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Sample records for epitaxial nbn films

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

    SciTech Connect

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

    2011-01-14

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

  2. Dependence of superconducting properties of NbN thin films on sputtering parameters

    NASA Astrophysics Data System (ADS)

    Khaire, Trupti; Carter, Faustin; Ding, Junjia; Posada, Chrystian; Bender, Amy; Wang, Gensheng; Yefremenko, Volodymyr; Pearson, John; Padin, Steve; Chang, Clarence; Hoffmann, Axel; Novosad, Valentyn; SPT3G Collaboration

    Recently, there has been growing interest in utilizing NbN, TiN, NbTiN thin films in superconducting device applications (e.g. detectors for CMB, mm and sub-mm astronomy). In this work, we have fabricated NbN superconducting thin films by DC reactive magnetron sputtering of Nb in the presence of argon and nitrogen gases. We found that the critical temperature of NbN films is sensitive to various deposition parameters like nitrogen flow rate, target voltage, base pressure, RF substrate bias, and the substrate temperature. By studying each of these factors we have been able to create highly reproducible NbN thin films. We obtained a Tc of 15.25 +/-0.25 K for 300 nm thick NbN film grown on silicon substrate at modest temperature of 250 C in the presence of RF substrate bias. We are also investigating the microwave properties of these NbN films at temperatures well below 50 mK by fabricating quarter wavelength CPW resonators out of NbN and characterizing their frequency shifts and quality factors as functions of temperature and power. In this work we present the results of these analyses. This work was supported by BES-DOE Grant DE-AC02-06CH11357.

  3. Effects of epitaxial structure and processing on electrical characteristics of InAs-based nBn infrared detectors

    NASA Astrophysics Data System (ADS)

    Du, X.; Savich, G. R.; Marozas, B. T.; Wicks, G. W.

    2017-02-01

    The conventional processing of the III-V nBn photodetectors defines mesa devices by etching the contact n-layer and stopping immediately above the barrier, i.e., a shallow etch. This processing enables great suppression of surface leakage currents without having to explore surface passivation techniques. However, devices that are made with this processing scheme are subject to lateral diffusion currents. To address the lateral diffusion current, we compare the effects of different processing approaches and epitaxial structures of nBn detectors. The conventional solution for eliminating lateral diffusion current, a deep etch through the barrier and the absorber, creates increased dark currents and an increased device failure rate. To avoid deep etch processing, a new device structure is proposed, the inverted-nBn structure. By comparing with the conventional nBn structure, the results show that the lateral diffusion current is effectively eliminated in the inverted-nBn structure without elevating the dark currents.

  4. 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.

  5. Nanomechanical properties of NbN films prepared by pulsed laser deposition using nanoindendation

    NASA Astrophysics Data System (ADS)

    Mamun, M. A.; Farha, A. H.; Er, A. O.; Ufuktepe, Y.; Gu, D.; Elsayed-Ali, H. E.; Elmustafa, A. A.

    2012-03-01

    Structural and mechanical properties of niobium nitride thin films deposited by pulsed laser deposition were investigated using X-ray diffraction, atomic force microscopy, and nanoindentation. Niobium nitride was deposited on Si(1 0 0) by pulsed laser deposition (PLD) of Nb in nitrogen background. A Nanoindenter XP equipped with a dynamic contact module (DCM II) head was used in conjunction with the continuous stiffness method (CSM) in depth and load control modes to measure the hardness and modulus of the NbN thin films. NbN film reveals simple cubic δ-NbN structure with the corresponding reflections of (1 1 1), (2 0 0), and (2 2 0) planes. Highly textured NbN film shows a strong (1 1 1) preferred orientation. The NbN thin films depict polycrystalline structure, with a wide range of grain sizes that range from 15 to 40 nm with an average surface roughness of 6 nm. The average modulus of the film is 420 ± 60 GPa, whereas for the substrate the average modulus is 180 GPa, which is considered higher than the average modulus for Si reported in the literature due to pile-up. The hardness of the film increases monotonically from an average of 12 GPa for deep indents (Si substrate) measured using XP CSM and load control (LC) modes to an average of 25 GPa measured using the DCM II head in CSM and LC modules. The average hardness of the Si substrate is 12 GPa.

  6. Materials Study of NbN and Ta x N Thin Films for SNS Josephson Junctions

    DOE PAGES

    Missert, Nancy; Brunke, Lyle; Henry, Michael D.; ...

    2017-02-15

    We investigated properties of NbN and TaxN thin films grown at ambient temperatures on SiO2/Si substrates by reactive-pulsed laser deposition and reactive magnetron sputtering (MS) as a function of N2 gas flow. Both techniques produced films with smooth surfaces, where the surface roughness did not depend on the N2 gas flow during growth. High crystalline quality, (111) oriented NbN films with Tc up to 11 K were produced by both techniques for N contents near 50%. The low temperature transport properties of the TaxN films depended upon both the N2 partial pressure used during growth and the film thickness. Furthermore,more » the root mean square surface roughness of TaxN films grown by MS increased as the film thickness decreased down to 10 nm.« less

  7. Local anodic oxidation of superconducting NbN thin films by an atomic force microscope

    NASA Astrophysics Data System (ADS)

    Y Yang, X.; You, L. X.; Wang, X.; Zhang, L. B.; Kang, L.; Wu, P. H.

    2009-12-01

    A local anodic oxidation technique has been applied to create oxidized nanowires on superconducting NbN thin films using an atomic force microscope (AFM) with a conductive probe. The AFM surface topography shows that both the width and height of the oxidized nanowires increase with increasing applied probe voltage under a certain relative humidity and a probe scan rate. The resistances of the NbN microbridges with and without an oxidized nanowire crossing were measured, and the results indicate that the oxidized nanowires with height of more than 8 nm are fully oxidized. The R-T and I-V characteristics of the NbN microbridges with the oxide wire of less than 8 nm were also obtained and analyzed. Methods for fabricating devices such as superconducting single photon detectors and superconducting hot electron bolometer mixers using this technology are discussed.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  10. 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.

  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. Superconducting fluctuations in a thin NbN film probed by the Hall effect

    NASA Astrophysics Data System (ADS)

    Destraz, Daniel; Ilin, Konstantin; Siegel, Michael; Schilling, Andreas; Chang, Johan

    2017-06-01

    We present a comprehensive study of how superconducting fluctuations in the normal state contribute to the conductivity tensor in a thin (119 Å) film of NbN. It is shown how these fluctuations drive a sign change in the Hall coefficient RH for low magnetic fields near the superconducting transition. The scaling behaviors as a function of distance to the transition ɛ =ln(T /Tc) of the longitudinal (σxx) and transverse (σxy) conductivity are found to be consistent with Gaussian fluctuation theory. Moreover, excellent quantitative agreement between theory and experiment is obtained without any adjustable parameters. Our experimental results thus provide a case study of the conductivity tensor originating from short-lived Cooper pairs.

  14. Anisotropic behaviour of transmission through thin superconducting NbN film in parallel magnetic field

    NASA Astrophysics Data System (ADS)

    Šindler, M.; Tesař, R.; Koláček, J.; Skrbek, L.

    2017-02-01

    Transmission of terahertz waves through a thin layer of the superconductor NbN deposited on an anisotropic R-cut sapphire substrate is studied as a function of temperature in a magnetic field oriented parallel with the sample. A significant difference is found between transmitted intensities of beams linearly polarised parallel with and perpendicular to the direction of applied magnetic field.

  15. 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.

  16. Epitaxial nucleation and growth of molecular films

    NASA Astrophysics Data System (ADS)

    Hooks, Daniel Edwin

    2000-10-01

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

  17. Study of the evolution of the atomic composition of thin NbN films under irradiation with mixed ion beams by methods of electron energy loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Dement'eva, M. M.; Prikhod'ko, K. E.; Gurovich, B. A.; Kutuzov, L. V.; Komarov, D. A.

    2016-11-01

    The variation in the atomic composition of ultrathin NbN films under irradiation by mixed ion beams to a doze of 4 dpa (for nitrogen) is experimentally studied by methods of electron energy loss spectroscopy with a transmission electron microscope in the transmission scan mode on cross-cut samples. The behavior of the substitution of nitrogen atoms by oxygen atoms has been established; it is characterized by changing the composition of the conducting part of the film from NbN to NbNO.

  18. FOURTH SEMINAR TO THE MEMORY OF D.N. KLYSHKO: Superconducting single-photon ultrathin NbN film detector

    NASA Astrophysics Data System (ADS)

    Korneev, A. A.; Minaeva, O. V.; Rubtsova, Inna A.; Milostnaya, I. I.; Chulkova, G. M.; Voronov, B. M.; Smirnov, K. V.; Seleznev, V. A.; Gol'tsman, G. N.; Pearlman, A.; Slysz, W.; Cross, A.; Alvarez, P.; Verevkin, A.; Sobolewski, R.

    2005-08-01

    Superconducting single-photon ultrathin NbN film detectors are studied. The development of manufacturing technology of detectors and the reduction of their operating temperature down to 2 K resulted in a considerable increase in their quantum efficiency, which reached in the visible region (at 0.56 μm) 30%—40%, i.e., achieved the limit determined by the absorption coefficient of the film. The quantum efficiency exponentially decreases with increasing wavelength, being equal to ~20% at 1.55 μm and ~0.02% at 5 μm. For the dark count rate of ~10-4s-1, the experimental equivalent noise power was 1.5×10-20 W Hz-1/2; it can be decreased in the future down to the record low value of 5×10-21 W Hz-1/2. The time resolution of the detector is 30 ps.

  19. Epitaxy of layered semiconductor thin films

    NASA Astrophysics Data System (ADS)

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

    1993-03-01

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

  20. Optical Properties of Epitaxially Grown Silver Films

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  1. Hot-Dipped Metal Films as Epitaxial Substrates

    NASA Technical Reports Server (NTRS)

    Shlichta, P. J.

    1985-01-01

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

  2. Transport properties of epitaxial lift off films

    NASA Technical Reports Server (NTRS)

    Mena, R. A.; Schacham, S. E.; Young, P. G.; Haugland, E. J.; Alterovitz, S. A.

    1993-01-01

    Transport properties of epitaxially lifted-off (ELO) films were characterized using conductivity, Hall, and Shubnikov-de Haas measurements. A 10-15 percent increase in the 2D electron gas concentration was observed in these films as compared with adjacent conventional samples. We believe this result to be caused by a backgating effect produced by a charge build up at the interface of the ELO film and the quartz substrate. This increase results in a substantial decrease in the quantum lifetime in the ELO samples, by 17-30 percent, but without a degradation in carrier mobility. Under persistent photoconductivity, only one subband was populated in the conventional structure, while in the ELO films the population of the second subband was clearly visible. However, the increase of the second subband concentration with increasing excitation is substantially smaller than anticipated due to screening of the backgating effect.

  3. Tailoring the surface chemical bond states of the NbN films by doping Ag: Achieving hard hydrophobic surface

    NASA Astrophysics Data System (ADS)

    Ren, Ping; Zhang, Kan; Du, Suxuan; Meng, Qingnan; He, Xin; Wang, Shuo; Wen, Mao; Zheng, Weitao

    2017-06-01

    Robust hydrophobic surfaces based on ceramics capable of withstanding harsh conditions such as abrasion, erosion and high temperature, are required in a broad range of applications. The metal cations with coordinative saturation or low electronegativity are commonly chosen to achieve the intrinsically hydrophobic ceramic by reducing Lewis acidity, and thus the ceramic systems are limited. In this work, we present a different picture that robust hydrophobic surface with high hardness (≥20 GPa) can be fabricated through doping Ag atoms into intrinsically hydrophilic ceramic film NbN by reactive co-sputtering. The transition of wettability from hydrophilic to hydrophobic of Nb-Ag-N films induced by Ag doping results from the appearance of Ag2O groups on the films surfaces through self-oxidation, because Ag cations (Ag+) in Ag2O are the filled-shell (4d105S0) electronic structure with coordinative saturation that have no tendency to interact with water. The results show that surface Ag2O benefited for hydrophobicity comes from the solute Ag atoms rather than precipitate metal Ag, in which the more Ag atoms incorporated into Nb-sublattice are able to further improve the hydrophobicity, whereas the precipitation of Ag nanoclusters would worsen it. The present work opens a window for fabricating robust hydrophobic surface through tailoring surface chemical bond states by doping Ag into transition metal nitrides.

  4. Epitaxial thick film high-Tc SQUIDs

    NASA Astrophysics Data System (ADS)

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

    2008-02-01

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

  5. 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.

  6. Sequential imposed layer epitaxy of cuprate films

    SciTech Connect

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

    1994-02-01

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

  7. 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)

  8. 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.

  9. Substrate heater for the growth of epitaxial silicon films

    NASA Astrophysics Data System (ADS)

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

    1999-03-01

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

  10. Growth of strontium ruthenate films by hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Marshall, Patrick B.; Kim, Honggyu; Ahadi, Kaveh; Stemmer, Susanne

    2017-09-01

    We report on the growth of epitaxial Sr2RuO4 films using a hybrid molecular beam epitaxy approach in which a volatile precursor containing RuO4 is used to supply ruthenium and oxygen. The use of the precursor overcomes a number of issues encountered in traditional molecular beam epitaxy that uses elemental metal sources. Phase-pure, epitaxial thin films of Sr2RuO4 are obtained. At high substrate temperatures, growth proceeds in a layer-by-layer mode with intensity oscillations observed in reflection high-energy electron diffraction. Films are of high structural quality, as documented by x-ray diffraction, atomic force microscopy, and transmission electron microscopy. The method should be suitable for the growth of other complex oxides containing ruthenium, opening up opportunities to investigate thin films that host rich exotic ground states.

  11. An XPS method for layer profiling of NbN thin films

    NASA Astrophysics Data System (ADS)

    Lubenchenko, A. V.; Batrakov, A. A.; Pavolotsky, A. B.; Krause, S.; Shurkaeva, I. V.; Lubenchenko, O. I.; Ivanov, D. A.

    2016-12-01

    Layer chemical and phase profiling of niobium nitride thin films on a silicon substrate oxidized on air was performed with the help of a method designed by us. The method includes: a new method of background subtraction of multiple inelastically scattered photoelectrons considering depth inhomogeneity of electron inelastic scattering; a new method of photoelectron line decomposition into component peaks considering physical nature of different decomposition parameters; joint solution of the background subtraction and photoelectron line decomposition problems; control of line decomposition accuracy with the help of a suggested performance criterion; calculation of layer thicknesses for a multilayer target using a simple formula.

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

    NASA Astrophysics Data System (ADS)

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

    1989-03-01

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

  13. Epitaxial patterning of thin-films: conventional lithographies and beyond

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Krishnan, Kannan M.

    2014-09-01

    Thin-film based novel magnetic and electronic devices have entered a new era in which the film crystallography, structural coherence, and epitaxy play important roles in determining their functional properties. The capabilities of controlling such structural and functional properties are being continuously developed by various physical deposition technologies. Epitaxial patterning strategies further allow the miniaturization of such novel devices, which incorporates thin-film components into nanoscale architectures while keeping their functional properties unmodified from their ideal single-crystal values. In the past decade, epitaxial patterning methods on the laboratory scale have been reported to meet distinct scientific inquires, in which the techniques and processes used differ from one to the other. In this review we summarize many of these pioneering endeavors in epitaxial patterning of thin-film devices that use both conventional and novel lithography techniques. These methods demonstrate epitaxial patterning for a broad range of materials (metals, oxides, and semiconductors) and cover common device length scales from micrometer to sub-hundred nanometer. Whilst we have been motivated by magnetic materials and devices, we present our outlook on developing systematic-strategies for epitaxial patterning of functional materials which will pave the road for the design, discovery and industrialization of next-generation advanced magnetic and electronic nano-devices.

  14. Terahertz Mixing Characteristics of NbN Superconducting Tunnel Junctions and Related Astronomical Observations

    NASA Astrophysics Data System (ADS)

    Li, J.

    2010-01-01

    High-sensitivity superconducting SIS (superconductor-insulator-superconductor) mixers are playing an increasingly important role in the terahertz (THz) astronomical observation, which is an emerging research frontier in modern astrophysics. Superconducting SIS mixers with niobium (Nb) tunnel junctions have reached a sensitivity close to the quantum limit, but have a frequency limit about 0.7 THz (i.e., gap frequency of Nb tunnel junctions). Beyond this frequency Nb superconducting films will absorb energetic photons (i.e., energy loss) to break Cooper pairs, thereby resulting in significant degradation of the mixer performance. Therefore, it is of particular interest to develop THz superconducting SIS mixers incorporating tunnel junctions with a larger energy gap. Niobium-nitride (NbN) superconducting tunnel junctions have been long known for their large energy gap, almost double that of Nb ones. With the introduction of epitaxially grown NbN films, the fabrication technology of NbN superconducting tunnel junctions has been considerably improved in the recent years. Nevertheless, their performances are still not as good as Nb ones, and furthermore they are not yet demonstrated in real astronomical applications. Given the facts mentioned above, in this paper we systematically study the quantum mixing behaviors of NbN superconducting tunnel junctions in the THz regime and demonstrate an astronomical testing observation with a 0.5 THz superconducting SIS mixer developed with NbN tunnel junctions. The main results of this study include: (1) successful design and fabrication of a 0.4˜0.6 THz waveguide mixing circuit with the high-dielectric-constant MgO substrate; (2) successful fabrication of NbN superconducting tunnel junctions with the gap voltage reaching 5.6 mV and the quality factor as high as 15; (3) demonstration of a 0.5 THz waveguide NbN superconducting SIS mixer with a measured receiver noise temperature (no correction) as low as five times the quantum limit

  15. Seed layer technique for high quality epitaxial manganite films.

    PubMed

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

    2016-08-01

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

  16. 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.

  17. 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

  18. Experimental Evidence for Epitaxial Silicene on Diboride Thin Films

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  19. High quality thick epitaxial films for power semiconductor devices

    NASA Astrophysics Data System (ADS)

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

    1986-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-10-01

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

  1. 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.

  2. 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.

  3. Magnetic Nanostructures by Adaptive Twinning in Strained Epitaxial Films

    NASA Astrophysics Data System (ADS)

    Kauffmann-Weiss, Sandra; Gruner, Markus E.; Backen, Anja; Schultz, Ludwig; Entel, Peter; Fähler, Sebastian

    2011-11-01

    We exploit the intrinsic structural instability of the Fe70Pd30 magnetic shape memory alloy to obtain functional epitaxial films exhibiting a self-organized nanostructure. We demonstrate that coherent epitaxial straining by 54% is possible. The combination of thin film experiments and large-scale first-principles calculations enables us to establish a lattice relaxation mechanism, which is not expected for stable materials. We identify a low twin boundary energy compared to a high elastic energy as key prerequisite for the adaptive nanotwinning. Our approach is versatile as it allows to control both, nanostructure and intrinsic properties for ferromagnetic, ferroelastic, and ferroelectric materials.

  4. Polydomain structures in ferroelectric and ferroelastic epitaxial films

    NASA Astrophysics Data System (ADS)

    Roytburd, Alexander L.; Ouyang, Jun; Artemev, Andrei

    2017-04-01

    A review of theoretical models, phase field modeling and experimental studies of domain structures in epitaxial films is presented. The thermodynamic theory of such domain structures is presented within the macroscopic thermo-mechanical framework. The theory allows for the evaluation of the main parameters of the domain structure using the energy minimization approach applied to the energy of elastic interactions. For homophase (polytwin) films, the thermodynamic theory provides a quantitative tool that can be used to estimate domain fractions in the film and the type of domain structure architecture. For heterophase films, the theory describes (a) the conditions under which two-phase structures can be obtained in epitaxial films, and (b) the phase and domain fractions in these films. The thermodynamic theory can also be used to describe the extrinsic contributions from domain structures to the functional properties of epitaxial ferroelectric films. The review of phase field modeling demonstrates that computational results reproduce the predictions of the thermodynamic theory. It is also shown that the phase field modeling that utilizes the energy minimization procedure for elastic and interfacial energies can be used to predict domain morphology for the films with two-phase structures produced either by phase transformation or through the co-deposition of immiscible phases. The experimental data presented in the review validate predictions of the thermodynamic model and the results of phase field modeling.

  5. 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.

  6. Nanoscale electrical properties of epitaxial Cu3Ge film.

    PubMed

    Wu, Fan; Cai, Wei; Gao, Jia; Loo, Yueh-Lin; Yao, Nan

    2016-07-01

    Cu3Ge has been pursued as next-generation interconnection/contact material due to its high thermal stability, low bulk resistivity and diffusion barrier property. Improvements in electrical performance and structure of Cu3Ge have attracted great attention in the past decades. Despite the remarkable progress in Cu3Ge fabrication on various substrates by different deposition methods, polycrystalline films with excess Ge were frequently obtained. Moreover, the characterization of nanoscale electrical properties remains challenging. Here we show the fabrication of epitaxial Cu3Ge thin film and its nanoscale electrical properties, which are directly correlated with localized film microstructures and supported by HRTEM observations. The average resistivity and work function of epitaxial Cu3Ge thin film are measured to be 6 ± 1 μΩ cm and ~4.47 ± 0.02 eV respectively, qualifying it as a good alternative to Cu.

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

    SciTech Connect

    Paranin, V. D.

    2016-04-13

    In work we investigated yttrium iron garnet epitaxial films with a thickness of 10 µm and 55 µm which were grown on the surface of garnet substrate. Using the polarizing microscopy method the branching domain structure of films was shown with the period of domains 21.5 µm and 42.5 µm. Disappearance of domains at presence of an external magnetic field up to 100 Oe was noted. The optical transmission of films for the polarized beam of HeNe laser is investigated and zero diffraction order and odd diffraction rings orders were shown. Interconnection of the period of chaotically oriented domains with angles of axially symmetric diffraction rings orders was shown. Diffraction patterns at various longitudinal magnetic fields are investigated. Disappearance of odd diffraction orders and increasing in intensity of zero diffraction order were fixed. Optical transmission of epitaxial films was measured in range of 500 - 900 nm.

  8. 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

  9. 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.

  10. Enhanced Luminescence in Epitaxial Oxide Thin-Film Phosphors

    SciTech Connect

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

    1999-11-08

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

  11. Measurement of magnetostriction coefficients of epitaxial garnet films.

    PubMed

    Vella-Coleiro, G P

    1979-09-01

    A technique for measuring the magnetostriction coefficients of epitaxial garnet films on 50-mm-diam wafers is described. The measurement is based on the shift of the microwave ferrimagnetic resonance produced by stressing the film, which is achieved by supporting the wafer around its circumference and reducing the atmospheric pressure on one side. A simple, nonresonant transmission microwave spectrometer which is well suited for measurements on large wafers is also described.

  12. 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

  13. 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.

  14. Strong circular photogalvanic effect in ZnO epitaxial films

    SciTech Connect

    Zhang, Q.; Wang, X. Q.; Yin, C. M.; Shen, B.; Chen, Y. H.; Chang, K.; Ge, W. K.

    2011-12-23

    A strong circular photogalvanic effect (CPGE) in ZnO epitaxial films was reported under interband excitation. It was observed that CPGE current is as large as 100 nA/W in ZnO, which is about one order in magnitude higher than that in InN film while the CPGE currents in GaN films are not detectable. The possible reasons for the above observations are the strong spin orbit coupling in ZnO or the inversed valence band structure of ZnO.

  15. Strong circular photogalvanic effect in ZnO epitaxial films

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Wang, X. Q.; Yin, C. M.; Shen, B.; Chen, Y. H.; Chang, K.; Ge, W. K.

    2011-12-01

    A strong circular photogalvanic effect (CPGE) in ZnO epitaxial films was reported under interband excitation. It was observed that CPGE current is as large as 100 nA/W in ZnO, which is about one order in magnitude higher than that in InN film while the CPGE currents in GaN films are not detectable. The possible reasons for the above observations are the strong spin orbit coupling in ZnO or the inversed valence band structure of ZnO.

  16. Strong circular photogalvanic effect in ZnO epitaxial films

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Wang, X. Q.; Yin, C. M.; Xu, F. J.; Tang, N.; Shen, B.; Chen, Y. H.; Chang, K.; Ge, W. K.; Ishitani, Y.; Yoshikawa, A.

    2010-07-01

    We report a strong circular photogalvanic effect (CPGE) in ZnO epitaxial films under interband excitation. It is observed that CPGE current is as large as 100 nA/W in ZnO, which is about one order in magnitude higher than that in InN film while the CPGE currents in GaN films are not detectable. The possible reasons for the above observations are the strong spin orbit coupling in ZnO or the inversed valence band structure of ZnO.

  17. 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.

  18. 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.

  19. Epitaxial growth of high quality WO3 thin films

    DOE PAGES

    Leng, X.; Pereiro, J.; Strle, J.; ...

    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.

  20. Substrate Preparations in Epitaxial ZnO Film Growth

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  1. Stress control of reactively sputtered thick NbN film on Si wafer changing the location of the substrate Si wafer against the Nb target on a magnetron cathode

    NASA Astrophysics Data System (ADS)

    Suzuki, Y.; Iguchi, N.; Adachi, K.; Hioki, T.; Ichiki, A.; Hsu, C.-W.; Kumagai, S.; Sasaki, M.; Motohiro, T.

    2017-07-01

    We have been developing a superconducting NbN thin film coil in a spiral trench on a Si-wafer using MEMS technology. Connecting the coils on the different wafers using waferbonding process, a cylindrical wafer stack is to be formed as a unit of a compact SMES. The critical current density of our NbN film was measured to be around 1100 A/mm2. We measured critical current I c of 47 mA for the previously fabricated coil of the film thickness t f = 0.5 μm. I c in the spiral coil increases with t f. However, if we make the NbN film thicker, the film is apt to have higher lateral force caused by tensile or compressive stress which can cause peeling of the film from the Si substrate. It is well known that the stress of the sputtered thin films can be controlled from tensile to compressive stress by controlling the bombardment of high energy particles including argon atoms backscattered from the target surface. Based on this knowledge, a specially designed sputter-deposition apparatus was fabricated in which the substrate can be located not only at the different target-to-substrate distances but also at several different lateral distances from the central axis of the target (off-axis lateral shift). Using this apparatus, various stress conditions could be realized which contributed to fabrication of thick NbN film spiral coil in the trench. The film stress was calculated from bending analysis of the substrate Si wafer by stylus method using Stoney’s formula. The maximum compressive stress of 2.5 GPa was measured. By an off-axis lateral shift, t f could be increased from 0.5 to 1 μm. By increasing sputtering gas pressure from 0.7 to 2 Pa, the compressive stress could be mitigated and t f could be further increased from 1.0 to 3 μm. Up to now, we measured I c of 220 mA for a NbN spiral coil at t f around 3 μm. More detailed adjustment of the deposition condition will bring further increase in t f, and hence I c into sight.

  2. Study of zinc oxide epitaxial film growth and UV photodetectors

    NASA Astrophysics Data System (ADS)

    Nahhas, Ahmed Mohammed

    ZnO is a versatile material, and has been extensively studied for various applications such as varistors, transducers, transparent conducting electrodes, sensors, and catalysts. While polycrystalline ZnO is commonly used in these conventional applications, there has been a growing interest in obtaining single-crystalline ZnO films on various substrates. ZnO is a II-VI wide bandgap semiconductor with a relatively large exciton binding energy, and holds a potential for light emitting/detecting or nonlinear optical devices in the UV range. ZnO is isomorphic to wurtzite GaN with good lattice match, and therefore there has been a great deal of interest in using ZnO as a buffer layer or a substrate in growing high quality GaN films (or vice versa ZnO growth on GaN). In this study, we have investigated epitaxial growth of ZnO films on sapphire and silicon substrates. High quality epitaxial ZnO films were grown on sapphire (0001) single crystal substrates using a rf magnetron sputtering technique. X-ray diffraction analysis shows that the ZnO films are of a monocrystalline wurtzite structure with their epitaxial relationship of ZnO[0001]//sapphire[0001] along the growth direction and ZnO[112&barbelow;0]//sapphire[11&barbelow;00] along the in-plane direction. ZnO on Si also offers an interesting opportunity that the various functional properties of ZnO can be combined with the advanced Si electronics on the same substrate. Direct growth of epitaxial ZnO on Si, however, is known to be an extremely difficult task due to the oxidation problem during the nucleation stage of a ZnO growth process. We have overcome this problem by introducing an epitaxial GaN buffer layer, and have successfully grown epitaxial ZnO films on Si(111) substrates. X-ray diffraction analysis confirms an epitaxial relationship of ZnO[0001]//GaN[0001]//Si[111] along the growth direction and ZnO[112&barbelow;0]//GaN[112&barbelow;0]//Si[11&barbelow;0] along the in-plane direction. As an application of the

  3. Gradient bounds for a thin film epitaxy equation

    NASA Astrophysics Data System (ADS)

    Li, Dong; Qiao, Zhonghua; Tang, Tao

    2017-02-01

    We consider a gradient flow modeling the epitaxial growth of thin films with slope selection. The surface height profile satisfies a nonlinear diffusion equation with biharmonic dissipation. We establish optimal local and global wellposedness for initial data with critical regularity. To understand the mechanism of slope selection and the dependence on the dissipation coefficient, we exhibit several lower and upper bounds for the gradient of the solution in physical dimensions d ≤ 3.

  4. Robust surface states in epitaxial Bi(111) thin films

    NASA Astrophysics Data System (ADS)

    Zhu, Kai; Jin, Xiaofeng

    Bulk Bi a prototype semimetal with trivial electronic band topology. Unanticipatedly, we show the Altshuler-Aronov-Spivak and Aharonov-Bohm effects in epitaxial Bi(111) thin films. Meanwhile, we clearly identify the interaction of the top and bottom surface states via quantum tunneling by the electrical conductance and weak anti-localization measurements. These results have significantly enriched our understanding about the electronic structure of Bi, which might be helpful for clearing up some of its longstanding subtle issues.

  5. Continuum elasticity modeling of nanostructure evolution in strained film epitaxy

    NASA Astrophysics Data System (ADS)

    Gamage, Champika G.

    The formation of surface nanostructures such as islands or quantum dots during strained film epitaxy has attracted great interest in recent years. The underlying mechanisms have been attributed to the occurrence of morphological instabilities of the strained films, for which the coupling between film-substrate material properties and growth conditions play a major role. Morphological properties of an epitaxially grown film and the self-organization process of coherent strained islands are analyzed via the development of a continuum elasticity model based on the 2nd order perturbation method. Effects of wetting stress due to film-substrate interactions have been incorporated in the resulting nonlinear dynamic equation governing the film morphological profile. We study the formation and evolution of surface strained islands or quantum dots for different film/substrate misfit strains, via analyzing the time-dependent behavior of the structure factor for surface heights, its various moments, and the surface roughness. Three regimes of island array evolution have been identified, including a film instability regime at early stage, a slow power-law-type coarsening at intermediate time, and the crossover to a saturated state, with detailed behavior dependent on misfit strains but not qualitatively on finite system sizes. It is found to be controlled by the strength of film-substrate wetting interaction which would constrain the valley-to-peak mass transport and hence the growth of island height, and also determined by the effect of elastic interaction between surface islands and the high-order strain energy of individual islands at late evolution stage. The results are compared to previous experimental and theoretical efforts on quantum dots coarsening and saturation. We also study the formation of these nanostructures on a nonplanar patterned substrate. The properties of islands formed are highly affected and controlled by the periodicity and amplitude of the pre

  6. Ultrafast transient reflectance of epitaxial semiconducting perovskite thin films

    NASA Astrophysics Data System (ADS)

    Smolin, S. Y.; Scafetta, M. D.; Guglietta, G. W.; Baxter, J. B.; May, S. J.

    2014-07-01

    Ultrafast pump-probe transient reflectance (TR) spectroscopy was used to study carrier dynamics in an epitaxial perovskite oxide thin film of LaFeO3 (LFO) with a thickness of 40 unit cells (16 nm) grown by molecular beam epitaxy on (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT). TR spectroscopy shows two negative transients in reflectance with local maxima at ˜2.5 eV and ˜3.5 eV which correspond to two optical transitions in LFO as determined by ellipsometry. The kinetics at these transients were best fit with an exponential decay model with fast (5-40 ps), medium (˜200 ps), and slow (˜ 3 ns) components that we attribute mainly to recombination of photoexcited carriers. Moreover, these reflectance transients did not completely decay within the observable time window, indicating that ˜10% of photoexcited carriers exist for at least 3 ns. This work illustrates that TR spectroscopy can be performed on thin (<20 nm) epitaxial oxide films to provide a quantitative understanding of recombination lifetimes, which are important parameters for the potential utilization of perovskite films in photovoltaic and photocatalytic applications.

  7. Optically transparent and electrically conducting epitaxial Ta2O films

    NASA Astrophysics Data System (ADS)

    Gnanarajan, S.; Lam, S. K. H.; Foley, C. P.

    2007-03-01

    An optically transparent and electrically conducting oxide Ta2O epitaxial thin film has been fabricated and characterized. In our experiments, we grew epitaxial Ta films on r-cut sapphire crystal substrates, which were subsequently oxidized into Ta2O films. The x-ray θ-2θ scan peaks match the American Society for Testing and Materials x-ray powder data card for Ta2O (18-1302) with a cubic structure. The x-ray photoelectron spectroscopic measurements indicated Ta 4f peak energy values between those for Ta and TaO whereas the O /Ta atomic ratio is between 0.5 and 1. Resistivity-temperature measurements showed a metallic behavior with resistivity values in the range of (1.5-3.3)×10-4Ωcm at 293K. Optical measurements on 25-100nm thick films indicated that they are transparent in the range of 400-2000nm and have an energy band gap between 2.04 and 2.17eV. The Hall mobility and carrier density of the films were in the range of 62-110cm2V-1s-1 and (1.9-3.0)×1020cm-3, respectively.

  8. 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.

  9. Effect of the Film-Growth Defects on the Magnetic Microstructure of Epitaxial FePt Thin Film.

    PubMed

    Lee, W H; Yoo, J H; Yang, J M; Park, J K

    2015-11-01

    Effect of the columnar grain boundaries on the perpendicular magnetic domain structure of epitaxial L10 FePt (001) thin film has been studied using electron holography. The analysis of stray fields shows that both the continuous and columnar epitaxial films of L10 FePt (001) consist of perpendicular magnetic domain walls. In the columnar epitaxial film, however, the perpendicular domain walls tend to be confined to columnar grain boundaries, because columnar boundaries act as pinning sites for the domain walls. The domain wall pinning by columnar grain boundaries leads to a significant hysteresis effect in the perpendicular magnetization of L10 FePt epitaxial films.

  10. A study on the epitaxial Bi2Se3 thin film grown by vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Lin, Yen-Cheng; Chen, Yu-Sung; Lee, Chao-Chun; Wu, Jen-Kai; Lee, Hsin-Yen; Liang, Chi-Te; Chang, Yuan Huei

    2016-06-01

    We report the growth of high quality Bi2Se3 thin films on Al2O3 substrates by using chemical vapor deposition. From the atomic force microscope, x-ray diffraction and transmission electron microscope measurements we found that the films are of good crystalline quality, have two distinct domains and can be grown epitaxially on the Al2O3 substrate. Carrier concentration in the sample is found to be 1.1 × 1019 cm-3 between T = 2 K to T = 300 K, and electron mobility can reach 954 cm2/V s at T = 2 K. Weak anti-localization effect is observed in the low temperature magneto-transport measurement for the sample which indicates that the thin film has topological surface state.

  11. 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.

  12. Antiferromagnetic domains in epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Scholl, Andreas

    2002-03-01

    Interface and surface effects play a central role in modern magnet structures. Magnetic exchange coupling and bias, spin injection across the boundary between magnetic and non-magnetic layers, and the surface and interface anisotropy in multilayers are examples for interface phenomena that are utilized in magneto-electronics. In particular, the microscopic origin of exchange bias at ferromagnet/antiferromagnet interfaces is still an unsolved problem despite of intense research, driven by the important application of exchange bias in hard disk read-heads and magnetic RAM. Knowledge of the microscopic magnetic structure in antiferromagnetic thin films and surfaces is of crucial importance for a better understanding of the exchange bias effect. Microscopic experiments on magnetically coupled ferromagnet/antiferromagnet layers using X-ray Photoemission Electron Microscopy (X-PEEM) now provide a new insight into the microscopic processes at this important interface. Using a combination of x-ray magnetic dichroism (XMD) contrast and microscopic electron yield detection we have resolved the magnetic domain structure in LaFeO3 and NiO thin films and crystals. The antiferromagnetic domain structure is linked to the crystallographic structure of the material and vanishes approaching the magnetic ordering temperature. Ferromagnetic films grown on the antiferromagnetic substrate show a corresponding ferromagnetic domain structure, an uniaxial exchange anistropy and a local bias which increases with decreasing domain size, suggesting a statistical origin of the bias effect. The role of uncompensated interface spins will also be discussed. We will present first experiments on magnetic interlayer coupling across metallic antiferromagnets, which suggest a similar origin of bias in full-metallic exchange bias system. A. Scholl et al., Science 287, 1014 (2000), F. Nolting et al., Nature 405, 767 (2000), H. Ohldag et al., Phys. Rev. Lett. 86, 2878 (2001)

  13. 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.

