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Sample records for insulating thin films

  1. Optical conductivity of topological insulator thin films

    SciTech Connect

    Li, L. L.; Xu, W.; Peeters, F. M.

    2015-05-07

    We present a detailed theoretical study on the optoelectronic properties of topological insulator thin film (TITFs). The k·p approach is employed to calculate the energy spectra and wave functions for both the bulk and surface states in the TITF. With these obtained results, the optical conductivities induced by different electronic transitions among the bulk and surface states are evaluated using the energy-balance equation derived from the Boltzmann equation. We find that for Bi{sub 2}Se{sub 3}-based TITFs, three characteristic regimes for the optical absorption can be observed. (i) In the low radiation frequency regime (photon energy ℏω<200 meV), the free-carrier absorption takes place due to intraband electronic transitions. An optical absorption window can be observed. (ii) In the intermediate radiation frequency regime (200<ℏω<300 meV), the optical absorption is induced mainly by interband electronic transitions from surface states in the valance band to surface states in the conduction band and an universal value σ{sub 0}=e{sup 2}/(8ℏ) for the optical conductivity can be obtained. (iii) In the high radiation frequency regime (ℏω>300 meV), the optical absorption can be achieved via interband electronic transitions from bulk and surface states in the valance band to bulk and surface states in the conduction band. A strong absorption peak can be observed. These interesting findings indicate that optical measurements can be applied to identify the energy regimes of bulk and surface states in the TITF.

  2. Quantum Hall Superfluids in Topological Insulator Thin Films

    NASA Astrophysics Data System (ADS)

    Tilahun, Dagim; Lee, Byounghak; Hankiewicz, Ewelina; MacDonald, Allan

    2011-10-01

    Three-dimensional topological insulators have protected Dirac-cone surface states. In this paper we propose magnetic field induced topological insulator thin film ordered states in which coherence is established spontaneously between top and bottom surfaces. We find that the large dielectric constants of these materials increases the layer separation range over which coherence survives and decreases the superfluid sound velocity, but has little influence on superfluid density or charge gap. The coherent state at total Landau-level filling factor νT=0 is predicted to be free of edge modes, qualitatively altering its transport phenomenology.

  3. Specular Andreev reflection in thin films of topological insulators

    NASA Astrophysics Data System (ADS)

    Majidi, Leyla; Asgari, Reza

    2016-05-01

    We theoretically reveal the possibility of specular Andreev reflection in a thin film topological insulator normal-superconductor (N/S) junction in the presence of a gate electric field. The probability of specular Andreev reflection increases with the electric field, and electron-hole conversion with unit efficiency happens in a wide experimentally accessible range of the electric field. We show that perfect specular Andreev reflection can occur for all angles of incidence with a particular excitation energy value. In addition, we find that the thermal conductance of the structure displays exponential dependence on the temperature. Our results reveal the potential of the proposed topological insulator thin-film-based N/S structure for the realization of intraband specular Andreev reflection.

  4. Superconductivity of very thin films: The superconductor-insulator transition

    NASA Astrophysics Data System (ADS)

    Lin, Yen-Hsiang; Nelson, J.; Goldman, A. M.

    2015-07-01

    The study of thin superconducting films has been an important component of the science of superconductivity for more than six decades. It played a major role in the development of currently accepted views of the macroscopic and microscopic nature of the superconducting state. In recent years the focus of research in the field has shifted to the study of ultrathin films and surface and interface layers. This has permitted the exploration of one of the important topics of condensed matter physics, the superconductor-insulator transition. This review will discuss this phenomenon as realized in the study of metallic films, cuprates, and metallic interfaces. These are in effect model systems for behaviors that may be found in more complex systems of contemporary interest.

  5. Quantum Hall Superfluids in Topological Insulator Thin Films

    NASA Astrophysics Data System (ADS)

    Tilahun, Dagim; Lee, Byounghak; Hankiewicz, E. M.; MacDonald, A. H.

    2011-12-01

    Three-dimensional topological insulators have protected Dirac-cone surface states. In this Letter we argue that gapped excitonic superfluids with spontaneous coherence between top and bottom surfaces can occur in the topological insulator (TI)-thin-film quantum Hall regime. We find that the large dielectric constants of TI materials increase the layer separation range over which coherence survives and decrease the superfluid sound velocity, but have little influence on the superfluid density or on the charge gap. The coherent state at total Landau-level filling factor νT=0 is predicted to be free of edge modes, qualitatively altering its transport phenomenology compared to the widely studied case of νT=1 in GaAs double-quantum wells.

  6. Quantum Hall superfluids in topological insulator thin films.

    PubMed

    Tilahun, Dagim; Lee, Byounghak; Hankiewicz, E M; MacDonald, A H

    2011-12-01

    Three-dimensional topological insulators have protected Dirac-cone surface states. In this Letter we argue that gapped excitonic superfluids with spontaneous coherence between top and bottom surfaces can occur in the topological insulator (TI)-thin-film quantum Hall regime. We find that the large dielectric constants of TI materials increase the layer separation range over which coherence survives and decrease the superfluid sound velocity, but have little influence on the superfluid density or on the charge gap. The coherent state at total Landau-level filling factor νT=0 is predicted to be free of edge modes, qualitatively altering its transport phenomenology compared to the widely studied case of νT=1 in GaAs double-quantum wells. PMID:22243013

  7. Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films.

    PubMed

    Figueroa, A I; van der Laan, G; Harrison, S E; Cibin, G; Hesjedal, T

    2016-01-01

    The breaking of time-reversal symmetry (TRS) in topological insulators is a prerequisite for unlocking their exotic properties and for observing the quantum anomalous Hall effect (QAHE). The incorporation of dopants which exhibit magnetic long-range order is the most promising approach for TRS-breaking. REBiTe3, wherein 50% of the Bi is substitutionally replaced by a RE atom (RE = Gd, Dy, and Ho), is a predicted QAHE system. Despite the low solubility of REs in bulk crystals of a few %, highly doped thin films have been demonstrated, which are free of secondary phases and of high crystalline quality. Here we study the effects of exposure to atmosphere of rare earth-doped Bi2(Se, Te)3 thin films using x-ray absorption spectroscopy. We demonstrate that these RE dopants are all trivalent and effectively substitute for Bi(3+) in the Bi2(Se, Te)3 matrix. We find an unexpected high degree of sample oxidation for the most highly doped samples, which is not restricted to the surface of the films. In the low-doping limit, the RE-doped films mostly show surface oxidation, which can be prevented by surface passivation, encapsulation, or in-situ cleaving to recover the topological surface state. PMID:26956771

  8. Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films

    PubMed Central

    Figueroa, A. I.; van der Laan, G.; Harrison, S. E.; Cibin, G.; Hesjedal, T.

    2016-01-01

    The breaking of time-reversal symmetry (TRS) in topological insulators is a prerequisite for unlocking their exotic properties and for observing the quantum anomalous Hall effect (QAHE). The incorporation of dopants which exhibit magnetic long-range order is the most promising approach for TRS-breaking. REBiTe3, wherein 50% of the Bi is substitutionally replaced by a RE atom (RE = Gd, Dy, and Ho), is a predicted QAHE system. Despite the low solubility of REs in bulk crystals of a few %, highly doped thin films have been demonstrated, which are free of secondary phases and of high crystalline quality. Here we study the effects of exposure to atmosphere of rare earth-doped Bi2(Se, Te)3 thin films using x-ray absorption spectroscopy. We demonstrate that these RE dopants are all trivalent and effectively substitute for Bi3+ in the Bi2(Se, Te)3 matrix. We find an unexpected high degree of sample oxidation for the most highly doped samples, which is not restricted to the surface of the films. In the low-doping limit, the RE-doped films mostly show surface oxidation, which can be prevented by surface passivation, encapsulation, or in-situ cleaving to recover the topological surface state. PMID:26956771

  9. Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films

    NASA Astrophysics Data System (ADS)

    Figueroa, A. I.; van der Laan, G.; Harrison, S. E.; Cibin, G.; Hesjedal, T.

    2016-03-01

    The breaking of time-reversal symmetry (TRS) in topological insulators is a prerequisite for unlocking their exotic properties and for observing the quantum anomalous Hall effect (QAHE). The incorporation of dopants which exhibit magnetic long-range order is the most promising approach for TRS-breaking. REBiTe3, wherein 50% of the Bi is substitutionally replaced by a RE atom (RE = Gd, Dy, and Ho), is a predicted QAHE system. Despite the low solubility of REs in bulk crystals of a few %, highly doped thin films have been demonstrated, which are free of secondary phases and of high crystalline quality. Here we study the effects of exposure to atmosphere of rare earth-doped Bi2(Se, Te)3 thin films using x-ray absorption spectroscopy. We demonstrate that these RE dopants are all trivalent and effectively substitute for Bi3+ in the Bi2(Se, Te)3 matrix. We find an unexpected high degree of sample oxidation for the most highly doped samples, which is not restricted to the surface of the films. In the low-doping limit, the RE-doped films mostly show surface oxidation, which can be prevented by surface passivation, encapsulation, or in-situ cleaving to recover the topological surface state.

  10. Quantum capacitance in thin film vanadium dioxide metal insulator transition

    NASA Astrophysics Data System (ADS)

    Wu, Zhe; Knighton, Talbot; Tarquini, Vinicio; Torres, David; Wang, Tongyu; Sepulveda, Nelson; Huang, Jian

    We present capacitance measurements of the electronic density of states performed in high quality vanadium dioxide (VO2) thin films on sapphire (Al2O3) substrate. These films show the expected metal insulator transition near 60 °C with resistivity changing by 3 orders of magnitude with a hysteresis of 10 °C. To make a capacitive probe, a gate is suspended above the film surface using a flip-chip method with microfabricated supports. The geometric capacitance per-area reached is 40 pF/mm2. Such a large capacitance can be significantly modified by electron interaction and band charging/discharging which appear as an extra term known as the quantum capacitance (Cq). An AC signal applied to the gate allows measurement of the changing density of states (DOS) across the MIT. The DOS abruptly increases as the sample is heated through the transition point. Conversely the low temperature drop of d μ / d n is consistent with an energy gap opening in the insulating phase. These parameters shed light on the transition mechanism. NSF DMR-1105183, NSF ECCS 1306311.

  11. Thin-film metal coated insulation barrier in a Josephson tunnel junction. [Patent application

    DOEpatents

    Hawkins, G.A.; Clarke, J.

    1975-10-31

    A highly stable, durable, and reproducible Josephson tunnel junction consists of a thin-film electrode of a hard superconductor, a thin oxide insulation layer over the electrode constituting a Josephson tunnel junction barrier, a thin-film layer of stabilizing metal over the barrier, and a second thin-film hard superconductive electrode over the stabilizing film. The thin stabilizing metal film is made only thick enough to limit penetration of the electrode material through the insulation layer so as to prevent a superconductive short.

  12. Unusual insulating phase at low temperature in thin indium films

    NASA Astrophysics Data System (ADS)

    Okuma, S.; Kokubo, N.

    1995-06-01

    We have prepared a series of thin indium films whose disorder is systematically introduced, and measured the temperature-dependent and magnetic-field-dependent Hall resistance Rxy as well as the longitudinal resistance Rxx at low temperatures. By increasing the field at fixed disorder, we have found, in addition to a usual critical field BxxC where Rxx(T-->0)-->∞, another critical field BxyC (>~BxxC) where Rxy(T-->0) diverges. With increasing disorder, BxxC decreases faster than BxyC, thus the region BxxCinsulator phase.

  13. Quantum Hall Super uids in Topological Insulator Thin Films

    NASA Astrophysics Data System (ADS)

    Tilahun, Dagim; Lee, Byounghak; Hankiewicz, Ewelina; MacDonald, Allan

    2012-02-01

    Three-dimensional topological insulators have protected Dirac-cone surface states. In this work we argue that gapped excitonic superfluids with spontaneous coherence between top and bottom surfaces can occur in the TI-thin-film quantum-Hall regime. We find that the large dielectric constants of TI materials increase the layer separation range over which coherence survives and decrease the superfluid sound velocity, but have little influence on the superfluid density or on the charge gap. The coherent state at total Landau-level filling factor νT= 0 is predicted to be free of edge modes, qualitatively altering its transport phenomenology compared to the widely studied case of νT= 1 in GaAs double quantum wells.

  14. Absorption of surface acoustic waves by topological insulator thin films

    SciTech Connect

    Li, L. L.; Xu, W.

    2014-08-11

    We present a theoretical study on the absorption of the surface acoustic waves (SAWs) by Dirac electrons in topological insulator (TI) thin films (TITFs). We find that due to momentum and energy conservation laws, the absorption of the SAWs in TITFs can only be achieved via intra-band electronic transitions. The strong absorption can be observed up to sub-terahertz frequencies. With increasing temperature, the absorption intensity increases significantly and the cut-off frequency is blue-shifted. More interestingly, we find that the absorption of the SAWs by the TITFs can be markedly enhanced by the tunable subgap in the Dirac energy spectrum of the TI surface states. Such a subgap is absent in conventional two-dimensional electron gases (2DEGs) and in the gapless Dirac 2DEG such as graphene. This study is pertinent to the exploration of the acoustic properties of TIs and to potential application of TIs as tunable SAW devices working at hypersonic frequencies.

  15. Laser assisted atom probe analysis of thin film on insulating substrate.

    PubMed

    Kodzuka, M; Ohkubo, T; Hono, K

    2011-05-01

    We demonstrate that the atom probe analyses of metallic thin films on insulating substrates are possible using laser assisted field evaporation. The tips with metallic thin film and insulating substrate (0.6-3 μm in thickness) were prepared by the lift-out and annular ion beam milling techniques on tungsten supports. In spite of the existence of thick insulating layer between the metallic film and the tungsten support, atom probe tomography with practical mass resolution, signal-to-noise ratio and spatial resolution was found to be possible using laser assisted field evaporation. PMID:21172729

  16. Photoexcitation dynamics in thin films of insulated molecular wires

    NASA Astrophysics Data System (ADS)

    Chang, M. H.; Frampton, M. J.; Anderson, H. L.; Herz, L. M.

    2006-12-01

    A study is presented on how encapsulation of conjugated polymer chains affects the motion of photoexcitations and the formation of interchain aggregates in solid films. It is shown that threading of a poly(diphenylene vinylene) backbone inside insulating cyclodextrins (rotaxination) and/or complexation of the chains with poly(ethylene oxide) are effective means of preventing the diffusion of excitons to nonradiative defect sites. Ultrafast time-resolved photoluminescence data reveal that excitation transfer between encapsulated chains is still possible and, for the case of rotaxination, is likely to be facilitated through close packing of end groups belonging to adjacent chains.

  17. Prototype thin-film thermocouple/heat-flux sensor for a ceramic-insulated diesel engine

    NASA Technical Reports Server (NTRS)

    Kim, Walter S.; Barrows, Richard F.

    1988-01-01

    A platinum versus platinum-13 percent rhodium thin-film thermocouple/heat-flux sensor was devised and tested in the harsh, high-temperature environment of a ceramic-insulated, low-heat-rejection diesel engine. The sensor probe assembly was developed to provide experimental validation of heat transfer and thermal analysis methodologies applicable to the insulated diesel engine concept. The thin-film thermocouple configuration was chosen to approximate an uninterrupted chamber surface and provide a 1-D heat-flux path through the probe body. The engine test was conducted by Purdue University for Integral Technologies, Inc., under a DOE-funded contract managed by NASA Lewis Research Center. The thin-film sensor performed reliably during 6 to 10 hr of repeated engine runs at indicated mean surface temperatures up to 950 K. However, the sensor suffered partial loss of adhesion in the thin-film thermocouple junction area following maximum cyclic temperature excursions to greater than 1150 K.

  18. Electronic Structure of Cu2N, a Thin-film Insulating Surface

    NASA Astrophysics Data System (ADS)

    Heidari, Sareh; Fisher, Andrew J.

    2013-03-01

    Thin-film insulators on metals have been used extensively as substrates when studying single molecule magnets (e.g. DyPc2) and magnetic atoms (e.g. Co) using inelastic tunneling spectroscopy (IETS). They decouple the states of the adsorbed molecule from the underlying metallic bulk, which is necessary for IETS measurements [C. F. Hirjibehedin et al., Science 312, 1021, (2006)] and also leads to higher resolution imaging of molecular states [J. Repp et al., Phys. Rev. Lett. 9, 026803, (2005)]. The Cu2N-Cu(100) surface has been shown by STM measurements to have insulating character, however the origin of the insulating behaviour has not been determined. By using Density Functional Theory calculations, we investigate the electronic structure of this surface. We show that the apparent insulating behaviour arises from a strong suppression of the Cu 4s density of states near the Fermi energy in the Cu2N thin film.

  19. Resistance noise in epitaxial thin films of ferromagnetic topological insulators

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Semonti; Kandala, Abhinav; Richardella, Anthony; Islam, Saurav; Samarth, Nitin; Ghosh, Arindam

    2016-02-01

    We report detailed temperature and gate-voltage dependence of 1/f resistance noise in magnetically doped topological insulators (TI) Crx(Bi,Sb)2-xTe3. The noise is remarkably sensitive to the gate voltage, increasing rapidly as the chemical potential is moved towards the charge neutrality point. Unlike in identically prepared (Bi,Sb)2Te3 films, where mobility-fluctuations in the surface states is the dominant mechanism, the noise in the magnetic Crx(Bi,Sb)2-xTe3 originates from transport in the localized band tail of the bulk valence band. A strong increase in noise with decreasing temperature supports this scenario. At higher temperature (≥10 K), we observed large noise peaks at gate voltage-dependent characteristic temperature scales. In line with similar observations in other non-magnetic TI systems, we attribute these peaks to generation-recombination in the Cr-impurity band.

  20. Metal-insulator transition induced in CaVO{sub 3} thin films

    SciTech Connect

    Gu Man; Laverock, Jude; Chen, Bo; Smith, Kevin E.; Wolf, Stuart A.; Lu Jiwei

    2013-04-07

    Stoichiometric CaVO{sub 3} (CVO) thin films of various thicknesses were grown on single crystal SrTiO{sub 3} (STO) (001) substrates using a pulsed electron-beam deposition technique. The CVO films were capped with a 2.5 nm STO layer. We observed a temperature driven metal-insulator transition (MIT) in CVO films with thicknesses below 4 nm that was not observed in either thick CVO films or STO films. The emergence of this MIT can be attributed to the reduction in effective bandwidth due to a crossover from a three-dimensional metal to a two-dimensional insulator. The insulating phase was only induced with a drive current below 0.1 {mu}A. X-ray absorption measurements indicated different electronic structures for thick and very thin films of CVO. Compared with the thick film ({approx}60 nm), thin films of CVO (2-4 nm) were more two-dimensional with the V charge state closer to V{sup 4+}.

  1. Pulsed laser deposition of high-quality thin films of the insulating ferromagnet EuS

    SciTech Connect

    Yang, Qi I.; Zhao, Jinfeng; Risbud, Subhash H.; Zhang, Li; Dolev, Merav; Fried, Alexander D.; Marshall, Ann F.; Kapitulnik, Aharon

    2014-02-24

    High-quality thin films of the ferromagnetic insulator europium(II) sulfide (EuS) were fabricated by pulsed laser deposition on Al{sub 2}O{sub 3} (0001) and Si (100) substrates. A single orientation was obtained with the [100] planes parallel to the substrates, with atomic-scale smoothness indicates a near-ideal surface topography. The films exhibit uniform ferromagnetism below 15.9 K, with a substantial component of the magnetization perpendicular to the plane of the films. Optimization of the growth condition also yielded truly insulating films with immeasurably large resistance. This combination of magnetic and electric properties opens the gate for future devices that require a true ferromagnetic insulator.

  2. Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

    SciTech Connect

    Si, W.; Zhang, C.; Wu, L.; Ozaki, T.; Gu, G.; Li, Q.

    2015-09-01

    Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF2 crystalline substrates respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk. With large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.

  3. Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

    DOE PAGESBeta

    Si, W.; Zhang, C.; Wu, L.; Ozaki, T.; Gu, G.; Li, Q.

    2015-09-01

    Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF2 crystalline substrates respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk.more » With large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.« less

  4. Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

    SciTech Connect

    Si, Weidong E-mail: qiangli@bnl.gov; Zhang, Cheng; Wu, Lijun; Ozaki, Toshinori; Gu, Genda; Li, Qiang E-mail: qiangli@bnl.gov

    2015-08-31

    Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF{sub 2} crystalline substrates, respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk. With large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.

  5. Quantum and classical contributions to linear magnetoresistance in topological insulator thin films

    NASA Astrophysics Data System (ADS)

    Singh, Sourabh; Gopal, R. K.; Sarkar, Jit; Mitra, Chiranjib

    2016-05-01

    Three dimensional topological insulators possess backscattering immune relativistic Dirac fermions on their surface due to nontrivial topology of the bulk band structure. Both metallic and bulk insulating topological insulators exhibit weak-antilocalization in the low magnetic field and linear like magnetoresistance in higher fields. We explore the linear magnetoresistance in bulk insulating topological insulator Bi2-xSbxTe3-ySey thin films grown by pulsed laser deposition technique. Thin films of Bi2-xSbxTe3-ySey were found to be insulating in nature, which conclusively establishes the origin of linear magnetoresistance from surface Dirac states. The films were thoroughly characterized for their crystallinity and composition and then subjected to transport measurements. We present a careful analysis taking into considerations all the existing models of linear magnetoresistance. We comprehend that the competition between classical and quantum contributions to magnetoresistance results in linear magnetoresistance in high fields. We observe that the cross-over field decreases with increasing temperature and the physical argument for this behavior is explained.

  6. Edge states and integer quantum Hall effect in topological insulator thin films.

    PubMed

    Zhang, Song-Bo; Lu, Hai-Zhou; Shen, Shun-Qing

    2015-01-01

    The integer quantum Hall effect is a topological state of quantum matter in two dimensions, and has recently been observed in three-dimensional topological insulator thin films. Here we study the Landau levels and edge states of surface Dirac fermions in topological insulators under strong magnetic field. We examine the formation of the quantum plateaux of the Hall conductance and find two different patterns, in one pattern the filling number covers all integers while only odd integers in the other. We focus on the quantum plateau closest to zero energy and demonstrate the breakdown of the quantum spin Hall effect resulting from structure inversion asymmetry. The phase diagrams of the quantum Hall states are presented as functions of magnetic field, gate voltage and chemical potential. This work establishes an intuitive picture of the edge states to understand the integer quantum Hall effect for Dirac electrons in topological insulator thin films. PMID:26304795

  7. Robust topological surface state in Kondo insulator SmB{sub 6} thin films

    SciTech Connect

    Yong, Jie Jiang, Yeping; Zhang, Xiaohang; Greene, Richard L.; Usanmaz, Demet; Curtarolo, Stefano; Li, Linze; Pan, Xiaoqing; Shin, Jongmoon; Takeuchi, Ichiro

    2014-12-01

    Fabrication of smooth thin films of topological insulators with true insulating bulk are extremely important for utilizing their novel properties in quantum and spintronic devices. Here, we report the growth of crystalline thin films of SmB{sub 6}, a topological Kondo insulator with true insulating bulk, by co-sputtering both SmB{sub 6} and B targets. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy indicate films that are polycrystalline with a (001) preferred orientation. When cooling down, resistivity ρ shows an increase around 50 K and saturation below 10 K, consistent with the opening of the hybridization gap and surface dominated transport, respectively. The ratio ρ{sub 2K}/ρ{sub 300K} is only about two, much smaller than that of bulk, which indicates a much larger surface-to-bulk ratio. Point contact spectroscopy using a superconductor tip on SmB{sub 6} films shows both a Kondo Fano resonance and Andeev reflection, indicating an insulating Kondo lattice with metallic surface states.

  8. Large-Chern-number quantum anomalous Hall effect in thin-film topological crystalline insulators.

    PubMed

    Fang, Chen; Gilbert, Matthew J; Bernevig, B Andrei

    2014-01-31

    We theoretically predict that thin-film topological crystalline insulators can host various quantum anomalous Hall phases when doped by ferromagnetically ordered dopants. Any Chern number between ±4 can, in principle, be reached as a result of the interplay between (a) the induced Zeeman field, depending on the magnetic doping concentration, (b) the structural distortion, either intrinsic or induced by a piezoelectric material through the proximity effect, and (c) the thickness of the thin film. We propose a heterostructure to realize quantum anomalous Hall phases with Chern numbers that can be tuned by electric fields. PMID:24580476

  9. Investigation of the magnetic properties of insulating thin films using the longitudinal spin Seebeck effect

    SciTech Connect

    Kehlberger, A. Jakob, G.; Kläui, M.; Onbasli, M. C.; Kim, D. H.; Ross, C. A.

    2014-05-07

    The longitudinal spin Seebeck effect is used as a detector for the magnetic properties and switching characteristics of magnetic thin insulating films. We use a 300 nm and a 20 nm thick Yttrium Iron Garnet (YIG, Y{sub 3}Fe{sub 5}O{sub 12}) film prepared by pulsed laser deposition and afterwards coated by platinum for the detection of the thermally excited magnons by the inverse spin Hall effect. The inverse spin Hall signals reveal a magnetic uniaxial anisotropy along the direction of the platinum stripe in the thicker film. For the thin film we find a more isotropic behavior, which is complementarily observed using the magnetoresistance occurring at the platinum/YIG interface. We explain our results on the basis of x-ray diffraction data, which reveal a miscut of the substrate and film surface and an expansion of the YIG lattice. Both findings favor a growth-induced magnetic anisotropy that we observe.

  10. Magnetotransport Methods to Probe Surface States of Topological Insulator Thin Films and Topological Insulator/Ferromagnet (TI/FM) Heterostructures

    NASA Astrophysics Data System (ADS)

    Kumar, Raj

    confirmed by the cos(theta) dependence of field titled MR measurements on the Bi2Se3 thin films. No switching in the AMR or hysteresis behavior in the MR was observed in control experiments performed on non TI materials with superconducting electrodes and metal electrodes on Bi2Se3 TI films. The growth and characterization of Bi2Se3/Bi 2Se3/La0.70Sr0.30MnO3 (TI/FM), a topological insulator/ferromagnet heterostructure is discussed in the last part of the thesis. We have grown Bi2Se3/Bi2Se 3/La0.70Sr0.30MnO3 (TI/FM) heterostructures by the method of pulsed laser deposition. Bi2Se3/La 0.70Sr0.30MnO3 (LSMO) is a strong ferromagnetic material with Tc ˜ 350 K and Bi2Se3 is the most studied topological insulator. XRD and phi scan measurements of Bi2Se3/La 0.70Sr0.30MnO3 (TI/FM) heterostructure showed that epitaxial thin films of Bi2Se3 were grown on the LSMO template. Strong in-plane magnetization was confirmed by magnetometry measurements of the Bi2Se3/LSMO heterostructure. Magnetotransport measurements showed a distorted weak anti-localization effect with hysteretic behavior due to interface induced ferromagnetism in the Bi2Se 3 TI films.

  11. Microthruster with integrated platinum thin film resistance temperature detector (RTD), heater, and thermal insulation

    NASA Astrophysics Data System (ADS)

    Miyakawa, N.; Legner, W.; Ziemann, T.; Telitschkin, D.; Fecht, H.-J.; Friedberger, A.

    2011-06-01

    We have fabricated microthruster chip pairs - one chip with microthruster structures such as injection capillaries, combustion chamber and nozzle, the other chip with platinum thin film devices such as resistance temperature detectors (RTDs) and a heater. The platinum thin film was sputtered on thermally oxidized silicon wafers WITHOUT adhesion layer. The effects of anneal up to 1050°C on the surface morphology of platinum thin films with varied geometry as well as with / without PECVD-SiO2 coating were investigated in air and N2 and results will also be presented. Electrical characterization of sensors was carried out in a furnace tube in which the sensors' temperature was varied between room temperature and 1000°C with a ramp of +/-5Kmin-1 in air and N2. The experiments showed that the temperature-resistance characteristics of sensors had stabilized after the first heating up to 1000°C in N2. After stabilization the sensors underwent further 8 temperature cycles which correspond to over 28h of operation time between 800 - 1000°C. To reduce the loss of combustion heat, chip material around the microthruster structures was partially removed. The effects of thermal insulation were investigated with microthruster chip pairs which were clamped together mechanically. The heater power was varied up to 20W and the temperature distribution in the chip pairs with / without thermal insulation was monitored with 7 integrated thin film sensors.

  12. Correlation Between Metal-Insulator Transition Characteristics and Electronic Structure Changes in Vanadium Oxide Thin Films

    SciTech Connect

    Ruzmetov,D.; Senanayake, S.; Narayanamurti, V.; Ramanathan, S.

    2008-01-01

    We correlate electron transport data directly with energy band structure measurements in vanadium oxide thin films with varying V-O stoichiometry across the VO2 metal-insulator transition. A set of vanadium oxide thin films were prepared by reactive dc sputtering from a V target at various oxygen partial pressures (O2 p.p.). Metal-insulator transition (MIT) characteristic to VO2 can be seen from the temperature dependence of electrical resistance of the films sputtered at optimal O2 p.p. Lower and higher O2 p.p. result in disappearance of the MIT. The results of the near edge x-ray absorption fine structure spectroscopy of the O K edge in identical VO films are presented. Redistribution of the spectral weight from {sigma}* to {pi}* bands is found in the vanadium oxide films exhibiting stronger VO2 MIT. This is taken as evidence of the strengthening of the metal-metal ion interaction with respect to the metal-ligand and indirect V-O-V interaction in vanadium oxide films featuring sharp MIT. We also observe a clear correlation between MIT and the width and area of the lower {pi}* band, which is likely to be due to the emergence of the d|| band overlapping with {pi}*. The strengthening of this d|| band near the Fermi level only in the vanadium oxide compounds displaying the MIT points out the importance of the role of the d|| band and electron correlations in the phase transition.

  13. Record surface state mobility and quantum Hall effect in topological insulator thin films via interface engineering

    NASA Astrophysics Data System (ADS)

    Koirala, Nikesh; Brahlek, Matthew; Salehi, Maryam; Wu, Liang; Dai, Jixia; Waugh, Justin; Nummy, Thomas; Han, Myung-Geun; Moon, Jisoo; Zhu, Yimei; Dessau, Daniel; Wu, Weida; Armitage, N. Peter; Oh, Seongshik

    Thin films of topological insulators (TIs) with conduction dominated by high mobility topological surface state (TSS) channel have been difficult to achieve due to increased material defects, thus making it difficult to probe TIs in quantum regime. Here by utilizing a structurally matched buffer layer based on In2Se3, we have achieved Bi2Se3 films with low defect density resulting in `order of magnitude' improvement in mobilities and carrier densities. This has led to TSS dominated transport and first observation of quantum Hall effect in Bi2Se3.

  14. Superconductor-Metal-Insulator transition in two dimensional Ta thin Films

    NASA Astrophysics Data System (ADS)

    Park, Sun-Gyu; Kim, Eunseong

    2013-03-01

    Superconductor-insulator transition has been induced by tuning film thickness or magnetic field. Recent electrical transport measurements of MoGe, Bi, Ta thin films revealed an interesting intermediate metallic phase which intervened superconducting and insulating phases at certain range of magnetic field. Especially, Ta thin films show the characteristic IV behavior at each phase and the disorder tuned intermediate metallic phase [Y. Li, C. L. Vicente, and J. Yoon, Physical Review B 81, 020505 (2010)]. This unexpected metallic phase can be interpreted as a consequence of vortex motion or contribution of fermionic quasiparticles. In this presentation, we report the scaling behavior during the transitions in Ta thin film as well as the transport measurements in various phases. Critical exponents v and z are obtained in samples with wide ranges of disorder. These results reveal new universality class appears when disorder exceeds a critical value. Dynamical exponent z of Superconducting sample is found to be 1, which is consistent with theoretical prediction of unity. z in a metallic sample is suddenly increased to be approximately 2.5. This critical exponent is much larger than the value found in other system and theoretical prediction. We gratefully acknowledge the financial support by the National Research Foundation of Korea through the Creative Research Initiatives.

  15. Electrically induced insulator to metal transition in epitaxial SmNiO{sub 3} thin films

    SciTech Connect

    Shukla, Nikhil Dasgupta, Sandeepan; Datta, Suman; Joshi, Toyanath; Borisov, Pavel; Lederman, David

    2014-07-07

    We report on the electrically induced insulator to metal transition (IMT) in SmNiO{sub 3} thin films grown on (001) LaAlO{sub 3} by pulsed laser deposition. The behavior of the resistivity as a function of temperature suggests that the primary transport mechanism in the SmNiO{sub 3} insulating state is dominated by Efros-Shklovskii variable range hopping (ES-VRH). Additionally, the magnetic transition in the insulating state of SmNiO{sub 3} modifies the characteristics of the ES-VRH transport. Systematic DC and pulsed current-voltage measurements indicate that current-induced joule heating is the fundamental mechanism driving the electrically induced IMT in SmNiO{sub 3}. These transport properties are explained in context of the IMT in SmNiO{sub 3} being related to the strong electron-lattice coupling.

  16. Metal-insulator transition in SrTi1-xVxO3 thin films

    NASA Astrophysics Data System (ADS)

    Gu, Man; Wolf, Stuart A.; Lu, Jiwei

    2013-11-01

    Epitaxial SrTi1-xVxO3 (0 ≤ x ≤ 1) thin films were grown on (001)-oriented (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) substrates using the pulsed electron-beam deposition technique. The transport study revealed a temperature driven metal-insulator transition (MIT) at 95 K for x = 0.67. The films with higher vanadium concentration (x > 0.67) were metallic corresponding to a Fermi liquid system. In the insulating phase (x < 0.67), the resistivity behavior was governed by Mott's variable range hopping mechanism. The possible mechanisms for the induced MIT are discussed, including the effects of electron correlation, lattice distortion, and Anderson localization.

  17. Electric field-induced superconducting transition of insulating FeSe thin film at 35 K

    NASA Astrophysics Data System (ADS)

    Hanzawa, Kota; Sato, Hikaru; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

    2016-04-01

    It is thought that strong electron correlation in an insulating parent phase would enhance a critical temperature (Tc) of superconductivity in a doped phase via enhancement of the binding energy of a Cooper pair as known in high-Tc cuprates. To induce a superconductor transition in an insulating phase, injection of a high density of carriers is needed (e.g., by impurity doping). An electric double-layer transistor (EDLT) with an ionic liquid gate insulator enables such a field-induced transition to be investigated and is expected to result in a high Tc because it is free from deterioration in structure and carrier transport that are in general caused by conventional carrier doping (e.g., chemical substitution). Here, for insulating epitaxial thin films (∼10 nm thick) of FeSe, we report a high Tc of 35 K, which is 4× higher than that of bulk FeSe, using an EDLT under application of a gate bias of +5.5 V. Hall effect measurements under the gate bias suggest that highly accumulated electron carrier in the channel, whose area density is estimated to be 1.4 × 1015 cm-2 (the average volume density of 1.7 × 1021 cm-3), is the origin of the high-Tc superconductivity. This result demonstrates that EDLTs are useful tools to explore the ultimate Tc for insulating parent materials.

  18. Electric field-induced superconducting transition of insulating FeSe thin film at 35 K.

    PubMed

    Hanzawa, Kota; Sato, Hikaru; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

    2016-04-12

    It is thought that strong electron correlation in an insulating parent phase would enhance a critical temperature (Tc) of superconductivity in a doped phase via enhancement of the binding energy of a Cooper pair as known in high-Tc cuprates. To induce a superconductor transition in an insulating phase, injection of a high density of carriers is needed (e.g., by impurity doping). An electric double-layer transistor (EDLT) with an ionic liquid gate insulator enables such a field-induced transition to be investigated and is expected to result in a high Tc because it is free from deterioration in structure and carrier transport that are in general caused by conventional carrier doping (e.g., chemical substitution). Here, for insulating epitaxial thin films (∼10 nm thick) of FeSe, we report a high Tc of 35 K, which is 4× higher than that of bulk FeSe, using an EDLT under application of a gate bias of +5.5 V. Hall effect measurements under the gate bias suggest that highly accumulated electron carrier in the channel, whose area density is estimated to be 1.4 × 10(15) cm(-2) (the average volume density of 1.7 × 10(21) cm(-3)), is the origin of the high-Tc superconductivity. This result demonstrates that EDLTs are useful tools to explore the ultimate Tc for insulating parent materials. PMID:27035956

  19. Metal-insulator transition in SrTi1-xVxO3 thin films

    NASA Astrophysics Data System (ADS)

    Gu, Man; Wolf, Stuart; Lu, Jiwei

    2014-03-01

    Epitaxial SrTi1-xVxO3 (0 <= x <= 1) thin films with thicknesses of ~ 16 nm were grown on (001)-oriented LSAT substrates using the pulsed electron-beam deposition technique. The transport study revealed a temperature driven metal-insulator transition (MIT) at 95 K for the film with x = 0.67. The films with higher vanadium concentration (x >0.67) were metallic, and the electrical resistivity followed the T2 law corresponding to a Fermi liquid system. In the insulating region of x <0.67, the temperature dependence of electrical resistivity for the x = 0.5 and 0.33 films can be scaled with Mott's variable range hopping model. The possible mechanism behind the observed MIT might be associated the interplay between electron-electron interactions and disorder-induced localization. The Ti4+ ion substitution introduces Anderson-localized states as well as lattice distortions that result in a reduction in the effective 3d bandwidth W. We gratefully acknowledge the financial support from the Army Research Office through MURI grant No. W911-NF-09-1-0398.

  20. Photoinduced Demagnetization and Insulator-to-Metal Transition in Ferromagnetic Insulating BaFeO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Tsuyama, T.; Chakraverty, S.; Macke, S.; Pontius, N.; Schüßler-Langeheine, C.; Hwang, H. Y.; Tokura, Y.; Wadati, H.

    2016-06-01

    We studied the electronic and magnetic dynamics of ferromagnetic insulating BaFeO3 thin films by using pump-probe time-resolved resonant x-ray reflectivity at the Fe 2 p edge. By changing the excitation density, we found two distinctly different types of demagnetization with a clear threshold behavior. We assigned the demagnetization change from slow (˜150 ps ) to fast (<70 ps ) to a transition into a metallic state induced by laser excitation. These results provide a novel approach for locally tuning magnetic dynamics. In analogy to heat-assisted magnetic recording, metallization can locally tune the susceptibility for magnetic manipulation, allowing one to spatially encode magnetic information.

  1. Photoinduced Demagnetization and Insulator-to-Metal Transition in Ferromagnetic Insulating BaFeO_{3} Thin Films.

    PubMed

    Tsuyama, T; Chakraverty, S; Macke, S; Pontius, N; Schüßler-Langeheine, C; Hwang, H Y; Tokura, Y; Wadati, H

    2016-06-24

    We studied the electronic and magnetic dynamics of ferromagnetic insulating BaFeO_{3} thin films by using pump-probe time-resolved resonant x-ray reflectivity at the Fe 2p edge. By changing the excitation density, we found two distinctly different types of demagnetization with a clear threshold behavior. We assigned the demagnetization change from slow (∼150  ps) to fast (<70  ps) to a transition into a metallic state induced by laser excitation. These results provide a novel approach for locally tuning magnetic dynamics. In analogy to heat-assisted magnetic recording, metallization can locally tune the susceptibility for magnetic manipulation, allowing one to spatially encode magnetic information. PMID:27391735

  2. Metal insulator transitions in perovskite SrIrO{sub 3} thin films

    SciTech Connect

    Biswas, Abhijit; Jeong, Yoon Hee; Kim, Ki-Seok

    2014-12-07

    Understanding of metal insulator transitions in a strongly correlated system, driven by Anderson localization (disorder) and/or Mott localization (correlation), is a long standing problem in condensed matter physics. The prevailing fundamental question would be how these two mechanisms contrive to accomplish emergent anomalous behaviors. Here, we have grown high quality perovskite SrIrO{sub 3} thin films, containing a strong spin orbit coupled 5d element Ir, on various substrates such as GdScO{sub 3} (110), DyScO{sub 3} (110), SrTiO{sub 3} (001), and NdGaO{sub 3} (110) with increasing lattice mismatch, in order to carry out a systematic study on the transport properties. We found that metal insulator transitions can be induced in this system; by either reducing thickness (on best lattice matched substrate) or changing degree of lattice strain (by lattice mismatch between film and substrates) of films. Surprisingly these two pathways seek two distinct types of metal insulator transitions; the former falls into disorder driven Anderson type whereas the latter turns out to be of unconventional Mott-Anderson type with the interplay of disorder and correlation. More interestingly, in the metallic phases of SrIrO{sub 3}, unusual non-Fermi liquid characteristics emerge in resistivity as Δρ ∝ T{sup ε} with ε evolving from 4/5 to 1 to 3/2 with increasing lattice strain. We discuss theoretical implications of these phenomena to shed light on the metal insulator transitions.

  3. Enhancing ferromagnetic resonance absorption for very thin insulating magnetic films with spin plasmonics

    SciTech Connect

    Chui, S. T.

    2015-05-14

    We consider enhancing the ferromagnetic resonance (FMR) absorption of very thin insulating magnetic films by placing it on top of a dielectric. We find that the signal is enhanced by at least an order of magnitude due to a new nonreciprocal interface resonance that is a mixture of the magnetic surface plasmon mode and a wave guide mode. This resonance occurs over a wide range of thicknesses of the dielectric that is still much less than the wavelength and is made possible by the negative magnetic susceptibility of the magnetic layer. The line width of absorption is reduced by an order of magnitude less than the Gilbert damping parameter. At some frequency, the group velocity of this resonance is negative. Experimentally, very thin yttrium iron garnet (YIG) films are grown on a Gadolinium Gallium Garnet (GGG) substrate which can be considered the dielectric. Our model applies to experiments performed in the YIG/GGG system. Indeed, our picture resolves the disagreement on the magnitude of the spin diffusion lengths obtained with the FMR and the Brillouin scattering techniques. It also provides for a way to make new adaptive thin film miniaturized photonic nonreciprocal devices with low loss.

  4. Propagation of Surface Plasmon Polaritons in Thin Films of Topological Insulators

    NASA Astrophysics Data System (ADS)

    Deshko, Yury; Chen, Zhiyi; Krusin-Elbaum, Lia; Menon, Vinod; Trevino, Jacob; Khanikaev, Alexander

    Surface Plasmon Polaritons (SPP) are coupled collective oscillations of surface charges and electromagnetic waves confined to the interface between a metal and a dielectric. Three dimensional topological insulators (TI), such as Bi2Se3, Bi2Te3, and Sb2Te3 are narrow band-gap semiconductors in the bulk while having conducting surface with the linear energy dispersion for the surface electronics states. Similar to double-layered graphene a thin single film of TI supports two SPP modes in the far-infrared range. We study the propagation of these modes in thin films of Bi2Se3, Bi2Te3, and Sb2Te3. The dispersion curves and the propagation lengths are estimated for all three materials. The explanation of the discrepancy between the theory and the first experimental observation of standing wave SPPs in Bi2Se3 is proposed. Finally, the possibilities of tuning the SPP dispersion relations in thin films of TI are discussed. Supported by NSF DMR-1420634 and DOD-W911NF-13-1-0159.

  5. Anomalous Hall effect sensors based on magnetic element doped topological insulator thin films

    NASA Astrophysics Data System (ADS)

    Ni, Yan; Zhang, Zhen; Nlebedim, Ikenna; Jiles, David

    Anomalous Hall effect (AHE) is recently discovered in magnetic element doped topological insulators (TIs), which promises low power consumption highly efficient spintronics and electronics. This discovery broaden the family of Hall effect (HE) sensors. In this work, both HE and AHE sensor based on Mn and Cr doped Bi2Te3 TI thin films will be systematically studied. The influence of Mn concentration on sensitivity of MnxBi2-xTe3 HE sensors will be discussed. The Hall sensitivity increase 8 times caused by quantum AHE will be reported. AHE senor based on Cr-doped Bi2Te3 TI thin films will also be studied and compared with Mn doped Bi2Te3 AHE sensor. The influence of thickness on sensitivity of CrxBi2-xTe3 AHE sensors will be discussed. Ultrahigh Hall sensitivity is obtained in Cr doped Bi2Te3. The largest Hall sensitivity can reach 2620 Ω/T in sensor which is almost twice higher than that of the normal semiconductor HE sensor. Our work indicates that magnetic element doped topological insulator with AHE are good candidates for ultra-sensitive Hall effect sensors.

  6. Thermoelectric transport in thin films of three-dimensional topological insulators

    NASA Astrophysics Data System (ADS)

    Ma, R.; Sheng, L.; Liu, M.; Sheng, D. N.

    2013-03-01

    We numerically study the thermoelectric transport properties based on the Haldane model of the three-dimensional topological insulator (3DTI) thin film in the presence of an exchange field g and a hybridization gap Δ. The thermoelectric coefficients exhibit rich behaviors as a consequence of the interplay between g and Δ in the 3DTI thin film. For Δ=0 but g≠0, the transverse thermoelectric conductivity αxy saturates to a universal value 1.38kBe/h at the center of each Landau level (LL) in the high-temperature regime, and displays a linear temperature dependence at low temperatures. The semiclassical Mott relation is found to remain valid at low temperatures. If g=0 but Δ≠0, the thermoelectric coefficients are consistent with those of a band insulator. For both g≠0 and Δ≠0, αxy saturates to a universal value 0.69kBe/h at the center of each LL in the high-temperature regime. We attribute this behavior to the split of all the LLs, caused by the simultaneous presence of nonzero g and Δ, which lifts the degeneracies between Dirac surface states.

  7. Temperature dependence of thermal conductivity of VO2 thin films across metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Kizuka, Hinako; Yagi, Takashi; Jia, Junjun; Yamashita, Yuichiro; Nakamura, Shinichi; Taketoshi, Naoyuki; Shigesato, Yuzo

    2015-05-01

    Thermal conductivity of a 300-nm-thick VO2 thin film and its temperature dependence across the metal-insulator phase transition (TMIT) were studied using a pulsed light heating thermoreflectance technique. The VO2 and Mo/VO2/Mo films with a VO2 thickness of 300 nm were prepared on quartz glass substrates: the former was used for the characterization of electrical properties, and the latter was used for the thermal conductivity measurement. The VO2 films were deposited by reactive rf magnetron sputtering using a V2O3 target and an Ar-O2 mixture gas at 645 K. The VO2 films consisted of single phase VO2 as confirmed by X-ray diffraction and electron beam diffraction. With increased temperature, the electrical resistivity of the VO2 film decreased abruptly from 6.3 × 10-1 to 5.3 × 10-4 Ω cm across the TMIT of around 325-340 K. The thermal conductivity of the VO2 film increased from 3.6 to 5.4 W m-1 K-1 across the TMIT. This discontinuity and temperature dependence of thermal conductivity can be explained by the phonon heat conduction and the Wiedemann-Franz law.

  8. Topological insulator thin films starting from the amorphous phase-Bi2Se3 as example

    NASA Astrophysics Data System (ADS)

    Barzola-Quiquia, J.; Lehmann, T.; Stiller, M.; Spemann, D.; Esquinazi, P.; Häussler, P.

    2015-02-01

    We present a new method to obtain topological insulator Bi2Se3 thin films with a centimeter large lateral length. To produce amorphous Bi2Se3 thin films, we have used a sequential flash-evaporation method at room temperature. Transmission electron microscopy has been used to verify that the prepared samples are in a pure amorphous state. During annealing, the samples transform into the rhombohedral Bi2Se3 crystalline structure which was confirmed using X-ray diffraction and Raman spectroscopy. Resistance measurements of the amorphous films show the expected Mott variable range hopping conduction process with a high specific resistance compared to the one obtained in the crystalline phase (metallic behavior). We have measured the magnetoresistance and the Hall effect at different temperatures between 2 K and 275 K. At temperatures T ≲ 50 K and fields B ≲ 1 T, we observe weak anti-localization in the MR; the Hall measurements confirm the n-type character of the samples. All experimental results of our films are in quantitative agreement with results from samples prepared using more sophisticated methods.

  9. Rutherford Backscattering Spectrometry analysis of iron-containing Bi2Se3 topological insulator thin films

    NASA Astrophysics Data System (ADS)

    Alarcon-Diez, V.; Eddrief, M.; Vickridge, I.

    2016-03-01

    Fe-containing Bi2Se3 topological insulators (TI) thin films have been grown to investigate the intricate interplay between topological order and the incorporation of ferromagnetic atoms. Here we present the quantitative characterisation of the Bi2Se3 thin films with up to 16 at% Fe incorporated during the growth process on GaAs (1 1 1) substrate by Molecular Beam Epitaxy. We report the elemental composition and depth profiles of the Bi2Se3:Fe films obtained using Rutherford Backscattering Spectrometry (RBS) and their formed crystalline phase obtained by X-ray diffraction (XRD). Resistance of the TI to beam-induced damage was investigated by channelling RBS. Using the elemental composition from RBS and the thickness from XRD measurements the Fe-free film density was deduced. For Fe-containing samples, the diffraction reveals the formation of two distinct crystalline phases, as well as their intergrowth pattern, in which the basal planes of Bi2Se3 coexist with an additional Fe-Se phase. This intergrown composite, with chemical compatibility of the Fe-Se phase with the crystalline Bi2Se3 structure, preserves the intrinsic topological surface states of the TI component despite the inhomogeneous distribution of the constituent phases. RBS analysis gives the stoichiometry of the Bi2Se3, and Bi2Se3:Fe samples (estimated between 0 and 16 at% Fe) and gives insights into the composition of FeSex phases present.

  10. Comparison of Classical and Charge Storage Methods for Determining Conductivity of Thin Film Insulators

    NASA Technical Reports Server (NTRS)

    Swaminathan, Prasanna; Dennison, J. R.; Sim, Alec; Brunson, Jerilyn; Crapo, Eric; Frederickson, A. R.

    2004-01-01

    Conductivity of insulating materials is a key parameter to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. Classical ASTM and IEC methods to measure thin film insulator conductivity apply a constant voltage to two electrodes around the sample and measure the resulting current for tens of minutes. However, conductivity is more appropriately measured for spacecraft charging applications as the "decay" of charge deposited on the surface of an insulator. Charge decay methods expose one side of the insulator in vacuum to sequences of charged particles, light, and plasma, with a metal electrode attached to the other side of the insulator. Data are obtained by capacitive coupling to measure both the resulting voltage on the open surface and emission of electrons from the exposed surface, as well monitoring currents to the electrode. Instrumentation for both classical and charge storage decay methods has been developed and tested at Jet Propulsion Laboratory (JPL) and at Utah State University (USU). Details of the apparatus, test methods and data analysis are given here. The JPL charge storage decay chamber is a first-generation instrument, designed to make detailed measurements on only three to five samples at a time. Because samples must typically be tested for over a month, a second-generation high sample throughput charge storage decay chamber was developed at USU with the capability of testing up to 32 samples simultaneously. Details are provided about the instrumentation to measure surface charge and current; for charge deposition apparatus and control; the sample holders to properly isolate the mounted samples; the sample carousel to rotate samples into place; the control of the sample environment including sample vacuum, ambient gas, and sample temperature; and the computer control and data acquisition systems. Measurements are compared here for a number of thin film insulators using both

  11. Ferroelectric domain inversion and its stability in lithium niobate thin film on insulator with different thicknesses

    NASA Astrophysics Data System (ADS)

    Shao, Guang-hao; Bai, Yu-hang; Cui, Guo-xin; Li, Chen; Qiu, Xiang-biao; Geng, De-qiang; Wu, Di; Lu, Yan-qing

    2016-07-01

    Ferroelectric domain inversion and its effect on the stability of lithium niobate thin films on insulator (LNOI) are experimentally characterized. Two sets of specimens with different thicknesses varying from submicron to microns are selected. For micron thick samples (˜28 μm), domain structures are achieved by pulsed electric field poling with electrodes patterned via photolithography. No domain structure deterioration has been observed for a month as inspected using polarizing optical microscopy and etching. As for submicron (540 nm) films, large-area domain inversion is realized by scanning a biased conductive tip in a piezoelectric force microscope. A graphic processing method is taken to evaluate the domain retention. A domain life time of 25.0 h is obtained and possible mechanisms are discussed. Our study gives a direct reference for domain structure-related applications of LNOI, including guiding wave nonlinear frequency conversion, nonlinear wavefront tailoring, electro-optic modulation, and piezoelectric devices.

  12. Record Surface State Mobility and Quantum Hall Effect in Topological Insulator Thin Films via Interface Engineering.

    PubMed

    Koirala, Nikesh; Brahlek, Matthew; Salehi, Maryam; Wu, Liang; Dai, Jixia; Waugh, Justin; Nummy, Thomas; Han, Myung-Geun; Moon, Jisoo; Zhu, Yimei; Dessau, Daniel; Wu, Weida; Armitage, N Peter; Oh, Seongshik

    2015-12-01

    Material defects remain as the main bottleneck to the progress of topological insulators (TIs). In particular, efforts to achieve thin TI samples with dominant surface transport have always led to increased defects and degraded mobilities, thus making it difficult to probe the quantum regime of the topological surface states. Here, by utilizing a novel buffer layer scheme composed of an In2Se3/(Bi0.5In0.5)2Se3 heterostructure, we introduce a quantum generation of Bi2Se3 films with an order of magnitude enhanced mobilities than before. This scheme has led to the first observation of the quantum Hall effect in Bi2Se3. PMID:26583739

  13. Quantum coherent transport in SnTe topological crystalline insulator thin films

    SciTech Connect

    Assaf, B. A.; Heiman, D.; Katmis, F.; Moodera, J. S.; Wei, P.; Satpati, B.; Bennett, S. P.; Harris, V. G.

    2014-09-08

    Topological crystalline insulators (TCI) are unique systems where a band inversion that is protected by crystalline mirror symmetry leads to a multiplicity of topological surface states. Binary SnTe is an attractive lead-free TCI compound; the present work on high-quality thin films provides a route for increasing the mobility and reducing the carrier density of SnTe without chemical doping. Results of quantum coherent magnetotransport measurements reveal a multiplicity of Dirac surface states that are unique to TCI. Modeling of the weak antilocalization shows variations in the extracted number of carrier valleys that reflect the role of coherent intervalley scattering in coupling different Dirac states on the degenerate TCI surface.

  14. Effective Hamiltonian for surface states of topological insulator thin films with hexagonal warping

    NASA Astrophysics Data System (ADS)

    Siu, Zhuo Bin; Tan, Seng Ghee; Jalil, Mansoor B. A.

    2016-05-01

    The effective Hamiltonian of the surface states on semi-infinite slabs of the topological insulators (TI) Bi2Te3 and Bi2Se3 require the addition of a cubic momentum hexagonal warping term on top of the usual Dirac fermion Hamiltonian in order to reproduce the experimentally measured constant energy contours at intermediate values of Fermi energy. In this work, we derive the effective Hamiltonian for the surface states of a Bi2Se3 thin film incorporating the corresponding hexagonal warping terms. We then calculate the dispersion relation of the effective Hamiltonian and show that the hexagonal warping leads distorts the equal energy contours from the circular cross sections of the Dirac cones.

  15. Record surface state mobility and quantum Hall effect in topological insulator thin films via interface engineering

    DOE PAGESBeta

    Koirala, Nikesh; Han, Myung -Geun; Brahlek, Matthew; Salehi, Maryam; Wu, Liang; Dai, Jixia; Waugh, Justin; Nummy, Thomas; Moon, Jisoo; Zhu, Yimei; et al

    2015-11-19

    Material defects remain as the main bottleneck to the progress of topological insulators (TIs). In particular, efforts to achieve thin TI samples with dominant surface transport have always led to increased defects and degraded mobilities, thus making it difficult to probe the quantum regime of the topological surface states. Here, by utilizing a novel buffer layer scheme composed of an In2Se3/(Bi0.5In0.5)2Se3 heterostructure, we introduce a quantum generation of Bi2Se3 films with an order of magnitude enhanced mobilities than before. Furthermore, this scheme has led to the first observation of the quantum Hall effect in Bi2Se3.

  16. Record surface state mobility and quantum Hall effect in topological insulator thin films via interface engineering

    SciTech Connect

    Koirala, Nikesh; Han, Myung -Geun; Brahlek, Matthew; Salehi, Maryam; Wu, Liang; Dai, Jixia; Waugh, Justin; Nummy, Thomas; Moon, Jisoo; Zhu, Yimei; Dessau, Daniel; Wu, Weida; Armitage, N. Peter; Oh, Seongshik

    2015-11-19

    Material defects remain as the main bottleneck to the progress of topological insulators (TIs). In particular, efforts to achieve thin TI samples with dominant surface transport have always led to increased defects and degraded mobilities, thus making it difficult to probe the quantum regime of the topological surface states. Here, by utilizing a novel buffer layer scheme composed of an In2Se3/(Bi0.5In0.5)2Se3 heterostructure, we introduce a quantum generation of Bi2Se3 films with an order of magnitude enhanced mobilities than before. Furthermore, this scheme has led to the first observation of the quantum Hall effect in Bi2Se3.

  17. Chiral magnetic conductivity and surface states of Weyl semimetals in topological insulator ultra-thin film multilayer

    NASA Astrophysics Data System (ADS)

    Owerre, S. A.

    2016-06-01

    We investigate an ultra-thin film of topological insulator (TI) multilayer as a model for a three-dimensional (3D) Weyl semimetal. We introduce tunneling parameters t S, {{t}\\bot} , and t D, where the former two parameters couple layers of the same thin film at small and large momenta, and the latter parameter couples neighbouring thin film layers along the z-direction. The Chern number is computed in each topological phase of the system and we find that for {{t}\\text{S}},{{t}\\text{D}}>0 , the tunneling parameter {{t}\\bot} changes from positive to negative as the system transits from Weyl semi-metallic phase to insulating phases. We further study the chiral magnetic effect (CME) of the system in the presence of a time dependent magnetic field. We compute the low-temperature dependence of the chiral magnetic conductivity and show that it captures three distinct phases of the system separated by plateaus. Furthermore, we propose and study a 3D lattice model of Porphyrin thin film, an organic material known to support topological Frenkel exciton edge states. We show that this model exhibits a 3D Weyl semi-metallic phase and also supports a 2D Weyl semi-metallic phase. We further show that this model recovers that of 3D Weyl semimetal in topological insulator thin film multilayer. Thus, paving the way for simulating a 3D Weyl semimetal in topological insulator thin film multilayer. We obtain the surface states (Fermi arcs) in the 3D model and the chiral edge states in the 2D model and analyze their topological properties.

  18. Chiral magnetic conductivity and surface states of Weyl semimetals in topological insulator ultra-thin film multilayer.

    PubMed

    Owerre, S A

    2016-06-15

    We investigate an ultra-thin film of topological insulator (TI) multilayer as a model for a three-dimensional (3D) Weyl semimetal. We introduce tunneling parameters t S, [Formula: see text], and t D, where the former two parameters couple layers of the same thin film at small and large momenta, and the latter parameter couples neighbouring thin film layers along the z-direction. The Chern number is computed in each topological phase of the system and we find that for [Formula: see text], the tunneling parameter [Formula: see text] changes from positive to negative as the system transits from Weyl semi-metallic phase to insulating phases. We further study the chiral magnetic effect (CME) of the system in the presence of a time dependent magnetic field. We compute the low-temperature dependence of the chiral magnetic conductivity and show that it captures three distinct phases of the system separated by plateaus. Furthermore, we propose and study a 3D lattice model of Porphyrin thin film, an organic material known to support topological Frenkel exciton edge states. We show that this model exhibits a 3D Weyl semi-metallic phase and also supports a 2D Weyl semi-metallic phase. We further show that this model recovers that of 3D Weyl semimetal in topological insulator thin film multilayer. Thus, paving the way for simulating a 3D Weyl semimetal in topological insulator thin film multilayer. We obtain the surface states (Fermi arcs) in the 3D model and the chiral edge states in the 2D model and analyze their topological properties. PMID:27157544

  19. Metal–insulator transition of valence-controlled VO2 thin film prepared by RF magnetron sputtering using oxygen radical

    NASA Astrophysics Data System (ADS)

    Suetsugu, Takaaki; Shimazu, Yuichi; Tsuchiya, Takashi; Kobayashi, Masaki; Minohara, Makoto; Sakai, Enju; Horiba, Koji; Kumigashira, Hiroshi; Higuchi, Tohru

    2016-06-01

    We have prepared b-axis-oriented VO2 thin films by RF magnetron sputtering using oxygen radicals as the reactive gas. The VO2 thin films consist of a mixed-valence V3+/V4+ state formed by oxygen vacancies. The V3+ ratio strongly depends on the film thickness and the oxygen partial pressure of the radical gun during deposition. The lattice constant of the b-axis increases and the metal–insulator transition (MIT) temperature decreases with decreasing V3+ ratio, although the VO2 thin films with a high V3+ ratio of 42% do not exhibit MIT. The bandwidths and spectral weights of V 3d a1g and \\text{e}\\text{g}σ bands at around the Fermi level, which correspond to the insulating phase at 300 K, are smaller in the VO2 thin films with a low V3+ ratio. These results indicate that the control of the mixed-valence V3+/V4+ state is important for the MIT of b-axis-oriented VO2 thin films.

  20. Intrinsic conduction through topological surface states of insulating Bi2Te3 epitaxial thin films.

    PubMed

    Hoefer, Katharina; Becker, Christoph; Rata, Diana; Swanson, Jesse; Thalmeier, Peter; Tjeng, L H

    2014-10-21

    Topological insulators represent a novel state of matter with surface charge carriers having a massless Dirac dispersion and locked helical spin polarization. Many exciting experiments have been proposed by theory, yet their execution has been hampered by the extrinsic conductivity associated with the unavoidable presence of defects in Bi2Te3 and Bi2Se3 bulk single crystals, as well as impurities on their surfaces. Here we present the preparation of Bi2Te3 thin films that are insulating in the bulk and the four-point probe measurement of the conductivity of the Dirac states on surfaces that are intrinsically clean. The total amount of charge carriers in the experiment is of the order of 10(12) cm(-2) only, and mobilities up to 4,600 cm(2)/Vs have been observed. These values are achieved by carrying out the preparation, structural characterization, angle-resolved and X-ray photoemission analysis, and temperature-dependent four-point probe conductivity measurement all in situ under ultra-high-vacuum conditions. This experimental approach opens the way to prepare devices that can exploit the intrinsic topological properties of the Dirac surface states. PMID:25294928

  1. Intrinsic conduction through topological surface states of insulating Bi2Te3 epitaxial thin films

    PubMed Central

    Hoefer, Katharina; Becker, Christoph; Rata, Diana; Swanson, Jesse; Thalmeier, Peter; Tjeng, L. H.

