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Sample records for grown nio thin

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

    SciTech Connect

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

    2011-03-01

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

  2. Growth mechanism of single-crystalline NiO thin films grown by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Roffi, Teuku Muhammad; Nozaki, Shinji; Uchida, Kazuo

    2016-10-01

    Nickel oxide (NiO) thin films were grown by atmospheric-pressure metal organic chemical vapor deposition (APMOCVD). Growth was carried out using various growth parameters, including the growth temperature, the input precursor (O2/Ni) ratio, and the type of substrate material. Effects of the growth parameters on the structural and electrical properties of the films were investigated. X-ray diffraction analysis revealed that the crystal structure and quality were strongly affected by the growth temperature and the type of substrate material. At an optimized growth temperature, single-crystalline NiO films were grown on MgO(100) and MgO(111) substrates in a cube-on-cube orientation relationship, while on an Al2O3(001) substrate, the film was grown in the NiO[111] direction. The use of MgO substrates successfully suppressed the formation of twin defects, which have been frequently reported in the growth of NiO. The difference in the formation of the twin defects on MgO and Al2O3 substrates was discussed. It was observed that the resistivity dependence on crystal quality was affected by the choice of substrate material. The effects of the precursor ratio on the transmittance and resistivity of the films were also investigated. Improved transparency in the visible wavelength region and higher conductivity were found in films grown with higher O2/Ni ratios.

  3. Surface electronic structure of polar NiO thin film grown on Ag(111)

    NASA Astrophysics Data System (ADS)

    Das, Jayanta; Menon, Krishnakumar S. R.

    2015-06-01

    The growth and structure of NiO thin films on top of Ag(111) substrate were studied where the formation of faceted surface was confirmed by Low Energy Electron Diffraction. The electronic structure of polar NiO(111) surface has been probed using photoemission techniques. The core energy levels and the valence band electronic structure were excited by x-ray and ultraviolet photons respectively. The modifications in physical structure and valence band electronic structure of the film under vacuum annealing have also been enlightened.

  4. Surface electronic structure of polar NiO thin film grown on Ag(111)

    SciTech Connect

    Das, Jayanta; Menon, Krishnakumar S. R.

    2015-06-24

    The growth and structure of NiO thin films on top of Ag(111) substrate were studied where the formation of faceted surface was confirmed by Low Energy Electron Diffraction. The electronic structure of polar NiO(111) surface has been probed using photoemission techniques. The core energy levels and the valence band electronic structure were excited by x-ray and ultraviolet photons respectively. The modifications in physical structure and valence band electronic structure of the film under vacuum annealing have also been enlightened.

  5. An analysis of the x-ray linear dichroism spectrum for NiO thin films grown on vicinal Ag(001)

    SciTech Connect

    Wu, Y.Z.; Zhao, Y.; Arenholz, E.; Young, A.T.; Sinkovic, B.; Qiu, Z.Q.

    2008-05-10

    Antiferromagnetic (AFM) NiO thin films are grown epitaxially on vicinal Ag(118) substrate and investigated by x-ray linear dichroism (XLD). We find that the NiO AFM spin exhibits an in-plane spin reorientation transition from parallel to perpendicular to the step edges with increasing the NiO film thickness. In addition to the conventional L{sub 2} adsorption edge, x-ray linear dichroism (XLD) effect at the Ni L{sub 3} adsorption edge is also measured and analyzed. The result identifies a small energy shift of the L{sub 3} peak. Temperature-dependent measurement confirms that the observed XLD effect in this system at the normal incidence of the x-rays originates entirely from the NiO magnetic ordering.

  6. Epitaxial NiO (1 0 0) and NiO (1 1 1) films grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Lindahl, E.; Lu, J.; Ottosson, M.; Carlsson, J.-O.

    2009-08-01

    Epitaxial NiO (1 1 1) and NiO (1 0 0) films have been grown by atomic layer deposition on both MgO (1 0 0) and α-Al 2O 3 (0 0 l) substrates at temperatures as low as 200 °C by using bis(2,2,6,6-tetramethyl-3,5-heptanedionato)Ni(II) and water as precursors. The films grown on the MgO (1 0 0) substrate show the expected cube on cube growth while the NiO (1 1 1) films grow with a twin rotated 180° on the α-Al 2O 3 (0 0 l) substrate surface. The films had columnar microstructures on both substrate types. The single grains were running throughout the whole film thickness and were significantly smaller in the direction parallel to the surface. Thin NiO (1 1 1) films can be grown with high crystal quality with a FWHM of 0.02-0.05° in the rocking curve measurements.

  7. Properties of NiO thin films deposited by intermittent spray pyrolysis process

    NASA Astrophysics Data System (ADS)

    Reguig, B. A.; Khelil, A.; Cattin, L.; Morsli, M.; Bernède, J. C.

    2007-02-01

    NiO thin films have been grown on glass substrates by intermittent spray pyrolysis deposition of NiCl 2·6H 2O diluted in distilled water, using a simple "perfume atomizer". The effect of the solution molarity on their properties was studied and compared to those of NiO thin films deposited with a classical spray system. It is shown that NiO thin films crystallized in the NiO structure are achieved after deposition. Whatever the precursor molarity, the grain size is around 25-30 nm. The crystallites are preferentially oriented along the (1 1 1) direction. All the films are p-type. However, the thickness and the conductivity of the NiO films depend on the precursor contraction. By comparison with the properties of films deposited by classical spray technique, it is shown that the critical precursor concentration, which induces strong thin films properties perturbations, is higher when a perfume atomizer is used. This broader stability domain can be attributed to better chlorides decomposition during the rest time used in the perfume atomizer technique.

  8. High-quality single crystalline NiO with twin phases grown on sapphire substrate by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Uchida, Kazuo; Yoshida, Ken-ichi; Zhang, Dongyuan; Koizumi, Atsushi; Nozaki, Shinji

    2012-12-01

    High-quality single crystalline twin phase NiO grown on sapphire substrates by metalorganic vapor phase epitaxy is reported. X-ray rocking curve analysis of NiO films grown at different temperatures indicates a minimum full width at half maximum of the cubic (111) diffraction peak of 0.107° for NiO film grown at as low as 550 °C. Detailed microstructural analysis by Φ scan X-ray diffraction and transmission electron microscopy reveal that the NiO film consists of large single crystalline domains with two different crystallographic orientations which are rotated relative to each other along the [111] axis by 60°. These single crystal domains are divided by the twin phase boundaries.

  9. Thickness dependent ferromagnetism in thermally decomposed NiO thin films

    NASA Astrophysics Data System (ADS)

    Ravikumar, Patta; Kisan, Bhagaban; Perumal, Alagarsamy

    2016-11-01

    We report the effects of film thickness, annealing temperature and annealing environments on thermal decomposition behavior and resulting magnetic properties of NiO (t=50-300 nm) thin films. All the NiO films were prepared directly on thermally oxidized Si at ambient temperature using magnetron sputtering technique and post annealed at different temperatures (TA) under vacuum and oxygen atmospheres. As-deposited films exhibit face centered cubic structure with large lattice constant due to strain induced during sputtering process. With increasing TA, the lattice constant decreases due to the release of strain and thickness dependent thermal decomposition reaction of NiO into Ni has been observed for the NiO films annealed at 500 °C under vacuum condition. As a result, the antiferromagnetic nature of the as-deposited NiO films transforms into ferromagnetic one with dominant thickness dependent ferromagnetic behavior at room temperature. In addition, the existence of both Ni and NiO phases in the annealed NiO films shows noticeable exchange bias under field cooling condition. The behavior of thermal decomposition was not observed for the NiO films annealed under oxygen condition which results in no detectable change in the magnetic properties. The observed results are discussed on the basis of thickness dependent thermal decomposition in NiO films with increasing TA and changing annealing conditions.

  10. Properties of Li-Doped NiO Thin Films Prepared by RF-Magnetron Sputtering.

    PubMed

    Kwon, Ho-Beom; Han, Joo-Hwan; Lee, Hee Young; Lee, Jai-Yeoul

    2016-02-01

    Li-doped NiO thin films were deposited on glass and c-axis (0001) sapphire single crystal substrates by radio frequency (RF)-niagnetron sputtering. The effects of the type of substrate, substrate temperature and atmosphere on the structural, electrical and optical properties of the NiO thin films were examined. The electrical conductivity of the NiO thin films depends on the type of substrate, substrate temperature and oxygen atmosphere. The electrical conductivity of the thin films on the glass and sapphire substrates was improved by the introduction of oxygen and decreased with increasing substrate temperature. The optical transmittance decreased with the introduction of oxygen and increased with increasing substrate temperature.

  11. A Thin Film of an Ni NiO Heterogeneous System for an Optical Recording Medium

    NASA Astrophysics Data System (ADS)

    Iida, Atsuko; Nishikawa, Reiji

    1994-07-01

    The authors have found a write once read many (WORM) type new optical recording medium of an Ni NiO heterogeneous system thin film. The structure of the recording medium is a single layer Ni NiO heterogeneous thin film on a transparent resin substrate. Irradiation of a converged laser diode beam causes a volume expansion of the film to form a swell. Information reading is done by using its reduction in reflectivity. The recordable composition region of this film is considered to be the transitive region from the metal to the oxide. The volume expansion is assumed to be induced by the oxidation of the Ni NiO heterogeneous thin film and the height of the swell is estimated. This value agrees well with the measured top height of the swell.

  12. Transformation from an atomically stepped NiO thin film to a nanotape structure: A kinetic study using x-ray diffraction

    SciTech Connect

    Sakata, Osami

    2008-12-15

    Transformation from an atomically stepped epitaxial thin film of NiO to a self-assemble nanotape structure at the step edge was observed in situ using synchrotron x-ray diffraction. The pristine NiO thin film was epitaxially grown on an ultrasmooth sapphire (0001) substrate with a regular step of 0.2 nm in height using laser molecular beam epitaxy. Transformation from the thin film to the nanotape structure was facilitated by postannealing in air from room temperature to 620 K. From the Arrhenius plot of ln(in-plane domain sizes) versus 1/T, an atomic-scale transformation energy of {approx}0.0135 eV/atom was derived.

  13. Properties of NiO thin films deposited by chemical spray pyrolysis using different precursor solutions

    NASA Astrophysics Data System (ADS)

    Cattin, L.; Reguig, B. A.; Khelil, A.; Morsli, M.; Benchouk, K.; Bernède, J. C.

    2008-07-01

    NiO thin films have been deposited by chemical spray pyrolysis using a perfume atomizer to grow the aerosol. The influence of the precursor, nickel chloride hexahydrate (NiCl 2·6H 2O), nickel nitrate hexahydrate (Ni(NO 3) 2·6H 2O), nickel hydroxide hexahydrate (Ni(OH) 2·6H 2O), nickel sulfate tetrahydrate (NiSO 4·4H 2O), on the thin films properties has been studied. In the experimental conditions used (substrate temperature 350 °C, precursor concentration 0.2-0.3 M, etc.), pure NiO thin films crystallized in the cubic phase can be achieved only with NiCl 2 and Ni(NO 3) 2 precursors. These films have been post-annealed at 425 °C for 3 h either in room atmosphere or under vacuum. If all the films are p-type, it is shown that the NiO films conductivity and optical transmittance depend on annealing process. The properties of the NiO thin films annealed under room atmosphere are not significantly modified, which is attributed to the fact that the temperature and the environment of this annealing is not very different from the experimental conditions during spray deposition. The annealing under vacuum is more efficient. This annealing being proceeded in a vacuum no better than 10 -2 Pa, it is supposed that the modifications of the NiO thin film properties, mainly the conductivity and optical transmission, are related to some interaction between residual oxygen and the films.

  14. Geometric structures of thin film: Pt on Pd(110) and NiO on Ni(100)

    SciTech Connect

    Warren, O.L.

    1993-07-01

    This thesis is divided into 3 papers: dynamical low-energy electron- diffraction investigation of lateral displacements in topmost layer of Pd(110); determination of (1{times}1) and (1{times}2) structures of Pt thin films on Pd(110) by dynamical low-energy electron-diffraction analysis; and structural determination of a NiO(111) film on Ni(100) by dynamical low-energy electron-diffraction analysis.

  15. Probing the redox states at the surface of electroactive nanoporous NiO thin films.

    PubMed

    Marrani, Andrea G; Novelli, Vittoria; Sheehan, Stephen; Dowling, Denis P; Dini, Danilo

    2014-01-01

    Nanoporous NiO thin film electrodes were obtained via plasma-assisted microwave sintering and characterized by means of a combination of electrochemical techniques and X-ray photoelectron spectroscopy (XPS). The aim of this study is the elucidation of the nature of the surface changes introduced by the redox processes of this nanostructured material. NiO undergoes two distinct electrochemical processes of oxidation in aqueous electrolyte with the progress of NiO anodic polarization. These findings are consistent with the sequential formation of oxyhydroxide species at the surface, the chemical nature of which was assessed by XPS. Electronic relaxation effects in the Ni 2p spectra clearly indicated that the superficial oxyhydroxide species resulted to be β-NiOOH and γ-NiOOH. We also show for the first time spectral evidence of an electrochemically generated Ni(IV) species. This study has direct relevance for those applications in which NiO electrodes are utilized in aqueous electrolyte, namely catalytic water splitting or electrochromism, and may constitute a starting point for the comprehension of electronic phenomena at the NiO/organic electrolyte interface of cathodic dye-sensitized solar cells (p-DSCs). PMID:24325361

  16. Effect of different nickel precursors on capacitive behavior of electrodeposited NiO thin films

    NASA Astrophysics Data System (ADS)

    Kore, R. M.; Ghadge, T. S.; Ambare, R. C.; Lokhande, B. J.

    2016-04-01

    In the present study, the effect of nickel precursors containing different anions like nitrate, chloride and sulphate on the morphology and pseudocapacitance behavior of NiO is investigated. The NiO samples were prepared by using a potentiondynamic electrodeposition technique in the three electrode cell. Cyclic voltammetry technique was exploited for potentiodynamic deposition of the films. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), etc. The XRD reveals the cubic crystal structure for all samples. The SEM micrograph shows nanoflakelike, up grown nanoflakes and honeycomb like nanostructured morphologies for nitrate, chloride and sulphate precursors respectively. The capacitive behavior of these samples was recorded using cyclic voltammetry (CV), charge-discharge and electrochemical impedance spectroscopy (EIS) in 1 M KOH electrolyte. The specific capacitance values of NiO samples obtained using CV for nitrate, chloride and sulphate precursors were 136, 214 and 893 Fg-1 respectively, at the scan rate of 5 mVs-1. The charge discharge study shows high specific energy for the sample obtained from sulphate (23.98 Whkg-1) as compared to chloride (9.67 Whkg-1) and nitrate (4.9 Whkg-1), whereas samples of cholride (13.9 kWkg-1 and nitrate (10.5 kWkg-1) shows comparatively more specific power than samples obtained from sulphate (7.6 kWkg-1). The equivalent series resistance of NiO samples observed from EIS study are 1.34, 1.29 and 1.27 Ω respectively for nitrate, chloride and sulphate precursors. These results emphasizes that the samples obtained from sulphate precursors provides very low impedance through honeycomb like nanostructured morphology which supports good capacitive behavior of NiO.

  17. Electronic and magnetic structure of epitaxial Fe3O4(001 ) /NiO heterostructures grown on MgO(001) and Nb-doped SrTiO3(001 )

    NASA Astrophysics Data System (ADS)

    Kuepper, K.; Kuschel, O.; Pathé, N.; Schemme, T.; Schmalhorst, J.; Thomas, A.; Arenholz, E.; Gorgoi, M.; Ovsyannikov, R.; Bartkowski, S.; Reiss, G.; Wollschläger, J.

    2016-07-01

    We study the underlying chemical, electronic, and magnetic properties of a number of magnetite-based thin films. The main focus is placed onto Fe3O4 (001)/NiO bilayers grown on MgO(001) and Nb-SrTiO3(001) substrates. We compare the results with those obtained on pure Fe3O4 (001) thin films. It is found that the magnetite layers are oxidized and Fe3 + dominates at the surfaces due to maghemite (γ -Fe2O3 ) formation, which decreases with increasing magnetite layer thickness. For layer thicknesses of around 20 nm and above, the cationic distribution is close to that of stoichiometric Fe3O4 . At the interface between NiO and Fe3O4 we find the Ni to be in a divalent valence state, with unambiguous spectral features in the Ni 2 p core level x-ray photoelectron spectra typical for NiO. The formation of a significant NiFe2O4 interlayer can be excluded by means of x-ray magnetic circular dichroism. Magneto-optical Kerr effect measurements reveal significant higher coercive fields compared to magnetite thin films grown on MgO(001), and an altered in-plane easy axis pointing in the <100 > direction. We discuss the spin magnetic moments of the magnetite layers and find that a thickness of 20 nm or above leads to spin magnetic moments close to that of bulk magnetite.

  18. Facile Route to NiO Nanostructured Electrode Grown by Oblique Angle Deposition Technique for Supercapacitors.

    PubMed

    Kannan, Vasudevan; Inamdar, Akbar I; Pawar, Sambaji M; Kim, Hyun-Seok; Park, Hyun-Chang; Kim, Hyungsang; Im, Hyunsik; Chae, Yeon Sik

    2016-07-13

    We report an efficient method for growing NiO nanostructures by oblique angle deposition (OAD) technique in an e-beam evaporator for supercapacitor applications. This facile physical vapor deposition technique combined with OAD presents a unique, direct, and economical route for obtaining high width-to-height ratio nanorods for supercapacitor electrodes. The NiO nanostructure essentially consists of nanorods with varying dimensions. The sample deposited at OAD 75° showed highest supercapacitance value of 344 F/g. NiO nanorod electrodes exhibits excellent electrochemical stability with no degradation in capacitance after 5000 charge-discharge cycles. The nanostructured film adhered well to the substrate and had 131% capacity retention. Peak energy density and power density of the NiO nanorods were 8.78 Wh/kg and 2.5 kW/kg, respectively. This technique has potential to be expanded for growing nanostructured films of other interesting metal/metal oxide candidates for supercapacitor applications. PMID:27322601

  19. Fabrication of NiO thin film electrode for supercapacitor applications

    SciTech Connect

    Mali, V. V.; Navale, S. T.; Chougule, M. A.; Khuspe, G. D.; Godse, P. R.; Patil, V. B.; Pawar, S. A.

    2014-04-24

    Nanocrystalline NiO electrode is successfully electrosynthesized for supercapacitor application. The nanocrystalline NiO electrode is characterized using scanning electron microscope (SEM). Nickel oxide is a highly porous and the film surface looked smooth and composed of fine elongated particles. The supercapacitive performance of NiO electrode is tested using cyclic voltammetry (C-V) technique in 0.5M Na{sub 2}S{sub 2}O{sub 3} electrolyte within potential range of −1.2 to +1.2 V. The effect of scan rate on the capacitance of NiO electrode is studied. The highest specific capacitance of 439 Fg{sup −1} at the voltage scan rate of 50mVs{sup −1} is achieved. Additionally stability and charging–discharging of NiO electrode are studied.

  20. Electrical properties of undoped and Li-doped NiO thin films deposited by RF sputtering without intentional heating

    NASA Astrophysics Data System (ADS)

    Sugiyama, Mutsumi; Nakai, Hiroshi; Sugimoto, Gaku; Yamada, Aika; Chichibu, Shigefusa F.

    2016-08-01

    The fundamental transmittance and electrical properties of undoped and Li-doped NiO thin films deposited by conventional RF sputtering without intentional heating were evaluated. Both the transmittance and resistivity of undoped and Li-doped NiO decreased with increasing O2 fraction in the sputtering gas, f(O2) = O2/(Ar + O2). The result is attributed to the increase in the concentration of acceptors of Ni vacancies (VNi) under oxygen-rich growth conditions. In addition to VNi, Li atom on the Ni site (LiNi) likely acts as a shallow accepter, which can explain the experimental finding that the carrier concentration of Li-doped NiO was approximately three orders of magnitude higher than that of the undoped case deposited under the same f(O2). The mobility of NiO was remarkably low (around 0.1–1.0 cm2 V‑1 s‑1) and almost independent of f(O2) or the amount of doping, reflecting the large hole effective mass.

  1. thin films grown with additional NaF layers

    NASA Astrophysics Data System (ADS)

    Kim, Gee Yeong; Kim, Juran; Jo, William; Son, Dae-Ho; Kim, Dae-Hwan; Kang, Jin-Kyu

    2014-10-01

    CZTS precursors [SLG/Mo (300 nm)/ZnS (460 nm)/SnS (480 nm)/Cu (240 nm)] were deposited by RF/DC sputtering, and then NaF layers (0, 15, and 30 nm) were grown by electron beam evaporation. The precursors were annealed in a furnace with Se metals at 590°C for 20 minutes. The final composition of the CZTSSe thin-films was of Cu/(Zn + Sn) ~ 0.88 and Zn/Sn ~ 1.05, with a metal S/Se ratio estimated at ~0.05. The CZTSSe thin-films have different NaF layer thicknesses in the range from 0 to 30 nm, achieving a ~3% conversion efficiency, and the CZTSSe thin-films contain ~3% of Na. Kelvin probe force microscopy was used to identify the local potential difference that varied according to the thickness of the NaF layer on the CZTSSe thin-films. The potential values at the grain boundaries were observed to increase as the NaF thickness increased. Moreover, the ratio of the positively charged GBs in the CZTSSe thin-films with an NaF layer was higher than that of pure CZTSSe thin-films. A positively charged potential was observed around the grain boundaries of the CZTSSe thin-films, which is a beneficial characteristic that can improve the performance of a device.

  2. Anisotropic magnetothermopower in ferromagnetic thin films grown on macroscopic substrates

    NASA Astrophysics Data System (ADS)

    Jayathilaka, P. B.; Belyea, D. D.; Fawcett, T. J.; Miller, Casey W.

    2015-05-01

    We report observing the anisotropic magnetothermopower in a variety of ferromagnetic thin films grown on macroscopic substrates. These measurements were enabled by eliminating spurious signals related to the Anomalous Nernst Effect by butt-mounting the sample to the heat source and sink, and appropriate positioning of electrical contacts to avoid unwanted thermal gradients. This protocol enabled detailed measurements of the magnetothermopower in the transverse and longitudinal configurations. This may enable Spin Seebeck Effect studies in the in-plane geometry.

  3. InSb thin films grown by electrodeposition

    SciTech Connect

    Singh, Joginder Rajaram, P.

    2014-04-24

    We have grown InSb thin films on Cu substrates using the electrodeposition technique. The electrochemical bath from which the InSb thin films were grown was made up of a mixture of aqueous solutions of 0.05 M InCl{sub 3} and 0.03M SbCl{sub 3}, 0 .20M citric acid and 0.30M sodium citrate. Citric acid and sodium citrate were used as complexing agents to bring the reduction potential of In and Sb closer to maintain binary growth. The electrodeposited films were characterized by structural, morphological and optical studies. X-ray diffraction studies show that the films are polycrystalline InSb having the zinc blende structure. Scanning electron microscopy (SEM) studies reveal that the surface of the films is uniformly covered with submicron sized spherical particles. FTIR spectra of InSb thin films show a sharp absorption peak at wave number 1022 cm{sup −1} corresponding to the band gap. Hot probe analysis shows that the InSb thin films have p type conductivity.

  4. InSb thin films grown by electrodeposition

    NASA Astrophysics Data System (ADS)

    Singh, Joginder; Rajaram, P.

    2014-04-01

    We have grown InSb thin films on Cu substrates using the electrodeposition technique. The electrochemical bath from which the InSb thin films were grown was made up of a mixture of aqueous solutions of 0.05 M InCl3 and 0.03M SbCl3, 0 .20M citric acid and 0.30M sodium citrate. Citric acid and sodium citrate were used as complexing agents to bring the reduction potential of In and Sb closer to maintain binary growth. The electrodeposited films were characterized by structural, morphological and optical studies. X-ray diffraction studies show that the films are polycrystalline InSb having the zinc blende structure. Scanning electron microscopy (SEM) studies reveal that the surface of the films is uniformly covered with submicron sized spherical particles. FTIR spectra of InSb thin films show a sharp absorption peak at wave number 1022 cm-1 corresponding to the band gap. Hot probe analysis shows that the InSb thin films have p type conductivity.

  5. Fabrication of hetero-junction diode using NiO thin film on ITO/glass substrate

    NASA Astrophysics Data System (ADS)

    Soni, Sonali; Sharma, Vinay; Kuanr, Bijoy K.

    2016-05-01

    Fabrication, characterization and testing of hetero-junctions of NiO thin films were done. Nickel films were evaporated on polished ITO coated glass substrates using thermal deposition. The films were annealed at high temperatures in the presence of oxygen to obtain NiO films. The rectifying current-voltage (I-V) properties confirmed that a hetero-junction diode was successfully formed. The AC and DC behavior of hetero-junction using DC silver-probes were determined. The threshold voltage, ideality factor and reverse saturation current of hetero junction were determined. We have compared these I-V characteristics with semiconducting PN junction diode. To test the device characteristics, we used the structure as a diode clipper at various frequencies. It is showed that our device is a better high-frequency junction-device than a normal PN junction diode.

  6. Preparation and electrochemical characterization of NiO nanostructure-carbon nanowall composites grown on carbon cloth

    NASA Astrophysics Data System (ADS)

    Chang, Hsuan-Chen; Chang, Hsin-Yueh; Su, Wei-Jhih; Lee, Kuei-Yi; Shih, Wen-Ching

    2012-09-01

    This study provided a simple method to form NiO nanostructures onto the carbon nanowalls (CNWs) surface to enhance the performance of electric double layer capacitor (EDLC) characteristics. The CNWs were synthesized on carbon cloth by rf magnetron sputtering without any catalyst. Ni film was then deposited on the synthesized CNWs by e-beam evaporator. Subsequently, the vacuum annealing process and oxygen plasma treatment were used to form the NiO nanostructures. The crystallize structures of NiO nanostructures and CNWs were examined by Raman scattering spectroscopy. To realize the electrochemical properties of NiO/CNWs/carbon cloth composite, cyclic voltammetry (CV) and galvanostatic charge-discharge tests were investigated. Due to the relatively larger surface area of CNWs and the quickly reversible redox reaction and pseudo-capacitive properties of NiO nanostructures, the measured results demonstrated that the NiO/CNWs/carbon cloth is a suitable electrode material for EDLC applications.

  7. Metastable oxygen incorporation into thin film NiO by low temperature active oxidation: Influence on hole conduction

    SciTech Connect

    Aydogdu, Gulgun H.; Ruzmetov, Dmitry; Ramanathan, Shriram

    2010-12-01

    The ability to controllably tune cation valence state and resulting electrical conductivity of transition metal-oxides such as NiO is of great interest for a range of solid state electronic and energy devices and more recently in understanding electron correlation phenomena at complex oxide interfaces. Here, we demonstrate that it is possible to enhance electrical conductivity of NiO thin films by one order of magnitude by photoexcitation and three orders of magnitude by ozone treatment at as low as 310 K. The change occurs within nearly 2000 s and, thereafter, reaches a self-limiting value. A surprising difference is seen at 400 K: ultraviolet photon and ozone treatments cause only a marginal reduction in resistance in the first few minutes and, then, the resistance begins to increase and recovers its original value. This unusual reversal is explained by considering metastable incorporation of oxygen in NiO and oxygen equilibration with the environment. Variation in nickel valence state prior to and after photoexcitation and ozone treatment, investigated by x-ray photoelectron spectroscopy, provides mechanistic insights into resistance trends. This study demonstrates photon-assisted and ozone oxidation as effective low temperature routes to tune the electrical properties as well as metastably incorporate oxygen into oxides with direct influence on electrical conduction properties.

  8. Applying computational nanomaterials design to the reactive ion etching of NiO thin films—a preliminary investigation

    NASA Astrophysics Data System (ADS)

    David, M.; Muhida, R.; Roman, T.; Kunikata, S.; Diño, W. A.; Nakanishi, H.; Kasai, H.; Takano, F.; Shima, H.; Akinaga, H.

    2007-09-01

    We have developed and proposed a model for reactive ion etching (RIE) process design of nickel oxide thin films using a computational materials design based on ab initio calculations. On etching NiO, we found that it was necessary to have hydrogen-based reactive gases in the initial state in order to enhance RIE (e.g. NH3, CH4). We strongly suggest the use of CH4 or any H-based gas source other than CHF3 to enhance RIE process.

  9. NiO nanosheets grown on graphene nanosheets as superior anode materials for Li-ion batteries

    NASA Astrophysics Data System (ADS)

    Zou, Yuqin; Wang, Yong

    2011-06-01

    This paper reports a hydrothermal preparation of NiO-graphene sheet-on-sheet and nanoparticle-on-sheet nanostructures. The sheet-on-sheet nanocomposite showed highly reversible large capacities at a common current of 0.1 C and good rate capabilities. A large initial charge capacity of 1056 mAh/g was observed for the sheet-on-sheet composite at 0.1 C, which decreased by only 2.4% to 1031 mAh/g after 40 cycles of discharge and charge. This cycling performance is better than that of NiO nanosheets, graphene nanosheets, NiO-graphene nanoparticle-on-sheet, and previous carbon/carbon nanotube supported NiO composites. It is believed that the mechanical stability and electrical conductivity of NiO nanosheets are increased by graphene nanosheets (GNS), the aggregation or restacking of which to graphite platelets are, on the other hand, effectively prevented by NiO nanosheets.

  10. An ultra-thin, un-doped NiO hole transporting layer of highly efficient (16.4%) organic-inorganic hybrid perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Seo, Seongrok; Park, Ik Jae; Kim, Myungjun; Lee, Seonhee; Bae, Changdeuck; Jung, Hyun Suk; Park, Nam-Gyu; Kim, Jin Young; Shin, Hyunjung

    2016-06-01

    NiO is a wide band gap p-type oxide semiconductor and has potential for applications in solar energy conversion as a hole-transporting layer (HTL). It also has good optical transparency and high chemical stability, and the capability of aligning the band edges to the perovskite (CH3NH3PbI3) layers. Ultra-thin and un-doped NiO films with much less absorption loss were prepared by atomic layer deposition (ALD) with highly precise control over thickness without any pinholes. Thin enough (5-7.5 nm in thickness) NiO films with the thickness of few time the Debye length (LD = 1-2 nm for NiO) show enough conductivities achieved by overlapping space charge regions. The inverted planar perovskite solar cells with NiO films as HTLs exhibited the highest energy conversion efficiency of 16.40% with high open circuit voltage (1.04 V) and fill factor (0.72) with negligible current-voltage hysteresis.NiO is a wide band gap p-type oxide semiconductor and has potential for applications in solar energy conversion as a hole-transporting layer (HTL). It also has good optical transparency and high chemical stability, and the capability of aligning the band edges to the perovskite (CH3NH3PbI3) layers. Ultra-thin and un-doped NiO films with much less absorption loss were prepared by atomic layer deposition (ALD) with highly precise control over thickness without any pinholes. Thin enough (5-7.5 nm in thickness) NiO films with the thickness of few time the Debye length (LD = 1-2 nm for NiO) show enough conductivities achieved by overlapping space charge regions. The inverted planar perovskite solar cells with NiO films as HTLs exhibited the highest energy conversion efficiency of 16.40% with high open circuit voltage (1.04 V) and fill factor (0.72) with negligible current-voltage hysteresis. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01601d

  11. Effects of anode materials on resistive characteristics of NiO thin films

    SciTech Connect

    Jia, Ze; Wang, Linkai; Zhang, Naiwen; Ren, Tianling; Liou, Juin J.

    2013-01-28

    This letter shows that the NiO-based structure with different anodes has different resistive switching properties. A conical conductive filament (CF) model is proposed for oxygen vacancies distributed in NiO films. Modeling analysis reveals much larger dissolution velocity of CF near anodes than near cathodes during the reset process. Different interfaces shown in Auger electron spectroscopy can be bound with the model to reveal that CF is dissolved in the structure with Pt or Au as anodes, while CF remains constant if the anode material is Ti or Al, which can explain whether switching properties occur in the specific NiO-based structures.

  12. An ultra-thin, un-doped NiO hole transporting layer of highly efficient (16.4%) organic-inorganic hybrid perovskite solar cells.

    PubMed

    Seo, Seongrok; Park, Ik Jae; Kim, Myungjun; Lee, Seonhee; Bae, Changdeuck; Jung, Hyun Suk; Park, Nam-Gyu; Kim, Jin Young; Shin, Hyunjung

    2016-06-01

    NiO is a wide band gap p-type oxide semiconductor and has potential for applications in solar energy conversion as a hole-transporting layer (HTL). It also has good optical transparency and high chemical stability, and the capability of aligning the band edges to the perovskite (CH3NH3PbI3) layers. Ultra-thin and un-doped NiO films with much less absorption loss were prepared by atomic layer deposition (ALD) with highly precise control over thickness without any pinholes. Thin enough (5-7.5 nm in thickness) NiO films with the thickness of few time the Debye length (LD = 1-2 nm for NiO) show enough conductivities achieved by overlapping space charge regions. The inverted planar perovskite solar cells with NiO films as HTLs exhibited the highest energy conversion efficiency of 16.40% with high open circuit voltage (1.04 V) and fill factor (0.72) with negligible current-voltage hysteresis.

  13. An ultra-thin, un-doped NiO hole transporting layer of highly efficient (16.4%) organic-inorganic hybrid perovskite solar cells.

    PubMed

    Seo, Seongrok; Park, Ik Jae; Kim, Myungjun; Lee, Seonhee; Bae, Changdeuck; Jung, Hyun Suk; Park, Nam-Gyu; Kim, Jin Young; Shin, Hyunjung

    2016-06-01

    NiO is a wide band gap p-type oxide semiconductor and has potential for applications in solar energy conversion as a hole-transporting layer (HTL). It also has good optical transparency and high chemical stability, and the capability of aligning the band edges to the perovskite (CH3NH3PbI3) layers. Ultra-thin and un-doped NiO films with much less absorption loss were prepared by atomic layer deposition (ALD) with highly precise control over thickness without any pinholes. Thin enough (5-7.5 nm in thickness) NiO films with the thickness of few time the Debye length (LD = 1-2 nm for NiO) show enough conductivities achieved by overlapping space charge regions. The inverted planar perovskite solar cells with NiO films as HTLs exhibited the highest energy conversion efficiency of 16.40% with high open circuit voltage (1.04 V) and fill factor (0.72) with negligible current-voltage hysteresis. PMID:27216291

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

    PubMed Central

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

    2015-01-01

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

  15. Multiferroic YCrO3 thin films grown on glass substrate: Resistive switching characteristics

    NASA Astrophysics Data System (ADS)

    Seo, Jeongdae; Ahn, Yoonho; Son, Jong Yeog

    2016-01-01

    Polycrystalline YCrO3 thin films were deposited on (111) Pt/Ta/glass substrates by pulsed laser deposition. The YCrO3 thin films exhibited good ferroelectric properties with remnant polarization of about 5 µC/cm2. Large leakage current was observed by I- V curve and ferroelectric hysteresis loop. The YCrO3 resistive random access memory (RRAM) capacitor showed unipolar switching behaviors with SET and RESET voltages higher than those of general NiO RRAM capacitors. [Figure not available: see fulltext.

  16. Creatinine biomaterial thin films grown by laser techniques.

    PubMed

    György, E; Axente, E; Mihailescu, I N; Predoi, D; Ciuca, S; Neamtu, J

    2008-03-01

    Creatinine thin films were synthesised by matrix assisted pulsed laser deposition (PLD) techniques for enzyme-based biosensor applications. An UV KrF* (lambda=248 nm, tau approximately 10 ns) excimer laser source was used for the irradiation of the targets at incident fluence values in the 0.3-0.5 J/cm2 range. For the matrix assisted PLD the targets consisted on a frozen composite obtained by dissolving the biomaterials in distilled water. The surface morphology, chemical composition and structure of the obtained biomaterial thin films were investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, and electron dispersive X-ray spectroscopy as a function of the target preparation procedure and incident laser fluence.

  17. Study of high [Tc] superconducting thin films grown by MOCVD

    SciTech Connect

    Erbil, A.

    1990-01-01

    Work is described briefly, which was carried out on development of techniques to grow metal-semiconductor superlattices (artificially layered materials) and on the copper oxide based susperconductors (naturally layered materials). The current growth technique utilized is metalorganic chemical vapor deposition (MOCVD). CdTe, PbTe, La, LaTe, and Bi[sub 2]Te[sub 3] were deposited, mostly on GaAs. Several YBa[sub 2]Cu[sub 3]O[sub 7] compounds were obtained with possible superconductivity at temperatures up to 550 K (1 part in 10[sup 4]). YBa[sub 2]Cu[sub 3]O[sub 7[minus]x] and Tl[sub 2]CaBa[sub 2]Cu[sub 2]O[sub y] thin films were deposited by MOCVD on common substrates such as glass.

  18. Thin film transistors using PECVD-grown carbon nanotubes.

    PubMed

    Ono, Yuki; Kishimoto, Shigeru; Ohno, Yutaka; Mizutani, Takashi

    2010-05-21

    Thin film transistors with a carbon nanotube (CNT) network as a channel have been fabricated using grid-inserted plasma-enhanced chemical vapor deposition (PECVD) which has the advantage of preferential growth of the CNTs with semiconducting behavior in the I-V characteristics of CNT field effect transistors (CNT-FETs). Taking advantage of the preferential growth and suppression of bundle formation, a large ON current of 170 microA mm(-1), which is among the largest in these kinds of devices with a large ON/OFF current ratio of about 10(5), has been realized in the relatively short channel length of 10 microm. The field effect mobility of the device was 5.8 cm(2) V(-1) s(-1). PMID:20418603

  19. Thin film transistors using PECVD-grown carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Ono, Yuki; Kishimoto, Shigeru; Ohno, Yutaka; Mizutani, Takashi

    2010-05-01

    Thin film transistors with a carbon nanotube (CNT) network as a channel have been fabricated using grid-inserted plasma-enhanced chemical vapor deposition (PECVD) which has the advantage of preferential growth of the CNTs with semiconducting behavior in the I-V characteristics of CNT field effect transistors (CNT-FETs). Taking advantage of the preferential growth and suppression of bundle formation, a large ON current of 170 µA mm - 1, which is among the largest in these kinds of devices with a large ON/OFF current ratio of about 105, has been realized in the relatively short channel length of 10 µm. The field effect mobility of the device was 5.8 cm2 V - 1 s - 1.

  20. Significance of microstructure for a MOCVD-grown YSZ thin film gas sensor

    SciTech Connect

    Vetrone, J.; Foster, C.; Bai, G.

    1996-11-01

    The authors report the fabrication and characterization of a low temperature (200--400 C) thin film gas sensor constructed from a MOCVD-grown yttria-stabilized zirconia (YSZ) layer sandwiched between two platinum thin film electrodes. A reproducible gas-sensing response is produced by applying a cyclic voltage which generates voltammograms with gas-specific current peaks and shapes. Growth conditions are optimized for preparing YSZ films having dense microstructures, low leakage currents, and maximum ion conductivities. In particular, the effect of growth temperature on film morphology and texture is discussed and related to the electrical and gas-sensing properties of the thin film sensor device.

  1. Polarity and microstructure in InN thin layers grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Kuwano, N.; Nakahara, Y.; Amano, H.

    2006-06-01

    Microstructures in InN grown on sapphire (0001) and yttria-stabilized zirconia (YSZ) (111) by metal-organic vapor phase epitaxy (MOVPE) were analyzed by means of transmission electron microscopy (TEM) in order to clarify the growth process. Special attention was paid to the selectivity of the crystal polarity of InN. The InN thin films grown on sapphire after nitridation has a flat surface while those grown on YSZ has hillocks on the surface. The crystal polarity was determined by comparing the experimentally observed intensity distribution in convergent beam electron diffraction (CBED) disks with those simulated by the Broch-wave method. It was found that the InN grown on the sapphire has a nitrogen-polarity and the one on YSZ has a mixture of In- and N-polarities. The effect of surface-nitridation of sapphire on the growth process is also discussed

  2. Strain induced modulation of the correlated transport in epitaxial Sm0.5Nd0.5NiO3 thin films

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Gardner, H. J.; Chen, X. G.; Singh, V. R.; Hong, X.

    2015-04-01

    We report a study of the effect of epitaxial strain on the correlated transport properties of 2-40 nm Sm0.5Nd0.5NiO3 (SNNO) films grown on different substrates. The metal-insulator transition (MIT) temperature TMI of the SNNO films increases with increasing tensile strain. While films on (0 0 1) LaAlO3 and (1 1 0) NdGaO3 substrates exhibit a sharp MIT and thermal hysteresis in the cooling-heating cycle, signaling a first-order transition, films on (0 0 1) SrTiO3 show a broad, second-order MIT. Hall effect measurements reveal hole-type charge carriers and thermally activated temperature dependence of the carrier density below TMI. The corresponding activation energy is ˜80 meV for films on LaAlO3 and NdGaO3, and is suppressed to 25 meV for films on SrTiO3. The carrier mobility in the metallic state and variable range hopping (VRH) transport at a low temperature point significantly enhanced electron localization in SNNO on STO, which we believe is not simply driven by extrinsic effects such as oxygen vacancies, but rather is an intrinsic characteristic for films subject to tensile strain due to the elongated Ni-O bond and hence enhanced dynamic Jahn-Teller distortion. In ultrathin films above the electrical dead layer thickness (2-3 nm), we observe a more than 100 K increase of TMI for films on LaAlO3, which has been correlated with a crossover from 3D to 2D transport as revealed from VRH. We attribute the distinct transport characteristics to strain induced modulation of various energy scales associated with the Ni-O-Ni bond angle and Ni-O bond length, which collectively determine the delocalization bandwidth of the system.

  3. Uniform GaN thin films grown on (100) silicon by remote plasma atomic layer deposition.

    PubMed

    Shih, Huan-Yu; Lin, Ming-Chih; Chen, Liang-Yih; Chen, Miin-Jang

    2015-01-01

    The growth of uniform gallium nitride (GaN) thin films was reported on (100) Si substrate by remote plasma atomic layer deposition (RP-ALD) using triethylgallium (TEG) and NH3 as the precursors. The self-limiting growth of GaN was manifested by the saturation of the deposition rate with the doses of TEG and NH3. The increase in the growth temperature leads to the rise of nitrogen content and improved crystallinity of GaN thin films, from amorphous at a low deposition temperature of 200 °C to polycrystalline hexagonal structures at a high growth temperature of 500 °C. No melting-back etching was observed at the GaN/Si interface. The excellent uniformity and almost atomic flat surface of the GaN thin films also infer the surface control mode of the GaN thin films grown by the RP-ALD technique. The GaN thin films grown by RP-ALD will be further applied in the light-emitting diodes and high electron mobility transistors on (100) Si substrate.

  4. Inverted fractal analysis of TiOx thin layers grown by inverse pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Égerházi, L.; Smausz, T.; Bari, F.

    2013-08-01

    Inverted fractal analysis (IFA), a method developed for fractal analysis of scanning electron microscopy images of cauliflower-like thin films is presented through the example of layers grown by inverse pulsed laser deposition (IPLD). IFA uses the integrated fractal analysis module (FracLac) of the image processing software ImageJ, and an objective thresholding routine that preserves the characteristic features of the images, independently of their brightness and contrast. IFA revealed fD = 1.83 ± 0.01 for TiOx layers grown at 5-50 Pa background pressures. For a series of images, this result was verified by evaluating the scaling of the number of still resolved features on the film, counted manually. The value of fD not only confirms the fractal structure of TiOx IPLD thin films, but also suggests that the aggregation of plasma species in the gas atmosphere may have only limited contribution to the deposition.

  5. Flexible cadmium telluride thin films grown on electron-beam-irradiated graphene/thin glass substrates

    SciTech Connect

    Seo, Won-Oh; Kim, Jihyun; Koo, Yong Hwan; Kim, Byungnam; Lee, Byung Cheol; Kim, Donghwan

    2014-08-25

    We demonstrate the close-spaced sublimation growth of polycrystalline cadmium telluride (CdTe) thin films on a flexible graphene electrode/thin glass substrate structure. Prior to the growth of CdTe films, chemical-vapor-deposited graphene was transferred onto a flexible glass substrate and subjected to electron-beam irradiation at an energy of 0.2 MeV in order to intentionally introduce the defects into it in a controlled manner. Micro-Raman spectroscopy and sheet resistance measurements were employed to monitor the damage and disorder in the electron-beam irradiated graphene layers. The morphology and optical properties of the CdTe thin films deposited on a graphene/flexible glass substrate were systematically characterized. The integration of the defective graphene layers with a flexible glass substrate can be a useful platform to grow various thin-film structures for flexible electronic and optoelectronic devices.

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

    SciTech Connect

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

    2011-01-01

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

  7. From Fe3O4 /NiO bilayers to NiFe2O4 -like thin films through Ni interdiffusion

    NASA Astrophysics Data System (ADS)

    Kuschel, O.; Buß, R.; Spiess, W.; Schemme, T.; Wöllermann, J.; Balinski, K.; N'Diaye, A. T.; Kuschel, T.; Wollschläger, J.; Kuepper, K.

    2016-09-01

    Ferrites with (inverse) spinel structure display a large variety of electronic and magnetic properties, making some of them interesting for potential applications in spintronics. We investigate the thermally induced interdiffusion of Ni2 + ions out of NiO into Fe3O4 ultrathin films, resulting in off-stoichiometric nickel ferrite-like thin layers. We synthesized epitaxial Fe3O4 /NiO bilayers on Nb-doped SrTiO3(001) substrates by means of reactive molecular beam epitaxy. Subsequently, we performed an annealing cycle comprising three steps at temperatures of 400 ∘C , 600 ∘C , and 800 ∘C under an oxygen background atmosphere. We studied the changes of the chemical and electronic properties as result of each annealing step with help of hard x-ray photoelectron spectroscopy and found a rather homogeneous distribution of Ni and Fe cations throughout the entire film after the overall annealing cycle. For one sample we observed a cationic distribution close to that of the spinel ferrite NiFe2O4 . Further evidence comes from low-energy electron diffraction patterns indicating a spinel-type structure at the surface after annealing. Site- and element-specific hysteresis loops performed by x-ray magnetic circular dichroism uncovered the antiferrimagnetic alignment between the octahedral coordinated Ni2 + and Fe3 + ions and the Fe3 + ion in tetrahedral coordination. We find a quite low coercive field of 0.02 T, indicating a rather low defect concentration within the thin ferrite films.

  8. Amorphous indium gallium zinc oxide thin film grown by pulse laser deposition technique

    NASA Astrophysics Data System (ADS)

    Mistry, Bhaumik V.; Joshi, U. S.

    2016-05-01

    Highly electrically conducting and transparent in visible light IGZO thin film were grown on glass substrate at substrate temperature of 400 C by a pulse laser deposition techniques. Structural, surface, electrical, and optical properties of IGZO thin films were investigated at room temperature. Smooth surface morphology and amorphous nature of the film has been confirmed from the AFM and GIXRD analysis. A resistivity down to 7.7×10-3 V cm was reproducibly obtained while maintaining optical transmission exceeding 70% at wavelengths from 340 to 780 nm. The carrier densities of the film was obtain to the value 1.9×1018 cm3, while the Hall mobility of the IGZO thin film was 16 cm2 V-1S-1.

  9. Biomolecular papain thin films grown by matrix assisted and conventional pulsed laser deposition: A comparative study

    NASA Astrophysics Data System (ADS)

    György, E.; Pérez del Pino, A.; Sauthier, G.; Figueras, A.

    2009-12-01

    Biomolecular papain thin films were grown both by matrix assisted pulsed laser evaporation (MAPLE) and conventional pulsed laser deposition (PLD) techniques with the aid of an UV KrF∗ (λ =248 nm, τFWHM≅20 ns) excimer laser source. For the MAPLE experiments the targets submitted to laser radiation consisted on frozen composites obtained by dissolving the biomaterial powder in distilled water at 10 wt % concentration. Conventional pressed biomaterial powder targets were used in the PLD experiments. The surface morphology of the obtained thin films was studied by atomic force microscopy and their structure and composition were investigated by Fourier transform infrared spectroscopy. The possible physical mechanisms implied in the ablation processes of the two techniques, under comparable experimental conditions were identified. The results showed that the growth mode, surface morphology as well as structure of the deposited biomaterial thin films are determined both by the incident laser fluence value as well as target preparation procedure.

  10. Raman spectroscopy of ZnMnO thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Orozco, S.; Riascos, H.; Duque, S.

    2016-02-01

    ZnMnO thin films were grown by Pulsed Laser Deposition (PLD) technique onto Silicon (100) substrates at different growth conditions. Thin films were deposited varying Mn concentration, substrate temperature and oxygen pressure. ZnMnO samples were analysed by using Raman Spectroscopy that shows a red shift for all vibration modes. Raman spectra revealed that nanostructure of thin films was the same of ZnO bulk, wurzite hexagonal structure. The structural disorder was manifested in the line width and shape variations of E2(high) and E2(low) modes located in 99 and 434cm-1 respectively, which may be due to the incorporation of Mn ions inside the ZnO crystal lattice. Around 570cm-1 was found a peak associated to E1(LO) vibration mode of ZnO. 272cm-1 suggest intrinsic host lattice defects. Additional mode centred at about 520cm-1 can be overlap of Si and Mn modes.

  11. Characterization of nanostructured iron selenide thin films grown by chemical route at room temperature

    SciTech Connect

    Ubale, A.U.; Sakhare, Y.S.; Belkedkar, M.R.; Singh, Arvind

    2013-02-15

    Highlights: ► Nanostructured FeSe thin films were successfully synthesized at room temperature by CBD method. ► The XRD and EDAX characterization confirms nanocrystalline nature of FeSe. ► The SEM and AFM show microporous morphology with nanorods and nanoplates of FeSe. -- Abstract: Iron selenide thin films have been deposited onto glass substrates by using chemical bath deposition technique. Structural characterization of iron selenide thin films was carried out by means of X-ray diffraction and Fourier transforms infrared spectrum. The morphological characterization of FeSe thin film was carried out using scanning electron microscopy and atomic force microscopy, which revealed porous grain morphology of FeSe with some nano rectangular rods and plates grown on it. The as-deposited thin films exhibited optical band gap energy 2.60 eV. The as deposited FeSe thin films are semiconducting in nature with p-type electrical conductivity. The room temperature electrical resistivity is of the order of 1.1 × 10{sup 5} Ω-cm with activation energy 0.26 and 0.95 eV, respectively, in low and high temperature region.

  12. Structural characterization of InSb thin films grown by electrodeposition

    SciTech Connect

    Singh, Joginder Rajaram, P.

    2015-06-24

    In the present work we have grown InSb thin films on brass substrates, using the electrodeposition technique. The electrochemical baths used in the growth were made up of aqueous solutions of InCl{sub 3} and SbCl{sub 3} mixed together in various proportions. The films grown were characterized by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive Analysis of X-rays (EDAX). Compositional studies show that stoichiometric InSb films can be prepared from a bath containing 0.05M InCl{sub 3} and 0.04M SbCl{sub 3}. XRD studies reveal that the films grown are polycrystalline having the zinc blende structure with (111) orientation. Crystallite size, dislocation density and strain were calculated using the XRD results. Optical transmission spectra were recorded using an FTIR spectrophotometer. The value of direct band gap was found to be around 0.20 eV for the thin films having the best stoichiometry.

  13. Strain induced modulation of the correlated transport in epitaxial Sm0.5Nd0.5NiO3 thin films.

    PubMed

    Zhang, L; Gardner, H J; Chen, X G; Singh, V R; Hong, X

    2015-04-10

    We report a study of the effect of epitaxial strain on the correlated transport properties of 2-40 nm Sm0.5Nd0.5NiO3 (SNNO) films grown on different substrates. The metal-insulator transition (MIT) temperature T(MI) of the SNNO films increases with increasing tensile strain. While films on (0 0 1) LaAlO3 and (1 1 0) NdGaO3 substrates exhibit a sharp MIT and thermal hysteresis in the cooling-heating cycle, signaling a first-order transition, films on (0 0 1) SrTiO3 show a broad, second-order MIT. Hall effect measurements reveal hole-type charge carriers and thermally activated temperature dependence of the carrier density below T(MI). The corresponding activation energy is ∼80 meV for films on LaAlO3 and NdGaO3, and is suppressed to 25 meV for films on SrTiO3. The carrier mobility in the metallic state and variable range hopping (VRH) transport at a low temperature point significantly enhanced electron localization in SNNO on STO, which we believe is not simply driven by extrinsic effects such as oxygen vacancies, but rather is an intrinsic characteristic for films subject to tensile strain due to the elongated Ni-O bond and hence enhanced dynamic Jahn-Teller distortion. In ultrathin films above the electrical dead layer thickness (2-3 nm), we observe a more than 100 K increase of T(MI) for films on LaAlO3, which has been correlated with a crossover from 3D to 2D transport as revealed from VRH. We attribute the distinct transport characteristics to strain induced modulation of various energy scales associated with the Ni-O-Ni bond angle and Ni-O bond length, which collectively determine the delocalization bandwidth of the system. PMID:25779981

  14. Space-charge behavior of 'Thin-MOS' diodes with MBE-grown silicon films

    NASA Technical Reports Server (NTRS)

    Lieneweg, U.; Bean, J. C.

    1984-01-01

    Basic theoretical and experimental characteristics of a novel 'Thin-MOS' technology, which has promising aspects for integrated high-frequency devices up to several hundred gigahertz are presented. The operation of such devices depends on charge injection into undoped silicon layers of about 1000-A thickness, grown by molecular beam epitaxy on heavily doped substrates, and isolation by thermally grown oxides of about 100-A thickness. Capacitance-voltage characteristics measured at high and low frequencies agree well with theoretical ones derived from uni and ambipolar space-charge models. It is concluded that after oxidation the residual doping in the epilayer is less than approximately 10 to the 16th/cu cm and rises by 3 orders of magnitude at the substrate interface within less than 100 A and that interface states at the oxide interface can be kept low.

  15. Low temperature magnetoresistance studies in MBE grown topological insulator thin films

    NASA Astrophysics Data System (ADS)

    Dey, Rik; Roy, Anupam; Pramanik, Tanmoy; Guchhait, Samaresh; Sonde, Sushant; Rai, Amritesh; Majumder, Sarmita; Ghosh, Bahniman; Register, Leonard; Banerjee, Sanjay

    2015-03-01

    We studied low temperature magnetoresistance in molecular beam epitaxy grown topological insulator Bi2Se3andBi2Te3 thin films. The surface and structural characterization of the grown films showed smooth epitaxial growth on Si(111). The magnetoresistance has been measured at low temperatures (2 - 20 K) with magnetic fields upto 9 T. The full range perpendicular field magnetoresistance has been explained with the original Hikami-Larkin-Nagaoka theory. Altshuler-Aronov theory of localization has been used to understand the full range parallel field magnetoresistance. Various scattering times have been estimated by fitting the magnetoresistance data with the theory. It is shown that the Zeeman effect is not needed to explain the magnetoresistance and has not been considered in the theory either. The angle dependent anisotropic magnetoresistance has also been observed and explained using the above theories. This work is funded by NRI-SWAN.

  16. Self-assembled hierarchical 3D - NiO microspheres with ultra-thin porous nanoflakes for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Jadhav, Harsharaj S.; Thorat, Gaurav M.; Mun, Junyoung; Seo, Jeong Gil

    2016-01-01

    Transition metal oxides have attracted great attention as an anode material for next generation lithium ion batteries. Here we report the preparation of self-assembled hierarchical 3D-NiO microspheres with ultra-thin porous nanoflakes by simple and cost effective urea assisted chemical co-precipitation method followed by annealing at different temperature. It is noteworthy that the annealing temperature has an impact on the formation of different morphologies and resultantly on the electrochemical performance. This hierarchical 3D-NiO microspheres with ultra-thin porous nanoflakes shows enhanced electrochemical performance with a large reversible capacity, superior cyclic performance, high rate capability, and improved ionic conductivity as an anode material for lithium ion batteries. A high reversible capacity up to 795 mA h g-1 after 150 cycles at a rate of 0.5 C, and a capacity higher than 460.2 mA h g-1 at a rate as high as 10 C were obtained for optimized NiO sample. In particular, enhancement of the electrochemical performance was attributed to the high specific surface area, good electric contact among the particles, and easier lithium ion diffusion.

  17. High-quality Bi2Te3 thin films grown on mica substrates for potential optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Wang, K.; Liu, Yanwen; Wang, Weiyi; Meyer, N.; Bao, L. H.; He, L.; Lang, M. R.; Chen, Z. G.; Che, X. Y.; Post, K.; Zou, J.; Basov, D. N.; Wang, K. L.; Xiu, Faxian

    2013-07-01

    We report high-quality topological insulator Bi2Te3 thin films grown on muscovite mica substrates by molecular beam epitaxy. The topographic and structural analysis revealed that the Bi2Te3 thin films exhibited atomically smooth terraces over a large area and a high crystalline quality. Both weak antilocalization effect and quantum oscillations were observed in the magnetotransport of the relatively thin samples. A phase coherence length of 277 nm for a 6 nm thin film and a high surface mobility of 0.58 m2 V-1 s-1 for a 4 nm thin film were achieved. These results confirm that the thin films grown on mica are of high quality.

  18. Spoof-like plasmonic behavior of plasma enhanced atomic layer deposition grown Ag thin films

    SciTech Connect

    Prokes, S. M.; Glembocki, O. J.; Cleveland, Erin; Caldwell, Josh D.; Foos, Edward; Niinistoe, Jaakko; Ritala, Mikko

    2012-01-30

    The plasmonic behavior of Ag thin films produced by plasma enhanced atomic layer deposition (PEALD) has been investigated. We show that as-deposited flat PEALD Ag films exhibit unexpected plasmonic properties, and the plasmonic enhancement can differ markedly, depending on the microstructure of the Ag film. Electromagnetic field simulations indicate that this plasmonic behavior is due to air gaps that are an inherent property of the mosaic-like microstructure of the PEALD-grown Ag film, suggesting that this is a metamaterial with behavior very similar to what would be expected in spoof plasmonics where gaps are fabricated in films to create plasmonic-like resonances.

  19. Synthesis and characterization of TiO2 nanostructure thin films grown by thermal CVD

    NASA Astrophysics Data System (ADS)

    Rizal, Umesh; Das, Soham; Kumar, Dhruva; Swain, Bhabani S.; Swain, Bibhu P.

    2016-04-01

    Thermal Chemical Vapor Deposition (CVD) deposited Titanium dioxide nanostructures (TiO2-NSs) were grown by using Ti powder and O2 precursors on Si/SiO2 (100) substrate. The microstructure and vibration properties of TiO2-NSs were characterized by Fourier transform infrared (FTIR), SEM, and photoluminescence (PL) spectroscopy. The role of O2 flow rate on TiO2-NSs revealed decreased deposition rate, however, surface roughness has been increased resulted into formation of nanostructure thin films.

  20. One-dimensional edge state of Bi thin film grown on Si(111)

    SciTech Connect

    Kawakami, Naoya; Lin, Chun-Liang; Kawai, Maki; Takagi, Noriaki; Arafune, Ryuichi

    2015-07-20

    The geometric and electronic structures of the Bi thin film grown on Si(111) were investigated by using scanning tunneling microscopy and spectroscopy. We have found two types of edges, one of which hosts an electronic state localized one-dimensionally. We also revealed the energy dispersion of the localized edge state from the evolution of quasiparticle interference patterns as a function of energy. These spectroscopic findings well reproduce those acquired for the cleaved surface of the bulk Bi crystal [I. K. Drozdov et al., Nat. Phys. 10, 664 (2014)]. The present results indicate that the deposited Bi film provides a tractable stage for further scrutiny of the one-dimensional edge state.

  1. Highly crystalline MoS{sub 2} thin films grown by pulsed laser deposition

    SciTech Connect

    Serrao, Claudy R.; You, Long; Gadgil, Sushant; Hu, Chenming; Salahuddin, Sayeef; Diamond, Anthony M.; Hsu, Shang-Lin; Clarkson, James; Carraro, Carlo; Maboudian, Roya

    2015-02-02

    Highly crystalline thin films of MoS{sub 2} were prepared over large area by pulsed laser deposition down to a single monolayer on Al{sub 2}O{sub 3} (0001), GaN (0001), and SiC-6H (0001) substrates. X-ray diffraction and selected area electron diffraction studies show that the films are quasi-epitaxial with good out-of-plane texture. In addition, the thin films were observed to be highly crystalline with rocking curve full width half maxima of 0.01°, smooth with a RMS roughness of 0.27 nm, and uniform in thickness based on Raman spectroscopy. From transport measurements, the as-grown films were found to be p-type.

  2. Microhardness studies on thin carbon films grown on P-type, (100) silicon

    NASA Technical Reports Server (NTRS)

    Kolecki, J. C.

    1982-01-01

    A program to grow thin carbon films and investigate their physical and electrical properties is described. Characteristics of films grown by rf sputtering and vacuum arc deposition on p type, (100) silicon wafers are presented. Microhardness data were obtained from both the films and the silicon via the Vickers diamond indentation technique. These data show that the films are always harder than the silicon, even when the films are thin (of the order of 1000 A). Vacuum arc films were found to contain black carbon inclusions of the order of a few microns in size, and clusters of inclusions of the order of tens of microns. Transmission electron diffraction showed that the films being studied were amorphous in structure.

  3. Characterization and Fabrication of ZnO Nanowires Grown on AlN Thin Film

    SciTech Connect

    Yousefi, Ramin; Kamaluddin, Burhanuddin; Ghoranneviss, Mahmood; Hajakbari, Fatemeh

    2009-07-07

    In this paper, we report ZnO nanowires grown on AlN thin film deposited on glass as substrate by physical vapour deposition. The temperature of substrates was kept between 600 deg. C and 500 deg. C during the growth. The typical average diameters of the obtained nanowires on substrate at 600 deg. C and 500 deg. C was about 57 nm and 22 nm, respectively with several micrometers in lengths. X-ray diffraction and Auger spectroscopy results showed Al diffused from AlN thin film into ZnO nanowires for sample at high temperature zone. In the photoluminescence spectra two emission bands appeared, one related to ultraviolet emission with a strong peak at 380-382 nm, and another related to deep level emission with a weak peak at 510 nm.

  4. Atomic Layer Deposition (ALD) grown thin films for ultra-fine pitch pixel detectors

    NASA Astrophysics Data System (ADS)

    Härkönen, J.; Ott, J.; Mäkelä, M.; Arsenovich, T.; Gädda, A.; Peltola, T.; Tuovinen, E.; Luukka, P.; Tuominen, E.; Junkes, A.; Niinistö, J.; Ritala, M.

    2016-09-01

    In this report we cover two special applications of Atomic Layer Deposition (ALD) thin films to solve these challenges of the very small size pixel detectors. First, we propose to passivate the p-type pixel detector with ALD grown Al2O3 field insulator with a negative oxide charge instead of using the commonly adopted p-stop or p-spray technologies with SiO2, and second, to use plasma-enhanced ALD grown titanium nitride (TiN) bias resistors instead of the punch through biasing structures. Surface passivation properties of Al2O3 field insulator was studied by Photoconductive Decay (PCD) method and our results indicate that after appropriate annealing Al2O3 provides equally low effective surface recombination velocity as thermally oxidized Si/SiO2 interface. Furthermore, with properly designed annealing steps, the TiN thin film resistors can be tuned to have up to several MΩ resistances with a few μm of physical size required in ultra-fine pitch pixel detectors.

  5. Growth mechanism of CuZnInSe2 thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tseng, Ya Hsin; Yang, Chu Shou; Wu, Chia Hsing; Chiu, Jai Wei; Yang, Min De; Wu, Chih-Hung

    2013-09-01

    CuZnInSe2 (CZIS) has potential application in solar cell for absorption layer, and give an advantage to change the band gap from CuInSe2 (1.02 eV) to ZnSe (2.67 eV). Using molecular beam epitaxy technology, the CZIS thin films were grown via CuInSe (CIS) and ZnSe base. In the case of CIS, thin films were grown on Mo-coated soda lime glass with various zinc flux. CIS was transformed into chalcopyrite and sphalerite coexisting CZIS easily but it is difficult to transform into the pure sphalerite CZIS. Zn/(Zn+In+Cu) ratio has limited to approximate 36 at% and the excess-Zn played a catalyst role. In the case of ZnSe base, which was grown on GaAs (001), various In and Cu flux defined as the TIn series and TCu series, respectively. There are four types of compound in the TIn series and TCu series, including ZnSe, InxSey, ZnIn2Se4 (ZIS) and CZIS. In the TIn series under the lowest In and Cu flux, selenium (Se) were randomly combined with cations to form the CZIS. When TIn is increased in this moment, the CZIS was transformed into ZIS. In the TCu series, CZIS demonstrated via In-rich ZIS (Zn(In, Cu)Se) and InxSey base ((Zn, Cu)InSe). It is chalcopyrite and sphalerite coexisting structure in the medium TCu region. In the high TCu region, it is transformed into the Zn-poor and Cu-rich CZIS.

  6. A scanning tunneling microscopy study of the structure of thin oxide films grown on Ni(111) single crystal surfaces by anodic polarization in acid electrolyte

    NASA Astrophysics Data System (ADS)

    Maurice, V.; Talah, H.; Marcus, P.

    1994-03-01

    Scanning tunneling microscopy has been used to study ex situ (in air) the thin oxide films (passive films) grown on Ni(111) by anodic polarization at +550, +650 and +750 mV/SHE in 0.05 M H 2SO 4. Atomic resolution imaging demonstrates the crystalline character of the oxide film and the epitaxy with the substrate. Two levels of roughening with respect to the non-polarized surfaces are observed: on a mesoscopic scale and on the atomic scale. The roughening on the mesoscopic scale increases with higher polarization potentials. The observed roughness is attributed to the result of the competition between metal dissolution and nucleation and growth of the oxide film. The roughening on the atomic scale is independent of the polarization potential. It is evidenced by the formation of a stepped crystalline lattice whose parameters fit those of a (111)-oriented NiO surface. The presence of steps indicates a tilt of (8 ± 5)° of the surface of the film with respect to the (111) orientation. The possible epitaxial relationships resulting from the surface tilt are discussed. Local variations of the film thickness at the step edges are likely to result from the surface tilt and may constitute preferential sites for the local breakdown of passivity.

  7. Hydroxyapatite thin films grown by pulsed laser deposition and radio-frequency magnetron sputtering: comparative study

    NASA Astrophysics Data System (ADS)

    Nelea, V.; Morosanu, C.; Iliescu, M.; Mihailescu, I. N.

    2004-04-01

    Hydroxyapatite (HA) thin films for applications in the biomedical field were grown by pulsed laser deposition (PLD) and radio-frequency magnetron sputtering (RF-MS) techniques. The depositions were performed from pure hydroxyapatite targets on Ti-5Al-2.5Fe (TiAlFe) alloys substrates. In order to prevent the HA film penetration by Ti atoms or ions diffused from the Ti-based alloy during and after deposition, the substrates were pre-coated with a thin buffer layer of TiN. In both cases, TiN was introduced by reactive PLD from TiN targets in low-pressure N 2. The PLD films were grown in vacuum onto room temperature substrates. The RF-MS films were deposited in low-pressure argon on substrates heated at 550 °C. The initially amorphous PLD thin films were annealed at 550 °C for 1 h in ambient air in order to restore the initial crystalline structure of HA target. The thickness of the PLD and RF-MS films were ˜1 μm and ˜350 nm, respectively. All films were structurally studied by scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXRD), energy dispersive X-ray spectrometry (EDS) and white light confocal microscopy (WLCM). The mechanical properties of the films were tested by Berkovich nano-indentation. Both PLD and RF-MS films mostly contain HA phase and exhibit good mechanical characteristics. Peaks of CaO were noticed as secondary phase in the GIXRD patterns only for RF-MS films. By its turn, the sputtered films were smoother as compared to the ones deposited by PLD (50 nm versus 250 nm average roughness). The RF-MS films were harder, more mechanically resistant and have a higher Young modulus.

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

    SciTech Connect

    Benaissa, M.

    1998-04-15

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

  9. Induced polarized state in intentionally grown oxygen deficient KTaO{sub 3} thin films

    SciTech Connect

    Mota, D. A.; Romaguera-Barcelay, Y.; Tkach, A.; Agostinho Moreira, J.; Almeida, A.; Perez de la Cruz, J.; Vilarinho, P. M.; Tavares, P. B.

    2013-07-21

    Deliberately oxygen deficient potassium tantalate thin films were grown by RF magnetron sputtering on Si/SiO{sub 2}/Ti/Pt substrates. Once they were structurally characterized, the effect of oxygen vacancies on their electric properties was addressed by measuring leakage currents, dielectric constant, electric polarization, and thermally stimulated depolarization currents. By using K{sub 2}O rich KTaO{sub 3} targets and specific deposition conditions, KTaO{sub 3-{delta}} oxygen deficient thin films with a K/Ta = 1 ratio were obtained. Room temperature X-ray diffraction patterns show that KTaO{sub 3-{delta}} thin films are under a compressive strain of 2.3% relative to KTaO{sub 3} crystals. Leakage current results reveal the presence of a conductive mechanism, following the Poole-Frenkel formalism. Furthermore, dielectric, polarization, and depolarization current measurements yield the existence of a polarized state below T{sub pol} {approx} 367 Degree-Sign C. A Cole-Cole dipolar relaxation was also ascertained apparently due to oxygen vacancies induced dipoles. After thermal annealing the films in an oxygen atmosphere at a temperature above T{sub pol}, the aforementioned polarized state is suppressed, associated with a drastic oxygen vacancies reduction emerging from annealing process.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  11. Ar ions irradiation effects in ZrN thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Craciun, D.; Socol, G.; Dorcioman, G.; Simeone, D.; Gosset, D.; Behdad, S.; Boesl, B.; Craciun, V.