  14. Epitaxies of chain compounds on monocrystalline polymer films

    SciTech Connect

    Kawaguchi, A.

    1993-12-31

    Various kinds of compounds with normal long hydrocarbon chain(s) were crystallized on the polyethylene (PE) substrate, whose surface was crystallographically well-defined. Their crystals grew in such an oriented way that the crystallographic plane of their subcells, which corresponded to that of the PE substrate surface, was in contact with the substrate surface. When isotactic polypropylene (iPP) and linear low density PE melt films were coupled and solidified from the side of iPP by cooling, a transparent PE-laminated iPP film was produced. When polyvinylcyclohexane was blended on the molecular level in iPP, it acted as a nucleating agent to give rise to a highly transparent iPP film. These textures are related to the epitaxy between the substrate and crystals grown on it. This paper will discuss their overgrowth mechanisms.

  15. Epitaxial Electrodeposition of Chiral Metal Oxide Films

    NASA Astrophysics Data System (ADS)

    Switzer, Jay

    2006-03-01

    Chirality is ubiquitous in Nature. One enantiomer of a molecule is often physiologically active, while the other enantiomer may be either inactive or toxic. Chiral surfaces offer the possibility of developing heterogeneous enantiospecific catalysts that can more readily be separated from the products and reused. Chiral surfaces might also serve as electrochemical sensors for chiral molecules- perhaps even implantable chiral sensors that could be used to monitor drug levels in the body. Our trick to produce chiral surfaces is to electrodeposit low symmetry metal oxide films with chiral orientations on achiral substrates (see, Nature 425, 490, 2003). The relationship between three-dimensional and two-dimensional chirality will be discussed. Chiral surfaces lack mirror or glide plane symmetry. It is possible to produce chiral surfaces of materials which do not crystallize in chiral space groups. We have deposited chiral orientations of achiral CuO onto single-crystal Au and Cu using both tartaric acid and the amino acids alanine and valine to control the handedness of the electrodeposited films. We will present results on the chiral recognition of molecules such as tartaric or malic acid and L-dopa on the chiral electrodeposited CuO. Initial work on the electrochemical biomineralization of chiral nanostructures of calcite will also be discussed.

  16. 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.

  17. Graphene Substrate for van der Waals Epitaxy of Layer-Structured Bismuth Antimony Telluride Thermoelectric Film.

    PubMed

    Kim, Eun Sung; Hwang, Jae-Yeol; Lee, Kyu Hyoung; Ohta, Hiromichi; Lee, Young Hee; Kim, Sung Wng

    2017-02-01

    Graphene as a substrate for the van der Waals epitaxy of 2D layered materials is utilized for the epitaxial growth of a layer-structured thermoelectric film. Van der Waals epitaxial Bi0.5 Sb1.5 Te3 film on graphene synthesized via a simple and scalable fabrication method exhibits good crystallinity and high thermoelectric transport properties comparable to single crystals.

  18. Different spin relaxation mechanisms between epitaxial and polycrystalline Ta thin films

    NASA Astrophysics Data System (ADS)

    Gamou, Hiromu; Ryu, Jeongchun; Kohda, Makoto; Nitta, Junsaku

    2017-02-01

    We demonstrate that spin relaxation mechanisms are different between epitaxial Ta and disordered polycrystalline Ta thin films by determining the relationship between spin relaxation time and diffusion constant. To control the diffusion constant, epitaxial Ta and polycrystalline Ta thin films are prepared by sputtering on different substrates and at different growth temperatures. The spin relaxation time is extracted from the results of weak antilocalization analysis including the superconducting fluctuation effect. The dominant spin relaxation mechanism for polycrystalline Ta thin films is the Elliot–Yafet mechanism, as is expected for centrosymmetric metal films. In contrast, the D’yakonov–Perel’ mechanism plays a role in epitaxial Ta thin films.

  19. Single-domain epitaxial silicene on diboride thin films

    SciTech Connect

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

    2016-04-11

    Epitaxial silicene, which forms spontaneously on ZrB{sub 2}(0001) thin films grown on Si(111) wafers, has a periodic stripe domain structure. By adsorbing additional Si atoms on this surface, we find that the domain boundaries vanish, and a single-domain silicene sheet can be prepared without altering its buckled honeycomb structure. The amount of Si required to induce this change suggests that the domain boundaries are made of a local distortion of the silicene honeycomb lattice. The realization of a single domain sheet with structural and electronic properties close to those of the original striped state demonstrates the high structural flexibility of silicene.

  20. Single-domain epitaxial silicene on diboride thin films

    DOE PAGES

    Fleurence, A.; Gill, T. G.; Friedlein, R.; ...

    2016-04-12

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

  1. Single-domain epitaxial silicene on diboride thin films

    SciTech Connect

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

    2016-04-12

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

  2. 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.

  3. Mobility enhanced photoactivity in sol-gel grown epitaxial anatase TiO2 films.

    PubMed

    Jung, Hyun Suk; Lee, Jung-Kun; Lee, Jaegab; Kang, Bo Soo; Jia, Quanxi; Nastasi, Michael; Noh, Jun Hong; Cho, Chin-Moo; Yoon, Sung Hoon

    2008-03-18

    Epitaxial anatase thin films were grown on single-crystal LaAlO3 substrates by a sol-gel process. The epitaxial relationship between TiO2 and LaAlO3 was found to be [100]TiO2||[100]LaAlO3 and (001)TiO2||(001)LaAlO3 based on X-ray diffraction and a high-resolution transmission electron microscopy. The epitaxial anatase films show significantly improved photocatalytic properties, compared with polycrystalline anatase film on fused silica substrate. The increase in the photocatalytic activity of epitaxial anatase films is explained by enhanced charge carrier mobility, which is traced to the decreased grain boundary density in the epitaxial anatase film.

  4. Piezomagnetism in Epitaxial Cr2O3 Thin Films

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Sahoo, Sarbeswar; Binek, Christian

    2007-03-01

    Recently, the magnetoelectric material Cr2O3 attracted renewed interest due to its potential for future spintronics applications which can be realized by novel magnetic thin film heterostructures [1]. Here we study thin films of Cr2O3 (111) on c-Al2O3 (111) substrate which are grown by thermal evaporation of Cr metal in an O2 atmosphere. X-ray diffraction data reveal stoichiometric epitaxially grown Cr2O3 (111) films. Owing to a lattice mismatch of ˜4% at the interface between the Al2O3 substrate and the film we observe a strong stress induced piezomagnetic moment in the Cr2O3 film. We measure the temperature dependence of this piezomoment by Superconducting Quantum Interference Device (SQUID) magnetometry and Kerr rotation. The presence of high inherent stress, a significant piezomagnetic moment and the possibility to realize high electric fields makes our Cr2O3 thin films ideal candidates for the challenging quest of the symmetry allowed but hitherto undiscovered piezomagnetoelectric effect. [1] Ch. Binek, B. Doudin, J. Phys. Condens. Matter 17, L39 (2005).

  5. 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

  6. Reversible metal-hydride phase transformation in epitaxial films

    NASA Astrophysics Data System (ADS)

    Roytburd, Alexander L.; Boyerinas, Brad M.; Bruck, Hugh A.

    2015-03-01

    Metal-hydride phase transformations in solids commonly proceed with hysteresis. The extrinsic component of hysteresis is the result of the dissipation of energy of internal stress due to plastic deformation and fracture. It can be mitigated on the nanoscale, where plastic deformation and fracture are suppressed and the transformation proceeds through formation and evolution of coherent phases. However, the phase coherency introduces intrinsic thermodynamic hysteresis, preventing reversible transformation. In this paper, it is shown that thermodynamic hysteresis of coherent metal-hydride transformation can be eliminated in epitaxial film due to substrate constraint. Film-substrate interaction leads to formation of heterophase polydomain nanostructure with variable phase fraction which can change reversibly by varying temperature in a closed system or chemical potential in an open system.

  7. Reversible metal-hydride phase transformation in epitaxial films.

    PubMed

    Roytburd, Alexander L; Boyerinas, Brad M; Bruck, Hugh A

    2015-03-11

    Metal-hydride phase transformations in solids commonly proceed with hysteresis. The extrinsic component of hysteresis is the result of the dissipation of energy of internal stress due to plastic deformation and fracture. It can be mitigated on the nanoscale, where plastic deformation and fracture are suppressed and the transformation proceeds through formation and evolution of coherent phases. However, the phase coherency introduces intrinsic thermodynamic hysteresis, preventing reversible transformation. In this paper, it is shown that thermodynamic hysteresis of coherent metal-hydride transformation can be eliminated in epitaxial film due to substrate constraint. Film-substrate interaction leads to formation of heterophase polydomain nanostructure with variable phase fraction which can change reversibly by varying temperature in a closed system or chemical potential in an open system.

  8. Spin Filtering in Epitaxial Spinel Films with Nanoscale Phase Separation.

    PubMed

    Li, Peng; Xia, Chuan; Li, Jun; Zhu, Zhiyong; Wen, Yan; Zhang, Qiang; Zhang, Junwei; Peng, Yong; Alshareef, Husam N; Zhang, Xixiang

    2017-05-23

    The coexistence of ferromagnetic metallic phase and antiferromagnetic insulating phase in nanoscaled inhomogeneous perovskite oxides accounts for the colossal magnetoresistance. Although the model of spin-polarized electron transport across antiphase boundaries has been commonly employed to account for large magnetoresistance (MR) in ferrites, the magnetic anomalies, the two magnetic phases and enhanced molecular moment, are still unresolved. We observed a sizable MR in epitaxial spinel films (NiCo2O4-δ) that is much larger than that commonly observed in spinel ferrites. Detailed analysis reveals that this MR can be attributed to phase separation, in which the perfect ferrimagnetic metallic phase and ferrimagnetic insulating phase coexist. The magnetic insulating phase plays an important role in spin filtering in these phase separated spinel oxides, leading to a sizable MR effect. A spin filtering model based on Zeeman effect and direct tunneling is developed to account for MR of the phase separated films.

  9. 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.

  10. Epitaxial growth of pentacene films on Cu110.

    PubMed

    Söhnchen, S; Lukas, S; Witte, G

    2004-07-01

    The molecular structure of thin pentacene (C(22)H(14)) films grown on a Cu(110) surface has been studied by means of He atom scattering, low energy electron diffraction, thermal desorption spectroscopy, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy. Depending on the actual film thickness three different crystalline phases have been identified which reveal a characteristic reorientation of the molecular plane relative to the substrate surface. In the monolayer regime the molecules form a highly ordered commensurate (6.5x2) structure with a planar adsorption geometry. For thin multilayers (thickness <2 nm) a second phase is observed which is characterized by a lateral ((-0.65 5.69) ( 1.90 1.37)) structure and a tilting of the molecular plane of about 28 degrees around their long axis which remains parallel to the surface. Finally, when exceeding a thickness of about 2 nm subsequent growth proceeds with an upright molecular orientation and leads to the formation of crystalline films which are epitaxially oriented with respect to the substrate. The present study thus demonstrates that also on metal substrates highly ordered pentacene films with an upright orientation of the molecular planes can be grown. Photoelectron spectroscopy data indicate further that thick films do not grow in a layer-by-layer mode but reveal a significant degree of roughness. (c) 2004 American Institute of Physics.

  11. Topological insulator film growth by molecular beam epitaxy: A review

    SciTech Connect

    Ginley, Theresa P.; Wang, Yong; Law, Stephanie

    2016-11-23

    In this article, we will review recent progress in the growth of topological insulator (TI) thin films by molecular beam epitaxy (MBE). The materials we focus on are the V2-VI3 family of TIs. These materials are ideally bulk insulating with surface states housing Dirac excitations which are spin-momentum locked. These surface states are interesting for fundamental physics studies (such as the search for Majorana fermions) as well as applications in spintronics and other fields. However, the majority of TI films and bulk crystals exhibit significant bulk conductivity, which obscures these states. In addition, many TI films have a high defect density. This review will discuss progress in reducing the bulk conductivity while increasing the crystal quality. We will describe in detail how growth parameters, substrate choice, and growth technique influence the resulting TI film properties for binary and ternary TIs. We then give an overview of progress in the growth of TI heterostructures. Furthermore, we close by discussing the bright future for TI film growth by MBE.

  12. Topological insulator film growth by molecular beam epitaxy: A review

    DOE PAGES

    Ginley, Theresa P.; Wang, Yong; Law, Stephanie

    2016-11-23

    In this article, we will review recent progress in the growth of topological insulator (TI) thin films by molecular beam epitaxy (MBE). The materials we focus on are the V2-VI3 family of TIs. These materials are ideally bulk insulating with surface states housing Dirac excitations which are spin-momentum locked. These surface states are interesting for fundamental physics studies (such as the search for Majorana fermions) as well as applications in spintronics and other fields. However, the majority of TI films and bulk crystals exhibit significant bulk conductivity, which obscures these states. In addition, many TI films have a high defectmore » density. This review will discuss progress in reducing the bulk conductivity while increasing the crystal quality. We will describe in detail how growth parameters, substrate choice, and growth technique influence the resulting TI film properties for binary and ternary TIs. We then give an overview of progress in the growth of TI heterostructures. Furthermore, we close by discussing the bright future for TI film growth by MBE.« less

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  14. Thermoelectric properties of epitaxial β-FeSi2 thin films grown on Si(111) substrates with various film qualities

    NASA Astrophysics Data System (ADS)

    Watanabe, Kentaro; Taniguchi, Tatsuhiko; Sakane, Shunya; Aoki, Shunsuke; Suzuki, Takeyuki; Fujita, Takeshi; Nakamura, Yoshiaki

    2017-05-01

    Si-based epitaxial β-FeSi2 thin films are attractive as materials for on-chip thermoelectric power generators. We investigated the structure, crystallinity, and thermoelectric properties of β-FeSi2 thin films epitaxially grown on Si(111) substrates by using three different techniques: conventional reactive deposition epitaxy followed by molecular beam epitaxy (RDE+MBE), solid phase epitaxy (SPE) based on codeposition of Fe and Si presented previously, and SPE followed by MBE (SPE+MBE) presented newly by this work. Their epitaxial growth temperatures were fixed at 530 °C for comparison. RDE+MBE thin films exhibited high crystalline quality, but rough surfaces and rugged β-FeSi2/Si(111) interfaces. On the other hand, SPE thin films showed flat surfaces and abrupt β-FeSi2/Si(111) interfaces but low crystallinity. We found that SPE+MBE thin films realized crystallinity higher than SPE thin films, and also had flatter surfaces and sharper interfaces than RDE+MBE thin films. In SPE+MBE thin film growth, due to the initial SPE process with low temperature codeposition, thermal interdiffusion of Fe and Si was suppressed, resulting in the surface flatness and abrupt interface. Second high temperature MBE process improved the crystallinity. We also investigated thermoelectric properties of these β-FeSi2 thin films. Structural factors affecting the thermoelectric properties of RDE+MBE, SPE, and SPE+MBE thin films were investigated.

  15. Search for quantum size effects in ultrathin epitaxial metallic films

    NASA Astrophysics Data System (ADS)

    Badoz, P. A.; D'Avitaya, F. Arnaud; Rosencher, E.

    In order to investigate quantum size effects in ultrathin metal films, tunneling spectroscopy measurements have been performed in the epitaxial CoSi2/Si system, with a metal thickness ranging from 1000 Å down to 35 A, i.e. a few de Broglie wavelengths of electrons in CoSi 2. The resulting spectra show extremely rich sets of features, the origin of which are investigated. The peaks observed at low energy (-100 meV, +100 meV) are thickness independent and attributed to phonon emission by hot electrons. The peaks observed at higher energy (up to 600 meV) are thickness dependent but their physical origin is not yet fully ascertained. The absence of unambiguous electron quantization effects in these epitaxial films is discussed and tentatively attributed to small thickness fluctuations (of the order of a few monolayers), which tend to blur the quantization of the electronic energies. Nous avons étudié les effets de quantification électronique dans les films métalliques minces par spectroscopie tunnel des jonctions CoSi2/Si épitaxiées, pour des épaisseurs de film métallique variant de 1000 ? 35 A, i.e. quelques longueurs d'ondes de de Broglie des électrons dans le CoSi 2. Les spectres obtenus montrent un ensemble de structures extrêmement riche dont nous discutons l'origine physique. Les pics observés à faible énergie (-100 meV, + 100 meV) sont indépendants de I'épaisseur du film de CoSi2, et attribués à l'émission de phonons par les électrons chauds dans le silicium. L'origine des pics observés à plus forte énergie (jusqu'à 600 meV) et dont la position dépend de l'épaisseur du film, est encore incomplètement comprise. Nous discutons l'absence d'effets clairement reliés à la quantification du gaz d'électrons bidimensionnel dans ces films épitaxiés: celle-ci pourrait provenir de faibles fluctuations d'épaisseur (quelques monocouches) qui tendent à brouiller la quantification des énergies électroniques.

  16. Cyclotron resonance in epitaxial Bi1-xSbx films grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Heremans, J.; Partin, D. L.; Thrush, C. M.; Karczewski, G.; Richardson, M. S.; Furdyna, J. K.

    1993-10-01

    The far-infrared magnetotransmission of thin films of semiconducting and semimetallic Bi1-xSbx alloys grown by molecular-beam epitaxy has been measured at fixed photon energies between 2.5 and 21.4 meV in magnetic fields up to 6 T, at T=1.8 K. The samples, grown on BaF2 substrates with composition 0<=x<=22.5%, were monocrystalline, with the trigonal axis perpendicular to the surface plane. The measurements were carried out in Faraday and Voigt geometries, with the magnetic field oriented parallel to binary, bisectrix, and trigonal axes of the films. Cyclotron-resonance lines of both electrons and holes were observed. From them, we establish the composition dependence of the effective-mass tensor, of the direct L-point band gap, and of the energy overlap in the semimetallic samples. We conclude that all band-structure parameters are the same in the films as in bulk Bi1-xSbx alloys, except for the energy overlap, which is increased by 16 meV independently of composition, possibly because of the strain induced by the substrate.

  17. Structure and magnetism of epitaxial PrVO3 films.

    PubMed

    Copie, O; Rotella, H; Boullay, P; Morales, M; Pautrat, A; Janolin, P-E; Infante, I C; Pravathana, D; Lüders, U; Prellier, W

    2013-12-11

    The interplay between charge, spin, orbital and lattice degrees of freedom in transition metal oxides has motivated extensive research aiming to understand the coupling phenomena in these multifunctional materials. Among them, rare earth vanadates are Mott insulators characterized by spin and orbital orderings strongly influenced by lattice distortions. Using epitaxial strain as a means to tailor the unit cell deformation, we report here on the first thin films of PrVO3 grown on (001)-oriented SrTiO3 substrate by pulsed laser deposition. An extensive structural characterization of the PrVO3 films, combining x-ray diffraction and high-resolution transmission electron microscopy studies, reveals the presence of oriented domains and a unit cell deformation tailored by the growth conditions. We have also investigated the physical properties of the PrVO3 films. We show that, while PrVO3 exhibits an insulating character, magnetic measurements indicate low-temperature hard-ferromagnetic behavior below 80 K. We discuss these properties in view of the thin-film structure.

  18. Growth of Atomically Flat DBCO Films Using Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Andrus, Aaron E.; Oh, Seongshik; Davidson, Bruce A.; O'Donnell, Jim; Eckstein, James N.

    2000-03-01

    We have grown atomically flat a-axis dysprosium barium copper oxide (DBCO) films by molecular beam epitaxy (MBE) using a pure ozone source. Such films can be used, for example, to exploit the inherent anisotropy of DBCO in spin injection devices using ferromagnetic polarized electron sources or all-superconducting Josephson junctions. The a-axis films are grown on a strontium titanate (STO) substrate using a low temperature DBCO template to achieve a-axis orientation. During growth, we use reflection high energy electron diffraction (RHEED) to observe the emergence of one-third order streaks in the diffraction pattern and a reduction in the surface roughness as we increase the growth temperature. Subsequent x-ray diffraction shows complete a-axis normal orientation with pseudomorphic growth (in-plane lattice constants identical to the substrate) and a slightly larger out of plane lattice constant than bulk crystals. Atomic force microscopy (AFM) shows an RMS roughness of 4 Å over several millimeters of the film surface, sufficient to construct tunnel junction devices.

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

    PubMed

    Halim, Joseph; Lukatskaya, Maria R; Cook, Kevin M; Lu, Jun; Smith, Cole R; Näslund, Lars-Åke; May, Steven J; Hultman, Lars; Gogotsi, Yury; Eklund, Per; Barsoum, Michel W

    2014-04-08

    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 cm(2) 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.

  20. Epitaxial growth of magnetic ZnCuO thin films by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Kim, Dong Hun; Kim, Tae Cheol; Lee, Seung Han; Jung, Hyun Kyu; Jeong, Jaeeun; Han, Seung Ho

    2017-02-01

    The crystal structure and magnetic properties of epitaxial ZnO thin films doped with 5 at% Cu on SrTiO3 (001) and (111) substrates were investigated. In the case of films deposited in oxygen, unique crystallographic growth directions on different substrates were observed, while a metallic phase was detected in films grown under vacuum. The Cu-doped ZnO thin films deposited on the SrTiO3 (111) substrates, with hexagonal structures, showed a single epitaxial relationship with the substrates, whereas those deposited on the SrTiO3 (001) substrates showed a double epitaxial growth mode. The epitaxial ZnCuO thin films deposited on the SrTiO3 (111) substrates under high vacuum exhibited a ferromagnetic signal at room temperature.

  1. Compensation in epitaxial cubic SiC films

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  2. 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

  3. Epitaxial thin films of novel multiferroic double perovskites.

    NASA Astrophysics Data System (ADS)

    Venimadhav, A.; Li, Qi

    2006-03-01

    Recently multiferroic materials have attracted great interest. However, relatively a few pure multiferroic compounds are currently known. Here we show the exploration of design of multiferroic properties in double perovskites by combining the ferrolectrisity driven by the Bi lone pairs and selectively choosing the 3d transition metals following Goodenough-Kanamori's rules to bring in ferromagnetism. We present growth issues in stabilizing the single phase, epitaxial thin films of new double perovskite multiferroic systems such as Bi2NiMnO6, Bi2FeCrO6 and La2NiMnO6 by pulsed laser deposition. Targets of these compositions were synthesized by solid state method with 15% of excess Bi in the composition to compensate the volatility of Bi during the deposition. We also present the synthesis of Bi2FeCrO6 by growing a superlattice structures from individual targets of Bi FeO3 and BiCrO3. In the cubic double perovskites, cations show rock salt kind of ordering in the (111) direction and hence growing these films on STO (111) substrates has an advantage. We present the growth, structural and multiferroic properties in these double perovskite thin films..

  4. 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.

  5. Epitaxial growth of AlN films via plasma-assisted atomic layer epitaxy

    SciTech Connect

    Nepal, N.; Qadri, S. B.; Hite, J. K.; Mahadik, N. A.; Mastro, M. A.; Eddy, C. R. Jr.

    2013-08-19

    Thin AlN layers were grown at 200–650 °C by plasma assisted atomic layer epitaxy (PA-ALE) simultaneously on Si(111), sapphire (1120), and GaN/sapphire substrates. The AlN growth on Si(111) is self-limited for trimethyaluminum (TMA) pulse of length > 0.04 s, using a 10 s purge. However, the AlN nucleation on GaN/sapphire is non-uniform and has a bimodal island size distribution for TMA pulse of ≤0.03 s. The growth rate (GR) remains almost constant for T{sub g} between 300 and 400 °C indicating ALE mode at those temperatures. The GR is increased by 20% at T{sub g} = 500 °C. Spectroscopic ellipsometry (SE) measurement shows that the ALE AlN layers grown at T{sub g} ≤ 400 °C have no clear band edge related features, however, the theoretically estimated band gap of 6.2 eV was measured for AlN grown at T{sub g} ≥ 500 °C. X-ray diffraction measurements on 37 nm thick AlN films grown at optimized growth conditions (T{sub g} = 500 °C, 10 s purge, 0.06 s TMA pulse) reveal that the ALE AlN on GaN/sapphire is (0002) oriented with rocking curve full width at the half maximum (FWHM) of 670 arc sec. Epitaxial growth of crystalline AlN layers by PA-ALE at low temperatures broadens application of the material in the technologies that require large area conformal growth at low temperatures with thickness control at the atomic scale.

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

    SciTech Connect

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

    2015-11-05

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

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

    PubMed

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

    2014-06-24

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

  8. Transport and magnetic properties of Fe3Si epitaxial films

    NASA Astrophysics Data System (ADS)

    Vinzelberg, H.; Schumann, J.; Elefant, D.; Arushanov, E.; Schmidt, O. G.

    2008-11-01

    The paper presents resistivity and magnetization measurements on nearly stoichiometric Fe3Si films epitaxially grown on GaAs substrates by electron-beam evaporation in an ultrahigh vacuum chamber. In the low-temperature resistivity a T3 term was found in all samples. A term like that is known to describe the anomalous single-magnon scattering processes in half-metallic materials and confirms so for our samples the hypothesis of half-metallic ferromagnetism in Fe3Si. The films show an anisotropic magnetoresistance in low magnetic fields. In high magnetic fields a negative longitudinal and transverse magnetoresistance (MR) has been observed linearly depending on the field strength. In the vicinity of 200 K the MR shows maximum absolute values up to 1.5% at magnetic fields of about 8 T. From the magnetization measurements a magnetic moment of 0.86μB/atom was obtained, which is close to that of bulk Fe3Si.

  9. Molecular beam epitaxy of thin HfTe2 semimetal films

    NASA Astrophysics Data System (ADS)

    Aminalragia-Giamini, S.; Marquez-Velasco, J.; Tsipas, P.; Tsoutsou, D.; Renaud, G.; Dimoulas, A.

    2017-03-01

    Epitaxial thin films of 1T-HfTe2 semimetal are grown by MBE on AlN(0001) substrates. The measured in-plane lattice parameter indicates an unstrained film which is also azimuthally aligned with the AlN substrate, albeit with an in-plane mosaic spread, as it would be expected for van der Waals epitaxy. Angle resolved photoemission spectroscopy combined with first principles electronic band structure calculations show steep linearly dispersing conduction and valence bands which cross near the Brillouin zone center, providing evidence that HfTe2/AlN is an epitaxial topological Dirac semimetal.

  10. Large-Area Dry Transfer of Single-Crystalline Epitaxial Bismuth Thin Films.

    PubMed

    Walker, Emily S; Na, Seung Ryul; Jung, Daehwan; March, Stephen D; Kim, Joon-Seok; Trivedi, Tanuj; Li, Wei; Tao, Li; Lee, Minjoo L; Liechti, Kenneth M; Akinwande, Deji; Bank, Seth R

    2016-11-09

    We report the first direct dry transfer of a single-crystalline thin film grown by molecular beam epitaxy. A double cantilever beam fracture technique was used to transfer epitaxial bismuth thin films grown on silicon (111) to silicon strips coated with epoxy. The transferred bismuth films retained electrical, optical, and structural properties comparable to the as-grown epitaxial films. Additionally, we isolated the bismuth thin films on freestanding flexible cured-epoxy post-transfer. The adhesion energy at the bismuth/silicon interface was measured to be ∼1 J/m(2), comparable to that of exfoliated and wet transferred graphene. This low adhesion energy and ease of transfer is unexpected for an epitaxially grown film and may enable the study of bismuth's unique electronic and spintronic properties on arbitrary substrates. Moreover, this method suggests a route to integrate other group-V epitaxial films (i.e., phosphorus) with arbitrary substrates, as well as potentially to isolate bismuthene, the atomic thin-film limit of bismuth.

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

    SciTech Connect

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

    2010-12-01

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

  12. Solid-liquid phase epitaxial growth of Li4Ti5O12 thin film

    NASA Astrophysics Data System (ADS)

    Li, Ning; Katase, Takayoshi; Zhu, Yanbei; Matsumoto, Takao; Umemura, Tomonari; Ikuhara, Yuichi; Ohta, Hiromichi

    2016-12-01

    A thin film of Li4Ti5O12, a candidate anode material for solid-state Li-ion batteries, was heteroepitaxially grown on a (001) SrTiO3 substrate using solid-liquid phase epitaxy. An amorphous Li4Ti5O12 film deposited at room temperature was first heated with LiNO3 powder in air and then washed with distilled water. The Li4Ti5O12 epitaxial film was obtained by heating with molten LiNO3 at 600 °C the liquid LiNO3 completely covered the film, suppressing the formation of Li deficiencies and enhancing the low-temperature crystal growth. Solid-liquid phase epitaxy is a powerful approach to grow Li-containing-oxide films, which are difficult to fabricate because of the loss of Li species at high temperature.

  13. Ferroelectric properties of highly c-oriented epitaxial Bi2WO6 thin films

    NASA Astrophysics Data System (ADS)

    Ahn, Yoonho; Son, Jong Yeog

    2017-03-01

    Bi2WO6 (BWO) thin films were epitaxially deposited onto single crystal Nb-doped SrTiO3 substrates via pulsed laser deposition (PLD). To control the growth mode of the BWO thin films, the deposition rate was varied from 0.01 to 0.4 nm/pulse. The BWO thin films yielded an island growth mode during a rapid deposition rate of 0.4 nm/pulse. On the other hand, a layer-by-layer growth mode was achieved with a low deposition rate of 0.01 nm/pulse. We could obtain highly c-oriented epitaxial BWO thin films by means of the layer-by-layer mode. Piezoresponse force microscopy revealed that the highly c-oriented epitaxial BWO thin films possessed spontaneous polarizations that were perpendicular to the c-axis.

  14. Langevin Equation for the Morphological Evolution of Strained Epitaxial Films

    NASA Astrophysics Data System (ADS)

    Vvedensky, Dimitri; Haselwandter, Christoph

    2006-03-01

    A stochastic partial differential equation for the morphological evolution of strained epitaxial films is derived from an atomistic master equation. The transition rules in this master equation are based on previous kinetic Monte Carlo (KMC) simulations of a model that incorporates the effects of strain through local environment-dependent energy barriers to adatom detachment from step edges. The morphological consequences of these rules are seen in the transition from layer-by-layer growth to the appearance of three-dimensional islands with increasing strain. The regularization of the exact Langevin description of these rules yields a continuum equation whose lowest-order terms provide a coarse-grained theory of this model. The coefficients in this equation are expressed in terms of the parameters of the original lattice model, so a direct comparison between the morphologies produced by KMC simulations and this Langevin equation are meaningful. Comparisons with previous approaches are made to provide an atomistic interpretation of a similar equation derived by Golovin et al. based on classical elasticity.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Microstructural and Magnetic Properties of Polycrystalline and Epitaxial Permalloy (NICKEL(80) IRON(20) Multilayered Thin Films.

    NASA Astrophysics Data System (ADS)

    Hashim, Imran

    Permalloy rm (Ni_{80 }Fe_{20}) thin films are of great scientific and technological interest because of their unique soft magnetic properties, and applications to magnetic recording. Chapter 1 provides an introduction to magnetic and magnetotransport properties of rm Ni_{80}Fe_{20} thin films, and how the film microstructure affects these properties. Chapter 2 discusses the instrumentation used for thin film fabrication, and for magnetic and structural characterization. Further details of instrumentation are discussed in Appendix A. Typically, the rm Ni_{80 }Fe_{20} films for magnetoresistive applications are capped with a refractory metal thin film such as Ta to prevent its oxidation and corrosion. We investigated the interdiffusion kinetics of polycrystalline Ta/rm Ni_{80}Fe_ {20} thin films and found that for 400 <= T <= 600 ^circC, there was significant grain-boundary interdiffusion which drastically affected soft magnetic properties of rm Ni_ {80}Fe_{20}. In Chapter 3, we present details of the microstructural evolution of these multilayers and the subsequent effects on their magnetic properties. An alternate method for reducing grain-boundary scattering would be to fabricate grain-boundary free epitaxial rm Ni_{80}Fe_{20 } films. The epitaxy of rm Ni _{80}Fe_{20} on MgO, NaCl and Cu had been demonstrated by investigators as early as the 60s. However, none of these substrates are available with as good atomic flatness as Si wafers. Following reports of epitaxial growth of Cu on Si, we proposed using it as a seed layer for growing rm Ni_ {80}Fe_{20} epitaxially on Si. However, there were conflicting reports of Cu epitaxy on Si, as some investigators claimed that Cu epitaxy on Si in UHV was not possible. We were able to resolve some of these controversies (see Chapter 4 for details) and thus fabricate epitaxial rm Ni_{80 }Fe_{20} films on Cu/Si. Chapter 5 examines the effect of the lattice mismatch between Cu and rm Ni_{80}Fe _{20} and the subsequent strain, on

  20. 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.

  1. Role of critical size of nuclei for liquid-phase epitaxy on polycrystalline Si films

    NASA Astrophysics Data System (ADS)

    Kühnle, Jürgen; Bergmann, Ralf B.; Werner, Jürgen H.

    1997-03-01

    Liquid-phase epitaxy of Si on fine-grained polycrystalline Si seeding films reveals the effect of a critical size of nuclei. As a consequence, during deposition appreciable parts of fine-grained polycrystalline Si films dissolve in the initially supersaturated growth solution. The observed dependences of the nucleation density on supersaturation and saturation temperature are in agreement with the concept of the critical size of nuclei as predicted by thermodynamic considerations. A comparison of nucleation densities obtained in liquid-phase epitaxy experiments and grain size distributions in seeding films allows to confirm the theoretically predicted critical grain size of about 500 nm.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Infrared Response and Optoelectronic Memory Device Fabrication Based on Epitaxial VO2 Film.

    PubMed

    Fan, Lele; Chen, Yuliang; Liu, Qianghu; Chen, Shi; Zhu, Lei; Meng, Qiangqiang; Wang, Baolin; Zhang, Qinfang; Ren, Hui; Zou, Chongwen

    2016-12-07

    In this work, high-quality VO2 epitaxial films were prepared on high-conductivity n-GaN (0001) crystal substrates via an oxide molecular beam epitaxy method. By fabricating a two-terminal VO2/GaN film device, we observed that the infrared transmittance and resistance of VO2 films could be dynamically controlled by an external bias voltage. Based on the hysteretic switching effect of VO2 in infrared range, an optoelectronic memory device was achieved. This memory device was operated under the "electrical writing-optical reading" mode, which shows promising applications in VO2-based optoelectronic device in the future.

  7. Adsorption-controlled growth of BiMnO3 films by molecular-beam epitaxy

    SciTech Connect

    Lee, H; Ke, X; Misra, R.; Ihlefeld, J.F.; Xu, Xiaoshan; Mei, Z.G.; Heeg, T.; Roeckerath, M.; Musfeldt, J.L.; Schiffer, P.; Schlom, D.G.

    2010-01-01

    We have developed the means to grow BiMnO3 thin films with unparalleled structural perfection by reactive molecular-beam epitaxy and determined its band gap. Film growth occurs in an adsorption-controlled growth regime. Within this growth window bounded by oxygen pressure and substrate temperature at a fixed bismuth overpressure, single-phase films of the metastable perovskite BiMnO3 may be grown by epitaxial stabilization. X-ray diffraction reveals phase-pure and epitaxial films with rocking curve full width at half maximum values as narrow as 11 arc sec 0.003 . Optical absorption measurements reveal that BiMnO3 has a direct band gap of 1.1 0.1 eV.

  8. Epitaxial growth of iridate pyrochlore Nd2Ir2O7 films

    PubMed Central

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

    2016-01-01

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

  9. Epitaxial growth of iridate pyrochlore Nd2Ir2O7 films

    DOE PAGES

    Gallagher, J. C.; Esser, B. D.; Morrow, R.; ...

    2016-02-29

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

  10. On the theory of electronic states of the "epitaxial graphene-quantum-well film" system

    NASA Astrophysics Data System (ADS)

    Alisultanov, Z. Z.; Meilanov, R. P.

