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Sample records for epitaxial nbn films

  1. Nano-meter bridge with epitaxially deposited NbN on MgO film

    SciTech Connect

    Yamashita, T.; Hamasaki, K.; Kodaira, Y.; Komata, T.

    1985-03-01

    Nano-meter(nm)-bridges with high-T /SUB c/ materials hold great technological interest because of their smaller capacitance and expected higher I /SUB o/ R /SUB n/ -product. They are promising especially for applications such as high speed logic and high frequency radiation detectors. Also they can operate over a wide temperature range and are stable against thermal cycles as are incorporating the refractory high-T /SUB c/ superconductors. One of the essential ingredient for high quality bridges is to have NbN films. Ultra-thin NbN films have been prepared by rf reactive-sputtering. NbN films deposited epitaxially on rf sputtered MgO films have high superconducting transition temperature T /SUB c/ . T /SUB c/ value of the film with thickness of about 5nm was about 14K, and is much higher than those deposited on Al/sub 2/O/sub 3/ films and Si substrates. Two types of nm-bridges were reproducibly fabricated with NbN films deposited epitaxially on MgO films. The obtained I /SUB o/ R /SUB n/ -products were in a range of 0.5 to 3.6mV. The microwaveinduced voltage steps were observed up to the voltage comparable to I /SUB o/ R /SUB n/ - product. The dc and ac quantum effects of the dc SQUIDS were observed in quite wide range of temperature, 4.2 to 11.4K.

  2. 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.

  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. Microwave surface resistance of reactively sputtered NbN thin films

    NASA Technical Reports Server (NTRS)

    Bautista, J. J.; Strayer, D. M.

    1987-01-01

    The surface resistance of niobium nitride (NBN) thin films was measured at 7.78 and 10.14 GHz in the temperature range of 1.5 to 4.2 K. The films were reactively sputtered on sapphire substrates to a thickness of approximately 1 micron. The surface resistance was determined by measuring the quality factor (Q) of the TE sub 011 mode of a lead-plated copper cavity where the NbN served as one end-cap of the cavity.

  5. High quality superconducting NbN thin films on GaAs

    NASA Astrophysics Data System (ADS)

    Marsili, Francesco; Gaggero, Alessandro; Li, Lianhe H.; Surrente, Alessandro; Leoni, Roberto; Lévy, Francis; Fiore, Andrea

    2009-09-01

    A very promising way to increase the detection efficiency of nanowire superconducting single-photon detectors (SSPDs) consists in integrating them with advanced optical structures such as distributed Bragg reflectors (DBRs) and optical waveguides. This requires transferring the challenging SSPD technology from the usual substrates, i.e. sapphire and MgO, to an optical substrate like GaAs, on which DBRs and waveguides can be easily obtained. Therefore, we optimized the deposition process of few-nm thick superconducting NbN films on GaAs and AlAs/GaAs-based DBRs at low temperatures (substrate temperature TS = 400 °C), in order to prevent As evaporation. NbN films ranging from 150 to 3 nm in thickness were then deposited on single-crystal MgO, GaAs, MgO-buffered GaAs and DBRs by current-controlled DC magnetron sputtering (planar, circular, balanced configuration) of Nb in an Ar+N2 plasma. 5.5 nm thick NbN films on GaAs exhibit TC = 10.7 K, ΔTC = 1.1 K and RRR = 0.7. The growth of such high quality thin NbN films on GaAs and DBRs has never been reported before.

  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. 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.

  8. Superconducting properties of very high quality NbN thin films grown by high temperature chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Hazra, D.; Tsavdaris, N.; Jebari, S.; Grimm, A.; Blanchet, F.; Mercier, F.; Blanquet, E.; Chapelier, C.; Hofheinz, M.

    2016-10-01

    Niobium nitride (NbN) is widely used in high-frequency superconducting electronics circuits because it has one of the highest superconducting transition temperatures ({T}{{c}}˜ 16.5 {{K}}) and largest gap among conventional superconductors. In its thin-film form, the T c of NbN is very sensitive to growth conditions and it still remains a challenge to grow NbN thin films (below 50 nm) with high T c. Here, we report on the superconducting properties of NbN thin films grown by high-temperature chemical vapor deposition (HTCVD). Transport measurements reveal significantly lower disorder than previously reported, characterized by a Ioffe-Regel parameter ({k}{{F}}{\\ell }) ˜ 12. Accordingly we observe {T}{{c}}˜ 17.06 {{K}} (point of 50% of normal state resistance), the highest value reported so far for films of thickness 50 nm or less, indicating that HTCVD could be particularly useful for growing high quality NbN thin films.

  9. 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.

  10. Monocrystalline NbN nanofilms on a 3C-SiC/Si substrate

    NASA Astrophysics Data System (ADS)

    Gao, J. R.; Hajenius, M.; Tichelaar, F. D.; Klapwijk, T. M.; Voronov, B.; Grishin, E.; Gol'tsman, G.; Zorman, C. A.; Mehregany, M.

    2007-08-01

    The authors have realized NbN (100) nanofilms on a 3C-SiC (100)/Si(100) substrate by dc reactive magnetron sputtering at 800°C. High-resolution transmission electron microscopy (HRTEM) is used to characterize the films, showing a monocrystalline structure and confirming epitaxial growth on the 3C-SiC layer. A film ranging in thickness from 3.4to4.1nm shows a superconducting transition temperature of 11.8K, which is the highest reported for NbN films of comparable thickness. The NbN nano-films on 3C-SiC offer a promising alternative to improve terahertz detectors. For comparison, NbN nanofilms grown directly on Si substrates are also studied by HRTEM.

  11. Scaling laws for the critical current density of NbN films in high magnetic fields

    SciTech Connect

    Hampshire, D.P. . Dept. of Physics); Gray, K.E.; Kampwirth, R.T. )

    1992-08-01

    We have measured the critical current density (Jc) of two NbN films (500 {Angstrom} and 1550 {Angstrom} thick) as a function of temperature in magnetic fields up to 25 Tesla using transport measurements. In both films, the functional form of the volume pinning force F{sub p} obeys the Fietz - Webb scaling law throughout the entire magnetic field and temperature range such that: F{sub p}=J{sub c} {times} B= {alpha}B{sub c2}{sup m}(T)b{sup {1/2}} (1-b){sup 2} = {alpha}*(1-T/T{sub c}){sup m}b{sup {1/2}}(1-b){sup 2} where {alpha} and {alpha}* are constants dependent on the film, B{sub c2}(T) is the upper critical field, b = B/B{sub c2}(T) is the reduced magnetic field, {Tc} is the critical temperature and we find m = 2.7 {plus minus} 0.1. Over a limited range of magnetic fields close to B{sub c2}(T), we can approximate this functional form by: F{sub p} = {Beta}B{sub c2}{sup M}(T)b(1-b){sup 2}={Beta}*(1-T/{Tc}){sup M}b(1-b){sup 2} where {Beta} and {Beta}* are constants and we find M = 2.6{plus minus}0.2. Values of J{sub c} derived from D.C. magnetisation data obtained using Bean's model show qualitative agreement with the transport measurements throughout the superconducting phase. Despite the marked granularity in the microstructure of these films, we interpret our results as evidence that a flux pinning mechanism determines the transport current density in NbN films in high magnetic fields.

  12. Scaling laws for the critical current density of NbN films in high magnetic fields

    SciTech Connect

    Hampshire, D.P.; Gray, K.E.; Kampwirth, R.T.

    1992-08-01

    We have measured the critical current density (Jc) of two NbN films (500 {Angstrom} and 1550 {Angstrom} thick) as a function of temperature in magnetic fields up to 25 Tesla using transport measurements. In both films, the functional form of the volume pinning force F{sub p} obeys the Fietz - Webb scaling law throughout the entire magnetic field and temperature range such that: F{sub p}=J{sub c} {times} B= {alpha}B{sub c2}{sup m}(T)b{sup {1/2}} (1-b){sup 2} = {alpha}*(1-T/T{sub c}){sup m}b{sup {1/2}}(1-b){sup 2} where {alpha} and {alpha}* are constants dependent on the film, B{sub c2}(T) is the upper critical field, b = B/B{sub c2}(T) is the reduced magnetic field, {Tc} is the critical temperature and we find m = 2.7 {plus_minus} 0.1. Over a limited range of magnetic fields close to B{sub c2}(T), we can approximate this functional form by: F{sub p} = {Beta}B{sub c2}{sup M}(T)b(1-b){sup 2}={Beta}*(1-T/{Tc}){sup M}b(1-b){sup 2} where {Beta} and {Beta}* are constants and we find M = 2.6{plus_minus}0.2. Values of J{sub c} derived from D.C. magnetisation data obtained using Bean`s model show qualitative agreement with the transport measurements throughout the superconducting phase. Despite the marked granularity in the microstructure of these films, we interpret our results as evidence that a flux pinning mechanism determines the transport current density in NbN films in high magnetic fields.

  13. Heteroepitaxial growth of GaN on various powder compounds (AlN, LaN, TiN, NbN, ZrN, ZrB 2 , VN, BeO) by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Park, Jinsub; Ha, Jun-Seok; Hong, Soon-Ku; Lee, Seog Woo; Cho, Meoung Whan; Yao, Takafumi; Lee, Hae Woo; Lee, Sang Hwa; Lee, Sung-Keun; Lee, Hyo-Jong

    2012-04-01

    We investigated the nucleation and growth behavior of GaN on various powders by hydride vapor phase epitaxy. In relative comparison, the nucleation tendency of GaN on each powder can be summarized as AlN > LaN, TiN, NbN > ZrN > ZrB2 > VN, BeO, indicating that the number of nucleation sites increased from right to left. LaN and NbN have not yet been reported as buffer materials for GaN growth. Of these, NbN is expected to be a good buffer material because the interatomic distance on the NbN (111) plane has only 2% difference from that on the GaN (0001) plane.

  14. Oxidation of epitaxial Ce films

    NASA Astrophysics Data System (ADS)

    Vescovo, E.; Carbone, C.

    1996-02-01

    Single-crystal Ce films of more than 300 Å thickness have been epitaxially grown on W(110). Their interaction with molecular oxygen at room temperature has been studied by angle-resolved photoemission, low-energy electron diffraction, and Auger spectroscopy. As a function of the oxygen exposure, the reaction is found to proceed through a sequence of three distinct stages: (i) ordered dissociative surface adsorption; (ii) formation of an ordered Ce2O3-like surface oxide; and (iii) gradual conversion of the sesquioxide into a disordered surface dioxide CeO2-x. A structurally different Ce2O3 oxide is obtained after high oxygen exposures followed by heating at 450 K. The formation of the epitaxial surface sesquioxides is favored by the good lattice match with the Ce substrate. The same type of structural relation might lead to the formation of ordered sesquioxides on other rare-earth surfaces exposing hexagonal planes.

  15. Epitaxial growth of single crystal films

    NASA Technical Reports Server (NTRS)

    Lind, M. D.; Kroes, R. L.; Immorlica, A. A., Jr.

    1981-01-01

    An experiment in gallium arsenide liquid phase epitaxy (LPE) on a flight of the SPAR 6 is described. A general purpose LPE processor suitable for either SPAR or Space Transportation System flights was designed and built. The process was started before the launch, and only the final step, in which the epitaxial film is grown, was performed during the flight. The experiment achieved its objectives; epitaxial films of reasonably good quality and very nearly the thickness predicted for convection free diffusion limited growth were produced. The films were examined by conventional analytical techniques and compared with films grown in normal gravity.

  16. 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.

  17. 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

  18. 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.

  19. 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

  20. Optimisation of NbN thin films on GaAs substrates for in-situ single photon detection in structured photonic devices

    NASA Astrophysics Data System (ADS)

    Reithmaier, G.; Senf, J.; Lichtmannecker, S.; Reichert, T.; Flassig, F.; Voss, A.; Gross, R.; Finley, J. J.

    2013-04-01

    We prepare NbN thin films by DC magnetron sputtering on [100] GaAs substrates, optimise their quality, and demonstrate their use for efficient single photon detection in the near-infrared. The interrelation between the Nb:N content, growth temperature, and crystal quality is established for 4-22 nm thick films. Optimised films exhibit a superconducting critical temperature of 12.6 ± 0.2K for a film thickness of 22 ± 0.5 nm and 10.2 ± 0.2 K for 4 ± 0.5 nm thick films that are suitable for single photon detection. The optimum growth temperature is shown to be ˜475 °C reflecting a trade-off between enhanced surface diffusion, which improves the crystal quality, and arsenic evaporation from the GaAs substrate. Analysis of the elemental composition of the films provides strong evidence that the δ-phase of NbN is formed in optimised samples, controlled primarily via the nitrogen partial pressure during growth. By patterning optimum 4 nm and 22 nm thick films into a 100 nm wide, 369μm long nanowire meander using electron beam lithography and reactive ion etching, we fabricated single photon detectors on GaAs substrates. Time-resolved studies of the photo-response, absolute detection efficiency, and dark count rates of these detectors as a function of the bias current reveal maximum single photon detection efficiencies as high as 21 ± 2% at 4.3 ± 0.1 K with ˜50 k dark counts per second for bias currents of 98%IC at a wavelength of 950 nm. As expected, similar detectors fabricated from 22 nm thick films exhibit much lower efficiencies (0.004%) with very low dark count rates ≤3 cps. The maximum lateral extension of a photo-generated resistive region is estimated to be 30 ± 8 nm, clearly identifying the low detection efficiency and dark count rate of the thick film detectors as arising from hotspot cooling via the heat reservoir provided by the NbN film.

  1. Photoluminescence studies in epitaxial CZTSe thin films

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  2. 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)

  3. 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)

  4. Epitaxial film transfer technique for producing single crystal Si film on an insulating substrate

    NASA Astrophysics Data System (ADS)

    Kimura, M.; Egami, K.; Kanamori, M.; Hamaguchi, T.

    1983-08-01

    Epitaxial film transfer, a new technique for producing a single crystal Si film with both large size and high quality on an insulating substrate, is demonstrated. The technique in which an epitaxial Si film is transferred to a secondary substrate by using three fundamental processes of epitaxial growth, bonding of two wafers, and substrate elimination, can produce a 2-in. single crystal Si film as thin as 1.5 μm on a insulating substrate. Thickness variation can be controlled to ±0.06 μm across a 2-in. wafer. An epitaxial Si film is transferred without significant degradation in quality although a fine film waving exists.

  5. 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.

  6. 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.

  7. Broadband ultrafast superconducting NbN detector for electromagnetic radiation

    NASA Astrophysics Data System (ADS)

    Gousev, Yu. P.; Gol'Tsman, G. N.; Semenov, A. D.; Gershenzon, E. M.; Nebosis, R. S.; Heusinger, M. A.; Renk, K. F.

    1994-04-01

    The paper shows that the NbN thin film detector combines, in an optimum way, both high sensitivity and short response, and it has, in addition, a broadband sensitivity from the submillimeter (or millimeter) wave range to visible light. Details of the experiment presents the performance and operating conditions of the broadband ultrafast superconducting NbN detector for electromagnetic radiation.

  8. Seed layer technique for high quality epitaxial manganite films

    PubMed Central

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O’Shea, K.; MacLaren, D. A.; Bergenti, I.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-01-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  9. Seed layer technique for high quality epitaxial manganite films

    NASA Astrophysics Data System (ADS)

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O'Shea, K.; MacLaren, D. A.; Riminucci, A.; Bergenti, I.; Fugattini, S.; Prezioso, M.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-08-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  10. Seed layer technique for high quality epitaxial manganite films

    PubMed Central

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O’Shea, K.; MacLaren, D. A.; Bergenti, I.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-01-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived. PMID:27648371

  11. 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.

  12. Characterization of epitaxially grown films of vanadium oxides

    SciTech Connect

    Rogers, K.D.; Coath, J.A.; Lovell, M.C. , Shrivenham, Swindon, Wiltshire, SN6 8LA, England )

    1991-08-01

    The growth of VO{sub 2} and V{sub 2}O{sub 3} thin films by reactive sputtering has been investigated. Previously reported studies of such thin films have often presented ambiguous results concerning the precise nature of the layers produced. A thorough and comprehensive characterization program including x-ray diffraction, scanning electron microscopy, Rutherford-backscattering spectroscopy, and electrical conductivity measurements has been undertaken to ensure that the films produced were of a true epitaxial nature.

  13. 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.

  14. Epitaxial growth of single crystal films

    NASA Technical Reports Server (NTRS)

    Lind, M. D.

    1980-01-01

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

  15. 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.

  16. 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

  17. 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.

  18. 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

  19. 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.

  20. Growth of Epitaxial Oxide Thin Films on Graphene

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    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.

  1. 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

  2. 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

  3. Structure and magnetic properties of epitaxial terbium- iron thin films

    NASA Astrophysics Data System (ADS)

    Wang, Chuei-Tang

    TbFe2 is a giant magnetostrictive material which has the largest known room temperature magnetostriction constant. The large magnetostriction constant suggests that we can manipulate the magnetic anisotropy of the material using small strains. Other research groups have grown amorphous and polycrystalline TbFe2 films; however, these films lose giant mangetostriction because of diordered atomic structure in the amorphous films and random grain orientation in the polycrystalline films. Single-crystal structure is needed to achieve the large magnetostriction, so epitaxial growth of TbFe2 thin films is necessary. The goal of this research is to grow epitaxial TbFe2 films and study the effect of film strain on magnetic anisotropy. A technique was developed to grow epitaxial TbFe2films using DC magnetron sputtering. The films were grown in a UHV system using elemental Tb and Fe sputtering targets and single-crystal Al2O3, MgO, and CaF2 substrates. (110) -oriented Mo, W, and Nb were used as buffer layers to provide the base for epitaxial growth and to prevent chemical reactions between the TbFe2 films and the substrates. On the Mo and W buffer layers the TbFe2 film is (111) -oriented but on the Nb buffer layer it is (110) -oriented. Preliminary calculation of magnetostrictive anisotropy in TbFe2(111) films predicts that compressive strain greater than 0.5% will induce perpendicular magnetization while tensile strain greater than 0.5% will induce an in- plane magnetization. Epitaxial growth on CaF2 provides compressive thermal strain of 0.51%, and SQUID measurements confirmed that these samples did have perpendicular magnetization. On the other hand, Al2O3 provides tensile thermal strain of 0.56%, and SQUID measurements showed the films on Al2O3 were in-plane. The values of strain on these three substrates were determined by strain measurement from synchrotron radiation. X-ray epitaxial quality measurements revealed a new orientation relationship, R30o, at the TbFe2

  4. Principle of direct van der Waals epitaxy of single-crystalline films on epitaxial graphene.

    PubMed

    Kim, Jeehwan; Bayram, Can; Park, Hongsik; Cheng, Cheng-Wei; Dimitrakopoulos, Christos; Ott, John A; Reuter, Kathleen B; Bedell, Stephen W; Sadana, Devendra K

    2014-09-11

    There are numerous studies on the growth of planar films on sp(2)-bonded two-dimensional (2D) layered materials. However, it has been challenging to grow single-crystalline films on 2D materials due to the extremely low surface energy. Recently, buffer-assisted growth of crystalline films on 2D layered materials has been introduced, but the crystalline quality is not comparable with the films grown on sp(3)-bonded three-dimensional materials. Here we demonstrate direct van der Waals epitaxy of high-quality single-crystalline GaN films on epitaxial graphene with low defectivity and surface roughness comparable with that grown on conventional SiC or sapphire substrates. The GaN film is released and transferred onto arbitrary substrates. The post-released graphene/SiC substrate is reused for multiple growth and transfer cycles of GaN films. We demonstrate fully functional blue light-emitting diodes (LEDs) by growing LED stacks on reused graphene/SiC substrates followed by transfer onto plastic tapes.

  5. Principle of direct van der Waals epitaxy of single-crystalline films on epitaxial graphene

    NASA Astrophysics Data System (ADS)

    Kim, Jeehwan; Bayram, Can; Park, Hongsik; Cheng, Cheng-Wei; Dimitrakopoulos, Christos; Ott, John A.; Reuter, Kathleen B.; Bedell, Stephen W.; Sadana, Devendra K.

    2014-09-01

    There are numerous studies on the growth of planar films on sp2-bonded two-dimensional (2D) layered materials. However, it has been challenging to grow single-crystalline films on 2D materials due to the extremely low surface energy. Recently, buffer-assisted growth of crystalline films on 2D layered materials has been introduced, but the crystalline quality is not comparable with the films grown on sp3-bonded three-dimensional materials. Here we demonstrate direct van der Waals epitaxy of high-quality single-crystalline GaN films on epitaxial graphene with low defectivity and surface roughness comparable with that grown on conventional SiC or sapphire substrates. The GaN film is released and transferred onto arbitrary substrates. The post-released graphene/SiC substrate is reused for multiple growth and transfer cycles of GaN films. We demonstrate fully functional blue light-emitting diodes (LEDs) by growing LED stacks on reused graphene/SiC substrates followed by transfer onto plastic tapes.

  6. 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.

  7. Ferroelectric switching in epitaxial GeTe films

    SciTech Connect

    Kolobov, A. V. Fons, P.; Tominaga, J.; Kim, D. J.; Gruverman, A.; Giussani, A.; Calarco, R.

    2014-06-01

    In this paper, using a resonance-enhanced piezoresponse force microscopy approach supported by density functional theory computer simulations, we have demonstrated the ferroelectric switching in epitaxial GeTe films. It has been shown that in films with thickness on the order of several nanometers reversible reorientation of polarization occurs due to swapping of the shorter and longer Ge-Te bonds in the interior of the material. It is also hinted that for ultra thin films consisting of just several atomic layers weakly bonded to the substrate, ferroelectric switching may proceed through exchange of Ge and Te planes within individual GeTe layers.

  8. Epitaxial growth of high quality WO3 thin films

    DOE PAGES

    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.

  9. 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.

  10. Pulsed organometallic beam epitaxy of complex oxide films

    NASA Astrophysics Data System (ADS)

    Duray, S. J.; Buchholz, D. B.; Song, S. N.; Richeson, D. S.; Ketterson, J. B.; Marks, T. J.; Chang, R. P. H.

    1991-09-01

    The results are reported of a pulsed organometallic beam epitaxy (POMBE) process for growing complex oxide films at low background gas pressure and low substrate temperature using organometallic precursors in an oxygen plasma environment. The results show that POMBE can extend the capability of organometallic chemical vapor deposition to growing complex oxide films with high precision both in composition and structure without the need for post-deposition oxidation and heat treatments. The growth of phase-pure, highly oriented Y-Ba-Cu-O superconducting oxide films is given as an example. Similar to the pulsed laser deposition process, the POMBE method has the potential for in situ processing of multilayer structures.

  11. Microstructure and twinning in epitaxial NiMnGa films

    NASA Astrophysics Data System (ADS)

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

    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.

  12. Chiral habit selection on nanostructured epitaxial quartz films.

    PubMed

    Carretero-Genevrier, Adrián; Gich, Martí; Picas, Laura; Sanchez, Clément; Rodriguez-Carvajal, Juan

    2015-01-01

    Understanding the crystallization of enantiomorphically pure systems can be relevant to diverse fields such as the study of the origins of life or the purification of racemates. Here we report on polycrystalline epitaxial thin films of quartz on Si substrates displaying two distinct types of chiral habits that never coexist in the same film. We combine Atomic Force Microscopy (AFM) analysis and computer-assisted crystallographic calculations to make a detailed study of these habits of quartz. By estimating the surface energies of the observed crystallites we argue that the films are enantiomorphically pure and we briefly outline a possible mechanism to explain the habit and chiral selection in this system.

  13. Conducting and interfacial properties of epitaxial SVO films

    NASA Astrophysics Data System (ADS)

    Ritums, D. L.; Wu, N. J.; Chen, X.; Liu, D.; Ignatiev, A.

    1998-01-01

    Epitaxial thin films (20-200 nm) of SrVO3 have been grown by pulsed laser deposition on Si, MgO, LaAlO3, and SrTiO3 substrates. These films range from insulating, to semiconducting, to metallic, depending on substrate and growth conditions, with resistivity found to be as low as 1 μΩ-cm for SrVO3 films deposited on a Si substrate with a YSZ buffer layer. This is comparable to 10 μΩ-cm for Pt. XPS depth profiling has been performed to study the interface reactions of the films and XRD studies have been done to determine the crystal structure of the films.

  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. 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.

  16. 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.

  17. Controlling magnetic anisotropy in epitaxial FePt(001) films

    SciTech Connect

    Lu Zhihong; Walock, M. J.; LeClair, P.; Butler, W. H.; Mankey, G. J.

    2009-07-15

    Epitaxial equiatomic Fe{sub 50}Pt{sub 50} thin films with a variable order parameter ranging from 0 to 0.9 and Fe{sub 100-x}Pt{sub x} thin films with x ranging from 33 to 50 were deposited on MgO (001) substrates by dc sputtering. A seed layer consisting of nonmagnetic Cr (4 nm)/Pt (12 nm) was used to promote the crystallinity of the magnetic films. The crystal structure and magnetic properties were gauged using x-ray diffraction and magnetometry. The magnetic anisotropy can be controlled by changing the order parameter. For Fe{sub 100-x}Pt{sub x} films, the increase in Fe composition leads to an increase in coercivity in the hard axis loop and causes a loss of perpendicular anisotropy.

  18. Magnetic anisotropy of epitaxial Co_2MnGa film

    NASA Astrophysics Data System (ADS)

    Pechan, Michael; Yu, Chentao; Carr, David; Palmstrom, Chris

    2004-03-01

    Magnetic Heusler alloys are gaining renewed interest due to the theoretical prediction of 100% polarization in the conduction electron bands -- an issue of particular importance in the the realization of spintronic devices. Co_2MnGa (001) films of 30 nm thick have been epitaxially grown on different substrate/buffer layers to produce various levels of strain in the magnetic layer. The present investigation utilizes ferromagnetic resonance (FMR) at both X- and Q-band. For the film grown on ErAs/InGaAs/InP, which exhibits a tensile strain, an induced uniaxial out-of-plane anisotropy (1.1× 10^6 erg/cm^3)^ is measured, which aids the shape anisotropy in constraining the magnetization to the film plane. In contrast, for the film grown on ScErAs/GaAs with a compression strain, a larger, negative induced anisotropy (- 3.3× 10^6 erg/cm^3) is measured whose easy axis perpendicular to the film plane. Both cases indicate a positive magnetostriction effect in Co_2MnGa film. In-plane angular dependence of FMR measurements shows the coexistence of a small 2-fold and 4-fold anisotropy in the order of 10^3 erg/cm^3 for these pseudomorphic films under both tensile and compression. The relationship between the in-plane easy axis and the crystalline orientations in these films depends upon strain.

  19. 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.

  20. 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

  1. Epitaxial orientation of Mg{sub 2}Si(110) thin film on Si(111) substrate

    SciTech Connect

    Wang, Y.; Wang, X. N.; Mei, Z. X.; Du, X. L.; Zou, J.; Jia, J. F.; Xue, Q. K.; Zhang, X. N.; Zhang, Z.

    2007-12-15

    Epitaxial Mg{sub 2}Si(110) thin film has been obtained on Si(111) substrate by thermally enhanced solid-phase reaction of epitaxial Mg film with underlying Si substrate. An epitaxial orientation relationship of Si(111) parallel Mg{sub 2}Si(110) and Si<110> parallel Mg{sub 2}Si<110> has been revealed by transmission electron microscopy. The formation of the unusual epitaxial orientation relationship is attributed to the strain relaxation of Mg{sub 2}Si film in a MgO/Mg{sub 2}Si/Si double heterostructure.

  2. 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.

  3. 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.

  4. Surface instabilities of epitaxial films on a substrate

    NASA Astrophysics Data System (ADS)

    Junqua, N.; Grilhé, J.

    1993-08-01

    The energy variation of an epitaxial film on a substrate is calculated when sinusoidal roughness appears at the surface, using the method of the surface dislocation model. The energy variation is negative beyond a critical value of wavelength which depends on the thickness of the film and on the ratio of the shear moduli of substrate and film. The kinetic of roughness development during film growing are discussed. La méthode des dislocations de surface est utilisée pour calculer la variation d'énergie d'un film mince en épitaxie sur un substrat lorsqu'une rugosité de forme sinusoïdale apparaît à sa surface. On détermine une longueur d'onde critique dépendant du rapport des coefficients d'élasticité du substrat et du film et aussi de l'épaisseur du film, au-delà de laquelle la variation d'énergie est négative. On discute également de la cinétique du développement de la rugosité.

  5. 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

  6. 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.

  7. Electronic properties of epitaxial silicene on diboride thin films.

    PubMed

    Friedlein, Rainer; Yamada-Takamura, Yukiko

    2015-05-27

    The Si counterpart of graphene—silicene—has partially similar but also unique electronic properties that relate to the presence of an extended π electronic system, the flexible crystal structure and the large spin-orbit coupling. Driven by predictions for exceptional electronic properties like the presence of massless charge carriers, the occurrence of the quantum Hall effect and perfect spin-filtering in free-standing, unreconstructed silicene, the recent experimental realization of largely sp(2)-hybridized, Si honeycomb lattices grown on a number of metallic substrates provided the opportunity for the systematic study of the electronic properties of epitaxial silicene phases. Following a discussion of theoretical predictions for free-standing silicene, we review properties of (√3 × √3)-reconstructed, epitaxial silicene phases but with the emphasis on the extensively studied case of silicene on ZrB2(0 0 0 1) thin films. As the experimental results show, the structural and electronic properties are highly interlinked and leave their fingerprint on the chemical states of individual Si atoms as revealed in core-level photoelectron spectra as well as in the valence electronic structure and low-energy interband transitions. With the critical role of substrates and of the chemical stability of epitaxial silicene highlighted, finally, benefits and challenges for any future silicene-based nanoelectronics are being put into perspective.

  8. 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

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. Epitaxial growth of MgB2 films at ambient temperature

    NASA Astrophysics Data System (ADS)

    Shishido, Hiroaki; Yoshida, Takuya; Nakagami, Takatoshi; Ishida, Takekazu

    We grew crystalline MgB2 thin films using molecular beam epitaxy at a low substrate temperature of 110 °C under an ultrahigh vacuum of about 10-6 Pa. MgB2 thin films were deposited on the (001) surface of a 4H-SiC substrate with an epitaxial Mg buffer layer. The epitaxial growth was confirmed by X-ray diffraction measurements. MgB2 thin films show a sharp superconducting transition at 27.2 K, with a relatively narrow superconducting transition width ΔTc = 0.9 K. The growth temperature was lower than any in prior reports on superconducting MgB2 thin films. The presence of the epitaxial Mg buffer layer is crucial for reducing the epitaxial temperature.

  14. 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.

  15. 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.

  16. 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.

  17. Pulsed organometallic beam epitaxy of complex oxide films

    SciTech Connect

    Duray, S.J.; Buchholz, D.B.; Song, S.N.; Richeson, D.S.; Ketterson, J.B.; Marks, T.J.; Chang, R.P.H. )

    1991-09-16

    We report the results of a pulsed organometallic beam epitaxy (POMBE) process for growing complex oxide films at low background gas pressure (10{sup {minus}4}--10{sup {minus}2} Torr) and low substrate temperature (600--680 {degree}C) using organometallic precursors in an oxygen plasma environment. Our results show that POMBE can extend the capability of organometallic chemical vapor deposition to growing complex oxide films with high precision both in composition and structure without the need for post-deposition oxidation and heat treatments. The growth of phase-pure, highly oriented Y-Ba-Cu-O superconducting oxide films {l brace}({ital T}{sub {ital c}} ({ital R}=0)=90.5 K) and {ital J}{sub {ital c}} (77 K, 50 K gauss)=1.1{times}10{sup 5} A/cm{sup 2}{r brace} is given as an example. Similar to the pulsed laser deposition process, the POMBE method has the potential for {ital in} {ital situ} processing of multilayer structures (e.g., junctions).

  18. 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

  19. 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.

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

    DOE PAGES

    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.

  1. Predicting epitaxial orientations and lattice structure in ultrathin magnetic thin films

    NASA Astrophysics Data System (ADS)

    Lu, Yong; Wang, Cuiping; Shi, Rongpei; Cui, Yuanyuan; Shi, Zhan; Yang, Shuiyuan; Cui, Yuwen; Liu, Xingjun

    2016-07-01

    Metastable phases, such as bcc Co or Ni and hcp Fe or Ni, reportedly possess extraordinary magnetic properties for epitaxial ultra-thin films. To understand phase stability of these epitaxy-oriented phases upon substrate lattices, we calculated novel phase diagrams of Co, Fe, and Ni ultrathin films by considering the chemical free energy, elastic strain energy, and surface energy. Verified by experimental data in the literatures, the stable epitaxy-oriented phases are readily identified from the phase diagrams. The stabilization of these metastable phases is determined by the interplay between orientation-dependent elastic strain energy and surface energy.

  2. Angular dependence of Raman spectrum for Pb(Zr,Ti)O3 epitaxial films

    NASA Astrophysics Data System (ADS)

    Fukushima, Hiroaki; Ichinose, Daichi; Funakubo, Hiroshi; Uchida, Hiroshi; Shima, Hiromi; Nishida, Ken

    2016-10-01

    Herein, we investigate the angular dependence of the Raman spectra of (001)/(100)-oriented tetragonal and (111)/(11\\bar{1})-oriented rhombohedral epitaxial lead zirconate titanate (PZT) films. The A 1 and E modes have the same angular dependence for the (111)/(11\\bar{1})-oriented rhombohedral epitaxial PZT film, but not for the (001)/(100)-oriented tetragonal epitaxial PZT film. These results agree well with theoretical predictions. On the basis of the fact that the angular dependence of the phonon mode in PZT films is linked to the crystal orientation and structure, the angular dependence of the Raman modes can be used to investigate the orientation and structure of PZT films.

  3. Epitaxial growth of B-doped high quality diamond film on cBN surface by chemical vapor deposition

    SciTech Connect

    Zou, G.T.; Gao, C.X.; Zhang, T.C.

    1995-12-31

    B-doped high quality diamond epitaxial films have been obtained on high-pressure synthesized cBN crystals by dc glow discharge chemical vapor deposition (CVD). The deposition conditions and the orientation of cBN crystal are important to diamond oriented nucleation and epitaxial growth. The micro-Raman spectroscopy measurement indicates that the quality of the diamond film grown on cBN (100) surface is close to that of natural diamond. The scanning electron microscopy (SEM) observation shows that the epitaxial film has very smooth surface. The specific resistance of the B-doped epitaxial film is about 0.1 ohm{center_dot}cm.

  4. 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.

  5. Strain-Tunable Magnetocrystalline Anisotropy in Epitaxial Y3 Fe5 O12 Thin Films

    NASA Astrophysics Data System (ADS)

    Wang, Hailong; Du, Chunhui; Hammel, P. Chris; Yang, Fengyuan

    2014-03-01

    Magnetocrystalline anisotropy plays an essential role in many applications and there is intense interest in understanding the role of magnetoelastic coupling in phonon-magnon interactions in thermal spintronics. It is important to understand magnetocrystalline anisotropy in the presence of lattice distortion induced by epitaxial strain and the underlying magnetization-lattice coupling. Y3Fe5O12 (YIG) has been widely used in microwave applications and spin pumping. Most YIG epitaxial film fabrication has employed Gd3Ga5O12 (GGG) substrates with nearly perfect lattice match. In order to probe the magnetocrystalline anisotropy and control magnetization by epitaxial strain in epitaxial YIG films, we grow YIG epitaxial thin films on (001)-oriented Y3Al5O12 (YAG) substrate with -3.0% lattice mismatch. We demonstrate strain-tuning of magnetocrystalline anisotropy over a range of more than one thousand Gauss in epitaxial YIG films of excellent crystalline quality grown on YAG substrates. Ferromagnetic resonance (FMR) measurements reveal a linear dependence of both out-of-plane and in-plane uniaxial anisotropy on the strain-induced tetragonal distortion of Y3Fe5O12. Importantly, we find the spin mixing conductance determined from inverse spin Hall effect and FMR linewidth broadening remains large in Pt/YIG/YAG heterostructures, quite comparable to the value found in Pt/YIG grown on lattice-matched GGG substrates.

  6. 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.

  7. Structure and magnetism of epitaxial rare-earth-transition-metal films

    SciTech Connect

    Fullerton, E.E.; Sowers, C.H.; Pearson, J.P.; Bader, S.D.

    1996-10-01

    Growth of epitaxial transition-metal superlattices; has proven essential in elucidating the role of crystal orientation and structure on magnetic properties such as giant magnetoresistance, interlayer coupling, and magnetic surface anisotropies. Extending these studies to the growth of epitaxial rare earth-transition metal (RE-TM) films and superlattices promises to play an equally important role in exploring and optimizing the properties of hard magnets. For instance, Skomski and Coey predict that a giant energy product (120 MG Oe) is possible in multilayer structures consisting of aligned hard-magnet layers exchanged coupled with soft-phase layers with high magnetization. Epitaxy provides one route to synthesizing such exchange-hardened magnets on controlled length scales. Epitaxial growth also allows the magnetic properties to be tailored by controlling the crystal orientation and the anisotropies of the magnetic layers and holds the possibility of stabilizing metastable phases. This paper describes the epitaxy and magnetic properties for several alloys.

  8. 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.

  9. 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.

  10. 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.

  11. Quantum transport in the surface states of epitaxial Bi(111) thin films

    NASA Astrophysics Data System (ADS)

    Zhu, Kai; Wu, Lin; Gong, Xinxin; Xiao, Shunhao; Jin, Xiaofeng

    2016-09-01

    Although bulk Bi is a prototypical semimetal with a topologically trivial electronic band structure, we show by various quantum transport measurements that epitaxial Bi(111) thin films have unexpected and nontrivial properties. Not only the top and the bottom but also the side surfaces of epitaxial Bi(111) thin films are always robustly metallic while the interior has already become insulating. We identify the coupling between the top and the bottom surface states that drives the two originally independent surface conducting channels into a single connected one. The properties of Bi(111) thin films realized could lead to promising applications in spintronics.

  12. 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.

  13. 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

  14. Epitaxial growth of iridate pyrochlore Nd2Ir2O7 films

    DOE PAGES

    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

  15. 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.

  16. 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

  17. Epitaxial growth of iridate pyrochlore Nd2Ir2O7 films.

    PubMed

    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. The epitaxial relationship between the YSZ and Nd2Ir2O7 is observed clearly while some interfacial regions show a thin region with polycrystalline Ir nanocrystals.

  18. High rate epitaxy of silicon thick films by medium pressure plasma chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Kambara, M.; Yagi, H.; Sawayanagi, M.; Yoshida, T.

    2006-04-01

    Homoepitaxial silicon thick films have been produced by medium pressure plasma chemical vapor deposition at rates as fast as 60 nm/s and at a temperature of around 700 °C, with a silane gas partial pressure of 4 mTorr. The continuous transition of the film structures from agglomerated to faceted columnar and to epitaxial planar structure was observed with an increase in the plasma power. The calorimetric analysis during deposition has also confirmed that the thermal boundary layer thickness between the plasma and substrate reduced with the increasing power and became comparable to the mean free path of the vapors when epitaxy was achieved at high rates. In addition, the rate for epitaxial growth was observed to increase linearly with silane gas partial pressure. These potentially indicate that less coagulated silicon atom clusters formed in the reduced boundary thickness have contributed effectively to the high rate epitaxial growth.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. InSb photodetectors with PIN and nBn designs

    NASA Astrophysics Data System (ADS)

    Evirgen, A.; Abautret, J.; Perez, J. P.; Aït-Kaci, H.; Christol, P.; Fleury, J.; Sik, H.; Nedelcu, A.; Cluzel, R.; Cordat, A.

    2013-12-01

    InSb pin photodiodes and nBn photodetectors were fabricated by Molecular Beam epitaxy (MBE) on InSb (100) n-type substrate and characterized. MBE Growth conditions were carefully studied to obtain high quality InSb layers, exhibiting in pin photodiode design dark current density values as low as 13nA.cm-2 at -50mV and R0A product as high as 6x106 WΩcm2 at 77K. Then, a new unipolar nBn InSb/InAlSb/InSb detector structure on InSb substrate were designed in order to suppress generation-recombination dark current. The first InSb nBn devices were fabricated and preliminary electrical characterizations are reported.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Photoluminescence from CdTe/sapphire films prepared by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Edwards, S. T.; Schreiner, A. F.; Myers, T. M.; Schetzina, J. F.

    1983-11-01

    Photoluminescence studies at 77 K are reported for CdTe/sapphire films prepared by molecular beam epitaxy. The CdTe/sapphire epilayers exhibited very bright photoluminescence spectra that were dominated by the near-edge emission band at 1.58 eV. The best CdTe/sapphire film proved to be the brightest source of luminescence of any CdTe specimen studied in our laboratories, including homoepitaxial films and bulk hydroplane polished samples. The CdTe/sapphire films also exhibited the best lateral uniformity as manifested by a nearly constant luminescence intensity over their surfaces. These results provide new evidence that high quality CdTe epitaxy on sapphire has been achieved.

  14. Epitaxial Growth of CaF2 Films on Si(111) Studied by Scanning Tunneling Microscopy

    NASA Astrophysics Data System (ADS)

    Kametani, Keisuke; Sudoh, Koichi; Iwasaki, Hiroshi

    2002-01-01

    Using ultrahigh vacuum scanning tunneling microscopy, we have studied the early stages of the epitaxial growth of CaF2 films on Si(111) at 630°C at a slow deposition rate of 0.2 monolayer (ML) per minute. After formation of CaF interface layer, we observe the film grows in the sequence of step edge decoration, one-dimensional islands growth on the terrace, formation of clusters of the islands, coalescence of the island cluster and filling of gaps between the one-dimensional islands in the cluster and between the island clusters to complete a layer. By such a sequence, epitaxial CaF2 films with atomically flat surface could be grown in layer-by-layer fashion up to 3 ML. The growth mode is discussed in relation to kinetic phase diagram [M. A. Olmstead: Thin Films: Heteroepitaxial Systems, eds. W. K. Liu and M. B. Santos (World Scientific, Singapore, 1999) Chap. 5].

  15. 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.

  16. 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.

  17. 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.

  18. Grazing-incidence X-ray diffraction study of rubrene epitaxial thin films.

    PubMed

    Fumagalli, Enrico; Campione, Marcello; Raimondo, Luisa; Sassella, Adele; Moret, Massimo; Barba, Luisa; Arrighetti, Gianmichele

    2012-09-01

    The growth of organic semiconductors as thin films with good and controlled electrical performances is nowadays one of the main tasks in the field of organic semiconductor-based electronic devices. In particular it is often required to grow highly crystalline and precisely oriented thin films. Here, thanks to grazing-incidence X-ray diffraction measurements carried out at the ELETTRA synchrotron facility, it is shown that rubrene thin films deposited by organic molecular beam epitaxy on the surface of tetracene single crystals have the structure of the known orthorhombic polymorph, with the (2 0 0) plane parallel to the substrate surface. Moreover, the exact epitaxial relationship between the film and the substrate crystalline structures is determined, demonstrating the presence of a unique in-plane orientation of the overlayer. PMID:22898945

  19. Photoresponse experiments on NbN proximized nanostructures

    NASA Astrophysics Data System (ADS)

    Pepe, G. P.; Parlato, L.; Pagliarulo, V.; Marrocco, N.; De Lisio, C.; Peluso, G.; Barone, A.; Taino, T.; Myoren, H.; Casaburi, A.; Ejrnaes, M.; Cristiano, R.

    2010-06-01

    Among superconducting materials used in developing high performance nanowire detectors, NbN demonstrated to have unique characteristics in terms of fast response time, quantum efficiency and photon-number resolving capability. We investigated the role of proximity effect on superconducting NbN thin films covered by a weak ferromagnetic NiCu thin layer. Hetero-structures NbN/NiCu have been deposited by DC magnetron sputtering on MgO substrates without any heating. Characterization in terms of morphological, transport, and ultra-fast optical properties has been done. Superconducting nanowires with meander-type geometries (48 micron lengths and <500 nm widths) have been designed and fabricated. Preliminary results concerning their photoresponse to 1550nm laser irradiation are presented.

  20. Strain-controlled optical absorption in epitaxial ferroelectric BaTiO{sub 3} films

    SciTech Connect

    Chernova, E.; Pacherova, O.; Chvostova, D.; Dejneka, A.; Kocourek, T.; Jelinek, M.; Tyunina, M.

    2015-05-11

    A lattice strain of 0.3%–1.3% is achieved in epitaxial tetragonal BaTiO{sub 3} films grown on (001)-oriented SrTiO{sub 3} single-crystal substrates. Our experimental studies of absorption spectra in the range of 0.74–9.0 eV demonstrate that epitaxy produces significant changes in the optical properties of the films compared with those of a reference polydomain BaTiO{sub 3} crystal: the absorption edge and the peak at 5 eV strongly blue-shift by 0.2–0.4 eV, the magnitude of the peak at 5 eV drops, and certain spectral features disappear, whereas the absorption peak at 8.5 eV remains unchanged. The observed behavior is attributed to ferroelectric polarization, which is enhanced by epitaxial strain in the films. Our results indicate that epitaxially induced variations of ferroelectric polarization may be used to tailor the optical properties of thin films for photonic and optoelectronic applications.

  1. 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.

  2. Epitaxial Ba-Y-Cu-O ceramic superconducting film on perovskite structure substrate

    SciTech Connect

    Chai, B.H.

    1991-07-09

    This patent describes a superconducting structure. It comprises a crystal substrate having a superconducting film epitaxially deposited thereon, wherein the substrate is a crystal selected from the group consisting of LaAlO{sub 3}, LaGaO{sub 3}, PrGaO{sub 3} and NdGaO{sub 3}, and wherein the superconducting film is a Ba- Y- Cu- O superconductor.

  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. 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.

  5. Enhanced Deposition Efficiency of Epitaxial Si Film from SiHCl3 by Mesoplasma Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Wu, Sudong; Kambara, Makoto; Yoshida, Toyonobu

    Epitaxial Si thick films have been deposited by mesoplasma chemical vapor deposition with SiHCl3-H2-Ar gas mixtures at high efficiency. Addition of hydrogen has been revealed to increase the deposition efficiency by removing Cl as a form of HCl. It also promotes the surface migration of deposition precursors for the attainment of epitaxial Si films. As a result, epitaxial Si films with a production yield of about 60% and a deposition rate of 430 nm/s were deposited at a H2/TCS ratio of 2-3.

  6. Sharp chemical interface in epitaxial Fe{sub 3}O{sub 4} thin films

    SciTech Connect

    Gálvez, S.; Rubio-Zuazo, J. Salas-Colera, E.; Muñoz-Noval, A.; Castro, G. R.

    2014-12-15

    Chemically sharp interface was obtained on single phase single oriented Fe{sub 3}O{sub 4} (001) thin film (7 nm) grown on NiO (001) substrate using oxygen assisted molecular beam epitaxy. Refinement of the atomic structure, stoichiometry, and oxygen vacancies were determined by soft and hard x-ray photoelectron spectroscopy, low energy electron diffraction and synchrotron based X-ray reflectivity, and X-ray diffraction. Our results demonstrate an epitaxial growth of the magnetite layer, perfect iron stoichiometry, absence of oxygen vacancies, and the existence of an intermixing free interface. Consistent magnetic and electrical characterizations are also shown.

  7. 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.

  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. Fluorination of epitaxial oxides: synthesis of perovskite oxyfluoride thin films.

    PubMed

    Moon, Eun Ju; Xie, Yujun; Laird, Eric D; Keavney, David J; Li, Christopher Y; May, Steven J

    2014-02-12

    While the synthesis of ABO3 perovskite films has enabled new strategies to control the functionality of this material class, the chemistries that have been realized in thin film form constitute only a fraction of those accessible to bulk chemists. Here, we report the synthesis of oxyfluoride films, where the incorporation of F may provide a new means to tune physical properties in thin films by modifying electronic structure. Fluorination is achieved by spin coating a poly(vinylidene fluoride) (PVDF) solution onto oxygen-deficient films. The film/polymer bilayer is then annealed, promoting the diffusion of F into the film. We have used this method to synthesize SrFeO(3-α)Fγ films, as confirmed by X-ray photoemission spectroscopy and X-ray absorption spectroscopy. PMID:24443775

  10. 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.

  11. 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.

  12. 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.

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

    DOE PAGES

    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

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

    DOE PAGES

    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

  15. Phase-controlled electrochemical activity of epitaxial Mg-spinel thin films

    DOE PAGES

    Feng, Zhenxing; Chen, Xiao; Qiao, Liang; Lipson, Albert L.; Fister, Timothy T.; Zeng, Li; Kim, Chunjoong; Yi, Tanghong; Sa, Niya; Proffit, Danielle L.; et al

    2015-12-07

    We report an approach to control the reversible electrochemical activity (i.e., extraction/insertion) of Mg2+ 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 Mg2+ activity with associated changes in film structure and Mn oxidation state. Lastly, these results demonstrate a novel strategy for identifying themore » factors that control multivalent cation mobility in next generation battery materials.« less

  16. Phase-controlled electrochemical activity of epitaxial Mg-spinel thin films

    SciTech Connect

    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

    2015-12-07

    We report an approach to control the reversible electrochemical activity (i.e., extraction/insertion) of Mg2+ 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 Mg2+ activity with associated changes in film structure and Mn oxidation state. Lastly, these results demonstrate a novel strategy for identifying the factors that control multivalent cation mobility in next generation battery materials.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  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.

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

    PubMed

    Carretero-Genevrier, Adrián; Gich, Martí

    2015-12-21

    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.

  3. 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.

  4. Photoresponse of YBa2Cu3O(7-delta) granular and epitaxial superconducting thin films

    NASA Technical Reports Server (NTRS)

    Valco, G. J.; Claspy, P.; Warner, J. D.; Varaljay, N.; Bhasin, K. B.