    2014-01-01

    Topological insulators represent a novel state of matter with surface charge carriers having a massless Dirac dispersion and locked helical spin polarization. Many exciting experiments have been proposed by theory, yet their execution has been hampered by the extrinsic conductivity associated with the unavoidable presence of defects in Bi2Te3 and Bi2Se3 bulk single crystals, as well as impurities on their surfaces. Here we present the preparation of Bi2Te3 thin films that are insulating in the bulk and the four-point probe measurement of the conductivity of the Dirac states on surfaces that are intrinsically clean. The total amount of charge carriers in the experiment is of the order of 1012 cm−2 only, and mobilities up to 4,600 cm2/Vs have been observed. These values are achieved by carrying out the preparation, structural characterization, angle-resolved and X-ray photoemission analysis, and temperature-dependent four-point probe conductivity measurement all in situ under ultra-high-vacuum conditions. This experimental approach opens the way to prepare devices that can exploit the intrinsic topological properties of the Dirac surface states. PMID:25294928

  2. Atomic-Scale Magnetism of Cr-Doped Bi2Se3 Thin Film Topological Insulators.

    PubMed

    Liu, Wenqing; West, Damien; He, Liang; Xu, Yongbing; Liu, Jun; Wang, Kejie; Wang, Yong; van der Laan, Gerrit; Zhang, Rong; Zhang, Shengbai; Wang, Kang L

    2015-10-27

    Magnetic doping is the most common method for breaking time-reversal-symmetry surface states of topological insulators (TIs) to realize novel physical phenomena and to create beneficial technological applications. Here we present a study of the magnetic coupling of a prototype magnetic TI, that is, Cr-doped Bi2Se3, in its ultrathin limit which is expected to give rise to quantum anomalous Hall (QAH) effect. The high quality Bi2-xCrxSe3 epitaxial thin film was prepared using molecular beam epitaxy (MBE), characterized with scanning transimission electron microscopy (STEM), electrical magnetotransport, and X-ray magnetic circularly dichroism (XMCD) techniques, and the results were simulated using density functional theory (DFT) with spin-orbit coupling (SOC). We observed a sizable spin moment mspin = (2.05 ± 0.20) μB/Cr and a small and negative orbital moment morb = (-0.05 ± 0.02) μB/Cr of the Bi1.94Cr0.06Se3 thin film at 2.5 K. A remarkable fraction of the (CrBi-CrI)(3+) antiferromagnetic dimer in the Bi2-xCrxSe3 for 0.02 < x < 0.40 was obtained using first-principles simulations, which was neglected in previous studies. The spontaneous coexistence of ferro- and antiferromagnetic Cr defects in Bi2-xCrxSe3 explains our experimental observations and those based on conventional magnetometry which universally report magnetic moments significantly lower than 3 μB/Cr predicted by Hund's rule. PMID:26348798

  3. Fractal Nature of Metallic and Insulating Domain Configurations in a VO2 Thin Film Revealed by Kelvin Probe Force Microscopy

    PubMed Central

    Sohn, Ahrum; Kanki, Teruo; Sakai, Kotaro; Tanaka, Hidekazu; Kim, Dong-Wook

    2015-01-01

    We investigated the surface work function (WS) and its spatial distribution for epitaxial VO2/TiO2 thin films using Kelvin probe force microscopy (KPFM). Nearly grain-boundary-free samples allowed observation of metallic and insulating domains with distinct WS values, throughout the metal–insulator transition. The metallic fraction, estimated from WS maps, describes the evolution of the resistance based on a two-dimensional percolation model. The KPFM measurements also revealed the fractal nature of the domain configuration. PMID:25982229

  4. High-mobility BaSnO3 thin-film transistor with HfO2 gate insulator

    NASA Astrophysics Data System (ADS)

    Kim, Young Mo; Park, Chulkwon; Kim, Useong; Ju, Chanjong; Char, Kookrin

    2016-01-01

    Thin-film transistors have been fabricated using La-doped BaSnO3 as n-type channels and (In,Sn)2O3 as source, drain, and gate electrodes. HfO2 was grown as gate insulators by atomic layer deposition. The field-effect mobility, Ion/Ioff ratio, and subthreshold swing of the device are 24.9 cm2 V-1 s-1, 6.0 × 106, and 0.42 V dec-1, respectively. The interface trap density, evaluated to be higher than 1013 cm-2 eV-1, was found to be slightly lower than that of the thin-film transistor with an Al2O3 gate insulator. We attribute the much smaller subthreshold swing values to the higher dielectric constant of HfO2.

  5. Shrinking of the Cooper Pair Insulator Phase in Thin Films with Ultrasmall Superconducting Islands

    NASA Astrophysics Data System (ADS)

    Joy, J. C.; Zhang, X.; Zhao, C.; Valles, J. M., Jr.; Fernandes, G.; Xu, J. M.

    The ubiquity of the bosonic Cooper Pair Insulator (CPI) phase near the two-dimensional superconductor to insulator transition (SIT) is a long standing question. While a number of two dimensional materials exhibit bosonic insulating phases similar to the Mott Insulator in arrays of ultrasmall, Josephson coupled superconducting islands, others show behaviors consistent with a fermionic insulating phase. Utilizing specially prepared anodized aluminum oxide substrates, we are able to fabricate films reminiscent of arrays of superconducting islands whose properties are tunable by varying the substrate morphology. Our recent work has focused on arrays of islands which possess an energy level spacing comparable to the mean field superconducting gap, where one expects pair breaking followed by fermionic Anderson Localization as the dominant mechanism by which superconductivity is destroyed. Early results show that the paradigmatic bosonic insulator exists only very near the disorder tuned SIT, while films only marginally deeper in the insulating phase exhibit transport distinct from the CPI's reentrant, activated transport. We are grateful for the support of NSF Grant No. DMR-1307290, the AFOSR, and the AOARD. Currently at Northwestern Polytechnical University, Xian, China.

  6. Massive Dirac Fermion Observed in Lanthanide-Doped Topological Insulator Thin Films

    PubMed Central

    Harrison, S. E.; Collins-McIntyre, L. J.; Schönherr, P.; Vailionis, A.; Srot, V.; van Aken, P. A.; Kellock, A. J.; Pushp, A.; Parkin, S. S. P.; Harris, J. S.; Zhou, B.; Chen, Y. L.; Hesjedal, T.

    2015-01-01

    The breaking of time reversal symmetry (TRS) in three-dimensional (3D) topological insulators (TIs), and thus the opening of a ‘Dirac-mass gap’ in the linearly dispersed Dirac surface state, is a prerequisite for unlocking exotic physical states. Introducing ferromagnetic long-range order by transition metal doping has been shown to break TRS. Here, we present the study of lanthanide (Ln) doped Bi2Te3, where the magnetic doping with high-moment lanthanides promises large energy gaps. Using molecular beam epitaxy, single-crystalline, rhombohedral thin films with Ln concentrations of up to ~35%, substituting on Bi sites, were achieved for Dy, Gd, and Ho doping. Angle-resolved photoemission spectroscopy shows the characteristic Dirac cone for Gd and Ho doping. In contrast, for Dy doping above a critical doping concentration, a gap opening is observed via the decreased spectral intensity at the Dirac point, indicating a topological quantum phase transition persisting up to room-temperature. PMID:26503435

  7. Artificial semiconductor/insulator superlattice channel structure for high-performance oxide thin-film transistors

    PubMed Central

    Ahn, Cheol Hyoun; Senthil, Karuppanan; Cho, Hyung Koun; Lee, Sang Yeol

    2013-01-01

    High-performance thin-film transistors (TFTs) are the fundamental building blocks in realizing the potential applications of the next-generation displays. Atomically controlled superlattice structures are expected to induce advanced electric and optical performance due to two-dimensional electron gas system, resulting in high-electron mobility transistors. Here, we have utilized a semiconductor/insulator superlattice channel structure comprising of ZnO/Al2O3 layers to realize high-performance TFTs. The TFT with ZnO (5 nm)/Al2O3 (3.6 nm) superlattice channel structure exhibited high field effect mobility of 27.8 cm2/Vs, and threshold voltage shift of only < 0.5 V under positive/negative gate bias stress test during 2 hours. These properties showed extremely improved TFT performance, compared to ZnO TFTs. The enhanced field effect mobility and stability obtained for the superlattice TFT devices were explained on the basis of layer-by-layer growth mode, improved crystalline nature of the channel layers, and passivation effect of Al2O3 layers. PMID:24061388

  8. Ultraviolet-Patternable Polymer Insulator for Organic Thin-Film Transistors on Flexible Substrates

    NASA Astrophysics Data System (ADS)

    Wu, Chung-Ming; Su, Shui-Hsiang; Wang, Hong-Tai; Yokoyama, Meiso; Fu, Shen-Li

    2011-04-01

    In this work, we describe the fabrication of pentacene-based organic thin-film transistors (OTFTs) on a flexible substrate using a UV-patternable polymer material, mr-UVCur06, as the gate insulator. The device structure is poly(ethylene terephthalate) (PET)/indium-tin oxide (ITO)/mr-UVCur06/pentacene/Au (source/drain). In addition to its solution-processable capability, mr-UVCur06 is directly patternable by UV light in a low-temperature process. The OTFT has an on-off ratio that approaches 105, and its pattern resolution can reach 5 µm. Additionally, UV/ozone post-treatment of the patterned mr-UVCur06 can illuminate the organic contaminants from its surface and significantly improve the performance of OTFTs. Moreover, the effect of UV/ozone post-treatment on the polymer dielectric is confirmed using a Fourier transform infrared (FT-IR) spectrometer. Owing to its highly desired characteristics such as photopatternability and low-temperature process, mr-UVCur06 is feasible for low-cost, large-area flexible device applications.

  9. Metal insulator transition with ferrimagnetic order in epitaxial thin films of spinel NiCo2O4

    NASA Astrophysics Data System (ADS)

    Silwal, Punam; Miao, Ludi; Stern, Ilan; Zhou, Xiaolan; Hu, Jin; Ho Kim, Dae

    2012-01-01

    We have grown epitaxial thin films of spinel NiCo2O4 on single crystalline MgAl2O4 (001) substrates by pulsed laser deposition. Magnetization measurement revealed hysteresis loops consistent with the reported ferrimagnetic order. The electrical transport exhibits a metallic behavior with the lowest resistivity of 0.8 mΩ cm and a metal insulator transition around the Néel temperature. The systematic variation in the properties of the films grown at different growth temperatures indicates a close relationship between the magnetic order and electrical transport.

  10. Metal—Insulator Transition in Bi2Sr2Cu1O6+d (Bi-2201) Thin Films

    NASA Astrophysics Data System (ADS)

    Pop, Aurel V.

    2009-05-01

    We have studied the influence of disorder induced by oxygen on the normal state resistivity of under doped Bi2Sr2Cu1O6+d (Bi-2201) thin films, deposited in situ onto heated SrTiO3 (100) substrates by using DC magnetron sputtering for an off-stoichiometric target. The compositions and structural characterization for the deposited films were carried by (EDX), (XPS) and X-ray diffraction measurements. The effect of partial oxygen pressure in the sputtering gas on the metal-insulator transition are presented.

  11. Selective area growth of Bi2Te3 and Sb2Te3 topological insulator thin films

    NASA Astrophysics Data System (ADS)

    Kampmeier, Jörn; Weyrich, Christian; Lanius, Martin; Schall, Melissa; Neumann, Elmar; Mussler, Gregor; Schäpers, Thomas; Grützmacher, Detlev

    2016-06-01

    The intrinsic bulk behavior of topological insulators (TI) is a key issue for their employment in future device applications. State of the art TIs predominantly suffer from large bulk charge carrier concentrations that mask their extraordinary surface states. In this paper we present the selective area growth of Bi2Te3 and Sb2Te3 TI thin films on prestructured Si(111) Si on insulator (SOI) substrates, paving the way to high quality TI nanostructures in which access to surface states is enhanced. Therefore high quality Bi2Te3 and Sb2Te3 thin films were deposited by means of solid source molecular beam epitaxy (MBE) and subsequently investigated by energy dispersive x-ray spectroscopy (EDX). To investigate the transport properties of the selectively grown thin films, magnetotransport measurements were performed at low temperatures. Nucleation in the SiO2 valleys next to the prepatterned Si(111) mesa structures was not observed. The structural and morphological qualities of crystals deposited on untreated Si(111) SOI wafers are completely preserved by employing the selective area growth on prepatterned substrates. The transport characteristics of the selectively-grown TI systems are comparable to those of the analogous postpatterned films.

  12. Voltage-induced Metal-Insulator Transitions in Perovskite Oxide Thin Films Doped with Strongly Correlelated Electrons

    NASA Astrophysics Data System (ADS)

    Wang, Yudi; Gil Kim, Soo; Chen, I.-Wei

    2007-03-01

    We have observed a reversible metal-insulator transition in perovskite oxide thin films that can be controlled by charge trapping pumped by a bipolar voltage bias. In the as-fabricated state, the thin film is metallic with a very low resistance comparable to that of the metallic bottom electrode, showing decreasing resistance with decreasing temperature. This metallic state switches to a high-resistance state after applying a voltage bias: such state is non-ohmic showing a negative temperature dependence of resistance. Switching at essentially the same voltage bias was observed down to 2K. The metal-insulator transition is attributed to charge trapping that disorders the energy of correlated electron states in the conduction band. By increasing the amount of charge trapped, which increases the disorder relative to the band width, increasingly more insulating states with a stronger temperature dependence of resistivity are accessed. This metal-insulator transition provides a platform to engineer new nonvolatile memory that does not require heat (as in phase transition) or dielectric breakdown (as in most other oxide resistance devices).

  13. Effects of reductive annealing on insulating polycrystalline thin films of Nb-doped anatase TiO2: recovery of high conductivity

    NASA Astrophysics Data System (ADS)

    Nakao, Shoichiro; Hirose, Yasushi; Hasegawa, Tetsuya

    2016-02-01

    We studied the effects of reductive annealing on insulating polycrystalline thin films of anatase Nb-doped TiO2 (TNO). The insulating TNO films were intentionally fabricated by annealing conductive TNO films in oxygen ambient at 400 °C. Reduced free carrier absorption in the insulating TNO films indicated carrier compensation due to excess oxygen. With H2-annealing, both carrier density and Hall mobility recovered to the level of conducting TNO, demonstrating that the excess oxygen can be efficiently removed by the annealing process without introducing additional scattering centers.

  14. Quantum anomalous Hall effect and a nontrivial spin-texture in ultra-thin films of magnetic topological insulators

    SciTech Connect

    Duong, Le Quy; Das, Tanmoy; Feng, Y. P.; Lin, Hsin

    2015-05-07

    We study the evolution of quantum anomalous Hall (QAH) effect for a Z{sub 2} topological insulator (TI) thin films in a proximity induced magnetic phase by a realistic layered k·p model with interlayer coupling. We examine three different magnetic configurations in which ferromagnetic (FM) layer(s) is added either from one side (FM-TI), from both sides (FM-TI-FM), or homogeneously distributed (magnetically doped) in a TI slab. We map out the thickness-dependent topological phase diagram under various experimental conditions. The critical magnetic exchange energy for the emergence of QAH effect in the latter two cases decreases monotonically with increasing number of quintuple layers (QLs), while it becomes surprisingly independent of the film thickness in the former case. The gap size of the emergent QAH insulator depends on the non-magnetic “parent” gap of the TI thin film and is tuned by the FM exchange energy, opening a versatile possibility to achieve room-temperature QAH insulator in various topological nanomaterials. Finally, we find that the emergent spin-texture in the QAH effect is very unconventional, non-“hedgehog” type; and it exhibits a chiral out-of-plane spin-flip texture within the same valence band which is reminiscent of dynamical “skyrmion” pattern, except our results are in the momentum space.

  15. Quantum anomalous Hall effect and a nontrivial spin-texture in ultra-thin films of magnetic topological insulators

    NASA Astrophysics Data System (ADS)

    Duong, Le Quy; Das, Tanmoy; Feng, Y. P.; Lin, Hsin

    2015-05-01

    We study the evolution of quantum anomalous Hall (QAH) effect for a Z2 topological insulator (TI) thin films in a proximity induced magnetic phase by a realistic layered k.p model with interlayer coupling. We examine three different magnetic configurations in which ferromagnetic (FM) layer(s) is added either from one side (FM-TI), from both sides (FM-TI-FM), or homogeneously distributed (magnetically doped) in a TI slab. We map out the thickness-dependent topological phase diagram under various experimental conditions. The critical magnetic exchange energy for the emergence of QAH effect in the latter two cases decreases monotonically with increasing number of quintuple layers (QLs), while it becomes surprisingly independent of the film thickness in the former case. The gap size of the emergent QAH insulator depends on the non-magnetic "parent" gap of the TI thin film and is tuned by the FM exchange energy, opening a versatile possibility to achieve room-temperature QAH insulator in various topological nanomaterials. Finally, we find that the emergent spin-texture in the QAH effect is very unconventional, non-"hedgehog" type; and it exhibits a chiral out-of-plane spin-flip texture within the same valence band which is reminiscent of dynamical "skyrmion" pattern, except our results are in the momentum space.

  16. Unusual M2-mediated metal-insulator transition in epitaxial VO2 thin films on GaN substrates

    NASA Astrophysics Data System (ADS)

    Yang, Hyoung Woo; Inn Sohn, Jung; Yang, Jae Hoon; Jang, Jae Eun; Cha, Seung Nam; Kim, Jongmin; Kang, Dae Joon

    2015-01-01

    We report on the epitaxial growth of vanadium dioxide (\\text{VO}2) thin films on (0001) GaN substrates using a radio frequency magnetron sputtering method and discuss their unusual M2-mediated metal-insulator transition (MIT) properties. We found that large lattice misfits between the \\text{VO}2 film and the GaN substrate could favor the stabilization of the intermediate insulating \\text{M}2 phase, which is known to be observed only in either doped or uniaxially strained samples. We demonstrated that the MIT in \\text{VO}2 films on GaN substrates could be mediated via a monoclinic \\text{M}2 phase during the transition from a monoclinic \\text{M}1 to a rutile R phase. This was confirmed by temperature-dependent Raman studies that exhibited both an evident upshift of a high-frequency phonon mode (ω\\text{V-O}) from 618 \\text{cm}-1 (\\text{M}1) to 645 \\text{cm}-1 (\\text{M}2) and a distinct peak splitting of a low-frequency phonon mode (ω\\text{V-V}) at 221 \\text{cm}-1 (\\text{M}2) for increasing temperatures. Moreover, a resistance change of four orders of magnitude was observed for \\text{VO}2 thin films on GaN substrates, being indicative of the high quality of \\text{VO}2 thin films. This study may offer great opportunities not only to improve the understanding of M2-mediated MIT behavior in \\text{VO}2 thin films, but also to realize novel electronic and optoelectronic devices.

  17. Thermopower analysis of metal-insulator transition temperature modulations in vanadium dioxide thin films with lattice distortion

    NASA Astrophysics Data System (ADS)

    Katase, Takayoshi; Endo, Kenji; Ohta, Hiromichi

    2015-07-01

    Insulator-to-metal (MI) phase transition in vanadium dioxide (V O2) thin films with controlled lattice distortion was investigated by thermopower measurements. V O2 epitaxial films with different crystallographic orientations, grown on (0001 ) α -A l2O3 , (11 2 ¯0 ) α -A l2O3 , and (001 ) Ti O2 substrates, showed significant decrease of absolute value of Seebeck coefficient (S ) from ˜200 to 23 μ V K-1 , along with a sharp drop in electrical resistivity (ρ ) , due to the transition from an insulator to a metal. The MI transition temperatures observed both in ρ (Tρ) and S (TS) for the V O2 films systematically decrease with lattice shrinkage in the pseudorutile structure along the c axis, accompanying a broadening of the MI transition temperature width. Moreover, the onset TS, where the insulating phase starts to become metallic, is much lower than the onset Tρ. This difference is attributed to the sensitivity of S for the detection of hidden metallic domains in the majority insulating phase, which cannot be detected in ρ measurements. Consequently, S measurements provide a straightforward and excellent approach for a deeper understanding of the MI transition process in V O2 .

  18. Metal-insulator transition with ferrimagnetic order in epitaxial thin films of spinel NiCo2O4

    NASA Astrophysics Data System (ADS)

    Silwal, Punam; Miao, Ludi; Stern, Ilan; Zhou, Xiaolan; Hu, Jin; Spinu, Leonard; Kim, Dae Ho; Talbayev, Diyar

    2014-03-01

    Spinel NiCo2O4 is attractive for various technological applications but is less studied partly because of the unavailability of NiCo2O4 single crystal or epitaxial thin film. We have grown high-quality crystalline epitaxial NiCo2O4 thin films on MgAl2O4 (001) substrates. The systematic investigation of the films grown at various temperatures reveals a strong correlation between the structural, magnetic, and electrical transport properties. The low-temperature grown films show metallic behavior with strong ferrimagnetic ordering while the high temperature grown films are insulating with suppressed magnetic order. In addition, these films show excellent transport and magnetic properties down to 2 unit-cell thickness. Our study of temperature- and growth-condition dependent optical conductivity provides further insight in the carrier transport of these films. We observed coherent band-like transport in both low- and high temperature grown films, whereas only thermally activated hopping conductivity was reported in previous studies. The confirmation of coherent band like transport provides a basis for further improving NiCo2O4 for the application as transparent conducting oxide.

  19. Ultrahigh sensitivity of anomalous Hall effect sensor based on Cr-doped Bi2Te3 topological insulator thin films

    DOE PAGESBeta

    Ni, Y.; Zhang, Z.; Nlebedim, I. C.; Jiles, D. C.

    2016-07-01

    Anomalous Hall effect (AHE) was recently discovered in magnetic element-doped topological insulators (TIs), which promises low power consumption and high efficiency spintronics and electronics. This discovery broadens the family of Hall sensors. In this paper, AHE sensors based on Cr-doped Bi2Te3 topological insulator thin films are studied with two thicknesses (15 and 65 nm). It is found, in both cases, that ultrahigh Hall sensitivity can be obtained in Cr-doped Bi2Te3. Hall sensitivity reaches 1666 Ω/T in the sensor with the 15 nm TI thin film, which is higher than that of the conventional semiconductor HE sensor. The AHE of 65more » nm sensors is even stronger, which causes the sensitivity increasing to 2620 Ω/T. Furthermore, after comparing Cr-doped Bi2Te3 with the previously studied Mn-doped Bi2Te3 TI Hall sensor, the sensitivity of the present AHE sensor shows about 60 times higher in 65 nm sensors. Furthermore, the implementation of AHE sensors based on a magnetic-doped TI thin film indicates that the TIs are good candidates for ultrasensitive AHE sensors.« less

  20. Collapse of the low temperature insulating state in Cr-doped V2O3 thin films

    NASA Astrophysics Data System (ADS)

    Homm, P.; Dillemans, L.; Menghini, M.; Van Bilzen, B.; Bakalov, P.; Su, C.-Y.; Lieten, R.; Houssa, M.; Nasr Esfahani, D.; Covaci, L.; Peeters, F. M.; Seo, J. W.; Locquet, J.-P.

    2015-09-01

    We have grown epitaxial Cr-doped V2O3 thin films with Cr concentrations between 0% and 20% on (0001)-Al2O3 by oxygen-assisted molecular beam epitaxy. For the highly doped samples (>3%), a regular and monotonous increase of the resistance with decreasing temperature is measured. Strikingly, in the low doping samples (between 1% and 3%), a collapse of the insulating state is observed with a reduction of the low temperature resistivity by up to 5 orders of magnitude. A vacuum annealing at high temperature of the films recovers the low temperature insulating state for doping levels below 3% and increases the room temperature resistivity towards the values of Cr-doped V2O3 single crystals. It is well-know that oxygen excess stabilizes a metallic state in V2O3 single crystals. Hence, we propose that Cr doping promotes oxygen excess in our films during deposition, leading to the collapse of the low temperature insulating state at low Cr concentrations. These results suggest that slightly Cr-doped V2O3 films can be interesting candidates for field effect devices.

  1. Collapse of the low temperature insulating state in Cr-doped V2O3 thin films

    NASA Astrophysics Data System (ADS)

    Homm, Pia; Dillemans, Leander; Menghini, Mariela; van Bilzen, Bart; Bakalov, Petar; Su, Chen-Yi; Lieten, Ruben; Houssa, Michel; Seo, Jin Won; Locquet, Jean-Pierre; Nasr Esfahani, Davoud; Covani, Lucian; Peeters, Francois

    We have grown epitaxial Cr-doped V2O3 thin films with Cr concentrations between 0 and 20% on (0001)-Al2O3 by oxygen-assisted molecular beam epitaxy. For the highly doped samples (> 3%), a regular and monotonous increase of the resistance with decreasing temperature is measured. Strikingly, in the low doping samples (between 1% and 3%), a collapse of the insulating state is observed with a reduction of the low temperature resistivity by up to 5 orders of magnitude. A vacuum annealing at high temperature of the films recovers the low temperature insulating state for doping levels below 3% and increases the room temperature resistivity towards the values of Cr-doped V2O3 single crystals. It is well known that oxygen excess stabilizes a metallic state in V2O3 single crystals. Hence, we propose that Cr doping promotes oxygen excess in our films during deposition, leading to the collapse of the low temperature insulating state at low Cr concentrations. These results suggest that slightly Cr-doped V2O3 films can be interesting candidates for field effect devices.

  2. Large-scale graphitic thin films synthesized on Ni and transferred to insulators: Structural and electronic properties

    NASA Astrophysics Data System (ADS)

    Cao, Helin; Yu, Qingkai; Colby, Robert; Pandey, Deepak; Park, C. S.; Lian, Jie; Zemlyanov, Dmitry; Childres, Isaac; Drachev, Vladimir; Stach, Eric A.; Hussain, Muhammad; Li, Hao; Pei, Steven S.; Chen, Yong P.

    2010-02-01

    We present a comprehensive study of the structural and electronic properties of ultrathin films containing graphene layers synthesized by chemical vapor deposition based surface segregation on polycrystalline Ni foils then transferred onto insulating SiO2/Si substrates. Films of size up to several mm's have been synthesized. Structural characterizations by atomic force microscopy, scanning tunneling microscopy, cross-sectional transmission electron microscopy (XTEM), and Raman spectroscopy confirm that such large-scale graphitic thin films (GTF) contain both thick graphite regions and thin regions of few-layer graphene. The films also contain many wrinkles, with sharply-bent tips and dislocations revealed by XTEM, yielding insights on the growth and buckling processes of the GTF. Measurements on mm-scale back-gated transistor devices fabricated from the transferred GTF show ambipolar field effect with resistance modulation ˜50% and carrier mobilities reaching ˜2000 cm2/V s. We also demonstrate quantum transport of carriers with phase coherence length over 0.2 μm from the observation of two-dimensional weak localization in low temperature magnetotransport measurements. Our results show that despite the nonuniformity and surface roughness, such large-scale, flexible thin films can have electronic properties promising for device applications.

  3. Combined gate-tunable Josephson junctions and normal state transport in Bi2Te3 topological insulator thin films

    NASA Astrophysics Data System (ADS)

    Ngabonziza, Prosper; Stehno, Martin, P.; Myoren, Hiroaki; Brinkman, Alexander

    In recent years, extensive efforts have been made to improve the coupling between topological insulators and s-wave superconductors in topological insulator Josephson devices (TIJDs). Despite significant progress, essential questions remain open such as the bulk contribution to the Josephson critical current or the existence (and number) of 4 π -periodic bound states (Majoranas) in TIJDs. To address these issues, we fabricated Nb/Bi2Te3/Nb Josephson junctions alongside Hall bar devices on MBE-grown Bi2Te3 topological insulator thin films. Using the SrTiO3 [111] substrate as a gate dielectric, we tuned the carrier density electrostatically and measured the Josephson supercurrent and the normal state transport properties of our thin film devices. We identify three gate voltage ranges with distinct behavior: A region of intermediate gate bias where the measured quantities change rapidly with the applied electric field, and two saturation regions for large bias of either polarity. We discuss carrier distribution and band alignment in the material as well as implications for the effective Josephson coupling in TIJDs. This work is financially supported by the Dutch Foundation for Fundamental Research on Matter (FOM), the Netherlands Organization for Scientific Research (NWO), and by the European Research Council (ERC).

  4. Thickness dependence oscillations of transport properties in thin films of a topological insulator Bi91Sb9

    NASA Astrophysics Data System (ADS)

    Rogacheva, E. I.; Orlova, D. S.; Nashchekina, O. N.; Dresselhaus, M. S.; Tang, S.

    2012-07-01

    The dependences of the electrical conductivity, Hall coefficient, magnetoresistance, and Seebeck coefficient on the thickness d (d = 15-400 nm) of the topological insulator Bi91Sb9 thin films grown on mica substrates were obtained at room temperature. In addition to the oscillations with a period Δd = (105 ± 5) nm in the thickness range d = 100-400 nm which are attributed to the quantization of the semiconductor electron energy spectrum, oscillations with a period Δd = (8 ± 2) nm in the range d = 15-60 nm were also revealed. It is suggested that the existence of the high-frequency oscillations in the thin films may be connected with the quantization of the metallic surface states energy spectrum.

  5. Electrolysis-induced protonation of VO2 thin film transistor for the metal-insulator phase modulation

    NASA Astrophysics Data System (ADS)

    Katase, Takayoshi; Endo, Kenji; Ohta, Hiromichi

    2016-02-01

    Compared to state-of-the-art modulation techniques, protonation is the most ideal to control the electrical and optical properties of transition metal oxides (TMOs) due to its intrinsic non-volatile operation. However, the protonation of TMOs is not typically utilized for solid-state devices because of imperative high-temperature annealing treatment in hydrogen source. Although one solution for room temperature (RT) protonation of TMOs is liquid-phase electrochemistry, it is unsuited for practical purposes due to liquid-leakage problem. Herein we demonstrate solid-state RT-protonation of vanadium dioxide (VO2), which is a well-known thermochromic TMO. We fabricated the three terminal thin-film-transistor structure on an insulating VO2 film using a water-infiltrated nanoporous glass, which serves as a solid electrolyte. For gate voltage application, water electrolysis and protonation/deprotonation of VO2 film surface occurred, leading to reversible metal-insulator phase conversion of ~11-nm-thick VO2 layer. The protonation was clearly accompanied by the structural change from an insulating monoclinic to a metallic tetragonal phase. Present results offer a new route for the development of electro-optically active solid-state devices with TMO materials by engineering RT protonation.

  6. Spin-orbit torque-assisted switching in magnetic insulator thin films with perpendicular magnetic anisotropy.

    PubMed

    Li, Peng; Liu, Tao; Chang, Houchen; Kalitsov, Alan; Zhang, Wei; Csaba, Gyorgy; Li, Wei; Richardson, Daniel; DeMann, August; Rimal, Gaurab; Dey, Himadri; Jiang, J S; Porod, Wolfgang; Field, Stuart B; Tang, Jinke; Marconi, Mario C; Hoffmann, Axel; Mryasov, Oleg; Wu, Mingzhong

    2016-01-01

    As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe12O19 bilayer where the BaFe12O19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control the up and down states of the remnant magnetization in the BaFe12O19 film when the film is magnetized by an in-plane magnetic field. It can reduce or increase the switching field of the BaFe12O19 film by as much as about 500 Oe when the film is switched with an out-of-plane field. PMID:27581060

  7. Mechanically-exfoliated stacks of thin films of Bi2Te3 topological insulators with enhanced thermoelectric performance

    NASA Astrophysics Data System (ADS)

    Goyal, V.; Teweldebrhan, D.; Balandin, A. A.

    2010-09-01

    The authors report on "graphene-like" mechanical exfoliation of single-crystal Bi2Te3 films and thermoelectric characterization of the stacks of such films. Thermal conductivity of the resulting "pseudosuperlattices" was measured by the "hot disk" and "laser flash" techniques. The room temperature in-plane (cross-plane) thermal conductivity of the stacks decreases by a factor of ˜2.4 (3.5) as compared to bulk. The thermal conductivity reduction with preserved electrical properties leads to strong increase in the thermoelectric figure of merit. It is suggested that the film thinning to few-quintuples and tuning of the Fermi level can help in achieving the topological-insulator surface transport regime with an extraordinary thermoelectric efficiency.

  8. Study of Ho-doped Bi{sub 2}Te{sub 3} topological insulator thin films

    SciTech Connect

    Harrison, S. E.; Collins-McIntyre, L. J.; Zhang, S. L.; Chen, Y. L.; Hesjedal, T.; Baker, A. A.; Figueroa, A. I.; Laan, G. van der; Kellock, A. J.; Pushp, A.; Parkin, S. S. P.; Harris, J. S.

    2015-11-02

    Breaking time-reversal symmetry through magnetic doping of topological insulators has been identified as a key strategy for unlocking exotic physical states. Here, we report the growth of Bi{sub 2}Te{sub 3} thin films doped with the highest magnetic moment element Ho. Diffraction studies demonstrate high quality films for up to 21% Ho incorporation. Superconducting quantum interference device magnetometry reveals paramagnetism down to 2 K with an effective magnetic moment of ∼5 μ{sub B}/Ho. Angle-resolved photoemission spectroscopy shows that the topological surface state remains intact with Ho doping, consistent with the material's paramagnetic state. The large saturation moment achieved makes these films useful for incorporation into heterostructures, whereby magnetic order can be introduced via interfacial coupling.

  9. Time-resolved terahertz dynamics in thin films of the topological insulator Bi2Se3

    DOE PAGESBeta

    Valdés Aguilar, R.; Qi, J.; Brahlek, M.; Bansal, N.; Azad, A.; Bowlan, J.; Oh, S.; Taylor, A. J.; Prasankumar, R. P.; Yarotski, D. A.

    2015-01-07

    We use optical pump–THz probe spectroscopy at low temperatures to study the hot carrier response in thin Bi2Se3 films of several thicknesses, allowing us to separate the bulk from the surface transient response. We find that for thinner films the photoexcitation changes the transport scattering rate and reduces the THz conductivity, which relaxes within 10 picoseconds (ps). For thicker films, the conductivity increases upon photoexcitation and scales with increasing both the film thickness and the optical fluence, with a decay time of approximately 5 ps as well as a much higher scattering rate. Furthermore, these different dynamics are attributed tomore » the surface and bulk electrons, respectively, and demonstrate that long-lived mobile surface photo-carriers can be accessed independently below certain film thicknesses for possible optoelectronic applications.« less

  10. Magnetic flux disorder and superconductor-insulator transition in nanohole thin films

    NASA Astrophysics Data System (ADS)

    Granato, Enzo

    2016-08-01

    We study the superconductor-insulator transition in nanohole ultrathin films in a transverse magnetic field by numerical simulation of a Josephson-junction array model. Geometrical disorder due to the random location of nanoholes in the film corresponds to random flux in the array model. Monte Carlo simulation in the path-integral representation is used to determine the critical behavior and the universal resistivity at the transition as a function of disorder and average number of flux quanta per cell, fo. The resistivity increases with disorder for noninteger fo while it decreases for integer fo, and reaches a common constant value in a vortex-glass regime above a critical value of the flux disorder Dfc. The estimate of Dfc and the resistivity increase for noninteger fo are consistent with recent experiments on ultrathin superconducting films with positional disordered nanoholes.

  11. Strain controlled systematic variation of metal-insulator transition in epitaxial NdNiO{sub 3} thin films

    SciTech Connect

    Kumar, Yogesh; Choudhary, R. J.; Kumar, Ravi

    2012-10-01

    We report here the strain dependent structural and electrical transport properties of epitaxial NdNiO{sub 3} thin films. Pulsed laser deposition technique was used to grow the NdNiO{sub 3} thin films on c-axis oriented SrTiO{sub 3} single crystals. Deposited films were irradiated using 200 MeV Ag{sup 15+} ion beam at the varying fluence (1 Multiplication-Sign 10{sup 11}, 5 Multiplication-Sign 10{sup 11}, and 1 Multiplication-Sign 10{sup 12} ions/cm{sup 2}). X-ray diffraction studies confirm the epitaxial growth of the deposited films, which is maintained even up to the highest fluence. Rise in the in-plane compressive strain has been observed after the irradiation. All the films exhibit metal-insulator transition, however, a systematic decrease in the transition temperature (T{sub MI}) has been observed after irradiation, which may be attributed to the increase in the in-plane compression. Raman spectroscopy data reveal that this reduction in T{sub MI}, with the irradiation, is related to the decrease in band gap due to the stress generated by the in-plane compressive strain.

  12. Topological insulator thin films starting from the amorphous phase-Bi{sub 2}Se{sub 3} as example

    SciTech Connect

    Barzola-Quiquia, J. Lehmann, T.; Stiller, M.; Spemann, D.; Esquinazi, P.; Häussler, P.

    2015-02-21

    We present a new method to obtain topological insulator Bi{sub 2}Se{sub 3} thin films with a centimeter large lateral length. To produce amorphous Bi{sub 2}Se{sub 3} thin films, we have used a sequential flash-evaporation method at room temperature. Transmission electron microscopy has been used to verify that the prepared samples are in a pure amorphous state. During annealing, the samples transform into the rhombohedral Bi{sub 2}Se{sub 3} crystalline structure which was confirmed using X-ray diffraction and Raman spectroscopy. Resistance measurements of the amorphous films show the expected Mott variable range hopping conduction process with a high specific resistance compared to the one obtained in the crystalline phase (metallic behavior). We have measured the magnetoresistance and the Hall effect at different temperatures between 2 K and 275 K. At temperatures T ≲ 50 K and fields B ≲ 1 T, we observe weak anti-localization in the MR; the Hall measurements confirm the n-type character of the samples. All experimental results of our films are in quantitative agreement with results from samples prepared using more sophisticated methods.

  13. Scaling Laws for Thin Films near the Superconducting-to-Insulating Transition.

    PubMed

    Tao, Yong

    2016-01-01

    We propose a Lagrangian function, which combines Landau-Ginzburg term and Chern-Simons term, for describing the competition between disorder and superconductivity. To describe the normal-to-superconducting transition in the thin superconducting films, we apply Wilson's renormalization group methods into this Lagrangian function. Finally, we obtain a scaling law between critical temperature (Tc), film thickness (d), sheet resistance of the film at the normal state (Rs), and number density of the electrons at the normal state (N). Such a scaling law is in agreement with recent experimental investigations [Ivry, Y. et al., Physical Review B 90, 214515 (2014)]. Our finding may have potential benefits for improving transition temperature Tc. PMID:27029338

  14. Scaling Laws for Thin Films near the Superconducting-to-Insulating Transition

    NASA Astrophysics Data System (ADS)

    Tao, Yong

    2016-03-01

    We propose a Lagrangian function, which combines Landau-Ginzburg term and Chern-Simons term, for describing the competition between disorder and superconductivity. To describe the normal-to-superconducting transition in the thin superconducting films, we apply Wilson’s renormalization group methods into this Lagrangian function. Finally, we obtain a scaling law between critical temperature (Tc), film thickness (d), sheet resistance of the film at the normal state (Rs), and number density of the electrons at the normal state (N). Such a scaling law is in agreement with recent experimental investigations [Ivry, Y. et al., Physical Review B 90, 214515 (2014)]. Our finding may have potential benefits for improving transition temperature Tc.

  15. Scaling Laws for Thin Films near the Superconducting-to-Insulating Transition

    PubMed Central

    Tao, Yong

    2016-01-01

    We propose a Lagrangian function, which combines Landau-Ginzburg term and Chern-Simons term, for describing the competition between disorder and superconductivity. To describe the normal-to-superconducting transition in the thin superconducting films, we apply Wilson’s renormalization group methods into this Lagrangian function. Finally, we obtain a scaling law between critical temperature (Tc), film thickness (d), sheet resistance of the film at the normal state (Rs), and number density of the electrons at the normal state (N). Such a scaling law is in agreement with recent experimental investigations [Ivry, Y. et al., Physical Review B 90, 214515 (2014)]. Our finding may have potential benefits for improving transition temperature Tc. PMID:27029338

  16. Surface grafting of octylamine onto poly(ethylene-alt-maleic anhydride) gate insulators for low-voltage DNTT thin-film transistors.

    PubMed

    Choe, Yun-Seo; Yi, Mi Hye; Kim, Ji-Heung; Kim, Yun Ho; Jang, Kwang-Suk

    2016-03-28

    This study investigates a spin-coating method for modifying the surface properties of a poly(ethylene-alt-maleic anhydride) (PEMA) gate insulator. The 60 nm-thick PEMA thin film exhibits excellent electrical insulating properties, and its surface properties could be easily modified by surface grafting of octylamine. Due to surface treatment via spin-coating, the surface energy of the PEMA gate insulator decreased, the crystal quality of the organic semiconductor improved, and consequently the performance of low-voltage organic thin-film transistors (TFTs) was enhanced. Our results suggest that the surface treatment of the PEMA gate insulator could be a simple and effective method for enhancing the performance of organic TFTs. PMID:26940136

  17. Fractal nature of metallic and insulating domain configurations in nearly grain-boundary-free VO2/TiO2 thin films

    NASA Astrophysics Data System (ADS)

    Sohn, Ahrum; Kanki, Teruo; Tanaka, Hidekazu; Kim, Dong-Wook

    We investigated evolution of the surface work function (WS) maps of epitaxial 15-nm-thick VO2/TiO2 thin films using Kelvin probe force microscopy (KPFM) measurements while the film undergoes the metal-insulator transition (MIT). The metallic and insulating domains coexist in the VO2 thin films during the transition, since the MIT is the first-order phase transition. Nearly grain-boundary-free samples allowed observation of metallic and insulating domains with distinct WS values, throughout the transition. Each domain allowed us to obtain real space domain maps with nanoscopic spatial resolution. The two-dimensional percolation model well explained the relationship between the metallic domain fraction and the measured the resistivity. The domain maps also suggested that the percolation clusters formed a fractal surface.

  18. Optical properties of TiN thin films close to the superconductor-insulator transition.

    SciTech Connect

    Pfuner, F.; Degiorgi, L.; Baturina, T. I.; Vinokur, V. M.; Baklanov, M. R.; Materials Science Division; ETH Zurich; Inst. Semiconductor Physics; IMEC Kapeldreef

    2009-11-10

    We present the intrinsic optical properties over a broad spectral range of TiN thin films deposited on an Si/SiO{sub 2} substrate. We analyze the measured reflectivity spectra of the film-substrate multilayer structure within a well-establish procedure based on the Fresnel equation and extract the real part of the optical conductivity of TiN. We identify the metallic contribution as well as the finite energy excitations and disentangle the spectral weight distribution among them. The absorption spectrum of TiN bears some similarities with the electrodynamic response observed in the normal state of the high-temperature superconductors. Particularly, a mid-infrared feature in the optical conductivity is quite reminiscent of a pseudogap-like excitation.

  19. Optical study of the insulator-to-metal transition in LaxMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Mohamed, W. S.; Maselli, P.; Calvani, P.; Baldassarre, L.; Orgiani, P.; Galdi, A.; Maritato, L.; Nucara, A.

    2014-09-01

    Lanthanum manganites with a massive concentration of La defects can be stabilized in the form of thin films, by exploiting the structural stress produced by a substrate such as SrTiO3. They undergo an insulator-to-metal transition (IMT) like those doped by divalent ions, which is here studied by measuring the optical conductivity of LaxMnO3-δ films with x = 0.66, 0.88, 0.98 and 1.10, and with δ ≃ 0, from the far infrared to the near ultraviolet, and between 20 and 300 K. The IMT is here a slow process which continues down to 100 K at least, more than 250 K below its onset at the Curie temperature Tc and at the TIMT measured from the dc resistivity. The metallization is here monitored through the increase of the Drude term and a transfer of spectral weight from a ‘hard’ midinfrared band MIR-2 peaked between 3000 and 5000 cm-1 at room temperature, to a ‘soft’ midinfrared band MIR-1 at ˜ 1000 cm-1 and to the Drude term. This evidence is in good agreement with a model of phase separation below Tc, where insulating and paramagnetic regions of small polarons coexist with conducting and ferromagnetic regions populated by large polarons and free carriers.

  20. Thickness-dependent transport channels in topological insulator Bi2Se3 thin films grown by magnetron sputtering

    PubMed Central

    Wang, Wen Jie; Gao, Kuang Hong; Li, Zhi Qing

    2016-01-01

    We study the low-temperature transport properties of Bi2Se3 thin films grown by magnetron sputtering. A positive magnetoresistance resulting from the weak antilocalization (WAL) effect is observed at low temperatures. The observed WAL effect is two dimensional in nature. Applying the Hikami-Larkin-Nagaoka theory, we have obtained the dephasing length. It is found that the temperature dependence of the dephasing length cannot be described only by the Nyquist electron-electron dephasing, in conflict with prevailing experimental results. From the WAL effect, we extract the number of the transport channels, which is found to increase with increasing the thickness of the films, reflecting the thickness-dependent coupling between the top and bottom surface states in topological insulator. On the other hand, the electron-electron interaction (EEI) effect is observed in temperature-dependent conductivity. From the EEI effect, we also extract the number of the transport channel, which shows similar thickness dependence with that obtained from the analysis of the WAL effect. The EEI effect, therefore, can be used to analyze the coupling effect between the top and bottom surface states in topological insulator like the WAL effect. PMID:27142578

  1. Thickness-dependent transport channels in topological insulator Bi2Se3 thin films grown by magnetron sputtering.

    PubMed

    Wang, Wen Jie; Gao, Kuang Hong; Li, Zhi Qing

    2016-01-01

    We study the low-temperature transport properties of Bi2Se3 thin films grown by magnetron sputtering. A positive magnetoresistance resulting from the weak antilocalization (WAL) effect is observed at low temperatures. The observed WAL effect is two dimensional in nature. Applying the Hikami-Larkin-Nagaoka theory, we have obtained the dephasing length. It is found that the temperature dependence of the dephasing length cannot be described only by the Nyquist electron-electron dephasing, in conflict with prevailing experimental results. From the WAL effect, we extract the number of the transport channels, which is found to increase with increasing the thickness of the films, reflecting the thickness-dependent coupling between the top and bottom surface states in topological insulator. On the other hand, the electron-electron interaction (EEI) effect is observed in temperature-dependent conductivity. From the EEI effect, we also extract the number of the transport channel, which shows similar thickness dependence with that obtained from the analysis of the WAL effect. The EEI effect, therefore, can be used to analyze the coupling effect between the top and bottom surface states in topological insulator like the WAL effect. PMID:27142578

  2. Role of laser energy density on growth of highly oriented topological insulator Bi2Se3 thin films

    NASA Astrophysics Data System (ADS)

    Chaturvedi, P.; Saha, B.; Saha, D.; Ganguly, S.

    2016-05-01

    Topological insulators (TIs) are very promising in the field of nanoelectronics due to their exotic properties. Bismuth Selenide, a 3D Topological insulator is considered as reference TI owing to its simple band structure and large bandgap. However, the presence of unintentional doping, which masks the metallic surface states, is still a major concern. In this work, we report the effect of laser energy density on the growth of highly oriented and stoichiometric thin films of Bi2Se3 by pulsed laser deposition (PLD). Structural characterizations by X-ray diffraction (XRD) and Raman Spectroscopy confirms the c-axis orientation and good crystallinity of films. Atomic force microscopy (AFM) study shows the increase in average grain size and rms roughness (from 3.1 nm to 5.1 nm) with the decrease in laser energy density. Compositional study by X-Ray Reflectivity (XRR) measurement is found to be in agreement with AFM results. Energy dispersive x-ray spectroscopy (EDS) measurements confirm the desired stoichiometry of the samples.

  3. Half-metallic ferromagnetism on surfaces of insulating and antiferromagnetic LaFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Mishra, Rohan; Kim, Young-Min; He, Qian; Kim, Seong-Keun; Chang, Seohyoung; Bhattacharya, Anand; Pantelides, Sokrates T.; Borisevich, Albina

    The surfaces of perovskite transition metal oxides having correlated electrons show novel electronic and magnetic phenomena. In this work, we combine scanning transmission electron microscopy imaging and electron energy loss spectroscopy (EELS) with density functional theory (DFT) calculations to study the surface of (LaFeO3)m /(SrFeO3)n heterostructure thin films. Using EELS, we observe a reduction in the oxidation state of Fe on moving from the bulk to the surface over a length of ~5 unit cells. Simultaneously acquired STEM images allow us to map the associated changes in their structure, such as cation displacements and changes in oxygen polyhedral tilts. DFT calculations coupled with the STEM results show that by reducing the surface layer of a LaFeO3 film such that the surface is terminated with FeO4 tetrahedra instead of the FeO6 octahedra as present in the bulk, it is possible to stabilize an exotic phase where the surface layer displays a half-metallic ferromagnetic behavior, while the bulk remains antiferromagnetic and insulating, similar to the class of topological insulators. The calculations also predict that the magnetism and conductivity at the surface can be controlled by the partial pressure of oxygen.

  4. Thickness-dependent transport channels in topological insulator Bi2Se3 thin films grown by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Wang, Wen Jie; Gao, Kuang Hong; Li, Zhi Qing

    2016-05-01

    We study the low-temperature transport properties of Bi2Se3 thin films grown by magnetron sputtering. A positive magnetoresistance resulting from the weak antilocalization (WAL) effect is observed at low temperatures. The observed WAL effect is two dimensional in nature. Applying the Hikami-Larkin-Nagaoka theory, we have obtained the dephasing length. It is found that the temperature dependence of the dephasing length cannot be described only by the Nyquist electron-electron dephasing, in conflict with prevailing experimental results. From the WAL effect, we extract the number of the transport channels, which is found to increase with increasing the thickness of the films, reflecting the thickness-dependent coupling between the top and bottom surface states in topological insulator. On the other hand, the electron-electron interaction (EEI) effect is observed in temperature-dependent conductivity. From the EEI effect, we also extract the number of the transport channel, which shows similar thickness dependence with that obtained from the analysis of the WAL effect. The EEI effect, therefore, can be used to analyze the coupling effect between the top and bottom surface states in topological insulator like the WAL effect.

  5. Thin-film palladium and silver alloys and layers for metal-insulator-semiconductor sensors

    NASA Astrophysics Data System (ADS)

    Hughes, R. C.; Schubert, W. K.; Zipperian, T. E.; Rodriguez, J. L.; Plut, T. A.

    1987-08-01

    The addition of Ag to Pd in the gate metal of a metal-insulator-semiconductor gas sensing diode can improve the performance and change the selectivity of the sensors for a variety of reactions. Data on the response of diodes with 12 different ratios of Ag to Pd in alloys and layers of Pd and Ag to hydrogen and other gases are reported. Diodes with as much as 32% Ag respond very well to H2 gas and the films are much more durable to high hydrogen exposure than pure Pd films. Improvements in the rate of response and aging behavior are found for certain Ag combinations; others give poorer performance. The presence of Ag on the surface changes the catalytic activity in some cases and examples of H2 mixed with O2 and/or NO2, propylene oxide, ethylene, and formic acid are given. Such selectivity forms the basis for miniature chemical sensor arrays which could analyze complex gas mixtures.

  6. Surface-to-surface scattering in three-dimensional (3D) topological insulator (TI) thin films

    NASA Astrophysics Data System (ADS)

    Yin, Gen; Wickramaratne, Darshana; Lake, Roger

    2013-03-01

    When the thickness of a 3D TI material is reduced below approximately 6nm, hybridization of the opposite surfaces states can result in inter-surface tunneling. Due to the rotational symmetry of the thin film, the k-s locking relation on opposite surfaces also has opposite chirality. Thus, in this inter-surface scattering mechanism, back-scattering is allowed without the flip of the spin. This effect breaks the protection of TI surface states against back-scattering. To investigate the influence of the inter-surface scattering mechanism, we study different near-elastic scattering mechanisms in the surface state transport using Boltzmann transport equations within the relaxation time approximation. The effect of screened Coulomb impurities, low-energy acoustic phonons and surface magnetic impurities on the TI surface states will be discussed. The response of the inter-surface scattering of TI states to various external stimuli such as a Rashba-like splitting and the orientation of the impurity magnetic moments will also be presented. Using our simulation results, we propose possible experimental methods to modulate the back-scatter protection of TI surface states in thin film TI materials.

  7. Thin Film?

    NASA Astrophysics Data System (ADS)

    Kariper, İ. Afşin

    2014-09-01

    This study focuses on the critical surface tension of lead sulfite (PbSO3) crystalline thin film produced with chemical bath deposition on substrates (commercial glass).The PbSO3 thin films were deposited at room temperature at different deposition times. The structural properties of the films were defined and examined according to X-ray diffraction (XRD) and the XRD results such as dislocation density, average grain size, and no. of crystallites per unit area. Atomic force microscopy was used to measure the film thickness and the surface properties. The critical surface tension of the PbSO3 thin films was measured with an optical tensiometer instrument and calculated using the Zisman method. The results indicated that the critical surface tension of films changed in accordance with the average grain size and film thickness. The film thickness increased with deposition time and was inversely correlated with surface tension. The average grain size increased according to deposition time and was inversely correlated with surface tension.

  8. Low Temperature Quantum Transport Properties of Bi2Se3 Topological Insulator Thin Films

    NASA Astrophysics Data System (ADS)

    Lederman, David; Babakiray, Sercan; Borisov, Pavel; Kc, Amit; Glinka, Yuri

    Bi2Se3 thin films with nominal thickness values of 12, 16, 20 and 25 quintuple layers (QLs) were grown by molecular beam epitaxy (MBE) on Al2O3 substrates. The magnetoconductance (MC) was analyzed using the two-dimensional Altshuler-Aronov (AA) and Hikami-Larkin-Nagaoka (HLN) mechanisms. Using a simple model where the channels for the bulk and surface states are independent from each other, and assuming that all channels undergo WAL, it was possible to determine the phase coherence length (Lϕ) of the carriers of the surface and bulk contributions independently from the MC with the field perpendicular to the surface. The value of Lϕ for the surface states was independent of thickness, as expected, while Lϕ for the bulk channel was strongly dependent on film thickness. WAL was also measured with the field applied parallel to the surface, and from the MC data in this configuration, it was possible to obtain values for Lϕ that were similar to the perpendicular configuration for all samples except for the thinnest sample (12 QL), which may be a result of interactions between the metallic surfaces states on opposite sides of the film. We will discuss these results in view of other results from the literature. This work was supported at WVU by a Research Challenge Grant from the West Virginia Higher Education Policy Commission and by the WVU Shared Research Facilities.

  9. Hidden landscapes in thin film topological insulators: between order and disorder, 2D and 3D, normal and topological phases

    NASA Astrophysics Data System (ADS)

    Oh, Seongshik

    Topological insulator (TI) is one of the rare systems in the history of condensed matter physics that is initiated by theories and followed by experiments. Although this theory-driven advance helped move the field quite fast despite its short history, apparently there exist significant gaps between theories and experiments. Many of these discrepancies originate from the very fact that the worlds readily accessible to theories are often far from the real worlds that are available in experiments. For example, the very paradigm of topological protection of the surface states on Z2 TIs such as Bi2Se3, Bi2Te3, Sb2Te3, etc, is in fact valid only if the sample size is infinite and the crystal momentum is well-defined in all three dimensions. On the other hand, many widely studied forms of TIs such as thin films and nano-wires have significant confinement in one or more of the dimensions with varying level of disorders. In other words, many of the real world topological systems have some important parameters that are not readily captured by theories, and thus it is often questionable how far the topological theories are valid to real systems. Interestingly, it turns out that this very uncertainty of the theories provides additional control knobs that allow us to explore hidden topological territories. In this talk, I will discuss how these additional knobs in thin film topological insulators reveal surprising, at times beautiful, landscapes at the boundaries between order and disorder, 2D and 3D, normal and topological phases. This work is supported by Gordon and Betty Moore Foundation's EPiQS Initiative (GBMF4418).

  10. Microstructural and magneto-transport characterization of Bi2SexTe3-x topological insulator thin films grown by pulsed laser deposition method

    NASA Astrophysics Data System (ADS)

    Jin, Zhenghe; Kumar, Raj; Hunte, Frank; Narayan, Jay; Kim, Ki Wook; North Carolina State University Team

    Bi2SexTe3-x topological insulator thin films were grown on Al2O3 (0001) substrate by pulsed laser deposition (PLD). XRD and other structural characterization measurements confirm the growth of the textured Bi2SexTe3-x thin films on Al2O3 substrate. The magneto-transport properties of thick and thin Þlms were investigated to study the effect of thickness on the topological insulator properties of the Bi2SexTe3 - x films. A pronounced semiconducting behavior with a highly insulating ground state was observed in the resistivity vs. temperature data. The presence of the weak anti-localization (WAL) effect with a sharp cusp in the magnetoresistance measurements confirms the 2-D surface transport originating from the TSS in Bi2SexTe3-x TI films. A high fraction of surface transport is observed in the Bi2SexTe3-x TI thin films which decreases in Bi2SexTe3-x TI thick films. The Cosine (θ) dependence of the WAL effect supports the observation of a high proportion of 2-D surface state contribution to overall transport properties of the Bi2SexTe3-x TI thin films. Our results show promise that high quality Bi2SexTe3-x TI thin films with significant surface transport can be grown by PLD method to exploit the exotic properties of the surface transport in future generation spintronic devices. This work was supported, in part, by National Science Foundation ECCS-1306400 and FAME.

  11. Thin Films

    NASA Astrophysics Data System (ADS)

    Khorshidi, Zahra; Bahari, Ali; Gholipur, Reza

    2014-11-01

    Effect of annealing temperature on the characteristics of sol-gel-driven Ta ax La(1- a) x O y thin film spin-coated on Si substrate as a high- k gate dielectric was studied. Ta ax La(1- a) x O y thin films with different amounts of a were prepared (as-prepared samples). X-ray diffraction measurements of the as-prepared samples indicated that Ta0.3 x La0.7 x Oy film had an amorphous structure. Therefore, Ta0.3 x La0.7 x O y film was chosen to continue the present studies. The morphology of Ta0.3 x La0.7 x O y films was studied using scanning electron microscopy and atomic force microscopy techniques. The obtained results showed that the size of grain boundaries on Ta0.3 x La0.7 x O y film surfaces was increased with increasing annealing temperature. Electrical and optical characterizations of the as-prepared and annealed films were investigated as a function of annealing temperature using capacitance-voltage ( C- V) and current density-voltage ( J- V) measurements and the Tauc method. The obtained results demonstrated that Ta0.3 x La0.7 x O y films had high dielectric constant (≈27), wide band gap (≈4.5 eV), and low leakage current density (≈10-6 A/cm2 at 1 V).

  12. Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Hirai, Kei; Kan, Daisuke; Ichikawa, Noriya; Mibu, Ko; Yoda, Yoshitaka; Andreeva, Marina; Shimakawa, Yuichi

    2015-01-01

    Oxygen coordination of transition metals is a key for functional properties of transition-metal oxides, because hybridization of transition-metal d and oxygen p orbitals determines correlations between charges, spins and lattices. Strain often modifies the oxygen coordination environment and affects such correlations in the oxides, resulting in the emergence of unusual properties and, in some cases, fascinating behaviors. While these strain effects have been studied in many of the fully-oxygenated oxides, such as ABO3 perovskites, those in oxygen-deficient oxides consisting of various oxygen coordination environments like tetrahedra and pyramids as well as octahedra remain unexplored. Here we report on the discovery of a strain-induced significant increase, by 550 K, in the metal-insulator transition temperature of an oxygen-deficient Fe oxide epitaxial thin film. The observed transition at 620 K is ascribed to charge disproportionation of Fe3.66+ into Fe4+ and Fe3+, associated with oxygen-vacancy ordering. The significant increase in the metal-insulator transition temperature, from 70 K in the bulk material, demonstrates that epitaxial growth of oxygen-deficient oxides under substrate-induced strain is a promising route for exploring novel functionality.

  13. Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films

    PubMed Central

    Hirai, Kei; Kan, Daisuke; Ichikawa, Noriya; Mibu, Ko; Yoda, Yoshitaka; Andreeva, Marina; Shimakawa, Yuichi

    2015-01-01

    Oxygen coordination of transition metals is a key for functional properties of transition-metal oxides, because hybridization of transition-metal d and oxygen p orbitals determines correlations between charges, spins and lattices. Strain often modifies the oxygen coordination environment and affects such correlations in the oxides, resulting in the emergence of unusual properties and, in some cases, fascinating behaviors. While these strain effects have been studied in many of the fully-oxygenated oxides, such as ABO3 perovskites, those in oxygen-deficient oxides consisting of various oxygen coordination environments like tetrahedra and pyramids as well as octahedra remain unexplored. Here we report on the discovery of a strain-induced significant increase, by 550 K, in the metal-insulator transition temperature of an oxygen-deficient Fe oxide epitaxial thin film. The observed transition at 620 K is ascribed to charge disproportionation of Fe3.66+ into Fe4+ and Fe3+, associated with oxygen-vacancy ordering. The significant increase in the metal-insulator transition temperature, from 70 K in the bulk material, demonstrates that epitaxial growth of oxygen-deficient oxides under substrate-induced strain is a promising route for exploring novel functionality. PMID:25600001

  14. Thin-Film Power Transformers

    NASA Technical Reports Server (NTRS)

    Katti, Romney R.

    1995-01-01

    Transformer core made of thin layers of insulating material interspersed with thin layers of ferromagnetic material. Flux-linking conductors made of thinner nonferromagnetic-conductor/insulator multilayers wrapped around core. Transformers have geometric features finer than those of transformers made in customary way by machining and mechanical pressing. In addition, some thin-film materials exhibit magnetic-flux-carrying capabilities superior to those of customary bulk transformer materials. Suitable for low-cost, high-yield mass production.

  15. Origins of enhanced thermoelectric power factor in topologically insulating Bi0.64Sb1.36Te3 thin films

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Chi, Hang; Walrath, J. C.; Chang, A. S.; Stoica, Vladimir A.; Endicott, Lynn; Tang, Xinfeng; Goldman, R. S.; Uher, Ctirad

    2016-01-01

    In this research, we report the enhanced thermoelectric power factor in topologically insulating thin films of Bi0.64Sb1.36Te3 with a thickness of 6-200 nm. Measurements of scanning tunneling spectroscopy and electronic transport show that the Fermi level lies close to the valence band edge, and that the topological surface state (TSS) is electron dominated. We find that the Seebeck coefficient of the 6 nm and 15 nm thick films is dominated by the valence band, while the TSS chiefly contributes to the electrical conductivity. In contrast, the electronic transport of the reference 200 nm thick film behaves similar to bulk thermoelectric materials with low carrier concentration, implying the effect of the TSS on the electronic transport is merely prominent in the thin region. The conductivity of the 6 nm and 15 nm thick film is obviously higher than that in the 200 nm thick film owing to the highly mobile TSS conduction channel. As a consequence of the enhanced electrical conductivity and the suppressed bipolar effect in transport properties for the 6 nm thick film, an impressive power factor of about 2.0 mW m-1 K-2 is achieved at room temperature for this film. Further investigations of the electronic transport properties of TSS and interactions between TSS and the bulk band might result in a further improved thermoelectric power factor in topologically insulating Bi0.64Sb1.36Te3 thin films.

