Showing papers by "Kandasamy Prabakar published in 2006"

Optimization and deposition of CdS thin films as applicable to TiO2∕CdS composite catalysis

Abstract: Methanol decomposition has been studied by in situ Fourier transform infrared spectroscopy on a CdS∕TiO2 bilayer deposited on glass substrates. First CdS thin films were deposited by chemical bath deposition method using the CdSO4 and thiourea as the precursors and ammonia as the complexing agent and have the optical band gap of 2.2–2.29 eV for the different CdSO4 solution concentrations. The structure of the CdS films was found to have mixed cubic and hexagonal phases, while the TiO2 films were polycrystalline anatase structure with an optical band-gap energy of 3.2 eV deposited at a total sputtering pressure of 0.1 Pa in an argon and oxygen gas mixture (Ar:O2=80:20) at 200 W sputtering power. The visible light active photocatalytic degradation efficiency of methanol over a TiO2∕CdS double layer is four times higher than that of a TiO2 single layer. The decomposition of methanol pathway proceeds via formaldehyde as the intermediate product.

Effect of nitrogen on the photocatalytic activity of TiOxNy thin films

Abstract: Visible light active nitrogen doped titanium oxide (TiOxNy) thin films were deposited by dc reactive magnetron sputtering on glass substrates at different nitrogen flow rates and sputtering pressures. All the deposited films consist of composite of TiOxNy and TiO2 phases of anatase and a small portion of the rutile (R) phase was embedded in the polycrystalline films. X-ray diffraction and optical studies confirmed that the prepared films had nitrogen substituted at some of the oxygen sites in TiO2, which formed narrow N 2p band above the valence band. The surface roughness of the films varied between 5 and 25 nm for the films deposited at nitrogen flow of 0.5–5 SCCM (standard cubic centimeter per minute), respectively. The photocatalytic decomposition of methanol was investigated using fourier transform infrared as a function of irradiation time. The formaldehyde and CO species are the main intermediates by increasing the irradiation time in the presence of pure methanol and CO2 is produced after the comp...

Sputtering pressure dependent photocatalytic properties of TiO2 thin films

Abstract: The TiO2 films were deposited on glass substrate by direct current reactive magnetron sputtering under various total sputtering gas pressures (PTot) of 02, 05, 08, and 5Pa and at the target to substrate distances (DT-S) of 40 and 70mm Argon and oxygen gas mixtures (Ar:O2=80:20) were used to deposit the films The optimum conditions to deposit the films with high photocatalytic activities were investigated in detail using in situ Fourier transform infrared spectra in relation to the sputter deposition processes The band gap energy was found to decrease from 325to313eV for the TiO2 films deposited at PTot of 5–02Pa and DT-S of 40mm For the films deposited at DT-S of 70mm, the band gap varied between 33 and 32eV The rate of decomposition of methanol is rapid for the films deposited at PTot of 02Pa and DT-S of 40mm and as the DT-S and PTot increase, the photo-oxidation of methanol by TiO2 decreases The formaldehyde and CO species are the main intermediates by increasing the irradiation time and

UV, Violet and Blue‐Green Luminescence from RF Sputter Deposited ZnO:Al Thin Films.

Abstract: The mechanism of ultraviolet (UV), violet and blue green emission from ZnO:Al (AZO) thin films deposited at different radio frequency (r.f.) powers on glass substrates was investigated. The structure and surface morphology of AZO films have also been observed. The optical transmittance spectra shows more than 80% transmittance in the visible region and the band gap is found to be directly allowed. From the photoluminescence measurement, intense UV and blue green luminescence is obtained for the samples deposited at higher sputtering powers. The mechanism of luminescence suggests that UV luminescence of AZO thin film is related to the transition from near band edge to the valence band and the concentration of antisite oxide (Ozn) increases with increase in r.f. power which in turn increases the intensity of green band emission while the violet PL is due to the defect level transition in the grain boundaries of AZO films. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)