitaxial ferromagnetic films with large lattice mismatch.

    PubMed

    Kim, Jang-Yong; Yao, Lide; van Dijken, Sebastiaan

    2013-02-27

    Strain control of epitaxial films using piezoelectric substrates has recently attracted significant scientific interest. Despite its potential as a powerful test bed for strain-related physical phenomena and strain-driven electronic, magnetic, and optical technologies, detailed studies on the efficiency and uniformity of piezoelectric strain transfer are scarce. Here, we demonstrate that full and uniform piezoelectric strain transfer to epitaxial films is not limited to systems with small lattice mismatch or limited film thickness. Detailed transmission electron microscopy (TEM) and x-ray diffraction (XRD) measurements of 100 nm thick CoFe(2)O(4) and La(2/3)Sr(1/3)MnO(3) epitaxial films on piezoelectric 0.72Pb(Mg(1/3)Nb(2/3))O(3)-0.28PbTiO(3) substrates (+4.3% and -3.8% lattice mismatch) indicate that misfit dislocations near the interface do not hamper the transfer of piezoelectric strain. Instead, the epitaxial magnetic oxide films and PMN-PT substrates are strained coherently and their lattice parameters change linearly as a function of applied electric field when their remnant growth-induced strain state is negligible. As a result, ferromagnetic properties such as the coercive field, saturation magnetization, and Curie temperature can be reversibly tuned by electrical means. The observation of efficient piezoelectric strain transfer in large-mismatch heteroepitaxial structures opens up new possibilities for the engineering of strain-controlled physical properties in a broad class of hybrid material systems. PMID:23370268

  12. Poisson Ratio of Epitaxial Germanium Films Grown on Silicon

    NASA Astrophysics Data System (ADS)

    Bharathan, Jayesh; Narayan, Jagdish; Rozgonyi, George; Bulman, Gary E.

    2013-01-01

    An accurate knowledge of elastic constants of thin films is important in understanding the effect of strain on material properties. We have used residual thermal strain to measure the Poisson ratio of Ge films grown on Si ⟨001⟩ substrates, using the sin2 ψ method and high-resolution x-ray diffraction. The Poisson ratio of the Ge films was measured to be 0.25, compared with the bulk value of 0.27. Our study indicates that use of Poisson ratio instead of bulk compliance values yields a more accurate description of the state of in-plane strain present in the film.

  13. Multilayer permalloy films grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Rook, K.; Zeltser, A. M.; Artman, J. O.; Laughlin, D. E.; Kryder, M. H.

    1991-04-01

    The magnetic properties of single-layer and multilayer 111-line textured Cu and Permalloy films, deposited by MBE on 111-plane Si substrates, have been measured by both ferromagnetic resonance and M-H loop tracer; microstructural characterizations were conducted by TEM, XRD, and reflection high-energy electron diffraction. The single-layer films had lower easy-axis coercivity H(ce) and a lower in-plane anisotropy field than sputter-deposited Permalloy films of similar thickness. The five-layer, Cu-interlayer separated Permalloy structures, having a magnetic thickness in excess of 100 nm, exhibited lower H(ce) than equivalent single-layer films.

  14. Magnetization reversal of in-plane uniaxial Co films and its dependence on epitaxial alignment

    SciTech Connect

    Idigoras, O. Suszka, A. K.; Berger, A.; Vavassori, P.; Obry, B.; Hillebrands, B.; Landeros, P.

    2014-02-28

    This work studies the influence of crystallographic alignment onto magnetization reversal in partially epitaxial Co films. A reproducible growth sequence was devised that allows for the continuous tuning of grain orientation disorder in Co films with uniaxial in-plane anisotropy by the controlled partial suppression of epitaxy. While all stable or meta-stable magnetization states occurring during a magnetic field cycle exhibit a uniform magnetization for fully epitaxial samples, non-uniform states appear for samples with sufficiently high grain orientation disorder. Simultaneously with the occurrence of stable domain states during the magnetization reversal, we observe a qualitative change of the applied field angle dependence of the coercive field. Upon increasing the grain orientation disorder, we observe a disappearance of transient domain wall propagation as the dominating reversal process, which is characterized by an increase of the coercive field for applied field angles away from the easy axis for well-ordered epitaxial samples. Upon reaching a certain disorder threshold level, we also find an anomalous magnetization reversal, which is characterized by a non-monotonic behavior of the remanent magnetization and coercive field as a function of the applied field angle in the vicinity of the nominal hard axis. This anomaly is a collective reversal mode that is caused by disorder-induced frustration and it can be qualitatively and even quantitatively explained by means of a two Stoner-Wohlfarth particle model. Its predictions are furthermore corroborated by Kerr microscopy and by Brillouin light scattering measurements.

  15. In situ reflection high-energy electron diffraction observation of epitaxial LaNiO3 thin films

    NASA Astrophysics Data System (ADS)

    Chen, P.; Xu, S. Y.; Zhou, W. Z.; Ong, C. K.; Cui, D. F.

    1999-03-01

    Epitaxial LaNiO3 (LNO) thin films were grown on (001) SrTiO3 substrates by laser molecular-beam epitaxy. The growth process of the LNO films was monitored by in situ reflection high-energy electron diffraction (RHEED). Clear RHEED patterns and the intensity oscillation of RHEED were observed during the epitaxial growth process. The morphology of the films was studied by atomic force microscopy. The results show that the films grown by this method have a nanoscale smooth surface with the root-mean-square surface roughness smaller than 7 nm on an area of 1×1 μm2. X-ray diffraction patterns indicate that the crystalline LNO films exhibited preferred (00l) orientation. The resistivity of the thin film is 0.28 mΩ cm at 278 K and 0.06 mΩ cm at 80 K, respectively.

  16. Extrinsic anomalous Hall effect in epitaxial Mn{sub 4}N films

    SciTech Connect

    Meng, M.; Wu, S. X. Ren, L. Z.; Zhou, W. Q.; Wang, Y. J.; Wang, G. L.; Li, S. W.

    2015-01-19

    Anomalous Hall effect (AHE) in ferrimagnetic Mn{sub 4}N epitaxial films grown by molecular-beam epitaxy is investigated. The longitudinal conductivity σ{sub xx} is within the superclean regime, indicating Mn{sub 4}N is a highly conducting material. We further demonstrate that the AHE signal in 40-nm-thick films is mainly due to the extrinsic contributions based on the analysis fitted by ρ{sub AH}=a′ρ{sub xx0}+bρ{sub xx}{sup 2} and σ{sub AH}∝σ{sub xx}. Our study not only provide a strategy for further theoretical work on antiperovskite manganese nitrides but also shed promising light on utilizing their extrinsic AHE to fabricate spintronic devices.

  17. Thin film GaAs solar cells on glass substrates by epitaxial liftoff

    SciTech Connect

    Lee, X.Y.; Goertemiller, M.; Boroditsky, M.; Ragan, R.; Yablonovitch, E.

    1997-02-01

    In this work, we describe the fabrication and operating characteristics of GaAs/AlGaAs thin film solar cells processed by the epitaxial liftoff (ELO) technique. This technique allows the transfer of these cells onto glass substrates. The performance of the lifted-off solar cell is demonstrated by means of electrical measurements under both dark and illuminated conditions. We have also optimized the light trapping conditions in this direct-gap material. The results show that good solar absorption is possible in active layers as thin as 0.32 {mu}m. In such a thin solar cell, the open circuit voltage would be enhanced. We believe that the combination of an epitaxial liftoff thin GaAs film, and nano-texturing can lead to record breaking performance. {copyright} {ital 1997 American Institute of Physics.}

  18. Strain-tunable extraordinary magnetocrystalline anisotropy in Sr2CrReO6 epitaxial films

    NASA Astrophysics Data System (ADS)

    Lucy, J. M.; Ball, M. R.; Restrepo, O. D.; Hauser, A. J.; Soliz, J. R.; Freeland, J. W.; Woodward, P. M.; Windl, W.; Yang, F. Y.