  16. Tuning the metal-insulator transition via epitaxial strain and Co doping in NdNiO3 thin films grown by polymer-assisted deposition

    NASA Astrophysics Data System (ADS)

    Yao, Dan; Shi, Lei; Zhou, Shiming; Liu, Haifeng; Zhao, Jiyin; Li, Yang; Wang, Yang

    2016-01-01

    The epitaxial NdNi1-xCoxO3 (0 ≤ x ≤ 0.10) thin films on (001) LaAlO3 and (001) SrTiO3 substrates were grown by a simple polymer-assisted deposition technique. The co-function of the epitaxial strain and Co doping on the metal-insulator transition in perovskite nickelate NdNiO3 thin films is investigated. X-ray diffraction and scanning electron microscopy reveal that the as-prepared thin films exhibit good crystallinity and heteroepitaxy. The temperature dependent resistivities of the thin films indicate that both the epitaxial strain and Co doping lower the metal-insulator (MI) transition temperature, which can be treated as a way to tune the MI transition. Furthermore, under the investigated Co-doping levels, the MI transition temperature (TMI) shifts to low temperatures with Co content increasing under both compressive and tensile strain, and the more distinction is in the former situation. When x is increased up to 0.10, the insulating phase is completely suppressed under the compressive strain. With the strain increases from compression to tension, the resistivities are enhanced both in the metal and insulating regions. However, the Co-doping effect on the resistivity shows a more complex situation. As Co content x increases from zero to 0.10, the resistivities are reduced both in the metal and insulating regions under the tensile strain, whereas they are enhanced in the high-temperature metal region under the compressive strain. Based on the temperature dependent resistivity in the metal regions, it is suggested that the electron-phonon coupling in the films becomes weaker with the increase of both the strain and Co-doping.

  17. Tuning the metal-insulator transition temperature of Sm0.5Nd0.5NiO3 thin films via strain

    NASA Astrophysics Data System (ADS)

    Gardner, H. Jeffrey; Singh, Vijay; Zhang, Le; Hong, Xia

    2014-03-01

    We have investigated the effect of substrate induced strain and film thickness on the metal-insulator transition of the correlated oxide Sm0.5Nd0.5NiO3 (SNNO). We have fabricated epitaxial 3 - 40 nm thick SNNO films on (001) LaAlO3 (LAO), (001) SrTiO3 (STO), and (110) NdGaO3 (NGO) via off-axis RF magnetron sputtering. The SNNO films are atomically smooth with (001) orientation as determined by atomic force microscopy and x-ray diffraction. SNNO films grown on LAO, subject to compressive strain, exhibit a sharp metal-insulator transition at lower temperatures. Conversely, films grown on STO and NGO, subject to tensile strain, exhibit a smeared albeit above room temperature metal-insulator transition. For all substrates, we have observed that the metal-insulator transition temperature (TMI) increases monotonically with decreasing film thickness until the electrically dead layer is reached (below 4 nm). We discuss the effect of strain and oxygen deficiencies on the TMI of SNNO thin films.

  18. Thin film three-dimensional topological insulator metal-oxide-semiconductor field-effect-transistors: A candidate for sub-10 nm devices

    SciTech Connect

    Akhavan, N. D. Jolley, G.; Umana-Membreno, G. A.; Antoszewski, J.; Faraone, L.

    2014-08-28

    Three-dimensional (3D) topological insulators (TI) are a new state of quantum matter in which surface states reside in the bulk insulating energy bandgap and are protected by time-reversal symmetry. It is possible to create an energy bandgap as a consequence of the interaction between the conduction band and valence band surface states from the opposite surfaces of a TI thin film, and the width of the bandgap can be controlled by the thin film thickness. The formation of an energy bandgap raises the possibility of thin-film TI-based metal-oxide-semiconductor field-effect-transistors (MOSFETs). In this paper, we explore the performance of MOSFETs based on thin film 3D-TI structures by employing quantum ballistic transport simulations using the effective continuous Hamiltonian with fitting parameters extracted from ab-initio calculations. We demonstrate that thin film transistors based on a 3D-TI structure provide similar electrical characteristics compared to a Si-MOSFET for gate lengths down to 10 nm. Thus, such a device can be a potential candidate to replace Si-based MOSFETs in the sub-10 nm regime.

  19. Improving the performance of organic thin film transistors formed on a vacuum flash-evaporated acrylate insulator

    SciTech Connect

    Ding, Z. Abbas, G. A.; Assender, H. E.; Morrison, J. J.; Sanchez-Romaguera, V.; Yeates, S. G.; Taylor, D. M.

    2013-12-02

    A systematic investigation has been undertaken, in which thin polymer buffer layers with different ester content have been spin-coated onto a flash-evaporated, cross-linked diacrylate gate-insulator to form bottom-gate, top-contact organic thin-film transistors. The highest device mobilities, ∼0.65 cm{sup 2}/V s and ∼1.00 cm{sup 2}/V s for pentacene and dinaphtho[2,3-b:2′,3′-f]-thieno[3,2-b]thiophene (DNTT), respectively, were only observed for a combination of large-grain (∼1–2 μm) semiconductor morphology coupled with a non-polar dielectric surface. No correlation was found between semiconductor grain size and dielectric surface chemistry. The threshold voltage of pentacene devices shifted from −10 V to −25 V with decreasing surface ester content, but remained close to 0 V for DNTT.

  20. Heteroepitaxial VO{sub 2} thin films on GaN: Structure and metal-insulator transition characteristics

    SciTech Connect

    Zhou You; Ramanathan, Shriram

    2012-10-01

    Monolithic integration of correlated oxide and nitride semiconductors may open up new opportunities in solid-state electronics and opto-electronics that combine desirable functional properties of both classes of materials. Here, we report on epitaxial growth and phase transition-related electrical properties of vanadium dioxide (VO{sub 2}) thin films on GaN epitaxial layers on c-sapphire. The epitaxial relation is determined to be (010){sub vo{sub 2}} parallel (0001){sub GaN} parallel (0001){sub A1{sub 2O{sub 3}}} and [100]{sub vo{sub 2}} parallel [1210]{sub GaN} parallel [0110]{sub A1{sub 2O{sub 3}}} from x-ray diffraction. VO{sub 2} heteroepitaxial growth and lattice mismatch are analyzed by comparing the GaN basal plane (0001) with the almost close packed corrugated oxygen plane in vanadium dioxide and an experimental stereographic projection describing the orientation relationship is established. X-ray photoelectron spectroscopy suggests a slightly oxygen rich composition at the surface, while Raman scattering measurements suggests that the quality of GaN layer is not significantly degraded by the high-temperature deposition of VO{sub 2}. Electrical characterization of VO{sub 2} films on GaN indicates that the resistance changes by about four orders of magnitude upon heating, similar to epitaxial VO{sub 2} films grown directly on c-sapphire. It is shown that the metal-insulator transition could also be voltage-triggered at room temperature and the transition threshold voltage scaling variation with temperature is analyzed in the framework of a current-driven Joule heating model. The ability to synthesize high quality correlated oxide films on GaN with sharp phase transition could enable new directions in semiconductor-photonic integrated devices.

  1. Effects of nonequilibrium growth, nonstoichiometry, and film orientation on the metal-to-insulator transition in NdNiO₃ thin films.

    PubMed

    Breckenfeld, Eric; Chen, Zuhuang; Damodaran, Anoop R; Martin, Lane W

    2014-12-24

    Next-generation devices will rely on exotic functional properties not found in traditional systems. One class of materials of particular interest for applications are those possessing metal-to-insulator transitions (MITs). In this work, we probe the relationship between variations in the growth process, subsequent variations in cation stoichiometry, and the MIT in NdNiO3 thin films. Slight variations in the growth conditions, in particular the laser fluence, during pulsed-laser deposition growth of NdNiO3 produces films that are both single-phase and coherently strained to a range of substrates despite possessing as much as 15% Nd-excess. Subsequent study of the temperature-dependence of the electronic transport reveals dramatic changes in both the onset and magnitude of the resistivity change at the MIT with increasing cation nonstoichiometry giving rise to a decrease (and ultimately a suppression) of the transition and the magnitude of the resistivity change. From there, the electronic transport of nearly ideal NdNiO3 thin films are studied as a function of epitaxial strain, thickness, and orientation. Overall, transitioning from tensile to compressive strain results in a systematic reduction of the onset and magnitude of the resistivity change across the MIT, thinner films are found to possess sharper MITs with larger changes in the resistivity at the transition, and (001)-oriented films exhibit sharper and larger MITs as compared to (110)- and (111)-oriented films as a result of highly anisotropic in-plane transport in the latter. PMID:25454898

  2. Thin film hydrogen sensor

    DOEpatents

    Lauf, Robert J.; Hoffheins, Barbara S.; Fleming, Pamela H.

    1994-01-01

    A hydrogen sensor element comprises an essentially inert, electrically-insulating substrate having a thin-film metallization deposited thereon which forms at least two resistors on the substrate. The metallization comprises a layer of Pd or a Pd alloy for sensing hydrogen and an underlying intermediate metal layer for providing enhanced adhesion of the metallization to the substrate. An essentially inert, electrically insulating, hydrogen impermeable passivation layer covers at least one of the resistors, and at least one of the resistors is left uncovered. The difference in electrical resistances of the covered resistor and the uncovered resistor is related to hydrogen concentration in a gas to which the sensor element is exposed.

  3. Advanced thin film thermocouples

    NASA Astrophysics Data System (ADS)

    Kreider, K. G.; Semancik, S.; Olson, C.

    1984-10-01

    The fabrication, materials characterization, and performance of thin film platinum rhodium thermocouples on gas turbine alloys was investigated. The materials chosen for the study were the turbine blade alloy systems MAR M200+Hf with NiCoCrAlY and FeCrAlY coatings, and vane alloy systems MAR M509 with FeCrAlY. Research was focussed on making improvements in the problem areas of coating substrate stability, adhesion, and insulation reliability and durability. Diffusion profiles between the substrate and coating with and without barrier coatings of Al2O3 are reported. The relationships between fabrication parameters of thermal oxidation and sputtering of the insulator and its characterization and performance are described. The best thin film thermocouples were fabricated with the NiCoCrAlY coatings which were thermally oxidized and sputter coated with Al2O3.

  4. Advanced thin film thermocouples

    NASA Technical Reports Server (NTRS)

    Kreider, K. G.; Semancik, S.; Olson, C.

    1984-01-01

    The fabrication, materials characterization, and performance of thin film platinum rhodium thermocouples on gas turbine alloys was investigated. The materials chosen for the study were the turbine blade alloy systems MAR M200+Hf with NiCoCrAlY and FeCrAlY coatings, and vane alloy systems MAR M509 with FeCrAlY. Research was focussed on making improvements in the problem areas of coating substrate stability, adhesion, and insulation reliability and durability. Diffusion profiles between the substrate and coating with and without barrier coatings of Al2O3 are reported. The relationships between fabrication parameters of thermal oxidation and sputtering of the insulator and its characterization and performance are described. The best thin film thermocouples were fabricated with the NiCoCrAlY coatings which were thermally oxidized and sputter coated with Al2O3.

  5. Thin Films

    NASA Astrophysics Data System (ADS)

    Naffouti, Wafa; Nasr, Tarek Ben; Mehdi, Ahmed; Kamoun-Turki, Najoua

    2014-11-01

    Titanium dioxide (TiO2) thin films were synthesized on glass substrates by spray pyrolysis. The effect of solution flow rate on the physical properties of the films was investigated by use of x-ray diffraction (XRD), scanning electron microscopy, atomic force microscopy (AFM), and spectrophotometry techniques. XRD analysis revealed the tetragonal anatase phase of TiO2 with highly preferred (101) orientation. AFM images showed that grain size on top of TiO2 thin films depended on solution flow rate. An indirect band gap energy of 3.46 eV was determined by means of transmission and reflection measurements. The envelope method, based on the optical transmission spectrum, was used to determine film thickness and optical constants, for example real and imaginary parts of the dielectric constant, refractive index, and extinction coefficient. Ultraviolet and visible photoluminescence emission peaks were observed at room temperature. These peaks were attributed to the intrinsic emission and to the surface defect states, respectively.

  6. A 350 mK, 9 T scanning tunneling microscope for the study of superconducting thin films on insulating substrates and single crystals

    SciTech Connect

    Kamlapure, Anand; Saraswat, Garima; Ganguli, Somesh Chandra; Bagwe, Vivas; Raychaudhuri, Pratap; Pai, Subash P.

    2013-12-15

    We report the construction and performance of a low temperature, high field scanning tunneling microscope (STM) operating down to 350 mK and in magnetic fields up to 9 T, with thin film deposition and in situ single crystal cleaving capabilities. The main focus lies on the simple design of STM head and a sample holder design that allows us to get spectroscopic data on superconducting thin films grown in situ on insulating substrates. Other design details on sample transport, sample preparation chamber, and vibration isolation schemes are also described. We demonstrate the capability of our instrument through the atomic resolution imaging and spectroscopy on NbSe{sub 2} single crystal and spectroscopic maps obtained on homogeneously disordered NbN thin film.

  7. Design of a compact waveguide optical isolator based on multimode interferometers using magneto-optical oxide thin films grown on silicon-on-insulator substrates.

    PubMed

    Shui, Keyi; Nie, Lixia; Zhang, Yan; Peng, Bo; Xie, Jianliang; Deng, Longjiang; Bi, Lei

    2016-06-13

    We report the design of a waveguide optical isolator based on multimode interferometer (MMI) structure using silicon on insulator (SOI) and deposited magneto-optical (MO) thin films. The optical isolator is based on a vertical 1 × 2 SOI MMI utilizing the nonreciprocal phase shift (NRPS) difference of different TM modes of the MO garnet thin film/SOI waveguide. By constructing a silicon/MO thin film/silicon structure, we demonstrate that the NRPS of the fundamental and first order TM modes can show opposite signs for certain device dimensions, therefore significantly reduce the device length. For a 310.42 μm long device, 20 dB isolation bandwidth larger than 1.6 nm with total insertion loss of 0.817 dB is achieved at 1550 nm wavelength. The fabrication tolerances and materials losses are also discussed to satisfy the state-of-the-art fabrication technology and material properties. PMID:27410305

  8. Electric breakdown effect in the current-voltage characteristics of amorphous indium oxide thin films near the superconductor-insulator transition

    NASA Astrophysics Data System (ADS)

    Cohen, O.; Ovadia, M.; Shahar, D.

    2011-09-01

    Current-voltage characteristics in the insulator bordering superconductivity in disordered thin films exhibit current jumps of several orders of magnitude due to the development of a thermally bistable electronic state at very low temperatures. In this high-resolution study we find that the jumps can be composed of many (up to 100) smaller jumps that appear to be random. This indicates that inhomogeneity develops near the transition to the insulator and that the current breakdown proceed via percolative paths spanning from one electrode to the other.

  9. Ab-initio study of structural and electronic properties of thin film and bulk forms of Bi2Q3 (Q = Se, Te) as topological insulators

    NASA Astrophysics Data System (ADS)

    Ranjbardizaj, Ahmad; Mizuseki, Hiroshi; Kawazoe, Yoshiyuki

    2013-03-01

    Bi2Q3 (Q =Se, Te) are the best-known bulk thermoelectric materials, which have been demonstrated to be topological insulators (TI). TI's are insulators with conductive surface states consisting of a single Dirac cones. These materials have layered structures consisting of stacked quintuple layers (QL), with relatively weak coupling between the QL's. Therefore, it might be easy to prepare the Bi2Q3 in the form of thin films with particular thicknesses using the available experimental techniques. In this study, the electronic and structural properties of bulk Bi2Se3 are investigated using density functional theory. Our results show that the Bi2Se3 is an indirect semiconductor with energy gap of ~ 0.27 eV. Additionally, the electronic structure dependence of Bi2Se3to the thicknesses of thin films (n-QL's with n =1,2...9) is considered. It is observed that the electronic structure of this kind of thin films depends on the number of QL's. For n-QL's with n larger than three, the thin film has a bulk band gap and has protected conducting states on its surface. Moreover, the effect of number of layers (n) on band-gap energy is studied. Similar calculations and discussions are carried out for Bi2Te3 and the results are compared to the Bi2Se3 case and also the available theoretical and experimental results.

  10. Ultrafast terahertz spectroscopy study of Kondo insulating thin film SmB6: evidence for an emergent surface state

    NASA Astrophysics Data System (ADS)

    Zhang, Jingdi; Yong, Jie; Takeuchi, Ichiro; Greene, Richard; Averitt, Richard

    We utilize terahertz time domain spectroscopy to investigate thin films of the heavy fermion compound SmB6, a prototype Kondo insulator. Temperature dependent terahertz (THz) conductivity measurements reveal a rapid decrease in the Drude weight and carrier scattering rate at ~T* =20 K, well below the hybridization gap onset temperature (100 K). Moreover, a low-temperature conductivity plateau (below 20K) indicates the emergence of a surface state with an effective electron mass of 0.1me. Conductivity dynamics following optical excitation are also measured and interpreted using Rothwarf-Taylor (R-T) phenomenology, yielding a hybridization gap energy of 17 meV. However, R-T modeling of the conductivity dynamics reveals a deviation from the expected thermally excited quasiparticle density at temperatures below 20K, indicative of another channel opening up in the low energy electrodynamics. Taken together, these results suggest the onset of a surface state well below the crossover temperature (100K) after long-range coherence of the f-electron Kondo lattice is established. JZ and RDA acknowledge support from DOE - Basic Energy Sciences under Grant No. DE-FG02-09ER46643, under which the THz measurements and data analysis were performed. JY, IT and RLG acknowledge support from ONR N00014-13-1-0635 and NSF DMR 1410665.

  11. A Roadmap for Controlled Production of Topological Insulator Nanostructures and Thin Films.

    PubMed

    Guo, Yunfan; Liu, Zhongfan; Peng, Hailin

    2015-07-15

    The group V-VI chalcogenide semiconductors (Bi2 Se3 , Bi2 Te3 , and Sb2 Te3 ) have long been known as thermoelectric materials. Recently, they have been once more generating interest because Bi2 Se3 , Bi2 Te3 and Sb2 Te3 have been crowned as 3D topological insulators (TIs), which have insulating bulk gaps and metallic Dirac surface states. One big challenge in the study of TIs is the lack of high-quality materials with few defects and insulating bulk states. To manifest the topological surface states, it is critical to suppress the contribution from the bulk carriers. Controlled production of TI nanostructures that have a large surface-to-volume ratio is an efficient way to reduce the bulk conductance and to significantly enhance the topological surface conduction. In this review article, the recent progress on the preparation of TI nanostructures is highlighted. Basic production methods for TI nanostructures are introduced in detail. Furthermore, several specific production approaches to reduce the residual bulk carriers from defects are summarized. Finally, the progress and the prospects of the production of TI-based heterostructures, which hold promise in both fundamental study and novel applications are discussed. PMID:25727694

  12. Topological insulator Bi{sub 2}Se{sub 3} thin films grown on double-layer graphene by molecular beam epitaxy

    SciTech Connect

    Song Canli; Jiang Yeping; Chang Cuizu; Xue Qikun; Wang Yilin; Zhang Yi; Wang Lili; He Ke; Fang Zhong; Dai Xi; Xie Xincheng; Ma Xucun; Chen Xi; Jia Jinfeng; Wang Yayu; Qi Xiaoliang; Zhang Shoucheng

    2010-10-04

    Atomically flat thin films of topological insulator Bi{sub 2}Se{sub 3} have been grown on double-layer graphene formed on 6H-SiC(0001) substrate by molecular beam epitaxy. By a combined study of reflection high energy electron diffraction and scanning tunneling microscopy, we identified the Se-rich condition and temperature criterion for layer-by-layer growth of epitaxial Bi{sub 2}Se{sub 3} films. The as-grown films without doping exhibit a low defect density of 1.0{+-}0.2x10{sup 11}/cm{sup 2}, and become a bulk insulator at a thickness of ten quintuple layers, as revealed by in situ angle resolved photoemission spectroscopy measurement.

  13. Influence of the surface properties of polymeric insulators on the electrical stability of 6,13-bis(triisopropylsilylethynyl)-pentacene thin-film transistors

    NASA Astrophysics Data System (ADS)

    Baang, Sungkeun; Lee, Hyeonju; Ham, Youngjin; Zhang, Xue; Park, Jaehoon; Lee, Ho Won; Kim, Young Kwan; Piao, Shang Hao; Choi, Hyoung Jin

    2015-12-01

    We investigated the electrical stabilities of 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) thin-film transistors (TFTs) fabricated with cross-linked polymeric insulators, i.e., poly(4-vinylphenol) (PVP) and poly(4-vinylphenol-co-methyl methacrylate) (PVP- co-PMMA). Compared to the cross-linked PVP insulator, the TIPS-pentacene TFTs containing a cross-linked PVP- co-PMMA insulator exhibit less hysteresis upon reversal of the gate-voltage sweep direction and a lower shift in the threshold voltage during consecutive operations, which is ascribed to the relatively hydrophobic surface of the cross-linked PVP- co-PMMA insulator. When these polymer solutions are mixed with yttrium-oxide nanoparticles, the rough surfaces of both nanocomposite insulators lead to larger shifts in the threshold voltage during consecutive operations, but its effect on the hysteretic behavior in the transfer characteristics of the TIPS-pentacene TFTs is negligible. Thus, the influence of the surface properties of the polymeric insulators on the electrical stability of TIPS-pentacene TFTs can be explained through hole-trapping and the delayed-depletion of the holes at the insulator/semiconductor interface.

  14. Metal--Insulator Transition in Bi{sub 2}Sr{sub 2}Cu{sub 1}O{sub 6+d}(Bi-2201) Thin Films

    SciTech Connect

    Pop, Aurel V.

    2009-05-22

    We have studied the influence of disorder induced by oxygen on the normal state resistivity of under doped Bi{sub 2}Sr{sub 2}Cu{sub 1}O{sub 6+d}(Bi-2201) thin films, deposited in situ onto heated SrTiO{sub 3}(100) substrates by using DC magnetron sputtering for an off-stoichiometric target. The compositions and structural characterization for the deposited films were carried by (EDX), (XPS) and X-ray diffraction measurements. The effect of partial oxygen pressure in the sputtering gas on the metal-insulator transition are presented.

  15. Disorder induced superconductor-insulator transition in epitaxial La1.85Sr0.15CuO4 thin films

    NASA Astrophysics Data System (ADS)

    Jang, Han-Byul; Yang, Chan-Ho

    La2-xSrxCuO4is a well-known superconducting system showing various electronic properties as a function of Sr content. Especially, epitaxial thin layers of the compound show enormous increase of superconducting critical temperature (Tc) by a compressive strain. It has been reported that Tc can be controlled by misfit strain, thickness, and oxygen annealing. In this study, we report structural and transport properties of high quality epitaxial La1.85Sr0.15CuO4thin films. According to x-ray diffraction study, c-axis lattice parameter shows no significant change for various film thicknesses and the in-plane lattice parameters of the films are coherently matched with that of substrate. Electronic transport measurements show a clear superconductor-to-insulator transition (SIT), accompanying variation of Tc depending on film thickness. These results are analyzed by using the McMillan equation to find the relation between the Tc and a disorder correlating with film thickness. We have found the disorder exhibits an explicit power-law behavior with respect to film thickness in our La1.85Sr0.15CuO4 thin films.

  16. Use of cermet thin film resistors with nitride passivated metal insulator field effect transistor

    NASA Technical Reports Server (NTRS)

    Brown, G. A.; Harrap, V.

    1971-01-01

    Film deposition of cermet resistors on same chip with metal nitride oxide silicon field effect transistors permits protection of contamination sensitive active devices from contaminants produced in cermet deposition and definition processes. Additional advantages include lower cost, greater reliability, and space savings.

  17. Electric-field-driven Mott metal-insulator transition in correlated thin films: An inhomogeneous dynamical mean-field theory approach

    NASA Astrophysics Data System (ADS)

    Bakalov, P.; Nasr Esfahani, D.; Covaci, L.; Peeters, F. M.; Tempere, J.; Locquet, J.-P.

    2016-04-01

    Simulations are carried out based on the dynamical mean-field theory (DMFT) in order to investigate the properties of correlated thin films for various values of the chemical potential, temperature, interaction strength, and applied transverse electric field. Application of a sufficiently strong field to a thin film at half filling leads to the appearance of conducting regions near the surfaces of the film, whereas in doped slabs the application of a field leads to a conductivity enhancement on one side of the film and a gradual transition to the insulating state on the opposite side. In addition to the inhomogeneous DMFT, a local density approximation (LDA) is considered in which the particle density n , quasiparticle residue Z , and spectral weight at the Fermi level A (ω =0 ) of each layer are approximated by a homogeneous bulk environment. A systematic comparison between the two approaches reveals that the less expensive LDA results are in good agreement with the DMFT approach, except close to the metal-to-insulator transition points and in the layers immediately at the film surfaces. LDA values for n are overall more reliable than those for Z and A (ω =0 ) . The hysteretic behavior (memory effect) characteristic of the bulk doping driven Mott transition persists in the slab.

  18. Stability of low-carrier-density topological-insulator Bi{sub 2}Se{sub 3} thin films and effect of capping layers

    SciTech Connect

    Salehi, Maryam; Brahlek, Matthew; Koirala, Nikesh; Moon, Jisoo; Oh, Seongshik; Wu, Liang; Armitage, N. P.

    2015-09-01

    Although over the past number of years there have been many advances in the materials aspects of topological insulators (TIs), one of the ongoing challenges with these materials is the protection of them against aging. In particular, the recent development of low-carrier-density bulk-insulating Bi{sub 2}Se{sub 3} thin films and their sensitivity to air demands reliable capping layers to stabilize their electronic properties. Here, we study the stability of the low-carrier-density Bi{sub 2}Se{sub 3} thin films in air with and without various capping layers using DC and THz probes. Without any capping layers, the carrier density increases by ∼150% over a week and by ∼280% over 9 months. In situ-deposited Se and ex situ-deposited poly(methyl methacrylate) suppress the aging effect to ∼27% and ∼88%, respectively, over 9 months. The combination of effective capping layers and low-carrier-density TI films will open up new opportunities in topological insulators.

  19. Coulomb drag in topological insulator films

    NASA Astrophysics Data System (ADS)

    Liu, Hong; Liu, Weizhe Edward; Culcer, Dimitrie

    2016-05-01

    We study Coulomb drag between the top and bottom surfaces of topological insulator films. We derive a kinetic equation for the thin-film spin density matrix containing the full spin structure of the two-layer system, and analyze the electron-electron interaction in detail in order to recover all terms responsible for Coulomb drag. Focusing on typical topological insulator systems, with a film thicknesses d up to 6 nm, we obtain numerical and approximate analytical results for the drag resistivity ρD and find that ρD is proportional to T2d-4 na-3/2 np-3/2 at low temperature T and low electron density na,p, with a denoting the active layer and p the passive layer. In addition, we compare ρD with graphene, identifying qualitative and quantitative differences, and we discuss the multi-valley case, ultra thin films and electron-hole layers.

  20. Metal-insulator transition in SrTi{sub 1−x}V{sub x}O{sub 3} thin films

    SciTech Connect

    Gu, Man; Wolf, Stuart A.; Lu, Jiwei

    2013-11-25

    Epitaxial SrTi{sub 1−x}V{sub x}O{sub 3} (0 ≤ x ≤ 1) thin films were grown on (001)-oriented (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (LSAT) substrates using the pulsed electron-beam deposition technique. The transport study revealed a temperature driven metal-insulator transition (MIT) at 95 K for x = 0.67. The films with higher vanadium concentration (x > 0.67) were metallic corresponding to a Fermi liquid system. In the insulating phase (x < 0.67), the resistivity behavior was governed by Mott's variable range hopping mechanism. The possible mechanisms for the induced MIT are discussed, including the effects of electron correlation, lattice distortion, and Anderson localization.

  1. 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.

  2. Nonvolatile memory thin-film transistors using biodegradable chicken albumen gate insulator and oxide semiconductor channel on eco-friendly paper substrate.

    PubMed

    Kim, So-Jung; Jeon, Da-Bin; Park, Jung-Ho; Ryu, Min-Ki; Yang, Jong-Heon; Hwang, Chi-Sun; Kim, Gi-Heon; Yoon, Sung-Min

    2015-03-01

    Nonvolatile memory thin-film transistors (TFTs) fabricated on paper substrates were proposed as one of the eco-friendly electronic devices. The gate stack was composed of chicken albumen gate insulator and In-Ga-Zn-O semiconducting channel layers. All the fabrication processes were performed below 120 °C. To improve the process compatibility of the synthethic paper substrate, an Al2O3 thin film was introduced as adhesion and barrier layers by atomic layer deposition. The dielectric properties of biomaterial albumen gate insulator were also enhanced by the preparation of Al2O3 capping layer. The nonvolatile bistabilities were realized by the switching phenomena of residual polarization within the albumen thin film. The fabricated device exhibited a counterclockwise hysteresis with a memory window of 11.8 V, high on/off ratio of approximately 1.1 × 10(6), and high saturation mobility (μsat) of 11.5 cm(2)/(V s). Furthermore, these device characteristics were not markedly degraded even after the delamination and under the bending situration. When the curvature radius was set as 5.3 cm, the ION/IOFF ratio and μsat were obtained to be 5.9 × 10(6) and 7.9 cm(2)/(V s), respectively. PMID:25679117

  3. Collapse of the low temperature insulating state in Cr-doped V{sub 2}O{sub 3} thin films

    SciTech Connect

    Homm, P. Dillemans, L.; Menghini, M.; Van Bilzen, B.; Bakalov, P.; Su, C.-Y.; Lieten, R.; Houssa, M.; Locquet, J.-P.; Nasr Esfahani, D.; Covaci, L.; Peeters, F. M.; Seo, J. W.

    2015-09-14

    We have grown epitaxial Cr-doped V{sub 2}O{sub 3} thin films with Cr concentrations between 0% and 20% on (0001)-Al{sub 2}O{sub 3} by oxygen-assisted molecular beam epitaxy. For the highly doped samples (>3%), a regular and monotonous increase of the resistance with decreasing temperature is measured. Strikingly, in the low doping samples (between 1% and 3%), a collapse of the insulating state is observed with a reduction of the low temperature resistivity by up to 5 orders of magnitude. A vacuum annealing at high temperature of the films recovers the low temperature insulating state for doping levels below 3% and increases the room temperature resistivity towards the values of Cr-doped V{sub 2}O{sub 3} single crystals. It is well-know that oxygen excess stabilizes a metallic state in V{sub 2}O{sub 3} single crystals. Hence, we propose that Cr doping promotes oxygen excess in our films during deposition, leading to the collapse of the low temperature insulating state at low Cr concentrations. These results suggest that slightly Cr-doped V{sub 2}O{sub 3} films can be interesting candidates for field effect devices.

  4. Structural properties of Bi2Te3 topological insulator thin films grown by molecular beam epitaxy on (111) BaF2 substrates

    NASA Astrophysics Data System (ADS)

    Fornari, Celso I.; Rappl, Paulo H. O.; Morelhão, Sérgio L.; Abramof, Eduardo

    2016-04-01

    Structural properties of topological insulator bismuth telluride films grown epitaxially on (111) BaF2 with a fixed Bi2Te3 beam flux were systematically investigated as a function of substrate temperature and additional Te flux. A layer-by-layer growth mode is observed since the early stages of epitaxy and remains throughout the whole deposition. Composition of the epitaxial films produced here stays between Bi2Te3 and Bi4Te5, as determined from the comparison of the measured x-ray diffraction curves with calculations. The substrate temperature region, where the growth rate remains constant, is found to be the most appropriate to obtain ordered Bi2Te3 films. Line width of the L = 18 Bi2Te3 diffraction peaks as low as 140 arcsec was obtained, indicating high crystalline quality. Twinning domains density rises with increasing growth temperature and reducing Te extra flux. X-ray reflectivity curves of pure Bi2Te3 films with thickness from 165 to 8 nm exhibited well defined interference fringes, evidencing homogeneous layers with smooth surface. Our results demonstrate that Bi2Te3 films with very well controlled structural parameters can be obtained. High structural quality Bi2Te3 films as thin as only eight quintuple layers grown here are promising candidates for intrinsic topological insulator.

  5. Magnetic thin-film insulator with ultra-low spin wave damping for coherent nanomagnonics.

    PubMed

    Yu, Haiming; Kelly, O d'Allivy; Cros, V; Bernard, R; Bortolotti, P; Anane, A; Brandl, F; Huber, R; Stasinopoulos, I; Grundler, D

    2014-01-01

    Wave control in the solid state has opened new avenues in modern information technology. Surface-acoustic-wave-based devices are found as mass market products in 100 millions of cellular phones. Spin waves (magnons) would offer a boost in today's data handling and security implementations, i.e., image processing and speech recognition. However, nanomagnonic devices realized so far suffer from the relatively short damping length in the metallic ferromagnets amounting to a few 10 micrometers typically. Here we demonstrate that nm-thick YIG films overcome the damping chasm. Using a conventional coplanar waveguide we excite a large series of short-wavelength spin waves (SWs). From the data we estimate a macroscopic of damping length of about 600 micrometers. The intrinsic damping parameter suggests even a record value about 1 mm allowing for magnonics-based nanotechnology with ultra-low damping. In addition, SWs at large wave vector are found to exhibit the non-reciprocal properties relevant for new concepts in nanoscale SW-based logics. We expect our results to provide the basis for coherent data processing with SWs at GHz rates and in large arrays of cellular magnetic arrays, thereby boosting the envisioned image processing and speech recognition. PMID:25355200

  6. Magnetic thin-film insulator with ultra-low spin wave damping for coherent nanomagnonics

    PubMed Central

    Yu, Haiming; Kelly, O. d'Allivy; Cros, V.; Bernard, R.; Bortolotti, P.; Anane, A.; Brandl, F.; Huber, R.; Stasinopoulos, I.; Grundler, D.

    2014-01-01

    Wave control in the solid state has opened new avenues in modern information technology. Surface-acoustic-wave-based devices are found as mass market products in 100 millions of cellular phones. Spin waves (magnons) would offer a boost in today's data handling and security implementations, i.e., image processing and speech recognition. However, nanomagnonic devices realized so far suffer from the relatively short damping length in the metallic ferromagnets amounting to a few 10 micrometers typically. Here we demonstrate that nm-thick YIG films overcome the damping chasm. Using a conventional coplanar waveguide we excite a large series of short-wavelength spin waves (SWs). From the data we estimate a macroscopic of damping length of about 600 micrometers. The intrinsic damping parameter suggests even a record value about 1 mm allowing for magnonics-based nanotechnology with ultra-low damping. In addition, SWs at large wave vector are found to exhibit the non-reciprocal properties relevant for new concepts in nanoscale SW-based logics. We expect our results to provide the basis for coherent data processing with SWs at GHz rates and in large arrays of cellular magnetic arrays, thereby boosting the envisioned image processing and speech recognition. PMID:25355200

  7. Magnetic thin-film insulator with ultra-low spin wave damping for coherent nanomagnonics

    NASA Astrophysics Data System (ADS)

    Yu, Haiming; Kelly, O. D'allivy; Cros, V.; Bernard, R.; Bortolotti, P.; Anane, A.; Brandl, F.; Huber, R.; Stasinopoulos, I.; Grundler, D.

    2014-10-01

    Wave control in the solid state has opened new avenues in modern information technology. Surface-acoustic-wave-based devices are found as mass market products in 100 millions of cellular phones. Spin waves (magnons) would offer a boost in today's data handling and security implementations, i.e., image processing and speech recognition. However, nanomagnonic devices realized so far suffer from the relatively short damping length in the metallic ferromagnets amounting to a few 10 micrometers typically. Here we demonstrate that nm-thick YIG films overcome the damping chasm. Using a conventional coplanar waveguide we excite a large series of short-wavelength spin waves (SWs). From the data we estimate a macroscopic of damping length of about 600 micrometers. The intrinsic damping parameter suggests even a record value about 1 mm allowing for magnonics-based nanotechnology with ultra-low damping. In addition, SWs at large wave vector are found to exhibit the non-reciprocal properties relevant for new concepts in nanoscale SW-based logics. We expect our results to provide the basis for coherent data processing with SWs at GHz rates and in large arrays of cellular magnetic arrays, thereby boosting the envisioned image processing and speech recognition.

  8. Ferromagnetism of magnetically doped topological insulators in Cr{sub x}Bi{sub 2−x}Te{sub 3} thin films

    SciTech Connect

    Ni, Y.; Zhang, Z. Hadimani, R. L.; Tuttle, G.; Jiles, D. C.; Nlebedim, I. C.

    2015-05-07

    We investigated the effect of magnetic doping on magnetic and transport properties of Bi{sub 2}Te{sub 3} thin films. Cr{sub x}Bi{sub 2−x}Te{sub 3} thin films with x = 0.03, 0.14, and 0.29 were grown epitaxially on mica substrate with low surface roughness (∼0.4 nm). It is found that Cr is an electron acceptor in Bi{sub 2}Te{sub 3} and increases the magnetization of Cr{sub x}Bi{sub 2−x}Te{sub 3}. When x = 0.14 and 0.29, ferromagnetism appears in Cr{sub x}Bi{sub 2−x}Te{sub 3} thin films, where anomalous Hall effect and weak localization of magnetoconductance were observed. The Curie temperature, coercivity, and remnant Hall resistance of thin films increase with increasing Cr concentration. The Arrott-Noakes plot demonstrates that the critical mechanism of the ferromagnetism can be described better with 3D-Heisenberg model than with mean field model. Our work may benefit for the practical applications of magnetic topological insulators in spintronics and magnetoelectric devices.

  9. Low temperature plasma enhanced chemical vapor deposition of thin films combining mechanical stiffness, electrical insulation, and homogeneity in microcavities

    SciTech Connect

    Peter, S.; Guenther, M.; Hauschild, D.; Richter, F.

    2010-08-15

    The deposition of hydrogenated amorphous carbon (a-C:H) as well as hydrogenated amorphous silicon carbonitride (SiCN:H) films was investigated in view of a simultaneous realization of a minimum Young's modulus (>70 GPa), a high electrical insulation ({>=}1 MV/cm), a low permittivity and the uniform coverage of microcavities with submillimeter dimensions. For the a-C:H deposition the precursors methane (CH{sub 4}) and acetylene (C{sub 2}H{sub 2}) were used, while SiCN:H films were deposited from mixtures of trimethylsilane [SiH(CH{sub 3}){sub 3}] with nitrogen and argon. To realize the deposition of micrometer thick films with the aforementioned complex requirements at substrate temperatures {<=}200 deg. C, several plasma enhanced chemical vapor deposition methods were investigated: the capacitively coupled rf discharge and the microwave electron cyclotron resonance (ECR) plasma, combined with two types of pulsed substrate bias. SiCN:H films deposited at about 1 Pa from ECR plasmas with pulsed high-voltage bias best met the requirements. Pulsed biasing with pulse periods of about 1 {mu}s and amplitudes of about -2 kV was found to be most advantageous for the conformal low temperature coating of the microtrenches, thereby ensuring the required mechanical and insulating film properties.

  10. Electrical Conduction Mechanisms in Metal-Insulator-Metal (MIM) Structure with TiO x N y Thin Films Deposited with Different O/N Ratios

    NASA Astrophysics Data System (ADS)

    Libardi, Juliano; Grigorov, Korneli G.; Moraes, Rodrigo S.; Guerino, Marciel; Da Silva Sobrinho, Argemiro S.; Massi, Marcos

    2015-01-01

    In this work, the current-voltage characteristics of titanium oxynitride thin films were measured and the charge carrier transport mechanisms established as a function of film composition. The films were deposited by magnetron sputtering, where the oxygen/nitrogen ratio was varied via a pulsing technique to enable the achievement of desired concentrations. Thus, the obtained films showed metallic titanium nitrate (TiN) or semiconductor titanium dioxide (TiO2) character and were used to fabricate metal-insulator-metal structures. An ohmic conduction mechanism was identified in the films with higher nitrogen incorporation or presenting TiN-rich phase. Decrease in the nitrogen content resulted in films with TiO2-rich phase. In this case, Poole-Frenkel and space-charge-limited current conduction mechanisms were observed. The dielectric constants were calculated from the high-frequency capacitance-voltage dependences, with a reduction from 10 to 3 being observed due to the stoichiometric changes and probable incorporation of defects into the film structure. Finally, the film composition and structural characteristics of the films were revealed by Rutherford backscattering and x-ray diffraction techniques, respectively.

  11. Optimization of a Solution-Processed SiO2 Gate Insulator by Plasma Treatment for Zinc Oxide Thin Film Transistors.

    PubMed

    Jeong, Yesul; Pearson, Christopher; Kim, Hyun-Gwan; Park, Man-Young; Kim, Hongdoo; Do, Lee-Mi; Petty, Michael C

    2016-01-27

    We report on the optimization of the plasma treatment conditions for a solution-processed silicon dioxide gate insulator for application in zinc oxide thin film transistors (TFTs). The SiO2 layer was formed by spin coating a perhydropolysilazane (PHPS) precursor. This thin film was subsequently thermally annealed, followed by exposure to an oxygen plasma, to form an insulating (leakage current density of ∼10(-7) A/cm(2)) SiO2 layer. Optimized ZnO TFTs (40 W plasma treatment of the gate insulator for 10 s) possessed a carrier mobility of 3.2 cm(2)/(V s), an on/off ratio of ∼10(7), a threshold voltage of -1.3 V, and a subthreshold swing of 0.2 V/decade. In addition, long-term exposure (150 min) of the pre-annealed PHPS to the oxygen plasma enabled the maximum processing temperature to be reduced from 180 to 150 °C. The resulting ZnO TFT exhibited a carrier mobility of 1.3 cm(2)/(V s) and on/off ratio of ∼10(7). PMID:26704352

  12. Thermoelectric properties of topological insulator Bi2Te3, Sb2Te3, and Bi2Se3 thin film quantum wells

    NASA Astrophysics Data System (ADS)

    Osterhage, Hermann; Gooth, Johannes; Hamdou, Bacel; Gwozdz, Paul; Zierold, Robert; Nielsch, Kornelius

    2014-09-01

    The thermoelectric (TE) figure of merit ZT of topological insulator Bi2Te3, Sb2Te3, and Bi2Se3 thin film quantum wells is calculated for thicknesses below 10 nm, for which hybridization of the surface states as well as quantum confinement in the bulk are individually predicted to enhance ZT. Here, the question is addressed what ZT can be expected from coexisting surface and bulk states in such quantum wells. It is demonstrated that the parallel contributing bulk and surface channels tend to cancel each other out. This is because the surface-to-volume ratios of the thin films prevent the domination of transport through a single channel and because the individual bulk and surface ZTs are optimized at different Fermi levels.

  13. Metal-insulator transition in low dimensional La{sub 0.75}Sr{sub 0.25}VO{sub 3} thin films

    SciTech Connect

    Dao, Tran M.; Mondal, Partha S.; Takamura, Y.; Arenholz, E.; Lee, Jaichan

    2011-06-15

    We report on the metal-insulator transition that occurs as a function of film thickness in ultrathin La{sub 0.75}Sr{sub 0.25}VO{sub 3} films. The metal-insulator transition displays a critical thickness of 5 unit cell. Above the critical thickness, metallic films exhibit a temperature driven metal-insulator transition with weak localization behavior. With decreasing film thickness, oxygen octahedron rotation in the films increases, causing enhanced electron-electron correlation. The electronelectron correlations in ultrathin films induce the transition from metal to insulator in addition to Anderson localization.

  14. Acoustic phonon dynamics in thin-films of the topological insulator Bi{sub 2}Se{sub 3}

    SciTech Connect

    Glinka, Yuri D.; Babakiray, Sercan; Johnson, Trent A.; Holcomb, Mikel B.; Lederman, David

    2015-04-28

    Transient reflectivity traces measured for nanometer-sized films (6–40 nm) of the topological insulator Bi{sub 2}Se{sub 3} revealed GHz-range oscillations driven within the relaxation of hot carriers photoexcited with ultrashort (∼100 fs) laser pulses of 1.51 eV photon energy. These oscillations have been suggested to result from acoustic phonon dynamics, including coherent longitudinal acoustic phonons in the form of standing acoustic waves. An increase of oscillation frequency from ∼35 to ∼70 GHz with decreasing film thickness from 40 to 15 nm was attributed to the interplay between two different regimes employing traveling-acoustic-waves for films thicker than 40 nm and the film bulk acoustic wave resonator (FBAWR) modes for films thinner than 40 nm. The amplitude of oscillations decays rapidly for films below 15 nm thick when the indirect intersurface coupling in Bi{sub 2}Se{sub 3} films switches the FBAWR regime to that of the Lamb wave excitation. The frequency range of coherent longitudinal acoustic phonons is in good agreement with elastic properties of Bi{sub 2}Se{sub 3}.

  15. Enhanced ferromagnetic and metal insulator transition in Sm0.55Sr0.45MnO3 thin films: Role of oxygen vacancy induced quenched disorder

    NASA Astrophysics Data System (ADS)

    Srivastava, M. K.; Siwach, P. K.; Kaur, A.; Singh, H. K.

    2010-11-01

    Effect of quenched disorder (QD) caused by oxygen vacancy (OV) and substrate induced inhomogeneous compressive strain, on the magnetic and transport properties of oriented polycrystalline Sm0.55Sr0.45MnO3 thin films is investigated. QD is related intimately to the ordering/disordering of the OVs and controls the paramagnetic-ferromagnetic/insulator-metal transition. OV ordered films show enhanced TC/TIM˜165 K, which is depressed by oxygen annealing. OV disordering realized by quenching reduces TC/TIM. The first order IM transition observed in SSMO single crystals is transformed into nonhysteretic and continuous one in the OV ordered films. QD appears to be diluted by OV disorder/annihilation and results in stronger carrier localization.

  16. Metal-insulator transition characteristics of vanadium dioxide thin films synthesized by ultrasonic nebulized spray pyrolysis of an aqueous combustion mixture

    NASA Astrophysics Data System (ADS)

    Bharathi, R.; Naorem, Rameshwari; Umarji, A. M.

    2015-08-01

    We report the synthesis of high quality vanadium dioxide (VO2) thin films by a novel spray pyrolysis technique, namely ultrasonic nebulized spray pyrolysis of aqueous combustion mixture (UNSPACM). This simple and cost effective two step process involves synthesis of a V2O5 film on an LaAlO3 substrate followed by a controlled reduction to form single phase VO2. The formation of M1 phase (P21/c) is confirmed by Raman spectroscopic studies. A thermally activated metal-insulator transition (MIT) was observed at 61 ^\\circ C, where the resistivity changes by four orders of magnitude. Activation energies for the low conduction phase and the high conduction phase were obtained from temperature variable resistance measurements. The infrared spectra also show a dramatic change in reflectance from 13% to over 90% in the wavelength range of 7-15 μ m. This indicates the suitability of the films for optical switching applications at infrared frequencies.

  17. Domain formation due to surface steps in topological insulator Bi{sub 2}Te{sub 3} thin films grown on Si (111) by molecular beam epitaxy

    SciTech Connect

    Borisova, S.; Kampmeier, J.; Mussler, G.; Grützmacher, D.; Luysberg, M.

    2013-08-19

    The atomic structure of topological insulators Bi{sub 2}Te{sub 3} thin films on Si (111) substrates grown in van der Waals mode by molecular beam epitaxy has been investigated by in situ scanning tunneling microscopy and scanning transmission electron microscopy. Besides single and multiple quintuple layer (QL) steps, which are typical for the step-flow mode of growth, a number of 0.4 QL steps is observed. We determine that these steps originate from single steps at the substrate surface causing domain boundaries in the Bi{sub 2}Te{sub 3} film. Due to the peculiar structure of these domain boundaries the domains are stable and penetrate throughout the entire film.

  18. Low-temperature (180 °C) formation of large-grained Ge (111) thin film on insulator using accelerated metal-induced crystallization

    SciTech Connect

    Toko, K. Numata, R.; Oya, N.; Suemasu, T.; Fukata, N.; Usami, N.

    2014-01-13

    The Al-induced crystallization (AIC) yields a large-grained (111)-oriented Ge thin film on an insulator at temperatures as low as 180 °C. We accelerated the AIC of an amorphous Ge layer (50-nm thickness) by initially doping Ge in Al and by facilitating Ge diffusion into Al. The electron backscatter diffraction measurement demonstrated the simultaneous achievement of large grains over 10 μm and a high (111) orientation fraction of 90% in the polycrystalline Ge layer formed at 180 °C. This result opens up the possibility for developing Ge-based electronic and optical devices fabricated on inexpensive flexible substrates.

  19. Time-resolved terahertz dynamics in thin films of the topological insulator Bi{sub 2}Se{sub 3}

    SciTech Connect

    Valdés Aguilar, R.; Qi, J.; Brahlek, M.; Bansal, N.; Oh, S.; Azad, A.; Bowlan, J.; Taylor, A. J.; Prasankumar, R. P.; Yarotski, D. A.

    2015-01-05

    We use optical pump–THz probe spectroscopy at low temperatures to study the hot carrier response in thin Bi{sub 2}Se{sub 3} films of several thicknesses, allowing us to separate the bulk from the surface transient response. We find that for thinner films the photoexcitation changes the transport scattering rate and reduces the THz conductivity, which relaxes within 10 picoseconds (ps). For thicker films, the conductivity increases upon photoexcitation and scales with increasing both the film thickness and the optical fluence, with a decay time of approximately 5 ps as well as a much higher scattering rate. These different dynamics are attributed to the surface and bulk electrons, respectively, and demonstrate that long-lived mobile surface photo-carriers can be accessed independently below certain film thicknesses for possible optoelectronic applications.

  20. Magnetotransport phenomena in Bi{sub 2}Se{sub 3} thin film topological insulators grown by hybrid physical chemical vapor deposition

    SciTech Connect

    Kumar, Raj; Hunte, Frank; Brom, Joseph E.; Redwing, Joan M.

    2015-02-14

    Intrinsic defects in Bi{sub 2}Se{sub 3} topological insulators tend to produce a high carrier concentration and current leakage through the bulk material. Bi{sub 2}Se{sub 3} thin films were grown by hybrid physical chemical vapor deposition on (0001) Al{sub 2}O{sub 3} substrates with high Se vapor pressure to reduce the occurrence of Se vacancies as the main type of defect. Consequently, the carrier concentration was reduced to ∼5.75 × 10{sup 18} cm{sup −3} comparable to reported carrier concentration in Bi{sub 2}Se{sub 3} thin films. Magnetotransport measurements were performed on the films and the data were analyzed for weak anti-localization using the Hikami-Larkin-Nagaoka model. The estimated α and l{sub ϕ} values showed good agreement with the symplectic case of 2-D transport of topological surface states in the quantum diffusion regime. The temperature and angular dependence of magnetoresistance indicate a large contribution of the 2-D surface carriers to overall transport properties of Bi{sub 2}Se{sub 3} thin film.

  1. Enhanced electrical properties of pentacene-based organic thin-film transistors by modifying the gate insulator surface

    NASA Astrophysics Data System (ADS)

    Tang, J. X.; Lee, C. S.; Chan, M. Y.; Lee, S. T.

    2008-09-01

    A reliable surface treatment for the pentacene/gate dielectric interface was developed to enhance the electrical transport properties of organic thin-film transistors (OTFTs). Plasma-polymerized fluorocarbon (CFx) film was deposited onto the SiO 2 gate dielectric prior to pentacene deposition, resulting in a dramatic increase of the field-effect mobility from 0.015 cm 2/(V s) to 0.22 cm 2/(V s), and a threshold voltage reduction from -14.0 V to -9.9 V. The observed carrier mobility increase by a factor of 10 in the resulting OTFTs is associated with various growth behaviors of polycrystalline pentacene thin films on different substrates, where a pronounced morphological change occurs in the first few molecular layers but the similar morphologies in the upper layers. The accompanying threshold voltage variation suggests that hole accumulation in the conduction channel-induced weak charge transfer between pentacene and CFx.

  2. Electrical properties of the Sm2Ti2O7 thin films for metal-insulator-metal capacitor applications

    NASA Astrophysics Data System (ADS)

    Jeong, Y. H.; Kim, J. C.; Lim, J. B.; Hong, K. P.; Nahm, S.; Sun, H. J.; Ghong, T. H.; Kim, Y. D.; Lee, H. J.

    2007-04-01

    A homogeneous crystalline Sm2Ti2O7 (ST) phase was formed in films grown at temperatures ranging between 100 and 200 °C and subsequently annealed at 900 °C. The ST film had a large dielectric constant of 58, which is similar to that of ST ceramics. The leakage current density of the ST film was low and the Poole-Frenkel emission was suggested as being the leakage current mechanism. The ST film had a negative quadratic voltage coefficient of capacitance (VCC), possibly due to the dipolar relaxation. The 100-nm-thick ST film had a high capacitance density of 5.2 fF/μm2 with a low leakage current density of 1.34 nA/cm2 at 2 V. Its quadratic and linear VCCs were -99.5 ppm/V2 and 11 ppm/V, respectively, with a low temperature coefficient of capacitance of 135 ppm/°C at 100 kHz. These results confirmed the potential for the ST film to be used as a high performance metal-insulator-metal capacitor.

  3. Finite-size driven topological and metal-insulator transition in (Bi1-xInx)2 Se3thin films

    NASA Astrophysics Data System (ADS)

    Salehi, Maryam; Shapourian, Hassan; Koirala, Nikesh; Brahlek, Matthew; Moon, Jisoo; Oh, Seongshik

    In a topological insulator (TI), if one of its heavy elements is replaced by a light one, the spin-orbit coupling (SOC) strength decreases and eventually the TI transforms into a normal insulator beyond a critical level of substitution.This is the standard description of the topological phase transition (TPT). However, this notion of TPT, driven solely by the SOC (or something equivalent), is not complete for finite size samples considering that the thickness of the topological surface states diverges at the critical point. Here, on specially-engineered (BixIn1-x)2 Se3 thin films, using systematic transport measurments we show that not only the SOC but also the finite sample size can induce TPT. This study sheds light on the role of spatial confinement as an extra tuning parameter controlling the topological critical point.

  4. Effect of Mn doping on ultrafast carrier dynamics in thin films of the topological insulator Bi2Se3.

    PubMed

    Glinka, Yuri D; Babakiray, Sercan; Holcomb, Mikel B; Lederman, David

    2016-04-27

    Transient reflectivity (TR) measured at laser photon energy 1.51 eV from the indirectly intersurface-coupled topological insulator Bi2-x Mn x Se3 films (12 nm thick) revealed a strong dependence of the rise-time and initial decay-time constants on photoexcited carrier density and Mn content. In undoped samples (x  =  0), these time constants are exclusively governed by electron-electron and electron-phonon scattering, respectively, whereas in films with x  =  0.013-0.27 ultrafast carrier dynamics are completely controlled by photoexcited electron trapping by ionized Mn(2+) acceptors and their dimers. The shortest decay-time (~0.75 ps) measured for the film with x  =  0.27 suggests a great potential of Mn-doped Bi2Se3 films for applications in high-speed optoelectronic devices. Using Raman spectroscopy exploiting similar laser photon energy (1.58 eV), we demonstrate that due to indirect intersurface coupling in the films, the photoexcited electron trapping in the bulk enhances the electron-phonon interaction strength in Dirac surface states. PMID:27001950

  5. Effects of oxygen pressure in preparation of insulating Sr 2AlTaO 6 thin films by MOCVD

    NASA Astrophysics Data System (ADS)

    Takahashi, Yoshihiro; Nakajima, Yuuichi; Morishita, Tadataka; Tanabe, Keiichi

    2002-10-01

    Approximately 300-nm-thick insulating Sr 2AlTaO 6 (SAT) films were prepared on 10-μm-thick YBa 2Cu 3O 7- δ (YBCO) films by metalorganic chemical vapor deposition (MOCVD) in the range of oxygen partial pressure from 13 Pa (0.1 Torr) to 667 Pa (5 Torr) for total deposition pressure of 13 hPa (10 Torr). Stoichiometric SAT films with good crystallinity and square-like grains originating from the cubic structure of SAT were obtained for all the oxygen partial pressure conditions. However, extraordinary areas were partially observed on the sample prepared in the low oxygen partial pressure below 67 Pa (0.5 Torr), which are supposed to be caused by unstableness of YBCO surface. Under the highest oxygen partial pressure condition of 667 Pa, the lower tetragonal YBCO film exhibited a Tc of 80 K, indicating a possibility of in situ oxygenation during cooling. It was also confirmed that the SAT film fabricated under this condition has good dielectric properties such as the dielectric constant of approximately 24 and the conductance below 10 -8 S.

  6. Effect of Mn doping on ultrafast carrier dynamics in thin films of the topological insulator Bi2Se3

    NASA Astrophysics Data System (ADS)

    Glinka, Yuri D.; Babakiray, Sercan; Holcomb, Mikel B.; Lederman, David

    2016-04-01

    Transient reflectivity (TR) measured at laser photon energy 1.51 eV from the indirectly intersurface-coupled topological insulator Bi2-x Mn x Se3 films (12 nm thick) revealed a strong dependence of the rise-time and initial decay-time constants on photoexcited carrier density and Mn content. In undoped samples (x  =  0), these time constants are exclusively governed by electron-electron and electron-phonon scattering, respectively, whereas in films with x  =  0.013-0.27 ultrafast carrier dynamics are completely controlled by photoexcited electron trapping by ionized Mn2+ acceptors and their dimers. The shortest decay-time (~0.75 ps) measured for the film with x  =  0.27 suggests a great potential of Mn-doped Bi2Se3 films for applications in high-speed optoelectronic devices. Using Raman spectroscopy exploiting similar laser photon energy (1.58 eV), we demonstrate that due to indirect intersurface coupling in the films, the photoexcited electron trapping in the bulk enhances the electron-phonon interaction strength in Dirac surface states.

  7. Improvement in performance of solution-processed indium-zinc-tin oxide thin-film transistors by UV/O3 treatment on zirconium oxide gate insulator

    NASA Astrophysics Data System (ADS)

    Naik, Bukke Ravindra; Avis, Christophe; Delwar Hossain Chowdhury, Md; Kim, Taehun; Lin, Tengda; Jang, Jin

    2016-03-01

    We studied solution-processed amorphous indium-zinc-tin oxide (a-IZTO) thin-film transistors (TFTs) with spin-coated zirconium oxide (ZrOx) as the gate insulator. The ZrOx gate insulator was used without and with UV/O3 treatment. The TFTs with an untreated ZrOx gate dielectric showed a saturation mobility (μsat) of 0.91 ± 0.29 cm2 V-1 s-1, a threshold voltage (Vth) of 0.28 ± 0.36 V, a subthreshold swing (SS) of 199 ± 37.17 mV/dec, and a current ratio (ION/IOFF) of ˜107. The TFTs with a UV/O3-treated ZrOx gate insulator exhibited μsat of 2.65 ± 0.43 cm2 V-1 s-1, Vth of 0.44 ± 0.35 V, SS of 133 ± 24.81 mV/dec, and ION/IOFF of ˜108. Hysteresis was 0.32 V in the untreated TFTs and was eliminated by UV/O3 treatment. Also, the leakage current decreased significantly when the IZTO TFT was coated onto a UV/O3-treated ZrOx gate insulator.

  8. Damping of confined modes in a ferromagnetic thin insulating film: angular momentum transfer across a nanoscale field-defined interface.

    PubMed

    Adur, Rohan; Du, Chunhui; Wang, Hailong; Manuilov, Sergei A; Bhallamudi, Vidya P; Zhang, Chi; Pelekhov, Denis V; Yang, Fengyuan; Hammel, P Chris

    2014-10-24

    We observe a dependence of the damping of a confined mode of precessing ferromagnetic magnetization on the size of the mode. The micron-scale mode is created within an extended, unpatterned yttrium iron garnet film by means of the intense local dipolar field of a micromagnetic tip. We find that the damping of the confined mode scales like the surface-to-volume ratio of the mode, indicating an interfacial damping effect (similar to spin pumping) due to the transfer of angular momentum from the confined mode to the spin sink of ferromagnetic material in the surrounding film. Though unexpected for insulating systems, the measured intralayer spin-mixing conductance g_↑↓=5.3×10(19)  m(-2) demonstrates efficient intralayer angular momentum transfer. PMID:25379927

  9. In situ spectroscopy of intrinsic Bi2Te3 topological insulator thin films and impact of extrinsic defects

    NASA Astrophysics Data System (ADS)

    Ngabonziza, P.; Heimbuch, R.; de Jong, N.; Klaassen, R. A.; Stehno, M. P.; Snelder, M.; Solmaz, A.; Ramankutty, S. V.; Frantzeskakis, E.; van Heumen, E.; Koster, G.; Golden, M. S.; Zandvliet, H. J. W.; Brinkman, A.

    2015-07-01

    Combined in situ x-ray photoemission spectroscopy, scanning tunneling spectroscopy, and angle resolved photoemission spectroscopy of molecular beam epitaxy grown Bi2Te3 on lattice mismatched substrates reveal high quality stoichiometric thin films with topological surface states without a contribution from the bulk bands at the Fermi energy. The absence of bulk states at the Fermi energy is achieved without counterdoping. We observe that the surface morphology and electronic band structure of Bi2Te3 are not affected by in vacuo storage and exposure to oxygen, whereas major changes are observed when exposed to ambient conditions. These films help define a pathway towards intrinsic topological devices.

  10. 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.