    2015-05-01

    Thin ZrN films (<500 nm) were grown on (1 0 0)Si substrates at a substrate temperature of 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under CH4 or N2 atmosphere. Glancing incidence X-ray diffraction showed that films were nanocrystalline, while X-ray reflectivity studies indicated that the films were very dense and with a smooth surface. The films were used to study the effect of 800 keV Ar ion irradiation on their structure and properties. After irradiation with a dose of 1014 at/cm2 the lattice parameter and crystallites size did marginally change. However, after irradiation with a 1015 at/cm2 dose, a clear increase in the lattice parameter accompanied by a significant decrease in nanohardness and Young modulus were observed.

  12. Lithium outdiffusion in LiTi2O4 thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Mesoraca, S.; Kleibeuker, J. E.; Prasad, B.; MacManus-Driscoll, J. L.; Blamire, M. G.

    2016-11-01

    We report surface chemical cation composition analysis of high quality superconducting LiTi2O4 thin films, grown epitaxially on MgAl2O4 (111) substrates by pulsed laser deposition. The superconducting transition temperature of the films was 13.8 K. Surface chemical composition is crucial for the formation of a good metal/insulator interface for integrating LiTi2O4 into full-oxide spin-filtering devices in order to minimize the formation of structural defects and increase the spin polarisation efficiency. In consideration of this, we report a detailed angle resolved x-ray photoelectron spectroscopy analysis. Results show Li segregation at the surface of LiTi2O4 films. We attribute this process due to outdiffusion of Li toward the outermost LiTi2O4 layers.

  13. Optical and mechanical properties of nanocrystalline ZrC thin films grown by pulsed laser deposition.

    DOE PAGES

    Craciun, D.; Socol, G.; Lambers, E.; McCumiskey, E. J.; Taylor, C. R.; Martin, C.; Argibay, Nicolas; Craciun, V.; Tanner, D. B.

    2015-01-17

    Thin ZrC films (<500 nm) were grown on (100) Si substrates at a substrate temperature of 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under different CH4 pressures. Glancing incidence X-ray diffraction showed that films were nanocrystalline, while X-ray reflectivity studies found out films were very dense and exhibited a smooth surface morphology. Optical spectroscopy data shows that the films have high reflectivity (>90%) in the infrared region, characteristic of metallic behavior. Nanoindentation results indicated that films deposited under lower CH4 pressures exhibited slightly higher nanohardness and Young modulus values than films deposited undermore » higher pressures. As a result, tribological characterization revealed that these films exhibited relatively high wear resistance and steady-state friction coefficients on the order of μ = 0.4.« less

  14. Nanocolumnar association and domain formation in porous thin films grown by evaporation at oblique angles.

    PubMed

    Lopez-Santos, C; Alvarez, R; Garcia-Valenzuela, A; Rico, V; Loeffler, M; Gonzalez-Elipe, A R; Palmero, A

    2016-09-30

    Porous thin films grown at oblique angles by evaporation techniques are formed by tilted nanocolumnar structures which, depending on the material type and growth conditions, associate along certain preferential directions, giving rise to large domains. This arrangement, commonly denoted as bundling association, is investigated in the present work by performing fundamental experiments and growth simulations. It is proved that trapping processes of vapor species at the film surface, together with the shadowing mechanism, mediate the anisotropic widening of the nanocolumns and promote their preferential coalescence along certain directions, giving rise to domains with different shape and size. The role of these two processes is thoroughly studied in connection with the formation of these domains in materials as different as SiO2 and TiO2.

  15. Nanocolumnar association and domain formation in porous thin films grown by evaporation at oblique angles

    NASA Astrophysics Data System (ADS)

    Lopez-Santos, C.; Alvarez, R.; Garcia-Valenzuela, A.; Rico, V.; Loeffler, M.; Gonzalez-Elipe, A. R.; Palmero, A.

    2016-09-01

    Porous thin films grown at oblique angles by evaporation techniques are formed by tilted nanocolumnar structures which, depending on the material type and growth conditions, associate along certain preferential directions, giving rise to large domains. This arrangement, commonly denoted as bundling association, is investigated in the present work by performing fundamental experiments and growth simulations. It is proved that trapping processes of vapor species at the film surface, together with the shadowing mechanism, mediate the anisotropic widening of the nanocolumns and promote their preferential coalescence along certain directions, giving rise to domains with different shape and size. The role of these two processes is thoroughly studied in connection with the formation of these domains in materials as different as SiO2 and TiO2.

  16. Nanocolumnar association and domain formation in porous thin films grown by evaporation at oblique angles.

    PubMed

    Lopez-Santos, C; Alvarez, R; Garcia-Valenzuela, A; Rico, V; Loeffler, M; Gonzalez-Elipe, A R; Palmero, A

    2016-09-30

    Porous thin films grown at oblique angles by evaporation techniques are formed by tilted nanocolumnar structures which, depending on the material type and growth conditions, associate along certain preferential directions, giving rise to large domains. This arrangement, commonly denoted as bundling association, is investigated in the present work by performing fundamental experiments and growth simulations. It is proved that trapping processes of vapor species at the film surface, together with the shadowing mechanism, mediate the anisotropic widening of the nanocolumns and promote their preferential coalescence along certain directions, giving rise to domains with different shape and size. The role of these two processes is thoroughly studied in connection with the formation of these domains in materials as different as SiO2 and TiO2. PMID:27535651

  17. Optical and mechanical properties of nanocrystalline ZrC thin films grown by pulsed laser deposition.

    SciTech Connect

    Craciun, D.; Socol, G.; Lambers, E.; McCumiskey, E. J.; Taylor, C. R.; Martin, C.; Argibay, Nicolas; Craciun, V.; Tanner, D. B.

    2015-01-17

    Thin ZrC films (<500 nm) were grown on (100) Si substrates at a substrate temperature of 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under different CH4 pressures. Glancing incidence X-ray diffraction showed that films were nanocrystalline, while X-ray reflectivity studies found out films were very dense and exhibited a smooth surface morphology. Optical spectroscopy data shows that the films have high reflectivity (>90%) in the infrared region, characteristic of metallic behavior. Nanoindentation results indicated that films deposited under lower CH4 pressures exhibited slightly higher nanohardness and Young modulus values than films deposited under higher pressures. As a result, tribological characterization revealed that these films exhibited relatively high wear resistance and steady-state friction coefficients on the order of μ = 0.4.

  18. Highly Crystalline CVD-grown Multilayer MoSe2 Thin Film Transistor for Fast Photodetector

    PubMed Central

    Jung, Chulseung; Kim, Seung Min; Moon, Hyunseong; Han, Gyuchull; Kwon, Junyeon; Hong, Young Ki; Omkaram, Inturu; Yoon, Youngki; Kim, Sunkook; Park, Jozeph

    2015-01-01

    Hexagonal molybdenum diselenide (MoSe2) multilayers were grown by chemical vapor deposition (CVD). A relatively high pressure (>760 Torr) was used during the CVD growth to achieve multilayers by creating multiple nuclei based on the two-dimensional crystal growth model. Our CVD-grown multilayer MoSe2 thin-film transistors (TFTs) show p-type-dominant ambipolar behaviors, which are attributed to the formation of Se vacancies generated at the decomposition temperature (650 °C) after the CVD growth for 10 min. Our MoSe2 TFT with a reasonably high field-effect mobility (10 cm2/V · s) exhibits a high photoresponsivity (93.7 A/W) and a fast photoresponse time (τrise ~ 0.4 s) under the illumination of light, which demonstrates the practical feasibility of multilayer MoSe2 TFTs for photodetector applications. PMID:26477744

  19. Influence of solution viscosity on hydrothermally grown ZnO thin films for DSSC applications

    NASA Astrophysics Data System (ADS)

    Marimuthu, T.; Anandhan, N.; Thangamuthu, R.; Surya, S.

    2016-10-01

    Zinc oxide (ZnO) nanowire arrays (NWAs) were grown onto zinc oxide-titanium dioxide (ZnO-TiO2) seeded fluorine doped tin oxide (FTO) conductive substrate by hydrothermal technique. X-ray diffraction (XRD) patterns depict that ZnO thin films are preferentially oriented along the (002) plane with hexagonal wurtzite structure. Viscosity measurements reveal that viscosity of the solutions linearly increases as the concentrations of the polyvinyl alcohol (PVA) increase in the growth solution. Field emission scanning electron microscope (FE-SEM) images show that the NWAs are vertically grown to seeded FTO substrate with hexagonal structure, and the growth of NWAs decreases as the concentration of the PVA increases. Stylus profilometer and atomic force microscopic (AFM) studies predict that the thickness and roughness of the films decrease with increasing the PVA concentrations. The NWAs prepared at 0.1% of PVA exhibits a lower transmittance and higher absorbance than that of the other films. The band gap of the optimized films prepared at 0.0 and 0.1% of PVA is found to be 3.270 and 3.268 eV, respectively. The photo to current conversion efficiency of the DSSC based on photoanodes prepared at 0.0 and 0.1% of PVA exhibits about 0.64 and 0.82%, respectively. Electrochemical impedance spectra reveal that the DSSC based on photoanode prepared at 0.1% of PVA has the highest charge transfer recombination resistance.

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

    NASA Astrophysics Data System (ADS)

    Li, Wei; Varlamov, Sergey; Xue, Chaowei

    2014-09-01

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

  1. A kinetic model for stress generation in thin films grown from energetic vapor fluxes

    NASA Astrophysics Data System (ADS)

    Chason, E.; Karlson, M.; Colin, J. J.; Magnfält, D.; Sarakinos, K.; Abadias, G.

    2016-04-01

    We have developed a kinetic model for residual stress generation in thin films grown from energetic vapor fluxes, encountered, e.g., during sputter deposition. The new analytical model considers sub-surface point defects created by atomic peening, along with processes treated in already existing stress models for non-energetic deposition, i.e., thermally activated diffusion processes at the surface and the grain boundary. According to the new model, ballistically induced sub-surface defects can get incorporated as excess atoms at the grain boundary, remain trapped in the bulk, or annihilate at the free surface, resulting in a complex dependence of the steady-state stress on the grain size, the growth rate, as well as the energetics of the incoming particle flux. We compare calculations from the model with in situ stress measurements performed on a series of Mo films sputter-deposited at different conditions and having different grain sizes. The model is able to reproduce the observed increase of compressive stress with increasing growth rate, behavior that is the opposite of what is typically seen under non-energetic growth conditions. On a grander scale, this study is a step towards obtaining a comprehensive understanding of stress generation and evolution in vapor deposited polycrystalline thin films.

  2. Electrochromism and photocatalysis in dendrite structured Ti:WO3 thin films grown by sputtering

    NASA Astrophysics Data System (ADS)

    Karuppasamy, A.

    2015-12-01

    Titanium doped tungsten oxide (Ti:WO3) thin films with dendrite surface structures were grown by co-sputtering titanium and tungsten in Ar + O2 atmosphere. Ti:WO3 thin films were deposited at oxygen flow rates corresponding to pressures in the range 1.0 × 10-3-5.0 × 10-3 mbar. Argon flow rate and sputtering power densities for titanium (2 W/cm2) and tungsten (3 W/cm2) were kept constant. Ti:WO3 films deposited at an oxygen pressure of 5 × 10-3 mbar are found to be better electrochromic and photocatalytic. They have high optical modulation (80% at λ = 550 nm), coloration efficiency (60 cm2/C at λ = 550 nm), electron/ion storage and removal capacity (Qc: -22.01 mC/cm2, Qa: 17.72 mC/cm2), reversibility (80%) and methylene blue decomposition rate (-1.38 μmol/l d). The combined effects of titanium doping, dendrite surface structures and porosity leads to significant enhancement in the electrochromic and photocatalytic properties of Ti:WO3 films.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  4. Electron backscatter diffraction analysis applied to [0 0 1] magnetite thin films grown on MgO substrates

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.; Zhou, Y.; Murphy, S.; Mücklich, F.; Hartmann, U.; Shvets, I. V.

    2007-09-01

    Electron backscatter diffraction (EBSD) analysis is applied to [0 0 1] oriented magnetite thin films grown on MgO substrates. A high image quality of the Kikuchi patterns was achieved enabling multi-phase scans. Several types of magnetite thin films were analyzed; one as-grown and the others after different annealing steps in oxygen atmosphere. From the EBSD mappings, we learn that the optimum orientation in [0 0 1]-direction is not yet achieved for the as-grown sample, but develops upon oxygen treatment. Furthermore, the distribution of misorientation angles within the investigated area (=1 grain) is found to change during the annealing steps. After 3 min of annealing, most of the misorientations around 30°-40° have vanished, and some islands with high misorientation angles remain, which may play a role as antiferromagnetic pinning centers.

  5. Systematic process development towards high performance transferred thin silicon solar cells based on epitaxially grown absorbers

    NASA Astrophysics Data System (ADS)

    Murcia Salazar, Clara Paola

    ). First principles modeling, however, predicts that efficiencies of 20+% are achievable with less than 20 mum of c-Si. In addition to a high voltage design, this work reports state of the art epitaxial c-Si solar cell performance and a path towards 20+%-efficient transferred epitaxial solar cells. The design and fabrication approach is based on high open circuit voltage first, high short circuit current second. A first design is a thin solar cell grown on a conductive silicon wafer. This structure allows developing processes to increase bulk lifetime and reduce surface recombination. Important processes that can be used for a transferred solar cell such as increased fill factor (FF) are developed at this stage. A second design is based on the use of a separation layer prior to the solar cell growth. We achieve a comparable performance with the second design. A third design includes the transfer of the solar cell to a secondary substrate. Initial processing development is reported for the transferred solar cells. Improvements in solar cell critical parameters have been characterized with a combination of predictive modeling and solar cell diagnostic tools such as quantum efficiency and voltage measurements. Fabrication processes have been developed to improve solar cell performance. The combination of process development, test structures, systematic fabrication, testing and analysis concludes with a path to high voltage, transferred thin c-Si solar cells towards 20+% efficiencies.

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

    NASA Astrophysics Data System (ADS)

    Jaeckel, Felix Till

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

  7. Electronic properties of high-temperature superconducting thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Abrecht, M.; Ariosa, Daniel; Cloetta, D.; Margaritondo, Giorgio; Pavuna, Davor

    2002-11-01

    We use a pulsed laser deposition (PLD) setup to grow ultra-thin films of high temperature superconductors (HTSC) and transfer them in-situ into a photoemission chamber. Photoemission measurements on such films allow us to study non-cleavable materials, but can also give insights into aspects never measured before, like the influence of strain on the low energy electronic structure. Systematic studies of many different materials grown as films showed that Bi2Sr2CaCu2O8+x, Bi2Sr2Cu1O6+x, Bi2Sr2Ca2Cu3O10+x and La2-xSrxCuO4 films exhibit a conductor-like Fermi edge, but materials containing chains (such as YBa2Cu3O7-x) are prone to very rapid surface degradation, possibly related to critical oxygen loss at the surface. Among HTSC materials, La2-xSrxCuO4 is extremely interesting because of its rather simple structure and the fact that its critical temperature Tc can be enhanced by epitaxial strain. Here we present our first high resolution angular resolved photoemission spectroscopy (ARPES) results on 8 unit-cell thin La2-xSrxCuO4 films on SrLaAlO4 [001] substrates. Due to the lattice mismatch, such films are compressed in the copper oxygen planes and expanded in the c-axis direction. Results show a surprisingly modified Fermi surface compared to the one of non-strained samples.

  8. Comparative study of ITO and FTO thin films grown by spray pyrolysis

    SciTech Connect

    Ait Aouaj, M.; Diaz, R.; Belayachi, A.; Rueda, F.; Abd-Lefdil, M.

    2009-07-01

    Tin doped indium oxide (ITO) and fluorine doped tin oxide (FTO) thin films have been prepared by one step spray pyrolysis. Both film types grown at 400 deg. C present a single phase, ITO has cubic structure and preferred orientation (4 0 0) while FTO exhibits a tetragonal structure. Scanning electron micrographs showed homogeneous surfaces with average grain size around 257 and 190 nm for ITO and FTO respectively. The optical properties have been studied in several ITO and FTO samples by transmittance and reflectance measurements. The transmittance in the visible zone is higher in ITO than in FTO layers with a comparable thickness, while the reflectance in the infrared zone is higher in FTO in comparison with ITO. The best electrical resistivity values, deduced from optical measurements, were 8 x 10{sup -4} and 6 x 10{sup -4} {Omega} cm for ITO (6% of Sn) and FTO (2.5% of F) respectively. The figure of merit reached a maximum value of 2.15 x 10{sup -3} {Omega}{sup -1} for ITO higher than 0.55 x 10{sup -3} {Omega}{sup -1} for FTO.

  9. Scanning Tunneling Microscopy and Transport study of Pb Thin Films Grown on Si Substrates

    NASA Astrophysics Data System (ADS)

    Yu, Hongbin

    2002-03-01

    By varying the interface structures and thus changing the interface energy, Pb film morphology can be modified from Stranski-Krastanov growth mode in the case of Si(111)7x7, to Frank van der Merwe growth mode when Pb is deposited onto Si(111)6x6-Au surface at room temperature. Different superstructures are observed on the Pb films formed on Au interfaces which can be interpreted as the moiré patterns due to the lattice mismatch between Pb film and Si substrate. The Pb(111) film tends to align with Si(111)1x1 when the thickness is between 1ML to 4ML, but in registry with Si(111)root 3 by root3 orientation when layers are thicker than 6ML. Furthermore, atomic lattices of the buried Si(111)root 3 by root 3 interface can be imaged by STM through conduction electrons in the Pb films because of the anisotropic effective mass in Pb layers. Quantum well (QW) states have been observed in Pb films and QW peak positions change due to different thicknesses and thus different confinement condition of electrons. Transport measurement of Pb thin films grown on Si substrate will be discussed.

  10. Crystal structure and energy gap of CdTe thin films grown by radio frequency sputtering

    NASA Astrophysics Data System (ADS)

    Jiménez-Sandoval, S.; Meléndez-Lira, M.; Hernández-Calderón, I.

    1992-11-01

    We have investigated the influence of structural characteristics on the band gap of rf sputtered CdTe thin films grown at substrate temperatures in the 69-232 °C range. The results of scanning electron microscopy and x-ray diffraction studies indicated that the films are a polycrystalline mixture of cubic and hexagonal phases with preferential growth of columnar type parallel to the cubic [111] direction. The band gap of the films was obtained from photoreflectance spectroscopy experiments carried out at room temperature. It was found that the films had a band gap larger than that of CdTe single crystals. This result has been correlated with the existence of lattice strain, quantum size effects, and hexagonal phase regions. By using theoretical models it was possible to estimate the contribution to the band gap shift due to strain and quantum size effects obtaining results in good agreement with the experiment. The study of annealed samples indicated that the effects of thermal treatments were to promote the change of the hexagonal phase to cubic, increase grain size, and shift the band gap towards lower energies reducing its difference with respect to that of single crystals.

  11. Dynamics of surface evolution in semiconductor thin films grown from a chemical bath.

    PubMed

    Gupta, Indu; Mohanty, Bhaskar Chandra

    2016-01-01

    Dynamics of surface evolution in CdS thin films grown by chemical bath deposition technique has been studied from time sequence of atomic force micrographs. Detailed scaling analysis of surface fluctuation in real and Fourier space yielded characteristic exponents αloc = 0.78 ± 0.07, α = 2.20 ± 0.08, αs = 1.49 ± 0.22, β = 0.86 ± 0.05 and βloc = 0.43 ± 0.10, which are very different from those predicted by the local growth models and are not related to any known universality classes. The observed anomalous scaling pattern, characterized by power law scaling dependence of interface width on deposition time differently at local and global scale, with rapid roughening of the growth front has been discussed to arise as a consequence of a nonlocal effect in the form of diffusional instability. PMID:27615367

  12. Dynamics of surface evolution in semiconductor thin films grown from a chemical bath

    NASA Astrophysics Data System (ADS)

    Gupta, Indu; Mohanty, Bhaskar Chandra

    2016-09-01

    Dynamics of surface evolution in CdS thin films grown by chemical bath deposition technique has been studied from time sequence of atomic force micrographs. Detailed scaling analysis of surface fluctuation in real and Fourier space yielded characteristic exponents αloc = 0.78 ± 0.07, α = 2.20 ± 0.08, αs = 1.49 ± 0.22, β = 0.86 ± 0.05 and βloc = 0.43 ± 0.10, which are very different from those predicted by the local growth models and are not related to any known universality classes. The observed anomalous scaling pattern, characterized by power law scaling dependence of interface width on deposition time differently at local and global scale, with rapid roughening of the growth front has been discussed to arise as a consequence of a nonlocal effect in the form of diffusional instability.

  13. Dynamics of surface evolution in semiconductor thin films grown from a chemical bath

    PubMed Central

    Gupta, Indu; Mohanty, Bhaskar Chandra

    2016-01-01

    Dynamics of surface evolution in CdS thin films grown by chemical bath deposition technique has been studied from time sequence of atomic force micrographs. Detailed scaling analysis of surface fluctuation in real and Fourier space yielded characteristic exponents αloc = 0.78 ± 0.07, α = 2.20 ± 0.08, αs = 1.49 ± 0.22, β = 0.86 ± 0.05 and βloc = 0.43 ± 0.10, which are very different from those predicted by the local growth models and are not related to any known universality classes. The observed anomalous scaling pattern, characterized by power law scaling dependence of interface width on deposition time differently at local and global scale, with rapid roughening of the growth front has been discussed to arise as a consequence of a nonlocal effect in the form of diffusional instability. PMID:27615367

  14. Dysprosium oxide and dysprosium-oxide-doped titanium oxide thin films grown by atomic layer deposition

    SciTech Connect

    Tamm, Aile Kozlova, Jekaterina; Aarik, Lauri; Aarik, Jaan; Kukli, Kaupo; Link, Joosep; Stern, Raivo

    2015-01-15

    Dysprosium oxide and dysprosium-oxide-doped titanium oxide thin films were grown by atomic layer deposition on silicon substrates. For depositing dysprosium and titanium oxides Dy(thd){sub 3}-O{sub 3} and TiCl{sub 4}-O{sub 3} were used as precursors combinations. Appropriate parameters for Dy(thd){sub 3}-O{sub 3} growth process were obtained by using a quartz crystal microbalance system. The Dy{sub 2}O{sub 3} films were deposited on planar substrates and on three-dimensional substrates with aspect ratio 1:20. The Dy/Ti ratio of Dy{sub 2}O{sub 3}-doped TiO{sub 2} films deposited on a planar silicon substrate ranged from 0.04 to 0.06. Magnetometry studies revealed that saturation of magnetization could not be observed in planar Dy{sub 2}O{sub 3} films, but it was observable in Dy{sub 2}O{sub 3} films on 3D substrates and in doped TiO{sub 2} films with a Dy/Ti atomic ratio of 0.06. The latter films exhibited saturation magnetization 10{sup −6} A cm{sup 2} and coercivity 11 kA/m at room temperature.

  15. Magnetic and structural properties of Co2FeAl thin films grown on Si substrate

    NASA Astrophysics Data System (ADS)

    Belmeguenai, Mohamed; Tuzcuoglu, Hanife; Gabor, Mihai; Petrisor, Traian; Tiusan, Coriolan; Berling, Dominique; Zighem, Fatih; Mourad Chérif, Salim

    2015-01-01

    The correlation between magnetic and structural properties of Co2FeAl (CFA) thin films of different thicknesses (10 nmgrown at room temperature on MgO-buffered Si/SiO2 substrates and annealed at 600 °C has been studied. x-ray diffraction (XRD) measurements revealed an (011) out-of-plane textured growth of the films. The deduced lattice parameter increases with the film thickness. Moreover, pole figures showed no in-plane preferential growth orientation. The magneto-optical Kerr effect hysteresis loops showed the presence of a weak in-plane uniaxial anisotropy with a random easy axis direction. The coercive field, measured with the applied field along the easy axis direction, and the uniaxial anisotropy field increase linearly with the inverse of the CFA thickness. The microstrip line ferromagnetic resonance measurements for in-plane and perpendicular applied magnetic fields revealed that the effective magnetization and the uniaxial in-plane anisotropy field follow a linear variation versus the inverse CFA thickness. This allows deriving a perpendicular surface anisotropy coefficient of -1.86 erg/cm2.

  16. Surface structural analysis of LiF(100) thin films grown on Pt(111)

    SciTech Connect

    Roberts, J.G.; Van Hove, M.A.; Somorjai, G.A.

    2002-08-29

    The surface structure of a multilayer LiF(100) thin film grown on Pt(111) from the vapor has been determined by the automated tensor low energy electron diffraction (LEED) method. The final structure, which refined to a Pendry R-factor (RP) of 0.24, had a surface corrugation (D1) of 0.24+-0.04 Angstrom due to the Li+ being displaced towards the bulk, leaving the initially coplanar F - unshifted. A similar intralayer corrugation due to the movement of the Li+ was also observed in the layer immediately under the surface layer, although to a lesser degree: D2=0.07+-0.04 Angstrom. This asymmetric relaxation resulted in the reduction of the first interlayer spacing, d(F2-Li1), to 1.77+-0.0 6 Angstrom from the ideal value of 2.01 Angstrom. The second interlayer spacing, d(Li3-F2), was within error bars of the bulk value, 2.01 Angstrom.

  17. Electrochemical Energy Storage Applications of CVD Grown Niobium Oxide Thin Films.

    PubMed

    Fiz, Raquel; Appel, Linus; Gutiérrez-Pardo, Antonio; Ramírez-Rico, Joaquín; Mathur, Sanjay

    2016-08-24

    We report here on the controlled synthesis, characterization, and electrochemical properties of different polymorphs of niobium pentoxide grown by CVD of new single-source precursors. Nb2O5 films deposited at different temperatures showed systematic phase evolution from low-temperature tetragonal (TT-Nb2O5, T-Nb2O5) to high temperature monoclinic modifications (H-Nb2O5). Optimization of the precursor flux and substrate temperature enabled phase-selective growth of Nb2O5 nanorods and films on conductive mesoporous biomorphic carbon matrices (BioC). Nb2O5 thin films deposited on monolithic BioC scaffolds produced composite materials integrating the high surface area and conductivity of the carbonaceous matrix with the intrinsically high capacitance of nanostructured niobium oxide. Heterojunctions in Nb2O5/BioC composites were found to be beneficial in electrochemical capacitance. Electrochemical characterization of Nb2O5/BioC composites showed that small amounts of Nb2O5 (as low as 5%) in conjunction with BioCarbon resulted in a 7-fold increase in the electrode capacitance, from 15 to 104 F g(-1), while imparting good cycling stability, making these materials ideally suited for electrochemical energy storage applications.

  18. Photoinduced Br Desorption from CsBr Thin Films Grown on Cu(100)

    SciTech Connect

    Halliday, Matthew T.; Joly, Alan G.; Hess, Wayne P.; Shluger, AL

    2015-10-22

    Thin films of CsBr deposited onto metals such as copper are potential photocathode materials for light sources and other applications. We investigate desorption dynamics of Br atoms from CsBr films grown on insulator (KBr, LiF) and metal (Cu) substrates induced by sub-bandgap 6.4 eV laser pulses. The experimental results demonstrate that the peak kinetic energy of Br atoms desorbed from CsBr/Cu films is much lower than that for the hyperthermal desorption from CsBr/LiF films. Kelvin probe measurements indicate negative charge at the surface following Br desorption from CsBr/Cu films. Our ab initio calculations of excitons at CsBr surfaces demonstrate that this behavior can be explained by an exciton model of desorption including electron trapping at the CsBr surface. Trapped negative charges reduce the energy of surface excitons available for Br desorption. We examine the electron-trapping characteristics of low-coordinated sites at the surface, in particular, divacancies and kink sites. We also provide a model of cation desorption caused by Franck-Hertz excitation of F centers at the surface in the course of irradiation of CsBr/Cu films. These results provide new insights into the mechanisms of photoinduced structural evolution of alkali halide films on metal substrates and activation of metal photocathodes coated with CsBr.

  19. Electrochemical Energy Storage Applications of CVD Grown Niobium Oxide Thin Films.

    PubMed

    Fiz, Raquel; Appel, Linus; Gutiérrez-Pardo, Antonio; Ramírez-Rico, Joaquín; Mathur, Sanjay

    2016-08-24

    We report here on the controlled synthesis, characterization, and electrochemical properties of different polymorphs of niobium pentoxide grown by CVD of new single-source precursors. Nb2O5 films deposited at different temperatures showed systematic phase evolution from low-temperature tetragonal (TT-Nb2O5, T-Nb2O5) to high temperature monoclinic modifications (H-Nb2O5). Optimization of the precursor flux and substrate temperature enabled phase-selective growth of Nb2O5 nanorods and films on conductive mesoporous biomorphic carbon matrices (BioC). Nb2O5 thin films deposited on monolithic BioC scaffolds produced composite materials integrating the high surface area and conductivity of the carbonaceous matrix with the intrinsically high capacitance of nanostructured niobium oxide. Heterojunctions in Nb2O5/BioC composites were found to be beneficial in electrochemical capacitance. Electrochemical characterization of Nb2O5/BioC composites showed that small amounts of Nb2O5 (as low as 5%) in conjunction with BioCarbon resulted in a 7-fold increase in the electrode capacitance, from 15 to 104 F g(-1), while imparting good cycling stability, making these materials ideally suited for electrochemical energy storage applications. PMID:27420568

  20. Surface structure determinations of crystalline ionic thin films grown on transition metal single crystal surfaces by low energy electron diffraction

    SciTech Connect

    Roberts, J.G.

    2000-05-01

    The surface structures of NaCl(100), LiF(100) and alpha-MgCl2(0001) adsorbed on various metal single crystals have been determined by low energy electron diffraction (LEED). Thin films of these salts were grown on metal substrates by exposing the heated metal surface to a molecular flux of salt emitted from a Knudsen cell. This method of investigating thin films of insulators (ionic salts) on a conducting substrate (metal) circumvents surface charging problems that plagued bulk studies, thereby allowing the use of electron-based techniques to characterize the surface.

  1. Diamond thin films grown by microwave plasma assisted chemical vapor deposition

    SciTech Connect

    Leksono, M.

    1991-09-05

    Undoped and boron doped diamond thin films have been successfully grown by microwave plasma chemical vapor deposition from CH{sub 4}, H{sub 2}, and B{sub 2}H{sub 6}. The films were characterized using x- ray diffraction techniques, Raman and infrared spectroscopies, scanning electron microscopy, secondary ion mass spectrometry, and various electrical measurements. The deposition rates of the diamond films were found to increase with the CH{sub 4} concentration, substrate temperature, and/or pressure, and at 1.0% methane, 900{degrees}C, and 35 Torr, the value was measured to be 0.87 {mu}m/hour. The deposition rate for boron doped diamond films, decreases as the diborane concentration increases. The morphologies of the undoped diamond films are strongly related to the deposition parameters. As the temperature increases from 840 to 925 C, the film morphology changes from cubo-octahedron to cubic structures, while as the CH{sub 4} concentration increases from 0.5 to 1.0%, the morphology changes from triangular (111) faces with a weak preferred orientation to square (100) faces. At 2.0% Ch{sub 4} or higher the films become microcrystalline with cauliflower structures. Scanning electron microscopy analyses also demonstrate that selective deposition of undoped diamond films has been successfully achieved using a lift-off process with a resolution of at least 2 {mu}m. The x-ray diffraction and Raman spectra demonstrate that high quality diamond films have been achieved. The concentration of the nondiamond phases in the films grown at 1.0% CH{sub 4} can be estimated from the Raman spectra to be at less than 0.2% and increases with the CH{sub 4} concentration. The Raman spectra of the boron doped diamond films also indicate that the presence of boron tends to suppress the nondiamond phases in the films. Infrared spectra of the undoped diamond films show very weak CH stretch peaks which suggest that the hydrogen concentration is very low.

  2. Defect-free thin InAs nanowires grown using molecular beam epitaxy.

    PubMed

    Zhang, Zhi; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2016-01-21

    In this study, we designed a simple method to achieve the growth of defect-free thin InAs nanowires with a lateral dimension well below their Bohr radius on different substrate orientations. By depositing and annealing a thin layer of Au thin film on a (100) substrate surface, we have achieved the growth of defect-free uniform-sized thin InAs nanowires. This study provides a strategy to achieve the growth of pure defect-free thin nanowires.

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

    NASA Astrophysics Data System (ADS)

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

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

  4. Postdeposition relaxation of internal stress in sputter-grown thin films caused by ion bombardment

    NASA Astrophysics Data System (ADS)

    Nowak, R.; Yoshida, F.; Morgiel, J.; Major, B.

    1999-01-01

    A hitherto unreported postdeposition method of relaxing ultrahigh internal stresses prevailing in sputter-grown thin films is the subject of the present research. A significant reduction of stress has been confirmed by x-ray diffraction and independent substrate deflection measurements for HfN films treated with Si+ ions of various energies (450 keV, 500 keV, and 1.1 MeV). The particular sequence of the performed experiments has allowed us to deduce the most likely scenario of the resulting stress relaxation. We argue that the observed reduction of internal stress had been caused by structural changes, namely the transport of interstitial defects occurring within the thermal spikes induced by ion bombardment and an increase in vacancy concentration. Simple theoretical considerations proved that the existence of an amorphous silicon interlayer formed right under the HfN film during the bombardment cannot be the cause of the observed stress relaxation. The employed Auger electron spectroscopy, transmission electron microscopy, and x-ray diffraction technique confirmed that the ion bombardment did not seriously affect either the composition, dislocation structure, or texture of nitride films. The relative softening of HfN after ion bombardment was found to be caused by amorphization of the substrate directly under the film. The penetration of incident particles deeper than predicted by a numerical simulation was attributed to a distinct crystallographic texture determined experimentally for HfN films. It was confirmed that modification with Si+ ions does not affect the resistivity of HfN films.

  5. Optical properties of metal oxynitride thin films grown with atmospheric plasma deposition

    NASA Astrophysics Data System (ADS)

    Hovish, Michael Q.; Dauskardt, Reinhold H.

    2016-10-01

    Thin films of tantalum oxynitride (TaO x N y ) and titanium oxynitride (TiO x N y ) are deposited using atmospheric plasma deposition and a suite of optical properties are reported. Tantalum and titanium ethoxide are introduced into the afterglow of a radio-frequency capacitively coupled plasma, facilitating the growth of oxynitride films on silicon and polycarbonate at temperatures below 180 °C. The plasma power and nitrogen flow within the plasma are varied between 60 and 120 W and between 0.1 and 0.3 LPM respectively. We use spectroscopic ellipsometry to show that the optical properties of the metal oxynitride films grown in this study are comparable to those synthesized with sol-gel methods. Measurement of both the extinction coefficient and the transmission on polycarbonate substrates indicates good transparency in the visible wavelengths of light. Additionally, the refractive index increases when increasing the number of reactive nitrogen species within the discharge. We use x-ray photoelectron spectroscopy to correlate the higher indexes observed at large secondary gas flows to the presence of metal oxynitride bonding. Single layer anti-reflection coatings are deposited on silicon, with a five-fold and seven-fold reduction in reflection for TaO x N y and TiO x N y coatings, respectively. In total, we have found that the modulation of nitrogen concentration within the plasma discharge results in good control over optical constants. In addition, we observe similarities between films deposited with atmospheric plasma and those reported for sol-gel, indicating an alternative processing route where solution chemistries are currently applied.

  6. Ultrafast carrier dynamics and the role of grain boundaries in polycrystalline silicon thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Titova, Lyubov V.; Cocker, Tyler L.; Xu, Sijia; Baribeau, Jean-Marc; Wu, Xiaohua; Lockwood, David J.; Hegmann, Frank A.

    2016-10-01

    We have used time-resolved terahertz spectroscopy to study microscopic photoconductivity and ultrafast photoexcited carrier dynamics in thin, pure, non-hydrogenated silicon films grown by molecular beam epitaxy on quartz substrates at temperatures ranging from 335 °C to 572 °C. By controlling the growth temperature, thin silicon films ranging from completely amorphous to polycrystalline with minimal amorphous phase can be achieved. Film morphology, in turn, determines its photoconductive properties: in the amorphous phase, carriers are trapped in bandtail states on sub-picosecond time scales, while the carriers excited in crystalline grains remain free for tens of picoseconds. We also find that in polycrystalline silicon the photoexcited carrier mobility is carrier-density-dependent, with higher carrier densities mitigating the effects of grain boundaries on inter-grain transport. In a film grown at the highest temperature of 572 °C, the morphology changes along the growth direction from polycrystalline with needles of single crystals in the bulk of the film to small crystallites interspersed with amorphous silicon at the top of the film. Depth profiling using different excitation wavelengths shows corresponding differences in the photoconductivity: the photoexcited carrier lifetime and mobility are higher in the first 100-150 nm from the substrate, suggesting that thinner, low-temperature grown polycrystalline silicon films are preferable for photovoltaic applications.

  7. Nucleation and stochiometry dependence of rutile-TiO2 thin films grown by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Constantin, Costel; Sun, Kai; Feenstra, R. M.

    2008-03-01

    Considerable interest has been shown of late in transition-metal oxides. One case is the titanium dioxide system, which can have applications as a high-k dielectric gate insulator for Si-based devicesootnotetextZ. J. Luo et al., Appl. Phys. Lett. 79, 2803. In this study, rutile-TiO2 thin films were grown on GaN(0001) substrates by oxygen plasma-assisted molecular beam epitaxy. Two sets of films were grown, one in which the initial GaN surface is prepared WITH the pseudo 1x1 Ga-rich surface reconstruction, and the other set, WITHOUT the pseudo 1x1. On top of these two type of surfaces, the rutile-TiO2 thin films were grown at Ts˜ 600 ^oC, and with a thickness ˜ 40 - 50 nm. During growth, reflection high-energy electron diffraction indicated a reversible stoichiometry transition from O-rich to Ti-rich growth. Post-growth x-ray diffraction measurements performed on the samples WITHOUT the GaN pseudo 1x1, show the presence of additional peaks at 2θ = 52.9^o, which implies the existence of additional phases. In addition, the high-resolution transmission electron microscopy performed on these samples show a high degree of disorder, as compared to the samples prepared WITH the pseudo 1x1. Work supported by ONR.

  8. Embedded polytypes in Bi2Sr2-xLaxCuO6 thin films grown by laser ablation

    NASA Astrophysics Data System (ADS)

    Cancellieri, C.; Lin, P. H.; Ariosa, D.; Pavuna, D.

    2007-11-01

    We investigate the presence of secondary phases in La-doped Bi-2201 thin films grown by laser ablation. The cation ratios in the target material, the oxygen pressure, and the substrate temperature during the deposition are the main parameters determining the presence of diluted intergrowth and/or polytype aggregates. A statistical model of random intergrowth is used to analyze the x-ray diffraction (XRD) anomalies caused by hidden defects and to characterize the latter. A detailed structural XRD refinement on oriented aggregates allows us to identify the guest phase as a Bi deficient phase, Bi-1201. The occurrence of this particular embedded polytype is accompanied by a global Bi deficiency introduced in the films by the growing process and/or by the annealing treatment. The presence of La favors the Bi-1201 formation mostly as La-rich c -axis oriented aggregates. Bi excess in the target material improves considerably the crystallographic structure of Bi-2201, avoids intergrowth formation, but does not prevent the phase separation of Bi-1201 in La-doped thin films. We also investigate the influence of the deposition parameters on the type of intergrowth as well as their variation with La doping. This work introduces a specific methodology for optimizing the growth of thin films grown by laser ablation, which applies to layered oxides that admit polytypes with close formation enthalpies in their phase diagram.

  9. Structure disorder degree of polysilicon thin films grown by different processing: Constant C from Raman spectroscopy

    SciTech Connect

    Wang, Quan; Zhang, Yanmin; Hu, Ran; Ren, Naifei; Ge, Daohan

    2013-11-14

    Flat, low-stress, boron-doped polysilicon thin films were prepared on single crystalline silicon substrates by low pressure chemical vapor deposition. It was found that the polysilicon films with different deposition processing have different microstructure properties. The confinement effect, tensile stresses, defects, and the Fano effect all have a great influence on the line shape of Raman scattering peak. But the effect results are different. The microstructure and the surface layer are two important mechanisms dominating the internal stress in three types of polysilicon thin films. For low-stress polysilicon thin film, the tensile stresses are mainly due to the change of microstructure after thermal annealing. But the tensile stresses in flat polysilicon thin film are induced by the silicon carbide layer at surface. After the thin film doped with boron atoms, the phenomenon of the tensile stresses increasing can be explained by the change of microstructure and the increase in the content of silicon carbide. We also investigated the disorder degree states for three polysilicon thin films by analyzing a constant C. It was found that the disorder degree of low-stress polysilicon thin film larger than that of flat and boron-doped polysilicon thin films due to the phase transformation after annealing. After the flat polysilicon thin film doped with boron atoms, there is no obvious change in the disorder degree and the disorder degree in some regions even decreases.

  10. Crystallization of bismuth titanate and bismuth silicate grown as thin films by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Harjuoja, Jenni; Väyrynen, Samuli; Putkonen, Matti; Niinistö, Lauri; Rauhala, Eero

    2006-01-01

    Bismuth silicate and bismuth titanate thin films were deposited by atomic layer deposition (ALD). A novel approach with pulsing of two Bi-precursors was studied to control the Si/Bi atomic ratio in bismuth silicate thin films. The crystallization of compounds formed in the Bi 2O 3-SiO 2 and Bi 2O 3-TiO 2 systems was investigated. Control of the stoichiometry of Bi-Si-O thin films was studied when deposited on Si(1 0 0) and crystallization was studied for films on sapphire and MgO-, ZrO 2- and YSZ-buffered Si(1 0 0). The Bi-Ti-O thin films were deposited on Si(1 0 0) substrate. Both Bi-Si-O and Bi-Ti-O thin films were amorphous after deposition. Highly a-axis oriented Bi 2SiO 5 thin films were obtained when the Bi-Si-O thin films deposited on MgO-buffered Si(1 0 0) were annealed at 800 °C in nitrogen. The full-width half-maximum values for 200 peak were also studied. An excess of bismuth was found to improve the crystallization of Bi-Ti-O thin films and the best crystallinity was observed with Ti/Bi atomic ratio of 0.28 for films annealed at nitrogen at 1000 °C. Roughness of the thin films as well as the concentration depth distribution were also examined.

  11. Properties of CsI, CsBr and GaAs thin films grown by pulsed laser deposition

    SciTech Connect

    Brendel, V M; Garnov, S V; Yagafarov, T F; Iskhakova, L D; Ermakov, R P

    2014-09-30

    CsI, CsBr and GaAs thin films have been grown by pulsed laser deposition on glass substrates. The morphology and structure of the films have been studied using X-ray diffraction and scanning electron microscopy. The CsI and CsBr films were identical in stoichiometry to the respective targets and had a polycrystalline structure. Increasing the substrate temperature led to an increase in the density of the films. All the GaAs films differed in stoichiometry from the target. An explanation was proposed for this fact. The present results demonstrate that, when the congruent transport condition is not fulfilled, films identical in stoichiometry to targets can be grown by pulsed laser deposition in the case of materials with a low melting point and thermal conductivity. (interaction of laser radiation with matter)

  12. Enhancement of supercapacitance property of electrochemically deposited MnO2 thin films grown in acidic medium

    NASA Astrophysics Data System (ADS)

    Jana, S. K.; Rao, V. P.; Banerjee, S.

    2014-02-01

    In this communication we present supercapacitance property of MnO2 thin-films which are fabricated on stainless steel (SS) substrate by electro-deposition method carried out in different pH of the electrolyte. A significant improvement of the device performance of acid mediated grown (AMG) MnO2 over normal MnO2 (grown in neutral medium) has been achieved. We have also investigated role of interfacial structure on the internal resistance of the device material. AMG MnO2 film exhibits superior device performance with specific capacitance of 652 F/g which is 2 times better than that obtained in normal MnO2 and also energy density of 90.69 Wh/kg.

  13. High-quality Bi{sub 2}Te{sub 3} thin films grown on mica substrates for potential optoelectronic applications

    SciTech Connect

    Wang, K.; Bao, L. H.; Liu Yanwen; Wang Weiyi; Xiu Faxian; Meyer, N.; Che, X. Y.; He, L.; Lang, M. R.; Wang, K. L.; Chen, Z. G.; Post, K.; Basov, D. N.; Zou, J.

    2013-07-15

    We report high-quality topological insulator Bi{sub 2}Te{sub 3} thin films grown on muscovite mica substrates by molecular beam epitaxy. The topographic and structural analysis revealed that the Bi{sub 2}Te{sub 3} thin films exhibited atomically smooth terraces over a large area and a high crystalline quality. Both weak antilocalization effect and quantum oscillations were observed in the magnetotransport of the relatively thin samples. A phase coherence length of 277 nm for a 6 nm thin film and a high surface mobility of 0.58 m{sup 2} V{sup -1} s{sup -1} for a 4 nm thin film were achieved. These results confirm that the thin films grown on mica are of high quality.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

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

    SciTech Connect

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

    2013-05-07

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

  16. Atomic-layer-deposited Al2O3 thin films with thin SiO2 layers grown by in situ O3 oxidation

    NASA Astrophysics Data System (ADS)

    Kim, Seong Keun; Hwang, Cheol Seong

    2004-08-01

    The growth, thermal annealing behaviors, and electrical properties of Al2O3 thin films grown by atomic layer deposition (ALD) on bare (100)Si and various oxidized Si wafers, by in situ O3 oxidation at 400°C and ex situ rapid thermal annealing (RTA) under O2 atmosphere at 900°C, were investigated. The ALD process was performed using Al(CH3)3 and high concentration of O3(400gm3). The high oxidation potential of O3 oxidized the Si surface at a very early stage of film growth and eliminated the incubation period even on a bare Si surface. The as-grown Al2O3 films had excess oxygen in the films, which diffused to the film Si interface and increased the interfacial layer by oxidizing the Si substrates during postannealing. The Al2O3 films grown on a bare Si substrate had the highest concentration of excess oxygen which resulted in the largest increase in the interfacial layer thickness during postannealing. As a result, the initial oxidation of the Si wafer did not significantly decrease the capacitance density compared to the films grown on a nonoxidized Si wafer at the as-deposited and postannealed states. Therefore, the Al2O3 layers grown using a high concentration of O3 oxidant on the in situ O3 oxidized Si wafers showed real high-k gate dielectric performance although the dielectric constants of the Al2O3 films were rather small (˜9) compared to other high-k gate dielectric films.

  17. Structural and optical characterization of ZrO2 thin films grown on silicon and quartz substrates

    NASA Astrophysics Data System (ADS)

    Hojabri, Alireza

    2016-09-01

    Zirconium oxide thin films were grown successfully by thermal annealing of zirconium thin films deposited on quartz and silicon substrates by direct current magnetron sputtering technique. The structural and optical properties in relation to thermal annealing times were investigated. The X-ray diffraction patterns revealed that structure of films changes from amorphous to crystalline by increase of annealing times in range 60-240 min. The composition of films was determined by Rutherford back scattering spectroscopy. Atomic force microscopy results exhibited that surface morphology and roughness of films depend on the annealing time. The refractive index of the films was calculated using Swanepoel's method. The optical band gap energy of annealed films decreased from 5.50 to 5.34 eV with increasing thermal annealing time.

  18. Superconducting YBa 2Cu 3O 7- δ thin film grown on metallic film evaporated on MgO

    NASA Astrophysics Data System (ADS)

    Verdyan, A.; Azoulay, J.; Lapsker, I.

    2001-03-01

    At present it is commonly accepted that thin film formation of YBa 2Cu 3O 7- δ (YBCO) on conducting substrate is one of the keys to further development of advanced devices in the microelectronic and other applications. We have grown YBCO thin films by resistive evaporation technique on MgO coated with metallic layers (Ni or Ag). A simple inexpensive vacuum system equipped with resistively heated boats for metal and precursor mixture of yttrium, copper and barium fluoride powders was used. X-ray diffraction (XRD) and scanning electron microscopy techniques were used for texture, morphology and surface analyses respectively. Electrical and magnetical properties were determined by a standard dc four-probe method. The way of heating process is shown to be critical parameter in the film quality. The physical and electrical properties of the YBCO films are discussed in light of the fact that XRD measurements done on the metallic buffer layers have revealed a multicrystalline structure.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  20. Co2FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

    NASA Astrophysics Data System (ADS)

    Belmeguenai, M.; Tuzcuoglu, H.; Gabor, M. S.; Petrisor, T.; Tiusan, C.; Zighem, F.; Chérif, S. M.; Moch, P.

    2014-01-01

    10 nm and 50 nm Co2FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (Ta), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing Ta, while the uniaxial anisotropy field is nearly unaffected by Ta within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with Ta. Finally, the FMR linewidth decreases when increasing Ta, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10-3 and 1.3×10-3 for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively).

  1. Pseudo capacitive performance of copper oxide thin films grown by RF sputtering

    SciTech Connect

    Reddy, B. Purusottam; Ganesh, K. Sivajee; Hussain, O. M.

    2015-06-24

    Thin films of Copper Oxide were prepared by radio frequency magnetron sputtering on steel substrates maintained at 250°C under different RF powers ranging from 150W to 250W by keeping the sputtering pressure at 5.7×10{sup −3} mbar and O{sub 2}:Ar ratio of 1:7. The influence of RF power on the pseudo capacitive performance of thin films was studied. The X-ray diffraction studies and Raman studies indicates that all the thin films exhibits CuO phase. The electrochemical studies was done by using three electrode configuration with platinum as reference electrode. From the cyclic voltammetry studies a high rate pseudocapacitance of 227 mFcm{sup −2} at 0.5 mVs{sup −1} and 77% of capacity retention after 1000 cycles was obtained for the CuO thin films prepared at an RF power of 220W.

  2. Conductivity of Thin Films Based on Single-Walled Carbon Nanotubes Grown by Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Rybakov, M. S.; Kosobutsky, A. V.; Sevostyanov, O. G.; Russakov, D. M.; Lomakin, M. V.; Chirkova, I. M.; Shandakov, S. D.

    2015-03-01

    Electrical and optical properties of thin films of single-walled carbon nanotubes (SWCNT) obtained by aerosol chemical vapor deposition using ethanol, ferrocene, and sulfur are studied. Structural and geometrical characteristics of the synthesis products are determined by the methods of Raman spectroscopy and transmission electron microscopy. The effect of sulfur on the properties of the SWCNTs and thin films based on them is found.

  3. 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.

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

    SciTech Connect

    Punugupati, Sandhyarani Narayan, Jagdish; Hunte, Frank

    2015-05-21

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

  5. KCl ultra-thin films with polar and non-polar surfaces grown on Si(111)7 × 7

    PubMed Central

    Beinik, Igor; Barth, Clemens; Hanbücken, Margrit; Masson, Laurence

    2015-01-01

    The growth of ultra-thin KCl films on the Si(111)7 × 7 reconstructed surface has been investigated as a function of KCl coverage and substrate temperature. The structure and morphology of the films were characterized by means of scanning tunneling microscopy (STM) under ultra-high vacuum (UHV) conditions. Detailed analysis of the atomically resolved STM images of islands grown at room and high temperatures (400 K–430 K) revealed the presence of KCl(001) and KCl(111) islands with the ratio between both structures depending on the growth temperature. At room temperature, the growth of the first layer, which covers the initial Si(111)7 × 7 surface, contains double/triple atomic layers of KCl(001) with a small fraction of KCl(111) islands. The high temperature growth promotes the appearance of large KCl(111) areas, which are built up by three atomic layers. At room and high temperatures, flat and atomically well-defined ultra-thin KCl films can be grown on the Si(111)7 × 7 substrate. The formation of the above mentioned (111) polar films is interpreted as a result of the thermally activated dissociative adsorption of KCl molecules on Si(111)7 × 7, which produces an excess of potassium on the Si surface. PMID:25650038

  6. Characterization of ZnO thin films grown on different p-Si substrate elaborated by solgel spin-coating method

    SciTech Connect

    Chebil, W.; Fouzri, A.; Fargi, A.; Azeza, B.; Zaaboub, Z.; and others

    2015-10-15

    Highlights: • High quality ZnO thin films grown on different p-Si substrates were successful obtained by sol–gel process. • PL measurement revealed that ZnO thin film grown on porous Si has the better optical quality. • I–V characteristics for all heterojunctions exhibit successful diode formation. • The diode ZnO/PSi shows a better photovoltaic effect under illumination with a maximum {sub Voc} of 0.2 V. - Abstract: In this study, ZnO thin films are deposited by sol–gel technique on p-type crystalline silicon (Si) with [100] orientation, etched silicon and porous silicon. The structural analyses showed that the obtained thin films were polycrystalline with a hexagonal wurtzite structure and preferentially oriented along the c-axis direction. Morphological study revealed the presence of rounded and facetted grains irregularly distributed on the surface of all samples. PL spectra at room temperature revealed that ZnO thin film grown on porous Si has a strong UV emission with low defects in the visible region comparing with ZnO grown on plat Si and etched Si surface. The heterojunction parameters were evaluated from the (I–V) under dark and illumination at room temperature. The ideality factor, barrier height and series resistance of heterojunction grown on different p-Si substrates are determined by using different methods. Best electrical properties are obtained for ZnO layer deposited on porous silicon.

  7. Photonic bandgap amorphous chalcogenide thin films with multilayered structure grown by pulsed laser deposition method

    NASA Astrophysics Data System (ADS)

    Zhang, Shao-qian; Němec, Petre; Nazabal, Virginie; Jin, Yu-qi

    2016-05-01

    Amorphous chalcogenide thin films were fabricated by the pulsed laser deposition technique. Thereafter, the stacks of multilayered thin films for reflectors and microcavity were designed for telecommunication wavelength. The prepared multilayered thin films for reflectors show good compatibility. The microcavity structure consists of Ge25Ga5Sb10S65 (doped with Er3+) spacer layer surrounded by two 5-layer As40Se60/Ge25Sb5S70 reflectors. Scanning/transmission electron microscopy results show good periodicity, great adherence and smooth interfaces between the alternating dielectric layers, which confirms a suitable compatibility between different materials. The results demonstrate that the chalcogenides can be used for preparing vertical Bragg reflectors and microcavity with high quality.

  8. Elevated temperature dependence of energy band gap of ZnO thin films grown by e-beam deposition

    SciTech Connect

    Rai, R. C.; Guminiak, M.; Wilser, S.; Cai, B.; Nakarmi, M. L.

    2012-04-01

    We report the surface, structural, electronic, and optical properties of the epitaxial ZnO thin films grown on (0001) sapphire substrate at 600 deg. C by an electron-beam deposition technique. ZnO thin films have been deposited in an oxygen environment and post-deposition annealed to improve the stoichiometry and the crystal quality. In order to investigate the free exciton binding energy and the temperature dependence of the energy bandgap, we carried out variable temperature (78-450 K) transmittance measurements on ZnO thin films. The absorption data below the energy bandgap have been modeled with the Urbach tail and a free exciton, while the data above the gap have been modeled with the charge transfer excitations. The exciton binding energy is measured to be E{sub 0}= 64 {+-} 7 meV, and the energy band gaps of the ZnO film are measured to be E{sub g}-tilde 3.51 and 3.48 eV at 78 and 300 K, respectively. The temperature dependence of the energy gap has been fitted with the Varshni model to extract the fitting parameters {alpha}= 0.00020 {+-} 0.00002 eV/K, {beta}= 325 {+-} 20 K, and E{sub g} (T = 0 K) = 3.516 {+-} 0.0002 eV.

  9. Substrate dependent structural, optical and electrical properties of ZnS thin films grown by RF sputtering

    NASA Astrophysics Data System (ADS)

    Pathak, Trilok K.; Kumar, Vinod; Purohit, L. P.; Swart, H. C.; Kroon, R. E.

    2016-10-01

    Zinc sulphide (ZnS) films are of great importance for applications in various optoelectronic devices. ZnS thin films were grown on glass, indium tin oxide (ITO) and Corning glass substrates by radio-frequency magnetron sputtering at a temperature of 373 K and a comparative study of the structural, optical and electrical properties was performed using X-ray diffraction (XRD), scanning electron microscopy, optical and current-voltage (I-V) measurements. The XRD patterns showed that the sputtered thin films exhibited good crystallinity with the (111) peak around 2θ=28.3° indicating preferential orientation of the cubic structure. The maximum strain and most densely packed grains were obtained for the Corning glass substrate. The transmittance spectra of the films were measured in the wavelength range from 200 to 800 nm, showing that the films are about 77% transparent in the visible region. A slight change of 3.50 eV to 3.54 eV was found for the bandgap of the films deposited on different substrates. The ZnS thin films deposited on Corning glass show better crystallinity, morphology and I-V characteristics than that deposited on ordinary glass and ITO substrates.

  10. Cu(In,Ga)Se 2 thin-film solar cells grown with cracked selenium

    NASA Astrophysics Data System (ADS)

    Kawamura, Masahiro; Fujita, Toshiyuki; Yamada, Akira; Konagai, Makoto

    2009-01-01

    Cu(In 1-xGa x)Se 2 (CIGS) films have been grown by using cracked selenium. In conventional evaporation system, the Se atoms were supplied as large clusters (Se x, x>5). However, the size of clusters can be reduced by the thermal cracking. The film qualities grown with small clusters (Se x, x<4) would be improved, since the smaller size molecules easily react with elemental metals, resulting in the reduction of selenium vacancies and the enhancement of surface migration. The CIGS films were deposited by the three-stage method with cracked selenium, and the films were evaluated by SEM, XRD, EDX, C- V measurement and admittance spectroscopy. It was found from the C- V characteristics that the carrier concentrations of the CIGS films grown with cracked selenium were increased with increasing the cracking temperature. The result clearly showed that the use of cracked selenium was effective for reduction of selenium vacancies. The conversion efficiency of 15.4% was obtained by using cracked selenium at a cracking temperature of 500 °C.

  11. Enhancement in the photocatalytic nature of nitrogen-doped PVD-grown titanium dioxide thin films

    SciTech Connect

    Tavares, C. J.; Marques, S. M.; Viseu, T.; Teixeira, V.; Carneiro, J. O.; Alves, E.; Barradas, N. P.; Munnik, F.; Girardeau, T.; Riviere, J.-P.

    2009-12-01

    Nitrogen-doped titanium dioxide semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron physical vapor deposition on glass substrates for self-cleaning applications. In order to increase the photocatalytic efficiency of the titania coatings, it is important to enhance the catalysts absorption of light from the solar spectra. Bearing this fact in mind, a reduction in the titania semiconductor band-gap has been attempted by using nitrogen doping from a coreactive gas mixture of N{sub 2}:O{sub 2} during the titanium sputtering process. Rutherford backscattering spectroscopy was used in order to assess the composition of the titania thin films, whereas heavy-ion elastic recoil detection analysis granted the evaluation of the doping level of nitrogen. X-ray photoelectron spectroscopy provided valuable information about the cation-anion binding within the semiconductor lattice. The as-deposited thin films were mostly amorphous, however, after a thermal annealing in vacuum at 500 deg. C the crystalline polymorph anatase and rutile phases have been developed, yielding an enhancement in the crystallinity. Spectroscopic ellipsometry experiments enabled the determination the refractive index of the thin films as a function of the wavelength, while from the optical transmittance it was possible to estimate the semiconductor indirect band-gap of these coatings, which has been proven to decrease as the N-doping increases. The photocatalytic performance of the titania films has been characterized by the degradation rate of an organic reactive dye under UV/visible irradiation. It has been found that for a certain critical limit of 1.19 at. % of nitrogen doping in the titania anatase crystalline lattice enhances the photocatalytic behavior of the thin films and it is in accordance with the observed semiconductor band-gap narrowing to 3.18 eV. By doping the titania lattice with nitrogen, the photocatalytic activity is enhanced under both UV and

  12. Local Structures and Interface Morphology of InGaAsN Thin Films Grown on GaAs

    SciTech Connect

    Allerman, A.A.; Chen, J.G.; Geisz, J.F.; Huang, S.; Hulbert, S.L.; Jones, E.D.; Kao, Y.H.; Kurtz, S.; Kurtz, S.R.; Olson, J.M.; Soo, Y.L.

    1999-02-23

    The compound semiconductor system InGaAsN exhibits many intriguing properties which are particularly useful for the development of innovative high efficiency thin film solar cells and long wavelength lasers. The bandgap in these semiconductors can be varied by controlling the content of N and In and the thin films can yet be lattice-matched to GaAs. In the present work, x-ray absorption fine structure (XAFS) and grazing incidence x-ray scattering (GIXS) techniques have been employed to probe the local environment surrounding both N and In atoms as well as the interface morphology of InGaAsN thin films epitaxially grown on GaAs. The soft x-ray XAFS results around nitrogen K-edge reveal that N is in the sp{sup 3} hybridized bonding configuration in InGaAsN and GaAsN, suggesting that N impurities most likely substitute for As sites in these two compounds. The results of In K-edge XAFS suggest a possible trend of a slightly larger coordination number of As nearest neighbors around In atoms in InGaAsN samples with a narrower bandgap whereas the In-As interatomic distance remains practically the same as in InAs within the experimental uncertainties. These results combined suggest that N-substitution of the As sites plays an important role of bandgap-narrowing while in the meantime counteracting the compressive strain caused by In-doping. Grazing incidence x-ray scattering (GIXS) experiments verify that InGaAsN thin films can indeed form very smooth interfaces with GaAs yielding an average interfacial roughness of 5-20{angstrom}.

  13. Paramagnetic dysprosium-doped zinc oxide thin films grown by pulsed-laser deposition

    SciTech Connect

    Lo, Fang-Yuh Ting, Yi-Chieh; Chou, Kai-Chieh; Hsieh, Tsung-Chun; Ye, Cin-Wei; Hsu, Yung-Yuan; Liu, Hsiang-Lin; Chern, Ming-Yau

    2015-06-07

    Dysprosium(Dy)-doped zinc oxide (Dy:ZnO) thin films were fabricated on c-oriented sapphire substrate by pulsed-laser deposition with doping concentration ranging from 1 to 10 at. %. X-ray diffraction (XRD), Raman-scattering, optical transmission spectroscopy, and spectroscopic ellipsometry revealed incorporation of Dy into ZnO host matrix without secondary phase. Solubility limit of Dy in ZnO under our deposition condition was between 5 and 10 at. % according to XRD and Raman-scattering characteristics. Optical transmission spectroscopy and spectroscopic ellipsometry also showed increase in both transmittance in ultraviolet regime and band gap of Dy:ZnO with increasing Dy density. Zinc vacancies and zinc interstitials were identified by photoluminescence spectroscopy as the defects accompanied with Dy incorporation. Magnetic investigations with a superconducting quantum interference device showed paramagnetism without long-range order for all Dy:ZnO thin films, and a hint of antiferromagnetic alignment of Dy impurities was observed at highest doping concentration—indicating the overall contribution of zinc vacancies and zinc interstitials to magnetic interaction was either neutral or toward antiferromagnetic. From our investigations, Dy:ZnO thin films could be useful for spin alignment and magneto-optical applications.

  14. Properties of anodic oxides grown on a hafnium-tantalum-titanium thin film library

    NASA Astrophysics Data System (ADS)

    Ionut Mardare, Andrei; Ludwig, Alfred; Savan, Alan; Hassel, Achim Walter

    2014-02-01

    A ternary thin film combinatorial materials library of the valve metal system Hf-Ta-Ti obtained by co-sputtering was studied. The microstructural and crystallographic analysis of the obtained compositions revealed a crystalline and textured surface, with the exception of compositions with Ta concentration above 48 at.% which are amorphous and show a flat surface. Electrochemical anodization of the composition spread thin films was used for analysing the growth of the mixed surface oxides. Oxide formation factors, obtained from the potentiodynamic anodization curves, as well as the dielectric constants and electrical resistances, obtained from electrochemical impedance spectroscopy, were mapped along two dimensions of the library using a scanning droplet cell microscope. The semiconducting properties of the anodic oxides were mapped using Mott-Schottky analysis. The degree of oxide mixing was analysed qualitatively using x-ray photoelectron spectroscopy depth profiling. A quantitative analysis of the surface oxides was performed and correlated to the as-deposited metal thin film compositions. In the concurrent transport of the three metal cations during oxide growth a clear speed order of Ti > Hf > Ta was proven.

  15. Electrical property measurements of Cr-N codoped TiO2 epitaxial thin films grown by pulsed laser deposition

    SciTech Connect

    Jacimovic, J; Gaal, R; Magrez, Arnaud; Forro, Laszlo; Regmi, Murari; Eres, Gyula

    2013-01-01

    The temperature dependent resistivity and thermo-electric power of Cr-N codoped TiO2 were compared with that of single element N and Cr doped and undoped TiO2 using epitaxial anatase thin films grown by pulsed laser deposition on (100) LaAlO3 substrates. The resistivity plots and especially the thermoelectric power data confirm that codoping is not a simple sum of single element doping. However, the negative sign of the Seebeck coefficient indicates electron dominated transport independent of doping. The narrowing distinction among the effects of different doping methods combined with increasing resistivity of the films with improving crystalline quality of TiO2 suggest that structural defects play a critical role in the doping process.

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

    SciTech Connect

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

    2014-03-03

    We investigated the formation of cubic boron nitride (c-BN) thin films on diamond (001) and (111) substrates by ion-beam-assisted molecular beam epitaxy (MBE). The metastable c-BN (sp{sup 3}-bonded BN) phase can be epitaxially grown as a result of the interplay between competitive phase formation and selective etching. We show that a proper adjustment of acceleration voltage for N{sub 2}{sup +} and Ar{sup +} ions is a key to selectively discriminate non-sp{sup 3} BN phases. At low acceleration voltage values, the sp{sup 2}-bonded BN is dominantly formed, while at high acceleration voltages, etching dominates irrespective of the bonding characteristics of BN.

  17. Perpendicular Magnetic Anisotropy and Spin Glass-like Behavior in Molecular Beam Epitaxy Grown Chromium Telluride Thin Films.

    PubMed

    Roy, Anupam; Guchhait, Samaresh; Dey, Rik; Pramanik, Tanmoy; Hsieh, Cheng-Chih; Rai, Amritesh; Banerjee, Sanjay K

    2015-04-28

    Reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), vibrating sample magnetometry, and other physical property measurements are used to investigate the structure, morphology, magnetic, and magnetotransport properties of (001)-oriented Cr2Te3 thin films grown on Al2O3(0001) and Si(111)-(7×7) surfaces by molecular beam epitaxy. Streaky RHEED patterns indicate flat smooth film growth on both substrates. STM studies show the hexagonal arrangements of surface atoms. Determination of the lattice parameter from the atomically resolved STM image is consistent with the bulk crystal structures. Magnetic measurements show the film is ferromagnetic, having a Curie temperature of about 180 K, and a spin glass-like behavior was observed below 35 K. Magnetotransport measurements show the metallic nature of the film with a perpendicular magnetic anisotropy along the c-axis.

  18. Synthesis of nanocrystalline Cu2ZnSnS4 thin films grown by the spray-pyrolysis technique

    NASA Astrophysics Data System (ADS)

    Chandel, Tarun; Singh, Joginder; Rajaram, P.

    2015-08-01

    Spray pyrolysis was used to deposit Cu2ZnSnS4 (CZTS) thin films on soda lime glass substrates at 300 °C. Aqueous solutions of copper chloride, zinc chloride, stannous chloride and thiourea were mixed together to form the spray liquid. The sprayed films were annealed under vacuum at 350 °C, 400 °C and 450 °C. Structural and optical characterization was performed on the CZTS films using X-ray diffraction (XRD) and UV-VIS spectrophotometry. XRD results indicate that the films are single phase nanocrystalline CZTS. Optical studies show that the optical gap values are 1.44 eV for the as-grown film and 1.46 eV, 1.48 eV and 1.49 eV for the films annealed at 350 °C, 400 °C and 450 °C, respectively.

  19. Correlation of Crystalline and Structural Properties of C60 Thin Films Grown at Various Temperature with Charge Carrier Mobility

    SciTech Connect

    Singh,T.; Sarciftci, N.; Yang, H.; Yang, L.; Plochberger, B.; Sitter, H.

    2007-01-01

    Transistors fabricated from C{sub 60} films grown by hot wall epitaxy at higher substrate temperature, showed an order of magnitude increased charge carrier mobility up to 6 cm{sup 2}/V s. In this letter, the authors present an extensive study of morphology and crystallinity of the fullerene films using atomic force microscopy and grazing-incidence x-ray diffraction. A clear correlation of crystalline quality of the C{sub 60} film and charge carrier mobility was found. A higher substrate temperature leads to a single crystal-like faceted fullerene crystals. The high crystalline quality solely brings a drastic improvement in the charge carrier mobility. A gate voltage independent mobility is also observed in these devices which can be attributed to the highly conjugated nature of the C{sub 60} thin film.