    2014-11-01

    We report the discovery of extraordinarily large anisotropy fields and strain-tunable magnetocrystalline anisotropy in Sr2CrReO6 epitaxial films. We determine the strain-induced tetragonal distortions and octahedral rotations in Sr2CrReO6 epitaxial films grown on (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT), SrTiO3 (STO), and SrCr0.5Nb0.5O3/LSAT substrates using x-ray diffraction and density functional theory. The structural distortions drive dramatic changes in magnetocrystalline anisotropy. We use magnetometry measurements and first principles calculations to determine the atomic origins of the large anisotropy observed. These techniques elucidate the interplay between structural deformations and magnetic behavior and lay the groundwork for the study of other strongly correlated systems in this class of ferromagnetic oxides.

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

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

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

  20. Epitaxial single crystalline ferrite films for high frequency applications

    SciTech Connect

    Suzuki, Y.; Dover, R.B. van; Korenivski, V.; Werder, D.; Chen, C.H.; Felder, R.J.; Phillips, J.M.

    1996-11-01

    The successful growth of single crystal ferrites in thin film form is an important step towards their future incorporation into integrated circuits operating at microwave frequencies. The authors have successfully grown high quality single crystalline spinel ferrite thin films of (Mn,Zn)Fe{sub 2}O{sub 4} and CoFe{sub 2}O{sub 4} on (100) and (110) SrTiO{sub 3} and MgAl{sub 2}O{sub 4} at low temperature. These ferrite films are buffered with spinel structure layers that are paramagnetic at room temperature. In contrast to ferrite films grown directly on the substrates, ferrite films grown on buffered substrates exhibit excellent crystallinity and bulk saturation magnetization values, thus indicating the importance of lattice match and structural similarity between the film and the immediately underlying layer. X-ray, RBS, AFM and TEM analysis provide a consistent picture of the structural properties of these ferrite films. The authors then use this technique to grow exchange-coupled bilayers of single crystalline CoFe{sub 2}O{sub 4} and (Mn,Zn)Fe{sub 2}O{sub 4}. In these bilayers, they observe strong exchange coupling across the interface that is similar in strength to the exchange coupling in the individual layers.

  1. Epitaxial Zinc Oxide Semiconductor Film deposited on Gallium Nitride Substrate

    NASA Astrophysics Data System (ADS)

    McMaster, Michael; Oder, Tom

    2011-04-01

    Zinc oxide (ZnO) is a wide bandgap semiconductor which is very promising for making efficient electronic and optical devices. The goal of this research was to produce high quality ZnO film on gallium nitride (GaN) substrate by optimizing the substrate temperature. The GaN substrates were chemically cleaned and mounted on a ceramic heater and loaded into a vacuum deposition chamber that was pumped down to a base pressure of 3 x 10-7 Torr. The film deposition was preceded by a 30 minute thermal desorption carried in vacuum at 500 ^oC. The ZnO thin film was then sputter-deposited using an O2/Ar gas mixture onto GaN substrates heated at temperatures varying from 20 ^oC to 500 ^oC. Post-deposition annealing was done in a rapid thermal processor at 900 ^oC for 5 min in an ultrapure N2 ambient to improve the crystal quality of the films. The films were then optically characterized using photoluminescence (PL) measurement with a UV laser excitation. Our measurements reveal that ZnO films deposited on GaN substrate held at 200 ^oC gave the best film with the highest luminous intensity, with a peak energy of 3.28 eV and a full width half maximum of 87.4 nm. Results from low temperature (10 K) PL measurements and from x-ray diffraction will also be presented.

  2. Growth of sputter-deposited metamagnetic epitaxial Ni-Co-Mn-In films

    SciTech Connect

    Niemann, R.; Schultz, L.; Faehler, S.

    2012-05-01

    Metamagnetic thin films represent a promising geometry for more efficient magnetocaloric cooling applications due to a fast heat transfer. Here, we identify suitable growth conditions to obtain epitaxial Ni-Mn-In-Co films with a metamagnetic transition in vicinity of room temperature. We show that both increased substrate temperature and target aging result in loss of indium. This can be attributed to evaporation and preferential sputtering, respectively. We present a model that treats the effect of target aging and temperature dependence of evaporation on the film composition independently and enables predictions of the film composition as a function of initial target composition, target age, and deposition temperature. Furthermore, our analysis reveals that a sufficient degree of chemical B2 order is required for a transformation, in addition to an appropriate film composition.

  3. Thickness-dependent metal-insulator transition in epitaxial SrRuO3 ultrathin films

    DOE PAGESBeta

    Shen, Xuan; Qiu, Xiangbiao; Su, Dong; Zhou, Shengqiang; Li, Aidong; Wu, Di

    2015-01-06

    Transport characteristics of ultrathin SrRuO₃ films, deposited epitaxially on TiO₂-terminated SrTiO₃ (001) single-crystal substrates, were studied as a function of film thickness. Evolution from a metallic to an insulating behavior is observed as the film thickness decreases from 20 to 4 unit cells. In films thicker than 4 unit cells, the transport behavior obeys the Drude low temperature conductivity with quantum corrections, which can be attributed to weak localization. Fitting the data with 2-dimensional localization model indicates that electron-phonon collisions are the main inelastic relaxation mechanism. In the film of 4 unit cells in thickness, the transport behavior follows variablemore » range hopping model, indicating a strongly localized state. As a result, magnetoresistance measurements reveal a likely magnetic anisotropy with the magnetic easy axis along the out-of-plane direction.« less

  4. Absence of low-temperature phase transitions in epitaxial BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Tenne, D. A.; Xi, X. X.; Li, Y. L.; Chen, L. Q.; Soukiassian, A.; Zhu, M. H.; James, A. R.; Lettieri, J.; Schlom, D. G.; Tian, W.; Pan, X. Q.

    2004-05-01

    We have studied phase transitions in epitaxial BaTiO3 thin films by Raman spectroscopy. The films are found to remain in a single ferroelectric phase over the temperature range from 5 to 325 K. The low-temperature phase transitions characteristic of bulk BaTiO3 (tetragonal-orthorhombic-rhombohedral) are absent in the films. X-ray diffraction shows that the BaTiO3 films are under tensile strain due to the thermal expansion mismatch with the buffer layer. A phase-field calculation of the phase diagram and domain structures in BaTiO3 thin films predicts, without any priori assumption, that an orthorhombic phase with in-plane polarization is the thermodynamically stable phase for such values of tensile strain and temperature, consistent with the experimental Raman results.

  5. Equilibrium State and Magnetic Permeability Tensor of the Epitaxial Ferrite Films

    NASA Astrophysics Data System (ADS)

    Bobkov, V. B.; Zavislyak, I. V.

    1997-12-01

    The analysis of the equilibrium state of an arbitrarily oriented epitaxial ferrite film with basic cubic symmetry has been carried out. The equilibrium orientation of the magnetization has been shown to coincide with the direction of the applied magnetic field for (n, n, m), (m, n, 0) and (112) films that are magnetized parallel to the surface along the axes 110, 100 and 111, respectively. Conditions of the stability of the equilibrium state have been found. For (100), (110) and (111) films a simple technique for determining the magnetic parameters of the films by the use of the spectra of magnetostatic waves has been proposed. For those films the magnetic permeability tensor has been obtained. Different algorithms have been proposed for processing the MSW spectra.

  6. XRD and AFM characterization of epitaxial Nb films before and after hydrogen exposure

    NASA Astrophysics Data System (ADS)

    Allain, Monica; Heuser, Brent; Durfee, Curtis

    2001-03-01

    Epitaxial Nb films have been characterized with x-ray diffraction (XRD) and atomic force microscopy (AFM) before and after hydrogenation at 100 C and 760 Torr. Two 1000 Angstrom epitaxial Nb films were grown on a-plane sapphire with two different miscut angles, 0.08 and 1.4 degrees. Both Nb films were capped with a 100 Angstrom thick Pd layer to facilitate molecular hydrogen dissociation. While the as-grow film mosaic did not depend on miscut angle, the surface morphology was significantly different. In particular, the high miscut film exhibited a fingered topography that was absent in the low miscut film. Hydrogen absorption under the conditions stated above induce a complete conversion of Nb to the alpha prime hydride phase. The Nb hydride phase transformation process is known to create dislocations as incoherent phase boundaries pass through the lattice. The surface morphology and lattice mosaic from post-hydrogen AFM and XRD measurements, respectively, show the extreme effect of the phase transformation process. Discussion will focus on the lattice mosaic broadening, residual strain, and surface features after hydrogen exposure.