    1990-01-01

    The response is reported of thin films of YBa2Cu3O(7-delta) with either a very grainy or a smooth epitaxial morphology to visible radiation. SrTiO3 substrates were employed for both types of films. The grainy films were formed by sequential multi-layer electron beam evaporation while the epitaxial films were formed by laser ablation. Both films were patterned into H shaped detectors via a negative photolithographic process employing a Br/ethanol etchant. The bridge region of the H was 50 microns wide. The patterned films formed by laser ablation and sequential evaporation had critical temperatures of 74 K and 72 K respectively. The bridge was current biased and illuminated with chopped He-Ne laser radiation and the voltage developed in response to the illumination was measured. A signal was detected only above the critical temperature and the peak of the response coincided with the resistive transition for both types of films although the correspondence was less exact for the grainy film. The details of the responses and their analysis are presented.

  5. Molecular beam epitaxy and characterization of thin Bi2Se3 films on Al2O3 (110)

    NASA Astrophysics Data System (ADS)

    Tabor, Phillip; Keenan, Cameron; Urazhdin, Sergei; Lederman, David

    2011-07-01

    The structural and electronic properties of thin Bi2Se3 films grown on Al2O3 (110) by molecular beam epitaxy are investigated. The epitaxial films grow in the Frank-van der Merwe mode and are c-axis oriented. They exhibit the highest crystallinity, the lowest carrier concentration, and optimal stoichiometry at a substrate temperature of 200 °C determined by the balance between surface kinetics and desorption of Se. The crystallinity of the films improves with increasing Se/Bi flux ratio. Our results enable studies of thin topological insulator films on inert, non-conducting substrates that allow optical access to both film surfaces.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Terahertz surface impedance of epitaxial MgB2 thin film

    NASA Astrophysics Data System (ADS)

    Jin, B. B.; Kuzel, P.; Kadlec, F.; Dahm, T.; Redwing, J. M.; Pogrebnyakov, A. V.; Xi, X. X.; Klein, N.

    2005-08-01

    We report on terahertz (THz) surface impedance measurement of an epitaxial MgB2 thin film using time domain THz spectroscopy. We show that the surface resistance of the MgB2 film is much lower than that of YBa2Cu3O7-δ and copper in the THz range. A linear dependence of the surface reactance on frequency is observed, yielding a penetration depth of about 100nm at low temperatures. The measurements agree qualitatively with calculations based on impurity scattering in the Born limit. Our results clearly indicate that MgB2 thin films have a great potential for THz electronic applications.

  11. 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.

  12. 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.

  13. Growth of epitaxial thin films of scandium nitride on 100-oriented silicon

    NASA Astrophysics Data System (ADS)

    Moram, M. A.; Novikov, S. V.; Kent, A. J.; Nörenberg, C.; Foxon, C. T.; Humphreys, C. J.

    2008-05-01

    A series of 100-oriented ScN films was grown under N-rich conditions on 100-oriented Si using different Sc fluxes. The ScN films grew in an epitaxial cube-on-cube orientation, with [0 0 1] ScN//[0 0 1] Si and [1 0 0] ScN//[1 0 0] Si, despite the high (11%) lattice mismatch between ScN and Si. The film grain size increases and the film ω-FWHM decreases with increasing Sc flux, but the film roughness increases. Films grown under similar conditions on 111-oriented Si resulted in mixed 111 and 100 orientations, indicating that the 100 orientation is favoured both due to texture inheritance from the substrate and due to the growth conditions used.

  14. Epitaxial growth and electronic structure of oxyhydride SrVO2H thin films

    NASA Astrophysics Data System (ADS)

    Katayama, Tsukasa; Chikamatsu, Akira; Yamada, Keisuke; Shigematsu, Kei; Onozuka, Tomoya; Minohara, Makoto; Kumigashira, Hiroshi; Ikenaga, Eiji; Hasegawa, Tetsuya

    2016-08-01

    Oxyhydride SrVO2H epitaxial thin films were fabricated on SrTiO3 substrates via topotactic hydridation of oxide SrVO3 films using CaH2. Structural and composition analyses suggested that the SrVO2H film possessed one-dimensionally ordered V-H--V bonds along the out-of-plane direction. The synthesis temperature could be lowered by reducing the film thickness, and the SrVO2H film was reversible to SrVO3 by oxidation through annealing in air. Photoemission and X-ray absorption spectroscopy measurements revealed the V3+ valence state in the SrVO2H film, indicating that the hydrogen existed as hydride. Furthermore, the electronic density of states was highly suppressed at the Fermi energy, consistent with the prediction that tetragonal distortion induces metal to insulation transition.

  15. 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.

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

    DOE PAGES

    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

  17. Strain control of Morin temperature in epitaxial α-Fe2O3(0001) film

    NASA Astrophysics Data System (ADS)

    Park, SeongHun; Jang, H.; Kim, J.-Y.; Park, B.-G.; Koo, T.-Y.; Park, J.-H.

    2013-07-01

    We present comprehensive studies of strain effects on the spin reorientation transition (SRT), the so-called Morin transition, in α-Fe2O3(0001) films. The α-Fe2O3(0001) epitaxial films were grown with a Cr2O3 buffer layer on Al2O3(0001) substrates through an oxide molecular beam epitaxy. The antiferromagnetic spin axis was monitored by using the Fe L2-edge X-ray magnetic linear dichroism. The buffer layer was found to introduce compressive strain into the α-Fe2O3(0001) film due to its 1.6% smaller in-plane lattice constant. The degree of strain is monotonically reduced with the increase of the α-Fe2O3 film thickness and becomes relaxed in the thick region (> 20 nm). The transition temperature TM, which increases up to ≃360 K, well above the bulk TM = 263 K, for the film thickness ≃3 nm, gradually decreases as the film thickness increases. We also examined the Néel temperature TN in the ultra-thin region (< 3 nm), which rapidly drops with the decrease of the film thickness. The correlation between TM and the strain in the α-Fe2O3(0001) epitaxial films was found to be well explained in terms of two competing energies of magnetic dipole anisotropy and single-ion magnetocrystalline anisotropy except for the ultra-thin region, in which TN is dominated by the finite-size effects.

  18. 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.

  19. 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.

  20. Suppression of superconductivity in epitaxial MgB2 ultrathin films

    NASA Astrophysics Data System (ADS)

    Zhang, Chen; Wang, Yue; Wang, Da; Zhang, Yan; Liu, Zheng-Hao; Feng, Qing-Rong; Gan, Zi-Zhao

    2013-07-01

    MgB2 ultrathin films have potential to make sensitive superconducting devices such as superconducting single-photon detectors working at relatively high temperatures. We have grown epitaxial MgB2 films in thicknesses ranging from about 40 nm to 6 nm by using the hybrid physical-chemical vapor deposition method and performed electrical transport measurements to study the thickness dependence of the superconducting critical temperature Tc. With reducing film thickness d, although a weak depression of the Tc has been observed, which could be attributed to an increase of disorder (interband impurity scattering) in the film, the Tc retains close to the bulk value of MgB2 (39 K), being about 35 K in the film of 6 nm thick. We show that this result, beneficial to the application of MgB2 ultrathin films and in accordance with recent theoretical calculations, is in contrast to previous findings in MgB2 films prepared by other methods such as co-evaporation and molecular-beam epitaxy, where a severe Tc suppression has been observed with Tc about one third of the bulk value in films of ˜5 nm thick. We discuss this apparent discrepancy in experiments and suggest that, towards the ultrathin limit, the different degrees of Tc suppression displayed in currently obtained MgB2 films by various techniques may arise from the different levels of disorder present in the film or different extents of proximity effect at the film surface or film-substrate interface.

  1. 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.

  2. Epitaxial growth of nanostructured gold films on germanium via galvanic displacement.

    PubMed

    Sayed, Sayed Y; Buriak, Jillian M

    2010-12-01

    This work focuses on the synthesis and characterization of gold films grown via galvanic displacement on Ge(111) substrates. The synthetic approach uses galvanic displacement, a type of electroless deposition that takes place in an efficient manner under aqueous, room temperature conditions. Investigations involving X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques were performed to study the crystallinity and orientation of the resulting gold-on-germanium films. A profound effect of HF(aq) concentration was noted, and although the SEM images did not show significant differences in the resulting gold films, a host of X-ray diffraction studies demonstrated that higher concentrations of HF(aq) led to epitaxial gold-on-germanium, whereas in the absence of HF(aq), lower degrees of order (fiber texture) resulted. Cross-sectional nanobeam diffraction analyses of the Au-Ge interface confirmed the epitaxial nature of the gold-on-germanium film. This epitaxial behavior can be attributed to the simultaneous etching of the germanium oxides, formed during the galvanic displacement process, in the presence of HF. High-resolution TEM analyses showed the coincident site lattice (CSL) interface of gold-on-germanium, which results in a small 3.8% lattice mismatch due to the coincidence of four gold lattices with three of germanium.

  3. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  5. 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.

  6. van der Waals epitaxy of CdTe thin film on graphene

    NASA Astrophysics Data System (ADS)

    Mohanty, Dibyajyoti; Xie, Weiyu; Wang, Yiping; Lu, Zonghuan; Shi, Jian; Zhang, Shengbai; Wang, Gwo-Ching; Lu, Toh-Ming; Bhat, Ishwara B.

    2016-10-01

    van der Waals epitaxy (vdWE) facilitates the epitaxial growth of materials having a large lattice mismatch with the substrate. Although vdWE of two-dimensional (2D) materials on 2D materials have been extensively studied, the vdWE for three-dimensional (3D) materials on 2D substrates remains a challenge. It is perceived that a 2D substrate passes little information to dictate the 3D growth. In this article, we demonstrated the vdWE growth of the CdTe(111) thin film on a graphene buffered SiO2/Si substrate using metalorganic chemical vapor deposition technique, despite a 46% large lattice mismatch between CdTe and graphene and a symmetry change from cubic to hexagonal. Our CdTe films produce a very narrow X-ray rocking curve, and the X-ray pole figure analysis showed 12 CdTe (111) peaks at a chi angle of 70°. This was attributed to two sets of parallel epitaxy of CdTe on graphene with a 30° relative orientation giving rise to a 12-fold symmetry in the pole figure. First-principles calculations reveal that, despite the relatively small energy differences, the graphene buffer layer does pass epitaxial information to CdTe as the parallel epitaxy, obtained in the experiment, is energetically favored. The work paves a way for the growth of high quality CdTe film on a large area as well as on the amorphous substrates.

  7. Synchrotron X-ray studies of epitaxial ferroelectric thin films and nanostructures

    NASA Astrophysics Data System (ADS)

    Klug, Jeffrey A.

    The study of ferroelectric thin films is a field of considerable scientific and technological interest. In this dissertation synchrotron x-ray techniques were applied to examine the effects of lateral confinement and epitaxial strain in ferroelectric thin films and nanostructures. Three materials systems were investigated: laterally confined epitaxial BiFeO3 nanostructures on SrTiO3 (001), ultra-thin commensurate SrTiO 3 films on Si (001), and coherently strained films of BaTiO3 on DyScO3 (110). Epitaxial films of BiFeO3 were deposited by radio frequency magnetron sputtering on SrRuO3 coated SrTiO 3 (001) substrates. Laterally confined nanostructures were fabricated using focused ion-beam processing and subsequently characterized with focused beam x-ray nanodiffraction measurements with unprecedented spatial resolution. Results from a series of rectangular nanostructures with lateral dimensions between 500 nm and 1 mum and a comparably-sized region of the unpatterned BiFeO3 film revealed qualitatively similar distributions of local strain and lattice rotation with a 2-3 times larger magnitude of variation observed in those of the nanostructures compared to the unpatterned film. This indicates that lateral confinement leads to enhanced variation in the local strain and lattice rotation fields in epitaxial BiFeO3 nanostructures. A commensurate 2 nm thick film of SrTiO3 on Si was characterized by the x-ray standing wave (XSW) technique to determine the Sr and Ti cation positions in the strained unit cell in order to verify strain-induced ferroelectricity in SrTiO3/Si. A Si (004) XSW measurement at 10°C indicated that the average Ti displacement from the midpoint between Sr planes was consistent in magnitude to that predicted by a density functional theory (DFT) calculated ferroelectric structure. The Ti displacement determined from a 35°C measurement better matched a DFT-predicted nonpolar structure. The thin film extension of the XSW technique was employed to

  8. 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.

  9. 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.

  10. Effect of buffer layer growth temperature on epitaxial GaN films deposited by magnetron sputtering

    SciTech Connect

    Mohanta, P.; Singh, D.; Kumar, R.; Ganguli, T.; Srinivasa, R. S.; Major, S. S.

    2012-06-05

    Epitaxial GaN films were deposited by reactive sputtering of a GaAs target in 100 % nitrogen at 700 deg. C on ZnO buffer layers grown at different substrate temperatures over sapphire substrates. High resolution X-ray diffraction measurements and the corresponding analysis show that the growth temperature of buffer layers significantly affects the micro-structural parameters of GaN epilayer, such as lateral coherence length, tilt and twist, while the vertical coherence length remains unaffected. The optimum substrate temperature for buffer layer growth has been found to be 300 deg. C. High epitaxial quality GaN film grown on such a buffer layer exhibited micro strain of 1.8x10{sup -4} along with screw and edge type dislocation densities of 7.87x10{sup 9} and 1.16x10{sup 11}, respectively.

  11. 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.}

  12. Ferromagnetic resonance in epitaxial films: Effects of lattice strains and voltage control via ferroelectric substrate

    NASA Astrophysics Data System (ADS)

    Pertsev, N. A.; Kohlstedt, H.; Knöchel, R.

    2011-07-01

    The phenomenon of ferromagnetic resonance (FMR) provides fundamental information on the physics of magnetic materials and lies at the heart of a variety of signal processing microwave devices. Here we demonstrate theoretically that substrate-induced lattice strains can change the FMR frequency of an epitaxial ferromagnetic film dramatically, leading to ultralow and ultrahigh resonance frequencies at room temperature. Remarkably, the FMR frequency varies with the epitaxial strain nonmonotonically, reaching minimum at a critical strain corresponding to the strain-induced spin reorientation transition. Furthermore, by coupling the ferromagnetic film to a ferroelectric substrate, it becomes possible to achieve an efficient voltage control of FMR parameters. In contrast to previous studies, we found that the tunability of FMR frequency varies with the applied electric field and strongly increases at critical field intensity.

  13. Evolution of properties of epitaxial bismuth iron garnet films with increasing thickness

    NASA Astrophysics Data System (ADS)

    Kahl, S.; Grishin, A. M.

    2004-07-01

    Bismuth iron garnet (BIG) films of thicknesses from 470 to 2560 nm were prepared by pulsed laser deposition under identical deposition conditions. All films are epitaxial, bismuth deficient, and show rms surface roughnesses between 15 and 40 nm. X-ray coherence lengths decrease with increasing film thickness. Films below approximately 1 μm are free of cracks, thicker films possess a network of cracks. From fits of optical transmission spectra, real and imaginary parts of the refractive indices were found for wavelengths from 500 to 850 nm. The effects of thin film interference and surface roughness were included. With these data as input information, each of our experimental Faraday rotation spectra was described by a single diamagnetic line in visible light. The measured spectra could be reproduced and parameters of the magneto-optical transition were obtained. We observed a broadening of the transition with increasing film thickness and a red shift of the center frequency. This corresponds to our experimental observation that the wavelength of maximum Faraday rotation for BIG films in visible light shifts to longer wavelengths by almost 40 nm for a 2560-nm-thick film as compared to a 470-nm-thick film. As BIG is not thermodynamically stable, aging is a crucial question. We found that careful annealing in oxygen below the deposition temperature increases the angle of Faraday rotation, while film properties deteriorate during long annealing times at the deposition temperature.

  14. Metastable fcc-Fe film epitaxially grown on Cu(100) single-crystal underlayer

    NASA Astrophysics Data System (ADS)

    Ohtake, Mitsuru; Shimamoto, Kohei; Futamoto, Masaaki

    2013-05-01

    Fe film of 40 nm thickness is prepared on fcc-Cu(100) single-crystal underlayer at room temperature by ultra-high vacuum molecular beam epitaxy. The film growth and the detailed structure are investigated by reflection high-energy electron diffraction, cross-sectional high-resolution transmission electron microscopy (HR-TEM), and x-ray diffraction (XRD). An Fe single-crystal with metastable fcc structure nucleates on the underlayer. The HR-TEM shows that fcc lattice is formed from the Fe/Cu interface up to the film surface. A large number of misfit dislocations are introduced around the Fe/Cu interface due to an accommodation of lattice mismatch. Dislocations exist up to the film near surface. The lattice constant is estimated by XRD to be a = 0.3607 nm. The film shows a ferromagnetic property, which reflects the property of fcc-Fe crystal with high-spin ferromagnetic state.

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

    DOE PAGES

    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

  16. 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.

  17. 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.

  18. 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.

  19. Tunable epitaxial growth of magnetoresistive La2/3Sr1/3MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Fontcuberta, J.; Bibes, M.; Martínez, B.; Trtik, V.; Ferrater, C.; Sánchez, F.; Varela, M.

    1999-04-01

    We report on the growth of epitaxial La2/3Sr1/3MnO3 thin films on buffered Si(001) substrates. We show that a suitable choice of the buffer heterostructure allows one to obtain epitaxial (00h), (0hh), and (hhh) manganite thin films. The magnetotransport properties are investigated and we have found that the low-field magnetoresistance is directly related to the width of the normal-to-plane rocking curves, irrespective of the film orientation. The magnetic anisotropy of these films has also been determined.

  20. Epitaxial growth of biaxially oriented YBCO films on silver

    NASA Astrophysics Data System (ADS)

    Liu, Danmin; Zhou, Meiling; Wang, Xue; Suo, Hongli; Zuo, Tieyong; Schindl, Michael; Flükiger, René

    2001-09-01

    YBCO films were deposited on (100), (110) and (111) oriented silver single crystals and { 100} <100>, { 110} <211> and { 012} <100> biaxially textured Ag substrates by pulsed laser deposition. It is shown that the (100) and (110) orientated single crystals and the { 110} biaxially textured Ag tape are all suitable for the deposition of YBCO thin films with c-axis in-plane alignment. The Jc of YBCO film deposited on { 110} <211> biaxially textured Ag foil is 7×105A cm-2 at 77 K, 0 T. A scheme for the regular growth of YBCO on silver was put forward.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Molecular beam epitaxy growth and optical properties of single crystal Zn3N2 films

    NASA Astrophysics Data System (ADS)

    Wu, Peng; Tiedje, T.; Alimohammadi, H.; Bahrami-Yekta, V.; Masnadi-Shirazi, M.; Wang, Cong

    2016-10-01

    Single crystal Zn3N2 films with (100) orientation have been grown by plasma-assisted molecular beam epitaxy on MgO and A-plane sapphire substrates with in situ optical reflectance monitoring of the growth. The optical bandgap was found to be 1.25-1.28 eV and an electron Hall mobility as high as 395 cm2 V-1 s-1 was measured. The films were n-type with carrier concentrations in the 1018-1019 cm-3 range.

  8. 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.

  9. Strain Effects on the Structural and Magnetic Properties of La- Ca-Mn-O Epitaxial Films

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P; Yeh, N. -C.; Beam, D. A.; Foote, M. C.

    1995-01-01

    La0.7Ca0.3MnO3 (a = 3.86 angstroms) epitaxial thin films have been grown on SrTiO3 (a = 3.905 angstroms), LaAlO3 (a = 3.79 angstroms), and YAlO3 (a/square root of 2 = 3.66 angstroms, b/square root of 2 = 3.77 angstroms) substrates. The films were analyzed with x-ray diffraction, x-ray photoemission spectroscopy, dc and ac resistivity, and dc magnetization.

  10. 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.

  11. 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.

  12. Structure and roughness analysis of thin epitaxial Pd films grown on Cu/Si(111) surface

    NASA Astrophysics Data System (ADS)

    Davydenko, A. V.; Kozlov, A. G.; Ognev, A. V.; Stebliy, M. E.; Chebotkevich, L. A.

    2016-10-01

    We investigated growth processes of epitaxial Pd(111) films on Cu(10 ML)/Si(111) substrate. We found three stages of growth. In the first stage, up to Pd thickness of 2.6 ML, the Pd film is the most disordered. Most of the strains in the Pd film relax in this stage. In the second stage, in the thickness interval from 2.6 to 13 ML, the roughness of the Pd does not change significantly and the Pd grows in a layer-by-layer like mode. During the second stage, the lattice parameter of the Pd film gradually increases to volume value. With increasing coverage after 13 ML, in the third stage, the lattice parameter does not change, but the roughness of the Pd films increases rapidly. Pd islands grow in height and in lateral size. Epitaxial growth of Pd on Cu(10 ML)/Si(111) substrate is compared with the growth of Pd on Cu(111) single crystal; the results obtained are discussed.

  13. Epitaxial aluminum-doped zinc oxide thin films on sapphire. 2: Defect equilibria and electrical properties

    SciTech Connect

    Srikant, V.; Sergo, V.; Clarke, D.R.

    1995-07-01

    The electrical transport properties of epitaxial ZnO films grown on different orientations of sapphire substrates have been measured as a function of partial pressure of oxygen. After equilibration, the carrier concentration is found to change from a p{sub O{sub 2}}{sup {minus}1/4} to a p{sub O{sub 2}}{sup {minus}3/8} dependence with increasing oxygen partial pressure. The partial pressure dependence is shown to be consistent with zinc vacancies being the rate-controlling diffusive species. In addition, the carrier concentration in ZnO films grown on A-, C-, and M-plane sapphire are the same but that of R-plane sapphire is systematically lower. Electron Hall mobility measurements as a function of carrier concentration for all the substrate orientations exhibit a transition from ``single-crystal`` behavior at high carrier concentrations to ``polycrystalline`` behavior at low carrier concentrations. This behavior is attributed to the effective height of potential barriers formed at the low-angle grain boundaries in the epitaxial ZnO films. The trap density at the grain boundaries is deduced to be {approximately}7 {times} 10{sup 12}/cm{sup 2}. The electron mobility, at constant carrier concentration, varies with the substrate orientation on which the ZnO films were grown. The difference is attributed to the difference in dislocation density in the films produced as a result of lattice mismatch with the different sapphire orientations.

  14. Dielectric response of epitaxially strained CoFe2O4 spinel thin films

    NASA Astrophysics Data System (ADS)

    Gutiérrez, Diego; Foerster, Michael; Fina, Ignasi; Fontcuberta, Josep; Fritsch, Daniel; Ederer, Claude

    2012-09-01

    Aiming to explore strain effects on the dielectric permittivity of ultrathin films of oxides with spinel structure, we report here on the thickness (4-160 nm) dependence of the dielectric response of CoFe2O4 (CFO) epitaxial films grown on La2/3Sr1/3MnO3 buffered SrTiO3(001) substrates. It is found that films thicker than ˜30 nm display bulklike permittivity values (ɛr≈14); however, a pronounced and gradual ɛr reduction is observed for thinner films when the in-plane compressive strain induced by the substrate increases. First-principle calculations are used to simulate the variation of the permittivity of CFO spinel thin films under epitaxial strain; in agreement with simple bond-length considerations, the out-of-plane permittivity is predicted to increase under in-plane compressive strain due to the resulting out-of-plane lattice expansion, but this enhancement can be overcompensated if this expansion is suppressed, resulting in an effective reduction of permittivity. However, the predicted reduction is substantially smaller than observed experimentally. We discuss possible mechanisms to account for this observation.

  15. 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.

  16. Single orientation graphene synthesized on iridium thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Dangwal Pandey, A.; Krausert, K.; Franz, D.; Grânäs, E.; Shayduk, R.; Müller, P.; Keller, T. F.; Noei, H.; Vonk, V.; Stierle, A.

    2016-08-01

    Heteroepitaxial iridium thin films were deposited on (0001) sapphire substrates by means of molecular beam epitaxy, and subsequently, one monolayer of graphene was synthesized by chemical vapor deposition. The influence of the growth parameters on the quality of the Ir films, as well as of graphene, was investigated systematically by means of low energy electron diffraction, x-ray reflectivity, x-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, and atomic force microscopy. Our study reveals (111) oriented iridium films with high crystalline quality and extremely low surface roughness, on which the formation of large-area epitaxial graphene is achieved. The presence of defects, like dislocations, twins, and 30° rotated domains in the iridium films is also discussed. The coverage of graphene was found to be influenced by the presence of 30° rotated domains in the Ir films. Low iridium deposition rates suppress these rotated domains and an almost complete coverage of graphene was obtained. This synthesis route yields inexpensive, air-stable, and large-area graphene with a well-defined orientation, making it accessible to a wider community of researchers for numerous experiments or applications, including those which use destructive analysis techniques or irreversible processes. Moreover, this approach can be used to tune the structural quality of graphene, allowing a systematic study of the influence of defects in various processes like intercalation below graphene.

  17. Epitaxial GaN films by hyperthermal ion-beam nitridation of Ga droplets

    SciTech Connect

    Gerlach, J. W.; Ivanov, T.; Neumann, L.; Hoeche, Th.; Hirsch, D.; Rauschenbach, B.

    2012-06-01

    Epitaxial GaN film formation on bare 6H-SiC(0001) substrates via the process of transformation of Ga droplets into a thin GaN film by applying hyperthermal nitrogen ions is investigated. Pre-deposited Ga atoms in well defined amounts form large droplets on the substrate surface which are subsequently nitridated at a substrate temperature of 630 Degree-Sign C by a low-energy nitrogen ion beam from a constricted glow-discharge ion source. The Ga deposition and ion-beam nitridation process steps are monitored in situ by reflection high-energy electron diffraction. Ex situ characterization by x-ray diffraction and reflectivity techniques, Rutherford backscattering spectrometry, and electron microscopy shows that the thickness of the resulting GaN films depends on the various amounts of pre-deposited gallium. The films are epitaxial to the substrate, exhibit a mosaic like, smooth surface topography and consist of coalesced large domains of low defect density. Possible transport mechanisms of reactive nitrogen species during hyperthermal nitridation are discussed and the formation of GaN films by an ion-beam assisted process is explained.

  18. Epitaxial deposition of highly enriched 28Si films with <1 nm roughness

    NASA Astrophysics Data System (ADS)

    Dwyer, K. J.; Kim, Hyun-Soo; Ramanayaka, A. N.; Simons, D. S.; Oleshko, Vladimir; Pomeroy, J. M.

    Low temperature epitaxial deposition of thin films with less than 1 nm rms roughness is achieved using a 28Si ion beam deposition source. These films are enriched in situ to <140 ppb 29Si isotope fraction for quantum computing devices. Removal of the 4.7 % 29Si nuclear spins in natural silicon allows for exceedingly long coherence (T2) times of qubits, making incorporation of highly enriched 28Si into devices critical for solid state quantum information. Low roughness epitaxial 28Si thin films are achieved by depositing in an island growth mode at temperatures of 300 °C to 400 °C, and the morphology is verified using scanning tunneling microscopy. Further, the crystalline quality of the films is shown using cross-sectional transmission electron microscopy. Finally, the chemical purity and broader electrical properties of the 28Si films are assessed by secondary ion mass spectroscopy as well as capacitance-voltage profiling, schottky diode measurements, and hall measurements.

  19. 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.

  20. Epitaxial yttrium iron garnet film for fabrication of high frequency on-chip inductors

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Liu, Houfang; Wu, Hao; Li, Xiaoning; Qiu, Haochuan; Yang, Yi; Qu, Bingjun; Ren, Tian-Ling; Han, Xiufeng; Zhang, Ruyi; Wang, Hong

    2016-10-01

    The application of epitaxial yttrium iron garnet (YIG) thin film on high frequency on-chip spiral inductors is investigated. The YIG thin film with the thickness of 3.6 μm was grown on GGG(111) substrate using the liquid phase method, which exhibits relatively high saturation magnetization 4πMs of 1615 Oe close to the bulk value of 1750 Oe and low initial coercivity Hc of 0.5 Oe that minimizes the hysteretic losses. Subsequently, the spiral inductors were directly fabricated on the YIG/GGG(111) substrate. The results show substantial improvement in the optimum operating frequency and self-resonance frequency of the on-chip spiral inductor with the YIG thin film with an increase of 50% up to ˜7.5 GHz and 14.2 GHz, respectively, implying that on-chip spiral inductors with the YIG thin film can be applied to much higher frequency RF circuits.

  1. 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.

  2. Superconductivity in Epitaxial Thin Films of Fe1:08Te:Ox

    SciTech Connect

    Gu, G.; Si, W.; Jie, Q.; Wu, L.; Zhou, J.; Johnson, P.D.; Li, Q.

    2010-03-01

    Superconducting thin films of Fe{sub 1.08}Te:O{sub x} have been epitaxially grown on SrTiO{sub 3} substrates by pulsed-laser deposition in controlled oxygen atmosphere. Although the bulk Fe{sub 1.08}Te is not superconducting, thin films with oxygen are superconducting with an onset and a zero resistance transition temperature around 12 and 8 K, respectively. Oxygen was found to be crucial to the superconducting properties of these films, suggesting that the oxygen incorporation can induce superconductivity in FeTe thin films. A metal-insulator transition is found at about 60 K, lower than that of bulk ({approx}70 K). From magnetoresistive measurements, we obtained the irreversibility line and the upper critical field.

  3. 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)].

  4. 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.

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

    DOE PAGES

    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

  6. 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.

  7. Surface control of epitaxial manganite films via oxygen pressure

    DOE PAGES

    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

  8. 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.

  9. Epitaxial Ni{sub 3}FeN thin films: A candidate for spintronic devices and magnetic sensors

    SciTech Connect

    Loloee, Reza

    2012-07-15

    A new type of epitaxial ferromagnetic nitride (Ni{sub 3} Fe N = permalloy nitride = 'PyN') compound films were grown on Al{sub 2}O{sub 3}(1120) substrates using reactive triode magnetron sputtering. The results of electron back-scattering diffraction and x-ray diffraction techniques indicate a high quality epitaxial crystalline structure with growth normal of (100). Magnetization measurements of epitaxial PyN films revealed several unique results. (1) A textbook square hysteresis loop that suggest existence of single magnetic domain in these films. (2) A coercive field is tunable from a few mOe up to a few Oe by changing the film thickness. (3) A magnetization that switches (rotate) over a very small field range of {delta}H{sub C} {<=} 0.05 Oe, independent of the film thickness. This small {delta}H indicates a very large resistive sensitivity ({delta}R/{delta}H) of the epitaxial PyN. (4) The epitaxial PyN thermal cycling through several cycles between '2 and 800 K' (-271 Degree-Sign C to +527 Degree-Sign C) shows much less degradation only about 2-5% compared to 40% degradation of a simple Py film. Four-probe transport measurements give an anisotropic magnetoresistance of Almost-Equal-To 6%, sufficiently higher than other known ferromagnetic materials. These interesting properties are ideal for a variety of spintronic devices and magnetic sensors.

  10. 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.

  11. 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.

  12. 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.

  13. Pulsed laser deposition: Prospects for commercial deposition of epitaxial films

    SciTech Connect

    Muenchausen, R.E.

    1999-03-01

    Pulsed laser deposition (PLD) is a physical vapor deposition (PVD) technique for the deposition of thin films. The vapor source is induced by the flash evaporation that occurs when a laser pulse of sufficient intensity (about 100 MW/cm{sup 2}) is absorbed by a target. In this paper the author briefly defines pulsed laser deposition, current applications, research directed at gaining a better understanding of the pulsed laser deposition process, and suggests some future directions to enable commercial applications.

  14. Suppression of creep-regime dynamics in epitaxial ferroelectric BiFeO3 films.

    PubMed

    Shin, Y J; Jeon, B C; Yang, S M; Hwang, I; Cho, M R; Sando, D; Lee, S R; Yoon, J-G; Noh, T W

    2015-05-27

    Switching dynamics of ferroelectric materials are governed by the response of domain walls to applied electric field. In epitaxial ferroelectric films, thermally-activated 'creep' motion plays a significant role in domain wall dynamics, and accordingly, detailed understanding of the system's switching properties requires that this creep motion be taken into account. Despite this importance, few studies have investigated creep motion in ferroelectric films under ac-driven force. Here, we explore ac hysteretic dynamics in epitaxial BiFeO3 thin films, through ferroelectric hysteresis measurements, and stroboscopic piezoresponse force microscopy. We reveal that identically-fabricated BiFeO3 films on SrRuO3 or La0.67Sr0.33MnO3 bottom electrodes exhibit markedly different switching behaviour, with BiFeO3/SrRuO3 presenting essentially creep-free dynamics. This unprecedented result arises from the distinctive spatial inhomogeneities of the internal fields, these being influenced by the bottom electrode's surface morphology. Our findings further highlight the importance of controlling interface and defect characteristics, to engineer ferroelectric devices with optimised performance.

  15. Nucleation and growth of epitaxial metal-oxide films based on polymer-assisted deposition.

    PubMed

    McCleskey, T M; Shi, P; Bauer, E; Highland, M J; Eastman, J A; Bi, Z X; Fuoss, P H; Baldo, P M; Ren, W; Scott, B L; Burrell, A K; Jia, Q X

    2014-04-01

    Polymer-assisted deposition (PAD) is one of the chemical solution deposition methods which have been successfully used to grow films, form coatings, and synthesize nanostructured materials. In comparison with other conventional solution-based deposition techniques, PAD differs in its use of water-soluble polymers in the solution that prevent the metal ions from unwanted chemical reactions and keep the solution stable. Furthermore, filtration to remove non-coordinated cations and anions in the PAD process ensures well controlled nucleation, which enables the growth of high quality epitaxial films with desired structural and physical properties. The precursor solution is prepared by mixing water-soluble polymer(s) with salt(s). Thermal treatment of the precursor films in a controlled environment leads to the formation of desired materials. Using BaTiO3 grown on SrTiO3 and LaMnO3 on LaAlO3 as model systems, we show the effect of filtration on the nucleation and growth of epitaxial complex metal-oxide films based on the PAD process. PMID:24158602

  16. Influence of the polarization anisotropy on the electrocaloric effect in epitaxial PMN-PT thin films

    NASA Astrophysics Data System (ADS)

    Mietschke, M.; Chekhonin, P.; Molin, C.; Gebhardt, S.; Fähler, S.; Nielsch, K.; Schultz, L.; Hühne, R.

    2016-09-01

    Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) compounds, which are typically used for high performance actuator applications due to their outstanding piezoelectric properties, show, in addition, a pronounced electrocaloric (EC) effect. The study of epitaxial films is a useful tool to analyze the correlation between the microstructure and EC properties in order to optimize the performance of these materials. Therefore, the 0.9PMN-0.1PT films were grown by a pulsed laser deposition on (001) as well as (111) oriented SrTiO3 single crystalline substrates using a La0.7Sr0.3CoO3 buffer as the bottom electrode and additional Au top electrodes. The structural properties determined by a high resolution X-ray and electron microscopy techniques indicated an undisturbed epitaxial growth. The anisotropy of the ferroelectric domain structure was investigated by a vertical and lateral piezoresponse force microscopy showing clear differences between the two orientations. A significant reduction of the thermal hysteresis was observed in the T-dependent polarization measurements for (111) oriented PMN-PT films, whereas the indirectly determined EC properties yield a maximum ΔT of around 15 K at 40 °C for a field of about 400 kV/cm for both film orientations.

  17. Metal-insulator transition in epitaxial perovskite SrIrO3 thin films via strain

    NASA Astrophysics Data System (ADS)

    Gruenewald, J. H.; Terzic, J.; Nichols, J.; Cao, G.; Seo, S. S. A.

    2014-03-01

    Iridates have drawn considerable interest due to their exotic phases arising from the interplay of the strong spin-orbit interaction and the electronic correlation. Here we will discuss our experimental investigations of the electronic properties of epitaxially strained SrIrO3 thin-films. The orthorhombic perovskite crystal phase of SrIrO3 is synthesized as a thin film (~ 20 nm) on various substrates of (LaAlO3)0.3-(Sr2AlTaO6)0.7, SrTiO3, GdScO3, and MgO using pulsed laser deposition. We have observed that when the in-plane lattice parameters are tuned from tensile to compressive strain, the electronic behavior of the strained SrIrO3 thin-films changes from metallic to insulating. All samples have sheet resistance below 13 k Ω/ □, and the insulating samples were fit using the Mott variable-range-hopping equation at low temperatures (< 15 K), which is believed to be the conducing mechanism of Anderson localization at finite temperature. The strain-dependent metal-insulator transition in epitaxial perovskite SrIrO3 thin-films offers an important insight into the electronic structure of these strongly correlated, spin-orbit-coupled materials. This work was supported by grants EPS-0814194, DMR-0856234, DMR-1265162, and KSEF-148-502-12-303.

  18. Straining to observe the M2 phase in epitaxial VO2 films

    NASA Astrophysics Data System (ADS)

    Quackenbush, Nicholas; Wahila, Matthew; Piper, Louis; Paik, Hanjong; Holtz, Megan; Huang, Xin; Brock, Joel; Muller, David; Schlom, Darrell; Woicik, Joseph; Arena, Dario

    It has been more than a decade since it was shown that the transition temperature TMIT of VO2 in epitaxial thin films can be tuned by compressive and tensile strain along the rutile c-axis. Since this discovery, uniaxial strain studies of VO2 nanobeams have demonstrated that compressive strain indeed lowers TMIT, thus stabilizing the metallic rutile phase. However, even minor tensile strain induces an intermediate insulating monoclinic M2 phase. Whether this phase can be stabilized in thin films remains contentious owing to the constraints of sample and/or interface quality. Here, we present hard x-ray photoelectron spectroscopy and temperature-dependent soft x-ray absorption spectroscopy of high quality ultrathin epitaxial VO2 films on TiO2 (001) and (100) substrates. The VO2/TiO2(001) are absent of intermediate phases and maintain a MIT similar to unstrained VO2, while the VO2/TiO2(100) films display a stable M2 phase between the M1 and rutile endpoint phases. We discuss our findings in terms of differences between uniaxial and biaxial strain. This research is supported by the National Science Foundation under DMR-1409912.

  19. Microstructure and Transport properties of epitaxial VO2 thin films on TiO2 substrates

    NASA Astrophysics Data System (ADS)

    Lu, Jiwei

    2008-10-01

    Vanadium oxides are paradigms of strongly correlated oxides and have attracted attention because of the metal insulator transitions (MIT) that several of the oxides and sub-oxides exhibit. In particular, VO2 has a metal--semiconductor transition at 340 K. This transition in VO2 combines the properties of a pure Mott Hubbard electronic transition with those of a Peierls structural transition. The Mott transition is responsible for the extreme speed of the optical switching that has been observed (faster than 100 fs). Understanding this transition and how to control it remains a challenge for both theory and experimental physics. We used a novel deposition technique, Reactive Bias Target Ion Beam Deposition, to grow 40 nm epitaxial VO2 thin films on rutile TiO2 substrates with various crystal orientations. X-ray diffraction (XRD) was used to explore the epitaxy of VO2 and we found that all VO2 thin films on TiO2 substrates showed tetragonal symmetry at room temperature due to the constrain from rutile substrates. We also characterized the metal-insulator transition of VO2 films as the function of the crystal orientation of rutile TiO2. We also characterized the anisotropy of VO2 thin films. In collaboration with Kevin West and Stuart Wolf, University of Virginia.

  20. Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

    PubMed Central

    Dral, A. Petra; Dubbink, David; Nijland, Maarten; ten Elshof, Johan E.; Rijnders, Guus; Koster, Gertjan

    2014-01-01

    Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO3 (001) and DyScO3 (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca2Nb3O10- nanosheets were used, prepared by delamination of their layered parent compound HCa2Nb3O10. A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material. PMID:25549000

  1. Suppression of creep-regime dynamics in epitaxial ferroelectric BiFeO3 films

    PubMed Central

    Shin, Y. J.; Jeon, B. C.; Yang, S. M.; Hwang, I.; Cho, M. R.; Sando, D.; Lee, S. R.; Yoon, J.-G.; Noh, T. W.

    2015-01-01

    Switching dynamics of ferroelectric materials are governed by the response of domain walls to applied electric field. In epitaxial ferroelectric films, thermally-activated ‘creep’ motion plays a significant role in domain wall dynamics, and accordingly, detailed understanding of the system’s switching properties requires that this creep motion be taken into account. Despite this importance, few studies have investigated creep motion in ferroelectric films under ac-driven force. Here, we explore ac hysteretic dynamics in epitaxial BiFeO3 thin films, through ferroelectric hysteresis measurements, and stroboscopic piezoresponse force microscopy. We reveal that identically-fabricated BiFeO3 films on SrRuO3 or La0.67Sr0.33MnO3 bottom electrodes exhibit markedly different switching behaviour, with BiFeO3/SrRuO3 presenting essentially creep-free dynamics. This unprecedented result arises from the distinctive spatial inhomogeneities of the internal fields, these being influenced by the bottom electrode’s surface morphology. Our findings further highlight the importance of controlling interface and defect characteristics, to engineer ferroelectric devices with optimised performance. PMID:26014521

  2. Defect formation and carrier doping in epitaxial films of the infinite layer compound

    SciTech Connect

    Feenstra, R.; Pennycook, S.J.; Chisholm, M.F.

    1996-02-01

    The correlation between defect formation and carrier doping in epitaxial films of the infinite layer compound SrCuO{sub 2} has been studied via molecular beam epitaxy controlled layer-by-layer growth experiments, chemically resolved scanning transmission electron microscopy, scanning tunneling microscopy, x-ray diffraction, electrical transport measurements, and post-growth oxidation-reduction annealing. Based on the complementary information provided by these experiments, it is concluded that the carrier doping is dominated by the formation of an electron-doped, Sr and O deficient matrix under mildly oxidizing growth conditions. Hole-doping is induced by extended defects containing excess Sr atoms and may lead to superconductivity after high-temperature oxidation.

  3. Acceptor states in heteroepitaxial CdHgTe films grown by molecular-beam epitaxy

    SciTech Connect

    Mynbaev, K. D.; Shilyaev, A. V. Bazhenov, N. L.; Izhnin, A. I.; Izhnin, I. I.; Mikhailov, N. N.; Varavin, V. S.; Dvoretsky, S. A.

    2015-03-15

    The photoluminescence method is used to study acceptor states in CdHgTe heteroepitaxial films (HEFs) grown by molecular-beam epitaxy. A comparison of the photoluminescence spectra of HEFs grown on GaAs substrates (CdHgTe/GaAs) with the spectra of CdHgTe/Si HEFs demonstrates that acceptor states with energy depths of about 18 and 27 meV are specific to CdHgTe/GaAs HEFs. The possible nature of these states and its relation to the HEF synthesis conditions and, in particular, to the vacancy doping occurring under conditions of a mercury deficiency during the course of epitaxy and postgrowth processing are discussed.

  4. Predictive Models for Nanostructure Evolution during Epitaxial Thin Film Growth

    NASA Astrophysics Data System (ADS)

    Evans, Jim

    2004-03-01

    We describe the development of a realistic atomistic lattice-gas (LG) model for multilayer homoepitaxial growth of metal(100) films at higher deposition temperatures (T). The model is tailored to incorporate the essential physical processes underlying growth, and is thus efficiently simulated using KMC [1]. It is shown to reliably predict film morphologies up to 1000's layers for a broad range of deposition conditions (T, flux), in fact revealing quite unexpected behavior. Specifically, we consider the Ag/Ag(100) system - the perceived prototype for smooth quasi-layer-by-layer growth at higher T. We predict the formation of mounds (multilayer stacks of islands) above 150K due to a small non-uniform step edge barrier. Initial growth at 300K is indeed smooth, but subsequent growth is actually extremely rough, corresponding to prolonged mound steepening. Thin films grow rougher at lower T down to 200K, but thick films grow smoother. Experiments confirm these surprising predictions [1,2]. We also find that long-time mound dynamics is quite distinct from predictions of standard continuum theories. For Ag/Ag(100) growth below 150K in the absence of terrace diffusion, one finds self-affine growth of films containing bulk vacancies [3], the latter feature being confirmed by X-ray scattering studies [4]. This regime can be modeled by accelerated MD [5], generic self-teaching KMC [6], or tailored LG models (distinct from the above model for higher T) [3,7]. Using the latter, we identify the key processes controlling morphology from 0-150K as capture of deposited atoms on the sides of nanoprotrusions, and the activation of low-barrier interlayer thermal diffusion processes. [1] Caspersen et al. PRB 65 (2002) 193407. [2] Elliott et al. PRB 54 (1996) 17938. [3] Stoldt et al. PRL 85 (2000) 800. [4] Botez et al. PRB 66 (2002) 075418. [5] Montalenti et al. PRL 87 (2001) 126101. [6] Henkelman et al. PRL 90 (2003) 116101. [7] Caspersen et al. PRB 64 (2001) 075401.

  5. Pyroelectric and piezoelectric responses of thin AlN films epitaxy-grown on a SiC/Si substrate

    NASA Astrophysics Data System (ADS)

    Kukushkin, S. A.; Osipov, A. V.; Sergeeva, O. N.; Kiselev, D. A.; Bogomolov, A. A.; Solnyshkin, A. V.; Kaptelov, E. Yu.; Senkevich, S. V.; Pronin, I. P.

    2016-05-01

    This paper presents the results of pyroelectric and piezoelectric studies of AlN films formed by chloride-hydride epitaxy (CHE) and molecular beam epitaxy (MBE) on epitaxial SiC nanolayers grown on Si by the atom substitution method. The surface topography and piezoelectric and pyroelecrtric responses of AlN films have been analyzed. The results of the study have shown that the vertical component of the piezoresponse in CHE-grown AlN films is more homogeneous over the film area than that in MBE-grown AlN films. However, the signal from the MBE-synthesized AlN films proved to be stronger. The inversion of the polar axis (polarization vector) on passage from MBE-grown AlN films to CHE-grown AlN films has been found experimentally. It has been shown that the polar axis in MBE-grown films is directed from the free surface of the film toward the Si substrate while, in CHE-grown films, the polarization vector is directed toward the free surface.

  6. Study of structural properties of cubic InN films on GaAs(001) substrates by molecular beam epitaxy and migration enhanced epitaxy

    SciTech Connect

    Casallas-Moreno, Y. L.; Perez-Caro, M.; Gallardo-Hernandez, S.; Ramirez-Lopez, M.; Martinez-Velis, I.; Lopez-Lopez, M.; Escobosa-Echavarria, A.

    2013-06-07

    InN epitaxial films with cubic phase were grown by rf-plasma-assisted molecular beam epitaxy (RF-MBE) on GaAs(001) substrates employing two methods: migration-enhanced epitaxy (MEE) and conventional MBE technique. The films were synthesized at different growth temperatures ranging from 490 to 550 Degree-Sign C, and different In beam fluxes (BEP{sub In}) ranging from 5.9 Multiplication-Sign 10{sup -7} to 9.7 Multiplication-Sign 10{sup -7} Torr. We found the optimum conditions for the nucleation of the cubic phase of the InN using a buffer composed of several thin layers, according to reflection high-energy electron diffraction (RHEED) patterns. Crystallographic analysis by high resolution X-ray diffraction (HR-XRD) and RHEED confirmed the growth of c-InN by the two methods. We achieved with the MEE method a higher crystal quality and higher cubic phase purity. The ratio of cubic to hexagonal components in InN films was estimated from the ratio of the integrated X-ray diffraction intensities of the cubic (002) and hexagonal (1011) planes measured by X-ray reciprocal space mapping (RSM). For MEE samples, the cubic phase of InN increases employing higher In beam fluxes and higher growth temperatures. We have obtained a cubic purity phase of 96.4% for a film grown at 510 Degree-Sign C by MEE.

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

    SciTech Connect

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

    2014-05-19

    Ultra-thin films of the electron doped manganite La{sub 0.8}Ce{sub 0.2}MnO{sub 3} were grown in a layer-by-layer growth mode on SrTiO{sub 3} (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 Ce{sup 4+} and Mn{sup 2+} 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-T{sub c} cuprates.

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

    SciTech Connect

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

    2009-04-01

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

  9. Local vibrational modes competitions in Mn-doped ZnO epitaxial films with tunable ferromagnetism

    SciTech Connect

    Cao, Qiang; Fu, Maoxiang; Liu, Guolei Zhang, Huaijin; Yan, Shishen; Chen, Yanxue; Mei, Liangmo; Jiao, Jun

    2014-06-28

    We reported spectroscopic investigations of high quality Mn-doped ZnO (ZnMnO) films grown by oxygen plasma-assisted molecular beam epitaxy. Raman scattering spectra revealed two local vibrational modes (LVMs) associated with Mn dopants at 523 and 712 cm{sup −1}. The LVMs and magnetic properties of ZnMnO films can be synchronously modulated by post annealing processing or by introducing tiny Co. The relative intensity of two LVMs clearly shows competitions arising from uncompensated acceptor and donor defects competition for ferromagnetic and nonmagnetic films. The experimental results indicated that LVM at 523 cm{sup −1} is attributed to Mn—(Zinc-vacancy) complexes, while LVM at 712 cm{sup −1} is attributed to Mn—(Oxygen-vacancy) complexes.

  10. Epitaxial ferroelectric BiFeO3 thin films for unassisted photocatalytic water splitting

    NASA Astrophysics Data System (ADS)

    Ji, Wei; Yao, Kui; Lim, Yee-Fun; Liang, Yung C.; Suwardi, Ady

    2013-08-01

    Considering energy band alignment and polarization effect, ferroelectric BiFeO3 thin films are proposed as the photoanode in a monolithic cell to achieve unassisted photocatalytic water splitting. Significant anodic photocurrent was observed in our epitaxial ferroelectric BiFeO3 films prepared from sputter deposition. Both negative polarization charges and thinner films were found to promote the anodic photocatalytic reaction. Ultraviolet photoelectron spectroscopy proved that the conduction and valence band edges of BiFeO3 straddle the water redox levels. Theoretical analyses show that the large switchable polarization can modify the surface properties to promote the hydrogen and oxygen evolutions on the surfaces with positive and negative polarization charges, respectively.