  11. Predicted Growth of Two-Dimensional Topological Insulator Thin Films of III-V Compounds on Si(111) Substrate.

    PubMed

    Yao, Liang-Zi; Crisostomo, Christian P; Yeh, Chun-Chen; Lai, Shu-Ming; Huang, Zhi-Quan; Hsu, Chia-Hsiu; Chuang, Feng-Chuan; Lin, Hsin; Bansil, Arun

    2015-01-01

    We have carried out systematic first-principles electronic structure computations of growth of ultrathin films of compounds of group III (B, Al, In, Ga, and Tl) with group V (N, P, As, Sb, and Bi) elements on Si(111) substrate, including effects of hydrogenation. Two bilayers (BLs) of AlBi, InBi, GaBi, TlAs, and TlSb are found to support a topological phase over a wide range of strains, in addition to BBi, TlN, and TlBi which can be driven into the nontrivial phase via strain. A large band gap of 134 meV is identified in hydrogenated 2 BL film of InBi. One and two BL films of GaBi and 2 BL films of InBi and TlAs on Si(111) surface possess nontrivial phases with a band gap as large as 121 meV in the case of 2 BL film of GaBi. Persistence of the nontrivial phase upon hydrogenations in the III-V thin films suggests that these films are suitable for growing on various substrates. PMID:26537227

  12. Predicted Growth of Two-Dimensional Topological Insulator Thin Films of III-V Compounds on Si(111) Substrate

    NASA Astrophysics Data System (ADS)

    Yao, Liang-Zi; Crisostomo, Christian P.; Yeh, Chun-Chen; Lai, Shu-Ming; Huang, Zhi-Quan; Hsu, Chia-Hsiu; Chuang, Feng-Chuan; Lin, Hsin; Bansil, Arun

    2015-11-01

    We have carried out systematic first-principles electronic structure computations of growth of ultrathin films of compounds of group III (B, Al, In, Ga, and Tl) with group V (N, P, As, Sb, and Bi) elements on Si(111) substrate, including effects of hydrogenation. Two bilayers (BLs) of AlBi, InBi, GaBi, TlAs, and TlSb are found to support a topological phase over a wide range of strains, in addition to BBi, TlN, and TlBi which can be driven into the nontrivial phase via strain. A large band gap of 134 meV is identified in hydrogenated 2 BL film of InBi. One and two BL films of GaBi and 2 BL films of InBi and TlAs on Si(111) surface possess nontrivial phases with a band gap as large as 121 meV in the case of 2 BL film of GaBi. Persistence of the nontrivial phase upon hydrogenations in the III-V thin films suggests that these films are suitable for growing on various substrates.

  13. Predicted Growth of Two-Dimensional Topological Insulator Thin Films of III-V Compounds on Si(111) Substrate

    DOE PAGESBeta

    Yao, Liang-Zi; Crisostomo, Christian P.; Yeh, Chun-Chen; Lai, Shu-Ming; Huang, Zhi-Quan; Hsu, Chia-Hsiu; Chuang, Feng-Chuan; Lin, Hsin; Bansil, Arun

    2015-11-05

    We have carried out systematic first-principles electronic structure computations of growth of ultrathin films of compounds of group III (B, Al, In, Ga, and Tl) with group V (N, P, As, Sb, and Bi) elements on Si(111) substrate, including effects of hydrogenation. Two bilayers (BLs) of AlBi, InBi, GaBi, TlAs, and TlSb are found to support a topological phase over a wide range of strains, in addition to BBi, TlN, and TlBi which can be driven into the nontrivial phase via strain. A large band gap of 134 meV is identified in hydrogenated 2 BL film of InBi. One andmore » two BL films of GaBi and 2 BL films of InBi and TlAs on Si(111) surface possess nontrivial phases with a band gap as large as 121 meV in the case of 2 BL film of GaBi. Persistence of the nontrivial phase upon hydrogenations in the III-V thin films suggests that these films are suitable for growing on various substrates.« less

  14. Predicted Growth of Two-Dimensional Topological Insulator Thin Films of III-V Compounds on Si(111) Substrate

    SciTech Connect

    Yao, Liang-Zi; Crisostomo, Christian P.; Yeh, Chun-Chen; Lai, Shu-Ming; Huang, Zhi-Quan; Hsu, Chia-Hsiu; Chuang, Feng-Chuan; Lin, Hsin; Bansil, Arun

    2015-11-05

    We have carried out systematic first-principles electronic structure computations of growth of ultrathin films of compounds of group III (B, Al, In, Ga, and Tl) with group V (N, P, As, Sb, and Bi) elements on Si(111) substrate, including effects of hydrogenation. Two bilayers (BLs) of AlBi, InBi, GaBi, TlAs, and TlSb are found to support a topological phase over a wide range of strains, in addition to BBi, TlN, and TlBi which can be driven into the nontrivial phase via strain. A large band gap of 134 meV is identified in hydrogenated 2 BL film of InBi. One and two BL films of GaBi and 2 BL films of InBi and TlAs on Si(111) surface possess nontrivial phases with a band gap as large as 121 meV in the case of 2 BL film of GaBi. Persistence of the nontrivial phase upon hydrogenations in the III-V thin films suggests that these films are suitable for growing on various substrates.

  15. Plasmon-enhanced electron-phonon coupling in Dirac surface states of the thin-film topological insulator Bi{sub 2}Se{sub 3}

    SciTech Connect

    Glinka, Yuri D.; Babakiray, Sercan; Lederman, David

    2015-10-07

    Raman measurements of a Fano-type surface phonon mode associated with Dirac surface states (SS) in Bi{sub 2}Se{sub 3} topological insulator thin films allowed an unambiguous determination of the electron-phonon coupling strength in Dirac SS as a function of film thickness ranging from 2 to 40 nm. A non-monotonic enhancement of the electron-phonon coupling strength with maximum for the 8–10 nm thick films was observed. The non-monotonicity is suggested to originate from plasmon-phonon coupling which enhances electron-phonon coupling when free carrier density in Dirac SS increases with decreasing film thickness and becomes suppressed for thinnest films when anharmonic coupling between in-plane and out-of-plane phonon modes occurs. The observed about four-fold enhancement of electron-phonon coupling in Dirac SS of the 8–10 nm thick Bi{sub 2}Se{sub 3} films with respect to the bulk samples may provide new insights into the origin of superconductivity in this-type materials and their applications.

  16. Electron-beam induced damage in thin insulating films on compound semiconductors. M.S. Thesis, 1988

    NASA Technical Reports Server (NTRS)

    Pantic, Dragan M.

    1989-01-01

    Phosphorus rich plasma enhanced chemical vapor deposition (PECVD) of silicon nitride and silicon dioxide films on n-type indium phosphide (InP) substrates were exposed to electron-beam irradiation in the 5 to 40 keV range for the purpose of characterizing the damage induced in the dielectric. The electron-beam exposure was on the range of 10(exp -7) to 10(exp -3) C/sq cm. The damage to the devices was characterized by capacitance-voltage (C-V) measurements of the metal insulator semiconductor (MIS) capacitors. These results were compared to results obtained for radiation damage of thermal silicon dioxide on silicon (Si) MOS capacitors with similar exposures. The radiation induced damage in the PECVD silicon nitride films on InP was successfully annealed out in an hydrogen/nitrogen (H2/N2) ambient at 400 C for 15 min. The PECVD silicon dioxide films on InP had the least radiation damage, while the thermal silicon dioxide films on Si had the most radiation damage.

  17. Superconductor-Insulator Transition in Amorphous NbxSi1-x Thin Films. Comparison between Thickness, Density of State and Microscopic Disorder.

    NASA Astrophysics Data System (ADS)

    Crauste, O.; Couedo, F.; Bergé, L.; Marrache, C.; Dumoulin, L.

    2012-12-01

    We report on the study of the Disordered-induced Superconductor-Insulator Transition (D-SIT) in NbxSi1-x thin films. These films, synthesized by electron-beam co-deposition, are continuous, amorphous, homogeneously disordered and structurally stable for a wide range of compositions, thicknesses and annealing temperature and thus particularly well suited for the study of D-SIT. We present an analysis of the D-SIT induced by three different parameters: the thickness, the Nb composition that changes the electronic density of states and the annealing temperature that changes the microscopic disorder. The annealing changes quantum interference patterns that decreases the local conductance. Our results show that the effect of the thickness on the destruction of superconductivity is very distinct from those of the composition or the annealing. We point out this material is particularly interesting to disentangle the effect of the parameters driving this quantum phase transition.

  18. Structural, magnetic, and electronic properties of GdTiO{sub 3} Mott insulator thin films grown by pulsed laser deposition

    SciTech Connect

    Grisolia, M. N.; Bruno, F. Y.; Sando, D.; Jacquet, E.; Barthélémy, A.; Bibes, M.; Zhao, H. J.; Chen, X. M.; Bellaiche, L.

    2014-10-27

    We report on the optimization process to synthesize epitaxial thin films of GdTiO{sub 3} on SrLaGaO{sub 4} substrates by pulsed laser deposition. Optimized films are free of impurity phases and are fully strained. They possess a magnetic Curie temperature T{sub C} = 31.8 K with a saturation magnetization of 4.2 μ{sub B} per formula unit at 10 K. Transport measurements reveal an insulating response, as expected. Optical spectroscopy indicates a band gap of ∼0.7 eV, comparable to the bulk value. Our work adds ferrimagnetic orthotitanates to the palette of perovskite materials for the design of emergent strongly correlated states at oxide interfaces using a versatile growth technique such as pulsed laser deposition.

  19. Effect of carrier recombination on ultrafast carrier dynamics in thin films of the topological insulator Bi{sub 2}Se{sub 3}

    SciTech Connect

    Glinka, Yuri D.; Babakiray, Sercan; Johnson, Trent A.; Holcomb, Mikel B.; Lederman, David

    2014-10-27

    Transient reflectivity (TR) from thin films (6–40 nm thick) of the topological insulator Bi{sub 2}Se{sub 3} revealed ultrafast carrier dynamics, which suggest the existence of both radiative and non-radiative recombination between electrons residing in the upper cone of initially unoccupied high energy Dirac surface states (SS) and holes residing in the lower cone of occupied low energy Dirac SS. The modeling of measured TR traces allowed us to conclude that recombination is induced by the depletion of bulk electrons in films below ∼20 nm thick due to the charge captured on the surface defects. We predict that such recombination processes can be observed using time-resolved photoluminescence techniques.

  20. Semiconductor-insulator transition in VO{sub 2} (B) thin films grown by pulsed laser deposition

    SciTech Connect

    Rúa, Armando; Díaz, Ramón D.; Lysenko, Sergiy; Fernández, Félix E.

    2015-09-28

    Thin films of B-phase VO{sub 2} were grown by pulsed-laser deposition on glass and (100)-cut MgO substrates in a temperature range from 375 to 425 °C and at higher gas pressures than usual for this technique. The films were strongly oriented, with ab-planes parallel to the substrate surface. Detailed study of surface morphology through Atomic Force Microscopy images suggest significant differences in evolution as a function of growth temperature for films on the two types of substrates. Measurements of electrical conductivities through cooling-heating cycles from room temperature to 120 K showed changes of five orders of magnitude, with steeper changes between room temperature and ∼150 K, which corresponds with the extended and reversible phase transition known to occur for this material. At lower temperatures conductivities exhibited Arrhenius behavior, indicating that no further structural change was occurring and that conduction is thermally activated. In this lower temperature range, conductivity of the samples can be described by the near-neighbor hopping model. No hysteresis was found between the cooling and heating braches of the cycles, which is at variance with previous results published for VO{sub 2} (B). This apparent lack of hysteresis for thin films grown in the manner described and the large conductivity variation as a function of temperature observed for the samples suggests this material could be of interest for infrared sensing applications.

  1. Size-dependent metal-insulator transition in platinum-dispersed silicon dioxide thin film: A candidate for future non-volatile memory

    NASA Astrophysics Data System (ADS)

    Chen, Albert B. K.

    Non-volatile random access memories (NVRAM) are promising data storage and processing devices. Various NVRAM, such as FeRAM and MRAM, have been studied in the past. But resistance switching random access memory (RRAM) has demonstrated the most potential for replacing flash memory in use today. In this dissertation, a novel RRAM material design that relies upon an electronic transition, rather than a phase change (as in chalcogenide Ovonic RRAM) or a structural change (such in oxide and halide filamentary RRAM), is investigated. Since the design is not limited to a single material but applicable to general combinations of metals and insulators, the goal of this study is to use a model material to delineate the intrinsic features of the electronic metal/insulator transition in random systems and to demonstrate their relevance to reliable memory storage and retrieval. We fabricated amorphous SiO2 thin films embedded with randomly dispersed Pt atoms. Macroscopically, this random material exhibits a percolation transition in electric conductivity similar to the one found in various insulator/metal granular materials. However, at Pt concentrations well below the bulk percolation limit, a distinct insulator to metal transition occurs in the thickness direction as the film thickness falls below electron's "diffusion" distance, which is the tunneling distance at 0K. The thickness-triggered metal- to-insulator transition (MIT) can be similarly triggered by other conditions: (a) a changing Pt concentration (a concentration-triggered MIT), (b) a changing voltage/polarity (voltage-triggered MIT), and (c) an UV irradiation (photon-triggered MIT). The resistance switching characteristics of this random material were further investigated in several device configurations under various test conditions. These include: materials for the top and bottom electrodes, fast pulsing, impedance spectroscopy, static stressing, retention, fatigue and temperature from 10K to 448K. The SiO2-Pt

  2. Predicted Growth of Two-Dimensional Topological Insulators Consisting of Hydrogenated III-V Thin films on Si(111) Substrate

    NASA Astrophysics Data System (ADS)

    Chuang, Feng-Chuan; Crisostomo, Christian; Yao, Liang-Zi; Yeh, Chun-Chen; Lai, Shu-Ming; Huang, Zhi-Quan; Hsu, Chia-Hsiu; Lin, Hsin; Albao, Marvin; Bansil, Arun

    We have carried out systematic first-principles electronic structure calculations of growth of ultrathin films of compounds of group III (B, Al, In, Ga and Tl) with group V (N, P, As, Sb and Bi) elements on Si(111) substrate, including effects of hydrogenation. A total of six compounds (GaBi, InBi, TlBi, TlAs, TlSb and TlN) are identified to be nontrivial in unhydrogenated case; whereas for hydrogenated case, only four (GaBi, InBi, TlBi and TlSb) remains nontrivial. The band gap is found to be as large as 855 meV for the hydrogenated TlBi film, making this class of III-V materials suitable for room temperature applications. TlBi remains topologically nontrivial with a large band gap at various hydrogen coverages, indicating the robustness of its band topology against bonding effects of substrates. Two bilayers (BLs) of AlBi, InBi, GaBi, TlAs and TlSb are found to support a topological phase over a wide range of strains, in addition to BBi, TlN and TlBi which can be driven into the nontrivial phase via strain. One and two BL films of GaBi and 2 BL films of InBi and TlAs on Si(111) surface possess nontrivial phases with a band gap as large as 121 meV in the case of 2 BL film of GaBi. Persistence of the nontrivial phase upon hydrogenations in the III-V thin films suggests that these films are suitable for growing on various substrates.

  3. Spatial Inhomogeneity in Oxygen Modulated Potassium Tungsten Oxide Thin Films: implications for superconductivity and metal-insulator transitions

    NASA Astrophysics Data System (ADS)

    Munakata, Ko; Luna, Katherine; Tsukada, Akio; Risbud, Subhash; Geballe, Theodore; Beasley, Malcolm

    2012-02-01

    High quality potassium tungsten oxide (K0.33 WOy) films were synthesized by pulsed laser deposition followed by annealing in vacuum. Oxygen concentration modulated anomalous correlation of metal-insulator and superconductivity transitions were studied; a similar scenario was recently suggested in the literature [1] for polycrystalline rubidium tungsten oxide samples. Detailed studies of the transport properties below and above the superconducting transition temperature exhibit a diversity of unexpected behavior. Some of our results can be interpreted as a signature of reduced dimensionality in the ab-plane in oxygen-rich insulating samples, implying a formation of spatially inhomogeneous electronic structure. We compare such phenomenology to the behavior of other materials with strong electron-phonon interactions, and discuss its implication for the possible high temperature superconducting anomaly in sodium tungsten oxides reported in the literature [2]. [1] D. C. Ling et. al., J. Phys. Conf. Ser. 150, 052141 (2009). [2] S. Reich, and Y. Tsabba, Eur. Phys. J. B 9, 1 (1999).

  4. Characterization of the pentacene thin-film transistors with an epoxy resin-based polymeric gate insulator

    NASA Astrophysics Data System (ADS)

    Kim, C. H.; Tondelier, D.; Geffroy, B.; Bonnassieux, Y.; Horowitz, G.

    2012-02-01

    The organic thin-film transistors (OTFTs) incorporating pentacene/SU-8 interface were fabricated and characterized. SU-8, a reliable epoxy-based photoresist, is tested as a potential highly-stable polymeric gate dielectric for OTFTs. The fabricated devices showed promising electrical performance with on-off ratio up to 107 and field-effect mobility up to 0.56 cm2/V s. Several device characteristics are further analyzed. There existed a leakage current path due to the uncontrolled pentacene coverage and we revealed that precise alignment of the evaporation mask of pentacene is critical for eliminating this problem. Pentacene grain formation largely depended on the growth condition on the SU-8 surface and small-grain films offered outstanding performance possibly owing to enhanced inter-domain connections. Natural degradation of the OTFTs is also discussed in terms of environmental stability and the pentacene/SU-8 transistor operated with noticeable air stability under ambient conditions.

  5. Metal-to-Insulator Transition in Anatase TiO2 Thin Films Induced by Growth Rate Modulation

    SciTech Connect

    Tachikawa, T; Minohara, M.; Nakanishi, Y.; Hikita, Y.; Yoshita, M.; Akiyama, H.; Bell, C.; Hwang, H.Y.

    2012-06-21

    We demonstrate control of the carrier density of single phase anatase TiO{sub 2} thin films by nearly two orders of magnitude by modulating the growth kinetics during pulsed laser deposition, under fixed thermodynamic conditions. The resistivity and the intensity of the photoluminescence spectra of these TiO{sub 2} samples, both of which correlate with the number of oxygen vacancies, are shown to depend strongly on the growth rate. A quantitative model is used to explain the carrier density changes.

  6. Pyrolyzed thin film carbon

    NASA Technical Reports Server (NTRS)

    Tai, Yu-Chong (Inventor); Liger, Matthieu (Inventor); Harder, Theodore (Inventor); Konishi, Satoshi (Inventor); Miserendino, Scott (Inventor)

    2010-01-01

    A method of making carbon thin films comprises depositing a catalyst on a substrate, depositing a hydrocarbon in contact with the catalyst and pyrolyzing the hydrocarbon. A method of controlling a carbon thin film density comprises etching a cavity into a substrate, depositing a hydrocarbon into the cavity, and pyrolyzing the hydrocarbon while in the cavity to form a carbon thin film. Controlling a carbon thin film density is achieved by changing the volume of the cavity. Methods of making carbon containing patterned structures are also provided. Carbon thin films and carbon containing patterned structures can be used in NEMS, MEMS, liquid chromatography, and sensor devices.

  7. BaTi4O9 thin films for high-performance metal-insulator-metal capacitors

    NASA Astrophysics Data System (ADS)

    Jang, Bo-Yun; Kim, Beom-Jong; Lee, Suk-Jin; Lee, Kyong-Jae; Nahm, Sahn; Sun, Ho-Jung; Lee, Hwack-Joo

    2005-09-01

    The dielectric and electrical properties of a BaTi4O9 film were investigated in order to evaluate its potential use in metal-insulator-metal (MIM) capacitors for rf/mixed signal integrated circuits. A high capacitance density of 4.62fF/μm2 along with a low tanδ of 0.0025 were obtained at 100 kHz. A high capacitance density of 4.12fF /μm2 and a high quality factor of 322 were also achieved at 2 GHz. The leakage current density was approximately 1nA/cm2 at ±2V. Small linear and quadratic voltage coefficients of capacitance of 110ppm/V and 40.05ppm/V2, respectively, and a small temperature coefficient of capacitance of -92.157ppm/°C at 100 kHz were obtained. These results demonstrate that the BaTi4O9 film is a good candidate material for MIM capacitors.

  8. Test results for electron beam charging of flexible insulators and composites. [solar array substrates, honeycomb panels, and thin dielectric films

    NASA Technical Reports Server (NTRS)

    Staskus, J. V.; Berkopec, F. D.

    1979-01-01

    Flexible solar-array substrates, graphite-fiber/epoxy - aluminum honeycomb panels, and thin dielectric films were exposed to monoenergetic electron beams ranging in energy from 2 to 20 keV in the Lewis Research Center's geomagnetic-substorm-environment simulation facility to determine surface potentials, dc currents, and surface discharges. The four solar-array substrate samples consisted of Kapton sheet reinforced with fabrics of woven glass or carbon fibers. They represented different construction techniques that might be used to reduce the charge accumulation on the array back surface. Five honeycomb-panel samples were tested, two of which were representative of Voyager antenna materials and had either conductive or nonconductive painted surfaces. A third sample was of Navstar solar-array substrate material. The other two samples were of materials proposed for use on Intelsat V. All the honeycomb-panel samples had graphite-fiber/epoxy composite face sheets. The thin dielectric films were 2.54-micrometer-thick Mylar and 7.62-micrometer-thick Kapton.

  9. Effect of Al2O3 insulator thickness on the structural integrity of amorphous indium-gallium-zinc-oxide based thin film transistors.

    PubMed

    Kim, Hak-Jun; Hwang, In-Ju; Kim, Youn-Jea

    2014-12-01

    The current transparent oxide semiconductors (TOSs) technology provides flexibility and high performance. In this study, multi-stack nano-layers of TOSs were designed for three-dimensional analysis of amorphous indium-gallium-zinc-oxide (a-IGZO) based thin film transistors (TFTs). In particular, the effects of torsional and compressive stresses on the nano-sized active layers such as the a-IGZO layer were investigated. Numerical simulations were carried out to investigate the structural integrity of a-IGZO based TFTs with three different thicknesses of the aluminum oxide (Al2O3) insulator (δ = 10, 20, and 30 nm), respectively, using a commercial code, COMSOL Multiphysics. The results are graphically depicted for operating conditions. PMID:25971080

  10. Tunable metal-insulator transition in Nd1-xYxNiO3 (x = 0.3, 0.4) perovskites thin film at near room temperature

    NASA Astrophysics Data System (ADS)

    Shao, Tao; Qi, Zeming; Wang, Yuyin; Li, Yuanyuan; Yang, Mei; Wang, Yu; Zhang, Guobin; Liu, Miao

    2015-07-01

    Metal-insulator transition (MIT) occurs due to the charge disproportionation and lattice distortions in rare-earth nickelates. Existing studies revealed that the MIT behavior of rare-earth nickelates is fairly sensitive to external stress/pressure, suggesting a viable route for MIT strain engineering. Unlike applying extrinsic strain, the MIT can also be modulated by through rare-earth cation mixing, which can be viewed as intrinsic quantum stress. We choose Nd1-XYXNiO3 (x = 0.3, 0.4) perovskites thin films as a prototype system to exhibit the tunable sharp MIT at near room temperature. By adjusting Y concentration, the transition temperature of the thin films can be changed within the range of 340-360 K. X-ray diffraction, X-ray absorption fine structure (XAFS), and in situ infrared spectroscopy are employed to probe the structural and optical property variation affected by composition and temperature. The infrared transmission intensity decreases with temperature across the MIT, indicating a pronounced thermochromic effect. Meanwhile, the XAFS result exhibits that the crystal atomistic structure changes accompanying with the Y atoms incorporation and MIT phase transition. The heavily doped Y atoms result in the pre-edge peak descent and Ni-O bond elongation, suggesting an enhanced charge disproportionation effect and the weakening of hybridization between Ni-3d and O-2p orbits.

  11. Antiferromagnetic and xy ferro-orbital order in insulating SrRuO3 thin films with SrO termination.

    PubMed

    Autieri, C

    2016-10-26

    By means of first-principles calculations we study the structural, magnetic and electronic properties of SrRuO3 surface for the SrO termination. We find that the RuO6 octahedra and the structure of the SrO layers at the surface are strongly modified as well as the Ru-O-Ru bond angles. We find in the thin films a d xy ferro-orbital order. The d xy orbital becomes the lowest in energy as in other quasitwodimensional ruthenates. Such structural rearrangement, together with a band reduction, leads to a modification of the magnetic properties. We compare the Jahn-Teller effect between the ferromagnetic and antiferromagnetic phases. We show that an insulating G-type antiferromagnetic phase takes place in SrRuO3 thin films, substituting the metallic phase experimentally found in every bulk Sr-ruthenates. The single layer SrRuO3 presents many similarities with the Ca2RuO4 low temperature phase, these similarities disappear with a larger number of layers. A study of the ground state of the as function of the number of layers is presented, the competition between bandwidth and Coulomb repulsion determines the ground state. We propose the disorder as responsible for the exchange bias effect observed. PMID:27588503

  12. Thin-film morphology of inkjet-printed single-droplet organic transistors using polarized Raman spectroscopy: effect of blending TIPS-pentacene with insulating polymer.

    PubMed

    James, David T; Kjellander, B K Charlotte; Smaal, Wiljan T T; Gelinck, Gerwin H; Combe, Craig; McCulloch, Iain; Wilson, Richard; Burroughes, Jeremy H; Bradley, Donal D C; Kim, Ji-Seon

    2011-12-27

    We report thin-film morphology studies of inkjet-printed single-droplet organic thin-film transistors (OTFTs) using angle-dependent polarized Raman spectroscopy. We show this to be an effective technique to determine the degree of molecular order as well as to spatially resolve the orientation of the conjugated backbones of the 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene) molecules. The addition of an insulating polymer, polystyrene (PS), does not disrupt the π-π stacking of the TIPS-Pentacene molecules. Blending in fact improves the uniformity of the molecular morphology and the active layer coverage within the device and reduces the variation in molecular orientation between polycrystalline domains. For OTFT performance, blending enhances the saturation mobility from 0.22 ± 0.05 cm(2)/(V·s) (TIPS-Pentacene) to 0.72 ± 0.17 cm(2)/(V·s) (TIPS-Pentacene:PS) in addition to improving the quality of the interface between TIPS-Pentacene and the gate dielectric in the channel, resulting in threshold voltages of ∼0 V and steep subthreshold slopes. PMID:22032725

  13. A Low Temperature, Solution-Processed Poly(4-vinylphenol), YO(x) Nanoparticle Composite/Polysilazane Bi-Layer Gate Insulator for ZnO Thin Film Transistor.

    PubMed

    Shin, Hyeonwoo; Kang, Chan-Mo; Chae, Hyunsik; Kim, Hyun-Gwan; Baek, Kyu-Ha; Choi, Hyoung Jin; Park, Man-Young; Do, Lee-Mi; Lee, Changhee

    2016-03-01

    Low temperature, solution-processed metal oxide thin film transistors (MEOTFTs) have been widely investigated for application in low-cost, transparent, and flexible electronics. To enlarge the application area, solution-processed gate insulators (GI) have been investigated in recent years. We investigated the effects of the organic/inorganic bi-layer GI to ZnO thin film transistors (TFTs). PVP, YO(x) nanoparticle composite, and polysilazane bi-layer showed low leakage current (-10(-8) A/cm2 in 2 MV), which are applicable in low temperature processed MEOTFTs. Polysilazane was used as an interlayer between ZnO and PVP, YO(x) nanoparticle composite as a good charge transport interface with ZnO. By applying the PVP, YO(x), nanoparticle composite/polysilazane bi-layer structure to ZnO TFTs, we successfully suppressed the off current (I(off)) to -10(-11) and fabricated good MEOTFTs in 180 degrees C. PMID:27455680

  14. Plasma-assisted hot filament chemical vapor deposition of AlN thin films on ZnO buffer layer: toward highly c-axis-oriented, uniform, insulative films

    NASA Astrophysics Data System (ADS)

    Alizadeh, M.; Mehdipour, H.; Ganesh, V.; Ameera, A. N.; Goh, B. T.; Shuhaimi, A.; Rahman, S. A.

    2014-12-01

    c-Axis-oriented aluminum nitride (AlN) thin film with improved quality was deposited on Si(111) substrate using ZnO buffer layer by plasma-assisted hot filament chemical vapor deposition. The optical and electrical properties and surface morphology as well as elemental composition of the AlN films deposited with and without ZnO buffer layer were investigated using a host of measurement techniques: X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and current-voltage (I-V) characteristic measurement. The XRD and XPS results reveal that the AlN/ZnO/Si films are free of metallic Al particles. Also, cross-sectional FESEM observations suggest formation of a well-aligned, uniform, continuous, and highly (002) oriented structure for a bi-layered AlN film when Si(111) is covered with ZnO buffer. Moreover, a decrease in full width at half maximum of the E2 (high)-mode peak in Raman spectrum indicates a better crystallinity for the AlN films formed on ZnO/Si substrate. Finally, I-V curves obtained indicate that the electrical behavior of the AlN thin films switches from conductive to insulative when film is grown on a ZnO-buffered Si substrate.

  15. Electric field induced metal-insulator transition in VO2 thin film based on FTO/VO2/FTO structure

    NASA Astrophysics Data System (ADS)

    Hao, Rulong; Li, Yi; Liu, Fei; Sun, Yao; Tang, Jiayin; Chen, Peizu; Jiang, Wei; Wu, Zhengyi; Xu, Tingting; Fang, Baoying

    2016-03-01

    A VO2 thin film has been prepared using a DC magnetron sputtering method and annealing on an F-doped SnO2 (FTO) conductive glass substrate. The FTO/VO2/FTO structure was fabricated using photolithography and a chemical etching process. The temperature dependence of the I-V hysteresis loop for the FTO/VO2/FTO structure has been analyzed. The threshold voltage decreases with increasing temperature, with a value of 9.2 V at 20 °C. The maximum transmission modulation value of the FTO/VO2/FTO structure is 31.4% under various temperatures and voltages. Optical modulation can be realized in the structure by applying an electric field.

  16. Thin-film metal hydrides.

    PubMed

    Remhof, Arndt; Borgschulte, Andreas

    2008-12-01

    The goal of the medieval alchemist, the chemical transformation of common metals into nobel metals, will forever be a dream. However, key characteristics of metals, such as their electronic band structure and, consequently, their electric, magnetic and optical properties, can be tailored by controlled hydrogen doping. Due to their morphology and well-defined geometry with flat, coplanar surfaces/interfaces, novel phenomena may be observed in thin films. Prominent examples are the eye-catching hydrogen switchable mirror effect, the visualization of solid-state diffusion and the formation of complex surface morphologies. Thin films do not suffer as much from embrittlement and/or decrepitation as bulk materials, allowing the study of cyclic absorption and desorption. Therefore, thin-metal hydride films are used as model systems to study metal-insulator transitions, for high throughput combinatorial research or they may be used as indicator layers to study hydrogen diffusion. They can be found in technological applications as hydrogen sensors, in electrochromic and thermochromic devices. In this review, we discuss the effect of hydrogen loading of thin niobium and yttrium films as archetypical examples of a transition metal and a rare earth metal, respectively. Our focus thereby lies on the hydrogen induced changes of the electronic structure and the morphology of the thin films, their optical properties, the visualization and the control of hydrogen diffusion and on the study of surface phenomena and catalysis. PMID:18980236

  17. Thin film metrology.

    PubMed

    Nitsch, Gerald; Flinn, Gregory

    2007-10-01

    Thin film metrology is suitable for characterising and performing quality control of a variety of coatings and films used in medical applications. The capabilities of today's systems are described. PMID:18078184

  18. Thin transparent films formed from powdered glass

    NASA Technical Reports Server (NTRS)

    1965-01-01

    Glass film less than five mils thick is formed from powdered glass dispersed in an organic liquid, deposited on a substrate, and fused into place. The thin films can be cut and shaped for contact lenses, optical filters and insulating layers.

  19. Ceramic Composite Thin Films

    NASA Technical Reports Server (NTRS)

    Ruoff, Rodney S. (Inventor); Stankovich, Sasha (Inventor); Dikin, Dmitriy A. (Inventor); Nguyen, SonBinh T. (Inventor)

    2013-01-01

    A ceramic composite thin film or layer includes individual graphene oxide and/or electrically conductive graphene sheets dispersed in a ceramic (e.g. silica) matrix. The thin film or layer can be electrically conductive film or layer depending the amount of graphene sheets present. The composite films or layers are transparent, chemically inert and compatible with both glass and hydrophilic SiOx/silicon substrates. The composite film or layer can be produced by making a suspension of graphene oxide sheet fragments, introducing a silica-precursor or silica to the suspension to form a sol, depositing the sol on a substrate as thin film or layer, at least partially reducing the graphene oxide sheets to conductive graphene sheets, and thermally consolidating the thin film or layer to form a silica matrix in which the graphene oxide and/or graphene sheets are dispersed.

  20. Magnetotransport study of (Sb1-xBix)2Te3 thin films on mica substrate for ideal topological insulator

    NASA Astrophysics Data System (ADS)

    Ni, Yan; Zhang, Zhen; Nlebedim, Cajetan I.; Jiles, David C.

    2016-05-01

    We deposited high quality (Sb1-xBix)2Te3 on mica substrate by molecular beam epitaxy and investigated their magnetotransport properties. It is found that the average surface roughness of thin films is lower than 2 nm. Moreover, a local maxima on the sheet resistance is obtained with x = 0.043, indicating a minimization of bulk conductivity at this composition. For (Sb0.957Bi0.043)2Te3, weak antilocalization with coefficient of -0.43 is observed, confirming the existence of 2D surface states. Moreover Shubnikov-de Hass oscillation behavior occurs under high magnetic field. The 2D carrier density is then determined as 0.81 × 1016 m-2, which is lower than that of most TIs reported previously, indicating that (Sb0.957Bi0.043)2Te3 is close to ideal TI composition of which the Dirac point and Fermi surface cross within the bulk bandgap. Our results thus demonstrate the best estimated composition for ideal TI is close to (Sb0.957Bi0.043)2Te3 and will be helpful for designing TI-based devices.

  1. Low-voltage pentacene thin-film transistors with Ta{sub 2}O{sub 5} gate insulators and their reversible light-induced threshold voltage shift

    SciTech Connect

    Liang Yan; Dong Guifang; Hu Yan; Wang Liduo; Qiu Yong

    2005-03-28

    We have fabricated pentacene thin-film transistors using Ta{sub 2}O{sub 5} films prepared by magnetron reactive sputtering as gate insulators. These transistors exhibit good electrical characteristics at an operating voltage as low as 5 V, with a field-effect mobility of 0.32 cm{sup 2}/Vs, an on/off ratio of 10{sup 4}, and a subthreshold slope of 0.5 V/decade. We have also investigated the optical properties of these transistors and observed a reversible light-induced threshold voltage shift. Under illumination, the threshold voltage shifts towards the positive direction while the field-effect mobility and on/off ratio remain almost unchanged. In the dark, however, the threshold voltage can slowly be restored to its original state. At a gate voltage of -5 V, the transistors show a broadband responsivity of 3.7 A/W after illumination at 60 {mu}W/cm{sup 2} for 10 min.

  2. Electric field-assisted metal insulator transition in vanadium dioxide (VO2) thin films: optical switching behavior and anomalous far-infrared emissivity variation

    NASA Astrophysics Data System (ADS)

    Crunteanu, Aurelian; Fabert, Marc; Cornette, Julie; Colas, Maggy; Orlianges, Jean-Christophe; Bessaudou, Annie; Cosset, Françoise

    2014-03-01

    We present the vanadium dioxide (VO2) thin films deposition using e-beam evaporation of a vanadium target under oxygen atmosphere on different substrates (sapphire, Si, SiO2/Si…) and we focus on their electrical and optical properties variations as the material undergoes a metal-insulator transition under thermal and electrical stimuli. The phase transition induces extremely abrupt changes in the electronic and optical properties of the material: the electrical resistivity increases up to 5 orders of magnitude while the optical properties (transmission, reflection, refractive index) are drastically modified. We present the integration of these films in simple planar optical devices and we demonstrate electrical-activated optical modulators for visible-infrared signals with high discrimination between the two states. We will highlight a peculiar behavior of the VO2 material in the infrared and far infrared regions (2- 20 μm), namely its anomalous emissivity change under thermal- end electrical activation (negative differential emittance phenomenon) with potential applications in active coatings for thermal regulation, optical limiting or camouflage coatings.

  3. Theory of strain-controlled magnetotransport and stabilization of the ferromagnetic insulating phase in manganite thin films.

    PubMed

    Mukherjee, Anamitra; Cole, William S; Woodward, Patrick; Randeria, Mohit; Trivedi, Nandini

    2013-04-12

    We show that applying strain on half-doped manganites makes it possible to tune the system to the proximity of a metal-insulator transition and thereby generate a colossal magnetoresistance (CMR) response. This phase competition not only allows control of CMR in ferromagnetic metallic manganites but can be used to generate CMR response in otherwise robust insulators at half-doping. Further, from our realistic microscopic model of strain and magnetotransport calculations within the Kubo formalism, we demonstrate a striking result of strain engineering that, under tensile strain, a ferromagnetic charge-ordered insulator, previously inaccessible to experiments, becomes stable. PMID:25167302

  4. Metal insulator transition and magnetotransport anomalies in perovskite SrIr{sub 0.5}Ru{sub 0.5}O{sub 3} thin films

    SciTech Connect

    Biswas, Abhijit; Lee, Yong Woo; Kim, Sang Woo; Jeong, Yoon Hee

    2015-03-21

    We investigated the nature of transport and magnetic properties in SrIr{sub 0.5}Ru{sub 0.5}O{sub 3} (SIRO), which has characteristics intermediate between a correlated non-Fermi liquid state and an itinerant Fermi liquid state, by growing perovskite thin films on various substrates (e.g., SrTiO{sub 3} (001), (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}TaAlO{sub 6}){sub 0.7} (001), and LaAlO{sub 3} (001)). We observed systematic variation of underlying substrate dependent metal-to-insulator transition temperatures (T{sub MIT} ∼ 80 K on SrTiO{sub 3}, ∼90 K on (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}TaAlO{sub 6}){sub 0.7}, and ∼100 K on LaAlO{sub 3}) in resistivity. At temperature 300 K ≥ T ≥ T{sub MIT}, SIRO is metallic and its resistivity follows a T{sup 3/2} power law, whereas insulating nature at T < T{sub MIT} is due to the localization effect. Magnetoresistance (MR) measurement of SIRO on SrTiO{sub 3} (001) shows negative MR at T < 25 K and positive MR at T > 25 K, with negative MR ∝ B{sup 1/2} and positive MR ∝ B{sup 2}; consistent with the localized-to-normal transport crossover dynamics. Furthermore, observed spin glass like behavior of SIRO on SrTiO{sub 3} (001) at T < 25 K in the localized regime validates the hypothesis that (Anderson) localization favors glassy ordering. These remarkable features provide a promising approach for future applications and of fundamental interest in oxide thin films.

  5. Carbon thin film thermometry

    NASA Technical Reports Server (NTRS)

    Collier, R. S.; Sparks, L. L.; Strobridge, T. R.

    1973-01-01

    The work concerning carbon thin film thermometry is reported. Optimum film deposition parameters were sought on an empirical basis for maximum stability of the films. One hundred films were fabricated for use at the Marshall Space Flight Center; 10 of these films were given a precise quasi-continuous calibration of temperature vs. resistance with 22 intervals between 5 and 80 K using primary platinum and germanium thermometers. Sensitivity curves were established and the remaining 90 films were given a three point calibration and fitted to the established sensitivity curves. Hydrogen gas-liquid discrimination set points are given for each film.

  6. The metal-insulator transition in vanadium dioxide: A view at bulk and surface contributions for thin films and the effect of annealing

    SciTech Connect

    Yin, W.; West, K. G.; Lu, J. W.; Pei, Y.; Wolf, S. A.; Reinke, P.; Sun, Y.

    2009-06-01

    Vanadium dioxide is investigated as potential oxide barrier in spin switches, and in order to incorporate VO{sub 2} layers in complex multilayer devices, it is necessary to understand the relation between bulk and surface/interface properties. Highly oriented VO{sub 2} thin films were grown on (0001) sapphire single crystal substrates with reactive bias target ion beam deposition. In the analysis of the VO{sub 2} films, bulk-sensitive methods [x-ray diffraction (XRD) and transport measurements] and surface sensitive techniques [photoelectron spectroscopy (PES) and scanning tunneling microscopy and spectroscopy] were employed. The samples were subjected to heating cycles with annealing temperatures of up to 425 and 525 K. Prior to annealing the VO{sub 2} films exhibit the transition from the monoclinic to the tetragonal phase with the concurrent change in conductivity by more than a factor of 10{sup 3} and their phase purity is confirmed by XRD. Annealing to 425 K and thus cycling across the metal-insulator transition (MIT) temperature has no impact on the bulk properties of the VO{sub 2} film but the surface undergoes irreversible electronic changes. The observation of the valence band with PES during the annealing illustrates that the surface adopts a partially metallic character, which is retained after cooling. Annealing to a higher temperature (525 K) triggers a modification of the bulk, which is evidenced by a considerable reduction in the MIT characteristics, and a degradation in crystallite morphology. The local measurement of the conductivity with scanning tunneling spectroscopy shows the transition of the surface from predominantly semiconducting surface prior to annealing to a surface with an overwhelming contribution from metallic sections afterward. The spatial distribution of metallic regions cannot be linked in a unique manner to the crystallite size or location within the crystallites. The onset of oxygen depletion at the surface is held responsible

  7. Reentrant Insulating State in Ultrathin Manganite Films

    SciTech Connect

    Bell, Christopher

    2011-08-11

    The transport and magnetic properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin-films grown by pulsed laser deposition on (LaAlO{sub 3}){sub 0.3}(SrAl{sub 0.5}Ta{sub 0.5}O{sub 3}){sub 0.7} single crystal substrates have been investigated. A systematic series with various thicknesses of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} was used to establish a phase diagram - which showed a clear difference compared to films grown on SrTiO{sub 3} substrates, highlighting the importance of film thickness and substrate strain. At 8 unit cells, the boundary between the metallic and insulating ground states, a second abrupt metal-insulator transition was observed at low temperatures, which could be tuned with by magnetic field, and is interpreted as a signature of electronic phase separation.

  8. Conductance modulation in topological insulator Bi{sub 2}Se{sub 3} thin films with ionic liquid gating

    SciTech Connect

    Son, Jaesung; Banerjee, Karan; Yang, Hyunsoo; Brahlek, Matthew; Koirala, Nikesh; Oh, Seongshik; Lee, Seoung-Ki; Ahn, Jong-Hyun

    2013-11-18

    A Bi{sub 2}Se{sub 3} topological insulator field effect transistor is investigated by using ionic liquid as an electric double layer gating material, leading to a conductance modulation of 365% at room temperature. We discuss the role of charged impurities on the transport properties. The conductance modulation with gate bias is due to a change in the carrier concentration, whereas the temperature dependent conductance change is originated from a change in mobility. Large conductance modulation at room temperature along with the transparent optical properties makes topological insulators as an interesting (opto)electronic material.

  9. Flexible Thin Metal Film Thermal Sensing System

    NASA Technical Reports Server (NTRS)

    Thomsen, Donald Laurence (Inventor)

    2012-01-01

    A flexible thin metal film thermal sensing system is provided. A thermally-conductive film made from a thermally-insulating material is doped with thermally-conductive material. At least one layer of electrically-conductive metal is deposited directly onto a surface of the thermally-conductive film. One or more devices are coupled to the layer(s) to measure an electrical characteristic associated therewith as an indication of temperature.

  10. Thin film hydrogen sensor

    DOEpatents

    Cheng, Y.T.; Poli, A.A.; Meltser, M.A.

    1999-03-23

    A thin film hydrogen sensor includes a substantially flat ceramic substrate with first and second planar sides and a first substrate end opposite a second substrate end; a thin film temperature responsive resistor on the first planar side of the substrate proximate to the first substrate end; a thin film hydrogen responsive metal resistor on the first planar side of the substrate proximate to the fist substrate end and proximate to the temperature responsive resistor; and a heater on the second planar side of the substrate proximate to the first end. 5 figs.

  11. Biomimetic thin film synthesis

    SciTech Connect

    Graff, G.L.; Campbell, A.A.; Gordon, N.R.

    1995-05-01

    The purpose of this program is to develop a new process for forming thin film coatings and to demonstrate that the biomimetic thin film technology developed at PNL is useful for industrial applications. In the biomimetic process, mineral deposition from aqueous solution is controlled by organic functional groups attached to the underlying substrate surface. The coatings process is simple, benign, inexpensive, energy efficient, and particularly suited for temperature sensitive substrate materials (such as polymers). In addition, biomimetic thin films can be deposited uniformly on complex shaped and porous substrates providing a unique capability over more traditional line-of-sight methods.

  12. Thin film hydrogen sensor

    DOEpatents

    Cheng, Yang-Tse; Poli, Andrea A.; Meltser, Mark Alexander

    1999-01-01

    A thin film hydrogen sensor, includes: a substantially flat ceramic substrate with first and second planar sides and a first substrate end opposite a second substrate end; a thin film temperature responsive resistor on the first planar side of the substrate proximate to the first substrate end; a thin film hydrogen responsive metal resistor on the first planar side of the substrate proximate to the fist substrate end and proximate to the temperature responsive resistor; and a heater on the second planar side of the substrate proximate to the first end.

  13. Thin Nanoporous Metal-Insulator-Metal Membranes.

    PubMed

    Aramesh, Morteza; Djalalian-Assl, Amir; Yajadda, Mir Massoud Aghili; Prawer, Steven; Ostrikov, Kostya Ken

    2016-02-01

    Insulating nanoporous materials are promising platforms for soft-ionizing membranes; however, improvement in fabrication processes and the quality and high breakdown resistance of the thin insulator layers are needed for high integration and performance. Here, scalable fabrication of highly porous, thin, silicon dioxide membranes with controlled thickness is demonstrated using plasma-enhanced chemical-vapor-deposition. The fabricated membranes exhibit good insulating properties with a breakdown voltage of 1 × 10(7) V/cm. Our calculations suggest that the average electric field inside a nanopore of the membranes can be as high as 1 × 10(6) V/cm; sufficient for ionization of wide range of molecules. These metal-insulator-metal nanoporous arrays are promising for applications such soft ionizing membranes for mass spectroscopy. PMID:26846250

  14. Influence of Mn concentration on magnetic topological insulator MnxBi2−xTe3 thin-film Hall-effect sensor

    DOE PAGESBeta

    Ni, Y.; Zhang, Z.; Nlebedim, I. C.; Hadimani, R. L.; Jiles, D. C.

    2015-06-11

    Hall-effect (HE) sensors based on high-quality Mn-doped Bi2Te3 topological insulator (TI) thin films have been systematically studied in this paper. Improvement of Hall sensitivity is found after doping the magnetic element Mn into Bi2Te3. The sensors with low Mn concentrations, MnxBi2-xTe3, x = 0.01 and 0.08 show the linear behavior of Hall resistance with sensitivity about 5 Ω/T. And their Hall sensitivity shows weak dependence on temperature. For sensors with high Mn concentration (x = 0.23), the Hall resistance with respect to magnetic field shows a hysteretic behavior. Moreover, its sensitivity shows almost eight times as high as that ofmore » the HE sensors with low Mn concentration. The highest sensitivity can reach 43 Ω/T at very low magnetic field. This increase of Hall sensitivity is caused by the occurrence of anomalous HE (AHE) after ferromagnetic phase transition. Our work indicates that the magnetic-element-doped TIs with AHE are good candidates for HE sensors.« less

  15. Multifunctional thin film surface

    SciTech Connect

    Brozik, Susan M.; Harper, Jason C.; Polsky, Ronen; Wheeler, David R.; Arango, Dulce C.; Dirk, Shawn M.

    2015-10-13

    A thin film with multiple binding functionality can be prepared on an electrode surface via consecutive electroreduction of two or more aryl-onium salts with different functional groups. This versatile and simple method for forming multifunctional surfaces provides an effective means for immobilization of diverse molecules at close proximities. The multifunctional thin film has applications in bioelectronics, molecular electronics, clinical diagnostics, and chemical and biological sensing.

  16. Thin film tritium dosimetry

    DOEpatents

    Moran, Paul R.

    1976-01-01

    The present invention provides a method for tritium dosimetry. A dosimeter comprising a thin film of a material having relatively sensitive RITAC-RITAP dosimetry properties is exposed to radiation from tritium, and after the dosimeter has been removed from the source of the radiation, the low energy electron dose deposited in the thin film is determined by radiation-induced, thermally-activated polarization dosimetry techniques.

  17. Evaporated VOx Thin Films

    NASA Astrophysics Data System (ADS)

    Stapinski, Tomasz; Leja, E.

    1989-03-01

    VOx thin films on glass were obtained by thermal evaporation of V205, powder. The structural investigations were carried out with the use of X-ray diffractometer. The electrical properties of the film were examined by means of temperature measurements of resistivity for the samples heat-treated in various conditions. Optical transmission and reflection spectra of VOX films of various composition showed the influence of the heat treatment.

  18. Microwave-enhanced thin-film deposition

    NASA Technical Reports Server (NTRS)

    Chitre, S.

    1984-01-01

    The deposition of semiconducting and insulating thin films at low temperatures using microwave technology was explored. The method of plasma formations, selection of a power source, the design of the microwave plasma cavity, the microwave circuitry, impedance matching, plasma diagnostics, the deposition chamber and the vacuum system were studied.

  19. Thin Film Transistors On Plastic Substrates

    DOEpatents

    Carey, Paul G.; Smith, Patrick M.; Sigmon, Thomas W.; Aceves, Randy C.

    2004-01-20

    A process for formation of thin film transistors (TFTs) on plastic substrates replaces standard thin film transistor fabrication techniques, and uses sufficiently lower processing temperatures so that inexpensive plastic substrates may be used in place of standard glass, quartz, and silicon wafer-based substrates. The silicon based thin film transistor produced by the process includes a low temperature substrate incapable of withstanding sustained processing temperatures greater than about 250.degree. C., an insulating layer on the substrate, a layer of silicon on the insulating layer having sections of doped silicon, undoped silicon, and poly-silicon, a gate dielectric layer on the layer of silicon, a layer of gate metal on the dielectric layer, a layer of oxide on sections of the layer of silicon and the layer of gate metal, and metal contacts on sections of the layer of silicon and layer of gate metal defining source, gate, and drain contacts, and interconnects.

  20. Metal-insulator transition at room temperature and infrared properties of Nd0.7Eu0.3NiO3 thin films

    NASA Astrophysics Data System (ADS)

    Capon, F.; Laffez, P.; Bardeau, J.-F.; Simon, P.; Lacorre, P.; Zaghrioui, M.

    2002-07-01

    Nd0.7Eu0.3NiO3 thin films are deposited by rf sputtering and subsequent oxygen pressure annealing on (100) oriented silicon substrate. We characterize the thermochromic properties of films by measuring electrical transition, infrared transmittance, and reflectance. The thermochromic effect at room temperature is observed. Resistivity measurements exhibit a sharper hysteresis loop than is usually observed in NdNiO3 thin films. Infrared properties in the 8-14 mum wavelength range spectra reveal a contrast of 30% in reflectance and 55% in transmittance.

  1. Anomalous photoelectric effect of a polycrystalline topological insulator film.

    PubMed

    Zhang, Hongbin; Yao, Jiandong; Shao, Jianmei; Li, Hai; Li, Shuwei; Bao, Dinghua; Wang, Chengxin; Yang, Guowei

    2014-01-01

    A topological insulator represents a new state of quantum matter that possesses an insulating bulk band gap as well as a spin-momentum-locked Dirac cone on the surface that is protected by time-reversal symmetry. Photon-dressed surface states and light-induced surface photocurrents have been observed in topological insulators. Here, we report experimental observations of an anomalous photoelectric effect in thin films of Bi2Te3, a polycrystalline topological insulator. Under illumination with non-polarised light, transport measurements reveal that the resistance of the topological surface states suddenly increases when the polycrystalline film is illuminated. The resistance variation is positively dependent on the light intensity but has no relation to the applied electric field; this finding can be attributed to the gap opening of the surface Dirac cone. This observation of an anomalous photoelectric effect in polycrystalline topological insulators offers exciting opportunities for the creation of photodetectors with an unusually broad spectral range. Moreover, polycrystalline topological insulator films provide an attractive material platform for exploring the nature and practical application of topological insulators. PMID:25069391

  2. Single-ion magnetic anisotropy of transition metal impurities in Bi2Se3 bulk and thin film topological insulators

    NASA Astrophysics Data System (ADS)

    Islam, Fhokrul; Pertsova, Anna; Mahani, Reza; Canali, Carlo

    The breaking of time reversal symmetry in a topological insulator (TI) by magnetic doping is one of the most studied phenomena among the properties of Dirac materials. The robustness of the topological surface states (TSS) against magnetic impurities is of critical importance for spin-dependent transport in these systems. The interaction between TSS and magnetic impurities can open a gap, provided that the magnetic order is oriented normal to the surface of the TI. Such gap opening is crucial for realizing TI-based spintronic devices and for the observation of different fundamental phenomena, such as the anomalous quantum Hall effect. Using density functional theory as implemented in the WIEN2k ab-initio package, we have investigated the effect of the magnetization orientation on the gap opening at the Dirac point, for substitutional Mn and Fe impurities on the Bi2Se3 surface, and have calculated the associated single-ion anisotropy (SIA). We also have studied bulk SIA in order to compare the role played by TSS on the surface SIA.

  3. The preparation of ACEL thin films

    NASA Astrophysics Data System (ADS)

    Vecht, Aron

    1990-05-01

    Although thin film ACEL devices have become commercially available, the number of companies producing these displays has continued to diminish. The cause of their demise was not display performance, as both sufficient brightness and efficiency has been achieved, but the low return on the heavy capital investment due to the poor yields obtained in production. In order to make ACEL thin film devices more viable, the capital investment needs to be low and/or the production yields high. Opting for relatively expensive sputtering or ALE techniques as the sole methods of fabricating EL structures, is both commercially and scientifically ill-advised. Considerable effort was spent in developing cheaper alternative techniques for thin film deposition. The main objectives of the contract can be summarized as follows: (1) to deposit high quality ZnS thin films by MOCVD, (2) to dope the ZnS thin film with Mn, (3) to deposit high quality dielectric films using a novel spray pyrolysis process, (4) to evaluate optimized insulator/ZnS-Mn/insulator structures, and (5) the fabrication of large area XY matrix ACEL structures.

  4. Thin film temperature sensor

    NASA Technical Reports Server (NTRS)

    Grant, H. P.; Przybyszewski, J. S.

    1980-01-01

    Thin film surface temperature sensors were developed. The sensors were made of platinum-platinum/10 percent rhodium thermocouples with associated thin film-to-lead wire connections and sputtered on aluminum oxide coated simulated turbine blades for testing. Tests included exposure to vibration, low velocity hydrocarbon hot gas flow to 1250 K, and furnace calibrations. Thermal electromotive force was typically two percent below standard type S thermocouples. Mean time to failure was 42 hours at a hot gas flow temperature of 1250 K and an average of 15 cycles to room temperature. Failures were mainly due to separation of the platinum thin film from the aluminum oxide surface. Several techniques to improve the adhesion of the platinum are discussed.

  5. Thin film photovoltaics

    SciTech Connect

    Zweibel, K; Ullal, H S

    1989-05-01

    Thin films are considered a potentially attractive technological approach to making cost-effective electricity by photovoltaics. Over the last twenty years, many have been investigated and some (cadmium telluride, copper indium diselenide, amorphous silicon) have become leading candidates for future large-scale commercialization. This paper surveys the past development of these key thin films and gives their status and future prospects. In all cases, significant progress toward cost-effective PV electricity has been made. If this progress continues, it appears that thin film PV could provide electricity that is competitive for summer daytime peaking power requirements by the middle of the 1990s; and electricity in a range that is competitive with fossil fuel costs (i.e., 6 cents/kilowatt-hour) should be available from PV around the turn of the century. 22 refs., 9 figs.

  6. Dielectric films improve life of polymeric insulators

    NASA Technical Reports Server (NTRS)

    Hudis, M.; Wydeven, T.

    1975-01-01

    Degradation of polymeric insulators may be significantly reduced when polymer surfaces are coated with film having gradation of dielectric constants, larger where it is in contact with polymer and smaller at its exposed surface.

  7. Photo-induced insulator-metal transition in Pr0.6Ca0.4MnO3 thin films grown by pulsed laser deposition: Effect of thickness dependent structural and transport properties

    NASA Astrophysics Data System (ADS)

    Elovaara, Tomi; Huhtinen, Hannu; Majumdar, Sayani; Paturi, Petriina

    2016-09-01

    We report photo-induced colossal magnetoresistive insulator-metal transition (IMT) in Pr0.6Ca0.4MnO3 thin films under much reduced applied magnetic field. The colossal effect was studied as a function of film thickness and thus with variable structural properties. Thorough structural, magnetic and magnetotransport characterization under light shows that the highest effect on the transition field can be obtained in the thinnest film (38 nm). However, due to the substrate induced strain of this film the required magnetic field for IMT is quite high. The best crystalline properties of the 110 nm film lead to the lowest IMT field under light and 109% change in resistance at 10 K. With increasing thickness, the film properties start to move more toward the bulk material and, hence, IMT is no more observed under the applied field of 9 T. Our results indicate that for obtaining large photo-induced CMR, the best epitaxial quality of thin films is essential.

  8. Thin film ceramic thermocouples

    NASA Technical Reports Server (NTRS)

    Gregory, Otto (Inventor); Fralick, Gustave (Inventor); Wrbanek, John (Inventor); You, Tao (Inventor)

    2011-01-01

    A thin film ceramic thermocouple (10) having two ceramic thermocouple (12, 14) that are in contact with each other in at least on point to form a junction, and wherein each element was prepared in a different oxygen/nitrogen/argon plasma. Since each element is prepared under different plasma conditions, they have different electrical conductivity and different charge carrier concentration. The thin film thermocouple (10) can be transparent. A versatile ceramic sensor system having an RTD heat flux sensor can be combined with a thermocouple and a strain sensor to yield a multifunctional ceramic sensor array. The transparent ceramic temperature sensor that could ultimately be used for calibration of optical sensors.

  9. Thin film photovoltaic device

    DOEpatents

    Catalano, Anthony W.; Bhushan, Manjul

    1982-01-01

    A thin film photovoltaic solar cell which utilizes a zinc phosphide semiconductor is of the homojunction type comprising an n-type conductivity region forming an electrical junction with a p-type region, both regions consisting essentially of the same semiconductor material. The n-type region is formed by treating zinc phosphide with an extrinsic dopant such as magnesium. The semiconductor is formed on a multilayer substrate which acts as an opaque contact. Various transparent contacts may be used, including a thin metal film of the same chemical composition as the n-type dopant or conductive oxides or metal grids.

  10. Thin film photovoltaic device

    DOEpatents

    Catalano, A.W.; Bhushan, M.

    1982-08-03

    A thin film photovoltaic solar cell which utilizes a zinc phosphide semiconductor is of the homojunction type comprising an n-type conductivity region forming an electrical junction with a p-type region, both regions consisting essentially of the same semiconductor material. The n-type region is formed by treating zinc phosphide with an extrinsic dopant such as magnesium. The semiconductor is formed on a multilayer substrate which acts as an opaque contact. Various transparent contacts may be used, including a thin metal film of the same chemical composition as the n-type dopant or conductive oxides or metal grids. 5 figs.

  11. 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.

  12. Thin films for material engineering

    NASA Astrophysics Data System (ADS)

    Wasa, Kiyotaka

    2016-07-01

    Thin films are defined as two-dimensional materials formed by condensing one by one atomic/molecular/ionic species of matter in contrast to bulk three-dimensional sintered ceramics. They are grown through atomic collisional chemical reaction on a substrate surface. Thin film growth processes are fascinating for developing innovative exotic materials. On the basis of my long research on sputtering deposition, this paper firstly describes the kinetic energy effect of sputtered adatoms on thin film growth and discusses on a possibility of room-temperature growth of cubic diamond crystallites and the perovskite thin films of binary compound PbTiO3. Secondly, high-performance sputtered ferroelectric thin films with extraordinary excellent crystallinity compatible with MBE deposited thin films are described in relation to a possible application for thin-film MEMS. Finally, the present thin-film technologies are discussed in terms of a future material science and engineering.

  13. Thin film solar cell workshop

    NASA Technical Reports Server (NTRS)

    Armstrong, Joe; Jeffrey, Frank

    1993-01-01

    A summation of responses to questions posed to the thin-film solar cell workshop and the ensuing discussion is provided. Participants in the workshop included photovoltaic manufacturers (both thin film and crystalline), cell performance investigators, and consumers.

  14. Thin-film optical initiator

    DOEpatents

    Erickson, Kenneth L.

    2001-01-01

    A thin-film optical initiator having an inert, transparent substrate, a reactive thin film, which can be either an explosive or a pyrotechnic, and a reflective thin film. The resultant thin-film optical initiator system also comprises a fiber-optic cable connected to a low-energy laser source, an output charge, and an initiator housing. The reactive thin film, which may contain very thin embedded layers or be a co-deposit of a light-absorbing material such as carbon, absorbs the incident laser light, is volumetrically heated, and explodes against the output charge, imparting about 5 to 20 times more energy than in the incident laser pulse.

  15. Thermoelectric properties of topological insulator Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3}, and Bi{sub 2}Se{sub 3} thin film quantum wells

    SciTech Connect

    Osterhage, Hermann Gooth, Johannes; Hamdou, Bacel; Gwozdz, Paul; Zierold, Robert; Nielsch, Kornelius

    2014-09-22

    The thermoelectric (TE) figure of merit ZT of topological insulator Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3}, and Bi{sub 2}Se{sub 3} thin film quantum wells is calculated for thicknesses below 10 nm, for which hybridization of the surface states as well as quantum confinement in the bulk are individually predicted to enhance ZT. Here, the question is addressed what ZT can be expected from coexisting surface and bulk states in such quantum wells. It is demonstrated that the parallel contributing bulk and surface channels tend to cancel each other out. This is because the surface-to-volume ratios of the thin films prevent the domination of transport through a single channel and because the individual bulk and surface ZTs are optimized at different Fermi levels.

  16. NMR characterization of thin films

    DOEpatents

    Gerald II, Rex E.; Klingler, Robert J.; Rathke, Jerome W.; Diaz, Rocio; Vukovic, Lela

    2010-06-15

    A method, apparatus, and system for characterizing thin film materials. The method, apparatus, and system includes a container for receiving a starting material, applying a gravitational force, a magnetic force, and an electric force or combinations thereof to at least the starting material, forming a thin film material, sensing an NMR signal from the thin film material and analyzing the NMR signal to characterize the thin film of material.