    2012-07-01

    The problem of an epitaxial graphene formed on a thin metal film in an external magnetic field has been considered. It has been shown that the problem can be solved using the Green's function method within the Kadanoff-Baym formalism. Analytical expressions for the transferred charge as a function of the magnetic field and the thickness of the film have been obtained.

  11. Aligned carbon nanotubes sandwiched in epitaxial NbC film for enhanced superconductivity.

    PubMed

    Zhang, Yingying; Ronning, Filip; Gofryk, Krzysztof; Mara, Nathan A; Haberkorn, Nestor; Zou, Guifu; Wang, Haiyan; Lee, Joon H; Bauer, Eve; McCleskey, Thomas M; Burell, Anthony K; Civale, Leonardo; Zhu, Y T; Jia, Quanxi

    2012-04-07

    Highly aligned carbon nanotube (CNT) ribbons were sandwiched in epitaxial superconducting NbC films by a chemical solution deposition method. The incorporation of aligned long CNTs into NbC film enhances the normal-state conductivity and improves the superconducting properties of the assembly.

  12. Structural and electronic properties of molecular beam epitaxially grown Ni1+xTiSn films

    NASA Astrophysics Data System (ADS)

    Rice, A. D.; Kawasaki, J. K.; Verma, N.; Pennachio, D. J.; Schultz, B. D.; Palmstrøm, C. J.

    2017-06-01

    This paper demonstrates the molecular beam epitaxial growth of metallic full-Heusler Ni2TiSn precipitates within semiconducting NiTiSn host matrix, and discusses the structural and chemical stability of this biphasic epitaxial composite and its influence on the electronic properties. Structural properties of the epitaxial films were characterized by in-situ reflection high-energy electron diffraction and ex-situ by X-ray diffraction and transmission electron microscopy. The results indicate the presence of a secondary phase with full Heusler ordering within half-Heusler host matrix. Both the parent half-Heusler and the secondary full-Heusler phases in the epitaxial films are strained from their bulk lattice parameters. Electronic properties show an increase in resistivity at low Ni excess.

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  14. Neutron Diffraction Investigations of Magnetism in BiFeO3 Epitaxial Films

    DTIC Science & Technology

    2011-01-01

    ordering temperatures are far too low for device applications. Perovskite-structured BiFeO 3 (BFO) with a rhom- bohedral distortion along the [111...where the magnetic moment lies in the HHL plane. Neutron Diffraction Investigations of Magnetism in BiFeO 3 Epitaxial Films The recovery of a...modulated magnetic structure in epitaxial BiFeO 3 thin fi lms as revealed by neutron diffraction is reported. The magnetic structure in thin fi lms is

  15. Epitaxial growth of AlN films on single-crystalline Ta substrates

    SciTech Connect

    Hirata, S.; Okamoto, K.; Inoue, S. Kim, T-W.; Ohta, J.; Fujioka, H.; Oshima, M.

    2007-08-15

    We have demonstrated the first epitaxial growth of AlN films on single-crystalline Ta substrates by the use of a low-temperature growth technique based on pulsed laser deposition (PLD). Although previous AlN films grown on Ta(100) and (111) substrates have exhibited quite poor crystallinity, an epitaxial AlN(0001) film with an in-plane epitaxial relationship of AlN[112-bar 0]//Ta[001] has been obtained on a Ta(110) substrate at a growth temperature of 450 deg. C. We found that the full-width at half-maximum values for the crystal orientation distribution in the tilt and twist directions of the AlN film were 0.37{sup o} and 0.41{sup o}, respectively. Grazing-incidence X-ray reflection (GIXR) and X-ray photoelectron spectroscopy (XPS) measurements have revealed that the AlN/Ta heterointerface is quite abrupt, and that its abruptness remains unchanged even after annealing at 1000 deg. C. - Graphical abstract: An epitaxial AlN(0001) film with an in-plane epitaxial relationship of AlN[112-bar 0]//Ta[001] has been obtained for the first time on a Ta(110) substrate by the use of a PLD low-temperature growth technique.

  16. Fabrication of Epitaxial Fe3O4 Film on a Si(111) Substrate.

    PubMed

    Takahashi, Nozomi; Huminiuc, Teodor; Yamamoto, Yuta; Yanase, Takashi; Shimada, Toshihiro; Hirohata, Atsufumi; Nagahama, Taro

    2017-08-01

    The application of magnetic oxides in spintronics has recently attracted much attention. The epitaxial growth of magnetic oxide on Si could be the first step of new functional spintronics devices with semiconductors. However, epitaxial spinel ferrite films are generally grown on oxide substrates, not on semiconductors. To combine oxide spintronics and semiconductor technology, we fabricated Fe3O4 films through epitaxial growth on a Si(111) substrate by inserting a γ-Al2O3 buffer layer. Both of γ-Al2O3 and Fe3O4 layer grew epitaxially on Si and the films exhibited the magnetic and electronic properties as same as bulk. Furthermore, we also found the buffer layer dependence of crystal structure of Fe3O4 by X-ray diffraction and high-resolution transmission electron microscope. The Fe3O4 films on an amorphous-Al2O3 buffer layer grown at room temperature grew uniaxially in the (111) orientation and had a textured structure in the plane. When Fe3O4 was deposited on Si(111) directly, the poly-crystal Fe3O4 films were obtained due to SiOx on Si substrate. The epitaxial Fe3O4 layer on Si substrates enable us the integration of highly functional spintoronic devices with Si technology.

  17. 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.

  18. Growth of GaN epitaxial films on polycrystalline diamond by metal-organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Jiang, Quanzhong; Allsopp, Duncan W. E.; Bowen, Chris R.

    2017-04-01

    Heat extraction is often essential in ensuring efficient performance of semiconductor devices and requires minimising the thermal resistance between the functional semiconductor layers and any heat sink. This paper reports the epitaxial growth of N-polar GaN films on polycrystalline diamond substrates of high thermal conductivity with metal-organic vapor phase epitaxy, by using a Si x C layer formed during deposition of polycrystalline diamond on a silicon substrate. The Si x C layer acts to provide the necessary structure ordering information for the formation of a single crystal GaN film at the wafer scale. It is shown that a three-dimensional island (3D) growth process removes hexagonal defects that are induced by the non-single crystal nature of the Si x C layer. It is also shown that intensive 3D growth and the introduction of a convex curvature of the substrate can be deployed to reduce tensile stress in the GaN epitaxy to enable the growth of a crack-free layer up to a thickness of 1.1µm. The twist and tilt can be as low as 0.65° and 0.39° respectively, values broadly comparable with GaN grown on Si substrates with a similar structure.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    He, Zhen

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

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

    SciTech Connect

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

    2012-03-15

    We have investigated the influence of the deposition variables on photocatalytic properties of epitaxial rutile films. Despite a large lattice misfit of rutile with sapphire substrate, (2 0 0) epitaxial layers were grown on (0 0 0 1)sapphire by domain matching epitaxy paradigm. Using {phi}-scan XRD and cross section TEM, the epitaxial relationship was determined to be rutile(1 0 0)||sapphire(0 0 0 1), rutile(0 0 1)||sapphire(1 0 -1 0), and rutile(0 1 0)||sapphire(1 -2 1 0). Based on the XRD patterns, increasing the repetition rate introduced tensile stress along the film normal direction, which may arise as a result of trapped defects. Formation of such defects was studied by UV-VIS, PL, and XPS techniques. AFM studies showed that the film roughness increases with the repetition rate. Finally, photocatalytic performance of the layers was investigated through measuring decomposition rate of 4-chlorophenol on the films surface. The films grown at higher frequencies revealed higher photocatalytic efficiency. This behavior was mainly related to formation of point defects which enhance the charge separation. - Graphical abstract: In this report, epitaxial rutile TiO{sub 2} thin films were deposited by PLD process under various deposition rates (frequencies) and their physical and chemical properties, especially photocatalytic performance, were investigated. It was found that photocatalytic efficiency improves when frequency increases. This behavior was mainly related to formation of point defects which enhance the charge separation. Highlights: Black-Right-Pointing-Pointer Rutile epitaxial thin films were deposited via PLD process under different frequencies. Black-Right-Pointing-Pointer Defect characteristic was studied. Black-Right-Pointing-Pointer Photocatalytic performance of the layers was investigated.

  2. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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.

  4. Atomic Layer Epitaxy of Group IV Materials: Surface Processes, Thin Films, Devices and their Characterization

    DTIC Science & Technology

    1993-12-01

    U AD-A274 325 Semiannual Technical Report U Atomic Layer Epitaxy of Group IV Materials: Surface Processes, Thin Films, Devices and Their... Group IV Materials: Surface Processes, Thin 414v001---01 Films, Devices and Their Characterization 1114SS S. AUTHOS) N00179 Robert F. Davis, Salah... Conformal deposition of SiC has been demonstrated within trenches etched into Si(100) wafers. P-type films have also been achieved using Al as a

  5. Ferroelectric Tungsten Bronze Bulk Crystals and Epitaxial Thin Films for Electro-Optic Device Applications

    DTIC Science & Technology

    1983-05-01

    23 FERROELECTRIC TUNGSTEN BRONZE BULK CRYSTALS AND EPITAXIAL THIN FILMS FOR ELECTRO-OPTIC DEVICE APPLICATIONS 10 CO O Semi-Annual Technical... THIN FILMS FOR ELECTRO-OPTIC DEVICE APPLICATIONS s TV^C or REPORT * pcmoo COVCHCO Semi-Annual Tec1! Rpt #1 for period 09/30/82-03/31/83...months, considerable progress has been made in several areas, including single crystal and thin film growth and characteriza- tion. The new

  6. 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.

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

    DOEpatents

    Wang, Qi [Littleton, CO; Stradins, Paul [Golden, CO; Teplin, Charles [Boulder, CO; Branz, Howard M [Boulder, CO

    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.

  8. A study on the epitaxial Bi{sub 2}Se{sub 3} thin film grown by vapor phase epitaxy

    SciTech Connect

    Lin, Yen-Cheng; Chen, Yu-Sung; Lee, Chao-Chun; Wu, Jen-Kai; Lee, Hsin-Yen E-mail: hyli@ntu.edu.tw; Liang, Chi-Te; Chang, Yuan Huei E-mail: hyli@ntu.edu.tw

    2016-06-15

    We report the growth of high quality Bi{sub 2}Se{sub 3} thin films on Al{sub 2}O{sub 3} substrates by using chemical vapor deposition. From the atomic force microscope, x-ray diffraction and transmission electron microscope measurements we found that the films are of good crystalline quality, have two distinct domains and can be grown epitaxially on the Al{sub 2}O{sub 3} substrate. Carrier concentration in the sample is found to be 1.1 × 10{sup 19} cm{sup −3} between T = 2 K to T = 300 K, and electron mobility can reach 954 cm{sup 2}/V s at T = 2 K. Weak anti-localization effect is observed in the low temperature magneto-transport measurement for the sample which indicates that the thin film has topological surface state.

  9. Perpendicularly magnetized τ-MnAl (001) thin films epitaxied on GaAs

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    Perpendicularly magnetized τ-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/cm3, perpendicular magnetic anisotropy constant of 13.65 Merg/cm3, 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.

  10. Mott-barrier diodes based on epitaxially grown n-GaAs films

    NASA Astrophysics Data System (ADS)

    Averin, S. V.; Azakian, E. A.; Guliaev, Iu. V.; Dmitriev, M. D.; Liubchenko, V. E.; Petrenko, I. V.; Sveshnikov, Iu. N.

    The fabrication and properties of epitaxially grown n-GaAs film Mott-barrier diodes are examined. The doping profile of a film grown via gas-phase epitaxy is presented, and the volt-farad characteristics of Schottky and Mott diodes are compared. An investigation of frequency conversion shows that the optimal heterodyne power for the Mott diode is significantly lower than that for the Schottky diode, which makes it possible to reduce the mixer noise temperature. It is noted that Mott-barrier diodes are particularly suitable for the submillimeter range.

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

    NASA Astrophysics Data System (ADS)

    Boyerinas, Brad Michael

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

  12. Thermoelectric Properties of Epitaxial β-FeSi2 Thin Films on Si(111) and Approach for Their Enhancement

    NASA Astrophysics Data System (ADS)

    Taniguchi, Tatsuhiko; Sakane, Shunya; Aoki, Shunsuke; Okuhata, Ryo; Ishibe, Takafumi; Watanabe, Kentaro; Suzuki, Takeyuki; Fujita, Takeshi; Sawano, Kentarou; Nakamura, Yoshiaki

    2016-10-01

    We have investigated the intrinsic thermoelectric properties of epitaxial β-FeSi2 thin films and the impact of phosphorus (P) doping. Epitaxial β-FeSi2 thin films with single phase were grown on Si(111) substrates by two different techniques in an ultrahigh-vacuum molecular beam epitaxy (MBE) system: solid-phase epitaxy (SPE), where iron silicide films formed by codeposition of Fe and Si at room temperature were recrystallized by annealing at 530°C to form epitaxial β-FeSi2 thin films on Si(111) substrates, and MBE of β-FeSi2 thin films on epitaxial β-FeSi2 templates formed on Si(111) by reactive deposition epitaxy (RDE) at 530°C (RDE + MBE). Epitaxial SPE thin films based on codeposition had a flatter surface and more abrupt β-FeSi2/Si(111) interface than epitaxial RDE + MBE thin films. We investigated the intrinsic thermoelectric properties of the epitaxial β-FeSi2 thin films on Si(111), revealing lower thermal conductivity and higher electrical conductivity compared with bulk β-FeSi2. We also investigated the impact of doping on the Seebeck coefficient of bulk and thin-film β-FeSi2. A route to enhance the thermoelectric performance of β-FeSi2 is proposed, based on (1) fabrication of thin-film structures for high electrical conductivity and low thermal conductivity, and (2) proper choice of doping for high Seebeck coefficient.

  13. Thermoelectric Properties of Epitaxial β-FeSi2 Thin Films on Si(111) and Approach for Their Enhancement

    NASA Astrophysics Data System (ADS)

    Taniguchi, Tatsuhiko; Sakane, Shunya; Aoki, Shunsuke; Okuhata, Ryo; Ishibe, Takafumi; Watanabe, Kentaro; Suzuki, Takeyuki; Fujita, Takeshi; Sawano, Kentarou; Nakamura, Yoshiaki

    2017-05-01

    We have investigated the intrinsic thermoelectric properties of epitaxial β-FeSi2 thin films and the impact of phosphorus (P) doping. Epitaxial β-FeSi2 thin films with single phase were grown on Si(111) substrates by two different techniques in an ultrahigh-vacuum molecular beam epitaxy (MBE) system: solid-phase epitaxy (SPE), where iron silicide films formed by codeposition of Fe and Si at room temperature were recrystallized by annealing at 530°C to form epitaxial β-FeSi2 thin films on Si(111) substrates, and MBE of β-FeSi2 thin films on epitaxial β-FeSi2 templates formed on Si(111) by reactive deposition epitaxy (RDE) at 530°C (RDE + MBE). Epitaxial SPE thin films based on codeposition had a flatter surface and more abrupt β-FeSi2/Si(111) interface than epitaxial RDE + MBE thin films. We investigated the intrinsic thermoelectric properties of the epitaxial β-FeSi2 thin films on Si(111), revealing lower thermal conductivity and higher electrical conductivity compared with bulk β-FeSi2. We also investigated the impact of doping on the Seebeck coefficient of bulk and thin-film β-FeSi2. A route to enhance the thermoelectric performance of β-FeSi2 is proposed, based on (1) fabrication of thin-film structures for high electrical conductivity and low thermal conductivity, and (2) proper choice of doping for high Seebeck coefficient.

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

    SciTech Connect

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

    2014-05-07

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

  15. 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.

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

    SciTech Connect

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

    2015-09-01

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

  17. Magnetoresistance in polycrystalline and epitaxial Fe1-xCoxSi thin films

    NASA Astrophysics Data System (ADS)

    Porter, N. A.; Creeth, G. L.; Marrows, C. H.

    2012-08-01

    Thin films of Fe1-xCoxSi were grown using molecular beam epitaxy on Si(111). These 20-nm-thick films, with compositions x=0 or 0.5, were produced by two methods: the first produced large (111)-textured crystallites of the B20 phase; the second produced phase-pure B20 (111) epilayers. The lattice mismatch with the substrate causes biaxial tensile strain in the layers, greater in the epilayers, that distorts the (111)-oriented material to a rhombohedral form. Magnetotransport measurements show that a combination of additional scattering arising from crystal grain boundaries and strain-free polycrystalline films results in a higher resistivity than for the epitaxial films. Magnetometry for x=0.5 suggests an increase in the ordering temperature in strained films relative to the polycrystalline films of 15±4 K. Moreover, the characteristic linear magnetoresistance, typical of bulk single-crystal material of this composition, is retained in the polycrystalline film but reduced in the epitaxial film. While the bulk properties of these materials are reproduced qualitatively, there are small quantitative modifications, due to the strain, to properties such as band gap, Curie temperature, and magnetoresistance.

  18. 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.

  19. Magnetic properties of epitaxial hexagonal HoFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Wang, Xiao; Xiao, Zhuyun; Xu, Xiaoshan; Wang, Wenbin; Keavney, David; Liu, Yaohua; Cheng, X. M.

    2014-03-01

    Multiferroic materials exhibit multiple ferroic orders simultaneously and thus have great potential applications in information technology, sensing and actuation. Epitaxial hexagonal HoFeO3 (h-HFO) films are very promising candidates as multiferroic materials with room temperature ferromagnetism, because magnetic Ho3+ ions are expected to have stronger exchange interactions with Fe3+ ions than the well-studied h-LuFeO3 films. We report study of magnetic properties of epitaxial h-HFO thin films deposited using laser molecular beam epitaxy on Yttria-stabilized zirconia (YSZ) substrates. X-ray diffraction measurements confirmed the epitaxial registry and six-fold symmetry of the film. Temperature dependence of magnetization of the film measured by a Quantum Design SQUID magnetometer shows dominating paramagnetic characteristic. Element specific x-ray magnetic circular dichroism measurements performed at beamline 4-ID-C of the Advanced Photon Source show a ferromagnetic ordering of Fe and an exchange coupling between Ho3+ and Fe3+ ions. Work at BMC is supported by NSF Career award (DMR 1053854). Work at ANL is supported by US-DOE, Office of Science, BES (No. DE-AC02-06CH11357).

  20. Polarization-control of the potential barrier at the electrode interfaces in epitaxial ferroelectric thin films.

    PubMed

    Pintilie, Ioana; Teodorescu, Cristian Mihail; Ghica, Corneliu; Chirila, Cristina; Boni, Andra Georgia; Hrib, Luminita; Pasuk, Iuliana; Negrea, Raluca; Apostol, Nicoleta; Pintilie, Lucian

    2014-02-26

    Electrode interface is a key element in controlling the macroscopic electrical properties of the ferroelectric capacitors based on thin films. In the case of epitaxial ferroelectrics, the electrode interface is essential in controlling the leakage current and the polarization switching, two important elements in the read/write processes of nonvolatile memories. However, the relation between the polarization bound charges and the electronic properties of the electrode interfaces is not yet well understood. Here we show that polarization charges are controlling the height of the potential barriers at the electrode interfaces in the case of Pb(Zr,Ti)O3 and BaTiO3 epitaxial films. The results suggest that the height is set to a value allowing rapid compensation of the depolarization field during the polarization switching, being almost independent of the metals used for electrodes. This general behavior open a new perspective in engineering interface properties and designing new devices based on epitaxial ferroelectrics.

  1. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Study of Phase Transition Properties in Epitaxial Ferroelectric Film

    NASA Astrophysics Data System (ADS)

    Wang, Chun-Dong; Teng, Bao-Hua; Ju, Yong-Feng; Cheng, Deng-Mu; Zhang, Chun-Lai

    2010-10-01

    Based on the transverse Ising model and using decoupling approximation to the Fermi-type Green's function, we study the phase transition properties of the epitaxial ferroelectric film with one substrate. A general recursive equation of the ferroelectric thin film with two n-layer materials is obtained, which enables us to study the phase transition properties for any number layers for epitaxial ferroelectric thin film. With the help of this equation, we analyze the effect of the exchange interaction and the transverse field in the phase diagram, the influence to the polarizations and Curie temperature numerically. The results show that epitaxial ferroelectric film are able to induce a strong increase or decrease of Curie temperature to different exchange interactions and transverse fields within the epitaxial film layers. The theoretical results are in reasonable accordance with experimental data of different ferroelectric thin film.

  2. 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.

  3. 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.

  4. Strain induced giant magnetism in epitaxial Fe16N2 thin film

    NASA Astrophysics Data System (ADS)

    Ji, Nian; Lauter, Valeria; Zhang, Xiaowei; Ambaye, Hailemariam; Wang, Jian-Ping

    2013-02-01

    We report a direct observation of giant saturation magnetization in Fe16N2. By exploiting thin film epitaxy, which provides controlled biaxial stress to create lattice distortion, we demonstrate that giant magnetism can be established in Fe16N2 thin film coherently grown on MgO (001) substrate. Explored by polarized neutron reflectometry, the depth-dependent saturation magnetic induction (Bs) of epitaxial Fe16N2 thin films is visualized, which reveals a strong correlation with the in-plane lattice parameter and tensile strain developed at near substrate interface. With controlled growth process and dimension adjustment, the Bs of these films can be modulated over a broad range, from ˜2.1 Tesla (T) (normal Bs) up to ˜3.1 T (giant Bs).

  5. Correlation among Channeling, Morphological and Micro-structural Properties in Epitaxial CeO2 Films

    SciTech Connect

    Saraf, Laxmikant V.; McCready, David E.; Shutthanandan, V.; Wang, Chong M.; Engelhard, Mark H.; Thevuthasan, Suntharampillai

    2006-03-20

    We report an evidence of a critical thickness at ~ 64 nm in epitaxial CeO2 films grown at 750 0C on YSZ substrates by dc magnetron sputtering where optimum ion channeling can be correlated with overall strain relaxation and film surface roughness. The occurrence of saturation in ion channeling yield, enhancement in the average surface roughness and relaxation in c-axis strain is clearly evident in thicker films beyond the critical thickness. Despite excellent surface smoothness and overall epitaxial growth, CeO2 films grown at 650 0C did not show optimum ion channeling properties due to high misfit dislocation and defect density. These results are discussed from a viewpoint of the need for such an optimum thickness to develop multilayers with smooth interfaces with relative overall lattice relaxation.

  6. Effect of microstructures on electrical conduction properties of β-FeSi2 epitaxial films

    NASA Astrophysics Data System (ADS)

    Akiyama, Kensuke; Kadowaki, Teiko; Hirabayashi, Yasuo; Funakubo, Hiroshi

    2017-06-01

    We investigated the carrier concentration and Hall mobility of epitaxial β-FeSi2 films grown on semi-insulating 4H-SiC(001) single crystals to clarify the contribution of the microstructures to their electrical conduction properties. These electrical conduction properties of epitaxial β-FeSi2 films were changed by their grain size. The Hall mobility of the films consisting of the grains of 250-350 nm in size was limited by the grain boundaries, while it was not limited by grain boundaries for the films consisting of the coarse grains of 20-40 μm in size but limited by defects inside the grains.

  7. Growth of MoO3 films by oxygen plasma assisted molecular beam epitaxy

    SciTech Connect

    Altman, Eric I.; Droubay, Timothy C.; Chambers, Scott A.

    2002-07-22

    The growth of MoO₃ films on SrLaAlO₄(0 0 1), a substrate lattice-matched to b-MoO , by oxygen plasma assisted molecular beam epitaxy was characterized using reflection high-energy electron diffraction (RHEED), X-ray photoelectron spectroscopy, Xray diffraction (XRD), and atomic force and scanning tunneling microscopies (AFM and STM).It was found that the flux of reactive oxygen species to the surface was not high enough to maintain the proper stoichiometry, even at the lowest measurable deposition rates. Therefore, the films were grown by depositing Mo in small increments and then allowing the Mo to oxidize. At 675 K, the films grew epitaxially but in a three-dimensional manner. XRD of films grown under these conditions revealed atetragonal structure that has not been previously observed in bulk MoO₃ samples.

  8. Epitaxial growth and electronic properties of mixed valence YbAl{sub 3} thin films

    SciTech Connect

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

    2016-07-21

    We report the growth of thin films of the mixed valence compound YbAl{sub 3} 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 f{sup 13} and f{sup 12} final states establishing that YbAl{sub 3} is a mixed valence compound and shows the presence of a Kondo Resonance peak near the Fermi-level.

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

    NASA Astrophysics Data System (ADS)

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

    2005-08-01

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

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

    SciTech Connect

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

    2005-08-29

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

  11. Microbolometers Based On Epitaxial YBa(2)Cu(3)O(7-x) Thin Films

    NASA Technical Reports Server (NTRS)

    Foote, Marc C.; Hunt, Brian D.; Johnson, Burgess R.; Marsh, Holly A.

    1995-01-01

    Improved microbolometers of superconducting-transition type developed with view toward eventual fabrication of staring, infrared-imaging planar arrays of such microbolometers integrated with addressing electronic circuitry. Superconducting thin films in microbolometers epitaxial. These devices exhibit high sensitivity and low noise.

  12. 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.

  13. Ionized cluster beam deposition and epitaxy of metal films on large lattice misfit substrates

    NASA Astrophysics Data System (ADS)

    Yamada, Isao

    1991-01-01

    This paper reviews the metal film formation by the ionized cluster beam (ICB) technique on various kinds of substrates. The ICB enables heteroepitaxy of metal films for lattice misfit larger than 25 percent. The film growth process was studied by in situ MEED, AES and XPS analyses. The films were also examined by ex situ electron diffraction and atomic resolution TEM. On Si(111), single crystal Al film was formed. The Al deposited on Si(100) formed a bicrystal structure. The film-substrate interface and the bicrystal grain boundary were very sharp and had little distortion of atomic arrangement. This explains the high thermal stability of the metal films deposited by ICB. Epitaxial Al films were also formed on CaF2, Ge, GaAs, and sapphire substrates.

  14. Fast magnetization precession for perpendicularly magnetized MnAlGe epitaxial films with atomic layered structures

    NASA Astrophysics Data System (ADS)

    Mizukami, S.; Sakuma, A.; Kubota, T.; Kondo, Y.; Sugihara, A.; Miyazaki, T.

    2013-09-01

    Epitaxial growth and magnetization precessional dynamics for tetragonal MnAlGe films are investigated. The films are grown on MgO (100) with c axis parallel to the film normal and well-ordered layered structures. The film exhibits rectangular hysteresis loop with perpendicular magnetic anisotropy constant of 4.7 Merg/cm3 and saturation magnetization of 250 emu/cm3. Magnetization precession with precession frequency of ˜100 GHz is observed by time-resolved magneto-optical Kerr effect. Further, the Gilbert damping constant is found to be less than ˜0.05, which is much larger than that obtained using the first principles calculations.

  15. Growth of layered superconductor β-PdBi2 films using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Denisov, N. V.; Matetskiy, A. V.; Tupkalo, A. V.; Zotov, A. V.; Saranin, A. A.

    2017-04-01

    Bulk β-PdBi2 layered material exhibits advanced properties and is supposed to be probable topological superconductor. We present a method based on molecular beam epitaxy that allows us to grow β-PdBi2 films from a single β-PdBi2 triple layer up to the dozens of triple layers, using Bi(111) film on Si(111) as a template. The grown films demonstrate structural, electronic and superconducting properties similar to those of bulk β-PdBi2 crystals. Ability to grow the β-PdBi2 films of desired thickness opens the promising possibilities to explore fascinating properties of this advanced material.

  16. Self-organization of quantum dots in epitaxially strained solid films.

    PubMed

    Golovin, A A; Davis, S H; Voorhees, P W

    2003-11-01

    A nonlinear evolution equation for surface-diffusion-driven Asaro-Tiller-Grinfeld instability of an epitaxially strained thin solid film on a solid substrate is derived in the case where the film wets the substrate. It is found that the presence of a weak wetting interaction between the film and the substrate can substantially retard the instability and modify its spectrum in such a way that the formation of spatially regular arrays of islands or pits on the film surface becomes possible. It is shown that the self-organization dynamics is significantly affected by the presence of the Goldstone mode associated with the conservation of mass.

  17. Pure electron-electron dephasing in percolative aluminum ultrathin film grown by molecular beam epitaxy.

    PubMed

    Lin, Shih-Wei; Wu, Yue-Han; Chang, Li; Liang, Chi-Te; Lin, Sheng-Di

    2015-01-01

    We have successfully grown ultrathin continuous aluminum film by molecular beam epitaxy. This percolative aluminum film is single crystalline and strain free as characterized by transmission electron microscopy and atomic force microscopy. The weak anti-localization effect is observed in the temperature range of 1.4 to 10 K with this sample, and it reveals that, for the first time, the dephasing is purely caused by electron-electron inelastic scattering in aluminum.

  18. Tuning morphology and magnetism in epitaxial L10 -FePt films

    NASA Astrophysics Data System (ADS)

    Lupo, P.; Orna, J.; Casoli, F.; Nasi, L.; Ranzieri, P.; Calestani, D.; Algarabel, P.; Morellón, L.; Albertini, F.

    2013-01-01

    In this work, well-ordered epitaxial FePt thin films have been grown by RF sputtering on two different substrates (MgO (100) and SrTiO3 (100)) and the effect of different lattice parameters between the substrate and FePt film on morphology and magnetic behavior has been considered. Growth conditions have been optimized to obtain different morphologies and magnetic behaviors.

  19. 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.

  20. Epitaxial growth of barium titanate thin films on germanium via atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Lin, Edward L.; Posadas, Agham B.; Wu, Hsin Wei; Smith, David J.; Demkov, Alexander A.; Ekerdt, John G.

    2017-10-01

    Barium titanate BaTiO3 (BTO) thin films were epitaxially grown at 225 °C on 2 × 1-reconstructed Ge(001) surfaces via atomic layer deposition (ALD). Approximately 2 nm of BTO film was grown directly on Ge(001) as an amorphous film. Electron diffraction confirmed the epitaxy of the BTO films after post-deposition annealing at 650 °C. Additional BTO layers grown on the crystalline BTO/Ge(001) film were crystalline as-deposited. X-ray diffraction indicated that the epitaxial BTO films had a c-axis out-of-plane orientation, and the abrupt BTO/Ge interface was preserved with no sign of any interfacial germanium oxide. Scanning transmission electron microscopy provided evidence of Ba atoms occupying the troughs of the dimer rows of the 2 × 1-reconstructed Ge(001) surface, as well as preservation of the 2 × 1-reconstructed Ge(001) surface. This study presents a low-temperature process to fabricate BTO/Ge heterostructures.

  1. Structural characterization of epitaxial Cr(x)Mo(1-x) alloy thin films.

    PubMed

    Kaspar, T C; Bowden, M E; Varga, T; Wang, C M; Shutthanandan, V; Joly, A G; Wirth, B D; Kurtz, R J

    2012-03-07

    To develop a model system containing regularly spaced misfit dislocations for studies of the radiation resistance of nanoscale defects, epitaxial thin films of Cr, Mo, and Cr(x)Mo(1-x) alloys were deposited on MgO(001) by molecular beam epitaxy. Film compositions were chosen to vary the lattice mismatch with MgO. The film structure was investigated by x-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and scanning transmission electron microscopy (STEM). Epitaxial films with reasonably high crystalline quality and abrupt interfaces were achieved at a relatively low deposition temperature, as confirmed by STEM. However, it was found by XRD and RBS in the channeling geometry that increasing the Mo content of the CrMo alloy films degraded the crystalline quality, despite the improved lattice match with MgO. XRD rocking curve data indicated that regions of different crystalline order may be present within the films with higher Mo content. This is tentatively ascribed to spinodal decomposition into Cr-rich and Mo-rich regions, as predicted by the Cr(x)Mo(1-x) phase diagram.

  2. Thin film evolution equations from (evaporating) dewetting liquid layers to epitaxial growth

    NASA Astrophysics Data System (ADS)

    Thiele, U.

    2010-03-01

    In the present contribution we review basic mathematical results for three physical systems involving self-organizing solid or liquid films at solid surfaces. The films may undergo a structuring process by dewetting, evaporation/condensation or epitaxial growth, respectively. We highlight similarities and differences of the three systems based on the observation that in certain limits all of them may be described using models of similar form, i.e. time evolution equations for the film thickness profile. Those equations represent gradient dynamics characterized by mobility functions and an underlying energy functional. Two basic steps of mathematical analysis are used to compare the different systems. First, we discuss the linear stability of homogeneous steady states, i.e. flat films, and second the systematics of non-trivial steady states, i.e. drop/hole states for dewetting films and quantum-dot states in epitaxial growth, respectively. Our aim is to illustrate that the underlying solution structure might be very complex as in the case of epitaxial growth but can be better understood when comparing the much simpler results for the dewetting liquid film. We furthermore show that the numerical continuation techniques employed can shed some light on this structure in a more convenient way than time-stepping methods. Finally we discuss that the usage of the employed general formulation does not only relate seemingly unrelated physical systems mathematically, but does allow as well for discussing model extensions in a more unified way.

  3. Mechanism of Charge Transport in Cobalt and Iron Phthalocyanine Thin Films Grown by Molecular Beam Epitaxy

    SciTech Connect

    Kumar, Arvind; Samanta, Soumen; Singh, Ajay; Debnath, A. K.; Aswal, D. K.; Gupta, S. K.

    2011-12-12

    Cobalt phthalocyanine (CoPc), iron phthalocyanine (FePc) and their composite (CoPc-FePc) films have been grown by molecular beam epitaxy (MBE). Grazing incidence X-ray diffraction (GIXRD) and scanning electron microscope (SEM) studies showed that composite films has better structural ordering compared to individual CoPc and FePc films. The temperature dependence of resistivity (in the temperature range 25 K- 100 K) showed that composite films are metallic, while individual CoPc and FePc films are in the critical regime of metal-to-insulator (M-I) transition The composite films show very high mobility of 110 cm{sup 2} V{sup -1} s{sup -1} at room temperature i.e. nearly two order of magnitude higher compared to pure CoPc and FePc films.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2007-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    Epitaxial Fe-Ga thin films in disordered bcc α-Fe crystal structure (A2) have been grown on GaAs(001) by molecular beam epitaxy. The saturated magnetization (MS) 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.

  7. 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.

  8. Epitaxy of mercury-based high temperature superconducting films on oxide and metal substrates

    NASA Astrophysics Data System (ADS)

    Xie, Yi-Yuan

    High-Tc superconducting (HTS) cuprates are highly anisotropic thus epitaxy along certain crystalline directions is essential to realize high-current-carrying capability at temperatures above 77 K. Hg-based HTS (Hg-HTS) cuprates have the record-high Tc up to 135 K, therefore are of great interest for fundamental research and practical applications. However, growth Of epitaxial Hg-HTS films is extremely difficult in conventional thermal-reaction process since Hg is highly volatile. Motivated by this, we first developed a cation-exchange process for growing epitaxial Hg-HTS films, which involves two steps: selection of precursor matrices with predesigned structure and composition followed by cation-exchange processing. New materials are formed via "atomic surgery" on an existing structure rather than thermal reaction among amorphous oxides in conventional process, thus the structural features of the precursor are inherited by the new material. Using epitaxial Tl-based HTS films as precursor and annealing them in Hg-vapor, epitaxial Hg-HTS films with superior quality have been obtained. This success encouraged us to develop epitaxy on metal tapes for coated conductors and On large-area wafers for electronic devices. For coated conductors, we addressed three critical issues: epitaxy on metal substrates, enhancement of in-field Jcs and scale-up in thickness and length. First, using a fabrication scheme that combines two processes: cation-exchange and fast-temperature-ramping-annealing, epitaxial HgBa2CaCu2O6+delta films were grown on rolling-assisted-biaxially-textured Ni substrates buffered with CeO 2/YSZ/CeO2 for the first time. We fabricated HgBa2CaCu 2O6+delta coated conductors with Tc = 122--124 K and self-field Jc > 1 x 106A/cm2 at 92 K which are record-high for HTS coated conductors. Second, we demonstrated improved in-field J cs via overdoping HgBa2CaCu 2O6+delta films (by means Of charge "overdoped"), heavy-ion-irradiation and substrate engineering. Finally

  9. Characterization of off-axis MgB2 epitaxial thin films for planar junctions

    NASA Astrophysics Data System (ADS)

    Iavarone, M.; Karapetrov, G.; Menzel, A.; Komanicky, V.; You, H.; Kwok, W. K.; Orgiani, P.; Ferrando, V.; Xi, X. X.