  11. Epitaxial ferroelectric BiFeO{sub 3} thin films for unassisted photocatalytic water splitting

    SciTech Connect

    Ji, Wei; Yao, Kui; Lim, Yee-Fun; Suwardi, Ady; Liang, Yung C.

    2013-08-05

    Considering energy band alignment and polarization effect, ferroelectric BiFeO{sub 3} thin films are proposed as the photoanode in a monolithic cell to achieve unassisted photocatalytic water splitting. Significant anodic photocurrent was observed in our epitaxial ferroelectric BiFeO{sub 3} films prepared from sputter deposition. Both negative polarization charges and thinner films were found to promote the anodic photocatalytic reaction. Ultraviolet photoelectron spectroscopy proved that the conduction and valence band edges of BiFeO{sub 3} straddle the water redox levels. Theoretical analyses show that the large switchable polarization can modify the surface properties to promote the hydrogen and oxygen evolutions on the surfaces with positive and negative polarization charges, respectively.

  12. Effects of oxygen-reducing atmosphere annealing on LaMnO3 epitaxial thin films

    SciTech Connect

    Choi, W. S.; Marton, Zsolt; Jang, S. Y.; Moon, S. J.; Jeon, B. C.; Shin, J. H.; Seo, Sung Seok A; Noh, Tae Won; Myung-Whun, Kim; Lee, Ho Nyung; Lee, Y. S.

    2009-01-01

    We investigated the effects of annealing on LaMnO{sub 3} epitaxial thin films grown by pulsed laser deposition (PLD) and propose an efficient method of characterizing their stoichiometry. Structural, magnetic and optical properties coherently indicate non-stoichiometric ferromagnetic and semiconducting phases for as-grown LaMnO{sub 3} films. By annealing in an oxygen-reducing atmosphere, we recovered the antiferromagnetic and insulating phases of bulk-like stoichiometric LaMnO{sub 3}. We show that non-destructive optical spectroscopy at room temperature is one of the most convenient tools for identifying the phases of LaMnO{sub 3} films. Our results serve as a prerequisite for studying LaMnO{sub 3} based heterostructures grown by PLD.

  13. Resistance switching in epitaxial SrCoO{sub x} thin films

    SciTech Connect

    Tambunan, Octolia T.; Parwanta, Kadek J.; Acharya, Susant K.; Lee, Bo Wha; Jung, Chang Uk; Kim, Yeon Soo; Park, Bae Ho; Jeong, Huiseong; Park, Ji-Yong; Cho, Myung Rae; Park, Yun Daniel; Choi, Woo Seok; Kim, Dong-Wook; Jin, Hyunwoo; Lee, Suyoun; Song, Seul Ji; Kang, Sung-Jin; Kim, Miyoung; Hwang, Cheol Seong

    2014-08-11

    We observed bipolar switching behavior from an epitaxial strontium cobaltite film grown on a SrTiO{sub 3} (001) substrate. The crystal structure of strontium cobaltite has been known to undergo topotactic phase transformation between two distinct phases: insulating brownmillerite (SrCoO{sub 2.5}) and conducting perovskite (SrCoO{sub 3−δ}) depending on the oxygen content. The current–voltage characteristics of the strontium cobaltite film showed that it could have a reversible insulator-to-metal transition triggered by electrical bias voltage. We propose that the resistance switching in the SrCoO{sub x} thin film could be related to the topotactic phase transformation and the peculiar structure of SrCoO{sub 2.5}.

  14. Light scattering by epitaxial VO{sub 2} films near the metal-insulator transition point

    SciTech Connect

    Lysenko, Sergiy Fernández, Felix; Rúa, Armando; Figueroa, Jose; Vargas, Kevin; Cordero, Joseph; Aparicio, Joaquin; Sepúlveda, Nelson

    2015-05-14

    Experimental observation of metal-insulator transition in epitaxial films of vanadium dioxide is reported. Hemispherical angle-resolved light scattering technique is applied for statistical analysis of the phase transition processes on mesoscale. It is shown that the thermal hysteresis strongly depends on spatial frequency of surface irregularities. The transformation of scattering indicatrix depends on sample morphology and is principally different for the thin films with higher internal elastic strain and for the thicker films where this strain is suppressed by introduction of misfit dislocations. The evolution of scattering indicatrix, fractal dimension, surface power spectral density, and surface autocorrelation function demonstrates distinctive behavior which elucidates the influence of structural defects and strain on thermal hysteresis, twinning of microcrystallites, and domain formation during the phase transition.

  15. Polarized Raman scattering study of PSN single crystals and epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Pokorný, J.; Rafalovskyi, I.; Gregora, I.; Borodavka, F.; Savinov, M.; Drahokoupil, J.; Tyunina, M.; Kocourek, T.; Jelinek, M.; Bing, Y.; Ye, Z.-G.; Hlinka, J.

    2015-06-01

    This paper describes a detailed analysis of the dependence of Raman scattering intensity on the polarization of the incident and inelastically scattered light in PbSc0.5Nb0.5O3 (PSN) single crystals and epitaxially compressed thin films grown on (100)-oriented MgO substrates. It is found that there are significant differences between the properties of the crystals and films, and that these differences can be attributed to the anticipated structural differences between these two forms of the same material. In particular, the scattering characteristics of the oxygen octahedra breathing mode near 810 cm-1 indicate a ferroelectric state for the crystals and a relaxor state for the films, which is consistent with the dielectric behaviors of these materials.

  16. Synthesis of atomically thin hexagonal boron nitride films on nickel foils by molecular beam epitaxy

    SciTech Connect

    Nakhaie, S.; Wofford, J. M.; Schumann, T.; Jahn, U.; Ramsteiner, M.; Hanke, M.; Lopes, J. M. J. Riechert, H.

    2015-05-25

    Hexagonal boron nitride (h-BN) is a layered two-dimensional material with properties that make it promising as a dielectric in various applications. We report the growth of h-BN films on Ni foils from elemental B and N using molecular beam epitaxy. The presence of crystalline h-BN over the entire substrate is confirmed by Raman spectroscopy. Atomic force microscopy is used to examine the morphology and continuity of the synthesized films. A scanning electron microscopy study of films obtained using shorter depositions offers insight into the nucleation and growth behavior of h-BN on the Ni substrate. The morphology of h-BN was found to evolve from dendritic, star-shaped islands to larger, smooth triangular ones with increasing growth temperature.

  17. Exchange-spring behavior in epitaxial hard/soft magnetic bilayer films.

    SciTech Connect

    Bader, S. D.; Fullerton, E. E.; Grimsditch, M.; Jiang, J. S.; Sowers, C. H.

    1997-12-05

    We present results on the magnetic reversal process in epitaxial Sm-Co (1{bar 1}00)/TM (TM = Fe, Co) bilayer films prepared via magnetron sputtering onto Cr-buffered single-crystal MgO substrates. The magnetically hard Sm-Co films have 20-T uniaxial anisotropy and coercivities >3 T at room temperature. The magnetization of the soft layer is pinned at the interface to the hard-magnet layer and switches reversibly as expected for an exchange-spring magnet. With increasing soft layer thickness, the coercive field of the hard layer becomes significantly less than that of a single layer. We also present numerical solutions of a one-dimensional model that provide the spin configuration for each atomic layer. Comparison of the experimental results with the model simulations indicates that the exchange-spring behavior of our bilayer films can be understood from the intrinsic parameters of the hard and soft layers.

  18. Magnetic properties and interlayer coupling of epitaxial Co/Cu films on Si

    SciTech Connect

    Mansell, R.; Petit, D. C. M. C.; Fernández-Pacheco, A.; Lavrijsen, R.; Lee, J. H.; Cowburn, R. P.

    2014-08-14

    Thin films of Co and Co/Cu/Co trilayers with wedged Cu interlayers were grown epitaxially on Cu buffer layers on hydrogen passivated Si(001) wafers. We find that single Co layers have a well-defined four-fold anisotropy but with smaller in-plane anisotropies than observed in Co grown on Cu crystals. Ruderman–Kittel–Kasuya–Yosida (RKKY) interlayer coupling is observed in one Co/Cu/Co sample which is the smoothest of the films as measured by atomic force microscopy. Some of the films also form a dot-like structure on the surface. Intermixing at elevated temperatures between the Cu buffer and Si limits the ability to form flat surfaces to promote RKKY coupling.

  19. Prediction of first-order martensitic transitions in strained epitaxial films

    NASA Astrophysics Data System (ADS)

    Schönecker, S.; Richter, M.; Koepernik, K.; Eschrig, H.

    2015-02-01

    Coherent epitaxial growth allows us to produce strained crystalline films with structures that are unstable in the bulk. Thereby, the overlayer lattice parameters in the interface plane, (a, b), determine the minimum-energy out-of-plane lattice parameter, {{c}min }(a,b). We show by means of density-functional total energy calculations that this dependence can be discontinuous and predict related first-order phase transitions in strained tetragonal films of the elements V, Nb, Ru, La, Os, and Ir. The abrupt change of {{c}min } can be exploited to switch properties specific to the overlayer material. This is demonstrated for the example of the superconducting critical temperature of a vanadium film which we predict to jump by 20% at a discontinuity of {{c}min }.

  20. Lanthanum gallate substrates for epitaxial high-temperature superconducting thin films

    SciTech Connect

    Sandstrom, R.L.; Giess, E.A.; Gallagher, W.J.; Segmueller, A.; Cooper, E.I.; Chisholm, M.F.; Gupta, A.; Shinde, S.; Laibowitz, R.B.

    1988-11-07

    We demonstrate that lanthanum gallate (LaGaO/sub 3/) has considerable potential as an electronic substrate material for high-temperature superconducting films. It provides a good lattice and thermal expansion match to YBa/sub 2/Cu/sub 3/O/sub 7-//sub x/, can be grown in large crystal sizes, is compatible with high-temperature film processing, and has a reasonably low dielectric constant (epsilonapprox. =25) and low dielectric losses. Epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-//sub x/ films grown on LaGaO/sub 3/ single-crystal substrates by three techniques have zero resistance between 87 and 91 K.

  1. Ferroelectric domain structure of anisotropically strained NaNbO{sub 3} epitaxial thin films

    SciTech Connect

    Schwarzkopf, J. Braun, D.; Schmidbauer, M.; Duk, A.; Wördenweber, R.

    2014-05-28

    NaNbO{sub 3} thin films have been grown under anisotropic biaxial strain on several oxide substrates by liquid-delivery spin metalorganic chemical vapor deposition. Compressive lattice strain of different magnitude, induced by the deposition of NaNbO{sub 3} films with varying film thickness on NdGaO{sub 3} single crystalline substrates, leads to modifications of film orientation and phase symmetry, which are similar to the phase transitions in Pb-containing oxides near the morphotropic phase boundary. Piezoresponse force microscopy measurements exhibit large out-of-plane polarization components, but no distinctive domain structure, while C-V measurements indicate relaxor properties in these films. When tensile strain is provoked by the epitaxial growth on DyScO{sub 3}, TbScO{sub 3}, and GdScO{sub 3} single crystalline substrates, NaNbO{sub 3} films behave rather like a normal ferroelectric. The application of these rare-earth scandate substrates yields well-ordered ferroelectric stripe domains of the type a{sub 1}/a{sub 2} with coherent domain walls aligned along the [001] substrate direction as long as the films are fully strained. With increasing plastic lattice relaxation, initially, a 2D domain pattern with still exclusively in-plane electric polarization, and finally, domains with in-plane and out-of-plane polar components evolve.

  2. Pulsed laser deposition of epitaxial BeO thin films on sapphire and SrTiO{sub 3}

    SciTech Connect

    Peltier, Thomas; Takahashi, Ryota; Lippmaa, Mikk

    2014-06-09

    Epitaxial beryllia thin films were grown by pulsed laser deposition on Al{sub 2}O{sub 3}(001) and SrTiO{sub 3}(111) substrates. Nearly relaxed epitaxial films were obtained on both substrates at growth temperatures of up to about 600 °C. Crystalline films with expanded lattice parameters were obtained even at room temperature. The maximum growth temperature was limited by a loss of beryllium from the film surface. The volatility of beryllium appeared to be caused by the slow oxidation kinetics at the film surface and the re-sputtering effect of high-energy Be and BeO species in the ablation plume. Time-of-flight plume composition analysis suggested that the target surface became Be metal rich at low oxygen pressures, reducing the growth rate of beryllia films.

  3. Epitaxial yttria-stabilized zirconia on (1 -1 0 2) sapphire for YBa2Cu3O(7-delta) thin films

    NASA Technical Reports Server (NTRS)

    Wu, X. D.; Muenchausen, R. E.; Nogar, N. S.; Pique, A.; Edwards, R.

    1991-01-01

    Epitaxial yttria-stabilized zirconia (YSZ) films were deposited on (1 -1 0 2) sapphire by pulsed laser deposition. The films are formed in a cubic phase with the a axis normal to the substrate surface. Ion beam channeling measurements show that the YSZ films are highly crystalline with a channeling minimum yield of 8 percent. The epitaxial relationship between the film and substrate is further confirmed by a cross-section TEM study. Epitaxial YBa2Cu3O(7-delta) thin films deposited on YSZ/sapphire have Tc and Jc of up to 89 K and 10 to the 6th A/sq cm at 77 K, respectively.

  4. Epitaxial growth and physical properties of ternary nitride thin films by polymer-assisted deposition

    DOE PAGES

    Enriquez, Erik M.; Zhang, Yingying; Chen, Aiping; Bi, Zhenxing; Wang, Yongqiang; Fu, Engang; Harrell, Zachary John; Lu, Xujie; Dowden, Paul Charles; Wang, Haiyan; et al

    2016-08-26

    Epitaxial layered ternary metal-nitride FeMoN2, (Fe0.33 Mo0.67)MoN2, CoMoN2, and FeWN2 thin films have been grown on c-plane sapphire substrates by polymer-assisted deposition. The ABN2 layer sits on top of the oxygen sublattices of the substrate with three possible matching configurations due to the significantly reduced lattice mismatch. The doping composition and elements affect not only the out-of-plane lattice parameters but also the temperature-dependent electrical properties. These films have resistivity in the range of 0.1–1 mΩ·cm, showing tunable metallic or semiconducting behaviors by adjusting the composition. A modified parallel connection channel model has been used to analyze the grain boundary andmore » Coulomb blockade effect on the electrical properties. Furthermore, the growth of the high crystallinity layered epitaxial thin films provides an avenue to study the composition-structure-property relationship in ABN2 materials through A and B-site substitution.« less

  5. Interplay between magnetocrystalline anisotropy and exchange bias in epitaxial CoO/Co films

    NASA Astrophysics Data System (ADS)

    Liu, Hao-Liang; Brems, Steven; Zeng, Yu-Jia; Temst, Kristiaan; Vantomme, André; Van Haesendonck, Chris

    2016-05-01

    The interplay between magnetocrystalline anisotropy and exchange bias is investigated in CoO/Co bilayer films, which are grown epitaxially on MgO (0 0 1), by magnetization reversal measurements based on the anisotropic magnetoresistance (AMR) effect. While an asymmetric magnetization reversal survives after training for cooling field (CF) along the hard axis, the magnetization reversal becomes symmetric and is dominated in both branches of the hysteresis loop by domain wall motion before and after training for CF along the easy axis. When performing an in-plane hysteresis loop perpendicular to the CF, the hysteresis loop along the easy axis becomes asymmetric: magnetization rotation dominates in the ascending branch, while there is a larger contribution of domain wall motion in the descending branch. Furthermore, the azimuthal angular dependence of the AMR shows two minima after performing a perpendicular hysteresis loop, instead of only one minimum after training. Relying on the extended Fulcomer and Charap model, these effects can be related to an increased deviation of the average uncompensated antiferromagnetic magnetization from the CF direction. This model provides a consistent interpretation of training and asymmetry of the magnetization reversal for epitaxial films with pronounced magnetocrystalline anisotropy as well as for the previously investigated polycrystalline films.

  6. Large magneto-optic enhancement in ultra-thin liquid-phase-epitaxy iron garnet films

    SciTech Connect

    Levy, Miguel; Chakravarty, A.; Huang, H.-C.; Osgood, R. M.

    2015-07-06

    Significant departures from bulk-like magneto-optic behavior are found in ultra-thin bismuth-substituted iron-garnet films grown by liquid-phase-epitaxy. These changes are due, at least in part, to geometrical factors and not to departures from bulk-composition in the transient layer at the film-substrate interface. A monotonic increase in specific Faraday rotation with reduced thickness is the signature feature of the observed phenomena. These are traced to size-dependent modifications in the diamagnetic transition processes responsible for the Faraday rotation. These processes correspond to the electronic transitions from singlet {sup 6}S ground states to spin-orbit split excited states of the Fe{sup 3+} ions in the garnet. A measurable reduction in the corresponding ferrimagnetic resonance linewidths is found, thus pointing to an increase in electronic relaxation times and longer lived excitations at reduced thicknesses. These changes together with a shift in vibrational frequency of the Bi-O bonds in the garnet at reduced thicknesses result in greatly enhanced magneto-optical performance. These studies were conducted on epitaxial monocrystalline Bi{sub 0.8}Gd{sub 0.2}Lu{sub 2}Fe{sub 5}O{sub 12} films.

  7. The demonstration of significant ferroelectricity in epitaxial Y-doped HfO2 film.

    PubMed

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

    2016-01-01

    Ferroelectricity and Curie temperature are demonstrated for epitaxial Y-doped HfO2 film grown on (110) yttrium oxide-stabilized zirconium oxide (YSZ) single crystal using Sn-doped In2O3 (ITO) as bottom electrodes. The XRD measurements for epitaxial film enabled us to investigate its detailed crystal structure including orientations of the film. The ferroelectricity was confirmed by electric displacement filed - electric filed hysteresis measurement, which revealed saturated polarization of 16 μC/cm(2). Estimated spontaneous polarization based on the obtained saturation polarization and the crystal structure analysis was 45 μC/cm(2). This value is the first experimental estimations of the spontaneous polarization and is in good agreement with the theoretical value from first principle calculation. Curie temperature was also estimated to be about 450 °C. This study strongly suggests that the HfO2-based materials are promising for various ferroelectric applications because of their comparable ferroelectric properties including polarization and Curie temperature to conventional ferroelectric materials together with the reported excellent scalability in thickness and compatibility with practical manufacturing processes. PMID:27608815

  8. Epitaxial growth and physical properties of ternary nitride thin films by polymer-assisted deposition

    NASA Astrophysics Data System (ADS)

    Enriquez, Erik; Zhang, Yingying; Chen, Aiping; Bi, Zhenxing; Wang, Yongqiang; Fu, Engang; Harrell, Zachary; Lü, Xujie; Dowden, Paul; Wang, Haiyan; Chen, Chonglin; Jia, Quanxi

    2016-08-01

    Epitaxial layered ternary metal-nitride FeMoN2, (Fe0.33Mo0.67)MoN2, CoMoN2, and FeWN2 thin films have been grown on c-plane sapphire substrates by polymer-assisted deposition. The ABN2 layer sits on top of the oxygen sublattices of the substrate with three possible matching configurations due to the significantly reduced lattice mismatch. The doping composition and elements affect not only the out-of-plane lattice parameters but also the temperature-dependent electrical properties. These films have resistivity in the range of 0.1-1 mΩ.cm, showing tunable metallic or semiconducting behaviors by adjusting the composition. A modified parallel connection channel model has been used to analyze the grain boundary and Coulomb blockade effect on the electrical properties. The growth of the high crystallinity layered epitaxial thin films provides an avenue to study the composition-structure-property relationship in ABN2 materials through A and B-site substitution.

  9. The demonstration of significant ferroelectricity in epitaxial Y-doped HfO2 film

    PubMed Central

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

    2016-01-01

    Ferroelectricity and Curie temperature are demonstrated for epitaxial Y-doped HfO2 film grown on (110) yttrium oxide-stabilized zirconium oxide (YSZ) single crystal using Sn-doped In2O3 (ITO) as bottom electrodes. The XRD measurements for epitaxial film enabled us to investigate its detailed crystal structure including orientations of the film. The ferroelectricity was confirmed by electric displacement filed – electric filed hysteresis measurement, which revealed saturated polarization of 16 μC/cm2. Estimated spontaneous polarization based on the obtained saturation polarization and the crystal structure analysis was 45 μC/cm2. This value is the first experimental estimations of the spontaneous polarization and is in good agreement with the theoretical value from first principle calculation. Curie temperature was also estimated to be about 450 °C. This study strongly suggests that the HfO2-based materials are promising for various ferroelectric applications because of their comparable ferroelectric properties including polarization and Curie temperature to conventional ferroelectric materials together with the reported excellent scalability in thickness and compatibility with practical manufacturing processes. PMID:27608815

  10. The demonstration of significant ferroelectricity in epitaxial Y-doped HfO2 film

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    Ferroelectricity and Curie temperature are demonstrated for epitaxial Y-doped HfO2 film grown on (110) yttrium oxide-stabilized zirconium oxide (YSZ) single crystal using Sn-doped In2O3 (ITO) as bottom electrodes. The XRD measurements for epitaxial film enabled us to investigate its detailed crystal structure including orientations of the film. The ferroelectricity was confirmed by electric displacement filed – electric filed hysteresis measurement, which revealed saturated polarization of 16 μC/cm2. Estimated spontaneous polarization based on the obtained saturation polarization and the crystal structure analysis was 45 μC/cm2. This value is the first experimental estimations of the spontaneous polarization and is in good agreement with the theoretical value from first principle calculation. Curie temperature was also estimated to be about 450 °C. This study strongly suggests that the HfO2-based materials are promising for various ferroelectric applications because of their comparable ferroelectric properties including polarization and Curie temperature to conventional ferroelectric materials together with the reported excellent scalability in thickness and compatibility with practical manufacturing processes.

  11. Magnetoelectric properties of epitaxial Fe3O4 thin films on (011) PMN-PT piezosubstrates

    NASA Astrophysics Data System (ADS)

    Tkach, Alexander; Baghaie Yazdi, Mehrdad; Foerster, Michael; Büttner, Felix; Vafaee, Mehran; Fries, Maximilian; Kläui, Mathias

    2015-01-01

    We determine the magnetic and magnetotransport properties of 33 nm thick Fe3O4 films epitaxially deposited by rf-magnetron sputtering on unpoled (011) [PbMg1/3Nb2/3O3] 0.68-[PbTiO3]0.32 (PMN-PT) substrates. The magnetoresistance (MR), as well as the magnetization reversal, strongly depend on the in-plane crystallographic direction of the epitaxial (011) Fe3O4 film and strain. When the magnetic field is applied along [100], the magnetization loops are slanted and the sign of the longitudinal MR changes from positive to negative around the Verwey transition at 125 K on cooling. Along the [01 1 ¯] direction, the loops are square shaped and the MR is negative above the switching field across the whole temperature range, just increasing in absolute value when cooling from 300 K to 150 K. The value of the MR is found to be strongly affected by poling the PMN-PT substrate, decreasing in the [100] direction and slightly increasing in the [01 1 ¯] direction upon poling, which results in a strained film.

  12. Epitaxial growth and electrical transport properties of Cr{sub 2}GeC thin films

    SciTech Connect

    Eklund, Per; Bugnet, Matthieu; Mauchamp, Vincent; Dubois, Sylvain; Tromas, Christophe; Jaouen, Michel; Cabioc'h, Thierry; Jensen, Jens; Piraux, Luc; Gence, Loiek

    2011-08-15

    Cr{sub 2}GeC thin films were grown by magnetron sputtering from elemental targets. Phase-pure Cr{sub 2}GeC was grown directly onto Al{sub 2}O{sub 3}(0001) at temperatures of 700-800 deg. C. These films have an epitaxial component with the well-known epitaxial relationship Cr{sub 2}GeC(0001)//Al{sub 2}O{sub 3}(0001) and Cr{sub 2}GeC(1120)//Al{sub 2}O{sub 3}(1100) or Cr{sub 2}GeC(1120)//Al{sub 2}O{sub 3}(1210). There is also a large secondary grain population with (1013) orientation. Deposition onto Al{sub 2}O{sub 3}(0001) with a TiN(111) seed layer and onto MgO(111) yielded growth of globally epitaxial Cr{sub 2}GeC(0001) with a virtually negligible (1013) contribution. In contrast to the films deposited at 700-800 deg. C, the ones grown at 500-600 deg. C are polycrystalline Cr{sub 2}GeC with (1010)-dominated orientation; they also exhibit surface segregations of Ge as a consequence of fast Ge diffusion rates along the basal planes. The room-temperature resistivity of our samples is 53-66 {mu}{Omega}cm. Temperature-dependent resistivity measurements from 15-295 K show that electron-phonon coupling is important and likely anisotropic, which emphasizes that the electrical transport properties cannot be understood in terms of ground state electronic structure calculations only.

  13. Anomalous thickness-dependent strain states and strain-tunable magnetization in Zn-doped ferrite epitaxial films

    NASA Astrophysics Data System (ADS)

    Yang, Y. J.; Yang, M. M.; Luo, Z. L.; Hu, C. S.; Bao, J.; Huang, H. L.; Zhang, S.; Wang, J. W.; Li, P. S.; Liu, Y.; Zhao, Y. G.; Chen, X. C.; Pan, G. Q.; Jiang, T.; Liu, Y. K.; Li, X. G.; Gao, C.

    2014-05-01

    A series of ZnxFe3-xO4 (ZFO, x = 0.4) thin films were epitaxially deposited on single-crystal (001)-SrTiO3 (STO) substrates by radio frequency magnetron sputtering. The anomalous thickness-dependent strain states of ZFO films were found, i.e., a tensile in-plane strain exists in the thinner ZFO film and which monotonously turns into compressive in the thicker films. Considering the lattice constant of bulk ZFO is bigger than that of STO, this strain state cannot be explained in the conventional framework of lattice-mismatch-induced strain in the hetero-epitaxial system. This unusual phenomenon is proposed to be closely related to the Volmer-Weber film growth mode in the thinner films and incorporation of the interstitial atoms into the island's boundaries during subsequent epitaxial growth of the thicker films. The ZFO/STO epitaxial film is found in the nature of magnetic semiconductor by transport measurements. The in-plane magnetization of the ZFO/STO films is found to increase as the in-plane compressive strain develops, which is further proved in the (001)-ZFO/PMN-PT film where the film strain state can be in situ controlled with applied electric field. This compressive-strain-enhanced magnetization can be attributed to the strain-mediated electric-field-induced in-plane magnetic anisotropy field enhancement. The above results indicate that strain engineering on magnetic oxide semiconductor ZFO films is promising for novel oxide-electronic devices.

  14. Anomalous thickness-dependent strain states and strain-tunable magnetization in Zn-doped ferrite epitaxial films

    SciTech Connect

    Yang, Y. J.; Bao, J.; Gao, C. E-mail: cgao@ustc.edu.cn; Yang, M. M.; Luo, Z. L. E-mail: cgao@ustc.edu.cn; Hu, C. S.; Chen, X. C.; Pan, G. Q.; Huang, H. L.; Zhang, S.; Wang, J. W.; Li, P. S.; Liu, Y.; Zhao, Y. G.; Jiang, T.; Liu, Y. K.; Li, X. G.

    2014-05-07

    A series of Zn{sub x}Fe{sub 3−x}O{sub 4} (ZFO, x = 0.4) thin films were epitaxially deposited on single-crystal (001)-SrTiO{sub 3} (STO) substrates by radio frequency magnetron sputtering. The anomalous thickness-dependent strain states of ZFO films were found, i.e., a tensile in-plane strain exists in the thinner ZFO film and which monotonously turns into compressive in the thicker films. Considering the lattice constant of bulk ZFO is bigger than that of STO, this strain state cannot be explained in the conventional framework of lattice-mismatch-induced strain in the hetero-epitaxial system. This unusual phenomenon is proposed to be closely related to the Volmer-Weber film growth mode in the thinner films and incorporation of the interstitial atoms into the island's boundaries during subsequent epitaxial growth of the thicker films. The ZFO/STO epitaxial film is found in the nature of magnetic semiconductor by transport measurements. The in-plane magnetization of the ZFO/STO films is found to increase as the in-plane compressive strain develops, which is further proved in the (001)-ZFO/PMN-PT film where the film strain state can be in situ controlled with applied electric field. This compressive-strain-enhanced magnetization can be attributed to the strain-mediated electric-field-induced in-plane magnetic anisotropy field enhancement. The above results indicate that strain engineering on magnetic oxide semiconductor ZFO films is promising for novel oxide-electronic devices.

  15. Crystallographic dependence of photocatalytic activity of WO3 thin films prepared by molecular beam epitaxy.

    PubMed

    Li, Guoqiang; Varga, Tamas; Yan, Pengfei; Wang, Zhiguo; Wang, Chongmin; Chambers, Scott A; Du, Yingge

    2015-06-21

    We investigated the impact of crystallographic orientation on the photocatalytic activity of single crystalline WO3 thin films prepared by molecular beam epitaxy on the photodegradation of rhodamine B (RhB). A clear effect is observed, with (111) being the most reactive surface, followed by (110) and (001). Photoreactivity is directly correlated with the surface free energy determined by density functional theory calculations. The RhB photodegradation mechanism is found to involve hydroxyl radicals in solution formed from photo-generated holes and differs from previous studies performed on nanoparticles and composites.

  16. Continuous spin reorientation transition in epitaxially grown antiferromagnetic NiO thin films

    SciTech Connect

    Li, J.; Arenholz, E.; Meng, Y.; Tan, A.; Park, J.; Jin, E.; Son, H.; Wu, J.; Jenkins, C. A.; Scholl, A.; Hwang, Chanyong; Qiu, Z. Q.

    2011-03-01

    Fe/NiO/MgO/Ag(001) films were grown epitaxially, and the Fe and NiO spin orientations were determined using x-ray magnetic dichroism. We find that the NiO spins are aligned perpendicularly to the in-plane Fe spins. Analyzing both the in-plane and out-of-plane spin components of the NiO layer, we demonstrate unambiguously that the antiferromagnetic NiO spins undergo a continuous spin reorientation transition from the in-plane to out-of-plane directions with increasing of the MgO thickness.

  17. ARPES studies on FeTe1-x Se x iron chalcogenides epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Innocenti, Davide; Moreschini, Luca; Chang, Young Jun; Walter, Andrew; Bostwick, Aaron; di Castro, Daniele; Tebano, Antonello; Medaglia, Pier Gianni; Bellingeri, Emilio; Pallecchi, Ilaria; Ferdeghini, Carlo; Balestrino, Giuseppe; Rotenberg, Eli

    2011-03-01

    The physics of iron-based chalcogenides raises fundamental questions on the interplay of magnetic order and electron pairing at the origin of the superconducting state. We have performed angle-resolved photemission spectroscopy (ARPES) studies on high-quality epitaxial thin films of FeTe 1-x Se x , grown by in situ pulsed laser deposition (PLD) on beamline 7.0.1 at the ALS. Specifically, we are able to show the evolution of the band structure as a function of x. We discuss our experimental results in comparison to the available theoretical band calculations.

  18. Tailoring exchange bias through chemical order in epitaxial FePt3 films

    NASA Astrophysics Data System (ADS)

    Saerbeck, T.; Zhu, H.; Lott, D.; Lee, H.; LeClair, P. R.; Mankey, G. J.; Stampfl, A. P. J.; Klose, F.

    2013-07-01

    Intentional introduction of chemical disorder into mono-stoichiometric epitaxial FePt3 films allows to create a ferro-/antiferromagnetic two-phase system, which shows a pronounced and controllable exchange bias effect. In contrast to conventional exchange bias systems, granular magnetic interfaces are created within the same crystallographic structure by local variation of chemical order. The amount of the exchange bias can be controlled by the relative amount and size of ferromagnetic and antiferromagnetic volume fractions and the interface between them. The tailoring of the magnetic composition alone, without affecting the chemical and structural compositions, opens the way to study granular magnetic exchange bias concepts separated from structural artifacts.

  19. Fabrication of superconducting NbN meander nanowires by nano-imprint lithography

    NASA Astrophysics Data System (ADS)

    Mei, Yang; Li-Hua, Liu; Lu-Hui, Ning; Yi-Rong, Jin; Hui, Deng; Jie, Li; Yang, Li; Dong-Ning, Zheng

    2016-01-01

    Superconducting nanowire single photon detector (SNSPD), as a new type of superconducting single photon detector (SPD), has a broad application prospect in quantum communication and other fields. In order to prepare SNSPD with high performance, it is necessary to fabricate a large area of uniform meander nanowires, which is the core of the SNSPD. In this paper, we demonstrate a process of patterning ultra-thin NbN films into meander-type nanowires by using the nano-imprint technology. In this process, a combination of hot embossing nano-imprint lithography (HE-NIL) and ultraviolet nano-imprint lithography (UV-NIL) is used to transfer the meander nanowire structure from the NIL Si hard mold to the NbN film. We have successfully obtained a NbN nanowire device with uniform line width. The critical temperature (Tc) of the superconducting NbN meander nanowires is about 5 K and the critical current (Ic) is about 3.5 μA at 2.5 K. Project supported by the National Basic Research Program of China (Grant Nos. 2011CBA00106 and 2009CB929102) and the National Natural Science Foundation of China (Grant Nos. 11104333 and 10974243).

  20. Epitaxially grown polycrystalline silicon thin-film solar cells on solid-phase crystallised seed layers

    NASA Astrophysics Data System (ADS)

    Li, Wei; Varlamov, Sergey; Xue, Chaowei

    2014-09-01

    This paper presents the fabrication of poly-Si thin film solar cells on glass substrates using seed layer approach. The solid-phase crystallised P-doped seed layer is not only used as the crystalline template for the epitaxial growth but also as the emitter for the solar cell structure. This paper investigates two important factors, surface cleaning and intragrain defects elimination for the seed layer, which can greatly influence the epitaxial grown solar cell performance. Shorter incubation and crystallisation time is observed using a simplified RCA cleaning than the other two wet chemical cleaning methods, indicating a cleaner seed layer surface is achieved. Cross sectional transmission microscope images confirm a crystallographic transferal of information from the simplified RCA cleaned seed layer into the epi-layer. RTA for the SPC seed layer can effectively eliminate the intragrain defects in the seed layer and improve structural quality of both of the seed layer and the epi-layer. Consequently, epitaxial grown poly-Si solar cell on the RTA treated seed layer shows better solar cell efficiency, Voc and Jsc than the one on the seed layer without RTA treatment.

  1. Growth temperature-dependent metal-insulator transition of vanadium dioxide epitaxial films on perovskite strontium titanate (111) single crystals

    NASA Astrophysics Data System (ADS)

    Wang, Liangxin; Yang, Yuanjun; Zhao, Jiangtao; Hong, Bin; Hu, Kai; Peng, Jinlan; Zhang, Haibin; Wen, Xiaolei; Luo, Zhenlin; Li, Xiaoguang; Gao, Chen

    2016-04-01

    Vanadium dioxide (VO2) epitaxial films were grown on perovskite single-crystal strontium titanate (SrTiO3) substrates by reactive radio-frequency magnetron sputtering. The growth temperature-dependent metal-insulator transition (MIT) behavior of the VO2 epitaxial films was then investigated. We found that the order of magnitude of resistance change across the MIT increased from 102 to 104 with increasing growth temperature. In contrast, the temperature of the MIT does not strongly depend on the growth temperature and is fairly stable at about 345 K. On one hand, the increasing magnitude of the MIT is attributed to the better crystallinity and thus larger grain size in the (010)-VO2/(111)-SrTiO3 epitaxial films at elevated temperature. On the other hand, the strain states do not change in the VO2 films deposited at various temperatures, resulting in stable V-V chains and V-O bonds in the VO2 epitaxial films. The accompanied orbital occupancy near the Fermi level is also constant and thus the MIT temperatures of VO2 films deposited at various temperatures are nearly the same. This work demonstrates that high-quality VO2 can be grown on perovskite substrates, showing potential for integration into oxide heterostructures and superlattices.

  2. Structure and magnetic properties of tetragonal Heusler D022-Mn3Ge compound epitaxial films with high perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Sugihara, A.; Suzuki, K.; Mizukami, S.; Miyazaki, T.

    2015-04-01

    We investigated the structure and magnetic properties of epitaxial films of D022-Mn3Ge tetragonal Heusler like compounds in detail. Epitaxial films with a stoichiometric composition were grown on Cr-buffered single crystalline (0 0 1) MgO substrates using ultra-high vacuum sputtering at different growth temperatures. X-ray diffraction showed that D022-ordered films were formed at growth temperatures of ⩾200 °C. Epitaxial growth was indicated by cross-sectional high-resolution transmission electron microscopy. Nanobeam diffraction patterns from the D022-Mn3Ge film grown at 400 °C suggests the absence of planar defects such as stacking faults and twins in the film. Out-of-plane magnetic hysteresis curves with perfect squareness were observed for the films grown at ⩾300 °C. These films also showed abrupt magnetization reversal at a coercivity of about 1 T, which is higher than that of other thin film materials with perpendicular magnetic anisotropy such as CoPt and FePt. A huge domain diameter in the D022-Mn3Ge films was indicated by the initial magnetization curves that were measured by the polar magneto-optical Kerr effect.

  3. Epitaxial Thin Films of Y doped HfO2

    NASA Astrophysics Data System (ADS)

    Serrao, Claudy; Khan, Asif; Ramamoorthy, Ramesh; Salahuddin, Sayeef

    Hafnium oxide (HfO2) is one of a few metal oxides that is thermodynamically stable on silicon and silicon oxide. There has been renewed interest in HfO2 due to the recent discovery of ferroelectricity and antiferroelectricity in doped HfO2. Typical ferroelectrics - such as strontium bismuth tantalate (SBT) and lead zirconium titanate (PZT) - contain elements that easily react with silicon and silicon oxide at elevated temperatures; therefore, such ferroelectrics are not suited for device applications. Meanwhile, ferroelectric HfO2 offers promise regarding integration with silicon. The stable phase of HfO2 at room temperature is monoclinic, but HfO2 can be stabilized in the tetragonal, orthorhombic or even cubic phase by suitable doping. We stabilized Y-doped HfO2 thin films using pulsed laser deposition. The strain state can be controlled using various perovskite substrates and controlled growth conditions. We report on Y-doped HfO2 domain structures from piezo-response force microscopy (PFM) and structural parameters via X-ray reciprocal space maps (RSM). We hope this work spurs further interest in strain-tuned ferroelectricity in doped HfO2.

  4. Preparation and characterization of epitaxially grown unsupported yttria-stabilized zirconia (YSZ) thin films

    NASA Astrophysics Data System (ADS)

    Götsch, Thomas; Mayr, Lukas; Stöger-Pollach, Michael; Klötzer, Bernhard; Penner, Simon

    2015-03-01

    Epitaxially grown, chemically homogeneous yttria-stabilized zirconia thin films ("YSZ", 8 mol% Y2O3) are prepared by direct-current sputtering onto a single-crystalline NaCl(0 0 1) template at substrate temperatures ≥493 K, resulting in unsupported YSZ films after floating off NaCl in water. A combined methodological approach by dedicated (surface science) analytical characterization tools (transmission electron microscopy and diffraction, atomic force microscopy, angle-resolved X-ray photoelectron spectroscopy) reveals that the film grows mainly in a [0 0 1] zone axis and no Y-enrichment in surface or bulk regions takes place. In fact, the Y-content of the sputter target is preserved in the thin films. Analysis of the plasmon region in EEL spectra indicates a defective nature of the as-deposited films, which can be suppressed by post-deposition oxidation at 1073 K. This, however, induces considerable sintering, as deduced from surface morphology measurements by AFM. In due course, the so-prepared unsupported YSZ films might act as well-defined model systems also for technological applications.

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

    NASA Astrophysics Data System (ADS)

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

    2010-04-01

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

  6. Growth temperature dependent structural and magnetic properties of epitaxial Co2FeAl Heusler alloy films

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    The structural and magnetic properties of a series of Co2FeAl Heusler alloy films grown on GaAs(001) substrate by molecular beam epitaxy have been studied. The epitaxial Co2FeAl films with an ordered L21 structure have been successfully obtained at growth temperature of 433 K, with an in-plane cubic magnetic anisotropy superimposed with an unusual uniaxial magnetic anisotropy. With increasing growth temperature, the ordered L21 structure degrades. Meanwhile, the uniaxial anisotropy decreases and eventually disappears above 673 K. The interfacial bonding between As and Co or Fe atom is suggested to be responsible for the additional uniaxial anisotropy.

  7. Epitaxial growth of Bi{sub 2}Se{sub 3} topological insulator thin films on Si (111)

    SciTech Connect

    He Liang; Xiu Faxian; Huang Guan; Kou Xufeng; Lang Murong; Wang, Kang L.; Wang Yong; Fedorov, Alexei V.; Beyermann, Ward P.; Zou Jin

    2011-05-15

    In this paper, we report the epitaxial growth of Bi{sub 2}Se{sub 3} thin films on Si (111) substrate, using molecular beam epitaxy (MBE). We show that the as-grown samples have good crystalline quality, and their surfaces exhibit terracelike quintuple layers. Angel-resolved photoemission experiments demonstrate single-Dirac-conelike surface states. These results combined with the temperature- and thickness-dependent magneto-transport measurements, suggest the presence of a shallow impurity band. Below a critical temperature of {approx}100K, the surface states of a 7 nm thick film contribute up to 50% of the total conduction.

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

    SciTech Connect

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

    2013-05-07

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

  9. Quantitative nanoscale characterization of undulated silicon-germanium/silicon(100) epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Wu, Chi-Chin

    Heteroepitaxial thin films are important for the fabrication of advanced devices and as model systems for understanding fundamental materials phenomena. Depending on the growth conditions, film thickness, and extent of lattice mismatch at the film/substrate interface during growth, the epitaxial film will undergo morphological surface evolution to help release the stored elastic strain energy. For low-mismatched structures, a compressively-strained film often roughens and/or forms misfit dislocations after achieving a characteristic thickness. Using undulated Si1-xGex/Si(100) thin films, this work focuses on measurement of quantitative nanoscale variations of compositional and strain/stress fields within roughened heteroepitaxial films. The research was initiated by calculating local and overall stresses for roughened films assuming a sinusoidal film geometry with finite element (FE) models. Chemical wet etching was then applied to experimentally determine the lateral variations of Ge composition within the undulated film. Additional FE modeling results indicated that such composition variations would contribute further overall stress reduction in the film. In-situ transmission electron microscopy (TEM) annealing experiments were performed to measure the dislocation propagation velocity in strained Si1-xGex films to explore the nanoscale correlations between stress variations and surface morphology. The local dislocation velocity data were translated into stresses using previously established stress-velocity relations developed for this system. The inferred stress variations correlated well spatially to the period of surface undulations. However, there was a large discrepancy in the stress variations between undulation peaks and troughs inferred from the local dislocation velocities compared to those calculated by FE models. A stress-dependent single-kink nucleation model was then successfully applied to reconcile these differences. The detailed local

  10. Room-temperature laser annealing for solid-phase epitaxial crystallization of β-Ga2O3 thin films

    NASA Astrophysics Data System (ADS)

    Shiojiri, Daishi; Fukuda, Daiji; Yamauchi, Ryosuke; Tsuchimine, Nobuo; Koyama, Koji; Kaneko, Satoru; Matsuda, Akifumi; Yoshimoto, Mamoru

    2016-10-01

    The epitaxial crystallization of β-Ga2O3 thin films on NiO-buffered α-Al2O3(0001) substrates via the solid-phase crystallization of amorphous Ga2O3 thin films by KrF excimer laser annealing at room temperature (RT) was examined. The results of X-ray and reflection high-energy electron diffraction measurements indicated that the epitaxial β-Ga2O3 (\\bar{2}01) thin films were fabricated by RT laser annealing. The optical bandgap of the thin films was estimated to be 4.9 eV from the results of UV/vis transmittance measurements. In the cathodoluminescence spectrum, UV-green luminescence was observed for the thin films. These optical properties are similar to those of bulk β-Ga2O3.

  11. Structural properties of SrO thin films grown by molecular beam epitaxy on LaAlO3 substrates

    NASA Astrophysics Data System (ADS)

    Maksimov, O.; Heydemann, V. D.; Fisher, P.; Skowronski, M.; Salvador, P. A.

    2006-12-01

    SrO films were grown on LaAlO3 substrates by molecular beam epitaxy and characterized using reflection high-energy electron diffraction (RHEED) and x-ray diffraction (XRD). The evolution of the RHEED pattern is discussed as a function of film thickness. 500Å thick SrO films were relaxed and exhibited RHEED patterns indicative of an atomically smooth surface having uniform terrace heights. Films had the epitaxial relationship (001)SrO‖(001)LaAlO3; [010]SrO‖[110]LaAlO3. This 45° in-plane rotation minimizes mismatch and leads to films of high crystalline quality, as verified by Kikuchi lines in the RHEED patterns and narrow rocking curves of the (002) XRD peak.

  12. Tailoring of magnetic properties of ultrathin epitaxial Fe films by Dy doping

    NASA Astrophysics Data System (ADS)

    Baker, A. A.; Figueroa, A. I.; van der Laan, G.; Hesjedal, T.

    2015-07-01

    We report on the controlled modification of relaxation parameters and magnetic moments of epitaxial Fe thin films through Dy doping. Ferromagnetic resonance measurements show that an increase of Dy doping from 0.1% to 5% gives a tripling in Gilbert damping, and more importantly a strongly enhanced anisotropic damping that can be qualitatively understood through the slow-relaxing impurity model. X-ray magnetic circular dichroism measurements show a pronounced suppression of the orbital moment of the Fe with Dy doping, leading to an almost threefold drop in the orbital to spin moment ratio, ml/ms. Doping with Dy can therefore be used to control both dynamic and static properties of thin ferromagnetic films for improved performance in spintronics device applications, mediated through the antiferromagnetic interaction of the 4f and 3d states.

  13. Tailoring of magnetic properties of ultrathin epitaxial Fe films by Dy doping

    SciTech Connect

    Baker, A. A.; Figueroa, A. I.; Laan, G. van der; Hesjedal, T.

    2015-07-15

    We report on the controlled modification of relaxation parameters and magnetic moments of epitaxial Fe thin films through Dy doping. Ferromagnetic resonance measurements show that an increase of Dy doping from 0.1% to 5% gives a tripling in Gilbert damping, and more importantly a strongly enhanced anisotropic damping that can be qualitatively understood through the slow-relaxing impurity model. X-ray magnetic circular dichroism measurements show a pronounced suppression of the orbital moment of the Fe with Dy doping, leading to an almost threefold drop in the orbital to spin moment ratio, m{sub l}/m{sub s}. Doping with Dy can therefore be used to control both dynamic and static properties of thin ferromagnetic films for improved performance in spintronics device applications, mediated through the antiferromagnetic interaction of the 4f and 3d states.

  14. Oxidized film structure and method of making epitaxial metal oxide structure

    DOEpatents

    Gan, Shupan [Richland, WA; Liang, Yong [Richland, WA

    2003-02-25

    A stable oxidized structure and an improved method of making such a structure, including an improved method of making an interfacial template for growing a crystalline metal oxide structure, are disclosed. The improved method comprises the steps of providing a substrate with a clean surface and depositing a metal on the surface at a high temperature under a vacuum to form a metal-substrate compound layer on the surface with a thickness of less than one monolayer. The compound layer is then oxidized by exposing the compound layer to essentially oxygen at a low partial pressure and low temperature. The method may further comprise the step of annealing the surface while under a vacuum to further stabilize the oxidized film structure. A crystalline metal oxide structure may be subsequently epitaxially grown by using the oxidized film structure as an interfacial template and depositing on the interfacial template at least one layer of a crystalline metal oxide.

  15. Hidden magnetic configuration in epitaxial La1-rSrzMnO3 films

    SciTech Connect

    Kao, Chi-Chang

    2011-05-23

    We present an unreported magnetic configuration in epitaxial La{sub 1-x}Sr{sub x}MnO{sub 3} (x {approx} 0.3) (LSMO) films grown on strontium titanate (STO). X-ray magnetic circular dichroism indicates that the remanent magnetic state of thick LSMO films is opposite to the direction of applied magnetic field. Spectroscopic and scattering measurements reveal that the average Mn valence varies from mixed Mn{sup 3+}/Mn{sup 4+} to an enriched Mn{sup 3+} region near the STO interface, resulting in a compressive lattice along a, b-axis and a possible electronic reconstruction in the Mn e{sub g} orbital (d{sub 3z{sup 2}-r{sup 2}}). This reconstruction may provide a mechanism for coupling the Mn{sup 3+} moments antiferromagnetically along the surface normal direction, and in turn may lead to the observed reversed magnetic configuration.

  16. Epitaxial aluminum-doped zinc oxide thin films on sapphire. 1: Effect of substrate orientation

    SciTech Connect

    Srikant, V.; Sergo, V.; Clarke, D.R.

    1995-07-01

    Epitaxial thin films of Al-doped zinc oxide have been grown on sapphire substrates by pulsed laser ablation. The effect of substrate temperature, background pressure of oxygen, and substrate orientation (A, M, R, C) on the orientation relationships between ZnO and sapphire have been evaluated using on- and off-axis X-ray diffractometry. Under all growth conditions zinc oxide, on A- and C-plane sapphire, grew with the c-axis perpendicular to the substrate. In contrast, on M and R orientations of sapphire, ZnO grew with its c-axis parallel or perpendicular to the substrate depending on the substrate temperature and background pressure employed during growth. In all cases only one unique in-plane relationship between the sapphire substrate and the zinc oxide film was found with the exception of the M-plane at high substrate temperatures.

