Nanocrystalline SnO 2 thin films were successfully prepared using sol-gel dip coating technique. The starting precursor was used as tin chloride dihydrate (SnCl 2 .2H 2 O), ethanol and glycerin. As the prepared films were fired at 500 o C. These films were characterized using XRD, FE-SEM and TEM to known crystal structure, surface morphology and microstructure property. Elemental composition was studied using energy dispersive spectrophotometer (EDAX). The H 2 gas sensing performance of nanocrystalline SnO 2 thin films were investigated and presented. It was found that the nanocrystalline SnO 2 thin films gives maximum gas response (S= 360) at 75 o C. The sensor shows fast speed of response (T Response = 2 s) and quick recover (T recover = 8 s).

Thick films of AR grade In2O3were prepared by standard screen-printing technique. The gas sensing performances of thick films were tested for various gases. It showed maximum sensitivity to ethanol vapour at 350°C for 80 ppm concentration. To improve the sensitivity and selectivity of the film towards a particular gas, In2O3sensors were surface-modified by dipping them in a solution of 2% nanosilver for different intervals of time. Obtained results indicated that spherical nano-Ag grains are highly dispersed on the surface of In2O3sensor. The surface area of the nano-Ag/ In2O3sensor is several times larger than that of pure In2O3sensor. In comparison with pure In2O3sensor, all of the nano-Ag-doped sensors showed better sensing performance in respect of response, selectivity, and optimum operating temperature. The surface-modified (30 min) In2O3sensor showed larger sensitivity to H2S gas (10 ppm) at 100°C. Nano silver on the surface of the film shifts the reactivity of film from ethanol vapour to H2S gas. A systematic study of gas sensing performance of the sensor indicates the key role played by the nano silver species on the surface. The sensitivity, selectivity, response, and recovery time of the sensor were measured and presented.

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Abstract-Strontium titanate (SrTiO 3 ) nanopowder has been synthesized through a sol-gelhydrothermal method. The X-ray diffraction studies of SrTiO 3 nanopowder have shown that the asprepared powder was single phase, crystalline, and has a cubic perovskite structure (ABO 3 ) with a lattice constant a = 3.903 Å. The particle size calculated from FWHM was ∼22 nm. SrTiO 3 nanopowder was examined using thermo gravimetric analysis; differential thermal analysis and UVvisible absorption spectroscopy. The transmission electron microscopic investigations have shown that the particle size of the as-prepared powder has a mean size of 34 nm. Then highly sensitive and selective sensors to H 2 S based on glass substrate were fabricated successfully by screen-printing

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