Growth and applications of superconducting and nonsuperconducting oxide epitaxial films

Growth and characterization of high-temperature-superconducting YBa2Cu3O7 and several metallic-oxide thin films by pulsed laser deposition is described here. An overview of substrates employed for epitaxial growth of perovskite-related oxides is presented. Ag-doped YBa2Cu3O7 films grown on bare sapphire are shown to give T-c = 90 K, critical current > 10(6) A/cm(2) at 77 K and surface resistance = 450 mu Omega. Application of epitaxial metallic LaNiO3 thin films as an electrode for ferroelectric oxide and as a normal metal layer barrier in the superconductor-normal metal-superconductor (SNS) Josephson junction is presented. Observation of giant magnetoresistance (GMR) in the metallic La0-6Pb0-4MnO3 thin films up to 50% is highlighted.

Growth and characterization of laser-deposited Ag-doped YBa2Cu3O7−x thin films on bare sapphire

Microstructural and superconducting properties of YBa2Cu3O7-x thin films grown in situ on bare sapphire by pulsed laser deposition using YBa2Cu3O7-x targets doped with 7 and 10 wt% Ag have been studied. Ag-doped films grown at 730 degrees C on sapphire have shown very significant improvement over the undoped YBa2Cu3O7-x films grown under identical condition. A zero resistance temperature of 90 K and a critical current density of 1.2 x 10(6) A/cm(2) at 77 K have been achieved on bare sapphire for the first time. Improved connectivity among grains and reduced reaction rate between the substrate and the film caused due to Ag in the film are suggested to be responsible for this greatly improved transport properties.

Spectroscopic Studies on Silver Selenide Thin Films

Silver selenide thin films of thickness between 80 nm and 160 nm were prepared by thermal evaporation technique at a high vacuum better than 2x10(-5)mbar on well cleaned glass substrates at a deposition rate of 0.2 nm/sec. Silver selenide thin films were polycrystalline with orthorhombic structure. Ellipsometric spectra of silver selenide thin films have been recorded in the wavelength range between 300 nm and 700 nm. Optical constants like refractive index, extinction coefficient, absorption coefficient, and optical band gap of silver selenide thin film have been calculated from the recorded spectra. The refractive index of silver selenide has been found to vary between 1.9 and 3.2 and the extinction coefficient varies from 0.5 to 1.6 with respect to their corresponding thickness of the films. Transmittance spectra of these films have been recorded in the wavelength range between 300 nm and 900 nm and its spectral data are analysed. The photoluminescence studies have been carried out on silver selenide thin films and the strong emission peak is found around 1.7 eV. The calculated optical band of thermally evaporated silver selenide thin films is found to be around 1.7 eV from their Ellipsometric, UV-Visible and Photoluminescence spectroscopic studies.

Substrate-dependent structure, microstructure, composition and properties of nanostructured TiN films

Titanium nitride films of a thickness of similar to 1.5 mu m were deposited on amorphous and crystalline substrates by DC reactive magnetron sputtering at ambient temperature with 100% nitrogen in the sputter gas. The growth of nanostructured, i.e. crystalline nano-grain sized, films at ambient temperature is demonstrated. The microstructure of the films grown on crystalline substrates reveals a larger grain size/crystallite size than that of the films deposited on amorphous substrates. Specular reflectance measurements on films deposited on different substrates indicate that the position of the Ti-N 2s band at 2.33 eV is substrate-dependent, indicating substrate-mediated stoichiometry. This clearly demonstrates that not only structure and microstructure, but also chemical composition of the films is substrate-influenced. The films deposited on amorphous substrates display lower hardness and modulus values than the films deposited on crystalline substrates, with the highest value of hardness being 19 GPa on a lanthanum aluminate substrate. (C) 2011 Elsevier Ltd. All rights reserved.

Scanning tunneling microscopy and spectroscopy of C70 thin films

Scanning tunneling microscopy of C-70 films deposited on HOPG and gold substrates has been carried but to investigate the 2D packing, defects and disorder. Besides providing direct evidence for orientational disorder, high resolution; images showing the carbon skeleton as well as the molecular arrangement in a solid solution of C-70 and C-60 are presented. Tunneling conductance measurements Indicate a small gap in the C-70 film deposited on HOPG substrate.

Surface barrier effects in non-resonant microwave absorption by superconducting thin films of YBa2Cu3O7??

We present an unusual temperature dependence of hysteresis in the Lion resonant microwave absorption (NRMA) signals from superconducting thin films of YBa2Cu3O7-delta. We observe that the hysteresis increases with increase in temperature till T-c which we interpret as evidence for the presence of Bean-Livingston surface barriers (BLSB) in the single crystalline films.