  17. Thermodynamic guiding principles in selective synthesis of strontium iridate Ruddlesden-Popper epitaxial films

    NASA Astrophysics Data System (ADS)

    Nishio, Kazunori; Hwang, Harold Y.; Hikita, Yasuyuki

    2016-03-01

    We demonstrate the selective fabrication of Ruddlesden-Popper (RP) type SrIrO3, Sr3Ir2O7, and Sr2IrO4 epitaxial thin films from a single SrIrO3 target using pulsed laser deposition (PLD). We identified that the growth conditions stabilizing each phase directly map onto the phase diagram expected from thermodynamic equilibria. This approach allows precise cation stoichiometry control as evidenced by the stabilization of single phase Sr3Ir2O7 for the first time, overcoming the close thermodynamic stability between neighboring RP phases. Despite the non-equilibrium nature of PLD, these results highlight the importance of thermodynamic guiding principles to strategically synthesize the targeted phase in complex oxide thin films.

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

    DOEpatents

    McKee, Rodney Allen; Walker, Frederick Joseph

    1997-01-01

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

  19. Scintillation properties of the Ce-doped multicomponent garnet epitaxial films

    NASA Astrophysics Data System (ADS)

    Prusa, P.; Kucera, M.; Mares, J. A.; Hanus, M.; Beitlerova, A.; Onderisinova, Z.; Nikl, M.

    2013-10-01

    (Lu,Y,Gd)3(Al,Ga)5O12:Ce garnet scintillator single crystalline films were grown onto LuAG, YAG and GGG substrates by liquid phase epitaxy method. Absorption, radioluminescence spectra and photoluminescence excitation, emission spectra, and decay kinetics were measured. Photoelectron yield, its dependence on amplifier shaping time and energy resolution were determined to evaluate scintillation performance. Most of the samples exhibited strong UV emission caused by trapped excitons and/or Gd3+ 4f-4f transition. However, emission spectrum of the best performing Gd2YAl5O12:Ce is dominated by the Ce3+ fast 5d-4f luminescence. This sample has outperformed photoelectron yield of all the garnet films studied so far.

  20. Octahedral tilt transitions in relaxed epitaxial Pb(Zr1-xTix)O3 films

    NASA Astrophysics Data System (ADS)

    Tinberg, Daniel S.; Johnson-Wilke, Raegan L.; Fong, Dillon D.; Fister, Timothy T.; Streiffer, Stephen K.; Han, Yisong; Reaney, Ian M.; Trolier-McKinstry, Susan

    2011-05-01

    Relaxed epitaxial {100}pc and {111}pc oriented films (350 nm) of Pb(Zr1-xTix)O3 (0.2 ≤ x ≤ 0.4) on SrRuO3/SrTiO3 substrates were grown by pulsed laser deposition and studied using high resolution synchrotron X-ray diffraction and transmission electron microscopy. The dielectric behavior and ferroelectric phase transition temperatures of the films were consistent with bulk PZT. However, weak 1/2{311}pc reflections in x-ray diffraction profiles were recorded above bulk TTilt (as indicated in the Jaffe, Cooke, and Jaffe phase diagram, where pc denotes pseudocubic indices). Moreover, anomalies in the dielectric and ferroelectric response were detected above TTilt which are explained by coupling of short coherence or weakly tilted regions to the ferroelectric polarization.

  1. Hidden Magnetic Configuration in Epitaxial La1-x SrxMnO3 Films

    SciTech Connect

    Lee, J.S.; Arena, D.A.; Yu, P.; Nelson, C.S.; Fan, R.; Kinane, C.J.; Langridge, S.; Rossell, M.D.; Ramesh, R.; Kao, C.C.

    2010-12-17

    We present an unreported magnetic configuration in epitaxial La{sub 1-x}Sr{sub x}MnO{sub 3} (x {approx} 0.3) (LSMO) films grown on strontium titanate (STO). X-ray magnetic circular dichroism indicates that the remanent magnetic state of thick LSMO films is opposite to the direction of the applied magnetic field. Spectroscopic and scattering measurements reveal that the average Mn valence varies from mixed Mn{sup 3+}/Mn{sup 4+} to an enriched Mn{sup 3+} region near the STO interface, resulting in a compressive lattice along the a, b axis and a possible electronic reconstruction in the Mn e{sub g} orbital (d{sub 3z{sup 2}-r{sup 2}}). This reconstruction may provide a mechanism for coupling the Mn{sup 3+} moments antiferromagnetically along the surface normal direction, and in turn may lead to the observed reversed magnetic configuration.

  2. Unstrained Epitaxial Zn-Substituted Fe3O4 Films for Ferromagnetic Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Ichimura, Takashi; Fujiwara, Kohei; Kushizaki, Takayoshi; Kanki, Teruo; Tanaka, Hidekazu

    2013-06-01

    A field-effect transistor has been fabricated utilizing an epitaxial film of unstrained zinc-substituted magnetite (Fe3O4) as the active channel. A thin film of Fe2.5Zn0.5O4 was grown on a lattice-matched MgO(001) substrate by pulsed-laser deposition and covered by a parylene gate insulator to dope charge carriers by a field effect. The device showed a field-effect mobility of 1.2 ×10-2 cm2 V-1 s-1 at 300 K, which is higher by a factor of 15 than those of the devices with strained Fe2.5Zn0.5O4 channels on perovskite-type substrates. The enhanced response to the gate electric field is useful in exploring gate-tunable magnetism in magnetite.

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

    DOEpatents

    McKee, Rodney Allen; Walker, Frederick Joseph

    1998-01-01

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

  4. Optical properties of epitaxial ZnGeAs2 thin film

    NASA Astrophysics Data System (ADS)

    Choi, S. G.; Aspnes, D. E.; van Schilfgaarde, M.; Peshek, T. J.; Coutts, T. J.; Norman, A. G.; Olson, J. M.; Levi, D. H.

    2009-03-01

    Chalcopyrite ZnGeAs2 lattice-matched to GaAs(001) is a promising 1.1 eV band gap semiconductor for applications in nonlinear photonic devices and multijunction solar cells. Knowledge of the optical functions of a material over a wide photon energy range is of importance to optimize photonic and photovoltaic device structures. We present room-temperature optical properties of a ZnGeAs2 thin film grown epitaxially on a GaAs(001) substrate by metalorganic vapor phase epitaxy. Spectroscopic ellipsometry was employed to measure the pseudodielectric function of the ZnGeAs2 thin film, and was compared with a theoretical calculation within the quasiparticle self-consistent GW approximation. The interband-transition critical-point energies were obtained from a standard lineshape analysis of the measured spectrum. We will also present a comparison of the optical properties of ZnGeAs2 with those of other II-IV-V2 chalcopyrite compounds as well as their corresponding III-V zincblende compounds. This abstract is subject to government rights.

  5. Process for selectively patterning epitaxial film growth on a semiconductor substrate

    DOEpatents

    Sheldon, P.; Hayes, R.E.

    1984-12-04

    Disclosed is a process for selectively patterning epitaxial film growth on a semiconductor substrate. The process includes forming a masking member on the surface of the substrate, the masking member having at least two layers including a first layer disposed on the substrate and the second layer covering the first layer. A window is then opened in a selected portion of the second layer by removing that portion to expose the first layer thereunder. The first layer is then subjected to an etchant introduced through the window to dissolve the first layer a sufficient amount to expose the substrate surface directly beneath the window, the first layer being adapted to preferentially dissolve at a substantially greater rate than the second layer so as to create an overhanging ledge portion with the second layer by undercutting the edges thereof adjacent the window. The epitaxial film is then deposited on the exposed substrate surface directly beneath the window. Finally, an etchant is introduced through the window to dissolve the remainder of the first layer so as to lift-off the second layer and materials deposited thereon to fully expose the balance of the substrate surface.

  6. Process for selectively patterning epitaxial film growth on a semiconductor substrate

    DOEpatents

    Sheldon, Peter; Hayes, Russell E.

    1986-01-01

    A process is disclosed for selectively patterning epitaxial film growth on a semiconductor substrate. The process includes forming a masking member on the surface of the substrate, the masking member having at least two layers including a first layer disposed on the substrate and the second layer covering the first layer. A window is then opened in a selected portion of the second layer by removing that portion to expose the first layer thereunder. The first layer is then subjected to an etchant introduced through the window to dissolve a sufficient amount of the first layer to expose the substrate surface directly beneath the window, the first layer being adapted to preferentially dissolve at a substantially greater rate than the second layer so as to create an overhanging ledge portion with the second layer by undercutting the edges thereof adjacent to the window. The epitaxial film is then deposited on the exposed substrate surface directly beneath the window. Finally, an etchant is introduced through the window to dissolve the remainder of the first layer so as to lift-off the second layer and materials deposited thereon to fully expose the balance of the substrate surface.

  7. Epitaxial growth of higher transition-temperature VO2 films on AlN/Si

    NASA Astrophysics Data System (ADS)

    Slusar, Tetiana; Cho, Jin-Cheol; Kim, Bong-Jun; Yun, Sun Jin; Kim, Hyun-Tak

    2016-02-01

    We report the epitaxial growth and the mechanism of a higher temperature insulator-to-metal-transition (IMT) of vanadium dioxide (VO2) thin films synthesized on aluminum nitride (AlN)/Si (111) substrates by a pulsed-laser-deposition method; the IMT temperature is TIMT ≈ 350 K. X-ray diffractometer and high resolution transmission electron microscope data show that the epitaxial relationship of VO2 and AlN is VO2 (010) ‖ AlN (0001) with VO2 [101] ‖ AlN [ 2 1 ¯ 1 ¯ 0 ] zone axes, which results in a substrate-induced tensile strain along the in-plane a and c axes of the insulating monoclinic VO2. This strain stabilizes the insulating phase of VO2 and raises TIMT for 10 K higher than TIMT single crystal ≈ 340 K in a bulk VO2 single crystal. Near TIMT, a resistance change of about four orders is observed in a thick film of ˜130 nm. The VO2/AlN/Si heterostructures are promising for the development of integrated IMT-Si technology, including thermal switchers, transistors, and other applications.

  8. Magnetic structure of dysprosium in epitaxial Dy films and in Dy/Er superlattices

    SciTech Connect

    Dumesnil, K.; Dufour, C.; Mangin, P.; Marchal, G.; Hennion, M.

    1996-09-01

    We present a magnetization and neutron-diffraction study of the basal plane magnetic structure of Dy epitaxial films and Dy/Er superlattices. The thermal evolution of the magnetic phases, the stability of the helical phase under a magnetic field, the thermal variation of the dysprosium in-plane and {ital c} parameters, and of the dysprosium turn angle are successively shown. In Dy/Er superlattices, the dysprosium helix propagates coherently through paramagnetic erbium; at low temperature, individual dysprosium layers undergo a ferromagnetic transition and are coupled antiferromagnetically to each other for erbium layers thicknesses larger than 20 A. In dysprosium films, as expected from the epitaxy effect, the Curie temperature of dysprosium is reduced if dysprosium is grown on yttrium and increased if it is grown on erbium, whereas it is unexpectedly close to the bulk value in Dy/Er superlattices. This amazing value of the Curie temperature in superlattices is correlated to two main experimentally observed effects: (i) the magnetoelastic driving force is reduced compared to bulk dysprosium because of the clamped {gamma} distortion; (ii) the difference between the exchange energies in the helical and the ferromagnetic phases is increased compared to the bulk value. {copyright} {ital 1996 The American Physical Society.}

  9. Effect of Polar Discontinuity on the Growth of Epitaxial LaNiO3 Ultrathin Films

    NASA Astrophysics Data System (ADS)

    Tung, I.-Cheng; Luo, G.; Morgan, D.; Lee, J. H.; Hong, H.; Chang, S. H.; Eastman, J. A.; Fong, D. D.; Bedzyk, M. J.; Freeland, J. W.

    2014-03-01

    We have conducted a detailed microscopic study of epitaxial LaNiO3 ultrathin films grown on (001) SrTiO3 as a function of thickness by using oxide molecular beam epitaxy with in-situ surface x-ray diffraction and soft x-ray absorption spectroscopy at the Advanced Photon Source to explore the influence of polar mismatch on the resulting structural and electronic properties. Our data demonstrate that the initial layers on the nonpolar SrTiO3 surface exhibit a smaller than expected out-of-plane lattice-spacing with a Ni valence of 2+. As the film becomes thicker, the lattice constant expands to its elastic limit, and the Ni valence approaches 3+. We will also discuss the energetics for vacancy formation during the initial growth as determined by density functional theory calculations. Work at the APS, Argonne is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Advanced Photon Source, Argonne National Laboratory.

  10. Effect of residual stress on the microstructure of GaN epitaxial films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Wang, Haiyan; Wang, Wenliang; Yang, Weijia; Zhu, Yunnong; Lin, Zhiting; Li, Guoqiang

    2016-04-01

    The stress-free GaN epitaxial films have been directly grown by pulsed laser deposition (PLD) at 850 °C, and the effect of different stress on the microstructure of as-grown GaN epitaxial films has been explored in detail. The as-grown stress-free GaN epitaxial films exhibit very smooth surface without any particles and grains, which is confirmed by the smallest surface root-mean-square roughness of 2.3 nm measured by atomic force microscopy. In addition, they also have relatively high crystalline quality, which is proved by the small full-width at half maximum values of GaN(0002) and GaN (10 1 bar 2) X-ray rocking curves as 0.27° and 0.68°, respectively. However, when the growth temperature is lower or higher than 850 °C, internal or thermal stress would be increased in as-grown GaN epitaxial films. To release the larger stress, a great number of dislocations are generated. Many irregular particulates, hexagonal GaN gains and pits are therefore produced on the films surface, and the crystalline quality is greatly reduced consequently. This work has demonstrated the direct growth of stress-free GaN epitaxial films with excellent surface morphology and high crystalline quality by PLD, and presented a comprehensive study on the origins and the effect of stress in GaN layer. It is instructional to achieve high-quality nitride films by PLD, and shows great potential and broad prospect for the further development of high-performance GaN-based devices.

  11. Exchange bias and crystal structure of epitaxial (111) FePt/BiFeO{sub 3} sputtered thin films

    SciTech Connect

    Chiu, Shang-Jui; Hsiao, Shih-Nan Lee, Hsin-Yi; Huang, Li-Chun; Yu, Ge-Ping; Chang, Huang-Wei

    2014-05-07

    Crystallographic structure and magnetic properties of the epitaxial FePt (10 nm)/BiFeO{sub 3} (BFO) (10 nm) bilayer films grown on (111) SrTiO{sub 3} (STO) substrates with different deposition temperatures of FePt layers (T{sub d}) have been investigated using magnetron sputtering. Out-of-plane radial scan along (111) direction and off-normal (002) azimuthal scan, determined by synchrotron radiation x-ray diffractometry, evidence that the FePt layers were well epitaxially grown on the (111) epitaxial BFO layers for the samples with T{sub d} = 300 and 700 °C. On the contrary, for the bilayer films with T{sub d} = 500 °C, the FePt and BFO layers exhibit low epitaxial quality. Large in-plane exchange bias field (H{sub eb}) values of 45–412 Oe are obtained for the L1{sub 0}-FePt/BFO bilayer films measured with applied field of 12 kOe at room temperature. The change of effective interfacial area, observed by scanning electron microscopy, between FePt island-like particles and BFO continuous layers, and epitaxiality of the bilayer were correlated with the evolution of H{sub eb}.

  12. Conduction-type control of Ge films grown on (NH 4) 2S-treated GaAs by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Inada, M.; Fujishima, T.; Umezu, I.; Sugimura, A.; Yamada, S.

    2001-07-01

    We have performed epitaxial growth of Ge films on (NH 4) 2S-treated GaAs (0 0 1) substrates under various growth temperatures using molecular beam epitaxy. We confirmed that this sulfur passivation is quite effective for preventing the oxidation of GaAs surface. Thus, the Ge films were grown epitaxially on GaAs substrate without thermal cleaning. The electric properties of Ge films were investigated using Hall measurement and it was found that the conduction type of Ge films can be controlled by growth temperature. The Ga-S bond is thought to be the key for conduction type control, although the details are not identified yet.

  13. Epitaxial Growth of Ca2IrO4 Single-Crystal Thin-Films

    NASA Astrophysics Data System (ADS)

    Souri, Maryam; Gruenewald, John H.; Terzic, Jasminka; Cao, Gang; Brill, Joseph W.; Seo, Sung S. Ambrose

    2015-03-01

    Complex oxides containing 5 d transition metals including iridates have attracted substantial attention due to their potential to create novel electronic and magnetic states that originate from strong spin-orbit coupling and the electron-correlation of 5 d electrons. However, the progress of experimental research on the 5 d transition-metal oxides is hindered by the limited number of available materials. To further understand the layered iridates (A2IrO4, A: alkaline-earth elements) featuring the Jeff = 1/2 Mott state, we have synthesized epitaxial thin-films of Ca2IrO4. The single crystal Ruddlesden-Popper (R-P) phase of Can+1IrnO3n+1 (n =1) is thermodynamically unstable; hence, we have used epitaxial-stabilization strategies to grow metastable thin-films of Ca2IrO4. The R-P phase of Ca2IrO4 is synthesized on yttrium aluminum oxide and lanthanum aluminum oxide substrates by pulsed laser deposition. We have studied the electronic structure of these films by transport and optical spectroscopic measurements. The dc-resistivity shows that these Ca2IrO4 thin-films are insulating with activation energy of about 100 meV. The optical spectroscopy shows that the optical gap energy is about 0.5 eV. We will discuss the electronic structure of Ca2IrO4 by comparing with Sr2IrO4andBa2IrO4.

  14. InGaN-based thin film solar cells: Epitaxy, structural design, and photovoltaic properties

    NASA Astrophysics Data System (ADS)

    Sang, Liwen; Liao, Meiyong; Koide, Yasuo; Sumiya, Masatomo

    2015-03-01

    InxGa1-xN, with the tunable direct bandgaps from ultraviolet to near infrared region, offers a promising candidate for the high-efficiency next-generation thin-film photovoltaic applications. Although the adoption of thick InGaN film as the active region is desirable to obtain efficient light absorption and carrier collection compared to InGaN/GaN quantum wells structure, the understanding on the effect from structural design is still unclear due to the poor-quality InGaN films with thickness and difficulty of p-type doping. In this paper, we comprehensively investigate the effects from film epitaxy, doping, and device structural design on the performances of the InGaN-based solar cells. The high-quality InGaN thick film is obtained on AlN/sapphire template, and p-In0.08Ga0.92N is achieved with a high hole concentration of more than 1018 cm-3. The dependence of the photovoltaic performances on different structures, such as active regions and p-type regions is analyzed with respect to the carrier transport mechanism in the dark and under illumination. The strategy of improving the p-i interface by using a super-thin AlN interlayer is provided, which successfully enhances the performance of the solar cells.

  15. Columnar structured FePt films epitaxially grown on large lattice mismatched intermediate layer

    PubMed Central

    Dong, K. F.; Deng, J. Y.; Peng, Y. G.; Ju, G.; Chow, G. M.; Chen, J. S.

    2016-01-01

    The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) <100>//ZrN (001) <100>//TiN (001) <100> among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained. PMID:27686046

  16. InGaN-based thin film solar cells: Epitaxy, structural design, and photovoltaic properties

    SciTech Connect

    Sang, Liwen; Liao, Meiyong; Koide, Yasuo; Sumiya, Masatomo

    2015-03-14

    In{sub x}Ga{sub 1−x}N, with the tunable direct bandgaps from ultraviolet to near infrared region, offers a promising candidate for the high-efficiency next-generation thin-film photovoltaic applications. Although the adoption of thick InGaN film as the active region is desirable to obtain efficient light absorption and carrier collection compared to InGaN/GaN quantum wells structure, the understanding on the effect from structural design is still unclear due to the poor-quality InGaN films with thickness and difficulty of p-type doping. In this paper, we comprehensively investigate the effects from film epitaxy, doping, and device structural design on the performances of the InGaN-based solar cells. The high-quality InGaN thick film is obtained on AlN/sapphire template, and p-In{sub 0.08}Ga{sub 0.92}N is achieved with a high hole concentration of more than 10{sup 18 }cm{sup −3}. The dependence of the photovoltaic performances on different structures, such as active regions and p-type regions is analyzed with respect to the carrier transport mechanism in the dark and under illumination. The strategy of improving the p-i interface by using a super-thin AlN interlayer is provided, which successfully enhances the performance of the solar cells.

  17. Mosaic and facet structures of epitaxial MnO films on Au (110)

    NASA Astrophysics Data System (ADS)

    Meinel, K.; Huth, M.; Beyer, H.; Neddermeyer, H.; Widdra, W.

    2014-01-01

    Growth and annealing behavior of epitaxial MnO films on an Au (110)-(1 × 2) substrate have been studied by means of Auger electron spectroscopy, low energy electron diffraction, and scanning tunneling microscopy. MnO (110) films have been successfully grown by Mn evaporation in an oxygen atmosphere at room temperature with subsequent annealing to 750 K. Instead of the expected (110)-like diffraction pattern complex mosaic and facet structures are found depending on annealing conditions. The mosaics are misfit-induced and display along [001] directions a misorientation of ± 1.5°. At temperatures around 850 K, mosaics gradually vanish and simultaneously a saw-tooth-like film morphology develops which is formed by ribbons of narrow (100) and (010) MnO facets. At temperatures above 850 K the film partially dewets from the substrate, and the film transforms to three-dimensional MnO islands that have a roof-like shape where large roof sides and small end sides are composed by {100} and by {111} facets, respectively. The experiments corroborate the theoretical predicted tendency of facet formation of MnO (110) surfaces.

  18. Epitaxial growth and electrical properties of perovskite HoMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Kan, Daisuke; Murakami, M.; Yu, W.; Greene, R. L.; Cheong, S. W.; Takeuchi, I.

    2008-03-01

    Recently, it was predicted that orthorhombic HoMnO3 would exhibit relatively large polarization (of the order of μC/cm^ 2) due to the existence of a ferroelectric order in the E- type magnetic structure [1]. We have fabricated perovskite HoMnO3 thin films on SrTiO3 (001) substrates by pulsed laser deposition. X-ray 2θ-θ scan shows (00 l) peaks only indicating that there are no secondary phases. The reciprocal space mapping around the SrTiO3 (103) Bragg reflection and the φ scan of the HoMnO3 (103) peak reveals the tetragonal symmetry of the films and the epitaxial relationship, [100]HoMnO3 // [100]SrTiO3 and [001] HoMnO3 // [001]SrTiO3, confirming that the film has the perovskite structure and not the hexagonal one. The films show good insulating properties at low temperatures. We will present electrical properties of the films including results of PUND measurements in applied magnetic field below the Neel temperature. This work is supported by NSF MRSEC, ARO, and the W. M. Keck Foundation. [1] Sergienko et al., PRL 97, 227204 (2006).

  19. Epitaxial growth of metal fluoride thin films by pulsed-laser deposition

    SciTech Connect

    Norton, D.P.; Budal, J.D.; Chakoumakos, B.C.; Geohegan, D.B.; Puretzky, A.

    1995-12-01

    We have studied growth of GdLiF4 thin films for optical waveguide applications. Epitaxial, c-axis oriented GdLiF4 films wer grown from undoped GdLiF4 targets in an on-axis Pulsed-laser deposition geometry on (100) CaF2. These films exhibit a high density of particulates on the surface which are ejected from the target in the ablation process. Growth from Nd-doped polycrystalline GdLiF4 ablation targets results in smooth films with lower particulate densities, as Nd doping increases the optical absorption of GdLiF4 at the ablation laser wavelength 193 nm and permits efficient pulsed-laser deposition. Optical emission spectra of the ablation pume reveals the presence of atomic F, Gd, and Li, indicating the dissociation of the metal-fluorine bonds in the ablation process. In addition, we find that the residual background oxygen pressure must be reduced to avoid formation of Gd4O3F6 as an impurity oxyfluoride phase in the films.

  20. Photoluminescence of localized excitons in ZnCdO thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wu, T. Y.; Huang, Y. S.; Hu, S. Y.; Lee, Y. C.; Tiong, K. K.; Chang, C. C.; Shen, J. L.; Chou, W. C.

    2016-07-01

    We have investigated the luminescence characteristics of Zn1-xCdxO thin films with different Cd contents grown by molecular beam epitaxy system. The temperature-dependent photoluminescence (PL) and excitation power-dependent PL spectra were measured to clarify the luminescence mechanisms of the Zn1-xCdxO thin films. The peak energy of the Zn1-xCdxO thin films with increasing the Cd concentration is observed as redshift and can be fitted by the quadratic function of alloy content. The broadened full-width at half-maximum (FWHM) estimated from the 15 K PL spectra as a function of Cd content shows a larger deviation between the experimental values and theoretical curve, which indicates that experimental FWHM values are affected not only by alloy compositional disorder but also by localized excitons occupying states in the tail of the density of states. The Urbach energy determined from an analysis of the lineshape of the low-energy side of the PL spectrum and the degree of localization effect estimated from the temperature-induced S-shaped PL peak position described an increasing mean exciton-localization effects in ZnCdO films with increasing the Cd content. In addition, the PL intensity and peak position as a function of excitation power are carried out to clarify the types of radiative recombination and the effects of localized exciton in the ZnCdO films with different Cd contents.

  1. Structural, magnetic, and transport properties of Fe-doped CoTiSb epitaxial thin films

    SciTech Connect

    Sun, N. Y.; Zhang, Y. Q.; Che, W. R.; Shan, R.; Qin, J.

    2015-11-07

    Epitaxial intrinsic and Fe-doped CoTiSb thin films with C1{sub b} structure were grown on MgO(100) substrates by magnetron sputtering. The semiconducting-like behavior in both intrinsic and Fe-doped thin films was demonstrated by temperature dependence of longitudinal resistivity. The Fe-doped CoTiSb films with a wide range of doping concentrations can maintain semiconducting-like and magnetic properties simultaneously, while the semiconducting behavior is weakening with the increasing Fe concentration. For 21 at. % Fe-doped film, low lattice magnetic moment (around 0.65 μ{sub B}) and high resistivity (larger than 800 μΩ cm) are beneficial to its application as a magnetic electrode in spintronic devices. Anomalous Hall effect of 21 at. % Fe-doped film was also investigated and its behaviors can be treated well by recent-reported anomalous Hall scaling including the contribution of spin-phonon skew scattering.

  2. A new approach to epitaxially grow high-quality GaN films on Si substrates: the combination of MBE and PLD

    PubMed Central

    Wang, Wenliang; Wang, Haiyan; Yang, Weijia; Zhu, Yunnong; Li, Guoqiang

    2016-01-01

    High-quality GaN epitaxial films have been grown on Si substrates with Al buffer layer by the combination of molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) technologies. MBE is used to grow Al buffer layer at first, and then PLD is deployed to grow GaN epitaxial films on the Al buffer layer. The surface morphology, crystalline quality, and interfacial property of as-grown GaN epitaxial films on Si substrates are studied systematically. The as-grown ~300 nm-thick GaN epitaxial films grown at 850 °C with ~30 nm-thick Al buffer layer on Si substrates show high crystalline quality with the full-width at half-maximum (FWHM) for GaN(0002) and GaN(102) X-ray rocking curves of 0.45° and 0.61°, respectively; very flat GaN surface with the root-mean-square surface roughness of 2.5 nm; as well as the sharp and abrupt GaN/AlGaN/Al/Si hetero-interfaces. Furthermore, the corresponding growth mechanism of GaN epitaxial films grown on Si substrates with Al buffer layer by the combination of MBE and PLD is hence studied in depth. This work provides a novel and simple approach for the epitaxial growth of high-quality GaN epitaxial films on Si substrates. PMID:27101930

  3. A new approach to epitaxially grow high-quality GaN films on Si substrates: the combination of MBE and PLD.

    PubMed

    Wang, Wenliang; Wang, Haiyan; Yang, Weijia; Zhu, Yunnong; Li, Guoqiang

    2016-04-22

    High-quality GaN epitaxial films have been grown on Si substrates with Al buffer layer by the combination of molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) technologies. MBE is used to grow Al buffer layer at first, and then PLD is deployed to grow GaN epitaxial films on the Al buffer layer. The surface morphology, crystalline quality, and interfacial property of as-grown GaN epitaxial films on Si substrates are studied systematically. The as-grown ~300 nm-thick GaN epitaxial films grown at 850 °C with ~30 nm-thick Al buffer layer on Si substrates show high crystalline quality with the full-width at half-maximum (FWHM) for GaN(0002) and GaN(102) X-ray rocking curves of 0.45° and 0.61°, respectively; very flat GaN surface with the root-mean-square surface roughness of 2.5 nm; as well as the sharp and abrupt GaN/AlGaN/Al/Si hetero-interfaces. Furthermore, the corresponding growth mechanism of GaN epitaxial films grown on Si substrates with Al buffer layer by the combination of MBE and PLD is hence studied in depth. This work provides a novel and simple approach for the epitaxial growth of high-quality GaN epitaxial films on Si substrates.

  4. Kinematical calculations of RHEED intensity oscillations during the growth of thin epitaxial films

    NASA Astrophysics Data System (ADS)

    Daniluk, Andrzej

    2005-08-01

    A practical computing algorithm working in real time has been developed for calculating the reflection high-energy electron diffraction (RHEED) from the molecular beam epitaxy (MBE) growing surface. The calculations are based on the use of kinematical diffraction theory. Simple mathematical models are used for the growth simulation in order to investigate the fundamental behaviors of reflectivity change during the growth of thin epitaxial films prepared using MBE. Program summaryTitle of program:GROWTH Catalogue identifier:ADVL Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADVL Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Distribution format: tar.gz Computer for which the program is designed and others on which is has been tested:Pentium-based PC Operating systems or monitors under which the program has been tested:Windows 9x, XP, NT Programming language used:Object Pascal Memory required to execute with typical data:more than 1 MB Number of bits in a word: 64 bits Number of processors used: 1 Number of lines in distributed program, including test data, etc.: 10 989 Number of bytes in distributed program, including test data, etc.:103 048 Nature of the physical problem:Reflection high-energy electron diffraction (RHEED) is a very useful technique for studying growth and surface analysis of thin epitaxial structures prepared using the molecular beam epitaxy (MBE). The simplest approach to calculating the RHEED intensity during the growth of thin epitaxial films is the kinematical diffraction theory (often called kinematical approximation), in which only a single scattering event is taken into account. The biggest advantage of this approach is that we can calculate RHEED intensity in real time. Also, the approach facilitates intuitive understanding of the growth mechanism and surface morphology [P.I. Cohen, G.S. Petrich, P.R. Pukite, G.J. Whaley, A.S. Arrott, Surf. Sci. 216 (1989) 222]. Method of solution:Epitaxial

  5. The in-plane anisotropic magnetic damping of ultrathin epitaxial Co{sub 2}FeAl film

    SciTech Connect

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

    2015-08-15

    The in-plane orientation-dependent effective damping of ultrathin Co{sub 2}FeAl 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 Co{sub 2}FeAl thin films.

  6. Improving dielectric properties of epitaxial Gd{sub 2}O{sub 3} thin films on silicon by nitrogen doping

    SciTech Connect

    Roy Chaudhuri, Ayan; Osten, H. J.; Fissel, A.; Archakam, V. R.

    2013-01-14

    We report about the effect of nitrogen doping on the electrical properties of epitaxial Gd{sub 2}O{sub 3} thin films. Epitaxial Gd{sub 2}O{sub 3}:N thin films were grown on Si (111) substrates by solid source molecular beam epitaxy using nitrous oxide as the nitridation agent. Substitutional nitrogen incorporation into the dielectric layer was confirmed by secondary ion mass spectroscopy and X-ray photoelectron spectroscopy analysis. Substantial reduction of the leakage current density and disappearance of hysteresis in capacitance-voltage characteristics observed in the Gd{sub 2}O{sub 3}:N layers indicate that nitrogen incorporation in Gd{sub 2}O{sub 3} effectively eliminates the adverse effects of the oxygen vacancy induced defects in the oxide layer.

  7. KTa0.65Nb0.35O3 thin films epitaxially grown by pulsed laser deposition on metallic and oxide epitaxial electrodes

    NASA Astrophysics Data System (ADS)

    Bouyasfi, A.; Mouttalie, M.; Demange, V.; Gautier, B.; Grandfond, A.; Députier, S.; Ollivier, S.; Hamedi, L.'H.; Guilloux-Viry, M.

    2012-09-01

    Ferroelectric KTa0.65Nb0.35O3 (KTN) thin films were grown by pulsed laser deposition on Pt and LaNiO3 epitaxial electrodes, on (1 0 0) and (1 1 0) SrTiO3 substrates. The effect of the nature of the electrode on structural and microstructural quality of KTN films was investigated. While epitaxial KTN thin films were successfully obtained on both electrodes, two orientations compete on Pt, whatever the main orientation of Pt is (1 0 0) or (1 1 0). On LaNiO3 in contrast, pure (1 0 0) and (1 1 0) oriented KTN films were achieved with a high crystalline quality illustrated by narrow ω-scans (Δω = 0.56° and Δω = 0.80° for (1 0 0) and (1 1 0) KTN, to be compared to 0.048° and 0.22° for (1 0 0) and (1 1 0) LaNiO3, respectively). Electrical measurements performed in tunneling atomic force microscopy (TUNA mode) on a KTN/Pt heterostructure showed a high asymmetry of the conduction mechanisms when a positive or a negative bias is applied on the sample. In particular leakage currents appear even at very low positive applied voltage. TUNA imaging operated at a moderate negative applied voltage of -3 V shows that some areas corresponding to grain boundaries seem to be more leaky than others.

  8. Non-Epitaxial Thin-Film Indium Phosphide Photovoltaics: Growth, Devices, and Cost Analysis

    NASA Astrophysics Data System (ADS)

    Zheng, Maxwell S.

    In recent years, the photovoltaic market has grown significantly as module prices have continued to come down. Continued growth of the field requires higher efficiency modules at lower manufacturing costs. In particular, higher efficiencies reduce the area needed for a given power output, thus reducing the downstream balance of systems costs that scale with area such as mounting frames, installation, and soft costs. Cells and modules made from III-V materials have the highest demonstrated efficiencies to date but are not yet at the cost level of other thin film technologies, which has limited their large-scale deployment. There is a need for new materials growth, processing and fabrication techniques to address this major shortcoming of III-V semiconductors. Chapters 2 and 3 explore growth of InP on non-epitaxial Mo substrates by MOCVD and CSS, respectively. The results from these studies demonstrate that InP optoelectronic quality is maintained even by growth on non-epitaxial metal substrates. Structural characterization by SEM and XRD show stoichiometric InP can be grown in complete thin films on Mo. Photoluminescence measurements show peak energies and widths to be similar to those of reference wafers of similar doping concentrations. In chapter 4 the TF-VLS growth technique is introduced and cells fabricated from InP produced by this technique are characterized. The TF-VLS method results in lateral grain sizes of >500 mum and exhibits superior optoelectronic quality. First generation devices using a n-TiO2 window layer along with p-type TF-VLS grown InP have reached ˜12.1% power conversion efficiency under 1 sun illumination with VOC of 692 mV, JSC of 26.9 mA/cm2, and FF of 65%. The cells are fabricated using all non-epitaxial processing. Optical measurements show the InP in these cells have the potential to support a higher VOC of ˜795 mV, which can be achieved by improved device design. Chapter 5 describes a cost analysis of a manufacturing process using an

  9. Effect of GaN interlayer on polarity control of epitaxial ZnO thin films grown by molecular beam epitaxy

    SciTech Connect

    Wang, X. Q.; Sun, H. P.; Pan, X. Q.

    2010-10-11

    Epitaxial ZnO thin films were grown on nitrided (0001) sapphire substrates with an intervening GaN layer by rf-plasma-assisted molecular beam epitaxy. It was found that polarity of the ZnO epilayer could be controlled by modifying the GaN interlayer. ZnO grown on a distorted 3-nm-thick GaN interlayer has Zn-polarity while ZnO on a 20-nm-thick GaN interlayer with a high structural quality has O-polarity. High resolution transmission electron microscopy analysis indicates that the polarity of ZnO epilayer is controlled by the atomic structure of the interface between the ZnO buffer layer and the intervening GaN layer.

  10. Preparation and structure characterization of SmCo{sub 5}(0001) epitaxial thin films grown on Cu(111) underlayers

    SciTech Connect

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

    2009-04-01

    SmCo{sub 5}(0001) epitaxial films were prepared on Cu(111) single-crystal underlayers formed on Al{sub 2}O{sub 3}(0001) substrates at 500 deg. C. The nucleation and growth mechanism of (0001)-oriented SmCo{sub 5} crystal on Cu(111) underlayer is investigated and a method to control the nucleation is proposed. The SmCo{sub 5} epitaxial thin film formed directly on Cu underlayer consists of two types of domains whose orientations are rotated around the film normal by 30 deg. each other. By introducing a thin Co seed layer on the Cu underlayer, a SmCo{sub 5}(0001) single-crystal thin film is successfully obtained. Nucleation of SmCo{sub 5} crystal on Cu underlayer seems controllable by varying the interaction between the Cu underlayer and the SmCo{sub 5} layer.

  11. Growth rate induced monoclinic to tetragonal phase transition in epitaxial BiFeO{sub 3} (001) thin films

    SciTech Connect

    Liu Huajun; Yang Ping; Yao Kui; Wang, John

    2011-03-07

    Epitaxial BiFeO{sub 3} thin films were deposited on SrRuO{sub 3} buffered SrTiO{sub 3} (001) substrates at different growth rates by varying the radio frequency sputtering power. With increasing growth rate, the crystal structure of BiFeO{sub 3} films develops from monoclinic lattice to a mixture phase of tetragonal lattice T{sub 1} with c/a{approx}1.05 and giant tetragonal lattice T{sub 2} with c/a{approx}1.23, finally to a single tetragonal phase T{sub 2}, as shown by high resolution synchrotron x-ray diffraction reciprocal space mappings. The observed phase transitions, induced by film growth rate, offer an alternative strategy to manipulate crystalline phases in epitaxial ferroelectric thin films.

  12. Pulsed laser deposition of epitaxial yttrium iron garnet films with low Gilbert damping and bulk-like magnetization

    SciTech Connect

    Onbasli, M. C. Kim, D. H.; Ross, C. A.; Kehlberger, A.; Jakob, G.; Kläui, M.; Chumak, A. V.; Hillebrands, B.

    2014-10-01

    Yttrium iron garnet (YIG, Y {sub 3}Fe{sub 5}O{sub 12}) films have been epitaxially grown on Gadolinium Gallium Garnet (GGG, Gd{sub 3}Ga{sub 5}O{sub 12}) substrates with (100) orientation using pulsed laser deposition. The films were single-phase, epitaxial with the GGG substrate, and the root-mean-square surface roughness varied between 0.14 nm and 0.2 nm. Films with thicknesses ranging from 17 to 200 nm exhibited low coercivity (<2 Oe), near-bulk room temperature saturation moments (∼135 emu cm{sup −3}), in-plane easy axis, and damping parameters as low as 2.2 × 10{sup −4}. These high quality YIG thin films are useful in the investigation of the origins of novel magnetic phenomena and magnetization dynamics.

  13. Microwave surface resistance of YBa 2Cu 3O 7-δ thin films deposited by pulsed organometallic beam epitaxy

    NASA Astrophysics Data System (ADS)

    DeGroot, D. C.; Hogan, T. P.; Kannewurf, C. R.; Buchholz, D. B.; Chang, R. P. H.; Gao, F.; Feng, M.; Nordin, R. A.

    1994-03-01

    The microwave surface resistance of superconducting YBa 2Cu 3O 7-δ thin films deposited by pulsed organometallic beam epitaxy (POMBE) has been characterized using the parallel plate transmission line resonator method. POMBE is an advanced organometric chemical vapor deposition technique where precursor vapors are precisely metered onto the substrate under computer control. In this study, the POMBE reactor was used to deposit epitaxial films of varying thickness onto LaAlO 3 substrates. The deposition procedure and surface-resistance results for films of varying thicknesses are described. The reduction of surface resistance achieved supports the use of the POMBE technique as a possible method for preparing device-quality high- Tc films and multi-layer structures.

  14. Molecular beam epitaxy deposition of Gd2O3 thin films on SrTiO3 (100) substrate

    NASA Astrophysics Data System (ADS)

    Wang, Jinxing; Hao, Jinghua; Zhang, Yangyang; Wei, Hongmei; Mu, Juyi

    2016-06-01

    Gd2O3 thin films are grown on the SrTiO3 (100) substrate by molecular beam epitaxy (MBE) deposition. X-ray diffraction (XRD) analysis, conventional transmission electron microscopy (TEM) and aberration-corrected scanning transmission electron microscopy (STEM) are performed to investigate the microstructure of deposited thin films. It is found that the as-deposited thin film possesses a very uniform thickness of ∼40 nm and is composed of single cubic phase Gd2O3 grains. STEM and TEM observations reveal that Gd2O3 thin film grows epitaxially on the SrTiO3 (100) substrate with (001)Gd2O3//(100)STO and [110]Gd2O3//[001]STO orientations. Furthermore, the Gd atoms are found to diffuse into the SrTiO3 substrate for a depth of one unit cell and substitute for the Sr atoms near the interface.

  15. Metallic transport and large anomalous Hall effect at room temperature in ferrimagnetic Mn{sub 4}N epitaxial thin film

    SciTech Connect

    Shen, Xi; Shigematsu, Kei; Chikamatsu, Akira Fukumura, Tomoteru; Hirose, Yasushi; Hasegawa, Tetsuya

    2014-08-18

    We report the electrical transport properties of ferrimagnetic Mn{sub 4}N (001) epitaxial thin films grown by pulsed laser deposition on MgO (001) substrates. The Mn{sub 4}N thin films were tetragonally distorted with a ratio of out-of-plane to in-plane lattice constants of 0.987 and showed perpendicular magnetic anisotropy with an effective magnetic anisotropy constant of 0.16 MJ/m{sup 3}, which is comparable with that of a recently reported molecular-beam-epitaxy-grown film. The thin films exhibited metallic transport with a room temperature resistivity of 125 μΩ cm in addition to a large anomalous Hall effect with a Hall angle tangent of 0.023.

  16. Pulsed laser deposition of epitaxial yttrium iron garnet films with low Gilbert damping and bulk-like magnetization

    NASA Astrophysics Data System (ADS)

    Onbasli, M. C.; Kehlberger, A.; Kim, D. H.; Jakob, G.; Kläui, M.; Chumak, A. V.; Hillebrands, B.; Ross, C. A.

    2014-10-01

    Yttrium iron garnet (YIG, Y 3Fe5O12) films have been epitaxially grown on Gadolinium Gallium Garnet (GGG, Gd3Ga5O12) substrates with (100) orientation using pulsed laser deposition. The films were single-phase, epitaxial with the GGG substrate, and the root-mean-square surface roughness varied between 0.14 nm and 0.2 nm. Films with thicknesses ranging from 17 to 200 nm exhibited low coercivity (<2 Oe), near-bulk room temperature saturation moments (˜135 emu cm-3), in-plane easy axis, and damping parameters as low as 2.2 × 10-4. These high quality YIG thin films are useful in the investigation of the origins of novel magnetic phenomena and magnetization dynamics.

  17. MWIR InSb detector with nBn architecture for high operating temperature

    NASA Astrophysics Data System (ADS)

    Perez, J.-P.; Evirgen, A.; Abautret, J.; Christol, P.; Cordat, A.; Nedelcu, A.

    2015-01-01

    In this communication, we report results obtained on a new InSb/InAlSb/InSb `bariode', grown by MBE on (100)- oriented InSb substrate. Because of a very weak valence band offset with InSb (~ 25meV), InAlSb is a good candidate as a barrier layer for electrons. However, due to lattice mismatch with the InSb substrate, careful growth study of InAlSb was made to insure high crystal quality. As a result, InSb-based nBn detector device exhibits dark current density equals to 1x10-9A.cm-2 at 77K: two decades lower than Insb standard pin photodiode with similar cut-off wavelength. Moreover, compared to standard pn (or pin) InSb-based photodetectors fabricated by implanted planar process or by molecular beam epitaxy (MBE), we demonstrate that the reachable working temperature, around 120 K, of the InSbbased nBn detector is respectively higher than 40 K and 20 K than the previous. Such result demonstrates the potentiality of Insb detectors with nBn architecture to reach the high operating temperature.

  18. Preparation and study of epitaxial Cr{sup 4+} : GGG films for passive Q switches in neodymium lasers

    SciTech Connect

    Bufetova, G A; Gusev, M Yu; Ivanov, I A; Nikolaev, D A; Seregin, V F; Tsvetkov, V B; Shcherbakov, Ivan A E-mail: tsvetkov@lsk.gpi.r

    2006-07-31

    The efficient technology is developed for growing Cr- and Ca-doped gadolinium-gallium garnet single-crystal films of thickness up to 100 {mu}m on large substrates (76 mm) by the method of liquid-phase epitaxy from a solution-melt. The dependences of the absorption spectra of films and optical losses at 1 {mu}m on the growth conditions and the solution-melt composition are studied. It is shown that Cr{sup 4+} ions are formed in the films, and these films can be used as passive Q switches in lasers. (special issue devoted to the 90th anniversary of a.m. prokhorov)

  19. Intrinsic high electrical conductivity of stoichiometric SrNb O3 epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Oka, Daichi; Hirose, Yasushi; Nakao, Shoichiro; Fukumura, Tomoteru; Hasegawa, Tetsuya

    2015-11-01

    SrV O3 and SrNb O3 are perovskite-type transition-metal oxides with the same d1 electronic configuration. Although SrNb O3 (4 d1 ) has a larger d orbital than SrV O3 (3 d1 ), the reported electrical resistivity of SrNb O3 is much higher than that of SrV O3 , probably owing to nonstoichiometry. In this paper, we grew epitaxial, high-conductivity stoichiometric SrNb O3 using pulsed laser deposition. The growth temperature strongly affected the Sr/Nb ratio and the oxygen content of the films, and we obtained stoichiometric SrNb O3 at a very narrow temperature window around 630 °C. The stoichiometric SrNb O3 epitaxial thin films grew coherently on KTa O3 (001) substrates with high crystallinity. The room-temperature resistivity of the stoichiometric film was 2.82 ×10-5Ω cm , one order of magnitude lower than the lowest reported value of SrNb O3 and comparable with that of SrV O3 . We observed a T -square dependence of resistivity below T*=180 K and non-Drude behavior in near-infrared absorption spectroscopy, attributable to the Fermi-liquid nature caused by electron correlation. Analysis of the T -square coefficient A of resistivity experimentally revealed that the 4 d orbital of Nb that is larger than the 3 d ones certainly contributes to the high electrical conduction of SrNb O3 .

  20. Plasmonic arrays of titanium nitride nanoparticles fabricated from epitaxial thin films.

    PubMed

    Murai, Shunsuke; Fujita, Koji; Daido, Yohei; Yasuhara, Ryuichiro; Kamakura, Ryosuke; Tanaka, Katsuhisa

    2016-01-25

    We have fabricated two-dimensional periodic arrays of titanium nitride (TiN) nanoparticles from epitaxial thin films. The thin films of TiN, deposited on sapphire and single crystalline magnesium oxide substrates by a pulsed laser deposition, are metallic and show reasonably small optical loss in the visible and near infrared regions. The thin films prepared were structured to the arrays of nanoparticles with the pitch of 400 nm by the combination of nanoimprint lithography and reactive ion etching. Optical transmission indicates that the arrays support the collective plasmonic modes, where the localized surface plasmon polaritons in TiN nanoparticles are radiatively coupled through diffraction. Numerical simulation visualizes the intense fields accumulated both in the nanoparticles and in between the particles, confirming that the collective mode originates from the simultaneous excitation of localized surface plasmon polaritons and diffraction. This study experimentally verified that the processing of TiN thin films with the nanoimprint lithography and reactive ion etching is a powerful and versatile way of preparing plasmonic nanostructures. PMID:26832498

  1. Thin film growth of CaFe2As2 by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hatano, T.; Kawaguchi, T.; Fujimoto, R.; Nakamura, I.; Mori, Y.; Harada, S.; Ujihara, T.; Ikuta, H.

    2016-01-01

    Film growth of CaFe2As2 was realized by molecular beam epitaxy on six different substrates that have a wide variation in the lattice mismatch to the target compound. By carefully adjusting the Ca-to-Fe flux ratio, we obtained single-phase thin films for most of the substrates. Interestingly, an expansion of the CaFe2As2 lattice to the out-of-plane direction was observed for all films, even when an opposite strain was expected. A detailed microstructure observation of the thin film grown on MgO by transmission electron microscope revealed that it consists of cube-on-cube and 45°-rotated domains. The latter domains were compressively strained in plane, which caused a stretching along the c-axis direction. Because the domains were well connected across the boundary with no appreciable discontinuity, we think that the out-of-plane expansion in the 45°-rotated domains exerted a tensile stress on the other domains, resulting in the unexpectedly large c-axis lattice parameter, despite the apparently opposite lattice mismatch.

  2. Electronic Properties of High-Quality Epitaxial Topological Dirac Semimetal Thin Films.

    PubMed

    Hellerstedt, Jack; Edmonds, Mark T; Ramakrishnan, Navneeth; Liu, Chang; Weber, Bent; Tadich, Anton; O'Donnell, Kane M; Adam, Shaffique; Fuhrer, Michael S

    2016-05-11

    Topological Dirac semimetals (TDS) are three-dimensional analogues of graphene, with linear electronic dispersions in three dimensions. Nanoscale confinement of TDSs in thin films is a necessary step toward observing the conventional-to-topological quantum phase transition (QPT) with increasing film thickness, gated devices for electric-field control of topological states, and devices with surface-state-dominated transport phenomena. Thin films can also be interfaced with superconductors (realizing a host for Majorana Fermions) or ferromagnets (realizing Weyl Fermions or T-broken topological states). Here we report structural and electrical characterization of large-area epitaxial thin films of TDS Na3Bi on single crystal Al2O3[0001] substrates. Charge carrier mobilities exceeding 6,000 cm(2)/(V s) and carrier densities below 1 × 10(18) cm(-3) are comparable to the best single crystal values. Perpendicular magnetoresistance at low field shows the perfect weak antilocalization behavior expected for Dirac Fermions in the absence of intervalley scattering. At higher fields up to 0.5 T anomalously large quadratic magnetoresistance is observed, indicating that some aspects of the low field magnetotransport (μB < 1) in this TDS are yet to be explained.