  20. Spin-resolved photoemssion study of epitaxially grown MoSe2 and WSe2 thin films.

    PubMed

    Mo, Sung-Kwan; Hwang, Choongyu; Zhang, Yi; Fanciulli, Mauro; Muff, Stefan; Hugo Dil, J; Shen, Zhi-Xun; Hussain, Zahid

    2016-11-16

    Few-layer thick MoSe2 and WSe2 possess non-trivial spin textures with sizable spin splitting due to the inversion symmetry breaking embedded in the crystal structure and strong spin-orbit coupling. We report a spin-resolved photoemission study of MoSe2 and WSe2 thin film samples epitaxially grown on a bilayer graphene substrate. We only found spin polarization in the single- and trilayer samples-not in the bilayer sample-mostly along the out-of-plane direction of the sample surface. The measured spin polarization is found to be strongly dependent on the light polarization as well as the measurement geometry, which reveals intricate coupling between the spin and orbital degrees of freedom in this class of material. PMID:27617696

  1. Spin-resolved photoemssion study of epitaxially grown MoSe2 and WSe2 thin films

    NASA Astrophysics Data System (ADS)

    Mo, Sung-Kwan; Hwang, Choongyu; Zhang, Yi; Fanciulli, Mauro; Muff, Stefan; Dil, J. Hugo; Shen, Zhi-Xun; Hussain, Zahid

    2016-11-01

    Few-layer thick MoSe2 and WSe2 possess non-trivial spin textures with sizable spin splitting due to the inversion symmetry breaking embedded in the crystal structure and strong spin-orbit coupling. We report a spin-resolved photoemission study of MoSe2 and WSe2 thin film samples epitaxially grown on a bilayer graphene substrate. We only found spin polarization in the single- and trilayer samples—not in the bilayer sample—mostly along the out-of-plane direction of the sample surface. The measured spin polarization is found to be strongly dependent on the light polarization as well as the measurement geometry, which reveals intricate coupling between the spin and orbital degrees of freedom in this class of material.

  2. Ferroelectric properties of (Ba,Sr)TiO3 thin films grown on YBa2Cu3O7 layers

    NASA Astrophysics Data System (ADS)

    Tao, K.; Hao, Z.; Xu, B.; Chen, B.; Miao, J.; Yang, H.; Zhao, B. R.

    2003-09-01

    Ferroelectric and superconductor bilayers of Ba1-xSrxTiO3(BST)/YBa2Cu3 O7 (YBCO) are grown on (001) SrTiO3 substrates by magnetron sputtering and pulsed laser deposition. The BST thin films exhibit typical ferroelectric behavior in their hysteresis loops. Capacitance-voltage curves are measured. From the capacitance, a dielectric constant of 1250 is obtained. The current-voltage curve is fitted to investigate the mechanism of leakage. The Schottky barrier height at the Ag/BST interface is calculated to be 0.521 eV. The trapped level Et in BST is estimated to be 0.335 eV below the conduction-band edge. An energy band diagram of the Ag/BST/YBCO structure is proposed to explain the experimental results.

  3. Study of optical and structural properties of CZTS thin films grown by co-evaporation and spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Moreno, R.; Ramirez, E. A.; Gordillo Guzmán, G.

    2016-02-01

    Results regarding optical and structural properties of Cu2ZnSnS4 (CZTS) thin films prepared by co-evaporation using a novel procedure are compared with those obtained with CZTS films grown using a solution based route. The lattice strain ε and crystallite size D of CZTS films prepared by co-evaporation and by spray pyrolysis were estimated through X-ray diffraction (XRD) measurements using Williamson-Hall-isotropic strain model. The results of estimated average crystallite size of CZTS films by Scherrer and Williamson-Hall plot methods were compared with AFM (atomic force microscopy) measurements. It was found that the average crystallite size measured by Williamson-Hall plot methods agree quite well with AFM results. Further, information regarding the influence of preparation method on both, crystalline phases and the formation of structural defects was achieved through Raman and Urbach energy measurements.

  4. Group III-nitride thin films grown using MBE and bismuth

    DOEpatents

    Kisielowski, Christian K.; Rubin, Michael

    2000-01-01

    The present invention comprises growing gallium nitride films in the presence of bismuth using MBE at temperatures of about 1000 K or less. The present invention further comprises the gallium nitride films fabricated using the inventive fabrication method. The inventive films may be doped with magnesium or other dopants. The gallium nitride films were grown on sapphire substrates using a hollow anode Constricted Glow Discharge nitrogen plasma source. When bismuth was used as a surfactant, two-dimensional gallium nitride crystal sizes ranging between 10 .mu.m and 20 .mu.m were observed. This is 20 to 40 times larger than crystal sizes observed when GaN films were grown under similar circumstances but without bismuth. It is thought that the observed increase in crystal size is due bismuth inducing an increased surface diffusion coefficient for gallium. The calculated value of 4.7.times.10.sup.-7 cm.sup.2 /sec. reveals a virtual substrate temperature of 1258 K which is 260 degrees higher than the actual one.

  5. Group III-nitride thin films grown using MBE and bismuth

    DOEpatents

    Kisielowski, Christian K.; Rubin, Michael

    2002-01-01

    The present invention comprises growing gallium nitride films in the presence of bismuth using MBE at temperatures of about 1000 K or less. The present invention further comprises the gallium nitride films fabricated using the inventive fabrication method. The inventive films may be doped with magnesium or other dopants. The gallium nitride films were grown on sapphire substrates using a hollow anode Constricted Glow Discharge nitrogen plasma source. When bismuth was used as a surfactant, two-dimensional gallium nitride crystal sizes ranging between 10 .mu.m and 20 .mu.m were observed. This is 20 to 40 times larger than crystal sizes observed when GaN films were grown under similar circumstances but without bismuth. It is thought that the observed increase in crystal size is due bismuth inducing an increased surface diffusion coefficient for gallium. The calculated value of 4.7.times.10.sup.-7 cm.sup.2 /sec. reveals a virtual substrate temperature of 1258 K which is 260 degrees higher than the actual one.

  6. Structural, morphological and optical characterizations of ZnO:Al thin films grown on silicon substrates by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Alyamani, A.; Sayari, A.; Albadri, A.; Albrithen, H.; El Mir, L.

    2016-09-01

    The pulsed laser deposition (PLD) technique is used to grow Al-doped ZnO (AZO) thin films at 500 ° C on silicon substrates under vacuum or oxygen gas background from ablating AZO nanoparticle targets synthesized via the sol-gel process. The structural, morphological and optical properties were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE) techniques. XRD and TEM images show that AZO powder has a wurtzite-type structure and is composed of small prismatic-like shape nanoparticles with an average size of 30nm. The structural properties of the AZO films grown under oxygen show no significant changes compared to those of the film grown under vacuum. However, the optical properties show a dependence on the growth conditions of the AZO films. Highly c -axis-oriented AZO thin films were obtained with grain size ˜ 15 nm. The stress in the AZO films is tensile as measured from the c -parameter. The dielectric function, the refractive index and the extinction coefficient as a function of the photon energy for the AZO films were determined by using spectroscopic ellipsometry measurements in the photon energy region from 1 to 6eV. The band gap energy was observed to slightly decrease in the presence of the O2 gas background and this may be attributed to the stress. The surface and volume energy loss functions are calculated and exhibit different behaviors in the energy range 1-6eV. Refractive indices of 1.9-2.1 in the visible region were obtained for the AZO films. Also, the electronic carrier concentration appears to be related to the presence of O2 during the growth process.

  7. Effects of substrate on the structure and orientation of ZnO thin film grown by rf-magnetron sputtering

    SciTech Connect

    Liu, H. F.; Chua, S. J.; Hu, G. X.; Gong, H.; Xiang, N.

    2007-10-15

    X-ray diffractions, Nomarski microscopy, scanning electron microscopy, and photoluminescence have been used to study the effects of substrate on the structure and orientation of ZnO thin films grown by rf-magnetron sputtering. GaAs(001), GaAs(111), Al{sub 2}O{sub 3}(0002) (c-plane), and Al{sub 2}O{sub 3}(1102) (r-plane) wafers have been selected as substrates in this study. X-ray diffractions reveal that the ZnO film grown on GaAs(001) substrate is purely textured with a high c-axis orientation while that grown on GaAs(111) substrate is a single ZnO(0002) crystal; a polycrystalline structure with a large-single-crystal area of ZnO(0002) is obtained on a c-plane Al{sub 2}O{sub 3} substrate while a ZnO(1120) single crystal is formed on an r-plane Al{sub 2}O{sub 3} substrate. There is absence of significant difference between the photoluminescence spectra collected from ZnO/GaAs(001), ZnO/GaAs(111), and ZnO/Al{sub 2}O{sub 3}(0002), while the photoluminescence from ZnO/Al{sub 2}O{sub 3}(1102) shows a reduced intensity together with an increased linewidth, which is, likely, due to the increased incorporation of native defects during the growth of ZnO(1120)

  8. Defect Analysis in III-V Semiconductor Thin Films Grown by Hydride Vapor Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Schulte, Kevin Louis

    Hydride vapor phase epitaxy (HVPE) is an epitaxial growth technique renowned for its ability to grow III-V semiconductors at high growth rates using lower cost reagents compared to metal-organic vapor phase epitaxy (MOVPE), the current industry standard. Recent interest in III-V photovoltaics has led to increased attention on HVPE. While the technique came to maturity in the 70s, much is unknown about how defects incorporate in HVPE-grown materials. Further understanding of how defects incorporate in III-V materials grown by HVPE is necessary to facilitate wider adoption of the technique. This information would inform strategies for minimizing and eliminating defects in HVPE materials, allowing for the formation of high performance devices. This investigation presents a study of multiple defects in III-V semiconductors grown by HVPE in the context of specific device applications, spanning point defects comprised of individual atoms to extended defects which propagate throughout the crystal. The incorporation of the arsenic anti-site defect, AsGa, intrinsic point defect was studied in high growth rate GaAs layers with potential photovoltaic applications. Relationships between growth conditions and incorporation of AsGa in GaAs epilayers were determined. The incorporation of AsGa depended strongly on the growth conditions employed, and a model was developed to predict the concentration of anti-site defects as a function of those growth conditions. Dislocations and anti-phase domain boundaries (APDBs), two types of extended defects, were investigated in the heteroepitaxial GaAs/Ge system. It was found that the use of 6° miscut substrates and specific growth temperatures led to elimination of APDBs. Dislocation densities were reduced through the use of high growth temperatures. The third and final application investigated was the growth of InxGa1-xAs metamorphic buffer layers (MBLs) by HVPE. The relationships between the growth conditions and the alloy composition

  9. Investigation of thin films of organic-based magnets grown by physical vapor deposition

    SciTech Connect

    Kao, C. Y.; Lu, Y.; Li, B.; Yoo, J.-W.; Epstein, A. J.

    2014-10-06

    Thin films of organic-based magnet, V[TCNE]{sub x} (TCNE: tetracyanoethylene), were deposited by physical vapor deposition (PVD) based reactive evaporation. The growth conditions were studied in detail. A saturated composition of V[TCNE]{sub ∼1.9} was determined by optimizing the growth condition. Two sets of films with different V to TCNE ratios were characterized. Both films were magnetic ordered up to 400 K and held coercive field of 60 Oe at room temperature. With the presence of excess vanadium within the film, the increase of defects created by PVD results in significant change in electronic property.

  10. On detection of the Fermi edge in in situ grown thin films of high- Tc oxides

    NASA Astrophysics Data System (ADS)

    Abrecht, M.; Ariosa, D.; Saleh, S. A.; Rast, S.; Margaritondo, G.; Onellion, M.; Pavuna, D.

    2001-11-01

    We discuss our systematic series of experiments on the photoelectric detection of the Fermi edge using a cylindrical mirror analyser on films of high- Tc oxides, grown in situ by pulsed laser ablation. The Fermi edge (comparable to the edge of the reference Ag) is very easily observed even in the two-phase BSCCO-2212 film that exhibits onsets of superconducting transitions, at 85 and 45 K. In contrast, the Fermi edge is weaker and more difficult to observe even in the state-of-the-art, highly epitaxial, monophase YBa 2Cu 3O 7- y (YBCO) and NdBa 2Cu 3O 7- y (NBCO-123) films (both with Tc=92 K). So far we could not detect the Fermi edge in the films of the double-`chain' YBCO-124.

  11. Structural evolution of platinum thin films grown by atomic layer deposition

    SciTech Connect

    Geyer, Scott M.; Methaapanon, Rungthiwa; Bent, Stacey; Johnson, Richard; Clemens, Bruce; Brennan, Sean; Toney, Mike F.

    2014-08-14

    The structural properties of Pt films grown by atomic layer deposition (ALD) are investigated with synchrotron based x-ray scattering and x-ray diffraction techniques. Using grazing incidence small angle scattering, we measure the lateral growth rate of the Pt islands to be 1.0 Å/cycle. High resolution x-ray diffraction reveals that the in-plane strain of the Pt lattice undergoes a transition from compressive strain to tensile strain when the individual islands coalescence into a continuous film. This transition to tensile strain is attributed to the lateral expansion that occurs when neighboring islands merge to reduce their surface energy. Using 2D grazing incidence x-ray diffraction, we show that the lattice orientation becomes more (111) oriented during deposition, with a sharp transition occurring during coalescence. Pt ALD performed at a lower deposition temperature (250 °C) is shown to result in significantly more randomly oriented grains.

  12. Photoresponse in thin films of WO{sub 3} grown by pulsed laser deposition

    SciTech Connect

    Roy Moulik, Samik; Samanta, Sudeshna; Ghosh, Barnali

    2014-06-09

    We report, the photoresponse behaviour of Tungsten trioxide (WO{sub 3}) films of different surface morphology, grown by using pulsed laser deposition (PLD). The Growth parameters for PLD were changed for two substrates SiO{sub 2}/Si (SO) and SrTiO{sub 3} (STO), such a way which, result nanocrystalline film on SO and needle like structured film on STO. The photoresponse is greatly modified in these two films because of two different surface morphologies. The nanocrystalline film (film on SO) shows distinct photocurrent (PC) ON/OFF states when light was turned on/off, the enhancement of PC is ∼27%. Whereas, the film with needle like structure (film on STO) exhibits significantly enhanced persistent photocurrent even in light off condition, in this case, the enhancement of PC ∼ 50% at room temperature at lowest wavelength (λ = 360 nm) at a nominal bias voltage of 0.1 V.

  13. Enhanced photocatalytic performance in atomic layer deposition grown TiO{sub 2} thin films via hydrogen plasma treatment

    SciTech Connect

    Sasinska, Alexander; Singh, Trilok; Wang, Shuangzhou; Mathur, Sanjay; Kraehnert, Ralph

    2015-01-15

    The authors report the effect of hydrogen plasma treatment on TiO{sub 2} thin films grown by atomic layer deposition as an effective approach for modifying the photoanode materials in order to enhance their photoelectrochemical performance. Hydrogen plasma treated TiO{sub 2} thin films showed an improved absorption in the visible spectrum probably due to surface reduction. XPS analysis confirmed the formation of Ti{sup 3+} states upon plasma treatment. Hydrogen plasma treatment of TiO{sub 2} films enhanced the measured photocurrent densities by a factor of 8 (1 mA/cm{sup 2} at 0.8 V versus normal hydrogen electrode) when compared to untreated TiO{sub 2} (0.12 mA/cm{sup 2}). The enhancement in photocurrent is attributed to the formation of localized electronic states in mid band-gap region, which facilitate efficient separation and transportation of photo excited charge carriers in the UV region of electromagnetic spectrum.

  14. Thermoelectric transport and Hall measurements of low defect Sb2Te3 thin films grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Zastrow, S.; Gooth, J.; Boehnert, T.; Heiderich, S.; Toellner, W.; Heimann, S.; Schulz, S.; Nielsch, K.

    2013-03-01

    Sb2Te3 has recently been an object of intensive research since its promising applicability in thermoelectric, in phase-change memory devices and as a topological insulator. In this work, we report highly textured Sb2Te3 thin films, grown by atomic layer deposition on Si/SiO2 wafers based on the reaction of SbCl3 and (Et3Si)2Te. The low deposition temperature at 80 °C allows the pre-patterning of the Sb2Te3 by standard lithography processes. A platform to characterize the Seebeck coefficient S, the electrical conductivity σ as well as the Hall coefficient RH on the same film has been developed. Comparing all temperature-dependent transport properties, three different conductive regions in the temperature range of 50-400 K are found. Room temperature values of S = 146 × 10-6 VK-1, σ = 104 Sm-1 and mobility µ = 270.5 × 10-4 m2 V-1 s-1 are determined. The low carrier concentration in the range of n = 2.4 × 1018 cm-3 at 300 K quantifies the low defect content of the Sb2Te3 thin films.

  15. Anomalous thickness-dependent optical energy gap of ALD-grown ultra-thin CuO films

    NASA Astrophysics Data System (ADS)

    Tripathi, T. S.; Terasaki, I.; Karppinen, M.

    2016-11-01

    Usually an inverse square relation between the optical energy gap and the size of crystallites is observed for semiconducting materials due to the strong quantum localization effect. Coulomb attraction that may lead to a proportional dependence is often ignored or considered less important to the optical energy gap when the crystallite size or the thickness of a thin film changes. Here we report a proportional dependence between the optical energy gap and the thickness of ALD-grown CuO thin films due to a strong Coulomb attraction. The ultrathin films deposited in the thickness range of 9-81 nm show a p-type semiconducting behavior when analyzed by Seebeck coefficient and electrical resistivity measurements. The indirect optical energy gap nature of the films is verified from UV-vis spectrophotometric measurements. A progressive increase in the indirect optical energy gap from 1.06 to 1.24 eV is observed with the increase in the thickness of the films. The data are analyzed in the presence of Coulomb attractions using the Brus model. The optical energy gap when plotted against the cubic root of the thickness of the films shows a linear dependence.

  16. Anomalous thickness-dependent optical energy gap of ALD-grown ultra-thin CuO films.

    PubMed

    Tripathi, T S; Terasaki, I; Karppinen, M

    2016-11-30

    Usually an inverse square relation between the optical energy gap and the size of crystallites is observed for semiconducting materials due to the strong quantum localization effect. Coulomb attraction that may lead to a proportional dependence is often ignored or considered less important to the optical energy gap when the crystallite size or the thickness of a thin film changes. Here we report a proportional dependence between the optical energy gap and the thickness of ALD-grown CuO thin films due to a strong Coulomb attraction. The ultrathin films deposited in the thickness range of 9-81 nm show a p-type semiconducting behavior when analyzed by Seebeck coefficient and electrical resistivity measurements. The indirect optical energy gap nature of the films is verified from UV-vis spectrophotometric measurements. A progressive increase in the indirect optical energy gap from 1.06 to 1.24 eV is observed with the increase in the thickness of the films. The data are analyzed in the presence of Coulomb attractions using the Brus model. The optical energy gap when plotted against the cubic root of the thickness of the films shows a linear dependence.

  17. Advanced APCVD-processes for high-temperature grown crystalline silicon thin film solar cells.

    PubMed

    Driessen, Marion; Merkel, Benjamin; Reber, Stefan

    2011-09-01

    Crystalline silicon thin film (cSiTF) solar cells based on the epitaxial wafer-equivalent (EpiWE) concept combine advantages of wafer-based and thin film silicon solar cells. In this paper two processes beyond the standard process sequence for cSiTF cell fabrication are described. The first provides an alternative to wet chemical saw damage removal by chemical vapor etching (CVE) with hydrogen chloride in-situ prior to epitaxial deposition. This application decreases the number of process and handling steps. Solar cells fabricated with different etching processes achieved efficiencies up to 14.7%. 1300 degrees C etching temperature led to better cell results than 1200 degrees C. The second investigated process aims for an improvement of cell efficiency by implementation of a reflecting interlayer between substrate and active solar cell. Some characteristics of epitaxial lateral overgrowth (ELO) of a patterned silicon dioxide film in a lab-type reactor constructed at Fraunhofer ISE are described and first solar cell results are presented.

  18. Nanostructured and wide bandgap CdS:O thin films grown by reactive RF sputtering

    SciTech Connect

    Islam, M. A.; Rahman, K. S.; Haque, F.; Rashid, M. J.; Akhtaruzzaman, M.; Sopian, K.; Sulaiman, Y.; Amin, N.

    2015-05-15

    In this study, CdS:O thin films were prepared from a 99.999% CdS target by reactive sputtering in a Ar:O{sub 2} (99:1) ambient with different RF power at room temperature. The deposited films were studied by means of XRD, SEM, EDX, Hall Effect and UV-Vis spectrometry. The incorporations of O{sub 2} into the films were observed to increase with the decrease of deposition power. The cryatallinity of the films were reduced, whereas the band gaps of the films were increased by the increase of O{sub 2} content on the films. The films were found in nano-structured grains with a compact surface. It has been seen that the highest carrier density is observed in the film with O{sub 2} at.% 21.10, while the values decreased with the further increase or decrease of O{sub 2} content on the films; indicating that specific amount of donor like O{sub 2} atoms substitute to the S atoms can improve the carrier density of the CdS:O thin film.

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

    NASA Astrophysics Data System (ADS)

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

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

  20. Biocompatible Mn2+-doped carbonated hydroxyapatite thin films grown by pulsed laser deposition.

    PubMed

    György, E; Toricelli, P; Socol, G; Iliescu, M; Mayer, I; Mihailescu, I N; Bigi, A; Werckman, J

    2004-11-01

    Mn(2+)-doped carbonated hydroxyapatite (Mn-CHA) thin films were obtained by pulsed laser deposition on Ti substrates. The results of the performed complementary diagnostic techniques, X-ray diffraction, infrared spectroscopy, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectroscopy investigations indicate that the films are crystalline with a Ca/P ratio of about 1.64-1.66. The optimum conditions, when nearly stoichiometric crystalline thin films were deposited, were found to be 10 Pa oxygen pressure, 400 degrees C substrate temperature, and postdeposition heat treatment in water vapors at the same substrate temperature. The films were seeded with L929 fibroblast and hFOB1.19 osteoblast cells and subjected to in vitro tests. Both fibroblast and osteoblast cells have a good adherence on the Mn-CHA film and on the Ti or polystyrene references. Proliferation and viability tests showed that osteoblast cells growth on Mn-CHA-coated Ti was enhanced as compared to uncoated pure Ti surfaces. Caspase-1 activity was not affected significantly by the material, showing that Mn-CHA does not induce apoptosis of cultured cells. These results demonstrate that Mn-CHA films on Ti should provoke a faster osteointegration of the coated implants as compared to pure Ti. (c) 2004 Wiley Periodicals, Inc. J Biomed Mater Res 71A: 353-358, 2004.

  1. Reduced Cu concentration in CuAl-LPE-grown thin Si layers

    SciTech Connect

    Wang, T.H.; Ciszek, T.F.; Asher, S.; Reedy, R.

    1995-08-01

    Cu-Al has been found to be a good solvent system to grow macroscopically smooth Si layers with thicknesses in tens of microns on cast MG-Si substrates by liquid phase epitaxy (LPE) at temperatures near 900{degrees}C. This solvent system utilizes Al to ensure good wetting between the solution and substrate by removing silicon native oxides, and employs Cu to control Al doping into the layers. Isotropic growth is achieved because of a high concentration of solute silicon in the solution and the resulting microscopically rough interface. The incorporation of Cu in the Si layers, however, was a concern since Cu is a major solution component and is generally regarded as a bad impurity for silicon devices due to its fast diffusivity and deep energy levels in the band gap. A study by Davis shows that Cu will nonetheless not degrade solar cell performance until above a level of 10{sup 17} cm{sup -3}. This threshold is expected to be even higher for thin layer silicon solar cells owing to the less stringent requirement on minority carrier diffusion length. But to ensure long term stability of solar cells, lower Cu concentrations in the thin layers are still preferred.

  2. Synthesis of LECBD grown cluster assembled SeO 2 thin films

    NASA Astrophysics Data System (ADS)

    Rath, S.; Das, K.; Sarangi, S. N.; Dash, A. K.; Ray, S. K.; Sahu, S. N.

    2006-12-01

    Cluster assembled selenium oxide (SeO 2) thin films, as a function of oxygen flow pressure (OFP) have been synthesized by a low energy cluster beam deposition (LECBD) technique. The OFP dependent surface morphology leading to well separated nanoclusters (size ranging from 50 to 200 nm) and fractal features are confirmed from transmission electron microscopic (TEM) measurements. A diffusion limited aggregation (DLA) mediated fractal growth with dimension as 1.71 ± 0.01 has been observed for high OFP (60 mbar). Structural analysis by glancing angle X-ray diffraction (GXRD) and selected area diffraction (SAD) studies identify the presence of tetragonal phase SeO 2 in the deposit. Micro-Raman studies indicate the shifts in bending and stretching vibrational phonon modes in cluster assembled SeO 2 as compared to their bulk counter part due to the phonon confinement effect.

  3. Intermodulation distortion measurements of MgB2 thin films grown by HPCVD

    NASA Astrophysics Data System (ADS)

    Cifariello, G.; Aurino, M.; di Gennaro, E.; Lamura, G.; Orgiani, P.; Villegier, J.-C.; Xi, X. X.; Andreone, A.

    2006-06-01

    The two tone intermodulation distortion (IMD) arising in MgB2 thin films synthesized by hybrid physical-chemical vapour deposition (HPCVD) is studied in order to probe the influence of the two bands on the symmetry of the gap function. The measurements are carried out by using a dielectrically loaded copper cavity operating at 7 GHz. Microwave data on samples having critical temperatures above 41 K, very low resistivity values, and residual resistivity ratio larger than 10, are shown. The dependence of the nonlinear surface losses and of the third order intermodulation products on the power feeding the cavity and on the temperature is analyzed. At low power, IMD versus temperature data show the intrinsic s-wave behaviour expected for this compound

  4. Crystallization kinetics of GeTe phase-change thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Sun, Xinxing; Thelander, Erik; Gerlach, Jürgen W.; Decker, Ulrich; Rauschenbach, Bernd

    2015-07-01

    Pulsed laser deposition was employed to the growth of GeTe thin films on Silicon substrates. X-ray diffraction measurements reveal that the critical crystallization temperature lies between 220 and 240 °C. Differential scanning calorimetry was used to investigate the crystallization kinetics of the as-deposited films, determining the activation energy to be 3.14 eV. Optical reflectivity and in situ resistance measurements exhibited a high reflectivity contrast of ~21% and 3-4 orders of magnitude drop in resistivity of the films upon crystallization. The results show that pulsed laser deposited GeTe films can be a promising candidate for phase-change applications.

  5. Microstructure investigation and magnetic study of permalloy thin films grown by thermal evaporation

    NASA Astrophysics Data System (ADS)

    Lamrani, Sabrina; Guittoum, Abderrahim; Schäfer, Rudolf; Pofahl, Stefan; Neu, Volker; Hemmous, Messaoud; Benbrahim, Nassima

    2016-06-01

    We study the effect of thickness on the structural and magnetic properties of permalloy thin films, evaporated on glass substrate. The films thicknesses range from 16 to 90 nm. From X-ray diffraction spectra analysis, we show that the thinner films present a "1,1,1" preferred orientation. However, the thicker films exhibit a random orientation. The grains size increases and the lattice parameter decreases with increasing thickness. The magnetic force microscopy observations display cross-tie walls features only for the two thicker films (60 and 90 nm thick films). The magnetic microstructure, carried out by Kerr microscopy technique, shows the presence of magnetic domains changing with the direction of applied magnetic field. The coercive field, Hc, was found to decrease from 6.5 for 16 to 1.75 Oe for 90 nm. All these results will be discussed and correlated.

  6. Effects of Precursor Concentration on Structural and Optical Properties of ZnO Thin Films Grown on Muscovite Mica Substrates by Sol-Gel Spin-Coating.

    PubMed

    Kim, Younggyu; Leem, Jae-Young

    2016-05-01

    The structural and optical properties of the ZnO thin films grown on mica substrates for different precursor concentrations were investigated. The surface morphologies of all the samples indicated that they consisted of granular structures with spherical nano-sized crystallites. The thickness of the ZnO thin films increased significantly and the optical band gap exhibited a blue shift with an increase in the precursor concentration. It is remarkable that the highest I(NBE)/I(DLE) ratio was observed for the ZnO thin film with 0.8 M precursor concentration, even though cracks formed on the surface of this film. PMID:27483897

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

    NASA Astrophysics Data System (ADS)

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

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

  8. Photoluminescence study of epitaxially grown ZnSnAs2:Mn thin films

    NASA Astrophysics Data System (ADS)

    Mammadov, E.; Haneta, M.; Toyota, H.; Uchitomi, N.

    2011-03-01

    The photoluminescence (PL) properties of heavily Mn-doped ZnSnAs2 layers epitaxially grown on nearly lattice-matched semi-insulating InP substrates are studied. PL spectra are obtained for samples with Mn concentrations of 5, 12 and 24 mol% relative to the combined concentrations of Zn and Sn. A broad emission band centered at ~ 1 eV is detected for Mn-doped layers at room temperature. The emission is a intense broad asymmetric line at low temperatures. The line is reconstructed by superposition of two bands with peak energies of ~ 0.99 and 1.07 eV, similar to those reported for InP. These bands are superimposed onto a 1.14 eV band with well-resolved phonon structure for the layer doped with 12 % Mn. Recombination mechanism involving the split-off band of the ZnSnAs2 is suggested. Temperature dependence of integrated intensities of the PL bands indicates to thermally activated emission with activation energies somewhat different from those found for InP. Mn substitution at cationic sites increases the concentration of holes which may act as recombination centers. Recombination to the holes bound to Mn ions with the ground state located below the top of the valence band has been proposed as a possible PL mechanism.

  9. Visible and infrared emission from GaN:Er thin films grown by sputtering

    SciTech Connect

    Chen, H.; Gurumurugan, K.; Kordesch, M.E.; Jadwisienczak, W.M.; Lozykowski, H.J.

    2000-07-01

    Erbium-doped films were grown on sapphire and silicon substrates by reactive sputtering, with different Er concentrations in the film. GaN films deposited at 800 K were determined to be polycrystalline by x-ray diffraction analysis, and retained their polycrystalline structure after annealing in nitrogen at 1,250 K. The Er-doped films showed optical transmission beginning at about 360 nm, and the Er dose and film purity were determined with Rutherford backscattering spectroscopy. Photoluminescence and cathodoluminescence spectroscopy showed sharp emission lines corresponding to Er{sup 3+} intra 4f{sup n} shell transitions over the range from 9--300 K. At above-bandgap optical and electron excitation, the {sup 4}S{sub 3/2} and {sup 4}F{sub 9/2} transition dominate, and are superposed on the yellow band emission. The infrared emission line at 1,543 nm, corresponding to the Er {sup 4}I{sub 13/2} to {sup 4}I{sub 5/2} transition is also observed.

  10. Influence of Postdeposition Cooling Atmosphere on Thermoelectric Properties of 2% Al-Doped ZnO Thin Films Grown by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Saini, S.; Mele, P.; Honda, H.; Matsumoto, K.; Miyazaki, K.; Luna, L. Molina; Hopkins, P. E.

    2015-06-01

    We have investigated the thermoelectric properties of 2% Al-doped ZnO (AZO) thin films depending on the postdeposition cooling atmosphere [in oxygen pressure (AZO-O) or vacuum (AZO-V)]. Thin films were grown by pulsed laser deposition on sapphire () substrates at various deposition temperatures ( to ). All films were c-axis oriented. The electrical conductivity of AZO-V thin films was higher than that of AZO-O thin films across the whole temperature range from 300 K to 600 K, due to the optimal carrier concentration () of AZO-V samples. Furthermore, the thermoelectric performance of AZO-V films increased with the deposition temperature; for instance, the highest power factor of and dimensionless figure of merit of 0.07 at 600 K were found for AZO-V thin film deposited at.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  12. Characterization of diamond-like nanocomposite thin films grown by plasma enhanced chemical vapor deposition

    SciTech Connect

    Santra, T. S.; Liu, C. H.; Bhattacharyya, T. K.; Patel, P.; Barik, T. K.

    2010-06-15

    Diamond-like nanocomposite (DLN) thin films, comprising the networks of a-C:H and a-Si:O were deposited on pyrex glass or silicon substrate using gas precursors (e.g., hexamethyldisilane, hexamethyldisiloxane, hexamethyldisilazane, or their different combinations) mixed with argon gas, by plasma enhanced chemical vapor deposition technique. Surface morphology of DLN films was analyzed by atomic force microscopy. High-resolution transmission electron microscopic result shows that the films contain nanoparticles within the amorphous structure. Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS) were used to determine the structural change within the DLN films. The hardness and friction coefficient of the films were measured by nanoindentation and scratch test techniques, respectively. FTIR and XPS studies show the presence of C-C, C-H, Si-C, and Si-H bonds in the a-C:H and a-Si:O networks. Using Raman spectroscopy, we also found that the hardness of the DLN films varies with the intensity ratio I{sub D}/I{sub G}. Finally, we observed that the DLN films has a better performance compared to DLC, when it comes to properties like high hardness, high modulus of elasticity, low surface roughness and low friction coefficient. These characteristics are the critical components in microelectromechanical systems (MEMS) and emerging nanoelectromechanical systems (NEMS).

  13. Design of step composition gradient thin film transistor channel layers grown by atomic layer deposition

    SciTech Connect

    Ahn, Cheol Hyoun; Hee Kim, So; Gu Yun, Myeong; Koun Cho, Hyung

    2014-12-01

    In this study, we proposed the artificially designed channel structure in oxide thin-film transistors (TFTs) called a “step-composition gradient channel.” We demonstrated Al step-composition gradient Al-Zn-O (AZO) channel structures consisting of three AZO layers with different Al contents. The effects of stacking sequence in the step-composition gradient channel on performance and electrical stability of bottom-gate TFT devices were investigated with two channels of inverse stacking order (ascending/descending step-composition). The TFT with ascending step-composition channel structure (5 → 10 → 14 at. % Al composition) showed relatively negative threshold voltage (−3.7 V) and good instability characteristics with a reduced threshold voltage shift (Δ 1.4 V), which was related to the alignment of the conduction band off-set within the channel layer depending on the Al contents. Finally, the reduced Al composition in the initial layer of ascending step-composition channel resulted in the best field effect mobility of 4.5 cm{sup 2}/V s. We presented a unique active layer of the “step-composition gradient channel” in the oxide TFTs and explained the mechanism of adequate channel design.

  14. Nanobrick wall multilayer thin films grown faster and stronger using electrophoretic deposition

    NASA Astrophysics Data System (ADS)

    Cho, Chungyeon; Wallace, Kevin L.; Hagen, David A.; Stevens, Bart; Regev, Oren; Grunlan, Jaime C.

    2015-05-01

    In an effort to speed up the layer-by-layer (LbL) deposition technique, electrophoretic deposition (EPD) is employed with weak polyelectrolytes and clay nanoplatelets. The introduction of an electric field results in nearly an order of magnitude increase in thickness relative to conventional LbL deposition for a given number of deposited layers. A higher clay concentration also results with the EPD-LbL process, which produces higher modulus and strength with fewer deposited layers. A 20 quadlayer (QL) assembly of linear polyethyleneimine (LPEI)/poly(acrylic acid)/LPEI/clay has an elastic modulus of 45 GPa, tensile strength of 70 MPa, and thickness of 4.4 μm. Traditional LbL requires 40 QL to achieve the same thickness, with lower modulus and strength. This study reveals how these films grow and maintain a highly ordered nanobrick wall structure that is commonly associated with LbL deposition. Fewer layers required to achieve improved properties will open up many new opportunities for this multifunctional thin film deposition technique.

  15. The Seebeck Coefficient in Oxygen Enriched La2NiO4

    NASA Astrophysics Data System (ADS)

    Bach, Paul; Leboran, Victor; Rivadulla, Francisco

    2013-03-01

    Oxide-based devices show promise for themoelectric applications due to their chemical stability and straightforward fabrication. The La2NiO4+δ system has been predicted to show an increased thermopower coupled with an increased electrical conductivity around δ = 0 . 05 [Pardo et al. PRB 86, 165114 (2012)] that could lead to a large thermoelectric figure of merit (ZT). We investigate the suitability of lanthanum nickelate as a candidate material for high-ZT devices through a systematic study of oxygenated thin films grown by pulsed laser deposition. We report the electrical conductivity, Seebeck coefficient, and structural morphology of La2NiO4 grown in a range of oxidizing atmospheres and discuss their implications for controlled engineering of thermoelectric properties. We have explored the possibility of gate-tuning these systems in order to fabricate single-oxide based devices. This work was supported by the Ministerio de Ciencia e Innovación (Spain), grant MAT2010-16157, and the European Research Council, grant ERC-2010-StG 259082 2D THERMS.

  16. Structural, optical and electrical properties of chemically grown Pb 1- xFe xSe nanoparticle thin films

    NASA Astrophysics Data System (ADS)

    Bhardwaj, Asha; Varadarajan, E.; Srivastava, P.; Sehgal, H. K.

    2008-04-01

    Single phase Pb 1- xFe xSe ( 0.00≤x≤0.07) thin films, with typical rocksalt structure, are grown by the chemical bath deposition method. An additional segregated phase of Fe 2O 3 is observed in the x≥0.08 films. The average grain size in the films grown at a fixed bath temperature (Tb) is observed to remain constant with increase in Fe concentration from x=0.00 to x=0.07. A decrease in Tb, for fixed x, results in a decrease in grain size in the films. The Tb induced decrease in grain size is seen to result in an increase of direct optical band gap (Eg) in films with the same x. In the typical case of x=0.06 films, decrease in grain size from 9 nm to 3 nm due to change in Tb from 85 to 55 ∘C, results in an increase in Eg from 2.09 eV to 2.89 eV. The blue shift is attributed to enhanced quantum confinement in the nanograins. However, at a fixed Tb, while grain size remains constant with increase in x, Eg is observed to decrease. Eg is seen to decrease from 2.20 to 1.84 eV with change in x from 0.02 to 0.07 in Tb of 85 ∘C films. This decrease is attributed to tailoring of Eg due to alloying between PbSe (Ebulk=0.28 eV) and FeSe (Ebulk=0.14 eV) in the single-phase nanoparticle films of Pb 1- xFe xSe. Resistivity decreases while Hall mobility increases with the increase in x ( 0.00≤x≤0.06) in the films.

  17. NiO(s) (Bunsenite) is not Available to Alyssum species

    Technology Transfer Automated Retrieval System (TEKTRAN)

    AIMS: To determine if the Ni-hyperaccumulator Alyssum corsicum can absorb Ni from the kinetically inert crystalline mineral NiO(s) (bunsenite). METHODS: A. corsicum and A. montanum plants were grown for 30 days in a serpentine Hoagland solution. NiO was provided at 0 or 0.1 g L-1 (1.34 mmol L-1) ...

  18. Thin Silicon-Dioxide Films Grown on Silicon by Low Temperature Plasma Anodization and Rapid Thermal Processing: AN Electrostructural Analysis.

    NASA Astrophysics Data System (ADS)

    Nelson, Scott Alan

    1988-06-01

    Capacitance-voltage (CV) techniques and x-ray photoelectron spectroscopy (XPS) have been used to study the electrical and structural properties of thin (< 200A) SiO_2 films grown on silicon by two reduced thermal load (RTL) processes, RF plasma anodization and rapid thermal processing (RTP), and compare them to furnace oxides. The electrical quality and structural characteristics of the thin films have been monitored as a function of process conditions and parameters. In particular, the plasma process has been studied and an optimal process configuration established which produces oxides with midgap interface state densities of 1 times 10^{11} eV^{-1} cm^ {-2}, Q_{ox} values of 1 times 10 ^{11} cm^{ -2}, and breakdown fields of 13 MV/cm. X-ray photoelectron spectroscopy has been used to compare the average SiO_4 tetrahedral ring structures and the suboxide content of the ~3 nm thick interfacial region of the plasma and rapid thermal oxides and significant structural differences have been identified. By correlating these structural differences with measured electrical differences the structural causes of some of the electrical characteristics found to be particularly prominent in plasma and RTP oxides have been identified. In plasma oxides larger amounts of silicon dangling bonds, P_{b} centers at the Si-SiO_2 interface have been identified as the source of a localized peak of interface states found at 0.3 eV above the silicon valence band. The larger P_{b} center density is probably caused by radiation damage from hot electrons and photons from the plasma, as evidenced by increased numbers of P_{b} centers in oxides grown in higher power and higher voltage plasmas, and by incomplete oxidation of the interface, as evidenced by a decreased P_{b} center density with increased oxidant flux via increased bias current density. Low temperature, 800-850C, rapid thermal annealing of the plasma oxides relieves localized compressive interfacial strain, apparently by allowing

  19. Thin yttrium iron garnet films grown by pulsed laser deposition: Crystal structure, static, and dynamic magnetic properties

    NASA Astrophysics Data System (ADS)

    Sokolov, N. S.; Fedorov, V. V.; Korovin, A. M.; Suturin, S. M.; Baranov, D. A.; Gastev, S. V.; Krichevtsov, B. B.; Maksimova, K. Yu.; Grunin, A. I.; Bursian, V. E.; Lutsev, L. V.; Tabuchi, M.

    2016-01-01

    Pulsed laser deposition has been used to grow thin (10-84 nm) epitaxial layers of Yttrium Iron Garnet Y3Fe5O12 (YIG) on (111)-oriented Gadolinium Gallium Garnet substrates at different growth conditions. Atomic force microscopy showed flat surface morphology both on micrometer and nanometer scales. X-ray diffraction measurements revealed that the films are coherent with the substrate in the interface plane. The interplane distance in the [111] direction was found to be by 1.2% larger than expected for YIG stoichiometric pseudomorphic film indicating presence of rhombohedral distortion in this direction. Polar Kerr effect and ferromagnetic resonance measurements showed existence of additional magnetic anisotropy, which adds to the demagnetizing field to keep magnetization vector in the film plane. The origin of the magnetic anisotropy is related to the strain in YIG films observed by XRD. Magneto-optical Kerr effect measurements revealed important role of magnetization rotation during magnetization reversal. An unusual fine structure of microwave magnetic resonance spectra has been observed in the film grown at reduced (0.5 mTorr) oxygen pressure. Surface spin wave propagation has been demonstrated in the in-plane magnetized films.

  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. Structural, morphological, and optoelectrical characterization of Bi2S3 thin films grown by co-evaporation

    NASA Astrophysics Data System (ADS)

    Mesa, F.; Arredondo, C. A.; Vallejo, W.

    2016-03-01

    This work presents the results of synthesis and characterization of polycrystalline n-type Bi2S3 thin films. The films were grown through a chemical reaction from co-evaporation of their precursor elements in a soda-lime glass substrate. The effect of the experimental conditions on the optical, morphological structural properties, the growth rate, and the electrical conductivity (σ) was studied through spectral transmittance, X-ray diffraction (XRD), atomic force microscopy (AFM) and σ versus T measurements, respectively. The results showed that the films grow only in the orthorhombic Bi2S3 bismuthinite phase. It was also found that the Bi2S3 films present an energy band gap (Eg) of about 1.38 eV. In addition to these results, the electrical conductivity of the Bi2S3 films was affected by both the transport of free carriers in extended states of the conduction band and for variable range hopping transport mechanisms, each one predominating in a different temperature range.

  2. Surface sulfurization on MBE-grown Cu(In1-x,Gax)Se2 thin films and devices

    NASA Astrophysics Data System (ADS)

    Khatri, Ishwor; Matsuyama, Isamu; Yamaguchi, Hiroshi; Fukai, Hirofumi; Nakada, Tokio

    2015-08-01

    Molecular beam epitaxy (MBE) grown Cu(In1-x,Gax)Se2 (CIGS) thin films were sulfurized at temperatures of 450-550 °C for 30 min in a 10% H2S-N2 mixture gas. The micro-roughness together with the S diffusion in the CIGS surfaces increased with increasing sulfurization temperature. Both near-band-edge PL intensity and decay time of the CIGS absorber layer enhanced after sulfurization. PL sub-peak around 80 meV below the main peak almost disappeared after sulfurization above 500 °C, which is expected due to the occupation of Se vacancies (Vse) with S. The open-circuit voltage (Voc), hence conversion efficiency, improved after sulfurization. The photovoltaic performance of the solar cells was consistent with PL intensity. Moreover, it is found for the first time from the SIMS analysis that the Cu atoms were depleted at the surface of CIGS layer after sulfurization, which could result in the improved Voc.

  3. Magnetic properties of Sm-Co thin films grown on MgO(100) deposited from a single alloy target

    SciTech Connect

    Verhagen, T. G. A.; Boltje, D. B.; Ruitenbeek, J. M. van; Aarts, J.

    2014-08-07

    We have grown epitaxial Sm-Co thin films by sputter deposition from a single alloy target with a nominal SmCo{sub 5} composition on Cr(100)-buffered MgO(100) single-crystal substrates. By varying the Ar gas pressure, we can change the composition of the film from a SmCo{sub 5}-like to a Sm{sub 2}Co{sub 7}-like phase. The composition, crystal structure, morphology, and magnetic properties of these films have been determined using Rutherford Backscattering, X-ray diffraction, and magnetization measurements. We find that we can grow films with, at room temperature, coercive fields as high as 3.3 T, but with a remanent magnetization which is lower than can be expected from the texturing. This appears to be due to the Sm content of the films, which is higher than expected from the content of the target, even at the lowest possible sputtering pressures. Moreover, we find relatively large variations of film properties using targets of nominally the same composition. At low temperatures, the coercive fields increase, as expected for these hard magnets, but in the magnetization, we observe a strong background signal from the paramagnetic impurities in the MgO substrates.

  4. Structural properties of Bi2-xMnxSe3 thin films grown via molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Babakiray, Sercan; Johnson, Trent A.; Borisov, Pavel; Holcomb, Mikel B.; Lederman, David; Marcus, Matthew A.; Tarafder, Kartick

    2015-07-01

    The effects of Mn doping on the structural properties of the topological insulator Bi2Se3 in thin film form were studied in samples grown via molecular beam epitaxy. Extended x-ray absorption fine structure measurements, supported by density functional theory calculations, indicate that preferential incorporation occurs substitutionally in Bi sites across the entire film volume. This finding is consistent with x-ray diffraction measurements which show that the out of plane lattice constant expands while the in plane lattice constant contracts as the Mn concentration is increased. X-ray photoelectron spectroscopy indicates that the Mn valency is 2+ and that the Mn bonding is similar to that in MnSe. The expansion along the out of plane direction is most likely due to weakening of the Van der Waals interactions between adjacent Se planes. Transport measurements are consistent with this Mn2+ substitution of Bi sites if additional structural defects induced by this substitution are taken into account.

  5. 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.

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

    PubMed

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

    2016-05-04

    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.

  7. Impact of low temperature annealing on structural, optical, electrical and morphological properties of ZnO thin films grown by RF sputtering for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Purohit, Anuradha; Chander, S.; Sharma, Anshu; Nehra, S. P.; Dhaka, M. S.

    2015-11-01

    This paper presents effect of low temperature annealing on the physical properties of ZnO thin films for photovoltaic applications. The thin films of thickness 50 nm were grown on glass and indium tin oxide (ITO) coated glass substrates employing radio frequency magnetron sputtering technique followed by thermal annealing within low temperature range 150-450 °C. These as-grown and annealed films were subjected to the X-ray diffraction (XRD), UV-Vis spectrophotometer, source meter and scanning electron microscopy (SEM) for structural, optical, electrical and surface morphological analysis respectively. The compositional analysis of the as-grown ZnO film was also carried out using energy dispersive spectroscopy (EDS). The XRD patterns reveal that the films have wurtzite structure of hexagonal phase with preferred orientation (1 0 0) and polycrystalline in nature. The crystallographic and optical parameters are calculated and discussed in detail. The optical band gap was found in the range 3.30-3.52 eV and observed to decrease with annealing temperature except 150 °C. The current-voltage characteristics show that the films exhibit approximately ohmic behavior. The SEM studies show that the films are uniform, homogeneous and free from crystal defects and voids. The experimental results reveal that ZnO thin films may be used as alternative materials for eco-friendly buffer layer to the thin film solar cell applications.

  8. The orientational relationship between monoclinic β-Ga2O3 and cubic NiO

    NASA Astrophysics Data System (ADS)

    Nakagomi, Shinji; Kubo, Shohei; Kokubun, Yoshihiro

    2016-07-01

    The orientational relationship between β-Ga2O3 and NiO was studied by X-ray diffraction measurements and cross-sectional high resolution transmission electron microscopy. A β-Ga2O3 thin film was formed on a (100) NiO layer on a (100) MgO substrate by gallium evaporation in an oxygen plasma. It was found that the resulting β-Ga2O3 had a four-fold domain structure satisfying both (100) β-Ga2O3 ‖ (100) NiO and (010) β-Ga2O3 ‖ {011} NiO. A γ-Ga2O3 layer was observed at the interface between the β-Ga2O3 and the NiO. An NiO film was also formed on a (100) β-Ga2O3 single-crystal substrate by the sol-gel method. An epitaxial (100) NiO film was formed on a (100) β-Ga2O3 substrate, and satisfied (011) NiO ‖ (010) β-Ga2O3. The crystal orientations of β-Ga2O3 on (100) NiO and NiO on (100) β-Ga2O3 can be explained using atomic arrangement models of the (100) plane of NiO and the (100) plane of β-Ga2O3.

  9. Nanoscale observation of surface potential and carrier transport in Cu2ZnSn(S,Se)4 thin films grown by sputtering-based two-step process

    PubMed Central

    2014-01-01

    Stacked precursors of Cu-Zn-Sn-S were grown by radio frequency sputtering and annealed in a furnace with Se metals to form thin-film solar cell materials of Cu2ZnSn(S,Se)4 (CZTSSe). The samples have different absorber layer thickness of 1 to 2 μm and show conversion efficiencies up to 8.06%. Conductive atomic force microscopy and Kelvin probe force microscopy were used to explore the local electrical properties of the surface of CZTSSe thin films. The high-efficiency CZTSSe thin film exhibits significantly positive bending of surface potential around the grain boundaries. Dominant current paths along the grain boundaries are also observed. The surface electrical parameters of potential and current lead to potential solar cell applications using CZTSSe thin films, which may be an alternative choice of Cu(In,Ga)Se2. PACS number: 08.37.-d; 61.72.Mm; 71.35.-y PMID:24397924

  10. Synthesis and frequency-dependent dielectric properties of epitaxial La1.875Sr0.125NiO4 thin films

    SciTech Connect

    Podpirka, Adrian; Tselev, Alexander; Ramanathan, Shriram

    2012-01-01

    Epitaxial thin films of La{sub 1.875}Sr{sub 0.125}NiO{sub 4} (lanthanum strontium nickelate, LSNO) have been synthesized by sputtering onto single crystal oxide substrates and their structural and dielectric properties are reported. High dielectric constants on the order of 10{sup 7} have been measured up to 1 MHz in interdigitated capacitors with a frequency dependence that correlates with substrate imposed strain and texture. The observation of a high dielectric constant albeit with moderate loss tangent at high frequencies motivates further explorations of charge ordering phenomena in such complex oxides and serves to examine size effects on dielectric response by comparison with studies on bulk single crystal LSNO.

  11. Enhancement of critical current density in YBa2Cu3O7-dgr thin films grown using PLD on YSZ (001) surface modified with Ag nano-dots

    NASA Astrophysics Data System (ADS)

    Ionescu, M.; Li, A. H.; Zhao, Y.; Liu, H. K.; Crisan, A.

    2004-07-01

    Y123 thin films were grown by pulsed laser deposition (PLD) on YSZ (001) substrate. Prior to the film deposition, a discontinuous layer of Ag was deposited on the substrate, also using PLD, in the form of separate islands. Atomic force microscopy (AFM) investigation of the Ag layer showed that its morphology consisted of self-assembled islands of nanometre size, randomly distributed on the surface of the substrate, called nano-dots. The Y123 superconducting films grown on such a surface were characterized using AFM, x-ray diffraction, secondary electron microscopy, ac susceptibility and dc magnetization. The results show that there is no significant difference in surface morphology, crystallographic orientation, phase composition or superconducting transition temperature between the Y123 films grown on YSZ (001) with an Ag nano-dots layer and a control Y123 film grown on a virgin YSZ (001) surface. On the other hand, at 77 K, the magnetic critical current density ( J_c^m ) was three times higher for the Y123 film grown on YSZ with the modified (001) surface than for the film grown on YSZ with a virgin (001) surface. At 5 K the enhancement of J_c^m was approximately seven times, at both low and high fields. This suggests an increase in pinning, caused presumably by point defects formed in the Y123 film above the Ag islands.

  12. Effect of growth temperature on magnetic and electronic properties of epitaxially grown MnAs thin films on GaAs(100) substrates

    SciTech Connect

    Song, J. H.; Cui, Y.; Ketterson, J. B.

    2013-05-07

    We grew epitaxial MnAs thin films on GaAs(100) substrates using molecular-beam epitaxy and investigated the growth temperature dependences of their physical properties. With increasing growth temperature from 200 Degree-Sign C to 350 Degree-Sign C, the crystal orientation of the film changed from type-A to type-B. The Curie temperatures of all type-B samples were {approx}346 K, while the type-A sample showed a lower bulk-like value of {approx}318 K, indicating an improvement in magnetic properties. Samples grown at above 550 Degree-Sign C exhibited semiconducting behavior, whereas the lower temperature grown samples show metallic behavior as expected. Our results indicate that growth temperature plays an important role in determining the crystal structure, magnetic, and electrical-transport properties of MnAs/GaAs(100) thin films.

  13. Surface oxygen exchange properties of Sr doped La2NiO4+δ as SOFC cathode: Thin-film electrical conductivity relaxation investigation

    DOE PAGES

    Guan, Bo; Li, Wenyuan; Zhang, Xinxin; Liu, Xingbo

    2015-06-02

    La2-xSrxNiO4+δ dense films are prepared by a novel spray-modified pressing method. The surface reaction kinetics is investigated via electrical conductivity relaxation (ECR). The layer thickness, 5~10 μm, is much less than the characteristic length of lanthanum nickelates, resulting in surface-controlled situation and allowing more accurate fitting than the traditional pellets ECR on the surface exchange coefficient (k). k for LNO is 1.6×10-5 cm/s in 0.2 atm at 700°C. Sr doping impairs the exchange kinetics, and k of Sr40 is about one order of magnitude smaller than undoped one. Interstitial oxygen and Ni oxidation state are suggested the predominant roles inmore » determining surface kinetics. In conclusion, given the properties of the thin-film herein developed by spray-modified pressing is closer to those in practical porous electrode compared to pulsed laser deposited film in terms of preferential orientation and strain, it warrants the use of such a method in a variety of pertinent investigations.« less

  14. Angle-resolved photoemission spectroscopy of strontium lanthanum copper oxide thin films grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Harter, John Wallace

    Among the multitude of known cuprate material families and associated structures, the archetype is "infinite-layer" ACuO2, where perfectly square and flat CuO2 planes are separated by layers of alkaline earth atoms. The infinite-layer structure is free of magnetic rare earth ions, oxygen chains, orthorhombic distortions, incommensurate superstructures, ordered vacancies, and other complications that abound among the other material families. Furthermore, it is the only cuprate that can be made superconducting by both electron and hole doping, making it a potential platform for decoding the complex many-body interactions responsible for high-temperature superconductivity. Research on the infinite-layer compound has been severely hindered by the inability to synthesize bulk single crystals, but recent progress has led to high-quality superconducting thin film samples. Here we report in situ angle-resolved photoemission spectroscopy measurements of epitaxially-stabilized Sr1-chiLa chiCuO2 thin films grown by molecular-beam epitaxy. At low doping, the material exhibits a dispersive lower Hubbard band typical of other cuprate parent compounds. As carriers are added to the system, a continuous evolution from Mott insulator to superconducting metal is observed as a coherent low-energy band develops on top of a concomitant remnant lower Hubbard band, gradually filling in the Mott gap. For chi = 0.10, our results reveal a strong coupling between electrons and (pi,pi) anti-ferromagnetism, inducing a Fermi surface reconstruction that pushes the nodal states below the Fermi level and realizing nodeless superconductivity. Electron diffraction measurements indicate the presence of a surface reconstruction that is consistent with the polar nature of Sr1-chiLachiCuO2. Most knowledge about the electron-doped side of the cuprate phase diagram has been deduced by generalizing from a single material family, Re2-chi CechiCuO4, where robust antiferromagnetism has been observed past chi

  15. An amorphous-to-crystalline phase transition within thin silicon films grown by ultra-high-vacuum evaporation and its impact on the optical response

    NASA Astrophysics Data System (ADS)

    Orapunt, Farida; Tay, Li-Lin; Lockwood, David J.; Baribeau, Jean-Marc; Noël, Mario; Zwinkels, Joanne C.; O'Leary, Stephen K.

    2016-02-01

    A number of thin silicon films are deposited on crystalline silicon, native oxidized crystalline silicon, and optical quality fused quartz substrates through the use of ultra-high-vacuum evaporation at growth temperatures ranging from 98 to 572 °C. An analysis of their grazing incidence X-ray diffraction and Raman spectra indicates that a phase transition, from amorphous-to-crystalline, occurs as the growth temperature is increased. Through a peak decomposition process, applied to the Raman spectroscopy results, the crystalline volume fractions associated with these samples are plotted as a function of the growth temperature for the different substrates considered. It is noted that the samples grown on the crystalline silicon substrates have the lowest crystallanity onset temperature, whereas those grown on the optical quality fused quartz substrates have the highest crystallanity onset temperature; the samples grown on the native oxidized crystalline silicon substrates have a crystallanity onset temperature between these two limits. These resultant dependencies on the growth temperature provide a quantitative means of characterizing the amorphous-to-crystalline phase transition within these thin silicon films. It is noted that the thin silicon film grown on an optical quality fused quartz substrate at 572 °C, possessing an 83% crystalline volume fraction, exhibits an optical absorption spectrum which is quite distinct from that associated with the other thin silicon films. We suggest that this is due to the onset of sufficient long-range order in the film for wave-vector conservation to apply, at least partially. Finally, we use a semi-classical optical absorption analysis to study how this phase transition, from amorphous-to-crystalline, impacts the spectral dependence of the optical absorption coefficient.

  16. Some optical and electron microscope comparative studies of excimer laser-assisted and nonassisted molecular-beam epitaxically grown thin GaAs films on Si

    NASA Technical Reports Server (NTRS)

    Lao, Pudong; Tang, Wade C.; Rajkumar, K. C.; Guha, S.; Madhukar, A.; Liu, J. K.; Grunthaner, F. J.

    1990-01-01

    The quality of GaAs thin films grown via MBE under pulsed excimer laser irradiation on Si substrates is examined in both laser-irradiated and nonirradiated areas using Raman scattering, Rayleigh scattering, and by photoluminescence (PL), as a function of temperature, and by TEM. The temperature dependence of the PL and Raman peak positions indicates the presence of compressive stress in the thin GaAs films in both laser-irradiated and nonirradiated areas. This indicates incomplete homogeneous strain relaxation by dislocations at the growth temperature. The residual compressive strain at the growth temperature is large enough such that even with the introduction of tensile strain arising from the difference in thermal expansion coefficients of GaAs and Si, a compressive strain is still present at room temperature for these thin GaAs/Si films.

  17. Study of the optical properties and structure of ZnSe/ZnO thin films grown by MOCVD with varying thicknesses

    NASA Astrophysics Data System (ADS)

    Jabri, S.; Amiri, G.; Sallet, V.; Souissi, A.; Meftah, A.; Galtier, P.; Oueslati, M.

    2016-05-01

    ZnSe layers were grown on ZnO substrates by the metal organic chemical vapor deposition technique. A new structure appeared at lower thicknesses films. The structural properties of the thin films were studied by the X-ray diffraction (XRD) and Raman spectroscopy methods. First, Raman selection rules are explicitly put forward from a theoretical viewpoint. Second, experimentally-retrieved-intensities of the Raman signal as a function of polarization angle of incident light are fitted to the obtained theoretical dependencies in order to confirm the crystallographic planes of zinc blend ZnSe thin film, and correlate with DRX measurements. Raman spectroscopy has been used to characterize the interfacial disorder that affects energy transport phenomena at ZnSe/ZnO interfaces and the Photoluminescence (PL) near the band edge of ZnSe thin films.

  18. X-ray analysis of strain distribution in two-step grown epitaxial SrTiO{sub 3} thin films

    SciTech Connect

    Panomsuwan, Gasidit E-mail: g.panomsuwan@gmail.com; Takai, Osamu; Saito, Nagahiro

    2014-08-04

    Epitaxial SrTiO{sub 3} (STO) thin films were grown on (001)-oriented LaAlO{sub 3} (LAO) substrates using a two-step growth method by ion beam sputter deposition. An STO buffer layer was initially grown on the LAO substrate at a low temperature of 150 °C prior to growing the STO main layer at 750 °C. The thickness of the STO buffer layer was varied at 3, 6, and 10 nm, while the total film thickness was kept constant at approximately 110 nm. According to x-ray structural analysis, we show that the STO buffer layer plays an essential role in controlling the strain in the STO layer grown subsequently. It is found that the strains in the STO films are more relaxed with an increase in buffer layer thickness. Moreover, the strain distribution in two-step grown STO films becomes more homogeneous across the film thickness when compared to that in directly grown STO film.

  19. 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.

  20. Fabricating superconducting interfaces between artificially grown LaAlO{sub 3} and SrTiO{sub 3} thin films

    SciTech Connect

    Li, Danfeng Gariglio, Stefano; Cancellieri, Claudia; Fête, Alexandre; Stornaiuolo, Daniela; Triscone, Jean-Marc

    2014-01-01

    Realization of a fully metallic two-dimensional electron gas (2DEG) at the interface between artificially grown LaAlO{sub 3} and SrTiO{sub 3} thin films has been an exciting challenge. Here we present for the first time the successful realization of a superconducting 2DEG at interfaces between artificially grown LaAlO{sub 3} and SrTiO{sub 3} thin films. Our results highlight the importance of two factors—the growth temperature and the SrTiO{sub 3} termination. We use local friction force microscopy and transport measurements to determine that in normal growth conditions the absence of a robust metallic state at low temperature in the artificially grown LaAlO{sub 3}/SrTiO{sub 3} interface is due to the nanoscale SrO segregation occurring on the SrTiO{sub 3} film surface during the growth and the associated defects in the SrTiO{sub 3} film. By adopting an extremely high SrTiO{sub 3} growth temperature, we demonstrate a way to realize metallic, down to the lowest temperature, and superconducting 2DEG at interfaces between LaAlO{sub 3} layers and artificially grown SrTiO{sub 3} thin films. This study paves the way to the realization of functional LaAlO{sub 3}/SrTiO{sub 3} superlattices and/or artificial LaAlO{sub 3}/SrTiO{sub 3} interfaces on other substrates.

  1. NIO1 diagnostics

    SciTech Connect

    Zaniol, B. Barbisan, M.; Pasqualotto, R.; Serianni, G.; Cavenago, M.; De Muri, M.; Mimo, A.

    2015-04-08

    The radio frequency ion source NIO1, jointly developed by Consorzio RFX and INFN-LNL, will generate a 60kV-135mA hydrogen negative ion beam, composed of 9 beamlets over an area of about 40 × 40 mm{sup 2}. This experiment will operate in continuous mode and in conditions similar to those foreseen for the larger ion sources of the Neutral Beam Injectors for ITER. The modular design of NIO1 is convenient to address the several still open important issues related to beam extraction, optics, and performance optimization. To this purpose a set of diagnostics is being implemented. Electric and water cooling plant related measurements will allow monitoring current, pressure, flow, and temperature. The plasma in the source will be characterized by emission spectroscopy, cavity ring-down and laser absorption spectroscopy. The accelerated beam will be analyzed with a fast emittance scanner, its intensity profile and divergence with beam emission spectroscopy and visible tomography. The power distribution of the beam on the calorimeter will be monitored by thermocouples and by an infrared camera. This contribution presents the implementation and initial operation of some of these diagnostics in the commissioning phase of the experiment, in particular the cooling water calorimetry and emission spectroscopy.

  2. Effect of particle size and inter-electrode distance on the field-emission properties of nanocrystalline CdS thin films grown in a polymer matrix by chemical bath deposition

    NASA Astrophysics Data System (ADS)

    Ghosh, P. K.; Jana, S.; Maity, U. N.; Chattopadhyay, K. K.

    2006-10-01

    The field-emission property of transparent nanocrystalline CdS thin films, grown by chemical bath deposition (CBD) within the pores of polyvinyl alcohol (PVA) on Si and glass substrates, has been studied. X-ray diffraction and transmission electron microscopy studies confirmed the nanocrystalline nature of the CdS particles with sizes lying in the range 6-12 nm. The Fowler-Nordhiem plots of the emission current from the nano-CdS/PVA thin films are almost straight line. The turn-on fields of the grown nano-CdS/PVA thin films are found to be in the range of 3.6-6.6 V/μm. The turn-on field decreases with the decrease of particle size. Only PVA thin film and bulk CdS/PVA composite thin film grown on Si substrates have not showed field-emission property under the same conditions.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  4. Structural, electrical, and optical properties of transparent gallium oxide thin films grown by plasma-enhanced atomic layer deposition

    SciTech Connect

    Shan, F.K.; Liu, G.X.; Lee, W.J.; Lee, G.H.; Kim, I.S.; Shin, B.C.

    2005-07-15

    Gallium oxide (Ga{sub 2}O{sub 3}) thin films were deposited on silicon (100) and sapphire (001) substrates using the plasma-enhanced atomic layer deposition (PEALD) technique with an alternating supply of reactant source, [(CH{sub 3}){sub 2}GaNH{sub 2}]{sub 3}, and oxygen plasma. The thin films were annealed at different temperatures (500, 700, and 900 deg. C, respectively) in a rapid thermal annealing system for 1 min. It was found that Ga{sub 2}O{sub 3} thin films deposited by PEALD showed excellent step coverage characteristics. X-ray diffraction measurements showed that the as-deposited thin film was amorphous. However, the thin films annealed at temperatures higher than 700 deg. C showed a (400) orientation of the monoclinic structure. An atomic force microscope was used to investigate the surface morphologies of the thin films. The thin films showed very smooth surfaces; the roughness of the as-deposited thin film was about 4 A . With increasing annealing temperature, the thin film became rougher compared with that annealed at lower temperatures. A double-beam spectrophotometer was used to measure the transmittances of the thin films on the sapphire substrates. The thin films showed a very high transmittance (nearly 100%). The band-gap energies of the thin films were determined by a linear fit of the transmittance spectra and were calculated to be between 5.0 and 5.24 eV. The electrical properties of thin films of Pt/film/Si structure were also investigated. It was found that, with increasing annealing temperature, the insulating characteristics of the Ga{sub 2}O{sub 3} thin films were significantly improved. Spectroscopic ellipsometry was used to derive the refractive indices and the thicknesses of the thin films. The refractive indices of the thin films showed normal dispersion behavior. The refractive indices of the thin films annealed at low temperatures were smaller than those annealed at high temperatures.

  5. Thermal stability and relaxation mechanisms in compressively strained Ge0.94Sn0.06 thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Fleischmann, C.; Lieten, R. R.; Hermann, P.; Hönicke, P.; Beckhoff, B.; Seidel, F.; Richard, O.; Bender, H.; Shimura, Y.; Zaima, S.; Uchida, N.; Temst, K.; Vandervorst, W.; Vantomme, A.

    2016-08-01

    Strained Ge1-xSnx thin films have recently attracted a lot of attention as promising high mobility or light emitting materials for future micro- and optoelectronic devices. While they can be grown nowadays with high crystal quality, the mechanism by which strain energy is relieved upon thermal treatments remains speculative. To this end, we investigated the evolution (and the interplay) of composition, strain, and morphology of strained Ge0.94Sn0.06 films with temperature. We observed a diffusion-driven formation of Sn-enriched islands (and their self-organization) as well as surface depressions (pits), resulting in phase separation and (local) reduction in strain energy, respectively. Remarkably, these compositional and morphological instabilities were found to be the dominating mechanisms to relieve energy, implying that the relaxation via misfit generation and propagation is not intrinsic to compressively strained Ge0.94Sn0.06 films grown by molecular beam epitaxy.

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

    SciTech Connect

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

    2010-10-11

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

  7. High electron mobility thin-film transistors based on Ga{sub 2}O{sub 3} grown by atmospheric ultrasonic spray pyrolysis at low temperatures

    SciTech Connect

    Thomas, Stuart R. E-mail: thomas.anthopoulos@imperial.ac.uk; Lin, Yen-Hung; Faber, Hendrik; Anthopoulos, Thomas D. E-mail: thomas.anthopoulos@imperial.ac.uk; Adamopoulos, George; Sygellou, Labrini; Stratakis, Emmanuel; Pliatsikas, Nikos; Patsalas, Panos A.