    2005-12-01

    Using scanning tunneling spectroscopy, we perform a full mapping of the quasiparticle density of states of magnesium diboride (MgB2) epitaxial thin films grown on (110) yttrium stabilized zirconia (YSZ) by hybrid physical-chemical vapor deposition. The films have critical temperatures of 40 K. X-ray measurements show an epitaxial MgB2 growth having the c-axis tilted by 32° with respect to the normal to the substrate, consistent with the atomic force microscopy images of the sample. Scanning tunneling spectroscopy clearly finds that the spectroscopic peak associated to the π gap is reduced on most of the film surface and the feature representative of the σ gap is present, with different intensity, on the majority of the sample's surface, which is consistent with x-ray measurements.

  10. 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.; ...

    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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Tunable band gap in epitaxial ferroelectric Ho(Mn,Ga)O{sub 3} films

    SciTech Connect

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

    2016-05-09

    Ferroelectrics have recently attracted attention as a new class of materials for use in optical and photovoltaic devices. We studied the electronic properties in epitaxially stabilized ferroelectric hexagonal Ho(Mn{sub 1−x}Ga{sub x})O{sub 3} (x = 0, 0.33, 0.67, and 1) thin films. Our films exhibited systematic changes in electronic structures, such as bandgap and optical transitions, according to the Ga concentration. In particular, the bandgap increased systematically from 1.4 to 3.2 eV, including the visible light region, with increasing Ga concentration from x = 0 to 1. These systematic changes, attributed to lattice parameter variations in epitaxial Ho(Mn{sub 1−x}Ga{sub x})O{sub 3} films, should prove useful for the design of optoelectronic devices based on ferroelectrics.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  17. 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.

  18. 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.

  19. Epitaxial growth and properties of MoOx(2films

    NASA Astrophysics Data System (ADS)

    Bhosle, V.; Tiwari, A.; Narayan, J.

    2005-04-01

    We report the growth of epitaxial molybdenum oxide (MoOx,2films on c plane of sapphire substrate using pulsed laser deposition in oxygen environment. The structure was characterized using x-ray diffraction, high resolution transmission electron microscopy and x-ray photoelectron spectroscopy (XPS). Electrical resistivity and optical properties were investigated using four-point-probe resistivity measurements and spectroscopy techniques, respectively. It was found that the film had a monoclinic structure based on MoO2 phase and showed an unusual combination of high conductivity and high transmittance in the visible region after annealing. The unusual combination of these properties was realized by systematically controlling the relative fraction of different oxidation states of molybdenum, namely Mo4+, Mo5+, and Mo6+ in the monoclinic phase. For a film 60nm thick and annealed at 250°C for 1h, the ratio of Mo6+/(Mo4++Mo5+) was determined to be ˜2.9/1 using XPS, and a typical value of transmittance was ˜65% and resistivity close to 1×10-3Ωcm. These results demonstrate growth of epitaxial MoOx films with tunable electrical and optical properties. Further optimization of these properties is expected to result in applications related to display panels, solar cells, chromogenic (photochromic, electrochromic, gasochromic) devices, and transparent conducting oxides. Our ability to grow epitaxial MoOx films can further aid their integration with optoelectronic and photonic devices.

  20. Diamagnetism to ferromagnetism in Sr-substituted epitaxial BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Punugupati, Sandhyarani; Prater, John T.; Narayan, Jagdish

    2016-04-01

    We report on the ferromagnetic-like behavior in otherwise diamagnetic BaTiO3 (BTO) thin films upon doping with non-magnetic element Sr having the composition Ba0.4Sr0.6TiO3 (BST). The epitaxial integration of BST (˜800 nm) thick films on Si (100) substrate was achieved using MgO (40 nm) and TiN (20 nm) as buffer layers to prepare BST/MgO/TiN/Si (100) heterostructure by pulsed laser deposition. The c-axis oriented and cube-on-cube epitaxial BST is formed on Si (100) as evidenced by the in-plane and out-of-plane X-ray diffraction. All the deposited films are relaxed through domain matching epitaxy paradigm as observed from X-ray diffraction pattern and A1TO3 mode (at 521.27 cm-1) of Raman spectra. As-deposited BST thin films reveal ferromagnetic-like properties, which persist up to 400 K. The magnetization decreases two-fold upon oxygen annealing. In contrast, as-deposited un-doped BTO films show diamagnetism. Electron spin resonance measurements reveal no evidence of external magnetic impurities. XRD and X-ray photoelectron spectroscopy spectra show significant changes influenced by Sr doping in BTO. The ferromagnetic-like behavior in BST could be due to the trapped electron donors from oxygen vacancies resulting from Sr-doping.

  1. Ordering of defects induced by epitaxy in LaCoO3 films

    NASA Astrophysics Data System (ADS)

    Mehta, Virat; Biskup, Neven; Wong, Franklin; Arenholz, Elke; Varela, Maria; Suzuki, Yuri

    2012-02-01

    In the bulk, LaCoO3 (LCO) undergoes a spin state transition from a diamagnet to a paramagnet with increasing temperature. Recent studies of epitaxial LCO thin films have resulted in the stabilization of a higher spin state and ferromagnetic ordering at low temperatures. Here, we explore the effects of epitaxy on the electronic structure of LCO films with X-ray absorption spectroscopy (XAS) and scanning transmission electron microscopy (STEM). We find differences in XAS spectra in coherently strained thinner films compared to the thicker partially relaxed films which may be due to differences in Co valence and bonding. STEM and electron energy loss spectroscopy of thinner LCO films reveal ordered defect planes that appear to be associated with a change in the O and Co bonding environments. In films on LaAlO3 strained in compression periodic planes occur parallel to the substrate-film interface, while films on SrTiO3 strained in tension have perpendicular defect planes. Correlation with magnetic data suggests that defect rich regions may exhibit greater ferromagnetism.

  2. Epitaxial Growth and Electronic Properties of Large Hexagonal Graphene Domains on Cu(111) Thin Film

    NASA Astrophysics Data System (ADS)

    Ago, Hiroki; Kawahara, Kenji; Ogawa, Yui; Tanoue, Shota; Bissett, Mark A.; Tsuji, Masaharu; Sakaguchi, Hidetsugu; Koch, Roland J.; Fromm, Felix; Seyller, Thomas; Komatsu, Katsuyoshi; Tsukagoshi, Kazuhito

    2013-07-01

    Large hexagonal single-crystalline domains of single-layer graphene are epitaxially grown by ambient-pressure chemical vapor deposition over a thin Cu(111) film deposited on c-plane sapphire. The hexagonal graphene domains with a maximum size of 100 µm are oriented in the same direction due to the epitaxial growth. Reflecting high crystallinity, a clear band structure with the Dirac cone is observed by angle-resolved photoelectron spectroscopy (ARPES), and a high carrier mobility exceeding 4,000 cm2 V-1 s-1 is obtained on SiO2/Si at room temperature. Our epitaxial approach combined with large domain growth is expected to contribute to future electronic applications.

  3. Epitaxial strain-engineered self-assembly of magnetic nanostructures in FeRh thin films

    NASA Astrophysics Data System (ADS)

    Witte, Ralf; Kruk, Robert; Molinari, Alan; Wang, Di; Schlabach, Sabine; Brand, Richard A.; Provenzano, Virgil; Hahn, Horst

    2017-01-01

    In this paper we introduce an innovative bottom-up approach for engineering self-assembled magnetic nanostructures using epitaxial strain-induced twinning and phase separation. X-ray diffraction, 57Fe Mössbauer spectroscopy, scanning tunneling microscopy, and transmission electron microscopy show that epitaxial films of a near-equiatomic FeRh alloy respond to the applied epitaxial strain by laterally splitting into two structural phases on the nanometer length scale. Most importantly, these two structural phases differ with respect to their magnetic properties, one being paramagnetic and the other ferromagnetic, thus leading to the formation of a patterned magnetic nanostructure. It is argued that the phase separation directly results from the different strain-dependence of the total energy of the two competing phases. This straightforward relation directly enables further tailoring and optimization of the nanostructures’ properties.

  4. 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.

  5. 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.

  6. Strain in epitaxial high-index Bi2Se3(221) films grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Li, Bin; Chen, Weiguang; Guo, Xin; Ho, Wingkin; Dai, Xianqi; Jia, Jinfeng; Xie, Maohai

    2017-02-01

    High-index Bi2Se3(221) film has been grown on In2Se3-buffered GaAs(001), in which a much retarded strain relaxation dynamics is recorded. The slow strain-relaxation process of in epitaxial Bi2Se3(221) can be attributed to the layered structure of Bi2Se3 crystal, where the epifilm grown along [221] is like a pile of weakly-coupled quintuple layer slabs stacked side-by-side on substrate. Finally, we reveal strong chemical bonding at the interface of Bi2Se3 and In2Se3 by plotting differential charge contour calculated by first-principle method. This study points to the feasibility of achieving strained TIs for manipulating the properties of topological systems.

  7. Highly aligned epitaxial nanorods with a checkerboard pattern in oxide films.

    PubMed

    Park, S; Horibe, Y; Asada, T; Wielunski, L S; Lee, N; Bonanno, P L; O'Malley, S M; Sirenko, A A; Kazimirov, A; Tanimura, M; Gustafsson, T; Cheong, S-W

    2008-02-01

    One of the central challenges of nanoscience is fabrication of nanoscale structures with well-controlled architectures using planar thin-film technology. Herein, we report that ordered nanocheckerboards in ZnMnGaO4 films were grown epitaxially on single-crystal MgO substrates by utilizing a solid-state method of the phase separation-induced self-assembly. The films consist of two types of chemically distinct and regularly spaced nanorods with mutually coherent interfaces, approximately 4 x 4 x 750 nm3 in size and perfectly aligned along the film growth direction. Surprisingly, a significant in-plane strain, more than 2%, from the substrate is globally maintained over the entire film thickness of about 820 nm. The strain energy from Jahn-Teller distortions and the film-substrate lattice mismatch induce the coherent three-dimensional (3D) self-assembled nanostructure, relieving the volume strain energy while suppressing the formation of dislocations.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  9. 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.

  10. 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.

  11. X-ray absorption spectroscopy on epitaxial BaTiO3 thin film

    NASA Astrophysics Data System (ADS)

    Panchal, Gyanendra; Shukla, D. K.; Choudhary, R. J.; Reddy, V. Raghavendra; Phase, D. M.

    2017-05-01

    We report the soft X-ray absorption spectroscopy (XAS) on pulsed laser deposition (PLD) grown epitaxial BaTiO3 thin film on (001) oriented SrTiO3 substrate. X-ray diffraction studies confirm that film is grown along the [001] direction and is compressed along surface normal. XAS around O K edge and Ti L3,2 edges performed on BaTiO3 thin film along with bulk BaTiO3 depicts considerable changes in crystal field parameters in thin film form due to strain present in the film. Modifications observed in t2g and eg sub bands of Ti ions are explained considering structural anisotropies present in the thin film.

  12. Epitaxial growth and electronic structure of oxyhydride SrVO{sub 2}H thin films

    SciTech Connect

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

    2016-08-28

    Oxyhydride SrVO{sub 2}H epitaxial thin films were fabricated on SrTiO{sub 3} substrates via topotactic hydridation of oxide SrVO{sub 3} films using CaH{sub 2}. Structural and composition analyses suggested that the SrVO{sub 2}H film possessed one-dimensionally ordered V-H{sup −}-V bonds along the out-of-plane direction. The synthesis temperature could be lowered by reducing the film thickness, and the SrVO{sub 2}H film was reversible to SrVO{sub 3} by oxidation through annealing in air. Photoemission and X-ray absorption spectroscopy measurements revealed the V{sup 3+} valence state in the SrVO{sub 2}H 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.

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

    DOE PAGES

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

    2016-11-07

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

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

    DOE PAGES

    Demaurex, Bénédicte; Bartlome, Richard; Seif, Johannes P.; ...

    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

  15. 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.

  16. 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.

  17. Epitaxial film growth of zirconium diboride on Si(0 0 1)

    NASA Astrophysics Data System (ADS)

    Roucka, R.; Tolle, J.; Chizmeshya, A. V. G.; Tsong, I. S. T.; Kouvetakis, J.

    2005-04-01

    The structure of epitaxial ZrB 2 films grown on Si(0 0 1) substrates via the thermal decomposition of the unimolecular precursor Zr(BH 4) 4 was studied by X-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy (XTEM). In spite of the large lattice mismatch between the Si(0 0 1) substrate and ZrB 2, epitaxy occurs via a coincidence-misfit mechanism in which the strain between film and substrate is accommodated by edge dislocations along the film-substrate interface. While the growth axis of the ZrB 2 film lies along the [1 1̲ 0 0] direction, i.e. [1 1̲ 0 0]//[0 0 1], the epitaxy produces two orthogonal domains as the result of a 6:5 misfit for [1 1 2̲ 0]//[1 1̲ 0] and a 13:12 misfit for [0 0 0 1̲ ]//[1 1̲ 0] along the same direction on the interface plane. These domains take the form of two-dimensional rectangular islands orthogonal to each other. The island-substrate and island-island interfaces were examined in detail with high-resolution XTEM and compared with theoretical models.

  18. Formation of V-grooves in SrRuO3 epitaxial film

    NASA Astrophysics Data System (ADS)

    Liu, Guiju; Feng, Honglei; Liu, Bin; Wang, Yiqian; Liu, Wei; Zou, Bin; Alford, Neil McN.; Petrov, Peter K.

    2016-12-01

    SrRuO3 thin films were epitaxially grown on a (001) SrTiO3 substrate using pulsed laser deposition technique. Various defects such as V-grooves, threading dislocations and dislocation dipoles are observed in the SrRuO3 epitaxial film. It is found that the sidewalls of most V-grooves are {101} facets, and the dominant angle between the sidewalls is 90°. Some threading dislocations end at the apexes of the V-grooves while the others penetrate the entire film. The threading dislocations and V-grooves can partially relieve the strain in the epitaxial SrRuO3 film. During the relaxation process, a two-dimensional growth mode transforms into a three-dimensional one, along with the formation of mesa-like islands separated by V-grooves. The dimensions and distributions of V-grooves are associated with the growth conditions. The control of growth mechanism and surface morphology are very important for the fabrication of novel perovskite oxide devices.

  19. 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.

  20. 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.

  1. 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).

  2. Epitaxial electrodeposition of metal oxide films and superlattices which exhibit resistance switching

    NASA Astrophysics Data System (ADS)

    Gudavarthy, Rakesh Vathsal

    This dissertation presents an investigation of the electrodeposition of metal oxide films and superlattices on conducting polycrystalline and single crystal substrates. In the first part of the study, electrodeposition of magnetite (Fe3O4) films and superlattices in the magnetite/zinc ferrite system which exhibit resistance switching is studied. Paper I reports the electrodeposition of superlattices in the magnetite/zinc ferrite system and shows that only superlattices exhibit multi state resistance switching. In paper II, simple polycrystalline magnetite films electrodeposited on stainless steel crystals exhibit multistate resistance switching which can be tuned by controlling the composition of the films. Paper III describes the epitaxial electrodeposition of Fe3O4films on Ni(111) substrates. In the second part, electrodeposited epitaxial films of CuO onto achiral Cu single crystals using chiral precursors are studied. Paper IV describes chiral electrodeposition of CuO from copper(II) complexes of malic acid on Cu single crystals. X-ray pole figures in conjunction with stereographic projections are used to determine the absolute configuration of the films. X-ray crystal structures of copper(II) malate crystals are analyzed to understand the mechanism of chiral electrodeposition.

  3. Catalytic Activity Enhancement for Oxygen Reduction on Epitaxial Perovskite Thin Films for Solid-Oxide Fuel Cells

    SciTech Connect

    La O', Gerardo Jose; Ahn, Sung Jin; Crumlin, Ethan; Orikasa, Yuki; Biegalski, Michael D; Christen, Hans M; Shao-Horn, Yang

    2010-01-01

    The active ingredient: La{sub 0.8}Sr{sub 0.2}CoO{sub 3-{delta}} (LSC) epitaxial thin films are prepared on (001)-oriented yttria-stabilized zirconia (YSZ) single crystals with a gadolinium-doped ceria (GDC) buffer layer. The LSC epitaxial films exhibit better oxygen reduction kinetics than bulk LSC. The enhanced activity is attributed in part to higher oxygen nonstoichiometry.

  4. 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.

  5. Air-bridged lateral epitaxial overgrowth of GaN thin films

    NASA Astrophysics Data System (ADS)

    Kidoguchi, Isao; Ishibashi, Akihiko; Sugahara, Gaku; Ban, Yuzaburoh

    2000-06-01

    A promising technique of selective lateral epitaxy, namely air-bridged lateral epitaxial overgrowth, is demonstrated in order to reduce the wing tilt as well as the threading dislocation density in GaN thin films. A seed GaN layer was etched to make ridge-stripe along <11¯00>GaN direction and a GaN material was regrown from the exposed (0001) top facet of the ridged GaN seed structures, whose sidewalls and etched bottoms were covered with silicon nitride mask, using low-pressure metalorganic vapor phase epitaxy. The density of dislocations in the wing region was reduced to be <107cm-2, which was at least two orders of magnitude lower than that of underlying GaN. The magnitude of the wing tilt was determined to be 0.08° by x-ray diffraction (XRD) measurements, which was smaller than other lateral epitaxial overgrown GaN thin films. The full width at half maximum of XRD for the wing region was 138 arc sec, indicating high uniformity of c-axis orientation.

  6. 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

  7. Complete Fabrication of a Traversable 3 µm Thick NbN Film Superconducting Coil with Cu plated layer of 42m in Length in a Spiral Three-Storied Trench Engraved in a Si Wafer of 76.2 mm in Diameter Formed by MEMS Technology for a Compact SMES with High Energy Storage Volume Density

    NASA Astrophysics Data System (ADS)

    Suzuki, Yasuhiro; Iguchi, Nobuhiro; Adachi, Kazuhiro; Ichiki, Akihisa; Hioki, Tatsumi; Hsu, Che-Wei; Sato, Ryoto; Kumagai, Shinya; Sasaki, Minoru; Noh, Joo-Hyong; Sakurahara, Yuuske; Okabe, Kyohei; Takai, Osamu; Honma, Hideo; Watanabe, Hideo; Sakoda, Hitoshi; Sasagawa, Hiroaki; Doy, Hideyuki; Zhou, Shuliang; Hori, H.; Nishikawa, Shigeaki; Nozaki, Toshihiro; Sugimoto, Noriaki; Motohiro, Tomoyoshi

    2017-09-01

    Based on the concept of a novel approach to make a compact SMES unit composed of a stack of Si wafers using MEMS process proposed previously, a complete fabrication of a traversable 3 µam thick NbN film superconducting coil lined with Cu plated layer of 42m in length in a spiral three-storied trench engraved in and extended over a whole Si-wafer of 76.2 mm in diameter was attained for the first time. With decrease in temperature, the DC resistivity showed a metallic decrease indicating the current pass was in the Cu plated layer and then made a sudden fall to residual contact resistance indicating the shift of current pass from the Cu plated layer to the NbN film at the critical temperature Tc of 15.5K by superconducting transition. The temperature dependence of I-V curve showed the increase in the critical current with decrease in the temperature and the highest critical current measured was 220 mA at 4K which is five times as large as that obtained in the test fabrication as the experimental proof of concept presented in the previous report. This completion of a one wafer superconducting NbN coil is an indispensable step for the next proof of concept of fabrication of series-connected two wafer coils via superconductive joint which will read to series connected 600 wafer coils finally, and for replacement of NbN by high Tc superconductor such as YBa2Cu3O7-x for operation under the cold energy of liquid hydrogen or liquid nitrogen.

  8. Chemical beam epitaxy of GaAs films using single-source precursors

    NASA Astrophysics Data System (ADS)

    Ekerdt, J. G.; Sun, Y. M.; Jackson, M. S.; Lakhotia, V.; Pacheco, K. A.; Koschmieder, S. U.; Cowley, A. H.; Jones, R. A.

    1992-11-01

    Two types of single-source precursors were studied that contained different Ga : As stoichiometry, [Me 2Ga(μ-AS- t-Bu 2)] 2 with a 1 : 1 stoichoimetry and Ga(As>- t-Bu 2) 3 with a 1 : 3 stoichiometry. Epitaxial films were grown from Ga(As- t-Bu 2) 3 on (100) GaAs in a chemical beam epitaxy system at 750 K and 6 × 10 -5 Torr. Temperature programmed desorption (TPD) studies for [Me 2Ga(μ- As- t-Bu 2)] 2 and Ga(As- t-Bu 2) 3 have been undertaken in a surface analysis chamber to develop an understanding of how precursor structure and reaction chemistry influence film properties. tert-Butyl ligands appear to react by β-hydride elimination process to isobutene and AsH. The methyl ligands appear to desorb rather than react with surface hydride to methane.

  9. Epitaxial growth of lead zirconium titanate thin films on Ag buffered Si substrates using rf sputtering

    NASA Astrophysics Data System (ADS)

    Wang, Chun; Laughlin, David E.; Kryder, Mark H.

    2007-04-01

    Epitaxial lead zirconium titanate (PZT) (001) thin films with a Pt bottom electrode were deposited by rf sputtering onto Si(001) single crystal substrates with a Ag buffer layer. Both PZT(20/80) and PZT(53/47) samples were shown to consist of a single perovskite phase and to have the (001) orientation. The orientation relationship was determined to be PZT(001)[110]‖Pt(001)[110]‖Ag(001)[110]‖Si(001)[110]. The microstructure of the multilayer was studied using transmission electron microscopy (TEM). The electron diffraction pattern confirmed the epitaxial relationship between each layer. The measured remanent polarization Pr and coercive field Ec of the PZT(20/80) thin film were 26μC /cm2 and 110kV/cm, respectively. For PZT(53/47), Pr was 10μC /cm2 and Ec was 80kV/cm.

  10. Surfactant-assisted epitaxial growth and magnetism of Fe films on Cu(111).

    PubMed

    Niño, M A; Camarero, J; Gómez, L; Ferrón, J; de Miguel, J J; Miranda, R

    2008-07-02

    The magnetic properties of thin epitaxial layers of Fe grown on Cu(111) depend sensitively on the films' structure and morphology. A combination of experiments and numerical simulations reveals that the use of a surfactant monolayer (ML) of Pb during molecular beam epitaxy (MBE) growth at room temperature reduces the amount of interdiffusion at the Cu-Fe interface, retards the fcc-to-bcc transformation by about 2 ML and substantially increases the films' coercivity. The origin of all these alterations to the magnetic behavior can be traced back to the structural modifications provoked by the surfactant during the early growth stages. These results open the way for the controlled fabrication of custom-designed materials with specific magnetic characteristics.

  11. Improvement of Crystalline Quality in GaN Films by Air-Bridged Lateral Epitaxial Growth

    NASA Astrophysics Data System (ADS)

    Kidoguchi, Isao; Ishibashi, Akihiko; Sugahara, Gaku; Tsujimura, Ayumu; Ban, Yuzaburoh

    2000-05-01

    Air-bridged lateral epitaxial growth (ABLEG), a new technique of lateral growth of GaN films, has been developed using low-pressure metalorganic vapor phase epitaxy. A previously grown 1-μm-thick GaN film is grooved along the < 1{\\bar 1}00 >\\textrm{GaN} direction, and the bottoms of the trenches and the sidewalls are covered with a silicon nitride mask. A free-standing GaN material is regrown from the exposed (0001) surface of the ridged GaN seed structure. Cross-sectional transmission electron microscopy analysis reveals that the dislocations originating from the underlying seed GaN extend straight in the < 0001 > direction and dislocations do not propagate into the wing region. The wing region also exhibits a smooth surface and the root mean square roughness is found to be 0.088 nm by atomic force microscopy measurement of the (0001) face of the wing region.

  12. Growth of In[sub 2]O[sub 3] thin films by atomic layer epitaxy

    SciTech Connect

    Asikainen, T.; Ritala, M.; Leskelae, M. . Dept. of Chemistry)

    1994-11-01

    Simultaneously occurring transparency and electrical conductivity give rise to numerous thin film applications for indium oxide doped with tin (ITO), e.g., as transparent electrodes in flat panel displays and electrochromic windows, as active and passive components in photovoltaic devices, and as long wavelength IR radiation reflecting heat mirror layers in energy saving windows. Indium oxide thin films were deposited by atomic layer epitaxy technique at 400 and 500 C using InCl[sub 3] and water as reactants. The films were characterized by means of X-ray diffraction, Rutherford backscattering spectrometry, nuclear reaction analysis, scanning electron microscopy, and by optical and electrical measurements. The highest deposition rate obtained was only 0.27 [angstrom]/cycle. The films were polycrystalline In[sub 2]O[sub 3] having the [100] direction as the most pronounced orientation. The resistivities of the highly transparent films were in the order of 3 [times] 10[sup [minus]3] [Omega]-cm.

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

    SciTech Connect

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

    2012-05-01

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

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

    DOE PAGES

    Shen, Xuan; Qiu, Xiangbiao; Su, Dong; ...

    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

  15. Controlled growth of antimony-doped tin dioxide thin films by atomic layer epitaxy

    NASA Astrophysics Data System (ADS)

    Viirola, H.; Niinistoe, L.

    1994-11-01

    Antimony-doped tin dioxide thin films were deposited on glass substrates by atomic layer epitaxy using SnCl4, SbCl5 and H2O as reactants. The growth experiments were carried out at 500 C. The effect of Sb doping on the growth rate, crystal texture and electrical and optical properties was studied. Spectrophotometry, secondary ion mass spectrometry, X-ray diffraction and electron spectroscopy for chemical analysis, as well as sheet resistance and Hall measurements were used to characterize the films. The films were highly uniform with only small thickness and sheet resistance variations. The films were polycrystalline with their crystallites having a preferred orientation, which depended on the Sb doping level and film thickness.

  16. Thermal process effect on microstructure and magnetic properties of epitaxial FePd(001) multilayer films.

    PubMed

    Wei, D H; Fong, S C

    2011-03-01

    Thermal process effect on the microstructure and magnetic characterizations of epitaxial FePd multilayer films grown on MgO(001) substrates via electron-beam deposition have been investigated. For the FePd films directly grown at 400 degrees C, the isolated island-like morphology was observed and displayed a perpendicular magnetic anisotropy with a large coercivity of 8000 Oe. On the other hand, the FePd films grown at 100 degrees C and then post-annealed at 400 degrees C showed continuous film morphology and with a lower remanence corresponded to the alternate up and down orientations of the magnetization. The significant distinction in magnetic exhibition of the FePd films was due to the remarkable change in surface and magnetic domain structures caused by varied interfacial energy during different thermal processes.

  17. 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.

  18. Effects of Growth Temperature on Epitaxial Thin Films of Vanadium Dioxide Grown by Pulsed Laser Deposition

    SciTech Connect

    Nag, Joyeeta; HaglundJr., Richard F; Payzant, E Andrew

    2011-01-01

    Stoichiometric vanadium dioxide in all of its bulk, thin film and nanostructured forms exhibits an insulator-to-metal transition (IMT) accompanied by structural change, induced by various physical and chemical stimuli such as temperature, ultrashort light pulses, electric field, doping or strain. In these applications, the optical qualities of the films are of paramount importance, but are often highly variable depending on fabrication procedure. We have grown epitaxial films of vanadium dioxide on c-plane (0001) of sapphire using two different procedures involving room temperature growth followed by annealing and direct high temperature growth. Strain at the interface of the substrate and the film due to growth at different temperatures leads to significant differences in morphologies and phase transition characteristics. We present a comparative study of the morphologies and switching characteristics of the two films and conclude that contrary to conventional wisdom, the room-temperature grown films have smoother, more continuous morphologies and better switching performance. Our observation is supported by theoretical and experimental studies of epitaxial growth of semiconductors.

  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. Layer-by-layer epitaxial thin films of the pyrochlore Tb2Ti2O7

    NASA Astrophysics Data System (ADS)

    Bovo, Laura; Rouleau, Christopher M.; Prabhakaran, Dharmalingam; Bramwell, Steven T.

    2017-02-01

    Layer-by-layer epitaxial growth of the pyrochlore magnet Tb2Ti2O7 on the isostructural substrate Y2Ti2O7 results in high-quality single crystal films of up to 60 nm thickness. Substrate-induced strain is shown to act as a strong and controlled perturbation to the exotic magnetism of Tb2Ti2O7, opening up the general prospect of strain-engineering the diverse magnetic and electrical properties of pyrochlore oxides.

  1. Layer-by-layer epitaxial thin films of the pyrochlore Tb2Ti2O7.

    PubMed

    Bovo, Laura; Rouleau, Christopher M; Prabhakaran, Dharmalingam; Bramwell, Steven T

    2017-02-03

    Layer-by-layer epitaxial growth of the pyrochlore magnet Tb2Ti2O7 on the isostructural substrate Y2Ti2O7 results in high-quality single crystal films of up to 60 nm thickness. Substrate-induced strain is shown to act as a strong and controlled perturbation to the exotic magnetism of Tb2Ti2O7, opening up the general prospect of strain-engineering the diverse magnetic and electrical properties of pyrochlore oxides.

  2. 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.

  3. 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.

  4. 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.

  5. Epitaxial growth of REBa 2Cu 3O 7- y films on various substrates by chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Yamagiwa, K.; Araki, T.; Takahashi, Y.; Hiei, H.; Kim, S. B.; Matsumoto, K.; Shibata, J.; Hirayama, T.; Ikuta, H.; Mizutani, U.; Hirabayashi, I.

    2001-07-01

    We have investigated the processing conditions for solid phase epitaxial growth of REBa 2Cu 3O 7- y (RE=rare earth and Y; RE123) by chemical solution deposition (CSD) using metalorganic precursors. We selected two kinds of starting materials, metal naphthenates and metal trifluoroacetates, for RE123 films. The films are crystallized through barium carbonate and fluoride, respectively. Superconducting properties of RE123 films were strongly dependent on microstructure of the calcined film. In the case of the metal naphthenates route, the calcined films had to be amorphous in order to realize solid phase epitaxial growth. However, Jc of the epitaxially grown film was low. On the other hand, using the metal trifluoroacetates, RE123 films were grown epitaxially even if the calcined films were crystallized in metal oxyfluoride. To prepare thicker RE123 films, single step coating controlling concentration and/or viscosity of coating solution is necessary because F-contained reactive gas was formed during heat-treatment. Using chemically stable CeO 2-buffered YSZ as substrates, we have succeeded in preparing the YBCO films, having high Jc of 3.6 MA/cm 2 and 4700 Å in thickness.

  6. Epitaxial SrTiO3 films with electron mobilities exceeding 30,000cm2V-1s-1

    NASA Astrophysics Data System (ADS)

    Son, Junwoo; Moetakef, Pouya; Jalan, Bharat; Bierwagen, Oliver; Wright, Nicholas J.; Engel-Herbert, Roman; Stemmer, Susanne

    2010-06-01

    The study of quantum phenomena in semiconductors requires epitaxial structures with exceptionally high charge-carrier mobilities. Furthermore, low-temperature mobilities are highly sensitive probes of the quality of epitaxial layers, because they are limited by impurity and defect scattering. Unlike many other complex oxides, electron-doped SrTiO3 single crystals show high (~104cm2V-1s-1) electron mobilities at low temperatures. High-mobility, epitaxial heterostructures with SrTiO3 have recently attracted attention for thermoelectric applications, field-induced superconductivity and two-dimensional (2D) interface conductivity. Epitaxial SrTiO3 thin films are often deposited by energetic techniques, such as pulsed laser deposition. Electron mobilities in such films are lower than those of single crystals. In semiconductor physics, molecular beam epitaxy (MBE) is widely established as the deposition method that produces the highest mobility structures. It is a low-energetic, high-purity technique that allows for low defect densities and precise control over doping concentrations and location. Here, we demonstrate controlled doping of epitaxial SrTiO3 layers grown by MBE. Electron mobilities in these films exceed those of single crystals. At low temperatures, the films show Shubnikov-de Haas oscillations. These high-mobility SrTiO3 films allow for the study of the intrinsic physics of SrTiO3 and can serve as building blocks for high-mobility oxide heterostructures.

  7. 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.

  8. Ta-doped Anatase TiO2 Epitaxial Film as Transparent Conducting Oxide

    NASA Astrophysics Data System (ADS)

    Hitosugi, Taro; Furubayashi, Yutaka; Ueda, Atsuki; Itabashi, Kinnosuke; Inaba, Kazuhisa; Hirose, Yasushi; Kinoda, Go; Yamamoto, Yukio; Shimada, Toshihiro; Hasegawa, Tetsuya

    2005-08-01

    We present electrical transport and optical properties of Ta-doped TiO2 epitaxial thin films with varying Ta concentration grown by the pulsed laser deposition method. The Ti0.95Ta0.05O2 film exhibited a resistivity of 2.5× 10-4 Ω cm at room temperature, and an internal transmittance of 95% in the visible light region. These values are comparable to those of a widely used transparent conducting oxide (TCO), indium tin oxide. Furthermore, this new material falls into a new category of TCOs that utilizes d electrons.

  9. Robust Zero-Field Skyrmion Formation in FeGe Epitaxial Thin Films

    NASA Astrophysics Data System (ADS)

    Gallagher, J. C.; Meng, K. Y.; Brangham, J. T.; Wang, H. L.; Esser, B. D.; McComb, D. W.; Yang, F. Y.

    2017-01-01

    B 20 phase magnetic materials have been of significant interest because they enable magnetic Skyrmions. One major effort in this emerging field is the stabilization of Skyrmions at room temperature and zero magnetic field. We grow phase-pure, high crystalline quality FeGe epitaxial films on Si(111). Hall effect measurements reveal a strong topological Hall effect after subtracting the ordinary and anomalous Hall effects, demonstrating the formation of high density Skyrmions in FeGe films between 5 and 275 K. In particular, a substantial topological Hall effect was observed at a zero magnetic field, showing a robust Skyrmion phase without the need of an external magnetic field.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1995-01-01

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

  12. Thickness dependent exchange bias in martensitic epitaxial Ni-Mn-Sn thin films

    SciTech Connect

    Behler, Anna; Teichert, Niclas; Auge, Alexander; Hütten, Andreas; Dutta, Biswanath; Hickel, Tilmann; Waske, Anja; Eckert, Jürgen

    2013-12-15

    A thickness dependent exchange bias in the low temperature martensitic state of epitaxial Ni-Mn-Sn thin films is found. The effect can be retained down to very small thicknesses. For a Ni{sub 50}Mn{sub 32}Sn{sub 18} thin film, which does not undergo a martensitic transformation, no exchange bias is observed. Our results suggest that a significant interplay between ferromagnetic and antiferromagnetic regions, which is the origin for exchange bias, is only present in the martensite. The finding is supported by ab initio calculations showing that the antiferromagnetic order is stabilized in the phase.

  13. Room temperature nanoscale ferroelectricity in magnetoelectric GaFeO3 epitaxial thin films.

    PubMed

    Mukherjee, Somdutta; Roy, Amritendu; Auluck, Sushil; Prasad, Rajendra; Gupta, Rajeev; Garg, Ashish

    2013-08-23

    We demonstrate room temperature ferroelectricity in the epitaxial thin films of magnetoelectric gallium ferrite. Piezoforce measurements show a 180° phase shift of piezoresponse upon switching the electric field indicating nanoscale ferroelectricity in the thin films. Further, temperature-dependent impedance analysis with and without the presence of an external magnetic field clearly reveals a pronounced magnetodielectric effect across the magnetic transition temperature. In addition, our first principles calculations show that Fe ions are not only responsible for ferrimagnetism as observed earlier but also give rise to the observed ferroelectricity, making gallium ferrite a unique single phase multiferroic.

  14. Magnetic domain pattern in hierarchically twinned epitaxial Ni-Mn-Ga films.

    PubMed

    Diestel, Anett; Neu, Volker; Backen, Anja; Schultz, Ludwig; Fähler, Sebastian

    2013-07-03

    Magnetic shape memory alloys exhibit a hierarchically twinned microstructure, which has been examined thoroughly in epitaxial Ni-Mn-Ga films. Here we analyze the consequences of this 'twin within twins' microstructure on the magnetic domain pattern. Atomic and magnetic force microscopy are used to probe the correlation between the martensitic microstructure and magnetic domains. We examine the consequences of different twin boundary orientations with respect to the substrate normal as well as variant boundaries between differently aligned twinned laminates. A detailed micromagnetic analysis is given which describes the influence of the finite film thickness on the formation of magnetic band domains in these multiferroic materials.

  15. 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.

  16. 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.