Synthesis and properties of zirconia thin films

Thin films of zirconia have been synthesized using reactive DC magnetron sputtering. It has been found that films with good optical constants, high refractive index (1.9 at 600 nm) and low extinction coefficient can be prepared al ambient temperatures. The optical constants and band gnp and hence the composition nle dependent on the deposition parameters such as target power, rate of deposition and oxygen background pressure. Thermal annealing of the films revealed that tile films showed optical and crystalline inhomogeneity and also large variations in optical constants.

Structural and electrical properties of radio frequency magnetron sputtered tantalum oxide films: Influence of post-deposition annealing

The as-deposited and annealed radio frequency reactive magnetron sputtered tantalum oxide (Ta2O5) films were characterized by studying the chemical binding configuration, structural and electrical properties. X-ray photoelectron spectroscopy and X-ray diffraction analysis of the films elucidate that the film annealed at 673 K was stoichiometric with orthorhombic beta-phase Ta2O5. The dielectric constant values of the tantalum oxide capacitors with the sandwich structure of Al/Ta2O5/Si were in the range from 14 to 26 depending on the post-deposition annealing temperature. The leakage current density was < 20 nA cm(-2) at the gate bias voltage of 0.04 MV/cm for the annealed films. The electrical conduction mechanism observed in the films was Poole-Frenkel. (C) 2010 Elsevier Ltd. All rights reserved.

Thickness-dependent fcc-hcp phase transformation in polycrystalline titanium thin films

Polycrystalline Ti thin films are shown to gradually transform from face-centered cubic (fcc) to hexagonal close-packed structure (hcp) with increasing film thickness. Diffraction stress analysis revealed that the fcc phase is formed in a highly compressive hcp matrix (>= 2 GPa), the magnitude of which decreases with increasing film thickness. A correlation between stress and crystallographic texture vis-a-vis the fcc-hcp phase transformation has been established. The total free energy change of the system upon phase transformation calculated using the experimental results shows that the fcc-hcp transformation is theoretically possible in the investigated film thickness regime (144-720 nm) and the hcp structure is stable for films thicker than 720 nm, whereas the fcc structure can be stabilized in Ti films much thinner than 144 nm. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Conductivity and structural studies on disordered amorphous conducting carbon films

Amorphous carbon films are prepared by the pyrolysis of Tetra Chloro Phthalic Anhydride (TCPA) at different temperatures (700 degrees C to 900 degrees C). DC Conductivity measurements are done on the films in the temperature range 300K to 4.2K. It shows an activated temperature dependence with a small activation energy (0.02eV to 0.003eV). Variable range hopping is observed at low temperatures. The films are characterised by XRD, SEM, TEM, AFM and microRaman. The electronic structure of the film is used to explain the electrical behaviour.

Sputter deposited LiPON thin films from powder target as electrolyte for thin film battery applications

Lithium phosphorus oxynitride (LiPON) thin films as solid electrolytes were prepared by reactive radio frequency (rf) magnetron sputtering from Li3PO4 powder compact target. High deposition rates and ease of manufacturing powder target compared with conventional ceramic Li3PO4 targets offer flexibility in handling and reduce the cost associated. Rf power density varied from 1.7 Wcm(-2) to 3 Wcm(-2) and N-2 flow from 10 to 30 sccm for a fixed substrate to target distance of 4 cm for best ionic conductivity. The surface chemical analysis done by X-ray photoelectron spectroscopy showed incorporation of nitrogen into the film as both triply, NE and doubly. Nd coordinated form. With increased presence of NE, ionic conductivity of LiPON was found to be increasing. The electrochemical impedance spectroscopy of LiPON films confirmed an ionic conductivity of 1.1 x 10(-6) Scm(-1) for optimum rf power and N-2 flow conditions. (C) 2011 Elsevier B.V. All rights reserved.

Buckling patterns in diamond-like carbon films

An optical microscopy study of stress relief patterns in diamond-like carbon films is presented. Interesting stress relief patterns are observed which include the well-known sinusoidal type, branching pattern and string-of-beads pattern. The last one is shown to relieve stresses under marginal conditions. Two new stress relief patterns are noted in the present study. One of them is of sinusoidal shape with two extra branches at every peak position. The distribution of different stress relief forms from the outer edge of the films towards the interior is markedly dependent on the film thickness. Our new patterns support the approach in which the stress relief forms have been analysed earlier using the theory of plate buckling.