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

    SciTech Connect

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

    2015-10-28

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

  8. Bulk-like pentacene epitaxial films on hydrogen-terminated Si(111)

    SciTech Connect

    Shimada, Toshihiro; Nogawa, Hiroyuki; Hasegawa, Tetsuya; Okada, Ryusuke; Ichikawa, Hisashi; Ueno, Keiji; Saiki, Koichiro

    2005-08-08

    The epitaxial growth of pentacene on hydrogen-terminated Si(111) is reported. Reflection high energy electron diffraction (RHEED) revealed that the crystal packing resembles that in the bulk crystal even at a monolayer thickness, which was maintained in multilayers. A ripening effect was clearly observed by atomic force microscopy (AFM). These results are important to obtain oriented crystalline films of pentacene combined with silicon microdevices with reduced defect densities.

  9. Carrier dynamics in ZnxCd1-xO films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Cheng, F. J.; Lee, Y. C.; Hu, S. Y.; Lin, Y. C.; Tiong, K. K.; Chou, W. C.

    2016-05-01

    In this work, the carrier dynamics in Zn1-xCdxO thin films with different Cd contents grown by molecular beam epitaxy system have been investigated using photoluminescence and time-resolved photoluminescence measurements. The carrier lifetime can be estimated from the PL decay curve fitted by triple exponential function. The emission energy dependence and temperature dependence of the PL decay time indicate that carrier localization dominate the luminescence mechanism of the ZnCdO alloy semiconductor.

  10. Epitaxial Growth and Characterization of Silicon Carbide Films

    SciTech Connect

    Dhanaraj,G.; Dudley, M.; Chen, Y.; Ragothamachar, B.; Wu, B.; Zhang, H.

    2006-01-01

    Silicon carbide (SiC) epitaxial layers have been grown in a chemical vapor deposition (CVD) system designed and fabricated in our laboratory. Silicon tetrachloride-propane as well as silane-propane were used as precursor gases. The hot zone was designed based on simulation by using numerical modeling. Growth rates up to 200 {mu}m could be achieved. A new growth-assisted hydrogen etching was developed to show the distribution of the micropipes present in the substrate. Higher growth rate was observed on off-axis (0 0 0 1) 4 H SiC compared to the on-axis (0 0 0 1) wafer and growth mechanism was explained.

  11. Epitaxial growth of cadmium sulfide films on silicon

    NASA Astrophysics Data System (ADS)

    Antipov, V. V.; Kukushkin, S. A.; Osipov, A. V.

    2016-03-01

    A 300-nm-thick cadmium sulfide epitaxial layer on silicon was grown for the first time. The grown was performed by the method of evaporation and condensation in a quasi-closed volume at a substrate temperature of 650°C and a growth time of 4 s. In order to avoid a chemical reaction between silicon and cadmium sulfide (at this temperature, the rate constant of the reaction is ~103) and to prevent etching of silicon by sulfur, a high-quality silicon carbide buffer layer ~100 nm thick was preliminarily synthesized by the substitution of atoms on the silicon surface. The ellipsometric, Raman, electron diffraction, and trace element analyses showed a high structural perfection of the CdS layer and the absence of a polycrystalline phase.

  12. Epitaxial Ni-Mn-Ga-Co thin films on PMN-PT substrates for multicaloric applications

    SciTech Connect

    Schleicher, B. Niemann, R.; Schultz, L.; Fähler, S.; Diestel, A.; Hühne, R.

    2015-08-07

    Multicaloric stacks consisting of a magnetocaloric film on a piezoelectric substrate promise improved caloric properties as the transition temperature can be controlled by both magnetic and electric fields. We present epitaxially grown magnetocaloric Ni-Mn-Ga-Co thin films on ferroelectric Pb(Mg{sub 1/3}Nb{sub 2/3}){sub 0.72}Ti{sub 0.28}O{sub 3} substrates. Structure and microstructure of two samples, being in the austenitic and martensitic state at room temperature, are investigated by X-ray diffraction in two- and four-circle geometry and by atomic force microscopy. In addition, high temperature magnetometry was performed on the latter sample. The combination of these methods allows separating the influence of epitaxial growth and martensitic transformation. A preferential alignment of twin boundaries is observed already in the as-deposited state, which indicates the presence of prestress, without applying an electric field to the substrate. A temperature-magnetic field phase diagram is presented, which demonstrates the inverse magnetocaloric effect of the epitaxial Ni-Mn-Ga-Co film.

  13. Epitaxial Ni-Mn-Ga-Co thin films on PMN-PT substrates for multicaloric applications

    NASA Astrophysics Data System (ADS)

    Schleicher, B.; Niemann, R.; Diestel, A.; Hühne, R.; Schultz, L.; Fähler, S.

    2015-08-01

    Multicaloric stacks consisting of a magnetocaloric film on a piezoelectric substrate promise improved caloric properties as the transition temperature can be controlled by both magnetic and electric fields. We present epitaxially grown magnetocaloric Ni-Mn-Ga-Co thin films on ferroelectric Pb(Mg1/3Nb2/3)0.72Ti0.28O3 substrates. Structure and microstructure of two samples, being in the austenitic and martensitic state at room temperature, are investigated by X-ray diffraction in two- and four-circle geometry and by atomic force microscopy. In addition, high temperature magnetometry was performed on the latter sample. The combination of these methods allows separating the influence of epitaxial growth and martensitic transformation. A preferential alignment of twin boundaries is observed already in the as-deposited state, which indicates the presence of prestress, without applying an electric field to the substrate. A temperature-magnetic field phase diagram is presented, which demonstrates the inverse magnetocaloric effect of the epitaxial Ni-Mn-Ga-Co film.

  14. Room temperature deposition of superconducting NbN for superconductor-insulator-superconductor junctions

    NASA Technical Reports Server (NTRS)

    Thakoor, S.; Leduc, H. G.; Thakoor, A. P.; Lambe, J.; Khanna, S. K.

    1986-01-01

    The deposition of stoichiometric B1-crystal-structure (111) NbN films on glass or sapphire substrates by reactive dc magnetron sputtering is reported. High-purity Ar-N2 mixtures are used in the apparatus described by Thakoor et al. (1985), and typical deposition parameters are given as background pressure about 10 ntorr, voltage -325 V, current 1 A, deposition rate 1.35 nm/s, film thickness 500 nm, P(Ar) 5-17 mtorr, initial P(N2) 2-6 mtorr, and room temperature. The N2 consumption-injection characteristics are studied and found to control NbN formation using well-conditioned Nb targets. Films with transition temperatures 15-16 K are obtained at P(Ar) = 12.9 + or - 0.2 mtorr and P(N2) = 3.7 + or - 0.1 mtorr. SIS junctions of area about 0.001 sq cm fabricated using the NbN films are shown to have I-V characteristics with nonlinearity parameter about 110 and NbN superconducting-gap parameter Delta = about 2.8 meV.

  15. Epitaxial YBa2Cu3O7-x nanocomposite thin films from colloidal solutions

    NASA Astrophysics Data System (ADS)

    Cayado, P.; De Keukeleere, K.; Garzón, A.; Perez-Mirabet, L.; Meledin, A.; De Roo, J.; Vallés, F.; Mundet, B.; Rijckaert, H.; Pollefeyt, G.; Coll, M.; Ricart, S.; Palau, A.; Gázquez, J.; Ros, J.; Van Tendeloo, G.; Van Driessche, I.; Puig, T.; Obradors, X.

    2015-12-01

    A methodology of general validity to prepare epitaxial nanocomposite films based on the use of colloidal solutions containing different crystalline preformed oxide nanoparticles (ex situ nanocomposites) is reported. The trifluoroacetate (TFA) metal-organic chemical solution deposition route is used with alcoholic solvents to grow epitaxial YBa2Cu3O7 (YBCO) films. For this reason stabilizing oxide nanoparticles in polar solvents is a challenging goal. We have used scalable nanoparticle synthetic methodologies such as thermal and microwave-assisted solvothermal techniques to prepare CeO2 and ZrO2 nanoparticles. We show that stable and homogeneous colloidal solutions with these nanoparticles can be reached using benzyl alcohol, triethyleneglycol, nonanoic acid, trifluoroacetic acid or decanoic acid as protecting ligands, thereby allowing subsequent mixing with alcoholic TFA solutions. An elaborate YBCO film growth analysis of these nanocomposites allows the identification of the different relevant growth phenomena, e.g. nanoparticles pushing towards the film surface, nanoparticle reactivity, coarsening and nanoparticle accumulation at the substrate interface. Upon mitigation of these effects, YBCO nanocomposite films with high self-field critical currents (J c ˜ 3-4 MA cm-2 at 77 K) were reached, indicating no current limitation effects associated with epitaxy perturbation, while smoothed magnetic field dependences of the critical currents at high magnetic fields and decreased effective anisotropic pinning behavior confirm the effectiveness of the novel developed approach to enhance vortex pinning. In conclusion, a novel low cost solution-derived route to high current nanocomposite superconducting films and coated conductors has been developed with very promising features.