  17. Angular dependence of magnetization reversal in epitaxial chromium telluride thin films with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Pramanik, Tanmoy; Roy, Anupam; Dey, Rik; Rai, Amritesh; Guchhait, Samaresh; Movva, Hema C. P.; Hsieh, Cheng-Chih; Banerjee, Sanjay K.

    2017-09-01

    We investigate magnetic anisotropy and magnetization reversal mechanism in chromium telluride thin films grown by molecular beam epitaxy. We report existence of strong perpendicular magnetic anisotropy in these thin films, along with a relatively strong second order anisotropy contribution. The angular variation of the switching field observed from the magnetoresistance measurement is explained quantitatively using a one-dimensional defect model. The model reveals the relative roles of nucleation and pinning in the magnetization reversal, depending on the applied field orientation. Micromagnetic simulations are performed to visualize the domain structure and switching process.

  18. Atomic Layer Deposition of Ultrathin Crystalline Epitaxial Films of V2O5.

    PubMed

    Sreedhara, M B; Ghatak, J; Bharath, B; Rao, C N R

    2017-01-25

    Ultrathin epitaxial films (10-90 nm thick) of V2O5 have been grown on c-Al2O3 by atomic layer deposition using vanadyl acetylacetonate as the vanadium precursor along with oxygen plasma. Various process parameters have been optimized for the purpose, and excellent crystalline films could be obtained below 200 °C, without the need for post-heat treatment. With a moderate temperature window, the process yields a growth rate of 0.45 Å/cycle. The films have been characterized by electron microscopy, atomic force microscopy, Raman spectroscopy, and other means. The films exhibit a (001) preferred orientation with respect to c-Al2O3 and undergo compressive strain at the initial few monolayer growth to adjust epitaxially with the substrate. Heterojunction diodes based on TiO2(p)-(n)V2O5 as well as a humidity sensor have been fabricated using the V2O5 films.

  19. 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.

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

    SciTech Connect

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

    2016-08-21

    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.

  1. 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.

  2. Big-data reflection high energy electron diffraction analysis for understanding epitaxial film growth processes.

    PubMed

    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 images, 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 data set are now feasible. Here, we develop such an approach to the analysis of the fundamental growth processes through multivariate statistical analysis of a RHEED image sequence. This approach is illustrated for growth of La(x)Ca(1-x)MnO(3) films grown on etched (001) SrTiO(3) 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 asymmetric 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.

  3. 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.

  4. 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.

  5. Interface and Electronic Characterization of Thin Epitaxial Co3O4 Films

    SciTech Connect

    Vaz, C.A.; Zhu, Y.; Wang, H.-Q.; Ahn, C.H.; Henrich, V.E.; Baykara, M.Z.; Schwendemann, T.C.; Pilet, N.; Albers, B.J.; Schwarz, U.D.; Zhang, L.H,; Wang, J.; Altman, E.I.

    2009-01-15

    The interface and electronic structure of thin ({approx} 20-74 nm) Co{sub 3}O{sub 4}(1 1 0) epitaxial films grown by oxygen-assisted molecular beam epitaxy on MgAl{sub 2}O{sub 4}(1 1 0) single crystal substrates have been investigated by means of real and reciprocal space techniques. As-grown film surfaces are found to be relatively disordered and exhibit an oblique low energy electron diffraction (LEED) pattern associated with the O-rich CoO{sub 2} bulk termination of the (1 1 0) surface. Interface and bulk film structure are found to improve significantly with post-growth annealing at 820 K in air and display sharp rectangular LEED patterns, suggesting a surface stoichiometry of the alternative Co{sub 2}O{sub 2} bulk termination of the (1 1 0) surface. Non-contact atomic force microscopy demonstrates the presence of wide terraces separated by atomic steps in the annealed films that are not present in the as-grown structures; the step height of {approx}2.7 {angstrom} corresponds to two atomic layers and confirms a single termination for the annealed films, consistent with the LEED results. A model of the (1 x 1) surfaces that allows for compensation of the polar surfaces is presented.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  8. 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.

  9. Diamagnetism to ferromagnetism in Sr-substituted epitaxial BaTiO{sub 3} thin films

    SciTech Connect

    Singamaneni, Srinivasa Rao Prater, John T.; Punugupati, Sandhyarani; Narayan, Jagdish

    2016-04-04

    We report on the ferromagnetic-like behavior in otherwise diamagnetic BaTiO{sub 3} (BTO) thin films upon doping with non-magnetic element Sr having the composition Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} (BST). The epitaxial integration of BST (∼800 nm) thick films on Si (100) substrate was achieved using MgO (40 nm) and TiN (20 nm) as buffer layers to prepare BST/MgO/TiN/Si (100) heterostructure by pulsed laser deposition. The c-axis oriented and cube-on-cube epitaxial BST is formed on Si (100) as evidenced by the in-plane and out-of-plane X-ray diffraction. All the deposited films are relaxed through domain matching epitaxy paradigm as observed from X-ray diffraction pattern and A{sub 1}TO{sub 3} mode (at 521.27 cm{sup −1}) of Raman spectra. As-deposited BST thin films reveal ferromagnetic-like properties, which persist up to 400 K. The magnetization decreases two-fold upon oxygen annealing. In contrast, as-deposited un-doped BTO films show diamagnetism. Electron spin resonance measurements reveal no evidence of external magnetic impurities. XRD and X-ray photoelectron spectroscopy spectra show significant changes influenced by Sr doping in BTO. The ferromagnetic-like behavior in BST could be due to the trapped electron donors from oxygen vacancies resulting from Sr-doping.

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

    NASA Astrophysics Data System (ADS)

    McClure, Adam Marc

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

  11. 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)].

  12. Strain relaxation and oxygen superstructure modulation in epitaxial Sr4Fe6O13+/-δ films

    NASA Astrophysics Data System (ADS)

    Santiso, J.; Pardo, J. A.; Solís, C.; Garcia, G.; Figueras, A.; Rossell, M. D.; Van Tendeloo, G.

    2005-03-01

    The compressive strain induced in epitaxial Sr4Fe6O13±δ (SFO) films of different thicknesses grown on SrTiO3 substrates is partially released by the modulation of the incommensurate oxygen superstructure along the a-axis parallel to the substrate [q =αam*, superspace group Xmmm(α00)0s0]. The modulation α value varies proportionally to the in-plane a-parameter in a continuous range from 0.41, for fully strained thin films of about 20-30nm, to 0.44 for partially-relaxed thicker films of about 280nm. This mechanism is responsible for the observed slow relaxation of the cell structure upon the film thickness increase in comparison with an equilibrium misfit dislocation-mediated relaxation.

  13. 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.

  14. Epitaxial Growth of Oriented Metalloporphyrin Network Thin Film for Improved Selectivity of Volatile Organic Compounds.

    PubMed

    Li, De-Jing; Gu, Zhi-Gang; Vohra, Ismail; Kang, Yao; Zhu, Yong-Sheng; Zhang, Jian

    2017-03-03

    This study reports an oriented and homogenous cobalt-metalloporphyrin network (PIZA-1) thin film prepared by liquid phase epitaxial (LPE) method. The thickness of the obtained thin films can be well controlled, and their photocurrent properties can also be tuned by LPE cycles or the introduction of conductive guest molecules (tetracyanoquinodimethane and C60 ) into the PIZA-1 pores. The study of quartz crystal microbalance adsorption confirms that the PIZA-1 thin film with [110]-orientation presents much higher selectivity of benzene over toluene and p-xylene than that of the PIZA-1 powder with mixed orientations. These results reveal that the selective adsorption of volatile organic compounds highly depends on the growth orientations of porphyrin-based metal-organic framework thin films. Furthermore, the work will provide a new perspective for developing important semiconductive sensing materials with improved selectivity of guest compounds.

  15. Electrical transport and magnetic properties of epitaxial LSMO films grown on STO substrates

    NASA Astrophysics Data System (ADS)

    Yuan, Wei; Zhao, Yuelei; Su, Tang; Song, Qi; Han, Wei; Shi, Jing

    2015-03-01

    La0.7Sr0.3MnO3 (LSMO) is a very attractive material for spintronics due to its half-metallic ferromagnetic properties. The LSMO films are epitaxially grown on STO (100) substrates using pulsed laser deposition. The effects of substrate temperature, laser power, oxygen pressure, and annealing on the LSMO growth are systematically investigated by the reflection high energy electron diffraction and atomic force microscopy. Under the optimized growth condition, we have achieved atomically flat LSMO thin films with a wide terrace width of more than 5 micro-meters. The electrical transport properties of LSMO thin films of various thicknesses ranging from 8 to 20 monolayers are studied by measuring the resistivity as a function of temperature. We find that the growth condition plays an important role in the critical film thickness for the metal-insulator transition and the Curie temperature. The Ministry of Science and Technology of China.

  16. 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.

  17. Optical characteristics of an epitaxial Fe3Si/Si(111) iron silicide film

    NASA Astrophysics Data System (ADS)

    Tarasov, I. A.; Popov, Z. I.; Varnakov, S. N.; Molokeev, M. S.; Fedorov, A. S.; Yakovlev, I. A.; Fedorov, D. A.; Ovchinnikov, S. G.

    2014-07-01

    The dispersion of the relative permittivity ɛ of a 27-nm-thick epitaxial Fe3Si iron silicide film has been measured within the E = 1.16-4.96 eV energy range using the spectroscopic ellipsometry technique. The experimental data are compared to the relative permittivity calculated in the framework of the density functional theory using the GGA-PBE approximation. For Fe3Si, the electronic structure and the electronic density of states (DOS) are calculated. The analysis of the frequencies corresponding to the transitions between the DOS peaks demonstrates qualitative agreement with the measured absorption peaks. The analysis of the single wavelength laser ellipsometry data obtained in the course of the film growth demonstrates that a continuous layer of Fe3Si iron silicide film is formed if the film thickness achieves 5 nm.

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

    PubMed

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

    2014-11-12

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

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

    SciTech Connect

    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 in 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.

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

    DOE PAGES

    Jeen, Hyoung Jeen; Choi, Woo Seok; Reboredo, Fernando A.; ...

    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

  1. Strain Control of Oxygen Vacancies in Epitaxial Strontium Cobaltite Films

    SciTech Connect

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

    2016-03-08

    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 degrees C. By applying a small biaxial tensile strain (2%), the oxygen activation energy barrier decreases by approximate to 30%, resulting in a tunable oxygen defi cient 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.

  2. Study of optoelectronic devices using epitaxial barium titanate thin films grown by RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Barrios, Pedro Jose

    Barium titanate in crystalline form presents ferroelectricity and a variety of significant effects. Its large piezoelectric, pyroelectric, electrooptic and photoelastic coefficients as well as its high dielectric constant make BaTiO3 (BTO) an excellent choice for transducers, sensors, and optoelectronic devices. Essential to the development of such devices on a microscale basis are to prepare films of high quality, similar to those of bulk crystals, and also to develop a proper fabrication process for low-loss waveguides that allow two-dimensional confinement of light. In this thesis we have studied the deposition of epitaxial BaTiO3 films on MgO single crystal substrates using an RF magnetron sputtering technique. The BaTiO3 films were found to have a single crystal structure with an in-plane epitaxial relationship of BTO (100) ∥MgO (100) as confirmed by X-ray diffraction pole figure measurement. BaTiO3 films' electrical, optical, and structural properties were studied and compared to those of the bulk material. Erbium-doped epitaxial BaTiO3 thin films were also developed using RF magnetron sputtering. The Er-doped BaTiO3 films show clear room temperature photoluminescence at 1.54 μm which corresponds to 4I13/2/to[4I]15/2 transitions of Er3+ ions. This new, added, property may be useful for the design of a new generation of guided optic devices presenting optical gain. We have also developed a novel method for forming channel waveguides in BaTiO3 films. The method exploits the photoelastic effect of BTO induced by thin-film stress. We have carried out numerical analyses on the stress distribution by solving the coupled equations that describe the elastomechanical and piezoelectric effects in the ferroelectric material. The refractive index changes were then calculated taking into account both the photoelastic and electrooptic effect of BaTiO3. The simulation result shows a good agreement with the measurement result. The waveguide structure developed in this

  3. Surface control of epitaxial manganite films via oxygen pressure

    DOE PAGES

    Tselev, Alexander; Vasudevan, Rama K.; Gianfrancesco, Anthony G.; ...

    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

  4. Surface Control of Epitaxial Manganite Films via Oxygen Pressure.

    PubMed

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

    2015-04-28

    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. 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. 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.

  5. Growth and Properties of Epitaxial Films of Ferroelectric Bismuth Titanate.

    DTIC Science & Technology

    mode, and MgAl2O4 giving the (010) orientation required for the extinction mode. The latter is obtained untwinned, a result attributed to the thermal...alleviated by a novel stress compensation growth technique. The films on MgAl2O4 , showing minimal substrate clamping effects, were converted by electrical

  6. 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.

  7. Surface and interface of epitaxial CdTe film on CdS buffered van der Waals mica substrate

    DOE PAGES

    Yang, Y. -B.; Seewald, L.; Mohanty, Dibyajyoti; ...

    2017-03-31

    We report single crystal CdTe films are desirable for optoelectronic device applications. An important strategy of creating films with high crystallinity is through epitaxial growth on a proper single crystal substrate. We report the metalorganic chemical vapor deposition of epitaxial CdTe films on the CdS/mica substrate. The epitaxial CdS film was grown on a mica surface by thermal evaporation. Due to the weak van der Waals forces, epitaxy is achieved despite the very large interface lattice mismatch between CdS and mica (~21–55%). The surface morphology of mica, CdS and CdTe were quantified by atomic force microscopy. The near surface structures, orientations and texture of CdTe and CdS films were characterized by the unique reflection high-energy electron diffraction surface pole figure technique. The interfaces of CdTe and CdS films and mica were characterized by X-ray pole figure technique and transmission electron microscopy. The out-of-plane and in-plane epitaxy of the heteroepitaxial films stack are determined to be CdTe(111)//CdS(0001)//mica(001) and [more » $$\\overline{1}2\\overline{1}$$]CdTe//[$$\\overline{1}100$$]CdS//[010]mica, respectively. The measured photoluminescence (PL), time resolved PL, photoresponse, and Hall mobility of the CdTe/CdS/mica indicate quality films. Finally, the use of van der Waals surface to grow epitaxial CdTe/CdS films offers an alternative strategy towards infrared imaging and solar cell applications.« less

  8. Surface and interface of epitaxial CdTe film on CdS buffered van der Waals mica substrate

    NASA Astrophysics Data System (ADS)

    Yang, Y.-B.; Seewald, L.; Mohanty, Dibyajyoti; Wang, Y.; Zhang, L. H.; Kisslinger, K.; Xie, Weiyu; Shi, J.; Bhat, I.; Zhang, Shengbai; Lu, T.-M.; Wang, G.-C.

    2017-08-01

    Single crystal CdTe films are desirable for optoelectronic device applications. An important strategy of creating films with high crystallinity is through epitaxial growth on a proper single crystal substrate. We report the metalorganic chemical vapor deposition of epitaxial CdTe films on the CdS/mica substrate. The epitaxial CdS film was grown on a mica surface by thermal evaporation. Due to the weak van der Waals forces, epitaxy is achieved despite the very large interface lattice mismatch between CdS and mica (∼21-55%). The surface morphology of mica, CdS and CdTe were quantified by atomic force microscopy. The near surface structures, orientations and texture of CdTe and CdS films were characterized by the unique reflection high-energy electron diffraction surface pole figure technique. The interfaces of CdTe and CdS films and mica were characterized by X-ray pole figure technique and transmission electron microscopy. The out-of-plane and in-plane epitaxy of the heteroepitaxial films stack are determined to be CdTe(111)//CdS(0001)//mica(001) and [ 1 bar2 1 bar]CdTe//[1 bar100]CdS//[010]mica, respectively. The measured photoluminescence (PL), time resolved PL, photoresponse, and Hall mobility of the CdTe/CdS/mica indicate quality films. The use of van der Waals surface to grow epitaxial CdTe/CdS films offers an alternative strategy towards infrared imaging and solar cell applications.

  9. Reversal of lattice, electronic structure, and magnetism in epitaxial SrCoOx thin films

    NASA Astrophysics Data System (ADS)

    Jeen, H.; Choi, W. S.; Lee, J. H.; Cooper, V. R.; Lee, H. N.; Seo, S. S. A.; Rabe, K. M.

    2014-03-01

    SrCoOx (x = 2.5 - 3.0, SCO) is an ideal material to study the role of oxygen content for electronic structure and magnetism, since SCO has two distinct topotactic phases: the antiferromagnetic insulating brownmillerite SrCoO2.5 and the ferromagnetic metallic perovskite SrCoO3. In this presentation, we report direct observation of a reversible lattice and electronic structure evolution in SrCoOx epitaxial thin films as well as different magnetic and electronic ground states between the topotactic phases.[2] By magnetization measurements, optical absorption, and transport measurements drastically different electronic and magnetic ground states are found in the epitaxially grown SrCoO2.5 and SrCoO3 thin films by pulsed laser epitaxy. First-principles calculations confirm substantial, which originate from the modification in the Co valence states and crystallographic structures. By real-time spectroscopic ellipsometry, the two electronically and magnetically different phases can be reversibly changed by changing the ambient pressure at greatly reduced temperatures. Our finding provides an important pathway to understanding the novel oxygen-content-dependent phase transition uniquely found in multivalent transition metal oxides. The work was supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.

  10. Defects Induced by Carbon Contamination in Low-Temperature Epitaxial Silicon Films Grown with Monosilane

    NASA Astrophysics Data System (ADS)

    Sato, Shin'ya; Mizushima, Ichiro; Miyano, Kiyotaka; Sato, Tsutomu; Nakamura, Shin'ichi; Tsunashima, Yoshitaka; Arikado, Tsunetoshi; Uchitomi, Naotaka

    2005-03-01

    The structures of the defects induced by carbon contamination in epitaxial silicon films grown with monosilane (SiH4) on silicon substrates were investigated. A new formation mechanism of defects associated with carbon in silicon epitaxial growth processes is proposed. The carbon contaminants were introduced prior to the growth by chemical vapor deposition (CVD), where the growth chamber was intentionally contaminated with organic materials. The carbon contaminant concentration was changed by adjusting the annealing conditions at temperatures ranging from 900°C to 1100°C. Silicon epitaxial films were grown by CVD at a temperature of 700°C. In this experiment, we found that pits were formed as dominant surface defects under the condition of a relatively low carbon concentration of less than 4.5× 1013 cm-2, while mound defects were formed at a carbon concentration of more than 4.5× 1013 cm-2. These defects can be explained by the formation of silicon carbide (SiC) islands resulting from the carbon contamination.

  11. 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.

  12. Adsorption-controlled growth of BiMnO{sub 3} films by molecular-beam epitaxy

    SciTech Connect

    Lee, J. H.; Ke, X.; Misra, R.; Schiffer, P.; Ihlefeld, J. F.; Mei, Z. G.; Liu, Z. K.; Xu, X. S.; Musfeldt, J. L.; Heeg, T.; Schlom, D. G.; Roeckerath, M.; Schubert, J.

    2010-06-28

    We have developed the means to grow BiMnO{sub 3} thin films with unparalleled structural perfection by reactive molecular-beam epitaxy and determined its band gap. Film growth occurs in an adsorption-controlled growth regime. Within this growth window bounded by oxygen pressure and substrate temperature at a fixed bismuth overpressure, single-phase films of the metastable perovskite BiMnO{sub 3} may be grown by epitaxial stabilization. X-ray diffraction reveals phase-pure and epitaxial films with omega rocking curve full width at half maximum values as narrow as 11 arc sec (0.003 deg. ). Optical absorption measurements reveal that BiMnO{sub 3} has a direct band gap of 1.1+-0.1 eV.

  13. The magnetic and chemical structural property of the epitaxially-grown multilayered thin film

    NASA Astrophysics Data System (ADS)

    Lee, Hwachol

    L10 FePt- and Fe-related alloys such as FePtRh, FeRh and FeRhPd have been studied for the high magnetocrystalline anisotropy and magnetic phase transition property for the future application. In this work, the thin film structural and magnetic property is investigated for the selected FePtRh and FeRhPd alloys. The compositionally-modulated L10 FePtRh multilayered structure is grown epitaxially on a-plane Al2O3 with Cr and Pt buffer layer at 600degC growth temperature by DC sputtering technique and examined for the structural, interfacial and magnetic property. For the epitaxially grown L10 [Fe50Pt45Rh5 (FM) (10nm) / Fe50Pt25Rh25 (AFM) (20nm)]x8 superlattice, the magnetically and chemically sharp interface formation between layers was observed in X-ray diffraction, transmission electron microscopy and polarized neutron reflectivity measurements with the negligible exchange bias at room and a slight coupling effect at lower temperature regime. For FeRhPd, the magnetic phase transition of epitaxially-grown 111-oriented Fe46Rh48Pd6 thin film is studied. The applied Rhodium buffer layer on a-plane Al2O3 (11 20) at 600degC shows the extraordinarily high quality of epitaxial film in (111) orientation, where two broad and coherent peak in rocking curve, and Laue oscillations are observed. The epitaxially-grown Pd-doped FeRh on Pt (111) grown at 600degC, 700degC exhibits the co-existing stable L10 (111) and B2 (110) structures and magnetic phase transition around 300degC. On the other hand, the partially-ordered FeRhPd structure grown at 400degC, 500degC shows background high ferromagnetic state over 5K˜350K temperature. For the reduced thickness of Fe46Rh48Pd 6, the ferromagnetic state becomes dominant with a reduced portion of the film undergoing a magnetic phase transition. For some epitaxial FeRhPd film, the spin-glass-like disordered state is also observed in field dependent SQUID measurement. For the tri-layered FeRhPd with thin Pt spacer, the background

  14. Preparation and characterization of Co epitaxial thin films on Al2O3(0001) single-crystal substrates

    NASA Astrophysics Data System (ADS)

    Yabuhara, Osamu; Ohtake, Mitsuru; Nukaga, Yuri; Futamoto, Masaaki

    2011-01-01

    Co epitaxial thin films were prepared on Al2O3(0001) single-crystal substrates in a substrate temperature range between 50 and 500 °C by ultra high vacuum molecular beam epitaxy. Effects of substrate temperature on the structure and the magnetic properties of the films were investigated. The films grown at temperatures lower than 150 °C consist of fcc- Co(111) crystal. With increasing the substrate temperature, hcp-Co(0001) crystal coexists with the fcc crystal and the volume ratio of hcp to fcc crystal increases. The films prepared at temperatures higher than 250 °C consist primarily of hcp crystal. The film growth seems to follow island-growth mode. The films consisting primarily of hcp crystal show perpendicular magnetic anisotropy. The domain structure and the magnetization properties are influenced by the magnetocrystalline anisotropy and the shape anisotropy caused by the film surface roughness.

  15. Enhancement of lower critical field by reducing the thickness of epitaxial and polycrystalline MgB₂ thin films

    DOE PAGES

    Tan, Teng; Wolak, M. A.; Acharya, Narendra; ...

    2015-04-01

    For potential applications in superconducting RF cavities, we have investigated the properties of polycrystalline MgB₂ films, including the thickness dependence of the lower critical field Hc₁. MgB₂ thin films were fabricated by hybrid physical-chemical vapor deposition on (0001) SiC substrate either directly (for epitaxial films) or with a MgO buffer layer (for polycrystalline films). When the film thickness decreased from 300 nm to 100 nm, Hc₁ at 5 K increased from around 600 Oe to 1880 Oe in epitaxial films and to 1520 Oe in polycrystalline films. The result is promising for using MgB₂/MgO multilayers to enhance the vortex penetrationmore » field.« less

  16. 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.

  17. 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.

  18. 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

  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. 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.

  1. High-Temperature Ionic Epitaxy of Halide Perovskite Thin Film and the Hidden Carrier Dynamics.

    PubMed

    Wang, Yiping; Sun, Xin; Chen, Zhizhong; Sun, Yi-Yang; Zhang, Shengbai; Lu, Toh-Ming; Wertz, Esther; Shi, Jian

    2017-09-01

    High-temperature vapor phase epitaxy (VPE) has been proved ubiquitously powerful in enabling high-performance electro-optic devices in III-V semiconductor field. A typical example is the successful growth of p-type GaN by VPE for blue light-emitting diodes. VPE excels as it controls film defects such as point/interface defects and grain boundary, thanks to its high-temperature processing condition and controllable deposition rate. For the first time, single-crystalline high-temperature VPE halide perovskite thin film has been demonstrated-a unique platform on unveiling previously uncovered carrier dynamics in inorganic halide perovskites. Toward wafer-scale epitaxial and grain boundary-free film is grown with alkali halides as substrates. It is shown the metal alkali halides could be used as universal substrates for VPE growth of perovskite due to their similar material chemistry and lattice constant. With VPE, hot photoluminescence and nanosecond photo-Dember effect are revealed in inorganic halide perovskite. These two phenomena suggest that inorganic halide perovskite could be as compelling as its organic-inorganic counterpart regarding optoelectronic properties and help explain the long carrier lifetime in halide perovskite. The findings suggest a new avenue on developing high-quality large-scale single-crystalline halide perovskite films requiring precise control of defects and morphology. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. 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

  3. Effects of Dopant Ionic Radius on Cerium Reduction in Epitaxial Cerium Oxide Thin Films

    DOE PAGES

    Yang, Nan; Orgiani, Pasquale; Di Bartolomeo, Elisabetta; ...

    2017-04-17

    The role of trivalent rare-earth dopants in ceria epitaxial films on surface ion exchange reactivity and ion conductivity has been systematically studied. Single-crystal epitaxial films with unique crystal orientation and micro-structure nature have allowed us to rule out the influence of structural defects on both transport and surface ion exchange properties. The films conductivities were larger than those reported in literature for both polycrystalline ceramic pellets and crystalline films. An increase in oxygen vacancies and Ce3+ concentration while decreasing the dopant ionic radius from La3+ to Yb3+ was observed, thus explaining the measured increased activation energy and enhanced surface reactivity.more » The more significant ability of smaller dopant ionic radius in releasing the stress strength induced by the larger Ce3+ ionic radius allows promoting the formation of oxygen vacancies and Ce3+, which are two precious species in determining the efficiency of ion transport and surface ion exchange processes. This can open new perspectives in designing ceria-based materials in tailoring functional properties, either ion migration or surface reactivity, by rational cation substitutions.« less

  4. 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.

  5. Fabrication of high critical current density superconducting tapes by epitaxial deposition of YBCO thick films on biaxially textured metal substrates

    SciTech Connect

    Goyal, A.; Norton, D.P.; Paranthaman, M.

    1996-12-31

    High critical current density YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) tapes were fabricated by epitaxial deposition on rolling- assisted-biaxially-textured-substrates (RABiTS). The RABiTS technique uses well established, industrially scaleable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers to yield chemically and structurally compatible surfaces. Epitaxial YBCO films grown on such substrates have critical current densities approaching 10{sup 6} A/cm{sup 2} at 77K in zero field and have field dependences similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for fabricating long lengths of high J{sub c} wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

  6. Research of surface-oxidation epitaxy of NiO films on cube textured Ni tapes

    NASA Astrophysics Data System (ADS)

    Shi, D. Q.; Ionescu, M.; McKinnon, J.; Chen, W. M.; Dou, S. X.

    2002-05-01

    Thin films of NiO were fabricated in air by surface-oxidation epitaxy (SOE) on biaxially-textured Ni substrate, for use as buffer layers for YBCO coated conductors. The surface-oxidation conditions such as the temperature and the reaction time, as well as the cooling rate, play a determining role in the process of epitaxial growth of the NiO layer. A continuous, biaxially-aligned textured NiO layer, was obtained for a 10 min oxidation in air at 1120 °C, and a cooling rate of 150 K/h. The roughness of the NiO layer is mostly controlled by a coarsening of some NiO grains.

  7. 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.

  8. How to enable bulk-like martensitic transformation in epitaxial films

    NASA Astrophysics Data System (ADS)

    Wodniok, Marius; Teichert, Niclas; Helmich, Lars; Hütten, Andreas

    2017-05-01

    The present study is dedicated to the influence of different substrate and buffer layer materials on the martensitic transformation in sputter deposited epitaxial shape memory Heusler alloys. For this, the magnetocaloric Heusler alloy Ni-Co-Mn-Al [N. Teichert et al., Phys. Rev. B 91, 184405 (2015)] is grown on MgO(001), MgAl2O4(001), and MgO(001)/V substrates, which exhibit a lattice misfit to the Ni-Co-Mn-Al between -1.2% and 3.6%. By temperature dependent X-ray diffraction measurements it is shown that the optimum buffer layer for shape memory Heusler films is not one with minimum lattice misfit, but one with minimum Young's modulus and moderate misfit because an elastic buffer layer can deform during the martensitic transformation of the Heusler layer. Furthermore, epitaxial strain caused by a moderate lattice misfit does not significantly change the martensitic transformation temperatures.

  9. Growth of superconducting SmFeAs(O, F) epitaxial films by F diffusion

    NASA Astrophysics Data System (ADS)

    Takeda, S.; Ueda, S.; Takano, S.; Yamamoto, A.; Naito, M.

    2012-03-01

    We report on our growth of superconducting SmFeAs(O, F) films by F diffusion. In our process, F-free SmFeAsO films were grown by molecular beam epitaxy (MBE) first, and subsequently F was introduced to the films via F diffusion from an overlayer of SmF3. We compared the growth conditions and also the properties of resultant films for CaF2 and LaAlO3 substrates. The best films on CaF2 exhibited a high transition temperature, {T}_{{c}}^{{on}}~({T}_{{c}}^{{end}})=57.8 K (56.4 K) at the highest, which may exceed the highest Tc ever reported for bulk samples. Furthermore, the films on CaF2 also showed high critical current density over 1 MA cm-2 in self-field at 5 K. On the other hand, the {T}_{{c}}^{{on}}~({T}_{{c}}^{{end}}) of the film on LaAlO3 was 50.3 K (49.3 K). The deteriorated superconducting properties on LaAlO3 appear to be due to oxygen diffusion from LaAlO3 to films.

  10. Bias sputtered NbN and superconducting nanowire devices

    NASA Astrophysics Data System (ADS)

    Dane, Andrew E.; McCaughan, Adam N.; Zhu, Di; Zhao, Qingyuan; Kim, Chung-Soo; Calandri, Niccolo; Agarwal, Akshay; Bellei, Francesco; Berggren, Karl K.

    2017-09-01

    Superconducting nanowire single photon detectors (SNSPDs) promise to combine near-unity quantum efficiency with >100 megacounts per second rates, picosecond timing jitter, and sensitivity ranging from x-ray to mid-infrared wavelengths. However, this promise is not yet fulfilled, as superior performance in all metrics is yet to be combined into one device. The highest single-pixel detection efficiency and the widest bias windows for saturated quantum efficiency have been achieved in SNSPDs based on amorphous materials, while the lowest timing jitter and highest counting rates were demonstrated in devices made from polycrystalline materials. Broadly speaking, the amorphous superconductors that have been used to make SNSPDs have higher resistivities and lower critical temperature (Tc) values than typical polycrystalline materials. Here, we demonstrate a method of preparing niobium nitride (NbN) that has lower-than-typical superconducting transition temperature and higher-than-typical resistivity. As we will show, NbN deposited onto unheated SiO2 has a low Tc and high resistivity but is too rough for fabricating unconstricted nanowires, and Tc is too low to yield SNSPDs that can operate well at liquid helium temperatures. By adding a 50 W RF bias to the substrate holder during sputtering, the Tc of the unheated NbN films was increased by up to 73%, and the roughness was substantially reduced. After optimizing the deposition for nitrogen flow rates, we obtained 5 nm thick NbN films with a Tc of 7.8 K and a resistivity of 253 μΩ cm. We used this bias sputtered room temperature NbN to fabricate SNSPDs. Measurements were performed at 2.5 K using 1550 nm light. Photon count rates appeared to saturate at bias currents approaching the critical current, indicating that the device's quantum efficiency was approaching unity. We measured a single-ended timing jitter of 38 ps. The optical coupling to these devices was not optimized; however, integration with front-side optical

  11. Characterization of epitaxial films of CdTe and CdS grown by hot-wall epitaxy

    NASA Astrophysics Data System (ADS)

    Sitter, H.; Humenberger, J.; Huber, W.; Lopez-Otero, A.

    1983-09-01

    Layers of n-type CdTe and CdS doped with indium are grown on single-crystal BaF2 and SrF2 substrates, respectively, using the method of hot-wall epitaxy. The electron concentrations are typically up to 2 x 10 to the 17th/cu cm in CdTe and 3 x 10 to the 18th/cu cm in CdS. Mobilities of 600 sq cm/Vs for CdTe and 230 sq cm/Vs for CdS are measured at room temperature. The mobility of some of the samples is found to increase exponentially with temperature in the range from 300 to 100 K. It is noted that this effect can be explained by means of a grain boundary model. In other samples, however, bulk scattering mechanisms figure prominently for tempperatures lower than 100 K. Attention is also given to mobility as a function of grain size. Deep level transient spectroscopy measurements are made in characterizing the carrier traps in the CdTe films. Six different defect levels are found in the upper half of the forbidden gap. It is determined that the concentration of the defects and their distribution with depth away from the interface in heterojunction diodes are a function of the growth conditions.

  12. Large-scale molecular dynamics simulations of TiN/TiN(001) epitaxial film growth

    SciTech Connect

    Edström, Daniel Sangiovanni, Davide G.; Hultman, Lars; Chirita, Valeriu; Petrov, Ivan; Greene, J. E.

    2016-07-15

    Large-scale classical molecular dynamics simulations of epitaxial TiN/TiN(001) thin film growth at 1200 K are carried out using incident flux ratios N/Ti = 1, 2, and 4. The films are analyzed as a function of composition, island size distribution, island edge orientation, and vacancy formation. Results show that N/Ti = 1 films are globally understoichiometric with dispersed Ti-rich surface regions which serve as traps to nucleate 111-oriented islands, leading to local epitaxial breakdown. Films grown with N/Ti = 2 are approximately stoichiometric and the growth mode is closer to layer-by-layer, while N/Ti = 4 films are stoichiometric with N-rich surfaces. As N/Ti is increased from 1 to 4, island edges are increasingly polar, i.e., 110-oriented, and N-terminated to accommodate the excess N flux, some of which is lost by reflection of incident N atoms. N vacancies are produced in the surface layer during film deposition with N/Ti = 1 due to the formation and subsequent desorption of N{sub 2} molecules composed of a N adatom and a N surface atom, as well as itinerant Ti adatoms pulling up N surface atoms. The N vacancy concentration is significantly reduced as N/Ti is increased to 2; with N/Ti = 4, Ti vacancies dominate. Overall, our results show that an insufficient N/Ti ratio leads to surface roughening via nucleation of small dispersed 111 islands, whereas high N/Ti ratios result in surface roughening due to more rapid upper-layer nucleation and mound formation. The growth mode of N/Ti = 2 films, which have smoother surfaces, is closer to layer-by-layer.

  13. Epitaxially grown BaM hexaferrite films having uniaxial axis in the film plane for self-biased devices

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaozhi; Meng, Siqin; Song, Dongsheng; Zhang, Yao; Yue, Zhenxing; Harris, Vincent G.

    2017-03-01

    Barium hexaferrite (BaM) films with in-plane c-axis orientation are promising and technically important materials for self-biased magnetic microwave devices. In this work, highly oriented BaM films with different thickness and an in-plane easy axis (c-axis) of magnetization were grown on a-plane single-crystal sapphire substrates by direct current magnetron sputtering. A procedure involving seed layers, layer-by-layer annealing was adopted to reduce the substrate-induced strains and allow for the growth of thick (~3.44 μm) films. The epitaxial growth of the BaM film on sapphire was revealed by high-resolution transmission electron microscopy with dislocations being observed at the film-substrate interface. The orientation was also verified by X-ray diffraction and more notably, polarized Raman scattering. The magnetic properties and ferromagnetic resonant frequencies were experimentally characterized by a vibrating sample magnetometry and a frequency-swept ferromagnetic resonant flip-chip technique, respectively. The micron-thick BaM films exhibited a large remanence ratio of 0.92 along in-plane easy axis and a small one of 0.09 for the in-plane hard axis loop measurement. The FMR frequency was 50.3 GHz at zero field and reached 57.9 GHz under a magnetic field of 3 kOe, indicating that the epitaxial BaM films with strong self-biased behaviors have good electromagnetic properties in millimeter-wave range.

  14. Epitaxially grown BaM hexaferrite films having uniaxial axis in the film plane for self-biased devices

    PubMed Central

    Zhang, Xiaozhi; Meng, Siqin; Song, Dongsheng; Zhang, Yao; Yue, Zhenxing; Harris, Vincent G.