    2014-09-01

    We report on thin-film transistors based on Ga{sub 2}O{sub 3} films grown by ultrasonic spray pyrolysis in ambient atmosphere at 400–450 °C. The elemental, electronic, optical, morphological, structural, and electrical properties of the films and devices were investigated using a range of complementary characterisation techniques, whilst the effects of post deposition annealing at higher temperature (700 °C) were also investigated. Both as-grown and post-deposition annealed Ga{sub 2}O{sub 3} films are found to be slightly oxygen deficient, exceptionally smooth and exhibit a wide energy bandgap of ∼4.9 eV. Transistors based on as-deposited Ga{sub 2}O{sub 3} films show n-type conductivity with the maximum electron mobility of ∼2 cm{sup 2}/V s.

  8. High-efficiency blue LEDs with thin AlGaN interlayers in InGaN/GaN MQWs grown on Si (111) substrates

    NASA Astrophysics Data System (ADS)

    Kimura, Shigeya; Yoshida, Hisashi; Ito, Toshihide; Okada, Aoi; Uesugi, Kenjiro; Nunoue, Shinya

    2016-02-01

    We demonstrate high-efficiency blue light-emitting diodes (LEDs) with thin AlGaN interlayers in InGaN/GaN multiquantum wells (MQWs) grown on Si (111) substrates. The peak external quantum efficiency (EQE) ηEQE of 82% at room temperature and the hot/cold factor (HCF) of 94% have been obtained by using the functional thin AlGaN interlayers in the MQWs in addition to reducing threading dislocation densities (TDDs) in the blue LEDs. An HCF is defined as ηEQE(85°C)/ηEQE(25°C). The blue LED structures were grown by metal-organic chemical vapor deposition on Si (111) substrates. The MQWs applied as an active layer have 8- pairs of InGaN/AlyGa1-yN/GaN (0<=y<=1) heterostructures. Thinfilm LEDs were fabricated by removing the Si (111) substrates from the grown layers. It is observed by high-resolution transmission electron microscopy and three-dimensional atom probe analysis that the 1 nm-thick AlyGa1-yN interlayers, whose Al content is y=0.3 or less, are continuously formed. EQE and the HCFs of the LEDs with thin Al0.15Ga0.85N interlayers are enhanced compared with those of the samples without the interlayers in the low-current-density region. We consider that the enhancement is due to both the reduction of the nonradiative recombination centers and the increase of the radiative recombination rate mediated by the strain-induced hole carriers indicated by the simulation of the energy band diagram.

  9. Optical properties of ZnO thin films grown on diamond-like carbon by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Li, Shao-lan; Zhang, Li-chun; Dong, Yan-feng; Zhao, Feng-zhou

    2012-11-01

    ZnO/diamond-like carbon (DLC) thin films are deposited by pulsed laser deposition (PLD), and the room-temperature photoluminescence (PL) is investigated. Using a fluorescence spectrophotometer, we obtain the PL spectra of DLC/Si and ZnO/Si thin films deposited at different substrate temperatures. The ZnO/DLC thin films show a broadband emission almost containing the entire visible spectrum. The Gaussian fitting curves of PL spectra reveal that the visible emission of ZnO/DLC thin films consists of three peaks centered at 381 nm, 526 nm and 682 nm, which are attributed to the radiative recombination of ZnO and DLC, respectively. The Commission International de l'Eclairage (CIE) 1931 ( x, y) chromaticity space of ZnO/DLC thin films indicates that the visible PL spectrum is very close to the standard white-light region.

  10. High hole concentration Li-doped NiZnO thin films grown by photo-assisted metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhao, Y. D.; Dong, X.; Ma, Z. Z.; Zhang, Y. T.; Wu, B.; Zhuang, S. W.; Zhang, B. L.; Li, W. C.; Du, G. T.

    2016-11-01

    High hole concentration Li-doped NiZnO thin films were grown by metal-organic chemical vapor deposition (MOCVD). The crystalline, optical, electrical, and morphological characteristics of the NiZnO films were studied as a function of lithium content. The resistance of the films decreased and the hole concentration greatly increased with increasing lithium content. However, the crystalline and optical properties were observed to degrade as the lithium content was increased. To relieve the degradation, a photo-assisted MOCVD method was used in order to restrict this degradation and this represents a new way to obtain stable high hole concentration NiZnO films.

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

    SciTech Connect

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

    2007-05-01

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

  12. Data storage applications based on LiCoO2 thin films grown on Al2O3 and Si substrates

    NASA Astrophysics Data System (ADS)

    Svoukis, E.; Mihailescu, C. N.; Mai, V. H.; Schneegans, O.; Breza, K.; Lioutas, C.; Giapintzakis, J.

    2016-09-01

    In this study, LiCoO2 thin films were investigated for data storage applications based on scanning probe mediated approaches. LiCoO2, compared to other materials proposed for scanning probe mediated nanoscale patterning, is highly stable and exhibits reversible electrochemical surface modifications. LiCoO2 thin films have been grown by pulsed laser deposition on Al2O3 and Si substrates over a range of deposition temperatures. The crystal structure and the microstructure of the films has been inferred through in- and out-of-plane X-ray diffraction studies and high-resolution transmission electron microscopy, respectively. The influence of the film deposition temperature on the surface electrical properties of the LiCoO2 films is discussed along with the relevant mechanism of surface resistance modification.

  13. Positive magnetoresistance in ferromagnetic Nd-doped In{sub 2}O{sub 3} thin films grown by pulse laser deposition

    SciTech Connect

    Xing, G. Z. Yi, J. B.; Li, S.; Yan, F.; Wu, T.

    2014-05-19

    We report the magnetic and magnetotransport properties of (In{sub 0.985}Nd{sub 0.015}){sub 2}O{sub 2.89} thin films grown by pulse laser deposition. The clear magnetization hysteresis loops with the complementary magnetic domain structure reveal the intrinsic room temperature ferromagnetism in the as-prepared films. The strong sp-f exchange interaction as a result of the rare earth doping is discussed as the origin of the magnetotransport behaviours. A positive magnetoresistance (∼29.2%) was observed at 5 K and ascribed to the strong ferromagnetic sp-f exchange interaction in (In{sub 0.985}Nd{sub 0.015}){sub 2}O{sub 2.89} thin films due to a large Zeeman splitting in an external magnetic field of 50 KOe.

  14. Variation of bandgap with oxygen ambient pressure in Mg xZn 1- xO thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Misra, P.; Bhattacharya, P.; Mallik, K.; Rajagopalan, S.; Kukreja, L. M.; Rustagi, K. C.

    2001-03-01

    Thin films of Mg xZn 1- xO were grown by pulsed laser deposition technique at various oxygen background pressures in the range of 10 -2-10 -5 Torr on single crystal (0001) alumina substrates. The films were found to be c-axis oriented with a high crystalline quality having FWHM of rocking curve of about 0.16°. The bandgap of Mg xZn 1- xO thin films was found to increase from 3.45 to 3.78 eV with decrease of oxygen pressure from 10 -2 to 10 -5 Torr during the deposition. This has been attributed to the increase in the Mg concentration in the films on decreasing the O 2 pressure.

  15. Effect of laser fluence on electrical properties of (Sr0.75,La0.25)TiO3 thin films grown by pulsed-laser-deposition.

    PubMed

    Eom, Kitae; Kim, Taemin; Seo, Jiwon; Choi, Jaedu; Lee, Jaichan

    2014-11-01

    We have grown Sr0.75La0.25TiO3 (SLTO) thin films using pulsed laser deposition (PLD) with various laser energy fluences. We investigated the effect of energy fluence on the compositions of SLTO films. The stoichiometry of SLTO films was controlled by adjusting the laser energy density. At low energy densities below 1.0 J/cm2, SLTO films become non-stoichiometric with Ti deficiency. The Ti deficiency increases with decreasing the laser energy fluence. We have also investigated the effect of laser energy fluence on the electrical properties of the thin films. The electrical resistivity and carrier density intimately depend on the laser energy fluence as a result of the non-stoichiometry. After eliminating the effect of oxygen vacancies by post-annealing, the electrical properties are dependent on the cation stoichiometry in the oxide films.

  16. Direct observation of fatigue in epitaxially grown Pb(Zr,Ti)O3 thin films using second harmonic piezoresponse force microscopy

    SciTech Connect

    Murari, Nishit M; Hong, Seungbum; Lee, Ho Nyung; Katiyar, Ram S.

    2011-01-01

    Here, we present a direct observation of fatigue phenomena in epitaxially grown Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3} (PZT) thin films using second harmonic piezoresponse force microscopy (SH-PFM). We observed strong correlation between the SH-PFM amplitude and phase signals with the remnant piezoresponse at different switching cycles. The SH-PFM results indicate that the average fraction of switchable domains decreases globally and the phase delays of polarization switching differ locally. In addition, we found that the fatigue developed uniformly over the whole area without developing region-by-region suppression of switchable polarization as in polycrystalline PZT thin films.

  17. Optical properties of epitaxial BiFeO3 thin film grown on SrRuO3-buffered SrTiO3 substrate.

    PubMed

    Xu, Ji-Ping; Zhang, Rong-Jun; Chen, Zhi-Hui; Wang, Zi-Yi; Zhang, Fan; Yu, Xiang; Jiang, An-Quan; Zheng, Yu-Xiang; Wang, Song-You; Chen, Liang-Yao

    2014-01-01

    The BiFeO3 (BFO) thin film was deposited by pulsed-laser deposition on SrRuO3 (SRO)-buffered (111) SrTiO3 (STO) substrate. X-ray diffraction pattern reveals a well-grown epitaxial BFO thin film. Atomic force microscopy study indicates that the BFO film is rather dense with a smooth surface. The ellipsometric spectra of the STO substrate, the SRO buffer layer, and the BFO thin film were measured, respectively, in the photon energy range 1.55 to 5.40 eV. Following the dielectric functions of STO and SRO, the ones of BFO described by the Lorentz model are received by fitting the spectra data to a five-medium optical model consisting of a semi-infinite STO substrate/SRO layer/BFO film/surface roughness/air ambient structure. The thickness and the optical constants of the BFO film are obtained. Then a direct bandgap is calculated at 2.68 eV, which is believed to be influenced by near-bandgap transitions. Compared to BFO films on other substrates, the dependence of the bandgap for the BFO thin film on in-plane compressive strain from epitaxial structure is received. Moreover, the bandgap and the transition revealed by the Lorentz model also provide a ground for the assessment of the bandgap for BFO single crystals.

  18. A bow-tie photoconductive antenna using a low-temperature-grown GaAs thin-film on a silicon substrate for terahertz wave generation and detection

    NASA Astrophysics Data System (ADS)

    Darío Velásquez Ríos, Rubén; Bikorimana, Siméon; Ummy, Muhammad Ali; Dorsinville, Roger; Seo, Sang-Woo

    2015-12-01

    This paper presents heterogeneously integrated bow-tie emitter-detector photoconductive antennas (PCAs) based on low-temperature grown-gallium arsenide (LTG-GaAs) thin-film devices on silicon-dioxide/silicon (SiO2/Si) host substrates for integrated terahertz (THz) systems. The LTG-GaAs thin-film devices are fabricated with standard photolithography and thermal evaporation of metal-contact layers of chromium (Cr), nickel (Ni) and gold (Au). They are etched selectively and separated from their growth GaAs substrate. The LTG-GaAs thin-film devices are then heterogeneously integrated on bow-tie antenna electrodes patterned on the surface of a SiO2/Si host substrate for THz emitters and THz detectors. Cost-effective and selective integration of LTG-GaAs thin-film devices on a Si platform is demonstrated. THz radiation from the fabricated THz PCAs is successfully measured using a pump-probe THz time-domain configuration. The THz temporal duration was measured at full width half maximum of 0.36 ps. Its frequency spectrum exhibits a broadband response with a peak resonant frequency of about 0.31 THz. The demonstration illustrates the feasibility of creating heterogeneously integrated THz systems using separately optimized LTG-GaAs devices and Si based electronics.

  19. Co{sub 2}FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

    SciTech Connect

    Belmeguenai, M. Tuzcuoglu, H.; Zighem, F.; Chérif, S. M.; Moch, P.; Gabor, M. S. Petrisor, T.; Tiusan, C.

    2014-01-28

    10 nm and 50 nm Co{sub 2}FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (T{sub a}), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing T{sub a}, while the uniaxial anisotropy field is nearly unaffected by T{sub a} within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with T{sub a}. Finally, the FMR linewidth decreases when increasing T{sub a}, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10{sup −3} and 1.3×10{sup −3} for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively)

  20. Evolution of morphology and structure of Pb thin films grown by pulsed laser deposition at different substrate temperatures

    SciTech Connect

    Lorusso, Antonella Maiolo, Berlinda; Perrone, Alessio; Gontad, Francisco; Maruccio, Giuseppe; Tasco, Vittorianna

    2014-03-15

    Pb thin films were prepared by pulsed laser deposition on a Si (100) substrate at different growth temperatures to investigate their morphology and structure. The morphological analysis of the thin metal films showed the formation of spherical submicrometer grains whose average size decreased with temperature. X-ray diffraction measurements confirmed that growth temperature influences the Pb polycrystalline film structure. A preferred orientation of Pb (111) normal to the substrate was achieved at 30 °C and became increasingly pronounced along the Pb (200) plane as the substrate temperature increased. These thin films could be used to synthesize innovative materials, such as metallic photocathodes, with improved photoemission performances.

  1. Nano-indentation of single-layer optical oxide thin films grown by electron-beam deposition

    SciTech Connect

    Mehrotra, K.; Oliver, J. B.; Lambropoulos, J. C.

    2015-01-01

    Mechanical characterization of optical oxide thin films is performed using nano-indentation, and the results are explained based on the deposition conditions used. These oxide films are generally deposited to have a porous microstructure that optimizes laser induced damage thresholds, but changes in deposition conditions lead to varying degrees of porosity, density, and possibly the microstructure of the thin film. This can directly explain the differences in the mechanical properties of the film studied here and those reported in literature. Of the four single-layer thin films tested, alumina was observed to demonstrate the highest values of nano-indentation hardness and elastic modulus. This is likely a result of the dense microstructure of the thin film arising from the particular deposition conditions used.

  2. Characterization of high-{kappa} LaLuO{sub 3} thin film grown on AlGaN/GaN heterostructure by molecular beam deposition

    SciTech Connect

    Yang Shu; Huang Sen; Chen Hongwei; Chen, Kevin J.; Schnee, Michael; Zhao Qingtai; Schubert, Juergen

    2011-10-31

    We report the study of high-dielectric-constant (high-{kappa}) dielectric LaLuO{sub 3} (LLO) thin film that is grown on AlGaN/GaN heterostructure by molecular beam deposition (MBD). The physical properties of LLO on AlGaN/GaN heterostrucure have been investigated with atomic force microscopy, x-ray photoelectron spectroscopy, and TEM. It is revealed that the MBD-grown 16 nm-thick LLO film is polycrystalline with a thin ({approx}2 nm) amorphous transition layer at the LLO/GaN interface. The bandgap of LLO is derived as 5.3 {+-} 0.04 eV from O1s energy loss spectrum. Capacitance-voltage (C-V) characteristics of a Ni-Au/LLO/III-nitride metal-insulator-semiconductor diode exhibit small frequency dispersion (<2%) and reveal a high effective dielectric constant of {approx}28 for the LLO film. The LLO layer is shown to be effective in suppressing the reverse and forward leakage current in the MIS diode. In particular, the MIS diode forward current is reduced by 7 orders of magnitude at a forward bias of 1 V compared to a conventional Ni-Au/III-nitride Schottky diode.

  3. Preparation of regularly structured nanotubular TiO2 thin films on ITO and their modification with thin ALD-grown layers.

    PubMed

    Tupala, Jere; Kemell, Marianna; Härkönen, Emma; Ritala, Mikko; Leskelä, Markku

    2012-03-30

    Nanotubular titanium dioxide thin films were prepared by anodization of titanium metal films evaporated on indium tin oxide (ITO) coated glass. A facile method to enhance the adhesion of the titanium film to the ITO glass was developed. An optimum thickness of 550 nm for the evaporated titanium was found to keep the film adhered to ITO during the anodization. The films were further modified by growing amorphous titania, alumina and tantala thin films conformally in the nanotubes by atomic layer deposition (ALD). The optical, electrical and physical properties of the different structures were compared. It was shown that even 5 nm thin layers can modify the properties of the nanotubular titanium dioxide films.

  4. p-type conduction from Sb-doped ZnO thin films grown by dual ion beam sputtering in the absence of oxygen ambient

    SciTech Connect

    Kumar Pandey, Sushil; Kumar Pandey, Saurabh; Awasthi, Vishnu; Kumar, Ashish; Mukherjee, Shaibal; Deshpande, Uday P.; Gupta, Mukul

    2013-10-28

    Sb-doped ZnO (SZO) thin films were deposited on c-plane sapphire substrates by dual ion beam sputtering deposition system in the absence of oxygen ambient. The electrical, structural, morphological, and elemental properties of SZO thin films were studied for films grown at different substrate temperatures ranging from 200 °C to 600 °C and then annealed in situ at 800 °C under vacuum (pressure ∼5 × 10{sup −8} mbar). Films grown for temperature range of 200–500 °C showed p-type conduction with hole concentration of 1.374 × 10{sup 16} to 5.538 × 10{sup 16} cm{sup −3}, resistivity of 66.733–12.758 Ω cm, and carrier mobility of 4.964–8.846 cm{sup 2} V{sup −1} s{sup −1} at room temperature. However, the film grown at 600 °C showed n-type behavior. Additionally, current-voltage (I–V) characteristic of p-ZnO/n-Si heterojunction showed a diode-like behavior, and that further confirmed the p-type conduction in ZnO by Sb doping. X-ray diffraction measurements showed that all SZO films had (002) preferred crystal orientation. X-ray photoelectron spectroscopy analysis confirmed the formation of Sb{sub Zn}–2V{sub Zn} complex caused acceptor-like behavior in SZO films.

  5. A comparative study on in situ grown superconducting YBCO and YBCO-Ag thin films by PLD on polycrystalline SmBa2NbO6 substrate

    NASA Astrophysics Data System (ADS)

    Kurian, J.; John, Asha M.; Wariar, P. R. S.; Sajith, P. K.; Koshy, J.; Pai, S. P.; Pinto, R.

    2000-02-01

    The development and characterization of SmBa2NbO6, which is a new ceramic substrate material for the YBa2Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> superconductor, are reported. SmBa2NbO6 has a complex cubic perovskite structure with lattice constant a = 8.524 Å. The dielectric properties of SmBa2NbO6 are in a range suitable for its use as a substrate for microwave applications. SmBa2NbO6 was found to have a thermal conductivity of 77 W m-1 K-1 and a thermal expansion coefficient of 7.8 × 10-6 °C-1 at room temperature. Superconducting YBa2 Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> and YBa2Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> -Ag thin films have been grown in situ on polycrystalline SmBa2NbO6 by the pulsed laser ablation technique. The films exhibited (00l) orientation of an orthorhombic YBa2 Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> phase and gave a zero resistivity superconducting transition (TC(0)) at 90 K with a transition width of ~1.5 K. The critical current density of YBCO-Ag thin films grown on polycrystalline SmBa2NbO6 substrate was ~3 × 105 A cm-2 at 77 K. A comparative study of YBCO and YBCO-Ag thin films developed on polycrystalline SmBa2NbO6 substrate by PLD based on the crystallinity, orientation and critical current density of the YBCO film is discussed in detail.

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

    SciTech Connect

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

    2009-04-01

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

  7. Ferroelectric properties of highly a-oriented polycrystalline Bi2WO6 thin films grown on glass substrates

    NASA Astrophysics Data System (ADS)

    Ahn, Yoonho; Son, Jong Yeog

    2016-10-01

    Polycrystalline Bi2WO6 (BWO) thin films were deposited on Pt/Ta/glass substrates by pulsed laser deposition (PLD). In this study, we comparatively investigate the influence of oxygen partial pressure on structural and ferroelectric properties of the BWO films. In comparison with the BWO films deposited at oxygen partial pressure of 100 and 300 mTorr, the BWO film deposited at 300 mTorr exhibits a highly a-oriented crystalline structure. The highly a-oriented polycrystalline BWO thin film shows good ferroelectric properties with a remnant polarization of about 21.5 μ C /cm2 . The piezoresponse force microscope study reveals that the highly a-oriented BWO thin film possesses larger ferroelectric domain patterns due to smaller domain wall energy.

  8. Graphite Thin Films Consisting of Nanograins of Multilayer Graphene on Sapphire Substrates Directly Grown by Alcohol Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Miyasaka, Yuta; Nakamura, Atsushi; Temmyo, Jiro

    2011-04-01

    Graphene has been attracting a strong interest as a transparent electrode as well as a THz nanoelectronic device owing to its unique properties. To date, large-area graphene growth has been realized by chemical vapor deposition (CVD) with a catalyst metal. To avoid the transfer of segregated graphene, we have examined directly graphite thin film growth on nonpolar a-sapphire substrates without any catalyst metal by alcohol CVD. Graphite thin films consisting of nanograins of multilayer graphene on a-sapphire substrates were verified by a combination of transmission electron spectroscopy (TEM), and Raman analyses, and optical transparent and sheet resistance measurements.

  9. Numerical analysis on the origin of thickness unevenness and formation of pits at GaN thin film grown by HVPE

    NASA Astrophysics Data System (ADS)

    Han, Xue-Feng; Lee, Jae-Hak; Lee, Yoo-Jin; Song, Jae-Ho; Yi, Kyung-Woo

    2016-09-01

    In this study, we propose a 3D model for analyzing the fluid flow, mass fractions of reacting gases, GaN deposition thickness distribution and V/III ratio distribution at the GaN deposition surface in the multi-susceptor HVPE equipment. The GaN thin film is grown in the multi-susceptor HVPE equipment at 1213 K and 1 bar. The deposition thickness distribution from the calculation has been compared with the experimental results. Moreover, the standard deviations of deposition thickness of the films achieved from calculations and experiments have been compared. Besides, in the calculation results, we found that the V/III ratio at the GaN deposition surface increased from the center to the periphery and from low susceptor to high susceptor. Our calculation results have also been verified by 3D measuring laser microscope observation of the surface morphology of the GaN thin film. In according with the calculation results, the density of the pits also decreases from the center to the periphery as well as from low susceptor to high susceptor, demonstrating that the pit density at the surface of the GaN thin films could be reduced when the V/III ratio is increased.

  10. 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.

  11. Characterization of nanostructured photosensitive (NiS){sub x}(CdS){sub (1-x)} composite thin films grown by successive ionic layer adsorption and reaction (SILAR) route

    SciTech Connect

    Ubale, A.U.; Bargal, A.N.

    2011-07-15

    Highlights: {yields} Thin films of (NiS){sub x}(CdS){sub (1-x)} with variable composition (x = 1 to 0) were deposited onto glass substrates by the successive ionic layer adsorption and reaction (SILAR) method. {yields} The structural, surface morphological and electrical characterizations of the as deposited and annealed films were studied. {yields} The bandgap and activation energy of annealed (NiS){sub x}(CdS){sub (1-x)} film decrease with improvement in photosensitive nature. -- Abstract: Recently ternary semiconductor nanostructured composite materials have attracted the interest of researchers because of their photovoltaic applications. Thin films of (NiS){sub x}(CdS){sub (1-x)} with variable composition (x = 1-0) had been deposited onto glass substrates by the successive ionic layer adsorption and reaction (SILAR) method. As grown and annealed films were characterised by X-ray diffraction, scanning electron microscopy and EDAX to investigate structural and morphological properties. The (NiS){sub x}(CdS){sub (1-x)} films were polycrystalline in nature having mixed phase of rhombohedral and hexagonal crystal structure due to NiS and CdS respectively. The optical and electrical properties of (NiS){sub x}(CdS){sub (1-x)} thin films were studied to determine compsition dependent bandgap, activation energy and photconductivity. The bandgap and activation energy of annealed (NiS){sub x}(CdS){sub (1-x)} film decrease with improvement in photosensitive nature.

  12. Interaction of oxygen with samarium on Al{sub 2}O{sub 3} thin film grown on Ni{sub 3}Al(111)

    SciTech Connect

    Cheng, Dingling; Xu, Qian E-mail: jfzhu@ustc.edu.cn; Han, Yong; Ye, Yifan; Pan, Haibin; Zhu, Junfa E-mail: jfzhu@ustc.edu.cn

    2014-03-07

    The interaction between oxygen and samarium (Sm) on the well-ordered thin Al{sub 2}O{sub 3} film grown on Ni{sub 3}Al(111) has been investigated by X-ray photoelectron spectroscopy and synchrotron radiation photoemission spectroscopy. At Sm coverage higher than one monolayer, exposure of oxygen to the Sm films at room temperature leads to the formation of both samarium peroxide (O{sub 2}{sup 2−}) states and regular samarium oxide (O{sup 2−}) states. By contrast, when exposing O{sub 2} to Sm film less than one monolayer on Al{sub 2}O{sub 3}, no O{sub 2}{sup 2−} can be observed. Upon heating to higher temperatures, these metastable O{sub 2}{sup 2−} states dissociate, supplying active O atoms which can diffuse through the Al{sub 2}O{sub 3} thin film to further oxidize the underlying Ni{sub 3}Al(111) substrate, leading to the significant increase of the Al{sub 2}O{sub 3} thin film thickness. Therefore, it can be concluded that Sm, presumably in its peroxide form, acts as a catalyst for the further oxidation of the Ni{sub 3}Al substrate by supplying the active oxygen species at elevated temperatures.

  13. Characterization of deep acceptor level in as-grown ZnO thin film by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Asghar, M.; K., Mahmood; A. Hasan, M.; T. Ferguson, I.; Tsu, R.; Willander, M.

    2014-09-01

    We report deep level transient spectroscopy results from ZnO layers grown on silicon by molecular beam epitaxy (MBE). The hot probe measurements reveal mixed conductivity in the as-grown ZnO layers, and the current—voltage (I—V) measurements demonstrate a good quality p-type Schottky device. A new deep acceptor level is observed in the ZnO layer having activation energy of 0.49 ±0.03 eV and capture cross-section of 8.57 × 10-18 cm2. Based on the results from Raman spectroscopy, photoluminescence, and secondary ion mass spectroscopy (SIMS) of the ZnO layer, the observed acceptor trap level is tentatively attributed to a nitrogen-zinc vacancy complex in ZnO.

  14. Single-crystal p-i-n-Si thin-film solar cells grown on Si substrate by sputter epitaxy

    NASA Astrophysics Data System (ADS)

    Yeh, Wenchang; Tatebe, Kyohei

    2015-08-01

    An intrinsic sputter-epitaxial (SE) Si film with a thickness of 1000 nm and a 50-nm-thick n+ SE-Si film were successfully grown as the light-absorbing layer and emitter layer, respectively, on a heavily doped p-Si(100) wafer to form the p-i-n junction of a solar cell (SC). Heavily doped n+ SE-Si with an electron concentration n of 3 × 1020 cm-3 was grown by cosputtering of Sb with Si. The characteristics of SE-Si grown at 310 °C was investigated in relation to annealing temperature. The oxygen concentration in SE-Si was ˜1018 cm-3, which was found to originate from the gas released in the chamber. Oxygen-induced thermal donors then became the source of n in the film, and n was reduced to 1 × 1016 cm-3 after forming-gas annealing at 700 °C because the thermal donors were neutralized by hydrogen. The SC exhibited a maximum internal quantum efficiency of 73.7%.

  15. Defects in Ga(In)NAs thin films grown by atomic H-assisted molecular beam epitaxy

    SciTech Connect

    Shimizu, Yukiko; Mura, Yusuke; Uedono, Akira; Okada, Yoshitaka

    2006-09-15

    The vacancy-type defects in Ga{sub 1-y}In{sub y}N{sub x}As{sub 1-x} dilute nitride films grown by atomic H-assisted molecular beam epitaxy (H-MBE) were investigated. The positron annihilation measurements showed that the densities of vacancy-type defects in GaN{sub x}As{sub 1-x} (x=0%-1.3%) films grown under an optimized atomic H flux were as low as that for a liquid encapsulated Czochralski (LEC) GaAs substrate. Further, the influence of vacancy-type defects on the crystal quality and optical properties were studied by x-ray diffraction and photoluminescence (PL) measurements. The integrated PL intensity at 77 K drastically decreased as N composition was increased, but we found no clear correlation between the density or volume of vacancy defects and optical properties, and the S parameters were nearly constant at a value of {approx}0.516 in all Ga{sub 1-y}In{sub y}N{sub x}As{sub 1-x} films grown by our H-MBE technique.

  16. Characteristics of Fluorine-doped tin oxide thin films grown by Streaming process for Electrodeless Electrochemical Deposition

    NASA Astrophysics Data System (ADS)

    Yusuf, Gbadebo; Khalilzadeh-Rezaie, Farnood; Cleary, Justin W.; Oladeji, Isaiah O.; Suu, Koukou; Schoenfeld, Winston V.; Peale, Robert E.; Awodugba, Ayodeji O.

    2015-04-01

    This work investigated the characteristics of SnO2: F films grown by Streaming Process for Electrodeless Electrochemical Deposition (SPEED). Stannic chloride (SnCl4) and ammonium fluoride (NH4 F) was dissolved in a mixture of deionized water and organic solvents. The preheated substrate temperature was varied between 450 and 530° C. High quality SnO2: F films were grown at all the substrate temperatures studied. The typical film thickness was 250 nm. XRD shows that the grown films are polycrystalline SnO2 with a tetragonal crystal structure. The average optical transmission of the films was around 93% throughout the wavelength of 400 to 1000 nm. The lowest electrical resistivity achieved was 6 x 10-4 Ω cm. The Hall measurements showed that the film is an n-type semiconductor, with the highest carrier mobility of 8.3 cm2/V.s, and concentration of 1 x 1021 cm-3. The direct band gap was determined to be 4 eV from the transmittance spectrum.

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

    SciTech Connect

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

    2009-04-01

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

  18. Effects of pH on the characteristics of ZnS thin films grown by using the CBD method

    NASA Astrophysics Data System (ADS)

    Ahn, Heejin; Lee, Dongchan; Park, Sujung; Um, Youngho

    In CIGS-based thin film solar cells, a chemically deposited ZnS buffer layer with high resistivity is generally used between the absorber layer and transparent conducting oxide layer. In this work, we report a chemical process to prepare ZnS films by the CBD technique based on the typical bath deposition. The influences of ammonia (NH4OH) and Na2EDTA (Na2C10H16N2O8) as complexing agents on structural, morphological, and optical properties of ZnS thin films are investigated ranging pH concentration from 5 to 10. To investigate effects of pH on the characteristics of ZnS thin films, by using UV-visible transmittance, atomic force microscopy, and optical absorption were investigated. With changing the pH range, the ZnS thin films demonstrate high transmittance of 75~80% in the visible region, indicating the films are potentially useful in photovoltaic applications. The results will be presented in detail. This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education (2011-0024709).

  19. Structural and optical properties of La-doped BaSnO3 thin films grown by PLD

    NASA Astrophysics Data System (ADS)

    James, K. K.; Krishnaprasad, P. S.; Hasna, K.; Jayaraj, M. K.

    2015-01-01

    In this study the structural and optical properties of lanthanum-doped BaSnO3 powder samples and thin films deposited on fused silica were investigaed using laser ablation. Under an oxygen pressure of 5×10-4 mbar, phase pure BaSnO3 films with a lattice constant of 0.417 nm and grain size of 21 nm were prepared at 630 °C. The band gap of BaSnO3 powder sample and thin films was calculated to be 3.36 eV and 3.67 eV, respectively. There was a progressive increase in conductivity for thin films of BaSnO3 doped with 0~7 at% of La. The highest conductivity, 9 Scm-1, was obtained for 7 at% La-doped BaSnO3. Carrier concentration, obtained from Burstein-Moss (B-M) shift, nearly matches the measured values except for 3 at% and 10 at% La-doped BaSnO3 thin films.

  20. Thin, high quality GaInP compositionally graded buffer layers grown at high growth rates for metamorphic III-V solar cell applications

    NASA Astrophysics Data System (ADS)

    Garcia, I.; France, R. M.; Geisz, J. F.; Simon, J.

    2014-05-01

    The metamorphic growth of lattice-mismatched materials has allowed optimizing the bandgap combination in multijunction solar cells for the solar spectrum under consideration. Buffer structures are used to accommodate the lattice-mismatch by introducing dislocations and relaxing the material in a controlled way. However, the metamorphic buffers typically involve significant growth time and material usage, which increases the cost of these solar cells. In this work, the thinning of buffer structures with continuously, linearly graded misfit is addressed with the goal of increasing the cost-effectiveness of metamorphic multijunction solar cells. The relaxation dynamics and quality of the buffer layers analyzed were assessed by in-situ stress measurements and ex-situ measurements of residual strain, threading dislocation density and surface roughness. Their ultimate quality has been tested using these buffers as templates for the growth of 1 eV Ga0.73In0.27As solar cells. The deleterious effect of thinning the grade layer of these buffer structures from 2 to 1 μm was investigated. It is shown that prompting the relaxation of the buffer by using a stepwise misfit jump at the beginning of the grade layer improves the quality of the thinned buffer structure. The residual threading dislocation density of the optimized thin buffers, grown at a high growth rate of 7 μm/h, is 3×106 cm-2, and solar cells on these buffers exhibit near-ideal carrier collection efficiency and a Voc of 0.62 V at 1-sun direct terrestrial spectrum.

  1. Influence of Gas Adsorption and Gold Nanoparticles on the Electrical Properties of CVD-Grown MoS2 Thin Films.

    PubMed

    Cho, Yunae; Sohn, Ahrum; Kim, Sujung; Hahm, Myung Gwan; Kim, Dong-Ho; Cho, Byungjin; Kim, Dong-Wook

    2016-08-24

    Molybdenum disulfide (MoS2) has increasingly attracted attention from researchers and is now one of the most intensively explored atomic-layered two-dimensional semiconductors. Control of the carrier concentration and doping type of MoS2 is crucial for its application in electronic and optoelectronic devices. Because the MoS2 layers are atomically thin, their transport characteristics may be very sensitive to ambient gas adsorption and the resulting charge transfer. We investigated the influence of the ambient gas (N2, H2/N2, and O2) choice on the resistance (R) and surface work function (WF) of trilayer MoS2 thin films grown via chemical vapor deposition. We also studied the electrical properties of gold (Au)-nanoparticle (NP)-coated MoS2 thin films; their R value was found to be 2 orders of magnitude smaller than that for bare samples. While the WF largely varied for each gas, R was almost invariant for both the bare and Au-NP-coated samples regardless of which gas was used. Temperature-dependent transport suggests that variable range hopping is the dominant mechanism for electrical conduction for bare and Au-NP-coated MoS2 thin films. The charges transferred from the gas adsorbates might be insufficient to induce measurable R change and/or be trapped in the defect states. The smaller WF and larger localization length of the Au-NP-coated sample, compared with the bare sample, suggest that more carriers and less defects enhanced conduction in MoS2. PMID:27490096

  2. Influence of Gas Adsorption and Gold Nanoparticles on the Electrical Properties of CVD-Grown MoS2 Thin Films.

    PubMed

    Cho, Yunae; Sohn, Ahrum; Kim, Sujung; Hahm, Myung Gwan; Kim, Dong-Ho; Cho, Byungjin; Kim, Dong-Wook

    2016-08-24

    Molybdenum disulfide (MoS2) has increasingly attracted attention from researchers and is now one of the most intensively explored atomic-layered two-dimensional semiconductors. Control of the carrier concentration and doping type of MoS2 is crucial for its application in electronic and optoelectronic devices. Because the MoS2 layers are atomically thin, their transport characteristics may be very sensitive to ambient gas adsorption and the resulting charge transfer. We investigated the influence of the ambient gas (N2, H2/N2, and O2) choice on the resistance (R) and surface work function (WF) of trilayer MoS2 thin films grown via chemical vapor deposition. We also studied the electrical properties of gold (Au)-nanoparticle (NP)-coated MoS2 thin films; their R value was found to be 2 orders of magnitude smaller than that for bare samples. While the WF largely varied for each gas, R was almost invariant for both the bare and Au-NP-coated samples regardless of which gas was used. Temperature-dependent transport suggests that variable range hopping is the dominant mechanism for electrical conduction for bare and Au-NP-coated MoS2 thin films. The charges transferred from the gas adsorbates might be insufficient to induce measurable R change and/or be trapped in the defect states. The smaller WF and larger localization length of the Au-NP-coated sample, compared with the bare sample, suggest that more carriers and less defects enhanced conduction in MoS2.

  3. Optical and electrical characterization of CdS-Glycine thin films with ammonia free buffer grown at different temperatures for solar cells applications

    NASA Astrophysics Data System (ADS)

    Berman-Mendoza, D.; Quiñones-Urías, D.; Ferra-González, S.; Vera-Marquina, A.; Rojas-Hernández, A.; Gómez Fuentes, R.; García-Juárez, A.; Leal-Cruz, A. L.; Ramos-Carrasco, A.

    2013-11-01

    In this work we report the fabrication and electro-optical characterization of CdS thin films using glycine as complexing agent with ammonia and ammonia free buffer by the Chemical Bath Deposition (CBD) method. The CdS thin films were grown at different temperatures of 50, 60, 70 and 80 °C in a thermal water bath. The morphology of these films was determined using atomic force microscopy; the resultant films were homogeneous, well adhered to the substrate, and specularly reflecting with a varying color depending on the deposition temperature. Transmittance and reflectance measurements of thermally treated CdS films were carried to study the effect of the ammonia buffer on its optical properties and bandgap. The crystallinity of the CdS thin films was determined by means of X Ray diffraction measurements. Therefore, for this study, an ammonia-free complexing agent has been taken for the deposition of CdS. Among different methods, which are being used for the preparation of CdS films, Chemical Bath Deposition (CBD) is the most attractive due to its low cost, easy to handle and large possibilities regarding doping and deposition on various substrates. In particular it can be used to easily obtain field effect devices by depositing CdS thin films over a SiO2/Si substrate. Heterostructures with interesting physical properties can be imagined, realized and tested in this way.. Structures CdS/PbS also were realized and have shown good solar cell characteristics.

  4. Compositional inhomogeneities in AlGaN thin films grown by molecular beam epitaxy: Effect on MSM UV photodetectors

    NASA Astrophysics Data System (ADS)

    Pramanik, Pallabi; Sen, Sayantani; Singha, Chirantan; Roy, Abhra Shankar; Das, Alakananda; Sen, Susanta; Bhattacharyya, A.

    2016-10-01

    Ultraviolet (UV) MSM photodetectors (PD) based on AlGaN alloys find many applications, including flame sensing. In this work we investigate the dependence of AlGaN based photodetectors grown by MBE on the kinetics of growth. MSM photodetectors were fabricated in the interdigitated configuration with Ni/Au contacts having 400 μm finger length and 10 μm finger spacing. Bulk Al0.4Ga0.6N films were grown on to sapphire substrates using an AlN buffer layer. A series of PDs were developed using the Al0.4Ga0.6N films grown under different group III/V flux ratios ranging from stoichiometric conditions to much higher than unity. Upon testing, it was observed that the otherwise identical photodetectors show significant decrease in dark current as AlGaN deposition conditions change from stoichiometric to excess group III, due to reduction of unintentional incorporation of oxygen-related point defects. In addition, the intensity and spectral dependence of the photocurrent also change, showing an extended low energy tail for the former and a sharp and prominent excitonic peak for the latter. The optical transmission measurements indicate a variation in Urbach energy with deposition conditions of the AlGaN films, although they have the same absorption edge. While all samples show a single red-shifted photoluminescence peak at room temperature, upon cooling, multiple higher energy peaks appear in the photoluminescence (PL) spectra, indicating that the alloys contain complex compositional inhomogeneities. Two types of alloy fluctuations, determined by the growth conditions, have been identified that modulate the optoelectronic properties of AlGaN by changing the spatial localization of excitons, thereby altering their stability. We identified that growth under stoichiometric conditions leads to compositional inhomogeneities that play a detrimental role in the operation of MSM photodetectors, which reduces the sharpness of the sensitivity edge, while growth under excess metal

  5. Comparative Study of Thermal Stability of NiFe and NiFeTa Thin Films Grown by Cosputtering Technique

    NASA Astrophysics Data System (ADS)

    Phuoc, Nguyen N.; Ong, C. K.

    2016-08-01

    A comparative study of the thermal behavior of dynamic permeability spectra for compositionally graded NiFeTa and uniform-composition NiFe thin films has been carried out. We found that the resonance frequency of the compositionally graded NiFeTa film increased with increasing temperature, while it decreased for the case of the uniform-composition NiFe thin film. This finding unambiguously suggests that the compositional gradient of the film is the only reason for the increase of the magnetic anisotropy with temperature due to its stress-induced origin, while the cosputtering technique does not play any role in this peculiar behavior. The temperature dependence of the frequency linewidth is also presented and discussed.

  6. Control of the magnetic properties of LaMnO3 epitaxial thin films grown by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Martinez, Benjamin; Roqueta, Jaume; Pomar, Alberto; Balcells, Lluis; Frontera, Carlos; Konstantinovic, Zorica; Sandiumenge, Felip; Santiso, Jose; Advanced materials characterization Team; Thin films growth Team

    2015-03-01

    LaMnO3 (LMO), the parent compound of colossal magnetoresistance based manganites has gained renewed attention as a building block in heterostructures with unexpected properties. In its bulk phase, stoichiometric LMO is an A-type antiferromagnetic (AFM) insulator (TN = 140K) with orthorhombic structure that easily accommodate an oxygen excess by generating cationic (La or Mn) vacancies. As a result, a fraction of Mn 3+ changes to Mn 4+ leading to a double-exchange mediated ferromagnetic (FM) behavior. In thin films the AFM phase has been elusive up to now and thin films with FM ordering are usually reported. In this work, we have systematically studied the growth process of LaMnO3 thin films by pulsed laser deposition on SrTiO3 (001) substrates under different oxygen partial pressures (PO2) . A close correlation between the structure (explored by XRD) and the magnetic properties (SQUID measurements) of the films with PO2 has been identified. At high PO2 FM behavior is observed. In contrast, at very low PO2, the results obtained for unit cell volume (close to stoichiometric bulk values) and magnetic moment (0.2 μB/Mn) strongly indicate antiferromagnetic ordering. We acknowledge financial support from the Spanish MINECO (MAT2012-33207).

  7. Synthesis of nanocrystalline Cu{sub 2}ZnSnS{sub 4} thin films grown by the spray-pyrolysis technique

    SciTech Connect

    Chandel, Tarun Singh, Joginder; Rajaram, P.

    2015-08-28

    Spray pyrolysis was used to deposit Cu{sub 2}ZnSnS{sub 4} (CZTS) thin films on soda lime glass substrates at 300 °C. Aqueous solutions of copper chloride, zinc chloride, stannous chloride and thiourea were mixed together to form the spray liquid. The sprayed films were annealed under vacuum at 350 °C, 400 °C and 450 °C. Structural and optical characterization was performed on the CZTS films using X-ray diffraction (XRD) and UV-VIS spectrophotometry. XRD results indicate that the films are single phase nanocrystalline CZTS. Optical studies show that the optical gap values are 1.44 eV for the as-grown film and 1.46 eV, 1.48 eV and 1.49 eV for the films annealed at 350 °C, 400 °C and 450 °C, respectively.

  8. Electron spin resonance of Zn{sub 1-x}Mg{sub x}O thin films grown by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Wassner, T. A.; Stutzmann, M.; Brandt, M. S.; Laumer, B.; Althammer, M.; Goennenwein, S. T. B.; Eickhoff, M.

    2010-08-30

    Zn{sub 1-x}Mg{sub x}O thin films with a Mg content x between 0 and 0.42 grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates were investigated by electron spin resonance at 5 K. Above band gap illumination induces a persistent resonance signal, which is attributed to free conduction band electrons. The g-factors of the Zn{sub 1-x}Mg{sub x}O epitaxial layers and their anisotropy were determined experimentally and an increase from g{sub ||}=1.957 for x=0 to g{sub ||}=1.970 for x=0.42 was found, accompanied by a decrease in anisotropy. A comparison with g-factors of the Al{sub x}Ga{sub 1-x}N system is also given.

  9. Characterization of M-plane GaN thin films grown on misoriented γ-LiAlO2 (100) substrates

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Chiao; Lo, Ikai; Wang, Ying-Chieh; Yang, Chen-Chi; Hu, Chia-Hsuan; Chou, Mitch M. C.; Schaadt, D. M.

    2016-09-01

    M-plane GaN thin films were grown on 11° misoriented γ-LiAlO2 substrates without peeling off or cracking by plasma-assisted molecular beam epitaxy. Because of anisotropic growth kinetics, which leads to an anisotropic compressive in-plane strain in the M-plane GaN films, the surface presents a rough morphology with worse crystal quality. The crystal quality of sample was optimally improved, XRD rocking curve FWHM of which is about 900 arcsec, by raising growth temperature to 800 °C with proper Ga/N flux ratio. As the crystal quality was improved, the polarization ratio decreased from the unity (less than 0.8) which could be attributed to the effect of exciton localization due to the partial increased in-plane strain.

  10. Effect of post-growth rapid thermal annealing on bilayer InAs/GaAs quantum dot heterostructure grown with very thin spacer thickness

    SciTech Connect

    Sengupta, S.; Halder, N.; Chakrabarti, S.

    2010-11-15

    We have investigated the effect of post-growth rapid thermal annealing on self-assembled InAs/GaAs bilayer quantum dot samples having very thin barrier thickness (7.5-8.5 nm). In/Ga interdiffusion in the samples due to annealing is presumed to be controlled by the vertical strain coupling from the seed dots in bilayer heterostructure. Strain coupling from embedded seed QD layer maintains a strain relaxed state in active top islands of the bilayer quantum dot sample grown with comparatively thick spacer layer (8.5 nm). This results in minimum In/Ga interdiffusion. However controlled interdiffusion across the interface between dots and GaAs barrier, noticeably enhances the emission efficiency in such bilayer quantum dot heterostructure on annealing up to 700 {sup o}C.

  11. 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.

  12. Thin film transistors using preferentially grown semiconducting single-walled carbon nanotube networks by water-assisted plasma-enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Kim, Un Jeong; Lee, Eun Hong; Kim, Jong Min; Min, Yo-Sep; Kim, Eunseong; Park, Wanjun

    2009-07-01

    Nearly perfect semiconducting single-walled carbon nanotube random network thin film transistors were fabricated and their reproducible transport properties were investigated. The networked single-walled carbon nanotubes were directly grown by water-assisted plasma-enhanced chemical vapor deposition. Optical analysis confirmed that the nanotubes were mostly semiconductors without clear metallic resonances in both the Raman and the UV-vis-IR spectroscopy. The transistors made by the nanotube networks whose density was much larger than the percolation threshold also showed no metallic paths. Estimation based on the conductance change of semiconducting nanotubes in the SWNT network due to applied gate voltage difference (conductance difference for on and off state) indicated a preferential growth of semiconducting nanotubes with an advantage of water-assisted PECVD. The nanotube transistors showed 10-5 of on/off ratio and ~8 cm2 V-1 s-1 of field effect mobility.

  13. Thin film transistors using preferentially grown semiconducting single-walled carbon nanotube networks by water-assisted plasma-enhanced chemical vapor deposition.

    PubMed

    Kim, Un Jeong; Lee, Eun Hong; Kim, Jong Min; Min, Yo-Sep; Kim, Eunseong; Park, Wanjun

    2009-07-22

    Nearly perfect semiconducting single-walled carbon nanotube random network thin film transistors were fabricated and their reproducible transport properties were investigated. The networked single-walled carbon nanotubes were directly grown by water-assisted plasma-enhanced chemical vapor deposition. Optical analysis confirmed that the nanotubes were mostly semiconductors without clear metallic resonances in both the Raman and the UV-vis-IR spectroscopy. The transistors made by the nanotube networks whose density was much larger than the percolation threshold also showed no metallic paths. Estimation based on the conductance change of semiconducting nanotubes in the SWNT network due to applied gate voltage difference (conductance difference for on and off state) indicated a preferential growth of semiconducting nanotubes with an advantage of water-assisted PECVD. The nanotube transistors showed 10(-5) of on/off ratio and approximately 8 cm2 V(-1) s(-1) of field effect mobility. PMID:19567966

  14. Structural, morphological and mechanical properties of niobium nitride thin films grown by ion and electron beams emanated from plasma

    NASA Astrophysics Data System (ADS)

    Siddiqui, Jamil; Hussain, Tousif; Ahmad, Riaz; Umar, Zeeshan A.; Abdus Samad, Ubair

    2016-05-01

    The influence of variation in plasma deposition parameters on the structural, morphological and mechanical characteristics of the niobium nitride films grown by plasma-emanated ion and electron beams are investigated. Crystallographic investigation made by X-ray diffractometer shows that the film synthesized at 10 cm axial distance with 15 plasma focus shots (PFS) exhibits better crystallinity when compared to the other deposition conditions. Morphological analysis made by scanning electron microscope reveals a definite granular pattern composed of homogeneously distributed nano-spheroids grown as clustered particles for the film synthesized at 10 cm axial distance for 15 PFS. Roughness analysis demonstrates higher rms roughness for the films synthesized at shorter axial distance and by greater number of PFS. Maximum niobium atomic percentage (35.8) and maximum average hardness (19.4 ± 0.4 GPa) characterized by energy-dispersive spectroscopy and nano-hardness analyzer respectively are observed for film synthesized at 10 cm axial distance with 15 PFS.

  15. Structure and magnetism of Fe thin films grown on Rh(001) studied by spin-resolved photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Hayashi, K.; Sawada, M.; Harasawa, A.; Kimura, A.; Kakizaki, A.

    2001-06-01

    Bulk Fe is known to be a bcc structure at room temperature and ferromagnetic below 920 K. On the other hand Fe films grown on non-magnetic substrates show a variety of structures and magnetism depending on the degree of the lattice constant (a0) difference between substrate and a bulk bcc Fe (a0=2.87 Å). On Au(001) (a0=4.07 Å) and Ag(001), Fe films grow in bcc structure and are ferromagnetic due to the small lattice mismatch to the Fe(110). On Cu(001) and Co(001), Fe films thinner than 5 ML reveal a face centred tetragonal (fct) structure and ferromagnetism, while in 6-10 ML region Fe films show fcc structure and only the topmost few layers were found to be ferromagnetic. The origin of this complicated magnetic behavior has been considered due to the lattice mismatch at the interface and investigated by a first principle calculation of the total energy and magnetic moments [1]. In this report, we present the structural and electronic properties of the Fe films epitaxially grown on a Rh(001) surface. .

  16. Comparative study of LiMn 2O 4 thin film cathode grown at high, medium and low temperatures by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Tang, S. B.; Lai, M. O.; Lu, L.; Tripathy, S.

    2006-12-01

    LiMn 2O 4 thin films with different crystallizations were respectively grown at high, medium and low temperatures by pulsed laser deposition (PLD). Structures, morphologies and electrochemical properties of these three types of thin films were comparatively studied. Films grown at high temperature (⩾873 K) possessed flat and smooth surfaces and were highly crystallized with different textures and crystal sizes depending on the deposition pressure of oxygen. However, films deposited at low temperature (473 K) had rough surfaces with amorphous characteristics. At medium temperature (673 K), the film was found to consist mainly of nano-crystals less than 100 nm with relatively loose and rough surfaces, but very dense as observed from the cross-section. The film deposited at 873 K and 100 mTorr of oxygen showed an initial discharge capacity of 54.3 μAh/cm 2 μm and decayed at 0.28% per cycle, while the amorphous film had an initial discharge capacity of 20.2 μAh/cm 2 μm and a loss rate of 0.29% per cycle. Compared with the highly crystallized and the amorphous films, nano-crystalline film exhibited higher potential, more capacity and much better cycling stability. As high as 61 μAh/cm 2 μm of discharge capacity can be achieved with an average decaying rate of only 0.032% per cycle up to 500 cycles. The excellent performance of nano-crystalline film was correlated to its microstructures in the present study.

  17. Comparative study of Hg xCd 1-xTe films grown on CdTe thin films previously deposited from two different techniques

    NASA Astrophysics Data System (ADS)

    Ali, A.; Abbas Shah, N.; Maqsood, A.

    2009-04-01

    High quality cadmium telluride (CdTe) thin films were grown on glass substrates with two different techniques, two evaporation source (TES) and closed space sublimation (CSS). Further to the above mercury telluride (HgTe) was then deposited by using single source on both CdTe thin films for obtaining Hg xCd 1-xTe samples. The crystalline structure of the Hg xCd 1-xTe sample grown from CSS-CdTe showed the preferential (1 1 1) orientation with smoother and larger grain size than those of TES-CdTe. The optical transmission for TES-CdTe sample was above 90% in the 1000-1500 nm range whereas it was significantly below 80% for CSS-CdTe sample. The optical transmission for TES-Hg xCd 1-xTe and CSS-Hg xCd 1-xTe was ˜60%. The resistivity at room temperature of TES-CdTe and CSS-CdTe was ˜3.33×10 9 Ω cm and ˜2.20×10 8 Ω cm, respectively, while the resistivity of TES-Hg xCd 1-xTe and CSS-Hg xCd 1-xTe samples was ˜1.73 Ω cm and ˜5.34×10 5 Ω cm, respectively. The comparative study of ternary compound prepared with the above techniques has been carried out for the first time.

  18. Growth characteristics and properties of Ga-doped ZnO (GZO) thin films grown by thermal and plasma-enhanced atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Nam, Taewook; Lee, Chang Wan; Kim, Hyun Jae; Kim, Hyungjun

    2014-03-01

    The growth characteristics and electrical and optical properties of gallium-doped ZnO (GZO) grown by thermal atomic layer deposition (Th-ALD) and plasma-enhanced atomic layer deposition (PE-ALD) were investigated as a function of key growth parameters including the growth temperature. While GZO films are generally deposited at high growth temperatures above 300 °C, room temperature deposition is possible using PE-ALD. The chemical properties of the films were analyzed by X-ray photoelectron spectroscopy and their electrical properties including the carrier concentration, mobility, and resistivity were investigated by Hall measurements. The lowest resistivity of 1.49 × 10-3 Ω cm was obtained for the Th-ALD GZO film grown at 300 °C. The transmittance was enhanced to over 85% in the visible light range when Ga was doped on a ZnO film. In addition, a GZO bottom-gated thin film transistor (TFT) was fabricated and exhibited good electrical properties.

  19. Growth, microstructure and electrical properties of sputter-deposited hafnium oxide (HfO2) thin films grown using HfO2 ceramic target

    SciTech Connect

    Aguirre, B.; Vemuri, R. S.; Zubia, David; Engelhard, Mark H.; Shutthanandan, V.; Kamala Bharathi, K.; Ramana, Chintalapalle V.

    2011-01-01

    Hafnium oxide (HfO₂) thin films have been made by radio-frequency (rf) magnetron-sputtering onto Si(100) substrates under varying growth temperature (Ts). HfO₂ ceramic target has been employed for sputtering while varying the Ts from room temperature to 500⁰C during deposition. The effect of Ts on the growth and microstructure of deposited HfO₂ films has been studied using grazing incidence x-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), and high-resolution scanning electron microscopy (HR-SEM) coupled with energy dispersive x-ray spectrometry (EDS). The results indicate that the effect of Ts is significant on the growth, surface and interface structure, morphology and chemical composition of the HfO₂ films. Structural characterization indicates that the HfO₂ films grown at Ts<200 ⁰C are amorphous while films grown at Ts>200 ⁰C are nanocrystalline. An amorphous-to-crystalline transition occurs at Ts=200 ⁰C. Nanocrystalline HfO₂ films crystallized in a monoclinic structure with a (-111) orientation. XPS measurements indicated the high surface-chemical quality and stoichiometric nature of the grown HfO₂ films. An interface layer (IL) formation occurs due to reaction at the HfO₂-Si interface for HfO₂ films deposited at Ts>200 ⁰C. The thickness of IL increases with increasing Ts. XPS and EDS at the HfO₂-Si cross-section indicate the IL is a (Hf, Si)-O compound. The electrical characterization using capacitance-voltage measurements indicate that the dielectric constant decreases from 25 to 16 with increasing Ts.

  20. Atomic layer deposition grown MO{sub x} thin films for solar water splitting: Prospects and challenges

    SciTech Connect

    Singh, Trilok; Lehnen, Thomas; Leuning, Tessa; Mathur, Sanjay

    2015-01-15

    The magnitude of energy challenge not only calls for efficient devices but also for abundant, inexpensive, and stable photoactive materials that can enable efficient light harvesting, charge separation and collection, as well as chemical transformations. Photoelectrochemical systems based on semiconductor materials have the possibility to transform solar energy directly into chemical energy the so-called “solar hydrogen.” The current challenge lies in the harvesting of a larger fraction of electromagnetic spectrum by enhancing the absorbance of electrode materials. In this context, atomically precise thin films of metal oxide semiconductors and their multilayered junctions are promising candidates to integrate high surface areas with well-defined electrode–substrate interface. Given its self-limited growth mechanism, the atomic layer deposition (ALD) technique offers a wide range of capabilities to deposit and modify materials at the nanoscale. In addition, it opens new frontiers for developing precursor chemistry that is inevitable to design new processes. Herein, the authors review the properties and potential of metal oxide thin films deposited by ALD for their application in photoelectrochemical water splitting application. The first part of the review covers the basics of ALD processes followed by a brief discussion on the electrochemistry of water splitting reaction. The second part focuses on different MO{sub x} films deposited by atomic layer deposition for water splitting applications; in this section, The authors discuss the most explored MO{sub x} semiconductors, namely, Fe{sub 2}O{sub 3}, TiO{sub 2}, WO{sub 3}, and ZnO, as active materials and refer to their application as protective coatings, conductive scaffolds, or in heterojunctions. The third part deals with the current challenges and future prospects of ALD processed MO{sub x} thin films for water splitting reactions.

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

    SciTech Connect

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

    2010-05-15

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

  2. Molecular beam epitaxy-grown wurtzite MgS thin films for solar-blind ultra-violet detection

    SciTech Connect

    Lai, Y. H.; He, Q. L.; Cheung, W. Y.; Lok, S. K.; Wong, K. S.; Sou, I. K.; Ho, S. K.; Tam, K. W.

    2013-04-29

    Molecular beam epitaxy grown MgS on GaAs(111)B substrate was resulted in wurtzite phase, as demonstrated by detailed structural characterizations. Phenomenological arguments were used to account for why wurtzite phase is preferred over zincblende phase or its most stable rocksalt phase. Results of photoresponse and reflectance measurements performed on wurtzite MgS photodiodes suggest a direct bandgap at around 5.1 eV. Their response peaks at 245 nm with quantum efficiency of 9.9% and enjoys rejection of more than three orders at 320 nm and close to five orders at longer wavelengths, proving the photodiodes highly competitive in solar-blind ultraviolet detection.

  3. Molecular beam epitaxy-grown wurtzite MgS thin films for solar-blind ultra-violet detection

    NASA Astrophysics Data System (ADS)

    Lai, Y. H.; He, Q. L.; Cheung, W. Y.; Lok, S. K.; Wong, K. S.; Ho, S. K.; Tam, K. W.; Sou, I. K.

    2013-04-01

    Molecular beam epitaxy grown MgS on GaAs(111)B substrate was resulted in wurtzite phase, as demonstrated by detailed structural characterizations. Phenomenological arguments were used to account for why wurtzite phase is preferred over zincblende phase or its most stable rocksalt phase. Results of photoresponse and reflectance measurements performed on wurtzite MgS photodiodes suggest a direct bandgap at around 5.1 eV. Their response peaks at 245 nm with quantum efficiency of 9.9% and enjoys rejection of more than three orders at 320 nm and close to five orders at longer wavelengths, proving the photodiodes highly competitive in solar-blind ultraviolet detection.

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

    SciTech Connect

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

    2010-10-04

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

  6. Effects of O2 plasma post-treatment on ZnO: Ga thin films grown by H2O-thermal ALD

    NASA Astrophysics Data System (ADS)

    Lee, Yueh-Lin; Chuang, Jia-Hao; Huang, Tzu-Hsuan; Ho, Chong-Long; Wu, Meng-Chyi

    2013-03-01

    Transparent conducting oxides have been widely employed in optoelectronic devices using the various deposition methods such as sputtering, thermal evaporator, and e-gun evaporator technologies.1-3 In this work, gallium doped zinc oxide (ZnO:Ga) thin films were grown on glass substrates via H2O-thermal atomic layer deposition (ALD) at different deposition temperatures. ALD-GZO thin films were constituted as a layer-by-layer structure by stacking zinc oxides and gallium oxides. Diethylzinc (DEZ), triethylgallium (TEG) and H2O were used as zinc, gallium precursors and oxygen source, respectively. Furthermore, we investigated the influences of O2 plasma post-treatment power on the surface morphology, electrical and optical property of ZnO:Ga films. As the result of O2 plasma post-treatment, the characteristics of ZnO:Ga films exhibit a smooth surface, low resistivity, high carrier concentration, and high optical transmittance in the visible spectrum. However, the transmittance decreases with O2 plasma power in the near- and mid-infrared regions.

  7. Tuning of near-infrared luminescence of SrTiO3:Ni2+ thin films grown on piezoelectric PMN-PT via strain engineering

    PubMed Central

    Bai, Gongxun; Zhang, Yang; Hao, Jianhua

    2014-01-01

    We report the tunable near-infrared luminescence of Ni2+ doped SrTiO3 (STO:Ni) thin film grown on piezoelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrate via strain engineering differing from conventional chemical approach. Through controlling the thickness of STO:Ni film, the luminescent properties of the films including emission wavelength and bandwidth, as well as lifetime can be effectively tuned. The observed phenomena can be explained by the variation in the crystal field around Ni2+ ions caused by strain due to the lattice mismatch. Moreover, the modulation of strain can be controlled under an external electric field via converse piezoelectric effect of PMN-PT used in this work. Consequently, controllable emission of the STO:Ni thin film is demonstrated in a reversible and real-time way, arising from the biaxial strain produced by piezoelectric PMN-PT. Physical mechanism behind the observation is discussed. This work will open a door for not only investigating the luminescent properties of the phosphors via piezoelectric platform, but also potentially developing novel planar light sources. PMID:25030046

  8. Characterization of CuInS2 thin films prepared from materials grown by using the mechanochemical method and their photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Akaki, Yoji; Sugimoto, Kanta; Nakamura, Shigeyuki; Yamaguchi, Toshiyuki; Yoshino, Kenji

    2015-08-01

    Cu-In-S thin films were deposited on glass substrates using single-source thermal evaporation with ternary compounds as source materials. Polycrystalline CuInS2 powder grown using the mechanochemical method was employed as the source material. After deposition, the films were annealed in H2S gas at different temperatures from 250 to 500 °C for 60 min. X-ray diffraction patterns indicated that single-phase CuInS2 was formed when annealed above 400 °C. The grain size of the crystals in thin films was approximately 0.2 to 2.0 µm. The best Al/ZnO:Al/ZnO/CdS/CuInS2/Mo solar cell had an open-circuit voltage of 360 mV, a short-circuit current density of 18.6 mA/cm2, and a fill factor of 35.5%, resulting in 2.38% efficiency.

  9. AgGaSe2 thin films grown by chemical close-spaced vapor transport for photovoltaic applications: structural, compositional and optical properties.

    PubMed

    Merschjann, C; Mews, M; Mete, T; Karkatzinou, A; Rusu, M; Korzun, B V; Schorr, S; Schubert-Bischoff, P; Seeger, S; Schedel-Niedrig, Th; Lux-Steiner, M-Ch

    2012-05-01

    Thin films of chalcopyrite AgGaSe(2) have been successfully grown on glass and glass/molybdenum substrates using the technique of chemical close-spaced vapor transport. The high crystallinity of the samples is confirmed by grazing-incidence x-ray diffraction, scanning and transmission electron microscopy, and optical transmission/reflection spectroscopy. Here, two of the three expected direct optical bandgaps are found at 1.77(2) and 1.88(6) eV at 300 K. The lowest bandgap energy at 4 K is estimated to be 1.82(3) eV. Photoluminescence spectroscopy has further revealed the nature of the point defects within the AgGaSe(2), showing evidence for the existence of very shallow acceptor levels of 5(1) and 10(1) meV, and thus suggesting the AgGaSe(2) phase itself to exhibit a p-type conductivity. At the same time, electrical characterization by Hall, Seebeck and four-point-probe measurements indicate properties of a compensated semiconductor. The electrical properties of the investigated thin films are mainly influenced by the presence of Ag(2)Se and Ga(2)O(3) nanometer-scaled surface layers, as well as by Ag(2)Se inclusions in the bulk and Ag clusters at the layers' rear side. PMID:22469870

  10. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Structural and Electrical Properties of Single Crystalline Ga-Doped ZnO Thin Films Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Lu, Zhong-Lin; Zou, Wen-Qin; Xu, Ming-Xiang; Zhang, Feng-Ming; Du, You-Wei

    2009-11-01

    High-quality Ga-doped ZnO (ZnO:Ga) single crystalline films with various Ga concentrations are grown on a-plane sapphire substrates using molecular-beam epitaxy. The site configuration of doped Ga atoms is studied by means of x-ray absorption spectroscopy. It is found that nearly all Ga can substitute into ZnO lattice as electrically active donors, a generating high density of free carriers with about one electron per Ga dopant when the Ga concentration is no more than 2%. However, further increasing the Ga doping concentration leads to a decrease of the conductivity due to partial segregation of Ga atoms to the minor phase of the spinel ZnGa2O4 or other intermediate phase. It seems that the maximum solubility of Ga in the ZnO single crystalline film is about 2 at.% and the lowest resistivity can reach 1.92 × 10-4 Ω·cm at room temperature, close to the best value reported. In contrast to ZnO:Ga thin film with 1% or 2% Ga doping, the film with 4% Ga doping exhibits a metal semiconductor transition at 80 K. The scattering mechanism of conducting electrons in single crystalline ZnO:Ga thin film is discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

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

  12. Far-infrared transmission in GaN, AlN, and AlGaN thin films grown by molecular beam epitaxy

    SciTech Connect

    Ibanez, J.; Hernandez, S.; Alarcon-Llado, E.; Cusco, R.; Artus, L.; Novikov, S. V.; Foxon, C. T.; Calleja, E.

    2008-08-01

    We present a far-infrared transmission study on group-III nitride thin films. Cubic GaN and AlN layers and c-oriented wurtzite GaN, AlN, and Al{sub x}Ga{sub 1-x}N (x<0.3) layers were grown by molecular beam epitaxy on GaAs and Si(111) substrates, respectively. The Berreman effect allows us to observe simultaneously the transverse optic and the longitudinal optic phonons of both the cubic and the hexagonal films as transmission minima in the infrared spectra acquired with obliquely incident radiation. We discuss our results in terms of the relevant electromagnetic theory of infrared transmission in cubic and wurtzite thin films. We compare the infrared results with visible Raman-scattering measurements. In the case of films with low scattering volumes and/or low Raman efficiencies and also when the Raman signal of the substrate material obscures the weaker peaks from the nitride films, we find that the Berreman technique is particularly useful to complement Raman spectroscopy.

  13. Tuning of near-infrared luminescence of SrTiO3:Ni2+ thin films grown on piezoelectric PMN-PT via strain engineering

    NASA Astrophysics Data System (ADS)

    Bai, Gongxun; Zhang, Yang; Hao, Jianhua

    2014-07-01

    We report the tunable near-infrared luminescence of Ni2+ doped SrTiO3 (STO:Ni) thin film grown on piezoelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrate via strain engineering differing from conventional chemical approach. Through controlling the thickness of STO:Ni film, the luminescent properties of the films including emission wavelength and bandwidth, as well as lifetime can be effectively tuned. The observed phenomena can be explained by the variation in the crystal field around Ni2+ ions caused by strain due to the lattice mismatch. Moreover, the modulation of strain can be controlled under an external electric field via converse piezoelectric effect of PMN-PT used in this work. Consequently, controllable emission of the STO:Ni thin film is demonstrated in a reversible and real-time way, arising from the biaxial strain produced by piezoelectric PMN-PT. Physical mechanism behind the observation is discussed. This work will open a door for not only investigating the luminescent properties of the phosphors via piezoelectric platform, but also potentially developing novel planar light sources.