  16. Design and Fabrication of Microwave Kinetic Inductance Detectors using NbN Symmetric Spiral Resonator Array

    NASA Astrophysics Data System (ADS)

    Hayashi, K.; Saito, A.; Ogawa, Y.; Murata, M.; Sawada, T.; Nakajima, K.; Yamada, H.; Ariyoshi, S.; Taino, T.; Tanoue, H.; Otani, C.; Ohshima, S.

    2014-05-01

    We designed and fabricated a microwave kinetic inductance detector (MKID) using a niobium nitride (NbN) symmetric spiral resonator array. Previously we revealed that a rewound spiral structure works as not only a high-Q half-wavelength resonator but also as a broadband terahertz antenna. We conducted simulations for a 9 resonator array assuming NbN as the superconducting material and sapphire as the dielectric substrate, and obtained a maximum attenuation of over 30 dB and unloaded quality factors of over 2×105 for frequencies between 4.4 and 4.9 GHz. We fabricated the 9 resonator array MKID using NbN thin film deposited on an m-sapphire substrate by using dc magnetron sputtering. We observed half-wavelength resonances of around 4.5 GHz at 4 K. We measured the optical response of the MKID. The frequency shift was 0.5 MHz when illuminated with 650 nm photons.

  17. Growth of <1100> Epitaxial ZnO Film on Y-Plane LiNbO3 Substrate

    NASA Astrophysics Data System (ADS)

    Kadota, Michio; Ito, Yoshihiro; Kobayashi, Hideaki

    2008-05-01

    A <0001> oriented polycrystal ZnO film is deposited on many types of substrate. However, an epitaxial ZnO film is deposited on only specific substrates, because it depends greatly on the lattice constant of the substrate. An epitaxial ZnO film with the c-axis oriented horizontally on some types of substrate has been reported. In this study, a <1100> orientated epitaxial ZnO film has been deposited on a pre-heat-treated Y-plane (0110) LiNbO3 substrate for the first time. A <0001> oriented polycrystal ZnO film has also been deposited on this substrate without pre-heat-treatment. Thus, two orientation directions can be controlled by pre-heat-treatment for the first time. Moreover, their applications to shear bulk wave transducers and surface acoustic wave devices are discussed.

  18. Anisotropic intrinsic anomalous Hall effect in epitaxial Fe films on GaAs(111)

    NASA Astrophysics Data System (ADS)

    Wu, Lin; Li, Yufan; Xu, Jianli; Hou, Dazhi; Jin, Xiaofeng

    2013-04-01

    The anomalous Hall effect (AHE) in epitaxial Fe films on GaAs(111) has been investigated as a function of film thickness and temperature. The intrinsic contribution from the Berry curvature is singled out from the extrinsic ones and determined to be 821 Ω-1 cm-1, which agrees to the theoretical prediction of 842 Ω-1 cm-1 and is considerably smaller than 1100 Ω-1 cm-1 for Fe(001). This result provides a direct experimental evidence for the anisotropy of the intrinsic AHE in single crystal Fe, reflecting its electronic band structure.

  19. Epitaxial ferromagnetic oxide thin films on silicon with atomically sharp interfaces

    SciTech Connect

    Coux, P. de; Bachelet, R.; Fontcuberta, J.; Sánchez, F.; Warot-Fonrose, B.; Skumryev, V.; Lupina, L.; Niu, G.; Schroeder, T.

    2014-07-07

    A bottleneck in the integration of functional oxides with silicon, either directly grown or using a buffer, is the usual formation of an amorphous interfacial layer. Here, we demonstrate that ferromagnetic CoFe{sub 2}O{sub 4} films can be grown epitaxially on Si(111) using a Y{sub 2}O{sub 3} buffer layer, and remarkably the Y{sub 2}O{sub 3}/Si(111) interface is stable and remains atomically sharp. CoFe{sub 2}O{sub 4} films present high crystal quality and high saturation magnetization.

  20. Mechanical properties of metal-organic frameworks: An indentation study on epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Bundschuh, S.; Kraft, O.; Arslan, H. K.; Gliemann, H.; Weidler, P. G.; Wöll, C.

    2012-09-01

    We have determined the hardness and Young's modulus of a highly porous metal-organic framework (MOF) using a standard nanoindentation technique. Despite the very low density of these films, 1.22 g cm-3, Young's modulus reaches values of almost 10 GPa for HKUST-1, demonstrating that this porous coordination polymer is substantially stiffer than normal polymers. This progress in characterizing mechanical properties of MOFs has been made possible by the use of high quality, oriented thin films grown using liquid phase epitaxy on modified Au substrates.

  1. Surface and electronic structure of epitaxial PtLuSb (001) thin films

    SciTech Connect

    Patel, Sahil J.; Kawasaki, Jason K.; Logan, John; Schultz, Brian D.; Adell, J.; Thiagarajan, B.; Mikkelsen, A.; Palmstrøm, Chris J.

    2014-05-19

    The surface and electronic structure of single crystal thin films of PtLuSb (001) grown by molecular beam epitaxy were studied. Scanning tunneling spectroscopy (STS), photoemission spectroscopy, and temperature dependent Hall measurements of PtLuSb thin films are consistent with a zero-gap semiconductor or semi-metal. STS and photoemission measurements show a decrease in density of states approaching the Fermi level for both valence and conduction bands as well as a slight shift of the Fermi level position into the valence band. Temperature dependent Hall measurements also corroborate the Fermi level position by measurement of p-type carriers.

  2. Epitaxial growth and photoluminescence of hexagonal CdS 1- xSe x alloy films

    NASA Astrophysics Data System (ADS)

    Grün, M.; Gerlach, H.; Breitkopf, Th.; Hetterich, M.; Reznitsky, A.; Kalt, H.; Klingshirn, C.

    1995-01-01

    CdSSe ternary alloy films were grown on GaAs(111) by hot-wall beam epitaxy. The hexagonal crystal phase is obtained. The composition varies from 0 to 40% selenium. Luminescence spectroscopy at low temperatures shows a dominant effect by alloy disorder. Localization of carriers, for example, is still observed at a pulsed optical excitation density of 6 mJ/cm 2. The overall quality of the CdSSe films is sufficient to use them as buffer layers for the growth of hexagonal superlattices.

  3. Domain formation in epitaxial Pb(Zr, Ti)O3 thin films

    NASA Astrophysics Data System (ADS)

    Lee, K. S.; Choi, J. H.; Lee, J. Y.; Baik, S.

    2001-10-01

    Ferroelectric twin-domain structures in epitaxial Pb(Zr, Ti)O3 (PZT) thin films grown on various single-crystal substrates such as MgO(001), KTaO3(001), and SrTiO3(001) were investigated by two-dimensional reciprocal space mapping using synchrotron x-ray diffraction. Each system showed a characteristic domain structure. PbTiO3 thin films grown on MgO(001) showed highly c-axis oriented domain structures consisting of a periodic array of 90° twinlike domains. Perfectly c-axis oriented films were obtained on SrTiO3(001), while the films grown on KTaO3(001) showed a-domain dominant structures with a small amount of c domains embedded in matrix a domains. Contributions of net elastic strain stored in each heteroepitaxial layer and its relaxation to the final domain structures were evaluated considering thermodynamic equilibrium relief of coherency strain by misfit dislocation generation at the film growth temperature. A comparison between theoretical consideration and experimental results clearly demonstrates that the nature of effective misfit strain and its relaxation during film growth play a critical role in the formation of domain structures in epitaxial PZT thin films. Moreover, it was verified that the control of such critical strain factors by changing film composition could modify dominant domain structures in a drastic way. In addition, it was found that the crystalline quality of the films is closely correlated to the tilting nature of the domain structure in each system and coherency strain across the 90° domain boundary is accommodated mainly by the domain tilt of the minor domain.