  17. NMR characterization of thin films

    DOEpatents

    Gerald, II, Rex E.; Klingler, Robert J.; Rathke, Jerome W.; Diaz, Rocio; Vukovic, Lela

    2008-11-25

    A method, apparatus, and system for characterizing thin film materials. The method, apparatus, and system includes a container for receiving a starting material, applying a gravitational force, a magnetic force, and an electric force or combinations thereof to at least the starting material, forming a thin film material, sensing an NMR signal from the thin film material and analyzing the NMR signal to characterize the thin film of material.

  18. Selective inorganic thin films

    SciTech Connect

    Phillips, M.L.F.; Weisenbach, L.A.; Anderson, M.T.

    1995-05-01

    This project is developing inorganic thin films as membranes for gas separation applications, and as discriminating coatings for liquid-phase chemical sensors. Our goal is to synthesize these coatings with tailored porosity and surface chemistry on porous substrates and on acoustic and optical sensors. Molecular sieve films offer the possibility of performing separations involving hydrogen, air, and natural gas constituents at elevated temperatures with very high separation factors. We are focusing on improving permeability and molecular sieve properties of crystalline zeolitic membranes made by hydrothermally reacting layered multicomponent sol-gel films deposited on mesoporous substrates. We also used acoustic plate mode (APM) oscillator and surface plasmon resonance (SPR) sensor elements as substrates for sol-gel films, and have both used these modified sensors to determine physical properties of the films and have determined the sensitivity and selectivity of these sensors to aqueous chemical species.

  19. Thin film photovoltaic cell

    DOEpatents

    Meakin, John D.; Bragagnolo, Julio

    1982-01-01

    A thin film photovoltaic cell having a transparent electrical contact and an opaque electrical contact with a pair of semiconductors therebetween includes utilizing one of the electrical contacts as a substrate and wherein the inner surface thereof is modified by microroughening while being macro-planar.

  20. Thin film scintillators

    NASA Astrophysics Data System (ADS)

    McDonald, Warren; McKinney, George; Tzolov, Marian

    2015-03-01

    Scintillating materials convert energy flux (particles or electromagnetic waves) into light with spectral characteristic matching a subsequent light detector. Commercial scintillators such as yttrium aluminum garnet (YAG) and yttrium aluminum perovskite (YAP) are commonly used. These are inefficient at lower energies due to the conductive coating present on their top surface, which is needed to avoid charging. We hypothesize that nano-structured thin film scintillators will outperform the commercial scintillators at low electron energies. We have developed alternative thin film scintillators, zinc tungstate and zinc oxide, which show promise for higher sensitivity to lower energy electrons since they are inherently conductive. Zinc tungstate films exhibit photoluminescence quantum efficiency of 74%. Cathodoluminescence spectroscopy was applied in transmission and reflection geometries. The comparison between the thin films and the YAG and YAP commercial scintillators shows much higher light output from the zinc tungstate and zinc oxide at electron energies less than 5 keV. Our films were integrated in a backscattered electron detector. This detector delivers better images than an identical detector with commercial YAG scintillator at low electron energies. Dr. Nicholas Barbi from PulseTor LLC, Dr. Anura Goonewardene, NSF Grants: #0806660, #1058829, #0923047.

  1. Coalescence and percolation in thin metal films

    SciTech Connect

    Yu, X.; Duxbury, P.M.; Jeffers, G.; Dubson, M.A. Center for Fundamental Materials Research, Michigan State University, East Lansing, Michigan 48824-1116 )

    1991-12-15

    Metals thermally evaporated onto warm insulating substrates evolve to the thin-film state via the morphological sequence: compact islands, elongated islands, percolation, hole filling, and finally the thin-film state. The coverage at which the metal percolates ({ital p}{sub {ital c}}) is often considerably higher than that predicted by percolation models, such as inverse swiss cheese or lattice percolation. Using a simple continuum model, we show that high-{ital p}{sub {ital c}}'s arise naturally in thin films that exhibit a crossover from full coalescence of islands at early stages of growth to partial coalescence at later stages. In this interrupted-coalescence model, full coalescence of islands occurs up to a critical island radius {ital R}{sub {ital c}}, after which islands overlap, but do not fully coalesce. We present the morphology of films and the critical area coverages generated by this model.

  2. Thin film solar cell module

    SciTech Connect

    Gay, R.R.

    1987-01-20

    A thin film solar cell module is described comprising a first solar cell panel containing an array of solar cells consisting of a TFS semiconductor sandwiched between a transparent conductive zinc oxide layer and a transparent conductive layer selected from the group consisting of tin oxide, indium tin oxide, and zinc oxide deposited upon a transparent superstrate, and a second solar cell panel containing an array of solar cells consisting of a CIS semiconductor layer sandwiched between a zinc oxide semiconductor layer and a conductive metal layer deposited upon an insulating substrate. The zinc oxide semiconductor layer contains a first relatively thin layer of high resistivity zinc oxide adjacent the CIS semiconductor and a second relatively thick layer of low resistivity zinc oxide overlying the high resistivity zinc oxide layer. The transparent conductive zinc oxide layer of the first panel faces the low resistivity zinc oxide layer of the second panel, the first and second panels being positioned optically in series and separated by a transparent insulating layer.

  3. Carrier tuning the metal-insulator transition of epitaxial La0.67Sr0.33MnO3 thin film on Nb doped SrTiO3 substrate

    NASA Astrophysics Data System (ADS)

    Zhan, J. M.; Li, P. G.; Liu, H.; Tao, S. L.; Ma, H.; Shen, J. Q.; Pan, M. J.; Zhang, Z. J.; Wang, S. L.; Yuan, G. L.

    2016-04-01

    La0.67Sr0.33MnO3 (LSMO) thin films were deposited on (001)SrTiO3(STO) and n-type doped Nb:SrTiO3(NSTO) single crystal substrates respectively. The metal to insulator transition temperature(TMI) of LSMO film on NSTO is lower than that on STO, and the TMI of LSMO can be tuned by changing the applied current in the LSMO/NSTO p-n junction. Such behaviors were considered to be related to the carrier concentration redistribution in LSMO film caused by the change of depletion layer thickness in p-n junction which depends greatly on the applied electric field. The phenomenon could be used to configure artificial devices and exploring the underlying physics.

  4. DC current induced metal-insulator transition in epitaxial Sm{sub 0.6}Nd{sub 0.4}NiO{sub 3}/LaAlO{sub 3} thin film

    SciTech Connect

    Huang, Haoliang; Luo, Zhenlin Yang, Yuanjun; Yang, Mengmeng; Wang, Haibo; Hu, Sixia; Bao, Jun; Yun, Yu; Meng, Dechao; Lu, Yalin; Gao, Chen

    2014-05-15

    The metal-insulator transition (MIT) in strong correlated electron materials can be induced by external perturbation in forms of thermal, electrical, optical, or magnetic fields. We report on the DC current induced MIT in epitaxial Sm{sub 0.6}Nd{sub 0.4}NiO{sub 3} (SNNO) thin film deposited by pulsed laser deposition on (001)-LaAlO{sub 3} substrate. It was found that the MIT in SNNO film not only can be triggered by thermal, but also can be induced by DC current. The T{sub MI} of SNNO film decreases from 282 K to 200 K with the DC current density increasing from 0.003 × 10{sup 9} A•m{sup −2} to 4.9 × 10{sup 9} A•m{sup −2}. Based on the resistivity curves measured at different temperatures, the MIT phase diagram has been successfully constructed.

  5. Time-resolved terahertz dynamics in thin films of the topological insulator Bi2Se3

    SciTech Connect

    Valdés Aguilar, R.; Qi, J.; Brahlek, M.; Bansal, N.; Azad, A.; Bowlan, J.; Oh, S.; Taylor, A. J.; Prasankumar, R. P.; Yarotski, D. A.

    2015-01-07

    We use optical pump–THz probe spectroscopy at low temperatures to study the hot carrier response in thin Bi2Se3 films of several thicknesses, allowing us to separate the bulk from the surface transient response. We find that for thinner films the photoexcitation changes the transport scattering rate and reduces the THz conductivity, which relaxes within 10 picoseconds (ps). For thicker films, the conductivity increases upon photoexcitation and scales with increasing both the film thickness and the optical fluence, with a decay time of approximately 5 ps as well as a much higher scattering rate. Furthermore, these different dynamics are attributed to the surface and bulk electrons, respectively, and demonstrate that long-lived mobile surface photo-carriers can be accessed independently below certain film thicknesses for possible optoelectronic applications.

  6. Effect of annealing temperature of Bi1.5Zn1.0Nb1.5O7 gate insulator on performance of ZnO based thin film transistors

    NASA Astrophysics Data System (ADS)

    Wei, Ye; Wei, Ren; Peng, Shi; Zhuangde, Jiang

    2016-07-01

    The bottom-gate structure ZnO based thin film transistors (ZnO-TFTs) using Bi1.5Zn1.0Nb1.5O7 (BZN) thin films as gate insulator were fabricated on Pt/SiO2/Si substrate by radio frequency magnetic sputtering. We investigated the effect of annealing temperature at 300, 400, and 500 °C on the performance of BZN thin films and ZnO-TFTs. XRD measurement confirmed that BZN thin films were amorphous in nature. BZN thin films annealed at 400 °C obtain the high capacitance density of 249 nF/cm2, high dielectric constant of 71, and low leakage current density of 10‑7 A/cm2 on/off current ratio and field effect mobility of ZnO-TFTs annealed at 400 °C are approximately one order of magnitude and two times, respectively higher than that of ZnO-TFTs annealed at 300 °C. When the annealing temperature is 400 °C, the electrical performance of ZnO-TFTs is enhanced remarkably. Devices obtain a low sub-threshold swing of 470 mV/dec and surface states density of 3.21 × 1012cm‑2. Project supported by the National Natural Science Foundation of China (Nos. 51332003, 51202184), the International Science & Technology Cooperation Program of China (Nos. 2010DFB13640, 2011DFA51880), and the “111 Project” of China (No. B14040).

  7. Thin film superconductor magnetic bearings

    DOEpatents

    Weinberger, Bernard R.

    1995-12-26

    A superconductor magnetic bearing includes a shaft (10) that is subject to a load (L) and rotatable around an axis of rotation, a magnet (12) mounted to the shaft, and a stator (14) in proximity to the shaft. The stator (14) has a superconductor thin film assembly (16) positioned to interact with the magnet (12) to produce a levitation force on the shaft (10) that supports the load (L). The thin film assembly (16) includes at least two superconductor thin films (18) and at least one substrate (20). Each thin film (18) is positioned on a substrate (20) and all the thin films are positioned such that an applied magnetic field from the magnet (12) passes through all the thin films. A similar bearing in which the thin film assembly (16) is mounted on the shaft (10) and the magnet (12) is part of the stator (14) also can be constructed.

  8. Thin film superconductor magnetic bearings

    SciTech Connect

    Weinberger, B.R.

    1995-12-26

    A superconductor magnetic bearing includes a shaft that is subject to a load (L) and rotatable around an axis of rotation, a magnet mounted to the shaft, and a stator in proximity to the shaft. The stator has a superconductor thin film assembly positioned to interact with the magnet to produce a levitation force on the shaft that supports the load (L). The thin film assembly includes at least two superconductor thin films and at least one substrate. Each thin film is positioned on a substrate and all the thin films are positioned such that an applied magnetic field from the magnet passes through all the thin films. A similar bearing in which the thin film assembly is mounted on the shaft and the magnet is part of the stator also can be constructed. 8 figs.

  9. Electric Properties and Interface Charge Trap Density of Ferroelectric Gate Thin Film Transistor Using (Bi,La)4Ti3O12/Pb(Zr,Ti)O3 Stacked Gate Insulator

    NASA Astrophysics Data System (ADS)

    Van Thanh, Pham; Trinh, Bui Nguyen Quoc; Miyasako, Takaaki; Trong Tue, Phan; Tokumitsu, Eisuke; Shimoda, Tatsuya

    2012-09-01

    We successfully fabricated ferroelectric gate thin film transistors (FGTs) using solution-processed (Bi,La)4Ti3O12 (BLT)/Pb(Zr,Ti)O3 (PZT) stacked films and an indium-tin oxide (ITO) film as ferroelectric gate insulators and an oxide channel, respectively. The typical n-type channel transistors were obtained with the counterclockwise hysteresis loop due to the ferroelectric property of the BLT/PZT stacked gate insulators. These FGTs exhibited good device performance characteristics, such as a high ON/OFF ratio of 106, a large memory window of 1.7-3.1 V, and a large ON current of 0.5-2.5 mA. In order to investigate interface charge trapping for these devices, we applied the conductance method to MFS capacitors, i.e., Pt/ITO/BLT/PZT/Pt capacitors. As a result, the interface charge trap density (Dit) between the ITO and BLT/PZT stacked films was estimated to be in the range of 10-11-10-12 eV-1 cm-2. The small Dit value suggested that good interfaces were achieved.

  10. Electric Properties and Interface Charge Trap Density of Ferroelectric Gate Thin Film Transistor Using (Bi,La)4Ti3O12/Pb(Zr,Ti)O3 Stacked Gate Insulator

    NASA Astrophysics Data System (ADS)

    Thanh, Pham Van; Trinh, Bui Nguyen Quoc; Miyasako, Takaaki; Tue, Phan Trong; Tokumitsu, Eisuke; Shimoda, Tatsuya

    2012-09-01

    We successfully fabricated ferroelectric gate thin film transistors (FGTs) using solution-processed (Bi,La)4Ti3O12 (BLT)/Pb(Zr,Ti)O3 (PZT) stacked films and an indium--tin oxide (ITO) film as ferroelectric gate insulators and an oxide channel, respectively. The typical n-type channel transistors were obtained with the counterclockwise hysteresis loop due to the ferroelectric property of the BLT/PZT stacked gate insulators. These FGTs exhibited good device performance characteristics, such as a high ON/OFF ratio of 106, a large memory window of 1.7--3.1 V, and a large ON current of 0.5--2.5 mA. In order to investigate interface charge trapping for these devices, we applied the conductance method to MFS capacitors, i.e., Pt/ITO/BLT/PZT/Pt capacitors. As a result, the interface charge trap density (Dit) between the ITO and BLT/PZT stacked films was estimated to be in the range of 10-11--10-12 eV-1 cm-2. The small Dit value suggested that good interfaces were achieved.

  11. Chiral atomically thin films

    NASA Astrophysics Data System (ADS)

    Kim, Cheol-Joo; Sánchez-Castillo, A.; Ziegler, Zack; Ogawa, Yui; Noguez, Cecilia; Park, Jiwoong

    2016-06-01

    Chiral materials possess left- and right-handed counterparts linked by mirror symmetry. These materials are useful for advanced applications in polarization optics, stereochemistry and spintronics. In particular, the realization of spatially uniform chiral films with atomic-scale control of their handedness could provide a powerful means for developing nanodevices with novel chiral properties. However, previous approaches based on natural or grown films, or arrays of fabricated building blocks, could not offer a direct means to program intrinsic chiral properties of the film on the atomic scale. Here, we report a chiral stacking approach, where two-dimensional materials are positioned layer-by-layer with precise control of the interlayer rotation (θ) and polarity, resulting in tunable chiral properties of the final stack. Using this method, we produce left- and right-handed bilayer graphene, that is, a two-atom-thick chiral film. The film displays one of the highest intrinsic ellipticity values (6.5 deg μm–1) ever reported, and a remarkably strong circular dichroism (CD) with the peak energy and sign tuned by θ and polarity. We show that these chiral properties originate from the large in-plane magnetic moment associated with the interlayer optical transition. Furthermore, we show that we can program the chiral properties of atomically thin films layer-by-layer by producing three-layer graphene films with structurally controlled CD spectra.

  12. Chiral atomically thin films.

    PubMed

    Kim, Cheol-Joo; Sánchez-Castillo, A; Ziegler, Zack; Ogawa, Yui; Noguez, Cecilia; Park, Jiwoong

    2016-06-01

    Chiral materials possess left- and right-handed counterparts linked by mirror symmetry. These materials are useful for advanced applications in polarization optics, stereochemistry and spintronics. In particular, the realization of spatially uniform chiral films with atomic-scale control of their handedness could provide a powerful means for developing nanodevices with novel chiral properties. However, previous approaches based on natural or grown films, or arrays of fabricated building blocks, could not offer a direct means to program intrinsic chiral properties of the film on the atomic scale. Here, we report a chiral stacking approach, where two-dimensional materials are positioned layer-by-layer with precise control of the interlayer rotation (θ) and polarity, resulting in tunable chiral properties of the final stack. Using this method, we produce left- and right-handed bilayer graphene, that is, a two-atom-thick chiral film. The film displays one of the highest intrinsic ellipticity values (6.5 deg μm(-1)) ever reported, and a remarkably strong circular dichroism (CD) with the peak energy and sign tuned by θ and polarity. We show that these chiral properties originate from the large in-plane magnetic moment associated with the interlayer optical transition. Furthermore, we show that we can program the chiral properties of atomically thin films layer-by-layer by producing three-layer graphene films with structurally controlled CD spectra. PMID:26900756

  13. Uncooled thin film pyroelectric IR detector with aerogel thermal isolation

    DOEpatents

    Ruffner, Judith A.; Bullington, Jeff A.; Clem, Paul G.; Warren, William L.; Brinker, C. Jeffrey; Tuttle, Bruce A.; Schwartz, Robert W.

    1999-01-01

    A monolithic infrared detector structure which allows integration of pyroelectric thin films atop low thermal conductivity aerogel thin films. The structure comprises, from bottom to top, a substrate, an aerogel insulating layer, a lower electrode, a pyroelectric layer, and an upper electrode layer capped by a blacking layer. The aerogel can offer thermal conductivity less than that of air, while providing a much stronger monolithic alternative to cantilevered or suspended air-gap structures for pyroelectric thin film pixel arrays. Pb(Zr.sub.0.4 Ti.sub.0.6)O.sub.3 thin films deposited on these structures displayed viable pyroelectric properties, while processed at 550.degree. C.

  14. Tuning the Fermi level with topological phase transition by internal strain in a topological insulator Bi2Se3 thin film

    NASA Astrophysics Data System (ADS)

    Kim, Tae-Hyeon; Jeong, Kwangsik; Park, Byung Cheol; Choi, Hyejin; Park, Sang Han; Jung, Seonghoon; Park, Jaehun; Jeong, Kwang-Ho; Kim, Jeong Won; Kim, Jae Hoon; Cho, Mann-Ho

    2015-12-01

    In a three-dimensional topological insulator Bi2Se3, a stress control for band gap manipulation was predicted but no systematic investigation has been performed yet due to the requirement of large external stress. We report herein on the strain-dependent results for Bi2Se3 films of various thicknesses that are grown via a self-organized ordering process. Using small angle X-ray scattering and Raman spectroscopy, the changes of d-spacings in the crystal structure and phonon vibration shifts resulted from stress are clearly observed when the film thickness is below ten quintuple layers. From the UV photoemission/inverse photoemission spectroscopy (UPS/IPES) results and ab initio calculations, significant changes of the Fermi level and band gap were observed. The deformed band structure also exhibits a Van Hove singularity at specific energies in the UV absorption experiment and ab initio calculations. Our results, including the synthesis of a strained ultrathin topological insulator, suggest a new direction for electronic and spintronic applications for the future.In a three-dimensional topological insulator Bi2Se3, a stress control for band gap manipulation was predicted but no systematic investigation has been performed yet due to the requirement of large external stress. We report herein on the strain-dependent results for Bi2Se3 films of various thicknesses that are grown via a self-organized ordering process. Using small angle X-ray scattering and Raman spectroscopy, the changes of d-spacings in the crystal structure and phonon vibration shifts resulted from stress are clearly observed when the film thickness is below ten quintuple layers. From the UV photoemission/inverse photoemission spectroscopy (UPS/IPES) results and ab initio calculations, significant changes of the Fermi level and band gap were observed. The deformed band structure also exhibits a Van Hove singularity at specific energies in the UV absorption experiment and ab initio calculations. Our

  15. Biomimetic thin film deposition

    SciTech Connect

    Rieke, P.R.; Graff, G.E.; Campbell, A.A.; Bunker, B.C.; Baskaran, S.; Song, L.; Tarasevich, B.J.; Fryxell, G.E.

    1995-09-01

    Biological mineral deposition for the formation of bone, mollusk shell and other hard tissues provides materials scientists with illustrative materials processing strategies. This presentation will review the key features of biomineralization and how these features can be of technical importance. We have adapted existing knowledge of biomineralization to develop a unique method of depositing inorganic thin films and coating. Our approach to thin film deposition is to modify substrate surfaces to imitate the proteins found in nature that are responsible for controlling mineral deposition. These biomimetic surfaces control the nucleation and growth of the mineral from a supersaturated aqueous solution. This has many processing advantages including simple processing equipment, environmentally benign reagents, uniform coating of highly complex shapes, and enhanced adherence of coating. Many different types of metal oxide, hydroxide, sulfide and phosphate materials with useful mechanical, optical, electronic and biomedical properties can be deposited.

  16. thin films as absorber

    NASA Astrophysics Data System (ADS)

    González, J. O.; Shaji, S.; Avellaneda, D.; Castillo, G. A.; Das Roy, T. K.; Krishnan, B.

    2014-09-01

    Photovoltaic structures were prepared using AgSb(S x Se1- x )2 as absorber and CdS as window layer at various conditions via a hybrid technique of chemical bath deposition and thermal evaporation followed by heat treatments. Silver antimony sulfo selenide thin films [AgSb(S x Se1- x )2] were prepared by heating multilayers of sequentially deposited Sb2S3/Ag dipped in Na2SeSO3 solution, glass/Sb2S3/Ag/Se. For this, Sb2S3 thin films were deposited from a chemical bath containing SbCl3 and Na2S2O3. Then, Ag thin films were thermally evaporated on glass/Sb2S3, followed by selenization by dipping in an acidic solution of Na2SeSO3. The duration of dipping was varied as 3, 4 and 5 h. Two different heat treatments, one at 350 °C for 20 min in vacuum followed by a post-heat treatment at 325 °C for 2 h in Ar, and the other at 350 °C for 1 h in Ar, were applied to the multilayers of different configurations. X-ray diffraction results showed the formation of AgSb(S x Se1- x )2 thin films as the primary phase and AgSb(S,Se)2 and Sb2S3 as secondary phases. Morphology and elemental detection were done by scanning electron microscopy and energy dispersive X-ray analysis. X-ray photoelectron spectroscopic studies showed the depthwise composition of the films. Optical properties were determined by UV-vis-IR transmittance and reflection spectral analysis. AgSb(S x Se1- x )2 formed at different conditions was incorporated in PV structures glass/FTO/CdS/AgSb(S x Se1- x )2/C/Ag. Chemically deposited post-annealed CdS thin films of various thicknesses were used as window layer. J- V characteristics of the cells were measured under dark and AM1.5 illumination. Analysis of the J- V characteristics resulted in the best solar cell parameters of V oc = 520 mV, J sc = 9.70 mA cm-2, FF = 0.50 and η = 2.7 %.

  17. Microstructure and transport properties of epitaxial topological insulator Bi2Se3 thin films grown on MgO (100), Cr2O3 (0001), and Al2O3 (0001) templates

    NASA Astrophysics Data System (ADS)

    Lee, Y. F.; Kumar, R.; Hunte, F.; Narayan, J.; Schwartz, J.

    2015-09-01

    We report the epitaxial integration of defect-induced room temperature ferromagnetic insulators, Cr2O3 and MgO, with topological insulators Bi2Se3 on c-sapphire substrate by pulsed laser deposition. The structural, magnetic, and magnetotransport properties of ˜15 nm Bi2Se3 thin films are investigated on each template. The lattice misfits of Cr2O3/Bi2Se3 and MgO/Bi2Se3 are ˜16% and ˜39%, respectively, where the critical thickness for pseudomorphic growth is less than one monolayer. The insulating behavior is more pronounced due to the additional scattering of the surface states of the Bi2Se3 layer by interfacing with MgO and Cr2O3. The weak antilocalization effect from the surface states is clearly suppressed, accounting for the presence of magnetic bottom layers. This work demonstrates an effective way to study the emergence of a ferromagnetic phase in topological insulators by the magnetic proximity effect in Bi2Se3, a step toward unveiling their exotic properties.

  18. Polycrystalline thin film photovoltaics

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Ullal, H. S.; Mitchell, R. L.

    Significant progress has recently been made towards improving the efficiencies of polycrystalline thin-film solar cells and modules using CuInSe2 and CdTe. The history of using CuInSe2 and CdTe for solar cells is reviewed. Initial outdoor stability tests of modules are encouraging. Progress in semiconductor deposition techniques has also been substantial. Both CuInSe2 and CdTe are positioned for commercialization during the 1990s. The major participants in developing these materials are described. The US DOE/SERI (Solar Energy Research Institute) program recognizes the rapid progress and important potential of polycrystalline thin films to meet ambitious cost and performance goals. US DOE/SERI is in the process of funding an initiative in this area with the goal of ensuring US leadership in the development of these technologies. The polycrystalline thin-film module development initiative, the modeling and stability of the devices, and health and safety issues are discussed.

  19. Ferroelectric/Dielectric Double Gate Insulator Spin-Coated Using Barium Titanate Nanocrystals for an Indium Oxide Nanocrystal-Based Thin-Film Transistor.

    PubMed

    Pham, Hien Thu; Yang, Jin Ho; Lee, Don-Sung; Lee, Byoung Hun; Jeong, Hyun-Dam

    2016-03-23

    Barium titanate nanocrystals (BT NCs) were prepared under solvothermal conditions at 200 °C for 24 h. The shape of the BT NCs was tuned from nanodot to nanocube upon changing the polarity of the alcohol solvent, varying the nanosize in the range of 14-22 nm. Oleic acid-passivated NCs showed good solubility in a nonpolar solvent. The effect of size and shape of the BT NCs on the ferroelectric properties was also studied. The maximum polarization value of 7.2 μC/cm(2) was obtained for the BT-5 NC thin film. Dielectric measurements of the films showed comparable dielectric constant values of BT NCs over 1-100 kHz without significant loss. Furthermore, the bottom gate In2O3 NC thin film transistors exhibited outstanding device performance with a field-effect mobility of 11.1 cm(2) V(-1) s(-1) at a low applied gate voltage with BT-5 NC/SiO2 as the gate dielectric. The low-density trapped state was observed at the interface between the In2O3 NC semiconductor and the BT-5 NCs/SiO2 dielectric film. Furthermore, compensation of the applied gate field by an electric dipole-induced dipole field within the BT-5 NC film was also observed. PMID:26927618

  20. Tuning the Fermi level with topological phase transition by internal strain in a topological insulator Bi2Se3 thin film.

    PubMed

    Kim, Tae-Hyeon; Jeong, KwangSik; Park, Byung Cheol; Choi, Hyejin; Park, Sang Han; Jung, Seonghoon; Park, Jaehun; Jeong, Kwang-Ho; Kim, Jeong Won; Kim, Jae Hoon; Cho, Mann-Ho

    2016-01-14

    In a three-dimensional topological insulator Bi2Se3, a stress control for band gap manipulation was predicted but no systematic investigation has been performed yet due to the requirement of large external stress. We report herein on the strain-dependent results for Bi2Se3 films of various thicknesses that are grown via a self-organized ordering process. Using small angle X-ray scattering and Raman spectroscopy, the changes of d-spacings in the crystal structure and phonon vibration shifts resulted from stress are clearly observed when the film thickness is below ten quintuple layers. From the UV photoemission/inverse photoemission spectroscopy (UPS/IPES) results and ab initio calculations, significant changes of the Fermi level and band gap were observed. The deformed band structure also exhibits a Van Hove singularity at specific energies in the UV absorption experiment and ab initio calculations. Our results, including the synthesis of a strained ultrathin topological insulator, suggest a new direction for electronic and spintronic applications for the future. PMID:26659120

  1. Thin film mechanics

    NASA Astrophysics Data System (ADS)

    Cooper, Ryan C.

    This doctoral thesis details the methods of determining mechanical properties of two classes of novel thin films suspended two-dimensional crystals and electron beam irradiated microfilms of polydimethylsiloxane (PDMS). Thin films are used in a variety of surface coatings to alter the opto-electronic properties or increase the wear or corrosion resistance and are ideal for micro- and nanoelectromechanical system fabrication. One of the challenges in fabricating thin films is the introduction of strains which can arise due to application techniques, geometrical conformation, or other spurious conditions. Chapters 2-4 focus on two dimensional materials. This is the intrinsic limit of thin films-being constrained to one atomic or molecular unit of thickness. These materials have mechanical, electrical, and optical properties ideal for micro- and nanoelectromechanical systems with truly novel device functionality. As such, the breadth of applications that can benefit from a treatise on two dimensional film mechanics is reason enough for exploration. This study explores the anomylously high strength of two dimensional materials. Furthermore, this work also aims to bridge four main gaps in the understanding of material science: bridging the gap between ab initio calculations and finite element analysis, bridging the gap between ab initio calculations and experimental results, nanoscale to microscale, and microscale to mesoscale. A nonlinear elasticity model is used to determine the necessary elastic constants to define the strain-energy density function for finite strain. Then, ab initio calculations-density functional theory-is used to calculate the nonlinear elastic response. Chapter 2 focuses on validating this methodology with atomic force microscope nanoindentation on molybdenum disulfide. Chapter 3 explores the convergence criteria of three density functional theory solvers to further verify the numerical calculations. Chapter 4 then uses this model to investigate

  2. Resonance-type thickness dependence of optical second-harmonic generation in thin films of the topological insulator B i2S e3

    NASA Astrophysics Data System (ADS)

    Glinka, Yuri D.; Babakiray, Sercan; Johnson, Trent A.; Holcomb, Mikel B.; Lederman, David

    2015-05-01

    Optical second-harmonic generation (SHG) has been measured in a reflection from the nanometer-thick films (6 to 40 nm) of the topological insulator B i2S e3 using 1.51 eV (820 nm) Ti:Sapphire laser photons and revealed a strong dependence of the integral SHG intensity on the film thickness. The integral SHG intensity was determined by area integration of the SHG rotational anisotropy patterns measured for different input-output light polarization geometries. A ˜100-fold enhancement of the integral SHG intensity with decreasing film thickness has been suggested to result from the dc-electric-field-induced SHG (EFISHG) effects. Two sources of dynamically created dc electric field were proposed: (i) the capacitor-type dc electric field that gradually increases with decreasing film thickness from 40 to 6 nm due to a dynamical imbalance of photoexcited long-lived carriers between the opposite-surface Dirac surface states and (ii) a dc electric field associated with a nonlinearly excited Dirac plasmon, which is responsible for the resonant enhancement of the integral SHG intensity for the 10 nm thick film with a Lorentz-shaped resonance of ˜1.6 nm full width at half maximum. In addition to the general SHG enhancement trends with decreasing film thickness, a relative decrease of the out-of-plane contribution with respect to the in-plane contribution was observed. Using a theoretical treatment of the measured SHG rotational anisotropy patterns, this effect has been suggested to result from the joint contributions of the linear and quadratic dc electric field effects to the EFISHG response.

  3. Polycrystalline thin film photovoltaic technology

    SciTech Connect

    Ullal, H.S.; Zweibel, K.; Mitchell, R.L.; Noufi, R.

    1991-03-01

    Low-cost, high-efficiency thin-film modules are an exciting photovoltaic technology option for generating cost-effective electricity in 1995 and beyond. In this paper we review the significant technical progress made in the following thin films: copper indium diselenide, cadmium telluride, and polycrystalline thin silicon films. Also, the recent US DOE/SERI initiative to commercialize these emerging technologies is discussed. 6 refs., 9 figs.

  4. Center for thin film studies

    NASA Astrophysics Data System (ADS)

    Shannon, Robert P.; Gibson, Ursula J.

    1987-11-01

    This report covers the first year of operation of the URI Thin Film Center (TFC), and describes a diverse array of studies on thin-film materials, substrates, and their processing and analysis. Individual efforts are highlighted in sections on nucleation studies, ion-assisted deposition, Rutherford backscattering spectrometry, Brillouin scattering, a continuum theory of the evolution of structure in thin films, a study of polishing parameters relevant to the preparation of substrates, and the setup of a characterization facility for the Center.

  5. High temperature polymer dielectric film insulation

    NASA Technical Reports Server (NTRS)

    Jones, Robert J.

    1994-01-01

    PFPI polymers were invented in the late 1970's. Assessment of emerging requirements has dictated that 300 C performance is the goal for next generation wire insulation. TRW PFPI as superior 300 C polymer candidates is presented. Included is a comparison of promising PFPI film properties with Kapton. Also included are the promising bulk polymer or coating properties.

  6. Interfacial reaction between metal-insulator transition material NbO2 thin film and wide band gap semiconductor GaN

    NASA Astrophysics Data System (ADS)

    Posadas, Agham; Kvit, Alexander; Demkov, Alexander

    Materials that undergo a metal-insulator transition (MIT) are potentially useful for a wide variety of applications including electronic and opto-electronic switches, memristors, sensors, and coatings. In most such materials, the MIT is driven by temperature. In one such material, NbO2, the MIT mechanism is primarily of the Peierls-type, in which the dimerization of the Nb atoms without electron correlation causes the transition from metallic to semiconducting. We describe our initial work at combining NbO2 and GaN in epitaxial form, which could be potentially useful in resistive switching devices operating at very high temperatures. We grow NbO2 films on GaN(0001)/Si(111) substrates using reactive molecular beam epitaxy from a metal evaporation source and molecular oxygen. X-ray diffraction shows that the films are found to grow with a single out of plane orientation but with three symmetry-related orientation domains in the plane. In situ x-ray photoelectron spectroscopy confirms that the phase pure NbO2 is formed but that a chemical reaction occurs between the GaN and NbO2 during the growth forming a polycrystalline interfacial layer. We perform STEM-EELS analysis of the film and the interface to further elucidate their chemical and structural properties.

  7. Polycrystalline thin-films

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Mitchell, R.

    1986-02-01

    This annual report summarizes the status, accomplishments, and projected future research directions of the Polycrystalline Thin Film Task in the Photovoltaic Program Branch of the Solar Energy Research Institute's Solar Electric Research Division. Major subcontracted work in this area has concentrated on development of CuInSe2 and CdTe technologies. During FY 1985, major progress was achieved by subcontractors in: (1) developing a new, low-cost method of fabricating CuInSe2, and (2) improving the efficiency of CuInSe2 devices by about 10% (relative). The report also lists research planned to meet the Department of Energy's goals in these technologies.

  8. Nonlinear optical thin films

    NASA Technical Reports Server (NTRS)

    Leslie, Thomas M.

    1993-01-01

    A focused approach to development and evaluation of organic polymer films for use in optoelectronics is presented. The issues and challenges that are addressed include: (1) material synthesis, purification, and the tailoring of the material properties; (2) deposition of uniform thin films by a variety of methods; (3) characterization of material physical properties (thermal, electrical, optical, and electro-optical); and (4) device fabrication and testing. Photonic materials, devices, and systems were identified as critical technology areas by the Department of Commerce and the Department of Defense. This approach offers strong integration of basic material issues through engineering applications by the development of materials that can be exploited as the active unit in a variety of polymeric thin film devices. Improved materials were developed with unprecedented purity and stability. The absorptive properties can be tailored and controlled to provide significant improvement in propagation losses and nonlinear performance. Furthermore, the materials were incorporated into polymers that are highly compatible with fabrication and patterning processes for integrated optical devices and circuits. By simultaneously addressing the issues of materials development and characterization, keeping device design and fabrication in mind, many obstacles were overcome for implementation of these polymeric materials and devices into systems. We intend to considerably improve the upper use temperature, poling stability, and compatibility with silicon based devices. The principal device application that was targeted is a linear electro-optic modulation etalon. Organic polymers need to be properly designed and coupled with existing integrated circuit technology to create new photonic devices for optical communication, image processing, other laser applications such as harmonic generation, and eventually optical computing. The progression from microscopic sample to a suitable film

  9. Host thin films incorporating nanoparticles

    NASA Astrophysics Data System (ADS)

    Qureshi, Uzma

    The focus of this research project was the investigation of the functional properties of thin films that incorporate a secondary nanoparticulate phase. In particular to assess if the secondary nanoparticulate material enhanced a functional property of the coating on glass. In order to achieve this, new thin film deposition methods were developed, namely use of nanopowder precursors, an aerosol assisted transport technique and an aerosol into atmospheric pressure chemical vapour deposition system. Aerosol assisted chemical vapour deposition (AACVD) was used to deposit 8 series of thin films on glass. Five different nanoparticles silver, gold, ceria, tungsten oxide and zinc oxide were tested and shown to successfully deposit thin films incorporating nanoparticles within a host matrix. Silver nanoparticles were synthesised and doped within a titania film by AACVD. This improved solar control properties. A unique aerosol assisted chemical vapour deposition (AACVD) into atmospheric pressure chemical vapour deposition (APCVD) system was used to deposit films of Au nanoparticles and thin films of gold nanoparticles incorporated within a host titania matrix. Incorporation of high refractive index contrast metal oxide particles within a host film altered the film colour. The key goal was to test the potential of nanopowder forms and transfer the suspended nanopowder via an aerosol to a substrate in order to deposit a thin film. Discrete tungsten oxide nanoparticles or ceria nanoparticles within a titanium dioxide thin film enhanced the self-cleaning and photo-induced super-hydrophilicity. The nanopowder precursor study was extended by deposition of zinc oxide thin films incorporating Au nanoparticles and also ZnO films deposited from a ZnO nanopowder precursor. Incorporation of Au nanoparticles within a VO: host matrix improved the thermochromic response, optical and colour properties. Composite VC/TiC and Au nanoparticle/V02/Ti02 thin films displayed three useful

  10. Robust Mechanical Properties of Electrically Insulative Alumina Films by Supersonic Aerosol Deposition

    NASA Astrophysics Data System (ADS)

    Lee, Jong-Gun; Cha, You-Hong; Kim, Do-Yeon; Lee, Jong-Hyuk; Lee, Tae-Kyu; Kim, Woo-Young; Park, Jieun; Lee, Dongyun; James, Scott C.; Al-Deyab, Salem S.; Yoon, Sam S.

    2015-08-01

    Electrically insulating alumina films were fabricated on steel substrates using supersonic aerosol deposition and their hardness and scratchability were measured. Alumina particles (0.4-μm diameter) were supersonically sprayed inside a low-pressure chamber using between 1 and 20 nozzle passes. These alumina particles were annealed between 300 and 800 K to determine the temperature's effect on film crystal size (37-41 nm). Smoother surface morphology and increased electrical resistance of the thin films were observed as their thicknesses grew by increasing the number of passes. Resistances of up to 10,000 MΩ demonstrate robust electrical insulation. Significant hardness was measured (1232 hv or 13.33 GPa), but the alumina films could be peeled off with normal loads of 36 and 47 N for films deposited on stainless steel and SKD11 substrates, respectively. High insulation and hardness confirm that these alumina films would make excellent electrical insulators.

  11. Thickness tunable quantum interference between surface phonon and Dirac plasmon states in thin films of the topological insulator Bi₂Se₃.

    PubMed

    Glinka, Yuri D; Babakiray, Sercan; Johnson, Trent A; Lederman, David

    2015-02-11

    We report on a >100-fold enhancement of Raman responses from Bi2Se3 thin films if laser photon energy switches from 2.33 eV (532 nm) to 1.58 eV (785 nm), which is due to direct optical coupling to Dirac surface states (SS) at the resonance energy of ∼1.5 eV (a thickness-independent enhancement) and due to nonlinearly excited Dirac plasmon (a thickness-dependent enhancement). Owing to the direct optical coupling, we observed an in-plane phonon mode of hexagonally arranged Se-atoms associated with a continuous network of Dirac SS. This mode revealed a Fano lineshape for films <15 nm thick, resulting from quantum interference between surface phonon and Dirac plasmon states. PMID:25614684

  12. Surface and substrate induced effects on thin films of the topological insulators Bi2Se3 and Bi2Te3

    SciTech Connect

    Liu, Wenliang; Peng, Xiangyang; Wei, Xiaolin; Yang, Hong; Stocks, George Malcolm; Zhong, Jianxin

    2013-01-01

    Based on van der Waals density functional calculations, we have studied few-quintuple-layer (QL) films of Bi2Se3 and Bi2Te3. The separation between the QLs near the surface is found to have a large increase after relaxation, whereas, the separation between the inner QLs is smaller and approaches the bulk value as the thickness grows, showing a two-dimensional to three-dimensional structural crossover. Accordingly, the surface Dirac cone of the Bi2Se3 film is evidently gapped for small thicknesses (two to four QLs), and the gap is reduced and, finally, is closed with the increasing thickness, agreeing well with the experiments. We further studied the substrate effect by investigating the Bi2Se3/graphene system. It is found that the underlying graphene induces a giant thickness-dependent Rashba splitting and Dirac point shift. Because Bi2Te3 films have smaller relative inter-QL expansion and stronger spin-orbit coupling, the topological features start to appear in the film as thin as two QLs in good accord with the experiments.

  13. Tuning thermoelectricity in a Bi2Se3 topological insulator via varied film thickness

    NASA Astrophysics Data System (ADS)

    Guo, Minghua; Wang, Zhenyu; Xu, Yong; Huang, Huaqing; Zang, Yunyi; Liu, Chang; Duan, Wenhui; Gan, Zhongxue; Zhang, Shou-Cheng; He, Ke; Ma, Xucun; Xue, Qikun; Wang, Yayu

    2016-01-01

    We report thermoelectric transport studies on Bi2Se3 topological insulator thin films with varied thickness grown by molecular beam epitaxy. We find that the Seebeck coefficient and thermoelectric power factor decrease systematically with the reduction of film thickness. These experimental observations can be explained quantitatively by theoretical calculations based on realistic electronic band structure of the Bi2Se3 thin films. This work illustrates the crucial role played by the topological surface states on the thermoelectric transport of topological insulators, and sheds new light on further improvement of their thermoelectric performance.

  14. Tuning thermoelectricity in a Bi2Se3 topological insulator via varied film thickness

    DOE PAGESBeta

    Guo, Minghua; Wang, Zhenyu; Xu, Yong; Huang, Huaqing; Zang, Yunyi; Liu, Chang; Duan, Wenhui; Gan, Zhongxue; Zhang, Shou-Cheng; He, Ke; et al

    2016-01-12

    We report thermoelectric transport studies on Bi2Se3 topological insulator thin films with varied thickness grown by molecular beam epitaxy. We find that the Seebeck coefficient and thermoelectric power factor decrease systematically with the reduction of film thickness. These experimental observations can be explained quantitatively by theoretical calculations based on realistic electronic band structure of the Bi2Se3 thin films. Lastly, this work illustrates the crucial role played by the topological surface states on the thermoelectric transport of topological insulators, and sheds new light on further improvement of their thermoelectric performance.

  15. Epitaxial growth of in-plane-dimerized, single phase NbO2 thin films for metal-insulator transition applications

    NASA Astrophysics Data System (ADS)

    Posadas, Agham; Hadamek, Tobias; O'Hara, Andy; Demkov, Alexander

    2015-03-01

    NbO2 is a exhibits a metal-insulator transition that may have potential applications in electronic devices. The strong conductivity change in NbO2 occurs along the dimerization direction and for devices utilizing NbO2 as a channel material (in-plane transport) such as transistors, one would like the dimerization direction to be in the plane of the film. The electrical properties of Nb oxides are strongly dependent on the oxidation state of Nb. It is therefore critical to be able to control the oxidation state of Nb during growth. Here, we describe the epitaxial growth of in-plane-dimerized NbO2 using molecular beam epitaxy on a variety of substrates (STO, LSAT, MgO, BTO and GaN), growth temperatures, and oxygen-to-niobium flux ratios. We show that the particular substrate used significantly affects the bulk and surface crystallinity, as well as the degree of oxidation. We also show the evolution of the valence and core level photoemission spectra of Nb oxides as a function of oxygen-to-niobium flux ratio and point out the optimum growth conditions to achieve phase-pure, epitaxial NbO2 films.

  16. Thin film atomic hydrogen detectors

    NASA Technical Reports Server (NTRS)

    Gruber, C. L.

    1977-01-01

    Thin film and bead thermistor atomic surface recombination hydrogen detectors were investigated both experimentally and theoretically. Devices were constructed on a thin Mylar film substrate. Using suitable Wheatstone bridge techniques sensitivities of 80 microvolts/2x10 to the 13th power atoms/sec are attainable with response time constants on the order of 5 seconds.

  17. Polysilicon thin films and interfaces

    SciTech Connect

    Kamins, T. ); Raicu, B. ); Thompson, C.V. )

    1990-01-01

    This volume contains the proceedings of a symposium on polysilicon thin films and interfaces, held as part of the 1990 Materials Research Society Spring Meeting. Topics covered include: crystal grown fo silicon and germanium wafers for photovoltaic devices, microanalysis of tungsten silicide interface, thermal processing of polysilicon thin films, and electrical and optical properties of polysilicon sheets for photovoltaic devices.

  18. Thin film ion conducting coating

    DOEpatents

    Goldner, Ronald B.; Haas, Terry; Wong, Kwok-Keung; Seward, George

    1989-01-01

    Durable thin film ion conducting coatings are formed on a transparent glass substrate by the controlled deposition of the mixed oxides of lithium:tantalum or lithium:niobium. The coatings provide durable ion transport sources for thin film solid state storage batteries and electrochromic energy conservation devices.

  19. Effect of ZnO channel thickness on the device behaviour of nonvolatile memory thin film transistors with double-layered gate insulators of Al2O3 and ferroelectric polymer

    NASA Astrophysics Data System (ADS)

    Yoon, Sung-Min; Yang, Shin-Hyuk; Park, Sang-Hee Ko; Jung, Soon-Won; Cho, Doo-Hee; Byun, Chun-Won; Kang, Seung-Youl; Hwang, Chi-Sun; Yu, Byoung-Gon

    2009-12-01

    Poly(vinylidene fluoride trifluoroethylene) and ZnO were employed for nonvolatile memory thin film transistors as ferroelectric gate insulator and oxide semiconducting channel layers, respectively. It was proposed that the thickness of the ZnO layer be carefully controlled for realizing the lower programming voltage, because the serially connected capacitor by the formation of a fully depleted ZnO channel had a critical effect on the off programming voltage. The fabricated memory transistor with Al/P(VDF-TrFE) (80 nm)/Al2O3 (4 nm)/ZnO (5 nm) exhibits encouraging behaviour such as a memory window of 3.8 V at the gate voltage of -10 to 12 V, and 107 on/off ratio, and a gate leakage current of 10-11 A.

  20. Polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Mitchell, R.; Ullal, H.

    1987-02-01

    This annual report for fiscal year 1986 summarizes the status, accomplishments, and projected future research directions of the Polycrystalline Thin Film Task in the Photovoltaic Program Branch of the Solar Energy Research Institute's Solar Electric Research Division. Subcontracted work in this area has concentrated on the development of CuInSe2 and CdTe technologies. During FY 1986, major progress was achieved by subcontractors in (1) achieving 10.5% (SERI-verified) efficiency with CdTe, (2) improving the efficiency of selenized CuInSe2 solar cells to nearly 8%, and (3) developing a transparent contact to CdTe cells for potential use in the top cells of tandem structures.

  1. Polyimide Aerogel Thin Films

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann; Guo, Haiquan

    2012-01-01

    Polyimide aerogels have been crosslinked through multifunctional amines. This invention builds on "Polyimide Aerogels With Three-Dimensional Cross-Linked Structure," and may be considered as a continuation of that invention, which results in a polyimide aerogel with a flexible, formable form. Gels formed from polyamic acid solutions, end-capped with anhydrides, and cross-linked with the multifunctional amines, are chemically imidized and dried using supercritical CO2 extraction to give aerogels having density around 0.1 to 0.3 g/cubic cm. The aerogels are 80 to 95% porous, and have high surface areas (200 to 600 sq m/g) and low thermal conductivity (as low as 14 mW/m-K at room temperature). Notably, the cross-linked polyimide aerogels have higher modulus than polymer-reinforced silica aerogels of similar density, and can be fabricated as both monoliths and thin films.

  2. Ferromagnetic thin films

    DOEpatents

    Krishnan, Kannan M.

    1994-01-01

    A ferromagnetic .delta.-Mn.sub.1-x Ga.sub.x thin film having perpendicular anisotropy is described which comprises: (a) a GaAs substrate, (b) a layer of undoped GaAs overlying said substrate and bonded thereto having a thickness ranging from about 50 to about 100 nanometers, (c) a layer of .delta.-Mn.sub.1-x Ga.sub.x overlying said layer of undoped GaAs and bonded thereto having a thickness ranging from about 20 to about 30 nanometers, and (d) a layer of GaAs overlying said layer of .delta.-Mn.sub.1-x Ga.sub.x and bonded thereto having a thickness ranging from about 2 to about 5 nanometers, wherein x is 0.4 .+-.0.05.

  3. Ferromagnetic thin films

    DOEpatents

    Krishnan, K.M.

    1994-12-20

    A ferromagnetic [delta]-Mn[sub 1[minus]x]Ga[sub x] thin film having perpendicular anisotropy is described which comprises: (a) a GaAs substrate, (b) a layer of undoped GaAs overlying said substrate and bonded thereto having a thickness ranging from about 50 to about 100 nanometers, (c) a layer of [delta]-Mn[sub 1[minus]x]Ga[sub x] overlying said layer of undoped GaAs and bonded thereto having a thickness ranging from about 20 to about 30 nanometers, and (d) a layer of GaAs overlying said layer of [delta]-Mn[sub 1[minus]x]Ga[sub x] and bonded thereto having a thickness ranging from about 2 to about 5 nanometers, wherein x is 0.4[+-]0.05. 7 figures.

  4. Tunable metal-insulator transition in Nd{sub 1−x}Y{sub x}NiO{sub 3} (x = 0.3, 0.4) perovskites thin film at near room temperature

    SciTech Connect

    Shao, Tao; Qi, Zeming Wang, Yuyin; Li, Yuanyuan; Yang, Mei; Zhang, Guobin; Wang, Yu; Liu, Miao

    2015-07-13

    Metal-insulator transition (MIT) occurs due to the charge disproportionation and lattice distortions in rare-earth nickelates. Existing studies revealed that the MIT behavior of rare-earth nickelates is fairly sensitive to external stress/pressure, suggesting a viable route for MIT strain engineering. Unlike applying extrinsic strain, the MIT can also be modulated by through rare-earth cation mixing, which can be viewed as intrinsic quantum stress. We choose Nd{sub 1−X}Y{sub X}NiO{sub 3} (x = 0.3, 0.4) perovskites thin films as a prototype system to exhibit the tunable sharp MIT at near room temperature. By adjusting Y concentration, the transition temperature of the thin films can be changed within the range of 340–360 K. X-ray diffraction, X-ray absorption fine structure (XAFS), and in situ infrared spectroscopy are employed to probe the structural and optical property variation affected by composition and temperature. The infrared transmission intensity decreases with temperature across the MIT, indicating a pronounced thermochromic effect. Meanwhile, the XAFS result exhibits that the crystal atomistic structure changes accompanying with the Y atoms incorporation and MIT phase transition. The heavily doped Y atoms result in the pre-edge peak descent and Ni-O bond elongation, suggesting an enhanced charge disproportionation effect and the weakening of hybridization between Ni-3d and O-2p orbits.

  5. Thin-film microextraction.

    PubMed

    Bruheim, Inge; Liu, Xiaochuan; Pawliszyn, Janusz

    2003-02-15

    The properties of a thin sheet of poly(dimethylsiloxane) (PDMS) membrane as an extraction phase were examined and compared to solid-phase microextraction (SPME) PDMS-coated fiber for application to semivolatile analytes in direct and headspace modes. This new PDMS extraction approach showed much higher extraction rates because of the larger surface area to extraction-phase volume ratio of the thin film. Unlike the coated rod formats of SPME using thick coatings, the high extraction rate of the membrane SPME technique allows larger amounts of analytes to be extracted within a short period of time. Therefore, higher extraction efficiency and sensitivity can be achieved without sacrificing analysis time. In direct membrane SPME extraction, a linear relationship was found between the initial rate of extraction and the surface area of the extraction phase. However, for headspace extraction, the rates were somewhat lower because of the resistance to analyte transport at the sample matrix/headspace barrier. It was found that the effect of this barrier could be reduced by increasing either agitation, temperature, or surface area of the sample matrix/headspace interface. A method for the determination of PAHs in spiked lake water samples was developed based on the membrane PDMS extraction coupled with GC/MS. A linearity of 0.9960 and detection limits in the low-ppt level were found. The reproducibility was found to vary from 2.8% to 10.7%. PMID:12622398

  6. Optical response and activity of ultrathin films of topological insulators

    NASA Astrophysics Data System (ADS)

    Parhizgar, Fariborz; Moghaddam, Ali G.; Asgari, Reza

    2015-07-01

    We investigate the optical properties of ultrathin film of a topological insulator in the presence of an in-plane magnetic field. We show that due to the combination of the overlap between the surface states of the two layers and the magnetic field, the optical conductivity can show strong anisotropy. This leads to the effective optical activity of the ultrathin film by influencing the circularly polarized incident light. Intriguingly, for a range of magnetic fields, the reflected and transmitted lights exhibit elliptic character. Even for certain values almost linear polarizations are obtained, indicating that the thin film can act as a polaroid in reflection. All these features are discussed in the context of the time-reversal symmetry breaking as one of the key ingredients for the optical activity.

  7. Thin film thermocouples for high temperature measurement

    NASA Astrophysics Data System (ADS)

    Kreider, Kenneth G.

    1989-05-01

    Thin film thermocouples have unique capabilities for measuring surface temperatures at high temperatures (above 800 K) under harsh conditions. Their low mass, approximately 2 x 10(-5) g/mm permits very rapid response and very little disturbance of heat transfer to the surface being measured. This has led to applications inside gas turbine engines and diesel engines measuring the surface temperature of first stage turbine blades and vanes and ceramic liners in diesel cylinders. The most successful high temperature (up to 1300 K) thin film thermocouples are sputter deposited from platinum and platinum-10 percent rhodium targets although results using base metal alloys, gold, and platinel will also be presented. The fabrication techniques used to form the thermocouples, approaches used to solve the high temperature insulation and adherence problems, current applications, and test results using the thin film thermocouples are reviewed. In addition a discussion will be presented on the current problems and future trends related to applications of thin film thermocouples at higher temperatures up to 1900 K.

  8. A versatile platform for magnetostriction measurements in thin films

    NASA Astrophysics Data System (ADS)

    Pernpeintner, M.; Holländer, R. B.; Seitner, M. J.; Weig, E. M.; Gross, R.; Goennenwein, S. T. B.; Huebl, H.

    2016-03-01

    We present a versatile nanomechanical sensing platform for the investigation of magnetostriction in thin films. It is based on a doubly clamped silicon nitride nanobeam resonator covered with a thin magnetostrictive film. Changing the magnetization direction within the film plane by an applied magnetic field generates a magnetoelastic stress and thus changes the resonance frequency of the nanobeam. A measurement of the resulting resonance frequency shift, e.g., by optical interferometry, allows to quantitatively determine the magnetostriction constants of the thin film. In a proof-of-principle experiment, we determine the magnetostriction constants of a 10 nm thick polycrystalline cobalt film, showing very good agreement with literature values. The presented technique aims, in particular, for the precise measurement of magnetostriction in a variety of (conducting and insulating) thin films, which can be deposited by, e.g., electron beam deposition, thermal evaporation, or sputtering.

  9. Anomalous C-V response correlated to relaxation processes in TiO2 thin film based-metal-insulator-metal capacitor: Effect of titanium and oxygen defects

    NASA Astrophysics Data System (ADS)

    Kahouli, A.; Marichy, C.; Sylvestre, A.; Pinna, N.

    2015-04-01

    Capacitance-voltage (C-V) and capacitance-frequency (C-f) measurements are performed on atomic layer deposited TiO2 thin films with top and bottom Au and Pt electrodes, respectively, over a large temperature and frequency range. A sharp capacitance peak/discontinuity (C-V anomalous) is observed in the C-V characteristics at various temperatures and voltages. It is demonstrated that this phenomenon is directly associated with oxygen vacancies. The C-V peak irreversibility and dissymmetry at the reversal dc voltage are attributed to difference between the Schottky contacts at the metal/TiO2 interfaces. Dielectric analyses reveal two relaxation processes with degeneration of the activation energy. The low trap level of 0.60-0.65 eV is associated with the first ionized oxygen vacancy at low temperature, while the deep trap level of 1.05 eV is associated to the second ionized oxygen vacancy at high temperature. The DC conductivity of the films exhibits a transition temperature at 200 °C, suggesting a transition from a conduction regime governed by ionized oxygen vacancies to one governed by interstitial Ti3+ ions. Both the C-V anomalous and relaxation processes in TiO2 arise from oxygen vacancies, while the conduction mechanism at high temperature is governed by interstitial titanium ions.

  10. Interference Colors in Thin Films.

    ERIC Educational Resources Information Center

    Armstrong, H. L.

    1979-01-01

    Explains interference colors in thin films as being due to the removal, or considerable reduction, of a certain color by destructive inteference that results in the complementary color being seen. (GA)

  11. Thin film phase transition materials development program

    NASA Astrophysics Data System (ADS)

    Case, W. E.

    1985-04-01

    A number of application concepts have emerged based on the idea that a phase transition thin film such as vanadium dioxide provides a high resolution, two-dimensional format for switching, recording, and processing optical signals. These applications range from high density optical disk recording systems and optical data processing to laser protection devices, infrared FLIRS and seekers, laser radar systems and IR scene simulators. All application candidates have a potential for providing either a totally new capability, an improved performance, a lower cost, or combinations of the three. Probably of greatest significance is the emergence of agile sensor concepts arising out of some of the film's special properties. These are represented by the above FLIRs, seekers and laser radar systems. A three year research program has been completed to advance the state-of-the-art in the preparation and characterization of selected thin film phase transition materials. The objectives of the program were: (1) to expand the data base and improve operational characteristics of Vought prepared vanadium dioxide thin films, (2) to evolve process chemistry and subsequently characterize several new program materials, including rare-earth chalcogenides, organic semiconductor charge complexes, alloys of transition metal oxides, and metal-insulator cermets, and (3) to spin-off new applications and concepts.

  12. Thin film cell development workshop report

    NASA Technical Reports Server (NTRS)

    Woodyard, James R.

    1991-01-01

    The Thin Film Development Workshop provided an opportunity for those interested in space applications of thin film cells to debate several topics. The unique characteristics of thin film cells as well as a number of other issues were covered during the discussions. The potential of thin film cells, key research and development issues, manufacturing issues, radiation damage, substrates, and space qualification of thin film cells were discussed.

  13. Vapor deposition of thin films

    DOEpatents

    Smith, David C.; Pattillo, Stevan G.; Laia, Jr., Joseph R.; Sattelberger, Alfred P.

    1992-01-01

    A highly pure thin metal film having a nanocrystalline structure and a process of preparing such highly pure thin metal films of, e.g., rhodium, iridium, molybdenum, tungsten, rhenium, platinum, or palladium by plasma assisted chemical vapor deposition of, e.g., rhodium(allyl).sub.3, iridium(allyl).sub.3, molybdenum(allyl).sub.4, tungsten(allyl).sub.4, rhenium(allyl).sub.4, platinum(allyl).sub.2, or palladium(allyl).sub.2 are disclosed. Additionally, a general process of reducing the carbon content of a metallic film prepared from one or more organometallic precursor compounds by plasma assisted chemical vapor deposition is disclosed.

  14. Fabrication of Thin Film Heat Flux Sensors

    NASA Technical Reports Server (NTRS)

    Will, Herbert A.

    1992-01-01

    Prototype thin film heat flux sensors have been constructed and tested. The sensors can be applied to propulsion system materials and components. The sensors can provide steady state and fast transient heat flux information. Fabrication of the sensor does not require any matching of the mounting surface. Heat flux is proportional to the temperature difference across the upper and lower surfaces of an insulation material. The sensor consists of an array of thermocouples on the upper and lower surfaces of a thin insulating layer. The thermocouples for the sensor are connected in a thermopile arrangement. A 100 thermocouple pair heat flux sensor has been fabricated on silicon wafers. The sensor produced an output voltage of 200-400 microvolts when exposed to a hot air heat gun. A 20 element thermocouple pair heat flux sensor has been fabricated on aluminum oxide sheet. Thermocouples are Pt-Pt/Rh with silicon dioxide as the insulating material. This sensor produced an output of 28 microvolts when exposed to the radiation of a furnace operating at 1000 C. Work is also underway to put this type of heat flux sensor on metal surfaces.

  15. Calorimetry of epitaxial thin films.

    PubMed

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

    2011-02-01

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

  16. Amorphous silicon Schottky barrier solar cells incorporating a thin insulating layer and a thin doped layer

    DOEpatents

    Carlson, David E.

    1980-01-01

    Amorphous silicon Schottky barrier solar cells which incorporate a thin insulating layer and a thin doped layer adjacent to the junction forming metal layer exhibit increased open circuit voltages compared to standard rectifying junction metal devices, i.e., Schottky barrier devices, and rectifying junction metal insulating silicon devices, i.e., MIS devices.

  17. Preparation of Epoxy Resin Thin Film by Electroless Deposition Method

    NASA Astrophysics Data System (ADS)

    Fukui, Hitoshi; Hirai, Makoto; Shinagawa, Tsutomu; Kobayashi, Yasuyuki; Chigane, Masaya; Fujiwara, Yutaka; Fujita, Naoyuki

    The electrodeposition coating process, which is a polymer film deposition method using water electrolysis, is widely used for automobile body primers. Recently this process is being used in the insulating polymer films deposition for the microelectromechanical system (MEMS) or micro electric components. However, this process has difficulty in depositing polymer film on complex shapes and non-conductive surfaces. In this paper, we demonstrate that epoxy resin thin films used extensively as insulating polymer films were successfully deposited using the electroless chemical reaction in aqueous solution on a non-conductive surface and high aspect glass tube. The substrates catalyzed using a commercialized three-step Sn/Ag/Pd activation process were immersed in the reaction solution containing water-soluble resin and NO3- ion, reducing agent (DMAB). The pH near the substrate rose when NO3- was reduced by released electrons from DMAB. Water-soluble resin combined with OH- hence, polymer thin film was deposited by the electroless deposition reaction. By FE-SEM and FT-IR measurement, it was clear that the conformal and dense epoxy resin films were deposited. Using the present method, epoxy films could be deposited on the surface of a high aspect ratio glass tube 50 mm in length and φ3 in inner diameter. These films had high insulation resistivity of 108∼1011Ωm with applied voltage of 250 V.

  18. The Thin Oil Film Equation

    NASA Technical Reports Server (NTRS)

    Brown, James L.; Naughton, Jonathan W.