    2017-01-01

    Barium hexaferrite (BaM) films with in-plane c-axis orientation are promising and technically important materials for self-biased magnetic microwave devices. In this work, highly oriented BaM films with different thickness and an in-plane easy axis (c-axis) of magnetization were grown on a-plane single-crystal sapphire substrates by direct current magnetron sputtering. A procedure involving seed layers, layer-by-layer annealing was adopted to reduce the substrate-induced strains and allow for the growth of thick (~3.44 μm) films. The epitaxial growth of the BaM film on sapphire was revealed by high-resolution transmission electron microscopy with dislocations being observed at the film-substrate interface. The orientation was also verified by X-ray diffraction and more notably, polarized Raman scattering. The magnetic properties and ferromagnetic resonant frequencies were experimentally characterized by a vibrating sample magnetometry and a frequency-swept ferromagnetic resonant flip-chip technique, respectively. The micron-thick BaM films exhibited a large remanence ratio of 0.92 along in-plane easy axis and a small one of 0.09 for the in-plane hard axis loop measurement. The FMR frequency was 50.3 GHz at zero field and reached 57.9 GHz under a magnetic field of 3 kOe, indicating that the epitaxial BaM films with strong self-biased behaviors have good electromagnetic properties in millimeter-wave range. PMID:28276492

  15. Control of magnetic properties of epitaxial Mn5Ge3Cx films induced by carbon doping

    NASA Astrophysics Data System (ADS)

    Spiesser, A.; Slipukhina, I.; Dau, M.-T.; Arras, E.; Le Thanh, V.; Michez, L.; Pochet, P.; Saito, H.; Yuasa, S.; Jamet, M.; Derrien, J.

    2011-10-01

    We report the effects of carbon incorporation on the structural and magnetic properties of epitaxial Mn5Ge3Cx films grown on Ge(111) by the solid phase epitaxy method. This variation of molecular beam epitaxy favors the diffusion process of carbon atoms. We show that up to a carbon molar concentration x of ˜0.6-0.7, the atoms are incorporated in the interstitial sites of the Mn5Ge3 lattice. Such a process results in a linear increase of the Curie temperature TC of the alloy, which can reach a value as high as ˜430 K [TC≈460 K at M(TC)=0]. Above this carbon content, TC is found to decrease. Structural characterizations reveal that Mn5Ge3Cx films are in perfect epitaxy when x ≤ 0.6, whereas cluster formation in the grown layers is detected above that threshold. The clusters can be attributed to manganese carbide (MnC) compounds which are formed when the carbon content exceeds the saturation value of 0.6 by consuming previously deposited carbon. Theoretical calculations accurately reproduce the main trend of TC variation as well as the cluster formation for x larger than the saturation content. In addition, we also show that after post-thermal annealing, the carbon-doped Mn5Ge3Cx alloys remain magnetically and structurally stable up to a temperature as high as 850 °C. The results are very promising for integrating Mn5Ge3Cx into ferromagnetic-semiconductor heterostructures, the ultimate goal being the realization of spintronic devices.

  16. Study of CdS epitaxial films chemically deposited from aqueous solutions on InP single crystals

    SciTech Connect

    Froment, M.; Bernard, M.C.; Cortes, R.; Mokili, B.; Lincot, D.

    1995-08-01

    Epitaxial growth of cadmium sulfide on InP single crystals is achieved by chemical bath deposition (CBD) in ammonia solutions at near room temperature. A better understanding of the correlations between the deposition parameters (temperature, bath composition) and the epitaxial quality is obtained by using electron diffraction and transmission techniques, x-ray diffraction, in combination with Raman spectroscopy. They are supplemented by electrochemical impedance and photocurrent experiments which give information on energetic structures between InP and CBD-CdS. Direct relations between the substrate properties and the growth habits of the CdS film (hexagonal vs. cubic, epitaxial vs. polycrystalline) are found.

  17. The growth of strontium titanate and lutetium ferrite thin films by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Brooks, Charles M.

    Included in this work is a range of studies on films of homoeptaxial and heteroepitaxial films of SrTiO3 and the first reported phase-pure films of LuFe2O4. We report the structural properties of homoepitaxial (100) SrTiO3 films grown by reactive molecular-beam epitaxy (MBE). The lattice spacing and x-ray diffraction (XRD) rocking curves of stoichiometric MBEgrown SrTiO3 films are indistinguishable from the underlying SrTiO3 substrates. The effect of off-stoichiometry for both strontium-rich and strontium-poor compositions results in lattice expansion with significant changes to the shuttered reflection high-energy electron diffraction oscillations, XRD, film microstructure, and thermal conductivity. Up to an 80% reduction in Sr(1+x)TiO3 film thermal conductivity is measured for x = -0.1 to 0.5. Significant reduction, from 11.5 to ˜2 W˙m-1K-1, occurs through the formation of Ruddlesden-Popper planar faults. The ability to deposit films with a reduction in thermal conductivity is applicable to thermal barrier coatings and thermoelectrics. Scanning transmission electron microscopy is used to examine the formation of Ruddlesden-Popper planar faults in films with strontium excess. We also show that the band gap of SrTiO3 can be altered by >10% (0.3 eV) by using experimentally realizable biaxial strains providing a new means to accomplish band gap engineering of SrTiO3 and related perovskites. Such band gap manipulation is relevant to applications in solar cells water splitting, transparent conducting oxides, superconductivity, two-dimensional electron liquids, and other emerging oxide electronics. This work also presents the adsorption-controlled growth of single-phase (0001)-oriented epitaxial films of charge ordered multiferroic, LuFe2O4, on (111) MgAl2O4, (111) MgO, and (0001) 6H-SiC substrates in an iron-rich environment at pressures and temperatures where excess iron desorbs from the film surface during growth. Scanning transmission electron microscopy reveals

  18. 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.

  19. 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.

  20. 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.

  1. Samarium monoxide epitaxial thin film as a possible heavy-fermion compound

    NASA Astrophysics Data System (ADS)

    Uchida, Yutaka; Kaminaga, Kenichi; Fukumura, Tomoteru; Hasegawa, Tetsuya

    2017-03-01

    SmO (001) epitaxial thin films were grown on YAl O3 (110) substrates by pulsed laser deposition method. X-ray photoemission spectroscopy indicated coexistence of S m2 + and S m3 + , suggesting a valence fluctuating state. A SmO thin film showed a metallic conductionlike SmO polycrystal in a previous study. However, a SmO thin film showed nonmonotonical temperature dependence at low temperature in contrast with the polycrystal. A local resistivity minimum was observed at 16 K, probably caused by the dense Kondo effect, and the resistivity below 2 K was proportional to T2. These features suggest the heavy-fermionic nature of SmO.

  2. 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.

  3. 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.

  4. Modeling the transport properties of epitaxially grown thermoelectric oxide thin films using spectroscopic ellipsometry

    NASA Astrophysics Data System (ADS)

    Sarath Kumar, S. R.; Abutaha, Anas I.; Hedhili, M. N.; Alshareef, H. N.

    2012-01-01

    The influence of oxygen vacancies on the transport properties of epitaxial thermoelectric (Sr,La)TiO3 thin films is determined using electrical and spectroscopic ellipsometry (SE) measurements. Oxygen vacancy concentration was varied by ex-situ annealing in Ar and Ar/H2. All films exhibited degenerate semiconducting behavior, and electrical conductivity decreased (258-133 S cm-1) with increasing oxygen content. Similar decrease in the Seebeck coefficient is observed and attributed to a decrease in effective mass (7.8-3.2 me), as determined by SE. Excellent agreement between transport properties deduced from SE and direct electrical measurements suggests that SE is an effective tool for studying oxide thin film thermoelectrics.

  5. YCo5±x thin films with perpendicular anisotropy grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sharma, S.; Hildebrandt, E.; Sharath, S. U.; Radulov, I.; Alff, L.

    2017-06-01

    The synthesis conditions of buffer-free (00l) oriented YCo5 and Y2Co17 thin films onto Al2O3 (0001) substrates have been explored by molecular beam epitaxy (MBE). The manipulation of the ratio of individual atomic beams of Yttrium, Y and Cobalt, Co, as well as growth rate variations allows establishing a thin film phase diagram. Highly textured YCo5±x thin films were stabilized with saturation magnetization of 517 emu/cm3 (0.517 MA/m), coercivity of 4 kOe (0.4 T), and anisotropy constant, K1, equal to 5.34 ×106 erg/cm3 (0.53 MJ/m3). These magnetic parameters and the perpendicular anisotropy obtained without additional underlayers make the material system interesting for application in magnetic recording devices.

  6. Thin film phase diagram of iron nitrides grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Gölden, D.; Hildebrandt, E.; Alff, L.

    2017-01-01

    A low-temperature thin film phase diagram of the iron nitride system is established for the case of thin films grown by molecular beam epitaxy and nitrided by a nitrogen radical source. A fine-tuning of the nitridation conditions allows for growth of α ‧ -Fe8Nx with increasing c / a -ratio and magnetic anisotropy with increasing x until almost phase pure α ‧ -Fe8N1 thin films are obtained. A further increase of nitrogen content below the phase decomposition temperature of α ‧ -Fe8N (180 °C) leads to a mixture of several phases that is also affected by the choice of substrate material and symmetry. At higher temperatures (350 °C), phase pure γ ‧ -Fe4N is the most stable phase.

  7. Chemical and Magnetic Properties of NiO Thin Films Epitaxially Grown on Fe(001)

    NASA Astrophysics Data System (ADS)

    Brambilla, Alberto

    2008-01-01

    Very high quality NiO films have been grown on Fe(001) by means of Molecular Beam Epitaxy. The chemical and magnetic properties of the NiO/Fe(001) interface have been evaluated by means of X-ray Absorption Spectroscopy and X-ray Magnetic Circular Dichroism. Furthermore, combined use of X-ray Magnetic Linear Dichroism and PhotoElectron Emission Microscopy allowed to observe an in-plane uniaxial magnetic anisotropy in very thin NiO films. For NiO films thinner than about 9 atomic layers the NiO magnetic moments align in-plane perpendicular to the Fe substrate magnetization. Above such critical thickness the coupling turns out to be collinear. The effects of thermal treatments, fundamental to produce exchange-biased structures, have also been considered.

  8. The effect of thin epitaxial films on the early deformation of copper single crystals

    NASA Astrophysics Data System (ADS)

    Ravindhran, K. S.

    1980-08-01

    The film substrate combinations studied were Nickel-Copper, Ruthenium-Copper, Platinum-Copper and Titanium-Tungsten-Copper. The single crystals were characterized by the subgrain size and initial dislocation density. The films were applied by electroplating and sputtering. The interface regions were examined qualitatively by Rutherford Backscattering Spectrometry technique. The presence of the epitaxial films raised the easy glide resolved shear stress and the slope of Stage 1. The extent of easy glide was unchanged. It was proposed that the strengthening in coated crystals resulted from a plastic constraint leading to plastic incompatibility across the interface. Automations diffusion across the interface resulting in an impurity atmosphere at the surface was also proposed as a mechanism to account for the observed strengthening. This was substantiated by Rutherford Backscattering Spectrometry.

  9. Anomalous resistivity upturn in epitaxial L21-Co2MnAl films.

    PubMed

    Zhu, L J; Zhao, J H

    2017-02-20

    Despite of the great scientific and technology interest, highly ordered full-Heusler L21-Co2MnAl films have remained a big challenge in terms of the availability and the electrical transport. Here we report the controllable growth and the intriguing transport behavior of epitaxial L21-Co2MnAl films, which exhibit a low-temperature (T) resistivity upturn with a pronounced T(1/2) dependence, a robust independence of magnetic fields, and a close relevance to structural disorder. The resistivity upturn turns out to be qualitatively contradictory to weak localization, particle-particle channel electron-electron interaction (EEI), and orbital two-channel Kondo effect, leaving a three-dimensional particle-hole channel EEI the most likely physical source. Our result highlights a considerable tunability of the structural and electronic disorder of magnetic films by varying growth temperature, affording unprecedented insights into the origin of the resistivity upturn.

  10. Anomalous resistivity upturn in epitaxial L21-Co2MnAl films

    NASA Astrophysics Data System (ADS)

    Zhu, L. J.; Zhao, J. H.

    2017-02-01

    Despite of the great scientific and technology interest, highly ordered full-Heusler L21-Co2MnAl films have remained a big challenge in terms of the availability and the electrical transport. Here we report the controllable growth and the intriguing transport behavior of epitaxial L21-Co2MnAl films, which exhibit a low-temperature (T) resistivity upturn with a pronounced T1/2 dependence, a robust independence of magnetic fields, and a close relevance to structural disorder. The resistivity upturn turns out to be qualitatively contradictory to weak localization, particle-particle channel electron-electron interaction (EEI), and orbital two-channel Kondo effect, leaving a three-dimensional particle-hole channel EEI the most likely physical source. Our result highlights a considerable tunability of the structural and electronic disorder of magnetic films by varying growth temperature, affording unprecedented insights into the origin of the resistivity upturn.

  11. Strained Pd films, by epitaxial growth on Au( 1 1 0 ), to control catalytic properties

    NASA Astrophysics Data System (ADS)

    Dolle, P.; Baudoing-Savois, R.; De Santis, M.; Saint-Lager, M. C.; Abel, M.; Bertolini, J. C.; Delichère, P.

    2002-10-01

    Pd ultra thin films on Au(1 1 0)-(1×2) have been prepared at 300 K by vapour deposition and studied using medium energy electron diffraction (MEED), surface X-ray diffraction (SXRD), low energy electron diffraction, low energy ion scattering (LEIS) and Auger electron spectroscopy (AES). The (1×2) superstructure intensities are strongly attenuated during the deposition of the first 0.5 ML. Simultaneously, LEIS indicates that gold atoms cover a large fraction of the deposited Pd atoms. A quantitative SXRD analysis of the 0.5 ML Pd film reveals a significantly ordered interface alloy covered by two incomplete Au layers. When more Pd is deposited up to about three layers, the growth proceeds in a quasi layer by layer mode, while the surfactant effect of gold persists. In this range of thickness, the film, mainly composed of Pd atoms, is under tensile strain in coherent epitaxy with the Au(1 1 0) substrate.

  12. Enhancement of piezoelectric response in Ga doped BiFeO3 epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Jaber, N.; Wolfman, J.; Daumont, C.; Négulescu, B.; Ruyter, A.; Feuillard, G.; Bavencoffe, M.; Fortineau, J.; Sauvage, T.; Courtois, B.; Bouyanfif, H.; Longuet, J. L.; Autret-Lambert, C.; Gervais, F.

    2015-06-01

    The piezoelectric properties of compositional spread (1 - x)BiFeO3-xGaFeO3 epitaxial thin films are investigated where Ga3+ substitution for Bi3+ is attempted in Bi1-xGaxFeO3 compounds. Ga content x was varied from 0 to 12% (atomic). Ferroelectric characterizations are reported at various length scales. Around 6.5% of Ga content, an enhancement of the effective piezoelectric coefficient d33 eff is observed together with a change of symmetry of the film. Measured d33 eff values in 135 nm thick films increased from 25 pm/V for undoped BiFeO3 to 55 pm/V for 6.5% Ga with no extrinsic contribution from ferroelastic domain rearrangement.

  13. 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.

  14. 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}.

  15. Photoluminescence properties of MgxZn1-xO 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.; Chou, W. C.; Shen, J. L.

    2017-02-01

    The optical properties of MgxZn1-xO films with x=0.03, 0.06, 0.08, and 0.11 grown by molecular beam epitaxy (MBE) have been studied by temperature-dependent photoluminescence (PL) measurement. It is presented that the full-width at half-maximum (FWHM) of the 12 K PL spectrum of MgZnO films increases with increasing Mg concentration and would deviate significantly from the simulation curve of Schubert model with higher Mg contents. The abnormal broader PL FWHM is inferred from larger compositional fluctuation by incorporating higher Mg contents, which results in larger effect of excitonic localization to induce more significant S-shaped behavior of the PL peak energy with temperature dependence. Additionally, the degree of localization increases as the linear proportion of the PL FWHM, indicating that the excitonic behavior in MgZnO films belong to the strong localization effect.

  16. Molecular beam epitaxy growth and scanning tunneling microscopy study of TiSe2 ultrathin films

    NASA Astrophysics Data System (ADS)

    Peng, Jun-Ping; Guan, Jia-Qi; Zhang, Hui-Min; Song, Can-Li; Wang, Lili; He, Ke; Xue, Qi-Kun; Ma, Xu-Cun

    2015-03-01

    Molecular beam epitaxy is used to grow TiSe2 ultrathin films on a graphitized SiC(0001) substrate. TiSe2 films proceed via a nearly layer-by-layer growth mode and exhibit two dominant types of defects, identified as Se vacancy and interstitial, respectively. By means of scanning tunneling microscopy, we demonstrate that the well-established charge density waves can survive in a single unit-cell (one triple-layer) regime, and find a gradual reduction in their correlation length as the density of surface defects in TiSe2 ultrathin films increases. Our findings offer important insights into the nature of charge density waves in TiSe2, and also pave a material foundation for potential applications based on the collective electronic states.

  17. Surface charge accumulation of InN films grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lu, Hai; Schaff, William J.; Eastman, Lester F.; Stutz, C. E.

    2003-03-01

    A series of thin InN films down to 10 nm in thickness were prepared by molecular-beam epitaxy on either AlN or GaN buffers under optimized growth conditions. By extrapolating the fitted curve of sheet carrier density versus film thickness to zero film thickness, a strong excess sheet charge was derived, which must come from either the surface or the interface between InN and its buffer layer. Since metal contacts, including Ti, Al, Ni, and a Hg probe, can always form an ohmic contact on InN without any annealing, it is determined that at least part of the excess charge is surface charge, which was also confirmed by capacitance-voltage measurements.

  18. Epitaxy of Fe/Cu/Si(1 1 1) ultrathin films: an Auger electron diffraction study

    NASA Astrophysics Data System (ADS)

    Castrucci, P.; Gunnella, R.; Bernardini, R.; Montecchiari, A.; Carboni, R.; De Crescenzi, M.

    2001-06-01

    Epitaxial Fe films, with thickness in the range between 1 and 50 ML (monolayer, ML), were grown in ultrahigh vacuum conditions on the 7×7 reconstructed (1 1 1)-Si surface. The films were evaporated on a Cu thick buffer layer to avoid iron silicides formation. Auger electron diffraction (AED) technique has been used to investigate the growth of the pseudomorphic film of fcc γ-Fe(1 1 1) and the successive growth of bcc Fe(1 1 0) domains in the Kurdjumov-Sachs orientation. The early stages of growth have been carefully investigated through AED to assess the pseudomorphism of iron γ-phase. AED patterns clearly show the presence of diffraction features that are fingerprints of the existence of a few bcc arranged atomic structures even for 1 ML iron coverage.

  19. 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.

  20. 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.

  1. Anomalous resistivity upturn in epitaxial L21-Co2MnAl films

    PubMed Central

    Zhu, L. J.; Zhao, J. H.

    2017-01-01

    Despite of the great scientific and technology interest, highly ordered full-Heusler L21-Co2MnAl films have remained a big challenge in terms of the availability and the electrical transport. Here we report the controllable growth and the intriguing transport behavior of epitaxial L21-Co2MnAl films, which exhibit a low-temperature (T) resistivity upturn with a pronounced T1/2 dependence, a robust independence of magnetic fields, and a close relevance to structural disorder. The resistivity upturn turns out to be qualitatively contradictory to weak localization, particle-particle channel electron-electron interaction (EEI), and orbital two-channel Kondo effect, leaving a three-dimensional particle-hole channel EEI the most likely physical source. Our result highlights a considerable tunability of the structural and electronic disorder of magnetic films by varying growth temperature, affording unprecedented insights into the origin of the resistivity upturn. PMID:28218300

  2. 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.

  3. Pinning effects on flux flow instability in epitaxial Nb thin films

    NASA Astrophysics Data System (ADS)

    Dobrovolskiy, Oleksandr V.; Shklovskij, Valerij A.; Hanefeld, Marc; Zörb, Markus; Köhs, Lukas; Huth, Michael

    2017-08-01

    The flux flow properties of epitaxial niobium films with different pinning strengths are investigated by dc electrical resistance measurements and mapped to results derived within the framework of a theoretical model. The cases of weak random pinning in as-grown films, strong random pinning in Ga ion-irradiated films, and strong periodic pinning induced by a nanogroove array milled by a focused ion beam are investigated. The generic feature of the current-voltage curves of the films consists of instability jumps to the normal state at some instability current density j * as the vortex lattice reaches its critical velocity v *. While {v}* (B) monotonically decreases for as-grown films, the irradiated films exhibit a non-monotonic dependence {v}* (B) attaining a maximum in the low-field range. In the case of nanopatterned films, this broad maximum is accompanied by a much sharper maximum in both {v}* (B) and {j}* (B), which we attribute to the commensurability effect when the spacing between the vortex rows coincides with the location of the grooves. We argue that the observed behavior of {v}* (B) can be explained by the pinning effect on the vortex flow instability and support our claims by fitting the experimental data to theoretical expressions derived within a model accounting for the field dependence of the depinning current density.

  4. Structural and electrical properties of large area epitaxial VO2 films grown by electron beam evaporation

    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.

    2017-02-01

    Large area (up to 4 squared inches) epitaxial VO2 films, with a uniform thickness and exhibiting an abrupt metal-insulator transition with a resistivity ratio as high as 2.85 × 10 4 , have been grown on (001)-oriented sapphire substrates by electron beam evaporation. The lattice distortions (mosaicity) and the level of strain in the films have been assessed by X-ray diffraction. It is demonstrated that the films grow in a domain-matching mode where the distortions are confined close to the interface which allows growth of high-quality materials despite the high film-substrate lattice mismatch. It is further shown that a post-deposition high-temperature oxygen annealing step is crucial to ensure the correct film stoichiometry and provide the best structural and electrical properties. Alternatively, it is possible to obtain high quality films with a RF discharge during deposition, which hence do not require the additional annealing step. Such films exhibit similar electrical properties and only slightly degraded structural properties.

  5. 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.

  6. Growth and characterization of ultrathin epitaxial MnO film on Ag(001)

    NASA Astrophysics Data System (ADS)

    Kundu, Asish K.; Menon, Krishnakumar S. R.

    2016-07-01

    We present here a comprehensive growth procedure to obtain a well-ordered MnO(001) ultrathin film on Ag(001) substrate. Depending upon the oxygen partial pressure during the growth, different phases of manganese oxide have been detected by Low Energy Electron Diffraction (LEED) and X-ray Photoelectron Spectroscopic (XPS) studies. A modified growth scheme has been adopted to get well-ordered and stoichiometric MnO(001) ultrathin film. The detailed growth mechanism of epitaxial MnO film on Ag(001) has been studied step by step, using LEED and XPS techniques. Observation of sharp (1 × 1) LEED pattern with a low inelastic background, corresponds to a long-range atomic order with low defect densities indicating the high structural quality of the film. The Mn 2p and Mn 3s core-level spectra confirm the oxidation state as well as the stoichiometry of the grown MnO films. Apart from the growth optimization, the evolution of strain relaxation of the MnO(001) film with film thickness has been explored.

  7. GaN film growth on LiNbO3 surfaces using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hoai Nam, Man; Goo, Son Chul; Deock Kim, Moon; Yang, Woochul

    2009-09-01

    GaN has been used for high power, high frequency electronic and optoelectronic devices such as light emitting diodes and laser diodes. Most of the GaN films grow on sapphire (0001) and silicon (111) substrates. In these work, we are trying to grow GaN films on lithium niobate (LiNbO3) substrates using molecular beam epitaxy (MBE). As a ferroelectric materials, LiNbO3 has a spontaneous polarization which may provide excellent control of polarity of GaN. The growth of GaN films on LiNbO3 has been performed after the LiNbO3 substrates was annealed in air at 1000°C for 2 hours. The annealed substrates allowed us to prepare atomically flat surfaces and improve adhesion of GaN on LiNbO3. The AlN buffer layer was deposited to get a smaller lattice mismatch with the GaN films. Compared with GaN films grown without a AlN layer, the crystal qualities of GaN films with AlN buffer layers are extremely improved. The surface morphology of LiNbO3 substrates and the grown GaN films were characterized by atomic force microscopy (AFM), and the crystal structures were studied by X-ray diffraction (XRD).

  8. Comparative study of electron transport mechanisms in epitaxial and polycrystalline zinc nitride films

    NASA Astrophysics Data System (ADS)

    Cao, Xiang; Yamaguchi, Yuuki; Ninomiya, Yoshihiko; Yamada, Naoomi

    2016-01-01

    Zn3N2 has been reported to have high electron mobility even in polycrystalline films. The high mobility in polycrystalline films is a striking feature as compared with group-III nitrides. However, the origins of the high mobility have not been elucidated to date. In this paper, we discuss the reason for high mobility in Zn3N2. We grew epitaxial and polycrystalline films of Zn3N2. Electron effective mass (m*) was determined optically and found to decrease with a decrease in electron density. Using a nonparabolic conduction band model, the m* at the bottom of the conduction band was derived to be (0.08 ± 0.03)m0 (m0 denotes the free electron mass), which is comparable to that in InN. Optically determined intra-grain mobility (μopt) in the polycrystalline films was higher than 110 cm2 V-1 s-1, resulting from the small m*. The Hall mobility (μH) in the polycrystalline films was significantly smaller than μopt, indicating that electron transport is impeded by scattering at the grain boundaries. Nevertheless, μH higher than 70 cm2 V-1 s-1 was achievable owing to the beneficial effect of the high μopt. As for the epitaxial films, we revealed that electron transport is hardly affected by grain boundary scattering and is governed solely by ionized impurity scattering. The findings in this study suggest that Zn3N2 is a high-mobility semiconductor with small effective mass.

  9. Ferromagnetic resonance in Mn5Ge3 epitaxial films with weak stripe domain structure

    NASA Astrophysics Data System (ADS)

    Kalvig, R.; Jedryka, E.; Aleshkevych, P.; Wojcik, M.; Bednarski, W.; Petit, M.; Michez, L.

    2017-03-01

    Extensive X-band and Q-band FMR experiments have been performed in the Mn5Ge3 epitaxial films with thicknesses varying between 4.5 and 68 nm. FMR signals were recorded in the temperature range between 15 and 295 K, at different orientations of magnetic field with respect to the film plane. In addition to the acoustic FMR mode with well defined resonance field, originating from inside the magnetic domains, a broad absorption line has been observed at low fields and attributed to the unresolved spectrum of FMR modes having the origin in flux closure caps. The FMR results have been discussed in the context of the domain structure computed with the use of OOMMF micromagnetic calculations and giving good agreement with the experimental hysteresis curves. From the Q-band experiments, where the FMR signal is observed in the magnetically saturated sample, the uniaxial anisotropy constant in films with different thicknesses has been determined as a function of temperature. This FMR study provides the evidence that the strong uniaxial anisotropy observed in epitaxial thin films of Mn5Ge3 leads to the formation of a stripe domain structure above 25 nm, in agreement with the published reports on magnetization studies in these films. It also eliminates a possible confusion that may arise from previously published FMR studies on films grown with the same method, which led their authors to conclude that the shape anisotropy can force the magnetization to the in-plane orientation in this thickness range and even above it.

  10. Comparative study of electron transport mechanisms in epitaxial and polycrystalline zinc nitride films

    SciTech Connect

    Cao, Xiang; Yamaguchi, Yuuki; Ninomiya, Yoshihiko; Yamada, Naoomi

    2016-01-14

    Zn{sub 3}N{sub 2} has been reported to have high electron mobility even in polycrystalline films. The high mobility in polycrystalline films is a striking feature as compared with group-III nitrides. However, the origins of the high mobility have not been elucidated to date. In this paper, we discuss the reason for high mobility in Zn{sub 3}N{sub 2}. We grew epitaxial and polycrystalline films of Zn{sub 3}N{sub 2}. Electron effective mass (m*) was determined optically and found to decrease with a decrease in electron density. Using a nonparabolic conduction band model, the m* at the bottom of the conduction band was derived to be (0.08 ± 0.03)m{sub 0} (m{sub 0} denotes the free electron mass), which is comparable to that in InN. Optically determined intra-grain mobility (μ{sub opt}) in the polycrystalline films was higher than 110 cm{sup 2} V{sup −1} s{sup −1}, resulting from the small m*. The Hall mobility (μ{sub H}) in the polycrystalline films was significantly smaller than μ{sub opt}, indicating that electron transport is impeded by scattering at the grain boundaries. Nevertheless, μ{sub H} higher than 70 cm{sup 2} V{sup −1} s{sup −1} was achievable owing to the beneficial effect of the high μ{sub opt}. As for the epitaxial films, we revealed that electron transport is hardly affected by grain boundary scattering and is governed solely by ionized impurity scattering. The findings in this study suggest that Zn{sub 3}N{sub 2} is a high-mobility semiconductor with small effective mass.

  11. Composition Shift as a Function of Thickness in Fe3-δO4(001) Epitaxial Films

    NASA Astrophysics Data System (ADS)

    Minagawa, Makoto; Yanagihara, Hideto; Uwabo, Kazuyuki; Kita, Eiji; Mibu, Ko

    2010-08-01

    We report on a thickness-dependent composition shift and a valency change in B-site Fe in Fe3-δO4(001) epitaxial films prepared by ozone-assisted molecular beam epitaxy. Conversion electron Mössbauer spectroscopy (CEMS) measurements for locally inserted 57Fe-enriched probe layers showed that a pure γ-Fe2O3 film can be obtained only if the film is sufficiently thin, and that the composition shift occurs when the thickness increases. The resistivity of Fe3-δO4 films having different thicknesses exhibited a significant decrease with an increase in the thickness, consistent with the CEMS experiment. These results indicate that γ-Fe2O3 films do not preferably grow homoepitaxially and that careful control of the growth is necessary to apply γ-Fe2O3 films to spintronics devices.

  12. 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.

  13. 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.

  14. 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

    2016-09-09

    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.

  15. 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.

  16. Surfactant-mediated epitaxy of thin germanium films on SiGe(001) virtual substrates

    NASA Astrophysics Data System (ADS)

    Schmidt, J.; Tetzlaff, D.; Bugiel, E.; Wietler, T. F.

    2017-01-01

    We report on the impact of a surfactant on the growth mode and strain relaxation of thin Ge films on Si0.21Ge0.79 virtual substrates grown by surfactant mediated epitaxy on Si(001) wafers. Ge epitaxy without surfactant results in island formation after deposition of only 5 nm Ge. A certain part of the strain in the Ge islands is relaxed via interfacial misfit dislocations, which are located within the core part of the islands. We discuss the possibilities for the occurrence of three-dimensional growth at low Ge layer thickness. The use of Sb as a surfactant suppresses three-dimensional islanding and enables the growth of smooth pseudomorphically strained Ge films on Si0.21Ge0.79(001) virtual substrates up to a thickness of 10 nm. At thicknesses higher than 20 nm, the films relax via the formation of a misfit dislocation network at the Ge/ Si1-xGex interface. The surface roughness of up to 30 nm thick layers is below 1.6 nm. Our experimental results corroborate the calculated thickness for plastic relaxation of Ge on Si1-xGex. The effect of the surfactant on the growth of the virtual substrate and on the subsequent growth of Ge on Si0.21Ge0.79 is discussed.

  17. 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

  18. 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.

  19. 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.

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

    SciTech Connect

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

    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 and 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.

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

    DOE PAGES

    Enriquez, Erik M.; Zhang, Yingying; Chen, Aiping; ...

    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

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

    SciTech Connect

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

    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 and 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.

  3. 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.

  4. 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.

  5. Van der Waals epitaxy of functional MoO{sub 2} film on mica for flexible electronics

    SciTech Connect

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

    2016-06-20

    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 MoO{sub 2} 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 MoO{sub 2} films are similar to those of the bulk. Flexible or free-standing MoO{sub 2} 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.

  6. Electronic and magnetic properties of epitaxial SrRhO3 films

    DOE PAGES

    Nichols, John A.; Yuk, Simuck F.; Sohn, Changhee; ...

    2017-06-16

    The strong interplay of fundamental order parameters in complex oxides is known to give rise to exotic physical phenomena. The 4$d$ transition-metal oxide SrRh O3 has generated much interest, but advances have been hindered by difficulties in preparing single-crystalline phases. Here we epitaxially stabilize high-quality single-crystalline SrRh O3 films and investigate their structural, electronic, and magnetic properties. Lastly, we determine that their properties significantly differ from the paramagnetic metallic ground state that governs bulk samples and are strongly related to rotations of Rh O6 octahedra.

  7. Spin Seebeck effect in insulating epitaxial γ-Fe2O3 thin films

    NASA Astrophysics Data System (ADS)

    Jiménez-Cavero, P.; Lucas, I.; Anadón, A.; Ramos, R.; Niizeki, T.; Aguirre, M. H.; Algarabel, P. A.; Uchida, K.; Ibarra, M. R.; Saitoh, E.; Morellón, L.

    2017-02-01

    We report the fabrication of high crystal quality epitaxial thin films of maghemite (γ-Fe2O3), a classic ferrimagnetic insulating iron oxide. Spin Seebeck effect (SSE) measurements in γ-Fe2O3/Pt bilayers as a function of sample preparation conditions and temperature yield a SSE coefficient of 0.5(1) μV/K at room temperature. Dependence on temperature allows us to estimate the magnon diffusion length in maghemite to be in the range of tens of nanometers, in good agreement with that of conducting iron oxide magnetite (Fe3O4), establishing the relevance of spin currents of magnonic origin in magnetic iron oxides.

  8. 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.

  9. 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.

  10. Symmetry rules in magnetic core-level photoelectron spectroscopy from epitaxial ferromagnetic ultrathin films

    NASA Astrophysics Data System (ADS)

    Schellenberg, R.; Meinert, H.; Perez, A.; Kisker, E.

    2001-09-01

    For two x-ray incidence directions onto an epitaxial FeNi(001) film, one to the left and a second one to the right side of the symmetry plane spanned by the magnetization direction and the photoelectron wave vector, we have measured distributions of the emission-angle dependence with respect to the crystallographic axes of the Fe 2p3/2 core-level photoelectron intensity asymmetry occurring upon magnetization reversal. The two angular distributions transform into each other when the signs of the magnetization and of the photoelectron emission angle are inverted, in accordance with the conservation of parity.

  11. Reversible plasma switching in epitaxial BiFeO{sub 3} thin films

    SciTech Connect

    Kim, Yunseok; Vrejoiu, Ionela; Hesse, Dietrich; Alexe, Marin

    2010-05-17

    Reversible plasma switching in epitaxial multiferroic BiFeO{sub 3} thin films was directly observed and analyzed using piezoresponse force microscopy. The polarization could be reversibly switched using oxygen plasma and a subsequent thermal annealing treatment in vacuum, respectively. The domain wall velocity during plasma switching, estimated to about 10{sup -8} m/s, is much slower compared to the normal electrical switching, however a large area of square centimeter scale could be stably switched. The results demonstrate that reversible plasma switching can be achieved by oxygen plasma treatment and it can be a useful tool for an electrode-less control of ferroelectric switching on large area.

  12. Electronic and magnetic properties of epitaxial SrRh O3 films

    NASA Astrophysics Data System (ADS)

    Nichols, John; Yuk, Simuck F.; Sohn, Changhee; Jeen, Hyoungjeen; Freeland, John W.; Cooper, Valentino R.; Lee, Ho Nyung

    2017-06-01

    The strong interplay of fundamental order parameters in complex oxides is known to give rise to exotic physical phenomena. The 4 d transition-metal oxide SrRh O3 has generated much interest, but advances have been hindered by difficulties in preparing single-crystalline phases. Here we epitaxially stabilize high-quality single-crystalline SrRh O3 films and investigate their structural, electronic, and magnetic properties. We determine that their properties significantly differ from the paramagnetic metallic ground state that governs bulk samples and are strongly related to rotations of Rh O6 octahedra.

  13. Bonding-site dependence of surface resistivity: CO on epitaxial Cu(100) films.

    PubMed

    Liu, Chang; Tobin, R G

    2007-03-28

    The authors have measured the contribution of CO adsorbed on different bonding sites to the resistivity of epitaxial Cu(100) films. Through an analysis of the correlation between surface resistivity and temperature-programed desorption measurements, CO on terraces is found to affect the resistance much more strongly than CO on defect sites. Two possible explanations are considered: a reduced scattering cross section of defect CO owing to the different local electronic structure at defect sites or strong scattering by the bare defect that is not significantly affected by the adsorption of CO.