  4. Epitaxial thin film growth of LiH using a liquid-Li atomic template

    SciTech Connect

    Oguchi, Hiroyuki; Ikeshoji, Tamio; Orimo, Shin-ichi; Ohsawa, Takeo; Shiraki, Susumu; Hitosugi, Taro; Kuwano, Hiroki

    2014-11-24

    We report on the synthesis of lithium hydride (LiH) epitaxial thin films through the hydrogenation of a Li melt, forming abrupt LiH/MgO interface. Experimental and first-principles molecular dynamics studies reveal a comprehensive microscopic picture of the crystallization processes, which sheds light on the fundamental atomistic growth processes that have remained unknown in the vapor-liquid-solid method. We found that the periodic structure that formed, because of the liquid-Li atoms at the film/MgO-substrate interface, serves as an atomic template for the epitaxial growth of LiH crystals. In contrast, films grown on the Al{sub 2}O{sub 3} substrates indicated polycrystalline films with a LiAlO{sub 2} secondary phase. These results and the proposed growth process provide insights into the preparation of other alkaline metal hydride thin films on oxides. Further, our investigations open the way to explore fundamental physics and chemistry of metal hydrides including possible phenomena that emerge at the heterointerfaces of metal hydrides.

  5. Colour centres investigation in pure and doped yttrium aluminium garnet epitaxial films

    NASA Astrophysics Data System (ADS)

    Ubizskii, S. B.; Syvorotka, I. M.; Melnyk, S. S.; Matkovskii, A. O.

    Epitaxial films with thickness of 10-250 μm of yttrium aluminium garnet (YAG) doped with Cr were grown by liquid phase epitaxy technique on YAG: Nd substrateds. Co-doping with Mg2+ was used to force the Cr4+ valent state formation. Dependence of absorption spectra of obtained films on melt-solution composition, growth conditiions and thermal treatment in reducing and oxidizing atmospheres is studied. The absorption being characteristic for YAG:Cr4+ crystals is found in co-doped films grown at higher temperatures (1000-1100°C). The chromium entering in the tetravalent state is confirmed by the annealing experiments. A very intensive absorption band in UV region with maximum at 275 nm was found both in co-doped and YAG: Mg2+ epifilms caused probbly by oxygen vacancies compensating the excess charge of Mg2+. Its intensity correlates with Cr4+ content in the film in the following way: it decreases with Cr4+ entering in the film.

  6. Growth, structural, dielectric and magnetic properties of epitaxial multiferroic NaMnF3 thin films

    NASA Astrophysics Data System (ADS)

    Kc, Amit; Borisov, Pavel; Lederman, David

    Epitaxial NaMnF3 thin films were grown on SrTiO3 (100) single crystal substrates via molecular beam epitaxy (MBE). The orthorhombically distorted perovskite fluoride NaMnF3 (Pnma space group) has been predicted to have a polar instability at low temperatures due to MnF6 octahedral tilts. Structural, magnetic and dielectric properties were studied. Thin film structural quality as a function of the substrate temperature and film thickness was investigated using X-ray diffraction (XRD), in-situ reflection high-energy electron diffraction (RHEED), and atomic force microscopy (AFM). The best films were smooth and single phase grown with four different twin domains. Magnetic characterization was performed using superconducting quantum interference device (SQUID) magnetometry. In-plane magnetization measurements revealed antiferromagnetic ordering with a Neel temperature TN = 66 K. For the dielectric studies, NaMnF3 films were grown on top of SrRuO3 (100) buffer layers grown via pulsed laser deposition that were used as bottom electrodes. Dielectric spectroscopy was performed at different temperatures between 11K and room temperature in a frequency range 100 Hz to 100 kHz. Significant temperature dependent dielectric properties were observed. This work was supported by the National Science Foundation.

  7. Structure and strain relaxation mechanisms of ultrathin epitaxial Pr2O3 films on Si(111)

    NASA Astrophysics Data System (ADS)

    Schroeder, T.; Lee, T.-L.; Libralesso, L.; Joumard, I.; Zegenhagen, J.; Zaumseil, P.; Wenger, C.; Lupina, G.; Lippert, G.; Dabrowski, J.; Müssig, H.-J.

    2005-04-01

    The structure of ultrathin epitaxial Pr2O3 films on Si(111) was studied by synchrotron radiation-grazing incidence x-ray diffraction. The oxide film grows as hexagonal Pr2O3 phase with its (0001) plane attached to the Si(111) substrate. The hexagonal (0001) Pr2O3 plane matches the in-plane symmetry of the hexagonal Si(111) surface unit cell by aligning the ⟨101¯0⟩Pr2O3 along the ⟨112¯⟩ Si directions. The small lattice mismatch of 0.5% results in the growth of pseudomorphic oxide films of high crystalline quality with an average domain size of about 50 nm. The critical thickness tc for pseudomorphic growth amounts to 3.0±0.5nm. The relaxation of the oxide film from pseudomorphism to bulk behavior beyond tc causes the introduction of misfit dislocations, the formation of an in-plane small angle mosaicity structure, and the occurence of a phase transition towards a (111) oriented cubic Pr2O3 film structure. The observed phase transition highlights the influence of the epitaxial interface energy on the stability of Pr2O3 phases on Si(111). A mechanism is proposed which transforms the hexagonal (0001) into the cubic (111) Pr2O3 epilayer structure by rearranging the oxygen network but leaving the Pr sublattice almost unmodified.

  8. Effects of epitaxial strain on oxygen vacancy ordering in LaCoO3 films

    NASA Astrophysics Data System (ADS)

    Biskup, Neven; Mehta, Virat; Pennycook, Steven; Suzuki, Yuri; Varela, Maria; Ornl Collaboration; Ucb Collaboration; Ucm Collaboration

    2013-03-01

    We report on atomically-resolved Z-contrast imaging and electron-energy-loss spectroscopy of epitaxial LaCoO3 thin films grown on SrTiO3, LaAlO3 and (LaAlO3)(SrTaO3) substrates. Regardless of the sign and magnitude of the epitaxial strain imposed by substrate, the LaCoO3 thin films contain oxygen vacancies to varying degrees. These oxygen vacancies tend to order parallel to the film/substrate interface in LCO films under tensile strain and perpendicular under compressive strain. Oxygen vacancy ordering results in charge ordering (CO) among the Co ions as observed by EELS through analysis of the Co L2,3 intensity ratio. We will discuss the amount of oxygen vacancies, the resulting superstructures and CO in the context of the ferromagnetismobserved in these films. Research at ORNL supported by the U.S. DOE-BES, MSED, and also by ORNL's ShaRE User Program (sponsored by DOE-BES), at UCM supported by the ERC Starting Investigator Award and at UC Berkeley and LBNL was supported by the Director, Office of Science, BES -

  9. Big-Data RHEED analysis for understanding epitaxial film growth processes

    SciTech Connect

    Vasudevan, Rama K; Tselev, Alexander; Baddorf, Arthur P; Kalinin, Sergei V

    2014-10-28

    Reflection high energy electron diffraction (RHEED) has by now become a standard tool for in-situ monitoring of film growth by pulsed laser deposition and molecular beam epitaxy. Yet despite the widespread adoption and wealth of information in RHEED image, most applications are limited to observing intensity oscillations of the specular spot, and much additional information on growth is discarded. With ease of data acquisition and increased computation speeds, statistical methods to rapidly mine the dataset are now feasible. Here, we develop such an approach to the analysis of the fundamental growth processes through multivariate statistical analysis of RHEED image sequence. This approach is illustrated for growth of LaxCa1-xMnO3 films grown on etched (001) SrTiO3 substrates, but is universal. The multivariate methods including principal component analysis and k-means clustering provide insight into the relevant behaviors, the timing and nature of a disordered to ordered growth change, and highlight statistically significant patterns. Fourier analysis yields the harmonic components of the signal and allows separation of the relevant components and baselines, isolating the assymetric nature of the step density function and the transmission spots from the imperfect layer-by-layer (LBL) growth. These studies show the promise of big data approaches to obtaining more insight into film properties during and after epitaxial film growth. Furthermore, these studies open the pathway to use forward prediction methods to potentially allow significantly more control over growth process and hence final film quality.