  3. Growth of SrVO{sub 3} thin films by hybrid molecular beam epitaxy

    SciTech Connect

    Eaton, Craig; Brahlek, Matthew; Engel-Herbert, Roman; Moyer, Jarrett A.; Alipour, Hamideh M.; Grimley, Everett D.; LeBeau, James M.

    2015-11-15

    The authors report the growth of stoichiometric SrVO{sub 3} thin films on (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (001) substrates using hybrid molecular beam epitaxy. This growth approach employs a conventional effusion cell to supply elemental A-site Sr and the metalorganic precursor vanadium oxytriisopropoxide (VTIP) to supply vanadium. Oxygen is supplied in its molecular form through a gas inlet. An optimal VTIP:Sr flux ratio has been identified using reflection high-energy electron-diffraction, x-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy, demonstrating stoichiometric SrVO{sub 3} films with atomically flat surface morphology. Away from the optimal VTIP:Sr flux, characteristic changes in the crystalline structure and surface morphology of the films were found, enabling identification of the type of nonstoichiometry. For optimal VTIP:Sr flux ratios, high quality SrVO{sub 3} thin films were obtained with smallest deviation of the lattice parameter from the ideal value and with atomically smooth surfaces, indicative of the good cation stoichiometry achieved by this growth technique.

  4. Surface state conductivity in epitaxially grown Bi1‑x Sb x (111) films

    NASA Astrophysics Data System (ADS)

    Koch, Julian; Kröger, Philipp; Pfnür, Herbert; Tegenkamp, Christoph

    2016-09-01

    Topologically non-trivial surface states were reported first on {{Bi}}1-xSb x bulk crystals. In this study we present transport measurements performed on thin {{Bi}}1-xSb x -films (up to 24 nm thickness) grown epitaxially on Si(111) with various Sb-concentrations (up to x = 0.22). The analysis of the temperature dependency allowed us to distinguish between different transport channels originating from surface and bulk bands as well as impurity states. At temperatures below 30 K the transport is mediated by surface states while at higher temperatures activated transport via bulk channels sets in. The surface state conductivity and bulk band gaps can be tuned by the Sb-concentration and film thickness, respectively. For films as thin as 4 nm the surface state transport is strongly suppressed in contrast to Bi(111) films grown under identical conditions. The impurity channel is of intrinsic origin due to the growth and alloy formation process and turns out to be located at the buried interface.

  5. Investigation of the growth of garnet films by liquid phase epitaxy

    NASA Technical Reports Server (NTRS)

    Moody, J. W.; Shaw, R. W.; Sandfort, R. M.

    1974-01-01

    Liquid phase expitaxy was investigated to determine its applicability to fabricating magnetic rare earth garnet films for spacecraft data recording systems. Two mixed garnet systems were investigated in detail: (1) Gd-Y and (2) Eu-Yb-Y. All films were deposited on Gd3Ga5012 substrates. The uniaxial anisotropy of the Gd-Y garnets is primarily stress-induced. These garnets are characterized by high-domain wall mobility, low coercivity and modest anisotropy. Characteristic length was found to be relatively sensitive to temperature. The Eu-Yb-Y garnets exhibit acceptable mobilities, good temperature stability and reasonable quality factors. The uniaxial anisotropy of these garnets is primarily growth-induced. The system is well suited for compositional "tailoring" to optimize specific desirable properties. Liquid phase epitaxy can be used to deposit Gd3Ga5012 spacing layers on magnetic garnet films and this arrangement possesses certain advantages over more conventional magnetic filmspacing layer combinations. However, it cannot be used if the magnetic film is to be ion implanted.

  6. Electronic structure of fully epitaxial Co2TiSn thin films

    SciTech Connect

    Meinert, Markus; Schmalhorst, Jan; Wulfmeier, Hendrik; Reiss, Gunter; Arenholz, Elke; Graf, Tanja; Felser, Claudia

    2010-10-28

    In this article we report on the properties of thin films of the full Heusler compound Co{sub 2}TiSn prepared by DC magnetron co-sputtering. Fully epitaxial, stoichiometric films were obtained by deposition on MgO (001) substrates at substrate temperatures above 600 C. The films are well ordered in the L2{sub 1} structure, and the Curie temperature exceeds slightly the bulk value. They show a significant, isotropic magnetoresistance and the resistivity becomes strongly anomalous in the paramagnetic state. The films are weakly ferrimagnetic, with nearly 1 {mu}{sub B} on the Co atoms, and a small antiparallel Ti moment, in agreement with theoretical expectations. From comparison of x-ray absorption spectra on the Co L{sub 3,2} edges, including circular and linear magnetic dichroism, with ab initio calculations of the x-ray absorption and circular dichroism spectra we infer that the electronic structure of Co{sub 2}TiSn has essentially non-localized character. Spectral features that have not been explained in detail before, are explained here in terms of the final state band structure.

  7. Enhanced UV detection by non-polar epitaxial GaN films

    SciTech Connect

    Mukundan, Shruti; Chandan, Greeshma; Mohan, Lokesh; Krupanidhi, S. B.; Roul, Basanta; Shetty, Arjun

    2015-12-15

    Nonpolar a-GaN (11-20) epilayers were grown on r-plane (1-102) sapphire substrates using plasma assisted molecular beam epitaxy. High resolution x-ray diffractometer confirmed the orientation of the grown film. Effect of the Ga/N ratio on the morphology and strain of a-GaN epilayers was compared and the best condition was obtained for the nitrogen flow of 1 sccm. Atomic force microscopy was used to analyze the surface morphology while the strain in the film was quantitatively measured using Raman spectroscopy and qualitatively analyzed by reciprocal space mapping technique. UV photo response of a-GaN film was measured after fabricating a metal-semiconductor-metal structure over the film with gold metal. The external quantum efficiency of the photodetectors fabricated in the (0002) polar and (11-20) nonpolar growth directions were compared in terms of responsivity and nonpolar GaN showed the best sensitivity at the cost of comparatively slow response time.

  8. Photoelectrochemical etching of epitaxial InGaN thin films: Self-limited kinetics and nanostructuring

    DOE PAGES

    Xiao, Xiaoyin; Fischer, Arthur J.; Coltrin, Michael E.; Lu, Ping; Koleske, Daniel D.; Wang, George T.; Polsky, Ronen; Tsao, Jeffrey Y.

    2014-10-22

    We report here the characteristics of photoelectrochemical (PEC) etching of epitaxial InGaN semiconductor thin films using narrowband lasers with linewidth less than ~1 nm. In the initial stages of PEC etching, when the thin film is flat, characteristic voltammogram shapes are observed. At low photo-excitation rates, voltammograms are S-shaped, indicating the onset of a voltage-independent rate-limiting process associated with electron-hole-pair creation and/or annihilation. At high photo-excitation rates, voltammograms are superlinear in shape, indicating, for the voltage ranges studied here, a voltage-dependent rate-limiting process associated with surface electrochemical oxidation. As PEC etching proceeds, the thin film becomes rough at the nanoscale,more » and ultimately evolves into an ensemble of nanoparticles. As a result, this change in InGaN film volume and morphology leads to a characteristic dependence of PEC etch rate on time: an incubation time, followed by a rise, then a peak, then a slow decay.« less

  9. Photoelectrochemical etching of epitaxial InGaN thin films: Self-limited kinetics and nanostructuring

    SciTech Connect

    Xiao, Xiaoyin; Fischer, Arthur J.; Coltrin, Michael E.; Lu, Ping; Koleske, Daniel D.; Wang, George T.; Polsky, Ronen; Tsao, Jeffrey Y.

    2014-10-22

    We report here the characteristics of photoelectrochemical (PEC) etching of epitaxial InGaN semiconductor thin films using narrowband lasers with linewidth less than ~1 nm. In the initial stages of PEC etching, when the thin film is flat, characteristic voltammogram shapes are observed. At low photo-excitation rates, voltammograms are S-shaped, indicating the onset of a voltage-independent rate-limiting process associated with electron-hole-pair creation and/or annihilation. At high photo-excitation rates, voltammograms are superlinear in shape, indicating, for the voltage ranges studied here, a voltage-dependent rate-limiting process associated with surface electrochemical oxidation. As PEC etching proceeds, the thin film becomes rough at the nanoscale, and ultimately evolves into an ensemble of nanoparticles. As a result, this change in InGaN film volume and morphology leads to a characteristic dependence of PEC etch rate on time: an incubation time, followed by a rise, then a peak, then a slow decay.

  10. Magnetic anisotropy and its microstructural origin in epitaxially grown SmCo thin films.

    SciTech Connect

    Benaissa, M.

    1998-04-15

    Microstructural features and magnetic behavior of epitaxially grown SmCo thin films with very high in-plane anisotropy are presented. Transmission electron microscopy was used to characterize the microstructure while magnetic measurements were performed using dc and SQUID magnetometers. Two substrate orientations were studied, i.e., MgO(100)/Cr(100)/SmCo(11{bar 2}0) and MgO(110)/Cr(211)/SmCo(1{bar 1}00). In the former, the SmCo(11{bar 2}0) film shows a bicrystalline microstructure, whereas in the latter, a uniaxial one is observed. Both microstructure consist of grains with a mixture of SmCo{sub 3} , Sm{sub 2}Co{sub 7} and SmCo{sub 3} polytypoids. A deviation from the c-axes was observed in the in-plane anisotropy of the SmCo(11{bar 2}0) thin film. A strong exchange interaction between the grains would, in principle, explain the observed deviation. On the other hand, both SmCo(11{bar 2}0) and (1{bar 1}00) thin films show very high coercivity values with pinning-type characteristics. Possible coercivity mechanisms related to intergranular exchange interactions and local variation in magnetocrystalline anisotropy constants are discussed.

  11. Electronic Properties of High-Quality Epitaxial Topological Dirac Semimetal Thin Films.

    PubMed

    Hellerstedt, Jack; Edmonds, Mark T; Ramakrishnan, Navneeth; Liu, Chang; Weber, Bent; Tadich, Anton; O'Donnell, Kane M; Adam, Shaffique; Fuhrer, Michael S

    2016-05-11

    Topological Dirac semimetals (TDS) are three-dimensional analogues of graphene, with linear electronic dispersions in three dimensions. Nanoscale confinement of TDSs in thin films is a necessary step toward observing the conventional-to-topological quantum phase transition (QPT) with increasing film thickness, gated devices for electric-field control of topological states, and devices with surface-state-dominated transport phenomena. Thin films can also be interfaced with superconductors (realizing a host for Majorana Fermions) or ferromagnets (realizing Weyl Fermions or T-broken topological states). Here we report structural and electrical characterization of large-area epitaxial thin films of TDS Na3Bi on single crystal Al2O3[0001] substrates. Charge carrier mobilities exceeding 6,000 cm(2)/(V s) and carrier densities below 1 × 10(18) cm(-3) are comparable to the best single crystal values. Perpendicular magnetoresistance at low field shows the perfect weak antilocalization behavior expected for Dirac Fermions in the absence of intervalley scattering. At higher fields up to 0.5 T anomalously large quadratic magnetoresistance is observed, indicating that some aspects of the low field magnetotransport (μB < 1) in this TDS are yet to be explained. PMID:27104635

  12. Epitaxial cobalt oxide films on Ir(100)-the importance of crystallographic analyses.

    PubMed

    Heinz, K; Hammer, L

    2013-05-01

    Epitaxial cobalt oxide films on Ir(100) exhibit a rich scenario of different structural phases which are reviewed in this paper. The great majority of phases could be, as a rare case, crystallographically described by the joint application of atomically resolved STM and quantitative LEED, whereby structural surprises were more the rule than the exception. So, the oxide grows in the polar (111) orientation for both the Co3O4 and CoO stoichiometry on the bare Ir substrate in spite of the latter's square symmetry. Moreover, the film orientation can be tuned to non-polar (100) growth when one or several pseudomorphic Co layers are introduced as an interface between oxide and Ir substrate. By using the nanostructured Ir(100)-(5 × 1)-H phase as a template a nanostructured Co film can be formed whose oxidation leads to a nanostructured oxide. The nominally polar films circumvent the polarity problem by appropriate surface terminations. That of CoO(111) is, again as a surprise, realized by a switch from rocksalt-type to wurtzite-type stacking near the surface, by which the latter becomes metallic. The stepwise oxidation of a pseudomorphic Co layer on the bare Ir substrate leads to the sequential formation of rocksalt-type tetrahedral Co-O building blocks (with intermediate BN-type blocks) whereby the Co species more and more assume positions determined by the inner-oxidic binding.

  13. Surface state conductivity in epitaxially grown Bi1-x Sb x (111) films

    NASA Astrophysics Data System (ADS)

    Koch, Julian; Kröger, Philipp; Pfnür, Herbert; Tegenkamp, Christoph

    2016-09-01

    Topologically non-trivial surface states were reported first on {{Bi}}1-xSb x bulk crystals. In this study we present transport measurements performed on thin {{Bi}}1-xSb x -films (up to 24 nm thickness) grown epitaxially on Si(111) with various Sb-concentrations (up to x = 0.22). The analysis of the temperature dependency allowed us to distinguish between different transport channels originating from surface and bulk bands as well as impurity states. At temperatures below 30 K the transport is mediated by surface states while at higher temperatures activated transport via bulk channels sets in. The surface state conductivity and bulk band gaps can be tuned by the Sb-concentration and film thickness, respectively. For films as thin as 4 nm the surface state transport is strongly suppressed in contrast to Bi(111) films grown under identical conditions. The impurity channel is of intrinsic origin due to the growth and alloy formation process and turns out to be located at the buried interface.

  14. Magnetic properties of ultra thin epitaxial Fe films on GaAs(001)

    SciTech Connect

    Morton, S A; Tobin, J G; Spangenberg, M; Neal, J R; Shen, T H; Waddill, G D; Matthew, J D; Greig, D; Malins, A R; Seddon, E A; Hopkinson, M

    2003-10-02

    The magnetic properties of epitaxial Fe films on GaAs in the range of the first few monolayers have been the subject of a considerable number of investigations in recent years. The absence of magnetic signatures at room temperature has been attributed to the existence of a magnetic ''dead'' layer as well as superparamagnetism. By examining the temperature dependence of the magnetic linear dichroism of the Fe core level photoelectrons, we found that these ''non-ferromagnetic'' layers had in fact a Curie temperature, T{sub c}, substantially lower than room temperature, e.g., a T{sub c} of about 240K for thin films of a nominal thickness of 0.9 nm. The values of Curie temperature were sensitive to the initial GaAs substrate conditions and the thickness of the Fe over-layer with a layer of thickness of 1.25 nm showing a T{sub c} above room temperature. The data suggest that the ultrathin Fe films on GaAs(001) are ferromagnetic, although a weaker exchange interaction in the films lead to a substantial reduction in Curie temperature.

  15. Tuning of magnetic properties for epitaxial Y2NiMnO6 thin film: Substrate is crucial

    NASA Astrophysics Data System (ADS)

    Xie, Changzheng; Shi, Lei

    2016-10-01

    The effects of epitaxial strain induced by lattice mismatch and substrate type on the structure and magnetic properties of Y2NiMnO6 thin films have been systematically investigated. Y2NiMnO6 thin films grown on (001)-oriented LaAlO3 (LAO), (La,Sr)(Al,Ta)O3 (LSAT), and SrTiO3 (STO) substrates with varying film thickness are obtained by a simple polymer assisted deposition method. X-ray diffraction and Raman scattering observations indicate that the single-phase epitaxial films are successfully obtained. By magnetic measurements, it is found that all the films show an obvious ferromagnetic transition with a lower transition temperatures (Tc) than that of the Y2NiMnO6 bulk. With the biaxial tensile strain decreasing or the film thickness increasing, the Tc of the film increases. Besides, due to the different strain states of the films and the different surface migrations of the substrates, the structure and magnetic properties show a strong dependence on the type of substrate. It is suggested that the biaxial tensile strain and substrate type have crucial effects on the structure, magnetic properties and the related Tc of the thin film, which can be utilized to engineer the magnetic properties of the films and the related ferroelectricity.

  16. Preparation and structural characterization of FeCo epitaxial thin films on insulating single-crystal substrates

    SciTech Connect

    Nishiyama, Tsutomu; Ohtake, Mitsuru; Futamoto, Masaaki; Kirino, Fumiyoshi

    2010-05-15

    FeCo epitaxial films were prepared on MgO(111), SrTiO{sub 3}(111), and Al{sub 2}O{sub 3}(0001) single-crystal substrates by ultrahigh vacuum molecular beam epitaxy. The effects of insulating substrate material on the film growth process and the structures were investigated. FeCo(110){sub bcc} films grow on MgO substrates with two type domains, Nishiyama-Wassermann (NW) and Kurdjumov-Sachs (KS) relationships. On the contrary, FeCo films grown on SrTiO{sub 3} and Al{sub 2}O{sub 3} substrates include FeCo(111){sub bcc} crystal in addition to the FeCo(110){sub bcc} crystals with NW and KS relationships. The FeCo(111){sub bcc} crystal consists of two type domains whose orientations are rotated around the film normal by 180 deg. each other. The out-of-plane and the in-plane lattice spacings of FeCo(110){sub bcc} and FeCo(111){sub bcc} crystals formed on the insulating substrates are in agreement with those of the bulk Fe{sub 50}Co{sub 50} (at. %) crystal with small errors ranging between +0.2% and +0.4%, showing that the strains in the epitaxial films are very small.

  17. Composition gradient effects on strain relaxation in Sr-doped LaMnO{sub 3} epitaxial thin films

    SciTech Connect

    Wang, Yishu; Meletis, Efstathios I.

    2015-07-15

    The authors report on a novel method to fabricate Sr-doped composition gradient epitaxial La{sub 1−x}Sr{sub x}MnO{sub 3} thin films by radio frequency magnetron sputtering. Biaxially strained epitaxial La{sub 1−x}Sr{sub x}MnO{sub 3} thin films were grown on (001) LaAlO{sub 3} substrates by following a cosputtering procedure from LaMnO{sub 3} and La{sub 0.67}Sr{sub 0.33}MnO{sub 3} targets. Three depositions were conducted by varying the substrate temperature (750 and 850 °C) and controlling the relative deposition rate from the two targets by varying their power rate during sputtering. The thickness of the thin films was about 20 and 30 nm for the short and long duration deposition, respectively. The films were studied by symmetric θ–2θ x-ray diffraction, pole figure analysis, atomic force microscopy, and x-ray photoelectron spectroscopy. Fabrication of smooth, composition gradient films of high epitaxial quality was achieved at a substrate temperature of 850 °C and low sputtering rate. A novel strain relaxation mechanism is also found that decreases significantly the mismatch between the film and substrate as the Sr doping level increases. The reported deposition procedure can produce new possibilities of designing nanoscale structures with cross coupled properties that may result in new materials.

  18. Long Range Ferromagnetic Order in LaCoO3-δ epitaxial films due to the interplay of epitaxial strain and oxygen vacancy ordering

    DOE PAGES

    Mehta, Virat; Biskup, Nevenko; Arenholz, E; Varela del Arco, Maria; Suzuki, Yuri

    2015-04-23

    We demonstrate that a combination of electronic structure modification and oxygen vacancy ordering can stabilize a long-range ferromagnetic ground state in epitaxial LaCoO3 thin films. Highest saturation magnetization values are found in the thin films in tension on SrTiO3 and (La,Sr)(Al,Ta)O3 substrates and the lowest values are found in thin films in compression on LaAlO3. Electron microscopy reveals oxygen vacancy ordering to varying degrees in all samples, although samples with the highest magnetization are the most defective. Element-specific x-ray absorption techniques reveal the presence of high spin Co2+ and Co3+ as well as low spin Co3+ in different proportions dependingmore » on the strain state. The interactions among the high spin Co ions and the oxygen vacancy superstructure are correlated with the stabilization of the long-range ferromagnetic order.« less

  19. Epitaxial growth and characterization of II-VI-semiconductor, one-dimensional nanostructures and thin films

    NASA Astrophysics Data System (ADS)

    Zhu, Zuoming

    In this thesis, I present the results of three material science studies on II-VI semiconductor nanostructures and thin films: (1) epitaxial growth and characterization of one-dimensional ZnO nanostructures, (2) crystal structure and self-assembly of ultrathin ZnO nanorods, and (3) investigations of surface chemistry for atomic layer epitaxy of ZnS thin film on silicon with chemical precursors. First, in Chapter 3, I present a comparative study of metal-surface-catalyzed growth of ZnO nanowires using four different metal catalysts and using substrates of differing materials and crystal orientation. Multiple material diagnostics were employed to compare the material, structural, and optical properties of the nanowires grown using these different surface systems. My study showed that the growth modes of nanowires are dependent on the choice of surface catalysts. Further, the study revealed that these differences in growth modes are also closely related to the differences in materials properties of these wires including the degree of nanowire alignment on substrates, and the atomic composition ratio of Zn/O, as well as the relative intensity of the oxygen vacancy-related emission in photoluminescence spectra. Second, in Chapter 4, I investigated the growth and self-assembly of ultrathin ZnO nanorods using a combination of small-angle and wide-angle synchrotron X-ray diffraction (SAXRD and WAXRD), and TEM. SAXRD and TEM were used to investigate nanorod self-assembly and the influence of surfactant/precursor ratio on self-assembly; WAXRD were used to study the effects of growth chemistry and physical parameters on the nanorod size and lattice constants. These measurements revealed that these rods self-assemble into periodic superstructures and that the surfactant ligands are important in controlling self-assembly. WAXRD results suggest that surface-dependent changes, such as the binding of surface ligands or other adsorbed species may dominate the changes in nanorod

  20. Structural Properties of Alternate Monatomic Layered [Fe/Co]n Epitaxial Films on MgO Substrate

    NASA Astrophysics Data System (ADS)

    Chu, In Chang; Saki, Yoshinobu; Kawasaki, Shohei; Doi, Masaaki; Sahashi, Masashi

    2008-06-01

    Body-centered-cubic (bcc) Fe50Co50 material is reported to show a high bulk spin scattering coefficient on current perpendicular to plane-giant magneto-resistance (CPP-GMR) system. But the origin of that phenomenon does not make sure yet. We prepared artificially alternate monatomic layered (AML) [Fe/Co] 41 MLs epitaxial films (Ts: 75, 250 °C) by monatomic deposition method and investigated the topology of AML [Fe/Co]n epitaxial films on MgO substrate with different orientation (001), (011) by the scanning tunnel microscopy (STM) and reflection high energy electron diffraction (RHEED), which we could confirm Frank-van der Merwe (FM) growth mode for AML [Fe/Co]n on MgO(001) and Volmer-Weber (VW) growth mode for that on Mg(011). The roughness of surface, Ra (0.20 nm) of AML [Fe/Co] 41 MLs epitaxial film grown at 75 °C on MgO(001) is smaller than that (0.46 nm) of AML [Fe/Co] grown at 250 °C on MgO(001), which has the large terraces of over 50 nm (Ra: 0.17 nm), even though there are some valleys between large terraces. Moreover we confirmed the structural properties of trilayered epitaxial films with AML [Fe/Co]n (Ra: 0.18 nm) and Fe50Co50 alloy epitaxial film on Au electrode by RHEED before confirming the characteristics of CPP-GMR devices.

  1. Mössbauer study on epitaxial Co{sub x}Fe{sub 4−x}N films grown by molecular beam epitaxy

    SciTech Connect

    Ito, Keita; Sanai, Tatsunori; Yasutomi, Yoko; Gushi, Toshiki; Toko, Kaoru; Yanagihara, Hideto; Kita, Eiji; Suemasu, Takashi; Tsunoda, Masakiyo

    2015-05-07

    We prepared Co{sub x}Fe{sub 4−x}N (x = 0, 1, 3) films on SrTiO{sub 3}(STO)(001) substrates by molecular beam epitaxy. The epitaxial relationship with Co{sub x}Fe{sub 4−x}N[100](001) || STO[100](001) was confirmed by ω-2θ (out-of-plane) and ϕ-2θ{sub χ} (in-plane) x-ray diffraction (XRD) measurements. The degree of order of atoms (S) in the Co{sub x}Fe{sub 4−x}N films was estimated to be ∼0.5 by the peak intensity ratio of Co{sub x}Fe{sub 4−x}N(100) (superlattice diffraction line) to (400) (fundamental diffraction line) in the ϕ-2θ{sub χ} XRD patterns. Conversion electron Mössbauer spectroscopy studies for the Co{sub x}Fe{sub 4−x}N films revealed that some N atoms are located at interstitial sites between the two nearest corner sites in the Co{sub x}Fe{sub 4−x}N films, and/or Fe atoms are located at both the corner and face-centered sites in the CoFe{sub 3}N and Co{sub 3}FeN films. In order to realize high spin-polarized Co{sub x}Fe{sub 4−x}N films having large S, further optimization of growth condition is required to prevent the site-disorders.

  2. Texture of Al thin films deposited by magnetron sputtering onto epitaxial W(001)

    SciTech Connect

    Madsen, Lynnette D.; Svedberg, Erik B.; Bergstrom, Daniel B.; Petrov, Ivan; Greene, Joseph E.

    2000-01-01

    Highly textured epitaxial metallizations will be required for the next generation of devices with the main driving force being a reduction in electromigration. Herein a model system of 190 nm of Al on a 140 nm layer of W grown on MgO <00l> substrates was studied. The W layer was <00l> oriented and rotated 45 degree sign with respect to the MgO substrate to minimize the misfit; the remaining strain was accommodated by dislocations, evident in transmission electron microscopy images. From high-resolution x-ray diffraction (XRD) measurements, the out-of-plane lattice parameter was determined to be 3.175 Aa, and the in-plane parameter was 3.153 Aa, i.e., the W film sustained a strain resulting in a tetragonal distortion of the lattice. XRD pole figures showed that the Al had four fold symmetry and two dominant orientations, <016> and <3 9 11>, which were twinned with multiple placements on the epitaxial W layer. The driving force for the tilted <001> and <011> orientations of Al on W is due to strain minimization through lattice matching. These results show that <00l> Al deposited at ambient conditions onto W is difficult to achieve and implies that electromigration difficulties are inherent. (c) 2000 American Institute of Physics.

  3. Structural evolution of epitaxial SrCoO{sub x} films near topotactic phase transition

    SciTech Connect

    Jeen, Hyoungjeen; Lee, Ho Nyung

    2015-12-15

    Control of oxygen stoichiometry in complex oxides via topotactic phase transition is an interesting avenue to not only modifying the physical properties, but utilizing in many energy technologies, such as energy storage and catalysts. However, detailed structural evolution in the close proximity of the topotactic phase transition in multivalent oxides has not been much studied. In this work, we used strontium cobaltites (SrCoO{sub x}) epitaxially grown by pulsed laser epitaxy (PLE) as a model system to study the oxidation-driven evolution of the structure, electronic, and magnetic properties. We grew coherently strained SrCoO{sub 2.5} thin films and performed post-annealing at various temperatures for topotactic conversion into the perovskite phase (SrCoO{sub 3-δ}). We clearly observed significant changes in electronic transport, magnetism, and microstructure near the critical temperature for the topotactic transformation from the brownmillerite to the perovskite phase. Nevertheless, the overall crystallinity was well maintained without much structural degradation, indicating that topotactic phase control can be a useful tool to control the physical properties repeatedly via redox reactions.

  4. Engineering of the Curie temperature of epitaxial Sr1-xBaxTiO3 films via strain

    NASA Astrophysics Data System (ADS)

    Dai, Y.; Schubert, J.; Hollmann, E.; Mussler, G.; Wördenweber, R.

    2016-09-01

    The impact of strain on the structural and electrical properties of epitaxial Sr1-xBaxTiO3 films grown on single crystalline DyScO3 (110), TbScO3 (110), and GdScO3 (110) substrates is presented. X-ray diffraction measurements demonstrate that all films are grown epitaxially. The tensile in-plane strain is only partially compensated by a contraction of the out-of-plane lattice parameter. As a result, the volume of the unit cell of the Sr1-xBaxTiO3 film increases due to the tensile strain, and the resulting Poisson ratio of the film is ν ≈ 0.33, which is larger than but still close to the literature values of ν ≈ 0.23 for unstrained defect-free SrTiO3. The Curie temperature derived from the temperature dependence of the in-plane dielectric response leads to a strain-temperature phase diagram for the epitaxial Sr1-xBaxTiO3 films. The experimental data show a deviation from the linear dependence predicted by the Landau thermodynamic theory for large strain (>1.2%). However, using the equilibrium thermodynamic analysis, we can demonstrate that this deviation arises from the relaxation of the strain due to defect formation in the film. The result reveals that in addition to the nominal misfit strain, the defect formation strongly affects the effective strain and, thus, the dielectric response of epitaxially grown ferroelectric films.

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

    PubMed Central

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

    2014-01-01

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

  6. Single-crystal cubic boron nitride thin films grown by ion-beam-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hirama, Kazuyuki; Taniyasu, Yoshitaka; Karimoto, Shin-ichi; Krockenberger, Yoshiharu; Yamamoto, Hideki

    2014-03-01

    We investigated the formation of cubic boron nitride (c-BN) thin films on diamond (001) and (111) substrates by ion-beam-assisted molecular beam epitaxy (MBE). The metastable c-BN (sp3-bonded BN) phase can be epitaxially grown as a result of the interplay between competitive phase formation and selective etching. We show that a proper adjustment of acceleration voltage for N2+ and Ar+ ions is a key to selectively discriminate non-sp3 BN phases. At low acceleration voltage values, the sp2-bonded BN is dominantly formed, while at high acceleration voltages, etching dominates irrespective of the bonding characteristics of BN.

  7. Summary of in situ epitaxial nucleation and growth measurements. [for semiconducting single crystal PbSe films

    NASA Technical Reports Server (NTRS)

    Poppa, H.; Moorhead, R. D.; Heinemann, K.

    1974-01-01

    In situ nucleation and growth measurements of Ag and Au on single-crystal PbSe thin films were made using a transmission electron microscope. Properties studied were polymorphism, crystalline perfection, and the stoichiometric composition of the initial and the autoepitaxially thickened PbSe substrates. The quantitative nucleation and cluster growth measurements were limited to low-saturation conditions. The epitaxial orientations are discussed, and evidence is presented as to the stage of deposition at which the epitaxial order for Ag is introduced. Strong substrate/overgrowth interaction manifested itself by alloying and interdiffusion.

  8. Strong growth orientation dependence of strain relaxation in epitaxial (Ba,Sr)TiO{sub 3} films and the resulting dielectric properties

    SciTech Connect

    Yamada, Tomoaki; Kamo, Takafumi; Funakubo, Hiroshi; Su Dong; Iijima, Takashi

    2011-05-01

    The growth orientation dependence of strain relaxation and the dielectric properties were investigated for (001)- and (111)-epitaxial (Ba,Sr)TiO{sub 3} films. The films were deposited on SrRuO{sub 3}/SrTiO{sub 3} and SrTiO{sub 3} substrates using rf magnetron sputtering. The residual strain was found to be remarkably different between the two orientations, although these lattice mismatches are identical; the strain relaxation of the (001)-epitaxial films is significantly slower than that of the (111)-epitaxial films and is promoted only when the growth rate is very low ({<=}5 nm/h). The observed orientation dependence is discussed with the surface energy for both growth orientations, which influences the growth mode of the films. Due to the large contrast of the strain in the (001)- and (111)-epitaxial films, the paraelectric to ferroelectric phase transition temperature of the (001)-epitaxial films is much higher than that of unstrained bulks, while the (111)-epitaxial films show a phase transition temperature corresponding to that of unstrained bulks regardless of the growth rates.

  9. High electron mobility in Ga(In)NAs films grown by molecular beam epitaxy

    SciTech Connect

    Miyashita, Naoya; Ahsan, Nazmul; Monirul Islam, Muhammad; Okada, Yoshitaka; Inagaki, Makoto; Yamaguchi, Masafumi

    2012-11-26

    We report the highest mobility values above 2000 cm{sup 2}/Vs in Si doped GaNAs film grown by molecular beam epitaxy. To understand the feature of the origin which limits the electron mobility in GaNAs, temperature dependences of mobility were measured for high mobility GaNAs and referential low mobility GaInNAs. Temperature dependent mobility for high mobility GaNAs is similar to the GaAs case, while that for low mobility GaInNAs shows large decrease in lower temperature region. The electron mobility of high quality GaNAs can be explained by intrinsic limiting factor of random alloy scattering and extrinsic factor of ionized impurity scattering.

  10. Modulation of Pb chemical state of epitaxial lead zirconate titanate thin films under high energy irradiation

    NASA Astrophysics Data System (ADS)

    Barala, Surendra Singh; Roul, Basanta; Banerjee, Nirupam; Kumar, Mahesh

    2016-09-01

    The chemical states of epitaxial PbZrxTi1-xO3 films were investigated by an X-ray photoelectron spectroscopy as a function of the gamma-ray doses. An anomalous behaviour was observed in Pb4f states, and a core level of Pb4f shifts towards a higher binding energy at 50 kGy and towards a lower binding energy at 200 kGy. The behaviour can be explained by a radiation induced reduction of PbO to metallic Pb. The metal-insulator-metal electrodes were fabricated by lithography, and the current-voltage characteristics were measured. A negative differential resistance (NDR) was observed in the leakage currents at room temperature. A higher current and disappearance of NDR characteristics were found in the 200 kGy irradiated samples, which further confirms the presence of metallic Pb.

  11. Evaluation of microindentation properties of epitaxial 3C-SiC/Si thin films

    NASA Astrophysics Data System (ADS)

    Geetha, D.; Sophia, P. Joice; Arivuoli, D.

    2016-06-01

    The microhardness characteristics of 3C-SiC/Si films grown by vapor phase epitaxy were investigated using Vickers and Knoop indenters. The observed hardness behavior at lower load range is being attributed to indentation size effect while the substrate hardness effect is found to be prominent at higher loads. The related mechanical properties such as fracture toughness, brittleness index, and yield stress were also evaluated. In order to study the nature and behavior of the surface topography during the deformation process for the applied load, detailed atomic force microscopy images were obtained around the indented regions of the samples. It revealed that the indents formed at higher loads showed fracture characteristics with a pattern of radial cracks propagating from the indent corners.

  12. Magnetic and structural anisotropies of Co2FeAl Heusler alloy epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Gabor, M. S.; Petrisor, T., Jr.; Tiusan, C.; Hehn, M.; Petrisor, T.

    2011-10-01

    This paper shows the correlation between chemical order, lattice strains, and magnetic properties of Heusler Co2FeAl films epitaxially grown on MgO(001). A detailed magnetic characterization is performed using vector-field magnetometery combined with a numerical Stoner-Wohlfarth analysis. We demonstrate the presence of three types of in-plane anisotropies: one biaxial, as expected for the cubic symmetry, and two uniaxial. The three anisotropies show different behavior with the annealing temperature. The biaxial anisotropy shows a monotonic increase. The uniaxial anisotropy that is parallel to the hard biaxial axes (related to chemical homogeneity) decreases, while the anisotropy that is supposed to have a magnetostatic origin remains constant.

  13. Epitaxial thin film GaAs solar cells using OM-CVD techniques. [Organometallics

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.; Wang, K. L.; Yeh, Y. C. M.

    1981-01-01

    A new approach has been initiated at JPL to fabricate thin-film, high efficiency GaAs solar cells on low-cost, single-crystal Si substrates having a thin CVD interlayer of Ge to minimize the lattice and thermal expansion mismatch. For initial experiments, n(+)/p GaAs cells were grown by OM-CVD on single-crystal GaAs and Ge wafers. Details of the growths and performance results will be presented. Subsequently, a combined epitaxial structure of OM-CVD GaAs on a strongly adherent Ge interlayer on (100) Si was grown. This is the first report of the successful growth of this composite structure. Low module costs projected by JPL SAMICS methodology calculations and the potential for 400-600W/kg space solar arrays will be discussed.

  14. Distribution of Pd clusters on ultrathin, epitaxial TiOx films on Pt3Ti(111)

    PubMed Central

    Breinlich, Christian; Buchholz, Maria; Pertram, Tobias; Becker, Conrad; Wandelt, Klaus

    2015-01-01

    Summary Scanning tunnelling microscopy (STM) was used to investigate the nucleation and growth of palladium clusters on two different, ultrathin, epitaxial, titania films grown on a Pt3Ti(111) surface. The first oxide phase, z'-TiOx, is anisotropic and consists of parallel stripes separated by trenches. Defects (i.e., oxygen vacancies) in this structure are confined to these trenches and act as nucleation sites. Therefore, the Pd clusters are mostly arranged in unidirectional rows along the trenches, creating a template effect. The second phase, w'-TiOx, exhibits a hexagonal, long range, (7 × 7)R21.8°, Moiré-type superstructure with fewer and shallower defects, making the template effect less discernible. PMID:26665071

  15. Large enhancement of positive magnetoresistance by Ce doping in Si epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Miyata, Y.; Ueno, K.; Togawa, Y.; Yoshimura, T.; Ashida, A.; Fujimura, N.

    2016-09-01

    We report the investigation into a large enhancement of the magnetoresistance (MR) by Ce doping in Si epitaxial thin films at room temperature. The positive MR is proportional to the square of the magnetic field at low magnetic fields below 5 T, while it increases linearly with regards to the strength of the magnetic field above 5 T. Based on the experimental finding that the change in the donor level corresponds to that of the MR ratio as a function of Ce concentration, the electronic state turns out to be influenced by Ce doping and strongly correlate the magnetotransport characteristics. It is concluded that this MR effect appears via the Lorentz force effect on the carrier motion, which is enhanced by the random scattering potential distribution arising from the Ce doping.

  16. Characteristic morphologies of triangular defects on Si-face 4H-SiC epitaxial films

    NASA Astrophysics Data System (ADS)

    Yamashita, T.; Naijo, T.; Matsuhata, H.; Momose, K.; Osawa, H.; Okumura, H.

    2016-01-01

    Triangular defects with a characteristic morphology consisting of a 3C-type structure were investigated on Si-face 4H-SiC epitaxial films using electron microscopy. Two types of triangular defects were investigated: one with a single valley on the surface along the [ 11 2 bar 0 ] direction and another with several parallel ridges and valleys called "washboard-like defects". The defects with a single valley had a characteristic domain structure consisting of four 3C crystals, which is similar to that of previously reported comet-shaped defects on the C-face. It is shown that the 3C domain in the washboard-like defect is covered by 4H layers with a washboard-like morphology.

  17. Ferroelastic twin structures in epitaxial WO{sub 3} thin films

    SciTech Connect

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

    2015-12-21

    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 YAlO{sub 3} 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.

  18. Synthesis, Structure, and Spectroscopy of Epitaxial EuFeO3 Thin Films

    SciTech Connect

    Choquette, Amber K.; Colby, Robert J.; Moon, E. J.; Schleputz, C. M.; Scafetta, Mark D.; Keavney, David J.; May, Steven J.

    2015-03-04

    Rare earth iron perovskites RFeO3, where R is a rare earth cation, exhibit an array of magnetic, catalytic, optical and electrochemical properties. Here we study EuFeO3 films synthesized by molecular beam epitaxy in order to better understand the optical properties of ferrites. A combination of x-ray diffraction, x-ray reflectivity, Rutherford backscattering spectroscopy, and scanning transmission electron microscopy were used to characterize the film structure and cation composition. X-ray absorption spectroscopy confirms the nominal 3+ valence states of Eu and Fe. The optical properties of EuFeO3 were investigated using variable angle spectroscopic ellipsometry between the phonon energies of 1.25 to 5 eV. We find that EuFeO3 is a semiconductor with an onset of optical absorption near 2.5 eV. The absorption spectrum of EuFeO3 is blue-shifted with respect to LaFeO3 films, a result that is attributed to the structural differences of the two materials.

  19. Interface control of surface photochemical reactivity in ultrathin epitaxial ferroelectric films

    SciTech Connect

    Chen, Jason; Lu, Haidong; Gruverman, Alexei; Liu, Heng-Jui; Chu, Ying-Hao; Dunn, Steve; Ostrikov, Kostya; Valanoor, Nagarajan

    2013-05-06

    Asymmetrical electrical boundary conditions in (001)-oriented Pb(Zr{sub 0.2}TiO{sub 0.8})O{sub 3} (PZT) epitaxial ultrathin ferroelectric films are exploited to control surface photochemical reactivity determined by the sign of the surface polarization charge. It is shown that the preferential orientation of polarization in the as-grown PZT layer can be manipulated by choosing an appropriate type of bottom electrode material. PZT films deposited on the SrRuO{sub 3} electrodes exhibit preferential upward polarization (C{sup +}) whilst the same films grown on the (La,Sr)CoO{sub 3}-electrodes are polarized downward (C{sup -}). Photochemical activity of the PZT surfaces with different surface polarization charges has been tested by studying deposition of silver nanoparticles from AgNO{sub 3} solution under UV irradiation. PZT surfaces with preferential C{sup +} orientation possess a more active surface for metal reduction than their C{sup -} counterparts, evidenced by large differences in the concentration of deposited silver nanoparticles. This effect is attributed to band bending at the bottom interface which varies depending on the difference in work functions of PZT and electrode materials.

  20. Enhancement of Magnetization in Y3Fe5O12 Epitaxial Thin Films

    NASA Astrophysics Data System (ADS)

    Brangham, Jack T.; Gallagher, James C.; Yang, Angela S.; White, Shane P.; Adur, Rohan; Ruane, Willam T.; Esser, Bryan D.; Page, Michael R.; Hammel, P. Chris; McComb, David W.; Yang, Fengyuan

    The ability to generate pure spin currents has applications in telecommunications, radar, and spin-based logic. Y3Fe5O12 (YIG) is one of the best materials for dynamic generation of spin currents due to its low damping, narrow ferromagnetic resonance (FMR) linewidth, and insulating behavior. We grow stoichiometric, high quality, epitaxial YIG thin films with thicknesses ranging from 4 to 250 nm on Gd3Ga5O12 by off-axis magnetron sputtering and characterize the YIG films by various techniques. The temperature dependence of the saturation magnetization was independently measured by in-plane vibrating sample magnetometry, out-of-plane magnetic shape anisotropy, and angular-dependent FMR absorption from 10 K to the Curie temperature of 530 K. The room temperature saturation magnetization was also measured with frequency dependent FMR. All measurements show a magnetization enhancement of 15% or greater when compared to reported magnetization values of bulk YIG crystals. We speculate this is due to suppression of the long wavelength magnons due to the finite size of the films.

  1. In situ epitaxial MgB2 thin films for superconducting electronics.

    PubMed

    Zeng, Xianghui; Pogrebnyakov, Alexej V; Kotcharov, Armen; Jones, James E; Xi, X X; Lysczek, Eric M; Redwing, Joan M; Xu, Shengyong; Li, Qi; Lettieri, James; Schlom, Darrell G; Tian, Wei; Pan, Xiaoqing; Liu, Zi-Kui

    2002-09-01

    The newly discovered 39-K superconductor MgB2 holds great promise for superconducting electronics. Like the conventional superconductor Nb, MgB2 is a phonon-mediated superconductor, with a relatively long coherence length. These properties make the prospect of fabricating reproducible uniform Josephson junctions, the fundamental element of superconducting circuits, much more favourable for MgB2 than for high-temperature superconductors. The higher transition temperature and larger energy gap of MgB2 promise higher operating temperatures and potentially higher speeds than Nb-based integrated circuits. However, success in MgB2 Josephson junctions has been limited because of the lack of an adequate thin-film technology. Because a superconducting integrated circuit uses a multilayer of superconducting, insulating and resistive films, an in situ process in which MgB2 is formed directly on the substrate is desirable. Here we show that this can be achieved by hybrid physical-chemical vapour deposition. The epitaxially grown MgB2 films show a high transition temperature and low resistivity, comparable to the best bulk samples, and their surfaces are smooth. This advance removes a major barrier for superconducting electronics using MgB2.

  2. Visible light carrier generation in co-doped epitaxial titanate films

    SciTech Connect

    Comes, Ryan B. Kaspar, Tiffany C.; Chambers, Scott A.; Smolin, Sergey Y.; Baxter, Jason B.; Gao, Ran; Apgar, Brent A.; Martin, Lane W.; Bowden, Mark E.

    2015-03-02

    Perovskite titanates such as SrTiO{sub 3} (STO) exhibit a wide range of important functional properties, including ferroelectricity and excellent photocatalytic performance. The wide optical band gap of titanates limits their use in these applications; however, making them ill-suited for integration into solar energy harvesting technologies. Our recent work has shown that by doping STO with equal concentrations of La and Cr, we can enhance visible light absorption in epitaxial thin films while avoiding any compensating defects. In this work, we explore the optical properties of photoexcited carriers in these films. Using spectroscopic ellipsometry, we show that the Cr{sup 3+} dopants, which produce electronic states immediately above the top of the O 2p valence band in STO reduce the direct band gap of the material from 3.75 eV to 2.4–2.7 eV depending on doping levels. Transient reflectance spectroscopy measurements are in agreement with the observations from ellipsometry and confirm that optically generated carriers are present for longer than 2 ns. Finally, through photoelectrochemical methylene blue degradation measurements, we show that these co-doped films exhibit enhanced visible light photocatalysis when compared to pure STO.

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

    NASA Astrophysics Data System (ADS)

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

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

  4. Evolution of Insulator-Metal Phase Transitions in Epitaxial Tungsten Oxide Films during Electrolyte-Gating.

    PubMed

    Nishihaya, Shinichi; Uchida, Masaki; Kozuka, Yusuke; Iwasa, Yoshihiro; Kawasaki, Masashi; Nishihaya, S; Uchida, M; Kozuka, Y; Iwasa, Y; Kawasaki, M; Iwasa, Y; Kawasaki, M

    2016-08-31

    An interface between an oxide and an electrolyte gives rise to various processes as exemplified by electrostatic charge accumulation/depletion and electrochemical reactions such as intercalation/decalation under electric field. Here we directly compare typical device operations of those in electric double layer transistor geometry by adopting A-site vacant perovskite WO3 epitaxial thin films as a channel material and two different electrolytes as gating agent. In situ measurements of X-ray diffraction and channel resistance performed during the gating revealed that in both the cases WO3 thin film reaches a new metallic state through multiple phase transitions, accompanied by the change in out-of-plane lattice constant. Electrons are electrostatically accumulated from the interface side with an ionic liquid, while alkaline metal ions are more uniformly intercalated into the film with a polymer electrolyte. We systematically demonstrate this difference in the electrostatic and electrochemical processes, by comparing doped carrier density, lattice deformation behavior, and time constant of the phase transitions. PMID:27502546

  5. Visible light carrier generation in co-doped epitaxial titanate films

    SciTech Connect

    Comes, Ryan B.; Smolin, Sergey Y.; Kaspar, Tiffany C.; Gao, Ran; Apgar, Brent A.; Martin, Lane W.; Bowden, Mark E.; Baxter, Jason; Chambers, Scott A.

    2015-03-02

    Perovskite titanates such as SrTiO3 (STO) exhibit a wide range of important functional properties, including high electron mobility, ferroelectricity—which may be valuable in photovoltaic applications—and excellent photocatalytic performance. The wide optical band gap of titanates limits their use in these applications, however, making them ill-suited for integration into solar energy harvesting technologies. Our recent work has shown that by doping STO with equal concentrations of La and Cr we can enhance visible light absorption in epitaxial thin films while avoiding any compensating defects. In this work, we explore the optical properties of photoexcited carriers in these films. Using spectroscopic ellipsometry, we show that the Cr3+ dopants, which produce electronic states immediately above the top of the O 2p valence band in STO reduce the direct band gap of the material from 3.75 eV to between 2.4 and 2.7 eV depending on doping levels. Transient reflectance measurements confirm that optically generated carriers have a recombination lifetime comparable to that of STO and are in agreement with the observations from ellipsometry. Finally, through photoelectrochemical yield measurements, we show that these co-doped films exhibit enhanced visible light photocatalysis when compared to pure STO.

  6. Epitaxial growth of high mobility Bi{sub 2}Se{sub 3} thin films on CdS

    SciTech Connect

    Kou, X. F.; He, L.; Xiu, F. X.; Lang, M. R.; Yu, X. X.; Tang, J. S.; Huang, G.; Jiang, X. W.; Zhu, J. F.; Wang, K. L.; Liao, Z. M.; Zou, J.; Wang, Y.; Fedorov, A. V.

    2011-06-13

    We report the experiment of high quality epitaxial growth of Bi{sub 2}Se{sub 3} thin films on hexagonal CdS (0001) substrates using a solid source molecular-beam epitaxy system. Layer-by-layer growth of single crystal Bi{sub 2}Se{sub 3} has been observed from the first quintuple layer. The size of surface triangular terraces has exceeded 1 {mu}m. Angle-resolved photoemission spectroscopy clearly reveals the presence of Dirac-cone-shape surface states. Magneto-transport measurements demonstrate a high Hall mobility of {approx}6000 cm{sup 2}/V s for the as-grown Bi{sub 2}Se{sub 3} thin films at temperatures below 30 K. These characteristics of Bi{sub 2}Se{sub 3} thin films promise a variety of potential applications in ultrafast, low-power dissipation devices.