  14. Epitaxial VO2 thin film-based radio-frequency switches with thermal activation

    NASA Astrophysics Data System (ADS)

    Lee, Jaeseong; Lee, Daesu; Cho, Sang June; Seo, Jung-Hun; Liu, Dong; Eom, Chang-Beom; Ma, Zhenqiang

    2017-08-01

    In this paper, we report on the demonstration of thermally triggered "normally ON" radio-frequency (RF) switches based on epitaxial vanadium dioxide (VO2) thin films with a SnO2 template on (001) TiO2 substrates. Fast insulator-to-metal phase transition of the epitaxial VO2 at a relatively low temperature allowed RF switches made of the VO2 to exhibit sharp changes in the RF insertion loss during cooling and heating at 60 °C and 66 °C, respectively. The change of RF insertion loss due to phase transition is greater than 15 dB. The VO2 RF switches also completed the transition of S21 within less than 3 °C and showed a low-loss operation frequency of up to 24.2 GHz with a low insertion loss of -1.36 dB and isolation of 17.56 dB at 12.03 GHz, respectively. The demonstration suggests that epitaxial VO2-based RF switches can be used in switching elements up to Ku-band RF circuits.

  15. 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.

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

    SciTech Connect

    Wang, Liangxin; Zhao, Jiangtao; Hong, Bin; Hu, Kai; Luo, Zhenlin; Yang, Yuanjun E-mail: cgao@ustc.edu.cn; Gao, Chen E-mail: cgao@ustc.edu.cn; Peng, Jinlan; Zhang, Haibin; Wen, Xiaolei; Li, Xiaoguang

    2016-04-14

    Vanadium dioxide (VO{sub 2}) epitaxial films were grown on perovskite single-crystal strontium titanate (SrTiO{sub 3}) substrates by reactive radio-frequency magnetron sputtering. The growth temperature-dependent metal–insulator transition (MIT) behavior of the VO{sub 2} epitaxial films was then investigated. We found that the order of magnitude of resistance change across the MIT increased from 10{sup 2} to 10{sup 4} 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)-VO{sub 2}/(111)-SrTiO{sub 3} epitaxial films at elevated temperature. On the other hand, the strain states do not change in the VO{sub 2} films deposited at various temperatures, resulting in stable V-V chains and V-O bonds in the VO{sub 2} epitaxial films. The accompanied orbital occupancy near the Fermi level is also constant and thus the MIT temperatures of VO{sub 2} films deposited at various temperatures are nearly the same. This work demonstrates that high-quality VO{sub 2} can be grown on perovskite substrates, showing potential for integration into oxide heterostructures and superlattices.

  17. 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.

  18. 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.

  19. Micromagnetics and microstructure of epitaxially grown Co and Co-Cr films for perpendicular magnetic recording

    NASA Astrophysics Data System (ADS)

    Krishnan, K. M.; Takeuchi, T.; Hirayama, Y.; Donnet, D. M.; Honda, Y.; Futamoto, M.

    1994-07-01

    Highly c-axis oriented, single crystal films of Co(1-x)Cr(x) (0 less than or equal to x less than 0.3) have been grown epitaxially on mica substrates by e-beam evaporation. Films grown on Ru underlayers have an average grain size of 50-80 nm, negligibe fcc content, and very narrow c-axis dispersions. For Co films (x = 0), the as-grown magnetization structure are mainly 180 degree domain walls with a uniform distribution of cross-ties for thinner samples (less than or equal to 300 Angstrom), while thicker (greater than 400 Angstrom) ones show stripe domains. These images were analyzed in detail to measure the wall widths and associated energy densities for as-grown, remanent, and ac-magnetized samples. As expected, the magnetic properties of these films are composition dependent. However, for any Cr concentration, these films exhibit the largest saturation magnetization when compared with either sputtered or evaporated samples. This enhancement can be attributed to a nanometer-scale segregation of Cr, which in these samples could be particularly aided by the diffusion on the close-packed planes of the films with very narrow c-axis dispersions. Preliminary x-ray microanalysis and NMR data support this interpretation.

  20. 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.

  1. Epitaxial growth and structure of monolayer cerium oxide films on Rh(111)

    NASA Astrophysics Data System (ADS)

    Chan, Lap Hong; Yuhara, Junji

    2017-07-01

    We prepared monolayer cerium (Ce) oxide films on Rh(111) to investigate their growth and structure using scanning tunneling microscopy (STM), low-energy electron diffraction, X-ray photoemission spectroscopy (XPS), and density functional theory (DFT) calculations. For quantitative analysis of Ce-oxide films, we used the combined techniques of XPS and Rutherford backscattering spectrometry to determine the concentration of Ce and O atoms. We prepared a monolayer (ML) Ce-oxide film by annealing a metallic Ce film at 0.3 ML coverage in an oxygen atmosphere. A well-ordered Ce-oxide phase with a (4×4) unit cell was obtained. The epitaxially grown Ce-oxide film aligned along the <110> azimuthal direction of Rh(111). The number of Ce and O atoms in the (4×4) unit cell was estimated. The STM images indicated that the two-dimensional island growth of the p(4×4) phase with p3m1 symmetry can be explained using the missing Ce atoms model. A simulated STM image of the p(4×4) structural model was in good agreement with the experimental STM image. The formation of Ce-oxide films on Rh(111) at submonolayer coverage was discussed on the basis of the results of DFT+U calculations.

  2. Measurements of magnetostriction constants of epitaxial garnet films by double-crystal x-ray diffraction

    SciTech Connect

    Mada, J.; Yamaguchi, K.

    1982-01-01

    Magnetostriction constants lambda/sub 111/ have been determined at room temperature with the double-crystal x-ray diffraction technique by measuring a small change in the lattice parameter. Measurements were carried out for epitaxial garnet films of Y/sub 3/Fe/sub 5/O/sub 12/ and Sm/sub 0.85/Tm/sub 2.15/Fe/sub 5/O/sub 12/ grown on (111) oriented Gd/sub 3/Ga/sub 5/O/sub 12/ substrates; and also for flux-grown bulk single crystal of Y/sub 3/Fe/sub 5/O/sub 12/. Values of lambda/sub 111/ obtained were -1.7 x 10/sup -6/ for film and -3.0 x 10/sup -6/ for bulk crystal. lambda/sub 111/ of Sm/sub 0.85/Tm/sub 2.15/Fe/sub 5/O/sub 12/ was -5.0 x 10/sup -6/. The discrepancy in lambda/sub 111/ values between film and bulk Y/sub 3/Fe/sub 5/O/sub 12/ is almost accounted for by the fact that the film can deform only perpendicular to the film plane due to the shear force of the substrate. It has been experimentally demonstrated that lambda/sub 111/ does not depend on film thickness or lattice mismatch, which is consistent with the present analysis.

  3. Epitaxial two dimensional aluminum films on silicon (111) by ultra-fast thermal deposition

    SciTech Connect

    Levine, Igal; Li Wenjie; Vilan, Ayelet; Yoffe, Alexander; Feldman, Yishay; Salomon, Adi

    2012-06-15

    Aluminum thin films are known for their extremely rough surface, which is detrimental for applications such as molecular electronics and photonics, where protrusions cause electrical shorts or strong scattering. We achieved atomically flat Al films using a highly non-equilibrium approach. Ultra-fast thermal deposition (UFTD), at rates >10 nm/s, yields RMS roughness of 0.4 to 0.8 nm for 30-50 nm thick Al films on variety of substrates. For UFTD on Si(111) substrates, the top surface follows closely the substrate topography (etch pits), indicating a 2D, layer-by-layer growth. The Al film is a mixture of (100) and (111) grains, where the latter are commensurate with the in-plane orientation of the underlying Si (epitaxy). We show the use of these ultra-smooth Al films for highly reproducible charge-transport measurements across a monolayer of alkyl phosphonic acid as well as for plasmonics applications by directly patterning them by focused ion beam to form a long-range ordered array of holes. UFTD is a one-step process, with no need for annealing, peeling, or primer layers. It is conceptually opposite to high quality deposition methods, such as MBE or ALD, which are slow and near-equilibrium processes. For Al, though, we find that limited diffusion length (and good wetting) is critical for achieving ultra-smooth thin films.

  4. Dislocation Reduction Mechanisms in Gallium Nitride Films Grown by Canti-Bridge Epitaxy Method

    NASA Astrophysics Data System (ADS)

    Xing, Zhi-Gang; Wang, Jing; Pei, Xiao-Jiang; Wan, Wei; Chen, Hong; Zhou, Jun-Ming

    2007-08-01

    By using the special maskless V-grooved c-plane sapphire as the substrate, we previously developed a novel GaN LEO method, or the so-called canti-bridge epitaxy (CBE), and consequently wing-tilt-free GaN films were obtained with low dislocation densities, with which all the conventional difficulties can be overcome [J. Vacuum Sci. Technol. B 23 (2005) 2476]. Here the evolution manner of dislocations in the CBE GaN films is investigated using transmission electron microscopy. The mechanisms of dislocation reduction are discussed. Dislocation behaviour is found to be similar to that in the conventional LEO GaN films except the enhanced dislocation-combination at the coalescence boundary that is a major dislocation-reduction mechanism for the bent horizontal-propagating dislocations in the CBE GaN films. The enhancement of this dislocation-combination probability is believed to result from the inclined shape and the undulate morphology of the sidewalls, which can be readily obtained in a wide range of applicable film-growth conditions during the GaN CBE process. Further development of the GaN CBE method and better crystal-quality of the GaN film both are expected.

  5. Epitaxial BiFeO3 nanostructures fabricated by differential etching of BiFeO3 films

    NASA Astrophysics Data System (ADS)

    Johann, Florian; Morelli, Alessio; Vrejoiu, Ionela

    2011-08-01

    We report on differential etching behavior of the different orientations of the polarization in BiFeO3 (BFO), similar to other ferroelectrics, such as LiNbO3. We show how this effect can be used to fabricate epitaxial BiFeO3 nanostructures. By means of piezoresponse force microscopy (PFM) domains of arbitrary shape and size can be poled in an epitaxial BiFeO3 film, which are then reproduced in the film morphology by differential etching. Structures with a lateral size smaller than 200 nm were fabricated and very good retention properties as well as a highly increased piezoelectric response were detected by PFM.

  6. 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.

  7. Structure and defects of a linear chain polymer film; GeO phthalocyanine epitaxially grown on KC1

    NASA Astrophysics Data System (ADS)

    Kobayashi, Takashi; Uyeda, Natsu

    1987-10-01

    Epitaxial film of GeO phthalocyanine polymer grown on KC1 has been investigated by direct observation of molecular images and electron diffraction. The film is composed of many crystallites oriented in two directions. The mechanism of the epitaxial growth of an organic crystal has been related to the determination of a staggering angle of the molecules stacked in polymer chains. Prominent diffuse scatterings have been observed and their origin has been revealed to be the existence of stacking faults in the crystal. The molecular orientation at the fault is discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  9. Epitaxial growth of aluminium-doped zinc oxide films by magnetron sputtering on (001), (110), and (012) oriented sapphire substrates

    NASA Astrophysics Data System (ADS)

    Kuppusami, P.; Vollweiler, G.; Rafaja, D.; Ellmer, K.

    2005-01-01

    Highly aluminium-doped zinc oxide (ZnO) films have been grown on differently oriented sapphire substrates by magnetron sputtering from an oxidic target. Rocking curve measurements, Rutherford backscattering analysis and transmission electron microscopy show that the films exhibit a disturbed film growth. However, despite the large nominal lattice mismatch between ZnO and sapphire (-31%), the films grow epitaxially on every sapphire orientation, even at room temperature. This was proven by pole figure analysis. The reason that epitaxial growth can be observed is an incommensurate lattice fitting between ZnO and sapphire by a mutual rotational alignment of their lattices. Films of the best crystallographic quality have been grown on (110)-oriented sapphire, which is also reflected by the highest Hall mobility in these layers.

  10. Oxygen vacancy induced photoluminescence and ferromagnetism in SrTiO3 thin films by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Xu, Wenfei; Yang, Jing; Bai, Wei; Tang, Kai; Zhang, Yuanyuan; Tang, Xiaodong

    2013-10-01

    SrTiO3 thin films were epitaxially grown on (100) SrTiO3 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 SrTiO3 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 d0 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 SrTiO3 films.

  11. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  13. GaAs thin film epitaxy and x-ray detector development

    NASA Astrophysics Data System (ADS)

    Wynne, Dawnelle I.; Cardozo, B.; Haller, Eugene E.

    1999-10-01

    We report on the growth of high purity n-GaAs using Liquid Phase Epitaxy and on the fabrication of Schottky barrier diodes for use as x-ray detectors using these layers. Our epilayers are grown form an ultra-pure Ga solvent in a graphite boat in a hydrogen atmosphere. Growth is started at a temperature of approximately 800 degrees C; the temperature is ramped down at 2 degrees C/min. to room temperature. Our best epilayers show a net-residual-donor concentration of approximately 2 X 1012 cm-3, measured by Hall effect. Electron mobilities as high as 150,000 cm2 V-1 s-1 at 77K have been obtained. The residual donors have been analyzed by far IR photothermal ionization spectroscopy and found to be sulfur and silicon. Up to approximately 200 micrometers of epitaxial GaAs have been deposited using several sequential growth runs on semi-insulating and n+-doped substrates. Schottky barrier diodes have been fabricated using this epitaxial material and have been electrically characterized by current-voltage and capacitance-voltage measurements. The Schottky barriers are formed by electron beam evaporation of Pt films. The ohmic contacts are made by electron beam evaporated and alloyed Ni-Ge-Au films on the backside of the substrate. Several of our diodes exhibit dark currents of the order of 0.3-3.3 nA/mm2 at reverse biases depleting approximately 50 micrometers of the epilayer. Electrical characteristics and preliminary performance results of our Schottky diodes using 109Cd and 241Am gamma and x- ray radiation will be discussed.

  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. Structural evolution of dilute magnetic (Sn,Mn)Se films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kanzyuba, Vasily; Dong, Sining; Liu, Xinyu; Li, Xiang; Rouvimov, Sergei; Okuno, Hanako; Mariette, Henri; Zhang, Xueqiang; Ptasinska, Sylwia; Tracy, Brian D.; Smith, David J.; Dobrowolska, Margaret; Furdyna, Jacek K.

    2017-02-01

    We describe the structural evolution of dilute magnetic (Sn,Mn)Se films grown by molecular beam epitaxy on GaAs (111) substrates, as revealed by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. When the Mn concentration is increased, the lattice of the ternary (Sn,Mn)Se films evolves quasi-coherently from a SnSe2 two-dimensional (2D) crystal structure into a more complex quasi-2D lattice rearrangement, ultimately transforming into the magnetically concentrated antiferromagnetic MnSe 3D rock-salt structure as Mn approaches 50 at. % of this material. These structural transformations are expected to underlie the evolution of magnetic properties of this ternary system reported earlier in the literature.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. HfSe2 thin films: 2D transition metal dichalcogenides grown by molecular beam epitaxy.

    PubMed

    Yue, Ruoyu; Barton, Adam T; Zhu, Hui; Azcatl, Angelica; Pena, Luis F; Wang, Jian; Peng, Xin; Lu, Ning; Cheng, Lanxia; Addou, Rafik; McDonnell, Stephen; Colombo, Luigi; Hsu, Julia W P; Kim, Jiyoung; Kim, Moon J; Wallace, Robert M; Hinkle, Christopher L

    2015-01-27

    In this work, we demonstrate the growth of HfSe2 thin films using molecular beam epitaxy. The relaxed growth criteria have allowed us to demonstrate layered, crystalline growth without misfit dislocations on other 2D substrates such as highly ordered pyrolytic graphite and MoS2. The HfSe2 thin films exhibit an atomically sharp interface with the substrates used, followed by flat, 2D layers with octahedral (1T) coordination. The resulting HfSe2 is slightly n-type with an indirect band gap of ∼ 1.1 eV and a measured energy band alignment significantly different from recent DFT calculations. These results demonstrate the feasibility and significant potential of fabricating 2D material based heterostructures with tunable band alignments for a variety of nanoelectronic and optoelectronic applications.

  1. Characteristics of Dy/W( 1 1 2 ) thin films during epitaxial growth

    NASA Astrophysics Data System (ADS)

    Moslemzadeh, N.; Barrett, S. D.; Ledieu, J.

    2002-12-01

    At RT a laminar growth has been found for Dy on W(1 1 2). For coverages more than 1 ML, epitaxial relations of Dy(0 0 0 1)∥W(1 1 2) with Dy[1 1 2¯ 0]∥W[1 1 1¯] were found. The high background intensity and the limited energy range over which the Dy LEED spots were visible suggests that the film was not well ordered. STM studies showed that the development of the second monolayer involved chain-like atomic rows, with irregular lengths and distances, on top of the first monolayer. For five monolayer films, flat terraces of Dy were observed by STM. Growth at 470 and 570 K was also found to be laminar, but LEED produced patterns with streaks.

  2. Roughness of CdTe thin films grown on glass by hot wall epitaxy

    NASA Astrophysics Data System (ADS)

    Leal, F. F.; Ferreira, S. O.; Menezes-Sobrinho, I. L.; Faria, T. E.

    2005-01-01

    Cadmium telluride films were grown on glass substrates using the hot wall epitaxy (HWE) technique. The samples were polycrystalline with a preferential (111) orientation. Scanning electron micrographs reveal a grain size between 0.1 and 0.5 µm. The surface morphology of the samples was studied by measuring the roughness profile using a stylus profiler. The roughness as a function of growth time and scale size were investigated to determine the growth and roughness exponents, β and α, respectively. From the results we can conclude that the growth surface has a self-affine character with a roughness exponent α equal to 0.69 ± 0.03 and almost independent of growth time. The growth exponent β was equal to 0.38 ± 0.06. These values agree with that determined previously for CdTe(111) films grown on GaAs(100).

  3. Preparation and rapid thermal annealing of AlN thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Liu, B.; Gao, J.; Wu, K. M.; Liu, C.

    2009-05-01

    AlN films were grown at 785 ∘C on (0001) sapphire substrates by radio-frequency assisted molecular beam epitaxy. Post-growth rapid thermal annealing (RTA) was carried out from 900 to 1200 ∘C for 10 s in flowing N 2. The morphological and structural properties of the AlN epilayers before and after the RTA were studied by atomic force microscopy, x-ray diffraction and transmission electron microscopy. It is found that the threading dislocations can be decreased to an order of magnitude by using an interlayer growth method. The surface roughness (RMS) of the AlN thin films becomes larger with the increase of annealing temperature. The full width at half maximum of AlN (0002) rocking curve reaches its minimum after the RTA at 1000 ∘C.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Epitaxial VO2 thin-film-based radio-frequency switches with electrical activation

    NASA Astrophysics Data System (ADS)

    Lee, Jaeseong; Lee, Daesu; Cho, Sang June; Seo, Jung-Hun; Liu, Dong; Eom, Chang-Beom; Ma, Zhenqiang

    2017-09-01

    Vanadium dioxide (VO2) is a correlated material exhibiting a sharp insulator-to-metal phase transition (IMT) caused by temperature change and/or bias voltage. We report on the demonstration of electrically triggered radio-frequency (RF) switches based on epitaxial VO2 thin films. The highly epitaxial VO2 and SnO2 template layer was grown on a (001) TiO2 substrate by pulsed laser deposition (PLD). A resistance change of the VO2 thin films of four orders of magnitude was achieved with a relatively low threshold voltage, as low as 13 V, for an IMT phase transition. VO2 RF switches also showed high-frequency responses of insertion losses of -3 dB at the on-state and return losses of -4.3 dB at the off-state over 27 GHz. Furthermore, an intrinsic cutoff frequency of 17.4 THz was estimated for the RF switches. The study on electrical IMT dynamics revealed a phase transition time of 840 ns.

  10. 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.

  11. 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.}

  12. Transport Anisotropy of Epitaxial VO2 films grown on (100) TiO2

    NASA Astrophysics Data System (ADS)

    Kittiwatanakul, Salinporn; Lu, Jiwei; Wolf, Stuart

    2011-03-01

    Vanadium dioxide (VO2) exhibits a metal semiconductor transition (MST) at 340 K. This transition is accompanied by the abrupt change in the electrical conductivity, optical transmittance and reflectance in infrared region, which can be used in the electronic devices such as temperature sensors and electric switches. In this study, Reactive Bias Target Ion Beam Deposition was used for epitaxial VO2 thin film growth on Ti O2 (100) substrates. The out-of-plane and the in-plane XRD scans have been performed to confirm the single phase VO2 and the epitaxial relationship between the film and the substrate. The hall bars along the in-plane c-axis and b-axis of R-VO2 were fabricated via the photolithographic process. It is found that the maximum conductivity was parallel to c-axis, while the minimum conductivity was parallel to b-axis. The conductivity anisotropy persisted through the metal semiconductor transition. The conductivity anisotropy ratio σc / σb was found to be ~ 16.2 at 300 K, much larger than that of single crystal VO2 . The temperature dependent anisotropy of the carrier concentration and the mobility is to be discussed.

  13. Exchange bias and crystal structure of epitaxial (111) FePt/BiFeO3 sputtered thin films

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    Crystallographic structure and magnetic properties of the epitaxial FePt (10 nm)/BiFeO3 (BFO) (10 nm) bilayer films grown on (111) SrTiO3 (STO) substrates with different deposition temperatures of FePt layers (Td) 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 Td = 300 and 700 °C. On the contrary, for the bilayer films with Td = 500 °C, the FePt and BFO layers exhibit low epitaxial quality. Large in-plane exchange bias field (Heb) values of 45-412 Oe are obtained for the L10-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 Heb.

  14. Modeling of light scattering from features on and within films and light scatter from epitaxial silicon defects

    NASA Astrophysics Data System (ADS)

    Zhang, Haiping

    The detection of particles and defects on or within films deposited on wafers using light scattering is of great interest to the semiconductor industry. Numerical calculation of light scattering characteristics from these features is very useful to the development and calibration of wafer inspection tools. A model and associated code is developed by using a modification of the discrete-dipole approximation (DDA) method to compute the light scattering from a feature with arbitrary shape on or within a filmed surface. The reflection interaction matrix is modified with the Sommerfeld integrals for filmed surfaces. Three-dimensional fast Fourier transform technique is used for accelerating the computation of light scatter from features associated with layered surfaces using the DDA method. Far field scatter is calculated approximately based on the reaction theorem. Model predictions of scattering signatures are compared with experimental results and other numerical models. Comparisons show good agreement for the cases considered, which demonstrates the accuracy and validity of the model. An epitaxial silicon wafer defect sample was fabricated containing typical epitaxial wafer defects such as epitaxial stacking faults, spikes and mounds. Atomic force microscopy was used to determine their physical sizes and shapes. The optical scattering characteristics of these epitaxial silicon wafer defects were studied using the numerical model. A method to discriminate epitaxial crystalline defects and particles is proposed.

  15. 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}.

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    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.

  18. 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

  19. Tuning the magnetism of epitaxial cobalt oxide thin films by electron beam irradiation

    NASA Astrophysics Data System (ADS)

    Lan, Q. Q.; Zhang, X. J.; Shen, X.; Yang, H. W.; Zhang, H. R.; Guan, X. X.; Wang, W.; Yao, Y.; Wang, Y. G.; Peng, Y.; Liu, B. G.; Sun, J. R.; Yu, R. C.

    2017-07-01

    Tuning magnetic properties of perovskite thin films is a central topic of recent studies because of its fundamental significance. In this work, we demonstrated the modification of the magnetism of L a0.9C a0.1Co O3 (LCCO) thin films by introducing a stripelike superstructure in a controllable manner using electron beam irradiation (EBI) in a transmission electron microscope. The microstructure, electronic structure, strain change, and origin of magnetism of the LCCO thin films were studied in detail using aberration-corrected scanning transmission electron microscopy, electron energy loss spectroscopy, and ab initio calculations based on density functional theory. The results indicate that the EBI-induced unit cell volume expansion accompanies the formation of oxygen vacancies and leads to the spin state transition of Co ions. The low spin state of C o4 + ions depress the stripelike superstructure, while higher spin states of Co ions with lower valences are conductive to the formation of "dark stripes". Our work clarifies the origin of magnetism of epitaxial LCCO thin films, benefiting a comprehensive understanding of correlated physics in cobalt oxide thin 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. Quantum Confinement Effects in PbSe Thin Films Formed Using Electrochemical Atomic Layer Epitaxy

    NASA Astrophysics Data System (ADS)

    Cox, Stephen M.; Happek, Uwe; Mathe, Mahlanyane K.; Stickney, John L.

    2004-03-01

    Electrochemical Atomic Layer Epitaxy (EC-ALE) is an alternative technique to MBE for the deposition of semiconductor films, heterostructures and nanodeposits. Advantages of this technique include room temperature deposition, deposition into templates and onto odd surfaces. Here we report on the deposition and characterization of PbSe thin films. The PbSe films were formed using EC-ALE as follows: A layer of Se was deposited onto a gold substrate at a potential less than that required to deposit Se onto Se, thus a Se monolayer is formed. Then, a monolayer of Pb was deposited onto the Se layer at a potential smaller than that required to deposit Pb onto itself. This technique is known as underpotential deposition (UPD). By alternately depositing Pb and Se layers using UPD, PbSe thin films of different thickness ranging from 10 to 85 layers of PbSe were formed. The dependence of the bandgap as a function of film thickness was obtained via IR absorption measurements and compared to models based on parabolic and hyperbolic band models.

  3. Creep-free ac hysteretic dynamics in epitaxial ferroelectric BiFeO3 films

    NASA Astrophysics Data System (ADS)

    Shin, Yeongjae; Jeon, Byung Chul; Yang, Sang Mo; Hwang, Inrok; Cho, Myung Rae; Sando, Daniel; Lee, Seung Ran; Yoon, Jong-Gul; Noh, Tae Won

    2015-03-01

    Dynamics of domain wall (DW) in ferroelectric (FE) films principally governs their switching properties under applied electric field (E) . At finite temperature (T) , the DW motion and their FE switching characteristics can be understood only by introducing the creep motion. Despite this importance, there have been little studies on creep motion of FE films under ac-driven force. In this work, we investigate ac-driven hysteretic dynamics of FE domains in epitaxial BiFeO3 (BFO) films through polarization-electric field hysteresis loops with varying frequency and other switching characters. All BFO films were grown at the optimized growth condition, by employing different bottom electrodes of La0.67Sr0.33MnO3 (LSMO) and SrRuO3 (SRO); only BFO/SRO shows nearly creep-free hysteretic dynamics. We argue that inhomogeneous internal E plays a significant role in such distinctive FE dynamics of BFO domains, which are affected by surface morphologies of bottom electrodes. Our results highlight that growth-mode-induced interfacial structure between an FE film and a bottom electrode result in engineering domain dynamics of FE switching characteristics. This work was supported by IBS-R009-D1.

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

    PubMed

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

    2016-09-30

    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.

  5. Epitaxial growth of WO3 films on SrTiO3 and sapphire

    NASA Astrophysics Data System (ADS)

    Garg, A.; Leake, J. A.; Barber, Z. H.

    2000-05-01

    Tungsten trioxide films were deposited on (100) SrTiO3 and R-plane (10icons/Journals/Common/1bar" ALT="bar" ALIGN="TOP"/> 2) cut sapphire substrates by dc magnetron sputtering, using a tungsten target in an Ar/O2 sputtering gas mixture at substrate temperatures ranging from 500 to 850 °C. Deposited films were characterized by x-ray diffraction using icons/Journals/Common/theta" ALT="theta" ALIGN="TOP"/> -2icons/Journals/Common/theta" ALT="theta" ALIGN="TOP"/> scans and pole figure analysis. X-ray results showed that films deposited on both types of substrate were epitaxial. The equilibrium phase was monoclinic icons/Journals/Common/gamma" ALT="gamma" ALIGN="TOP"/> -WO3 , confirmed by Raman spectroscopy. Films on both substrates were (001) oriented. This preferred orientation improved as the deposition temperature was reduced. The in-plane orientation relationship of the films with the substrate was obtained from the pole figures.

  6. Growth and ferroelectric properties of La and Al codoped BiFeO3 epitaxial films

    NASA Astrophysics Data System (ADS)

    Izumi, Hirokazu; Yoshimura, Takeshi; Fujimura, Norifumi

    2017-05-01

    Preparation of La and Al codoped BiFeO3 ((Bi1-xLax)(Fe1-xAlx)O3 (x = 0, 0.1, 0.2, 0.3, and 0.4): BFO-LA) thin films on Nb doped SrTiO3 (001) substrates was attempted by using a pulsed laser deposition (PLD) method. All obtained BFO-LA films grew epitaxially with a cube-on-cube relationship with the substrate. Upon La and Al codoping, the crystal system of the films changed from the rhombohedral-like monoclinic (MA) phase to the tetragonal phase, and the unit cell volume decreased monotonically. Although the ferroelectricity of the films was degraded by more than 20% La and Al codoping, 10% La and Al codoped BiFeO3 showed a larger remanent polarization than non-doped BiFeO3. The piezoelectric d constant (d33(AFM)) of the 10% La and Al codoped films was slightly reduced, in contrast to the drastic reduction observed for La doped BiFeO3.

  7. 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.

  8. 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

  9. Effect of residual impurities on transport properties of {beta}-FeSi{sub 2} epitaxial films grown by molecular beam epitaxy

    SciTech Connect

    Terai, Y.; Yoneda, K.; Noda, K.; Miura, N.; Fujiwara, Y.

    2012-07-01

    Unintentionally doped {beta}-FeSi{sub 2} epitaxial films were grown on silicon-on-insulator substrates by molecular beam epitaxy using a high-purity (5N) Fe source to investigate the effect of residual impurities on the transport properties of {beta}-FeSi{sub 2}. From secondary ion mass spectroscopy analysis, impurities of As, Al, and Mn ({approx}10{sup 17} cm{sup -3}); P and B ({approx}10{sup 16} cm{sup -3}); and Cr and Pb ({approx}10{sup 15} cm{sup -3}) were detected in the epitaxial layer. In Hall measurements at room temperature, the films exhibited n-type conduction with a carrier density of 4-6 Multiplication-Sign 10{sup 16} cm{sup -3} and a Hall mobility of 400-440 cm{sup 2}/Vs. In the temperature (T) dependence of the transport properties, a transition from band conduction to hopping conduction was observed at approximately T = 230 K. At temperatures of 110-150 K, both negative and positive magnetoresistance (MR) were observed depending on the temperature and magnetic field. The MR exhibits mixed conduction of defect band conduction and band conduction in this temperature range.

  10. 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

  11. Effects of the inhomogenous co doping on the magnetoresistance of Zn1-xCo(x)O epitaxial films.

    PubMed

    Ye, Shuangli; Klar, Limei; Ney, Andreas; Ney, Verena; Kammermeier, Tom; Ollefs, Katharina; Liu, Feng; Wang, Gaofeng

    2012-02-01

    A series of Zn1-xCo(x)O epitaxial films around 100 nm with nominal Co concentration from 5% to 15% was prepared by ultra high vacuum (UHV) magnetron reactive sputtering. The optical, magnetic and magneto-transport properties of this series of Zn1-xCo(x)O epitaxial films were investigated, respectively. Resonant Raman spectra indicate the high structural and crystalline quality of these Zn1-xCo(x)O (5 < or = x < or = 15%) films, and confirm a consistent correlation between the substituting Co ions content with the Co doping concentration as well. Paramagnetism, superparamagnetism and ferromagnetism with altered Curie temperature from low temperatures to above room temperatures have been observed in these films by SQUID magnetometry. The broad blocking temperature range indicates the presence of inhomogenous distribution of the magnetic nano-clusters in the superparamagnetic films. However, the magneto-transport behaviors do not strongly respond to the change of the magnetic properties from paramagnetism to ferromagnetism of these Zn1-xCo(x)O films. The lack of efficient coupling between the inhomogenous magnetic nanoclusters and the carrier system in ferromagnetic Zn1-xCo(x)O films highlights the absence of the intrinsic magnetic origins in high structural quality Zn1-xCo(x)O (5 < or = x < or = 15%) epitaxial films. On the other hand, the competition between the spin alignments and the inhomogenous local disorder effect by magnetic ions is suggested to be responsible for the carrier properties and the oberseved magnetoresistance in these Co doping Zn1-xCo(x)O (5 < or = x < or = 15%) epitaxial films.

  12. 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.

  13. Single domain Bi2Se3 films grown on InP(111)A by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Guo, X.; Xu, Z. J.; Liu, H. C.; Zhao, B.; Dai, X. Q.; He, H. T.; Wang, J. N.; Liu, H. J.; Ho, W. K.; Xie, M. H.

    2013-04-01

    We report the growth of single-domain epitaxial Bi2Se3 films on InP(111)A substrate by molecular-beam epitaxy. Nucleation of Bi2Se3 proceeds at steps, so the lattices of the substrate play the guiding role for a unidirectional crystalline film in the step-flow growth mode. There exists a strong chemical interaction between atoms at the heterointerface, so the growth does not follow the van der Waals epitaxy process. A mounded morphology of thick Bi2Se3 epilayers suggests a growth kinetics dictated by the Ehrlich-Schwoebel barrier. The Schubnikov de Haas oscillations observed in magnetoresistance measurements are attributed to Landau quantization of the bulk states of electrons.

  14. 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.

  15. 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

  16. 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.

  17. Growth and Characterization of N-Polar GaN Films on Si(111) by Plasma Assisted Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Dasgupta, Sansaptak; Nidhi; Wu, Feng; Speck, James S.; Mishra, Umesh K.

    2012-11-01

    Smooth N-polar GaN films were epitaxially grown by plasma assisted molecular beam epitaxy (PAMBE) on on-axis p-Si(111). The structural quality of the as-grown GaN films was further improved by insertion of AlGaN/GaN superlattice structures, resulting in reduced threading dislocation density and also efficient stress management in the GaN film to mitigate crack formation. The structural quality of these films was comparable to N-polar GaN grown on C-SiC by MBE. Convergent beam electron diffraction (CBED) imaging and KOH etch studies were performed to confirm the N-polarity of the sample. Room temperature photoluminescence measurements revealed strong GaN band-edge emission.

  18. 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.

  19. 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.

  20. Real structure of the ZnO epitaxial films on (0001) leucosapphire substrates coated by ultrathin gold layers

    SciTech Connect

    Muslimov, A. E. Butashin, A. V.; Kolymagin, A. B.; Vasilyev, A. L.; Kanevsky, V. M.

    2016-01-15

    The real structure of ZnO films formed by magnetron sputtering on (0001) leucosapphire substrates coated by an ultrathin (less than 0.7 nm) Au buffer layer has been studied by high-resolution microscopy. It is shown that modification of the leucosapphire substrate surface by depositing ultrathin Au layers does not lead to the formation of Au clusters at the film–substrate interface but significantly improves the structural quality of ZnO epitaxial films. It is demonstrated that the simplicity and scalability of the technique used to modify the substrate surface in combination with a high (above 2 nm/s) film growth rate under magnetron sputtering make it possible to obtain high-quality (0001) ZnO epitaxial films with an area of 5–6 cm{sup 2}.

  1. 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.

  2. Epitaxial growth and characterization of stoichiometric LiNbO{sub 3} films prepared by the sol-gel method

    SciTech Connect

    Takahashi, Makoto; Otowa, Ryouhei; Mori, Hidekazu; Sato, Shoji; Nishiwaki, Akira; Wakita, Koichi; Ohnishi, Naoyuki; Yagi, Touru; Uchida, Tetsuo

    2004-12-01

    After stoichiometric LiNbO{sub 3} thick films were deposited on z-cut LiNbO{sub 3} substrates using the sol-gel method from a precursor solution containing various polyvinyl alcohol (PVA) concentrations, their characteristics were investigated. The film thickness increased linearly with the increase in PVA and precursor concentrations. The orientation relationships between films and substrates were determined by x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, and the results showed that (006) oriented LiNbO{sub 3} epitaxial layers with parallel epitaxial relationships could be grown on a z-cut LiNbO{sub 3} substrate. The refractive indexes of the films were n{sub 0}=2.28{+-}0.02 and n{sub e}=2.19{+-}0.02 at a wavelength of 632.8 nm, and their transmission loss was 0.50{+-}0.04 dB/cm.

