Optical properties change in amorphous (As2S3)(0.87)Sb-0.13 thin films by photo and thermal induced process

Exposure with above band gap light and thermal annealing at a temperature near to glass transition temperature, of thermally evaporated amorphous (As2S3)(0.87)Sb-0.13 thin films of 1 mu m thickness, were found to be accompanied by structural effects, which in turn, lead to changes in the optical properties. The optical properties of thin films induced by illumination and annealing were studied by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Photo darkening or photo bleaching was observed in the film depending upon the conditions of the light exposure or annealing. These changes of the optical properties are assigned to the change of homopolar bond densities. (C) 2010 Elsevier B.V. All rights reserved.

Effect of sodium diffusion on the structural and electrical properties of Cu2ZnSnS4 thin films

Cu2ZnSnS4 (CZTS) is a kesterite semiconductor consisting of abundantly available elements. It has a band gap of 1.5 eV and a large absorption coefficient. Hence, thin films made of this material can be used as absorber layers of a solar cell. CZTS films were deposited on soda lime and Na free borosilicate glass substrates through Ultrasonic Spray Pyrolysis. The diffusion of sodium from soda lime glass was found to have a profound effect on characteristics like grain size, crystal texture and conductivity of CZTS thin films. Copper ion concentration also varied during the deposition and it was observed that the carrier concentration was enhanced when there was a deficiency of copper in the films. The effect of sodium diffusion and copper deficiency in enhancing the structural and electrical properties of CZTS films are presented in this paper. (C) 2010 Elsevier B.V. All rights reserved.

Photocatalytic Inactivation of Escherichia coli with LbL Fabricated Immobilized TiO2 Thin Films

Photocatalysis using semiconductor catalyst such as TiO2, in presence of UV light, is a promising technique for the inactivation of various microorganisms present in water. In the current study, the photocatalytic inactivation of Escherichia coli bacteria was studied with commercial Degussa Aeroxide TiO2 P25 (Aeroxide) and combustion synthesized TiO2 (CS TiO2) catalysts immobilized on glass slides in presence of UV irradiation. Thin films of the catalyst and polyelectrolytes, poly(allyl amine hydrochloride) and poly(styrene sulfonate sodium salt), were deposited on glass slides by layer by layer (LbL) deposition method and characterized by SEM and AFM imaging. The effect of various parameters, namely, catalyst concentration, surface area and number of bilayers, on inactivation was studied. Maximum inactivation of 8-log reduction in the viable count was observed with 1.227 mg/cm(2) of catalyst loaded slides. With this loading, complete inactivation was observed within 90 min and 75 min of irradiation, for Aeroxide and CS TiO2, respectively. Further increase in the catalyst concentration or increasing number of bilayers had no significant effect on inactivation. The effect of surface area on the inactivation was studied by increasing the number of slides and the inactivation was observed to increase with increasing surface area. It was also observed that the immobilized catalyst slides can be used for several cycles leading to an economic process. The study shows potential application of TiO2, for the inactivation of bacteria, in its fixed form by a simple immobilization technique.

Ferromagnetic La0.6Pb0.4MnO3 thin films with giant magnetoresistance at 300 K

Highly textured, as-deposited La0.6Pb0.4MnO3 thin films have been grown on LaAlO3 by pulsed laser deposition. The films are ferromagnetic metals below 300 K. Giant negative magnetoresistance of over 40% is observed at 300 K at 6 T.

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.

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.

Chemical and microstructural modifications in LiPON thin films exposed to atmospheric humidity

Lithium phosphorus oxynitride (LiPON), the widely used solid electrolyte for thin film microbatteries, is not compatible with the ambient humid temperatures. The reasons for reduction in ionic conductivity of LiPON thin films from 2.8 x 10(-6) Scm(-1) to 9.9 x 10(-10) Scm(-1) when exposed to air are analyzed with the aid of AC impedance measurements, SEM, XPS and stylus profilometry. Initially, particulate-free film surfaces obtained soon after rf sputter deposition in N-2 ambient conditions becomes covered with microstructures, forming pores in the film when exposed to air. LiPON films are deposited on Ti coated silicon in addition to bare silicon, ruling out the possibility of stress-related rupturing from the LiPON/Si interface. The reduction of nitrogen, phosphorus, and increased presence of lithium, oxygen and carbon over the film surface lowers the ionic conductivity of LiPON films when exposed to air. (c) 2011 Elsevier B.V. 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.

Metal-insulator transition and giant magnetoresistance in La1-xMnO3-delta thin films and superlattices

The first fabrication of self-doped La1-xMnO3-delta films which are unique among the other La(1-x)M(x)MnO(3) (M = Ca, Ba and Pb) thin films showing giant magnetoresistance is reported. Ag-doped La0.7MnO3-delta films were grown on LaAlO3[100] substrates. These films show ferromagnetic and metal-insulator transition at 220 K and exhibit giant magnetoresistance (GMR) with Delta R/R(o) = 85% and Delta R/R(H) > 550%. Without silver addition these self-doped films are non-magnetic, Enhancement in GMR up to 8% has been observed in superlattices having alternate magnetic and non-magnetic La1-xMnO3-delta layers.

A Comparative Study of Electrical Switching Behavior of Certain Tellurium based Chalcogenide Thin Films for Phase Change Memory (PCM) Applications

This work describes the electrical switching behavior of three telluride based amorphous chalcogenide thin film samples, Al-Te, Ge-Se-Te and Ge-Te-Si. These amorphous thin films are made using bulk glassy ingots, prepared by conventional melt quenching technique, using flash evaporation technique; while Al-Te sample has been coated in coplanar electrode geometry, Ge-Se-Te and Ge-Te-Si samples have been deposited with sandwich electrodes. It is observed that all the three samples studied, exhibit memory switching behavior in thin film form, with Ge-Te-Si sample exhibiting a faster switching characteristic. The difference seen in the switching voltages of the three samples studied has been understood on the basis of difference in device geometry and thickness. Scanning electron microscopic image of switched region of a representative Ge15Te81Si4 sample shows a structural change and formation of crystallites in the electrode region, which is responsible for making a conducting channel between the two electrodes during switching.

Structural and optical properties of RF sputtered Bi2VO5.5 thin films

Thin films of Bismuth Vanadate Bi2VO5.5 (BiV) have been deposited on amorphous quartz and polycrystalline silicon substrates by r.f. sputtering technique and characterised for their structural and optical properties. The os-deposited films at room temperature are found to be amorphous and transparent over the spectral range of 0.55 mu m to 12 mu m. Post-deposition annealing at 400 degrees C in air shows the formation of the BiV crystalline phase. The optical constants namely refractive index. extinction coefficient and optical bandgap of both amorphous and crystalline films have been determined. The refractive index of the as-deposited film is around 2.4 at 0.7 mu m and drops to 2.26 at 1.56 mu m. The optical bandgap of the material has been determined from the computed values of the absorption coefficients.