  7. Morphology and grain structure evolution during epitaxial growth of Ag films on native-oxide-covered Si surface

    SciTech Connect

    Hur, Tae-Bong; Kim, Hong Koo; Perello, David; Yun, Minhee; Kulovits, Andreas; Wiezorek, Joerg

    2008-05-15

    Epitaxial nanocrystalline Ag films were grown on initially native-oxide-covered Si(001) substrates using radio-frequency magnetron sputtering. Mechanisms of grain growth and morphology evolution were investigated. An epitaxially oriented Ag layer ({approx}5 nm thick) formed on the oxide-desorbed Si surface during the initial growth phase. After a period of growth instability, characterized as kinetic roughening, grain growth stagnation, and increase of step-edge density, a layer of nanocrystalline Ag grains with a uniform size distribution appeared on the quasi-two-dimensional layer. This hierarchical process of film formation is attributed to the dynamic interplay between incoming energetic Ag particles and native oxide. The cyclic interaction (desorption and migration) of the oxide with the growing Ag film is found to play a crucial role in the characteristic evolution of grain growth and morphology change involving an interval of grain growth stagnation.

  8. AlN thin films grown on epitaxial 3C-SiC (100) for piezoelectric resonant devices

    SciTech Connect

    Lin, Chih-Ming; Senesky, Debbie G.; Pisano, Albert P.; Lien, Wei-Cheng; Felmetsger, Valery V.; Hopcroft, Matthew A.

    2010-10-04

    Highly c-axis oriented heteroepitaxial aluminum nitride (AlN) films were grown on epitaxial cubic silicon carbide (3C-SiC) layers on Si (100) substrates using alternating current reactive magnetron sputtering at temperatures between approximately 300-450 deg. C. The AlN films were characterized by x-ray diffraction, scanning electron microscope, and transmission electron microscopy. A two-port surface acoustic wave device was fabricated on the AlN/3C-SiC/Si composite structure, and an expected Rayleigh mode exhibited a high acoustic velocity of 5200 m/s. The results demonstrate the potential of utilizing AlN films on epitaxial 3C-SiC layers to create piezoelectric resonant devices.

  9. Surface and Interface Properties of 10–12 Unit Cells Thick Sputter Deposited Epitaxial CeO 2 Films

    DOE PAGES

    Saraf, L. V.; Wang, C. M.; Engelhard, M. H.; Nachimuthu, P.

    2008-01-01

    Ulmore » trathin and continuous epitaxial films with relaxed lattice strain can potentially maintain more of its bulk physical and chemical properties and are useful as buffer layers. We study surface, interface, and microstructural properties of ultrathin ( ∼ 10–12 unit cells thick) epitaxial ceria films grown on single crystal YSZ substrates. The out-of -plane and in-plane lattice parameters indicate relaxation in the continuous film due to misfit dislocations seen by high-resolution transmission electron microscopy (HRTEM) and substrate roughness of ∼ 1-2 unit cells, confirmed by atomic force microscopy and HRTEM. A combination of secondary sputtering, lattice mismatch, substrate roughness, and surface reduction creating secondary phase was likely the cause of surface roughness which should be reduced to a minimum level for effective use of it as buffer layers.« less

  10. Nanoparticle-Sintered BaTiO3 Thin Films and Its Orientation Control by Solid Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Nakasone, Fumi; Kobayashi, Keisuke; Suzuki, Toshimasa; Mizuno, Youichi; Chazono, Hirokazu; Imai, Hiroaki

    2008-11-01

    A novel powder-sintering thin-film process using nanocrystals of sol-gel-derived BaTiO3 without sintering additives yields a highly densified microstructure containing columnar grains at low temperatures of 800 °C. The BaTiO3 thin film fabricated on a (111)-oriented Pt/TiO2/Al2O3 substrate shows high crystallinity and a relatively high dielectric constant of 635 at 10 kHz with a low loss tangent of 0.007. Furthermore, the controllability of the crystallographic orientations of thin films by solid phase epitaxy is demonstrated on the basis of the optimization of surface nucleation and the subsequent grain growth on epitaxially grown platinum electrodes and single-crystal SrTiO3 substrates.

  11. Shift of morphotropic phase boundary in high-performance [111]-oriented epitaxial Pb (Zr, Ti) O3 thin films

    NASA Astrophysics Data System (ADS)

    Yu, Qi; Li, Jing-Feng; Zhu, Zhi-Xiang; Xu, Ying; Wang, Qing-Ming

    2012-07-01

    High-performance epitaxial niobium-doped lead zirconate titanate thin films [Pb(ZrxTi1-x)0.98Nb0.02O3] with a fixed thickness were deposited on [111]-cut single-crystalline SrTiO3 substrates by a sol-gel process as a function of Zr/Ti ratio ranging from 20/80 to 80/20. An obvious shift of morphotropic phase boundary (MPB) was observed in the [111]-oriented epitaxial films. Deviating from the Zr/Ti ratio of 52/48 in bulk materials, the MPB composition in the as-deposited films was found to move to a lower Zr/Ti ratio between 30/70 and 40/60, which agrees with the theoretical analysis on the basis of lattice mismatch between films and substrates and is further confirmed by the XRD patterns and Raman spectrum as well as ferroelectric test. Furthermore, a superior remnant polarization (Pr) value among all the compositions was obtained at a Zr/Ti ratio of 30/70, indicating that the extrinsic ferroelectric polarization near the new morphotropic phase boundary will lead to outstanding dielectric and piezoelectric performance in the epitaxial PZT thin film system.

  12. Epitaxial growth of highly-crystalline spinel ferrite thin films on perovskite substrates for all-oxide devices

    PubMed Central

    Moyer, Jarrett A.; Gao, Ran; Schiffer, Peter; Martin, Lane W.

    2015-01-01

    The potential growth modes for epitaxial growth of Fe3O4 on SrTiO3 (001) are investigated through control of the energetics of the pulsed-laser deposition growth process (via substrate temperature and laser fluence). We find that Fe3O4 grows epitaxially in three distinct growth modes: 2D-like, island, and 3D-to-2D, the last of which is characterized by films that begin growth in an island growth mode before progressing to a 2D growth mode. Films grown in the 2D-like and 3D-to-2D growth modes are atomically flat and partially strained, while films grown in the island growth mode are terminated in islands and fully relaxed. We find that the optimal structural, transport, and magnetic properties are obtained for films grown on the 2D-like/3D-to-2D growth regime boundary. The viability for including such thin films in perovskite-based all-oxide devices is demonstrated by growing a Fe3O4/La0.7Sr0.3MnO3 spin valve epitaxially on SrTiO3. PMID:26030835

  13. Epitaxial Deposition of Low-Defect Aluminum Nitride and Aluminum Gallium Nitride Films

    NASA Astrophysics Data System (ADS)

    Jain, Rakesh

    The bjective of my research was to develop low-defect AlN and AlGaN templates to enable pseudo-homoepitaxial deposition of UV-LEDs. Two approaches have been used to achieve this objective. Firstly, hydride vapor phase epitaxy (HVPE) process was used to prepare thick AlN films with lower defect density. Interactions of dislocations in thicker films result in their annihilation. Secondly, since thick films grown on sapphire tend to crack beyond a critical thickness (3-5 mum), epitaxial lateral overgrowth (ELOG) approach was employed to eliminate cracking and to further reduce the defect density. The growth technique was switched from HVPE to Metalorganic chemical vapor deposition (MOCVD) due to much improved material quality with the later method. An HVPE growth system was first designed and constructed from ground up [1]. It is a vertical system with a quartz chamber and a resistively heated furnace. AlCl3 and NH3 were used as the precursors. AlCl3 was generated by passing HCl gas (diluted with H2) through Al metal source. A linear relationship between growth rate and HCl flow rate indicated that the growth rate is limited by mass transportation. Growth parameters including temperature, chamber pressure and V/III ratio were optimized to improve the film quality. Thick films of AlN with thicknesses exceeding 25 mum were grown with growth rates as high as 20 mum/hr [2]. AFM study revealed that surface roughness of HVPE grown AlN films strongly depends on the growth rate. The lowest RMS roughness for HVPE grown film was 1.9 nm. These films had typical (002) full-width at half maximum (FWHM) values ranging from 24 -- 400 arcsec, depending on the growth rate of the respective films. The crystalline quality of the films was also found to be deteriorating as the growth rate increased. It is inferred that the growth mode changes from two dimensional to three dimensional at higher growth rates due to reduced adatom migration length. PL spectrum exhibited near-band-edge (NBE

  14. Structural and electrical properties of epitaxial YBCO films on Si (Abstract Only).

    NASA Astrophysics Data System (ADS)

    Fork, David K.; Barrera, A.; Phillips, Julia M.; Newman, N.; Fenner, David B.; Geballe, Theodore H.; Connell, G. A. N.; Boyce, James B.

    1991-03-01

    Efforts to grow high quality films of YBCO on Si have been complicated by factors discussed in Ref. 1, chief among them being the reaction between YBCO and Si, which is damaging even at 550 C. This is well below the customary temperatures for YBCO film growth. To avoid the reaction problem, epitaxial YBCO films were grown on Si (100) using an intermediate buffer layer of yttria-stabilized zirconia (YSZ).2 Both layers are grown via an entirely in situ process by pulsed laser deposition (PLD). Although the buffer layer prevents reaction, another problem arises; the large difference in thermal expansion coefficients between silicon and YBCO causes strain at room temperature. Thin (<500 A) YBCO films are unrelaxed and under tensile strain with a distorted unit cell. Thicker films are cracked and have poorer electrical properties. The thermal strain may be reduced by growing on silicon-on-sapphire (SOS) rather than silicon.3 This allows the growth of films of arbitrary thickness. Ion channeling reveals a high degree of crystalline perfection with a channeling minimum yield for Ba as low as 12% on either silicon or SOS. The normal state resistivity is 250-300 i-cm at 300 K; the critical temperature, Tc (R=0), is 86-88 K with a transition width (ATc) of I K. Critical current densities (J)°f 2x107 A/cm2 at 4.2 K and >2x106 A/cm2 at 77 K have been achieved. In addition, the surface resistance of a YBCO film on SOS was measured against Nb at 4.2 K. At 10 GHz, a value of 45 was obtained. This compares favorably to values reported for LaAlO3. Application of this technology to produce reaction patterned microstrip lines has been tested.4 This was done by ion milling away portions of the YSZ buffer layer prior to the YBCO deposition. YBCO landing on regions of exposed Si reacts to form an insulator. This technique was used to make 3 micron lines 1.5 mm long. The resulting structure had a Jc of l.6xl06 A/cm2 at 77 K. Isolation of separate structures exceeded 20 M. Several

  15. Study of the branching domain structures in epitaxial films of yttrium iron garnet by end face magnetic force microscopy

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

    The distribution of the magnetization vector on the free surface and end (cleaved facet) of thick epitaxial yttrium iron garnet films has been studied by the scanning magnetic-force microscopy method. Volume fractal-like branching of the domain structure has been found at the interface of the film and the free space with the refinement of the formed partial branches of the stripe (labyrinth) domains. Triangular closing domains have been observed at the interface between the film and the substrate. Direct experimental proof of the existence of the static horizontal Bloch lines within the stripe domain walls has been obtained.

  16. Voltage-current characteristics of epitaxial and misoriented Ba(Fe1-xCox) 2As2 thin films

    NASA Astrophysics Data System (ADS)

    Rodríguez, O.; Mariño, A.

    2015-06-01

    Ba(Fe1-xCox) 2As2 thin films were produced by Pulsed Laser Deposition (PLD). Epitaxial thin films were obtained when the deposition temperature was 700 °C while at 875 °C misoriented films were obtained. The presence of grain boundaries reduces the transport critical current Jc in almost two order of magnitude with respect to the textured thin films. The Voltage-Current (V-I) curves of misoriented films, exhibit a mixture of a non-ohmic linear differential (NOLD) and power law behaviors, due to the viscous flow of the flux lines along the grain boundaries lines, corresponding to the Jc limited by grain boundaries and Jc limited by intragrain, respectively. The misoriented thin films also present a kinked V-I curves attributed to a vortex channeling along the boundaries.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  18. Structural and Magnetic Phase Transitions in Manganese Arsenide Thin-Films Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Jaeckel, Felix Till

    Phase transitions play an important role in many fields of physics and engineering, and their study in bulk materials has a long tradition. Many of the experimental techniques involve measurements of thermodynamically extensive parameters. With the increasing technological importance of thin-film technology there is a pressing need to find new ways to study phase transitions at smaller length-scales, where the traditional methods are insufficient. In this regard, the phase transitions observed in thin-films of MnAs present interesting challenges. As a ferromagnetic material that can be grown epitaxially on a variety of technologically important substrates, MnAs is an interesting material for spintronics applications. In the bulk, the first order transition from the low temperature ferromagnetic alpha-phase to the beta-phase occurs at 313 K. The magnetic state of the beta-phase has remained controversial. A second order transition to the paramagnetic gamma-phase takes place at 398 K. In thin-films, the anisotropic strain imposed by the substrate leads to the interesting phenomenon of coexistence of alpha- and beta-phases in a regular array of stripes over an extended temperature range. In this dissertation these phase transitions are studied in films grown by molecular beam epitaxy on GaAs (001). The films are confirmed to be of high structural quality and almost purely in the A0 orientation. A diverse set of experimental techniques, germane to thin-film technology, is used to probe the properties of the film: Temperature-dependent X-ray diffraction and atomic-force microscopy (AFM), as well as magnetotransport give insights into the structural properties, while the anomalous Hall effect is used as a probe of magnetization during the phase transition. In addition, reflectance difference spectroscopy (RDS) is used as a sensitive probe of electronic structure. Inductively coupled plasma etching with BCl3 is demonstrated to be effective for patterning MnAs. We show

  19. Thermodynamic Theory of Epitaxial Alloys: First-Principles Mixed-Basis Cluster Expansion of (In,Ga)N Alloy Film

    SciTech Connect

    Liu, J. Z.; Zunger, A.

    2009-01-01

    Epitaxial growth of semiconductor alloys onto a fixed substrate has become the method of choice to make high quality crystals. In the coherent epitaxial growth, the lattice mismatch between the alloy film and the substrate induces a particular form of strain, adding a strain energy term into the free energy of the alloy system. Such epitaxial strain energy can alter the thermodynamics of the alloy, leading to a different phase diagram and different atomic microstructures. In this paper, we present a general-purpose mixed-basis cluster expansion method to describe the thermodynamics of an epitaxial alloy, where the formation energy of a structure is expressed in terms of pair and many-body interactions. With a finite number of first-principles calculation inputs, our method can predict the energies of various atomic structures with an accuracy comparable to that of first-principles calculations themselves. Epitaxial (In, Ga)N zinc-blende alloy grown on GaN(001) substrate is taken as an example to demonstrate the details of the method. Two (210) superlattice structures, (InN){sub 2}/(GaN){sub 2} (at x = 0.50) and (InN){sub 4}/(GaN){sub 1} (at x = 0.80), are identified as the ground state structures, in contrast to the phase-separation behavior of the bulk alloy.

  20. Thermodynamic theory of epitaxial alloys: first-principles mixed-basis cluster expansion of (In, Ga)N alloy film.

    PubMed

    Liu, Jefferson Zhe; Zunger, Alex

    2009-07-22

    Epitaxial growth of semiconductor alloys onto a fixed substrate has become the method of choice to make high quality crystals. In the coherent epitaxial growth, the lattice mismatch between the alloy film and the substrate induces a particular form of strain, adding a strain energy term into the free energy of the alloy system. Such epitaxial strain energy can alter the thermodynamics of the alloy, leading to a different phase diagram and different atomic microstructures. In this paper, we present a general-purpose mixed-basis cluster expansion method to describe the thermodynamics of an epitaxial alloy, where the formation energy of a structure is expressed in terms of pair and many-body interactions. With a finite number of first-principles calculation inputs, our method can predict the energies of various atomic structures with an accuracy comparable to that of first-principles calculations themselves. Epitaxial (In, Ga)N zinc-blende alloy grown on GaN(001) substrate is taken as an example to demonstrate the details of the method. Two (210) superlattice structures, (InN)(2)/(GaN)(2) (at x = 0.50) and (InN)(4)/(GaN)(1) (at x = 0.80), are identified as the ground state structures, in contrast to the phase-separation behavior of the bulk alloy. PMID:21828531

  1. Epitaxial growth of YBCO films on metallic substrates buffered with yttria-stabilized zirconia

    NASA Astrophysics Data System (ADS)

    Ma, B.; Li, M.; Fisher, B. L.; Koritala, R. E.; Balachandran, U.

    2002-05-01

    Biaxially textured yttria-stabilized zirconia (YSZ) films were grown on polished Hastelloy C (HC) substrates by ion-beam-assisted deposition (IBAD) and electron-beam evaporation. A water-cooled sample stage was used to dissipate heat generated by the Kaufman ion source and to maintain the substrate temperature below 100 °C during deposition. X-ray pole figures were used for texture analysis. In-plane texture measured from the YSZ (111) φ-scan full-width-at-half-maximum (FWHM) was 13.2° and out-of-plane texture from the YSZ (002) ω-scan FWHM was 7.7°. In-plane texture improved with lowered substrate temperature during IBAD deposition. RMS surface roughness of 3.3 nm was measured by atomic force microscopy. A thin CeO2 buffer layer (≈10 nm) was deposited to improve the lattice match between the YSZ and YBCO films and to enhance the biaxial alignment of YBCO films. YBCO films were epitaxially grown on IBAD-YSZ buffered HC substrates with and without CeO2 buffer layers by pulsed laser deposition (PLD). In-plane texture FWHMs of 12° and 9° were observed for CeO2 (111) and YBCO (103), respectively. Tc=90 K, with sharp transition, and Jc values of ≈2×106 A/cm2 at 77 K in zero field were observed on 0.5-μm-thick, 5-mm-wide, and 1-cm-long samples.

  2. Ultrafast structural dynamics of LaVO3 thin films grown by hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Brahlek, Matthew; Lapano, Jason; Stoica, Vladimir; Zhang, Lei; Zhang, Hai-Tian; Akamatsu, Hirofumi; Eaton, Craig; Gopalan, Venkatraman; Freeland, John; Wen, Haidan; Engel-Herbert, Roman

    LaVO3, with a partially full d-shell is expected to be metallic, but due to electron-electron interactions a gap emerges and the ground state is a Mott insulator. Such effects are a strong function of the bonding geometry, and particularly the V-O-V bond angle. Controlling these structural effects on the ultrafast time scale can lead to control over the underlying electronic ground state. Here we report the ultrafast structural dynamics of 25 and 50 nm thick LaVO3 thin films grown by the hybrid molecular beam epitaxy technique on SrTiO3 when excited across the bandgap by 800 nm light. Using time-resolved x-ray diffraction on the 100 ps time scale at Sector 7 of the Advanced Photon Source, we directly measured the structural changes with atomic accuracy by monitoring integer Bragg diffraction peaks and find a large out-of-plane strain of 0.18% upon optical excitation; the recovery time is ~1 ns for the 25 nm film and ~2 ns for the 50 nm film, consistent with the thermal transport from the film to the substrate. Further, we will discuss the response of the oxygen octahedral rotation patterns indicated by changes of the half-order diffraction peaks. Understanding such ultrafast structural deformation is important for optimizing optical excitations to create new metastable phases starting from a Mott insulator. This work was supported by the Department of Energy under Grant DE-SC0012375, and DE-AC02-06CH11357.

  3. Evolution and regularity results for epitaxially strained thin films and material voids

    NASA Astrophysics Data System (ADS)

    Piovano, Paolo

    In this dissertation we study free boundary problems that model the evolution of interfaces in the presence of elasticity, such as thin film profiles and material void boundaries. These problems are characterized by the competition between the elastic bulk energy and the anisotropic surface energy. First, we consider the evolution equation with curvature regularization that models the motion of a two-dimensional thin film by evaporation-condensation on a rigid substrate. The film is strained due to the mismatch between the crystalline lattices of the two materials and anisotropy is taken into account. We present the results contained in [62] where the author establishes short time existence, uniqueness and regularity of the solution using De Giorgi's minimizing movements to exploit the L2-gradient flow structure of the equation. This seems to be the first analytical result for the evaporation-condensation case in the presence of elasticity. Second, we consider the relaxed energy introduced in [20] that depends on admissible pairs (E, u) of sets E and functions u defined only outside of E. For dimension three this energy appears in the study of the material voids in solids, where the pairs (E, u) are interpreted as the admissible configurations that consist of void regions E in the space and of displacements u of the atoms of the crystal. We provide the precise mathematical framework that guarantees the existence of minimal energy pairs (E, u). Then, we establish that for every minimal configuration (E, u), the function u is C1,gloc -regular outside an essentially closed subset of E. No hypothesis of starshapedness is assumed on the voids and all the results that are contained in [18] hold true for every dimension d ≥ 2. Key Words and Sentences: surface energy, elastic bulk energy, minimizing movements, evolution, gradient flow, motion by mean curvature, minimal configurations, existence, uniqueness, regularity, partial regularity, lower density bound, thin film

  4. Low temperature epitaxy of Ge-Sb-Te films on BaF{sub 2} (111) by pulsed laser deposition

    SciTech Connect

    Thelander, E. Gerlach, J. W.; Ross, U.; Lotnyk, A.; Rauschenbach, B.

    2014-12-01

    Pulsed laser deposition was employed to deposit epitaxial Ge{sub 2}Sb{sub 2}Te{sub 5}-layers on the (111) plane of BaF{sub 2} single crystal substrates. X-ray diffraction measurements show a process temperature window for epitaxial growth between 85 °C and 295 °C. No crystalline growth is observed for lower temperatures, whereas higher temperatures lead to strong desorption of the film constituents. The films are of hexagonal structure with lattice parameters consistent with existing models. X-ray pole figure measurements reveal that the films grow with one single out-of-plane crystal orientation, but rotational twin domains are present. The out-of-plane epitaxial relationship is determined to be Ge{sub 2}Sb{sub 2}Te{sub 5}(0001) || BaF{sub 2}(111), whereas the in-plane relationship is characterized by two directions, i.e., Ge{sub 2}Sb{sub 2}Te{sub 5} [-12-10] || BaF{sub 2}[1-10] and Ge{sub 2}Sb{sub 2}Te{sub 5}[1-210] || BaF{sub 2}[1-10]. Aberration-corrected high-resolution scanning transmission electron microscopy was used to resolve the local atomic structure and confirm the hexagonal structure of the films.

  5. The mechanism of sputter-induced epitaxy modification in YBCO (001) films grown on MgO (001) substrates

    SciTech Connect

    Huang, Y.; Vuchic, B.V.; Carmody, M.; Baldo, P.M.; Merkle, K.L.; Buchholz, D.B.; Mahajan, S.; Lei, J.S.; Markworth, P.R.; Chang, R.P.; Marks, L.D.

    1998-12-01

    The sputter-induced epitaxy change of in-plane orientation occurring in YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (001) thin films grown on MgO (001) substrates by pulsed organo-metallic beam epitaxy (POMBE) is investigated by a series of film growth and characterization experiments, including RBS and TEM. The factors influencing the orientation change are systematically studied. The experimental results suggest that the substrate surface morphology change caused by the ion sputtering and the Ar ion implantation in the substrate surface layer are not the major factors that affect the orientation change. Instead, the implantation of W ions, which come from the hot filament of the ion gun, and the initial Ba deposition layer in the YBCO film growth play the most important roles in controlling the epitaxy orientation change. Microstructure studies show that a Ba{sub x}Mg{sub 1{minus}x}O buffer layer is formed on top of the sputtered substrate surface due to Ba diffusion into the W implanted layer. It is believed that the formation of this buffer layer relieves the large lattice mismatch and changes the YBCO film from the 45{degree} oriented growth to the 0{degree} oriented growth. {copyright} {ital 1998 Materials Research Society.}

  6. Room temperature ferromagnetism in epitaxial Cr{sub 2}O{sub 3} thin films grown on r-sapphire

    SciTech Connect

    Punugupati, Sandhyarani Narayan, Jagdish; Hunte, Frank

    2015-05-21

    We report on the epitaxial growth and magnetic properties of Cr{sub 2}O{sub 3} thin films grown on r-sapphire substrate using pulsed laser deposition. The X-ray diffraction (XRD) (2θ and Φ) and TEM characterization confirm that the films are grown epitaxially. The r-plane (011{sup ¯}2) of Cr{sub 2}O{sub 3} grows on r-plane of sapphire. The epitaxial relations can be written as [011{sup ¯}2] Cr{sub 2}O{sub 3} ‖ [011{sup ¯}2] Al{sub 2}O{sub 3} (out-of-plane) and [1{sup ¯}1{sup ¯}20] Cr{sub 2}O{sub 3} ‖ [1{sup ¯}1{sup ¯}20] Al{sub 2}O{sub 3} (in-plane). The as-deposited films showed ferromagnetic behavior up to 400 K but ferromagnetism almost vanishes with oxygen annealing. The Raman spectroscopy data together with strain measurements using high resolution XRD indicate that ferromagnetism in r-Cr{sub 2}O{sub 3} thin films is due to the strain caused by defects, such as oxygen vacancies.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  8. Optical band gap of NpO2 and PuO2 from optical absorbance of epitaxial films

    NASA Astrophysics Data System (ADS)

    Mark McCleskey, T.; Bauer, Eve; Jia, Quanxi; Burrell, Anthony K.; Scott, Brian L.; Conradson, Steven D.; Mueller, Alex; Roy, Lindsay; Wen, Xiaodong; Scuseria, Gustavo E.; Martin, Richard L.

    2013-01-01

    We report a solution based synthesis of epitaxial thin films of neptunium oxide and plutonium oxide. Actinides represent a challenge to first principle calculations due to features that arise from f orbital interactions. Conventional semi-local density functional theory predicts NpO2 and PuO2 to be metallic, when they are well known insulators. Improvements in theory are dependent on comparison with accurate measurements of material properties, which in turn demand high-quality samples. The high melting point of actinide oxides and their inherent radioactivity makes single crystal and epitaxial film formation challenging. We report on the preparation of high quality epitaxial actinide films. The films have been characterized through a combination of X-ray diffraction and X-ray absorption fine structure (XANES and EXAFS) measurements. We report band gaps of 2.80 ± 0.1 eV and 2.85 ± 0.1 eV at room temperature for PuO2 and NpO2, respectively, and compare our measurements with state-of-the-art calculations.

  9. High in-plane anisotropy of epitaxial CoPt(110) alloy films prepared by cosputtering or molecular beam epitaxy on MgO

    SciTech Connect

    Abes, M.; Ersen, O.; Meny, C.; Schmerber, G.; Acosta, M.; Arabski, J.; Ulhaq-Bouillet, C.; Dinia, A.; Panissod, P.; Pierron-Bohnes, V.

    2007-03-15

    We present structural and magnetic properties of three sets of structures: as-deposited CoPt films cosputtered at 900 K on MgO(110) substrates with a Pt(110) buffer layer and CoPt films deposited by molecular beam epitaxy directly on MgO(110) substrates at 900 K, as prepared and annealed at 900 K. All layers have the L1{sub 0} tetragonal structure. The chemical long-range ordering for the as-deposited CoPt films is incomplete in contrast with the annealed CoPt films, where long-range order is the highest. The structural study of these CoPt films grown on MgO(110) has pointed out that three variants of the L1{sub 0} phase coexist. The proportion of x and y variants, with the concentration modulation along a vector oriented at 45 degree sign with respect to the growth direction, is higher than the proportion of the z variant with the concentration modulation within the plane. The magnetic study shows an in-plane easy magnetization axis with a large magnetic anisotropy. This is interesting for the magnetic recording media with classical longitudinal writing and reading heads. The simulation of the magnetization loops confirms that the easy magnetization axis is within the plane and along the [110] direction, favored by the dominant x and y variants.

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

    SciTech Connect

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

    2015-07-20

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

  11. Resistivity Effects of Cation Ordering in Highly-Doped La2-xSrxCu4 Epitaxial Thin Films

    NASA Astrophysics Data System (ADS)

    Burquest, Franklin; Marmol, Rodrigo; Cox, Nicholas; Nelson-Cheeseman, Brittany

    Highly-doped La2-xSrxCuO4 (LSCO) films (0.5 <= x <= 1.0) are promising for many applications due to their electronic, ionic, and phonon transport. In this study, we investigate the effect of ``electrostatic strain'' on the electrical transport of LSCO thin films with large doping (x =0.5, 0.75, and 1.0). This ``electrostatic strain'' is applied by ordering differently charged A-site cations (La3+ vs. Sr2+) into charged A-O layers within the crystal structure. This causes internal polar electrostatic forces, which have been shown to cause stretching of the apical oxygen bond in analogous epitaxial nickelate films. Thin film samples are grown concurrently to minimize extraneous effects on film structure and properties. Atomic force microscopy and x-ray reflectivity demonstrate that the films are single crystalline, epitaxial, and smooth. X-ray diffraction is used to measure the c-axis of the films as a function of doping and dopant cation ordering. Electrical transport data of the ordered samples is compared with transport data of conventional disordered cation samples. Preliminary data indicates significant differences in resistivity at both 300K and 10K between the cation-ordered and cation-disordered samples. This work indicates that dopant cation ordering within the layered cuprates could significantly modify the conduction mechanisms at play in these materials.

  12. The realization and performance of vibration energy harvesting MEMS devices based on an epitaxial piezoelectric thin film

    NASA Astrophysics Data System (ADS)

    Isarakorn, D.; Briand, D.; Janphuang, P.; Sambri, A.; Gariglio, S.; Triscone, J.-M.; Guy, F.; Reiner, J. W.; Ahn, C. H.; de Rooij, N. F.

    2011-02-01

    This paper focuses on the fabrication and evaluation of vibration energy harvesting devices by utilizing an epitaxial Pb(Zr0.2Ti0.8)O3 (PZT) thin film. The high quality of the c-axis oriented PZT layer results in a high piezoelectric coefficient and a low dielectric constant, which are key parameters for realizing high performance piezoelectric energy harvesters. Different cantilever structures, with and without a Si proof mass, are realized using micro-patterning techniques optimized for the epitaxial oxide layers, to maintain the piezoelectric properties throughout the process. The characteristics and the energy harvesting performances of the fabricated devices are experimentally investigated and compared against analytical calculations. The optimized device based on a 0.5 µm thick epitaxial PZT film, a cantilever beam of 1 mm × 2.5 mm × 0.015 mm, with a Si proof mass of 1 mm × 0.5 mm × 0.23 mm, generates an output power, current and voltage of, respectively, 13 µW g - 2, 48 µA g - 1 and 0.27 V g - 1 (g = 9.81 m s - 2) at the resonant frequency of 2.3 kHz for an optimal resistive load of 5.6 kΩ. The epitaxial PZT harvester exhibits higher power and current with usable voltage, while maintaining lower optimal resistive load as compared with other examples present in the literature. These results indicate the potential of epitaxial PZT thin films for the improvement of the performances of energy harvesting devices.

  13. Microstructure of Co/X (X=Cu,Ag,Au) epitaxial thin films grown on Al{sub 2}O{sub 3}(0001) substrates

    SciTech Connect

    Ohtake, Mitsuru; Akita, Yuta; Futamoto, Masaaki; Kirino, Fumiyoshi

    2007-05-01

    Epitaxial thin films of Co/X (X=Cu,Ag,Au) were prepared on Al{sub 2}O{sub 3}(0001) substrates at substrate temperatures of 100 and 300 degree sign C by UHV molecular beam epitaxy. A complicated microstructure was realized for the epitaxial thin films. In-situ reflection high-energy electron diffraction observation has shown that X atoms of the buffer layer segregated to the surface during Co layer deposition, and it yielded a unique epitaxial granular structure. The structure consists of small Co grains buried in the X buffer layer, where both the magnetic small Co grains and the nonmagnetic X layer are epitaxially grown on the single crystal substrate. The structure varied depending on the X element and the substrate temperature. The crystal structure of Co grains is influenced by the buffer layer material and determined to be hcp and fcc structures for the buffer layer materials of Au and Cu, respectively.

  14. Growth and magnetic property of antiperovskite manganese nitride films doped with Cu by molecular beam epitaxy

    SciTech Connect

    Yu, Fengmei; Ren, Lizhu; Meng, Meng; Wang, Yunjia; Yang, Mei; Wu, Shuxiang; Li, Shuwei

    2014-04-07

    Manganese nitrides thin films on MgO (100) substrates with and without Cu-doping have been fabricated by plasma assisted molecular beam epitaxy. Antiperovskite compounds Mn{sub 3.6}Cu{sub 0.4}N have been grown in the case of Cu-doping, and the pure Mn{sub 3}N{sub 2} single crystal has been obtained without Cu-doping. The Mn{sub 3.6}Cu{sub 0.4}N exhibits ferrimagnetism, and the magnetization of Mn{sub 3.6}Cu{sub 0.4}N increases upon the temperature decreasing from 300 K to 5 K, similar to Mn{sub 4}N. The exchange bias (EB) effects emerge in the Mn{sub 3.6}Cu{sub 0.4}N films. The EB behavior is originated from the interfaces between ferrimagnetic Mn{sub 3.6}Cu{sub 0.4}N and antiferromagnetic metal Mn, which is verified to be formed by the data of x-ray photoelectron spectroscopy. The present results not only provide a strategy for producing functional antiperovskite manganese nitrides, but also shed promising light on fabricating the exchange bias part of spintronic devices.

  15. Electrical properties of undoped GaN films grown by maskless epitaxial lateral overgrowth

    NASA Astrophysics Data System (ADS)

    Polyakov, A. Y.; Jeon, Dae-Woo; Lee, In-Hwan; Smirnov, N. B.; Govorkov, A. V.; Kozhukhova, E. A.; Yakimov, E. B.

    2013-02-01

    Electrical properties, deep traps spectra, microcathodoluminescence (MCL) spectra measurements, MCL imaging, and electron beam induced current (EBIC) imaging were performed for undoped GaN films grown by metalorganic chemical vapor deposition using maskless epitaxial lateral overgrowth on basal plane sapphire. The films showed a low dislocation density of ˜108 cm-2 in the laterally overgrown wings and an order of magnitude higher dislocation density in vertical growth seed regions, as determined by MCL and EBIC imaging. The polarity of EBIC signal measurements and the room temperature capacitance-voltage characteristics suggested that the high-dislocation-density seed regions were high-resistivity p-type, with the Fermi level pinned near Ev + 0.4 eV, as determined by admittance spectroscopy. The wing regions were n-type, with low residual donor concentration of some 1014 cm-3 near the surface. The donor concentration further decreased upon movement towards the sapphire substrate. Some possible explanations of the observed effects are discussed.

  16. Significant enhancement of the strength-to-resistivity ratio by using nanotwins in epitaxial Cu films

    SciTech Connect

    Misra, Amit; Ronningh, Filip; Anderoglu, Osman; Zhang, X

    2008-01-01

    Epitaxial nanotwinned Cu films, with an average twin spacing ranging from 7 to 16 nm, exhibit a high ratio of strength-to-electrical resisitivity, -400 MPa({mu}{Omega}cm){sup -1}. The hardness of these Cu films approaches 2.8 GPa, and their electrical resistivities are comparable to that of oxygen-free high-conductivity Cu. Compared to high-angle grain boundaries, coherent twin interfaces possess inherently high resistance to the transmission of single dislocations, and yet an order of magnitude lower electron scattering coefficient, determined to be 1.5-5 x 10{sup -7} {mu}{Omega}cm{sup 2} at room temperature. Analytical studies as well as experimental results show that, in polycrystalline Cu, grain refinement leads to a maximum of the strength-to-resistivity ratio, -250 MPa({mu}{Omega}cm){sup -1}, when grain size is comparable to the mean-free path of electrons. However, in twinned Cu, such a ratio increases continuously with decreasing twin spacing down to a few nanometers. Hence nanoscale growth twins are more effective to achieve a higher strength-to-resistivity ratio than high-angle grain boundaries.

  17. Direct observation of epitaxial organic film growth: temperature-dependent growth mechanisms and metastability.

    PubMed

    Marchetto, Helder; Schmidt, Thomas; Groh, Ullrich; Maier, Florian C; Lévesque, Pierre L; Fink, Rainer H; Freund, Hans-Joachim; Umbach, Eberhard

    2015-11-21

    The growth of the first ten layers of organic thin films on a smooth metallic substrate has been investigated in real-time using the model system PTCDA on Ag(111). The complex behaviour is comprehensively studied by electron microscopy, spectroscopy and diffraction in a combined PEEM/LEEM instrument revealing several new phenomena and yielding a consistent picture of this layer growth. PTCDA grows above room temperature in a Stranski-Krastanov mode, forming three-dimensional islands on a stable bi-layer, in competition with metastable 3rd and 4th layers. Around room temperature this growth mode changes into a quasi layer-by-layer growth, while at temperatures below about 250 K a Vollmer-Weber-like behaviour is observed. By means of laterally resolved soft X-ray absorption spectroscopy the orientation of all adsorbed molecules is found to be homogeneously flat lying on the surface, even during the growth process. The films grow epitaxially, showing long-range order with rotational domains. For the monolayer these domains could be directly analysed, showing an average size of several micrometers extending over substrate steps.

  18. Irreversible properties of YBCO thick films deposited by liquid phase epitaxy on single crystalline substrates

    NASA Astrophysics Data System (ADS)

    Vostner, A.; Tönies, S.; Weber, H. W.; Cheng, Y. S.; Kurumovic, A.; Evetts, J. E.; Mennema, S. H.; Zandbergen, H. W.

    2003-10-01

    We report on the field and temperature dependence of the critical transport current density Jc, the angular dependence of the transport current at various external magnetic fields and the irreversibility fields in YBa2Cu3O7-delta (Y-123) thick films prepared by liquid phase epitaxy (LPE). A comparison of the irreversible properties between specimens produced with and without silver additions to the melt is also presented. Transmission electron microscopy (TEM) was employed to obtain information on the correlation between the transport properties and the microstructure. The samples were deposited either directly on NdGaO3 (NGO) or on seeded (100) MgO substrates, where a 200 nm thin YBCO film deposited by pulsed laser deposition (PLD) acts as seed layer for the LPE process. The final thickness of the Y-123 layer is of the order of 1 µm for the NGO and between 2 and 10 µm for the MgO samples. The critical current densities reach 3 × 109 A m-2 at zero field and 77 K in the best case.

  19. Low-loss substrate for epitaxial growth of high-temperature superconductor thin films

    SciTech Connect

    Simon, R.W.; Platt, C.E.; Lee, A.E.; Lee, G.S.; Daly, K.P.; Wire, M.S.; Luine, J.A.; Urbanik, M.

    1988-12-26

    A perovskite-like single-crystal substrate material has been investigated that simultaneously permits epitaxial growth of 1-2-3 superconductor films and possesses desirable rf properties of low dielectric constant and loss tangent. The lattice constant of 3.792 A provides a lattice match to within 1% of the a axis of 1-2-3. Sputtered films of erbium-barium-copper-oxide have been produced on (100) LaAlO/sub 3/ substrates that exhibit sharp resistive transitions at 90 K (..delta..T = 1K), bulk superconductivity as determined by ac susceptibility measurements, and nearly single-crystal growth as evidenced by x-ray diffraction and high-resolution scanning electron microscopy. The high-frequency dielectric properties of LaAlO/sub 3/ were experimentally investigated at several temperatures. The low-frequency dielectric constant was measured to be 15 and the microwave loss tangent ranged from 6 x 10/sup -4/ at room temperature to 5 x 10/sup -6/ at 4 K.

  20. Direct observation of epitaxial organic film growth: temperature-dependent growth mechanisms and metastability.

    PubMed

    Marchetto, Helder; Schmidt, Thomas; Groh, Ullrich; Maier, Florian C; Lévesque, Pierre L; Fink, Rainer H; Freund, Hans-Joachim; Umbach, Eberhard

    2015-11-21

    The growth of the first ten layers of organic thin films on a smooth metallic substrate has been investigated in real-time using the model system PTCDA on Ag(111). The complex behaviour is comprehensively studied by electron microscopy, spectroscopy and diffraction in a combined PEEM/LEEM instrument revealing several new phenomena and yielding a consistent picture of this layer growth. PTCDA grows above room temperature in a Stranski-Krastanov mode, forming three-dimensional islands on a stable bi-layer, in competition with metastable 3rd and 4th layers. Around room temperature this growth mode changes into a quasi layer-by-layer growth, while at temperatures below about 250 K a Vollmer-Weber-like behaviour is observed. By means of laterally resolved soft X-ray absorption spectroscopy the orientation of all adsorbed molecules is found to be homogeneously flat lying on the surface, even during the growth process. The films grow epitaxially, showing long-range order with rotational domains. For the monolayer these domains could be directly analysed, showing an average size of several micrometers extending over substrate steps. PMID:26462749

  1. Molecular beam epitaxy growth and magnetic properties of Cr-Co-Ga Heusler alloy films

    SciTech Connect

    Feng, Wuwei Wang, Weihua; Zhao, Chenglong; Van Quang, Nguyen; Cho, Sunglae; Dung, Dang Duc

    2015-11-15

    We have re-investigated growth and magnetic properties of Cr{sub 2}CoGa films using molecular beam epitaxy technique. Phase separation and precipitate formation were observed experimentally again in agreement with observation of multiple phases separation in sputtered Cr{sub 2}CoGa films by M. Meinert et al. However, significant phase separation could be suppressed by proper control of growth conditions. We showed that Cr{sub 2}CoGa Heusler phase, rather than Co{sub 2}CrGa phase, constitutes the majority of the sample grown on GaAs(001) at 450 {sup o}C. The measured small spin moment of Cr{sub 2}CoGa is in agreement with predicted HM-FCF nature; however, its Curie temperature is not as high as expected from the theoretical prediction probably due to the off-stoichiometry of Cr{sub 2}CoGa and the existence of the disorders and phase separation.

  2. Current-phase relationship of granular NbN weak links, inferred from Josephson interferometer characteristics

    SciTech Connect

    Claassen, J.H.

    1982-05-01

    Small-area dc superconducting quantum interference devices (SQUID's) were made using ultra-short variable-thickness microbridges of NbN. The bridges had an effective length of approx.500 A and a width of approx.1.5 ..mu..m. Analysis of the response to magnetic flux permits interferences to be drawn about the current-phase relationship (CPR) of the bridges. Contrary to predictions of Ginzburg--Landau theory for microbridges of these dimensions, it is found that the CPR is single valued and probably close to ideal (sinusoidal) over a large temperature range (>2.5 K). The discrepancy with theory may be due to the granular nature of the NbN films.

  3. The electronic structure of epitaxially strained iridate thin films and superlattices from first principles

    NASA Astrophysics Data System (ADS)

    Voss, Johannes; Fennie, Craig J.

    2012-02-01

    Within the Ruddlesden-Popper iridates Srn+1IrnO3n+1, strong spin-orbit interactions lead to the formation of a half-filled, narrow Jeff=1/2 band and filled Jeff=3/2 bands. This places the iridates in the vicinity of a Mott transition, which is sensitive to perturbations in crystal structure, despite relatively weak on-site Coulomb interactions [1]. For example, Sr2IrO4 (n=1) is an antiferromagnetic Mott insulator that displays an almost rigid coupling between spin canting and IrO6 octahedron rotations [2], while epitaxially stabilized SrIrO3 (n=∞) is a correlated metal. In this talk, we will discuss from first-principles within the LDA+SO+U approach the possibility to engineer the electronic structure of SrIrO3 and CaIrO3 thin films using epitaxial strain and by creating superlattices of the form (AIrO3)m(A'BO3)m' with A, A' = Ca, Sr. [1] S.J. Moon, H. Jin, K.W. Kim, W.S. Choi, Y.S. Lee, J. Yu, G. Cao, A. Sumi, H. Funakubo, C. Bernhard, and T.W. Noh, PRL 101, 226402 (2008). [2] B.J. Kim, H. Jin, S.J. Moon, J.-Y. Kim, B.-G. Park, C.S. Leem, J. Yu, T.W. Noh, C. Kim, S.-J. Oh, J.-H. Park, V. Durairaj, G. Cao, and E. Rotenberg, PRL 101, 076402 (2008).

  4. Growth temperature dependent structural and magnetic properties of epitaxial Co{sub 2}FeAl Heusler alloy films

    SciTech Connect

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

    2013-06-21

    The structural and magnetic properties of a series of Co{sub 2}FeAl Heusler alloy films grown on GaAs(001) substrate by molecular beam epitaxy have been studied. The epitaxial Co{sub 2}FeAl films with an ordered L{sub 21} structure have been successfully obtained at growth temperature of 433 K, with an in-plane cubic magnetic anisotropy superimposed with an unusual uniaxial magnetic anisotropy. With increasing growth temperature, the ordered L{sub 21} structure degrades. Meanwhile, the uniaxial anisotropy decreases and eventually disappears above 673 K. The interfacial bonding between As and Co or Fe atom is suggested to be responsible for the additional uniaxial anisotropy.

  5. Role of microstructures on the M1-M2 phase transition in epitaxial VO2 thin films

    PubMed Central

    Ji, Yanda; Zhang, Yin; Gao, Min; Yuan, Zhen; Xia, Yudong; Jin, Changqing; Tao, Bowan; Chen, Chonglin; Jia, Quanxi; Lin, Yuan

    2014-01-01

    Vanadium dioxide (VO2) with its unique sharp resistivity change at the metal-insulator transition (MIT) has been extensively considered for the near-future terahertz/infrared devices and energy harvesting systems. Controlling the epitaxial quality and microstructures of vanadium dioxide thin films and understanding the metal-insulator transition behaviors are therefore critical to novel device development. The metal-insulator transition behaviors of the epitaxial vanadium dioxide thin films deposited on Al2O3 (0001) substrates were systematically studied by characterizing the temperature dependency of both Raman spectrum and Fourier transform infrared spectroscopy. Our findings on the correlation between the nucleation dynamics of intermediate monoclinic (M2) phase with microstructures will open a new avenue for the design and integration of advanced heterostructures with controllable multifunctionalities for sensing and imaging system applications. PMID:24798056

  6. Origin of the butterfly-shaped magnetoresistance in reactive sputtered epitaxial Fe{sub 3}O{sub 4} films

    SciTech Connect

    Li, P.; Zhang, L. T.; Mi, W. B.; Jiang, E. Y.; Bai, H. L.

    2009-08-01

    Epitaxial Fe{sub 3}O{sub 4} thin films were synthesized by facing-target reactive sputtering Fe targets. The epitaxy of the Fe{sub 3}O{sub 4} film on MgO (100) was examined macroscopically using x-ray diffraction, including conventional theta-2theta scan, tilting 2theta scan, phi scan, and pole figure. The observed low-field butterfly-shaped magnetoresistance (MR) are explained by the primary fast rotation of the spins far away from antiphase boundaries and the high-field MR changing linearly with magnetic field can be understood by the gradual rotation of the spins near the antiphase boundaries. It is magnetocrystalline anisotropy that causes an increase in MR below Verwey transition temperature.

  7. High quality CuInSe2 films grown on pseudo-lattice-matched substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Niki, S.; Fons, P. J.; Yamada, A.; Kurafuji, T.; Chichibu, S.; Nakanishi, H.; Bi, W. G.; Tu, C. W.

    1996-07-01

    CuInSe2 films have been grown by molecular beam epitaxy on pseudo-lattice-matched substrates that consist of a 1-μm-thick In0.29Ga0.71As layer grown on a linearly composition-graded InxGa1-xAs buffer (0≤x≤0.29) grown in turn on GaAs (001). The properties of these films have been compared with those of the films grown directly on GaAs (001). High resolution x-ray diffraction analysis on CuInSe2 grown on pseudo-lattice-matched substrates indicated substantial reduction on residual strain in the CuInSe2 films. A photoluminescence spectrum dominated by sharp free exciton emissions has been observed for the first time from CuInSe2 films indicative of significant improvement in crystalline quality and substantial reduction in the point defect density.

  8. Single-crystalline BaTiO3 films grown by gas-source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Matsubara, Yuya; Takahashi, Kei S.; Tokura, Yoshinori; Kawasaki, Masashi

    2014-12-01

    Thin BaTiO3 films were grown on GdScO3 (110) substrates by metalorganic gas-source molecular beam epitaxy. Titanium tetra-isopropoxide (TTIP) was used as a volatile precursor that provides a wide growth window of the supplied TTIP/Ba ratio for automatic adjustment of the film composition. Within the growth window, compressively strained films can be grown with excellent crystalline quality, whereas films grown outside of the growth window are relaxed with inferior crystallinity. This growth method will provide a way to study the intrinsic properties of ferroelectric BaTiO3 films and their heterostructures by precise control of the stoichiometry, structure, and purity.

  9. Negligible substrate clamping effect on piezoelectric response in (111)-epitaxial tetragonal Pb(Zr, Ti)O{sub 3} films

    SciTech Connect

    Yamada, Tomoaki; Yasumoto, Jun; Ito, Daisuke; Yoshino, Masahito; Nagasaki, Takanori; Sakata, Osami; Imai, Yasuhiko; Kiguchi, Takanori; Shiraishi, Takahisa; Shimizu, Takao; Funakubo, Hiroshi

    2015-08-21

    The converse piezoelectric responses of (111)- and (001)-epitaxial tetragonal Pb(Zr{sub 0.35}Ti{sub 0.65})O{sub 3} [PZT] films were compared to investigate the orientation dependence of the substrate clamping effect. Synchrotron X-ray diffraction (XRD) and piezoelectric force microscopy revealed that the as-grown (111)-PZT film has a polydomain structure with normal twin boundaries that are changed by the poling process to inclined boundaries, as predicted by Romanov et al. [Phys. Status Solidi A 172, 225 (1999)]. Time-resolved synchrotron XRD under bias voltage showed the negligible impact of substrate clamping on the piezoelectric response in the (111)-PZT film, unlike the case for (001)-PZT film. The origin of the negligible clamping effect in the (111)-PZT film is discussed from the viewpoint of the elastic properties and the compensation of lattice distortion between neighboring domains.