    1999-01-01

    A thin film of oil on a surface responds primarily to the wall shear stress generated on that surface by a three-dimensional flow. The oil film is also subject to wall pressure gradients, surface tension effects and gravity. The partial differential equation governing the oil film flow is shown to be related to Burgers' equation. Analytical and numerical methods for solving the thin oil film equation are presented. A direct numerical solver is developed where the wall shear stress variation on the surface is known and which solves for the oil film thickness spatial and time variation on the surface. An inverse numerical solver is also developed where the oil film thickness spatial variation over the surface at two discrete times is known and which solves for the wall shear stress variation over the test surface. A One-Time-Level inverse solver is also demonstrated. The inverse numerical solver provides a mathematically rigorous basis for an improved form of a wall shear stress instrument suitable for application to complex three-dimensional flows. To demonstrate the complexity of flows for which these oil film methods are now suitable, extensive examination is accomplished for these analytical and numerical methods as applied to a thin oil film in the vicinity of a three-dimensional saddle of separation.

  19. Thin film photovoltaic device and process of manufacture

    DOEpatents

    Albright, Scot P.; Chamberlin, Rhodes

    1997-10-07

    Provided is a thin film photovoltaic device and a method of manufacturing the device. The thin film photovoltaic device comprises a film layer having particles which are smaller than about 30 microns in size held in an electrically insulating matrix material to reduce the potential for electrical shorting through the film layer. The film layer may be provided by depositing preformed particles onto a surrogate substrate and binding the particles in a film-forming matrix material to form a flexible sheet with the film layer. The flexible sheet may be separated from the surrogate substrate and cut into flexible strips. A plurality of the flexible strips may be located adjacent to and supported by a common supporting substrate to form a photovoltaic module having a plurality of electrically interconnected photovoltaic cells.

  20. Thin film photovoltaic device and process of manufacture

    DOEpatents

    Albright, Scot P.; Chamberlin, Rhodes

    1999-02-09

    Provided is a thin film photovoltaic device and a method of manufacturing the device. The thin film photovoltaic device comprises a film layer having particles which are smaller than about 30 microns in size held in an electrically insulating matrix material to reduce the potential for electrical shorting through the film layer. The film layer may be provided by depositing preformed particles onto a surrogate substrate and binding the particles in a film-forming matrix material to form a flexible sheet with the film layer. The flexible sheet may be separated from the surrogate substrate and cut into flexible strips. A plurality of the flexible strips may be located adjacent to and supported by a common supporting substrate to form a photovoltaic module having a plurality of electrically interconnected photovoltaic cells.

  1. Thin film photovoltaic device and process of manufacture

    DOEpatents

    Albright, S.P.; Chamberlin, R.

    1997-10-07

    Provided is a thin film photovoltaic device and a method of manufacturing the device. The thin film photovoltaic device comprises a film layer having particles which are smaller than about 30 microns in size held in an electrically insulating matrix material to reduce the potential for electrical shorting through the film layer. The film layer may be provided by depositing preformed particles onto a surrogate substrate and binding the particles in a film-forming matrix material to form a flexible sheet with the film layer. The flexible sheet may be separated from the surrogate substrate and cut into flexible strips. A plurality of the flexible strips may be located adjacent to and supported by a common supporting substrate to form a photovoltaic module having a plurality of electrically interconnected photovoltaic cells. 13 figs.

  2. Thin film photovoltaic device and process of manufacture

    DOEpatents

    Albright, S.P.; Chamberlin, R.

    1999-02-09

    Provided is a thin film photovoltaic device and a method of manufacturing the device. The thin film photovoltaic device comprises a film layer having particles which are smaller than about 30 microns in size held in an electrically insulating matrix material to reduce the potential for electrical shorting through the film layer. The film layer may be provided by depositing preformed particles onto a surrogate substrate and binding the particles in a film-forming matrix material to form a flexible sheet with the film layer. The flexible sheet may be separated from the surrogate substrate and cut into flexible strips. A plurality of the flexible strips may be located adjacent to and supported by a common supporting substrate to form a photovoltaic module having a plurality of electrically interconnected photovoltaic cells. 13 figs.

  3. TI--CR--AL--O thin film resistors

    DOEpatents

    Jankowski, Alan F.; Schmid, Anthony P.

    2000-01-01

    Thin films of Ti--Cr--Al--O are used as a resistor material. The films are rf sputter deposited from ceramic targets using a reactive working gas mixture of Ar and O.sub.2. Resistivity values from 10.sup.4 to 10.sup.10 Ohm-cm have been measured for Ti--Cr--Al--O film <1 .mu.m thick. The film resistivity can be discretely selected through control of the target composition and the deposition parameters. The application of Ti--Cr--Al--O as a thin film resistor has been found to be thermodynamically stable, unlike other metal-oxide films. The Ti--Cr--Al--O film can be used as a vertical or lateral resistor, for example, as a layer beneath a field emission cathode in a flat panel display; or used to control surface emissivity, for example, as a coating on an insulating material such as vertical wall supports in flat panel displays.

  4. Thin-Film Resistance Heat-Flux Sensors

    NASA Technical Reports Server (NTRS)

    Fralick, Gustave C.; Wrbanek, John D.; Blaha, Charles A.

    2005-01-01

    Thin-film heat-flux sensors of a proposed type would offer advantages over currently available thin-film heat flux sensors. Like a currently available thin-film heat-flux sensor, a sensor according to the proposal would be based on measurement of voltages related to the temperatures of thin metal films on the hotter and colder faces of a layer of an electrically insulating and moderately thermally conductive material. The heat flux through such a device is proportional to the difference between the temperatures and to the thermal conductivity of the layer. The advantages of the proposed sensors over the commercial ones would arise from the manner in which the temperature-related voltages would be generated and measured.

  5. Thin film of biocompatible polysaccharides

    NASA Astrophysics Data System (ADS)

    Richert, Ludovic; Lavalle, Philippe; Schaaf, Pierre; Voegel, Jean-Claude; Picart, Catherine

    2003-03-01

    The layer-by-layer deposition method proposed by Decher et al. (1991) is a very simple and versatile method used to build thin films. These films are of interest for bioengineering because of their unique properties and of the possible insertion of bioactive molecules. We present here the peculiar properties of a new kind of film formed with natural biopolymers, namely hyaluronan (HA)and chitosan (CHI). The films may be used as biomimetic substrates to control bacterial and cell adhesion. These polysaccharides are of particular interest because they are biodegradable, non toxic, and can be found in various tissues. Hyaluronan is also a natural ligand for a numerous type of cells through the CD44 receptor. Chitosan has already largely been used for its biological and anti-microbial properties. (CHI/HA) films were built in acidic pH at different ionic strength. The buildup was followed in situ by optical waveguide lightmode spectroscopy (OWLS), quartz crystal microbalance, streaming potential measurements and atomic force microscopy. The kinetics of adsorption and desorption of the polyelectrolytes depended on the ionic strength. Small islands were initially present on the surface which grew by mutual coalescence until becoming a flat film. The films were around 200 nm in thickness. These results suggest that different types of thin films constituted of polysaccharides can be built on any type of surface. These films are currently investigated toward their cell adhesion and bacterial adhesion properties.

  6. (Thin films under chemical stress)

    SciTech Connect

    Not Available

    1990-01-01

    As stated above the purpose of this research is to enable workers in a variety of fields to understand the chemical and physical changes which take place when thin films (primarily organic films) are placed under chemical stress. This stress may occur because the film is being swelled by penetrant entrained in solvent, because interfacial reactions are occurring at one or more boundaries within the film structure, or because some component of the film is responding to an external stimulus (e.g. pH, temperature, electric field, or radiation). These questions are important within the context of our long-term goal of understanding the behavior of composite structures, composed of thin organic polymer films interspersed with Langmuir-Blodgett (LB) and self-assembled monolayers, which might have unique functional properties. In the past year we have concentrated on the following objectives: (1) understanding how the two possible diffusion mechanisms contribute to the swelling of thin films of organic polymers place in solution, (2) identifying systems which are appropriate polymer media for the construction of composite membranes for use in aqueous environments, and (3) understanding the self-assembly process for long chain fatty acids at model surfaces. Progress in meeting each of these objectives will be described in this report. 4 figs.

  7. Thin-film forces in pseudoemulsion films

    SciTech Connect

    Bergeron, V.; Radke, C.J. |

    1991-06-01

    Use of foam for enhanced oil recovery (EOR) has shown recent success in steam-flooding field applications. Foam can also provide an effective barrier against gas coning in thin oil zones. Both of these applications stem from the unique mobility-control properties a stable foam possesses when it exists in porous media. Unfortunately, oil has a major destabilizing effect on foam. Therefore, it is important for EOR applications to understand how oil destroys foam. Studies all indicate that stabilization of the pseudoemulsion film is critical to maintain foam stability in the presence of oil. Hence, to aid in design of surfactant formulations for foam insensitivity to oil the authors pursue direct measurement of the thin-film or disjoining forces that stabilize pseudoemulsion films. Experimental procedures and preliminary results are described.

  8. Thin films under chemical stress

    SciTech Connect

    Not Available

    1991-01-01

    The goal of work on this project has been develop a set of experimental tools to allow investigators interested in transport, binding, and segregation phenomena in composite thin film structures to study these phenomena in situ. Work to-date has focuses on combining novel spatially-directed optical excitation phenomena, e.g. waveguide eigenmodes in thin dielectric slabs, surface plasmon excitations at metal-dielectric interfaces, with standard spectroscopies to understand dynamic processes in thin films and at interfaces. There have been two main scientific thrusts in the work and an additional technical project. In one thrust we have sought to develop experimental tools which will allow us to understand the chemical and physical changes which take place when thin polymer films are placed under chemical stress. In principle this stress may occur because the film is being swelled by a penetrant entrained in solvent, because interfacial reactions are occurring at one or more boundaries within the film structure, or because some component of the film is responding to an external stimulus (e.g. pH, temperature, electric field, or radiation). However all work to-date has focused on obtaining a clearer understanding penetrant transport phenomena. The other thrust has addressed the kinetics of adsorption of model n-alkanoic acids from organic solvents. Both of these thrusts are important within the context of our long-term goal of understanding the behavior of composite structures, composed of thin organic polymer films interspersed with Langmuir-Blodgett (LB) and self-assembled monolayers. In addition there has been a good deal of work to develop the local technical capability to fabricate grating couplers for optical waveguide excitation. This work, which is subsidiary to the main scientific goals of the project, has been successfully completed and will be detailed as well. 41 refs., 10 figs.

  9. Beryllium thin films for resistor applications

    NASA Technical Reports Server (NTRS)

    Fiet, O.

    1972-01-01

    Beryllium thin films have a protective oxidation resistant property at high temperature and high recrystallization temperature. However, the experimental film has very low temperature coefficient of resistance.

  10. A new photosensitive dielectric insulating polyester film: Synthesis and characterization

    SciTech Connect

    Shi, F.F.; Economy, J.E.

    1996-10-01

    In this paper, we described the synthesis and the characterization of a new dielectric insulating film prepared from a photosensitive polyester. The unique feature of this new photosensitive polyester film is that it can be foamed when cured at 280{degrees}C though interchain transesterification reaction. This process can reduce the dielectric constant of the film to 2.5. Some important properties, such as photosensitivity, thermal stability, mechanical properties of this new dielectric insulating polymer film were discussed. The preliminary results show a good resolution and an acceptable profile of this new insulator after foaming.

  11. Influence of the charge trap density distribution in a gate insulator on the positive-bias stress instability of amorphous indium-gallium-zinc oxide thin-film transistors

    NASA Astrophysics Data System (ADS)

    Kim, Eungtaek; Kim, Choong-Ki; Lee, Myung Keun; Bang, Tewook; Choi, Yang-Kyu; Park, Sang-Hee Ko; Choi, Kyung Cheol

    2016-05-01

    We investigated the positive-bias stress (PBS) instability of thin film transistors (TFTs) composed of different types of first-gate insulators, which serve as a protection layer of the active surface. Two different deposition methods, i.e., the thermal atomic layer deposition (THALD) and plasma-enhanced ALD (PEALD) of Al2O3, were applied for the deposition of the first GI. When THALD was used to deposit the GI, amorphous indium-gallium-zinc oxide (a-IGZO) TFTs showed superior stability characteristics under PBS. For example, the threshold voltage shift (ΔVth) was 0 V even after a PBS time (tstress) of 3000 s under a gate voltage (VG) condition of 5 V (with an electrical field of 1.25 MV/cm). On the other hand, when the first GI was deposited by PEALD, the ΔVth value of a-IGZO TFTs was 0.82 V after undergoing an identical amount of PBS. In order to interpret the disparate ΔVth values resulting from PBS quantitatively, the average oxide charge trap density (NT) in the GI and its spatial distribution were investigated through low-frequency noise characterizations. A higher NT resulted during in the PEALD type GI than in the THALD case. Specifically, the PEALD process on a-IGZO layer surface led to an increasing trend of NT near the GI/a-IGZO interface compared to bulk GI owing to oxygen plasma damage on the a-IGZO surface.

  12. Influence of Mn concentration on magnetic topological insulator MnxBi2−xTe3 thin-film Hall-effect sensor

    SciTech Connect

    Ni, Y.; Zhang, Z.; Nlebedim, I. C.; Hadimani, R. L.; Jiles, D. C.

    2015-06-11

    Hall-effect (HE) sensors based on high-quality Mn-doped Bi2Te3 topological insulator (TI) thin films have been systematically studied in this paper. Improvement of Hall sensitivity is found after doping the magnetic element Mn into Bi2Te3. The sensors with low Mn concentrations, MnxBi2-xTe3, x = 0.01 and 0.08 show the linear behavior of Hall resistance with sensitivity about 5 Ω/T. And their Hall sensitivity shows weak dependence on temperature. For sensors with high Mn concentration (x = 0.23), the Hall resistance with respect to magnetic field shows a hysteretic behavior. Moreover, its sensitivity shows almost eight times as high as that of the HE sensors with low Mn concentration. The highest sensitivity can reach 43 Ω/T at very low magnetic field. This increase of Hall sensitivity is caused by the occurrence of anomalous HE (AHE) after ferromagnetic phase transition. Our work indicates that the magnetic-element-doped TIs with AHE are good candidates for HE sensors.

  13. Semiconductor-nanocrystal/conjugated polymer thin films

    DOEpatents

    Alivisatos, A. Paul; Dittmer, Janke J.; Huynh, Wendy U.; Milliron, Delia

    2014-06-17

    The invention described herein provides for thin films and methods of making comprising inorganic semiconductor-nanocrystals dispersed in semiconducting-polymers in high loading amounts. The invention also describes photovoltaic devices incorporating the thin films.

  14. Thin film-coated polymer webs

    DOEpatents

    Wenz, Robert P.; Weber, Michael F.; Arudi, Ravindra L.

    1992-02-04

    The present invention relates to thin film-coated polymer webs, and more particularly to thin film electronic devices supported upon a polymer web, wherein the polymer web is treated with a purifying amount of electron beam radiation.

  15. Semiconductor-nanocrystal/conjugated polymer thin films

    DOEpatents

    Alivisatos, A. Paul; Dittmer, Janke J.; Huynh, Wendy U.; Milliron, Delia

    2010-08-17

    The invention described herein provides for thin films and methods of making comprising inorganic semiconductor-nanocrystals dispersed in semiconducting-polymers in high loading amounts. The invention also describes photovoltaic devices incorporating the thin films.

  16. Low work function, stable thin films

    DOEpatents

    Dinh, Long N.; McLean, II, William; Balooch, Mehdi; Fehring, Jr., Edward J.; Schildbach, Marcus A.

    2000-01-01

    Generation of low work function, stable compound thin films by laser ablation. Compound thin films with low work function can be synthesized by simultaneously laser ablating silicon, for example, and thermal evaporating an alkali metal into an oxygen environment. For example, the compound thin film may be composed of Si/Cs/O. The work functions of the thin films can be varied by changing the silicon/alkali metal/oxygen ratio. Low work functions of the compound thin films deposited on silicon substrates were confirmed by ultraviolet photoelectron spectroscopy (UPS). The compound thin films are stable up to 500.degree. C. as measured by x-ray photoelectron spectroscopy (XPS). Tests have established that for certain chemical compositions and annealing temperatures of the compound thin films, negative electron affinity (NEA) was detected. The low work function, stable compound thin films can be utilized in solar cells, field emission flat panel displays, electron guns, and cold cathode electron guns.

  17. Polycrystalline VO2 thin films via femtosecond laser processing of amorphous VO x

    NASA Astrophysics Data System (ADS)

    Charipar, N. A.; Kim, H.; Breckenfeld, E.; Charipar, K. M.; Mathews, S. A.; Piqué, A.

    2016-05-01

    Femtosecond laser processing of pulsed laser-deposited amorphous vanadium oxide thin films was investigated. Polycrystalline VO2 thin films were achieved by femtosecond laser processing in air at room temperature. The electrical transport properties, crystal structure, surface morphology, and optical properties were characterized. The laser-processed films exhibited a metal-insulator phase transition characteristic of VO2, thus presenting a pathway for the growth of crystalline vanadium dioxide films on low-temperature substrates.

  18. Metal/insulator/semiconductor tunnel diodes formed by the oxidation of polycrystaline diamond films

    NASA Astrophysics Data System (ADS)

    Gonon, P.; Deneuville, A.; Gheeraert, E.; Fontaine, F.; Lenormand, F.

    1994-09-01

    Polycrystalline diamond films have been annealed under O2 at 600 C, or have been dipped in a H2SO4/CrO3 solution. Both treatments result in the formation of a thin electrically insulating layer at the top of the films. Subsequent metallization results in the formation of a metal/insulator/diamond tunnel diode with a potential barrier for holes of 0.85 eV, and with a Fermi level localized at about 0.45 eV above the diamond valence band.

  19. Thin film polymeric gel electrolytes

    DOEpatents

    Derzon, D.K.; Arnold, C. Jr.; Delnick, F.M.

    1996-12-31

    Novel hybrid thin film electrolytes, based on an organonitrile solvent system, which are compositionally stable, environmentally safe, can be produced efficiently in large quantity and which, because of their high conductivities {approx_equal}10{sup {minus}3}{Omega}{sup {minus}1} cm{sup {minus}1} are useful as electrolytes for rechargeable lithium batteries. 1 fig.

  20. Thin Film Solid Lubricant Development

    NASA Technical Reports Server (NTRS)

    Benoy, Patricia A.

    1997-01-01

    Tribological coatings for high temperature sliding applications are addressed. A sputter-deposited bilayer coating of gold and chromium is investigated as a potential solid lubricant for protection of alumina substrates during sliding at high temperature. Evaluation of the tribological properties of alumina pins sliding against thin sputtered gold films on alumina substrates is presented.

  1. Hybrid thin-film amplifier

    NASA Technical Reports Server (NTRS)

    Cleveland, G.

    1977-01-01

    Miniature amplifier for bioelectronic instrumentation consumes only about 100 mW and has frequency response flat to within 0.5 dB from 0.14 to 450 Hz. Device consists of five thin film substrates, which contain eight operational amplifiers and seven field-effect transistor dice.

  2. Thin film polymeric gel electrolytes

    DOEpatents

    Derzon, Dora K.; Arnold, Jr., Charles; Delnick, Frank M.

    1996-01-01

    Novel hybrid thin film electrolyte, based on an organonitrile solvent system, which are compositionally stable, environmentally safe, can be produced efficiently in large quantity and which, because of their high conductivities .apprxeq.10.sup.-3 .OMEGA..sup.-1 cm.sup.-1 are useful as electrolytes for rechargeable lithium batteries.

  3. Thin films and uses

    DOEpatents

    Baskaran, Suresh; Graff, Gordon L.; Song, Lin

    1998-01-01

    The invention provides a method for synthesizing a titanium oxide-containing film comprising the following steps: (a) preparing an aqueous solution of a titanium chelate with a titanium molarity in the range of 0.01M to 0.6M. (b) immersing a substrate in the prepared solution, (c) decomposing the titanium chelate to deposit a film on the substrate. The titanium chelate maybe decomposed acid, base, temperature or other means. A preferred method provides for the deposit of adherent titanium oxide films from C2 to C5 hydroxy carboxylic acids. In another aspect the invention is a novel article of manufacture having a titanium coating which protects the substrate against ultraviolet damage. In another aspect the invention provides novel semipermeable gas separation membranes, and a method for producing them.

  4. Polyimide thin-film dielectrics on ferroelectrics

    NASA Technical Reports Server (NTRS)

    Galiardi, R. V.

    1977-01-01

    Conducting layers of multi-layered thin-film ferroelectric device, such as is used in liquid crystal/ferroelectric display, can be electrically isolated using thin-film layer of polyimide. Ease of application and high electrical-breakdown strength allow dependable and economical means of providing dielectric for other thin-film microelectronic devices.

  5. Phase stabilization of VO2 thin films in high vacuum

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Tian; Eaton, Craig; Ye, Hansheng; Engel-Herbert, Roman

    2015-11-01

    A new growth approach to stabilize VO2 on Al2O3 in high vacuum is reported by reducing vanadium oxytriisopropoxide (VTIP) with vanadium metal. Phase stabilization and surface wetting behavior were studied as a function of growth parameters. The flux balance of VTIP to V in combination with growth temperature was identified to be critical for the growth of high quality VO2 thin films. High V fluxes were required to suppress the island formation and to ensure a coalesced film, while too high V fluxes ultimately favored the formation of the undesired, epitaxially stabilized V2O3 phase. Careful optimization of growth temperature, VTIP to V ratio, and growth rate led to high quality single phase VO2 thin films with >3.5 orders of magnitude change in resistivity across the metal-to-insulator transition. This approach opens up another synthesis avenue to stabilize oxide thin films into desired phases.

  6. Probing crystalline insulator surfaces with neutral helium atom scattering: A study of mixed potassium tantalate/niobate and thin films of potassium chloride and p-quaterphenyl on sodium chloride(001)

    NASA Astrophysics Data System (ADS)

    Trelenberg, Thomas Walter

    Results from experiments using a thermal-energy beam of helium atoms as a probe in studying three crystalline insulator surfaces are presented. The primary focus is the simple ferroelectric perovskite, KTa1- xNbxO3 (or KTN when not specifying an Nb concentration) with x = 0.06, 0.10, 0.20, 0.30, and 0.52. Thin films of KCl and p-quaterphenyl grown onto NaCl(001) were also studied. Extending an earlier work on potassium tantalate (KTaO3), freshly cleaved (001) surfaces of niobium-doped potassium tantalate (KTN) were studied. While KTaO3 is an incipient ferroelectric undergoing no bulk phase changes, KTN, with Nb concentration greater than ˜1.5%, is a tunable ferroelectric, existing in several bulk phases depending on the temperature of the material. A metastable feature observed in KTN immediately after cleaving results in satellite peaks around the specular peak which decay over time. Also, small, broad half-order peaks were observed when the surface temperature was cycled between 50 K and 270 K for the first time. Surface hysteresis effects and responses to electric fields were also studied. Surface dispersion curves for the two high-symmetry directions are given for various Nb doping levels and substrate temperatures. This work compares the above phenomena to similar occurrences observed previously in KTaO3, and notes how the responses differ as a function of niobium doping. Also building on previous experience, the growth of KCl on NaCl was studied. Several recent works have focused on the physical interpretation of 3/4-order peaks observed during LEED investigations of this system. A HAS study of this system revealed, at best, a weak indication of several n/4-order peaks, but at film thicknesses well above those reported. In our first attempt to examine the surfaces of films of large organic molecules using HAS, p-quaterphenyl (p-4P) was deposited onto an NaCl surface held at 300K. Diffraction intensities from the NaCl were reduced but produced no other

  7. Phase Coarsening in Thin Films

    NASA Astrophysics Data System (ADS)

    Wang, K. G.; Glicksman, M. E.

    2015-08-01

    Phase coarsening (Ostwald ripening) phenomena are ubiquitous in materials growth processes such as thin film formation. The classical theory explaining late-stage phase coarsening phenomena was developed by Lifshitz and Slyozov, and by Wagner in the 1960s. Their theory is valid only for a vanishing volume fraction of the second phase in three dimensions. However, phase coarsening in two-dimensional systems is qualitatively different from that in three dimensions. In this paper, the many-body concept of screening length is reviewed, from which we derive the growth law for a `screened' phase island, and develop diffusion screening theory for phase coarsening in thin films. The coarsening rate constant, maximum size of phase islands in films, and their size distribution function will be derived from diffusion screening theory. A critical comparison will be provided of prior coarsening concepts and improvements derived from screening approaches.

  8. Straining graphene using thin film shrinkage methods.

    PubMed

    Shioya, Hiroki; Craciun, Monica F; Russo, Saverio; Yamamoto, Michihisa; Tarucha, Seigo

    2014-03-12

    Theoretical works suggest the possibility and usefulness of strain engineering of graphene by predicting remarkable properties, such as Dirac cone merging, bandgap opening and pseudo magnetic field generation. However, most of these predictions have not yet been confirmed because it is experimentally difficult to control the magnitude and type (e.g., uniaxial, biaxial, and so forth) of strain in graphene devices. Here we report two novel methods to apply strain without bending the substrate. We employ thin films of evaporated metal and organic insulator deposited on graphene, which shrink after electron beam irradiation or heat application. These methods make it possible to apply both biaxial strain and in-plane isotropic compressive strain in a well-controlled manner. Raman spectroscopy measurements show a clear splitting of the degenerate states of the G-band in the case of biaxial strain, and G-band blue shift without splitting in the case of in-plane isotropic compressive strain. In the case of biaxial strain application, we find out the ratio of the strain component perpendicular to the stretching direction is at least three times larger than what was previously observed, indicating that shrinkage of the metal or organic insulator deposited on graphene induces both tensile and compressive strain in this atomically thin material. Our studies present for the first time a viable way to apply strain to graphene without the need to bend the substrate. PMID:24490629

  9. Straining Graphene Using Thin Film Shrinkage Methods

    PubMed Central

    2014-01-01

    Theoretical works suggest the possibility and usefulness of strain engineering of graphene by predicting remarkable properties, such as Dirac cone merging, bandgap opening and pseudo magnetic field generation. However, most of these predictions have not yet been confirmed because it is experimentally difficult to control the magnitude and type (e.g., uniaxial, biaxial, and so forth) of strain in graphene devices. Here we report two novel methods to apply strain without bending the substrate. We employ thin films of evaporated metal and organic insulator deposited on graphene, which shrink after electron beam irradiation or heat application. These methods make it possible to apply both biaxial strain and in-plane isotropic compressive strain in a well-controlled manner. Raman spectroscopy measurements show a clear splitting of the degenerate states of the G-band in the case of biaxial strain, and G-band blue shift without splitting in the case of in-plane isotropic compressive strain. In the case of biaxial strain application, we find out the ratio of the strain component perpendicular to the stretching direction is at least three times larger than what was previously observed, indicating that shrinkage of the metal or organic insulator deposited on graphene induces both tensile and compressive strain in this atomically thin material. Our studies present for the first time a viable way to apply strain to graphene without the need to bend the substrate. PMID:24490629

  10. Thin film module development

    NASA Technical Reports Server (NTRS)

    Jester, T.

    1985-01-01

    The design of ARCO Solar, Inc.'s Genesis G100 photovoltaic module was driven by several criteria, including environmental stability (both electrical and mechanical), consumer aesthetics, low materials costs, and manufacturing ease. The module circuitry is designed as a 12 volt battery charger, using monolithic patterning techniques on a glass superstrate. This patterning and interconnect method proves amenable to high volume, low cost production throughput, and the use of glass serves the dual role of handling ease and availability. The mechanical design of the module centers on environmental stability. Packaging of the glass superstrate circuit must provide good resistance to thermal and humidity exposure along with hi-pot insulation and hailstone impact resistance. The options considered are given. Ethylene vinyl acetate (EVA) is chosen as the pottant material for its excellent weatherability.

  11. Electroluminescence in thin-film CaS:Ce

    NASA Astrophysics Data System (ADS)

    Shanker, Virendra; Tanaka, Shosaku; Shiiki, Masatoshi; Deguchi, Hiroshi; Kobayashi, Hiroshi; Sasakura, Hiroshi

    1984-11-01

    We report a double insulated CaS:Ce thin-film electroluminescent (EL) device which emits a bright green EL due to Ce3+ luminescent centers, being characteristic of parity allowed 5d-4f transitions. A brightness level of 500 cd/m2 and emission efficiency of 0.11 lm/W have been obtained under 5-kHz sinusoidal voltage excitation. The CaS:Ce thin film has been fabricated by coevaporation of CaS and sulfur.

  12. Thermoelectric properties of an ultra-thin topological insulator.

    PubMed

    Islam, S K Firoz; Ghosh, T K

    2014-04-23

    Thermoelectric coefficients of an ultra-thin topological insulator are presented here. The hybridization between top and bottom surface states of a topological insulator plays a significant role. In the absence of a magnetic field, the thermopower increases and thermal conductivity decreases with an increase in the hybridization energy. In the presence of a magnetic field perpendicular to the ultra-thin topological insulator, thermoelectric coefficients exhibit quantum oscillations with inverse magnetic field, whose frequency is strongly modified by the Zeeman energy and whose phase factor is governed by the product of the Landé g-factor and the hybridization energy. In addition to the numerical results, the low-temperature approximate analytical results for the thermoelectric coefficients are also provided. It is also observed that for a given magnetic field these transport coefficients oscillate with hybridization energy, at a frequency that depends on the Landé g-factor. PMID:24694878

  13. Electrical and Optical Properties of Organic Thin Films

    NASA Astrophysics Data System (ADS)

    Buckner, Spencer Lewis

    The purpose of this research was to examine the applicability of organic thin films as electrical insulators in metal-insulator-semiconductor (MIS) and metal-insulator -metal (MIM) devices and an anti-reflective (A-R) coatings for solar cells. Films of anthracene, stearic acid and diacetylene alcohol were examined for their electrical and optical properties. Two techniques were used to deposit the films for these studies. Thermal evaporation in vacuum was used to deposit aluminum as electrodes and contacts in MIS and MIM devices. The organic films were deposited by either thermal evaporation or the Langmuir-Blodgett (L-B) dipping technique. Several vacuum systems and an L-B trough were fabricated for these studies and their design and construction are outlined. Several types of measurements were used to examine the properties of the organic films. Optical reflectance measurements of the diacetylene alcohol and stearic acid, both deposited by the L-B technique, on commercial silicon solar cells were used to study the potential use of these types of films as A-R and protective coatings. Electrical breakdown studies of the MIM devices were conducted to determine the maximum electric fields the insulators could withstand without destruction. Capacitance versus voltage (C-V) measurements of the organic films in MIS devices were used to determine surface defect densities at the semicondcutor/insulator interface. For each type of measurements made on the devices, theories are outlined to analyze the data obtained. The optical reflectance data are analyzed using standard electromagnetic theory. The electrical breakdown data are examined using the theories of Forlani and Minnaja (F-M) and Klein. The C-V data are examined using several different theories to determine charge and defect densities and to analyze the effects of thermal stressing and annealing. Finally, conclusions are drawn as to the applicability of these types of organic materials as insulators and coatings

  14. Thin aerogel films for optical, thermal, acoustic, and electronic applications

    SciTech Connect

    Hrubesh, L.W.; Poco, J.F.

    1994-09-01

    Aerogels are a special class of continuously porous solid materials which are characterized by nanometer size particles and pores. Typically, aerogels are made using sol-gel chemistry to form a solvent filled, high porosity gel that is dried by removing the solvent without collapsing the tenuous solid phase. As bulk materials, aerogels are known to have many exceptional, and even some unique physical properties. Aerogels provide the highest thermal insulation and lowest dielectric constant of any other material known. However, some important applications require the aerogels in the form of thin films or sheets. For example, electronic applications require micrometer thin aerogel films bonded to a substrate, and others require thicker films, either on a substrate or as free standing sheets. Special methods are required to make aerogel thin films or sheets. In this paper, the authors discuss the special conditions needed to fabricate thin aerogel films and they describe methods to make films and thin sheets. They also give some specific applications for which aerogel films are being developed.

  15. Phase diagram of compressively strained nickelate thin films

    SciTech Connect

    Disa, Ankit S; Kumah, D.; Ngai, J H; Specht, Eliot D; Arena, D.A.; Walker, Frederick J.; Ahn, Charles H.

    2013-01-01

    The complex phase diagrams of strongly correlated oxides arise from the coupling between physical and electronic structure. This can lead to a renormalization of the phase boundaries when considering thin films rather than bulk crystals due to reduced dimensionality and epitaxial strain. The well-established bulk RNiO3 phase diagram shows a systematic dependence between the metal-insulator transition and the perovskite A-site rare-earth ion, R. Here, we explore the equivalent phase diagram for nickelate thin films under compressive epitaxial strain. We determine the metalinsulator phase diagram for the solid solution of Nd1-yLayNiO3 thin films within the range 0 y 1. We find qualitative similarity between the films and their bulk analogs, but with an overall renormalization in the metal-insulator transition to lower temperature. A combination of x-ray diffraction measurements and soft x-ray absorption spectroscopy indicates that the renormalization is due to increased Ni O bond hybridization for coherently strained thin films.

  16. Selective inorganic thin films

    SciTech Connect

    Phillips, M.L.F.; Pohl, P.I.; Brinker, C.J.

    1997-04-01

    Separating light gases using membranes is a technology area for which there exists opportunities for significant energy savings. Examples of industrial needs for gas separation include hydrogen recovery, natural gas purification, and dehydration. A membrane capable of separating H{sub 2} from other gases at high temperatures could recover hydrogen from refinery waste streams, and facilitate catalytic dehydrogenation and the water gas shift (CO + H{sub 2}O {yields} H{sub 2} + CO{sub 2}) reaction. Natural gas purification requires separating CH{sub 4} from mixtures with CO{sub 2}, H{sub 2}S, H{sub 2}O, and higher alkanes. A dehydrating membrane would remove water vapor from gas streams in which water is a byproduct or a contaminant, such as refrigeration systems. Molecular sieve films offer the possibility of performing separations involving hydrogen, natural gas constituents, and water vapor at elevated temperatures with very high separation factors. It is in applications such as these that the authors expect inorganic molecular sieve membranes to compete most effectively with current gas separation technologies. Cryogenic separations are very energy intensive. Polymer membranes do not have the thermal stability appropriate for high temperature hydrogen recovery, and tend to swell in the presence of hydrocarbon natural gas constituents. The authors goal is to develop a family of microporous oxide films that offer permeability and selectivity exceeding those of polymer membranes, allowing gas membranes to compete with cryogenic and adsorption technologies for large-scale gas separation applications.

  17. Improvement of electron mobility in La:BaSnO3 thin films by insertion of an atomically flat insulating (Sr,Ba)SnO3 buffer layer

    NASA Astrophysics Data System (ADS)

    Shiogai, Junichi; Nishihara, Kazuki; Sato, Kazuhisa; Tsukazaki, Atsushi

    2016-06-01

    One perovskite oxide, ASnO3 (A = Sr, Ba), is a candidate for use as a transparent conductive oxide with high electron mobility in single crystalline form. However, the electron mobility of films grown on SrTiO3 substrates does not reach the bulk value, probably because of dislocation scattering that originates from the large lattice mismatch. This study investigates the effect of insertion of bilayer BaSnO3 / (Sr,Ba)SnO3 for buffering this large lattice mismatch between La:BaSnO3 and SrTiO3 substrate. The insertion of 200-nm-thick BaSnO3 on (Sr,Ba)SnO3 bilayer buffer structures reduces the number of dislocations and improves surface smoothness of the films after annealing as proved respectively by scanning transmission electron microscopy and atomic force microscopy. A systematic investigation of BaSnO3 buffer layer thickness dependence on Hall mobility of the electron transport in La:BaSnO3 shows that the highest obtained value of mobility is 78 cm2V-1s-1 because of its fewer dislocations. High electron mobility films based on perovskite BaSnO3 can provide a good platform for transparent-conducting-oxide electronic devices and for creation of fascinating perovskite heterostructures.

  18. Thin film buried anode battery

    DOEpatents

    Lee, Se-Hee; Tracy, C. Edwin; Liu, Ping

    2009-12-15

    A reverse configuration, lithium thin film battery (300) having a buried lithium anode layer (305) and process for making the same. The present invention is formed from a precursor composite structure (200) made by depositing electrolyte layer (204) onto substrate (201), followed by sequential depositions of cathode layer (203) and current collector (202) on the electrolyte layer. The precursor is subjected to an activation step, wherein a buried lithium anode layer (305) is formed via electroplating a lithium anode layer at the interface of substrate (201) and electrolyte film (204). The electroplating is accomplished by applying a current between anode current collector (201) and cathode current collector (202).

  19. Joining lead wires to thin platinum alloy films

    NASA Technical Reports Server (NTRS)

    Przybyszewski, J. S.; Claing, R. G. (Inventor)

    1983-01-01

    A two step process of joining a lead wire to .000002 m thick platinum alloy film which rests upon an equally thin alumina insulating layer which is adhered to a metal substrate is described. Typically the platinum alloy film forms part of a thermocouple for measuring the surface temperature of a gas turbine airfoil. In the first step the lead wire is deformed 30 to 60% at room temperature while the characteristic one million ohm resistance of the alumina insulating layer is monitored for degradation. In the second step the cold pressed assembly is heated at 865 to 1025 C for 4 to 75 hr in air. During the heating step any degradation of insulating layer resistance may be reversed, provided the resistance was not decreased below 100 ohm in the cold pressing.

  20. Thin film concentrator panel development

    NASA Astrophysics Data System (ADS)

    Zimmerman, D. K.

    1982-07-01

    The development and testing of a rigid panel concept that utilizes a thin film reflective surface for application to a low-cost point-focusing solar concentrator is discussed. It is shown that a thin film reflective surface is acceptable for use on solar concentrators, including 1500 F applications. Additionally, it is shown that a formed steel sheet substrate is a good choice for concentrator panels. The panel has good optical properties, acceptable forming tolerances, environmentally resistant substrate and stiffeners, and adaptability to low to mass production rates. Computer simulations of the concentrator optics were run using the selected reflector panel design. Experimentally determined values for reflector surface specularity and reflectivity along with dimensional data were used in the analysis. The simulations provided intercept factor and net energy into the aperture as a function of aperture size for different surface errors and pointing errors. Point source and Sun source optical tests were also performed.

  1. Thin film characterization using spectroscopic ellipsometry

    NASA Technical Reports Server (NTRS)

    Alterovitz, Samuel A.

    1990-01-01

    The application of the multiple angle and wavelength (MAW) technique to measure the dielectric function of semiconducting films is discussed. This technique evaluates unambiguously the complex dielectric function, epsilon (E), of the film without any pre-assumptions. In some cases the effective medium approximation (EMA) was used to determine the volume fraction of the film components. Application of the MAW technique to several semiconducting films was published previously. Different applications and examples are given, including metal and insulator films.

  2. Thickness dependent metal-insulator transition and dimensional crossover for weak localization in Si{sub 0.02}Zn{sub 0.98}O thin films grown by pulsed laser deposition

    SciTech Connect

    Das, Amit K. Ajimsha, R. S.; Kukreja, L. M.

    2014-05-21

    Metal to insulator transition was observed in Si{sub 0.02}Zn{sub 0.98}O (SZO) films, grown by pulsed laser deposition on sapphire substrates, as the thicknesses of the films were reduced from ∼40 to 15 nm. The SZO film with thickness of ∼40 nm showed typical metallic behavior in temperature dependent resistivity measurements. On the contrary, the SZO film with thickness of ∼15 nm was found to exhibit strong localization where the transport at low temperature was dominated by variable range hopping conduction. In the intermediate thickness regime, quantum corrections were important and a dimensional crossover from 3D to 2D weak localization occurred in the SZO film with thickness of 20 nm.

  3. Cooper pair islanding model of insulating nanohoneycomb films

    NASA Astrophysics Data System (ADS)

    Hollen, S. M.; Valles, J. M., Jr.

    2012-07-01

    We first review evidence for the Cooper pair insulator (CPI) phase in amorphous nanohoneycomb (NHC) films. We then extend our analysis of superconducting islands induced by film thickness variations in NHC films to examine the evolution of island sizes through the magnetic field-driven SIT. Finally, using the islanding picture, we present a plausible model for the appearance and behavior of the CPI phase in amorphous NHC films.

  4. Bulk and Thin Film Contact Resistance with Dissimilar Materials

    NASA Astrophysics Data System (ADS)

    Lau, Y. Y.; Zhang, P.; Tang, W.; Gomez, M. R.; French, D. M.; Zier, J. C.; Gilgenbach, R. M.

    2011-10-01

    Contact resistance is important to integrated circuits, thin film devices, carbon nanotube based cathodes, MEMS relays and interconnectors, wire-array z-pinches, metal-insulator-vacuum junctions, and high power microwave sources, etc. This paper summarizes the recent modeling efforts at U of M, addressing the effect of dissimilar materials and of finite dimensions on the contact resistance of both bulk contacts and thin film contacts. Accurate analytical scaling laws are constructed for the contact resistance of both bulk and thin film contacts over a large range of resistivity ratios and aspect ratios in Cartesian and cylindrical geometries. They were validated against known limiting cases; and spot-checks with numerical simulations and experiments. Supported by AFOSR, AFRL, L-3, and Northrop-Grumman.

  5. Superconducting UBe 13 thin films

    NASA Astrophysics Data System (ADS)

    Quateman, J. H.; Tedrow, P. M.

    1985-12-01

    Of the known heavy fermion superconductors only UBe 13 can have a low resistivity ratio and still go superconducting. In addition, it is a line compound with a melting temperature of nearly twice that of the constituents. These facts make UBe 13 a promising choice for fabrication in thin film form. We have successfully made 2000 Å UBe 13 films by coevaporation of uranium and beryllium on 700°C substrates which were then heated in situ to 1100°C. These films were polycrystalline as shown by X-ray diffraction and have Tc's of 0.85 K, that of the bulk. The resistivity rise at approximately 2 K and the strong negative magnetoresistance were also of the same magnitude as that of the bulk, as were both the perpendicular and parallel critical fields. Thin films of UBe 13 will make more accessible tunneling and proximity effect experiments which can help elucidate the nature of the superconductivity of this compound.

  6. Thin Thermal-Insulation Blankets for Very High Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Michael K.

    2003-01-01

    Thermal-insulation blankets of a proposed type would be exceptionally thin and would endure temperatures up to 2,100 C. These blankets were originally intended to protect components of the NASA Solar Probe spacecraft against radiant heating at its planned closest approach to the Sun (a distance of 4 solar radii). These blankets could also be used on Earth to provide thermal protection in special applications (especially in vacuum chambers) for which conventional thermal-insulation blankets would be too thick or would not perform adequately.

  7. Preparation of Exfoliated Bi2Te3 Thin Films

    NASA Astrophysics Data System (ADS)

    Luo, Jiajun; Late, Dattatray; Wu, Isaac; Biswas, Kanishka; Kanatzidis, Mercouri; Grayson, Matthew

    2011-12-01

    Bi2Te3, recently recognized as a "topological insulator", is proposed to have enhanced electrical and thermoelectric properties due to the topological surface state. In this work, we describe our technique for synthesizing Bi2Te3 thin films with the Scotch tape method. We also describe strategies for fabricating samples for transport and thermoelectric measurements. Preliminary data of carrier density and mobility at room temperature was obtained.

  8. Fate of the Bose insulator in the limit of strong localization and low Cooper-pair density in ultrathin films

    NASA Astrophysics Data System (ADS)

    Hollen, S. M.; Fernandes, G. E.; Xu, J. M.; Valles, J. M.

    2014-10-01

    A Bose insulator composed of a low density of strongly localized Cooper pairs develops at the two-dimensional superconductor to insulator transition (SIT) in a number of thin film systems. Investigations of ultrathin amorphous PbBi films far from the SIT described here provide evidence that the Bose insulator gives way to a second insulating phase with decreasing film thickness. At a critical film thickness dc the magnetoresistance changes sign from positive, as expected for boson transport, to negative, as expected for fermion transport, signs of local Cooper-pair phase coherence effects on transport vanish, and the transport activation energy exhibits a kink. Below dc pairing fluctuation effects remain visible in the high-temperature transport while the activation energy continues to rise. These features show that Cooper pairing persists and suggest that the localized unpaired electron states involved in transport are interspersed among regions of strongly localized Cooper pairs in this strongly localized, low Cooper-pair density phase.

  9. Zinc oxide thin film acoustic sensor

    SciTech Connect

    Mohammed, Ali Jasim; Salih, Wafaa Mahdi; Hassan, Marwa Abdul Muhsien; Nusseif, Asmaa Deiaa; Kadhum, Haider Abdullah; Mansour, Hazim Louis

    2013-12-16

    This paper reports the implementation of (750 nm) thickness of Zinc Oxide (ZnO) thin film for the piezoelectric pressure sensors. The film was prepared and deposited employing the spray pyrolysis technique. XRD results show that the growth preferred orientation is the (002) plane. A polycrystalline thin film (close to mono crystallite like) was obtained. Depending on the Scanning Electron Microscopy photogram, the film homogeneity and thickness were shown. The resonance frequency measured (about 19 kHz) and the damping coefficient was calculated and its value was found to be about (2.5538), the thin film be haves as homogeneous for under and over damped. The thin film pressure sensing was approximately exponentially related with frequency, the thin film was observed to has a good response for mechanical stresses also it is a good material for the piezoelectric properties.

  10. Zinc oxide thin film acoustic sensor

    NASA Astrophysics Data System (ADS)

    Mohammed, Ali Jasim; Salih, Wafaa Mahdi; Hassan, Marwa Abdul Muhsien; Mansour, Hazim Louis; Nusseif, Asmaa Deiaa; Kadhum, Haider Abdullah

    2013-12-01

    This paper reports the implementation of (750 nm) thickness of Zinc Oxide (ZnO) thin film for the piezoelectric pressure sensors. The film was prepared and deposited employing the spray pyrolysis technique. XRD results show that the growth preferred orientation is the (002) plane. A polycrystalline thin film (close to mono crystallite like) was obtained. Depending on the Scanning Electron Microscopy photogram, the film homogeneity and thickness were shown. The resonance frequency measured (about 19 kHz) and the damping coefficient was calculated and its value was found to be about (2.5538), the thin film be haves as homogeneous for under and over damped. The thin film pressure sensing was approximately exponentially related with frequency, the thin film was observed to has a good response for mechanical stresses also it is a good material for the piezoelectric properties.

  11. Uncooled thin film pyroelectric IR detector with aerogel thermal isolation

    SciTech Connect

    Ruffner, J.A.; Clem, P.G.; Tuttle, B.A.

    1998-01-01

    Uncooled pyroelectric IR imaging systems, such as night vision goggles, offer important strategic advantages in battlefield scenarios and reconnaissance surveys. Until now, the current technology for fabricating these devices has been limited by low throughput and high cost which ultimately limit the availability of these sensor devices. We have developed and fabricated an alternative design for pyroelectric IR imaging sensors that utilizes a multilayered thin film deposition scheme to create a monolithic thin film imaging element on an active silicon substrate for the first time. This approach combines a thin film pyroelectric imaging element with a thermally insulating SiO{sub 2} aerogel thin film to produce a new type of uncooled IR sensor that offers significantly higher thermal, spatial, and temporal resolutions at a substantially lower cost per unit. This report describes the deposition, characterization and optimization of the aerogel thermal isolation layer and an appropriate pyroelectric imaging element. It also describes the overall integration of these components along with the appropriate planarization, etch stop, adhesion, electrode, and blacking agent thin film layers into a monolithic structure. 19 refs., 8 figs., 6 tabs.

  12. Analysis of Hard Thin Film Coating

    NASA Technical Reports Server (NTRS)

    Shen, Dashen

    1998-01-01

    MSFC is interested in developing hard thin film coating for bearings. The wearing of the bearing is an important problem for space flight engine. Hard thin film coating can drastically improve the surface of the bearing and improve the wear-endurance of the bearing. However, many fundamental problems in surface physics, plasma deposition, etc, need further research. The approach is using electron cyclotron resonance chemical vapor deposition (ECRCVD) to deposit hard thin film an stainless steel bearing. The thin films in consideration include SiC, SiN and other materials. An ECRCVD deposition system is being assembled at MSFC.

  13. Analysis of Hard Thin Film Coating

    NASA Technical Reports Server (NTRS)

    Shen, Dashen

    1998-01-01

    Marshall Space Flight Center (MSFC) is interested in developing hard thin film coating for bearings. The wearing of the bearing is an important problem for space flight engine. Hard thin film coating can drastically improve the surface of the bearing and improve the wear-endurance of the bearing. However, many fundamental problems in surface physics, plasma deposition, etc, need further research. The approach is using Electron Cyclotron Resonance Chemical Vapor Deposition (ECRCVD) to deposit hard thin film on stainless steel bearing. The thin films in consideration include SiC, SiN and other materials. An ECRCVD deposition system is being assembled at MSFC.

  14. Thin Aerogel as a Spacer in Multilayer Insulation

    NASA Technical Reports Server (NTRS)

    Moroz, Nancy

    2015-01-01

    Cryogenic fluid management is a critical technical area that is needed for future space exploration. A key challenge is the storability of liquid hydrogen (LH2), liquid methane (LCH4), and liquid oxygen (LOX) propellants for long-duration missions. The storage tanks must be well-insulated to prevent over-pressurization and venting, which can lead to unacceptable propellant losses for long-duration missions to Mars and beyond. Aspen Aerogels had validated the key process step to enable the fabrication of thin, low-density aerogel materials. The multilayer aerogel insulation (MLAI) system prototypes were prepared using sheets of aerogel materials with superior thermal performance exceeding current state-of-the-art insulation for space applications. The exceptional properties of this system include a new breakthrough in high-vacuum cryogenic thermal insulation, providing a durable material with excellent thermal performance at a reduced cost when compared to longstanding state-of-the-art multilayer insulation systems. During the Phase II project, further refinement and qualification/system-level testing of the MLAI system will be performed for use in cryogenic storage applications. Aspen has been in discussions with United Launch Alliance, LLC; NASA's Kennedy Space Center; and Yetispace, Inc., to test the MLAI system on rea-lworld tanks such as Vibro-Acoustic Test Article (VATA) or the Cryogenic Orbital Testbed (CRYOTE).

  15. Thin Aerogel as a Spacer in Multilayer Insulation

    NASA Technical Reports Server (NTRS)

    Moroz, Nancy

    2015-01-01

    Cryogenic fluid management is a critical technical area that is needed for future space exploration. A key challenge is the storability of liquid hydrogen (LH2), liquid methane (LCH4), and liquid oxygen (LOX) propellants for long-duration missions. The storage tanks must be well-insulated to prevent over-pressurization and venting, which can lead to unacceptable propellant losses for long-duration missions to Mars and beyond. Aspen Aerogels had validated the key process step to enable the fabrication of thin, low-density aerogel materials. The multilayer aerogel insulation (MLAI) system prototypes were prepared using sheets of aerogel materials with superior thermal performance exceeding current state-of-the-art insulation for space applications. The exceptional properties of this system include a new breakthrough in high-vacuum cryogenic thermal insulation, providing a durable material with excellent thermal performance at a reduced cost when compared to longstanding state-of-the-art multilayer insulation systems. During the Phase II project, further refinement and qualification/system-level testing of the MLAI system will be performed for use in cryogenic storage applications. Aspen has been in discussions with United Launch Alliance, LLC; NASA's Kennedy Space Center; and Yetispace, Inc., to test the MLAI system on real-world tanks such as Vibro-Acoustic Test Article (VATA) or the Cryogenic Orbital Testbed (CRYOTE).

  16. Ferroelectric films of barium strontium titanate on semi-insulating silicon carbide substrates

    NASA Astrophysics Data System (ADS)

    Tumarkin, A. V.; Razumov, S. V.; Gagarin, A. G.; Odinets, A. A.; Mikhailov, A. K.; Pronin, I. P.; Stozharov, V. M.; Senkevich, S. V.; Travin, N. K.

    2016-04-01

    Thin ferroelectric Ba x Sr1- x TiO3 (BST) layers have been grown for the first time on semi-insulating silicon carbide substrates by RF magnetron sputtering of a ceramic target without using buffer sublayers. Results of investigation of the structure of obtained BST films and the electrical properties of related planar capacitors are presented. The obtained structures are characterized by high nonlinearity and low dielectric losses at microwave frequencies.

  17. Thin film solar energy collector

    DOEpatents

    Aykan, Kamran; Farrauto, Robert J.; Jefferson, Clinton F.; Lanam, Richard D.

    1983-11-22

    A multi-layer solar energy collector of improved stability comprising: (1) a substrate of quartz, silicate glass, stainless steel or aluminum-containing ferritic alloy; (2) a solar absorptive layer comprising silver, copper oxide, rhodium/rhodium oxide and 0-15% by weight of platinum; (3) an interlayer comprising silver or silver/platinum; and (4) an optional external anti-reflective coating, plus a method for preparing a thermally stable multi-layered solar collector, in which the absorptive layer is undercoated with a thin film of silver or silver/platinum to obtain an improved conductor-dielectric tandem.

  18. Thin film based plasmon nanorulers

    NASA Astrophysics Data System (ADS)

    Taylor, Alexander D.; Lu, Chang; Geyer, Scott; Carroll, D. L.

    2016-07-01

    In this work, isolated metal nanoparticles are supported on a dielectric thin film that is placed on a conducting plane. The optical scattering characteristics of these metal nanoparticles are directly correlated with the localized surface plasmon states of the nanoparticle—image particle dimer, formed in the conducting plane below. Quantification of plasmon resonance shifts can be directly correlated with the application of the plasmon nanoruler equation. This simple geometry shows that direct optical techniques can be used to resolve thickness variations in dielectrics of only a few nanometers.

  19. Strain-induced properties of epitaxial VOx thin films

    NASA Astrophysics Data System (ADS)

    Rata, A. D.; Hibma, T.

    2005-01-01

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

  20. New devices using ferroelectric thin films

    SciTech Connect

    Land, C.E.; Butler, M.A.; Martin, S.J.

    1989-01-01

    Recent developments in the fabrication technologies of ferroelectric thin films in general and of PZT (lead zirconate titanate) and PLZT (lead lanthanum zirconate titanate) thin films in particular have suggested the feasibility of several new devices. Integrated optical devices for information processing and high-speed switching, high-density optical information processing and storage devices and spatial light modulators are some of the applications currently being investigated for these films. Ongoing studies of the longitudinal electrooptic effects and the photosensitivities of PZT and PLZT thin films have established the feasibility of erasable/rewritable optical memories with fast switching and potentially long lifetimes compared to current magneto-optic thin film devices. Some properties of PZT thin films and of new devices based on those properties are described in this paper. 15 refs., 5 figs., 1 tab.

  1. Aluminum nitride insulating films for MOSFET devices

    NASA Technical Reports Server (NTRS)

    Lewicki, G. W.; Maserjian, J.

    1972-01-01

    Application of aluminum nitrides as electrical insulator for electric capacitors is discussed. Electrical properties of aluminum nitrides are analyzed and specific use with field effect transistors is defined. Operational limits of field effect transistors are developed.

  2. Fully Integrated Applications of Thin Films on Low Temperature Cofired Ceramic (LTCC)

    SciTech Connect

    Ambrose Wolf; Ken Peterson; Matt O'Keefe; Wayne Huebner; Bill Kuhn

    2012-04-19

    Thin film multilayers have previously been introduced on multilayer low temperature cofired ceramic (LTCC), as well as initial thin film capacitors on LTCC. The ruggedness of a multipurpose Ti-Cu-Pt-Au stack for connectivity and RF conductivity has continued to benefit fabrication and reliability in state of-the-art modules, while the capacitors have followed the traditional Metal-Insulator-Metal (MIM) style. The full integration of thin film passives with thin film connectivity traces is presented. Certain passives, such as capacitors, require specifically tailored and separately patterned thin film (multi-)layers, including a dielectric. Different capacitance values are achieved by variation of both the insulator layer thickness and the active area of the capacitor. Other passives, such as filters, require only the conductor - a single thin film multilayer. This can be patterned from the same connectivity thin film material (Ti-Cu-Pt-Au), or a specially tailored thin film material (e.g. Ti-Cu-Au) can be deposited. Both versions are described, including process and integration details. Examples are discussed, ranging from patterning for maximum tolerances, to space and performance-optimized designs. Cross-sectional issues associated with integration are also highlighted in the discussion.

  3. Electrostatic thin film chemical and biological sensor

    DOEpatents

    Prelas, Mark A.; Ghosh, Tushar K.; Tompson, Jr., Robert V.; Viswanath, Dabir; Loyalka, Sudarshan K.

    2010-01-19

    A chemical and biological agent sensor includes an electrostatic thin film supported by a substrate. The film includes an electrostatic charged surface to attract predetermined biological and chemical agents of interest. A charge collector associated with said electrostatic thin film collects charge associated with surface defects in the electrostatic film induced by the predetermined biological and chemical agents of interest. A preferred sensing system includes a charge based deep level transient spectroscopy system to read out charges from the film and match responses to data sets regarding the agents of interest. A method for sensing biological and chemical agents includes providing a thin sensing film having a predetermined electrostatic charge. The film is exposed to an environment suspected of containing the biological and chemical agents. Quantum surface effects on the film are measured. Biological and/or chemical agents can be detected, identified and quantified based on the measured quantum surface effects.

  4. Thin films of mixed metal compounds

    DOEpatents

    Mickelsen, Reid A.; Chen, Wen S.

    1985-01-01

    A compositionally uniform thin film of a mixed metal compound is formed by simultaneously evaporating a first metal compound and a second metal compound from independent sources. The mean free path between the vapor particles is reduced by a gas and the mixed vapors are deposited uniformly. The invention finds particular utility in forming thin film heterojunction solar cells.

  5. Deposition of thin insulation layers from the gas phase

    NASA Technical Reports Server (NTRS)

    Behn, R.; Hagedorn, H.; Kammermaier, J.; Kobale, M.; Packonik, H.; Ristow, D.; Seebacher, G.

    1981-01-01

    The continuous deposition of thin organic dielectric films on metallized carrier foils by glow discharge in monomeric gases is described. Depending on the applied monomers, the films had a dissipation factor of .001 to .003 (1 kHz), a relative permittivity of 2.3 to 2.5 and a resistivity of about 10 to the 17th power omega cm. Additionally, they proved to have a high mechanical homogeneity. Self-healing rolled capacitors with a very high capacitance per volume and of consistently high quality were fabricated from the metallized carrier foils covered with the dielectric film.

  6. Characteristics Of Vacuum Deposited Sucrose Thin Films

    NASA Astrophysics Data System (ADS)

    Ungureanu, F.; Predoi, D.; Ghita, R. V.; Vatasescu-Balcan, R. A.; Costache, M.

    Thin films of sucrose (C12H22O11) were deposited on thin cut glass substrates by thermal evaporation technique (p ~ 10-5 torr). The surface morphology was putted into evidence by FT-IR and SEM analysis. The experimental results confirm a uniform deposition of an adherent sucrose layer. The biological tests (e.g., cell morphology and cell viability evaluated by measuring mitochondrial dehydrogenise activity with MTT assay) confirm the properties of sucrose thin films as bioactive material. The human fetal osteoblast system grown on thin sucrose film was used for the determination of cell proliferation, cell viability and cell morphology studies.

  7. Cellulose triacetate, thin film dielectric capacitor

    NASA Technical Reports Server (NTRS)

    Yen, Shiao-Ping S. (Inventor); Jow, T. Richard (Inventor)

    1995-01-01

    Very thin films of cellulose triacetate are cast from a solution containing a small amount of high boiling temperature, non-solvent which evaporates last and lifts the film from the casting surface. Stretched, oriented, crystallized films have high electrical breakdown properties. Metallized films less than about 2 microns in thickness form self-healing electrodes for high energy density, pulsed power capacitors. Thicker films can be utilized as a dielectric for a capacitor.

  8. Cellulose triacetate, thin film dielectric capacitor

    NASA Technical Reports Server (NTRS)

    Yen, Shiao-Ping S. (Inventor); Jow, T. Richard (Inventor)

    1993-01-01

    Very thin films of cellulose triacetate are cast from a solution containing a small amount of high boiling temperature, non-solvent which evaporates last and lifts the film from the casting surface. Stretched, oriented, crystallized films have high electrical breakdown properties. Metallized films less than about 2 microns in thickness form self-healing electrodes for high energy density, pulsed power capacitors. Thicker films can be utilized as a dielectric for a capacitor.

  9. Preparation and Characterization of PZT Thin Films

    SciTech Connect

    Bose, A.; Sreemany, M.; Bhattacharyya, D. K.; Sen, Suchitra; Halder, S. K.

    2008-07-29

    In analogy with Piezoelectric Wafer Active Sensors (PWAS), Lead Zirconate Titanate (PZT) thin films also seem to be promising for Structural Health Monitoring (SHM) due to a number of reasons. Firstly, PZT thin films with well oriented domains show enhanced piezoelectric response. Secondly, PWAS requires comparatively large voltage leading to a demand for thin PZT films (<< {mu}m in thickness) for low voltage operation at {<=}10 V. This work focuses on two different aspects: (a) growing oriented PZT thin films in ferroelectric perovskite phase in the range of (80-150) nm thickness on epitaxial Si/Pt without a seed layer and (b) synthesizing perovskite phase in PZT thin films on Corning glass 1737 using a seed layer of TiO{sub x} (TiO{sub x} thickness ranging between 30 nm to 500 nm)

  10. A monolithic thin film electrochromic window

    SciTech Connect

    Goldner, R.B.; Arntz, F.O.; Berera, G.; Haas, T.E.; Wong, K.K. . Electro-Optics Technology Center); Wei, G. ); Yu, P.C. )

    1991-01-01

    Three closely related thin film solid state ionic devices that are potentially important for applications are: electrochromic smart windows, high energy density thin film rechargeable batteries, and thin film electrochemical sensors. Each usually has at least on mixed ion/electron conductor, an electron-blocking ion conductor, and an ion-blocking electron conductor, and many of the technical issues associated with thin film solid state ionics are common to all three devices. Since the electrochromic window has the added technical requirement of electrically-controlled optical modulation, (over the solar spectrum), and since research at the authors' institution has focused primarily on the window structure, this paper will address the electrochromic window, and particularly a monolithic variable reflectivity electrochromic window, as an illustrative example of some of the challenges and opportunities that are confronting the thin film solid state ionics community. 33 refs.

  11. A monolithic thin film electrochromic window

    SciTech Connect

    Goldner, R.B.; Arntz, F.O.; Berera, G.; Haas, T.E.; Wong, K.K.; Wei, G.; Yu, P.C.