  14. Tuning of near-infrared luminescence of SrTiO3:Ni2+ thin films grown on piezoelectric PMN-PT via strain engineering.

    PubMed

    Bai, Gongxun; Zhang, Yang; Hao, Jianhua

    2014-01-01

    We report the tunable near-infrared luminescence of Ni(2+) doped SrTiO3 (STO:Ni) thin film grown on piezoelectric Pb(Mg(1/3)Nb(2/3))(0.7)Ti(0.3)O3 (PMN-PT) substrate via strain engineering differing from conventional chemical approach. Through controlling the thickness of STO:Ni film, the luminescent properties of the films including emission wavelength and bandwidth, as well as lifetime can be effectively tuned. The observed phenomena can be explained by the variation in the crystal field around Ni(2+) ions caused by strain due to the lattice mismatch. Moreover, the modulation of strain can be controlled under an external electric field via converse piezoelectric effect of PMN-PT used in this work. Consequently, controllable emission of the STO:Ni thin film is demonstrated in a reversible and real-time way, arising from the biaxial strain produced by piezoelectric PMN-PT. Physical mechanism behind the observation is discussed. This work will open a door for not only investigating the luminescent properties of the phosphors via piezoelectric platform, but also potentially developing novel planar light sources. PMID:25030046

  15. Absence of morphotropic phase boundary effects in BiFeO3-PbTiO3 thin films grown via a chemical multilayer deposition method

    NASA Astrophysics Data System (ADS)

    Gupta, Shashaank; Bhattacharjee, Shuvrajyoti; Pandey, Dhananjai; Bansal, Vipul; Bhargava, Suresh K.; Peng, Ju Lin; Garg, Ashish

    2011-07-01

    We report an unusual behavior observed in (BiFeO3)1- x -(PbTiO3) x (BF- xPT) thin films prepared using a multilayer chemical solution deposition method. Films of different compositions were grown by depositing several bilayers of BF and PT precursors of varying BF and PT layer thicknesses followed by heat treatment in air. X-ray diffraction showed that samples of all compositions show mixing of two compounds resulting in a single-phase mixture, also confirmed by transmission electron microscopy. In contrast to bulk compositions, samples show a monoclinic (MA-type) structure suggesting disappearance of the morphotropic phase boundary (MPB) at x=0.30 as observed in the bulk. This is accompanied by the lack of any enhancement of the remanent polarization at the MPB, as shown by the ferroelectric measurements. Magnetic measurements showed an increase in the magnetization of the samples with increasing BF content. Significant magnetization in the samples indicates melting of spin spirals in the BF- xPT films, arising from a random distribution of iron atoms. Absence of Fe2+ ions was corroborated by X-ray photoelectron spectroscopy measurements. The results illustrate that thin film processing methodology significantly changes the structural evolution, in contrast to predictions from the equilibrium phase diagram, besides modifying the functional characteristics of the BP- xPT system dramatically.

  16. Effect of substrate temperature on structure and luminescence properties of YVO4:Eu3+ thin films grown by PLD

    NASA Astrophysics Data System (ADS)

    Foka, K. E.; Dejene, B. F.; Swart, H. C.

    2016-03-01

    YVO4:Eu3+ thin films were deposited by pulse laser deposition at substrate temperatures of 200, 300 and 400 °C. The oxygen deposition background pressure was also changed from 20 to 85 mTorr at a substrate temperature of 400 °C. The films deposited at the higher temperatures showed a tetragonal phase in consistent with the standard JCPDS card 17-0341. The X-ray diffraction patterns obtained from the 200 °C sample showed only a very small peak at the (200) orientation. The other phosphor thin film showed an improved crystalline structure when the temperature was increased. Scanning electron microscope images indicated larger particles on the surface at the higher temperatures. Atomic force microscopy results showed smooth surfaces with small particles at lower temperatures and an increase in surface roughness at higher temperatures due to the improvement in crystallinity. The photoluminescence showed the typical emission peaks of Eu3+ in the red region at 594 and 618 nm attributed to the 5D0-7F1 and 5D0-7F2 transitions. The peaks at 652 and 699 nm corresponding to the 5D0-7F3 and 5D0-7F4 transitions were also observed. The spectra showed an increase in PL intensity when the deposition temperature and oxygen pressure were increased.

  17. Anisotropic spin structure along the easy axis of magnetization in epitaxially grown MnAs/GaAs(100) thin films

    SciTech Connect

    Song, J. H.; Cui, Y.; Lee, J. J.; Ketterson, J. B.

    2014-05-07

    We grew epitaxial MnAs thin films on GaAs(100) substrates using molecular-beam epitaxy and investigated their magnetic properties. The crystal orientation of the film was type-B. Measurements of the film's magnetization revealed two-fold symmetric magnetic anisotropy on its surface, with the easy and hard directions of magnetization along GaAs[1{sup ¯}10](MnAs[1{sup ¯}1{sup ¯}20]) and GaAs[110](MnAs[11{sup ¯}02]), respectively. We found breakage of the uniaxial anisotropy in magnetization along the easy direction of magnetization for both the magnetization versus magnetic field and magnetization versus temperature measurements. We suggest that the origin of this peculiar pinned ferromagnetism in the MnAs layer is the spin-exchange interaction between the MnAs film and the ultra-thin Mn layer formed at the interface of MnAs film and GaAs(100) substrate.

  18. Interface and electrical properties of ultra-thin HfO2 film grown by radio frequency sputtering

    NASA Astrophysics Data System (ADS)

    Nath, Madhuchhanda; Roy, Asim

    2016-02-01

    Interfacial composition and electrical properties of ultra-thin hafnium oxide (HfO2) films on p-type <100> Si substrate are reported. Hafnium oxide (HfO2) thin films are prepared using radio-frequency sputtering method and subsequently annealed at different temperature. The effect of post-deposition annealing on the interfacial and chemical state of HfO2/Si gate stack has been characterised by means of X-ray reflectivity and X-ray photoelectron spectroscopy studies. Peaks of X-ray photoelectron spectroscopy spectra at 530.50 and 532.25 eV originate from Hf-O-Si bond illustrated the creation of Hf-silicate based interfacial layer at the high-k/Si interface. X-ray reflectivity fitting result also corroborated the formation of Hf silicate interfacial layer. Capacitance-voltage measurements revealed insignificant hysteresis in case of film annealed at 600 °C. Interface trap density has been extracted using Terman method and is found to be 3.18×10-11 cm-2 eV-1 at -1.0 V. Minimum equivalent oxide thickness (EOT) of 1.3 nm was obtained for the film annealed at 600° C. The gate leakage current density of the HfO2 film annealed at 600 °C is 1.5×10-5 A/cm2 at a bias voltage of -2 V.

  19. Properties of barium titanate (BaTiO3) thin films grown on silicon by rf magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Evangelou, E. K.; Konofaos, N.; Thomas, C. B.

    2000-03-01

    Thin films of BaTiO3 were deposited on p-Si substrates by rf magnetron sputtering in order to investigate their suitability for use in ac thin film electroluminescent (ACTFEL) devices and dynamic RAM (DRAM) applications. Post-growth annealing at 700oC and the subsequent deposition of Al contacts resulted in the creation of Al/BaTiO3/p-Si metal-insulator-semiconductor devices. The electronic and structural properties of the films were examined by admittance spectroscopy, current-voltage and transient current measurements, and X-ray diffraction (XRD) characterization. Analysis of the XRD spectra showed the polycrystalline nature of the films but also the presence of an amorphous phase. The electrical measurements revealed a high dielectric constant, around 60, a charge storage capacity exceeding 3muC cm-2 and a total charge trapped inside the oxide of around 50nCcm-2 while the density of traps at the BaTiO3/p-Si interface was found to be as high as 1 x 1012 cm-2eV-1. These results indicate that the films are suitable for both DRAM and ACTFEL applications.

  20. Mixing ALD/MLD-grown ZnO and Zn-4-aminophenol layers into various thin-film structures.

    PubMed

    Sundberg, Pia; Sood, Anjali; Liu, Xuwen; Karppinen, Maarit

    2013-11-14

    Building 2D inorganic-organic hybrids by combining inorganic and organic constituents with molecular-layer precision is an attractive approach to fabricate novel materials with a tailored combination of properties from both entities. Here we demonstrate the potential of the combined atomic and molecular layer deposition (ALD/MLD) technique for the state-of-the-art synthesis of such materials and to fabricate both homogeneous thin-film mixtures and nanolaminates of ZnO and the Zn-4-aminophenol inorganic-organic hybrid. The thin films are deposited by varying the number of precursor cycles during the depositions. Diethyl zinc and 4-aminophenol (AP) are used as precursors for the Zn-AP hybrid depositions, and diethyl zinc and water for the ZnO depositions. The characterization of the mixed Zn-AP and ZnO films reveals that crystallinity, density, surface roughness, chemical stability, hardness and contact modulus are sensitively altered by even a minor insertion of Zn-AP hybrid into the ZnO structure. Fabrication of Zn-AP + ZnO nanolaminates with different thicknesses of the Zn-AP and ZnO layers provides us with an even better way to control the hardness and contact modulus, and also to enhance the chemical stability of the films.

  1. Influence of different aspect ratios on the structural and electrical properties of GaN thin films grown on nanoscale-patterned sapphire substrates

    NASA Astrophysics Data System (ADS)

    Lee, Fang-Wei; Ke, Wen-Cheng; Cheng, Chun-Hong; Liao, Bo-Wei; Chen, Wei-Kuo

    2016-07-01

    This study presents GaN thin films grown on nanoscale-patterned sapphire substrates (NPSSs) with different aspect ratios (ARs) using a homemade metal-organic chemical vapor deposition system. The anodic aluminum oxide (AAO) technique is used to prepare the dry etching mask. The cross-sectional view of the scanning electron microscope image shows that voids exist between the interface of the GaN thin film and the high-AR (i.e. ∼2) NPSS. In contrast, patterns on the low-AR (∼0.7) NPSS are filled full of GaN. The formation of voids on the high-AR NPSS is believed to be due to the enhancement of the lateral growth in the initial growth stage, and the quick-merging GaN thin film blocks the precursors from continuing to supply the bottom of the pattern. The atomic force microscopy images of GaN on bare sapphire show a layer-by-layer surface morphology, which becomes a step-flow surface morphology for GaN on a high-AR NPSS. The edge-type threading dislocation density can be reduced from 7.1 × 108 cm-2 for GaN on bare sapphire to 4.9 × 108 cm-2 for GaN on a high-AR NPSS. In addition, the carrier mobility increases from 85 cm2/Vs for GaN on bare sapphire to 199 cm2/Vs for GaN on a high-AR NPSS. However, the increased screw-type threading dislocation density for GaN on a low-AR NPSS is due to the competition of lateral growth on the flat-top patterns and vertical growth on the bottom of the patterns that causes the material quality of the GaN thin film to degenerate. Thus, the experimental results indicate that the AR of the particular patterning of a NPSS plays a crucial role in achieving GaN thin film with a high crystalline quality.

  2. Effects of Concentration and Substrate Type on Structure and Conductivity of p-Type CuS Thin Films Grown by Spray Pyrolysis Deposition

    NASA Astrophysics Data System (ADS)

    Sabah, Fayroz A.; Ahmed, Naser M.; Hassan, Z.

    2016-09-01

    Copper sulphide (CuS) thin films were grown upon Ti, indium tin oxide (ITO), and glass substrates by using spray pyrolysis deposition at 200°C. The films exhibited good adhesion compared to chemical bath deposition. CuCl2·2H2O and Na2S2O3·5H2O precursors were used as Cu2+ and S2- sources, respectively. Two concentrations (i.e., 0.2 M and 0.4 M) were selected in this study. X-ray diffraction analysis reveals that the films with 0.2 M showed only the formation of a covellite CuS phase having a hexagonal crystal structure with diffraction peaks of low intensity. For 0.4 M concentration, in addition to the covellite CuS phase, chalcocite Cu2S phase having a hexagonal crystal structure also appeared with relatively higher intensity peaks for all thin films. Field-emission scanning electron microscopy observations showed the formation of small grains for 0.2 M, whereas a mixture of grains with square-like shape and nanoplates were formed for 0.4 M. Depending on the 0.2 M and 0.4 M thin films thicknesses (3.2 μm and 4 μm, respectively), the band gap energy was obtained from optical measurements to be approximately 2.64 eV for 0.2 M (pure CuS phase), which slightly decreased up to 2.56 eV for 0.4 M concentration. Hall effect measurements showed that all grown films are p-type. The 0.2 M film exhibited much lower sheet resistance (R sh = 33.96 Ω/Sq-55.70 Ω/Sq) compared to 0.4 M film (R sh = 104.33 Ω/Sq-466.6 Ω/Sq). Moreover, for both concentrations, the films deposited onto ITO substrate showed the lowest sheet resistance (R sh = 33.96 Ω/Sq-104.33 Ω/Sq).

  3. Solution-grown small-molecule organic semiconductor with enhanced crystal alignment and areal coverage for organic thin film transistors

    DOE PAGES

    Bi, Sheng; He, Zhengran; Chen, Jihua; Li, Dawen

    2015-07-24

    Drop casting of small-molecule organic semiconductors typically forms crystals with random orientation and poor areal coverage, which leads to significant performance variations of organic thin-film transistors (OTFTs). In this study, we utilize the controlled evaporative self-assembly (CESA) method combined with binary solvent system to control the crystal growth. A small-molecule organic semiconductor,2,5-Di-(2-ethylhexyl)-3,6-bis(5"-n-hexyl-2,2',5',2"]terthiophen-5-yl)-pyrrolo[3,4-c]pyrrole-1,4-dione (SMDPPEH), is used as an example to demonstrate the effectiveness of our approach. By optimizing the double solvent ratios, well-aligned SMDPPEH crystals with significantly improved areal coverage were achieved. As a result, the SMDPPEH based OTFTs exhibit a mobility of 1.6 × 10-2 cm2/V s, which is themore » highest mobility from SMDPPEH ever reported.« less

  4. Ultra-narrow ferromagnetic resonance in organic-based thin films grown via low temperature chemical vapor deposition

    SciTech Connect

    Yu, H.; Harberts, M.; Adur, R.; Hammel, P. Chris; Johnston-Halperin, E. E-mail: epstein@physics.osu.edu; Lu, Y.; Epstein, A. J. E-mail: epstein@physics.osu.edu

    2014-07-07

    We present the growth of thin films of the organic-based ferrimagnetic semiconductor V[TCNE]{sub x} (x ∼ 2, TCNE: tetracyanoethylene) via chemical vapor deposition. Under optimized growth conditions, we observe a significant increase in magnetic homogeneity, as evidenced by a Curie temperature above 600 K and sharp magnetization switching. Further, ferromagnetic resonance studies reveal a single resonance with full width at half maximum linewidth of 1.4 G, comparable to the narrowest lines measured in inorganic magnetic materials and in contrast to previous studies that showed multiple resonance features. These characteristics are promising for the development of high frequency electronic devices that take advantage of the unique properties of this organic-based material, such as the potential for low cost synthesis combined with low temperature and conformal deposition on a wide variety of substrates.

  5. Study of high {Tc} superconducting thin films grown by MOCVD. Final report, July 1, 1986--April 30, 1990

    SciTech Connect

    Erbil, A.

    1990-12-31

    Work is described briefly, which was carried out on development of techniques to grow metal-semiconductor superlattices (artificially layered materials) and on the copper oxide based susperconductors (naturally layered materials). The current growth technique utilized is metalorganic chemical vapor deposition (MOCVD). CdTe, PbTe, La, LaTe, and Bi{sub 2}Te{sub 3} were deposited, mostly on GaAs. Several YBa{sub 2}Cu{sub 3}O{sub 7} compounds were obtained with possible superconductivity at temperatures up to 550 K (1 part in 10{sup 4}). YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} and Tl{sub 2}CaBa{sub 2}Cu{sub 2}O{sub y} thin films were deposited by MOCVD on common substrates such as glass.

  6. Structure and composition of zirconium carbide thin-film grown by ion beam sputtering for optical applications

    NASA Astrophysics Data System (ADS)

    Singh, Amol; Modi, Mohammed H.; Dhawan, Rajnish; Lodha, G. S.

    2014-04-01

    Thin film of compound material ZrC was deposited on Si (100) wafer using ion beam sputtering method. The deposition was carried out at room temperature and at base pressure of 3×10-5 Pa. X-ray photoelectron spectroscopy (XPS) measurements were performed for determining the surface chemical compositions. Grazing incidence x-ray reflectivity (GIXRR) measurements were performed to study the film thickness, roughness and density. From GIXRR curve roughness value of the film was found less than 1 nm indicating smooth surface morphology. Films density was found 6.51 g/cm3, which is close to bulk density. Atomic force microscopy (AFM) measurements were performed to check the surface morphology. AFM investigation showed that the film surface is smooth, which corroborate the GIXRR data. Figure 2 of the original article PDF file, as supplied to AIP Publishing, contained a PDF processing error. This article was updated on 12 May 2014 to correct that error.

  7. Deposition And Characterization of (Ti,Zr)N Thin Films Grown Through PAPVD By The Pulsed Arc Technique

    SciTech Connect

    Marulanda, D. M.; Trujillo, O.; Devia, A.

    2006-12-04

    The Plasma Assisted Physic Vapor Deposition (PAPVD) by the pulsed arc technique has been used for deposition of Titanium Zirconium Nitride (Ti,Zr)N coatings, using a segmented target of TiZr. The deposition was performed in a vacuum chamber with two faced electrodes (target and substrate) using nitrogen as working gas, and a power-controlled source used to produce the arc discharges. Films were deposited on stainless steel 304, and they were characterized using the X-Ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD), Energy Dispersion Spectroscopy (EDS) and Scanning Probe Microscopy (SPM) techniques. The XRD patterns show different planes in which the film grows. Through SPM, using Atomic Force Microscopy (AFM) and Lateral Force Microscopy (LFM) modes, a nanotribologic study of the thin film was made, determining hardness and friction coefficient.

  8. Defect study of molecular beam epitaxy grown undoped GaInNAsSb thin film using junction-capacitance spectroscopy

    SciTech Connect

    Monirul Islam, Muhammad; Miyashita, Naoya; Ahsan, Nazmul; Okada, Yoshitaka

    2013-02-18

    Defects in undoped GaInNAsSb thin film (i-GaInNAsSb) were investigated by junction-capacitance technique using admittance and transient photocapacitance (TPC) spectroscopy. An electron trap D2 was identified at 0.34 eV below the conduction band (E{sub C}) of i-GaInNAsSb using admittance spectroscopy. Optical transition of valance band (E{sub V}) electrons to a localized state OH1 (E{sub V} + 0.75 eV) was manifested in negative TPC signal. Combined activation energy of OH1 and D2 defect corresponds to the band-gap of i-GaInNAsSb, suggesting that OH1/D2 acts as an efficient recombination center. TPC signal at {approx}1.59 eV above E{sub V} was attributed to the nitrogen-induced localized state in GaInNAsSb.

  9. Structural and magnetic properties of epitaxial delafossite CuFeO{sub 2} thin films grown by pulsed laser deposition

    SciTech Connect

    Joshi, Toyanath; Senty, Tess R.; Trappen, Robbyn; Zhou, Jinling; Borisov, Pavel; Holcomb, Mikel B.; Bristow, Alan D.; Lederman, David; Chen, Song; Song, Xueyan; Ferrari, Piero; Cabrera, Alejandro L.

    2015-01-07

    Growth of pure phase delafossite CuFeO{sub 2} thin films on Al{sub 2}O{sub 3} (00.1) substrates by pulsed laser deposition was systematically investigated as a function of growth temperature and oxygen pressure. X-ray diffraction, transmission electron microscopy, Raman scattering, and x-ray absorption spectroscopy confirmed the existence of the delafossite phase. Infrared reflectivity spectra determined a band edge at 1.15 eV, in agreement with the bulk delafossite data. Magnetization measurements on CuFeO{sub 2} films demonstrated a phase transition at T{sub C} ≈ 15 ± 1 K, which agrees with the first antiferromagnetic transition at 14 K in the bulk CuFeO{sub 2}. Low temperature magnetic phase is best described by commensurate, weak ferromagnetic spin ordering along the c-axis.

  10. Solution-grown small-molecule organic semiconductor with enhanced crystal alignment and areal coverage for organic thin film transistors

    SciTech Connect

    Bi, Sheng; He, Zhengran; Chen, Jihua; Li, Dawen

    2015-07-24

    Drop casting of small-molecule organic semiconductors typically forms crystals with random orientation and poor areal coverage, which leads to significant performance variations of organic thin-film transistors (OTFTs). In this study, we utilize the controlled evaporative self-assembly (CESA) method combined with binary solvent system to control the crystal growth. A small-molecule organic semiconductor,2,5-Di-(2-ethylhexyl)-3,6-bis(5"-n-hexyl-2,2',5',2"]terthiophen-5-yl)-pyrrolo[3,4-c]pyrrole-1,4-dione (SMDPPEH), is used as an example to demonstrate the effectiveness of our approach. By optimizing the double solvent ratios, well-aligned SMDPPEH crystals with significantly improved areal coverage were achieved. As a result, the SMDPPEH based OTFTs exhibit a mobility of 1.6 × 10-2 cm2/V s, which is the highest mobility from SMDPPEH ever reported.

  11. Structural and optical properties of TiO2 thin films grown by sol-gel dip coating process

    NASA Astrophysics Data System (ADS)

    Bouachiba, Y.; Bouabellou, A.; Hanini, F.; Kermiche, F.; Taabouche, A.; Boukheddaden, K.

    2014-01-01

    The mono and bi-layer TiO2 thin films have been prepared by sol-gel method on glass. X-Ray diffraction, Raman spectroscopy, atomic force microscopy, spectroscopic ellipsometry and m-lines spectroscopy techniques have been used to characterize the TiO2 films. The mono-layer film is found to be amorphous, while the bi-layer film shows the presence of anatase phase. The bi-layer film exhibits more homogeneous surface with less roughness. The thickness effect on the refractive index, extinction ceofficient, packing density and optical band gap is analysed. The waveguiding measurements of the bi-layer film exhibit single-guided TE0 and TM0 polarized modes from which we can measure the refractive index and the film thickness.

  12. Large-area uniform graphene-like thin films grown by chemical vapor deposition directly on silicon nitride

    NASA Astrophysics Data System (ADS)

    Sun, Jie; Lindvall, Niclas; Cole, Matthew T.; Teo, Kenneth B. K.; Yurgens, August

    2011-06-01

    Large-area uniform carbon films with graphene-like properties are synthesized by chemical vapor deposition directly on Si3N4/Si at 1000 °C without metal catalysts. The as deposited films are atomically thin and wrinkle- and pinhole-free. The film thickness can be controlled by modifying the growth conditions. Raman spectroscopy confirms the sp2 graphitic structures. The films show ohmic behavior with a sheet resistance of ˜2.3-10.5 kΩ/◻ at room temperature. An electric field effect of ˜2-10% (VG=-20 V) is observed. The growth is explained by the self-assembly of carbon clusters from hydrocarbon pyrolysis. The scalable and transfer-free technique favors the application of graphene as transparent electrodes.

  13. Boron nitride phosphide thin films grown on quartz substrate by hot-filament and plasma-assisted chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhang, X. W.; Xu, S. Y.; Han, G. R.

    2004-10-01

    Boron nitride phosphide films are, for the first time, grown on transparent quartz substrate by hot filament and radio-frequency plasma co-assisted chemical vapor deposition technique. XPS, XRD, SEM, and UV measurements are performed to study the chemical composition, crystallization, microstructure, and optical absorption, respectively. A centipede-like microstructure and undulating ground morphology on the film surface are observed, and their growth mechanism is speculated upon. The chemical composition is determined as BN1-xPx, whose characteristic XRD peak is preliminarily identified. The optical band gap can be modulated between 5.52 eV and 3.74 eV, simply by adjusting the phosphorus content in BN1-xPx through modifying the PH3 flux during the film-deposition process. The merits of the BN1-xPx film, such as high ultraviolet photoelectric sensitivity with negligible sensitivity in the visible region, modifiable wide optical band gap, and good adhesion on transparent substrate, suggest potential applications for ultraviolet photo-electronics.

  14. Electrical and piezoelectric properties of BiFeO3 thin films grown on SrxCa1-xRuO3-buffered SrTiO3 substrates

    NASA Astrophysics Data System (ADS)

    Yao, Yingbang; Chen, Long; Wang, Zhihong; Alshareef, Husam; Zhang, X. X.

    2012-06-01

    (001)-oriented BiFeO3 (BFO) thin films were grown on SrxCa1-xRuO3- (SCRO; x = 1, 0.67, 0.33, 0) buffered SrTiO3 (001) substrates using pulsed laser deposition. The microstructural, electrical, ferroelectric, and piezoelectric properties of the thin films were considerably affected by the buffer layers. The interface between the BFO films and the SCRO-buffer layer was found to play a dominant role in determining the electrical and piezoelectric behaviors of the films. We found that films grown on SrRuO3-buffer layers exhibited minimal electrical leakage while films grown on Sr0.33Ca0.67RuO3-buffer layers had the largest piezoelectric response. The origin of this difference is discussed.

  15. NiO growth on Ag(001): A layer-by-layer vibrational study

    NASA Astrophysics Data System (ADS)

    Kostov, K. L.; Schumann, F. O.; Polzin, S.; Sander, D.; Widdra, W.

    2016-08-01

    The vibrational properties of NiO(001) films on Ag(001) with thicknesses up to 50 monolayers (ML) are characterized with high-resolution electron energy loss spectroscopy (HREELS). For NiO growth at 300 K, four different coverage regions are distinguished by HREELS. The film-thickness-dependent Fuchs-Kliewer (FK) phonon frequency shifts and intensity changes are identified from the NiO monolayer to bulklike thick films. Characteristic changes of the vibrational properties are analyzed to resolve restructuring processes during annealing and thermal decomposition of NiO films. A quantitative comparison of the experimental data, including a line shape analysis, with the calculated loss function based on dielectric theory reveals an excellent agreement between the bulk and the NiO(001) thin film phonon properties for film thicknesses above 15 ML. In contrast, a strong FK phonon softening is observed for thin films below 5 ML that cannot be explained by dielectric theory nor phonon standing waves. This softening is attributed to the presence of surface stress, which results from the -2 % lattice mismatch between NiO and Ag.

  16. Polycrystalline domain structure of pentacene thin films epitaxially grown on a hydrogen-terminated Si(111) surface

    SciTech Connect

    Nishikata, S.; Sadowski, J. T.; Al-Mahboob, A.; Nishihara, T.; Fujikawa, Y.; Sakurai, T.; Nakajima, K.; Sazaki, G.; Suto, S.

    2007-10-15

    Single-monolayer high pentacene (Pn) dendrites grown on a hydrogen-terminated Si(111) surface [H-Si(111)] under ultrahigh vacuum were observed by low-energy electron microscopy and microbeam low-energy electron diffraction analyses. We determined the epitaxial structure (type I) inside a unique polycrystalline domain structure of such dendrites, each of which has six equivalent epitaxial orientations of Pn two-dimensional (2D) unit cells. There are three sets of these cells, which are rotated {+-}120 deg. relative to each other. Domain boundaries inside each dendrite were successfully observed by scanning tunneling microscopy. In addition, we found another epitaxial relation (type II): the polycrystalline domain structure and lattice parameters are similar to those of the type-I dendrite; however, the 2D unit cells of the type-II dendrite are rotated approximately 90 deg. relative to those of the type-I dendrite. These results suggest that the crystal structure of the dendrites on H-Si(111) is determined mainly by the interaction between Pn molecules. Each dendrite is composed of domains that are exclusively of type I or II. The so-called point-on-line coincidences are found between the Pn 2D lattices of types I and II, and H-Si(111). The higher commensurability of the type-I dendrites than the type-II dendrites results in a higher probability of type-I dendrite formation. Moreover, for both the type-I and type-II dendrites, we found supercell structures. We estimated the minimum interface energy between the dendrite and H-Si(111) from an island's free energy, which is necessary to reproduce the growth of a single-monolayer high dendrite.

  17. The effects of oxygen pressure on disordering and magneto-transport properties of Ba{sub 2}FeMoO{sub 6} thin films grown via pulsed laser deposition

    SciTech Connect

    Kim, Kyeong-Won; Mhin, Sungwook; Jones, Jacob L.; Norton, David P.; Ghosh, Siddhartha Buvaev, Sanal; Hebard, Arthur F.

    2015-07-21

    Epitaxial Ba{sub 2}FeMoO{sub 6} thin films were grown via pulsed laser deposition under low oxygen pressure and their structural, chemical, and magnetic properties were examined, focusing on the effects of oxygen pressure. The chemical disorder, off-stoichiometry in B site cations (Fe and Mo) increased with increasing oxygen pressure and thus magnetic properties were degraded. Interestingly, in contrast, negative magneto-resistance, which is the characteristics of this double perovskite material, was enhanced with increasing oxygen pressure. It is believed that phase segregation of highly disordered thin films is responsible for the increased magneto-resistance of thin films grown at high oxygen pressure. The anomalous Hall effect, which behaves hole-like, was also observed due to spin-polarized itinerant electrons under low magnetic field below 1 T and the ordinary electron-like Hall effect was dominant at higher magnetic fields.

  18. Effect of sulfurization time on the properties of copper zinc tin sulfide thin films grown by electrochemical deposition

    NASA Astrophysics Data System (ADS)

    Aldalbahi, Ali; Mkawi, E. M.; Ibrahim, K.; Farrukh, M. A.

    2016-09-01

    We report growth of quaternary Cu2 ZnSnS4 (CZTS) thin films prepared by the electrochemical deposition from salt precursors containing Cu (II), Zn (II) and Sn (IV) metals. The influence of different sulfurization times t (t = 75, 90, 105, and 120 min) on the structural, compositional, morphological, and optical properties, as well as on the electrical properties is studied. The films sulfurized 2 hours showed a prominent kesterite phase with a nearly stoichiometric composition. Samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and Raman and UV-VIS-NIR spectrometer at different stages of work. X-ray diffraction and Raman spectroscopy analyses confirmed the formation of phase-pure CZTS films. (FESEM) shows that compact and dense morphology and enhanced photo-sensitivity. STEM - EDS elemental map of CZTS cross-section confirms homogeneous distribution. From optical study, energy gap was enlarged with a changed sulfurization times in the range of 1.37–1.47 eV.

  19. Optical properties of nanocrystalline Y2O3 thin films grown on quartz substrates by electron beam deposition

    NASA Astrophysics Data System (ADS)

    Wiktorczyk, Tadeusz; Biegański, Piotr; Serafińczuk, Jarosław

    2016-09-01

    Yttrium oxide thin films of a thickness 221-341 nm were formed onto quartz substrates by reactive physical vapor deposition in an oxygen atmosphere. An electron beam gun was applied as a deposition source. The effect of substrate temperature during film deposition (in the range of 323-673 K) on film structure, surface morphology and optical properties was investigated. The surface morphology studies (with atomic force microscopy and diffuse spectra reflectivity) show that the film surface was relatively smooth with RMS surface roughness in the range of 1.7-3.8 nm. XRD analysis has revealed that all diffraction lines belong to a cubic Y2O3 structure. The films consisted of small nanocrystals. Their average grain size increases from 1.6 nm to 22 nm, with substrate temperature rising from 323 K to 673 K. Optical examinations of transmittance and reflectance were performed in the spectral range of 0.2-2.5 μm. Optical constants and their dispersion curves were determined. Values of the refractive index of the films were in the range of n = 1.79-1.90 (at 0.55 μm) for substrate temperature during film deposition of 323-673 K. The changes in the refractive index upon substrate temperature correspond very well with the increase in the nanocrystals grain diameter and with film porosity.

  20. Effect of sulfurization time on the properties of copper zinc tin sulfide thin films grown by electrochemical deposition

    PubMed Central

    Aldalbahi, Ali; Mkawi, E. M.; Ibrahim, K.; Farrukh, M. A.

    2016-01-01

    We report growth of quaternary Cu2 ZnSnS4 (CZTS) thin films prepared by the electrochemical deposition from salt precursors containing Cu (II), Zn (II) and Sn (IV) metals. The influence of different sulfurization times t (t = 75, 90, 105, and 120 min) on the structural, compositional, morphological, and optical properties, as well as on the electrical properties is studied. The films sulfurized 2 hours showed a prominent kesterite phase with a nearly stoichiometric composition. Samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and Raman and UV-VIS-NIR spectrometer at different stages of work. X-ray diffraction and Raman spectroscopy analyses confirmed the formation of phase-pure CZTS films. (FESEM) shows that compact and dense morphology and enhanced photo-sensitivity. STEM - EDS elemental map of CZTS cross-section confirms homogeneous distribution. From optical study, energy gap was enlarged with a changed sulfurization times in the range of 1.37–1.47 eV. PMID:27600023

  1. Ultra-high mobility transparent organic thin film transistors grown by an off-centre spin-coating method

    NASA Astrophysics Data System (ADS)

    Yuan, Yongbo; Giri, Gaurav; Ayzner, Alexander L.; Zoombelt, Arjan P.; Mannsfeld, Stefan C. B.; Chen, Jihua; Nordlund, Dennis; Toney, Michael F.; Huang, Jinsong; Bao, Zhenan

    2014-01-01

    Organic semiconductors with higher carrier mobility and better transparency have been actively pursued for numerous applications, such as flat-panel display backplane and sensor arrays. The carrier mobility is an important figure of merit and is sensitively influenced by the crystallinity and the molecular arrangement in a crystal lattice. Here we describe the growth of a highly aligned meta-stable structure of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) from a blended solution of C8-BTBT and polystyrene by using a novel off-centre spin-coating method. Combined with a vertical phase separation of the blend, the highly aligned, meta-stable C8-BTBT films provide a significantly increased thin film transistor hole mobility up to 43 cm2 Vs-1 (25 cm2 Vs-1 on average), which is the highest value reported to date for all organic molecules. The resulting transistors show high transparency of >90% over the visible spectrum, indicating their potential for transparent, high-performance organic electronics.

  2. Effect of sulfurization time on the properties of copper zinc tin sulfide thin films grown by electrochemical deposition.

    PubMed

    Aldalbahi, Ali; Mkawi, E M; Ibrahim, K; Farrukh, M A

    2016-01-01

    We report growth of quaternary Cu2 ZnSnS4 (CZTS) thin films prepared by the electrochemical deposition from salt precursors containing Cu (II), Zn (II) and Sn (IV) metals. The influence of different sulfurization times t (t = 75, 90, 105, and 120 min) on the structural, compositional, morphological, and optical properties, as well as on the electrical properties is studied. The films sulfurized 2 hours showed a prominent kesterite phase with a nearly stoichiometric composition. Samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and Raman and UV-VIS-NIR spectrometer at different stages of work. X-ray diffraction and Raman spectroscopy analyses confirmed the formation of phase-pure CZTS films. (FESEM) shows that compact and dense morphology and enhanced photo-sensitivity. STEM - EDS elemental map of CZTS cross-section confirms homogeneous distribution. From optical study, energy gap was enlarged with a changed sulfurization times in the range of 1.37-1.47 eV. PMID:27600023

  3. Co2FeAl thin films grown on MgO substrates: Correlation between static, dynamic, and structural properties

    NASA Astrophysics Data System (ADS)

    Belmeguenai, M.; Tuzcuoglu, H.; Gabor, M. S.; Petrisor, T., Jr.; Tiusan, C.; Berling, D.; Zighem, F.; Chauveau, T.; Chérif, S. M.; Moch, P.

    2013-05-01

    Co2FeAl (CFA) thin films with thickness varying from 10 to 115 nm have been deposited on MgO(001) substrates by magnetron sputtering and then capped by a Ta or Cr layer. X-ray diffraction (XRD) revealed that the cubic [001] CFA axis is normal to the substrate and that all the CFA films exhibit full epitaxial growth. The chemical order varies from the B2 phase to the A2 phase when decreasing the thickness. Magneto-optical Kerr effect (MOKE) and vibrating sample magnetometer (VSM) measurements show that, depending on the field orientation, one- or two-step switchings occur. Moreover, the films present a quadratic MOKE signal increasing with the CFA thickness, due to the increasing chemical order. Ferromagnetic resonance (FMR), MOKE transverse bias initial inverse susceptibility and torque (TBIIST) measurements reveal that the in-plane anisotropy results from the superposition of a uniaxial and of a fourfold symmetry term. The fourfold anisotropy is in accord with the crystal structure of the samples and is correlated to the biaxial strain and to the chemical order present in the films. In addition, a large negative perpendicular uniaxial anisotropy is observed. Frequency and angular dependencies of the ferromagnetic resonance linewidth show two magnon scattering and mosaicity contributions, which depend on the CFA thickness. A Gilbert damping coefficient as low as 0.0011 is found.

  4. Role of surface-electrical properties on the cell-viability of carbon thin films grown in nanodomain morphology

    NASA Astrophysics Data System (ADS)

    Javid, Amjed; Kumar, Manish; Yoon, Seokyoung; Lee, Jung Heon; Tajima, Satomi; Hori, Masaru; Geon Han, Jeon

    2016-07-01

    Carbon thin films, having a combination of unique physical and chemical properties, exhibit an interesting biocompatibility and biological response to living entities. Here, the carbon films are developed in the morphology form of nano-domains with nanoscale inter-domain separations, tuned by plasma conditions in the facing target magnetron sputtering process. The wettability and surface energy are found to have a close relation to the inter-domain separations. The chemical structure of carbon films exhibited the relative enhancement of sp3 in comparison to sp2 with the increase of domain separations. The cell-viability of these films shows promising results for L929 mouse fibroblast and Saos-2 bone cells, when inter-domain separation is increased. Electrical conductivity and surface energy are identified to play the key role in different time-scales during the cell-proliferation process. The contribution from electrical conductivity is dominant in the beginning of the cultivation, whereas with the passage of time (~3-5 d) the surface energy takes control over conductivity to enhance the cell proliferation.

  5. Yb:YAG thin disk laser passively Q-switched by a hydro-thermal grown molybdenum disulfide saturable absorber

    NASA Astrophysics Data System (ADS)

    Zhan, Yi; Wang, Li; Wang, Jie Yu; Li, Hong Wei; Yu, Zhen Huang

    2015-02-01

    We demonstrate a passively Q-switched Yb:YAG thin disk solid-state laser based on nanoflake MoS2 as a saturable absorber. MoS2 is synthesized by a hydro-thermal process. The prepared MoS2 is transferred onto the BK7 glass for ease-of-use in the solid-state laser as a saturable absorber. The average output power could reach up to 250 mW, center wavelength 1030 nm corresponding to a pulse width, a pulse repetition rate, and a per pulse energy of 12 μs, 17 kHz, and 15 μJ, respectively. Our results show that nanoflake MoS2 could be a promising saturable absorber for Q-switching solid-state lasers. The over saturation of the MoS2 saturable absorber at a high pump strength limit in a solid-state laser could be also effective for high power operation.

  6. Role of surface-electrical properties on the cell-viability of carbon thin films grown in nanodomain morphology

    NASA Astrophysics Data System (ADS)

    Javid, Amjed; Kumar, Manish; Yoon, Seokyoung; Lee, Jung Heon; Tajima, Satomi; Hori, Masaru; Geon Han, Jeon

    2016-07-01

    Carbon thin films, having a combination of unique physical and chemical properties, exhibit an interesting biocompatibility and biological response to living entities. Here, the carbon films are developed in the morphology form of nano-domains with nanoscale inter-domain separations, tuned by plasma conditions in the facing target magnetron sputtering process. The wettability and surface energy are found to have a close relation to the inter-domain separations. The chemical structure of carbon films exhibited the relative enhancement of sp3 in comparison to sp2 with the increase of domain separations. The cell-viability of these films shows promising results for L929 mouse fibroblast and Saos-2 bone cells, when inter-domain separation is increased. Electrical conductivity and surface energy are identified to play the key role in different time-scales during the cell-proliferation process. The contribution from electrical conductivity is dominant in the beginning of the cultivation, whereas with the passage of time (~3–5 d) the surface energy takes control over conductivity to enhance the cell proliferation.

  7. Luminescent characteristics of Se-doped ZnGa2O4:Mn thin film phosphors grown by pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Jeong, J. H.; Bae, J. S.; Choi, B. C.; Yi, S. S.; Holloway, P. H.

    2004-07-01

    Mn-doped ZnGa2O4-xSex (x=0.00, 0.025, 0.05, 0.075 and 0.10) thin film phosphors have been grown using pulsed laser ablation under various growth conditions. Structural characterization was carried out on a series of ZnGa2O4-xSex:Mn2+ films grown on MgO(100) substrates using Zn-rich ceramic targets. Zn-rich ceramic targets were prepared to compensate for loss of vaporization of Zn during deposition. The oxygen pressure was fixed at 100 mTorr and the substrate temperatures were varied from 500 to 700 °C. Luminescence results indicated that MgO (100) is a promising substrate for the growth of high-quality of ZnGa2O4-xSex:Mn2+ films. The crystallinity and surface roughness of the ZnGa2O4-xSex:Mn2+ films are highly dependent on the growth conditions, in particular on the substrate temperature and composition ratio of targets. The crystallinity of the films improved with Se doping. Incorporation of Se into the ZnGa2O4 lattice led to a remarkable increase of photoluminescence. The highest green emission intensity was observed with ZnGa2O3.925Se0.075:Mn2+ films whose brightness was increased by a factor of 3.1 in comparison with that of ZnGa2O4:Mn2+ films. This phosphor is promising for application in flat panel displays. .

  8. Microstructure evolution and non-diamond carbon incorporation in CVD diamond thin films grown at low substrate temperatures

    NASA Astrophysics Data System (ADS)

    Michler, J.; Stiegler, J.; von Kaenel, Y.; Moeckli, P.; Dorsch, W.; Stenkamp, D.; Blank, E.

    1997-03-01

    We investigated the development of the microstructure and the incorporation of non-diamond carbon close to the low temperature border of the CVD diamond domain. Thin diamond films were deposited at low substrate temperatures (560°C-275°C) by microwave plasma-assisted CVD on silicon, varying only the substrate temperature. At elevated temperatures (560°C-430°C) the film mainly consists of nearly defect free near 112 oriented grains with smooth 111 facets, exhibiting steps and risers at the surface. Decreasing the substrate temperature an apparently sharp transition occurs, below which the film quality undergoes a rapid deterioration as evidenced by Raman spectroscopy, while crystalline faceted grains with a size of several microns and a growth texture of <100> remain. However, X-ray diffraction reveals a strongly decreasing crystal size (from about 1 μm to 10 nm) which can be attributed to an increased twin density within the macroscopic grains. High resolution transmission electron microscopy reveals that these twins consist of small twin lamellae with a spacing of only several atomic planes. Transmission electron microscopy of near surface areas evidences re-entrant corners at the grain surfaces formed by twin lamellae and the presence of steps and risers. Non-diamond carbon was detected in the form of amorphous inclusions at incoherent twin boundaries and probably at higher order twin boundaries. The observations will be discussed by means of two different competing nucleation mechanisms: above the low temperature limit the grains grow by lateral ledge motion and preferential nucleation at re-entrant corners. Approaching the low temperature limit, two-dimensional nucleation at growth facets becomes an alternate nucleation mechanism, which introduces a high density of microtwins. If two-dimensional nuclei grow together, non-diamond carbon is incorporated during growth at this interface.

  9. Atomic disorder of Li0.5Ni0.5O thin films caused by Li doping: estimation from X-ray Debye–Waller factors

    PubMed Central

    Yang, Anli; Sakata, Osami; Yamauchi, Ryosuke; Kumara, L. S. R.; Song, Chulho; Katsuya, Yoshio; Matsuda, Akifumi; Yoshimoto, Mamoru

    2015-01-01

    Cubic type room-temperature (RT) epitaxial Li0.5Ni0.5O and NiO thin films with [111] orientation grown on ultra-smooth sapphire (0001) substrates were examined using synchrotron-based thin-film X-ray diffraction. The 11 and 22 rocking curves including six respective equivalent reflections of the Li0.5Ni0.5O and NiO thin films were recorded. The RT B 1 factor, which appears in the Debye–Waller factor, of a cubic Li0.5Ni0.5O thin film was estimated to be 1.8 (4) Å2 from its 11 and 22 reflections, even though the Debye model was originally derived on the basis of one cubic element. The corresponding Debye temperature is 281 (39) K. Furthermore, the B 2 factor in the pseudo-Debye–Waller factor is proposed. This parameter, which is evaluated using one reflection, was also determined for the Li0.5Ni0.5O thin film by treating Li0.5Ni0.5O and NiO as ideal NaCl crystal structures. A structural parameter for the atomic disorder is introduced and evaluated. This parameter includes the combined effects of thermal vibration, interstitial atoms and defects caused by Li doping using the two Debye–Waller factors. PMID:26664345

  10. UV light induced insulator-metal transition in ultra-thin ZnO/TiOx stacked layer grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Saha, D.; Misra, P.; Joshi, M. P.; Kukreja, L. M.

    2016-08-01

    In the present study, atomic layer deposition has been used to grow a series of Ti incorporated ZnO thin films by vertically stacking different numbers (n = 1-7) of ZnO/TiOx layers on (0001) sapphire substrates. The effects of defect states mediated chemisorption of O2 and/OH groups on the electrical properties of these films have been investigated by illuminating the samples under UV light inside a high vacuum optical cryostat. The ultra-thin film having one stacked layer (n = 1) did not show any change in its electrical resistance upon UV light exposure. On the contrary, marginal drop in the electrical resistivity was measured for the samples with n ≥ 3. Most surprisingly, the sample with n = 2 (thickness ˜ 12 nm) showed an insulator to metal transition upon UV light exposure. The temperature dependent electrical resistivity measurement on the as grown film (n = 2) showed insulating behaviour, i.e., diverging resistivity on extrapolation to T→ 0 K. However, upon UV light exposure, it transformed to a metallic state, i.e., finite resistivity at T → 0 K. Such an insulator-metal transition plausibly arises due to the de-trapping of conduction electrons from the surface defect sites which resulted in an upward shift of the Fermi level above the mobility edge. The low-temperature electron transport properties on the insulating film (n = 2) were investigated by a combined study of zero field electrical resistivity ρ(T) and magnetoresistance (MR) measurements. The observed negative MR was found to be in good agreement with the magnetic field induced suppression of quantum interference between forward-going paths of tunnelling electrons. Both ρ(T) and MR measurements provided strong evidence for the Efros-Shklovskii type variable range hopping conduction in the low-temperature (≤40 K) regime. Such studies on electron transport in ultra-thin n-type doped ZnO films are crucial to achieve optimum functionality with long term reliability of ZnO based transparent

  11. The effect of deposition atmosphere on the chemical composition of TiN and ZrN thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Craciun, D.; Socol, G.; Stefan, N.; Dorcioman, G.; Hanna, M.; Taylor, C. R.; Lambers, E.; Craciun, V.

    2014-05-01

    Very thin TiN and ZrN films (<500 nm) were grown on (1 0 0) Si substrates at temperatures up to 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under residual vacuum or various mixtures of CH4 or N2. Auger electron spectroscopy investigations found that films contained a relatively low oxygen concentration, usually below 3.0 at%. Films deposited under residual vacuum or very low N2 pressures (<3 × 10-3 Pa) contained 3-6 at% C atoms in the bulk. This fraction grew to 8-10 at% when the deposition was performed under an atmosphere of 2 × 10-3 Pa CH4. To avoid C atoms incorporation into the bulk a deposition pressure of 10 Pa N2 was required. X-ray photoelectron spectroscopy investigations found that oxygen was mostly bonded in an oxynitride type of compound, while carbon was bonded into a metallic carbide. The presence of C atoms in the chemical composition of the TiN or ZrN improved the measured hardness of the films.

  12. Characterization of structural defects in SnSe2 thin films grown by molecular beam epitaxy on GaAs (111)B substrates

    NASA Astrophysics Data System (ADS)

    Tracy, Brian D.; Li, Xiang; Liu, Xinyu; Furdyna, Jacek; Dobrowolska, Margaret; Smith, David J.

    2016-11-01

    Tin selenide thin films have been grown by molecular beam epitaxy on GaAs (111)B substrates at a growth temperature of 150 °C, and a microstructural study has been carried out, primarily using the technique of transmission electron microscopy. The Se:Sn flux ratio during growth was systematically varied and found to have a strong impact on the resultant crystal structure and quality. Low flux ratios (Se:Sn=3:1) led to defective films consisting primarily of SnSe, whereas high flux ratios (Se:Sn>10:1) gave higher quality, single-phase SnSe2. The structure of the monoselenide films was found to be consistent with the Space Group Pnma with the epitaxial growth relationship of [011]SnSe// [ 1 1 bar 0 ] GaAs, while the diselenide films were consistent with the Space Group P 3 bar m1 , and had the epitaxial growth relationship [ 2 1 bar 1 bar 0 ]SnSe2// [ 1 1 bar 0 ] GaAs.

  13. Structural properties of Bi{sub 2−x}Mn{sub x}Se{sub 3} thin films grown via molecular beam epitaxy

    SciTech Connect

    Babakiray, Sercan; Johnson, Trent A.; Borisov, Pavel; Holcomb, Mikel B.; Lederman, David; Marcus, Matthew A.; Tarafder, Kartick

    2015-07-28

    The effects of Mn doping on the structural properties of the topological insulator Bi{sub 2}Se{sub 3} in thin film form were studied in samples grown via molecular beam epitaxy. Extended x-ray absorption fine structure measurements, supported by density functional theory calculations, indicate that preferential incorporation occurs substitutionally in Bi sites across the entire film volume. This finding is consistent with x-ray diffraction measurements which show that the out of plane lattice constant expands while the in plane lattice constant contracts as the Mn concentration is increased. X-ray photoelectron spectroscopy indicates that the Mn valency is 2+ and that the Mn bonding is similar to that in MnSe. The expansion along the out of plane direction is most likely due to weakening of the Van der Waals interactions between adjacent Se planes. Transport measurements are consistent with this Mn{sup 2+} substitution of Bi sites if additional structural defects induced by this substitution are taken into account.

  14. Electrical conduction and dielectric relaxation properties of AlN thin films grown by hollow-cathode plasma-assisted atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Altuntas, Halit; Bayrak, Turkan; Kizir, Seda; Haider, Ali; Biyikli, Necmi

    2016-07-01

    In this study, aluminum nitride (AlN) thin films were deposited at 200 °C, on p-type silicon substrates utilizing a capacitively coupled hollow-cathode plasma source integrated atomic layer deposition (ALD) reactor. The structural properties of AlN were characterized by grazing incidence x-ray diffraction, by which we confirmed the hexagonal wurtzite single-phase crystalline structure. The films exhibited an optical band edge around ˜5.7 eV. The refractive index and extinction coefficient of the AlN films were measured via a spectroscopic ellipsometer. In addition, to investigate the electrical conduction mechanisms and dielectric properties, Al/AlN/p-Si metal-insulator-semiconductor capacitor structures were fabricated, and current density-voltage and frequency dependent (7 kHz-5 MHz) dielectric constant measurements (within the strong accumulation region) were performed. A peak of dielectric loss was observed at a frequency of 3 MHz and the Cole-Davidson empirical formula was used to determine the relaxation time. It was concluded that the native point defects such as nitrogen vacancies and DX centers formed with the involvement of Si atoms into the AlN layers might have influenced the electrical conduction and dielectric relaxation properties of the plasma-assisted ALD grown AlN films.

  15. Tin-Incorporation Induced Changes in the Microstructural, Optical, and Electrical Behavior of Tungsten Oxide Nanocrystalline Thin Films Grown Via Spray Pyrolysis

    NASA Astrophysics Data System (ADS)

    Mukherjee, Ramnayan; Prajapati, C. S.; Sahay, P. P.

    2014-12-01

    Undoped and Sn-doped WO3 thin films were grown on cleaned glass substrates by chemical spray pyrolysis, using ammonium tungstate (NH4)2WO4 as the host precursor and tin chloride (SnCl4·5H2O) as the source of dopant. The XRD spectra confirm the monoclinic structure with a sharp narrow peak along (200) direction along with other peaks of low relative intensities for all the samples. On Sn doping, the films exhibit reduced crystallinity relative to the undoped film. The standard deviation for relative peak intensity with dopant concentration shows enhancement in heterogeneous nucleation growth. As evident from SEM images, on Sn doping, appearance of island-like structure (i.e., cluster of primary crystallites at few places) takes place. The transmittance has been found to decrease in all the Sn-doped films. The optical band gap has been calculated for both direct and indirect transitions. On Sn doping, the direct band gap shows a red shift and becomes 2.89 eV at 2 at.% doping. Two distinct peaks, one blue emission at 408 nm and other green emission at 533 nm, have been found in the PL spectra. Electrical conductivity has been found to increase with Sn doping.

  16. Observation of dopant-profile independent electron transport in sub-monolayer TiOx stacked ZnO thin films grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Saha, D.; Misra, P.; Das, Gangadhar; Joshi, M. P.; Kukreja, L. M.

    2016-01-01

    Dopant-profile independent electron transport has been observed through a combined study of temperature dependent electrical resistivity and magnetoresistance measurements on a series of Ti incorporated ZnO thin films with varying degree of static-disorder. These films were grown by atomic layer deposition through in-situ vertical stacking of multiple sub-monolayers of TiOx in ZnO. Upon decreasing ZnO spacer layer thickness, electron transport smoothly evolved from a good metallic to an incipient non-metallic regime due to the intricate interplay of screening of spatial potential fluctuations and strength of static-disorder in the films. Temperature dependent phase-coherence length as extracted from the magnetotransport measurement revealed insignificant role of inter sub-monolayer scattering as an additional channel for electron dephasing, indicating that films were homogeneously disordered three-dimensional electronic systems irrespective of their dopant-profiles. Results of this study are worthy enough for both fundamental physics perspective and efficient applications of multi-stacked ZnO/TiOx structures in the emerging field of transparent oxide electronics.

  17. Pressure effect on the magnetization of Sr{sub 2}FeMoO{sub 6} thin films grown by pulsed laser deposition

    SciTech Connect

    Fix, T.; Versini, G.; Loison, J.L.; Colis, S.; Schmerber, G.; Pourroy, G.; Dinia, A.

    2005-01-15

    Thin films of Sr{sub 2}FeMoO{sub 6} (SFMO) are grown on SrTiO{sub 3} (001) substrates by pulsed laser deposition. The best films provide 3.2{mu}{sub B}/f.u. at 5 K, a Curie temperature above 400 K, low roughness, high crystallinity, and low splashing. Therefore, the use of such SFMO electrodes in magnetic tunnel junctions patterned with conventional lithography is promising. Pseudomorphic epitaxial growth is obtained for thicknesses under 50 nm. Above this thickness the films do not relax homogeneously. A coherent and systematic variation of the magnetization with the deposition conditions is obtained, which highlights a high reproducibility. Under a reasonable O{sub 2} partial pressure to avoid parasite phases, the limiting factor for high magnetization is the total pressure or the deposition rate. Therefore, the deposition rate is suspected to have a strong influence on the Fe/Mo ordering. Highly magnetic samples are obtained under a low gas flow of either a 20% O{sub 2}+N{sub 2} or a 0.3% O{sub 2}+Ar.

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

    PubMed Central

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

    2014-01-01

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

  19. Characterisation of epitaxial TiO 2 thin films grown on MgO(0 0 1) using atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Mitchell, D. R. G.; Attard, D. J.; Triani, G.

    2005-11-01

    Thin films of TiO 2 have been deposited onto MgO(0 0 1) substrates using atomic layer deposition at 300 °C. Plan and cross-sectional transmission electron microscopy (TEM), X-ray diffraction and atomic force microscopy have been used to understand the nature of the films. X-ray and electron diffraction showed that a polycrystalline, epitaxial anatase film was produced. The c-axis of the anatase was parallel to the MgO(0 0 1) surface with two orientational variants at right angles to each other in the plane of the film, each aligned with an MgO cube axis. Plan-view and cross-sectional TEM showed that the grain structure of the film reflected this orientation relationship, with the grain morphology comprising two sets of roughly tetragonal grains. Also present was a small fraction of equiaxed, anatase grains which were randomly oriented. Roughness measurement using atomic force microscopy showed that the epitaxial anatase films were quite smooth, in comparison to equivalent non-aligned films grown on silicon.

  20. Electrical conduction and dielectric relaxation properties of AlN thin films grown by hollow-cathode plasma-assisted atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Altuntas, Halit; Bayrak, Turkan; Kizir, Seda; Haider, Ali; Biyikli, Necmi

    2016-07-01

    In this study, aluminum nitride (AlN) thin films were deposited at 200 °C, on p-type silicon substrates utilizing a capacitively coupled hollow-cathode plasma source integrated atomic layer deposition (ALD) reactor. The structural properties of AlN were characterized by grazing incidence x-ray diffraction, by which we confirmed the hexagonal wurtzite single-phase crystalline structure. The films exhibited an optical band edge around ∼5.7 eV. The refractive index and extinction coefficient of the AlN films were measured via a spectroscopic ellipsometer. In addition, to investigate the electrical conduction mechanisms and dielectric properties, Al/AlN/p-Si metal-insulator-semiconductor capacitor structures were fabricated, and current density–voltage and frequency dependent (7 kHz–5 MHz) dielectric constant measurements (within the strong accumulation region) were performed. A peak of dielectric loss was observed at a frequency of 3 MHz and the Cole–Davidson empirical formula was used to determine the relaxation time. It was concluded that the native point defects such as nitrogen vacancies and DX centers formed with the involvement of Si atoms into the AlN layers might have influenced the electrical conduction and dielectric relaxation properties of the plasma-assisted ALD grown AlN films.

  1. Effect of the annealing process on the microstructure of La 2Zr 2O 7 thin layers epitaxially grown on LaAlO 3 by metalorganic decomposition

    NASA Astrophysics Data System (ADS)

    Jiménez, C.; Caroff, T.; Rapenne, L.; Morlens, S.; Santos, E.; Odier, P.; Weiss, F.

    2009-05-01

    La 2Zr 2O 7 (LZO) films have been grown by metalorganic decomposition (MOD) to be used as buffer layers for coated conductors. A characteristic feature of LZO thin films deposited by MOD is the formation of nanovoids in an almost single crystal structure of LZO pyrochlore phase. Annealing parameters (heating ramp, temperature, pressure, etc.) were varied to establish their influence on the microstructure of the LZO layers. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for sample characterization. The epitaxial pyrochlore phase was obtained for annealing temperatures higher than 850 °C whatever the other annealing conditions. However, the film microstructure, in particular, nanovoids shape and size, is strongly dependent on heating ramp and pressure during annealing. When using low heating ramp, percolation of voids creates diffusion channels for oxygen which are detrimental for the substrate protection during coated conductor fabrication. From this point of view high heating rates are more adapted to the growth of LZO layers.

  2. Microstructure and dielectric properties of (Ba 0.6Sr 0.4)TiO 3 thin films grown on super smooth glazed-Al 2O 3 ceramics substrate

    NASA Astrophysics Data System (ADS)

    Chen, Hongwei; Yang, Chuanren; Zheng, Shanxue; Zhang, Jihua; Zhang, Qiaozhen; Lei, Guanhuan; Lou, Feizhi; Yang, Lijun

    2011-12-01

    Modified substrates with nanometer scale smooth surface were obtained via coating a layer of CaO-Al2O3-SiO2 (CaAlSi) high temperature glaze with proper additives on the rough-95% Al2O3 ceramics substrates. (Ba0.6Sr0.4)TiO3 (BST) thin films were deposited on modified Al2O3 substrates by radio-frequency magnetron sputtering. The microstructure, dielectric, and insulating properties of BST thin films grown on glazed-Al2O3 substrates were investigated by X-ray diffraction (XRD), atomic force microscope (AFM), and dielectric properties measurement. These results showed that microstructure and dielectric properties of BST thin films grown on glazed-Al2O3 substrates were almost consistent with that of BST thin films grown on LaAlO3 (1 0 0) single-crystal substrates. Thus, the expensive single-crystal substrates may be substituted by extremely cheap glazed-Al2O3 substrates.

  3. Surface structure determinations of crystalline ionic thin films grown on transition metal single crystal surfaces by low-energy electron diffraction

    NASA Astrophysics Data System (ADS)

    Roberts, Joel Glenn

    The surface structures of NaCl(100), LiF(100) and alpha-MgCl2 (0001) adsorbed on various metal single crystals have been determined by low energy electron diffraction (LEED). Thin films of these salts were grown on metal substrates by exposing the heated metal surface to a molecular flux of salt emitted from a Knudsen cell. This method of investigating thin films of insulators (ionic salts) on a conducting substrate (metal) circumvents surface charging problems that plagued bulk studies, thereby allowing the use of electron-based techniques to characterize the surface. The surface layer of NaCl(100) was found to have a 0.12 +/- 0.03 A corrugation due to movement of the Na+ ions towards the bulk. Additional deviations from the bulk structure were not seen in the deeper atomic layers. In order to determine if the metal substrate had an influence on the films' growth characteristics, multilayer films of NaCl(100) were grown on Pd(100) and Pt(111). An tensor LEED (TLEED) analysis of the diffraction beam intensities from the NaCl(100)-(1 x 1) on Pd(100) and NaCl(100)-(1 x 1) on Pt(111) LEED patterns showed that the multilayer NaCl(100) film had the same structure on both substrates to a depth sampled by the electrons in the individual experimental energy ranges. Additionally, these two films exhibited the same adsorbate-substrate interaction on Pd(100) and Pt(111) as evidenced by the lone multilayer (zero order) desorption peak observed in the temperature programmed desorption (TPD) spectra of NaCl. The surface structure of LiF(100) was studied to correlate the surface corrugation of the alkali halide (100) surface to the ions' polarizability. The LiF surface is less polarizable than the NaCl surface. TLEED calculations determined that the LiF(100) surface had a 0.24 +/- 0.04 A corrugation with a 0.06 +/- 0.04 A corrugation of the second layer. Both corrugations were due to the cations moving deeper into the bulk. Unlike NaCl and LiF, MgCl2 adsorbed on Pd(111) and Pt

  4. Potentiometric Zinc Ion Sensor Based on Honeycomb-Like NiO Nanostructures

    PubMed Central

    Abbasi, Mazhar Ali; Ibupoto, Zafar Hussain; Hussain, Mushtaque; Khan, Yaqoob; Khan, Azam; Nur, Omer; Willander, Magnus

    2012-01-01

    In this study honeycomb-like NiO nanostructures were grown on nickel foam by a simple hydrothermal growth method. The NiO nanostructures were characterized by field emission electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) techniques. The characterized NiO nanostructures were uniform, dense and polycrystalline in the crystal phase. In addition to this, the NiO nanostructures were used in the development of a zinc ion sensor electrode by functionalization with the highly selective zinc ion ionophore 12-crown-4. The developed zinc ion sensor electrode has shown a good linear potentiometric response for a wide range of zinc ion concentrations, ranging from 0.001 mM to 100 mM, with sensitivity of 36 mV/decade. The detection limit of the present zinc ion sensor was found to be 0.0005 mM and it also displays a fast response time of less than 10 s. The proposed zinc ion sensor electrode has also shown good reproducibility, repeatability, storage stability and selectivity. The zinc ion sensor based on the functionalized NiO nanostructures was also used as indicator electrode in potentiometric titrations and it has demonstrated an acceptable stoichiometric relationship for the determination of zinc ion in unknown samples. The NiO nanostructures-based zinc ion sensor has potential for analysing zinc ion in various industrial, clinical and other real samples. PMID:23202217

  5. Magnetic and structural properties of BiFeO{sub 3} thin films grown epitaxially on SrTiO{sub 3}/Si substrates

    SciTech Connect

    Laughlin, Ryan P.; Currie, Daniel A.; Contreras-Guererro, Rocio; Dedigama, Aruna; Priyantha, Weerasinghe; Droopad, Ravindranath; Theodoropoulou, Nikoleta; Gao Peng; Pan Xiaoqing

    2013-05-07

    The integration of oxides with semiconductors is important for the technological advancement of the next generation electronics. Concomitant ferroelectric and antiferromagnetic (AF) behavior is demonstrated in single crystal BiFeO{sub 3} (BFO) films grown on 20 nm SrTiO{sub 3} (STO) virtual substrates on Si(100) using molecular beam epitaxy (MBE). STO thin films are grown in an oxide MBE chamber by co-deposition of Sr, Ti, and molecular O{sub 2}. Careful control of the O{sub 2} during nucleation produced commensurate growth of STO on Si. The sequence of the steps allows for the suppression of an amorphous SiO{sub 2} layer. This STO(20 nm)/Si structure was used as a virtual substrate for MBE deposition of BFO on Si without breaking vacuum. BFO was deposited using Fe and O{sub 2} plasma with an overpressure of Bi flux, the growth rate was controlled by the incoming Fe flux. The reflection high energy electron diffraction image shows a 2-D growth front with a 6-fold surface reconstruction under optimized O{sub 2} pressure of 5 Multiplication-Sign 10{sup -8} mbar. Cross-sectional transmission electron microscopy (TEM) confirms the high crystallinity of the films and shows sharp, atomically flat interfaces. The selected area diffraction pattern (SADP) reveals that BFO grows in a distorted rhombohedral crystal structure. X-ray diffraction does not show formation of second phases and is consistent with the TEM and SADP results. The BFO films show AF behavior with a Neel temperature that exceeds 350 K, as expected (T{sub N} = 673 K) and with a residual ferromagnetic behavior that decreases with film thickness and is consistent with the G-type AF due to the canted spins. The saturation magnetization per unit volume for a 40 nm thick film was 180 emu/cm{sup 3} at an in-plane magnetic field of 8 kOe. The ferroelectric behavior of the films was verified using piezoresponse force microscopy.

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

    SciTech Connect

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

    2014-12-15

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

  7. Measuring relative performance of an EDS detector using a NiO standard.

    SciTech Connect

    Sugar, Joshua Daniel; Kotula, Paul Gabriel

    2013-09-01

    A method for measuring the relative performance of energy dispersive spectrometers (EDS) on a TEM is discussed. A NiO thin-film standard fabricated at Sandia CA is used. A performance parameter,, is measured and compared to values on several TEM systems.

  8. First principles exploration of NiO and its ions NiO+ and NiO-

    NASA Astrophysics Data System (ADS)

    Sakellaris, Constantine N.; Mavridis, Aristides

    2013-02-01

    We present a high level ab initio study of NiO and its ions, NiO+ and NiO-. Employing variational multireference configuration interaction (MRCI) and single reference coupled-cluster methods combined with basis sets of quintuple quality, 54, 20, and 10 bound states of NiO, NiO+, and NiO- have been studied. For all these states, complete potential energy curves have been constructed at the MRCI level of theory; in addition, for the ground states of the three species core subvalence (3s23p6/Ni) and scalar relativistic effects have been taken into account. We report energetics, spectroscopic parameters, dipole moments, and spin-orbit coupling constants. The agreement with experiment is in the case of NiO good, but certain discrepancies that need further investigation have arisen in the case of the anion whose ground state remains computationally a tantalizing matter. The cation is experimentally almost entirely unexplored, therefore, the study of many states shall prove valuable to further investigators. The ground state symmetry, bond distances, and binding energies of NiO and NiO+ are (existing experimental values in parenthesis), X3Σ-(X3Σ-), re = 1.606 (1.62712) Å, D0 = 88.5 (89.2 ± 0.7) kcal/mol, and X4Σ-(?), re = 1.60(?) Å, D0 = 55 (62.4 ± 2.4) kcal/mol, respectively. The ground state of NiO- is 4Σ- (but 2Π experimentally) with D0 = 85-87 (89.2 ± 0.7) kcal/mol.

  9. Structural, electronic, and magnetic investigation of magnetic ordering in MBE-grown CrxSb2-xTe3 thin films

    NASA Astrophysics Data System (ADS)

    Collins-McIntyre, L. J.; Duffy, L. B.; Singh, A.; Steinke, N.-J.; Kinane, C. J.; Charlton, T. R.; Pushp, A.; Kellock, A. J.; Parkin, S. S. P.; Holmes, S. N.; Barnes, C. H. W.; van der Laan, G.; Langridge, S.; Hesjedal, T.

    2016-07-01

    We report the structural, electronic, and magnetic study of Cr-doped Sb2Te3 thin films grown by a two-step deposition process using molecular-beam epitaxy (MBE). The samples were investigated using a variety of complementary techniques, namely, x-ray diffraction (XRD), atomic force microscopy, SQUID magnetometry, magneto-transport, and polarized neutron reflectometry (PNR). It is found that the samples retain good crystalline order up to a doping level of x=0.42 (in Cr x Sb2-x Te3), above which degradation of the crystal structure is observed by XRD. Fits to the recorded XRD spectra indicate a general reduction in the c-axis lattice parameter as a function of doping, consistent with substitutional doping with an ion of smaller ionic radius. The samples show soft ferromagnetic behavior with the easy axis of magnetization being out-of-plane. The saturation magnetization is dependent on the doping level, and reaches from ˜2 μ_\\text{B} to almost 3 μ_\\text{B} per Cr ion. The transition temperature (T{c}) depends strongly on the Cr concentration and is found to increase with doping concentration. For the highest achievable doping level for phase-pure films of x=0.42 , a T{c} of 125 K was determined. Electric transport measurements find surface-dominated transport below ˜10 K. The magnetic properties extracted from anomalous Hall effect data are in excellent agreement with the magnetometry data. PNR studies indicate a uniform magnetization profile throughout the film, with no indication of enhanced magnetic order towards the sample surface.

  10. A structural and electrical comparison of thin SiO2 films grown on silicon by plasma anodization and rapid thermal processing to furnace oxidation

    NASA Astrophysics Data System (ADS)

    Nelson, S. A.; Hallen, H. D.; Buhrman, R. A.