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

    SciTech Connect

    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 variable 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.

  11. Reduced leakage in epitaxial BiFeO{sub 3} films following oxygen radio frequency plasma treatment

    SciTech Connect

    Kothari, Deepti; Upadhyay, Sanjay K.; Raghavendra Reddy, V.; Jariwala, C.; Raole, P. M.

    2013-06-07

    Epitaxial BiFeO{sub 3} (BFO) films were deposited using pulsed laser deposition method. The prepared films were characterized using x-ray diffraction, x-ray reflectivity, ferroelectric loop tracer, and leakage current measurements before and after oxygen plasma treatment. The leakage current of the films, a crucial parameter in device applications, is observed to be reduced by two orders of magnitude with oxygen plasma treatment at room temperature. P-E hysteresis loops were observed in oxygen plasma treated BFO films. The observed results indicate the usefulness of oxygen radio frequency plasma treatment (RF 13.56 MHz), which is an effective and low temperature processing technique, in such lossy ferroelectric thin films.

  12. Negligible substrate clamping effect on piezoelectric response in (111)-epitaxial tetragonal Pb(Zr, Ti)O3 films

    NASA Astrophysics Data System (ADS)

    Yamada, Tomoaki; Yasumoto, Jun; Ito, Daisuke; Sakata, Osami; Imai, Yasuhiko; Kiguchi, Takanori; Shiraishi, Takahisa; Shimizu, Takao; Funakubo, Hiroshi; Yoshino, Masahito; Nagasaki, Takanori

    2015-08-01

    The converse piezoelectric responses of (111)- and (001)-epitaxial tetragonal Pb(Zr0.35Ti0.65)O3 [PZT] films were compared to investigate the orientation dependence of the substrate clamping effect. Synchrotron X-ray diffraction (XRD) and piezoelectric force microscopy revealed that the as-grown (111)-PZT film has a polydomain structure with normal twin boundaries that are changed by the poling process to inclined boundaries, as predicted by Romanov et al. [Phys. Status Solidi A 172, 225 (1999)]. Time-resolved synchrotron XRD under bias voltage showed the negligible impact of substrate clamping on the piezoelectric response in the (111)-PZT film, unlike the case for (001)-PZT film. The origin of the negligible clamping effect in the (111)-PZT film is discussed from the viewpoint of the elastic properties and the compensation of lattice distortion between neighboring domains.

  13. Growth, Crystal Structure, and Properties of Epitaxial BiScO3 Thin Films By Pulsed Laser Deposition

    SciTech Connect

    Trolier-McKinstry, Susan; Biegalski, Michael D; Wang, Junling; Belik, Alexei; Levin, Igor

    2008-01-01

    Epitaxial BiScO3 thin films were grown on BiFeO3 buffered SrTiO3 substrates. The crystallinity of the films is reasonable, given the very large lattice mismatch, with full width at half maximum of 0.58 in  peak), 0.80 in  (222 peak) and 0.28 in . It was found that the epitaxial thin films of BiScO3 on SrTiO3 retain the principal structural features of bulk BiScO3 (i.e. octahedral tilting and the pattern of Bi displacements) that give rise to a pseudo-orthorhombic unit cell 22ac 2ac 4ac (ac≈4 refers to the lattice parameter of an ideal cubic perovskite). Films grown on (100) substrates adopt the bulk monoclinic structure whereas films on the (110) substrates exhibit a somewhat different symmetry. The dielectric permittivities were modest (~35) with low loss tangents; no maxima were observed over the temperature range of -200 and +350 C. There is no evidence of significant hysteresis (either ferroelectric or antiferroelectric) at room temperature up to the breakdown strength of the films.

  14. Self-regulated growth of LaVO{sub 3} thin films by hybrid molecular beam epitaxy

    SciTech Connect

    Zhang, Hai-Tian; Engel-Herbert, Roman; Dedon, Liv R.; Martin, Lane W.

    2015-06-08

    LaVO{sub 3} thin films were grown on SrTiO{sub 3} (001) by hybrid molecular beam epitaxy. A volatile metalorganic precursor, vanadium oxytriisopropoxide (VTIP), and elemental La were co-supplied in the presence of a molecular oxygen flux. By keeping the La flux fixed and varying the VTIP flux, stoichiometric LaVO{sub 3} films were obtained for a range of cation flux ratios, indicating the presence of a self-regulated growth window. Films grown under stoichiometric conditions were found to have the largest lattice parameter, which decreased monotonically with increasing amounts of excess La or V. Energy dispersive X-ray spectroscopy and Rutherford backscattering measurements were carried out to confirm film compositions. Stoichiometric growth of complex vanadate thin films independent of cation flux ratios expands upon the previously reported self-regulated growth of perovskite titanates using hybrid molecular beam epitaxy, thus demonstrating the general applicability of this growth approach to other complex oxide materials, where a precise control over film stoichiometry is demanded by the application.

  15. Epitaxial strain induced phase transitions in La-doped BiFeO3 thin films on Si substrates

    NASA Astrophysics Data System (ADS)

    Chen, Deyang; Nelson, Christopher T.; Zhu, Xiaohong; Serrao, Claudy R.; Gao, Ya; Yi, Di; Liu, Jian; Ramesh, Ramamoorthy; Zeng, Dechang; Schlom, Darrel G.; South China University Of Technology Collaboration; Cornell University Collaboration; Concept Team

    2014-03-01

    Epitaxial strain is a powerful pathway to trigger phase transitions with emergent phenomena in oxide thin films, e.g., strain induced ferroelectric to ferroelectric (PE-PE) phase transition from tetragonal-like to rhombohedral-like phase in Pb(ZrxTi1-x) O3 and BiFeO3 films. In this study, we report a strain driven antiferroelectric to ferroelectric (AFE-FE) phase transition from orthorhombic (O) to rhombohedral (R) phase in LaxBi1-xFeO3 (LBFO) thin film on Si substrates. The ground state of LaxBi1-xFeO3 bulk is antiferroelectric PbZrO3 type orthorhombic phase. We show that epitaxial strain from Si substrates can stabilize a rhombohedral structure of LBFO in 20 nm films and intermediate strains position LBFO into a nanoscale mixture of rhombohedral and orthorhombic phases in 30-100 nm films and then strain relaxation in 125nm films leads to the orthorhombic phase. Transmission electron microscopy (TEM) shows atomically sharp O/R morphotropic phase boundary (MPB) with O phase domains larger than 10 nm in width. In summary, our findings open a new path to drive AFE-FE phase transition in LBFO and provide a route to study O/R MPB.

  16. Direct band-gap measurement on epitaxial Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} Heusler-alloy films

    SciTech Connect

    Alhuwaymel, Tariq F.; Carpenter, Robert; Yu, Chris Nga Tung; Kuerbanjiang, Balati; Lazarov, Vlado K.; Abdullah, Ranjdar M.; El-Gomati, Mohamed; Hirohata, Atsufumi

    2015-05-07

    In this study, a newly developed band-gap measurement technique has been used to characterise epitaxial Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} (CFAS) films. The CFAS films were deposited on MgO(001) substrate by ultra high vacuum molecular beam epitaxy. The band-gap for the as deposited films was found to be ∼110 meV when measured at room temperature. This simple technique provides a macroscopic analysis of the half-metallic properties of a thin film. This allows for simple optimisation of growth and annealing conditions.

  17. The non-epitaxial growth of c-axis YBa 2Cu 3O x films on high-index planes of silver

    NASA Astrophysics Data System (ADS)

    Huang, D. X.; Yamada, Y.; Hirabayashi, I.

    2000-11-01

    YBa 2Cu 3O x (YBCO) thin films were deposited by the pulsed-laser ablation on polycrystalline Ag substrates. The c-axis-oriented YBCO films on various high-index silver crystal planes have been observed using cross-sectional transmission electron microscopy (TEM). The obtained results show that, differing from the epitaxial growth of the YBCO films on low-index planes, the YBCO films grown on high-index planes have not a good epitaxial relationship. The c-axes of the YBCO grains keep to vertical to the substrate surface plane but the a- and b- axes of the grains are randomly oriented.

  18. Interplay of the strain and microstructure in ferroelectric epitaxial CaTiO3 Films

    NASA Astrophysics Data System (ADS)

    He, Qian; Liang, Qiao; Biegalski, Michael; Borisevich, Albina

    2014-03-01

    CaTiO3 (CTO) was predicted to become ferroelectric under lattice strain. However, other factors such as oxygen octahedral tilts or microstructural details can play a role. In this work, two 20 nm CTO films were grown on LSAT and NGO by PLD. They both show ferroelectricity, with Tc near 140 K on LSAT and near 70 K on NGO, and the remnant polarization at 10K of 5 and 2 μC/cm, respectively. This is surprising given that the strain of CTO on both substrates is similar. AC-STEM shows two major differences in microstructure between two CTO films: Firstly, the first few nm of CTO on NGO show perfect epitaxial growth, and after that grains start to develop, but the c-axis of CTO remains aligned with the c-axis of NGO, suggesting the presence of 180° grain boundaries only. However for CTO/LSAT, grains begin to develop at the interface and their c-axes have two possible orientations, resulting in both 180° and 90° grain boundaries. These grain boundaries are either dislocations or ferroelastic twins. Secondly, the octahedral tilt behavior at the film/substrate interface is different: CTO/LSAT has a 5-6 unit cell transition region from the untilted LSAT to the tilted CTO, which is not the case in CTO/NGO. The connection between the microstructure, substrate strain and connections to the ferroelectric properties will be discussed in detail. Research at ORNL supported by the MSE Division, BES, U.S. DOE, and through a user project supported by ORNL's CNMS, which is also sponsored by BES, U.S. DOE.

  19. Stranski-Krastanow islanding initiated on the stochastic rough surfaces of the epitaxially strained thin films

    SciTech Connect

    Tarik Ogurtani, Omer; Celik, Aytac; Emre Oren, Ersin

    2014-06-14

    Quantum dots (QD) have discrete energy spectrum, which can be adjusted over a wide range by tuning composition, density, size, lattice strain, and morphology. These features make quantum dots attractive for the design and fabrication of novel electronic, magnetic and photonic devices and other functional materials used in cutting-edge applications. The formation of QD on epitaxially strained thin film surfaces, known as Stranski-Krastanow (SK) islands, has attracted great attention due to their unique electronic properties. Here, we present a systematic dynamical simulation study for the spontaneous evolution of the SK islands on the stochastically rough surfaces (nucleationless growth). During the development of SK islands through the mass accumulation at randomly selected regions of the film via surface drift-diffusion (induced by the capillary and mismatch stresses) with and/or without growth, one also observes the formation of an extremely thin wetting layer having a thickness of a few Angstroms. Above a certain threshold level of the mismatch strain and/or the size of the patch, the formation of multiple islands separated by shallow wetting layers is also observed as metastable states such as doublets even multiplets. These islands are converted into a distinct SK islands after long annealing times by coalescence through the long range surface diffusion. Extensive computer simulation studies demonstrated that after an initial transient regime, there is a strong quadratic relationship between the height of the SK singlet and the intensity of the lattice mismatch strain (in a wide range of stresses up to 8.5 GPa for germanium thin crystalline films), with the exception at those critical points where the morphological (shape change with necking) transition takes place.

  20. Epitaxial Growth of GaN Nanowires with High Structural Perfection on a Metallic TiN Film.

    PubMed

    Wölz, M; Hauswald, C; Flissikowski, T; Gotschke, T; Fernández-Garrido, S; Brandt, O; Grahn, H T; Geelhaar, L; Riechert, H

    2015-06-10

    Vertical GaN nanowires are grown in a self-induced way on a sputtered Ti film by plasma-assisted molecular beam epitaxy. Both in situ electron diffraction and ex situ ellipsometry show that Ti is converted to TiN upon exposure of the surface to the N plasma. In addition, the ellipsometric data demonstrate this TiN film to be metallic. The diffraction data evidence that the GaN nanowires have a strict epitaxial relationship to this film. Photoluminescence spectroscopy of the GaN nanowires shows excitonic transitions virtually identical in spectral position, line width, and decay time to those of state-of-the-art GaN nanowires grown on Si. Therefore, the crystalline quality of the GaN nanowires grown on metallic TiN and on Si is equivalent. The freedom to employ metallic substrates for the epitaxial growth of semiconductor nanowires in high structural quality may enable novel applications that benefit from the associated high thermal and electrical conductivity as well as optical reflectivity.

  1. Microstructure and nonbasal-plane growth of epitaxial Ti2AlN thin films

    NASA Astrophysics Data System (ADS)

    Beckers, M.; Schell, N.; Martins, R. M. S.; Mücklich, A.; Möller, W.; Hultman, L.

    2006-02-01

    Thin films of the Mn+1AXn (MAX) phase (M: early transition metal; A:A-group element; X: C and/or N; n=1-3) Ti2AlN were epitaxially grown onto single-crystal MgO(111) and MgO(100) substrates by dc reactive magnetron cosputtering from Ti and Al targets in an Ar/N2 gas mixture at a temperature of 690 °C. To promote the nucleation of the MAX phase, a fcc (Ti0.63Al0.37)N seed layer was deposited before changing to Ti2AlN growth parameters. The nucleation processes have been studied by real-time in situ specular x-ray reflectivity. Independent of substrate orientation, the seed layer shows no roughening until its final thickness of approximately 100 A˚, indicating pseudomorphic layer-by-layer growth. The MAX phase shows heteroepitaxial layer-by-layer growth on MgO(111), with increased surface roughening up to approximately 200 A˚, whereas on MgO(100) the growth mode changes to Volmer-Weber-type already after three monolayers. X-ray scattering in Bragg-Brentano geometry of the final, approximately 1000 A˚ thick, Ti2AlN film reveals lattice parameters of c=13.463 A˚ and a=2.976 A˚ on the MgO(111) substrate and c=13.740 A˚ and a=2.224 A˚ on the MgO(100) substrate. From pole figure measurements the orientational relationship between film and substrate lattice was determined to be MgO{111}<110>//Ti2AlN{1012}<1210>, regardless of the substrate orientation. This tilted, nonbasal-plane growth leads to a threefold grain orientation of Ti2AlN along the MgO<110> directions and a polycrystalline morphology confirmed by cross-sectional transmission electron microscopy. The growth can be assumed to take place in a lateral step-flow mode, i.e., emerging low surface free-energy (0001) planes, on which arriving atoms can diffuse until finding a step where they are bound to A facets. This growth process is irrespective of orientational relationship between substrate and film. However, in the present low-temperature case the partitioning of arriving Al and Ti atoms during

  2. Growth and physical property of epitaxial Co{sub 70}Fe{sub 30} thin film on Si substrate via TiN buffer

    SciTech Connect

    Ji, C.-X.; Lu Feng; Chang, Y. Austin; Yang, J. Joshua; Rzchowski, M. S.

    2008-01-14

    Epitaxial Co{sub 70}Fe{sub 30} films with the bcc structure were grown on a Si(001) substrate with TiN as a buffer by sputtering technique. The x-ray diffraction results confirmed the epitaxial nature of the films and the crystallographic relationship was determined as Co{sub 70}Fe{sub 30}(002)<110>//TiN(002)<100>//Si(004)<100>. The surface morphology characterized by atomic force microscopy on our films revealed that smooth surfaces could be obtained at growth temperatures below 350 deg. C. The strain state of 60 nm epitaxial Co{sub 70}Fe{sub 30} films was studied as a function of growth temperature. Magnetization hysteresis loops of the films grown at 300 deg. C were measured using superconducting quantum interface device magnetometer.

  3. Epitaxial growth of group III-nitride films by pulsed laser deposition and their use in the development of LED devices

    NASA Astrophysics Data System (ADS)

    Li, Guoqiang; Wang, Wenliang; Yang, Weijia; Wang, Haiyan

    2015-11-01

    Recently, pulsed laser deposition (PLD) technology makes viable the epitaxial growth of group III-nitrides on thermally active substrates at low temperature. The precursors generated from the pulsed laser ablating the target has enough kinetic energy when arriving at substrates, thereby effectively suppressing the interfacial reactions between the epitaxial films and the substrates, and eventually makes the film growth at low temperature possible. So far, high-quality group III-nitride epitaxial films have been successfully grown on a variety of thermally active substrates by PLD. By combining PLD with other technologies such as laser rastering technique, molecular beam epitaxy (MBE), and metal-organic chemical vapor deposition (MOCVD), III-nitride-based light-emitting diode (LED) structures have been realized on different thermally active substrates, with high-performance LED devices being demonstrated. This review focuses on the epitaxial growth of group III-nitrides on thermally active substrates by PLD and their use in the development of LED devices. The surface morphology, interfacial property between film and substrate, and crystalline quality of as-grown group III-nitride films by PLD, are systematically reviewed. The corresponding solutions for film homogeneity on large size substrates, defect control, and InGaN films growth by PLD are also discussed in depth, together with introductions to some newly developed technologies for PLD in order to realize LED structures, which provides great opportunities for commercialization of LEDs on thermally active substrates.

  4. Electroreflectance study of the effect of {gamma} radiation on the optical properties of epitaxial GaN films

    SciTech Connect

    Belyaev, A. E.; Klyui, N. I. Konakova, R. V.; Lukyanov, A. N.; Danilchenko, B. A.; Sveshnikov, J. N.; Klyui, A. N.

    2012-03-15

    Experimental data on the electroreflectance spectra of {gamma}-irradiated epitaxial GaN films on sapphire are reported. The irradiation doses are 10{sup 5}-2 Multiplication-Sign 10{sup 6} rad. The theoretical electroreflectance spectra calculated on the basis of a model of three types of transitions are in agreement with experimental data with reasonable accuracy. The energies and broadenings of the transitions derived in the context of the model give grounds to infer that, in the GaN films, there are internal stresses dependent on the {gamma}-irradiation dose.

  5. Room temperature weak ferromagnetism in Sn1-xMnxSe2 2D films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Dong, Sining; Liu, Xinyu; Li, Xiang; Kanzyuba, Vasily; Yoo, Taehee; Rouvimov, Sergei; Vishwanath, Suresh; Xing, Huili G.; Jena, Debdeep; Dobrowolska, Margaret; Furdyna, Jacek K.

    2016-03-01

    We discuss growth and magnetic properties of high-quality two dimensional (2D) Sn1-xMnxSe2 films. Thin films of this 2D ternary alloy with a wide range of Mn concentrations were successfully grown by molecular beam epitaxy. Mn concentrations up to x ≈ 0.60 were achieved without destroying the crystal structure of the parent SnSe2 2D system. Most important, the specimens show clear weak ferromagnetic behavior above room temperature, which should be of interest for 2D spintronic applications.

  6. The thickness-dependent dynamic magnetic property of Co2FeAl films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    Co2FeAl films with different thickness were prepared at different temperature by molecular beam epitaxy. Their dynamic magnetic property was studied by the time-resolved magneto-optical Kerr effect measurements. It is observed that the intrinsic damping factor of Co2FeAl for [100] orientation is not related to the film's thickness and magnetic anisotropy as well as temperature at high-field regime, but increases with structural disorder of Co2FeAl. The dominant contribution from the inhomogeneous magnetic anisotropy is revealed to be responsible for the observed extremely nonlinear and drastic field-dependent damping factors at low-field regime.

  7. Microstructural, Magnetic Anisotropy, and Magnetic Domain Structure Correlations in Epitaxial FePd Thin Films with Perpendicular Magnetic Anisotropy

    NASA Technical Reports Server (NTRS)

    Skuza, J. R.; Clavero, C.; Yang, K.; Wincheski, B.; Lukaszew, R. A.

    2009-01-01

    L1(sub 0)-ordered FePd epitaxial thin films were prepared using dc magnetron sputter deposition on MgO (001) substrates. The films were grown with varying thickness and degree of chemical order to investigate the interplay between the microstructure, magnetic anisotropy, and magnetic domain structure. The experimentally measured domain size/period and magnetic anisotropy in this high perpendicular anisotropy system were found to be correlated following the analytical energy model proposed by Kooy and Enz that considers a delicate balance between the domain wall energy and the demagnetizing stray field energy.

  8. Band gap tuning of epitaxial SrTiO{sub 3-δ}/Si(001) thin films through strain engineering

    SciTech Connect

    Cottier, Ryan J.; Steinle, Nathan A.; Currie, Daniel A.; Theodoropoulou, Nikoleta

    2015-11-30

    We investigate the effect of strain and oxygen vacancies (V{sub O}) on the crystal and optical properties of oxygen deficient, ultra-thin (4–30 nm) films of SrTiO{sub 3-δ} (STO) grown heteroepitaxially on p-Si(001) substrates by molecular beam epitaxy. We demonstrate that STO band gap tuning can be achieved through strain engineering and show that the energy shift of the direct energy gap transition of SrTiO{sub 3-δ}/Si films has a quantifiable dimensional and doping dependence that correlates well with the changes in crystal structure.

  9. Oxygen vacancy induced photoluminescence and ferromagnetism in SrTiO{sub 3} thin films by molecular beam epitaxy

    SciTech Connect

    Xu, Wenfei; Yang, Jing; Bai, Wei; Tang, Kai; Zhang, Yuanyuan; Tang, Xiaodong

    2013-10-21

    SrTiO{sub 3} thin films were epitaxially grown on (100) SrTiO{sub 3} substrates using molecular beam epitaxy. The temperature for growth of the films was optimized, which was indicated by x-ray diffraction and further confirmed by microstructural characterization. Photoluminescence spectra show that oxygen-vacancy contributes to red and blue luminescence of oxygen-deficient post-annealed films, and a red shift was observed in blue region. On the other hand, ferromagnetism in film form SrTiO{sub 3} was observed from 5 K to 400 K and could be further enhanced with decreasing oxygen plasma partial pressure in annealing processes, which might be explained by the theory involving d{sup 0} magnetism related to oxygen-vacancy. From the cooperative investigations of optical and magnetic properties, we conclude that intrinsic defects, especially oxygen-vacancy, can induce and enhance luminescence and magnetism in SrTiO{sub 3} films.

  10. Strain controlled systematic variation of metal-insulator transition in epitaxial NdNiO{sub 3} thin films

    SciTech Connect

    Kumar, Yogesh; Choudhary, R. J.; Kumar, Ravi

    2012-10-01

    We report here the strain dependent structural and electrical transport properties of epitaxial NdNiO{sub 3} thin films. Pulsed laser deposition technique was used to grow the NdNiO{sub 3} thin films on c-axis oriented SrTiO{sub 3} single crystals. Deposited films were irradiated using 200 MeV Ag{sup 15+} ion beam at the varying fluence (1 Multiplication-Sign 10{sup 11}, 5 Multiplication-Sign 10{sup 11}, and 1 Multiplication-Sign 10{sup 12} ions/cm{sup 2}). X-ray diffraction studies confirm the epitaxial growth of the deposited films, which is maintained even up to the highest fluence. Rise in the in-plane compressive strain has been observed after the irradiation. All the films exhibit metal-insulator transition, however, a systematic decrease in the transition temperature (T{sub MI}) has been observed after irradiation, which may be attributed to the increase in the in-plane compression. Raman spectroscopy data reveal that this reduction in T{sub MI}, with the irradiation, is related to the decrease in band gap due to the stress generated by the in-plane compressive strain.

  11. Anisotropic spin structure along the easy axis of magnetization in epitaxially grown MnAs/GaAs(100) thin films

    SciTech Connect

    Song, J. H.; Cui, Y.; Lee, J. J.; Ketterson, J. B.

    2014-05-07

    We grew epitaxial MnAs thin films on GaAs(100) substrates using molecular-beam epitaxy and investigated their magnetic properties. The crystal orientation of the film was type-B. Measurements of the film's magnetization revealed two-fold symmetric magnetic anisotropy on its surface, with the easy and hard directions of magnetization along GaAs[1{sup ¯}10](MnAs[1{sup ¯}1{sup ¯}20]) and GaAs[110](MnAs[11{sup ¯}02]), respectively. We found breakage of the uniaxial anisotropy in magnetization along the easy direction of magnetization for both the magnetization versus magnetic field and magnetization versus temperature measurements. We suggest that the origin of this peculiar pinned ferromagnetism in the MnAs layer is the spin-exchange interaction between the MnAs film and the ultra-thin Mn layer formed at the interface of MnAs film and GaAs(100) substrate.

  12. Enhanced metallic properties of SrRuO3 thin films via kinetically controlled pulsed laser epitaxy

    NASA Astrophysics Data System (ADS)

    Thompson, J.; Nichols, J.; Lee, S.; Ryee, S.; Gruenewald, J. H.; Connell, J. G.; Souri, M.; Johnson, J. M.; Hwang, J.; Han, M. J.; Lee, H. N.; Kim, D.-W.; Seo, S. S. A.

    2016-10-01

    Metal electrodes are a universal element of all electronic devices. Conducting SrRuO3 (SRO) epitaxial thin films have been extensively used as electrodes in complex-oxide heterostructures due to good lattice mismatches with perovskite substrates. However, when compared to SRO single crystals, SRO thin films have shown reduced conductivity and Curie temperatures (TC), which can lead to higher Joule heating and energy loss in the devices. Here, we report that high-quality SRO thin films can be synthesized by controlling the plume dynamics and growth rate of pulsed laser epitaxy (PLE) with real-time optical spectroscopic monitoring. The SRO thin films grown under the kinetically controlled conditions, down to ca. 16 nm in thickness, exhibit both enhanced conductivity and TC as compared to bulk values, due to their improved stoichiometry and a strain-mediated increase of the bandwidth of Ru 4d electrons. This result provides a direction for enhancing the physical properties of PLE-grown thin films and paves a way to improved device applications.

  13. The structure and properties of phthalocyanine films grown by the molecular beam epitaxy technique. III. Preparation and characterization of lutetium diphthalocyanine films

    NASA Astrophysics Data System (ADS)

    Hoshi, Hajime; Dann, Anthony J.; Maruyama, Yusei

    1990-06-01

    Two types of epitaxial films of lutetium diphthalocyanine, LuPc2, have been obtained on KBr, LuPc2 /KBr, and on the film of fluoro-bridged aluminum phthalocyanine polymer, (AlPcF)n, on KBr, LuPc2 /(AlPcF)n /KBr, by the molecular beam epitaxy technique. Their structures have been studied by transmission electron microscopy as well as scanning electron microscopy. The phase of LuPc2 /KBr is bidirectionally oriented tetragonal, KBr(100)((10)1/2×(10)1/2) R±27°-LuPc2. The phase of LuPc2 /(AlPcF)n /KBr is predominantly unidirectionally oriented tetragonal, KBr(100)(3×3)R45°-LuPc2 /(AlPcF)n, but some bidirectional orthorhombic phase, KBr(100)C(6×3)R45°-LuPc2 /(AlPcF)n, is also present.

  14. Electronic structure, surface doping, and optical response in epitaxial WSe2 thin films

    DOE PAGES

    Zhang, Yi; Ugeda, Miguel M.; Jin, Chenhao; Shi, Su -Fei; Bradley, Aaron J.; Martin-Recio, Ana; Ryu, Hyejin; Kim, Jonghwan; Tang, Shujie; Kim, Yeongkwan; et al

    2016-03-14

    High quality WSe2 films have been grown on bilayer graphene (BLG) with layer-by-layer control of thickness using molecular beam epitaxy. The combination of angle-resolved photoemission, scanning tunneling microscopy/spectroscopy, and optical absorption measurements reveal the atomic and electronic structures evolution and optical response of WSe2/BLG. We observe that a bilayer of WSe2 is a direct bandgap semiconductor, when integrated in a BLG-based heterostructure, thus shifting the direct–indirect band gap crossover to trilayer WSe2. In the monolayer limit, WSe2 shows a spin-splitting of 475 meV in the valence band at the K point, the largest value observed among all the MX2 (Mmore » = Mo, W; X = S, Se) materials. The exciton binding energy of monolayer-WSe2/BLG is found to be 0.21 eV, a value that is orders of magnitude larger than that of conventional three-dimensional semiconductors, yet small as compared to other two-dimensional transition metal dichalcogennides (TMDCs) semiconductors. Lastly, our finding regarding the overall modification of the electronic structure by an alkali metal surface electron doping opens a route to further control the electronic properties of TMDCs.« less

  15. Point Contact Spin Spectroscopy of Ferromagnetic Fe3Si epitaxial Films

    NASA Astrophysics Data System (ADS)

    Chiu, Y. H.; Chiang, T. W.; Huang, S. Y.; Lee, S. F.; Kwo, J.

    2006-03-01

    We report transport study of ferromagnetic Fe3Si epitaxial films using point contact Andreev reflection technique. Fe3Si is a ferromagnetic metal with a high Curie temperature of 840K and nearly lattice-matched to GaAs. The Heusler-like structure makes it a good candidate of half metals for spintronics. The observed spectra of Nb and NbTi / Fe3Si point contacts using a Nb or NbTi etched tip are often broad, along with the presence of sharp dips at the superconducting Fermi energy possibly attributed to the proximity effect occurring at the interface of the contact. Using a modified Blonder-Tinkham-Klapwijk theory, the data analysis gave a spin polarization ranging from 27% to 47% under various contact conditions. The best-fit gave P= 41%, Z= 0.05, =1.49 meV at 2K. Since the thickness of our Fe3Si samples are often small, current distribution effects in the probed layer are specially considered by varying the sample thickness.

  16. Electronic Structure, Surface Doping, and Optical Response in Epitaxial WSe2 Thin Films.

    PubMed

    Zhang, Yi; Ugeda, Miguel M; Jin, Chenhao; Shi, Su-Fei; Bradley, Aaron J; Martín-Recio, Ana; Ryu, Hyejin; Kim, Jonghwan; Tang, Shujie; Kim, Yeongkwan; Zhou, Bo; Hwang, Choongyu; Chen, Yulin; Wang, Feng; Crommie, Michael F; Hussain, Zahid; Shen, Zhi-Xun; Mo, Sung-Kwan

    2016-04-13

    High quality WSe2 films have been grown on bilayer graphene (BLG) with layer-by-layer control of thickness using molecular beam epitaxy. The combination of angle-resolved photoemission, scanning tunneling microscopy/spectroscopy, and optical absorption measurements reveal the atomic and electronic structures evolution and optical response of WSe2/BLG. We observe that a bilayer of WSe2 is a direct bandgap semiconductor, when integrated in a BLG-based heterostructure, thus shifting the direct-indirect band gap crossover to trilayer WSe2. In the monolayer limit, WSe2 shows a spin-splitting of 475 meV in the valence band at the K point, the largest value observed among all the MX2 (M = Mo, W; X = S, Se) materials. The exciton binding energy of monolayer-WSe2/BLG is found to be 0.21 eV, a value that is orders of magnitude larger than that of conventional three-dimensional semiconductors, yet small as compared to other two-dimensional transition metal dichalcogennides (TMDCs) semiconductors. Finally, our finding regarding the overall modification of the electronic structure by an alkali metal surface electron doping opens a route to further control the electronic properties of TMDCs. PMID:26974978

  17. Large linear magnetoresistance in heavily-doped Nb:SrTiO3 epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Jin, Hyunwoo; Lee, Keundong; Baek, Seung-Hyub; Kim, Jin-Sang; Cheong, Byung-Ki; Park, Bae Ho; Yoon, Sungwon; Suh, B. J.; Kim, Changyoung; Seo, S. S. A.; Lee, Suyoun

    2016-10-01

    Interaction between electrons has long been a focused topic in condensed-matter physics since it has led to the discoveries of astonishing phenomena, for example, high-Tc superconductivity and colossal magnetoresistance (CMR) in strongly-correlated materials. In the study of strongly-correlated perovskite oxides, Nb-doped SrTiO3 (Nb:SrTiO3) has been a workhorse not only as a conducting substrate, but also as a host possessing high carrier mobility. In this work, we report the observations of large linear magnetoresistance (LMR) and the metal-to-insulator transition (MIT) induced by magnetic field in heavily-doped Nb:STO (SrNb0.2Ti0.8O3) epitaxial thin films. These phenomena are associated with the interplay between the large classical MR due to high carrier mobility and the electronic localization effect due to strong spin-orbit coupling, implying that heavily Nb-doped Sr(Nb0.2Ti0.8)O3 is promising for the application in spintronic devices.

  18. Magnetic and magnetoelastic properties of epitaxial SmFe2 thin film.

    PubMed

    de la Fuente, C; Arnaudas, J I; Ciria, M; del Moral, A; Dufour, C; Dumesnil, K

    2010-02-01

    We report on magnetic and magnetoelastic measurements for a 5000 Å (110) SmFe(2) thin film, which was successfully analyzed by means of a point charge model for describing the effect of the epitaxial growth in this kind of system. Some of the main conclusions of the Mössbauer and magnetoelastic results and the new magnetization results up to 5 T allow us to get a full description of the crystal electric field, exchange, and magnetoelastic behavior in this compound. So, new single-ion parameters are obtained for the crystal field interaction of samarium ions, A(4)(r(4)) = +755 K/ion and A(6)(r(6)) = -180 K/ion, and new single-ion magnetoelastic coupling B(γ,2) is approximately equal -200 MPa and B(ε,2) is approximately equal MPa, which represent the tetragonal and the in-plane shear deformations, respectively. Moreover, the new thermal behavior of the samarium magnetic moment, the exchange coupling parameter, and the magnetocrystalline anisotropy of the iron sublattice are obtained too. From these, the softening of the spin reorientation transition with respect to the bulk case could be accounted for.

  19. Orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films

    DOE PAGES

    Zhu, L. J.; Nie, S. H.; Xiong, P.; Schlottmann, P.; Zhao, J. H.

    2016-02-24

    The orbital two-channel Kondo effect displaying exotic non-Fermi liquid behaviour arises in the intricate scenario of two conduction electrons compensating a pseudo-spin-1/2 impurity of two-level system. Despite extensive efforts for several decades, no material system has been clearly identified to exhibit all three transport regimes characteristic of the two-channel Kondo effect in the same sample, leaving the interpretation of the experimental results a subject of debate. Here we present a transport study suggestive of a robust orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films, as evidenced by a magnetic field-independent resistivity upturn with a clear transition from logarithmic- tomore » square-root temperature dependence and deviation from it in three distinct temperature regimes. Lastly, our results also provide an experimental indication of the presence of two-channel Kondo physics in a ferromagnet, pointing to considerable robustness of the orbital two-channel Kondo effect even in the presence of spin polarization of the conduction electrons.« less

  20. Orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films

    PubMed Central

    Zhu, L. J.; Nie, S. H.; Xiong, P.; Schlottmann, P.; Zhao, J. H.

    2016-01-01

    The orbital two-channel Kondo effect displaying exotic non-Fermi liquid behaviour arises in the intricate scenario of two conduction electrons compensating a pseudo-spin-1/2 impurity of two-level system. Despite extensive efforts for several decades, no material system has been clearly identified to exhibit all three transport regimes characteristic of the two-channel Kondo effect in the same sample, leaving the interpretation of the experimental results a subject of debate. Here we present a transport study suggestive of a robust orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films, as evidenced by a magnetic field-independent resistivity upturn with a clear transition from logarithmic- to square-root temperature dependence and deviation from it in three distinct temperature regimes. Our results also provide an experimental indication of the presence of two-channel Kondo physics in a ferromagnet, pointing to considerable robustness of the orbital two-channel Kondo effect even in the presence of spin polarization of the conduction electrons. PMID:26905518

  1. Large linear magnetoresistance in heavily-doped Nb:SrTiO3 epitaxial thin films

    PubMed Central

    Jin, Hyunwoo; Lee, Keundong; Baek, Seung-Hyub; Kim, Jin-Sang; Cheong, Byung-ki; Park, Bae Ho; Yoon, Sungwon; Suh, B. J.; Kim, Changyoung; Seo, S. S. A.; Lee, Suyoun

    2016-01-01

    Interaction between electrons has long been a focused topic in condensed-matter physics since it has led to the discoveries of astonishing phenomena, for example, high-Tc superconductivity and colossal magnetoresistance (CMR) in strongly-correlated materials. In the study of strongly-correlated perovskite oxides, Nb-doped SrTiO3 (Nb:SrTiO3) has been a workhorse not only as a conducting substrate, but also as a host possessing high carrier mobility. In this work, we report the observations of large linear magnetoresistance (LMR) and the metal-to-insulator transition (MIT) induced by magnetic field in heavily-doped Nb:STO (SrNb0.2Ti0.8O3) epitaxial thin films. These phenomena are associated with the interplay between the large classical MR due to high carrier mobility and the electronic localization effect due to strong spin-orbit coupling, implying that heavily Nb-doped Sr(Nb0.2Ti0.8)O3 is promising for the application in spintronic devices. PMID:27703222

  2. Electronic Structure, Surface Doping, and Optical Response in Epitaxial WSe2 Thin Films.

    PubMed

    Zhang, Yi; Ugeda, Miguel M; Jin, Chenhao; Shi, Su-Fei; Bradley, Aaron J; Martín-Recio, Ana; Ryu, Hyejin; Kim, Jonghwan; Tang, Shujie; Kim, Yeongkwan; Zhou, Bo; Hwang, Choongyu; Chen, Yulin; Wang, Feng; Crommie, Michael F; Hussain, Zahid; Shen, Zhi-Xun; Mo, Sung-Kwan

    2016-04-13

    High quality WSe2 films have been grown on bilayer graphene (BLG) with layer-by-layer control of thickness using molecular beam epitaxy. The combination of angle-resolved photoemission, scanning tunneling microscopy/spectroscopy, and optical absorption measurements reveal the atomic and electronic structures evolution and optical response of WSe2/BLG. We observe that a bilayer of WSe2 is a direct bandgap semiconductor, when integrated in a BLG-based heterostructure, thus shifting the direct-indirect band gap crossover to trilayer WSe2. In the monolayer limit, WSe2 shows a spin-splitting of 475 meV in the valence band at the K point, the largest value observed among all the MX2 (M = Mo, W; X = S, Se) materials. The exciton binding energy of monolayer-WSe2/BLG is found to be 0.21 eV, a value that is orders of magnitude larger than that of conventional three-dimensional semiconductors, yet small as compared to other two-dimensional transition metal dichalcogennides (TMDCs) semiconductors. Finally, our finding regarding the overall modification of the electronic structure by an alkali metal surface electron doping opens a route to further control the electronic properties of TMDCs.

  3. Perpendicular Magnetic Anisotropy and Spin Glass-like Behavior in Molecular Beam Epitaxy Grown Chromium Telluride Thin Films.

    PubMed

    Roy, Anupam; Guchhait, Samaresh; Dey, Rik; Pramanik, Tanmoy; Hsieh, Cheng-Chih; Rai, Amritesh; Banerjee, Sanjay K

    2015-04-28

    Reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), vibrating sample magnetometry, and other physical property measurements are used to investigate the structure, morphology, magnetic, and magnetotransport properties of (001)-oriented Cr2Te3 thin films grown on Al2O3(0001) and Si(111)-(7×7) surfaces by molecular beam epitaxy. Streaky RHEED patterns indicate flat smooth film growth on both substrates. STM studies show the hexagonal arrangements of surface atoms. Determination of the lattice parameter from the atomically resolved STM image is consistent with the bulk crystal structures. Magnetic measurements show the film is ferromagnetic, having a Curie temperature of about 180 K, and a spin glass-like behavior was observed below 35 K. Magnetotransport measurements show the metallic nature of the film with a perpendicular magnetic anisotropy along the c-axis.

  4. Superior electrical properties of crystalline Er{sub 2}O{sub 3} films epitaxially grown on Si substrates

    SciTech Connect

    Chen, S.; Zhu, Y.Y.; Xu, R.; Wu, Y.Q.; Yang, X.J.; Fan, Y.L.; Lu, F.; Jiang, Z.M.; Zou, J.

    2006-05-29

    Crystalline Er{sub 2}O{sub 3} thin films were epitaxially grown on Si (001) substrates. The dielectric constant of the film with an equivalent oxide thickness of 2.0 nm is 14.4. The leakage current density as small as 1.6x10{sup -4} A/cm{sup 2} at a reversed bias voltage of -1 V has been measured. Atomically sharp Er{sub 2}O{sub 3}/Si interface, superior electrical properties, and good time stability of the Er{sub 2}O{sub 3} thin film indicate that crystalline Er{sub 2}O{sub 3} thin film can be an ideal candidate of future electronic devices.

  5. Low-relaxation spin waves in laser-molecular-beam epitaxy grown nanosized yttrium iron garnet films

    NASA Astrophysics Data System (ADS)

    Lutsev, L. V.; Korovin, A. M.; Bursian, V. E.; Gastev, S. V.; Fedorov, V. V.; Suturin, S. M.; Sokolov, N. S.

    2016-05-01

    Synthesis of nanosized yttrium iron garnet (Y3Fe5O12, YIG) films followed by the study of ferromagnetic resonance (FMR) and spin wave propagation in these films is reported. The YIG films were grown on gadolinium gallium garnet substrates by laser molecular beam epitaxy. It has been shown that spin waves propagating in YIG deposited at 700 °C have low damping. At the frequency of 3.29 GHz, the spin-wave damping parameter is less than 3.6 × 10-5. Magnetic inhomogeneities of the YIG films give the main contribution to the FMR linewidth. The contribution of the relaxation processes to the FMR linewidth is as low as 1.2%.

  6. Long Range Ferromagnetic Order in LaCoO3-δ epitaxial films due to the interplay of epitaxial strain and oxygen vacancy ordering

    SciTech Connect

    Mehta, Virat; Biskup, Nevenko; Arenholz, E; Varela del Arco, Maria; Suzuki, Yuri

    2015-04-23

    We demonstrate that a combination of electronic structure modification and oxygen vacancy ordering can stabilize a long-range ferromagnetic ground state in epitaxial LaCoO3 thin films. Highest saturation magnetization values are found in the thin films in tension on SrTiO3 and (La,Sr)(Al,Ta)O3 substrates and the lowest values are found in thin films in compression on LaAlO3. Electron microscopy reveals oxygen vacancy ordering to varying degrees in all samples, although samples with the highest magnetization are the most defective. Element-specific x-ray absorption techniques reveal the presence of high spin Co2+ and Co3+ as well as low spin Co3+ in different proportions depending on the strain state. The interactions among the high spin Co ions and the oxygen vacancy superstructure are correlated with the stabilization of the long-range ferromagnetic order.

  7. In-situ plume diagnosis during pulsed laser deposition of epitaxial-oxide thin films

    SciTech Connect

    Fenner, D.B.; Kung, P.J.; Goeres, J.; Li, Q.

    1996-12-31

    The visible plume, induced during pulsed-laser deposition (PLD) of epitaxial La{sub 0.5}Sr{sub 0.5}CoO{sub 3}/Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3}/La{sub 0.5}Sr{sub 0.5}CoO{sub 3}/YBa{sub 2}Cu{sub 3}O{sub 7}/YSZ heterostructures on silicon (100) wafers, was studied by optical-emission spectroscopy (OES). These films are suitable for the fabrication of ferroelectric capacitors and pyroelectric-sensor devices. A YAG laser, at 266 nm, is used for ablation. A collection lens transfers the PLD-plume emission into an optical fiber and onto a diffraction grating and a CCD array, for time-averaged spectroscopy from 410 to 640 nm. Plume emissions from ablated targets in the presence of an oxygen ambient, due to various atomic (Ba, Co, Cu, Sr, Ti, Y, Zr), ionic (Ba{sup +}, La{sup +}, Sr{sup +}, Y{sup +}), and a diatomic oxide (YO) species were identified. Emission intensity and evolution of ablated species are reported for distance away from the target surface, oxygen pressures, and laser fluences (1 to 4 J/cm{sup 2}). The behavior of reactive-product species, especially YO for plumes from yttria-stabilized zirconia (YSZ) and YBCO targets, is discussed. This simple and inexpensive OES system is suitable for use as a plume-quality monitor on routine PLD film synthesis.

  8. Growth mechanism of CuZnInSe2 thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tseng, Ya Hsin; Yang, Chu Shou; Wu, Chia Hsing; Chiu, Jai Wei; Yang, Min De; Wu, Chih-Hung

    2013-09-01

    CuZnInSe2 (CZIS) has potential application in solar cell for absorption layer, and give an advantage to change the band gap from CuInSe2 (1.02 eV) to ZnSe (2.67 eV). Using molecular beam epitaxy technology, the CZIS thin films were grown via CuInSe (CIS) and ZnSe base. In the case of CIS, thin films were grown on Mo-coated soda lime glass with various zinc flux. CIS was transformed into chalcopyrite and sphalerite coexisting CZIS easily but it is difficult to transform into the pure sphalerite CZIS. Zn/(Zn+In+Cu) ratio has limited to approximate 36 at% and the excess-Zn played a catalyst role. In the case of ZnSe base, which was grown on GaAs (001), various In and Cu flux defined as the TIn series and TCu series, respectively. There are four types of compound in the TIn series and TCu series, including ZnSe, InxSey, ZnIn2Se4 (ZIS) and CZIS. In the TIn series under the lowest In and Cu flux, selenium (Se) were randomly combined with cations to form the CZIS. When TIn is increased in this moment, the CZIS was transformed into ZIS. In the TCu series, CZIS demonstrated via In-rich ZIS (Zn(In, Cu)Se) and InxSey base ((Zn, Cu)InSe). It is chalcopyrite and sphalerite coexisting structure in the medium TCu region. In the high TCu region, it is transformed into the Zn-poor and Cu-rich CZIS.

  9. Growth of epitaxial tetragonal (Bi,K)TiO3 films and their ferroelectric and piezoelectric properties

    NASA Astrophysics Data System (ADS)

    Nemoto, Yuichi; Ichinose, Daichi; Shimizu, Takao; Uchida, Hiroshi; Yamaoka, Wakiko; Sato, Yusuke; Funakubo, Hiroshi

    2016-10-01

    (Bi,K)TiO3 films were grown on (001) c SrRuO3 // (100)SrTiO3 substrates by pulsed laser deposition (PLD) at various temperatures. The K/Ti and Bi/Ti ratios of the films were almost the same at 350 and 500 °C, but decreased markedly at 650 °C. The ferroelectric property was ascertained for epitaxial tetragonal (Bi,K)TiO3 films grown at 500 °C from polarization-electric field relationships, and their saturation polarization (P sat) and coercive field (E c) at a maximum electric field of 800 kV/cm were 18 µC/cm2 and 300 kV/cm, respectively. To improve the ferroelectric property, the films were heat-treated at 650 °C while keeping the films in the PLD chamber after film deposition. These films also maintained a (001)-oriented epitaxy and had a tetragonal symmetry. The P sat and E c obtained at an electric field of 800 kV/cm were changed to 22 µC/cm2 and 95 kV/cm, respectively. Moreover, these P sat and E c values increased to 31 µC/cm2 and 165 kV/cm, respectively, at a maximum electric field of 1500 kV/cm. These heat-treated (Bi,K)TiO3 films showed piezoelectricity with an apparent piezoelectric coefficient (d 33(AFM)) of 22 pm/V.

  10. Impact of Lattice Mismatch and Stoichiometry on the Structure and Bandgap of (Fe,Cr)2O3 Epitaxial Thin Films

    SciTech Connect

    Kaspar, Tiffany C.; Chamberlin, Sara E.; Bowden, Mark E.; Colby, Robert J.; Shutthanandan, V.; Manandhar, Sandeep; Wang, Yong; Sushko, Petr; Chambers, Scott A.

    2014-03-13

    The structural properties of high-quality epitaxial (Fe1-xCrx)2O3 thin films are investigated across the composition range. Epitaxial films are deposited on a-Al2O3(0001) substrates by oxygen-plasma-assisted molecular beam epitaxy. Corundum (Fe1-xCrx)2O3 supercells relaxed by density functional theory confirm that the non-linear behavior of the bulk lattice parameters originates in the magnetic structure of the alloy films. High-resolution x-ray diffraction reveals the degree of epitaxial strain relaxation in the films, with Cr-rich films remaining partially strained to the Al2O3 substrate. For intermediate compositions, a lattice expansion and non-Poisson-like tetragonal distortion are found. Scanning transmission electron microscopy and electron energy loss spectroscopy reveal a columnar grain structure in the films, with uniform mixing of cations on the nanometer scale. Oxygen non-stoichiometry is quantified by non-Rutherford resonant elastic scattering measurements utilizing 3.04 MeV He+. Intermediate-composition films are found to be slightly over-stoichiometric, resulting in the observed lattice expansion. Cr-rich films, in contrast, appear to be slightly oxygen deficient. A model is proposed to explain these results based on the energetics of oxygen defect formation and rate of oxygen diffusion in the corundum lattice. Compressive biaxial strain is found to reduce the bandgap of epitaxial Cr2O3 relative to the bulk value. The relationships which are elucidated between epitaxial film structure and optical properties can be applied to bandgap optimization in the (Fe,Cr)2O3 system.

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

    DOE PAGES

    Choi, Woo Seok; Lee, Ho Nyung

    2015-05-08

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

  12. Influence of pulsed nanosecond volume discharge in atmospheric-pressure air on the electrical characteristics of MCT epitaxial films

    NASA Astrophysics Data System (ADS)

    Grigoryev, Denis V.; Voitsekhovskii, Alexandr V.; Lozovoy, Kirill A.; Nesmelov, Sergey N.; Dzyadukh, Stanislav M.; Tarasenko, Viktor F.; Shulepov, Michail A.; Dvoretskii, Sergei A.

    2015-12-01

    The purpose of this paper was investigating the effect of volume nanosecond discharge in air at atmospheric pressure on the electro-physical properties of the HgCdTe (MCT) epitaxial films grown by molecular beam epitaxy. Hall measurements of electro-physical parameters of MCT samples after irradiation have shown that there is a layer of epitaxial films exhibiting n-type conductivity that is formed in the near-surface area. After more than 600 pulses of influence parameters and thickness of the resulting n-layer is such that the measured field dependence of Hall coefficient corresponds to the material of n-type conductivity. Also it is shown that the impact of the discharge leads to significant changes in electro-physical characteristics of MIS structures. This fact is demonstrated by increase in density of positive fixed charge, change in the hysteresis type of the capacitance-voltage characteristic, an increase in density of surface states. The preliminary results show that it is possible to use such actions in the development of technologies of the controlled change in the properties of MCT.