  3. Epitaxial Growth of Silicon Films on SiO2 Patterned Si(100) Substrates by Atmospheric Pressure Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Duan, Chunyan; Deng, Youjun; Ai, Bin; Liu, Chao; Zhuang, Lin; Shen, Hui

    2012-09-01

    In order to investigate the effect of selective area nucleation on epitaxial growth of silicon (Si) films, 35 µm thick Si films were deposited by atmospheric pressure chemical vapor deposition (APCVD) under the standard condition on two kinds of SiO2 patterned Si(100) wafers. One was circular patterns, and the other was striated patterns. Then, the structural properties of the as-deposited silicon thin films were investigated by metallurgical microscope, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM). The results show that normal epitaxial growth occurs on the exposed Si(100) regions, while just polycrystalline Si deposition happens on the SiO2 regions. Moreover, for the substrates with circular patterns, the as-deposited Si thin films possess pyramid surface morphology thus excellent light trapping performance being spontaneously formed, and the sizes of the pyramid grains approximately equal to the sum of the diameter and spacing of the round exposed Si regions.

  4. 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.

  5. Critical thickness and strain relaxation in molecular beam epitaxy-grown SrTiO3 films

    NASA Astrophysics Data System (ADS)

    Wang, Tianqi; Ganguly, Koustav; Marshall, Patrick; Xu, Peng; Jalan, Bharat

    2013-11-01

    We report on the study of the critical thickness and the strain relaxation in epitaxial SrTiO3 film grown on (La0.3Sr0.7)(Al0.65Ta0.35)O3 (001) (LSAT) substrate using the hybrid molecular beam epitaxy approach. No change in the film's lattice parameter (both the in-plane and the out-of-plane) was observed up to a film thickness of 180 nm, which is in sharp contrast to the theoretical critical thickness of ˜12 nm calculated using the equilibrium theory of strain relaxation. For film thicknesses greater than 180 nm, the out-of-plane lattice parameter was found to decrease hyperbolically in an excellent agreement with the relaxation via forming misfit dislocations. Possible mechanisms are discussed by which the elastic strain energy can be accommodated prior to forming misfit dislocations leading to such anomalously large critical thickness.

  6. 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.

  7. Metallic transport and large anomalous Hall effect at room temperature in ferrimagnetic Mn4N epitaxial thin film

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    We report the electrical transport properties of ferrimagnetic Mn4N (001) epitaxial thin films grown by pulsed laser deposition on MgO (001) substrates. The Mn4N 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/m3, 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.

  8. The structural state of epitaxial GaP films of different polarities grown on misoriented Si(001) substrates

    NASA Astrophysics Data System (ADS)

    Loshkarev, I. D.; Vasilenko, A. P.; Trukhanov, E. M.; Kolesnikov, A. V.; Putyato, M. A.; Esin, M. Yu.; Petrushkov, M. O.

    2017-02-01

    The structure of GaP films grown by molecular-beam epitaxy on vicinal Si(1113) substrates has been studied by X-ray diffraction. It is established that the crystalline lattice of a pseudomorphic film rotates about the <110> axis toward increasing deviation from the singular orientation, while the subsequent relaxation leads to rotation in the opposite direction. This is valid for the films of both (001) and (001¯) polarities. Differences between the surface morphologies of relaxed and pseudomorphic GaP films are revealed.

  9. Low-temperature photoluminescence study of thin epitaxial GaAs films on Ge substrates

    NASA Astrophysics Data System (ADS)

    Brammertz, Guy; Mols, Yves; Degroote, Stefan; Motsnyi, Vasyl; Leys, Maarten; Borghs, Gustaaf; Caymax, Matty

    2006-05-01

    Thin epitaxial GaAs films, with thickness varying from 140 to 1000 nm and different Si doping levels, were grown at 650 °C by organometallic vapor phase epitaxy on Ge substrates and analyzed by low-temperature photoluminescence (PL) spectroscopy. All spectra of thin GaAs on Ge show two different structures, one narrow band-to-band (B2B) structure at an energy of ~1.5 eV and a broad inner-band-gap (IB) structure at an energy of ~1.1 eV. Small strain in the thin GaAs films causes the B2B structure to be separated into a light-hole and a heavy-hole peak. At 2.5 K the good structural quality of the thin GaAs films on Ge can be observed from the narrow excitonic peaks. Peak widths of less than 1 meV are measured. GaAs films with thickness smaller than 200 nm show B2B PL spectra with characteristics of an n-type doping level of approximately 1018 at./cm3. This is caused by heavy Ge diffusion from the substrate into the GaAs at the heterointerface between the two materials. The IB structure observed in all films consists of two Gaussian peaks with energies of 1.04 and 1.17 eV. These deep trapping states arise from Ge-based complexes formed within the GaAs at the Ge-GaAs heterointerface, due to strong diffusion of Ge atoms into the GaAs. Because of similarities with Si-based complexes, the peak at 1.04 eV was identified to be due to a GeGa-GeAs complex, whereas the peak at 1.17 eV was attributed to the GeGa-VGa complex. The intensity of the IB structure decreases strongly as the GaAs film thickness is increased. PL intensity of undoped GaAs films containing antiphase domains (APDs) is four orders of magnitude lower than for similar films without APDs. This reduction in intensity is due to the electrically active Ga-Ga and As-As bonds at the boundaries between the different APDs. When the Si doping level is increased, the PL intensity of the APD-containing films is increased again as well. A film containing APDs with a Si doping level of ~1018 at./cm3 has only a factor 10

  10. Structural and Optical Properties of Thick Freestanding AlN Films Prepared by Hydride Vapor Phase Epitaxy

    DTIC Science & Technology

    2012-01-01

    electronic device applications, optoe- lectronic devices are the driving force of AlN based material research. Deep ultraviolet laser diodes and light...films deposited on Si and SiC substrates, removed from the substrates by etching techniques, were used as seeds to grow AlN boules with a diameter...ranging from 0.5 to 1.75 in. Selected wafers were employed as substrates to deposit epitaxial AlN films with improved structural and optical properties

  11. 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 .

  12. Atomic layer epitaxy group IV materials: Surface processes, thin films, devices and their characterization

    NASA Astrophysics Data System (ADS)

    Davis, Robert F.; Bedair, Salah; El-Masry, Nadia; Glass, Jeffrey T.

    1993-06-01

    The maximum temperature at which self-terminating monolayers of Si can be formed on Si(100) from Si2H6 has been determined to be 570 deg C. As such, the chemical reactivity of C2H4 has been determined to be insufficient at this temperature, and acetylene has been selected as the successor C precursor due to its superior reactivity and chemisorption properties. A cryogenic purifier for removing acetone has been commissioned. Trenched Si(100) wafers are also being made to assess the ALE process for sidewall deposition uniformity and future bipolar devices. Nonstoichiometric, Si-rich SiC has been produced with an associated decrease in the band gap. An AES/XPS UHV analytical system and associated ALE deposition system has been commissioned and integrated into a much larger surface science system. These dual systems will allow a thorough study and characterization of both the initial nucleation of SiC and the overall ALE growth process of SiC. Tetramethylsilane and hexamethyldisilane have been deposited onto Si substrates in a hot filament CVD chamber to investigate their ability to promote ALE of diamond under DC biasing and a variety of system parameters. An electron gun and heating stage has been added to the growth chamber to enable AES and substrate heating. Good quality diamond films have been nucleated on deposited interlayers of both precursor compounds. The films have been examined by SEM and Raman spectroscopy. Good quality epitaxial films of CeO2 have been grown on Si(111) using laser ablation. Atomically clean substrates and slow growth rates were determined necessary for epitaxy.

  13. Hall effect in semiconducting epitaxial and amorphous Y-Ba-Cu-O thin films

    NASA Astrophysics Data System (ADS)

    Shan, Pao-Chuan; Jahanzeb, Agha; Butler, Donald P.; ćelik-Butler, Zeynep; Kula, Witold; Sobolewski, Roman

    1997-05-01

    An experimental study of the Hall effect in nonmetallic Y-Ba-Cu-O thin films is reported. Both epitaxial crystalline YBa2Cuoverflow="scroll">3O6+x (x⩽0.5) and multiphase/amorphous Y-Ba-Cu-O thin films were studied. The structure of the samples was measured by x-ray diffraction and Raman microprobe. The amorphous Y-Ba-Cu-O samples were found to have a grain size of about 100 Å. The conduction properties were studied and analyzed for the two types of samples over a wide temperature range including room temperature. The Hall effect measurements showed positive charge carriers with a concentration ranging from 1017 to 1020 cm-3 at room temperature. The mobility was found to decrease with higher Hall carrier concentration. The empirical relationship for the mobility dependence on impurity concentration agreed with the relationship between mobility and the experimental Hall carrier concentration, suggesting that the same localized states were responsible for both providing the carriers and reducing the mobility through scattering. It was also observed that the mobility values for both amorphous and crystalline samples followed the same empirical curve, a result which showed that the conduction mechanisms in the epitaxial (tetragonal) and amorphous Y-Ba-Cu-O materials are very likely to be similar despite the differences in the composition and structure of the films. The similarity is consistent with other work that concludes that the conduction mechanism occurs along the copper oxide planes. Our work implies that the conduction mechanism operates over a short range, less than the 100 Å grain size of the amorphous, such that the lack of order in the amorphous samples was essentially irrelevant to the charge transport.

  14. Epitaxial thin films of Dirac semimetal antiperovskite Cu3PdN

    NASA Astrophysics Data System (ADS)

    Quintela, C. X.; Campbell, N.; Shao, D. F.; Irwin, J.; Harris, D. T.; Xie, L.; Anderson, T. J.; Reiser, N.; Pan, X. Q.; Tsymbal, E. Y.; Rzchowski, M. S.; Eom, C. B.

    2017-09-01

    The growth and study of materials showing novel topological states of matter is one of the frontiers in condensed matter physics. Among this class of materials, the nitride antiperovskite Cu3PdN has been proposed as a new three-dimensional Dirac semimetal. However, the experimental realization of Cu3PdN and the consequent study of its electronic properties have been hindered due to the difficulty of synthesizing this material. In this study, we report fabrication and both structural and transport characterization of epitaxial Cu3PdN thin films grown on (001)-oriented SrTiO3 substrates by reactive magnetron sputtering and post-annealed in NH3 atmosphere. The structural properties of the films, investigated by x-ray diffraction and scanning transmission electron microscopy, establish single phase Cu3PdN exhibiting cube-on-cube epitaxy (001)[100]Cu3PdN||(001)[100]SrTiO3. Electrical transport measurements of as-grown samples show metallic conduction with a small temperature coefficient of the resistivity of 1.5 × 10-4 K-1 and a positive Hall coefficient. Post-annealing in NH3 results in the reduction of the electrical resistivity accompanied by the Hall coefficient sign reversal. Using a combination of chemical composition analyses and ab initio band structure calculations, we discuss the interplay between nitrogen stoichiometry and magneto-transport results in the framework of the electronic band structure of Cu3PdN. Our successful growth of thin films of antiperovskite Cu3PdN opens the path to further investigate its physical properties and their dependence on dimensionality, strain engineering, and doping.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  16. 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.

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

    DOE PAGES

    Xiao, Xiaoyin; Fischer, Arthur J.; Coltrin, Michael E.; ...

    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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Coexistence of Low Damping and Strong Magnetoelastic Coupling in Epitaxial Spinel Ferrite Thin Films.

    PubMed

    Emori, Satoru; Gray, Benjamin A; Jeon, Hyung-Min; Peoples, Joseph; Schmitt, Maxwell; Mahalingam, Krishnamurthy; Hill, Madelyn; McConney, Michael E; Gray, Matthew T; Alaan, Urusa S; Bornstein, Alexander C; Shafer, Padraic; N'Diaye, Alpha T; Arenholz, Elke; Haugstad, Greg; Meng, Keng-Yuan; Yang, Fengyuan; Li, Dongyao; Mahat, Sushant; Cahill, David G; Dhagat, Pallavi; Jander, Albrecht; Sun, Nian X; Suzuki, Yuri; Howe, Brandon M

    2017-09-01

    Low-loss magnetization dynamics and strong magnetoelastic coupling are generally mutually exclusive properties due to opposing dependencies on spin-orbit interactions. So far, the lack of low-damping, magnetostrictive ferrite films has hindered the development of power-efficient magnetoelectric and acoustic spintronic devices. Here, magnetically soft epitaxial spinel NiZnAl-ferrite thin films with an unusually low Gilbert damping parameter (<3 × 10(-3) ), as well as strong magnetoelastic coupling evidenced by a giant strain-induced anisotropy field (≈1 T) and a sizable magnetostriction coefficient (≈10 ppm), are reported. This exceptional combination of low intrinsic damping and substantial magnetostriction arises from the cation chemistry of NiZnAl-ferrite. At the same time, the coherently strained film structure suppresses extrinsic damping, enables soft magnetic behavior, and generates large easy-plane magnetoelastic anisotropy. These findings provide a foundation for a new class of low-loss, magnetoelastic thin film materials that are promising for spin-mechanical devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. 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.

  4. 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.

  5. Growth of uniform CaGe2 films by alternating layer molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Xu, Jinsong; Katoch, Jyoti; Ahmed, Adam S.; Pinchuk, Igor V.; Young, Justin R.; Johnston-Halperin, Ezekiel; Pelz, Jonathan; Kawakami, Roland K.

    2017-02-01

    Layered Zintl phase van der Waals (vdW) materials are of interest due to their strong spin-orbit coupling and potential for high mobility. Here, we report the successful growth of large area CaGe2 films, as a model of layered Zintl phase materials, on atomically flat Ge(111) substrates by molecular beam epitaxy (MBE) using an alternating layer growth (ALG) protocol. Reflection high energy electron diffraction (RHEED) patterns of the Ge buffer layer and CaGe2 indicate high quality two dimensional surfaces, which is further confirmed by atomic force microscopy (AFM), showing atomically flat and uniform CaGe2 films. The appearance of Laue oscillations in X-ray diffraction (XRD) and Kiessig fringes in the X-ray reflectivity (XRR), which are absent in co-deposited CaGe2, confirms the uniformity of the CaGe2 film and the smoothness of the interface. These results demonstrate a novel method of deposition of CaGe2 that could be also applied to other layered Zintl phase vdW materials. Also, the high quality of the CaGe2 film is promising for the exploration of novel properties of germanane.

  6. Voltage Scaling of Graphene Device on SrTiO3 Epitaxial Thin Film.

    PubMed

    Park, Jeongmin; Kang, Haeyong; Kang, Kyeong Tae; Yun, Yoojoo; Lee, Young Hee; Choi, Woo Seok; Suh, Dongseok

    2016-03-09

    Electrical transport in monolayer graphene on SrTiO3 (STO) thin film is examined in order to promote gate-voltage scaling using a high-k dielectric material. The atomically flat surface of thin STO layer epitaxially grown on Nb-doped STO single-crystal substrate offers good adhesion between the high-k film and graphene, resulting in nonhysteretic conductance as a function of gate voltage at all temperatures down to 2 K. The two-terminal conductance quantization under magnetic fields corresponding to quantum Hall states survives up to 200 K at a magnetic field of 14 T. In addition, the substantial shift of charge neutrality point in graphene seems to correlate with the temperature-dependent dielectric constant of the STO thin film, and its effective dielectric properties could be deduced from the universality of quantum phenomena in graphene. Our experimental data prove that the operating voltage reduction can be successfully realized due to the underlying high-k STO thin film, without any noticeable degradation of graphene device performance.

  7. Strain relief through stair-rod dislocations in ultrathin epitaxial metal films: Defect geometry and energetics

    SciTech Connect

    Klein, A.; Meyer, W.; Schmidt, A.; Gumler, B.; Mueller, S.; Hammer, L.; Heinz, K.

    2008-07-15

    Epitaxial Ni films deposited on Ir(100) were investigated by tunneling microscopy (STM), quantitative low-energy electron diffraction (LEED), and density-functional theory (DFT). For film thicknesses beyond 3 monolayers the large tensile strain ({approx_equal}9%) is relieved by the formation of stair-rod-like dislocations. Their favorable energetics is revealed by DFT calculations which also determine the defects' structural parameters. On the unstructured Ir(100)-(1x1) surface they develop in an irregular way, i.e., without long-range order. In STM they are visible as shallow depressions or by decoration with further adsorbed adatoms. In contrast to this case of missing long-range order, the dislocations are ordered in films on the Ir(100)-(5x1)-H surface, whereby (5x1)-periodic Ir wires at the interface act as pinning centers. So, their detailed atomic structure is accessible experimentally by quantitative LEED with crystallographic precision. Features similar to Ni are also observed for Co films.

  8. 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.

  9. Dielectric relaxation and polaronic conduction in epitaxial BaFe12O19 hexaferrite thin film

    NASA Astrophysics Data System (ADS)

    Tang, Rujun; Zhou, Hao; Zhao, Run; Jian, Jie; Wang, Han; Huang, Jijie; Fan, Meng; Zhang, Wei; Wang, Haiyan; Yang, Hao

    2016-03-01

    The dielectric properties of epitaxial BaFe12O19 hexaferrite thin film have been investigated as a function of frequency (50 Hz  -  2 MHz) and temperature (100-375 K). The frequency dependent permittivity, impedance ({{Z}\\prime \\prime} ) and modulus ({{M}\\prime \\prime} ) spectra show that the dielectric responses of BaFe12O19 thin film are thermally activated. The activation energy of BaFe12O19 film (E a) is much smaller than that of the polycrystalline bulk BaFe12O19. In addition, E a increases with increasing temperature and there is a distribution of relaxation time in the sample. The scaling behavior of {{Z}\\prime \\prime} and {{M}\\prime \\prime} spectra of the sample further suggest that the distribution of relaxation time is temperature independent at low temperatures (<250 K) and temperature dependent at high temperatures. The temperature dependent dc conductivity shows that small polaron hopping is the most probable conduction mechanism for BaFe12O19 film.

  10. 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.

  11. 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.

  12. 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; ...

    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

  13. Long-range ferromagnetic order in LaCoO3 -δ epitaxial films due to the interplay of epitaxial strain and oxygen vacancy ordering

    NASA Astrophysics Data System (ADS)

    Mehta, V. V.; Biskup, N.; Jenkins, C.; Arenholz, E.; Varela, M.; Suzuki, Y.

    2015-04-01

    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.

  14. 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

  15. 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.

  16. Semiconducting p-type MgNiO:Li epitaxial films fabricated by cosputtering method

    SciTech Connect

    Kwon, Yong Hun; Chun, Sung Hyun; Cho, Hyung Koun

    2013-07-15

    Li-doped ternary Mg{sub x}Ni{sub 1-x}O thin films were deposited on (0001) Al{sub 2}O{sub 3} substrates by a radio frequency (RF) magnetron cosputtering method with MgO and NiO:Li targets. The Mg mole fraction and Li content were relatively controlled by changing RF power for the MgO target over a range of 0-300 W, while the NiO:Li target was kept at 150 W. As a result, all films were epitaxially grown on (0001) Al{sub 2}O{sub 3} substrates with the relationship of [110]{sub NiO}||[1110]{sub Al2O3}, [112]{sub NiO}||[2110]{sub Al2O3} (in-plane), and [111]{sub NiO}||[0001]{sub Al2O3} (out-of-plane), and showed p-type semiconducting properties. Furthermore, from x-ray diffraction patterns, the authors found that MgO was effectively mixed with NiO:Li without structural deformation due to low lattice mismatch (0.8%) between NiO and MgO. However, the excess Li contents degraded the crystallinity of the MgNiO films. The band-gap of films was continuously shifted from 3.66 eV (339 nm) to 4.15 eV (299 nm) by the RF power of the MgO target. A visible transmittance of more than 80% was exhibited at RF powers higher than 200 W. Ultimately, the electrical resistivity of p-type MgNiO films was improved from 7.5 to 673.5 {Omega}cm, indicating that the Li-doped MgNiO films are good candidates for transparent p-type semiconductors.

  17. Structural evolution of epitaxial SrCoOx films near topotactic phase transition

    NASA Astrophysics Data System (ADS)

    Jeen, Hyoungjeen; Lee, Ho Nyung

    2015-12-01

    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 (SrCoOx) 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 SrCoO2.5 thin films and performed post-annealing at various temperatures for topotactic conversion into the perovskite phase (SrCoO3-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.

  18. Structural evolution of epitaxial SrCoOx films near topotactic phase transition

    DOE PAGES

    Jeen, Hyoung Jeen; Lee, Ho Nyung

    2015-12-18

    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 (SrCoOx) 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 SrCoO2.5thin films and performed post-annealing at various temperatures for topotacticmore » conversion into the perovskite phase (SrCoO3-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. Furthermore, 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.« less

  19. Ultralow 1/f Noise in a Heterostructure of Superconducting Epitaxial Cobalt Disilicide Thin Film on Silicon.

    PubMed

    Chiu, Shao-Pin; Yeh, Sheng-Shiuan; Chiou, Chien-Jyun; Chou, Yi-Chia; Lin, Juhn-Jong; Tsuei, Chang-Chyi

    2017-01-24

    High-precision resistance noise measurements indicate that the epitaxial CoSi2/Si heterostructures at 150 and 2 K (slightly above its superconducting transition temperature Tc of 1.54 K) exhibit an unusually low 1/f noise level in the frequency range of 0.008-0.2 Hz. This corresponds to an upper limit of Hooge constant γ ≤ 3 × 10(-6), about 100 times lower than that of single-crystalline aluminum films on SiO2 capped Si substrates. Supported by high-resolution cross-sectional transmission electron microscopy studies, our analysis reveals that the 1/f noise is dominated by excess interfacial Si atoms and their dimer reconstruction induced fluctuators. Unbonded orbitals (i.e., dangling bonds) on excess Si atoms are intrinsically rare at the epitaxial CoSi2/Si(100) interface, giving limited trapping-detrapping centers for localized charges. With its excellent normal-state properties, CoSi2 has been used in silicon-based integrated circuits for decades. The intrinsically low noise properties discovered in this work could be utilized for developing quiet qubits and scalable superconducting circuits for future quantum computing.

  20. Cationic Redistribution at Epitaxial Interfaces in Superconducting Two-Dimensionally Doped Lanthanum Cuprate Films.

    PubMed

    Baiutti, Federico; Gregori, Giuliano; Wang, Yi; Suyolcu, Y Eren; Cristiani, Georg; van Aken, Peter A; Maier, Joachim; Logvenov, Gennady

    2016-10-12

    The exploration of interface effects in complex oxide heterostructures has led to the discovery of novel intriguing phenomena in recent years and has opened the path toward the precise tuning of material properties at the nanoscale. One recent example is space-charge superconductivity. Among the complex range of effects which may arise from phase interaction, a crucial role is played by cationic intermixing, which defines the final chemical composition of the interface. In this work, we performed a systematic study on the local cationic redistribution of two-dimensionally doped lanthanum cuprate films grown by oxide molecular beam epitaxy, in which single LaO layers in the epitaxial crystal structure were substituted by layers of differently sized and charged dopants (Ca, Sr, Ba, and Dy). In such a model system, in which the dopant undergoes an asymmetric redistribution across the interface, the evolution of the cationic concentration profile can be effectively tracked by means of atomically resolved imaging and spectroscopic methods. This allowed for the investigation of the impact of the dopant chemistry (ionic size and charge) and of the growth conditions (temperature) on the final superconducting and structural properties. A qualitative model for interface cationic intermixing, based on thermodynamic considerations, is proposed. This work highlights the key role which cationic redistribution may have in the definition of the final interface properties and represents a further step forward the realization of heterostructures with improved quality.

  1. 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.

  2. 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

  3. Epitaxial PZT thin films on YSZ-buffered Si (001) substrates for piezoelectric MEMS or NEMS applications

    NASA Astrophysics Data System (ADS)

    Jorel, Corentin; Colder, Héloïse; Galdi, Alice; Méchin, Laurence

    2012-12-01

    We report the growth of epitaxial Pb(Zr0.54Ti0.46)O3 (PZT) thin films on yttria-stabilized zirconia buffered silicon substrates by pulsed laser deposition. We demonstrate a full in plane epitaxy of the buffer layer, showing a RMS roughness of less than 0.3 nm for a 120 nm thick layer. This buffer layer allows the growth of fully (110) textured oxide conducting SrRuO3 and subsequent functional oxide layers. Here the Pb(Zr,Ti)O3 oxide was chosen to demonstrate its possible integration in piezoelectric microelectromechanical systems on silicon.

  4. Influence of epitaxial strain on the magnetic properties of (110) SmFe{sub 2} thin film

    SciTech Connect

    Fuente, C. de la; Arnaudas, J. I.; Ciria, M.; Moral, A. del; Dufour, C.; Dumesnil, K.

    2009-03-30

    A novel nonlinear influence of the magnetoelastic energy because of the epitaxial strain allows us to explain the spontaneous magnetization and the cubic magnetostriction of a molecular-beam-epitaxy-grown SmFe{sub 2} thin film. Under this scope, new crystal-field parameters A{sub 4} and A{sub 6} and exchange coupling parameter {lambda}{sub ex} have been found. These new parameters could account for the change of the energy balance in the spin reorientation transition and explain the softening it has with respect to the bulk case.

  5. Epitaxial Ag film formation on NaCl crystals in Knudsen gases of Ar

    NASA Astrophysics Data System (ADS)

    Ogura, Iwao; Suzuki, Shoetu; Nagashima, Seiichi

    Transportation of Ag atoms onto NaCl substrate in Knudsen Ar gas is studied according to the kinetic theory of gas. The results, as compared with our experiment, are as follows: (1) The temperature of Ar-Ag gas in a deposition chamber is estimated to be ˜900 K. (2) The concentration n( r) in radial flow of Ag atoms oto the substrate is given as n( r) = 4.7 × 10 16r-1 atoms m -3. (3) Estimated deposition rate, 1 nm/s, 9 cm of the Ag source agrees with the experimental value. (4) The number of dimers formed in the Ar sbnd Ag gas is ˜3% of the numbers of Ag atoms reaching the substrate. (5) Epitaxial Ag film formation on the NaCl at room temperature will be controlled by temperature and/or pressure of Ar gas.

  6. Composition dependence of magnetic properties in perpendicularly magnetized epitaxial thin films of Mn-Ga alloys

    NASA Astrophysics Data System (ADS)

    Mizukami, S.; Kubota, T.; Wu, F.; Zhang, X.; Miyazaki, T.; Naganuma, H.; Oogane, M.; Sakuma, A.; Ando, Y.

    2012-01-01

    Mn-Ga binary alloys show strong magnetism and large uniaxial magnetic anisotropy even though these alloys do not contain any noble, rare-earth metals or magnetic elements. We investigate the composition dependence of saturation magnetization MS and uniaxial magnetic anisotropy Ku in epitaxial films of MnxGa1-x alloys (x˜0.5-0.75) grown by magnetron sputtering. The MS values decrease linearly from approximately 600 to 200 emu/cm3 with increasing x, whereas the Ku values decrease slightly from approximately 15 to 10 Merg/cm3 with increasing x. These trends are distinct from those for known tetragonal hard magnets obtained in a limited composition range in Mn-Al and Fe-Pt binary alloys. These data are analyzed using a localized magnetic moment model.

  7. Structural and optical characterizations of InPBi thin films grown by molecular beam epitaxy.

    PubMed

    Gu, Yi; Wang, Kai; Zhou, Haifei; Li, Yaoyao; Cao, Chunfang; Zhang, Liyao; Zhang, Yonggang; Gong, Qian; Wang, Shumin

    2014-01-13

    InPBi thin films have been grown on InP by gas source molecular beam epitaxy. A maximum Bi composition of 2.4% is determined by Rutherford backscattering spectrometry. X-ray diffraction measurements show good structural quality for Bi composition up to 1.4% and a partially relaxed structure for higher Bi contents. The bandgap was measured by optical absorption, and the bandgap reduction caused by the Bi incorporation was estimated to be about 56 meV/Bi%. Strong and broad photoluminescence signals were observed at room temperature for samples with xBi < 2.4%. The PL peak position varies from 1.4 to 1.9 μm, far below the measured InPBi bandgap.

  8. Detection of current induced spin polarization in epitaxial Bi2Te3 thin film

    NASA Astrophysics Data System (ADS)

    Dey, Rik; Roy, Anupam; Pramanik, Tanmoy; Rai, Amritesh; Heon Shin, Seung; Majumder, Sarmita; Register, Leonard F.; Banerjee, Sanjay K.

    2017-03-01

    We electrically detect charge current induced spin polarization on the surface of a molecular beam epitaxy grown Bi2Te3 thin film in a two-terminal device with a ferromagnetic MgO/Fe contact and a nonmagnetic Ti/Au contact. The two-point resistance, measured in an applied magnetic field, shows a hysteresis tracking the magnetization of Fe. A theoretical estimate is obtained for the change in resistance on reversing the magnetization direction of Fe from coupled spin-charge transport equations based on the quantum kinetic theory. The order of magnitude and the sign of the hysteresis are consistent with the spin-polarized surface state of Bi2Te3.

  9. Influence of epitaxial strain on elastocaloric effect in ferroelectric thin films

    SciTech Connect

    Liu, Yang Dkhil, Brahim; Wei, Jie; Lou, Xiaojie; Bellaiche, L.; Scott, James F.

    2015-01-19

    We report the influence of epitaxial strain u{sub m} on the elastocaloric properties of BaTiO{sub 3} thin films. Using thermodynamic calculations, we show that there exists a critical compressive stress σ{sub 3c} at which the elastocaloric effect is maximized for any compressive misfit strain we investigate. Moreover, it is found that |σ{sub 3c}| decreases significantly with decreasing |u{sub m}|, which is accompanied by a reduction of the elastocaloric response. Interestingly, a several fold enhancement in the electrocaloric effect can be achieved for stress in proximity of σ{sub 3c}. The elastocaloric effect predicted here may find potential cooling applications by combining the stress-mediated electrocaloric effect or designing hybrid elastocaloric/electrocaloric devices in the future.

  10. Electrical properties of the amorphous interfacial layer between Al electrodes and epitaxial NiO films

    SciTech Connect

    Hyuck Jang, Jae; Kwon, Ji-Hwan; Kim, Miyoung; Ran Lee, Seung; Char, Kookrin

    2012-04-23

    The amorphous interfacial layer (a-IL) between Al electrode and epitaxial NiO films were studied using electron energy-loss spectroscopy (EELS) and energy-dispersive x-ray spectroscopy. Two distinct properties were found in the a-IL, i.e., a lower metallic and an upper insulating layer. EELS results revealed that the metallic Ni atoms were responsible for the conducting nature of the lower oxide amorphous layer. The resistance behavior of Al/a-IL/epi-NiO was changed from a high to a low resistance state after forming process. The resistance change could be explained by the formation of a nanocrystalline metal alloy in the insulating amorphous layer.

  11. Epitaxial growth of cadmium telluride films on silicon with a buffer silicon carbide layer

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

    An epitaxial 1-3-μm-thick cadmium telluride film has been grown on silicon with a buffer silicon carbide layer using the method of open thermal evaporation and condensation in vacuum for the first time. The optimum substrate temperature was 500°C at an evaporator temperature of 580°C, and the growth time was 4 s. In order to provide more qualitative growth of cadmium telluride, a high-quality 100-nm-thick buffer silicon carbide layer was previously synthesized on the silicon surface using the method of topochemical substitution of atoms. The ellipsometric, Raman, X-ray diffraction, and electron-diffraction analyses showed a high structural perfection of the CdTe layer in the absence of a polycrystalline phase.

  12. Carbon dioxide and water adsorption on highly epitaxial Delafossite CuFeO2 thin film

    NASA Astrophysics Data System (ADS)

    Rojas, S.; Joshi, T.; Borisov, P.; Sarabia, M.; Lederman, D.; Cabrera, A. L.

    2015-03-01

    Thermal programmed desorption (TPD) of CO2 and H2O from a 200 nm thick CuFeO2 Delafossite surface was performed in a standard UHV chamber, The CuFeO2 thin film grown using Pulsed Laser Deposition (PLD) over an Al2O3 (0001) substrate with controlled O2 atmosphere resulted with highly epitaxial crystal structure. The adsorption/desorption of CO2 and H2O process was also monitored with X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). Our results revealed that carbon dioxide interacts with CuFeO2 forming Fe carbonates compounds on its surface. Hydroxides were also formed on the surface due to water presence. Using TPD data, Arrhenius plots for CO2 and water desorption were done and activation energy for desorption was obtained. Funds FONDECyT 1130372; Thanks to P. Ferrari.

  13. 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.

  14. Time-resolved probing of magnon mass renormalization in epitaxial Fe films

    NASA Astrophysics Data System (ADS)

    Stoica, Vladimir; Schlepuetz, Christian; Walko, Donald; Li, Yuelin; Dufresne, Eric; Landahl, Eric; Clarke, Roy

    2011-03-01

    Irradiation of ferromagnetic metals with femtosecond laser pulses leads to sub-picosecond ultrafast demagnetization, followed by coherent spin wave dynamics on the picosecond to nanosecond timescales. Presently, it is of high interest to develop a cohesive picture that consistently accounts for these experimental observations. One way to address this is to refine the experimental techniques for improving the quantitative comparison with theory. Here, we present in-detail investigations of the coherent exchange spin waves in epitaxial Fe films, which are used for accurate determination the spin wave stiffness constant, D. These studies enabled to detect the effect of femtosecond laser excitation on D and correlate the results with time-resolved X-ray diffraction measurements of the thermal relaxation. Our data provide evidence for the magnon mass renormalization induced by electron-magnon interaction. Preliminary data obtained in Ni and Co seem to indicate the same effect.

  15. 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.

  16. Compliant ferroelastic domains in epitaxial Pb(Zr,Ti)O{sub 3} thin films

    SciTech Connect

    Feigl, L.; McGilly, L. J.; Sandu, C. S.; Setter, N.

    2014-04-28

    Ordered patterns of highly compliant ferroelastic domains have been created by use of tensile strained epitaxial Pb(Zr,Ti)O{sub 3} thin films, of very low defect density, grown on DyScO{sub 3} substrates. The effect of 180° switching on well-ordered a/c 90° domain patterns is investigated by a combination of transmission electron microscopy, piezoelectric force microscopy, and X-ray diffraction. It is shown that ferroelastic a-domains, having an in-plane polarization, can be created and completely removed on a local level by an out-of-plane electric field. The modifications of the ferroelastic domain pattern can be controlled by varying the parameters used during switching with a piezoresponse force microscope to produce the desired arrangement.

  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. Growth Parameters for Thin Film InBi Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Keen, B.; Makin, R.; Stampe, P. A.; Kennedy, R. J.; Sallis, S.; Piper, L. J.; McCombe, B.; Durbin, S. M.

    2014-04-01

    The alloying of bismuth with III-V semiconductors, in particular GaAs and InAs thin films grown by molecular beam epitaxy (MBE), has attracted considerable interest due to the accompanying changes in band structure and lattice constant. Specifically, bismuth incorporation in these compounds results in both a reduction in band gap (through shifting of the valence band) and an increase in the lattice constant of the alloy. To fully understand the composition of these alloys, a better understanding of the binary endpoints is needed. At present, a limited amount of literature exists on the III-Bi family of materials, most of which is theoretical work based on density functional theory calculations. The only III-Bi material known to exist (in bulk crystal form) is InBi, but its electrical properties have not been sufficiently studied and, to date, the material has not been fabricated as a thin film. We have successfully deposited crystalline InBi on (100) GaAs substrates using MBE. Wetting of the substrate is poor, and regions of varying composition exist across the substrate. To obtain InBi, the growth temperature had to be below 100 °C. It was found that film crystallinity improved with reduced Bi flux, into an In-rich regime. Additionally, attempts were made to grow AlBi and GaBi.

  19. The structure and morphology of (112)-oriented Cu(In,Ga)Se{sub 2} epitaxial films

    SciTech Connect

    Liao Dongxiang; Rockett, Angus

    2008-11-01

    The properties of the (112) surfaces of Cu(In,Ga)Se{sub 2} (CIGS) are important to the performance of photovoltaic devices based on these materials. Epitaxial CIGS films were grown on GaAs (111)A (cation-terminated) and B (anion-terminated) substrates and the structure and morphology of the films were studied. There are a large number of rotational twins in films grown on (111)B substrates, but not for (111)A substrates. The surfaces consist of shallow triangular pyramids bounded by one type of <110> step. The steps show both sharp inside and outside corners. New layers nucleated as islands at step edges. The step heights are a mixture of single and multiple atomic layers. The change in surface chemistry from cation to anion terminated affects the measured electronic states comprising the valence band and is probably accompanied by a shift in the valence band edge. There is a distinct difference in step edge shape that shows a difference in step kink density but the expected high kink energy on both surfaces indicates that this may be due to kinetic rather than thermodynamic effects.

  20. 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.