    1988-05-01

    We have used capacitance-voltage (C-V) techniques and x-ray photoelectron spectroscopy (XPS) to study for the first time the electrical and structural properties of thin SiO2 films grown on silicon by plasma anodization and rapid thermal processes (RTO) and then compared them to furnace oxides. We have compared the SiO4 tetrahedral ring structure and the suboxide content of the ˜3-nm-thick interfacial region of these oxides and have found significant structural differences. By correlating these differences with measured electrical differences, we have identified the structural causes of some of the electrical characteristics of the plasma and RTO oxides. In plasma oxides we see larger amounts of silicon dangling bonds, Pb centers, at the Si-SiO2 interface and have identified these dangling bonds as the source of a localized peak of interface states found at 0.3 eV above the silicon valence band. Low-temperature rapid thermal annealing of the plasma oxides relieves localized compressive interfacial strain, apparently by allowing the completion of oxidation at the interface, and reduces the amount of dangling bonds. However, this strain relief simultaneously increases the average SiO4 ring structure at the interface. A larger interfacial SiO4 ring structure is also seen in rapid thermal oxides and has been attributed to the very rapid cooling which takes place at the end of the rapid thermal process. Post-growth thermal processing has been shown to reduce the average ring structure by relieving localized tensile interfacial stress, but this stress relief is accompanied by the appearance of a peak of interface states at about 0.8 eV above the valence band which is attributed to Si-O bonds broken during the anneal. Long furnace anneals of rapid thermal oxides remove these states and give interface state densities comparable to those of furnace oxides.

  11. Structural, electronic, and magnetic investigation of magnetic ordering in MBE-grown CrxSb2‑xTe3 thin films

    NASA Astrophysics Data System (ADS)

    Collins-McIntyre, L. J.; Duffy, L. B.; Singh, A.; Steinke, N.-J.; Kinane, C. J.; Charlton, T. R.; Pushp, A.; Kellock, A. J.; Parkin, S. S. P.; Holmes, S. N.; Barnes, C. H. W.; van der Laan, G.; Langridge, S.; Hesjedal, T.

    2016-07-01

    We report the structural, electronic, and magnetic study of Cr-doped Sb2Te3 thin films grown by a two-step deposition process using molecular-beam epitaxy (MBE). The samples were investigated using a variety of complementary techniques, namely, x-ray diffraction (XRD), atomic force microscopy, SQUID magnetometry, magneto-transport, and polarized neutron reflectometry (PNR). It is found that the samples retain good crystalline order up to a doping level of x=0.42 (in Cr x Sb2‑x Te3), above which degradation of the crystal structure is observed by XRD. Fits to the recorded XRD spectra indicate a general reduction in the c-axis lattice parameter as a function of doping, consistent with substitutional doping with an ion of smaller ionic radius. The samples show soft ferromagnetic behavior with the easy axis of magnetization being out-of-plane. The saturation magnetization is dependent on the doping level, and reaches from ∼2 μ_\\text{B} to almost 3 μ_\\text{B} per Cr ion. The transition temperature (T{c}) depends strongly on the Cr concentration and is found to increase with doping concentration. For the highest achievable doping level for phase-pure films of x=0.42 , a T{c} of 125 K was determined. Electric transport measurements find surface-dominated transport below ∼10 K. The magnetic properties extracted from anomalous Hall effect data are in excellent agreement with the magnetometry data. PNR studies indicate a uniform magnetization profile throughout the film, with no indication of enhanced magnetic order towards the sample surface.

  12. Highly textured Sr, Nb co-doped BiFeO{sub 3} thin films grown on SrRuO{sub 3}/Si substrates by rf- sputtering

    SciTech Connect

    Ostos, C.; Raymond, O.; Siqueiros, J. M.; Suarez-Almodovar, N.; Bueno-Baques, D.; Mestres, L.

    2011-07-15

    In this study, (011)-highly oriented Sr, Nb co-doped BiFeO{sub 3} (BFO) thin films were successfully grown on SrRuO{sub 3}/Si substrates by rf-magnetron sputtering. The presence of parasite magnetic phases was ruled out based on the high resolution x-ray diffraction data. BFO films exhibited a columnar-like grain growth with rms surface roughness values of {approx_equal}5.3 nm and average grain sizes of {approx_equal}65-70 nm for samples with different thicknesses. Remanent polarization values (2P{sub r}) of 54 {mu}C cm{sup -2} at room temperature were found for the BFO films with a ferroelectric behavior characteristic of an asymmetric device structure. Analysis of the leakage mechanisms for this structure in negative bias suggests Schottky injection and a dominant Poole-Frenkel trap-limited conduction at room temperature. Oxygen vacancies and Fe{sup 3+}/Fe{sup 2+} trap centers are consistent with the surface chemical bonding states analysis from x-ray photoelectron spectroscopy data. The (011)-BFO/SrRuO{sub 3}/Si film structure exhibits a strong magnetic interaction at the interface between the multiferroic film and the substrate layer where an enhanced ferromagnetic response at 5 K was observed. Zero-field cooled (ZFC) and field cooled (FC) magnetization curves of this film system revealed a possible spin glass behavior at spin freezing temperatures below 30 K depending on the BFO film thickness.

  13. Status of NIO1 construction

    NASA Astrophysics Data System (ADS)

    Cavenago, M.; Fagotti, E.; Poggi, M.; Serianni, G.; Antoni, V.; Bigi, M.; Fellin, F.; Gazza, E.; Recchia, M.; Veltri, P.; Petrenko, S.; Kulevoy, T.

    2011-09-01

    The NIO1 (Negative Ion Optimization phase 1) project consists of a multiaperture negative ion source mounted on a 60 kV accelerating column; up to 9 beamlets (15 mA H- each one) arranged in 3×3 matrix with 14 mm spacing can be extracted. The moderate size and the modular concept make some relative rotation of the source magnetic filter and the electrodes possible, so that the effect of crossed and aligned field can be easily compared. Other goals of source experimental program are emittance (and beam profile) measurement at several distances (for simulation code validation), testing of diagnostic components and of radiofrequency coupling. A full set of construction drawing was completed; also the Fast Emittance Scanner (FES) and its vacuum chambers were built (four mounting positions are reserved to FES). Some low power rf matching boxes were developed for a test plasma, approximately half the source size. A cesium oven compatible with NIO1 is being also developed; by using some industrial standard 100 W heaters (with a proper driver) a careful control of temperature is planned.

  14. Polytype stability, microstructural evolution, and impurities at the interface of homoepitaxial 4H-silicon carbide(1120) thin films grown via hot-wall chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Bishop, Seann M. G.

    The electronic properties of 4H-SiC make it a leading semiconductor material for high-power applications. Despite advances in SiC crystal growth, devices fabricated in 4H-SiC(0001) continue to be limited by defects like micropipes, dislocations and stacking faults. Investigations performed here on non-basal 4H-SiC have demonstrated micropipe-free, 4H-SiC(112¯0) films comparable with conventional 4H-SiC(0001). Improved device performance has been achieved for p-i-n rectifiers fabricated in 4H-SiC(112¯0). Hot-wall chemical vapor deposition (CVD) is the most widely used growth process employed to meet the material demands for 4H-SiC-based high-power electronics; however, the suitability of this technique for the growth of thin films (<10 mum) is not well established. A detailed analysis of the epitaxial growth of 4H-SiC(112¯0) thin films by vertical, hot-wall CVD has been performed in this work. Two growth regimes were identified and termed sublimation growth and precursor growth. In the former, the SiC coating decomposes and results in the in-situ (sublimation) growth of epitaxial SiC films. It is proposed that in-situ layer aids in subsequent thin film growth from reactant gases. Transmission electron microscopy revealed areas without observable defects and an indistinguishable interface between the substrate and sublimation grown layer. Aluminum impurity concentrations to 3x10 18 cm-3 were identified near the interface with the substrate. The influence of these impurities on the cathodoluminescence spectrum of 4H-SiC was studied. A model based on boundary layer theory was developed to explain the origin and the profile of the aluminum impurities. Secondary ion mass spectrometry revealed the SiC coating to be the major source of aluminum impurities. An argon diluent reduced the concentration of aluminum at the interface to 2x1017 cm-3. Films deposited via precursor growth exhibited specular surfaces. Optical and structural characterization showed the films

  15. Spectroscopic ellipsometry-based study of optical properties of amorphous and crystalline ZnSnO alloys and Zn2SnO4 thin films grown using sputtering deposition: Dielectric function and subgap states

    NASA Astrophysics Data System (ADS)

    Ko, Kun Hee; So, Hyeon Seob; Jung, Dae Ho; Park, Jun Woo; Lee, Hosun

    2016-04-01

    We investigated the optical properties of amorphous and crystalline zinc tin oxide (ZTO) thin films grown on SiO2/Si substrates with varying compositions via a co-sputtering deposition method at room temperature. The co-sputtering targets consist of SnO2 and ZnO. By varying the relative power ratio of the two targets, we demonstrate the ability to control the Sn and Zn composition of the resulting ZTO thin films. The ratio of [Sn]/([Sn] + [Zn]) atomic compositions was estimated at 11%, 29%, 42%, 54%, and 60%. Using a 600 °C annealing process, the as-grown amorphous ZTO films were transformed into crystalline ZTO films. The dielectric functions were obtained based on the measured ellipsometric angles, ψ and Δ. We determined the dielectric functions, absorption coefficients, and optical gap energies of ZTO thin films with varying compositions. The dielectric functions, absorption coefficients, and optical gap energies of amorphous and crystalline Zn2SnO4 thin films were obtained at 29 at. % of Sn. Subgap states at 1.6 eV (A) and 2.8 eV (B) of ZnSnO alloys and Zn2SnO4 films were found in the imaginary part of the dielectric function spectra. The subgap state intensities were reduced via a nitrogen gas annealing. Possible origins of the observed subgap states will be discussed.

  16. Single-crystalline Ni(OH)2 and NiO nanoplatelet arrays as supercapacitor electrodes

    NASA Astrophysics Data System (ADS)

    Li, Jiangtian; Zhao, Wei; Huang, Fuqiang; Manivannan, Ayyakkannu; Wu, Nianqiang

    2011-12-01

    Vertically aligned Ni(OH)2 and NiO single-crystalline nanoplatelet arrays were directly grown on the fluorine-doped tin oxide (FTO) substrate by a simple hydrothermal method. The effects of the hydrothermal parameters on the morphology and crystal structure of the nanoarray film were investigated. Controlling the ammonia and persulfate concentrations was the key to controlling the morphology of the nanoarray film. The experimental results showed that the single-crystalline NiO nanoplatelet array was a promising candidate for the supercapacitor electrode. It exhibited a high specific capacitance, prompt charge/discharge rate, and good stability of cycling performance. It is believed that the vertically oriented aligned single-crystalline NiO nanoplatelet array is beneficial to the charge transfer in the electrode and to the ion transport in the solution during redox reaction.Vertically aligned Ni(OH)2 and NiO single-crystalline nanoplatelet arrays were directly grown on the fluorine-doped tin oxide (FTO) substrate by a simple hydrothermal method. The effects of the hydrothermal parameters on the morphology and crystal structure of the nanoarray film were investigated. Controlling the ammonia and persulfate concentrations was the key to controlling the morphology of the nanoarray film. The experimental results showed that the single-crystalline NiO nanoplatelet array was a promising candidate for the supercapacitor electrode. It exhibited a high specific capacitance, prompt charge/discharge rate, and good stability of cycling performance. It is believed that the vertically oriented aligned single-crystalline NiO nanoplatelet array is beneficial to the charge transfer in the electrode and to the ion transport in the solution during redox reaction. Electronic supplementary information (ESI) available: XRD patterns of Ni(OH)2 and NiO powders; SEM and TEM images of Ni(OH)2 and NiO nanoplatelet arrays; and electrochemical performances for NiO nanoarrays and powders. See

  17. Theoretical and experimental studies of surface physics: Theory of surface electromigration wind force felt by a sodium adatom on stepped sodium(110) surfaces; and magnetic order-disorder phase transition of antiferromagnetic nickel oxide thin films on silver(001)

    NASA Astrophysics Data System (ADS)

    Cheng, Jason Yu-Lin

    This dissertation is composed of theoretical and experimental work in surface physics. I have performed calculations of electromigration wind forces felt by a Na adatom on Na (110) stepped metal surfaces. Electromigration is a process which impurities are induced to drift in a particular direction when an electric field is applied across the sample. I find that the electromigration wind force felt by an adatom is changed due to the presence of step edge on the surface. My experimental work explores the magnetic order-disorder phase transition of antiferromagnetic nickel oxide thin films. I find that the Neel temperature is different for nickel oxide thin films and bulk samples. In my theoretical calculations I have applied multiple scattering theory to explore the variation of the electromigration wind force experienced by a Na adatom on Na (110) stepped metal surfaces. I find that the electromigration wind force felt by a migrating adatom is strongly perturbed as the adatom approaches a step edge. This is a result of multiple scattering of the carriers between the adatom and step which alters the local current density. In addition, the electromigration wind force felt by a Na adatom in the lower and the upper step regions is asymmetric. The implications of this inhomogeneity in the electromigration driving force for current-induced changes in surface morphology are discussed. In my experimental work, antiferromagnetic nickel oxide (NiO) thin films were grown on single crystal Ag (100) by means of electron beam deposition. My low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) results indicate that the magnetic order in NiO may be dependent upon the oxygen stoichiometry in the thin film. I show that in thin films approximately 13 monolayers thick, the Neel temperature, TN, of NiO is 631 K which is higher than the bulk value of TN = 523 K. Furthermore, I find that as the film thickness is increased, the Neel temperature decreases towards the

  18. Epitaxial Ba2IrO4 thin-films grown on SrTiO3 substrates by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Nichols, J.; Korneta, O. B.; Terzic, J.; Cao, G.; Brill, J. W.; Seo, S. S. A.

    2014-03-01

    We have synthesized epitaxial Ba2IrO4 (BIO) thin-films on SrTiO3 (001) substrates by pulsed laser deposition and studied their electronic structure by dc-transport and optical spectroscopic experiments. We have observed that BIO thin-films are insulating but close to the metal-insulator transition boundary with significantly smaller transport and optical gap energies than its sister compound, Sr2IrO4. Moreover, BIO thin-films have both an enhanced electronic bandwidth and electronic-correlation energy. Our results suggest that BIO thin-films have great potential for realizing the interesting physical properties predicted in layered iridates.

  19. Role of an ultra-thin AlN/GaN superlattice interlayer on the strain engineering of GaN films grown on Si(110) and Si(111) substrates by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Shen, X. Q.; Takahashi, T.; Matsuhata, H.; Ide, T.; Shimizu, M.; Rong, X.; Chen, G.; Wang, X. Q.; Shen, B.

    2013-12-02

    We investigate the role of an ultra-thin AlN/GaN superlattice interlayer (SL-IL) on the strain engineering of the GaN films grown on Si(110) and Si(111) substrates by plasma-assisted molecular beam epitaxy. It is found that micro-cracks limitted only at the SL-IL position are naturally generated. These micro-cracks play an important role in relaxing the tensile strain caused by the difference of the coefficient of thermal expansion between GaN and Si and keeping the residual strain in the crack-free GaN epilayers resulted from the SL-IL during the growth. The mechanism understanding of the strain modulation by the SL-IL in the GaN epilayers grown on Si substrates makes it possible to design new heterostructures of III-nitrides for optic and electronic device applications.

  20. Effects of air annealing on CdS quantum dots thin film grown at room temperature by CBD technique intended for photosensor applications

    SciTech Connect

    Shaikh, Shaheed U.; Desale, Dipalee J.; Siddiqui, Farha Y.; Ghosh, Arindam; Birajadar, Ravikiran B.; Ghule, Anil V.; Sharma, Ramphal

    2012-11-15

    Graphical abstract: The effect of different intensities (40, 60 100 and 200 W) of light on CdS quantum dots thin film annealed at 350 °C indicating enhancement in (a) photo-current and (b) photosensitivity. Highlights: ► The preparation of CdS nanodot thin film at room temperature by M-CBD technique. ► Study of air annealing on prepared CdS nanodots thin film. ► The optimized annealing temperature for CdS nanodot thin film is 350 °C. ► Modified CdS thin films can be used in photosensor application. -- Abstract: CdS quantum dots thin-films have been deposited onto the glass substrate at room temperature using modified chemical bath deposition technique. The prepared thin films were further annealed in air atmosphere at 150, 250 and 350 °C for 1 h and subsequently characterized by scanning electron microscopy, ultraviolet–visible spectroscopy, electrical resistivity and I–V system. The modifications observed in morphology and opto-electrical properties of the thin films are presented.

  1. Structural and electrical characterization of ultra-thin SrTiO3 tunnel barriers grown over YBa2Cu3O7 electrodes for the development of high Tc Josephson junctions.

    PubMed

    Félix, L Avilés; Sirena, M; Guzmán, L A Agüero; Sutter, J González; Vargas, S Pons; Steren, L B; Bernard, R; Trastoy, J; Villegas, J E; Briático, J; Bergeal, N; Lesueur, J; Faini, G

    2012-12-14

    The transport properties of ultra-thin SrTiO(3) (STO) layers grown over YBa(2)Cu(3)O(7) electrodes were studied by conductive atomic force microscopy at the nano-scale. A very good control of the barrier thickness was achieved during the deposition process. A phenomenological approach was used to obtain critical parameters regarding the structural and electrical properties of the system. The STO layers present an energy barrier of 0.9 eV and an attenuation length of 0.23 nm, indicating very good insulating properties for the development of high-quality Josephson junctions.

  2. Structural and electrical characterization of ultra-thin SrTiO3 tunnel barriers grown over YBa2Cu3O7 electrodes for the development of high Tc Josephson junctions.

    PubMed

    Félix, L Avilés; Sirena, M; Guzmán, L A Agüero; Sutter, J González; Vargas, S Pons; Steren, L B; Bernard, R; Trastoy, J; Villegas, J E; Briático, J; Bergeal, N; Lesueur, J; Faini, G

    2012-12-14

    The transport properties of ultra-thin SrTiO(3) (STO) layers grown over YBa(2)Cu(3)O(7) electrodes were studied by conductive atomic force microscopy at the nano-scale. A very good control of the barrier thickness was achieved during the deposition process. A phenomenological approach was used to obtain critical parameters regarding the structural and electrical properties of the system. The STO layers present an energy barrier of 0.9 eV and an attenuation length of 0.23 nm, indicating very good insulating properties for the development of high-quality Josephson junctions. PMID:23154521

  3. Giant magnetocaloric effect of Mn{sub 0.92}Ba{sub 0.08}As thin film grown on Al{sub 2}O{sub 3}(0001) substrate

    SciTech Connect

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

    2012-04-01

    The epitaxial Mn{sub 0.92}Ba{sub 0.08}As thin film was grown on Al{sub 2}O{sub 3}(0001) substrate by molecular beam epitaxy. The Curie temperature (T{sub C}) around 350 K was enhanced with the addition of Ba, compared to that of bulk MnAs (T{sub C} {approx} 318 K). We have observed the linear resistivity versus the square of temperature and high negative magnetoresistance near Curie temperature. Moreover, the giant magnetocaloric effect was found with maximum magnetic entropy change, 65 J/kgK, around room temperature at 5 T.

  4. Preparation and characterization of Cu2ZnSnSe4 thin films grown from ZnSe and Cu2SnS3 precursors in a two stage process

    NASA Astrophysics Data System (ADS)

    Moreno, R.; Leguizamon, A.; Hurtado, M.; Guzmán, F.; Gordillo, G.

    2014-04-01

    Compound of the kesterite familie has been considered as an alternative absorber layer in the manufacture of thin film solar cells due to its earth abundant and environmental friendly constituents and high absorption coefficient. In this work we propose a new route to grow single phase Cu2ZnSnSe4 (CZTSe) thin films with tetragonal-kesterite type structure; this consist in sequential evaporation of thin films of CuSe, SnSe and ZnSe in a two stage process. Measurements of X-ray diffraction (XRD) revealed the formation of the Cu2ZnSnSe4 compound, grown with tetragonal Kësterite type structure. Optical characterization performed through spectral transmittance measurements established that this compound has high absorption (absorption coefficient > 104 cm-1) and a forbidden energy gap of 1.46 eV; these results indicate that the CZTSe thin films we have prepared has properties suitable for later use as absorber layer in solar cells. Results regarding electrical transport properties determined from temperature dependent conductivity measurements are also reported.

  5. Full Field Birefringence Measurement of Grown-In Stresses in Thin Silicon Sheet: Final Technical Report, 2 January 2002 - 15 January 2008

    SciTech Connect

    Danyluk, S.; Ostapenka, S.

    2008-11-01

    This paper summarizes polariscopy work that led to prototype non-contact, near-infrared light-transmission system for inspecting thin, flat, large-area Si wafers. Acoustic work led to commercially viable system to inspect wafers for microcracks.

  6. An aberration-corrected STEM study of structural defects in epitaxial GaN thin films grown by ion beam assisted MBE.

    PubMed

    Poppitz, David; Lotnyk, Andriy; Gerlach, Jürgen W; Lenzner, Jörg; Grundmann, Marius; Rauschenbach, Bernd

    2015-06-01

    Ion-beam assisted molecular-beam epitaxy was used for direct growth of epitaxial GaN thin films on super-polished 6H-SiC(0001) substrates. The GaN films with different film thicknesses were studied using reflection high energy electron diffraction, X-ray diffraction, cathodoluminescence and primarily aberration-corrected scanning transmission electron microscopy techniques. Special attention was devoted to the microstructural characterization of GaN thin films and the GaN-SiC interface on the atomic scale. The results show a variety of defect types in the GaN thin films and at the GaN-SiC interface. A high crystalline quality of the produced hexagonal GaN thin films was demonstrated. The gained results are discussed.

  7. Epitaxial Ba{sub 2}IrO{sub 4} thin-films grown on SrTiO{sub 3} substrates by pulsed laser deposition

    SciTech Connect

    Nichols, J. Korneta, O. B.; Terzic, J.; Cao, G.; Brill, J. W.; Seo, S. S. A.

    2014-03-24

    We have synthesized epitaxial Ba{sub 2}IrO{sub 4} (BIO) thin-films on SrTiO{sub 3} (001) substrates by pulsed laser deposition and studied their electronic structure by dc-transport and optical spectroscopic experiments. We have observed that BIO thin-films are insulating but close to the metal-insulator transition boundary with significantly smaller transport and optical gap energies than its sister compound, Sr{sub 2}IrO{sub 4}. Moreover, BIO thin-films have both an enhanced electronic bandwidth and electronic-correlation energy. Our results suggest that BIO thin-films have great potential for realizing the interesting physical properties predicted in layered iridates.

  8. Ferroelectric properties and crystalline structures of BaMgF{sub 4} thin films grown on Pt(111)/SiO{sub 2}/Si(100)

    SciTech Connect

    Moriwaki, Masashi; Aizawa, Koji; Tokumitsu, Eisuke; Ishiwara, Hiroshi

    1997-07-01

    Crystalline quality and ferroelectric properties of (120)-oriented BaMgF{sub 4}(BMF) films grown on Pt(111)/SiO{sub 2}/Si(100) and n-Si(111) substrates have been investigated. The BaMgF{sub 4} films grown on Pt(111) have large and flat grains, while the films on Si(111) have small grains. The C-V curve of BaMgF{sub 4}/Pt(111)/SiO{sub 2}/Si(100) diodes showed a hysteresis loop with a memory window of 3.8V.

  9. Direct observation of infinite NiO2 planes in LaNiO2 films

    NASA Astrophysics Data System (ADS)

    Ikeda, Ai; Krockenberger, Yoshiharu; Irie, Hiroshi; Naito, Michio; Yamamoto, Hideki

    2016-06-01

    Epitaxial thin films of LaNiO2, which is an oxygen-deficient perovskite with “infinite layers” of Ni1+O2, were prepared by a low-temperature reduction of LaNiO3 single-crystal films on NdGaO3 substrates. We report the high-angle annular dark-field and bright-field scanning transmission electron microscopy observations of infinite NiO2 planes of c-axis-oriented LaNiO2 epitaxial thin films with a layer stacking sequence of NiO2/La/NiO2. Resistivity measurements on the films show T 2 dependence between 400 and 150 K and a negative Hall coefficient.

  10. Effects of substrate conductivity on cell morphogenesis and proliferation using tailored, atomic layer deposition-grown ZnO thin films

    PubMed Central

    Choi, Won Jin; Jung, Jongjin; Lee, Sujin; Chung, Yoon Jang; Yang, Cheol-Soo; Lee, Young Kuk; Lee, You-Seop; Park, Joung Kyu; Ko, Hyuk Wan; Lee, Jeong-O

    2015-01-01

    We demonstrate that ZnO films grown by atomic layer deposition (ALD) can be employed as a substrate to explore the effects of electrical conductivity on cell adhesion, proliferation, and morphogenesis. ZnO substrates with precisely tunable electrical conductivity were fabricated on glass substrates using ALD deposition. The electrical conductivity of the film increased linearly with increasing duration of the ZnO deposition cycle (thickness), whereas other physical characteristics, such as surface energy and roughness, tended to saturate at a certain value. Differences in conductivity dramatically affected the behavior of SF295 glioblastoma cells grown on ZnO films, with high conductivity (thick) ZnO films causing growth arrest and producing SF295 cell morphologies distinct from those cultured on insulating substrates. Based on simple electrostatic calculations, we propose that cells grown on highly conductive substrates may strongly adhere to the substrate without focal-adhesion complex formation, owing to the enhanced electrostatic interaction between cells and the substrate. Thus, the inactivation of focal adhesions leads to cell proliferation arrest. Taken together, the work presented here confirms that substrates with high conductivity disturb the cell-substrate interaction, producing cascading effects on cellular morphogenesis and disrupting proliferation, and suggests that ALD-grown ZnO offers a single-variable method for uniquely tailoring conductivity. PMID:25897486

  11. Effects of substrate conductivity on cell morphogenesis and proliferation using tailored, atomic layer deposition-grown ZnO thin films.

    PubMed

    Choi, Won Jin; Jung, Jongjin; Lee, Sujin; Chung, Yoon Jang; Yang, Cheol-Soo; Lee, Young Kuk; Lee, You-Seop; Park, Joung Kyu; Ko, Hyuk Wan; Lee, Jeong-O

    2015-04-21

    We demonstrate that ZnO films grown by atomic layer deposition (ALD) can be employed as a substrate to explore the effects of electrical conductivity on cell adhesion, proliferation, and morphogenesis. ZnO substrates with precisely tunable electrical conductivity were fabricated on glass substrates using ALD deposition. The electrical conductivity of the film increased linearly with increasing duration of the ZnO deposition cycle (thickness), whereas other physical characteristics, such as surface energy and roughness, tended to saturate at a certain value. Differences in conductivity dramatically affected the behavior of SF295 glioblastoma cells grown on ZnO films, with high conductivity (thick) ZnO films causing growth arrest and producing SF295 cell morphologies distinct from those cultured on insulating substrates. Based on simple electrostatic calculations, we propose that cells grown on highly conductive substrates may strongly adhere to the substrate without focal-adhesion complex formation, owing to the enhanced electrostatic interaction between cells and the substrate. Thus, the inactivation of focal adhesions leads to cell proliferation arrest. Taken together, the work presented here confirms that substrates with high conductivity disturb the cell-substrate interaction, producing cascading effects on cellular morphogenesis and disrupting proliferation, and suggests that ALD-grown ZnO offers a single-variable method for uniquely tailoring conductivity.

  12. Preparation and characterization of nanostructured nickel oxide thin films by spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Ismail, Raid A.; Ghafori, Sa'ad; Kadhim, Ghada A.

    2013-12-01

    Transparent crystalline nanostructured nickel oxide (NiO) thin films were prepared using a simple spray pyrolysis technique from hydrated nickel chloride salt solution (NiCl2·6H2O) onto glass and silicon (n-type) substrates at different temperatures (280, 320, 360, and 400 °C) and with different solution concentrations (0.025, 0.05, 0.075, and 0.1 M). Structural and morphological properties of the grown NiO films were studied using X-ray diffraction (XRD) and atomic force microscope. Optical properties and chemical analysis of the films were characterized by UV-visible absorption spectra and Fourier transform infrared spectroscopy, respectively. The XRD result showed that the deposited film has an amorphous structure when deposited at temperature of T s = 280 °C and concentration of 0.025 M. At higher temperatures ( T s = 320, 360, 400 °C) and solution concentrations (0.05, 0.075, 0.1 M), the deposited films have cubic polycrystalline structure formed with preferred orientation along (111) plane. The band gap of NiO film increases from 3.4 to 3.8 eV as the molarity decreased from 0.1 to 0.05 M.

  13. Effects of confinements on morphology of In{sub x}Ga{sub 1–x}As thin film grown on sub-micron patterned GaAs substrate: Elastoplastic phase field model

    SciTech Connect

    Arjmand, M.; Deng, J.; Swaminathan, N.; Morgan, D.; Szlufarska, I.

    2014-09-21

    An elastoplastic phase field model is developed to investigate the role of lateral confinement on morphology of thin films grown heteroepitaxially on patterned substrates. Parameters of the model are chosen to represent In{sub x}Ga{sub 1-x}As thin films growing on GaAs patterned with SiO₂. We determined the effect of misfit strain on morphology of thin films grown in 0.5 μm patterns with non-uniform deposition flux. Growth of islands inside patterns can be controlled by non-uniformity of deposition flux, misfit strain between film and the substrate, and also strain energy relaxation due to plastic deformation. Our results show that the evolution of island morphology depends non-monotonically on indium content and associated misfit strain due to coupling between the plastic relaxation and the confinements effects. Low indium concentration (0%–40%) causes formation of instabilities with relatively long wavelengths across the width of the pattern. Low surface diffusion (due to low indium concentration) and fewer islands across the pattern (due to small misfit strain) lead to formation and growth of islands near the walls driven by overflow flux. Further increase in indium concentration (40%–75%) increases the lattice mismatch and surface diffusivity of the film, and also activates plastic deformation mechanism, which leads to coalescence of islands usually away from the edges. By further increasing the indium concentration (up to 100%), plastic deformation relaxes most of the strain energy density of the film, which prevents formation of instabilities in the film. Hence, in this case, islands are only formed near the walls.

  14. Effects of confinements on morphology of InxGa1-xAs thin film grown on sub-micron patterned GaAs substrate: Elastoplastic phase field model

    NASA Astrophysics Data System (ADS)

    Arjmand, M.; Deng, J.; Swaminathan, N.; Morgan, D.; Szlufarska, I.

    2014-09-01

    An elastoplastic phase field model is developed to investigate the role of lateral confinement on morphology of thin films grown heteroepitaxially on patterned substrates. Parameters of the model are chosen to represent InxGa1-xAs thin films growing on GaAs patterned with SiO2. We determined the effect of misfit strain on morphology of thin films grown in 0.5 μm patterns with non-uniform deposition flux. Growth of islands inside patterns can be controlled by non-uniformity of deposition flux, misfit strain between film and the substrate, and also strain energy relaxation due to plastic deformation. Our results show that the evolution of island morphology depends non-monotonically on indium content and associated misfit strain due to coupling between the plastic relaxation and the confinements effects. Low indium concentration (0%-40%) causes formation of instabilities with relatively long wavelengths across the width of the pattern. Low surface diffusion (due to low indium concentration) and fewer islands across the pattern (due to small misfit strain) lead to formation and growth of islands near the walls driven by overflow flux. Further increase in indium concentration (40%-75%) increases the lattice mismatch and surface diffusivity of the film, and also activates plastic deformation mechanism, which leads to coalescence of islands usually away from the edges. By further increasing the indium concentration (up to 100%), plastic deformation relaxes most of the strain energy density of the film, which prevents formation of instabilities in the film. Hence, in this case, islands are only formed near the walls.

  15. Comparison of ZnO thin films grown on a polycrystalline 3C-SiC buffer layer by RF magnetron sputtering and a sol-gel method

    NASA Astrophysics Data System (ADS)

    Phan, Duy-Thach; Chung, Gwiy-Sang

    2011-02-01

    Zinc oxide (ZnO) thin films were deposited on a polycrystalline (poly) 3C-SiC buffer layer using RF magnetron sputtering and a sol-gel method. The post-deposition annealing was performed on ZnO thin films prepared using both methods. The formation of ZnO piezoelectric thin films with less residual stress was due to a close lattice mismatch of the ZnO and SiC layers as obtained by the sputtering method. Nanocrystalline, porous ZnO film prepared using the sol-gel method showed strong ultraviolet UV emission at a wavelength of 380 nm. The 3C-SiC buffer layer improved the optical and piezoelectric properties of the ZnO film produced by the two deposition methods. Moreover, the different structures of the ZnO films on the 3C-SiC intermediate layer caused by the different deposition techniques were also considered and discussed.

  16. 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

  17. Tuning of in-plane optical anisotropy by inserting ultra-thin InAs layer at interfaces in (001)-grown GaAs/AlGaAs quantum wells

    SciTech Connect

    Yu, J. L.; Cheng, S. Y.; Lai, Y. F.; Zheng, Q.

    2015-01-07

    The in-plane optical anisotropy (IPOA) in (001)-grown GaAs/AlGaAs quantum wells (QWs) with different well widths varying from 2 nm to 8 nm has been studied by reflectance difference spectroscopy. Ultra-thin InAs layers with thickness ranging from 0.5 monolayer (ML) to 1.5 ML have been inserted at GaAs/AlGaAs interfaces to tune the asymmetry in the QWs. It is demonstrated that the IPOA can be accurately tailored by the thickness of the inserted ultra-thin InAs layer at the interfaces. Strain-induced IPOA has also been extracted by using a stress apparatus. We find that the intensity of the strain-induced IPOA decreases with the thickness of the inserted InAs layer, while that of the interface-induced IPOA increases with the thickness of the InAs layer. Theoretical calculations based on 6 band k ⋅ p theory have been carried out, and good agreements with experimental results are obtained. Our results demonstrate that, the IPOA of the QWs can be greatly and effectively tuned by inserting an ultra-thin InAs layer with different thicknesses at the interfaces of QWs, which does not significantly influence the transition energies and the transition probability of QWs.

  18. High electron mobility and low carrier concentration of hydrothermally grown ZnO thin films on seeded a-plane sapphire at low temperature

    NASA Astrophysics Data System (ADS)

    Jayah, Nurul Azzyaty; Yahaya, Hafizal; Mahmood, Mohamad Rusop; Terasako, Tomoaki; Yasui, Kanji; Hashim, Abdul Manaf

    2015-01-01

    Hydrothermal zinc oxide (ZnO) thick films were successfully grown on the chemical vapor deposition (CVD)-grown thick ZnO seed layers on a-plane sapphire substrates using the aqueous solution of zinc nitrate dehydrate (Zn(NO3)2). The use of the CVD ZnO seed layers with the flat surfaces seems to be a key technique for obtaining thick films instead of vertically aligned nanostructures as reported in many literatures. All the hydrothermal ZnO layers showed the large grains with hexagonal end facets and were highly oriented towards the c-axis direction. Photoluminescence (PL) spectra of the hydrothermal layers were composed of the ultraviolet (UV) emission (370 to 380 nm) and the visible emission (481 to 491 nm), and the intensity ratio of the former emission ( I UV) to the latter emission ( I VIS) changed, depending on both the molarity of the solution and temperature. It is surprising that all the Hall mobilities for the hydrothermal ZnO layers were significantly larger than those for their corresponding CVD seed films. It was also found that, for the hydrothermal films grown at 70°C to 90°C, the molarity dependences of I UV/ I VIS resembled those of mobilities, implying that the mobility in the film is affected by the structural defects. The highest mobility of 166 cm2/Vs was achieved on the hydrothermal film with the carrier concentration of 1.65 × 1017 cm-3 grown from the aqueous solution of 40 mM at 70°C.

  19. High electron mobility and low carrier concentration of hydrothermally grown ZnO thin films on seeded a-plane sapphire at low temperature.

    PubMed

    Jayah, Nurul Azzyaty; Yahaya, Hafizal; Mahmood, Mohamad Rusop; Terasako, Tomoaki; Yasui, Kanji; Hashim, Abdul Manaf

    2015-01-01

    Hydrothermal zinc oxide (ZnO) thick films were successfully grown on the chemical vapor deposition (CVD)-grown thick ZnO seed layers on a-plane sapphire substrates using the aqueous solution of zinc nitrate dehydrate (Zn(NO3)2). The use of the CVD ZnO seed layers with the flat surfaces seems to be a key technique for obtaining thick films instead of vertically aligned nanostructures as reported in many literatures. All the hydrothermal ZnO layers showed the large grains with hexagonal end facets and were highly oriented towards the c-axis direction. Photoluminescence (PL) spectra of the hydrothermal layers were composed of the ultraviolet (UV) emission (370 to 380 nm) and the visible emission (481 to 491 nm), and the intensity ratio of the former emission (I UV) to the latter emission (I VIS) changed, depending on both the molarity of the solution and temperature. It is surprising that all the Hall mobilities for the hydrothermal ZnO layers were significantly larger than those for their corresponding CVD seed films. It was also found that, for the hydrothermal films grown at 70°C to 90°C, the molarity dependences of I UV/I VIS resembled those of mobilities, implying that the mobility in the film is affected by the structural defects. The highest mobility of 166 cm(2)/Vs was achieved on the hydrothermal film with the carrier concentration of 1.65 × 10(17) cm(-3) grown from the aqueous solution of 40 mM at 70°C.

  20. Laser damage properties of TiO{sub 2}/Al{sub 2}O{sub 3} thin films grown by atomic layer deposition

    SciTech Connect

    Wei Yaowei; Liu Hao; Sheng Ouyang; Liu Zhichao; Chen Songlin; Yang Liming

    2011-08-20

    Research on thin film deposited by atomic layer deposition (ALD) for laser damage resistance is rare. In this paper, it has been used to deposit TiO{sub 2}/Al{sub 2}O{sub 3} films at 110 deg. C and 280 deg. C on fused silica and BK7 substrates. Microstructure of the thin films was investigated by x-ray diffraction. The laser-induced damage threshold (LIDT) of samples was measured by a damage test system. Damage morphology was studied under a Nomarski differential interference contrast microscope and further checked under an atomic force microscope. Multilayers deposited at different temperatures were compared. The results show that the films deposited by ALD had better uniformity and transmission; in this paper, the uniformity is better than 99% over 100 mm {Phi} samples, and the transmission is more than 99.8% at 1064 nm. Deposition temperature affects the deposition rate and the thin film microstructure and further influences the LIDT of the thin films. As to the TiO{sub 2}/Al{sub 2}O{sub 3} films, the LIDTs were 6.73{+-}0.47 J/cm{sup 2} and 6.5{+-}0.46 J/cm{sup 2} at 110 deg. C on fused silica and BK7 substrates, respectively. The LIDTs at 110 deg. C are notably better than 280 deg. C.

  1. Highly transparent and lower resistivity of yttrium doped ZnO thin films grown on quartz glass by sol-gel method

    NASA Astrophysics Data System (ADS)

    Kaur, Narinder; Sharma, Sanjeev K.; Kim, Deuk Young; Singh, Narinder

    2016-11-01

    We prepared highly transparent yttrium-doped ZnO (YZO) thin films on quartz glass by a sol-gel method, and then annealed them at 600 °C in vacuum. All samples showed hexagonal wurtzite structure with a preferential orientation along the (002) direction. We observed the average grain size of Y: 2 at% thin film to be in the range of 15-20 nm. We observed blue shift in the optical bandgap (3.29 eV→3.32 eV) by increasing the Y concentration (0-2 at%), due to increasing the number of electrons, and replacing the di-valent (Zn2+) with tri-valent (Y3+) dopants. Replacing the higher ionic radii (Y3+) with smaller ionic radii (Zn2+) expanded the local volume of the lattice, which reduced the lattice defects, and increased the intensity ratio of NBE/DLE emission (INBE/IDLE). We also observed the lowest (172 meV) Urbach energy of Y: 2 at% thin film, and confirmed the high structural quality. Incorporation of the appropriate Y concentration (2 at%) improved the crystallinity of YZO thin films, which led to less carrier scattering and lower resistivity.

  2. Material properties of pulsed-laser crystallized Si thin films grown on yttria-stabilized zirconia crystallization-induction layers by two-step irradiation method

    NASA Astrophysics Data System (ADS)

    Thi Kieu Lien, Mai; Horita, Susumu

    2016-03-01

    Amorphous Si thin films on yttria-stabilized zirconia (YSZ) layers were crystallized widely in solid phase by the two-step method with a pulsed laser, moving the sample stage. The crystalline quality, impurity diffusion, and electrical properties of the crystallized Si films were investigated. It was found that the crystallinity of the Si thin films was improved and their surface was smooth without an incubation layer at the interface, indicating the uniform crystallinity of Si on YSZ. The diffusion of Zr and Y into the Si thin films was as small as or smaller than the order of 1017 atoms/cm3. We evaluated the electrical properties of carrier concentration and Hall mobility of the Si thin films with/without YSZ layers by using the resistivity and AC Hall effect measurements. The temperature and doping concentration dependences were measured for both undoped and P-doped films. It was found that both the undoped and P-doped Si/YSZ/glass films showed higher mobilities and carrier concentrations (and therefore higher conductivities), which indicate a smaller number of defects, than the Si/glass films. This suggested that the Si film crystallized on the YSZ layer is more suitable for application to electronic devices than the Si film on glass.

  3. Optical and electrochemical properties of Cu-doped NiO films prepared by electrochemical deposition

    NASA Astrophysics Data System (ADS)

    Zhao, Lili; Su, Ge; Liu, Wei; Cao, Lixin; Wang, Jing; Dong, Zheng; Song, Meiqin

    2011-02-01

    Cu-doped nickel oxide (NiO) thin films were prepared by electrochemial deposition (cathodic deposition) technique onto the fluorine doped tin oxide (F: SnO2; FTO) coated glass substrates from organic solutions. Effects of Cu content on the morphology, structure, optical and electrochromic properties of NiO films were investigated by means of scanning electron microscope (SEM), X-ray diffraction (XRD), ultraviolet-visible spectrophotometer (UV-vis) and cyclic voltammetry (CV), respectively. SEM images indicated the formation of nanorods after Cu was added. The films were formed with amorphous or short-range ordered NiO grains and a trace of face-centered cubic NixCu1-xO confirmed by XRD. The transmittances of both bleached state and colored state were significantly lowered when Cu was added. The NiO films doped with Cu (the molar ratio was 1/8) exhibited the optimum electrochromic behavior with a variation of transmittance (ΔT) up to ∼80% at the wavelength range of 350-600 nm. Cu doping reduces the response time for both the coloring and bleaching states, and the reversibility of the redox reaction was increased as well.

  4. Structural, optical, and electrical properties of p-type NiO films and composite TiO 2/NiO electrodes for solid-state dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Lee, Yi-Mu; Hsu, Cheng-Hsing; Chen, Hung-Wei

    2009-02-01

    p-Type nickel oxide thin films were prepared by sol-gel method, and their structural, optical and electrical properties were investigated. The Ni(OH) 2 sol was formed from nickel (II) acetate tetrahydrate, Ni(CH 3COO) 2·4H 2O, in a mixture of alcohol solution and poly(ethylene glycol), and deposited on an ITO substrate by spin coating followed by different heat treatments in air (50-800 °C). The formation and composition of NiO thin film was justified by EDX analysis. It is found that the thickness of the NiO film calcined at 450 °C for 1 h is about 120 nm with average particle size of 22 nm, and high UV transparency (˜75%) in the visible region is also observed. However, the transmittance is negligible for thin films calcined at 800 °C and below 200 °C due to larger particle size and the amorphous characteristics, respectively. Moreover, the composite electrode comprising n-type TiO 2 and p-type NiO is fabricated. The current-voltage ( I- V) characteristics of the composite TiO 2/NiO electrode demonstrate significant p-type behavior by the shape of the rectifying curve in dark. The effect of calcination temperature on the rectification behavior is also discussed.

  5. Doping effect on SILAR synthesized crystalline nanostructured Cu-doped ZnO thin films grown on indium tin oxide (ITO) coated glass substrates and its characterization

    NASA Astrophysics Data System (ADS)

    Dhaygude, H. D.; Shinde, S. K.; Velhal, Ninad B.; Takale, M. V.; Fulari, V. J.

    2016-08-01

    In the present study, a novel chemical route is used to synthesize the undoped and Cu-doped ZnO thin films in aqueous solution by successive ionic layer adsorption and reaction (SILAR) method. The synthesized thin films are characterized by x-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive x-ray analysis (EDAX), contact angle goniometer and UV-Vis spectroscopic techniques. XRD study shows that the prepared films are polycrystalline in nature with hexagonal crystal structure. The change in morphology for different doping is observed in the studies of FE-SEM. EDAX spectrum shows that the thin films consist of zinc, copper and oxygen elements. Contact angle goniometer is used to measure the contact angle between a liquid and a solid interface and after detection, the nature of the films is initiated from hydrophobic to hydrophilic. The optical band gap energy for direct allowed transition ranging between 1.60-2.91 eV is observed.

  6. The influence of voltage applied between the electrodes on optical and morphological properties of the InGaN thin films grown by thermionic vacuum arc.

    PubMed

    Özen, Soner; Şenay, Volkan; Pat, Suat; Korkmaz, Şadan

    2016-01-01

    The aim of this research is to investigate the optical and morphological properties of the InGaN thin films deposited onto amorphous glass substrates in two separate experiments with two different voltages applied between the electrodes, i.e. 500 and 600 V by means of the thermionic vacuum arc technique. This technique is original for thin film deposition and it enables thin film production in a very short period of time. The optical and morphological properties of the films were investigated by using field emission scanning electron microscope, atomic force microscope, spectroscopic ellipsometer, reflectometer, spectrophotometer, and optical tensiometer. Optical properties were also supported by empirical relations. The deposition rates were calculated as 3 and 3.3 nm/sec for 500 and 600 V, respectively. The increase in the voltage also increased the refractive index, grain size, root mean square roughness and surface free energy. According to the results of the wetting experiments, InGaN samples were low-wettable, also known as hydrophobic.

  7. Doping effect on SILAR synthesized crystalline nanostructured Cu-doped ZnO thin films grown on indium tin oxide (ITO) coated glass substrates and its characterization

    NASA Astrophysics Data System (ADS)

    Dhaygude, H. D.; Shinde, S. K.; Velhal, Ninad B.; Takale, M. V.; Fulari, V. J.

    2016-08-01

    In the present study, a novel chemical route is used to synthesize the undoped and Cu-doped ZnO thin films in aqueous solution by successive ionic layer adsorption and reaction (SILAR) method. The synthesized thin films are characterized by x-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive x-ray analysis (EDAX), contact angle goniometer and UV–Vis spectroscopic techniques. XRD study shows that the prepared films are polycrystalline in nature with hexagonal crystal structure. The change in morphology for different doping is observed in the studies of FE-SEM. EDAX spectrum shows that the thin films consist of zinc, copper and oxygen elements. Contact angle goniometer is used to measure the contact angle between a liquid and a solid interface and after detection, the nature of the films is initiated from hydrophobic to hydrophilic. The optical band gap energy for direct allowed transition ranging between 1.60–2.91 eV is observed.

  8. Photo-induced valence change of the sulfur atom in an L-cysteine thin film grown on a silver metal substrate in a saliva-emulated aqueous solution

    NASA Astrophysics Data System (ADS)

    Tsujibayashi, Toru; Azuma, Junpei; Yamamoto, Isamu; Takahashi, Kazutoshi; Kamada, Masao

    2015-04-01

    A thin film of L-cysteine (HSCH2CH(NH2)COOH) is grown on a silver substrate in saliva-emulated aqueous solution. X-ray photoemission spectroscopic measurements have revealed that the sulfur atom shows valence change under IR laser irradiation at 825 nm. The valence change maintains for about a minute at room temperature and more than an hour between 110 and 250 K after stopping the laser irradiation. It is not observed at all at temperatures lower than 110 K. This temperature-dependent behavior indicates that the photo-excited electronic change should be accompanied by a conformational change in the L-cysteine molecule. It is strongly suggested that the reversible valence change of the sulfur atom is applicable to a memory used around room temperature.

  9. Photo-induced valence change of the sulfur atom in an L-cysteine thin film grown on a silver metal substrate in a saliva-emulated aqueous solution

    SciTech Connect

    Tsujibayashi, Toru; Azuma, Junpei; Yamamoto, Isamu; Takahashi, Kazutoshi; Kamada, Masao

    2015-04-27

    A thin film of L-cysteine (HSCH{sub 2}CH(NH{sub 2})COOH) is grown on a silver substrate in saliva-emulated aqueous solution. X-ray photoemission spectroscopic measurements have revealed that the sulfur atom shows valence change under IR laser irradiation at 825 nm. The valence change maintains for about a minute at room temperature and more than an hour between 110 and 250 K after stopping the laser irradiation. It is not observed at all at temperatures lower than 110 K. This temperature-dependent behavior indicates that the photo-excited electronic change should be accompanied by a conformational change in the L-cysteine molecule. It is strongly suggested that the reversible valence change of the sulfur atom is applicable to a memory used around room temperature.

  10. In-plane dielectric properties of epitaxial Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} thin films grown on GaAs for tunable device application

    SciTech Connect

    Yang Zhibin; Hao Jianhua

    2012-09-01

    We have epitaxially deposited ferroelectric Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} (BST) thin films grown on GaAs substrate via SrTiO{sub 3} buffer layer by laser molecular beam epitaxy. Structural characteristics of the heterostructure were measured by various techniques. The in-plane dielectric properties of the heteroepitaxial structure under different applying frequency were investigated from -190 to 90 Degree-Sign C, indicating Curie temperature of the BST film to be around 52 Degree-Sign C. At room temperature, the dielectric constant of the heterostructure under moderate dc bias field can be tuned by more than 30% and K factor used for frequency agile materials is found to be close to 8. Our results offer the possibility to combine frequency agile electronics of ferroelectric titanate with the high-performance microwave capabilities of GaAs for room temperature tunable device application.

  11. Effects of laser energy fluence on the onset and growth of the Rayleigh-Taylor instabilities and its influence on the topography of the Fe thin film grown in pulsed laser deposition facility

    SciTech Connect

    Mahmood, S.; Rawat, R. S.; Wang, Y.; Lee, S.; Tan, T. L.; Springham, S. V.; Lee, P.; Zakaullah, M.

    2012-10-15

    The effect of laser energy fluence on the onset and growth of Rayleigh-Taylor (RT) instabilities in laser induced Fe plasma is investigated using time-resolved fast gated imaging. The snow plow and shock wave models are fitted to the experimental results and used to estimate the ablation parameters and the density of gas atoms that interact with the ablated species. It is observed that RT instability develops during the interface deceleration stage and grows for a considerable time for higher laser energy fluence. The effects of RT instabilities formation on the surface topography of the Fe thin films grown in pulsed laser deposition system are investigated (i) using different laser energy fluences for the same wavelength of laser radiation and (ii) using different laser wavelengths keeping the energy fluence fixed. It is concluded that the deposition achieved under turbulent condition leads to less smooth deposition surfaces with bigger sized particle agglomerates or network.

  12. Ferromagnetism and magneto-transport properties of Mn{sub 0.92}Ca{sub 0.08}As thin film grown on Al{sub 2}O{sub 3}(0001) substrate

    SciTech Connect

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

    2014-05-07

    The epitaxial Mn{sub 0.92}Ca{sub 0.08}As thin film was grown on Al{sub 2}O{sub 3}(0001) substrate by molecular beam epitaxy. The Curie temperature (T{sub C}) around 340 K was enhanced with the addition of Ca, compared to that of bulk MnAs (T{sub C} ∼ 318 K). The maxima magnetoresistance, ∼2.08% at 0.7 T, was observed near the critical magnetic transition temperature. Moreover, the giant magnetocaloric effect was found with the maximum magnetic entropy change, ∼200 J/kgK, around 330 K at 5 T.

  13. 2D Electronic Transport with Strong Spin-Orbit Coupling in Bi(2-) Square Net of Y2O2Bi Thin Film Grown by Multilayer Solid-Phase Epitaxy.

    PubMed

    Sei, Ryosuke; Fukumura, Tomoteru; Hasegawa, Tetsuya

    2015-11-18

    Highly crystalline Y2O2Bi epitaxial thin film with monatomic Bi(2-) square net layer was grown by newly developed multilayer solid phase epitaxy. High reactivity of the nanometer-scale multilayered precursor enabled efficient formation of single crystalline Y2O2Bi phase with one-step heating. The reductive state of Bi(2-) square net was observed by X-ray photoemission spectroscopy. The electrical resistivity was one order lower than that of polycrystalline powder in previous study. The magnetotransport showed weak antilocalization effect well fitted by the Hikami-Larkin-Nagaoka model, exhibiting two-dimensional electronic nature with strong spin-orbit coupling in the Bi(2-) square net.

  14. Two-dimensional weak anti-localization in Bi{sub 2}Te{sub 3} thin film grown on Si(111)-(7 Multiplication-Sign 7) surface by molecular beam epitaxy

    SciTech Connect

    Roy, Anupam; Guchhait, Samaresh; Sonde, Sushant; Dey, Rik; Pramanik, Tanmoy; Rai, Amritesh; Movva, Hema C. P.; Banerjee, Sanjay K.; Colombo, Luigi

    2013-04-22

    We report on low temperature transport studies of Bi{sub 2}Te{sub 3} topological insulator thin films grown on Si(111)-(7 Multiplication-Sign 7) surface by molecular beam epitaxy. A sharp increase in the magnetoresistance with magnetic field at low temperature indicates the existence of weak anti-localization. The measured weak anti-localization effect agrees well with the Hikami-Larkin-Nagaoka model, and the extracted phase coherence length shows a power-law dependence with temperature indicating the existence of a two-dimensional system. An insulating ground state has also been observed at low temperature showing a logarithmic divergence of the resistance that appears to be the influence of electron-electron interaction in a two-dimensional system.

  15. Ellipsometric investigation of nitrogen doped diamond thin films grown in microwave CH4/H2/N2 plasma enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Ficek, Mateusz; Sankaran, Kamatchi J.; Ryl, Jacek; Bogdanowicz, Robert; Lin, I.-Nan; Haenen, Ken; Darowicki, Kazimierz

    2016-06-01

    The influence of N2 concentration (1%-8%) in CH4/H2/N2 plasma on structure and optical properties of nitrogen doped diamond (NDD) films was investigated. Thickness, roughness, and optical properties of the NDD films in the VIS-NIR range were investigated on the silicon substrates using spectroscopic ellipsometry. The samples exhibited relatively high refractive index (2.6 ± 0.25 at 550 nm) and extinction coefficient (0.05 ± 0.02 at 550 nm) with a transmittance of 60%. The optical investigation was supported by the molecular and atomic data delivered by Raman studies, bright field transmission electron microscopy imaging, and X-ray photoelectron spectroscopy diagnostics. Those results revealed that while the films grown in CH4/H2 plasma contained micron-sized diamond grains, the films grown using CH4/H2/(4%)N2 plasma exhibited ultranano-sized diamond grains along with n-diamond and i-carbon clusters, which were surrounded by amorphous carbon grain boundaries.

  16. Structural and magnetic properties of Ge{sub 1-x}Mn{sub x} thin films grown on Ge (001) substrates

    SciTech Connect

    Yada, Shinsuke; Nam Hai, Pham; Tanaka, Masaaki; Sugahara, Satoshi

    2011-10-01

    We investigate the structural and magneto-optical properties of Mn-doped Ge (Ge{sub 1-x}Mn{sub x}) films with self-organized nanocolumns, grown on Ge (001) substrates by molecular beam epitaxy (MBE), in which the substrate temperature (T{sub S}) and growth rate (R{sub G}) are varied. Transmission electron microscopy (TEM) observations and magnetic circular dichroism (MCD) measurements reveal that Mn-rich nanocolumnar precipitation is formed in the Ge{sub 1-x}Mn{sub x} films grown at T{sub S} {<=} 100 deg. C, with keeping the size and spacing. At higher T{sub S} ({>=}150 deg. C), ferromagnetic Mn{sub 5}Ge{sub 3} clusters are formed. It is also found that the Mn distribution in the Ge{sub 1-x}Mn{sub x} films can be controlled: By lowering T{sub S} or increasing R{sub G}, the Mn content x{sub nc} in the nanocolumns decreases and Mn atoms are more distributed into the Ge matrix, and eventually the magnetic properties are changed. The formation of the nanocolumns is explained by the spinodal decomposition in the layer-by-layer growth mode. We analyzed the periodicity and Mn content x{sub nc} of nanocolumns by using the Cahn-Hilliard equation.

  17. Influence of the shape and surface oxidation in the magnetization reversal of thin iron nanowires grown by focused electron beam induced deposition

    PubMed Central

    Córdoba, Rosa; Magén, César; Snoeck, Etienne; Koopmans, Bert

    2015-01-01

    Summary Iron nanostructures grown by focused electron beam induced deposition (FEBID) are promising for applications in magnetic sensing, storage and logic. Such applications require a precise design and determination of the coercive field (H C), which depends on the shape of the nanostructure. In the present work, we have used the Fe2(CO)9 precursor to grow iron nanowires by FEBID in the thickness range from 10 to 45 nm and width range from 50 to 500 nm. These nanowires exhibit an Fe content between 80 and 85%, thus giving a high ferromagnetic signal. Magneto-optical Kerr characterization indicates that H C decreases for increasing thickness and width, providing a route to control the magnetization reversal field through the modification of the nanowire dimensions. Transmission electron microscopy experiments indicate that these wires have a bell-type shape with a surface oxide layer of about 5 nm. Such features are decisive in the actual value of H C as micromagnetic simulations demonstrate. These results will help to make appropriate designs of magnetic nanowires grown by FEBID. PMID:26199835

  18. Structural and optical properties of dense vertically aligned ZnO nanorods grown onto silver and gold thin films by galvanic effect with iron contamination

    SciTech Connect

    Scarpellini, D.; Paoloni, S.; Medaglia, P.G.; Pizzoferrato, R.; Orsini, A.; Falconi, C.

    2015-05-15

    Highlights: • ZnO nanorods were grown on Au and Ag films in aqueous solution by galvanic effect. • The method is prone to metal contamination which can influence the ZnO properties. • Iron doping improves the lattice matching between ZnO and the substrate. • Energy levels of point defects are lowered and the light emission is red-shifted. • Galvanic-induced nucleation starts and proceeds continuously during the growth. - Abstract: Dense arrays of vertically aligned ZnO nanorods have been grown onto either silver or gold seedless substrates trough a simple hydrothermal method by exploiting the galvanic effect between the substrate and metallic parts. The nanorods exhibit larger bases and more defined hexagonal shapes, in comparison with standard non-galvanic wet-chemistry synthesis. X-ray diffraction (XRD) shows that the iron contamination, associated with the galvanic contact, significantly improves the in-plane compatibility of ZnO with the Au and Ag cubic lattice. Photoluminescence (PL) measurements indicate that the contamination does not affect the number density of localized defects, but lowers their energy levels uniformly; differently, the band-edge emission is not altered appreciably. Finally, we have found that the ZnO hetero-nucleation by galvanic effect initiates at different times in different sites of the substrate area. Our results can be useful for the fabrication of high performance piezonanodevices comprising high-density metal-to-ZnO nanoscaled junctions without intermediate polycrystalline layers.

  19. Influence of the shape and surface oxidation in the magnetization reversal of thin iron nanowires grown by focused electron beam induced deposition.

    PubMed

    Rodríguez, Luis A; Deen, Lorenz; Córdoba, Rosa; Magén, César; Snoeck, Etienne; Koopmans, Bert; De Teresa, José M

    2015-01-01

    Iron nanostructures grown by focused electron beam induced deposition (FEBID) are promising for applications in magnetic sensing, storage and logic. Such applications require a precise design and determination of the coercive field (H C), which depends on the shape of the nanostructure. In the present work, we have used the Fe2(CO)9 precursor to grow iron nanowires by FEBID in the thickness range from 10 to 45 nm and width range from 50 to 500 nm. These nanowires exhibit an Fe content between 80 and 85%, thus giving a high ferromagnetic signal. Magneto-optical Kerr characterization indicates that H C decreases for increasing thickness and width, providing a route to control the magnetization reversal field through the modification of the nanowire dimensions. Transmission electron microscopy experiments indicate that these wires have a bell-type shape with a surface oxide layer of about 5 nm. Such features are decisive in the actual value of H C as micromagnetic simulations demonstrate. These results will help to make appropriate designs of magnetic nanowires grown by FEBID.

  20. Influence of the shape and surface oxidation in the magnetization reversal of thin iron nanowires grown by focused electron beam induced deposition.

    PubMed

    Rodríguez, Luis A; Deen, Lorenz; Córdoba, Rosa; Magén, César; Snoeck, Etienne; Koopmans, Bert; De Teresa, José M

    2015-01-01

    Iron nanostructures grown by focused electron beam induced deposition (FEBID) are promising for applications in magnetic sensing, storage and logic. Such applications require a precise design and determination of the coercive field (H C), which depends on the shape of the nanostructure. In the present work, we have used the Fe2(CO)9 precursor to grow iron nanowires by FEBID in the thickness range from 10 to 45 nm and width range from 50 to 500 nm. These nanowires exhibit an Fe content between 80 and 85%, thus giving a high ferromagnetic signal. Magneto-optical Kerr characterization indicates that H C decreases for increasing thickness and width, providing a route to control the magnetization reversal field through the modification of the nanowire dimensions. Transmission electron microscopy experiments indicate that these wires have a bell-type shape with a surface oxide layer of about 5 nm. Such features are decisive in the actual value of H C as micromagnetic simulations demonstrate. These results will help to make appropriate designs of magnetic nanowires grown by FEBID. PMID:26199835

  1. Mechanisms of the micro-crack generation in an ultra-thin AlN/GaN superlattice structure grown on Si(110) substrates by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Shen, X. Q.; Takahashi, T.; Ide, T.; Shimizu, M.

    2015-09-01

    We investigate the generation mechanisms of micro-cracks (MCs) in an ultra-thin AlN/GaN superlattice (SL) structure grown on Si(110) substrates by metalorganic chemical vapor deposition. The SL is intended to be used as an interlayer (IL) for relaxing tensile stress and obtaining high-quality crack-free GaN grown on Si substrates. It is found that the MCs can be generated by two different mechanisms, where large mismatches of the lattice constant (LC) and the coefficient of thermal expansion (CTE) play key roles in the issue. Different MC configurations (low-density and high-density MCs) are observed, which are considered to be formed during the different growth stages (SL growth and cooling down processes) due to the LC and the CTE effects. In-situ and ex-situ experimental results support the mechanism interpretations of the MCs generation. The mechanism understanding makes it possible to optimize the SL IL structure for growing high-quality crack-free GaN films on Si substrates for optical and electronic device applications.

  2. Mechanisms of the micro-crack generation in an ultra-thin AlN/GaN superlattice structure grown on Si(110) substrates by metalorganic chemical vapor deposition

    SciTech Connect

    Shen, X. Q. Takahashi, T.; Ide, T.; Shimizu, M.

    2015-09-28

    We investigate the generation mechanisms of micro-cracks (MCs) in an ultra-thin AlN/GaN superlattice (SL) structure grown on Si(110) substrates by metalorganic chemical vapor deposition. The SL is intended to be used as an interlayer (IL) for relaxing tensile stress and obtaining high-quality crack-free GaN grown on Si substrates. It is found that the MCs can be generated by two different mechanisms, where large mismatches of the lattice constant (LC) and the coefficient of thermal expansion (CTE) play key roles in the issue. Different MC configurations (low-density and high-density MCs) are observed, which are considered to be formed during the different growth stages (SL growth and cooling down processes) due to the LC and the CTE effects. In-situ and ex-situ experimental results support the mechanism interpretations of the MCs generation. The mechanism understanding makes it possible to optimize the SL IL structure for growing high-quality crack-free GaN films on Si substrates for optical and electronic device applications.

  3. Epitaxial single-crystal thin films of MnxTi1 - xO2 - δ grown on (rutile)TiO2 substrates with pulsed laser deposition: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Ilton, Eugene S.; Droubay, Timothy C.; Chaka, Anne M.; Kovarik, Libor; Varga, Tamas; Arey, Bruce W.; Kerisit, Sebastien N.

    2015-02-01

    Epitaxial rutile-structured single-crystal MnxTi1 - xO2 - δ films were synthesized on rutile- (110) and -(001) substrates using pulsed laser deposition. The films were characterized by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and aberration-corrected transmission electron microscopy (ACTEM). Under the present conditions, 400 °C and PO2 = 20 mTorr, single crystal epitaxial thin films were grown for x = 0.13, where x is the nominal average mole fraction of Mn. In fact, arbitrarily thick films could be grown with near invariant Mn/Ti concentration profiles from the substrate/film interface to the film surface. In contrast, at x = 0.25, Mn became enriched towards the surface and a secondary nano-scale phase formed which appeared to maintain the basic rutile structure but with enhanced z-contrast in the tunnels, or interstitial sites. Ab initio thermodynamic calculations provided quantitative estimates for the destabilizing effect of expanding the β-MnO2 lattice parameters to those of TiO2-rutile, the stabilizing effect of diluting Mn with increasing Ti concentration, and competing reaction pathways for surface oxide formation.

  4. Epitaxial single-crystal thin films of MnxTi1-xO2-δ grown on (rutile)TiO2 substrates with pulsed laser deposition: Experiment and theory

    SciTech Connect

    Ilton, Eugene S.; Droubay, Timothy C.; Chaka, Anne M.; Kovarik, Libor; Varga, Tamas; Arey, Bruce W.; Kerisit, Sebastien N.

    2015-02-01

    Epitaxial rutile-structured single-crystal MnxTi1-xO2-δ films were synthesized on rutile- (110) and -(001) substrates using pulsed laser deposition. The films were characterized by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and aberration-corrected transmission electron microscopy (ACTEM). Under the present conditions, 400oC and PO2 = 20 mTorr, single crystal epitaxial thin films were grown for x = 0.13, where x is the nominal average mole fraction of Mn. In fact, arbitrarily thick films could be grown with near invariant Mn/Ti concentration profiles from the substrate/film interface to the film surface. In contrast, at x = 0.25, Mn became enriched towards the surface and a secondary nano-scale phase formed which appeared to maintain the basic rutile structure but with enhanced z-contrast in the tunnels, or tetrahedral interstitial sites. Ab initio thermodynamic calculations provided quantitative estimates for the destabilizing effect of expanding the β-MnO2 lattice parameters to those of TiO2-rutile, the stabilizing effect of diluting Mn with increasing Ti concentration, and competing reaction pathways.

  5. Interstitial Boron-Doped TiO2 Thin Films: The Significant Effect of Boron on TiO2 Coatings Grown by Atmospheric Pressure Chemical Vapor Deposition.

    PubMed

    Quesada-González, Miguel; Boscher, Nicolas D; Carmalt, Claire J; Parkin, Ivan P

    2016-09-28

    The work presented here describes the preparation of transparent interstitial boron-doped TiO2 thin-films by atmospheric pressure chemical vapor deposition (APCVD). The interstitial boron-doping, on TiO2, proved by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), is shown to enhance the crystallinity and significantly improve the photocatalytic activity of the TiO2 films. The synthesis, highly suitable for a reel-to-reel process, has been carried out in one step. PMID:27622709

  6. Interstitial Boron-Doped TiO2 Thin Films: The Significant Effect of Boron on TiO2 Coatings Grown by Atmospheric Pressure Chemical Vapor Deposition.

    PubMed

    Quesada-González, Miguel; Boscher, Nicolas D; Carmalt, Claire J; Parkin, Ivan P

    2016-09-28

    The work presented here describes the preparation of transparent interstitial boron-doped TiO2 thin-films by atmospheric pressure chemical vapor deposition (APCVD). The interstitial boron-doping, on TiO2, proved by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), is shown to enhance the crystallinity and significantly improve the photocatalytic activity of the TiO2 films. The synthesis, highly suitable for a reel-to-reel process, has been carried out in one step.

  7. IR and electrochemical synthesis and characterization of thin films of PEDOT grown on platinum single crystal electrodes in [EMMIM]Tf2N ionic liquid.

    PubMed

    Sandoval, Andrea P; Suárez-Herrera, Marco F; Feliu, Juan M

    2015-01-01

    Thin films of PEDOT synthesized on platinum single electrodes in contact with the ionic liquid 1-ethyl-2,3-dimethylimidazolium triflimide ([EMMIM]Tf2N) were studied by cyclic voltammetry, chronoamperometry, infrared spectroscopy and atomic force microscopy. It was found that the polymer grows faster on Pt(111) than on Pt(110) or Pt(100) and that the redox reactions associated with the PEDOT p-doping process are much more reversible in [EMMIM]Tf2N than in acetonitrile. Finally, the ion exchange and charge carriers' formation during the p-doping reaction of PEDOT were studied using in situ FTIR spectroscopy. PMID:25815089

  8. Fabrication and characterization of molecular beam epitaxy grown thin-film GaAs waveguides for mid-infrared evanescent field chemical sensing.

    PubMed

    Charlton, Christy; Giovannini, Marcella; Faist, Jérôme; Mizaikoff, Boris

    2006-06-15

    Thin-film GaAs waveguides were designed and fabricated by molecular beam epitaxy for use in mid-infrared (MIR) evanescent field liquid sensing. Waveguides were designed to facilitate the propagation of a single mode at a wavelength of 10.3 microm emitted from a distributed feedback quantum cascade laser, which overlaps with molecular selective absorption features of acetic anhydride. The characterization of the waveguides shows transmission across a broad MIR band. Evanescent field absorption measurements indicate a significant sensitivity enhancement in contrast to multimode planar silver halide waveguides.