  13. Strain-relaxation and critical thickness of epitaxial La1.85Sr0.15CuO4 films

    DOE PAGES

    Meyer, Tricia L; Jiang, Lu; Park, Sungkyun; Egami, Takeshi; Lee, Ho Nyung

    2015-12-08

    We report the thickness-dependent strain-relaxation behavior and the associated impacts upon the superconductivity in epitaxial La1.85Sr0.15CuO4 films grown on different substrates, which provide a range of strain. We have found that the critical thickness for the onset of superconductivity in La1.85Sr0.15CuO4 films is associated with the finite thickness effect and epitaxial strain. In particular, thin films with tensile strain greater than ~0.25% revealed no superconductivity. We attribute this phenomenon to the inherent formation of oxygen vacancies that can be minimized via strain relaxation.

  14. Exceptionally high magnetization of stoichiometric Y3Fe5O12 epitaxial films grown on Gd3Ga5O12

    NASA Astrophysics Data System (ADS)

    Gallagher, James C.; Yang, Angela S.; Brangham, Jack T.; Esser, Bryan D.; White, Shane P.; Page, Michael R.; Meng, Keng-Yuan; Yu, Sisheng; Adur, Rohan; Ruane, William; Dunsiger, Sarah R.; McComb, David W.; Yang, Fengyuan; Hammel, P. Chris

    2016-08-01

    The saturation magnetization of Y3Fe5O12 (YIG) epitaxial films 4 to 250 nm in thickness has been determined by complementary measurements including the angular and frequency dependencies of the ferromagnetic resonance fields as well as magnetometry measurements. The YIG films exhibit state-of-the-art crystalline quality, proper stoichiometry, and pure Fe3+ valence state. The values of YIG magnetization obtained from all the techniques significantly exceed previously reported values for single crystal YIG and the theoretical maximum. This enhancement of magnetization, not attributable to off-stoichiometry or other defects in YIG, opens opportunities for tuning magnetic properties in epitaxial films of magnetic insulators.

  15. Changes in the electro-physical properties of MCT epitaxial films affected by a plasma volume discharge induced by an avalanche beam in atmospheric-pressure air

    NASA Astrophysics Data System (ADS)

    Grigoryev, D. V.; Voitsekhovskii, A. V.; Lozovoy, K. A.; Tarasenko, V. F.; Shulepov, M. A.

    2015-11-01

    In this paper the influence of the plasma volume discharge of nanosecond duration formed in a non-uniform electric field at atmospheric pressure on samples of epitaxial films HgCdTe (MCT) films are discussed. The experimental data show that the action of pulses of nanosecond volume discharge in air at atmospheric pressure leads to changes in the electrophysical properties of MCT epitaxial films due to formation of a near-surface high- conductivity layer of the n-type conduction. The preliminary results show that it is possible to use such actions in the development of technologies for the controlled change of the properties of MCT.

  16. Effects of substrate temperature and Cu underlayer thickness on the formation of SmCo{sub 5}(0001) epitaxial thin films

    SciTech Connect

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

    2010-05-15

    SmCo{sub 5}(0001) epitaxial thin films were prepared on Cu(111) underlayers heteroepitaxially grown on Al{sub 2}O{sub 3}(0001) single-crystal substrates by molecular beam epitaxy. The effects of substrate temperature and Cu underlayer thickness on the crystallographic properties of SmCo{sub 5}(0001) epitaxial films were investigated. The Cu atoms of underlayer diffuse into the SmCo{sub 5} film and substitute the Co sites in SmCo{sub 5} structure forming an alloy compound of Sm(Co,Cu){sub 5}. The ordered phase formation is enhanced with increasing the substrate temperature and with increasing the Cu underlayer thickness. The Cu atom diffusion into the SmCo{sub 5} film is assisting the formation of Sm(Co,Cu){sub 5} ordered phase.

  17. Growth study of nonpolar Zn{sub 1-x}Mg{sub x}O epitaxial films on a-plane bulk ZnO by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Laumer, Bernhard; Schuster, Fabian; Stutzmann, Martin; Bergmaier, Andreas; Dollinger, Guenther; Vogel, Stephen; Gries, Katharina I.; Volz, Kerstin; Eickhoff, Martin

    2012-09-17

    Nonpolar Zn{sub 1-x}Mg{sub x}O epitaxial films were grown by plasma-assisted molecular beam epitaxy on a-plane ZnO substrates. A smooth surface morphology was accomplished under oxygen-rich growth conditions. The benefits of the use of ZnO substrates on the structural properties are reflected by a low-density of threading dislocations. Furthermore, no indications for the generation of basal plane stacking faults are found. The pseudomorphic growth on a-plane ZnO substrates efficiently locks the epitaxial Zn{sub 1-x}Mg{sub x}O films to the wurtzite structure up to x = 0.25. The Mg concentration is not constant and increases with larger thickness. The optical properties reflect the influence of alloy disorder.

  18. Accurate determination of optical bandgap and lattice parameters of Zn{sub 1-x}Mg{sub x}O epitaxial films (0{<=}x{<=}0.3) grown by plasma-assisted molecular beam epitaxy on a-plane sapphire

    SciTech Connect

    Laumer, Bernhard; Schuster, Fabian; Stutzmann, Martin; Bergmaier, Andreas; Dollinger, Guenther; Eickhoff, Martin

    2013-06-21

    Zn{sub 1-x}Mg{sub x}O epitaxial films with Mg concentrations 0{<=}x{<=}0.3 were grown by plasma-assisted molecular beam epitaxy on a-plane sapphire substrates. Precise determination of the Mg concentration x was performed by elastic recoil detection analysis. The bandgap energy was extracted from absorption measurements with high accuracy taking electron-hole interaction and exciton-phonon complexes into account. From these results a linear relationship between bandgap energy and Mg concentration is established for x{<=}0.3. Due to alloy disorder, the increase of the photoluminescence emission energy with Mg concentration is less pronounced. An analysis of the lattice parameters reveals that the epitaxial films grow biaxially strained on a-plane sapphire.

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

    SciTech Connect

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

    2015-01-19

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    SciTech Connect

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

    2013-06-01

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

  2. High-temperature stability of epitaxial, non-isostructural Mo/NbN superlattices

    SciTech Connect

    Engstroem, C.; Madan, A.; Birch, J.; Nastasi, M.; Hultman, L.; Barnett, S. A.

    2000-02-01

    The effect of 1000 degree sign C vacuum annealing on the structure and hardness of epitaxial Mo/NbN superlattice thin films was studied. The intensity of superlattice satellite peaks, measured by x-ray diffraction, decreased during annealing while new peaks corresponding to a MoNbN ternary phase appeared. The results are consistent with the Mo-Nb-N phase diagram, which shows no mutual solubility between Mo, NbN, and MoNbN. Even after 3-h anneals and a loss of most of the superlattice peak intensity, the room-temperature hardness was the same as for as-deposited superlattices. The retained hardness suggests that a residual nanocomposite structure is retained even after the formation of the ternary structure. (c) 2000 Materials Research Society.

  3. Enhanced quality of epitaxial AlN thin films on 6H-SiC by ultra-high-vacuum ion-assisted reactive dc magnetron sputter deposition

    NASA Astrophysics Data System (ADS)

    Tungasmita, S.; Birch, J.; Persson, P. O. A.˚.; Järrendahl, K.; Hultman, L.

    2000-01-01

    Epitaxial AlN thin films have been grown on 6H-SiC substrates by ultra-high-vacuum (UHV) ion-assisted reactive dc magnetron sputtering. The low-energy ion-assisted growth (Ei=17-27 eV) results in an increasing surface mobility, promoting domain-boundary annihilation and epitaxial growth. Domain widths increased from 42 to 135 nm and strained-layer epitaxy was observed in this energy range. For Ei>52 eV, an amorphous interfacial layer of AlN was formed on the SiC, which inhibited epitaxial growth. Using UHV condition and very pure nitrogen sputtering gas yielded reduced impurity levels in the films (O: 3.5×1018cm-3). Analysis techniques used in this study are in situ reflection high-energy electron diffraction, secondary-ion-mass spectroscopy, atomic-force microscopy, x-ray diffraction, and cross-section high-resolution electron microscopy.

  4. Single-crystal cubic boron nitride thin films grown by ion-beam-assisted molecular beam epitaxy

    SciTech Connect

    Hirama, Kazuyuki Taniyasu, Yoshitaka; Karimoto, Shin-ichi; Krockenberger, Yoshiharu; Yamamoto, Hideki

    2014-03-03

    We investigated the formation of cubic boron nitride (c-BN) thin films on diamond (001) and (111) substrates by ion-beam-assisted molecular beam epitaxy (MBE). The metastable c-BN (sp{sup 3}-bonded BN) phase can be epitaxially grown as a result of the interplay between competitive phase formation and selective etching. We show that a proper adjustment of acceleration voltage for N{sub 2}{sup +} and Ar{sup +} ions is a key to selectively discriminate non-sp{sup 3} BN phases. At low acceleration voltage values, the sp{sup 2}-bonded BN is dominantly formed, while at high acceleration voltages, etching dominates irrespective of the bonding characteristics of BN.

  5. Raman spectroscopy of epitaxial topological insulator Bi2Te3 thin films on GaN substrates

    NASA Astrophysics Data System (ADS)

    Xu, Hao; Song, Yuxin; Gong, Qian; Pan, Wenwu; Wu, Xiaoyan; Wang, Shumin

    2015-05-01

    Bi2Te3 has drawn great attention in recent years as both a topological insulator and the best thermoelectric material at room temperature. We report on Raman spectroscopic study on Bi2Te3 thin films with thicknesses of 20-50 nm grown on GaN by molecular beam epitaxy. All the four classical optical phonon modes are clearly revealed for the first time in ex situ Raman for epitaxial Bi2Te3. Unusual and infrared-active vibration modes are also observed and analyzed. In the resonant Raman measurements, abnormal enhancement and suppression of different modes are studied. The interface modes caused by a large density of domain boundaries formed during coalescence of crystal islands with different lattice orientations and the Fröhlich electron-phonon interaction are found to play significant roles during the Raman scattering processes.

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

    NASA Astrophysics Data System (ADS)

    Ma, Wenhui

    2016-04-01

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

  7. Strain induced ferromagnetism in epitaxial Cr{sub 2}O{sub 3} thin films integrated on Si(001)

    SciTech Connect

    Punugupati, Sandhyarani Narayan, Jagdish; Hunte, Frank

    2014-09-29

    We report on the epitaxial growth and magnetic properties of antiferromagnetic and magnetoelectric (ME) Cr{sub 2}O{sub 3} thin films deposited on cubic yttria stabilized zirconia (c-YSZ)/Si(001) using pulsed laser deposition. The X-ray diffraction (2ϴ and Φ) and TEM characterizations confirm that the films were grown epitaxially. The Cr{sub 2}O{sub 3}(0001) growth on YSZ(001) occurs with twin domains. There are four domains of Cr{sub 2}O{sub 3} with in-plane rotation of 30° or 150° from each other about the [0001] growth direction. The epitaxial relation between the layers is given as [001]Si ‖ [001]YSZ ‖ [0001]Cr{sub 2}O{sub 3} and [100]Si ǁ [100]YSZ ǁ [101{sup ¯}0] Cr{sub 2}O{sub 3} or [112{sup ¯}0] Cr{sub 2}O{sub 3}. Though the bulk Cr{sub 2}O{sub 3} is an antiferromagnetic with T{sub N} = 307 K, we found that the films exhibit ferromagnetic like hysteresis loops with high saturation and finite coercive field up to 400 K. The thickness dependent magnetizations together with oxygen annealing results suggest that the ferromagnetism (FM) is due to oxygen related defects whose concentration is controlled by strain present in the films. This FM, in addition to the intrinsic magneto-electric properties of Cr{sub 2}O{sub 3}, opens the door to relevant spintronics applications.

  8. The tetragonal-like to rutile structural phase transition in epitaxial VO2/TiO2 (001) thick films

    NASA Astrophysics Data System (ADS)

    Qiu, Hongbo; Yang, Memgmeng; Dong, Yongqi; Xu, Han; Hong, Bin; Gu, Yueliang; Yang, Yuanjun; Zou, Chongwen; Luo, Zhenlin; Gao, Chen

    2015-11-01

    A controllable metal-insulator transition (MIT) of VO2 has been highly desired due to its huge potential applications in memory storage, smart windows or optical switching devices. Recently, interfacial strain engineering has been recognized as an effective approach to tuning the MIT of epitaxial VO2 films. However, the strain-involved structural evolution during the MIT process is still not clear, which prevents comprehensively understanding and utilizing interfacial strain engineering in VO2 films. In this work, we have systematically studied the epitaxial VO2 thick films grown on TiO2 (001) single crystal substrate and the structural transition at the boundary of MIT region. By using in situ temperature-dependent high-resolution x-ray diffractions, a tetragonal-like (‘T-like’) to ‘rutile’ structural phase transition is identified during the MIT process. The room-temperature crystal phase of epitaxial VO2/TiO2(001) thick film is clarified to be tetragonal-like, neither strained-rutile phase nor monoclinic phase. The calculated atomic structure of this T-like phase VO2 resembles that of the M1 phase VO2, which has been verified by their similar Raman spectra. More, the crystal lattices of the coexisted phases in the MIT region were revealed in detail. The current findings will not only show some clues on the MIT mechanism study from the structural point of view, but also favor the interface engineering assisted VO2-based devices and applications in the future.

  9. Epitaxial Growth of (0001)Ru Thin Films on (111)ZrN/(111)Si by Low-Temperature Process and Their Surface Morphologies

    NASA Astrophysics Data System (ADS)

    Sakurai, Junpei; Sasaki, Katsutaka; Yanagisawa, Hideto; Shinkai, Satoko; Abe, Yoshio

    2008-03-01

    We have investigated the epitaxial growth of (0001)Ru thin films on (111)ZrN/(111)Si epitaxial systems at room temperature using an ultrahigh-vacuum dc magnetron sputtering system. The film quality obtained and the epitaxial relationship were evaluated by X-ray diffraction, X-ray pole figure, grazing-incidence-angle X-ray reflectivity, and atomic force microscopy analyses. It was found that (0001)Ru films with a thickness of 100 nm were grown epitaxially on a (111)ZrN(40 nm)/(111)Si system even at room temperature with the directional relationship of Ru(0001)[1120]∥ZrN(111)[110]∥Si(111)[110]. In addition, it was also clarified that an epitaxial (0001)Ru film with a thickness of 3 nm on a (111)ZrN (6 nm)/(111)Si system can be regarded as a dense film with the same density as the bulk, and exhibits a fairly flat surface morphology with an average surface roughness of approximately 0.2-0.3 nm.

  10. Epitaxial Growth of Metastable hcp-Ni and hcp-NiFe Thin Films on Au(100)fcc Single-Crystal Underlayers and Their Structure Characterization

    NASA Astrophysics Data System (ADS)

    Ohtake, Mitsuru; Sato, Yoichi; Higuchi, Jumpei; Tanaka, Takahiro; Kirino, Fumiyoshi; Futamoto, Masaaki

    2011-10-01

    Metastable hcp-Ni and hcp-NiFe epitaxial thin films are prepared on Au(100)fcc single-crystal underlayers by molecular beam epitaxy. The epitaxial growth and the transformation from metastable hcp to more stable fcc phase are studied by in-situ reflection high-energy electron diffraction. In an early stage of film growth, hcp(1120) crystal is stabilized through hetero-epitaxial growth. The epitaxial orientation relationship between the film and the underlayer is determined to be hcp(1120)[0001], hcp(1120)[1100] ∥ Au(100)[001]fcc. With increasing the film thickness, the hcp structure starts to transform into fcc structure. High-resolution transmission electron microscopy shows that the film consists of a mixture of hcp and fcc crystals and that a large number of stacking faults exist parallel to the close-packed plane. The results suggest that the hcp structure starts to transform from these stacking faults into fcc structure in the lateral direction by atomic displacement parallel to the hcp(0001) close-packed plane. The crystallographic orientation relationships between the hcp and transformed fcc crystals are determined to be fcc(110)[111], fcc(110)[111] ∥ hcp(1120)[0001] and fcc(110)[112], fcc(110)[112] ∥ hcp(1120)[1100].

  11. Strain engineering of magnetic anisotropy: The epitaxial growth of cobalt-manganese-gallium Heusler alloy films on III-V semiconductors

    NASA Astrophysics Data System (ADS)

    Carr, David Michael

    This research is the first step towards manipulating thin film magnetic anisotropy through control of uniform epitaxial strain. Pseudomorphic Co 2MnGa films with thicknesses of 300 A have been grown on several III-V semiconductors to generate coherently-strained epitaxial films. Growth of Co2MnGa films at 200°C both directly on GaAs substrates and on thermodynamically stable Sc0.3Er0.7As interlayers resulted in similar physical and magnetic properties. The epitaxial strain generated an induced perpendicular anisotropy and magnetic stripe domains. This resulted in a reduced in-plane remnant magnetization, high coercivity, and a relatively low saturation field for the out-of-plane magnetization. For higher temperature growths, the interlayer was required to minimize interfacial reactions and maintain the magnetic properties of the films. When the growth temperature on the Sc0.3Er0.7As interlayers was increased from 0 to 400°C, the subsequent films had improved L21 atomic ordering, decreased out-of-plane lattice parameters, and enhanced strain-induced perpendicular anisotropy. Dramatic variations in the magnetic anisotropy were observed for films grown on different III-V semiconductors due to controlled strain-induced perpendicular anisotropy. For Co2MnGa films grown under tension on InP, the magnetization barely saturated out-of-plane with a field of 1.75 Tesla. These films displayed clear in-plane anisotropy and low coercivity switching. For films grown under compression on GaAs, the magnetization easily saturated out-of-plane with a field of a few thousand Oe. These films displayed no in-plane anisotropy in the hysteresis loops and had large coercivities. For comparison, bulk-like unstrained Co2MnGa films were grown on relaxed ErAs interlayers on InAs. These films displayed properties intermediate between films grown on GaAs and InP. Finally, growth of films on GaP resulted in partial relaxation, thereby reducing the induced perpendicular anisotropy and verifying

  12. Effect of thickness and strain on the metamagnetic transition temperature of ultra-thin epitaxial FeRh films

    NASA Astrophysics Data System (ADS)

    Ceballos, Alejandro; Bordel, Catherine; Schneider, Oliver; Hellman, Frances

    2015-03-01

    The antiferromagnetic to ferromagnetic transition in ultra-thin epitaxial FeRh films was studied as a function of film thickness and substrate-induced strain. The lattice mismatch from MgO, STO and KTO was used to provide different strain states on FeRh films with thicknesses spanning 5 to 22 nm. The interplay of these parameters was studied using magnetometry, diffractometry, atomic force microscopy and energy dispersive spectroscopy. Our results provide insight into the growth mechanisms of FeRh and how the onset of the magnetic transition can be controlled via strain engineering. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship and the Department of Energy.

  13. p-type ZnO films with solid-source phosphorus doping by molecular-beam epitaxy

    SciTech Connect

    Xiu, F.X.; Yang, Z.; Mandalapu, L.J.; Liu, J.L.; Beyermann, W. P.

    2006-01-30

    Phosphorus-doped p-type ZnO films were grown on r-plane sapphire substrates using molecular-beam epitaxy with a solid-source GaP effusion cell. X-ray diffraction spectra and reflection high-energy electron diffraction patterns indicate that high-quality single crystalline (1120) ZnO films were obtained. Hall and resistivity measurements show that the phosphorus-doped ZnO films have high hole concentrations and low resistivities at room temperature. Photoluminescence (PL) measurements at 8 K reveal a dominant acceptor-bound exciton emission with an energy of 3.317 eV. The acceptor energy level of the phosphorus dopant is estimated to be 0.18 eV above the valence band from PL spectra, which is also consistent with the temperature dependence of PL measurements.

  14. Electronic Degeneracy and Intrinsic Magnetic Properties of EpitaxialNb: SrTiO3 Thin Films Controlled by Defects.

    PubMed

    Sarantopoulos, A; Ferreiro-Vila, E; Pardo, V; Magén, C; Aguirre, M H; Rivadulla, F

    2015-10-16

    We report thermoelectric power experiments in e-doped thin films of SrTiO3 (STO) which demonstrate that the electronic band degeneracy can be lifted through defect management during growth. We show that even small amounts of cationic vacancies, combined with epitaxial stress, produce a homogeneous tetragonal distortion of the films, resulting in a Kondo-like resistance upturn at low temperature, large anisotropic magnetoresistance, and nonlinear Hall effect. Ab initio calculations confirm a different occupation of each band depending on the degree of tetragonal distortion. The phenomenology reported in this Letter for tetragonally distorted e-doped STO thin films, is similar to that observed in LaAlO3/STO interfaces and magnetic STO quantum wells.

  15. Growth and structure of photosensitive Pb{sub 1-x}Mn{sub x}Te(Ga) epitaxial films

    SciTech Connect

    Nuriev, I. R.; Sadygov, R. M.; Nazarov, A. M.

    2008-05-15

    The growth and structure of (1-1.5)-{mu}m-thick Pb{sub 1-x}Mn{sub x}Te(Ga)(x = 0.06) films with 0.4-0.9 at % of gallium, grown on BaF{sub 2}(111) and Pb{sub 1-x}Sn{sub x}Te (x = 0.2) (100) substrates by molecular beam epitaxy, have been investigated. It is established that the films are crystallized into an fcc structure, and their growth planes are (111) and (100), according to the substrate orientation. The optimal conditions for obtaining high-resistivity photosensitive p-and n-type films with a perfect crystal structure (W{sub 1/2} = 80''-100'') have been determined.

  16. Scanning reflection electron microscopy study of surface defects in GaN films formed by epitaxial lateral overgrowth

    NASA Astrophysics Data System (ADS)

    Watanabe, Heiji; Kuroda, Naotaka; Sunakawa, Haruo; Usui, Akira

    2000-09-01

    We have used scanning reflection electron microscopy (SREM) to detect surface defects in GaN films formed by facet-initiated epitaxial lateral overgrowth. SREM revealed individual threading dislocations and single atomic steps on the GaN surface, and provided images of crystallographic tilting near the surfaces. We found that one of the two tilted GaN crystals in the overgrown areas became dominant and that the surface changed to a single domain after 50-μm-thick GaN deposition. Our SREM results also showed that the deposition of thick (over 100 μm) GaN films significantly improves the crystallographic structures of the overgrown regions, and reduces the threading dislocations in the GaN films.

  17. Electronic Degeneracy and Intrinsic Magnetic Properties of EpitaxialNb: SrTiO3 Thin Films Controlled by Defects.

    PubMed

    Sarantopoulos, A; Ferreiro-Vila, E; Pardo, V; Magén, C; Aguirre, M H; Rivadulla, F

    2015-10-16

    We report thermoelectric power experiments in e-doped thin films of SrTiO3 (STO) which demonstrate that the electronic band degeneracy can be lifted through defect management during growth. We show that even small amounts of cationic vacancies, combined with epitaxial stress, produce a homogeneous tetragonal distortion of the films, resulting in a Kondo-like resistance upturn at low temperature, large anisotropic magnetoresistance, and nonlinear Hall effect. Ab initio calculations confirm a different occupation of each band depending on the degree of tetragonal distortion. The phenomenology reported in this Letter for tetragonally distorted e-doped STO thin films, is similar to that observed in LaAlO3/STO interfaces and magnetic STO quantum wells. PMID:26550891

  18. Correlation of nanochemistry and electrical properties in HfO2 films grown by metalorganic molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Moon, Tae-Hyoung; Ham, Moon-Ho; Myoung, Jae-Min

    2005-03-01

    We present the annealing effects on nanochemistry and electrical properties in HfO2 dielectrics grown by metalorganic molecular-beam epitaxy. After the postannealing treatment of HfO2 films in the temperature range of 600-800°C, the thicknesses and chemical states of the films were examined by high-resolution transmission electron microscopy and angle-resolved x-ray photoelectron spectroscopy. By comparing the line shapes of core-level spectra for the samples with different annealing temperatures, the concentrations of SiO and Hf-silicate with high dielectric constant are found to be highest for HfO2 film annealed at 700°C. This result supports that the accumulation capacitance of the sample annealed at 700°C is not deteriorated in spite of a steep increase in interfacial layer thickness compared with that of the sample annealed at 600°C.

  19. Ultrafast carrier dynamics and the role of grain boundaries in polycrystalline silicon thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Titova, Lyubov V.; Cocker, Tyler L.; Xu, Sijia; Baribeau, Jean-Marc; Wu, Xiaohua; Lockwood, David J.; Hegmann, Frank A.

    2016-10-01

    We have used time-resolved terahertz spectroscopy to study microscopic photoconductivity and ultrafast photoexcited carrier dynamics in thin, pure, non-hydrogenated silicon films grown by molecular beam epitaxy on quartz substrates at temperatures ranging from 335 °C to 572 °C. By controlling the growth temperature, thin silicon films ranging from completely amorphous to polycrystalline with minimal amorphous phase can be achieved. Film morphology, in turn, determines its photoconductive properties: in the amorphous phase, carriers are trapped in bandtail states on sub-picosecond time scales, while the carriers excited in crystalline grains remain free for tens of picoseconds. We also find that in polycrystalline silicon the photoexcited carrier mobility is carrier-density-dependent, with higher carrier densities mitigating the effects of grain boundaries on inter-grain transport. In a film grown at the highest temperature of 572 °C, the morphology changes along the growth direction from polycrystalline with needles of single crystals in the bulk of the film to small crystallites interspersed with amorphous silicon at the top of the film. Depth profiling using different excitation wavelengths shows corresponding differences in the photoconductivity: the photoexcited carrier lifetime and mobility are higher in the first 100-150 nm from the substrate, suggesting that thinner, low-temperature grown polycrystalline silicon films are preferable for photovoltaic applications.

  20. Strain-controlled easy axis orientation of epitaxial CoFe2O4 films by He implantation

    NASA Astrophysics Data System (ADS)

    Herklotz, Andreas; Wong, Antony T.; Rus, Stefania F.; Ward, Thomas Z.

    2015-03-01

    Heteroepitaxial strain engineering is an essential tool in the strongly correlated systems for investigating fundamental coupling effects and for more practical control of thin film properties. Here, we use strain doping by He implantation as an alternative technique to control thin film functionalities. We demonstrate the tuning of the magnetic anisotropy of CoFe2O4 (CFO) films through He implantation. Compressively strained thin films of CFO are grown coherently on MgO substrates and show pronounced out-of-plane magnetic anisotropy. Successive doping of the CFO films with He using a commercial ion gun results in an expansion of the out-of-plane lattice parameter while maintaining in-plane epitaxial lock to the substrate. We observe a continuous rotation of the magnetic easy axis towards the film plane with increasing unit cell tetragonality. The results are in agreement with the strain-induced change of the magnetic anisotropy due to the large negative magnetostriction of CFO and demonstrate that strain doping via He implantation is an elegant path to tune desired characteristics of transition metal oxide thin films. This work was supported by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division.

  1. Gas Sensing Properties of Epitaxial LaBaCo2O5.5+δ Thin Films

    PubMed Central

    Liu, M.; Ren, S. P.; Zhang, R. Y.; Xue, Z. Y.; Ma, C. R.; Yin, M. L.; Xu, X.; Bao, S. Y.; Chen, C. L.

    2015-01-01

    Chemical reactivity and stability of highly epitaxial mixed-conductive LaBaCo2O5.5+δ (LBCO) thin films on (001) LaAlO3 (LAO) single-crystalline substrates, fabricated by using pulsed laser deposition system, were systematically investigated. Microstructure studies from x-ray diffraction indicate that the films are c-axis oriented with the interface relationship of [100]LBCO//[100]LAO and (001)LBCO//(001)LAO. LBCO thin films can detect the ethanol vapor concentration as low as 10ppm and the response of LBCO thin film to various ethanol vapor concentrations is very reliable and reproducible with the switch between air and ethanol vapor. Moreover, the fast response of the LBCO thin film, as the p-type gas sensor, is better than some n-type oxide semiconductor thin films and comparable with some nanorods and nanowires. These findings indicate that the LBCO thin films have great potential for the development of gas sensors in reducing/oxidizing environments. PMID:26146369

  2. An aberration-corrected STEM study of structural defects in epitaxial GaN thin films grown by ion beam assisted MBE.

    PubMed

    Poppitz, David; Lotnyk, Andriy; Gerlach, Jürgen W; Lenzner, Jörg; Grundmann, Marius; Rauschenbach, Bernd

    2015-06-01

    Ion-beam assisted molecular-beam epitaxy was used for direct growth of epitaxial GaN thin films on super-polished 6H-SiC(0001) substrates. The GaN films with different film thicknesses were studied using reflection high energy electron diffraction, X-ray diffraction, cathodoluminescence and primarily aberration-corrected scanning transmission electron microscopy techniques. Special attention was devoted to the microstructural characterization of GaN thin films and the GaN-SiC interface on the atomic scale. The results show a variety of defect types in the GaN thin films and at the GaN-SiC interface. A high crystalline quality of the produced hexagonal GaN thin films was demonstrated. The gained results are discussed.

  3. Spin-state configuration induced faster spin dynamics in epitaxial La1-xSrxCoO3 thin films

    NASA Astrophysics Data System (ADS)

    Cui, W. Y.; Li, P.; Bai, H. L.

    2015-05-01

    Two important features: spin-state configuration and spin dynamics in phase-separated ferromagnetic/spin-glass epitaxial La1-xSrxCoO3 thin films (x=0.07, 0.17, 0.26, 0.30, 0.40, 0.60) have been investigated and elaborated, proved by both magnetic analyses and first principle calculations. The configuration with high-spin (HS) state Co3+ and low-spin (LS) state Co4+ is considered to be the most stable spin-state configuration for La1-xSrxCoO3 at ground state, which was demonstrated by calculating the magnetic moments of La1-xSrxCoO3, as well as first principle calculation. The stretched Co-O bond by Sr doping causes the decrease of crystal field splitting, resulting in the HS state Co3+ and LS state Co4+. The spin dynamics in the La1-xSrxCoO3 thin films was found to be faster than the classic spin-glass compounds, which is attributed to the higher-spin Co3+, and rather smaller ferromagnetic cluster size (~2.16 to ~21.5 nm) in the epitaxial films than that in referenced polycrystalline compounds (~35 to ~240 nm).

  4. Epitaxial LiCoO2 films as a model system for fundamental electrochemical studies of positive electrodes.

    PubMed

    Takeuchi, Saya; Tan, Haiyan; Bharathi, K Kamala; Stafford, Gery R; Shin, Jongmoon; Yasui, Shintaro; Takeuchi, Ichiro; Bendersky, Leonid A

    2015-04-22

    Epitaxial LiCoO2 (LCO) thin films of different orientations were fabricated by pulsed laser deposition (PLD) in order to model single-crystal behavior during electrochemical reaction. This paper demonstrates that deposition of conductive SrRuO3 between a SrTiO3 (STO) substrate and an LCO film allows (1) epitaxial growth of LCO with orientation determined by STO and (2) electrochemical measurements, such as cyclic voltammetry and impedance spectroscopy. Scanning transmission electron microscopy (S/TEM and SEM) has demonstrated an orientation relationship between LCO and STO of three orientations, (111), (110) and (100), and identified a LCO/electrolyte surface as consisting of two crystallographic facets of LCO, (001) and {104}. The difference in the orientation of LCO accounts for the difference in the exposed area of {104} planes to the electrolyte, where lithium ions have easy access to fast diffusion planes. The resistance for lithium ion transfer measured by electrochemical impedance spectroscopy had inverse correlation with exposed area of {104} plane measured by TEM. Chemical diffusivity of lithium ions in LCO was measured by fitting electrochemical impedance spectroscopy data to a modified Randles equivalent circuit and allowed us to determine its dependence on film orientation.

  5. Growth mechanism and electronic properties of epitaxial In{sub 2}O{sub 3} films on sapphire

    SciTech Connect

    Wang, Ch. Y.; Kirste, L.; Roehlig, C. C.; Koehler, K.; Cimalla, V.; Ambacher, O.; Morales, F. M.; Manuel, J. M.; Garcia, R.

    2011-11-01

    In this work, we report on the epitaxial growth of high-quality cubic indium oxide thick films on c-plane sapphire substrates using a two-step growth process. The epitaxial relationship of In{sub 2}O{sub 3} on (0001) Al{sub 2}O{sub 3} has been investigated. The (222) plane spacing and lattice parameter of a most strain-relaxed high-quality In{sub 2}O{sub 3} film have been determined to be 292.58 pm and 1013.53 pm, respectively. The electronic properties in dependence of the film thickness are interpreted using a three-region model. The density at the surface and interface totals (3.3{+-}1.5)x10{sup 13}cm{sup -2}, while the background electron density in the bulk was determined to be (2.4{+-}0.5)x10{sup 18}cm{sup -3}. Furthermore, post treatments such as irradiation via ultraviolet light and ozone oxidation have been found to influence only the surface layer, while the bulk electronic properties remain unchanged.

  6. Self-assembled, vertically aligned, epitaxial nanoscale p-n heterojunctions for thin film based photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Bogorin, Daniela F.; Aytug, Tolga; Paranthaman, Parans M.; Lupini, Andrew A.; Rondinone, Adam; Winters, Kyle

    2012-02-01

    Using rf- sputtering technique we have exploited phase-separated self-assembly and developed epitaxial, nanostructured composite films composed of phase separated, and vertically oriented p-n interfacial nanocolumns of Cu2O (p type; 2eV bandgap) and TiO2 (n type; 3.2 eV bandgap). The characteristic band gaps of these phases allow extension of the solar capture from ultraviolet to a visible wavelenght. The composite films were grown on perovskite substrates and exhibit single crystalline epitaxy in both phases. We have investigated crystalline structure, interfacial quality and optical properties of the nanopillar arrays using XRD, TEM, SEM, AFM, and optical absorption techniques. Here, we show nearly complete atomic order at Cu2O-TiO2 interface (i.e., p-n junction) and an absorption profile that captures a wide range of solar spectrum extending from ultraviolet to visible wavelengths. Compared to layered thin film architectures, the use of such vertically aligned nanostructures in solar cells can promote cost-effective fabrication of high efficiency PV devices by providing low defect concentrations, improved absorption and light trapping capabilities, and increased minority carrier diffusion lengths.

  7. Superconductivity in epitaxial thin films of NaxCoO2•yD2O

    NASA Astrophysics Data System (ADS)

    Krockenberger, Y.; Fritsch, I.; Christiani, G.; Habermeier, H.-U.; Yu, Li; Bernhard, C.; Keimer, B.; Alff, L.

    2006-04-01

    The observation of superconductivity in the layered transition metal oxide NaxCoO2•yH2O [K. Takada et al., Nature (London) 422, 53 (2003)] has caused a tremendous upsurge of scientific interest due to its similarities and its differences to the copper based high-temperature superconductors. Two years after the discovery, we report the fabrication of single-phase superconducting epitaxial thin films of Na0.3CoO2•1.3D2O grown by pulsed laser deposition technique. This opens additional roads for experimental research exploring the superconducting state and the phase diagram of this unconventional material.

  8. Simulation for deposition of cadmium telluride thin films in hot wall epitaxial system using Monte Carlo technique

    NASA Astrophysics Data System (ADS)

    Venkatachalam, T.; Ganesan, S.; Sakthivel, K.

    2006-04-01

    The molecular flow in the hot wall epitaxial system has been studied by computer simulation using the Monte Carlo technique for the deposition of CdTe thin films. The number of wall collisions, intermolecular collisions, direct transmissions, number of molecules and flux density distributions along each volume of the tube, with different source temperatures and wall temperatures for various lengths and radii of the hot wall setup, have been simulated, then the optimal deposition conditions for the thermodynamic equilibrium of vapour transport are determined and experimentally validated.

  9. Formation of epitaxial metastable NiGe{sub 2} thin film on Ge(100) by pulsed excimer laser anneal

    SciTech Connect

    Lim, Phyllis S. Y.; Yeo, Yee-Chia; Chi, Dong Zhi; Lim, Poh Chong; Wang, Xin Cai; Chan, Taw Kuei; Osipowicz, Thomas

    2010-11-01

    Epitaxial nickel digermanide (NiGe{sub 2}), a metastable phase, was formed by laser annealing Ni on (100) germanium-on-silicon substrates. The NiGe{sub 2} formation was investigated using transmission electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, Rutherford backscattering spectroscopy, and first-principles calculations. The formation mechanism of NiGe{sub 2} is discussed and is attributed to both the reduced interfacial energy at the NiGe{sub 2}/Ge(100) interface and the kinetic aspects of the laser annealing reaction associated with phase transformation and film agglomeration.

  10. Electronic Structure of Tl2Ba2CuO(6+Delta) Epitaxial Films Measured by X-Ray Photoemission

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Ren, Z. F.; Wang, J. H.

    1996-01-01

    The valence electronic structure and core levels of Tl2Ba2CuO(6 + delta) (Tl-2201) epitaxial films have been measured with X-ray photoelectron spectroscopy and are compared to those of Tl2Ba2CaCu2O(8 + delta) (Tl-2212). Changes in the Tl-2201 core-level binding energies with oxygen doping are consistent with a change in the chemical potential. Differences between the Tl-2201 and Tl-2212 measured densities of states are consistent with the calculated Cu 3d and Tl 6s partial densities of states.

  11. Advanced Fabrication Method for the Preparation of MOF Thin Films: Liquid-Phase Epitaxy Approach Meets Spin Coating Method.

    PubMed

    Chernikova, Valeriya; Shekhah, Osama; Eddaoudi, Mohamed

    2016-08-10

    Here, we report a new and advanced method for the fabrication of highly oriented/polycrystalline metal-organic framework (MOF) thin films. Building on the attractive features of the liquid-phase epitaxy (LPE) approach, a facile spin coating method was implemented to generate MOF thin films in a high-throughput fashion. Advantageously, this approach offers a great prospective to cost-effectively construct thin-films with a significantly shortened preparation time and a lessened chemicals and solvents consumption, as compared to the conventional LPE-process. Certainly, this new spin-coating approach has been implemented successfully to construct various MOF thin films, ranging in thickness from a few micrometers down to the nanometer scale, spanning 2-D and 3-D benchmark MOF materials including Cu2(bdc)2·xH2O, Zn2(bdc)2·xH2O, HKUST-1, and ZIF-8. This method was appraised and proved effective on a variety of substrates comprising functionalized gold, silicon, glass, porous stainless steel, and aluminum oxide. The facile, high-throughput and cost-effective nature of this approach, coupled with the successful thin film growth and substrate versatility, represents the next generation of methods for MOF thin film fabrication. Therefore, paving the way for these unique MOF materials to address a wide range of challenges in the areas of sensing devices and membrane technology. PMID:27415640

  12. Semipolar and nonpolar GaN epi-films grown on m-sapphire by plasma assisted molecular beam epitaxy

    SciTech Connect

    Mukundan, Shruti; Mohan, Lokesh; Chandan, Greeshma; Krupanidhi, S. B.; Roul, Basanta

    2014-11-28

    We hereby report the development of non-polar epi-GaN films of usable quality, on an m-plane sapphire. Generally, it is difficult to obtain high-quality nonpolar material due to the planar anisotropic nature of the growth mode. However, we could achieve good quality epi-GaN films by involving controlled steps of nitridation. GaN epilayers were grown on m-plane (10-10) sapphire substrates using plasma assisted molecular beam epitaxy. The films grown on the nitridated surface resulted in a nonpolar (10-10) orientation while without nitridation caused a semipolar (11-22) orientation. Room temperature photoluminescence study showed that nonpolar GaN films have higher value of compressive strain as compared to semipolar GaN films, which was further confirmed by room temperature Raman spectroscopy. The room temperature UV photodetection of both films was investigated by measuring the I-V characteristics under UV light illumination. UV photodetectors fabricated on nonpolar GaN showed better characteristics, including higher external quantum efficiency, compared to photodetectors fabricated on semipolar GaN. X-ray rocking curves confirmed better crystallinity of semipolar as compared to nonpolar GaN which resulted in faster transit response of the device.

  13. Vibrational properties of epitaxial Bi{sub 4}Te{sub 3} films as studied by Raman spectroscopy

    SciTech Connect

    Xu, Hao; Pan, Wenwu; Chen, Qimiao; Wu, Xiaoyan; Song, Yuxin E-mail: shumin@chalmers.se; Gong, Qian; Lu, Pengfei; Wang, Shumin E-mail: shumin@chalmers.se

    2015-08-15

    Bi{sub 4}Te{sub 3}, as one of the phases of the binary Bi–Te system, shares many similarities with Bi{sub 2}Te{sub 3}, which is known as a topological insulator and thermoelectric material. We report the micro-Raman spectroscopy study of 50 nm Bi{sub 4}Te{sub 3} films on Si substrates prepared by molecular beam epitaxy. Raman spectra of Bi{sub 4}Te{sub 3} films completely resolve the six predicted Raman-active phonon modes for the first time. Structural features and Raman tensors of Bi{sub 4}Te{sub 3} films are introduced. According to the wavenumbers and assignments of the six eigenpeaks in the Raman spectra of Bi{sub 4}Te{sub 3} films, it is found that the Raman-active phonon oscillations in Bi{sub 4}Te{sub 3} films exhibit the vibrational properties of those in both Bi and Bi{sub 2}Te{sub 3} films.

  14. Epitaxial growth of multiferroic BiFeO3 thin films with (101) and (111) orientations on (100) Si substrates

    NASA Astrophysics Data System (ADS)

    Kyun Lee, Sung; Ho Choi, Bum; Hesse, Dietrich

    2013-06-01

    Multiferroic (101)- and (111)-oriented BiFeO3 thin films were grown on heteroepitaxial substrates of (110) SrRuO3/(100) YSZ/(100) Si and (111) SrRuO3/(111) Pt/(100) YSZ/(100) Si, respectively, by pulsed laser deposition. X-ray diffraction θ-2θ scans, ϕ scans, and pole figures showed the well-developed out-of-plane and in-plane orientations of the epitaxial BiFeO3 films. The (111) BiFeO3 films showed ˜√3 /√2 times higher remanent polarization (58.9 μC/cm2) than that of the (101) BiFeO3 films (44.3 μC/cm2), thus revealing the ferroelectric anisotropy. The (101) BiFeO3 films exhibited a good fatigue resistance up to 4.6 × 107 cycles, whereas the (111) BiFeO3 films proved to be vulnerable to fatigue, which is associated with the polarization switching path.

  15. Epitaxial Growth of Atomically Flat Yttrium Iron Garnet Thin Films on Gadolinium Gallium Garnet by Pulse Laser Deposition

    NASA Astrophysics Data System (ADS)

    Lin, Tao; Tang, Chi; Shi, Jing

    2013-03-01

    Yttrium iron garnet (YIG) is a ferrimagnetic insulator which is useful for magneto-optical, microwave, and more recently spintronic devices. Pulsed laser deposition (PLD) has emerged as a preferred technique to deposit complex oxide thin films, heterostructures, and superlattices with high quality. Deposition of YIG films using PLD has been reported by several groups. The layer-by-layer growth mode has been achieved with a high laser repetition rate. No details about surface morphology were discussed. Here we report our approach to grow YIG films with thickness ranging from 10 to 100 nm on (110)- and (111)-oriented gadolinium gallium garnet (GGG) substrates. In both orientations, we have successfully grown epitaxial YIG thin films confirmed by the patterns of the reflection high-energy electron diffraction. The magnetic properties are measured by a vibrating sample magnetometer. The in-plane easy-axis coercivity is less than 1 Oe, while the perpendicular saturation field is ~ 2000 Oe. For both orientations, the atomic force microscopy images show that the YIG surface is extremely flat with roughness ~ 0.6Å. Flat terraces are found with the atomic step height in films with both orientations. This work paves the way to engineering anisotropy of the thin films for YIG-based magnetic devices. This work was supported in part by DMEA and DOE.

  16. Comparison of morphology evolution of Ge(001) homoepitaxial films grown by pulsed laser deposition and molecular-beam epitaxy

    SciTech Connect

    Shin Byungha; Leonard, John P.; McCamy, James W.; Aziz, Michael J.

    2005-10-31

    Using a dual molecular-beam epitaxy (MBE)-pulsed laser deposition (PLD) ultrahigh vacuum chamber, we have conducted the first experiments under identical thermal, background, and surface preparation conditions to compare Ge(001) homoepitaxial growth morphology in PLD and MBE. We find that in PLD with low kinetic energy and in MBE the film morphology evolves in a similar fashion: initially irregularly shaped mounds form, followed by pyramidal mounds with edges of the square-base along the <100> directions; the film roughness and mound separation increase with film thickness. In PLD with high kinetic energy, well-defined pyramidal mounds are not observed and the morphology rather resembles that of an ion-etched Ge(001) surface. The areal feature density is higher for PLD films than for MBE films grown at the same average growth rate and temperature. Furthermore, the dependence upon film thickness of roughness and feature separation differ for PLD and MBE. We attribute these differences to the higher yield of defect generation by energetic species in PLD.

  17. Epitaxial NiO (1 0 0) and NiO (1 1 1) films grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Lindahl, E.; Lu, J.; Ottosson, M.; Carlsson, J.-O.

    2009-08-01

    Epitaxial NiO (1 1 1) and NiO (1 0 0) films have been grown by atomic layer deposition on both MgO (1 0 0) and α-Al 2O 3 (0 0 l) substrates at temperatures as low as 200 °C by using bis(2,2,6,6-tetramethyl-3,5-heptanedionato)Ni(II) and water as precursors. The films grown on the MgO (1 0 0) substrate show the expected cube on cube growth while the NiO (1 1 1) films grow with a twin rotated 180° on the α-Al 2O 3 (0 0 l) substrate surface. The films had columnar microstructures on both substrate types. The single grains were running throughout the whole film thickness and were significantly smaller in the direction parallel to the surface. Thin NiO (1 1 1) films can be grown with high crystal quality with a FWHM of 0.02-0.05° in the rocking curve measurements.

  18. Role of thermal strain in the metal-insulator and structural phase transition of epitaxial VO2 films

    NASA Astrophysics Data System (ADS)

    Théry, V.; Boulle, A.; Crunteanu, A.; Orlianges, J. C.; Beaumont, A.; Mayet, R.; Mennai, A.; Cosset, F.; Bessaudou, A.; Fabert, M.

    2016-05-01

    The metal-insulator switching characteristics of VO2 play a crucial role in the performances of VO2-based devices. In this paper we study high-quality (010)-oriented epitaxial films grown on (001) sapphire substrates by means of electron-beam evaporation and investigate the role of interface defects and thermal strain on the parallel evolution of the metal-insulator transition (MIT) and structural phase transition (SPT) between the monoclinic (insulator) and rutile (metal) phases. It is demonstrated that the highly-mismatched VO2/Al2O3 interface promotes a domain-matching epitaxial growth process where the film grows in a strain-relaxed state and the lattice distortions are confined at the interface in regions with limited spatial extent. Upon cooling down from the growth temperature, tensile strain is stored in the films as a consequence of the thermal expansion mismatch between VO2 and Al2O3 . The thinnest films exhibit the highest level of tensile strain in the interfacial plane resulting in a shift of both the MIT and the SPT temperatures towards higher values, pointing to a stabilization of the monoclinic/insulating phase. Concomitantly, the electrical switching characteristics are altered (lower resistivity ratio and broader transition) as a result of the presence of structural defects located at the interface. The SPT exhibits a similar evolution with, additionally, a broader hysteresis due to the formation of an intermediate, strain-stabilized phase in the M1-R transition. Films with thickness ranging between 100-300 nm undergo a partial strain relaxation and exhibit the best performances, with a sharp (10°C temperature range) and narrow (hysteresis <4°C) MIT extending over more than four orders of magnitude in resistivity (6 ×104 ).

  19. Semipolar Single-Crystal ZnO Films Deposited by Low-Temperature Aqueous Solution Phase Epitaxy on GaN Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Richardson, Jacob J.; Koslow, Ingrid; Pan, Chih-Chien; Zhao, Yuji; Ha, Jun-Seok; DenBaars, Steven P.

    2011-12-01

    Low-temperature aqueous solution deposition has been used for the first time to produce epitaxial ZnO layers on the semipolar (1011) surface of bulk GaN substrates and LEDs. Although the ZnO films have single in-plane and out-of-plane orientations, which are nominally the same as those of the (1011) GaN substrate, the ZnO lattice is observed to be slightly tilted with respect to that of the substrate. A (1011) light-emitting diode using an epitaxial ZnO film as a transparent current-spreading layer achieved a high external quantum efficiency of 48%.

  20. Orientation-dependent critical currents in Y sub 1 Ba sub 2 Cu sub 3 O sub 7-x epitaxial thin films: Evidence for intrinsic flux pinning

    SciTech Connect

    Christen, D.K.; Klabunde, C.E.; Feenstra, R.; Lowndes, D.H.; Norton, D.P.; Budai, J.D.; Kerchner, H.R.; Thompson, J.R.; Zhu, S. ); Marwick, A.D. )

    1990-01-01

    For YBCO epitaxial thin films the basal plane transport critical current density J{sub c}, flowing perpendicular to an applied magnetic field H, depends sensitively on the orientation of the crystal with respect to H. In particular, J{sub c} is sharply peaked and greatly enhanced when H is precisely parallel to the copper-oxygen planes. Experiments on a series of epitaxial monolithic and superconductor-insulator multilayer thin films provide clear evidence that the enhancement is a bulk, rather than surface or thin sample, phenomenon. Measurements of the orientation dependence are presented and compared with a model of intrinsic flux pinning'' by the layered crystal structure.