  10. Pulsed laser ablation growth and doping of epitaxial compound semiconductor films

    SciTech Connect

    Lowndes, D.H.; Rouleau, C.M.; Geohegan, D.B.; Budai, J.D.; Poker, D.B.; Puretzky, A.A.; Strauss, M.A.; Pedraza, A.J.; Park, J.W.

    1995-12-01

    Pulsed laser ablation (PLA) has several characteristics that are potentially attractive for the growth and doping of chemically complex compound semiconductors including (1) stoichiometric (congruent) transfer of composition from target to film, (2) the use of reactive gases to control film composition and/or doping via energetic-beam-induced reactions, and (3) low-temperature nonequilibrium phase formation in the laser-generated plasma ``plume.`` However, the electrical properties of compound semiconductors are far more sensitive to low concentrations of defects than are the oxide metals/ceramics for which PLA has been so successful. Only recently have doped epitaxial compound semiconductor films been grown by PLA. Fundamental studies are being carried out to relate film electrical and microstructural properties to the energy distribution of ablated species, to the temporal evolution of the ablation pulse in ambient gases, and to beam assisted surface and/or gas-phase reactions. In this paper the authors describe results of ex situ Hall effect, high-resolution x-ray diffraction, transmission electron microscopy, and Rutherford backscattering measurements that are being used in combination with in situ RHEED and time-resolved ion probe measurements to evaluate PLA for growth of doped epitaxial compound semiconductor films and heterostructures. Examples are presented and results analyzed for doped II-VI, I-III-VI, and column-III nitride materials grown recently in this and other laboratories.

  11. Effects of doping and epitaxy on optical behavior of NaNbO3 films

    NASA Astrophysics Data System (ADS)

    Kocourek, T.; Inkinen, S.; Pacherova, O.; Chernova, E.; Potucek, Z.; Yao, L. D.; Jelinek, M.; Dejneka, A.; van Dijken, S.; Tyunina, M.

    2015-10-01

    Cube-on-cube epitaxy of perovskite sub-cell of Pr-doped and undoped NaNbO3 is obtained in 130-nm-thick films on top of (La0.18Sr0.82)(Al0.59Ta0.41)O3 (001) substrates. Experimental studies show that the edge of optical absorption red-shifts and some interband transitions change in the films compared to crystals. Bright red luminescence is achieved at room-temperature under ultraviolet excitation in the Pr-doped film. An interband mechanism of luminescence excitation is detected in the film, which is in contrast to the intervalence charge transfer mechanism in the crystal. The results are discussed in terms of epitaxially induced changes of crystal symmetry and ferroelectric polarization in the films. It is suggested that the band structure and interband transitions in NaNbO3 and the transition probabilities in the Pr ions can be significantly modified by these changes.

  12. Disappearance of ferroelectric critical thickness in epitaxial ultrathin BaZr O3 films

    NASA Astrophysics Data System (ADS)

    Zhang, Yajun; Li, Gui-Ping; Shimada, Takahiro; Wang, Jie; Kitamura, Takayuki

    2014-11-01

    The intrinsic critical ferroelectric thickness of epitaxial ultrathin capacitors of incipient ferroelectric BaZr O3 (BZO) films with realistic SrRu O3 (SRO) electrodes is investigated by first-principles calculations based on density functional theory. We reveal that polarization can stably exist even in one-unit-cell thick BZO films, i.e., absence of critical thickness, whereas the widely investigated proper ferroelectrics like BaTi O3 and SrTi O3 films have no polarization. The influences of realistic ferroelectric-electrode interface and misfit strain on the ionic and electronic structures of the BZO-SRO thin film system have been examined under the short-circuited boundary condition. It is found that the ionic polarization of conductive SRO electrodes can effectively strengthen the screening of bound charges at the interface, which greatly reduces the depolarization field in the BZO films. Furthermore, the epitaxial misfit strain remarkably enhances the polarization through the enhancement of hybridization of Zr and O electron orbitals, resulting in the disappearance of ferroelectric critical thickness. Our findings are beyond the critical thickness of proper ferroelectrics and are thus promising for future nanometer-scale ferroelectric device such as high-density ferroelectric memory.

  13. Epitaxial composition-graded perovskite films grown by a dual-beam pulsed laser deposition method

    NASA Astrophysics Data System (ADS)

    Sakai, Joe; Autret-Lambert, Cécile; Sauvage, Thierry; Courtois, Blandine; Wolfman, Jérôme; Gervais, François

    2013-10-01

    We prepared SrTiO3 (STO) to Ba0.6Sr0.4TiO3 (BST06) out-of-plane composition-graded films on STO (100) substrates by means of a dual-beam dual-target pulsed laser deposition technique. In the deposition system, a sliding mirror divides one KrF excimer laser beam into two, realizing the dual-beam of controlled intensity ratio. X-ray diffraction reciprocal space mapping has revealed that the graded films deposited under oxygen pressure at or lower than 1×10-3 mbar were coherently strained with the same in-plane lattice parameter as the substrate. Their composition gradient along the growth direction was confirmed by Rutherford backscattering analysis to be uniform. We deposited BST06 top layers of various thickness on epitaxial composition-graded (ECG) buffer layers and examined their coherency and crystallinity. In comparison with the cases of STO homoepitaxial buffer layers, ECG buffer layers achieved better crystallinity of top BST06 layers, suggesting that the crystallinity of a heteroepitaxially-grown film is affected not only by the in-plane lattice matching but also by the out-of-plane lattice continuity with the substrate. ECG films that bridge compositions of substrate and top layer materials can be useful buffer layers for epitaxial growth of lattice-mismatched oxide films.

  14. High field properties of NbN conductors on practical substrates

    SciTech Connect

    Kampwirth, R.T.; Capone, D.W. II; Gray, K.E.; Ho, H.; Chumbley, S.

    1987-01-01

    A new UHV, oil free, two gun magnetron sputtering system has been developed to allow continuous production of NbN conductors. A scaling rule relating film properties to preparation conditions was successfully used to predict the preparation conditions necessary to achieve the best NbN film properties in the two gun system. Comparison of high field J/sub c/ results between the new two gun system and a diffusion pumped one gun system show similar results for NbN on sapphire substrates, suggesting no effect from oil backstreaming. Short sections of double side coated Ti tapes 25 ..mu..m thick with approx. = ..mu..m of NbN have J/sub c/ = 1 x 10/sup 4/ A/cm/sup 2/ at 18T with H/sub c2/(4.2K) of 22.5 to 23 T. Ta wires made under the same conditions with approx. =2.7 ..mu..m of NbN had J/sub c/(18T) a factor of two lower. An 11 turn coil with a 2.5 cm bending radius has been made by coating one side of a moving tape 1.3 m long with approx. =3..mu..m of NbN. The best section had a J/sub c/approx. = 1 x 10/sup 4/ A/cm/sup 2/ at 18T and J/sub c/approx. =4 x 10/sup 3/ A/cm/sub 2/ at 20T.

  15. Low-temperature epitaxy of Ge films by sputter deposition.

    NASA Technical Reports Server (NTRS)

    Khan, I. H.

    1973-01-01

    It is shown experimentally that isoepitaxial growth of Ge films on Ge substrates can be obtained by dc sputtering at substrate temperatures as low as 100 C. The crystallographic structure and orientation of the films are strongly influenced by such deposition parameters as substrate temperature, growth rate, surface contamination, and sputtering-gas purity. The amorphous-polycrystalline transition occurs between 110 and 115 C, while the polycrystalline-single crystalline transition occurs at roughly 140 C. The crystallographic order increases with increasing substrate temperature.

  16. Characterization of Epitaxial Film Silicon Solar Cells Grown on Seeded Display Glass: Preprint

    SciTech Connect

    Young, D. L.; Grover, S.; Teplin, C.; Stradins, P.; LaSalvia, V.; Chuang, T. K.; Couillard, J. G.; Branz, H. M.

