Undoped tin oxide (TO), palladium-doped tin oxide (PTO) and fluorine-doped tin oxide (FTO) thin films have been prepared by spray pyrolysis method, under optimized conditions. Transmission measurement of the TO, PTO and FTO films have been studied in the UV-Visible region. Band gap energy evaluated from the spectral data lies between 3.15 eV and 3.8 eV. The X-ray diffraction analysis of the films confirms a polycrystalline, tetragonal rutile structure of tin oxide, with preferred orientation along the (101) plane. The lattice constants, a and c, were evaluated as 4.7256 Å and 3.1768 Å . The average grain size lies between 470 nm and 850 nm and its variation as a function of annealing temperature have been studied and reported. The AFM micrographs of the films reveal smooth and uniform surface pattern without any dark pits, pinholes and microcracks. The sheet resistance (R) and electrical resistivity ( r) of the films under ambient condition and CO gas atmosphere have been studied at different operating temperatures, in a specially designed sensor test rig setup. From the resistance measurement, response and recovery characteristics, detection sensitivity and optimum operating temperature of the as-coated TO, FTO and PTO films towards CO gas have been investigated and the results are discussed. Studies show a maximum detection sensitivity of 13.6% with a minimum response time of 110 sec. for the PTO thin films, at the operating temperature of 3508 8 8 8 8C.

P-type porous silicon (PS) structure has been prepared by anodic electrochemical etching process under optimized conditions. Photoluminescence studies of the PS structure show emission at longer wavelengths (red) for the excitation at 365 nm. Scanning electron microscope investigations of the PS surface confirm the formation of uniform porous structure, and the pore diameter have been estimated as 25 μm. Pd:SnO 2 /PS/p-Si heterojunction with top gold ohmic contact developed by conventional methods has been used as the sensor device. Sensing properties of the device towards liquefied petroleum gas (LPG) and NO 2 gas have been investigated in an indigenously developed sensor test rig. The response and recovery characteristics of the sensor device at different operating temperatures show short response time for LPG. From the studies, maximum sensitivity and optimum operating temperature of the device towards LPG and NO 2 gas sensing has been estimated as 69% at 180°C and 52% at 220°C, respectively. The developed sensor device shows a short response time of 25 and 57 s for sensing LPG and NO 2 gases, respectively.

Abstract. Undoped and antimony doped tin oxide thin films of different thicknesses were prepared on mineral glass substrate by spray pyrolysis method via sol-gel route. Both the films show good transmittance in the visible region. Band gap energy of both films lies between 3 to 3.5 eV. X-ray diffraction studies of undoped and antimony doped tin oxide thin films for various annealing temperature show polycrystalline tetragonal structure of SnO2 with preferred orientation of (110) and (101), respectively and from the XRD data, grain size were also evaluated. AFM images of Undoped and antimony doped tin oxide thin films annealed at 375 ~ depict the film thickness and indicate uniform surface pattern without dark pits and with strains of some ups exceeding the specified limit. The prepared films were tested in a specially developed test rig for Liquefied Petroleum Gas detection at different operating temperatures. The response characteristics of the films for LPG detection show maximum sensitivity and minimum response time at the operating temperature 400 ~ Studies indicate that antimony doped tin oxide thin film are one among the suitable candidates for LPG detection with a detection sensitivity and response time (t90) of 11 and 140 seconds, respectively.

Abstract. Present work deals with the preparation of TiO2 thin films of different thicknesses by PVD technique using an electron beam and to characterize the films for oxygen gas detection. The films were characterized using optical transmission measurements, XRD and atomic force microscopy. From the spectral data, the extinction, absorption coefficient and refractive index of the films are evaluated and reported. The optical band gap energy varies between 3 and 3.68 eV. The XRD pattern confirms the formation of polycrystalline anatase structure of Titanium with preferred orientation of (110) plane. The AFM images indicate the presence of coarse and fine grains with uniform as well as smooth surfaces over the entire range of the analyzed surface. Response characteristics of TiO 2 thin films for oxygen gas detection are studied, which indicate a low response time of 120 seconds and high sensitivity of 16 at the operating temperature 450 ~