  9. IR and electrochemical synthesis and characterization of thin films of PEDOT grown on platinum single crystal electrodes in [EMMIM]Tf2N ionic liquid

    PubMed Central

    Sandoval, Andrea P; Suárez-Herrera, Marco F

    2015-01-01

    Summary Thin films of PEDOT synthesized on platinum single electrodes in contact with the ionic liquid 1-ethyl-2,3-dimethylimidazolium triflimide ([EMMIM]Tf2N) were studied by cyclic voltammetry, chronoamperometry, infrared spectroscopy and atomic force microscopy. It was found that the polymer grows faster on Pt(111) than on Pt(110) or Pt(100) and that the redox reactions associated with the PEDOT p-doping process are much more reversible in [EMMIM]Tf2N than in acetonitrile. Finally, the ion exchange and charge carriers’ formation during the p-doping reaction of PEDOT were studied using in situ FTIR spectroscopy. PMID:25815089

  10. Quality improvements of ZnxCdyMg1-x-ySe layers grown on InP substrates by a thin ZnCdSe interfacial layer

    NASA Astrophysics Data System (ADS)

    Zeng, L.; Yang, B. X.; Tamargo, M. C.; Snoeks, E.; Zhao, L.

    1998-03-01

    The quality of lattice-matched ZnxCdyMg1-x-ySe epitaxial layers grown on (001) InP substrates with a III-V buffer layer has been improved by initially growing a ZnCdSe interfacial layer (50 Å) at low temperature. The widths of double crystal x-ray rocking curves for ZnxCdyMg1-x-ySe epilayers with band gaps as high as 3.05 eV were reduced to about 70 arcsec. The defect density evaluated from etch pit density and plan-view transmission electron microscopy measurements was reduced by two orders of magnitude, to 106-107cm-2. The photoluminescence band edge emission became more symmetric and slightly narrower. It is proposed that an initial two-dimensional growth mode has been achieved by incorporating such a lattice-matched ZnCdSe layer.

  11. High oxidation state at the epitaxial interface of {gamma}-Al{sub 2}O{sub 3} thin films grown on Si(111) and Si(001)

    SciTech Connect

    El Kazzi, M.; Silly, M.; Sirotti, F.; Merckling, C.; Saint-Girons, G.; Grenet, G.; Hollinger, G.

    2010-10-11

    High resolution synchrotron radiation x-ray photoelectron spectroscopy allowed us to identify the chemical bonding at the interface between epitaxial {gamma}-Al{sub 2}O{sub 3} and Si substrate. The experiments were performed on 1 nm thick epitaxial {gamma}-Al{sub 2}O{sub 3} layers grown on both Si(111) and Si(001) substrates. In both cases, the Si 2p core level decomposition recorded at photon energy of 160 eV provided evidence for the absence of Si{sup 2+} and Si{sup 3+} species and the presence of two different Si{sup 4+} species. A microscopic model is proposed for the interface obtained with two incomplete SiO{sub 2} planes based on the Si 2p{sub 3/2} line shape.

  12. Magnetically Hard Fe3Se4 Embedded in Bi2Se3 Topological Insulator Thin Films Grown by Molecular Beam Epitaxy.

    PubMed

    Vasconcelos, Hugo Menezes do Nascimento; Eddrief, Mahmoud; Zheng, Yunlin; Demaille, Dominique; Hidki, Sarah; Fonda, Emiliano; Novikova, Anastasiia; Fujii, Jun; Torelli, Piero; Salles, Benjamin Rache; Vobornik, Ivana; Panaccione, Giancarlo; de Oliveira, Adilson Jesus Aparecido; Marangolo, Massimiliano; Vidal, Franck

    2016-01-26

    We investigated the structural, magnetic, and electronic properties of Bi2Se3 epilayers containing Fe grown on GaAs(111) by molecular beam epitaxy. It is shown that, in the window of growth parameters leading to Bi2Se3 epilayers with optimized quality, Fe atom clustering leads to the formation of FexSey inclusions. These objects have platelet shape and are embedded within Bi2Se3. Monoclinic Fe3Se4 is identified as the main secondary phase through detailed structural measurements. Due to the presence of the hard ferrimagnetic Fe3Se4 inclusions, the system exhibits a very large coercive field at low temperature and room temperature magnetic ordering. Despite this composite structure and the proximity of a magnetic phase, the surface electronic structure of Bi2Se3 is preserved, as shown by the persistence of a gapless Dirac cone at Γ.

  13. Electrical properties of InGaN thin films grown by RF sputtering at different temperatures, varying nitrogen and argon partial pressure ratios

    NASA Astrophysics Data System (ADS)

    Jakkala, Pratheesh; Kordesch, Martin E.

    2016-10-01

    Indium gallium nitride (InGaN) thin films of varying indium (In) and gallium (Ga) compositions have been fabricated on aluminosilicate glass and silicon (111) substrates using RF magnetron sputtering method at different growth temperatures, varied from 35 °C to 450 °C. Argon (Ar) and nitrogen (N2) are used as Inert and reactive gases respectively. Keeping the total pressure of gas mixture constant, partial pressures of N2 and Ar gases are varied. Ratio of Ar partial pressure to total pressure in the gas mixture is varied from 0 to 0.75. In this study, we present electrical properties of these InGaN thin films. Resistivity values of 2.6 × 10‑5 to 1.68 × 10‑2 Ω.cm, mobility values of 0.119 to 45.2 cm2/V.s, conductivity values of 0.595 × 103 to 37.3 × 103 mho/cm and bulk carrier concentration values ‑1020 to ‑1022/m3 are recorded that are measured through Hall-effect measurement technique.

  14. A study on the structural and mechanical properties of nanocrystalline CuS thin films grown by chemical bath deposition technique

    SciTech Connect

    Mukherjee, Nillohit; Sinha, Arijit; Khan, Gobinda Gopal; Chandra, Debraj; Bhaumik, Asim; Mondal, Anup

    2011-01-15

    We report a chemical route for the deposition of nanocrystalline thin films of CuS, using aqueous solutions of Cu(CH{sub 3}COO){sub 2}, SC(NH{sub 2}){sub 2} and N(CH{sub 2}CH{sub 2}OH){sub 3} [triethanolamine, i.e. TEA] in proper concentrations and ratios. The films were structurally characterized using X-ray diffraction technique (XRD), field emission scanning electron microscopy (FESEM) and optical analysis [both photo luminescence (PL) and ultraviolet-visible (UV-vis)]. Optical studies showed a large blue shift in the band gap energy of the films due to quantum confinement effect exerted by the nanocrystals. From both XRD and FESEM analyses, formation of CuS nanocrystals with sizes within 10-15 nm was evident. A study on the mechanical properties was carried out using nanoindentation and nanoscratch techniques, which showed good mechanical stability and high adherence of the films with the bottom substrate. Such study on the mechanical properties of the CuS thin films is being reported here for the first time. Current-voltage (I-V) measurements were also carried out for the films, which showed p-type conductivity.

  15. Performance enhancement of blue light-emitting diodes with InGaN/GaN multi-quantum wells grown on Si substrates by inserting thin AlGaN interlayers

    NASA Astrophysics Data System (ADS)

    Kimura, Shigeya; Yoshida, Hisashi; Uesugi, Kenjiro; Ito, Toshihide; Okada, Aoi; Nunoue, Shinya

    2016-09-01

    We have grown blue light-emitting diodes (LEDs) having InGaN/GaN multi-quantum wells (MQWs) with thin AlyGa1-yN (0 < y < 0.3) interlayers on Si(111) substrates. It was found by high-resolution transmission electron microscopy observations and three-dimensional atom probe analysis that 1-nm-thick interlayers with an AlN mole fraction of less than y = 0.3 were continuously formed between GaN barriers and InGaN wells, and that the AlN mole fraction up to y = 0.15 could be consistently controlled. The external quantum efficiency of the blue LED was enhanced in the low-current-density region (≤45 A/cm2) but reduced in the high-current-density region by the insertion of the thin Al0.15Ga0.85N interlayers in the MQWs. We also found that reductions in both forward voltage and wavelength shift with current were achieved by inserting the interlayers even though the inserted AlGaN layers had potential higher than that of the GaN barriers. The obtained peak wall-plug efficiency was 83% at room temperature. We suggest that the enhanced electroluminescence (EL) performance was caused by the introduction of polarization-induced hole carriers in the InGaN wells on the side adjacent to the thin AlGaN/InGaN interface and efficient electron carrier transport through multiple wells. This model is supported by temperature-dependent EL properties and band-diagram simulations. We also found that inserting the interlayers brought about a reduction in the Shockley-Read-Hall nonradiative recombination component, corresponding to the shrinkage of V-defects. This is another conceivable reason for the observed performance enhancement.

  16. Facile synthesis of a mechanically robust and highly porous NiO film with excellent electrocatalytic activity towards methanol oxidation

    NASA Astrophysics Data System (ADS)

    Wang, Luoyuan; Zhang, Guoge; Liu, Yan; Li, Wenfang; Lu, Wei; Huang, Haitao

    2016-05-01

    Considerable research is being conducted in searching for effective anode catalysts in alkaline direct methanol fuel cells (DMFCs). Although significant progress has been achieved, it is still challenging to prepare non-Pt catalysts with both excellent activity and good durability. Herein, a highly porous NiO film is developed by a facile and fast anodization approach. The anodic NiO film demonstrates a high surface area, large mesopore volume and small crystallite size, leading to facilitated adsorption of reaction species, easy electrolyte penetration and fast reaction kinetics. Furthermore, as anodic NiO is grown in situ on a metallic substrate with strong adhesion strength and good electrical contact, it can be used directly as an anode catalyst for methanol oxidation without the need to add any binder or conducting agent. Such an additive-free approach greatly expedites the catalyst preparation process. The anodic NiO shows lower methanol oxidation potential, higher oxidation current and better catalytic durability than most of the state-of-the-art Ni-based catalysts reported elsewhere. As anodization is a simple, low cost and easily scaled up method, the work described here provides an exciting direction to speed up the practical application of alkaline DMFCs.Considerable research is being conducted in searching for effective anode catalysts in alkaline direct methanol fuel cells (DMFCs). Although significant progress has been achieved, it is still challenging to prepare non-Pt catalysts with both excellent activity and good durability. Herein, a highly porous NiO film is developed by a facile and fast anodization approach. The anodic NiO film demonstrates a high surface area, large mesopore volume and small crystallite size, leading to facilitated adsorption of reaction species, easy electrolyte penetration and fast reaction kinetics. Furthermore, as anodic NiO is grown in situ on a metallic substrate with strong adhesion strength and good electrical contact

  17. Electron beam induced coloration and luminescence in layered structure of WO{sub 3} thin films grown by pulsed dc magnetron sputtering

    SciTech Connect

    Karuppasamy, A.; Subrahmanyam, A.

    2007-06-01

    Tungsten oxide thin films have been deposited by pulsed dc magnetron sputtering of tungsten in argon and oxygen atmosphere. The as-deposited WO{sub 3} film is amorphous, highly transparent, and shows a layered structure along the edges. In addition, the optical properties of the as-deposited film show a steplike behavior of extinction coefficient. However, the electron beam irradiation (3.0 keV) of the as-deposited films results in crystallization, coloration (deep blue), and luminescence (intense red emission). The above changes in physical properties are attributed to the extraction of oxygen atoms from the sample and the structural modifications induced by electron bombardment. The present method of coloration and luminescence has a potential for fabricating high-density optical data storage device.

  18. Electronic excitations and structure of Li{sub 2}IrO{sub 3} thin films grown on ZrO{sub 2}:Y (001) substrates

    SciTech Connect

    Jenderka, Marcus Schmidt-Grund, Rüdiger; Grundmann, Marius; Lorenz, Michael

    2015-01-14

    Thin films are a prerequisite for application of the emergent exotic ground states in iridates that result from the interplay of strong spin-orbit coupling and electronic correlations. We report on pulsed laser deposition of Li{sub 2}IrO{sub 3} films on ZrO{sub 2}:Y (001) single crystalline substrates. X-ray diffraction confirms preferential (001) and (10-1) out-of-plane crystalline orientations with well defined in-plane orientation. Resistivity between 35 and 300 K is dominated by a three-dimensional variable range hopping mechanism. The dielectric function is determined by means of spectroscopic ellipsometry and, complemented by Fourier transform infrared transmission spectroscopy, reveals a small optical gap of ≈300 meV, a splitting of the 5d-t{sub 2g} manifold, and several in-gap excitations attributed to phonons and possibly magnons.

  19. Transport properties of ultra-thin VO2 films on (001) TiO2 grown by reactive molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Paik, Hanjong; Moyer, Jarrett A.; Spila, Timothy; Tashman, Joshua W.; Mundy, Julia A.; Freeman, Eugene; Shukla, Nikhil; Lapano, Jason M.; Engel-Herbert, Roman; Zander, Willi; Schubert, Jürgen; Muller, David A.; Datta, Suman; Schiffer, Peter; Schlom, Darrell G.

    2015-10-01

    We report the growth of (001)-oriented VO2 films as thin as 1.5 nm with abrupt and reproducible metal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinner films with sharp MITs are discussed, including the Volmer-Weber type growth mode due to the high energy of the (001) VO2 surface. Another key limitation is interdiffusion with the (001) TiO2 substrate, which we quantify using low angle annular dark field scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy. We find that controlling island coalescence on the (001) surface and minimization of cation interdiffusion by using a low growth temperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO2 films with abrupt MIT behavior.

  20. Microstructure study of pinning sites of highly (0001) textured Sm(Co,Cu){sub 5} thin films grown on Ru underlayer

    SciTech Connect

    Zhao Haibao; Wang Hao; Liu Xiaoqi; Wang Jianping

    2012-04-01

    In this paper, microstructure study of pinning sites of highly (0001) textured Sm(Co,Cu){sub 5} thin films was presented. Various types of pinning sites were identified, such as voids, grain/matrix boundaries (or crystalline/amorphous boundaries), grain boundaries between crystalline grains, and composition inhomogeneity in grains. One key finding of TEM elemental mapping was that Cu atoms were rich in the inner part of Sm(Co,Cu){sub 5} grains (defined by Sm and Co concentrations), instead of the outer part of grains, such as grain boundaries. Cu served as an alloying element in Sm(Co,Cu){sub 5} grains, not as a doping element to form Cu-rich grain boundaries. A model of Sm(Co,Cu){sub 5} films with lateral graded anisotropy due to composition/crystallization variation can explain the huge difference between the H{sub C} and H{sub K}.

  1. Substrate-induced disorder in V{sub 2}O{sub 3} thin films grown on annealed c-plane sapphire substrates

    SciTech Connect

    Brockman, J.; Samant, M. G.; Roche, K. P.; Parkin, S. S. P.

    2012-07-30

    We investigate the structural and electronic properties of V{sub 2}O{sub 3} thin films deposited by oxygen plasma-assisted molecular beam epitaxy onto annealed and unannealed c-plane sapphire substrates. Annealing the substrates before growth to produce ultra-smooth surfaces improved initial epitaxy, according to in situ reflection high-energy electron diffraction. Surprisingly, films deposited on annealed substrates had a more island-like surface, broader x-ray diffraction peaks, and an increased resistivity of V{sub 2}O{sub 3}'s normally metallic high-temperature phase. We attribute these results to enhanced strain coupling at the interface between the substrate and film, highlighting the vulnerability of V{sub 2}O{sub 3}'s strongly correlated metallic phase to crystalline defects and structural disorder.

  2. Structural properties of relaxed thin film germanium layers grown by low temperature RF-PECVD epitaxy on Si and Ge (100) substrates

    SciTech Connect

    Cariou, R.; Ruggeri, R.; Tan, X.; Nassar, J.; Roca i Cabarrocas, P.; Mannino, Giovanni

    2014-07-15

    We report on unusual low temperature (175 °C) heteroepitaxial growth of germanium thin films using a standard radio-frequency plasma process. Spectroscopic ellipsometry and transmission electron microscopy (TEM) reveal a perfect crystalline quality of epitaxial germanium layers on (100) c-Ge wafers. In addition direct germanium crystal growth is achieved on (100) c-Si, despite 4.2% lattice mismatch. Defects rising from Ge/Si interface are mostly located within the first tens of nanometers, and threading dislocation density (TDD) values as low as 10{sup 6} cm{sup −2} are obtained. Misfit stress is released fast: residual strain of −0.4% is calculated from Moiré pattern analysis. Moreover we demonstrate a striking feature of low temperature plasma epitaxy, namely the fact that crystalline quality improves with thickness without epitaxy breakdown, as shown by TEM and depth profiling of surface TDD.

  3. Transport properties of ultra-thin VO{sub 2} films on (001) TiO{sub 2} grown by reactive molecular-beam epitaxy

    SciTech Connect

    Paik, Hanjong; Tashman, Joshua W.; Moyer, Jarrett A.; Schiffer, Peter; Spila, Timothy; Mundy, Julia A.; Freeman, Eugene; Shukla, Nikhil; Datta, Suman; Lapano, Jason M.; Engel-Herbert, Roman; Zander, Willi; Schubert, Jürgen; Muller, David A.; Schlom, Darrell G.

    2015-10-19

    We report the growth of (001)-oriented VO{sub 2} films as thin as 1.5 nm with abrupt and reproducible metal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinner films with sharp MITs are discussed, including the Volmer-Weber type growth mode due to the high energy of the (001) VO{sub 2} surface. Another key limitation is interdiffusion with the (001) TiO{sub 2} substrate, which we quantify using low angle annular dark field scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy. We find that controlling island coalescence on the (001) surface and minimization of cation interdiffusion by using a low growth temperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO{sub 2} films with abrupt MIT behavior.

  4. Structural and dielectric properties of Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} thin films grown by PLD

    SciTech Connect

    James, K. K.; Satish, B.; Jayaraj, M. K.

    2014-01-28

    Ferroelectric thin films of Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} (BST) were deposited on Si/SiO{sub 2}/TiO{sub 2}/Pt (PtSi) substrate by pulsed laser deposition (PLD). Crystalline films with perovskite structure were obtained without post-deposition annealing. Phase purity of the deposited films was confirmed by x-ray diffraction. The lowest value of FWHM obtained for the film deposited at oxygen pressure 5.4×10{sup −4} mbar and substrate temperature 600°C, indicates the high crystallinity of the film. The room temperature dielectric constant at 100 kHz was 85. Butterfly loop, which is the characteristic of ferroelectric materials, was obtained in the regime of −4 to +4V. The leakage current density was nearly 9×10{sup −13} Acm{sup −2}.

  5. Sapphire substrate-induced effects in VO{sub 2} thin films grown by oxygen plasma-assisted pulsed laser deposition

    SciTech Connect

    Skuza, J. R. E-mail: apradhan@nsu.edu; Scott, D. W.; Pradhan, A. K. E-mail: apradhan@nsu.edu

    2015-11-21

    We investigate the structural and electronic properties of VO{sub 2} thin films on c-plane sapphire substrates with three different surface morphologies to control the strain at the substrate-film interface. Only non-annealed substrates with no discernible surface features (terraces) provided a suitable template for VO{sub 2} film growth with a semiconductor-metal transition (SMT), which was much lower than the bulk transition temperature. In addition to strain, oxygen vacancy concentration also affects the properties of VO{sub 2}, which can be controlled through deposition conditions. Oxygen plasma-assisted pulsed laser deposition allows favorable conditions for VO{sub 2} film growth with SMTs that can be easily tailored for device applications.

  6. Enhanced self-field critical current density of nano-composite YBa2Cu3O7 thin films grown by pulsed-laser deposition

    NASA Astrophysics Data System (ADS)

    Siraj, K.; Pedarnig, J. D.; Moser, A.; Bäuerle, D.; Babu, N. Hari; Cardwell, D. A.

    2008-06-01

    Enhanced self-field critical current density Jc of novel, high-temperature superconducting thin films is reported. Layers are deposited on (001) MgO substrates by laser ablation of YBa2Cu3O7-δ(Y-123) ceramics containing Y2Ba4CuMOx (M-2411, M=Ag, Nb, Ru, Zr) nano-particles. The Jc of films depends on the secondary-phase content of the ceramic targets, which was varied between 0 and 15 mol%. Composite layers (2 mol% of Ag-2411 and Nb-2411) exhibit Jc values at 77 K of up to 5.1 MA/cm2, which is 3 to 4 times higher than those observed in films deposited from phase pure Y-123 ceramics. Nb-2411 grows epitaxially in the composite layers and the estimated crystallite size is ~10 nm.

  7. Electronic and crystalline structures of zero band-gap LuPdBi thin films grown epitaxially on MgO(100)

    SciTech Connect

    Shan, Rong; Ouardi, Siham; Fecher, Gerhard H.; ViolBarbosa, Carlos E.; Felser, Claudia; Gao, Li; Kellock, Andrew; Roche, Kevin P.; Samant, Mahesh G.; Parkin, Stuart S. P.; Ikenaga, Eiji

    2013-04-29

    Thin films of the proposed topological insulator LuPdBi-a Heusler compound with the C1{sub b} structure-were prepared on Ta-Mo-buffered MgO(100) substrates by co-sputtering from PdBi{sub 2} and Lu targets. Epitaxial growth of LuPdBi films was confirmed by X-ray diffraction and reflection high-energy electron diffraction. The root-mean-square roughness of the films was as low as 1.45 nm, even though the films were deposited at high temperature. The film composition is close to the ideal stoichiometric ratio. The valence band spectra of the LuPdBi films, observed by hard X-ray photoelectron spectroscopy, correspond very well with the ab initio-calculated density of states.

  8. Distinctions of the growth and structural-spectroscopic investigations of thin AlN films grown on the GaAs substrates

    NASA Astrophysics Data System (ADS)

    Seredin, P. V.; Kashkarov, V. M.; Arsentyev, I. N.; Bondarev, A. D.; Tarasov, I. S.

    2016-08-01

    Using X-ray diffraction analysis, atomic force microscopy, IR and UV spectroscopy, the properties of thin aluminium nitride films (<200 nm) that were obtained by ion-plasma reactive sputtering on GaAs substrates with different orientations were studied. The films of aluminium nitride can have a refractive index within the range of 1.6-4.0 for the wavelength band around ~250 nm and an optical band-gap of ~5 eV. It was shown that the morphology, surface composition and optical functional characteristics of AlN/GaAs heterophase systems can be controlled owing to the use of misoriented GaAs substrates as well choice of the technological parameters used for the film growth.

  9. Dielectric and ferroelectric properties of highly oriented (Pb,Nb)(Zr,Sn,Ti)O3 thin films grown by a sol-gel process

    NASA Astrophysics Data System (ADS)

    Jiwei, Zhai; Cheung, M. H.; Xu, Zheng Kui; Li, Xin; Chen, Haydn; Colla, Eugene V.; Wu, T. B.

    2002-11-01

    Antiferroelectric (Pb,Nb)(Zr,Sn,Ti)O3 thin films were deposited via a sol-gel process on LaNiO3-coated silicon substrates. Films showed a strong (001) preferred orientation upon annealing at 500-700 degC for 30 min. The dependence of electrical properties on film thickness has been studied, with the emphasis placed on field-induced phase switching from the antiferroelectric to the ferroelectric state. The decrease of film thickness led to an increase of the phase-switching field along with the appearance of remanent polarization. However, the dielectric constant and maximum polarization decreased with the reduction of film thickness. Saturation polarization was 35 muC/cm2, which is equal to that observed in bulk samples.

  10. 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.

  11. Surface segregation as a means of gettering Cu in liquid-phase-epitaxy silicon thin layers grown from Al-Cu-Si solutions

    SciTech Connect

    Wang, T.H.; Ciszek, T.F.; Reedy, R.; Asher, S.; King, D.

    1996-05-01

    The authors demonstrate that, by using the natural surface segregation phenomenon, Cu can be gettered to the surface from the bulk of silicon layers so that its concentrations in the liquid-phase-epitaxy (LPE) layers are much lower than its solubility at the layer growth temperature and the reported 10{sup 17} cm{sup {minus}3} degradation threshold for solar-cell performance. Secondary-ion mass spectroscopy (SIMS) analysis indicates that, within a micron-deep sub-surface region, Cu accumulates even in as-grown LPE samples. Slower cooling after growth to room temperature enhances this Cu enrichment. X-ray photoelectron spectroscopy (XPS) measurement shows as much as 3.2% Cu in a surface region of about 50 {Angstrom}. More surface-sensitive, ion-scattering spectroscopy (ISS) analysis further reveals about 7% of Cu at the top surface. These results translate to an areal gettering capacity of about 1.0 x 10{sup 16} cm{sup {minus}2}, which is higher than the available total-area density of Cu in the layer and substrate (3.6 x 10{sup 15} cm{sup {minus}2} for a uniform 1.2 x 10{sup 17}cm{sup {minus}3} Cu throughout the layer and substrate with a total thickness of 300 {mu}m).

  12. Wear resistance of ZrC/TiN and ZrC/ZrN thin multilayers grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Craciun, D.; Socol, G.; Dorcioman, G.; Niculaie, S.; Bourne, G.; Zhang, J.; Lambers, E.; Siebein, K.; Craciun, V.

    2013-03-01

    ZrC/TiN and ZrC/ZrN multilayers thinner than 350 nm were grown on (100) Si substrates at a temperature of 300 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser ( λ=248 nm, pulse duration τ=25 ns, 8.0 J/cm2 fluence and 40 Hz repetition rate). Cross-sectional transmission electron microscopy, Auger electron spectroscopy depth profiling and simulations of X-ray reflectivity curves indicated that there was intermixing between the deposited layers at the interfaces as well as between the first layer and the substrate. Nanoindentation investigations found hardness values between 35 and 38 GPa for the deposited multilayers. Linear unidirectional sliding wear tests were conducted using a ball-on-plate tribometer under 1 N normal force. Wear tracks were produced in a Hysitron nanoindenter with 1 μm radius diamond tip under a 500 μN load. High-resolution cross-sectional transmission electron microscopy studies of the wear tracks showed that the multilayers withstood these tests without significant damage. The results could be explained by the use of a high laser fluence during deposition that resulted in very dense and strongly adherent nanocrystalline layers.

  13. Densitometric validation and analysis of biomarker β-amyrin in different Acacia species (leaves) grown in Kingdom of Saudi Arabia by high performance thin-layer chromatography.

    PubMed

    Alam, Perwez; Alajmi, Mohamed Fahad; Siddiqui, Nasir Ali; Al-Rehaily, Adnan Jathlan; Alharbi, Hattan; Basudan, Omer Ahmed; Hussain, Afzal

    2015-07-01

    Biomarker β-amyrin was analyzed in the leaves of four different Acacia species (A. salicina, A. loreta, A. hamulosa and A. tortilis) grown in Kingdom of Saudi Arabia by a validated HPTLC method. The chromatography was performed on glass-backed silica gel 60 F254 HPTLC plates using solvents toluene: methanol (9:1, v/v) as mobile phase. The developed TLC plate was derivatized with anisaldehyde and scanned at 520 nm. A sharp peak of β-amyrin was found at Rf=0.58±0.01. The r2 and the linear regression equation for β-amyrin was found to be 0.991 and 19.913X+107.803, respectively in the concentration range of 100-800 ng. The percentage of β-amyrin was found to be maximum 2.70% w/w in A. tortilis, 1.85% w/w in A. loreta and 1.80% w/w in A. hamulosa while it was totally absent in A. salicina. This study conceives maiden reporting of quantification of β-amyrin in four different species of Acacia by validated HPTLC method. The developed method for the analysis of β-amyrin was proved to be reproducible by statistical analysis hence it can be employed for further analysis of β-amyrin in plasma, other biological fluids and in finished products available in the market.

  14. Effect of wettability on surface morphologies and optical properties of Ag thin films grown on glass and polymer substrates by thermal evaporation

    NASA Astrophysics Data System (ADS)

    Lv, Jing

    2013-05-01

    A series of Ag films with different thicknesses were deposited on BK-7 glass, PET and PC substrates under identical conditions by thermal evaporation. The effect of the wettability on the morphology and optical properties of Ag/glass and Ag/polymer films was studied by atomic force microscopy and spectrophotometry. The experimental results show that the wettability of Ag grains with polymer is stronger than with glass, which results in the aggregation of bigger grains in initial layer. During deposition the interaction of interlayer plays an important role for the formation of the surface morphology. The strong wettability activates the nonlinear optical properties of Ag grains grown on polymer substrates, which result in the strong absorbance in short wavelength. The effect of the bare substrate on the transmittance of Ag films is more obvious than the reflectance. With the increasing of the thickness, the effect of the wettability on the morphology and optical properties of Ag films decline. In this experiment when the thickness is above 50 nm, the effect almost vanished.

  15. Molecular-beam epitaxy of Co2MnSi Heusler alloy thin films epitaxially grown on Si(0 0 1)

    NASA Astrophysics Data System (ADS)

    Stephan, R.; Dulot, F.; Mehdaoui, A.; Berling, D.; Wetzel, P.

    We report on the investigation of structural and magnetic properties of the ternary Heusler alloy Co2MnSi grown on Si(0 0 1) by molecular-beam epitaxy. Low-energy electron diffraction (LEED), inelastic medium-energy electron diffraction (IMEED) and X-ray photoelectron diffraction (XPD) measurements clearly show the growth of crystalline Co2MnSi. The best crystallographic and magnetic quality of the Co2MnSi films have been achieved after codeposition of the three Co, Mn and Si elements on the Si(0 0 1) substrate held at 587 K. Quantitative determinations of magnetic anisotropies were performed using transverse bias initial inverse susceptibility and torque measurements (TBIIST). Co2MnSi reveals to have an in-plane fourfold magnetocrystalline anisotropy with easy axis along <0 1 0> directions for evaporation fluxes perpendicular to the substrate surface. On the other hand, grazing-incidence fluxes invariably generate a dominant uniaxial in-plane magnetic anisotropy contribution with easy axis perpendicular to the incidence plane.

  16. Angle-resolved photoemission study of thin molecular-beam-epitaxy-grown α-Sn1-xGex films with x~0.5

    NASA Astrophysics Data System (ADS)

    Höchst, Hartmut; Engelhardt, Michael A.; Hernández-Calderón, Isaac

    1989-11-01

    Angle-resolved synchrotron-radiation photoemission spectroscopy is used to study the electronic structure of metastable epitaxial films of α-Sn1-xGex alloys. Homogeneous crystalline alloy films were grown by molecular-beam epitaxy on Ge(100) substrates at ~400 °C up to a thickness of ~300 Å. Photoemission core-level analysis indicates a strong tendency to form a compound with a composition close to x~0.5. Angle-resolved spectra show a shift of the Γ8 valence band from ~0.6 eV in Ge(100) to ~0.16 eV below EF in the α-Sn0.48Ge0.52 alloy. The experimental information of a constant alloy Fermi level locates the top of the Γ8 valence band ~0.16 eV below EF. Assuming a linear band model, the direct band gap of Eg~0.2 eV for x~0.5 will then locate the bottom of the Γ7 conduction band ~0.04 eV above EF.

  17. Comprehensive strain and band gap analysis of PA-MBE grown AlGaN/GaN heterostructures on sapphire with ultra thin buffer

    SciTech Connect

    Mahata, Mihir Kumar; Ghosh, Saptarsi; Jana, Sanjay Kumar; Bag, Ankush; Kumar, Rahul; Chakraborty, Apurba; Biswas, Dhrubes; Mukhopadhyay, Partha

    2014-11-15

    In this work, cluster tool (CT) Plasma Assisted Molecular Beam Epitaxy (PA-MBE) grown AlGaN/GaN heterostructure on c-plane (0 0 0 1) sapphire (Al{sub 2}O{sub 3}) were investigated by High Resolution X-ray Diffraction (HRXRD), Room Temperature Raman Spectroscopy (RTRS), and Room Temperature Photoluminescence (RTPL). The effects of strain and doping on GaN and AlGaN layers were investigated thoroughly. The out-of-plane (‘c’) and in-plane (‘a’) lattice parameters were measured from RTRS analysis and as well as reciprocal space mapping (RSM) from HRXRD scan of (002) and (105) plane. The in-plane (out-of plane) strain of the samples were found to be −2.5 × 10{sup −3}(1 × 10{sup −3}), and −1.7 × 10{sup −3}(2 × 10{sup −3}) in GaN layer and 5.1 × 10{sup −3} (−3.3 × 10{sup −3}), and 8.8 × 10{sup −3}(−1.3 × 10{sup −3}) in AlGaN layer, respectively. In addition, the band structures of AlGaN/GaN interface were estimated by both theoretical (based on elastic theory) and experimental observations of the RTPL spectrum.

  18. Densitometric validation and analysis of biomarker β-amyrin in different Acacia species (leaves) grown in Kingdom of Saudi Arabia by high performance thin-layer chromatography.

    PubMed

    Alam, Perwez; Alajmi, Mohamed Fahad; Siddiqui, Nasir Ali; Al-Rehaily, Adnan Jathlan; Alharbi, Hattan; Basudan, Omer Ahmed; Hussain, Afzal

    2015-07-01

    Biomarker β-amyrin was analyzed in the leaves of four different Acacia species (A. salicina, A. loreta, A. hamulosa and A. tortilis) grown in Kingdom of Saudi Arabia by a validated HPTLC method. The chromatography was performed on glass-backed silica gel 60 F254 HPTLC plates using solvents toluene: methanol (9:1, v/v) as mobile phase. The developed TLC plate was derivatized with anisaldehyde and scanned at 520 nm. A sharp peak of β-amyrin was found at Rf=0.58±0.01. The r2 and the linear regression equation for β-amyrin was found to be 0.991 and 19.913X+107.803, respectively in the concentration range of 100-800 ng. The percentage of β-amyrin was found to be maximum 2.70% w/w in A. tortilis, 1.85% w/w in A. loreta and 1.80% w/w in A. hamulosa while it was totally absent in A. salicina. This study conceives maiden reporting of quantification of β-amyrin in four different species of Acacia by validated HPTLC method. The developed method for the analysis of β-amyrin was proved to be reproducible by statistical analysis hence it can be employed for further analysis of β-amyrin in plasma, other biological fluids and in finished products available in the market. PMID:26431661

  19. X-ray magnetic spectroscopy of MBE-grown Mn-doped Bi{sub 2}Se{sub 3} thin films

    SciTech Connect

    Collins-McIntyre, L. J.; Watson, M. D.; Zhang, S. L.; Coldea, A. I.; Hesjedal, T.; Baker, A. A.; Harrison, S. E.; Pushp, A.; Kellock, A. J.; Parkin, S. S. P.; Laan, G. van der

    2014-12-15

    We report the growth of Mn-doped Bi{sub 2}Se{sub 3} thin films by molecular beam epitaxy (MBE), investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), SQUID magnetometry and x-ray magnetic circular dichroism (XMCD). Epitaxial films were deposited on c-plane sapphire substrates by co-evaporation. The films exhibit a spiral growth mechanism typical of this material class, as revealed by AFM. The XRD measurements demonstrate a good crystalline structure which is retained upon doping up to ∼7.5 atomic-% Mn, determined by Rutherford backscattering spectrometry (RBS), and show no evidence of the formation of parasitic phases. However an increasing interstitial incorporation of Mn is observed with increasing doping concentration. A magnetic moment of 5.1 μ{sub B}/Mn is obtained from bulk-sensitive SQUID measurements, and a much lower moment of 1.6 μ{sub B}/Mn from surface-sensitive XMCD. At ∼2.5 K, XMCD at the Mn L{sub 2,3} edge, reveals short-range magnetic order in the films and indicates ferromagnetic order below 1.5 K.

  20. Strain-dependence Of The Structure And Ferroic Properties Of Epitaxial Ni-1 (-) Ti-x(1) (-) O-y(3) Thin Films Grown On Sapphire Substrates

    SciTech Connect

    Varga, Tamas; Droubay, Timothy C.; Bowden, Mark E.; Stephens, Sean A.; Manandhar, Sandeep; Shutthanandan, V.; Colby, Robert J.; Hu, Dehong; Shelton, William A.; Chambers, Scott A.

    2015-03-01

    Polarization-induced weak ferromagnetism has been predicted a few years back in perovskite MTiO3 (M = Fe, Mn, Ni) [Fennie, Phys. Rev. Lett. 100, 167203 (2008)]. We set out to stabilize this metastable perovskite structure by growing NiTiO3 epitaxially on sapphire Al2O3 (001) substrate, and to control the polar and magnetic properties via strain. Epitaxial Ni1-xTi1-yO3 films of different Ni/Ti ratios and thicknesses were deposited on Al2O3 substrates by pulsed laser deposition at different temperatures, and characterized using several techniques. The effect of film thickness, deposition temperature, and film stoichiometry on lattice strain, film structure, and physical properties was investigated. Our structural data from x-ray diffraction, electron microscopy, and x-ray absorption spectroscopy shows that substrate-induced strain has a marked effect on the structure and crystalline quality of the films. Physical property measurements reveal a dependence of the Néel transition and lattice polarization on strain, and highlight our ability to control the ferroic properties in NiTiO3 thin films by film stoichiometry and thickness.

  1. Structural and dynamical magnetic response of co-sputtered Co2FeAl heusler alloy thin films grown at different substrate temperatures

    NASA Astrophysics Data System (ADS)

    Yadav, Anjali; Chaudhary, Sujeet

    2014-04-01

    The interdependence between the dynamical magnetic response and the microstructural properties such as crystallinity, lateral crystallite size, structural ordering of the co-sputtered polycrystalline Co2FeAl thin films on Si (100) are studied by varying the growth temperature from room temperature (RT) to 600 °C. Frequency (7-11 GHz) dependent in-plane ferromagnetic resonance (FMR) studies were carried out by using co-planar waveguide to estimate Gilbert damping constant (α) and effective saturation magnetization (4πMeff). The improvement in crystallinity, larger crystallite and particle sizes of the films are critical in obtaining films with lower α and higher 4πMeff. Increase in the lattice constant with substrate temperature indicates the improvement in the structural ordering at higher temperatures. Minimum value of α is found to be 0.005 ± 0.0003 for the film deposited at 500 °C, which is comparable to the values reported for epitaxial Co2FeAl films. The value of 4πMeff is found to increase from 1.32 to 1.51 T with the increase in deposition temperature from RT to 500 °C. The study also shows that the root mean square (rms) roughness linearly affects the FMR in-homogenous line broadening and the anisotropy field.

  2. Strain-Dependence of the Structure and Ferroic Properties of Epitaxial NiTiO 3 Thin Films Grown on Different Substrates

    DOE PAGES

    Varga, Tamas; Droubay, Timothy C.; Bowden, Mark E.; Kovarik, Libor; Hu, Dehong; Chambers, Scott A.

    2015-01-01

    Polarization-induced weak ferromagnetism has been predicted a few years back in perovskite MTiO 3 (M = Fe, Mn, and Ni). We set out to stabilize this metastable perovskite structure by growing NiTiO 3 epitaxially on different substrates and to investigate the dependence of polar and magnetic properties on strain. Epitaxial NiTiO 3 films were deposited on Al 2 O 3 , Fe 2 O 3 , and LiNbO 3 substrates by pulsed laser deposition and characterized using several techniques. The effect of substrate choice on lattice strain, film structure, and physical properties was investigated. Our structural data from X-raymore » diffraction and electron microscopy shows that substrate-induced strain has a marked effect on the structure and crystalline quality of the films. Physical property measurements reveal a dependence of the weak ferromagnetism and lattice polarization on strain and highlight our ability to control the ferroic properties in NiTiO 3 thin films by the choice of substrate. Our results are also consistent with the theoretical prediction that the ferromagnetism in acentric NiTiO 3 is polarization induced. From the substrates studied here, the perovskite substrate LiNbO 3 proved to be the most promising one for strong multiferroism.« less

  3. Process optimization of deposition conditions of PbS thin films grown by a successive ionic layer adsorption and reaction (SILAR) method using response surface methodology

    NASA Astrophysics Data System (ADS)

    Yücel, Ersin; Yücel, Yasin; Beleli, Buse

    2015-07-01

    In this study, lead sulfide (PbS) thin films were synthesized by a successive ionic layer adsorption and reaction (SILAR) method with different pH, dipping time and dipping cycles. Response surface methodology (RSM) and central composite design (CCD) were successfully used to optimize the PbS films deposition parameters and understand the significance and interaction of the factors affecting the film quality. 5-level-3-factor central composite design was employed to evaluate the effects of the deposition parameters (pH, dipping time and dipping cycles) on the response (the optical band gap of the films). Data obtained from RSM were subjected to the analysis of variance (ANOVA) and analyzed using a second order polynomial equation. The optimal conditions for the PbS films deposition have been found to be: pH of 9.1, dipping time of 10 s and dipping cycles of 10 cycles. The predicted band gap of PbS film was 2.13 eV under the optimal conditions. Verification experiment (2.24 eV) confirmed the validity of the predicted model. The film structures were characterized by X-ray diffractometer (XRD). Morphological properties of the films were studied with a scanning electron microscopy (SEM). The optical properties of the films were investigated using a UV-visible spectrophotometer.

  4. Strain-dependence Of The Structure And Ferroic Properties Of Epitaxial NiTiO3 Thin Films Grown On Different Substrates

    SciTech Connect

    Varga, Tamas; Droubay, Timothy C.; Bowden, Mark E.; Kovarik, Libor; Hu, Dehong; Chambers, Scott A.

    2015-08-14

    Polarization-induced weak ferromagnetism has been predicted a few years back in perovskite MTiO3 (M = Fe, Mn, Ni) [Fennie, Phys. Rev. Lett. 100, 167203 (2008)]. We set out to stabilize this metastable perovskite structure by growing NiTiO3 epitaxially on different substrates, and to investigate the dependence of polar and magnetic properties on strain. Epitaxial NiTiO3 films were deposited on Al2O3, Fe2O3, and LiNbO3 substrates by pulsed laser deposition, and characterized using several techniques. The effect of substrate choice on lattice strain, film structure, and physical properties was investigated. Our structural data from x-ray diffraction and electron microscopy shows that substrate-induced strain has a marked effect on the structure and crystalline quality of the films. Physical property measurements reveal a dependence of the weak ferromagnetism and lattice polarization on strain, and highlight our ability to control the ferroic properties in NiTiO3 thin films by the choice of substrate. Our results are also consistent with the theoretical prediction that the ferromagnetism in acentric NiTiO3 is polarization-induced. From the substrates studied here, the perovskite substrate LiNbO3 proved to be the most promising one for strong multiferroism.

  5. Tuning of the surface plasmon resonance in TiO{sub 2}/Au thin films grown by magnetron sputtering: The effect of thermal annealing

    SciTech Connect

    Torrell, M.; Kabir, R.; Cunha, L.; Vasilevskiy, M. I.; Vaz, F.; Cavaleiro, A.; Alves, E.; Barradas, N. P.

    2011-04-01

    Nanocomposites consisting of a dielectric matrix, such as TiO{sub 2}, with embedded noble metal nanoparticles (NPs) possess specific optical properties due to the surface plasmon resonance (SPR) effect, interesting for several applications. The aim of this work is to demonstrate that these properties are sensitive to the nanostructure of magnetron-sputtered TiO{sub 2}/Au thin films, which can be tuned by annealing. We study the role of the shape and size distribution of the NPs, as well as the influence of the crystallinity and phase composition of the host matrix on the optical response of the films. All these characteristics can be modified by vacuum annealing treatments of the deposited films. A theoretical interpretation and modeling of the experimental results obtained is presented. The model involves a modified Maxwell-Garnett approach for the effective dielectric function of the composite (describing the SPR effect) and the transfer matrix formalism for multilayer optics. Input data are based on the experimental information obtained from the detailed structural characterization of the films. It is shown that the annealing treatments can be used for controlling the optical properties of the composite films, making them attractive for decorative coatings.

  6. Local structures and interface morphology of InxGa1-xAs1-yNy thin films grown on GaAs

    NASA Astrophysics Data System (ADS)

    Soo, Y. L.; Huang, S.; Kao, Y. H.; Chen, J. G.; Hulbert, S. L.; Geisz, J. F.; Kurtz, Sarah; Olson, J. M.; Kurtz, Steven R.; Jones, E. D.; Allerman, A. A.

    1999-11-01

    X-ray absorption fine-structure techniques have been utilized to probe the short-range structures around N and In in InxGa1-xAs1-yNy compounds containing about 3% of N and 8% of In. Our results indicate that N impurities most likely substitute for As atoms in the system. The In-As interatomic distance in these compounds remains practically the same as in InAs, while the coordination number of As atoms around In shows possible variations with changes in the material characteristics. The N atoms play an important role in affecting the changes of band gap while also serving as ``strain moderators'' by providing a tensile strain in the film to counteract the compressive strain caused by the In impurities. Further, grazing incidence x-ray scattering measurements of InxGa1-xAs1-yNy/GaAs heterojunctions provide direct evidence that the InxGa1-xAs1-yNy thin films can indeed be lattice matched to GaAs substrates resulting in a reasonably smooth heterointerface.

  7. Incorporation of La in epitaxial SrTiO{sub 3} thin films grown by atomic layer deposition on SrTiO{sub 3}-buffered Si (001) substrates

    SciTech Connect

    McDaniel, Martin D.; Ngo, Thong Q.; Ekerdt, John G.; Posadas, Agham; Demkov, Alexander A.; Karako, Christine M.; Bruley, John; Frank, Martin M.; Narayanan, Vijay

    2014-06-14

    Strontium titanate, SrTiO{sub 3} (STO), thin films incorporated with lanthanum are grown on Si (001) substrates at a thickness range of 5–25 nm. Atomic layer deposition (ALD) is used to grow the La{sub x}Sr{sub 1−x}TiO{sub 3} (La:STO) films after buffering the Si (001) substrate with four-unit-cells of STO deposited by molecular beam epitaxy. The crystalline structure and orientation of the La:STO films are confirmed via reflection high-energy electron diffraction, X-ray diffraction, and cross-sectional transmission electron microscopy. The low temperature ALD growth (∼225 °C) and post-deposition annealing at 550 °C for 5 min maintains an abrupt interface between Si (001) and the crystalline oxide. Higher annealing temperatures (650 °C) show more complete La activation with film resistivities of ∼2.0 × 10{sup −2} Ω cm for 20-nm-thick La:STO (x ∼ 0.15); however, the STO-Si interface is slightly degraded due to the increased annealing temperature. To demonstrate the selective incorporation of lanthanum by ALD, a layered heterostructure is grown with an undoped STO layer sandwiched between two conductive La:STO layers. Based on this work, an epitaxial oxide stack centered on La:STO and BaTiO{sub 3} integrated with Si is envisioned as a material candidate for a ferroelectric field-effect transistor.

  8. Layer-by-layer grown scalable redox-active ruthenium-based molecular multilayer thin films for electrochemical applications and beyond.

    PubMed

    Kaliginedi, Veerabhadrarao; Ozawa, Hiroaki; Kuzume, Akiyoshi; Maharajan, Sivarajakumar; Pobelov, Ilya V; Kwon, Nam Hee; Mohos, Miklos; Broekmann, Peter; Fromm, Katharina M; Haga, Masa-aki; Wandlowski, Thomas

    2015-11-14

    Here we report the first study on the electrochemical energy storage application of a surface-immobilized ruthenium complex multilayer thin film with anion storage capability. We employed a novel dinuclear ruthenium complex with tetrapodal anchoring groups to build well-ordered redox-active multilayer coatings on an indium tin oxide (ITO) surface using a layer-by-layer self-assembly process. Cyclic voltammetry (CV), UV-Visible (UV-Vis) and Raman spectroscopy showed a linear increase of peak current, absorbance and Raman intensities, respectively with the number of layers. These results indicate the formation of well-ordered multilayers of the ruthenium complex on ITO, which is further supported by the X-ray photoelectron spectroscopy analysis. The thickness of the layers can be controlled with nanometer precision. In particular, the thickest layer studied (65 molecular layers and approx. 120 nm thick) demonstrated fast electrochemical oxidation/reduction, indicating a very low attenuation of the charge transfer within the multilayer. In situ-UV-Vis and resonance Raman spectroscopy results demonstrated the reversible electrochromic/redox behavior of the ruthenium complex multilayered films on ITO with respect to the electrode potential, which is an ideal prerequisite for e.g. smart electrochemical energy storage applications. Galvanostatic charge-discharge experiments demonstrated a pseudocapacitor behavior of the multilayer film with a good specific capacitance of 92.2 F g(-1) at a current density of 10 μA cm(-2) and an excellent cycling stability. As demonstrated in our prototypical experiments, the fine control of physicochemical properties at nanometer scale, relatively good stability of layers under ambient conditions makes the multilayer coatings of this type an excellent material for e.g. electrochemical energy storage, as interlayers in inverted bulk heterojunction solar cell applications and as functional components in molecular electronics applications

  9. The cytotoxicity of NiO nanoparticle with borate capping.

    PubMed

    Liu, Zunjing; Wang, Yongjing; Pan, Danmei; Chen, Zhi; Pan, Xiaohong; Wang, Yonghao; Lin, Zhang

    2011-11-01

    The impact of surface capping on cytotoxicity of NiO nanoparticle was investigated with Escherichia coil (E.coli) in this work. The NiO nanoparticle and NiO nanoparticle capped by borate (denoted as NiO-borate) were synthesized by hydrothermal method. The average size of both nanoparticles is about 4.0 nm. The plate experiments demonstrated that NiO-borate nanoparticles show lower cytotoxicity than NiO nanopaticles. Further spectrophotometric analysis revealed that the concentration of both extracellular and intercellular Ni2+ in NiO-borate system were lower than that of uncapped one. Intracellular ICP-AES analysis also showed the concentration of Ni element was higher than Ni2+, suggesting the NiO nanoparticles might penetrate into the cellular interior. Comprehensive AFM, SEM and TEM observation illustrated both NiO-borate and NiO nanoparticles lead to the collapse of cellular body, the convex on the cell wall and the damage of cell wall ultimately. In summary, the surface capping with borate on NiO nanopaticles will suppress the release of the Ni2+ ions and impede the contact between the NiO nanoparticle and cell wall, which ultimately decreased the cytotoxicity of NiO nanoparticles.

  10. Aluminum doped nickel oxide thin film with improved electrochromic performance from layered double hydroxides precursor in situ pyrolytic route

    NASA Astrophysics Data System (ADS)

    Shi, Jingjing; Lai, Lincong; Zhang, Ping; Li, Hailong; Qin, Yumei; Gao, Yuanchunxue; Luo, Lei; Lu, Jun

    2016-09-01

    Electrochromic materials with unique performance arouse great interest on account of potential application values in smart window, low-power display, automobile anti-glare rearview mirror, and e-papers. In this paper, high-performing Al-doped NiO porous electrochromic film grown on ITO substrate has been prepared via a layered double hydroxides(LDHs) precursor in situ pyrolytic route. The Al3+ ions distributed homogenously within the NiO matrix can significantly influence the crystallinity of Ni-Al LDH and NiO:Al3+ films. The electrochromic performance of the films were evaluated by means of UV-vis absorption spectroscopy, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry(CA) measurements. In addition, the ratio of Ni3+/Ni2+ also varies with Al content which can lead to different electrochemical performances. Among the as-prepared films, NiO film prepared from Ni-Al (19:1) LDH show the best electrochromic performance with a high transparency of 96%, large optical modulation range (58.4%), fast switching speed (bleaching/coloration times are 1.8/4.2 s, respectively) and excellent durability (30% decrease after 2000 cycles). The improved performance was owed to the synergy of large NiO film specific surface area and porous morphology, as well as Al doping stifled the formation of Ni3+ making bleached state more pure. This LDHs precursor pyrolytic method is simple, low-cost and environmental benign and is feasible for the preparation of NiO:Al and other Al-doped oxide thin film.

  11. Effect of NiO crystallinity on forming characteristics in Pt/NiO/Pt cells as resistive switching memories

    NASA Astrophysics Data System (ADS)

    Nishi, Yusuke; Kimoto, Tsunenobu

    2016-09-01

    Resistive switching (RS) in metal/oxide/metal stack structures plays a key role in resistive RAM. The formation and rupture of conductive filaments have been widely accepted as an origin of RS mechanism especially in binary transition metal oxides. Forming exhibits some analogies with a dielectric breakdown of SiO2 thin films. In this study, Time-Dependent Forming (TDF) characteristics of Pt/NiO/Pt stack structures have been investigated. The results revealed that the formation of conductive filaments at the forming process by applying constant voltage followed a weakest-link theory and that the weakest spots were almost randomly distributed in NiO thin films according to the Poisson statistics. Furthermore, the distribution of TDF characteristics depends on NiO crystallinity. A small variation of initial resistance tends to result in a large variation of time to forming and vice versa.

  12. Solution-Processible Crystalline NiO Nanoparticles for High-Performance Planar Perovskite Photovoltaic Cells

    PubMed Central

    Kwon, Uisik; Kim, Bong-Gi; Nguyen, Duc Cuong; Park, Jong-Hyeon; Ha, Na Young; Kim, Seung-Joo; Ko, Seung Hwan; Lee, Soonil; Lee, Daeho; Park, Hui Joon

    2016-01-01

    In this work, we report on solution-based p-i-n-type planar-structured CH3NH3PbI3 perovskite photovoltaic (PV) cells, in which precrystallized NiO nanoparticles (NPs) without post-treatment are used to form a hole transport layer (HTL). X-ray diffraction and high-resolution transmission electron microscopy showed the crystallinity of the NPs, and atomic force microscopy and scanning electron microscopy confirmed the uniform surfaces of the resultant NiO thin film and the subsequent perovskite photoactive layer. Compared to the conventional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL, the NiO HTL had excellent energy-level alignment with that of CH3NH3PbI3 and improved electron-blocking capability, as analyzed by photoelectron spectroscopy and diode modeling, resulting in Voc ~0.13 V higher than conventional PEDOT:PSS-based devices. Consequently, a power conversion efficiency (PCE) of 15.4% with a high fill factor (FF, 0.74), short-circuit current density (Jsc, 20.2 mA·cm−2), and open circuit voltage (Voc, 1.04 V) having negligible hysteresis and superior air stability has been achieved. PMID:27465263

  13. Solution-Processible Crystalline NiO Nanoparticles for High-Performance Planar Perovskite Photovoltaic Cells

    NASA Astrophysics Data System (ADS)

    Kwon, Uisik; Kim, Bong-Gi; Nguyen, Duc Cuong; Park, Jong-Hyeon; Ha, Na Young; Kim, Seung-Joo; Ko, Seung Hwan; Lee, Soonil; Lee, Daeho; Park, Hui Joon

    2016-07-01

    In this work, we report on solution-based p-i-n-type planar-structured CH3NH3PbI3 perovskite photovoltaic (PV) cells, in which precrystallized NiO nanoparticles (NPs) without post-treatment are used to form a hole transport layer (HTL). X-ray diffraction and high-resolution transmission electron microscopy showed the crystallinity of the NPs, and atomic force microscopy and scanning electron microscopy confirmed the uniform surfaces of the resultant NiO thin film and the subsequent perovskite photoactive layer. Compared to the conventional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL, the NiO HTL had excellent energy-level alignment with that of CH3NH3PbI3 and improved electron-blocking capability, as analyzed by photoelectron spectroscopy and diode modeling, resulting in Voc ~0.13 V higher than conventional PEDOT:PSS-based devices. Consequently, a power conversion efficiency (PCE) of 15.4% with a high fill factor (FF, 0.74), short-circuit current density (Jsc, 20.2 mA·cm‑2), and open circuit voltage (Voc, 1.04 V) having negligible hysteresis and superior air stability has been achieved.

  14. Transport properties and c/a ratio of V{sub 2}O{sub 3} thin films grown on C- and R-plane sapphire substrates by pulsed laser deposition

    SciTech Connect

    Sakai, Joe; Limelette, Patrice

    2015-12-14

    We prepared V{sub 2}O{sub 3} thin films on C- or R-plane sapphire (Al{sub 2}O{sub 3}) substrates by a pulsed laser deposition method. X-ray diffraction analyses confirmed that single-phase V{sub 2}O{sub 3} films were epitaxially grown on both C- and R-planes under an Ar gas ambient of 2 × 10{sup −2} mbar at a substrate temperature of 873 K. Depending on the deposition conditions, c/a ratios at room temperature of (0001)-oriented V{sub 2}O{sub 3} films widely ranged from 2.79 to 2.88. Among them, the films of 2.81 ≤ c/a ≤ 2.84 showed complex metal (M)–insulator (I)–M transition during cooling from 300 to 10 K, while those of larger c/a ratios were accompanied by metallic properties throughout this temperature range. All the films on R-plane substrates underwent simple M-I transition at ∼150 K, which was more abrupt than the films on C-plane, whereas their c/a ratios were narrowly distributed. The distinct difference of M-I transition properties between C- and R-plane films is explained by the intrinsic a- and c-axes evolution through the transition from M to I phases.

  15. Synthesis and characterization of electron doped La{sub 0.85}Te{sub 0.15}MnO{sub 3} thin film grown on LaAlO{sub 3} substrate by pulsed laser deposition technique

    SciTech Connect

    Bhat, Irshad Husain, Shahid; Patil, S. I.; Khan, Wasi; Ali, S. Asad

    2015-06-24

    We report the structural, morphological and magneto-transport properties of electron doped La{sub 0.85}Te{sub 0.15}MnO{sub 3} (LTMO) thin film grown on (001) LaAlO{sub 3} single crystal substrate by pulsed laser deposition (PLD). X-ray diffraction (XRD) results confirm that the film has good crystalline quality, single phase, and c-axis orientation. The atomic force microscopy (AFM) results have revealed that the film consists of grains with the average size in a range of 20–30 nm and root-mean square (rms) roughness of 0.27nm. The resistivity versus temperature measurement exhibits an insulator to metal transition (MIT). We have noticed a huge value of magnetoresistance (∼93%) close to MIT in presence of 8T field. X-ray photoemission spectroscopy confirms the electron doping and suggests that Te ions could be in the Te{sup 4+} state, while the Mn ions stay in the Mn{sup 2+} and Mn{sup 3+} valence state.

  16. Heterogeneous distribution of B-site cations in BaZrxTi1-xO3 epitaxial thin films grown on (0 0 1) SrTiO3 by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Ventura, J.; Polo, M. C.; Ferrater, C.; Hernández, S.; Sancho-Parramón, J.; Coy, L. E.; Rodríguez, L.; Canillas, A.; Fábrega, L.; Varela, M.

    2016-09-01

    The isovalent susbstitution of Ti4+ by Zr4+ in BaZrxTi1-xO3 modifies the dielectric character of ferroelectric BaTiO3 yielding different behaviours such as relaxor, polar cluster, etc. The dynamic coupling between BaTiO3 polar nanoregions and BaZrO3 nonpolar ones as well as microstrain between them are thought to be behind such a rich phase diagram. However, these short-range compositonal variations are elusive to detect and this topic is thus rarely addressed. We have grown epitaxial thin films of BaZrxTi1-xO3 on (0 0 1)-oriented SrTiO3 substrates by pulsed laser deposition sweeping the entire composition range between BaTiO3 and BaZrO3 in increments of 0.1 in x. Several characterization techniques (AFM, TEM, XRD, Raman spectroscopy) were used for this research in order to understand the morphological and structural properties of the deposited films. Ellipsometric measurements allowed the calculation of the band gap energy of the films. This work demonstrates the existence of a heterogeneous distribution in the substitution of titanium by zirconium yielding relaxor and polar cluster nanoregions.

  17. Effect of nitrogen flow rate on structural, morphological and optical properties of In-rich InxAl1-xN thin films grown by plasma-assisted dual source reactive evaporation

    NASA Astrophysics Data System (ADS)

    Alizadeh, M.; Ganesh, V.; Goh, B. T.; Dee, C. F.; Mohmad, A. R.; Rahman, S. A.

    2016-08-01

    In-rich InxAl1-xN thin films were deposited on quartz substrate at various nitrogen flow rates by plasma-assisted dual source reactive evaporation technique. The elemental composition, surface morphology, structural and optical properties of the films were investigated by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Raman spectroscopy, X-ray diffraction (XRD), UV-vis spectrophotometer and photoluminescence (PL) measurements. XPS results revealed that the indium composition (x) of the InxAl1-xN films increases from 0.90 to 0.97 as the nitrogen flow rate is increased from 40 to 100 sccm, respectively. FESEM images of the surface and cross-sectional microstructure of the InxAl1-xN films showed that by increasing the N2 flow rate, the grown particles are highly agglomerated. Raman and XRD results indicated that by increasing nitrogen flow rate the In-rich InxAl1-xN films tend to turn into amorphous state. It was found that band gap energy of the films are in the range of 0.90-1.17 eV which is desirable for the application of full spectra solar cells.

  18. Structural and optical properties of Si-doped Al0.08In0.08Ga0.84N thin films grown on different substrates for optoelectronic devices

    NASA Astrophysics Data System (ADS)

    Ghazai, Alaa Jabbar; Hassan, Haslan Abu; Hassan, Zanuri Bint

    2016-07-01

    The objective of the current study is to characterize the optoelectronic properties of quaternary n-Al0.08In0.08Ga0.84N thin films grown via molecular beam epitaxy (MBE) on sapphire (Al2O3) and silicon (Si) substrates for different optoelectronic applications. Due to mismatch problems between the epilayer and substrates, the AlN buffer layer was inserted at low temperature to reduce the lattice mismatch to approximately 4% for the samples, to produce high-quality epitaxy films. Defect-free films with high structural, optical and electrical qualities were obtained. Their small full width at half maximum, low compressive strain, relatively large grain size and low dislocation density which produced smooth surfaces without any separation phases or cracks were characterized using X-ray diffraction analysis. Scanning electron microscopy, energy-dispersive X-ray microscopy and atomic force microscopy images confirmed these characterizations. Furthermore, high optical quality, as well as high absorption and absorption coefficients were observed using photoluminescence and UV-VIS spectroscopy; however, a red shift was observed in the PL peak of the near band edge of 3.158 eV of the sample on Si substrate compared with 3.37 eV for the sample on sapphire substrate which is attributed to the compressive strain and occurrence of the quantum confined Stark effect.

  19. Structural, magnetic, and Magneto optical properties of Fe3O4/NiO bilayers on MgO(001)

    NASA Astrophysics Data System (ADS)

    Wollschläger, Joachim; Schemme, Tobias; Kuschel, Olga; Witziok, Matthäus; Kuschel, Timo; Kuepper, Karsten

    2016-02-01

    Ultrathin magnetite (Fe3O4) films are attractive for applications in the field of spintronics due to their ferrimagnetic behavior with assumed high degree of spin polarized electrons at the Fermi energy. For these applications, it is necessary to form epitactical bilayer structure combining ferrimagnetic magnetite with an antiferromagnetic layer. Therefore, here we study Fe3O4/NiO bilayers on MgO(001) substrates. Bilayers grown by reactive molecular beam epitaxy are stoichiometric and have well-developed surface and interface structures. The NiO layers are laterally pinned to the structure of the MgO(001) substrate while the magnetite films gradually relax. The interfaces show smooth morphologies and the films have very homogeneous film thickness necessary for spintronical applications. The magnetic and magneto optical properties of the Fe3O4/NiO bilayers were probed by the magneto optical Kerr effect. Compared to single Fe3O4 layers on MgO(001), the bilayers show complicated ferrimagnetic behavior depending on the azimuthal direction of the external applied field. The coercive field of the bilayers, however, is increased with the coercive field of single layer Fe3O4/MgO(001) structures making the Fe3O4/NiO bilayers attractive for spintronic applications.

  20. Facile synthesis of a mechanically robust and highly porous NiO film with excellent electrocatalytic activity towards methanol oxidation.

    PubMed

    Wang, Luoyuan; Zhang, Guoge; Liu, Yan; Li, Wenfang; Lu, Wei; Huang, Haitao

    2016-06-01

    Considerable research is being conducted in searching for effective anode catalysts in alkaline direct methanol fuel cells (DMFCs). Although significant progress has been achieved, it is still challenging to prepare non-Pt catalysts with both excellent activity and good durability. Herein, a highly porous NiO film is developed by a facile and fast anodization approach. The anodic NiO film demonstrates a high surface area, large mesopore volume and small crystallite size, leading to facilitated adsorption of reaction species, easy electrolyte penetration and fast reaction kinetics. Furthermore, as anodic NiO is grown in situ on a metallic substrate with strong adhesion strength and good electrical contact, it can be used directly as an anode catalyst for methanol oxidation without the need to add any binder or conducting agent. Such an additive-free approach greatly expedites the catalyst preparation process. The anodic NiO shows lower methanol oxidation potential, higher oxidation current and better catalytic durability than most of the state-of-the-art Ni-based catalysts reported elsewhere. As anodization is a simple, low cost and easily scaled up method, the work described here provides an exciting direction to speed up the practical application of alkaline DMFCs. PMID:27189412

  1. Synthesis and electrochemical properties of NiO nanospindles

    SciTech Connect

    Zhou, Hai; Lv, Baoliang; Xu, Yao; Wu, Dong

    2014-02-01

    Graphical abstract: NiO nanospindles with a different electrochemical activity as compared to those previous reports were synthesized via an agglomeration–dissolution–recrystallization growth process without the addition of any surfactant. - Highlights: • NiO nanospindles were synthesized without the addition of any surfactant. • The agglomeration–dissolution–recrystallization growth process was used to explain the precursors’ formation process of the spindle-like NiO. • As-obtained spindle-like NiO showed a different electrochemical activity as compared to those previous reports. - Abstract: NiO nanospindles were successfully synthesized via a hydrothermal and post-treatment method. The as-synthesized nanospindles were about several hundred nanometers in width and about one micrometer in length. X-ray diffraction (XRD) analysis revealed that the spindle-like structure was cubic NiO phase crystalline. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) analysis indicated that these NiO nanospindles were of single crystal nature. On the basis of time-dependent experiments, a possible agglomeration–dissolution–recrystallization growth process was proposed to explain the formation process of the spindle-like precursors. The cyclic voltammetry (CV) measurement showed that the as-prepared spindle-like NiO exhibited a pseudo-capacitance behavior.

  2. NiO nanoarrays of a few atoms thickness on 3D nickel network for enhanced pseudocapacitive electrode applications

    NASA Astrophysics Data System (ADS)

    Senthilkumar, Velusamy; Kadumudi, Firoz Babu; Ho, Nhu Thuy; Kim, Ji-Woong; Park, Sungkyun; Bae, Jong-Seong; Choi, Won Mook; Cho, Shinuk; Kim, Yong Soo

    2016-01-01

    The present work focuses on the development of template-free mesoporous NiO nanoarrays with large surface area grown on 3D nickel foam networks by a seed mediated aqueous chemical growth technique and subsequent annealing process. The resultant binder-free, well-aligned and vertically grown NiO nanoarrays exhibits a micron-sized planar structure as well as an ultrathin thickness (˜7 nm). The unique surface and electronic structure facilitates surface-dependent electrochemical reaction processes with no dead volume. They deliver a high capacitance of 2065 F g-1 at a current density of 16 A g-1 as a three electrode system. A specific capacitance of 1247 F g-1 is maintained at a higher current rate of 70 A g-1 with 88.9% retention after 5000 cycles. Finally, in a solid-state asymmetric supercapacitor configuration using NiO//activated carbon, the device delivers an enhanced supercapacitive performance, with an energy density of 43.5 Wh kg-1 and power density of 2.1 kW kg-1. Thus, the current research paves the way for the use of NiO nanoarrays as an electrode material for practical supercapacitor devices with higher cycling retention and rate capacity.

  3. Electrical properties of (110) epitaxial lead-free ferroelectric Na0.5Bi0.5TiO3 thin films grown by pulsed laser deposition: Macroscopic and nanoscale data

    NASA Astrophysics Data System (ADS)

    Bousquet, M.; Duclère, J.-R.; Gautier, B.; Boulle, A.; Wu, A.; Députier, S.; Fasquelle, D.; Rémondière, F.; Albertini, D.; Champeaux, C.; Marchet, P.; Guilloux-Viry, M.; Vilarinho, P.