    2012-06-01

    We report characterizations of epitaxial film crystal silicon (c-Si) solar cells with open-circuit voltages (Voc) above 560 mV. The 2-um absorber cells are grown by low-temperature (<750 degrees C) hot-wire CVD (HWCVD) on Corning EAGLE XG display glass coated with a layer-transferred (LT) Si seed. The high Voc is a result of low-defect epitaxial Si (epi-Si) growth and effective hydrogen passivation of defects. The quality of HWCVD epitaxial growth on seeded glass substrates depends on the crystallographic quality of the seed and the morphology of the epitaxial growth surface. Heterojunction devices consist of glass/c-Si LT seed/ epi n+ Si:P/epi n- Si:P/intrinsic a-Si:H/p+ a-Si:H/ITO. Similar devices grown on electronically 'dead' n+ wafers have given Voc {approx}630 mV and {approx}8% efficiency with no light trapping features. Here we study the effects of the seed surface polish on epi-Si quality, how hydrogenation influences the device character, and the dominant junction transport physics.

  17. Highly resistive epitaxial Mg-doped GdN thin films

    SciTech Connect

    Lee, C.-M.; Warring, H.; Trodahl, H. J.; Ruck, B. J.; Natali, F.; Vézian, S.; Damilano, B.; Cordier, Y.; Granville, S.; Al Khalfioui, M.

    2015-01-12

    We report the growth by molecular beam epitaxy of highly resistive GdN, using intentional doping with magnesium. Mg-doped GdN layers with resistivities of 10{sup 3} Ω cm and carrier concentrations of 10{sup 16 }cm{sup −3} are obtained for films with Mg concentrations up to 5 × 10{sup 19} atoms/cm{sup 3}. X-ray diffraction rocking curves indicate that Mg-doped GdN films have crystalline quality very similar to undoped GdN films, showing that the Mg doping did not affect the structural properties of the films. A decrease of the Curie temperature with decreasing the electron density is observed, supporting a recently suggested magnetic polaron scenario [F. Natali, B. J. Ruck, H. J. Trodahl, D. L. Binh, S. Vézian, B. Damilano, Y. Cordier, F. Semond, and C. Meyer, Phys. Rev. B 87, 035202 (2013)].

  18. Improved epitaxy of ultrathin praseodymia films on chlorine passivated Si(111) reducing silicate interface formation

    SciTech Connect

    Gevers, S.; Bruns, D.; Weisemoeller, T.; Wollschlaeger, J.; Flege, J. I.; Kaemena, B.; Falta, J.

    2010-12-13

    Ultrathin praseodymia films have been deposited on both Cl-passivated and nonpassivated Si(111) substrates by molecular beam epitaxy. Comparative studies on the crystallinity and stoichiometry are performed by x-ray photoelectron spectroscopy, x-ray standing waves, and x-ray reflectometry. On nonpassivated Si(111) an amorphous silicate film is formed. In contrast, praseodymia deposited on Cl-passivated Si(111) form a well-ordered crystalline film with cubic-Pr{sub 2}O{sub 3} (bixbyite) structure. The vertical lattice constant of the praseodymia film is increased by 1.4% compared to the bulk value. Furthermore, the formation of an extended amorphous silicate interface layers is suppressed and confined to only one monolayer.

  19. The Long Forgotten Compound: CoTe, and its Epitaxial Film Growth and Properties

    NASA Astrophysics Data System (ADS)

    Zhang, Zhiwei; Zhu, Zhihai; Hines, William A.; Budnick, Joseph I.; Wells, Barrett O.

    As part of our investigation of Co-doped, Fe-chalcogenide superconductors, we have synthesized films of CoTe; a long forgotten binary compound. Using pulsed laser deposition, we have grown epitaxial films on MgO, CaF2, and SrTiO3 and have found that careful control of growth conditions allows for the synthesis of either (001) or (101) oriented films. X-ray diffraction shows the structure of the films is hexagonal. However, we also find the surprising presence of the nominally disallowed (001) peak. We also report temperature dependent transport and magnetic properties. This material may be of interest as a magnetic semiconductor and for its relationship to chemically doping Fe-based superconductors. DOE/BES Contract DE-FG02-00ER45801.

  20. Epitaxial thin film deposition of magnetostrictive materials and its effect on magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    McClure, Adam Marc

    Magnetostriction means that the dimensions of a material depend on its magnetization. The primary goal of this dissertation was to understand the effect of magnetostriction on the magnetic anisotropy of single crystal magnetostrictive thin films, where the epitaxial pinning of the material to a substrate could inhibit its conversion to new dimensions. In order to address this goal, several Fe-based binary alloys were deposited onto various substrates by molecular beam epitaxy. The samples were characterized by an array of techniques including electron diffraction, Rutherford backscattering, vibrating sample magnetometry, ferromagnetic resonance, and x-ray absorption spectroscopies. The attempted growths of crystalline magnetostrictive thin films resulted in successful depositions of Fe1-xGax and Fe1-x Znx. Depositions onto MgO(001) substrates result in an in-plane cubic magnetic anisotropy, as expected from the cubic symmetry of the Fe-based thin films, and a strong out-of-plane uniaxial anisotropy that forces the magnetization to lie in the plane of the films. Depositions onto ZnSe/GaAs(001) substrates feature an additional in-plane uniaxial anisotropy. The magnitudes and signs of the in-plane anisotropies depend on the Ga content. Furthermore, the cubic anisotropy constant of Fe1-xGax samples deposited onto MgO substrates switches sign at a lower Ga concentration than is seen in bulk Fe1-xGax. The effect on the magnetic anisotropy of depositing a magnetostrictive material as an epitaxial thin film is influenced by the material's magnetostrictive properties and the substrate upon which it is deposited. In particular, pinning a magnetoelastic material to a substrate will modify its cubic anisotropy, and depositions on substrates compliant to an anisotropic strain relaxation may result in a strong in-plane uniaxial anisotropy.

  1. Strain control of oxygen vacancies in epitaxial strontium cobaltite films

    DOE PAGESBeta

    Jeen, Hyoung Jeen; Choi, Woo Seok; Reboredo, Fernando A.; Freeland, John W.; Eres, Gyula; Lee, Ho Nyung; Petrie, Jonathan R.; Mitra, Chandrima; Meyer, Tricia L.

    2016-01-25

    In this study, the ability to manipulate oxygen anion defects rather than metal cations in complex oxides can facilitate creating new functionalities critical for emerging energy and device technologies. However, the difficulty in activating oxygen at reduced temperatures hinders the deliberate control of important defects, oxygen vacancies. Here, strontium cobaltite (SrCoOx) is used to demonstrate that epitaxial strain is a powerful tool for manipulating the oxygen vacancy concentration even under highly oxidizing environments and at annealing temperatures as low as 300 °C. By applying a small biaxial tensile strain (2%), the oxygen activation energy barrier decreases by ≈30%, resulting inmore » a tunable oxygen deficient steady-state under conditions that would normally fully oxidize unstrained cobaltite. These strain-induced changes in oxygen stoichiometry drive the cobaltite from a ferromagnetic metal towards an antiferromagnetic insulator. The ability to decouple the oxygen vacancy concentration from its typical dependence on the operational environment is useful for effectively designing oxides materials with a specific oxygen stoichiometry.« less

  2. Growth and phase transition characteristics of pure M-phase VO{sub 2} epitaxial film prepared by oxide molecular beam epitaxy

    SciTech Connect

    Fan, L. L.; Chen, S.; Wu, Y. F.; Chen, F. H.; Chu, W. S.; Chen, X.; Zou, C. W.; Wu, Z. Y.

    2013-09-23

    VO{sub 2} epitaxial film with large size has been prepared by oxide-molecular beam epitaxy method on Al{sub 2}O{sub 3} (0001) substrate. The VO{sub 2} film shows a perfect crystal orientation, uniformity, and distinct metal-insulator phase transition (MIT) characteristics. It is observed that the MIT character is closely associated with the crystal defects such as oxygen vacancies. By controlling the growth condition, the MIT temperature can be tuned through modifying the content of oxygen vacancies. The role of the oxygen vacancies on the phase transition behavior of this VO{sub 2} film is discussed in the framework of the hybridization theory and the valence state of vanadium.