    1991-12-31

    Three closely related thin film solid state ionic devices that are potentially important for applications are: electrochromic smart windows, high energy density thin film rechargeable batteries, and thin film electrochemical sensors. Each usually has at least on mixed ion/electron conductor, an electron-blocking ion conductor, and an ion-blocking electron conductor, and many of the technical issues associated with thin film solid state ionics are common to all three devices. Since the electrochromic window has the added technical requirement of electrically-controlled optical modulation, (over the solar spectrum), and since research at the authors` institution has focused primarily on the window structure, this paper will address the electrochromic window, and particularly a monolithic variable reflectivity electrochromic window, as an illustrative example of some of the challenges and opportunities that are confronting the thin film solid state ionics community. 33 refs.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  13. Thin-film decoupling capacitors for multi-chip modules

    SciTech Connect

    Dimos, D.: Lockwood, S.J.; Schwartz, R.W.; Rodgers, M.S.

    1994-03-01

    Thin-film decoupling capacitors based on ferroelectric lead lanthanum zirconate titanate (PLZT) films are being developed for use in advanced packages, such as multi-chip modules. These thin-film decoupling capacitors are intended to replace multi-layer ceramic capacitors for certain applications, since they can be more fully integrated into the packaging architecture. The increased integration that can be achieved should lead to decreased package volume and improved high-speed performance, due to a decrease in interconnect inductance. PLZT films are fabricated by spin coating using metal carboxylate/alkoxide solutions. These films exhibit very high dielectric constants ({var_epsilon} {ge} 900), low dielectric losses (tan{delta} = 0.01), excellent insulation resistances ({rho} > 10{sup 13} {Omega}-cm at 125{degrees}C), and good breakdown field strengths (E{sub B} = 900 kV/cm). For integrated circuit applications, the PLZT dielectric is less than 1 {mu}m thick, which results in a large capacitance/area (8--9 nF/mm{sup 2}). The thin-film geometry and processing conditions also make these capacitors suitable for direct incorporation onto integrated circuits and for packages that require embedded components.

  14. rf plasma oxidation of Ni thin films sputter deposited to generate thin nickel oxide layers

    NASA Astrophysics Data System (ADS)

    Hoey, Megan L.; Carlson, J. B.; Osgood, R. M.; Kimball, B.; Buchwald, W.

    2010-10-01

    Nickel oxide (NiO) layers were formed on silicon (Si) substrates by plasma oxidation of nickel (Ni) film lines. This ultrathin NiO layer acted as a barrier layer to conduction, and was an integral part of a metal-insulator-metal (MIM) diode, completed by depositing gold (Au) on top of the oxide. The electrical and structural properties of the NiO thin film were examined using resistivity calculations, current-voltage (I-V) measurements and cross-sectional transmission electron microscopy (XTEM) imaging. The flow rate of the oxygen gas, chamber pressure, power, and exposure time and their influence on the characteristics of the NiO thin film were studied.

  15. Planar thin film SQUID with integral flux concentrator

    NASA Technical Reports Server (NTRS)

    Peters, Palmer N. (Inventor); Sisk, Robert C. (Inventor)

    1988-01-01

    A thin film SQUID is disclosed having improved flux concentration combined with simplicity of design and fabrication. The SQUID starts with a wafer like substrate having simple planar geometry. A large area of superconducting film is coated on the substrate, with a small open or uncoated area remaining at its center to define a SQUID loop, and a gap in the film formed, beginning at the outer circumferential edge of the substrate and extending radially inward to the open area. A Josephson junction is formed across the gap near the open area to interrupt the electrical continuity of the SQUID loop. A coil is attached to the surface of the substrate, electrically insulated from the superconducting film, and is energized to induce flux within the SQUID which is concentrated within the open area.

  16. Metal-insulator transition in films of doped semiconductor nanocrystals.

    PubMed

    Chen, Ting; Reich, K V; Kramer, Nicolaas J; Fu, Han; Kortshagen, Uwe R; Shklovskii, B I

    2016-03-01

    To fully deploy the potential of semiconductor nanocrystal films as low-cost electronic materials, a better understanding of the amount of dopants required to make their conductivity metallic is needed. In bulk semiconductors, the critical concentration of electrons at the metal-insulator transition is described by the Mott criterion. Here, we theoretically derive the critical concentration nc for films of heavily doped nanocrystals devoid of ligands at their surface and in direct contact with each other. In the accompanying experiments, we investigate the conduction mechanism in films of phosphorus-doped, ligand-free silicon nanocrystals. At the largest electron concentration achieved in our samples, which is half the predicted nc, we find that the localization length of hopping electrons is close to three times the nanocrystals diameter, indicating that the film approaches the metal-insulator transition. PMID:26618885

  17. Metal-insulator transition in films of doped semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Chen, Ting; Reich, K. V.; Kramer, Nicolaas J.; Fu, Han; Kortshagen, Uwe R.; Shklovskii, B. I.

    2016-03-01

    To fully deploy the potential of semiconductor nanocrystal films as low-cost electronic materials, a better understanding of the amount of dopants required to make their conductivity metallic is needed. In bulk semiconductors, the critical concentration of electrons at the metal-insulator transition is described by the Mott criterion. Here, we theoretically derive the critical concentration nc for films of heavily doped nanocrystals devoid of ligands at their surface and in direct contact with each other. In the accompanying experiments, we investigate the conduction mechanism in films of phosphorus-doped, ligand-free silicon nanocrystals. At the largest electron concentration achieved in our samples, which is half the predicted nc, we find that the localization length of hopping electrons is close to three times the nanocrystals diameter, indicating that the film approaches the metal-insulator transition.

  18. Thin-film optical shutter

    NASA Astrophysics Data System (ADS)

    Matlow, S. L.

    1981-02-01

    The ideal solution to the excessive solar gain problem is an optical shutter, a device which switches from being highly transmissive to solar radiation to being highly reflective to solar radiation when a critical temperature is reached in the enclosure. The switching occurs because one or more materials in the device undergo a phase transition at the critical temperature. A specific embodiment of macroconjugated macromolecules, the poly (p-phenylene)'s, was chosen as the one most likely to meet all of the requirements of the thin film optical shutter project (TFOS). The reason for this choice is explored. In order to be able to make meaningful calculations of the thermodynamic and optical properties of the poly (p-phenylene)'s a quantum mechanical method, the equilibrium bond length (EBL) theory, was developed. Some results of EBL theory are included.

  19. Thin film bioreactors in space

    NASA Technical Reports Server (NTRS)

    Hughes-Fulford, M.; Scheld, H. W.

    1989-01-01

    Studies from the Skylab, SL-3 and D-1 missions have demonstrated that biological organisms grown in microgravity have changes in basic cellular functions such as DNA, mRNA and protein synthesis, cytoskeleton synthesis, glucose utilization, and cellular differentiation. Since microgravity could affect prokaryotic and eukaryotic cells at a subcellular and molecular level, space offers an opportunity to learn more about basic biological systems with one inmportant variable removed. The thin film bioreactor will facilitate the handling of fluids in microgravity, under constant temperature and will allow multiple samples of cells to be grown with variable conditions. Studies on cell cultures grown in microgravity would make it possible to identify and quantify changes in basic biological function in microgravity which are needed to develop new applications of orbital research and future biotechnology.

  20. Wrinkle motifs in thin films

    PubMed Central

    Budrikis, Zoe; Sellerio, Alessandro L.; Bertalan, Zsolt; Zapperi, Stefano

    2015-01-01

    On length scales from nanometres to metres, partial adhesion of thin films with substrates generates a fascinating variety of patterns, such as ‘telephone cord’ buckles, wrinkles, and labyrinth domains. Although these patterns are part of everyday experience and are important in industry, they are not completely understood. Here, we report simulation studies of a previously-overlooked phenomenon in which pairs of wrinkles form avoiding pairs, focusing on the case of graphene over patterned substrates. By nucleating and growing wrinkles in a controlled way, we characterize how their morphology is determined by stress fields in the sheet and friction with the substrate. Our simulations uncover the generic behaviour of avoiding wrinkle pairs that should be valid at all scales. PMID:25758174

  1. BDS thin film damage competition

    SciTech Connect

    Stolz, C J; Thomas, M D; Griffin, A J

    2008-10-24

    A laser damage competition was held at the 2008 Boulder Damage Symposium in order to determine the current status of thin film laser resistance within the private, academic, and government sectors. This damage competition allows a direct comparison of the current state-of-the-art of high laser resistance coatings since they are all tested using the same damage test setup and the same protocol. A normal incidence high reflector multilayer coating was selected at a wavelength of 1064 nm. The substrates were provided by the submitters. A double blind test assured sample and submitter anonymity so only a summary of the results are presented here. In addition to the laser resistance results, details of deposition processes, coating materials, and layer count will also be shared.

  2. Dynamic delamination of patterned thin films

    NASA Astrophysics Data System (ADS)

    Kandula, Soma S. V.; Tran, Phuong; Geubelle, Philippe H.; Sottos, Nancy R.

    2008-12-01

    We investigate laser-induced dynamic delamination of a patterned thin film on a substrate. Controlled delamination results from our insertion of a weak adhesion region beneath the film. The inertial forces acting on the weakly bonded portion of the film lead to stable propagation of a crack along the film/substrate interface. Through a simple energy balance, we extract the critical energy for interfacial failure, a quantity that is difficult and sometimes impossible to characterize by more conventional methods for many thin film/substrate combinations.

  3. AES analysis of barium fluoride thin films

    NASA Astrophysics Data System (ADS)

    Kashin, G. N.; Makhnjuk, V. I.; Rumjantseva, S. M.; Shchekochihin, Ju. M.

    1993-06-01

    AES analysis of thin films of metal fluorides is a difficult problem due to charging and decomposition of such films under electron bombardment. We have developed a simple algorithm for a reliable quantitative AES analysis of metal fluoride thin films (BaF 2 in our work). The relative AES sensitivity factors for barium and fluorine were determined from BaF 2 single-crystal samples. We have investigated the dependence of composition and stability of barium fluoride films on the substrate temperature during film growth. We found that the instability of BaF 2 films grown on GaAs substrates at high temperatures (> 525°C) is due to a loss of fluorine. Our results show that, under the optimal electron exposure conditions, AES can be used for a quantitative analysis of metal fluoride thin films.

  4. Infrared radiation of thin plastic films.

    NASA Technical Reports Server (NTRS)

    Tien, C. L.; Chan, C. K.; Cunnington, G. R.

    1972-01-01

    A combined analytical and experimental study is presented for infrared radiation characteristics of thin plastic films with and without a metal substrate. On the basis of the thin-film analysis, a simple analytical technique is developed for determining band-averaged optical constants of thin plastic films from spectral normal transmittance data for two different film thicknesses. Specifically, the band-averaged optical constants of polyethylene terephthalate and polyimide were obtained from transmittance measurements of films with thicknesses in the range of 0.25 to 3 mil. The spectral normal reflectance and total normal emittance of the film side of singly aluminized films are calculated by use of optical constants; the results compare favorably with measured values.

  5. Thin film nitinol microstent for aneurysm occlusion.

    PubMed

    Chun, Youngjae; Levi, Daniel S; Mohanchandra, K P; Vinuela, Fernando; Vinuela, Fernando; Carman, Gregory P

    2009-05-01

    Thin film nitinol produced by sputter deposition was used in the design of microstents intended to treat small vessel aneurysms. Thin film microstents were fabricated by "hot-target" dc sputter deposition. Both stress-strain curves and differential scanning calorimetry curves were generated for the film used to fabricate stents. The films used for stents had an A(f) temperature of approximately 36 degrees C allowing for body activated response from a microcatheter. The 10 microm film was only slightly radio-opaque; thus, a Td marker was attached to the stents to guide fluoroscopic delivery. Thin film microstents were tested in a flow loop with and without nitinol support skeletons to give additional radial support. Stents could be compressed into and easily delivered with <3 Fr catheters. Theoretical frictional and wall drag forces on a thin film nitinol small vessel vascular stent were calculated, and the radial force exerted by thin film stents was evaluated theoretically and experimentally. In vivo studies in swine confirmed that thin film nitinol microstents could be deployed accurately and consistently in the swine cranial vasculature. PMID:19388784

  6. Method of producing thin cellulose nitrate film

    DOEpatents

    Lupica, S.B.

    1975-12-23

    An improved method for forming a thin nitrocellulose film of reproducible thickness is described. The film is a cellulose nitrate film, 10 to 20 microns in thickness, cast from a solution of cellulose nitrate in tetrahydrofuran, said solution containing from 7 to 15 percent, by weight, of dioctyl phthalate, said cellulose nitrate having a nitrogen content of from 10 to 13 percent.

  7. Amorphous Insulator Films With Controllable Properties

    NASA Technical Reports Server (NTRS)

    Alterovitz, Samuel A.; Warner, Joseph D.; Liu, David C.; Pouch, John J.

    1987-01-01

    In experiments described in report, amorphous hydrogenated carbon films grown at room temperature by low-frequency plasma deposition, using methane or butane gas. Films have unique array of useful properties; (a) adhere to wide variety of materials; (b) contain only carbon and hydrogen; (c) smooth and free of pinholes; (d) resistant to attack by moisture and chemicals; and (e) have high electric-breakdown strength and electrical resistivity. Two of optical properties and hardness of this film controlled by deposition conditions. Amorphous a-C:H and BN films used for hermetic sealing and protection of optical, electronic, magnetic, or delicate mechanical systems, and for semiconductor field dielectrics.

  8. Detecting insulation defects in metal/plastic films

    NASA Technical Reports Server (NTRS)

    Buggle, R. N.

    1980-01-01

    Simple apparatus checks insulation between plastic and metal surfaces. Film can be inspected more accurately; apparatus can spot minute electrical contaminants between plastic and metal films. Steel roller connected to high-range ohmmeter is guided over entire plastic area of test sample. Roller weighs 2 lb. (0.9 kg), which effectively translates into 250-psi (1.76X10 to 6th power -N/sq m) contact pressure at plastic surface sufficient to locate microscopic defects.

  9. Topological insulator Bi2Te3 films synthesized by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Cao, Helin; Venkatasubramanian, Rama; Liu, Chang; Pierce, Jonathan; Yang, Haoran; Zahid Hasan, M.; Wu, Yue; Chen, Yong P.

    2012-10-01

    Topological insulator (TI) materials such as Bi2Te3 and Bi2Se3 have attracted strong recent interests. Large scale, high quality TI thin films are important for developing TI-based device applications. In this work, structural and electronic properties of Bi2Te3 thin films deposited by metal organic chemical vapor deposition (MOCVD) on GaAs (001) substrates were characterized via x-ray diffraction (XRD), Raman spectroscopy, angle-resolved photoemission spectroscopy (ARPES), and electronic transport measurements. The characteristic topological surface states with a single Dirac cone have been clearly revealed in the electronic band structure measured by ARPES, confirming the TI nature of the MOCVD Bi2Te3 films. Resistivity and Hall effect measurements have demonstrated relatively high bulk carrier mobility of ˜350 cm2/Vs at 300 K and ˜7400 cm2/Vs at 15 K. We have also measured the Seebeck coefficient of the films. Our demonstration of high quality topological insulator films grown by a simple and scalable method is of interests for both fundamental research and practical applications of thermoelectric and TI materials.

  10. Optical information storage in PLZT thin films

    SciTech Connect

    Land, C.E.

    1989-01-01

    The feasibility of storing and reading high density optical information in lead zirconate titanate (PZT) and in lead lanthanum zirconate titanate (PLZT) thin films depends on both the longitudinal electrooptic coefficients and the photosensitivities of the films. This paper describes the methods used to measure both the longitudinal electrooptic effects and the photosensitivities of the thin films. The results of these measurements were used to evaluate a longitudinal quadratic electrooptic R coefficient, a linear electrooptic r/sub c/ coefficient and the wavelength dependence of the photosensitivity of a composition of PZT polycrystalline thin film. The longitudinal electrooptic R and r/sub c/ coefficients are about an order of magnitude less than the transverse R and R/sub c/ coefficients of the bulk ceramics of similar compositions. This is attributed to clamping of the film by the rigid substrate. The large birefringence after poling (>10/sup /minus/2/) suggests that the optic axes of the films are preferentially oriented normal to the film surface. The techniques used for evaluating the photosensitivities of the thin films are based on measuring the photocurrent generated rather than the reduction in coercive voltage (used previously for bulk ceramics) when the film is exposed to light. The thin film photosensitivities appear to be about three orders of magnitude higher than those of bulk ceramics of similar compositions. 14 refs., 12 figs., 1 tab.

  11. VUV thin films, chapter 7

    NASA Technical Reports Server (NTRS)

    Zukic, Muamer; Torr, Douglas G.

    1993-01-01

    The application of thin film technology to the vacuum ultraviolet (VUV) wavelength region from 120 nm to 230 nm has not been fully exploited in the past because of absorption effects which complicate the accurate determination of the optical functions of dielectric materials. The problem therefore reduces to that of determining the real and imaginary parts of a complex optical function, namely the frequency dependent refractive index n and extinction coefficient k. We discuss techniques for the inverse retrieval of n and k for dielectric materials at VUV wavelengths from measurements of their reflectance and transmittance. Suitable substrate and film materials are identified for application in the VUV. Such applications include coatings for the fabrication of narrow and broadband filters and beamsplitters. The availability of such devices open the VUV regime to high resolution photometry, interferometry and polarimetry both for space based and laboratory applications. This chapter deals with the optics of absorbing multilayers, the determination of the optical functions for several useful materials, and the design of VUV multilayer stacks as applied to the design of narrow and broadband reflection and transmission filters and beamsplitters. Experimental techniques are discussed briefly, and several examples of the optical functions derived for selected materials are presented.

  12. Thin Film Physical Sensor Instrumentation Research and Development at NASA Glenn Research Center

    NASA Technical Reports Server (NTRS)

    Wrbanek, John D.; Fralick, Gustave C.

    2006-01-01

    A range of thin film sensor technology has been demonstrated enabling measurement of multiple parameters either individually or in sensor arrays including temperature, strain, heat flux, and flow. Multiple techniques exist for refractory thin film fabrication, fabrication and integration on complex surfaces and multilayered thin film insulation. Leveraging expertise in thin films and high temperature materials, investigations for the applications of thin film ceramic sensors has begun. The current challenges of instrumentation technology are to further develop systems packaging and component testing of specialized sensors, further develop instrumentation techniques on complex surfaces, improve sensor durability, and to address needs for extreme temperature applications. The technology research and development ongoing at NASA Glenn for applications to future launch vehicles, space vehicles, and ground systems is outlined.

  13. Thickness dependence of superconducting properties in magnesium diboride thin films

    NASA Astrophysics Data System (ADS)

    Beringer, Douglas; Clavero, Cesar; Tan, Teng; Xi, Xiaoxing; Lukaszew, Rosa

    2013-03-01

    Thin film MgB2 is a promising material currently researched for improvements in superconducting radio frequency (SRF) technology and applications. At present, bulk niobium SRF accelerating cavities suffer from a fundamental upper limit in maximally sustained accelerating gradients; however, a scheme involving multi-layered superstructures consisting of superconducting-insulating-superconducting (SIS) layers has been proposed to overcome this fundamental material limit of 50 MV/m. The SIS multi-layer paradigm is reliant upon implementing a thin shielding material with a suitably high Hc1 which may prevent early field penetration in a bulk material layer and consequently delay the high field breakdown. It has been predicted that for thin superconducting films -- thickness less than the London penetration depth (~ 140 nm in the case of MgB2) -- the lower critical field Hc1 will be enhanced with decreasing thickness. Thus, MgB2, with a high bulk Hc1 value is a prime candidate for such SIS structures. Here we present our study on the structure, surface morphology and superconducting properties on a series of MgB2 thin films and correlate the effects of film thickness and surface morphology on Hc1. This work was supported in part by the U.S. Department of Energy (DE-SC0004410 and DE-AC05-06OR23177) and Defense Threat Reduction Agency (HDTRA1-10-1-0072).

  14. Synthesis of periodic mesoporous silica thin films

    SciTech Connect

    Anderson, M.T.; Martin, J.E.; Odinek, J.G.; Newcomer, P.

    1996-06-01

    We have synthesized periodic mesoporous silica thin films from homogeneous solutions. To synthesize the films, a thin layer of a pH 7 micellar coating solution that contains TMOS (tetramethoxysilane) is dip or spin-coated onto Si wafers, borosilicate glass, or quartz substrates. NH3 gas is diffused into the solution and causes rapid hydrolysis and condensation of the TMOS and the formation of periodic mesoporous thin films within 10 seconds. Combination of homogenous solutions and rapid product formation maximizes the concentration of the desired product and provides a controlled, predictable microstructure. The films have been made continuous and crack-free by optimizing initial silica concentration and film thickness. The films are being evaluated as high surface area, size-selective coatings for surface acoustic wave (SAW) sensors.

  15. Flexible thin metal film thermal sensing system

    NASA Technical Reports Server (NTRS)

    Thomsen, Donald L. (Inventor)

    2010-01-01

    A flexible thin metal film thermal sensing system is provided. A self-metallized polymeric film has a polymeric film region and a metal surface disposed thereon. A layer of electrically-conductive metal is deposited directly onto the self-metallized polymeric film's metal surface. Coupled to at least one of the metal surface and the layer of electrically-conductive metal is a device/system for measuring an electrical characteristic associated therewith as an indication of temperature.

  16. Surface roughness evolution of nanocomposite thin films

    SciTech Connect

    Turkin, A. A.; Pei, Y. T.; Shaha, K. P.; Chen, C. Q.; Vainshtein, D. I.; Hosson, J. Th. M. de

    2009-01-01

    An analysis of dynamic roughening and smoothening mechanisms of thin films grown with pulsed-dc magnetron sputtering is presented. The roughness evolution has been described by a linear stochastic equation, which contains the second- and fourth-order gradient terms. Dynamic smoothening of the growing interface is explained by ballistic effects resulting from impingements of ions to the growing thin film. These ballistic effects are sensitive to the flux and energy of impinging ions. The predictions of the model are compared with experimental data, and it is concluded that the thin film roughness can be further controlled by adjusting waveform, frequency, and width of dc pulses.

  17. Macro stress mapping on thin film buckling

    SciTech Connect

    Goudeau, P.; Villain, P.; Renault, P.-O.; Tamura, N.; Celestre, R.S.; Padmore, H.A.

    2002-11-06

    Thin films deposited by Physical Vapour Deposition techniques on substrates generally exhibit large residual stresses which may be responsible of thin film buckling in the case of compressive stresses. Since the 80's, a lot of theoretical work has been done to develop mechanical models but only a few experimental work has been done on this subject to support these theoretical approaches and nothing concerning local stress measurement mainly because of the small dimension of the buckling (few 10th mm). This paper deals with the application of micro beam X-ray diffraction available on synchrotron radiation sources for stress mapping analysis of gold thin film buckling.

  18. Insulating phase at low temperature in ultrathin La0.8Sr0.2MnO3 films

    PubMed Central

    Feng, Yaqing; Jin, Kui-juan; Gu, Lin; He, Xu; Ge, Chen; Zhang, Qing-hua; He, Min; Guo, Qin-lin; Wan, Qian; He, Meng; Lu, Hui-bin; Yang, Guozhen

    2016-01-01

    Metal-insulator transition is observed in the La0.8Sr0.2MnO3 thin films with thickness larger than 5 unit cells. Insulating phase at lower temperature appeared in the ultrathin films with thickness ranging from 6 unit cells to 10 unit cells and it is found that the Mott variable range hopping conduction dominates in this insulating phase at low temperature with a decrease of localization length in thinner films. A deficiency of oxygen content and a resulting decrease of the Mn valence have been observed in the ultrathin films with thickness smaller than or equal to 10 unit cells by studying the aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy of the films. These results suggest that the existence of the oxygen vacancies in thinner films suppresses the double-exchange mechanism and contributes to the enhancement of disorder, leading to a decrease of the Curie temperature and the low temperature insulating phase in the ultrathin films. In addition, the suppression of the magnetic properties in thinner films indicates stronger disorder of magnetic moments, which is considered to be the reason for this decrease of the localization length. PMID:26928070

  19. Photonics applications of nanostructured thin films

    NASA Astrophysics Data System (ADS)

    Kennedy, Scott Ronald

    Using an advanced thin film fabrication technique known as Glancing Angle Deposition (GLAD), it is possible to fabricate unique thin film nanostructures with characteristic dimensions on the order of a wavelength of light. By tailoring the morphologies of the films, they can be designed to exhibit particular optical properties that can be customized through advanced substrate motion and highly oblique flux incidence angles. In applications to photonics, controlling the flow of light for a specified task, GLAD thin films can be fabricated to provide the ability to manipulate incident light through controlled interactions of optical frequency electromagnetic radiation with the thin film nanostructures. Tetragonal square spiral photonic band gap crystals, a new class of periodic dielectric material that is characterized by the elimination of the density of states for frequencies lying in the stop gap of the crystal, can be fabricated using GLAD in a virtual single step process. The design and fabrication of these unique devices has been performed and the resultant crystals characterized in terms of optical response with respect to forbidden propagation modes, material properties, and advanced deposition techniques used to improve the overall structure. Chiral or helical thin films deposited using GLAD were also investigated, and have been shown to exhibit optical activity and circular birefringence due to their inherent structural anisotropy. It has been shown that the addition of nematic liquid crystals (LCs) to chiral thin films enhances the overall device performance due to order induced in the LCs by the film structure. This effect was investigated for a variety of materials and film structures. Finally, by developing a modified GLAD technique whereby the deposited film porosity is controlled through the angle of flux incidence, porous broadband antireflection coatings were produced. Using an appropriate effective medium theory to describe the index of refraction

  20. Thin Thermal-Insulation Blankets for Very High Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Michael K.

    2003-01-01

    Thermal-insulation blankets of a proposed type would be exceptionally thin and would endure temperatures up to 2,100 C. These blankets were originally intended to protect components of the NASA Solar Probe spacecraft against radiant heating at its planned closest approach to the Sun (a distance of 4 solar radii). These blankets could also be used on Earth to provide thermal protection in special applications (especially in vacuum chambers) for which conventional thermal-insulation blankets would be too thick or would not perform adequately. A blanket according to the proposal (see figure) would be made of molybdenum, titanium nitride, and carbon- carbon composite mesh, which melt at temperatures of 2,610, 2,930, and 2,130 C, respectively. The emittance of molybdenum is 0.24, while that of titanium nitride is 0.03. Carbon-carbon composite mesh is a thermal insulator. Typically, the blanket would include 0.25-mil (.0.00635-mm)-thick hot-side and cold-side cover layers of molybdenum. Titanium nitride would be vapor-deposited on both surfaces of each cover layer. Between the cover layers there would be 10 inner layers of 0.15-mil (.0.0038-mm)-thick molybdenum with vapor-deposited titanium nitride on both sides of each layer. The thickness of each titanium nitride coat would be about 1,000 A. The cover and inner layers would be interspersed with 0.25-mil (0.00635-mm)-thick layers of carbon-carbon composite mesh. The blanket would have total thickness of 4.75 mils (approximately equal to 0.121 mm) and an areal mass density of 0.7 kilograms per square meter. One could, of course, increase the thermal- insulation capability of the blanket by increasing number of inner layers (thereby unavoidably increasing the total thickness and mass density).

  1. Passivation Effects in Copper Thin Films

    SciTech Connect

    Wiederhirn, G.; Nucci, J.; Richter, G.; Arzt, E.; Balk, T. J.; Dehm, G.

    2006-02-07

    We studied the influence of a 10 nm AlxOy passivation on the stress-temperature behavior of 100 nm and 1 {mu}m thick Cu films. At low temperatures, the passivation induces a large tensile stress increase in the 100 nm film; however, its effect on the 1 {mu}m film is negligible. At high temperatures, the opposite behavior is observed; while the passivation does not change the 100 nm film behavior, it strengthens the 1 {mu}m film by driving it deeper into compression. These observations are explained in light of a combination of constrained diffusional creep and dislocation dynamics unique to ultra-thin films.

  2. Research on Advanced Thin Film Batteries

    SciTech Connect

    Goldner, Ronald B.

    2003-11-24

    During the past 7 years, the Tufts group has been carrying out research on advanced thin film batteries composed of a thin film LiCo02 cathode (positive electrode), a thin film LiPON (lithium phosphorous oxynitride) solid electrolyte, and a thin film graphitic carbon anode (negative electrode), under grant DE FG02-95ER14578. Prior to 1997, the research had been using an rfsputter deposition process for LiCoOi and LiPON and an electron beam evaporation or a controlled anode arc evaporation method for depositing the carbon layer. The pre-1997 work led to the deposition of a single layer cell that was successfully cycled for more than 400 times [1,2] and the research also led to the deposition of a monolithic double-cell 7 volt battery that was cycled for more than 15 times [3]. Since 1997, the research has been concerned primarily with developing a research-worthy and, possibly, a production-worthy, thin film deposition process, termed IBAD (ion beam assisted deposition) for depositing each ofthe electrodes and the electrolyte of a completely inorganic solid thin film battery. The main focus has been on depositing three materials - graphitic carbon as the negative electrode (anode), lithium cobalt oxide (nominally LiCoCb) as the positive electrode (cathode), and lithium phosphorus oxynitride (LiPON) as the electrolyte. Since 1998, carbon, LiCoOa, and LiPON films have been deposited using the IBAD process with the following results.

  3. Performance Characterization of Monolithic Thin Film Resistors

    NASA Astrophysics Data System (ADS)

    Yin, Rong

    Thin film resistors have a large resistance range and stable performance under high temperature operating condition. Thin film resistors trimmed by laser beam are able to achieve very high precision on resistance value. As a result, thin film resistors have been widely used to improve the performance of integrated circuits such as operational amplifier, analog-to-digital (A/D) and digital -to-analog (D/A) converters, etc. In this dissertation, a new class of thin film resistors, silicon chrome (SiCr) thin film resistors, has been investigated at length. From thin film characterization to aging behavior modelling, we have carried out a series of engineering activities. The characteristics of the SiCr thin film incorporated into three bipolar processes were first determined. After laser trimming, we have measured a couple of physical parameters of the SiCr film in the heat affected zone (HAZ). This is the first time the sheet resistance and the temperature coefficient of resistance (TCR) of thin film in the HAZ have been characterized. Both thermal and d.c. load accelerated aging tests were performed. The test structures were subjected to the aging for 1000 hours. Based on the test data, we not only evaluated the classical thermal aging model for untrimmed thin film resistors, but also established several empirical thermal aging models for trimmed resistors and d.c. load aging models for both trimmed and untrimmed thin film resistors. All the experiments were carried out for both conventional bar resistors and our new Swiss Cheese (SC) resistors. For the first time, the performance of laser trimmed SC resistors, which was experimentally evaluated, shown a clear superiority over that of trimmed bar resistors. Besides these experiments, we have examined different die attach techniques and their effects on thin film resistors. Also, we have developed a number of hardware systems and software tools, such as a temperature controller, d.c. current source, temperature

  4. Permanent laser conditioning of thin film optical materials

    DOEpatents

    Wolfe, C. Robert; Kozlowski, Mark R.; Campbell, John H.; Staggs, Michael; Rainer, Frank

    1995-01-01

    The invention comprises a method for producing optical thin films with a high laser damage threshold and the resulting thin films. The laser damage threshold of the thin films is permanently increased by irradiating the thin films with a fluence below an unconditioned laser damage threshold.

  5. Permanent laser conditioning of thin film optical materials

    DOEpatents

    Wolfe, C.R.; Kozlowski, M.R.; Campbell, J.H.; Staggs, M.; Rainer, F.

    1995-12-05

    The invention comprises a method for producing optical thin films with a high laser damage threshold and the resulting thin films. The laser damage threshold of the thin films is permanently increased by irradiating the thin films with a fluence below an unconditioned laser damage threshold. 9 figs.

  6. Ferromagnetic properties of fcc Gd thin films

    SciTech Connect

    Bertelli, T. P. Passamani, E. C.; Larica, C.; Nascimento, V. P.; Takeuchi, A. Y.

    2015-05-28

    Magnetic properties of sputtered Gd thin films grown on Si (100) substrates kept at two different temperatures were investigated using X-ray diffraction, ac magnetic susceptibility, and dc magnetization measurements. The obtained Gd thin films have a mixture of hcp and fcc structures, but with their fractions depending on the substrate temperature T{sub S} and film thickness x. Gd fcc samples were obtained when T{sub S} = 763 K and x = 10 nm, while the hcp structure was stabilized for lower T{sub S} (300 K) and thicker film (20 nm). The fcc structure is formed on the Ta buffer layer, while the hcp phase grows on the fcc Gd layer as a consequence of the lattice relaxation process. Spin reorientation phenomenon, commonly found in bulk Gd species, was also observed in the hcp Gd thin film. This phenomenon is assumed to cause the magnetization anomalous increase observed below 50 K in stressed Gd films. Magnetic properties of fcc Gd thin films are: Curie temperature above 300 K, saturation magnetization value of about 175 emu/cm{sup 3}, and coercive field of about 100 Oe at 300 K; features that allow us to classify Gd thin films, with fcc structure, as a soft ferromagnetic material.

  7. Molecular Beam Epitaxial (MBE) Growth and Characterization of Thin Films of Semiconductor Tin

    NASA Astrophysics Data System (ADS)

    Folkes, P.; Taylor, P.; Rong, C.; Nichols, B.; Hier, H.; Burke, R.; Neupane, M.

    Recent theoretical predictions that a two-dimensional monolayer of semiconductor tin is a two-dimensional topological insulator and experimental evidence of three-dimensional topological insulator behavior in strained ultrathin films of semiconductor tin grown by MBE on InSb has generated intense research interest. This research is primarily focused on the MBE growth and topological characteristics of ultrathin films of semiconductor tin. In this talk we present results of a study on the MBE growth and the transport, structural and optical characterization of thin films of semiconductor tin on several different substrates.

  8. Thermally tunable ferroelectric thin film photonic crystals.

    SciTech Connect

    Lin, P. T.; Wessels, B. W.; Imre, A.; Ocola, L. E.; Northwestern Univ.

    2008-01-01

    Thermally tunable PhCs are fabricated from ferroelectric thin films. Photonic band structure and temperature dependent diffraction are calculated by FDTD. 50% intensity modulation is demonstrated experimentally. This device has potential in active ultra-compact optical circuits.

  9. Recent developments in thin film solar cells

    NASA Astrophysics Data System (ADS)

    Dhere, Neelkanth G.

    The present status of the development of thin film solar cells is reviewed, with emphasis on important areas for further research. The following aperture-area efficiencies were measured for thin film modules: a-Si:H, 9.8 percent, 933 sq cm; CuIn(Ga)Se2, 11.1 percent, 938 sq cm; and CdTe, 7.3 percent, 838 sq cm. CuIn(Ga)Se2 cells and modules demonstrated excellent efficiencies and stability. The cost advantage of thin film modules and the higher efficiency and improved stability resulting from multijunctions are shown. Engineering solutions are found to minimize light-induced degradation of a-Si:H solar cells. CdTe cells and modules, and cleaved epitaxial thin film III-V compound cells showed remarkable efficiencies.

  10. Thin film production method and apparatus

    DOEpatents

    Loutfy, Raouf O.; Moravsky, Alexander P.; Hassen, Charles N.

    2010-08-10

    A method for forming a thin film material which comprises depositing solid particles from a flowing suspension or aerosol onto a filter and next adhering the solid particles to a second substrate using an adhesive.

  11. Highly stretchable wrinkled gold thin film wires

    NASA Astrophysics Data System (ADS)

    Kim, Joshua; Park, Sun-Jun; Nguyen, Thao; Chu, Michael; Pegan, Jonathan D.; Khine, Michelle

    2016-02-01

    With the growing prominence of wearable electronic technology, there is a need to improve the mechanical reliability of electronics for more demanding applications. Conductive wires represent a vital component present in all electronics. Unlike traditional planar and rigid electronics, these new wearable electrical components must conform to curvilinear surfaces, stretch with the body, and remain unobtrusive and low profile. In this paper, the piezoresistive response of shrink induced wrinkled gold thin films under strain demonstrates robust conductive performance in excess of 200% strain. Importantly, the wrinkled metallic thin films displayed negligible change in resistance of up to 100% strain. The wrinkled metallic wires exhibited consistent performance after repetitive strain. Importantly, these wrinkled thin films are inexpensive to fabricate and are compatible with roll to roll manufacturing processes. We propose that these wrinkled metal thin film wires are an attractive alternative to conventional wires for wearable applications.

  12. Mechanical Properties of Silicon Carbonitride Thin Films

    NASA Astrophysics Data System (ADS)

    Peng, Xiaofeng; Hu, Xingfang; Wang, Wei; Song, Lixin

    2003-02-01

    Silicon carbonitride thin films were synthesized by reactive rf sputtering a silicon carbide target in nitrogen and argon atmosphere, or sputtering a silicon nitride target in methane and argon atmosphere, respectively. The Nanoindentation technique (Nanoindenter XP system with a continuous stiffness measurement technique) was employed to measure the hardness and elastic modulus of thin films. The effects of sputtering power on the mechanical properties are different for the two SiCN thin films. With increasing sputtering power, the hardness and the elastic modulus decrease for the former but increase for the latter. The tendency is similar to the evolution trend of Si-C bonds in SiCN materials. This reflects that Si-C bonds provide greater hardness for SiCN thin films than Si-N and C-N bonds.

  13. Microstructure Related Properties of Optical Thin Films.

    NASA Astrophysics Data System (ADS)

    Wharton, John James, Jr.

    Both the optical and physical properties of thin film optical interference coatings depend upon the microstructure of the deposited films. This microstructure is strongly columnar with voids between the columns. Computer simulations of the film growth process indicate that the two most important factors responsible for this columnar growth are a limited mobility of the condensing molecules and self-shadowing by molecules already deposited. During the vacuum deposition of thin films, the microstructure can be influenced by many parameters, such as substrate temperature and vacuum pressure. By controlling these parameters and introducing additional ones, thin film coatings can be improved. In this research, ultraviolet irradiation and ion bombardment were examined as additional parameters. Past studies have shown that post-deposition ultraviolet irradiation can be used to relieve stress and reduce absorption in the far ultraviolet of silicon dioxide films. Ion bombardment has been used to reduce stress, improve packing density, and increase resistance to moisture penetration. Three refractory oxide materials commonly used in thin film coatings were studied; they are silicon dioxide, titanium dioxide, and zirconium dioxide. Both single-layer films and narrowband filters made of these materials were examined. A 1000-watt mercury-xenon lamp was used to provide ultraviolet irradiation. An inverted magnetron ion source was used to produce argon and oxygen ions. Ultraviolet irradiation was found to reduce the absorption and slightly increase the index of refraction in zirconium oxide films. X-ray diffraction analysis revealed that ultraviolet irradiation caused titanium oxide films to become more amorphous; their absorption in the ultraviolet was slightly reduced. No changes were noted in film durability. Ion bombardment enhanced the tetragonal (lll) peak of zirconium oxide but increased the absorption of both zirconium oxide and titanium oxide films. The titanium oxide

  14. Nonreciprocal switching of VO2 thin films on microstructured surfaces

    NASA Astrophysics Data System (ADS)

    Adams, Charles; Karakurt, Ismail; Leiderer, Paul; Boneberg, Johannes; Haglund, Richard

    2010-10-01

    Vanadium dioxide is a strongly correlated electron material that undergoes an insulator-to-metal transition at approximately 340 K, with a corresponding large change in its optical and electronic properties. By depositing a VO2 thin film on a planar hexagonal close-packed array of 1.54 μm diameter silica microspheres, we constructed a laser-triggered thin film optical switch that exhibits different fluence thresholds for the insulator-metal transition (IMT) depending on the direction of illumination. The IMT was triggered by a ns Nd:YAG laser (532 nm) from two directions normal to the substrate while monitoring the transmission with a near-IR diode laser. Due to the focusing effects of the microspheres, the fluence required for switching the VO2 was 2.4 times higher when the switching laser was incident from the film (top) side of the array than from the microsphere (bottom) side. Through both the experiments and simulations, we find evidence for strong nonlinear near-field absorption in the VO2.

  15. Redox processes in silicon dioxide thin films using copper microelectrodes

    NASA Astrophysics Data System (ADS)

    Tappertzhofen, S.; Menzel, S.; Valov, I.; Waser, R.

    2011-11-01

    Although SiO2 is a typical insulator, we demonstrate an electrochemical characteristic of the Cu/Cu+ oxidation at the interface with 30 nm thick silicon dioxide thin films studied by cyclic voltammetry. This study reveals the process of anodic oxidation and subsequent reduction of oxidized Cu ions injected in the SiO2 layer with special attention to the kinetics of the redox process. We estimated the diffusion coefficient and the mobility of Cu ions in SiO2. The results gain deeper insight in the processes involved during resistive switching of Cu/SiO2 based nonvolatile memory devices.

  16. Thin-film reliability and engineering overview

    NASA Technical Reports Server (NTRS)

    Ross, R. G., Jr.

    1984-01-01

    The reliability and engineering technology base required for thin film solar energy conversions modules is discussed. The emphasis is on the integration of amorphous silicon cells into power modules. The effort is being coordinated with SERI's thin film cell research activities as part of DOE's Amorphous Silicon Program. Program concentration is on temperature humidity reliability research, glass breaking strength research, point defect system analysis, hot spot heating assessment, and electrical measurements technology.

  17. Epitaxial thin film growth in outer space

    NASA Technical Reports Server (NTRS)

    Ignatiev, Alex; Chu, C. W.

    1988-01-01

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

  18. Review of CdO thin films

    NASA Astrophysics Data System (ADS)

    Chandiramouli, R.; Jeyaprakash, B. G.

    2013-02-01

    Cadmium Oxide (CdO) thin film is one of the first transparent conducting oxide semiconductors. Its excellent optical and electronic properties have made CdO a promising material for flat panel displays. In this article, we provide a comprehensive review of the state-of-the-art research activities related to the 'preparation-property-application' triangle of CdO thin films.

  19. Advances in CZTS thin films and nanostructured

    NASA Astrophysics Data System (ADS)

    Ali, N.; Ahmed, R.; Bakhtiar-Ul-Haq; Shaari, A.

    2015-06-01

    Already published data for the optical band gap (Eg) of thin films and nanostructured copper zinc tin sulphide (CZTS) have been reviewed and combined. The vacuum (physical) and non-vacuum (chemical) processes are focused in the study for band gap comparison. The results are accumulated for thin films and nanostructured in different tables. It is inferred from the re- view that the nanostructured material has plenty of worth by engineering the band gap for capturing the maximum photons from solar spectrum.

  20. Thin wetting film lensless imaging

    NASA Astrophysics Data System (ADS)

    Allier, C. P.; Poher, V.; Coutard, J. G.; Hiernard, G.; Dinten, J. M.

    2011-03-01

    Lensless imaging has recently attracted a lot of attention as a compact, easy-to-use method to image or detect biological objects like cells, but failed at detecting micron size objects like bacteria that often do not scatter enough light. In order to detect single bacterium, we have developed a method based on a thin wetting film that produces a micro-lens effect. Compared with previously reported results, a large improvement in signal to noise ratio is obtained due to the presence of a micro-lens on top of each bacterium. In these conditions, standard CMOS sensors are able to detect single bacterium, e.g. E.coli, Bacillus subtilis and Bacillus thuringiensis, with a large signal to noise ratio. This paper presents our sensor optimization to enhance the SNR; improve the detection of sub-micron objects; and increase the imaging FOV, from 4.3 mm2 to 12 mm2 to 24 mm2, which allows the detection of bacteria contained in 0.5μl to 4μl to 10μl, respectively.

  1. Microstructural evolution of tungsten oxide thin films

    NASA Astrophysics Data System (ADS)

    Hembram, K. P. S. S.; Thomas, Rajesh; Rao, G. Mohan

    2009-10-01

    Tungsten oxide thin films are of great interest due to their promising applications in various optoelectronic thin film devices. We have investigated the microstructural evolution of tungsten oxide thin films grown by DC magnetron sputtering on silicon substrate. The structural characterization and surface morphology were carried out using X-ray diffraction and Scanning Electron Microscopy (SEM). The as deposited films were amorphous, where as, the films annealed above 400 °C were crystalline. In order to explain the microstructural changes due to annealing, we have proposed a "instability wheel" model for the evolution of the microstructure. This model explains the transformation of mater into various geometries within them selves, followed by external perturbation.

  2. Visualization of local phase transition behaviors in ultrathin VO2/TiO2 thin films

    NASA Astrophysics Data System (ADS)

    Sohn, Ahrum; Kanki, Terou; Tanaka, Hidekazu; Kim, Dong-Wook

    VO2 undergoes the first order phase transition and two electronic phases can coexist near the critical temperature. We investigated evolution of the surface work function maps of epitaxial VO2/TiO2 thin films (thickness: 15, 30, and 45 nm) using Kelvin probe force microscopy (KPFM) measurements in the temperature range of 285-330 K. Fully strained thin films were almost free of grain boundaries and thicker films had dislocations caused by strain relaxation. The sample's work function decreases, while spanning the metal-insulator transition (MIT). The work function maps clearly revealed coexistence of the two distinct phase domains. The surface area fraction of the insulating phase near the dislocations was higher than that in other regions. Thicker films have complicated domain patterns; hence, the three-dimensional percolation model properly described the MIT behaviors. In contrast, the two-dimensional percolation model well explained the transition behaviors of uniformly strained thinner films.

  3. Design and evaluation of thin metal surface insulation for hypersonic flight

    NASA Technical Reports Server (NTRS)

    Miller, R. C.; Petach, A. M.

    1976-01-01

    An all-metal insulation was studied as a thermal protection system for hypersonic vehicles. Key program goals included fabricating the insulation in thin packages which are optimized for high temperature insulation of an actively cooled aluminum structure, and the use of state-of-the-art alloys. The insulation was fabricated from 300 series stainless steel in thicknesses of 0.8 to 12 mm. The outer, 0.127 mm thick, skin was textured to accommodate thermal expansion and oxidized to increase emittance. The thin insulating package was achieved using an insulation concept consisting of foil radiation shields spaced within the package, and conical foil supports to carry loads from the skin and maintain package dimensions. Samples of the metal-insulation were tested to evaluate thermal insulation capability, rain and sand erosion resistance, high temperature oxidation resistance, applied load capability, and high temperature emittance.

  4. Printable CIGS thin film solar cells

    NASA Astrophysics Data System (ADS)

    Fan, Xiaojuan

    2014-03-01

    Among the various thin film solar cells in the market, CuInGaSe thin film cells have been considered as the most promising alternatives to silicon solar cells because of their high photo-electricity efficiency, reliability, and stability. However, many fabrication of CIGS thin film are based on vacuum processes such as evaporation sputtering techniques which are not cost efficient. This work develops a method using paste or ink liquid spin-coated on glass that would be to conventional ways in terms of cost effective, non-vacuum needed, quick processing. A mixture precursor was prepared by dissolving appropriate amounts of chemicals. After the mixture solution was cooled, a viscous paste prepared and ready for spin-coating process. A slight bluish CIG thin film substrate was then put in a tube furnace with evaporation of metal Se by depositing CdS layer and ZnO nanoparticle thin film coating to a solar cell fabrication. Structure, absorption spectrum, and photo-conversion efficiency for the as-grown CIGS thin film solar cell under study.

  5. Printable CIGS thin film solar cells

    NASA Astrophysics Data System (ADS)

    Fan, Xiaojuan

    2013-03-01

    Among the various thin film solar cells in the market, CuInGaSe thin film solar cells have been considered as the most promising alternatives to crystalline silicon solar cells because of their high photo-electricity conversion efficiency, reliability, and stability. However, many fabrication methods of CIGS thin film are based on vacuum processes such as evaporation and sputtering techniques which are not cost efficient. This work develops a solution method using paste or ink liquid spin-coated on glass that would be competitive to conventional ways in terms of cost effective, non-vacuum needed, and quick processing. A mixture precursor was prepared by dissolving appropriate amounts of composition chemicals. After the mixture solution was cooled, a viscous paste was prepared and ready for spin-coating process. A slight bluish CIG thin film on substrate was then put in a tube furnace with evaporation of metal Se followed by depositing CdS layer and ZnO nanoparticle thin film coating to complete a solar cell fabrication. Structure, absorption spectrum, and photo-electricity conversion efficiency for the as-grown CIGS thin film solar cell are under study.

  6. Carbon Nanotube Thin-Film Antennas.

    PubMed

    Puchades, Ivan; Rossi, Jamie E; Cress, Cory D; Naglich, Eric; Landi, Brian J

    2016-08-17

    Multiwalled carbon nanotube (MWCNT) and single-walled carbon nanotube (SWCNT) dipole antennas have been successfully designed, fabricated, and tested. Antennas of varying lengths were fabricated using flexible bulk MWCNT sheet material and evaluated to confirm the validity of a full-wave antenna design equation. The ∼20× improvement in electrical conductivity provided by chemically doped SWCNT thin films over MWCNT sheets presents an opportunity for the fabrication of thin-film antennas, leading to potentially simplified system integration and optical transparency. The resonance characteristics of a fabricated chlorosulfonic acid-doped SWCNT thin-film antenna demonstrate the feasibility of the technology and indicate that when the sheet resistance of the thin film is >40 ohm/sq no power is absorbed by the antenna and that a sheet resistance of <10 ohm/sq is needed to achieve a 10 dB return loss in the unbalanced antenna. The dependence of the return loss performance on the SWCNT sheet resistance is consistent with unbalanced metal, metal oxide, and other CNT-based thin-film antennas, and it provides a framework for which other thin-film antennas can be designed. PMID:27454334

  7. Laser processing for thin-film photovoltaics

    NASA Astrophysics Data System (ADS)

    Compaan, Alvin D.

    1995-04-01

    Over the past decade major advances have occurred in the field of thin- film photovoltaics (PV) with many of them a direct consequence of the application of laser processing. Improved cell efficiencies have been achieved in crystalline and polycrystalline Si, in hydrogenated amorphous silicon, and in two polycrystalline thin-film materials. The use of lasers in photovoltaics includes laser hole drilling for emitter wrap-through, laser trenching for buried bus lines, and laser texturing of crystalline and polycrystalline Si cells. In thin-film devices, laser scribing is gaining increased importance for module interconnects. Pulsed laser recrystallization of boron-doped hydrogenated amorphous silicon is used to form highly conductive p-layers in p-i-n amorphous silicon cells and in thin-film transistors. Optical beam melting appears to be an attractive method for forming metal semiconductor alloys for contact formation. Finally, pulsed lasers are used for deposition of the entire semiconductor absorber layer in two types of polycrystalline thin-film cells-those based on copper indium diselenide and those based on cadmium telluride. In our lab we have prepared and studied heavily doped polycrystalline silicon thin films and also have used laser physical vapor deposition (LPVD) to prepare 'all-LPVD' CdS/CdTe solar cells on glass with efficiencies tested at NREL at 10.5%. LPVD is highly flexible and ideally suited for prototyping PV cells using ternary or quaternary alloys and for exploring new dopant combinations.

  8. Organic ferroelectric gate field-effect transistor memory using high-mobility rubrene thin film

    NASA Astrophysics Data System (ADS)

    Kanashima, Takeshi; Katsura, Yuu; Okuyama, Masanori

    2014-01-01

    An organic ferroelectric gate field-effect transistor (FET) memory has been fabricated using an organic semiconductor of rubrene thin film with a high mobility and a gate insulating layer of poly(vinylidene fluoride-tetrafluoroethylene) [P(VDF-TeFE)] thin film. A rubrene thin-film sheet was grown by physical vapor transport (PVT), and placed onto a spin-coated P(VDF-TeFE) thin-film layer, and Au source and drain electrodes were formed on this rubrene thin film. A hysteresis loop of the drain current-gate voltage (ID-VG) characteristic has been clearly observed in the ferroelectric gate FET, and is caused by the ferroelectricity. The maximum drain current is 1.5 × 10-6 A, which is about two orders of magnitude larger than that of the P(VDF-TeFE) gate FET using a pentacene thin film. Moreover, the mobility of this organic ferroelectric gate FET using rubrene thin film is 0.71 cm2 V-1 s-1, which is 35 times larger than that of the FET with pentacene thin film.

  9. Thin-Film Nanocapacitor and Its Characterization

    ERIC Educational Resources Information Center

    Hunter, David N.; Pickering, Shawn L.; Jia, Dongdong

    2007-01-01

    An undergraduate thin-film nanotechnology laboratory was designed. Nanocapacitors were fabricated on silicon substrates by sputter deposition. A mask was designed to form the shape of the capacitor and its electrodes. Thin metal layers of Au with a 80 nm thickness were deposited and used as two infinitely large parallel plates for a capacitor.…

  10. An Extension of Thin Film Optics

    NASA Astrophysics Data System (ADS)

    Apell, P.

    1985-10-01

    The classical McIntyre formula for p-polarized light incident on a thin film on a substrate is extended in general terms to include a realistic description of the interfaces and the possible excitation of plasma waves in the film. An earlier extension is critized and criteria are given for when the classical result is applicable.

  11. Thin films, asphaltenes, and reservoir wettability

    SciTech Connect

    Kaminsky, R.; Bergeron, V.; Radke, C.J. |

    1993-04-01

    Reservoir wettability impacts the success of oil recovery by waterflooding and other methods. To understand wettability and its alteration, thin-film forces in solid-aqueous-oil systems must be elucidated. Upon rupture of thick aqueous films separating the oil and rock phases, asphaltene components in the crude oil adsorb irreversibly on the solid surface, changing it from water-wet to oil-wet. Conditions of wettability alteration can be found by performing adhesion tests, in which an oil droplet is brought into contact with a solid surface. Exceeding a critical capillary pressure destabilizes the film, causing spontaneous film rupture to a molecularly adsorbed layer and oil adhesion accompanied by pinning at the three-phase contact line. The authors conduct adhesion experiments similar to those of Buckley and Morrow and simultaneously examine the state of the underlying thin film using optical microscopy and microinterferometry. Aqueous thin films between an asphaltic Orcutt crude oil and glass surfaces are studied as a function of aqueous pH and salinity. For the first time, they prove experimentally that strongly water-wet to strongly oil-wet wettability alteration and contact-angle pinning occur when thick aqueous films thin to molecularly adsorbed films and when the oil phase contains asphaltene molecules.

  12. Liquid phase deposition of electrochromic thin films

    SciTech Connect

    Richardson, Thomas J.; Rubin, Michael D.

    2000-08-18

    Thin films of titanium, zirconium and nickel oxides were deposited on conductive SnO2:F glass substrates by immersion in aqueous solutions. The films are transparent, conformal, of uniform thickness and appearance, and adhere strongly to the substrates. On electrochemical cycling, TiO2, mixed TiO2-ZrO2, and NiOx films exhibited stable electrochromism with high coloration efficiencies. These nickel oxide films were particularly stable compared with films prepared by other non-vacuum techniques. The method is simple, inexpensive, energy efficient, and readily scalable to larger substrates.

  13. Adhesion and friction of thin metal films

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1976-01-01

    Sliding friction experiments were conducted in vacuum with thin films of titanium, chromium, iron, and platinum sputter deposited on quartz or mica substrates. A single crystal hemispherically tipped gold slider was used in contact with the films at loads of 1.0 to 30.0 and at a sliding velocity of 0.7 mm/min at 23 C. Test results indicate that the friction coefficient is dependent on the adhesion of two interfaces, that between the film and its substrate and the slider and the film. There exists a relationship between the percent d bond character of metals in bulk and in thin film form and the friction coefficient. Oxygen can increase adhesive bonding of a metal film (platinum) to a substrate.

  14. Induced electronic anisotropy in bismuth thin films

    SciTech Connect

    Liao, Albert D.; Yao, Mengliang; Opeil, Cyril; Katmis, Ferhat; Moodera, Jagadeesh S.; Li, Mingda; Tang, Shuang; Dresselhaus, Mildred S.

    2014-08-11

    We use magneto-resistance measurements to investigate the effect of texturing in polycrystalline bismuth thin films. Electrical current in bismuth films with texturing such that all grains are oriented with the trigonal axis normal to the film plane is found to flow in an isotropic manner. By contrast, bismuth films with no texture such that not all grains have the same crystallographic orientation exhibit anisotropic current flow, giving rise to preferential current flow pathways in each grain depending on its orientation. Extraction of the mobility and the phase coherence length in both types of films indicates that carrier scattering is not responsible for the observed anisotropic conduction. Evidence from control experiments on antimony thin films suggests that the anisotropy is a result of bismuth's large electron effective mass anisotropy.

  15. Weak Delocalization in Graphene on a Ferromagnetic Insulating Film.

    PubMed

    Pietrobon, Luca; Fallarino, Lorenzo; Berger, Andreas; Chuvilin, Andrey; Casanova, Fèlix; Hueso, Luis E

    2015-12-16

    Graphene has been predicted to develop a magnetic moment by proximity effect when placed on a ferromagnetic film, a promise that could open exciting possibilities in the fields of spintronics and magnetic data recording. In this work, the interplay between the magnetoresistance of graphene and the magnetization of an underlying ferromagnetic insulating film is studied in detail. A clear correlation between both magnitudes is observed but through a careful modeling of the magnetization and the weak localization measurements, that such correspondence can be explained by the effects of the magnetic stray fields arising from the ferromagnetic insulator is found. The results emphasize the complexity arising at the interface between magnetic and 2D materials. PMID:26505882

  16. Microcrystalline organic thin-film solar cells.

    PubMed

    Verreet, Bregt; Heremans, Paul; Stesmans, Andre; Rand, Barry P

    2013-10-11

    Microcrystalline organic films with tunable thickness are produced directly on an indium-tin-oxide substrate, by crystallizing a thin amorphous rubrene film followed by its use as a template for subsequent homoepitaxial growth. These films, with exciton diffusion lengths exceeding 200 nm, produce solar cells with increasing photocurrents at thicknesses up to 400 nm with a fill factor >65%, demonstrating significant potential for microcrystalline organic electronic devices. PMID:23939936

  17. Process for making thin film solar cell

    SciTech Connect

    Eberspacher, C.; Ermer, J.H.; Mitchell, K.W.

    1991-09-03

    This paper describes a semiconducting thin film forced on a substrate by the method. It comprises: depositing a composite film of copper and indium on a substrate, the film having an atomic copper to indium ratio of about one, depositing a film of selenium on the composite copper indium film, the selenium film thickness selected to provide an atomic ratio of selenium to copper and indium of less than one, and heating the substrate with the composite copper indium film and the selenium film in the presence of H{sub 2}S gas for a time and at a temperature sufficient to cause interdiffusion of copper, indium, selenium and sulfur to form a semiconductor of the class CuInSe{sub 2{minus}x}S{sub x} where x is less than two.

  18. Thin-film Rechargeable Lithium Batteries

    DOE R&D Accomplishments Database

    Dudney, N. J.; Bates, J. B.; Lubben, D.

    1995-06-01

    Thin film rechargeable lithium batteries using ceramic electrolyte and cathode materials have been fabricated by physical deposition techniques. The lithium phosphorous oxynitride electrolyte has exceptional electrochemical stability and a good lithium conductivity. The lithium insertion reaction of several different intercalation materials, amorphous V{sub 2}O{sub 5}, amorphous LiMn{sub 2}O{sub 4}, and crystalline LiMn{sub 2}O{sub 4} films, have been investigated using the completed cathode/electrolyte/lithium thin film battery.

  19. Thin-film rechargeable lithium batteries

    SciTech Connect

    Dudney, N.J.; Bates, J.B.; Lubben, D.

    1995-06-01

    Thin-film rechargeable lithium batteries using ceramic electrolyte and cathode materials have been fabricated by physical deposition techniques. The lithium phosphorous oxynitride electrolyte has exceptional electrochemical stability and a good lithium conductivity. The lithium insertion reaction of several different intercalation materials, amorphous V{sub 2}O{sub 5}, amorphous LiMn{sub 2}O{sub 4}, and crystalline LiMn{sub 2}O{sub 4} films, have been investigated using the completed cathode/electrolyte/lithium thin-film battery.

  20. Thin Ice Films at Mineral Surfaces.

    PubMed

    Yeşilbaş, Merve; Boily, Jean-François

    2016-07-21

    Ice films formed at mineral surfaces are of widespread occurrence in nature and are involved in numerous atmospheric and terrestrial processes. In this study, we studied thin ice films at surfaces of 19 synthetic and natural mineral samples of varied structure and composition. These thin films were formed by sublimation of thicker hexagonal ice overlayers mostly produced by freezing wet pastes of mineral particles at -10 and -50 °C. Vibration spectroscopy revealed that thin ice films contained smaller populations of strongly hydrogen-bonded water molecules than in hexagonal ice and liquid water. Thin ice films at the surfaces of the majority of minerals considered in this work [i.e., metal (oxy)(hydr)oxides, phyllosilicates, silicates, volcanic ash, Arizona Test Dust] produced intense O-H stretching bands at ∼3400 cm(-1), attenuated bands at ∼3200 cm(-1), and liquid-water-like bending band at ∼1640 cm(-1) irrespective of structure and composition. Illite, a nonexpandable phyllosilicate, is the only mineral that stabilized a form of ice that was strongly resilient to sublimation in temperatures as low as -50 °C. As mineral-bound thin ice films are the substrates upon which ice grows from water vapor or aqueous solutions, this study provides new constraints from which their natural occurrences can be understood. PMID:27377606

  1. Thin film absorber for a solar collector

    DOEpatents

    Wilhelm, William G.

    1985-01-01

    This invention pertains to energy absorbers for solar collectors, and more particularly to high performance thin film absorbers. The solar collectors comprising the absorber of this invention overcome several problems seen in current systems, such as excessive hardware, high cost and unreliability. In the preferred form, the apparatus features a substantially rigid planar frame with a thin film window bonded to one planar side of the frame. An absorber in accordance with the present invention is comprised of two thin film layers that are sealed perimetrically. In a preferred embodiment, thin film layers are formed from a metal/plastic laminate. The layers define a fluid-tight planar envelope of large surface area to volume through which a heat transfer fluid flows. The absorber is bonded to the other planar side of the frame. The thin film construction of the absorber assures substantially full envelope wetting and thus good efficiency. The window and absorber films stress the frame adding to the overall strength of the collector.