    2012-05-01

    We report the electrical properties, measured both at the macroscopic and nanometric scales, of epitaxial (110)-Na0.5Bi0.5TiO3 (NBT) thin films grown on (110)Pt/(110)SrTiO3 by pulsed laser deposition (PLD). The influence of the A-site composition (Na and/or Bi excess) on both the structural/microstructural characteristics and the electrical properties is discussed. Whatever the composition of the NBT target, the final layers are systematically epitaxially grown, with NBT crystallites mainly (110)-oriented, and as well (100)-oriented for some minor proportion. Atomic force microscopy (AFM) images reveal the coexistence of two kinds of grains presenting different shapes: namely flat and elongated grains, corresponding to (100)- and (110)-oriented NBT crystallites, respectively. The macroscopic ferroelectric properties were measured at room temperature. A rather well-defined shape of the hysteresis loops was obtained: the incorporation of a Bi excess in the target clearly improves the saturation of the loops. The ferroelectric performances are a remanent polarization (Pr) value, ranging from 7 to 14 μC/cm2, associated with a coercive field (Ec) in the range 68-85 kV/cm. In addition, at 105 Hz, the relative permittivity was about ɛr ˜ 255-410 and the dielectric losses (tan δ) were ˜6%-7%. Finally, the electrical properties at the local scale were investigated by coupling piezoresponse force microscopy (PFM) and tunneling AFM (TUNA) measurements. The collected data reveal that the two types of grains behave differently. The PFM amplitude signal of (110)-oriented grains is very contrasted and such grains are often divided in ferroelectric bi-domains of nanometric sizes, whereas the response of (100)-oriented grains is less contrasted and more homogeneous. The interpretation of the PFM signal is provided. The piezoloop recorded on a (110)NBT grain is strongly distorted and shifted along the vertical axis, in agreement with the vertical drift observed for macroscopic

  4. Pulsed laser deposition and characterization of highly tunable (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 thin films grown on LaNiO3/Si substrate

    NASA Astrophysics Data System (ADS)

    Bhardwaj, Chandan; Daniel, B. S. S.; Kaur, Davinder

    2013-01-01

    The structural and electric properties of Ba(Zr0.2Ti0.8)O3 {BZT}, (Ba0.7Ca0.3)TiO3 {BCT} and 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 {BCZT50} thin films grown on LaNiO3 coated Si(1 0 0) substrate by pulsed laser deposition (PLD) were thoroughly investigated. XRD results revealed relatively higher (1 0 0) preferred orientation and higher crystallinity for BCZT50 film in comparison to BZT and BCT thin films. FESEM showed that the average grain size of BCZT50 thin film is larger than that of BZT and BCT thin films. The optimal composition BCZT50 also exhibited maximum spontaneous polarization (Pm), maximum remanant polarization (Pr), minimum coercive field (Ec), maximum dielectric constant ɛr(0) and maximum tunability (nr). The increase in nr, ɛr(0) and polarization P(E) for BCZT50 thin film is attributed to (1 0 0) preferred orientation, microstructural homogeneity, large grain growth and most importantly to its proximity to the morphotropic phase boundary (MPB) causing very low energy barrier for polarization rotation and lattice distortion. It is also observed that BCZT50 thin film exhibits low leakage current density and good fatigue endurance as compared to BZT and BCT thin films.

  5. Spin reorientation in α-Fe2O3 nanoparticles induced by interparticle exchange interactions in α-Fe2O3/NiO nanocomposites

    NASA Astrophysics Data System (ADS)

    Frandsen, C.; Lefmann, K.; Lebech, B.; Bahl, C. R. H.; Brok, E.; Ancoña, S. N.; Theil Kuhn, L.; Keller, L.; Kasama, T.; Gontard, L. C.; Mørup, S.

    2011-12-01

    We report that the spin structure of α-Fe2O3 nanoparticles rotates coherently out of the basal (001) plane at low temperatures when interacting with thin plate-shaped NiO nanoparticles. The observed spin reorientation (up to ˜70∘) in α-Fe2O3 nanoparticles has, in appearance, similarities to the Morin transition in bulk α-Fe2O3, but its origin is different—it is caused by exchange coupling between aggregated nanoparticles of α-Fe2O3 and NiO with different directions of easy axes of magnetization.

  6. Enhanced microwave dielectric tunability of Ba0.5Sr0.5TiO3 thin films grown with reduced strain on DyScO3 substrates by three-step technique

    NASA Astrophysics Data System (ADS)

    Liu, Hongrui; Avrutin, Vitaliy; Zhu, Congyong; Özgür, Ümit; Yang, Juan; Lu, Changzhi; Morkoç, Hadis

    2013-01-01

    Tunable dielectric properties of epitaxial ferroelectric Ba0.5Sr0.5TiO3 (BST) thin films deposited on nearly lattice-matched DyScO3 substrates by radio frequency magnetron sputtering have been investigated at microwave frequencies and correlated with residual compressive strain. To reduce the residual strain of the BST films caused by substrate clamping and improve their microwave properties, a three-step deposition method was devised and employed. A high-temperature deposition at 1068 K of the nucleation layer was followed by a relatively low-temperature deposition (varied in the range of 673-873 K) of the BST interlayer and a high-temperature deposition at 1068 K of the top layer. Upon post-growth thermal treatment at 1298 K the films grown by the three-step method with the optimized interlayer deposition temperature of 873 K exhibited lower compressive strain compared to the control layer (-0.002 vs. -0.006). At 10 GHz, a high dielectric tunability of 47.9% at an applied electric field of 60 kV/cm was achieved for the optimized films. A large differential phase shift of 145°/cm and a figure of merit of 23°/dB were obtained using a simple coplanar waveguide phase shifter at 10 GHz. The low residual strain and improved dielectric properties of the films fabricated using the three-step deposition technique were attributed to reduced clamping of the BST films by the nearly lattice-matched substrate.

  7. Nanostructured light-absorbing crystalline CuIn{sub (1–x)}Ga{sub x}Se{sub 2} thin films grown through high flux, low energy ion irradiation

    SciTech Connect

    Hall, Allen J.; Hebert, Damon; Rockett, Angus A.; Shah, Amish B.; Bettge, Martin

    2013-10-21

    A hybrid effusion/sputtering vacuum system was modified with an inductively coupled plasma (ICP) coil enabling ion assisted physical vapor deposition of CuIn{sub 1−x}Ga{sub x}Se{sub 2} thin films on GaAs single crystals and stainless steel foils. With <80 W rf power to the ICP coil at 620–740 °C, film morphologies were unchanged compared to those grown without the ICP. At low temperature (600–670 °C) and high rf power (80–400 W), a light absorbing nanostructured highly anisotropic platelet morphology was produced with surface planes dominated by (112){sub T} facets. At 80–400 W rf power and 640–740 °C, both interconnected void and small platelet morphologies were observed while at >270 W and above >715 °C nanostructured pillars with large inter-pillar voids were produced. The latter appeared black and exhibited a strong (112){sub T} texture with interpillar twist angles of ±8°. Application of a negative dc bias of 0–50 V to the film during growth was not found to alter the film morphology or stoichiometry. The results are interpreted as resulting from the plasma causing strong etching favoring formation of (112){sub T} planes and preferential nucleation of new grains, balanced against conventional thermal diffusion and normal growth mechanisms at higher temperatures. The absence of effects due to applied substrate bias suggests that physical sputtering or ion bombardment effects were minimal. The nanostructured platelet and pillar films were found to exhibit less than one percent reflectivity at angles up to 75° from the surface normal.

  8. Spin Seebeck effect through antiferromagnetic NiO

    NASA Astrophysics Data System (ADS)

    Prakash, Arati; Brangham, Jack; Yang, Fengyuan; Heremans, Joseph P.

    2016-07-01

    We report temperature-dependent spin Seebeck measurements on Pt/YIG bilayers and Pt/NiO/YIG trilayers, where YIG (yttrium iron garnet, Y3F e5O12 ) is an insulating ferrimagnet and NiO is an antiferromagnet at low temperatures. The thickness of the NiO layer is varied from 0 to 10 nm. In the Pt/YIG bilayers, the temperature gradient applied to the YIG stimulates dynamic spin injection into the Pt, which generates an inverse spin Hall voltage in the Pt. The presence of a NiO layer dampens the spin injection exponentially with a decay length of 2 ± 0.6 nm at 180 K. The decay length increases with temperature and shows a maximum of 5.5 ± 0.8 nm at 360 K. The temperature dependence of the amplitude of the spin Seebeck signal without NiO shows a broad maximum of 6.5 ± 0.5 μV/K at 20 K. In the presence of NiO, the maximum shifts sharply to higher temperatures, likely correlated to the increase in decay length. This implies that NiO is most transparent to magnon propagation near the paramagnet-antiferromagnet transition. We do not see the enhancement in spin current driven into Pt reported in other papers when 1-2 nm NiO layers are sandwiched between Pt and YIG.

  9. Mesoscale assembly of NiO nanosheets into spheres

    SciTech Connect

    Zhang Meng; Yan Guojin; Hou Yonggai; Wang Chunhua

    2009-05-15

    NiO solid/hollow spheres with diameters about 100 nm have been successfully synthesized through thermal decomposition of nickel acetate in ethylene glycol at 200 deg. C. These spheres are composed of nanosheets about 3-5 nm thick. Introducing poly(vinyl pyrrolidone) (PVP) surfactant to reaction system can effectively control the products' morphology. By adjusting the quantity of PVP, we accomplish surface areas-tunable NiO assembled spheres from {approx}70 to {approx}200 m{sup 2} g{sup -1}. Electrochemical tests show that NiO hollow spheres deliver a large discharge capacity of 823 mA h g{sup -1}. Furthermore, these hollow spheres also display a slow capacity-fading rate. A series of contrastive experiments demonstrate that the surface area of NiO assembled spheres has a noticeable influence on their discharge capacity. - Graphical abstract: The mesoscale assembly of NiO nanosheets into spheres have been achieved by a solvothermal method. N{sub 2} adsorption/desorption isotherms show the S{sub BET} of NiO is tunable. NiO spheres show large discharge capacity and slow capacity-fading rate.

  10. Magnetic interactions in NiO at ultrahigh pressure

    DOE PAGES

    Potapkin, Vasily; Dubrovinsky, Leonid; Sergueev, I.; Ekholm, M.; Kantor, Innokenty; Bessas, D.; Bykova, E.; Prakapenka, V.; Hermann, Raphael P.; Rueffer, Rudolf; et al

    2016-05-24

    Here, magnetic properties of NiO have been studied in the multimegabar pressure range by nuclear forward scattering of synchrotron radiation using the 67.4 keV M ssbauer transition of 61Ni. The observed magnetic hyperfine splitting confirms the antiferromagnetic state of NiO up to 280 GPa, the highest pressure where magnetism has been observed so far, in any material. Remarkably, the hyperfine field increases from 8.47 T at ambient pressure to ~24 T at the highest pressure, ruling out the possibility of a magnetic collapse. A joint x-ray diffraction and extended x-ray-absorption fine structure investigation reveals that NiO remains in a distortedmore » sodium chloride structure in the entire studied pressure range. Ab initio calculations support the experimental observations, and further indicate a complete absence of Mott transition in NiO up to at least 280 GPa.« less

  11. Magnetic interactions in NiO at ultrahigh pressure

    NASA Astrophysics Data System (ADS)

    Potapkin, V.; Dubrovinsky, L.; Sergueev, I.; Ekholm, M.; Kantor, I.; Bessas, D.; Bykova, E.; Prakapenka, V.; Hermann, R. P.; Rüffer, R.; Cerantola, V.; Jönsson, H. J. M.; Olovsson, W.; Mankovsky, S.; Ebert, H.; Abrikosov, I. A.

    2016-05-01

    Magnetic properties of NiO have been studied in the multimegabar pressure range by nuclear forward scattering of synchrotron radiation using the 67.4 keV Mössbauer transition of 61Ni. The observed magnetic hyperfine splitting confirms the antiferromagnetic state of NiO up to 280 GPa, the highest pressure where magnetism has been observed so far, in any material. Remarkably, the hyperfine field increases from 8.47 T at ambient pressure to ˜24 T at the highest pressure, ruling out the possibility of a magnetic collapse. A joint x-ray diffraction and extended x-ray-absorption fine structure investigation reveals that NiO remains in a distorted sodium chloride structure in the entire studied pressure range. Ab initio calculations support the experimental observations, and further indicate a complete absence of Mott transition in NiO up to at least 280 GPa.

  12. Ni3Si2 nanowires grown in situ on Ni foam for high-performance supercapacitors

    NASA Astrophysics Data System (ADS)

    Jiang, Yizhe; Li, Zhihui; Li, Beibei; Zhang, Jinying; Niu, Chunming

    2016-07-01

    Ni3Si2 nanowires and nanoawls have grown in situ on the surface of Ni foams by a controlled low pressure chemical vapor deposition process. Structural characterization shows that the individual Ni3Si2 nanowire is single crystal covered with a thin layer (1-2 nm) of SiO2 with a diameter of ∼20-30 nm and length of ten's micrometers. Individual nanoawl with a circular cone shape is polycrystalline. Both Ni3Si2 nanowire and nanoawl samples are evaluated as potential electrode materials for supercapacitors. The nanowire electrode delivers a very high specific capacitance and excellent rate capability. A specific capacitance of 760 F g-1 is measured at current density of 0.5 A g-1, which decreases to 518 F g-1 when the current density increases to 10 A g-1. The capacitance is dominated by pseudocapacitance with a mechanism similar to that of NiO or Ni(OH)2 widely studied in the literature. An asymmetric supercapacitor fabricated by pairing Ni3Si2 nanowire electrode with an activated carbon electrode exhibits energy densities of 17.5 Wh kg-1 and 8.8 Wh kg-1 at power densites of 301 W kg-1 and 3000 W kg-1.

  13. Evolution of Ni nanofilaments and electromagnetic coupling in the resistive switching of NiO

    NASA Astrophysics Data System (ADS)

    Luo, Yuxiang; Zhao, Diyang; Zhao, Yonggang; Chiang, Fu-Kuo; Chen, Pengcheng; Guo, Minghua; Luo, Nannan; Jiang, Xingli; Miao, Peixian; Sun, Ying; Chen, Aitian; Lin, Zhu; Li, Jianqi; Duan, Wenhui; Cai, Jianwang; Wang, Yayu

    2014-12-01

    Resistive switching effect in conductor/insulator/conductor thin-film stacks is promising for resistance random access memory with high-density, fast speed, low power dissipation and high endurance, as well as novel computer logic architectures. NiO is a model system for the resistive switching effect and the formation/rupture of Ni nanofilaments is considered to be essential. However, it is not clear how the nanofilaments evolve in the switching process. Moreover, since Ni nanofilaments should be ferromagnetic, it provides an opportunity to explore the electromagnetic coupling in this system. Here, we report a direct observation of Ni nanofilaments and their specific evolution process for the first time by a combination of various measurements and theoretical calculations. We found that multi-nanofilaments are involved in the low resistance state and the nanofilaments become thin and rupture separately in the RESET process with subsequent increase of the rupture gaps. Theoretical calculations reveal the role of oxygen vacancy amount in the evolution of Ni nanofilaments. We also demonstrate electromagnetic coupling in this system, which opens a new avenue for multifunctional devices.Resistive switching effect in conductor/insulator/conductor thin-film stacks is promising for resistance random access memory with high-density, fast speed, low power dissipation and high endurance, as well as novel computer logic architectures. NiO is a model system for the resistive switching effect and the formation/rupture of Ni nanofilaments is considered to be essential. However, it is not clear how the nanofilaments evolve in the switching process. Moreover, since Ni nanofilaments should be ferromagnetic, it provides an opportunity to explore the electromagnetic coupling in this system. Here, we report a direct observation of Ni nanofilaments and their specific evolution process for the first time by a combination of various measurements and theoretical calculations. We found

  14. Preparation of nickel oxide thin films at different annealing temperature by sol-gel spin coating method

    NASA Astrophysics Data System (ADS)

    Abdullah, M. A. R.; Mamat, M. H.; Ismail, A. S.; Malek, M. F.; Alrokayan, Salman A. H.; Khan, Haseeb A.; Rusop, M.

    2016-07-01

    Preparation of NiO thin films at different annealing temperature by sol-gel method was conducted to synthesize the quality of the surface thin films. The effects of annealing temperature on the surface topology were systematically investigated. Our studies confirmed that the surface roughness of the thin films was increased whenever annealing temperature was increase. NiO thin films morphology structure analysis was confirmed by field emission scanning electron microscope. Surface roughness of the thin films was investigated by atomic force microscopy.

  15. High-performance hybrid (electrostatic double-layer and faradaic capacitor-based) polymer actuators incorporating nickel oxide and vapor-grown carbon nanofibers.

    PubMed

    Terasawa, Naohiro; Asaka, Kinji

    2014-12-01

    The electrochemical and electromechanical properties of polymeric actuators prepared using nickel peroxide hydrate (NiO2·xH2O) or nickel peroxide anhydride (NiO2)/vapor-grown carbon nanofibers (VGCF)/ionic liquid (IL) electrodes were compared with actuators prepared using solely VGCFs or single-walled carbon nanotubes (SWCNTs) and an IL. The electrode in these actuator systems is equivalent to an electrochemical capacitor (EC) exhibiting both electrostatic double-layer capacitor (EDLC)- and faradaic capacitor (FC)-like behaviors. The capacitance of the metal oxide (NiO2·xH2O or NiO2)/VGCF/IL electrode is primarily attributable to the EDLC mechanism such that, at low frequencies, the strains exhibited by the NiO2·xH2O/VGCF/IL and NiO2/VGCF/IL actuators primarily result from the FC mechanism. The VGCFs in the NiO2·xH2O/VGCF/IL and NiO2/VGCF/IL actuators strengthen the EDLC mechanism and increase the electroconductivity of the devices. The mechanism underlying the functioning of the NiO2·xH2O/VGCF/IL actuator in which NiO2·xH2O/VGCF = 1.0 was found to be different from that of the devices produced using solely VGCFs or SWCNTs, which exhibited only the EDLC mechanism. In addition, it was found that both NiO2 and VGCFs are essential with regard to producing actuators that are capable of exhibiting strain levels greater than those of SWCNT-based polymer actuators and are thus suitable for practical applications. Furthermore, the frequency dependence of the displacement responses of the NiO2·xH2O/VGCF and NiO2/VGCF polymer actuators were successfully simulated using a double-layer charging kinetic model. This model, which accounted for the oxidization and reduction reactions of the metal oxide, can also be applied to SWCNT-based actuators. The results of electromechanical response simulations for the NiO2·xH2O/VGCF and NiO2/VGCF actuators predicted the strains at low frequencies as well as the time constants of the devices, confirming that the model is applicable

  16. Influence of defects on the structural and magnetic properties of multifunctional La2NiMnO6 thin films

    SciTech Connect

    Guo, HZ; Burgess, J; Ada, E; Street, S; Gupta, A.; Iliev, M N; Kellock, A J; Magen Dominguez, Cesar; Varela del Arco, Maria; Pennycook, Stephen J

    2008-01-01

    Thin films of the double perovskite La2NiMnO6 (LNMO) have been grown on various lattice-matched substrates (SrTiO3, LaAlO3, NdGaO3 and MgO) by pulsed laser deposition under varying oxygen background pressure (25 - 800 mTorr). The out-of-plane lattice constant of the LNMO film initially decreases with increasing pressure, likely caused by a reduction in the defect concentration and improved structural ordering, before leveling off at higher pressures. Scanning transmission electron microscopy results show that the films are epitaxial, and the interface is sharp and coherent. While very few defects are observed by STEM in a film grown at high oxygen pressure (800 mTorr), a film grown at a lower pressure (100 mTorr) shows the formation of defects that extend throughout the thickness except for a very thin layer near the interface. The Raman spectra of the films are dominated by two broad peaks at around 540 cm-1 and 685 cm-1, which are assigned to the antisymmetric stretching (AS) and symmetric stretching (S) modes of MnO6 and NiO6 octahedra, respectively. The Raman peaks of the LNMO thin films grown in 800 mTorr background O2 are blue shifted in comparison to those of LNMO bulk, and the shift increases with decreasing film thickness, indicating the increased influence of strain. The critical thickness for strain relaxation as determined from the Raman spectra is between 40 - 80 nm. The strain is observed to have a negligible influence on the magnetic properties for films grown at high oxygen pressures. However, films grown at low pressures exhibit degraded magnetic properties, which can be attributed to a combination of B-site cation disorder and an increase in the concentration of Mn3+ and Ni3+ Jahn-Teller ions caused by oxygen defects. With increasing oxygen pressure during growth, the paramagnetic-ferromagnetic transition temperature (~280 K) gets sharper and the saturation magnetization at low temperatures is enhanced. Based on electron energy loss spectroscopy

  17. NiO as a peculiar support for metal nanoparticles in polyols oxidation

    SciTech Connect

    Villa, Alberto; Veith, Gabriel M; Ferri, Davide; Weidenkaff, Anke; Perry, Kelly A; Campisi, Sebastiano; Prati, Laura

    2013-01-01

    The peculiar influence of a NiO support was studied by preparing gold catalysts supported on NiO(1-x) TiO2(x) mixed oxides. PVA protected Au nanoparticles showed high activity when supported on NiO for the selective oxidation of glycerol and ethan-1,2-diol. A detailed characterization of the resulting Au catalysts revealed a preferential deposition of the metal nanoparticles on the NiO phase. However, the activity of Au on NiO(1-x)-TiO2(x) decreased with respect to pure NiO and the selectivity evolved with changes to the support.

  18. Vacuum-free, maskless patterning of Ni electrodes by laser reductive sintering of NiO nanoparticle ink and its application to transparent conductors.

    PubMed

    Lee, Daeho; Paeng, Dongwoo; Park, Hee K; Grigoropoulos, Costas P

    2014-10-28

    We introduce a method for direct patterning of Ni electrodes through selective laser direct writing (LDW) of NiO nanoparticle (NP) ink. High-resolution Ni patterns are generated from NiO NP thin films by a vacuum-free, lithography-free, and solution-processable route. In particular, a continuous wave laser is used for the LDW reductive sintering of the metal oxide under ambient conditions with the aid of reducing agents in the ink solvent. Thin (∼ 40 nm) Ni electrodes of glossy metallic surfaces with smooth morphology and excellent edge definition can be fabricated. By applying this method, we demonstrate a high transmittance (>87%), electrically conducting panel for a touch screen panel application. The resistivity of the Ni electrode is less than an order of magnitude higher compared to that of the bulk Ni. Mechanical bending test, tape-pull test, and ultrasonic bath test confirm the robust adhesion of the electrodes on glass and polymer substrates.

  19. First principles study of oxygen vacancies and iron impurities on electrical and optical properties of NiO

    NASA Astrophysics Data System (ADS)

    Petersen, John; Fidele, Twagirayezu; Borges, Pablo; Scolfaro, Luisa; Geerts, Wilhelmus

    We are studying the properties of iron doped NiO by Density Functional Theory. NiO is being considered for use in RRAM, based on the reversible switching of a thin transition metal oxide (TMO) layer between a low and high resistance state using the mechanism of soft breakdown. RRAM's high integration density, its high endurance and good retention, its low energy use, and its high speed make it a potential candidate for replacing Flash memory. Switching between the high and low resistance state is inhomogeneous, and low resistance nano-filaments are formed. Fe impurities are introduced to optimize the switching properties. The effects of oxygen vacancies and iron on the electronic structure and optical properties of NiO are calculated and compared with experiment. Antiferromagnetic rhombohedral 108 atom cells with 1.85% Fe concentration are considered. Due to the highly-correlated nature of d orbitals in TMOs, a Hubbard U correction is applied to calculations in this work via the GGA + U method of DFT using VASP. Hybrid HSE06 calculations will also be considered. Localized energy levels from iron and from oxygen vacancies are identified, and their effects on dielectric permittivity are presented. Texas State University (Research Enhancement grant) and DOD (HBCU/MI Grant W911NF-15-1-0394).

  20. Insulator-metal transition in highly compressed NiO.

    PubMed

    Gavriliuk, Alexander G; Trojan, Ivan A; Struzhkin, Viktor V

    2012-08-24

    The insulator-metal transition was observed experimentally in nickel monoxide (NiO) at very high pressures of ~240 GPa. The sample resistance becomes measurable at about 130 GPa and decreases substantially with the pressure increase to ~240 GPa. A sharp drop in resistance by about 3 orders of magnitude has been observed at ~240 GPa with a concomitant change of the resistance type from semiconducting to metallic. This is the first experimental observation of an insulator-metal transition in NiO, which was anticipated by Mott decades ago. From simple multielectron consideration, the metallic phase of NiO forms when the effective Hubbard energy U(eff) is almost equal to the estimated full bandwidth 2W. PMID:23002762

  1. Magnetic skin layer of NiO(100) probed by polarization-dependent spectromicroscopy

    SciTech Connect

    Mandal, Suman Menon, Krishnakumar S. R.; Maccherozzi, Francesco

    2014-06-16

    Using polarization-dependent x-ray photoemission electron microscopy, we have investigated the surface effects on antiferromagnetic (AFM) domain formation. Depth-resolved information obtained from our study indicates the presence of strain-induced surface AFM domains on some of the cleaved NiO(100) crystals, which are unusually thinner than bulk AFM domain wall widths (∼150 nm). Existence of such magnetic skin layer is substantiated by exchange-coupled ferromagnetic Fe domains in Fe/NiO(100), thereby evidencing the influence of this surface AFM domains on interfacial magnetic coupling. Our observations demonstrate a depth evolution of AFM structure in presence of induced surface strain, while the surface symmetry-breaking in absence of induced strain does not modify the bulk AFM domain structure. Realization of such thin surface AFM layer will provide better microscopic understanding of the exchange bias phenomena.

  2. Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

    NASA Astrophysics Data System (ADS)

    Ravikumar, Patta; Kisan, Bhagaban; Perumal, A.

    2015-08-01

    We report systematic investigations of structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling. Structural properties revealed that both pure NiO and as-milled NiO powders exhibit face centered cubic structure, but average crystallite size decreases to around 11 nm along with significant increase in strain with increasing milling speed. Vibrational properties show the enhancement in the intensity of one-phonon longitudinal optical (LO) band and disappearance of two-magnon band due to size reduction. In addition, two-phonon LO band exhibits red shift due to size-induced phonon confinement effect and surface relaxation. Pure NiO powder exhibit antiferromagnetic nature, which transforms into induced ferromagnetic after size reduction. The average magnetization at room temperature increases with decreasing the crystallite size and a maximum moment of 0.016 μB/f.u. at 12 kOe applied field and coercivity of 170 Oe were obtained for 30 hours milled NiO powders at 600 rotation per minute milling speed. The change in the magnetic properties is also supported by the vibrational properties. Thermomagnetization measurements at high temperature reveal a well-defined magnetic phase transition at high temperature (TC) around 780 K due to induced ferromagnetic phase. Electron paramagnetic resonance (EPR) studies reveal a good agreement between the EPR results and magnetic properties. The observed results are described on the basis of crystallite size variation, defect density, large strain, oxidation/reduction of Ni and interaction between uncompensated surfaces and particle core with lattice expansion. The obtained results suggest that nanoscale NiO powders with high TC and moderate magnetic moment at room temperature with cubic structure would be useful to expedite for spintronic devices.

  3. Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

    SciTech Connect

    Ravikumar, Patta; Kisan, Bhagaban; Perumal, A.

    2015-08-15

    We report systematic investigations of structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling. Structural properties revealed that both pure NiO and as-milled NiO powders exhibit face centered cubic structure, but average crystallite size decreases to around 11 nm along with significant increase in strain with increasing milling speed. Vibrational properties show the enhancement in the intensity of one-phonon longitudinal optical (LO) band and disappearance of two-magnon band due to size reduction. In addition, two-phonon LO band exhibits red shift due to size-induced phonon confinement effect and surface relaxation. Pure NiO powder exhibit antiferromagnetic nature, which transforms into induced ferromagnetic after size reduction. The average magnetization at room temperature increases with decreasing the crystallite size and a maximum moment of 0.016 μ{sub B}/f.u. at 12 kOe applied field and coercivity of 170 Oe were obtained for 30 hours milled NiO powders at 600 rotation per minute milling speed. The change in the magnetic properties is also supported by the vibrational properties. Thermomagnetization measurements at high temperature reveal a well-defined magnetic phase transition at high temperature (T{sub C}) around 780 K due to induced ferromagnetic phase. Electron paramagnetic resonance (EPR) studies reveal a good agreement between the EPR results and magnetic properties. The observed results are described on the basis of crystallite size variation, defect density, large strain, oxidation/reduction of Ni and interaction between uncompensated surfaces and particle core with lattice expansion. The obtained results suggest that nanoscale NiO powders with high T{sub C} and moderate magnetic moment at room temperature with cubic structure would be useful to expedite for spintronic devices.

  4. Study of single crystal CuInSe2 thin films and CuGaSe2/CuInSe2 single quantum well grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Thiru, Sathiabama; Asakawa, Masaki; Honda, Kazuki; Kawaharazuka, Atsushi; Tackeuchi, Atsushi; Makimoto, Toshiki; Horikoshi, Yoshiji

    2015-09-01

    High quality CuGaSe2 and CuInSe2 single crystalline layers are grown on GaAs (001) by employing the deposition sequence of migration enhanced epitaxy using a solid source molecular beam epitaxy system. When CuGaSe2 is grown on CuInSe2 at moderate temperatures, severe interdiffusion takes place at the heterojunction of CuGaSe2/CuInSe2. This problem has been solved by optimizing the growth temperature and deposition rates of the constituent elements. Thus, we have successfully grown CuGaSe2/CuInSe2 single quantum well with sharp interfaces on GaAs (001) for the first time. Intense photoluminescence from the single quantum well with 10 nm well width is demonstrated.

  5. Room temperature ferromagnetic properties of epitaxial (111) Y0.225Sr0.775CoO3-δ thin film grown on single crystalline (111) MgO substrate

    NASA Astrophysics Data System (ADS)

    Seo, Jeongdae; Ahn, Yoonho; Yeog Son, Jong

    2015-08-01

    Epitaxial (111) Y0.225Sr0.775CoO3-δ (YSCO) thin films were deposited on single crystalline (111) MgO substrates by a pulsed laser deposition method. The YSCO thin film exhibited room temperature ferromagnetism with a remanent magnetization of 1.5×10-5 emu. The magnetic force microscopy (MFM) study revealed that the YSCO thin film had a mosaic MFM domain structure. The comparison of domain wall energy for the YSCO and PZT indicates that the large domain wall energy induce the large domain size, though the large magnetization value reduce the magnetic domain size in the case of Co. According to the optical conductivity analysis by spectroscopic ellipsometry, it is inferred that the transition from the intermediate spin state to the high spin state of the YSCO thin film is attributed to the ferromagnetism of the Co4+ ion.

  6. Transparent nanoscale floating gate memory using self-assembled bismuth nanocrystals in Bi(2) Mg(2/3) Nb(4/3) O(7) (BMN) pyrochlore thin films grown at room temperature.

    PubMed

    Jung, Hyun-June; Yoon, Soon-Gil; Hong, Soon-Ku; Lee, Jeong-Yong

    2012-07-01

    Bismuth nanocrystals for a nanoscale floating gate memory device are self-assembled in Bi(2) Mg(2/3) Nb(4/3) O(7) (BMN) dielectric films grown at room temperature by radio-frequency sputtering. The TEM cross-sectional image shows the "real" structure grown on a Si (001) substrate. The image magnified from the dotted box (red color) in the the cross-sectional image clearly shows bismuth nanoparticles at the interface between the Al(2) O(3) and HfO(2) layer (right image). Nanoparticles approximately 3 nm in size are regularly distributed at the interface.

  7. Comment on: "Characterization of Microroughness Parameters in Titanium Nitride Thin Films Grown by DC Magnetron Sputtering" [J Fusion Energ DOI 10.1007/s10894-012-9510-z

    NASA Astrophysics Data System (ADS)

    Solaymani, Shahram; Ghaderi, Atefeh; Nezafat, Negin Beryani

    2012-12-01

    In recent article [Ali Gelali. Azin Ahmadpourian. Reza Bavadi. M. R. Hantehzadeh. Arman Ahmadpourian. J Fusion Energ DOI 10.1007/s10894-012-9510-z], Ali Geleli et al. studied the PSD and RMS Roughness parameters in Titanium Nitride thin films by AFM data and used the computed fractal dimension value of micrographs to describe the surface morphology of thin films. Here, the correct form of equations and relationship between PSD and RMS will be discussed.

  8. 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.

  9. Preparation and characterization of multilayer NiO nano-products via electrospinning

    NASA Astrophysics Data System (ADS)

    Liu, Mengzhu; Wang, Yongpeng; Li, Pengchong; Cheng, Zhiqiang; Zhang, Yongqiang; Zhang, Mingyue; Hu, Meijuan; Li, Junfeng

    2013-11-01

    NiO with multilayer structure was prepared by impregnating electrospun polylactic acid (PLA) nanofibrous webs with nickel acetate solution and subsequent calcination. From SEM images, it can be observed that the structures of NiO products from surface to center were nanogrooves inlaid film, hollow pores and honeycomb-like nanofibers with nanogrooves, successively. The formation mechanisms were studied in detail by TGA and DSC. FT-IR and XRD measurements demonstrated that the product was highly pure NiO with cubic structure. The sensitivity of the NiO products to formaldehyde was investigated. As a result, the multilayer NiO exhibited much higher sensing signal than NiO powders. This indicated that the prepared multilayer NiO could be used as a candidate to fabricate formaldehyde sensors.

  10. p-Type NiO Hybrid Visible Photodetector.

    PubMed

    Mallows, John; Planells, Miquel; Thakare, Vishal; Bhosale, Reshma; Ogale, Satishchandra; Robertson, Neil

    2015-12-23

    A novel hybrid visible-light photodetector was created using a planar p-type inorganic NiO layer in a junction with an organic electron acceptor layer. The effect of different oxygen pressures on formation of the NiO layer by pulsed laser deposition shows that higher pressure increases the charge carrier density of the film and lowers the dark current in the device. The addition of a monolayer of small molecules containing conjugated π systems and carboxyl groups at the device interface was also investigated and with correct alignment of the energy levels improves the device performance with respect to the quantum efficiency, responsivity, and photogeneration. The thickness of the organic layer was also optimized for the device, giving a responsivity of 1.54 × 10(-2) A W(-1) in 460 nm light. PMID:26654105

  11. Particle transport and heat loads in NIO1.

    PubMed

    Fonnesu, N; Cavenago, M; Serianni, G; Veltri, P

    2016-02-01

    NIO1 is a compact radio frequency ion source designed to generate a 60 kV-135 mA hydrogen negative ion beam and it aims at continuous operation, which implies a detailed thermo-mechanical analysis of the beam-facing components, in particular, the accelerator grids. A 3D analysis of the entire NIO1 beam has been performed for the first time with a fully 3D version of EAMCC, a relativistic particle tracking code for the calculation of the grid power deposition induced by particle impacts. According to the results presented in this paper, secondary and co-extracted electrons cause a non-negligible heat load on the grids, where different high-power density regions, within reasonable sustainable standard limits, are calculated.

  12. p-Type NiO Hybrid Visible Photodetector.

    PubMed

    Mallows, John; Planells, Miquel; Thakare, Vishal; Bhosale, Reshma; Ogale, Satishchandra; Robertson, Neil

    2015-12-23

    A novel hybrid visible-light photodetector was created using a planar p-type inorganic NiO layer in a junction with an organic electron acceptor layer. The effect of different oxygen pressures on formation of the NiO layer by pulsed laser deposition shows that higher pressure increases the charge carrier density of the film and lowers the dark current in the device. The addition of a monolayer of small molecules containing conjugated π systems and carboxyl groups at the device interface was also investigated and with correct alignment of the energy levels improves the device performance with respect to the quantum efficiency, responsivity, and photogeneration. The thickness of the organic layer was also optimized for the device, giving a responsivity of 1.54 × 10(-2) A W(-1) in 460 nm light.

  13. Particle transport and heat loads in NIO1.

    PubMed

    Fonnesu, N; Cavenago, M; Serianni, G; Veltri, P

    2016-02-01

    NIO1 is a compact radio frequency ion source designed to generate a 60 kV-135 mA hydrogen negative ion beam and it aims at continuous operation, which implies a detailed thermo-mechanical analysis of the beam-facing components, in particular, the accelerator grids. A 3D analysis of the entire NIO1 beam has been performed for the first time with a fully 3D version of EAMCC, a relativistic particle tracking code for the calculation of the grid power deposition induced by particle impacts. According to the results presented in this paper, secondary and co-extracted electrons cause a non-negligible heat load on the grids, where different high-power density regions, within reasonable sustainable standard limits, are calculated. PMID:26932077

  14. Dielectric and ferroelectric properties of Ba(Sn{sub 0.15}Ti{sub 0.85})O{sub 3} thin films grown by a sol-gel process

    SciTech Connect

    Zhai Jiwei; Shen Bo; Yao Xi; Zhang Liangying

    2004-09-01

    Ferroelectric Ba(Sn{sub 0.15}Ti{sub 0.85})O{sub 3} (BTS) thin films were deposited on LaNiO{sub 3}-coated silicon substrates via a sol-gel process. Films showed a strong (1 0 0) preferred orientation depending upon annealing temperature and concentration of the precursor solution. The dependence of dielectric and ferroelectric properties on film orientation has been studied. The leakage current density of thin films at 100 kV/cm was 7 x 10{sup -7} A/cm{sup 2} and 5 x 10{sup -5} A/cm{sup 2} and their capacitor tunability was 54 and 25% at an applied field of 200 kV/cm (measurement frequency of 1 MHz) for the thin films deposited with 0.1 and 0.4 M spin-on solution, respectively. This work clearly reveals the highly promising potential of BTS compared with BST films for application in tunable microwave devices.

  15. Impact of varying buffer thickness generated strain and threading dislocations on the formation of plasma assisted MBE grown ultra-thin AlGaN/GaN heterostructure on silicon

    SciTech Connect

    Chowdhury, Subhra; Biswas, Dhrubes

    2015-05-15

    Plasma-assisted molecular beam epitaxy (PAMBE) growth of ultra-thin Al{sub 0.2}Ga{sub 0.8}N/GaN heterostructures on Si(111) substrate with three buffer thickness (600 nm/400 nm/200 nm) have been reported. An unique growth process has been developed that supports lower temperature epitaxy of GaN buffer which minimizes thermally generated tensile strain through appropriate nitridation and AlN initiated epitaxy for achieving high quality GaN buffer which supports such ultra-thin heterostructures in the range of 10-15Å. It is followed by investigations of role of buffer thickness on formation of ultra-thin Al{sub 0.2}Ga{sub 0.8}N/GaN heterostructure, in terms of stress-strain and threading dislocation (TD). Structural characterization were performed by High-Resolution X-Ray Diffraction (HRXRD), room-temperature Photoluminescence (RT-PL), High Resolution Transmission Electron Microscopy (HRTEM) and Atomic Force Microscopy (AFM). Analysis revealed increasing biaxial tensile stress of 0.6918 ± 0.04, 1.1084, 1.1814 GPa in heterostructures with decreasing buffer thickness of 600, 400, 200 nm respectively which are summed up with residual tensile strain causing red-shift in RT-PL peak. Also, increasing buffer thickness drastically reduced TD density from the order 10{sup 10} cm{sup −2} to 10{sup 8} cm{sup −2}. Surface morphology through AFM leads to decrease of pits and root mean square value with increasing buffer thickness which are resulted due to reduction of combined effect of strain and TDs.

  16. Effect of postdeposition annealing on the electrical properties of β-Ga{sub 2}O{sub 3} thin films grown on p-Si by plasma-enhanced atomic layer deposition

    SciTech Connect

    Altuntas, Halit; Donmez, Inci; Ozgit-Akgun, Cagla; Biyikli, Necmi

    2014-07-01

    Ga{sub 2}O{sub 3} dielectric thin films were deposited on (111)-oriented p-type silicon wafers by plasma-enhanced atomic layer deposition using trimethylgallium and oxygen plasma. Structural analysis of the Ga{sub 2}O{sub 3} thin films was carried out using grazing-incidence x-ray diffraction. As-deposited films were amorphous. Upon postdeposition annealing at 700, 800, and 900 °C for 30 min under N{sub 2} ambient, films crystallized into β-form monoclinic structure. Electrical properties of the β-Ga{sub 2}O{sub 3} thin films were then investigated by fabricating and characterizing Al/β-Ga{sub 2}O{sub 3}/p-Si metal–oxide-semiconductor capacitors. The effect of postdeposition annealing on the leakage current densities, leakage current conduction mechanisms, dielectric constants, flat-band voltages, reverse breakdown voltages, threshold voltages, and effective oxide charges of the capacitors were presented. The effective oxide charges (Q{sub eff}) were calculated from the capacitance–voltage (C-V) curves using the flat-band voltage shift and were found as 2.6 × 10{sup 12}, 1.9 × 10{sup 12}, and 2.5 × 10{sup 12} cm{sup −2} for samples annealed at 700, 800, and 900 °C, respectively. Effective dielectric constants of the films decreased with increasing annealing temperature. This situation was attributed to the formation of an interfacial SiO{sub 2} layer during annealing process. Leakage mechanisms in the regions where current increases gradually with voltage were well fitted by the Schottky emission model for films annealed at 700 and 900 °C, and by the Frenkel–Poole emission model for film annealed at 800 °C. Leakage current density was found to improve with annealing temperature. β-Ga{sub 2}O{sub 3} thin film annealed at 800 °C exhibited the highest reverse breakdown field value.

  17. The influence of strain on the dielectric behavior of (Ba, Sr) Ti{sub 1+x}O{sub 3} thin films grown by LS-MOCVD on Pt/SiO{sub 2}/Si.

    SciTech Connect

    Streiffer, S. K.

    1998-10-14

    The strain state and its coupling to dielectric behavior have been investigated for (100) BST thin films deposited on Pt/SiO{sub 2}/Si at 640 C. It is estimated from x-ray diffraction that the in-plane biaxial strain is approximately 0.7%. We postulate that this is of sufficient magnitude to confine any spontaneous polarization to the plane of the film. The thickness-corrected dielectric behavior perpendicular to the substrate for these samples shows evidence of coupling to such an in-plane phase transition at approximately 390K, as manifested by deviation from Curie-Weiss-like behavior at this temperature.

  18. 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.

  19. Growth of Hierarchal Mesoporous NiO Nanosheets on Carbon Cloth as Binder-free Anodes for High-performance Flexible Lithium-ion Batteries

    PubMed Central

    Long, Hu; Shi, Tielin; Hu, Hao; Jiang, Shulan; Xi, Shuang; Tang, Zirong

    2014-01-01

    Mesoporous NiO nanosheets were directly grown on three-dimensional (3D) carbon cloth substrate, which can be used as binder-free anode for lithium-ion batteries (LIBs). These mesoporous nanosheets were interconnected with each other and forming a network with interval voids, which give rise to large surface area and efficient buffering of the volume change. The integrated hierarchical electrode maintains all the advantageous features of directly building two-dimensional (2D) nanostructues on 3D conductive substrate, such as short diffusion length, strain relaxation and fast electron transport. As the LIB anode, it presents a high reversible capacity of 892.6 mAh g−1 after 120 cycles at a current density of 100 mA g−1 and 758.1 mAh g−1 at a high charging rate of 700 mA g−1 after 150 cycles. As demonstrated in this work, the hierarchical NiO nanosheets/carbon cloth also shows high flexibility, which can be directly used as the anode to build flexible LIBs. The introduced facile and low-cost method to prepare NiO nanosheets on flexible and conductive carbon cloth substrate is promising for the fabrication of high performance energy storage devices, especially for next-generation wearable electronic devices. PMID:25491432

  20. Role of interface structure and chemistry in resistive switching of NiO nanocrystals on SrTiO{sub 3}

    SciTech Connect

    Cheng, Xuan; Sullaphen, Jivika; Valanoor, Nagarajan; Weyland, Matthew; Liu, Hongwei

    2014-03-01

    Nickel oxide (NiO) nanocrystals epitaxially grown on (001) strontium titanate (SrTiO{sub 3}) single crystal substrates were characterized to investigate interface morphology and chemistry. Aberration corrected high angle annular dark field scanning transmission electron microscopy reveals the interface between the NiO nanocrystals and the underlying SrTiO{sub 3} substrate to be rough, irregular, and have a lower average atomic number than the substrate or the nanocrystal. Energy dispersive x-ray spectroscopy and electron energy loss spectroscopy confirm both chemical disorder and a shift of the energy of the Ti L{sub 2,3} peaks. Analysis of the O K edge profiles in conjunction with this shift, implies the presence of oxygen vacancies at the interface. This sheds light into the origin of the previously postulated minority carriers’ model to explain resistive switching in NiO [J. Sullaphen, K. Bogle, X. Cheng, J. M. Gregg, and N. Valanoor, Appl. Phys. Lett. 100, 203115 (2012)].

  1. The interfacial and surface properties of thin Fe and Gd films grown on W(110) as studied by scanning tunneling microscopy, site-resolved photoelectron diffraction, and spin polarized photoelectron diffraction

    SciTech Connect

    Tober, E.D.

    1997-06-01

    Combined scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) measurements from Gd films grown on W(110) prepared with and without annealing have been used to provide a detailed picture of the growth of such films, permitting a quantitative structural explanation for previously-measured magnetic properties and the identification of a new two-dimensional structure for the first monolayer. The analysis of the film roughness of room-temperature-grown films as a function of coverage and lateral length scale reveals that the growing Gd surface follows scaling laws for a self-affine surface. Annealing these as-deposited films at elevated temperatures is found to drastically alter the morphology of the films, as seen by both STM and LEED. Nanometer-scale islands of relatively well-defined size and shape are observed under certain conditions. Finally, the first monolayer of Gd is observed to form a (7x14) superstructure with pseudo-(7x7) symmetry that is consistent with a minimally-distorted hexagonal two-dimensional Gd(0001) film. Furthermore, a new beamline and photoelectron spectrometer/diffractometer at the Advanced Light Source have been used to obtain full-solid-angle and site-specific photoelectron diffraction (PD) data from interface W atoms just beneath (1x1) Fe and (7x14) Gd monolayers on W(110) by utilizing the core level shift in the W 4f{sub 7/2} spectrum. A comparison of experiment with multiple scattering calculations permits determining the Fe adsorption site and the relative interlayer spacing to the first and second W layers. These Fe results are also compared to those from the very different Gd overlayer and from the clean W(110) surface. Such interface PD measurements show considerable promise for future studies. Finally, the rare-earth ferromagnetic system of Gd(0001) has been examined through the use of spin polarized photoelectron diffraction from the Gd 4s and 5s photoelectron multiplets.

  2. 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.

  3. Ferroelectric dielectric properties of Ba{sub 0.5}Sr{sub 0.5}(Ti{sub 0.80}Sn{sub 0.20})O{sub 3} thin films grown by the soft chemical method

    SciTech Connect

    Souza, I.A.; Cavalcante, L.S.; Cilense, M.

    2006-10-15

    Polycrystalline Ba{sub 0.5}Sr{sub 0.5}(Ti{sub 0.80}Sn{sub 0.20})O{sub 3} (BST:Sn) thin films with a perovskite structure were prepared by the soft chemical method on a platinum-coated silicon substrate from spin-coating technique. The resulting thin films showed a dense structure with uniforain size distribution. The dielectric constant of the films estimated from C-V curve is around 1134 and can be ascribed to a reduction in the oxygen vacancy concentration. The ferroelectric nature of the film indicated by butterfly-shaped C-V curves and confirmed by the hysteresis curve, showed remnant polarization of 14{mu}C/cm{sup 2} and coercive field of 74kV/cm at frequency of 1MHz. At the same frequency, the leakage current density at 1.0V is equal to 1.5x10{sup -7}A/cm{sup 2}. This work clearly reveals the highly promising potential of BST:Sn for application in memory devices.

  4. Facile approach to prepare hollow core–shell NiO microspherers for supercapacitor electrodes

    SciTech Connect

    Han, Dandan; Xu, Pengcheng; Jing, Xiaoyan; Wang, Jun; Song, Dalei; Liu, Jingyuan; Zhang, Milin

    2013-07-15

    A facile lamellar template method (see image) has been developed for the preparation of uniform hollow core–shell structure NiO (HCS–NiO) with a nanoarchitectured wall structure. The prepared NiO was found to be highly crystalline in uniform microstructures with high specific surface area and pore volume. The results indicated that ethanol interacted with trisodium citrate played an important role for the formation of hollow core–shell spheres. On the basis of the analysis of the composition and the morphology, a possible formation mechanism was investigated. NiO microspheres with hollow core–shell showed excellent capacitive properties. The exceptional cyclic, structural and electrochemical stability with ∼95% coulombic efficiency, and very low ESR value from impedance measurements promised good utility value of hollow core–shell NiO material in fabricating a wide range of high-performance electrochemical supercapacitors. - The hollow core–shell NiO was prepared with a facile lamellar template method. The prepared NiO show higher capacitance, lower ion diffusion resistance and better electroactive surface utilization for Faradaic reactions. - Highlights: • Formation of hollow core–shell NiO via a novel and facile precipitation route. • Exhibited uniform feature sizes and high surface area of hollow core–shell NiO. • Synthesized NiO has high specific capacitance ( 448 F g{sup 1}) and very low ESR value. • Increased 20% of long life cycles capability after 500 charge–discharge cycles.

  5. Novel combustion method to prepare octahedral NiO nanoparticles and its photocatalytic activity

    SciTech Connect

    Jegatha Christy, A.; Umadevi, M.

    2013-10-15

    Graphical abstract: - Highlights: • NiO nanoparticles were synthesized by solution combustion method. • Prepared NiO nanoparticles are fcc structure. • Synthesized NiO nanoparticles are octahedral shape. • Shows good photocatalytic activity. - Abstract: Nickel oxide nanoparticles (NiO NPs) were synthesized by solution combustion method using glycine and citric acid as fuels. The X-ray diffraction (XRD) result confirms the face centered cubic (fcc) structure of NiO. The octahedral shape of NiO NPs was confirmed by field emission scanning electron microscope (FESEM) and high resolution transmission electron microscopy (HRTEM). It is possible to suggest that the organic fuel (citric acid/glycine) is responsible for the formation of the octahedral shape due to the easier complex formation. Photocatalytic activity of NiO NPs also evaluated and found that the prepared NiO NPs have high photocatalytic degradation. In the present study, the crystalline nature and shape of the NiO nanoparticles plays a vital role in determining the photocatalytic activity.

  6. Self-organization processes in highly epitaxial La{sub 2/3}Sr{sub 1/3}MnO{sub 3} thin films grown on SrTiO{sub 3} (001) substrates

    SciTech Connect

    Konstantinovic, Z.; Balcells, Ll.; Martinez, B.; Santiso, J.; Colson, D.; Forget, A.

    2009-03-15

    We report on the growth of highly epitaxial La{sub 2/3}Sr{sub 1/3}MnO{sub 3} thin films on SrTiO{sub 3} (001) oriented substrates by rf magnetron sputtering. It is shown that structural strain caused by lattice mismatch between film and substrate and kinetics growing instabilities may offer unique opportunities to control the film morphologies. By increasing growth rate, the surface morphology undergoes a dramatic transformation: from very smooth surface through arrays of mounds or antidots to hatched morphology. All nano-objects form long-range ordered arrays running in the steps direction defined by the miscut angle of underlying substrate. These self-assembled structures are of high interest envisaging a new route for the fabrication of oxide-based magnetoelectronic devices by using a bottom-up approach.

  7. Enhanced Dielectric Properties of [Pb(Mg1/3Nb2/3)O3]0.9-PbTiO3]0.1 Thin Films Grown on BaPbO3 Perovskite Electrode

    NASA Astrophysics Data System (ADS)

    Ho, Sut Kam; Hau, Fei Fei; Wong, Kin Hung

    2004-11-01

    Polycrystalline and epitaxial [Pb(Mg1/3Nb2/3)O3]0.9-[PbTiO3]0.1 (PMN-PT) thin films were prepared by pulsed laser deposition on BaPbO3 (BPO) and La0.7Sr0.3MnO3 (LSMO) oxide electrodes. In comparison, the epitaxial films show higher dielectric constant and the polycrystalline films exhibit lower dielectric loss and smaller leakage current. It is also found that the use of lead based BPO electrodes helps to raise the dielectric constant of the PMN-PT layer by 30%, and to reduce the dielectric leakage by as much as three orders of magnitude. Our results have clearly demonstrated the superiority of using lead based electrodes for growing lead based dielectrics.

  8. Nios II hardware acceleration of the epsilon quadratic sieve algorithm

    NASA Astrophysics Data System (ADS)

    Meyer-Bäse, Uwe; Botella, Guillermo; Castillo, Encarnacion; García, Antonio

    2010-04-01

    The quadratic sieve (QS) algorithm is one of the most powerful algorithms to factor large composite primes used to break RSA cryptographic systems. The hardware structure of the QS algorithm seems to be a good fit for FPGA acceleration. Our new ɛ-QS algorithm further simplifies the hardware architecture making it an even better candidate for C2H acceleration. This paper shows our design results in FPGA resource and performance when implementing very long arithmetic on the Nios microprocessor platform with C2H acceleration for different libraries (GMP, LIP, FLINT, NRMP) and QS architecture choices for factoring 32-2048 bit RSA numbers.

  9. Methods for making thin layers of crystalline materials

    SciTech Connect

    Lagally, Max G; Paskiewicz, Deborah M; Tanto, Boy

    2013-07-23

    Methods for making growth templates for the epitaxial growth of compound semiconductors and other materials are provided. The growth templates are thin layers of single-crystalline materials that are themselves grown epitaxially on a substrate that includes a thin layer of sacrificial material. The thin layer of sacrificial material, which creates a coherent strain in the single-crystalline material as it is grown thereon, includes one or more suspended sections and one or more supported sections.

  10. L10 ordered phase formation in FePt, FePd, CoPt, and CoPd alloy thin films epitaxially grown on MgO(001) single-crystal substrates

    NASA Astrophysics Data System (ADS)

    Ohtake, Mitsuru; Ouchi, Shouhei; Kirino, Fumiyoshi; Futamoto, Masaaki

    2012-04-01

    The FePt, FePd, CoPt, and CoPd epitaxial thin films are prepared on MgO(001) single-crystal substrates by ultrahigh vacuum RF magnetron sputtering. The effects of the magnetic material and the substrate temperature on the film growth, the film structure, and the magnetic properties are investigated. The L10 ordered phase formation is observed for FePt, FePd, and CoPt films prepared at temperatures higher than 200, 400, and 600 °C, respectively, whereas that is not recognized for CoPd films. The L10-FePd(001) single-crystal films with the c-axis normal to the substrate surface are formed, whereas the FePt and CoPt epitaxial films include L10(100) crystals whose c-axis is parallel to the substrate surface, in addition to the L10(001) crystals. Upon increasing the substrate temperature, the ordering degree increases. A higher ordering parameter is observed in the order of FePd > FePt > CoPt. The magnetic properties are influenced by the crystal structure, the crystallographic orientation of the L10 crystal, and the ordering degree.

  11. Stress analysis and ferroelectric properties of Pb(Zr0.52Ti0.48)0.96Nb0.04O3 thin film grown on different thickness of BaPbO3 electrodes

    NASA Astrophysics Data System (ADS)

    Wen, Xin-Yi; Yu, Jun; Wang, Yun-Bo; Zhou, Wen-Li; Gao, Jun-Xiong

    2010-12-01

    Pb(Zr0.52Ti0.48)0.96Nb0.04O3 (PZTN) thin films were deposited on BaPbO3 (BPO) electrodes by rf-magnetron sputtering. 34, 68, 135, and 270 nm thick BPOs were adopted in this study. The preferred orientation changes from slightly (100)/(001) to slightly (101)/(110) as the BPO thickness increased. The mean grain sizes obtained by Williamson-Hall plots are 81 nm, 120 nm, 146 nm, and 90 nm, respectively. The same tendency was observed by atomic force microscopy method. In residual stress analysis, tensile stress was observed in every film. The stress magnitude is the maximum in the film with 135 nm thick BPO. Through a simple calculation, we suggest that the tensile stress in our films mainly originates from the phase transformation stresses. We also note that the ferroelectric and dielectrics properties are improved with the raise of tensile stresses. A possible reason is that the tensile stress benefits the tetragonal-monoclinic phase transition in the PZTN films with composition near morphotropic phase boundary. The other possible reason is that the raise of the tensile stress is consistent with the increasing of grain size, which decreases the grain boundary density and facilitate domain mobility.

  12. Semi-analytical modeling of the NIO1 source

    SciTech Connect

    Cazzador, M.; Cavenago, M.; Serianni, G.; Veltri, P.

    2015-04-08

    NIO1 is a compact and versatile negative ion source, with a total current of 130 mA accelerated to 60 keV. Negative ions are created inside the plasma, which is inductively coupled to an external rf cylindrical coil operating in the range of 2 ± 0.2 MHz. The plasma is confined in the source chamber (a 50 mm radius cylinder) by a multipole magnetic field and the ions are extracted through a 3x3 matrix of apertures. The use of cesium, to enhance the negative ion production by H{sub 0} bombardment of the surfaces, is foreseen in a second stage of the operation, so that at present time the source is operating in pure volume configuration. This paper presents a model aimed to describe the main physical phenomena occurring in the source, focusing on the rf coupling with the plasma and the evolution of plasma parameters in the source. With respect to more sophisticated models of negative ion sources here we aimed to develop a fast tool capable of qualitatively describing the response of the system to variations in the basic operating parameters. The findings of this models is finally compared with the first experimental results of NIO1.

  13. Custom instruction set NIOS-based OFDM processor for FPGAs

    NASA Astrophysics Data System (ADS)

    Meyer-Bäse, Uwe; Sunkara, Divya; Castillo, Encarnacion; Garcia, Antonio

    2006-05-01

    Orthogonal Frequency division multiplexing (OFDM) spread spectrum technique, sometimes also called multi-carrier or discrete multi-tone modulation, are used in bandwidth-efficient communication systems in the presence of channel distortion. The benefits of OFDM are high spectral efficiency, resiliency to RF interference, and lower multi-path distortion. OFDM is the basis for the European digital audio broadcasting (DAB) standard, the global asymmetric digital subscriber line (ADSL) standard, in the IEEE 802.11 5.8 GHz band standard, and ongoing development in wireless local area networks. The modulator and demodulator in an OFDM system can be implemented by use of a parallel bank of filters based on the discrete Fourier transform (DFT), in case the number of subchannels is large (e.g. K > 25), the OFDM system are efficiently implemented by use of the fast Fourier transform (FFT) to compute the DFT. We have developed a custom FPGA-based Altera NIOS system to increase the performance, programmability, and low power in mobil wireless systems. The overall gain observed for a 1024-point FFT ranges depending on the multiplier used by the NIOS processor between a factor of 3 and 16. A careful optimization described in the appendix yield a performance gain of up to 77% when compared with our preliminary results.

  14. First experiments with the negative ion source NIO1.

    PubMed

    Cavenago, M; Serianni, G; De Muri, M; Agostinetti, P; Antoni, V; Baltador, C; Barbisan, M; Baseggio, L; Bigi, M; Cervaro, V; Degli Agostini, F; Fagotti, E; Kulevoy, T; Ippolito, N; Laterza, B; Minarello, A; Maniero, M; Pasqualotto, R; Petrenko, S; Poggi, M; Ravarotto, D; Recchia, M; Sartori, E; Sattin, M; Sonato, P; Taccogna, F; Variale, V; Veltri, P; Zaniol, B; Zanotto, L; Zucchetti, S

    2016-02-01

    Neutral Beam Injectors (NBIs), which need to be strongly optimized in the perspective of DEMO reactor, request a thorough understanding of the negative ion source used and of the multi-beamlet optics. A relatively compact radio frequency (rf) ion source, named NIO1 (Negative Ion Optimization 1), with 9 beam apertures for a total H(-) current of 130 mA, 60 kV acceleration voltage, was installed at Consorzio RFX, including a high voltage deck and an X-ray shield, to provide a test bench for source optimizations for activities in support to the ITER NBI test facility. NIO1 status and plasma experiments both with air and with hydrogen as filling gas are described. Transition from a weak plasma to an inductively coupled plasma is clearly evident for the former gas and may be triggered by rising the rf power (over 0.5 kW) at low pressure (equal or below 2 Pa). Transition in hydrogen plasma requires more rf power (over 1.5 kW). PMID:26932048

  15. Flower-like NiO structures: Controlled hydrothermal synthesis and electrochemical characteristic

    SciTech Connect

    Chai, Hui; Chen, Xuan; Jia, Dianzeng; Bao, Shujuan; Zhou, Wanyong

    2012-12-15

    Graphical abstract: Flower-like porous NiO was obtained via thermal decomposition of the precursor prepared by a hydrothermal process using hexamethylenetetramine and polyethylene glycol as hydrolysis-controlling agent and surfactant, respectively. The morphology and microstructure of as-synthesized NiO were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results of electrochemical measurements demonstrated that the flower-like porous NiO has high capacity (340 F g{sup −1}) with excellent cycling performance as electrode materials of electrochemical capacitors (ECs), which may be attributed to the unique microstrcture of NiO. Data analyses indicated that NiO with novel porous structure attractive for practical and large-scale applications in electrochemical capacitors. Display Omitted Highlights: ► Synthesis and characterization of NiO with novel porous structure is presented in this work. ► The electrochemical performance of product was examined. ► NiO with excellent performance as electrode materials may be due to the unique microstrcture. ► NiO with novel porous structure attractive for practical with high capacity (340 F g{sup −1}). -- Abstract: Flower-like porous NiO was obtained by thermal decomposition of the precursor prepared by a hydrothermal process with hexamethylenetetramine and polyethylene glycol as hydrolysis-controlling agent and surfactant, respectively. The morphology and microstructure of as-synthesized NiO were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The resulting structures of NiO exhibited porous like petal building blocks. The electrochemical measurements’ results demonstrated that flower-like porous NiO has high capacity (340 F g{sup −1}) with excellent cycling performance as electrode materials for

  16. Properties of Pb(0.92)La(0.08)Zr(0.52)Ti(0.48)O(3) thin films grown on SrRuO(3) buffered nickel and silicon substrates by chemical solution deposition

    SciTech Connect

    Narayanan, M.; Ma, B.; Tong, S.; Koritala, R.; Balachandran, U.

    2012-01-01

    Ferroelectric film-on-foil capacitors are suitable to replace discrete passive components in the quest to develop electronic devices that show superior performance and are smaller in size. The film-on-foil approach is the most practical method to fabricate such components. Films of Pb{sub 0.92}La{sub 0.08}Zr{sub 0.52}Ti{sub 0.48}O{sub 3} (PLZT) were deposited on SrRuO{sub 3} (SRO) buffer films over nickel and silicon substrates. High-quality polycrystalline SRO thin-film electrodes were first deposited by chemical solution deposition. A phase pure, dense, uniform microstructure with grain size <100 nm was obtained in films crystallized at 700 C. The room-temperature resistivity of the SRO films crystallized at 700 C was {approx}800-900 {mu}{Omega}-cm. The dielectric properties of sol-gel derived PLZT capacitors on SRO-buffered nickel were evaluated as a function of temperature, bias field, and frequency, and the results were compared to those of the same films on silicon substrates. The comparison demonstrated the integrity of the buffer layer and its compatibility with nickel substrates. Device-quality dielectric properties were measured on PLZT films deposited on SRO-buffered nickel foils and found to be superior to those for PLZT on SRO-buffered silicon and expensive platinized silicon. These results suggest that SRO films can act as an effective barrier layer on nickel substrates suitable for embedded capacitor applications.

  17. Electric-field-controlled interface strain coupling and non-volatile resistance switching of La1-xBaxMnO3 thin films epitaxially grown on relaxor-based ferroelectric single crystals

    NASA Astrophysics Data System (ADS)

    Zheng, Ming; Zhu, Qiu-Xiang; Li, Xue-Yan; Yang, Ming-Min; Wang, Yu; Li, Xiao-Min; Shi, Xun; Luo, Hao-Su; Zheng, Ren-Kui

    2014-09-01

    We have fabricated magnetoelectric heterostructures by growing ferromagnetic La1-xBaxMnO3 (x = 0.2, 0.4) thin films on (001)-, (110)-, and (111)-oriented 0.31Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb1/2)O3-0.34PbTiO3 (PINT) ferroelectric single-crystal substrates. Upon poling along the [001], [110], or [111] crystal direction, the electric-field-induced non-180° domain switching gives rise to a decrease in the resistance and an enhancement of the metal-to-insulator transition temperature TC of the films. By taking advantage of the 180° ferroelectric domain switching, we identify that such changes in the resistance and TC are caused by domain switching-induced strain but not domain switching-induced accumulation or depletion of charge carriers at the interface. Further, we found that the domain switching-induced strain effects can be efficiently controlled by a magnetic field, mediated by the electronic phase separation. Moreover, we determined the evolution of the strength of the electronic phase separation against temperature and magnetic field by recording the strain-tunability of the resistance [(ΔR/R)strain] under magnetic fields. Additionally, opposing effects of domain switching-induced strain on ferromagnetism above and below 197 K for the La0.8Ba0.2MnO3 film and 150 K for the La0.6Ba0.4MnO3 film, respectively, were observed and explained by the magnetoelastic effect through adjusting the magnetic anisotropy. Finally, using the reversible ferroelastic domain switching of the PINT, we realized non-volatile resistance switching of the films at room temperature, implying potential applications of the magnetoelectric heterostructure in non-volatile memory devices.

  18. Electric-field-controlled interface strain coupling and non-volatile resistance switching of La{sub 1-x}Ba{sub x}MnO₃ thin films epitaxially grown on relaxor-based ferroelectric single crystals

    SciTech Connect

    Zheng, Ming; Zhu, Qiu-Xiang; Li, Xue-Yan; Yang, Ming-Min; Li, Xiao-Min; Shi, Xun; Luo, Hao-Su; Zheng, Ren-Kui; Wang, Yu

    2014-09-21

    We have fabricated magnetoelectric heterostructures by growing ferromagnetic La{sub 1-x}Ba{sub x}MnO₃ (x=0.2, 0.4) thin films on (001)-, (110)-, and (111)-oriented 0.31Pb(In{sub 1/2}Nb{sub 1/2})O₃-0.35Pb(Mg{sub 1/3}Nb{sub 1/2})O₃-0.34PbTiO₃ (PINT) ferroelectric single-crystal substrates. Upon poling along the [001], [110], or [111] crystal direction, the electric-field-induced non-180° domain switching gives rise to a decrease in the resistance and an enhancement of the metal-to-insulator transition temperature TC of the films. By taking advantage of the 180° ferroelectric domain switching, we identify that such changes in the resistance and TC are caused by domain switching-induced strain but not domain switching-induced accumulation or depletion of charge carriers at the interface. Further, we found that the domain switching-induced strain effects can be efficiently controlled by a magnetic field, mediated by the electronic phase separation. Moreover, we determined the evolution of the strength of the electronic phase separation against temperature and magnetic field by recording the strain-tunability of the resistance [(ΔR/R){sub strain}] under magnetic fields. Additionally, opposing effects of domain switching-induced strain on ferromagnetism above and below 197 K for the La₀.₈Ba₀.₂MnO₃ film and 150 K for the La₀.₆Ba₀.₄MnO₃ film, respectively, were observed and explained by the magnetoelastic effect through adjusting the magnetic anisotropy. Finally, using the reversible ferroelastic domain switching of the PINT, we realized non-volatile resistance switching of the films at room temperature, implying potential applications of the magnetoelectric heterostructure in non-volatile memory devices.

  19. Facile synthesis of self-assembled biporous NiO and its electrochemical properties

    NASA Astrophysics Data System (ADS)

    Muruganandham, M.; Suri, Rominder P. S.; Sillanpää, Mika; Lee, Gang-Juan; Wu, Jerry J.

    2016-09-01

    In this article, we report the synthesis of self-assembled bi-porous nickel oxide on a large scale without using any templates or matrix. Porous NiO microspheres composed of particles were obtained by thermal decomposition of nickel oxalate, which was prepared using nickel salt and oxalic acid as precursors. The as-obtained nickel oxalate and nickel oxide were characterized using X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), thermogravimetric analysis (TGA), and nitrogen adsorption-desorption analysis. The influence of various experimental conditions on the formation nickel oxalate and NiO were studied. The nitrogen adsorption-desorption analysis showed that the synthesized NiO possesses a biporous (both mesoporous and macroporous) surface structur. The NiO microspheres showed a discharge capacity of 2929 mAh g-1. A plausible mechanism for the NiO self-assembly was proposed.

  20. Microstructure and thermal conductivity of surfactant-free NiO nanostructures

    SciTech Connect

    Sahoo, Pranati; Misra, Dinesh K.; Salvador, Jim; Makongo, Julien P.A.; Chaubey, Girija S.; Takas, Nathan J.; Wiley, John B.; Poudeu, Pierre F.P.

    2012-06-15

    High purity, nanometer sized surfactant-free nickel oxide (NiO) particles were produced in gram scale using a solution combustion method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), gas pycnometry and gas adsorption analysis (BET). The average particle size of the as-synthesized NiO increases significantly with the preheating temperature of the furnace, while the specific surface area decreases. A BET specific surface area of {approx}100 m{sup 2}/g was obtained for NiO nanoparticles with size as small as 3 nm synthesized at 300 Degree-Sign C. The thermal conductivity ({kappa}) of pressed pellets of the synthesized NiO nanoparticles obtained using spark plasma sintering (SPS) and uniaxial hot pressing is drastically decreased ({approx}60%) compared to that of NiO single crystal. This strong reduction in {kappa} with particle size suggests the suitability of the synthesized surfactant-free NiO nanoparticles for use as nanoinclusions when designing high performance materials for waste heat recovery. - Graphical abstract: Highly efficient phonon scattering by surfactant-free NiO nanostructures obtained by solution combustion of a mixture of nickel (II) nitrate hexahydrate (oxidizer) and urea (fuel) at various temperatures. Highlights: Black-Right-Pointing-Pointer Fast synthesis of surfactant-free NiO nanoparticles with controllable size. Black-Right-Pointing-Pointer High specific surface area for NiO nanoparticles with size range from 3 to 7 nm. Black-Right-Pointing-Pointer Strong reduction of the thermal conductivity with decreasing particle size. Black-Right-Pointing-Pointer NiO as nanoinclusions in high performance materials for energy conversion.