  3. Surface control of epitaxial manganite films via oxygen pressure

    SciTech Connect

    Tselev, Alexander; Vasudevan, Rama K.; Gianfrancesco, Anthony G.; Qiao, Liang; Ganesh, Panchapakesan; Meyer, Tricia L.; Lee, Ho Nyung; Biegalski, Michael D.; Baddorf, Arthur P.; Kalinin, Sergei

    2015-03-11

    The trend to reduce device dimensions demands increasing attention to atomic-scale details of structure of thin films as well as to pathways to control it. We found that this is of special importance in the systems with multiple competing interactions. We have used in situ scanning tunneling microscopy to image surfaces of La5/8Ca3/8MnO3 films grown by pulsed laser deposition. The atomically resolved imaging was combined with in situ angle-resolved X-ray photoelectron spectroscopy. We find a strong effect of the background oxygen pressure during deposition on structural and chemical features of the film surface. Deposition at 50 mTorr of O2 leads to mixed-terminated film surfaces, with B-site (MnO2) termination being structurally imperfect at the atomic scale. Moreover, a relatively small reduction of the oxygen pressure to 20 mTorr results in a dramatic change of the surface structure leading to a nearly perfectly ordered B-site terminated surface with only a small fraction of A-site (La,Ca)O termination. This is accompanied, however, by surface roughening at a mesoscopic length scale. The results suggest that oxygen has a strong link to the adatom mobility during growth. The effect of the oxygen pressure on dopant surface segregation is also pronounced: Ca surface segregation is decreased with oxygen pressure reduction.

  4. Surface control of epitaxial manganite films via oxygen pressure

    DOE PAGESBeta

    Tselev, Alexander; Vasudevan, Rama K.; Gianfrancesco, Anthony G.; Qiao, Liang; Ganesh, Panchapakesan; Meyer, Tricia L.; Lee, Ho Nyung; Biegalski, Michael D.; Baddorf, Arthur P.; Kalinin, Sergei

    2015-03-11

    The trend to reduce device dimensions demands increasing attention to atomic-scale details of structure of thin films as well as to pathways to control it. We found that this is of special importance in the systems with multiple competing interactions. We have used in situ scanning tunneling microscopy to image surfaces of La5/8Ca3/8MnO3 films grown by pulsed laser deposition. The atomically resolved imaging was combined with in situ angle-resolved X-ray photoelectron spectroscopy. We find a strong effect of the background oxygen pressure during deposition on structural and chemical features of the film surface. Deposition at 50 mTorr of O2 leadsmore » to mixed-terminated film surfaces, with B-site (MnO2) termination being structurally imperfect at the atomic scale. Moreover, a relatively small reduction of the oxygen pressure to 20 mTorr results in a dramatic change of the surface structure leading to a nearly perfectly ordered B-site terminated surface with only a small fraction of A-site (La,Ca)O termination. This is accompanied, however, by surface roughening at a mesoscopic length scale. The results suggest that oxygen has a strong link to the adatom mobility during growth. The effect of the oxygen pressure on dopant surface segregation is also pronounced: Ca surface segregation is decreased with oxygen pressure reduction.« less

  5. BiFeO3 epitaxial thin films and devices: past, present and future.

    PubMed

    Sando, D; Barthélémy, A; Bibes, M

    2014-11-26

    The celebrated renaissance of the multiferroics family over the past ten years has also been that of its most paradigmatic member, bismuth ferrite (BiFeO3). Known since the 1960s to be a high temperature antiferromagnet and since the 1970s to be ferroelectric, BiFeO3 only had its bulk ferroic properties clarified in the mid-2000s. It is however the fabrication of BiFeO3 thin films and their integration into epitaxial oxide heterostructures that have fully revealed its extraordinarily broad palette of functionalities. Here we review the first decade of research on BiFeO3 films, restricting ourselves to epitaxial structures. We discuss how thickness and epitaxial strain influence not only the unit cell parameters, but also the crystal structure, illustrated for instance by the discovery of the so-called T-like phase of BiFeO3. We then present its ferroelectric and piezoelectric properties and their evolution near morphotropic phase boundaries. Magnetic properties and their modification by thickness and strain effects, as well as optical parameters, are covered. Finally, we highlight various types of devices based on BiFeO3 in electronics, spintronics, and optics, and provide perspectives for the development of further multifunctional devices for information technology and energy harvesting. PMID:25352066

  6. Epitaxial stabilization of ultra thin films of electron doped manganites

    NASA Astrophysics Data System (ADS)

    Middey, S.; Kareev, M.; Meyers, D.; Liu, X.; Cao, Y.; Tripathi, S.; Yazici, D.; Maple, M. B.; Ryan, P. J.; Freeland, J. W.; Chakhalian, J.

    2014-05-01

    Ultra-thin films of the electron doped manganite La0.8Ce0.2MnO3 were grown in a layer-by-layer growth mode on SrTiO3 (001) substrates by pulsed laser interval deposition. High structural quality and surface morphology were confirmed by a combination of synchrotron based x-ray diffraction and atomic force microscopy. Resonant X-ray absorption spectroscopy measurements confirm the presence of Ce4+ and Mn2+ ions. In addition, the electron doping signature was corroborated by Hall effect measurements. All grown films show a ferromagnetic ground state as revealed by both dc magnetization and x-ray magnetic circular dichroism measurements and remain insulating contrary to earlier reports of a metal-insulator transition. Our results hint at the possibility of electron-hole asymmetry in the colossal magnetoresistive manganite phase diagram akin to the high-Tc cuprates.

  7. Misfit strain phase diagrams of epitaxial PMN-PT films

    NASA Astrophysics Data System (ADS)

    Khakpash, N.; Khassaf, H.; Rossetti, G. A.; Alpay, S. P.

    2015-02-01

    Misfit strain-temperature phase diagrams of three compositions of (001) pseudocubic (1 - x).Pb (Mgl/3Nb2/3)O3 - x.PbTiO3 (PMN-PT) thin films are computed using a phenomenological model. Two (x = 0.30, 0.42) are located near the morphotropic phase boundary (MPB) of bulk PMN-PT at room temperature (RT) and one (x = 0.70) is located far from the MPB. The results show that it is possible to stabilize an adaptive monoclinic phase over a wide range of misfit strains. At RT, the stability region of this phase is much larger for PMN-PT compared to barium strontium titanate and lead zirconate titanate films.

  8. Misfit strain phase diagrams of epitaxial PMN–PT films

    SciTech Connect

    Khakpash, N.; Khassaf, H.; Rossetti, G. A.; Alpay, S. P.

    2015-02-23

    Misfit strain–temperature phase diagrams of three compositions of (001) pseudocubic (1 − x)·Pb (Mg{sub l/3}Nb{sub 2/3})O{sub 3} − x·PbTiO{sub 3} (PMN–PT) thin films are computed using a phenomenological model. Two (x = 0.30, 0.42) are located near the morphotropic phase boundary (MPB) of bulk PMN–PT at room temperature (RT) and one (x = 0.70) is located far from the MPB. The results show that it is possible to stabilize an adaptive monoclinic phase over a wide range of misfit strains. At RT, the stability region of this phase is much larger for PMN–PT compared to barium strontium titanate and lead zirconate titanate films.

  9. Epitaxial Cu{sub 2}ZnSnS{sub 4} thin film on Si (111) 4° substrate

    SciTech Connect

    Song, Ning; Liu, Fangyang; Huang, Yidan; Hao, Xiaojing E-mail: xj.hao@unsw.edu.au; Green, Martin A.; Young, Matthew; Erslev, Pete; Harvey, Steven P.; Teeter, Glenn E-mail: xj.hao@unsw.edu.au; Wilson, Samual

    2015-06-22

    To explore the possibility of Cu{sub 2}ZnSnS{sub 4} (CZTS)/Si based tandem solar cells, the heteroepitaxy of tetragonal Cu{sub 2}ZnSnS{sub 4} thin films on single crystalline cubic Si (111) wafers with 4° miscut is obtained by molecular beam epitaxy. The X-ray θ-2θ scan and selected area diffraction patterns of the CZTS thin films and Si substrates, and the high resolution transmission electron microscopy image of the CZTS/Si interface region demonstrate that the CZTS thin films are epitaxially grown on the Si substrates. A CZTS/Si P-N junction is formed and shows photovoltaic responses, indicating the promising application of epitaxial CZTS thin films on Si.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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