  2. Carrier lifetimes in thin-film photovoltaics

    NASA Astrophysics Data System (ADS)

    Baek, Dohyun

    2015-09-01

    The carrier lifetimes in thin-film solar cells are reviewed and discussed. Shockley-Read-Hall recombination is dominant at low carrier density, Auger recombination is dominant under a high injection condition and high carrier density, and surface recombination is dominant under any conditions. Because the surface photovoltage technique is insensitive to the surface condition, it is useful for bulk lifetime measurements. The photoconductance decay technique measures the effective recombination lifetime. The time-resolved photoluminescence technique is very useful for measuring thin-film semiconductor or solar-cell materials lifetime, because the sample is thin, other techniques are not suitable for measuring the lifetime. Many papers have provided time-resolved photoluminescence (TRPL) lifetimes for copper-indium-gallium-selenide (CIGS) and CdTe thin-film solar cell. The TRPL lifetime strongly depends on open-circuit voltage and conversion efficiency; however, the TRPL life time is insensitive to the short-circuit current.

  3. Use of thin film light detector

    NASA Technical Reports Server (NTRS)

    Lewicki, G. W.; Maserjian, J.

    1973-01-01

    A photovoltaic cell device with a trapezoidal barrier is described. An aluminum, magnesium, or tantalum base is vapor deposited on a quartz substrate. An oxide or nitride film of the base metal is produced as an insulator by reaction in a glow discharge plasma to a thickness of less than 100 Angstroms. A metal, preferably gold, conter-electrode is vapor deposited on the insulating layer. A bias generator of high impedance is used to set and shift or modulate the spectral response of the device.

  4. Collaboration of the NASA Glenn Research Center and Rolls-Royce Developed Thin Film Multilayered Dielectrics for Harsh Environments

    NASA Technical Reports Server (NTRS)

    Wrbanek, John D.; Fralick, Gustave C.; Busfield, A. Rachel; Thomas, Valarie D.; Blaha, Charles A.

    2003-01-01

    The use of thin films to electrically insulate thin film sensors on engine components minimizes the intrusiveness of the sensors and allows a more accurate measurement of the environment. A variety of insulating films were investigated for preventing electrical shorting caused by insulator failure between the sensor and the component. By alternating layers of sputtered high-temperature ceramics, a sequence of insulating layers was devised that (1) prevents pinholes from forming completely through the insulator and (2) maintains high electrical resistivity at high temperatures. The total thickness is only a fraction of that needed for conventional insulating techniques. The Sensors and Electronics Technology Branch of the NASA Glenn Research Center has an in-house effort to develop thin film sensors for surface measurement in propulsion system research. Thin film sensors do not require special machining of the components on which they are mounted, and they are considerably thinner (less than 10 mm thick) than wire or foil sensors. The thin film sensors are thus much less disturbing to the operating environment and have a minimal impact on the physical characteristics of the supporting component. To further this research, NASA Glenn and Rolls-Royce (Derby, UK), with assistance from the Ohio Aerospace Institute (OAI) and the Akima Corporation, pursued a joint investigation using multilayered thin film dielectrics as a reliable insulator in harsh environments. The use of a multilayered scheme is thought to be promising for the fabrication of electrically insulating thin films. A major cause of conduction in thin film dielectrics is the presence of defects, such as pinholes, that propagate through the film to the underlying substrate surface. By alternating the insulating material, each new growth pattern would deviate from the previous one, eliminating direct pathways for conduction to the substrate. The film depositions and testing were conducted in the Instrument

  5. 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.

  6. Interfacial Coupling-Induced Ferromagnetic Insulator Phase in Manganite Film.

    PubMed

    Zhang, Bangmin; Wu, Lijun; Yin, Wei-Guo; Sun, Cheng-Jun; Yang, Ping; Venkatesan, T; Chen, Jingsheng; Zhu, Yimei; Chow, Gan Moog

    2016-07-13

    Interfaces with subtle differences in atomic and electronic structures in perovskite ABO3 heterostructures often yield intriguingly different properties, yet their exact roles remain elusive. Here, we report an integrated study of unusual transport, magnetic, and structural properties of Pr0.67Sr0.33MnO3 film on SrTiO3 substrate. The variations in the out-of-plane lattice constant and BO6 octahedral rotation across the Pr0.67Sr0.33MnO3/SrTiO3 interface strongly depend on the thickness of the Pr0.67Sr0.33MnO3 film. In the 12 nm film, a new interface-sensitive ferromagnetic polaronic insulator (FI') phase is formed during the cubic-to-tetragonal phase transition of SrTiO3, apparently due to the enhanced electron-phonon interaction and atomic disorder in the film. The transport properties of the FI' phase in the 30 nm film are masked because of the reduced interfacial coupling and smaller interface-to-volume ratio. This work demonstrates how thickness-dependent interfacial coupling leads to the formation of a theoretically predicted ferromagnetic-polaronic insulator, as illustrated in a new phase diagram, that is otherwise ferromagnetic metal (FM) in bulk form. PMID:27276032

  7. Adhesive transfer of thin viscoelastic films.

    PubMed

    Shull, Kenneth R; Martin, Elizabeth F; Drzal, Peter L; Hersam, Mark C; Markowitz, Alison R; McSwain, Rachel L

    2005-01-01

    Micellar suspensions of acrylic diblock copolymers are excellent model materials for studying the adhesive transfer of viscoelastic solids. The micellar structure is maintained in films with a variety of thicknesses, giving films with a well-defined structure and viscoelastic character. Thin films were cast onto elastomeric silicone substrates from micellar suspensions in butanol, and the adhesive interactions between these coated elastomeric substrates and a rigid indenter were quantified. By controlling the adhesive properties of the film/indenter and film/substrate interfaces we were able to obtain very clean transfer of the film from the substrate to the portion of the glass indenter with which the film was in contact. Adhesive failure at the film/substrate interface occurs when the film/indenter interface is able to support an applied energy release rate that is sufficient to result in cavity nucleation at the film/substrate interface. Cavity formation is rapidly followed by delamination of the entire region under the indenter. The final stage in the transfer process involves the failure of the film that bridges the indenter and the elastomeric substrate. This film is remarkably robust and is extended to three times its original width prior to failure. Failure of this film occurs at the periphery of the indenter, giving a transferred film that conforms to the original contact area between the indenter and the coated substrate. PMID:15620300

  8. Method for making thin polypropylene film

    DOEpatents

    Behymer, R.D.; Scholten, J.A.

    1985-11-21

    An economical method is provided for making uniform thickness polypropylene film as thin as 100 Angstroms. A solution of polypropylene dissolved in xylene is formed by mixing granular polypropylene and xylene together in a flask at an elevated temperature. A substrate, such as a glass plate or microscope slide is immersed in the solution. When the glass plate is withdrawn from the solution at a uniform rate, a thin polypropylene film forms on a flat surface area of the glass plate as the result of xylene evaporation. The actual thickness of the polypropylene film is functional of the polypropylene in xylene solution concentration, and the particular withdrawal rate of the glass plate from the solution. After formation, the thin polypropylene film is floated from the glass plate onto the surface of water, from which it is picked up with a wire hoop.

  9. Simulated Thin-Film Growth and Imaging

    NASA Astrophysics Data System (ADS)

    Schillaci, Michael

    2001-06-01

    Thin-films have become the cornerstone of the electronics, telecommunications, and broadband markets. A list of potential products includes: computer boards and chips, satellites, cell phones, fuel cells, superconductors, flat panel displays, optical waveguides, building and automotive windows, food and beverage plastic containers, metal foils, pipe plating, vision ware, manufacturing equipment and turbine engines. For all of these reasons a basic understanding of the physical processes involved in both growing and imaging thin-films can provide a wonderful research project for advanced undergraduate and first-year graduate students. After producing rudimentary two- and three-dimensional thin-film models incorporating ballsitic deposition and nearest neighbor Coulomb-type interactions, the QM tunneling equations are used to produce simulated scanning tunneling microscope (SSTM) images of the films. A discussion of computational platforms, languages, and software packages that may be used to accomplish similar results is also given.

  10. Tungsten-doped thin film materials

    DOEpatents

    Xiang, Xiao-Dong; Chang, Hauyee; Gao, Chen; Takeuchi, Ichiro; Schultz, Peter G.

    2003-12-09

    A dielectric thin film material for high frequency use, including use as a capacitor, and having a low dielectric loss factor is provided, the film comprising a composition of tungsten-doped barium strontium titanate of the general formula (Ba.sub.x Sr.sub.1-x)TiO.sub.3, where X is between about 0.5 and about 1.0. Also provided is a method for making a dielectric thin film of the general formula (Ba.sub.x Sr.sub.1-x)TiO.sub.3 and doped with W, where X is between about 0.5 and about 1.0, a substrate is provided, TiO.sub.2, the W dopant, Ba, and optionally Sr are deposited on the substrate, and the substrate containing TiO.sub.2, the W dopant, Ba, and optionally Sr is heated to form a low loss dielectric thin film.

  11. Ambient pressure process for preparing aerogel thin films reliquified sols useful in preparing aerogel thin films

    DOEpatents

    Brinker, Charles Jeffrey; Prakash, Sai Sivasankaran

    1999-01-01

    A method for preparing aerogel thin films by an ambient-pressure, continuous process. The method of this invention obviates the use of an autoclave and is amenable to the formation of thin films by operations such as dip coating. The method is less energy intensive and less dangerous than conventional supercritical aerogel processing techniques.

  12. Fabrication of Poly (methyl methacrylate) and Poly(vinyl alcohol) Thin Film Capacitors on Flexible Substrates

    NASA Astrophysics Data System (ADS)

    Salim, Bindu; Meenaa Pria KNJ, Jaisree; Alagappan, M.; Kandaswamy, A.

    2015-11-01

    Flexible electronics is becoming more popular with introduction of more and more organic conducting materials and processes for making thin films. The use of polymers as gate dielectric has over ruled the usage of conventional inorganic oxides in Organic Thin Film Transistors (OTFTs) on account of its solution process ability and ease of making highly insulating thin film. In this work Capacitance is fabricated with polymeric dielectrics namely poly (methyl methacrylate) - PMMA and poly (vinyl alcohol) - PVA. The electrodes used for these capacitors are Indium Tin Oxide (ITO) and Aluminium. Capacitance value of 9.5nF/cm2 and 33.12nF/cm2 is achieved for thickness of 510 nm of PMMA and 80 nm of PVA respectively. This study on capacitance can be used for assessing the suitability of these polymers as gate insulators in OTFTs.

  13. Thin film heat flux sensor for Space Shuttle Main Engine turbine environment

    NASA Technical Reports Server (NTRS)

    Will, Herbert

    1991-01-01

    The Space Shuttle Main Engine (SSME) turbine environment stresses engine components to their design limits and beyond. The extremely high temperatures and rapid temperature cycling can easily cause parts to fail if they are not properly designed. Thin film heat flux sensors can provide heat loading information with almost no disturbance of gas flows or of the blade. These sensors can provide steady state and transient heat flux information. A thin film heat flux sensor is described which makes it easier to measure small temperature differences across very thin insulating layers.

  14. Nanostructured thin films for icephobic applications

    NASA Astrophysics Data System (ADS)

    Noormohammed, Saleema

    Icing on surfaces such as cables or high voltage insulators often leads to severe safety issues such as power outages in cold winter conditions. Conventional methods used to avoid such icing problems include mechanical deicing where the ice is scraped or broken and chemical deicing where deicers such as ethylene glycol are used. These methods have their own disadvantages of being destructive, expensive and time consuming. A better approach would be to prevent ice from forming in the first place by producing coating materials that are icephobic. Superhydrophobic surfaces, which demonstrate high water-repellency due to the negligible contact area of water with those surfaces, are also expected to minimize the contact area of ice. A low dielectric constant surface is also expected to reduce the adhesion of ice due to the screening of mirror charges, thereby eliminating one of the strongest interaction forces---the electrostatic forces of attraction at the ice-surface interface. In the present research work, both concepts were studied by producing superhydrophobic nanorough low-epsilon dielectric surfaces on aluminum or alumina substrates. Superhydrophobic properties were achieved on surfaces of aluminum or alumina by creating a certain nanoroughness using chemical methods followed by a low surface energy coating of rf-sputtered Teflon or fluoroalkyl-silane (FAS-17) providing a water contact angle greater than 160°. The same behavior is reported even when the nanorough substrates were coated with dielectric thin films of ZnO (lower epsilon) or TiO 2, (higher epsilon). It is found that the superhydrophobic nanorough low surface energy surfaces are also icephobic and the presence of a low dielectric constant surface coating of Teflon (lowest epsilon; epsilon = 2) allows a considerable reduction of the ice adhesion strength even on non-nanotextured surfaces where ice would stick. The superhydrophobic nanorough low-epsilon surfaces also demonstrate morphological and

  15. Monolayer-Mediated Patterning of Electroceramic Thin Films

    SciTech Connect

    Clem, P.G.; Payne, D.A.

    1998-10-11

    Integrated electroceramic thin film devices on semiconductor and insulator substrates feature a variety of attractive attributes, including high capacitance density, nonvolatile memory, sensor/actuator ability, and other unique electronic and optical properties. The ability to pattern such ceramic materials atop semiconductor substrates, thus, is a critical technology. Patterned oxide thin film devices are typically formed by uniform film deposition followed by somewhat complicated post-deposition ion-beam or chemical etching in a controlled environment. We review here the development of an ambient atmosphere technique which allows selective deposition of electroceramic thin layers without such post-deposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self-assembled monolayer to modify the adhesion of subsequently deposited solution-derived electroceramics. The selective fictionalization is achieved through microcontact printing (v-CP) of self-assembled monolayer of the chemical octadecyltrichlorosilane on substrates of technical interest. Subsequent sol-gel deposition of ceramic oxides on these functionalized substrates, followed by lift-off from the monolayer, yields high quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micron- scale dielectric oxide devices have been fabricated using this process, with lateral resolution as fine as 0.5Lm. In this paper, we review the monolayer patterning and electrical behavior of several patterned electroceramic thin films, including Pb(Zr,Ti)03 [PZT], LiNb03, and Ta205. An applied device example is also presented in combination with selective MOCVD deposition of metal electrodes: integrated, fully monolayer-patterned Pt//PZT//PSi(Si(100) ferroelectric memory cells.

  16. Crystallinity of tellurium capping and epitaxy of ferromagnetic topological insulator films on SrTiO3

    PubMed Central

    Park, Jihwey; Soh, Yeong-Ah; Aeppli, Gabriel; Feng, Xiao; Ou, Yunbo; He, Ke; Xue, Qi-Kun

    2015-01-01

    Thin films of topological insulators are often capped with an insulating layer since topological insulators are known to be fragile to degradation. However, capping can hinder the observation of novel transport properties of the surface states. To understand the influence of capping on the surface states, it is crucial to understand the crystal structure and the atomic arrangement at the interfaces. Here, we use x-ray diffraction to establish the crystal structure of magnetic topological insulator Cr-doped (Bi,Sb)2Te3 (CBST) films grown on SrTiO3 (1 1 1) substrates with and without a Te capping layer. We find that both the film and capping layer are single crystal and that the crystal quality of the film is independent of the presence of the capping layer, but that x-rays cause sublimation of the CBST film, which is prevented by the capping layer. Our findings show that the different transport properties of capped films cannot be attributed to a lower crystal quality but to a more subtle effect such as a different electronic structure at the interface with the capping layer. Our results on the crystal structure and atomic arrangements of the topological heterostructure will enable modelling the electronic structure and design of topological heterostructures. PMID:26123202

  17. Crystallinity of tellurium capping and epitaxy of ferromagnetic topological insulator films on SrTiO3.

    PubMed

    Park, Jihwey; Soh, Yeong-Ah; Aeppli, Gabriel; Feng, Xiao; Ou, Yunbo; He, Ke; Xue, Qi-Kun

    2015-01-01

    Thin films of topological insulators are often capped with an insulating layer since topological insulators are known to be fragile to degradation. However, capping can hinder the observation of novel transport properties of the surface states. To understand the influence of capping on the surface states, it is crucial to understand the crystal structure and the atomic arrangement at the interfaces. Here, we use x-ray diffraction to establish the crystal structure of magnetic topological insulator Cr-doped (Bi,Sb)2Te3 (CBST) films grown on SrTiO3 (1 1 1) substrates with and without a Te capping layer. We find that both the film and capping layer are single crystal and that the crystal quality of the film is independent of the presence of the capping layer, but that x-rays cause sublimation of the CBST film, which is prevented by the capping layer. Our findings show that the different transport properties of capped films cannot be attributed to a lower crystal quality but to a more subtle effect such as a different electronic structure at the interface with the capping layer. Our results on the crystal structure and atomic arrangements of the topological heterostructure will enable modelling the electronic structure and design of topological heterostructures. PMID:26123202

  18. Crystallinity of tellurium capping and epitaxy of ferromagnetic topological insulator films on SrTiO3

    NASA Astrophysics Data System (ADS)

    Park, Jihwey; Soh, Yeong-Ah; Aeppli, Gabriel; Feng, Xiao; Ou, Yunbo; He, Ke; Xue, Qi-Kun

    2015-06-01

    Thin films of topological insulators are often capped with an insulating layer since topological insulators are known to be fragile to degradation. However, capping can hinder the observation of novel transport properties of the surface states. To understand the influence of capping on the surface states, it is crucial to understand the crystal structure and the atomic arrangement at the interfaces. Here, we use x-ray diffraction to establish the crystal structure of magnetic topological insulator Cr-doped (Bi,Sb)2Te3 (CBST) films grown on SrTiO3 (1 1 1) substrates with and without a Te capping layer. We find that both the film and capping layer are single crystal and that the crystal quality of the film is independent of the presence of the capping layer, but that x-rays cause sublimation of the CBST film, which is prevented by the capping layer. Our findings show that the different transport properties of capped films cannot be attributed to a lower crystal quality but to a more subtle effect such as a different electronic structure at the interface with the capping layer. Our results on the crystal structure and atomic arrangements of the topological heterostructure will enable modelling the electronic structure and design of topological heterostructures.

  19. Niobium Thin Film Characterization for Thin Film Technology Used in Superconducting Radiofrequency Cavities

    NASA Astrophysics Data System (ADS)

    Dai, Yishu; Valente-Feliciano, Anne-Marie

    2015-10-01

    Superconducting RadioFrequency (SRF) penetrates about 40-100 nm of the top surface, making thin film technology possible in producing superconducting cavities. Thin film is based on the deposition of a thin Nb layer on top of a good thermal conducting material such as Al or Cu. Thin film allows for better control of the surface and has negligible response to the Earth's magnetic field, eliminating the need for magnetic shielding of the cavities. Thin film superconductivity depends heavily on coating process conditions, involving controllable parameters such as crystal plane orientation, coating temperature, and ion energy. MgO and Al2O3 substrates are used because they offer very smooth surfaces, ideal for studying film growth. Atomic Force Microscopy is used to characterize surface's morphology. It is evident that a lower nucleation energy and a long coating time increases the film quality in the r-plane sapphire crystal orientation. The quality of the film increases with thickness. Nb films coated on r-plane, grow along the (001) plane and yield a much higher RRR compared to the films grown on a- and c-planes. This information allows for further improvement on the research process for thin film technology used in superconducting cavities for the particle accelerators. National Science Foundation, Department of Energy, Jefferson Lab, Old Dominion University.

  20. Influence of the vacuum interface on the charge distribution in V2O3 thin films

    NASA Astrophysics Data System (ADS)

    Schwingenschlögl, U.; Frésard, R.; Eyert, V.

    2009-09-01

    The electronic structure of V2O3 thin films is studied by means of the augmented spherical wave method as based on density functional theory and the local density approximation. We establish that the effects of charge redistribution, induced by the vacuum interface, in such films are restricted to a very narrow surface layer of ≈15 Å thickness. As a consequence, charge redistribution can be ruled out as a source of the extraordinary thickness dependence of the metal-insulator transition observed in V2O3 thin films of ~100-1000 Å thickness.

  1. Synthesis and ionic liquid gating of hexagonal WO{sub 3} thin films

    SciTech Connect

    Wu, Phillip M. E-mail: beasley@stanford.edu; Munakata, Ko; Hammond, R. H.; Geballe, T. H.; Beasley, M. R. E-mail: beasley@stanford.edu; Ishii, Satoshi; Tanabe, Kenji; Tokiwa, Kazuyasu

    2015-01-26

    Via thin film deposition techniques, the meta-stable in bulk crystal hexagonal phase of tungsten oxide (hex-WO{sub 3}) is stabilized as a thin film. The hex-WO{sub 3} structure is potentially promising for numerous applications and is related to the structure for superconducting compounds found in WO{sub 3}. Utilizing ionic liquid gating, carriers were electrostatically induced in the films and an insulator-to-metal transition is observed. These results show that ionic liquid gating is a viable technique to alter the electrical transport properties of WO{sub 3}.

  2. Mirrorlike pulsed laser deposited tungsten thin film

    SciTech Connect

    Mostako, A. T. T.; Khare, Alika; Rao, C. V. S.

    2011-01-15

    Mirrorlike tungsten thin films on stainless steel substrate deposited via pulsed laser deposition technique in vacuum (10{sup -5} Torr) is reported, which may find direct application as first mirror in fusion devices. The crystal structure of tungsten film is analyzed using x-ray diffraction pattern, surface morphology of the tungsten films is studied with scanning electron microscope and atomic force microscope. The film composition is identified using energy dispersive x-ray. The specular and diffuse reflectivities with respect to stainless steel substrate of the tungsten films are recorded with FTIR spectra. The thickness and the optical quality of pulsed laser deposition deposited films are tested via interferometric technique. The reflectivity is approaching about that of the bulk for the tungsten film of thickness {approx}782 nm.

  3. Mirrorlike pulsed laser deposited tungsten thin film.

    PubMed

    Mostako, A T T; Rao, C V S; Khare, Alika

    2011-01-01

    Mirrorlike tungsten thin films on stainless steel substrate deposited via pulsed laser deposition technique in vacuum (10(-5) Torr) is reported, which may find direct application as first mirror in fusion devices. The crystal structure of tungsten film is analyzed using x-ray diffraction pattern, surface morphology of the tungsten films is studied with scanning electron microscope and atomic force microscope. The film composition is identified using energy dispersive x-ray. The specular and diffuse reflectivities with respect to stainless steel substrate of the tungsten films are recorded with FTIR spectra. The thickness and the optical quality of pulsed laser deposition deposited films are tested via interferometric technique. The reflectivity is approaching about that of the bulk for the tungsten film of thickness ∼782 nm. PMID:21280810

  4. Corrosion Behaviour of Sputtered Alumina Thin Films

    NASA Astrophysics Data System (ADS)

    Reddy, I. Neelakanta; Dey, Arjun; Sridhara, N.; Anoop, S.; Bera, Parthasarathi; Rani, R. Uma; Anandan, Chinnasamy; Sharma, Anand Kumar

    2015-10-01

    Corrosion studies of sputtered alumina thin films grown on stainless steel (SS) 304 were carried out by linear polarization and electrochemical impedance spectroscopy. Noticeable changes were not observed in morphology and surface roughness of films after carrying out the corrosion test. Corrosion current density (icorr) of alumina coated SS decreased up to 10-10 A cm-2 while icorr value in the range of 10-5-10-6 A cm-2 was observed for bare SS. The direct sputtered film showed superior corrosion resistance behaviour than the reactive sputtered film. This might be attributed to the difference in thickness of the films sputtered by direct and reactive methods. The electronic structure of deposited alumina films was studied both before and after corrosion test by X-ray photoelectron spectroscopy technique which also confirmed no structural changes of alumina film after exposing it to corrosive environment.

  5. Flat panel display using Ti-Cr-Al-O thin film

    DOEpatents

    Jankowski, Alan F.; Schmid, Anthony P.

    2002-01-01

    Thin films of Ti--Cr--Al--O are used as a resistor material. The films are rf sputter deposited from ceramic targets using a reactive working gas mixture of Ar and O.sub.2. Resistivity values from 10.sup.4 to 10.sup.10 Ohm-cm have been measured for Ti--Cr--Al--O film <1 .mu.m thick. The film resistivity can be discretely selected through control of the target composition and the deposition parameters. The application of Ti--Cr--Al--O as a thin film resistor has been found to be thermodynamically stable, unlike other metal-oxide films. The Ti--Cr--Al--O film can be used as a vertical or lateral resistor, for example, as a layer beneath a field emission cathode in a flat panel display; or used to control surface emissivity, for example, as a coating on an insulating material such as vertical wall supports in flat panel displays.

  6. Process for producing Ti-Cr-Al-O thin film resistors

    DOEpatents

    Jankowski, Alan F.; Schmid, Anthony P.

    2001-01-01

    Thin films of Ti-Cr-Al-O are used as a resistor material. The films are rf sputter deposited from ceramic targets using a reactive working gas mixture of Ar and O.sub.2. Resistivity values from 10.sup.4 to 10.sup.10 Ohm-cm have been measured for Ti-Cr-Al-O film <1 .mu.m thick. The film resistivity can be discretely selected through control of the target composition and the deposition parameters. The application of Ti-Cr-Al-O as a thin film resistor has been found to be thermodynamically stable, unlike other metal-oxide films. The Ti-Cr-Al-O film can be used as a vertical or lateral resistor, for example, as a layer beneath a field emission cathode in a flat panel display; or used to control surface emissivity, for example, as a coating on an insulating material such as vertical wall supports in flat panel displays.

  7. Electrical resistivity of assembled transparent inorganic oxide nanoparticle thin layers: Influence of silica, insulating impurities and surfactant layer thickness

    PubMed Central

    Bubenhofer, Stephanie B.; Schumacher, Christoph M.; Koehler, Fabian M.; Luechinger, Norman A.; Sotiriou, Georgios A.; Grass, Robert N.; Stark, Wendelin J.

    2013-01-01

    Transparent, conductive layers prepared from nanoparticle dispersion of doped oxides are highly sensitive to impurities. Currently investigated cost efficient and fast production of thin conducting films for use in consumer electronics relies on wet processing such as spin and/or dip coating of surfactant-stabilized nanoparticle dispersions. This inherently results in entrainment of organic and inorganic impurities into the conducting layer leading to largely varying electrical conductivity. Therefore this study provides a systematic investigation on the effect of insulating surfactants, small organic molecules and silica in terms of pressure dependent electrical conductivity as a result of different core/shell structure (layer thickness). Application of high temperature flame synthesis gives access to antimony-doped tin oxide (ATO) nanoparticles with high purity. This well-defined starting material was then subjected to representative film preparation processes using organic additives. In addition ATO nanoparticles were prepared with a homogeneous inorganic silica layer (silica layer thickness from 0.7 to 2 nm). Testing both organic and inorganic shell materials for the electronic transport through the nanoparticle composite allowed a systematic study on the influence of surface adsorbates (e.g. organic, insulating materials on the conducting nanoparticle’s surface) in comparison to well-known insulators such as silica. Insulating impurities or shells revealed a dominant influence of tunneling effect on the overall layer resistance. Mechanical relaxation phenomena were found for 2 nm insulating shells for both large polymer surfactants and (inorganic) SiO2 shells. PMID:22545730

  8. A high performance thin film thermoelectric cooler

    SciTech Connect

    Rowe, D.M.; Min, G.; Volklein, F.

    1998-07-01

    Thin film thermoelectric devices with small dimensions have been fabricated using microelectronics technology and operated successfully in the Seebeck mode as sensors or generators. However, they do not operate successfully in the Peltier mode as coolers, because of the thermal bypass provided by the relatively thick substrate upon which the thermoelectric device is fabricated. In this paper a processing sequence is described which dramatically reduces this thermal bypass and facilitates the fabrication of high performance integrated thin film thermoelectric coolers. In the processing sequence a very thin amorphous SiC (or SiO{sub 2}SiN{sub 4}) film is deposited on a silicon substrate using conventional thin film deposition and a membrane formed by removing the silicon substrate over a desired region using chemical etching or micro-machining. Thermoelements are deposited on the membrane using conventional thin film deposition and patterning techniques and configured so that the region which is to be cooled is abutted to the cold junctions of the Peltier thermoelements while the hot junctions are located at the outer peripheral area which rests on the silicon substrate rim. Heat is pumped laterally from the cooled region to the silicon substrate rim and then dissipated vertically through it to an external heat sink. Theoretical calculations of the performance of a cooler described above indicate that a maximum temperature difference of about 40--50K can be achieved with a maximum heat pumping capacity of around 10 milliwatts.

  9. Ion beam-based characterization of multicomponent oxide thin films and thin film layered structures

    SciTech Connect

    Krauss, A.R.; Rangaswamy, M.; Lin, Yuping; Gruen, D.M.; Schultz, J.A.; Schmidt, H.K.; Chang, R.P.H.

    1992-11-01

    Fabrication of thin film layered structures of multi-component materials such as high temperature superconductors, ferroelectric and electro-optic materials, and alloy semiconductors, and the development of hybrid materials requires understanding of film growth and interface properties. For High Temperature Superconductors, the superconducting coherence length is extremely short (5--15 {Angstrom}), and fabrication of reliable devices will require control of film properties at extremely sharp interfaces; it will be necessary to verify the integrity of thin layers and layered structure devices over thicknesses comparable to the atomic layer spacing. Analytical techniques which probe the first 1--2 atomic layers are therefore necessary for in-situ characterization of relevant thin film growth processes. However, most surface-analytical techniques are sensitive to a region within 10--40 {Angstrom} of the surface and are physically incompatible with thin film deposition and are typically restricted to ultra high vacuum conditions. A review of ion beam-based analytical methods for the characterization of thin film and multi-layered thin film structures incorporating layers of multicomponent oxides is presented. Particular attention will be paid to the use of time-of-flight techniques based on the use of 1- 15 key ion beams which show potential for use as nondestructive, real-time, in-situ surface diagnostics for the growth of multicomponent metal and metal oxide thin films.

  10. Thin film dielectric composite materials

    DOEpatents

    Jia, Quanxi; Gibbons, Brady J.; Findikoglu, Alp T.; Park, Bae Ho

    2002-01-01

    A dielectric composite material comprising at least two crystal phases of different components with TiO.sub.2 as a first component and a material selected from the group consisting of Ba.sub.1-x Sr.sub.x TiO.sub.3 where x is from 0.3 to 0.7, Pb.sub.1-x Ca.sub.x TiO.sub.3 where x is from 0.4 to 0.7, Sr.sub.1-x Pb.sub.x TiO.sub.3 where x is from 0.2 to 0.4, Ba.sub.1-x Cd.sub.x TiO.sub.3 where x is from 0.02 to 0.1, BaTi.sub.1-x Zr.sub.x O.sub.3 where x is from 0.2 to 0.3, BaTi.sub.1-x Sn.sub.x O.sub.3 where x is from 0.15 to 0.3, BaTi.sub.1-x Hf.sub.x O.sub.3 where x is from 0.24 to 0.3, Pb.sub.1-1.3x La.sub.x TiO.sub.3+0.2x where x is from 0.23 to 0.3, (BaTiO.sub.3).sub.x (PbFeo.sub.0.5 Nb.sub.0.5 O.sub.3).sub.1-x where x is from 0.75 to 0.9, (PbTiO.sub.3).sub.- (PbCo.sub.0.5 W.sub.0.5 O.sub.3).sub.1-x where x is from 0.1 to 0.45, (PbTiO.sub.3).sub.x (PbMg.sub.0.5 W.sub.0.5 O.sub.3).sub.1-x where x is from 0.2 to 0.4, and (PbTiO.sub.3).sub.x (PbFe.sub.0.5 Ta.sub.0.5 O.sub.3).sub.1-x where x is from 0 to 0.2, as the second component is described. The dielectric composite material can be formed as a thin film upon suitable substrates.

  11. Diamondlike carbon films on semiconductors for insulated-gate technology

    NASA Technical Reports Server (NTRS)

    Kapoor, V. J.; Mirtich, M. J.; Banks, B. A.

    1986-01-01

    MIS structures are fabricated on p-type InP, GaAs, and Si substrated by direct ionization of 25-percent CH4 in Ar and ion-beam deposition of 70-nm-thick diamondlike films, followed by application of Al gate electrodes and ohmic contacts. The films are found to have bandgap 0.9-1.1 eV, resistivity 8.1 Mohm cm, breakdown field strength 1 MV/cm, and density 1.8 g/cu cm, to be thermally stable up to 400 C, and to undergo rapid decomposition above 450 C. The electrical properties of the MIS structures are significantly improved by sputter cleaning the substrates with a 1-keV 2-mA/sq cm Ar beam for 2 min at 300 microtorr prior to C-film deposition. The resulting structures have fixed insulator charge number densities 4 x 10 to the 12th/sq cm (InP), 7.5 x 10 to the 12th/sq cm (GaAs), and 9 x 10 to the 11th/sq cm (Si) and interface state densities (5, 200, and 0.5) x 10 to the 12th/ sq cm eV, respectively. It is suggested that the low optical bandgap and resistivity of the C films and the high insulator-charge and interface-state densities make them unstable as gate dielectrics for microelectronics.

  12. Memory switches based on metal oxide thin films

    NASA Technical Reports Server (NTRS)

    Ramesham, Rajeshuni (Inventor); Thakoor, Anilkumar P. (Inventor); Lambe, John J. (Inventor)

    1990-01-01

    MnO.sub.2-x thin films (12) exhibit irreversible memory switching (28) with an OFF/ON resistance ratio of at least about 10.sup.3 and the tailorability of ON state (20) resistance. Such films are potentially extremely useful as a connection element in a variety of microelectronic circuits and arrays (24). Such films provide a pre-tailored, finite, non-volatile resistive element at a desired place in an electric circuit, which can be electrically turned OFF (22) or disconnected as desired, by application of an electrical pulse. Microswitch structures (10) constitute the thin film element, contacted by a pair of separate electrodes (16a, 16b) and have a finite, pre-selected ON resistance which is ideally suited, for example, as a programmable binary synaptic connection for electronic implementation of neural network architectures. The MnO.sub.2-x microswitch is non-volatile, patternable, insensitive to ultraviolet light, and adherent to a variety of insulating substrates (14), such as glass and silicon dioxide-coated silicon substrates.

  13. Cleaved thin-film probes for scanning tunneling microscopy.

    PubMed

    Siahaan, T; Kurnosikov, O; Barcones, B; Swagten, H J M; Koopmans, B

    2016-01-22

    We introduce an alternative type of probe for scanning tunneling microscopy (STM). Instead of using a needle-like tip made from a piece of metallic wire, a sharp-edged cleaved insulating substrate, which is initially covered by a thin conductive film, is used. The sharp tip is formed at the intersection of the two cleaved sides. Using this approach a variety of materials for STM probes can be used, and functionalization of STM probes is possible. The working principle of different probes made of metallic (Pt, Co, and CoB), indium-tin oxide, as well as Cu/Pt and Co/Pt multilayer films are demonstrated by STM imaging of clean Cu(001) and Cu(111) surfaces as well as the epitaxial Co clusters on Cu(111). PMID:26636763

  14. Crystallization of zirconia based thin films.

    PubMed

    Stender, D; Frison, R; Conder, K; Rupp, J L M; Scherrer, B; Martynczuk, J M; Gauckler, L J; Schneider, C W; Lippert, T; Wokaun, A

    2015-07-28

    The crystallization kinetics of amorphous 3 and 8 mol% yttria stabilized zirconia (3YSZ and 8YSZ) thin films grown by pulsed laser deposition (PLD), spray pyrolysis and dc-magnetron sputtering are explored. The deposited films were heat treated up to 1000 °C ex situ and in situ in an X-ray diffractometer. A minimum temperature of 275 °C was determined at which as-deposited amorphous PLD grown 3YSZ films fully crystallize within five hours. Above 325 °C these films transform nearly instantaneously with a high degree of micro-strain when crystallized below 500 °C. In these films the t'' phase crystallizes which transforms at T > 600 °C to the t' phase upon relaxation of the micro-strain. Furthermore, the crystallization of 8YSZ thin films grown by PLD, spray pyrolysis and dc-sputtering are characterized by in situ XRD measurements. At a constant heating rate of 2.4 K min(-1) crystallization is accomplished after reaching 800 °C, while PLD grown thin films were completely crystallized already at ca. 300 °C. PMID:26119755

  15. Optimization of YBa sub 2 Cu sub 3 O sub 7 thin films for multilayers

    SciTech Connect

    Humphreys, R.G.; Chew, N.G.; Satchell, J.S.; Goodyear, S.W.; Edwards, J.A.; Blenkinsop, S.E. )

    1991-03-01

    This paper studies the in situ growth of YBa{sub 2}Cu{sub 3}O{sub 7} thin films using e-beam coevaporation. The growth conditions for smooth YBa{sub 2}Cu{sub 3}O{sub 7} films with high T{sub c} and J{sub c} have been established. Superconductor-insulator and SIS structures have been grown using Y{sub 2}O{sub 3} as an epitaxial insulator, and preliminary vertical transport measurements in patterned structures are reported.

  16. Electrical control of terahertz nano antennas on VO2 thin film.

    PubMed

    Jeong, Young-Gyun; Bernien, Hannes; Kyoung, Ji-Soo; Park, Hyeong-Ryeol; Kim, Hyun-Sun; Choi, Jae-Wook; Kim, Bong-Jun; Kim, Hyun-Tak; Ahn, Kwang Jun; Kim, Dai-Sik

    2011-10-24

    We demonstrate an active metamaterial device that allows to electrically control terahertz transmission over more than one order of magnitude. Our device consists of a lithographically defined gold nano antenna array fabricated on a thin film of vanadium dioxide (VO(2)), a material that possesses an insulator to metal transition. The nano antennas let terahertz (THz) radiation funnel through when the VO(2) film is in the insulating state. By applying a dc-bias voltage through our device, the VO(2) becomes metallic. This electrically shorts the antennas and therefore switches off the transmission in two distinct regimes: reversible and irreversible switching. PMID:22108973

  17. History Dependent Magnetoresistance in Lightly Doped LaZxSrxCuO4Thin Films

    SciTech Connect

    Bozovic I.; Shi, X.; Popovic, D.; Panagopoulos, C.; Logvenov, G.; Bollinger, A.T.

    2012-06-01

    The in-plane magnetoresistance (MR) in atomically smooth La{sub 2-x}Sr{sub x}CuO{sub 4} thin films grown by molecular-beam-epitaxy was measured in magnetic fields B up to 9 T over a wide range of temperatures T. The films, with x = 0.03 and x = 0.05, are insulating, and the positive MR emerges at T < 4 K. The positive MR exhibits glassy features, including history dependence and memory, for all orientations of B. The results show that this behavior, which reflects the onset of glassiness in the dynamics of doped holes, is a robust feature of the insulating state.

  18. Evidence of Microscopic Phase Segregation in CMR thin films

    NASA Astrophysics Data System (ADS)

    Imtiaz, Atif; Anlage, Steven

    2003-03-01

    We have used a Near Field Scanning Microwave Microscope (NFMM) to study local sheet resistance (Rx) contrast in 100nm thick La_0.67Ca_0.33MnO3 thin films. These films show a transition from charge-ordered insulating or paramagnetic insulating to a ferro-magnetic metallic state at a transition temperature Tc ( 250K for the film we studied). No Magnetic Field is applied when performing the experiment. We used our NFMM to study this sample above and below the Tc. Probe/sample distance control is achieved by employing a Scanning Tunneling Microscope feedback. Scanning is done in constant tunnel current mode, and microwave data is collected simultaneously. Several models (transmission line model and lumped element model) of microwave microscope are used to extract the Rx from the data of frequency shift and Quality factor versus position. The Rx images show evidence of the phase transition: we find that the sheet resistance distribution is broader for the data below Tc. Upon closer examination, we see evidence of inhomogeneous conductivity on the scale of 2.5nm below Tc. Discussion of these results and their modeling will be presented. [1] Atif Imtiaz and Steven M. Anlage, "A novel STM-assisted microwave microscope with capacitance and loss imaging capability", Ultramicroscopy (in press); cond-mat/0203540.

  19. Capillary stress in microporous thin films

    SciTech Connect

    Samuel, J.; Hurd, A.J.; Frink, L.J.D.; Swol, F. van; Brinker, C.J. |; Raman, N.K.

    1996-06-01

    Development of capillary stress in porous xerogels, although ubiquitous, has not been systematically studied. The authors have used the beam bending technique to measure stress isotherms of microporous thin films prepared by a sol-gel route. The thin films were prepared on deformable silicon substrates which were then placed in a vacuum system. The automated measurement was carried out by monitoring the deflection of a laser reflected off the substrate while changing the overlying relative pressure of various solvents. The magnitude of the macroscopic bending stress was found to reach a value of 180 MPa at a relative pressure of methanol, P/Po = 0.001. The observed stress is determined by the pore size distribution and is an order of magnitude smaller in mesoporous thin films. Density Functional Theory (DFT) indicates that for the microporous materials, the stress at saturation is compressive and drops as the relative pressure is reduced.

  20. Vibration welding system with thin film sensor

    DOEpatents

    Cai, Wayne W; Abell, Jeffrey A; Li, Xiaochun; Choi, Hongseok; Zhao, Jingzhou

    2014-03-18

    A vibration welding system includes an anvil, a welding horn, a thin film sensor, and a process controller. The anvil and horn include working surfaces that contact a work piece during the welding process. The sensor measures a control value at the working surface. The measured control value is transmitted to the controller, which controls the system in part using the measured control value. The thin film sensor may include a plurality of thermopiles and thermocouples which collectively measure temperature and heat flux at the working surface. A method includes providing a welder device with a slot adjacent to a working surface of the welder device, inserting the thin film sensor into the slot, and using the sensor to measure a control value at the working surface. A process controller then controls the vibration welding system in part using the measured control value.

  1. Thin film ferroelectric electro-optic memory

    NASA Technical Reports Server (NTRS)

    Thakoor, Sarita (Inventor); Thakoor, Anilkumar P. (Inventor)

    1993-01-01

    An electrically programmable, optically readable data or memory cell is configured from a thin film of ferroelectric material, such as PZT, sandwiched between a transparent top electrode and a bottom electrode. The output photoresponse, which may be a photocurrent or photo-emf, is a function of the product of the remanent polarization from a previously applied polarization voltage and the incident light intensity. The cell is useful for analog and digital data storage as well as opto-electric computing. The optical read operation is non-destructive of the remanent polarization. The cell provides a method for computing the product of stored data and incident optical data by applying an electrical signal to store data by polarizing the thin film ferroelectric material, and then applying an intensity modulated optical signal incident onto the thin film material to generate a photoresponse therein related to the product of the electrical and optical signals.

  2. Mesoscale morphologies in polymer thin films.

    SciTech Connect

    Ramanathan, M.; Darling, S. B.

    2011-06-01

    In the midst of an exciting era of polymer nanoscience, where the development of materials and understanding of properties at the nanoscale remain a major R&D endeavor, there are several exciting phenomena that have been reported at the mesoscale (approximately an order of magnitude larger than the nanoscale). In this review article, we focus on mesoscale morphologies in polymer thin films from the viewpoint of origination of structure formation, structure development and the interaction forces that govern these morphologies. Mesoscale morphologies, including dendrites, holes, spherulites, fractals and honeycomb structures have been observed in thin films of homopolymer, copolymer, blends and composites. Following a largely phenomenological level of description, we review the kinetic and thermodynamic aspects of mesostructure formation outlining some of the key mechanisms at play. We also discuss various strategies to direct, limit, or inhibit the appearance of mesostructures in polymer thin films as well as an outlook toward potential areas of growth in this field of research.

  3. Method for synthesizing thin film electrodes

    DOEpatents

    Boyle, Timothy J.

    2007-03-13

    A method for making a thin-film electrode, either an anode or a cathode, by preparing a precursor solution using an alkoxide reactant, depositing multiple thin film layers with each layer approximately 500 1000 .ANG. in thickness, and heating the layers to above 600.degree. C. to achieve a material with electrochemical properties suitable for use in a thin film battery. The preparation of the anode precursor solution uses Sn(OCH.sub.2C(CH.sub.3).sub.3).sub.2 dissolved in a solvent in the presence of HO.sub.2CCH.sub.3 and the cathode precursor solution is formed by dissolving a mixture of (Li(OCH.sub.2C(CH.sub.3).sub.3)).sub.8 and Co(O.sub.2CCH.sub.3).H.sub.2O in at least one polar solvent.

  4. Magnetic Damping in Ferromagnetic Thin Films

    NASA Astrophysics Data System (ADS)

    Oogane, Mikihiko; Wakitani, Takeshi; Yakata, Satoshi; Yilgin, Resul; Ando, Yasuo; Sakuma, Akimasa; Miyazaki, Terunobu

    2006-05-01

    We determined the Gilbert damping constants of Fe-Co-Ni and Co-Fe-B alloys with various compositions and half-metallic Co2MnAl Heusler alloy films prepared by magnetron sputtering. The ferromagnetic resonance (FMR) technique was used to determine the damping constants of the prepared films. The out-of-plane angular dependences of the resonance field (HR) and line width (Δ Hpp) of FMR spectra were measured and fitted using the Landau-Lifshitz-Gilbert (LLG) equation. The experimental results fitted well, considering the inhomogeneities of the films in the fitting. The damping constants of the metallic films were much larger than those of bulk ferrimagnetic insulators and were roughly proportional to (g-2)2, where g is the Lande g factor. We discuss the origin of magnetic damping, considering spin-orbit and s-d interactions.

  5. Fabrication and Characterization of ZnO Langmuir-Blodgett Film and Its Use in Metal-Insulator-Metal Tunnel Diode.

    PubMed

    Azad, Ibrahim; Ram, Manoj K; Goswami, D Yogi; Stefanakos, Elias

    2016-08-23

    Metal-insulator-metal tunnel diodes have great potential for use in infrared detection and energy harvesting applications. The quantum based tunneling mechanism of electrons in MIM (metal-insulator-metal) or MIIM (metal-insulator-insulator-metal) diodes can facilitate rectification at THz frequencies. In this study, the required nanometer thin insulating layer (I) in the MIM diode structure was fabricated using the Langmuir-Blodgett technique. The zinc stearate LB film was deposited on Au/Cr coated quartz, FTO, and silicon substrates, and then heat treated by varying the temperature from 100 to 550 °C to obtain nanometer thin ZnO layers. The thin films were characterized by XRD, AFM, FTIR, and cyclic voltammetry methods. The final MIM structure was fabricated by depositing chromium/nickel over the ZnO on Au/Cr film. The current voltage (I-V) characteristics of the diode showed that the conduction mechanism is electron tunneling through the thin insulating layer. The sensitivity of the diodes was as high as 32 V(-1). The diode resistance was ∼80 Ω (at a bias voltage of 0.78 V), and the rectification ratio at that bias point was about 12 (for a voltage swing of ±200 mV). The diode response exhibited significant nonlinearity and high asymmetry at the bias point, very desirable diode performance parameters for IR detection applications. PMID:27464073

  6. Zeolite thin films: from computer chips to space stations.

    PubMed

    Lew, Christopher M; Cai, Rui; Yan, Yushan

    2010-02-16

    Zeolites are a class of crystalline oxides that have uniform and molecular-sized pores (3-12 A in diameter). Although natural zeolites were first discovered in 1756, significant commercial development did not begin until the 1950s when synthetic zeolites with high purity and controlled chemical composition became available. Since then, major commercial applications of zeolites have been limited to catalysis, adsorption, and ion exchange, all using zeolites in powder form. Although researchers have widely investigated zeolite thin films within the last 15 years, most of these studies were motivated by the potential application of these materials as separation membranes and membrane reactors. In the last decade, we have recognized and demonstrated that zeolite thin films can have new, diverse, and economically significant applications that others had not previously considered. In this Account, we highlight our work on the development of zeolite thin films as low-dielectric constant (low-k) insulators for future generation computer chips, environmentally benign corrosion-resistant coatings for aerospace alloys, and hydrophilic and microbiocidal coatings for gravity-independent water separation in space stations. Although these three applications might not seem directly related, they all rely on the ability to fine-tune important macroscopic properties of zeolites by changing their ratio of silicon to aluminum. For example, pure-silica zeolites (PSZs, Si/Al = infinity) are hydrophobic, acid stable, and have no ion exchange capacity, while low-silica zeolites (LSZs, Si/Al < 2) are hydrophilic, acid soluble, and have a high ion exchange capacity. These new thin films also take advantage of some unique properties of zeolites that have not been exploited before, such as a higher elastic modulus, hardness, and heat conductivity than those of amorphous porous silicas, and microbiocidal capabilities derived from their ion exchange capacities. Finally, we briefly discuss our

  7. Thin film oxygen partial pressure sensor

    NASA Technical Reports Server (NTRS)

    Wortman, J. J.; Harrison, J. W.; Honbarrier, H. L.; Yen, J.

    1972-01-01

    The development is described of a laboratory model oxygen partial pressure sensor using a sputtered zinc oxide thin film. The film is operated at about 400 C through the use of a miniature silicon bar. Because of the unique resistance versus temperature relation of the silicon bar, control of the operational temperature is achieved by controlling the resistance. A circuit for accomplishing this is described. The response of sputtered zinc oxide films of various thicknesses to oxygen, nitrogen, argon, carbon dioxide, and water vapor caused a change in the film resistance. Over a large range, film conductance varied approximately as the square root of the oxygen partial pressure. The presence of water vapor in the gas stream caused a shift in the film conductance at a given oxygen partial pressure. A theoretical model is presented to explain the characteristic features of the zinc oxide response to oxygen.

  8. Solid-state thin-film supercapacitor with ruthenium oxide and solid electrolyte thin films

    NASA Astrophysics Data System (ADS)

    Yoon, Y. S.; Cho, W. I.; Lim, J. H.; Choi, D. J.

    Direct current reactive sputtering deposition of ruthenium oxide thin films (bottom and top electrodes) at 400°C are performed to produce a solid-state thin-film supercapacitor (TFSC). The supercapacitor has a cell structure of RuO 2/Li 2.94PO 2.37N 0.75 (Lipon)/RuO 2/Pt. Radio frequency, reactive sputtering deposition of an Li 2.94PO 2.37N 0.75 electrolyte film is performed on the bottom RuO 2 film at room temperature to separate the bottom and top RuO 2 electrodes electrically. The stoichiometry of the RuO 2 thin film is investigated by Rutherford back-scattering spectrometry (RBS). X-ray diffraction (XRD) shows that the as-deposited RuO 2 thin film is an amorphous phase. Scanning electron microscopy (SEM) measurements reveal that the RuO 2/Lipon/RuO 2 hetero-interfaces have no inter-diffusion problems. Charge-discharge measurements with constant current at room temperature clearly reveal typical supercapacitor behaviour for a RuO 2/Lipon/RuO 2/Pt cell structure. Since the electrolyte thin film has low ionic mobility, the capacity and cycle performance are inferior to those of a bulk type of supercapacitor. These results indicate that a high performance, TFSC can be fabricated by a solid electrolyte thin film with high ionic conductivity.

  9. Fractal structure formation from Ag nanoparticle films on insulating substrates.

    PubMed

    Tang, Jing; Li, Zhiyong; Xia, Qiangfei; Williams, R Stanley

    2009-07-01

    Two dimensional (2D) fractal structures were observed to form from fairly uniform Ag island films (equivalent mass thicknesses of 1.5 and 5 nm) on insulating silicon dioxide surfaces (thermally grown silicon oxide on Si or quartz) upon immersion in deionized water. This result is distinctly different from the previously observed three-dimensional (3D) growth of faceted Ag nanocrystals on conductive surfaces (ITO and graphite) as the result of an electrochemical Ostwald ripening process, which also occurs on native oxide covered silicon surfaces as reported here. The fractal structures formed by diffusion-limited aggregation (DLA) of Ag species on the insulating surfaces. We present the experimental observation of this phenomenon and discuss some possible mechanisms for the DLA formation. PMID:19496573

  10. Feasibility Study of Thin Film Thermocouple Piles

    NASA Technical Reports Server (NTRS)

    Sisk, R. C.

    2001-01-01

    Historically, thermopile detectors, generators, and refrigerators based on bulk materials have been used to measure temperature, generate power for spacecraft, and cool sensors for scientific investigations. New potential uses of small, low-power, thin film thermopiles are in the area of microelectromechanical systems since power requirements decrease as electrical and mechanical machines shrink in size. In this research activity, thin film thermopile devices are fabricated utilizing radio frequency sputter coating and photoresist lift-off techniques. Electrical characterizations are performed on two designs in order to investigate the feasibility of generating small amounts of power, utilizing any available waste heat as the energy source.

  11. Borocarbide thin films and tunneling measurements.

    SciTech Connect

    Iavarone, M.; Andreone, A.; Cassinese, A.; Dicapual, R.; giannil, L.; Vagliol, R.; DeWilde, Y.; Crabtree, G. W.

    2000-06-15

    The results obtained by their group in thin film fabrication and STM tunneling on superconducting borocarbides YNi{sub 2}B{sub 2}C have been be briefly reviewed. Results concerning the microwave surface impedance and the S/N planar junctions on LuNi{sub 2}B{sub 2}C thin films have been also presented and analyzed. These new data unambiguously confirm the full BCS nature of the superconducting gap in borocarbides and the absence of significant pair-breaking effects in LuNi{sub 2}B{sub 2}C.

  12. Emittance Theory for Thin Film Selective Emitter

    NASA Technical Reports Server (NTRS)

    Chubb, Donald L.; Lowe, Roland A.; Good, Brian S.

    1994-01-01

    Thin films of high temperature garnet materials such as yttrium aluminum garnet (YAG) doped with rare earths are currently being investigated as selective emitters. This paper presents a radiative transfer analysis of the thin film emitter. From this analysis the emitter efficiency and power density are calculated. Results based on measured extinction coefficients for erbium-YAG and holmium-YAG are presented. These results indicated that emitter efficiencies of 50 percent and power densities of several watts/sq cm are attainable at moderate temperatures (less than 1750 K).

  13. Anomalous C-V response correlated to relaxation processes in TiO{sub 2} thin film based-metal-insulator-metal capacitor: Effect of titanium and oxygen defects

    SciTech Connect

    Kahouli, A.; Marichy, C.; Pinna, N.

    2015-04-21

    Capacitance-voltage (C–V) and capacitance-frequency (C–f) measurements are performed on atomic layer deposited TiO{sub 2} thin films with top and bottom Au and Pt electrodes, respectively, over a large temperature and frequency range. A sharp capacitance peak/discontinuity (C–V anomalous) is observed in the C–V characteristics at various temperatures and voltages. It is demonstrated that this phenomenon is directly associated with oxygen vacancies. The C–V peak irreversibility and dissymmetry at the reversal dc voltage are attributed to difference between the Schottky contacts at the metal/TiO{sub 2} interfaces. Dielectric analyses reveal two relaxation processes with degeneration of the activation energy. The low trap level of 0.60–0.65 eV is associated with the first ionized oxygen vacancy at low temperature, while the deep trap level of 1.05 eV is associated to the second ionized oxygen vacancy at high temperature. The DC conductivity of the films exhibits a transition temperature at 200 °C, suggesting a transition from a conduction regime governed by ionized oxygen vacancies to one governed by interstitial Ti{sup 3+} ions. Both the C–V anomalous and relaxation processes in TiO{sub 2} arise from oxygen vacancies, while the conduction mechanism at high temperature is governed by interstitial titanium ions.

  14. Annealed CVD molybdenum thin film surface

    DOEpatents

    Carver, Gary E.; Seraphin, Bernhard O.

    1984-01-01

    Molybdenum thin films deposited by pyrolytic decomposition of Mo(CO).sub.6 attain, after anneal in a reducing atmosphere at temperatures greater than 700.degree. C., infrared reflectance values greater than reflectance of supersmooth bulk molybdenum. Black molybdenum films deposited under oxidizing conditions and annealed, when covered with an anti-reflecting coating, approach the ideal solar collector characteristic of visible light absorber and infrared energy reflector.

  15. Dynamics of liquid films and thin jets

    NASA Technical Reports Server (NTRS)

    Zak, M.

    1979-01-01

    The theory of liquid films and thin jets as one- and two-dimensional continuums is examined. The equations of motion have led to solutions for the characteristic speeds of wave propagation for the parameters characterizing the shape. The formal analogy with a compressible fluid indicates the possibility of shock wave generation in films and jets and the formal analogy to the theory of threads and membranes leads to the discovery of some new dynamic effects. The theory is illustrated by examples.

  16. Superconducting thin films on potassium tantalate substrates

    DOEpatents

    Feenstra, Roeland; Boatner, Lynn A.

    1992-01-01

    A superconductive system for the lossless transmission of electrical current comprising a thin film of superconducting material Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7-x epitaxially deposited upon a KTaO.sub.3 substrate. The KTaO.sub.3 is an improved substrate over those of the prior art since the it exhibits small lattice constant mismatch and does not chemically react with the superconducting film.

  17. Influence of lattice distortion on phase transition properties of polycrystalline VO2 thin film

    NASA Astrophysics Data System (ADS)

    Lin, Tiegui; Wang, Langping; Wang, Xiaofeng; Zhang, Yufen; Yu, Yonghao

    2016-08-01

    In this work, high power impulse magnetron sputtering was used to control the lattice distortion in polycrystalline VO2 thin film. SEM images revealed that all the VO2 thin films had crystallite sizes of below 20 nm, and similar configurations. UV-vis-near IR transmittance spectra measured at different temperatures showed that most of the as-deposited films had a typical metal-insulator transition. Four-point probe resistivity results showed that the transition temperature of the films varied from 54.5 to 32 °C. The X-ray diffraction (XRD) patterns of the as-deposited films revealed that most were polycrystalline monoclinic VO2. The XRD results also confirmed that the lattice distortions in the as-deposited films were different, and the transition temperature decreased with the difference between the interplanar spacing of the as-deposited thin film and standard rutile VO2. Furthermore, a room temperature rutile VO2 thin film was successfully synthesized when this difference was small enough. Additionally, XRD patterns measured at varied temperatures revealed that the phase transition process of the polycrystalline VO2 thin film was a coordinative deformation between grains with different orientations. The main structural change during the phase transition was a gradual shift in interplanar spacing with temperature.

  18. Novel nanostructured thin film heterostructures: Growth, nanoscale characterization and properties

    NASA Astrophysics Data System (ADS)

    Chugh, Amit

    During my graduate study, I have been involved in the growth of new nano heterostructures grown by Pulsed Laser Deposition and by Laser MBE with the emphasis on understanding the thin film growth process by a new paradigm of Domain Matching Epitaxy (DME) and to integrate them on substrates like silicon, sapphire and new metallic substrates like Ni with exciting technological applications. The DME involves matching of integral multiples of lattice planes (diffracting as well as nondiffracting) between the film and the substrate, and this matching could be different in different directions. The idea of matching planes is derived from the basic fact that during thin film growth lattice relaxation involves generation of dislocations whose Burgers vectors correspond to missing or extra planes, rather than lattice constants. In the DME framework, the conventional lattice matching epitaxy (LME) becomes a special case where matching of lattice constants results from matching of lattice planes with a relatively small misfit of less than 7-8%. In large lattice mismatch systems, epitaxial growth of thin films is possible by matching of domains where integral multiples of lattice planes match across the interface. The work done in my doctoral study is divided into two main segments, (a) Growth of layered nanostructures and (b) growth of nanostructured composite thin films. The three systems studied under the first segment are (1) Growth of epitaxial self-aligned insulating films on metals (Cu) and its integration with Si (100). (2) Growth and integration of LSMO with Si (100). (3) Growth of Si on Ni substrates (highly textured) with TiN as a buffer layer. The heterostructures studied under the second part are (1) Role of Self-assembled Gold Nanodots in Improving the Electrical and Optical Characteristics of Zinc Oxide Films and (2) Growth of high quality epitaxial ZnO-Pt Nanocomposite and ZnO/Pt, Nanolayer Structures on Sapphire (0001). The epitaxial growth of these

  19. Hydrothermal Barium Titanate Thin-Film Characteristics and their Suitability as Decoupling Capacitors

    SciTech Connect

    Raj, P. Markondeya; Lee, Baik-Woo; Kang, Nam-Kee; Tummala, Rao R; Lance, Michael J; Meyer III, Harry M

    2010-01-01

    System integration and miniaturization demands are driving integrated thin film capacitor technologies towards ultrahigh capacitance densities for noise-free power supply, power conversion and efficient power management. Hydrothermal route can deposit crystalline ferroelectric films at low temperatures of less than 150 C. It is hence an attractive route for integrating high permittivity thin film capacitors on organic, silicon or flex substrates. However, hydrothermal films are not commercialized so far because of their inferior insulation characteristics. Embedded hydroxyl groups are attributed to be the cause for high leakage currents, temperature dependent properties and lower Breakdown Voltages (BDVs). This paper discusses the dielectric characteristics such as capacitance density, leakage currents and Temperature Coefficient of Capacitance (TCC) of hydrothermal barium titanate films and correlates them to the embedded water and OH groups, film morphology, stoichiometry and crystallinity. With thermal treatment, majority of the OH groups can be removed leading to improved insulation characteristics. The room temperature I-V characteristics agreed with ionic conduction models for films baked at 160 C while higher baking temperatures of above 300 C resulted in Poole-Frenkel type conduction. A brief perspective is provided on the suitability of hydrothermal thin film capacitors for power supply applications.

  20. Hydrogenated nanocrystalline silicon germanium thin films

    NASA Astrophysics Data System (ADS)

    Yusoff, A. R. M.; Syahrul, M. N.; Henkel, K.

    2007-08-01

    Hydrogenated nanocrystalline silicon germanium thin films (nc-SiGe:H) is an interesting alternative material to replace hydrogenated nanocrystalline silicon (nc-Si:H) as the narrow bandgap absorber in an a-Si/a-SiGe/nc-SiGe(nc-Si) triple-junction solar cell due to its higher optical absorption in the wavelength range of interest. In this paper, we present results of optical, structural investigations and electrical characterization of nc-SiGe:H thin films made by hot-wire chemical vapor deposition (HWCVD) with a coil-shaped tungsten filament and with a disilane/germane/hydrogen gas mixture. The optical band gaps of a-SiGe:H and nc-SiGe:H thin-films, which are deposited with the same disilane/germane/hydrogen gas mixture ratio of 3.4:1.7:7, are about 1.58 eV and 2.1 eV, respectively. The nc-SiGe:H thin film exhibits a larger optical absorption coefficient of about 2-4 in the 600-900 nm range when compared to nc-Si:H thin film. Therefore, a thinner nc-SiGe:H layer of sim500 nm thickness may be sufficient for the narrow bandgap absorber in an a-Si based multiple-junction solar cell. We enhanced the transport properties as measured by the photoconductivity frequency mixing technique. These improved alloys do not necessarily show an improvement in the degree of structural heterogeneity on the nanometer scale as measured by small-angle X-ray scattering. Decreasing both the filament temperature and substrate temperature produced a film with relatively low structural heterogeneity while photoluminescence showed an order of magnitude increase in defect density for a similar change in the process.