Pure ZnO thick film, prepared by screen-printing technique, was almost insensitive to NH 3 . Pure ZnO thick films were surface modified with MnO 2 by dipping them into 0.01 M aqueous solution of manganese chloride (MnCl 2 ) for different intervals of time and fired at 500˚C for 12 h. The grains of MnO 2 would disperse around the grains of ZnO base material. The MnO 2 modified ZnO films dipped for 30 min were observed to be sensitive and highly selective to NH 3 gas at room temperature. An exceptional sensitivity was found to low concentration (50 ppm) of NH 3 gas at room temperature and no cross sensitivity was observed even to high concentrations of other hazardous and polluting gases. The effects of surface microstructure and MnO 2 concentrations on the sensitivity, selectivity, response and recovery of the sensor in the presence of NH 3 and other gases were studied and discussed. The better performance could be attributed to an optimum number of surface misfits in terms of MnO 2 on the ZnO films.

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The objective of the present paper is to investigate the effect of variation of precursor concentration (0•01, 0•02 and 0•03 M) on the structural, microstructural, optical and gas sensing properties of TiO 2 thin films. Titanium dioxide (TiO 2) films were prepared from aqueous solution of titanium chloride (TiCl 3 •6H 2 O, 99•9% pure, Merck made, Germany) onto the glass substrates heated at a temperature of 350 • C by the spray pyrolysis technique. Bandgap energy of the films vary from 3•28 to 3•29 eV. X-ray diffraction shows that films to be nanocrystalline with anatase phase having tetragonal crystal structure. The d values calculated from electron diffraction patterns (TEM) were observed to be matching with d values calculated from XRD. Transmission electron microscopy (TEM) reveled that grain sizes were observed to increase (10-29 nm) with an increase in the concentration of precursor solution. The gas sensing performance of the films was tested. Keywords. Spray pyrolysis; nanocrystalline TiO 2 ; electron diffraction pattern.

Nanostructured pure and Pt-doped TiO 2 thin films were prepared by chemical spray pyrolysis technique. Aqueous solution of TiCl 3 ⋅6H 2 O (0⋅01 M) was chosen as the starting solution for the preparation of pure TiO 2 thin film. Aqueous solutions of PtCl 6 ⋅6H 2 O (0⋅01 M) and TiCl 3 ⋅6H 2 O (0⋅01 M) were mixed in volume % of 1 : 99, 2⋅5 : 97⋅5 and 5 : 95 respectively to obtain Pt-doped TiO 2 thin films. The solutions were sprayed onto quartz substrate heated at 350 °C temperature to obtain the films. These thin films were fired for one hour at 550 °C. The sensing performance of these films was tested for various gases such as LPG, H 2 , CO 2 , ethanol, NH 3 and Cl 2 (1000 ppm). The Pt-doped TiO 2 (1 : 99) was observed to be most sensitive (572) to H 2 at 400 °C with high selectivity against other gases. Its response time was short (10 s) and recovery was also fast (14 s). To understand the reasons behind the gas-sensing performance of the films, their structural and microstructral properties were studied using X-ray diffraction and electron microscopy (FE-SEM and TEM), respectively. Thicknesses of all these samples were determined using Surface Profiler. The results are interpreted. Keywords. Spray pyrolysis techniques; TiO 2 thin films; hydrogen gas response.

Highly textured ZnO thin films were prepared using ultrasonic nebulizer and pyrolysis technique in horizontal quartz reactor double zone furnace. The thin films were prepared by varying the first zone temperature from 25 o C to 400 o C while keeping second zone at 500 o C while using 0.1M (300 ml) solution of Zn (NO3)2.6H2O. The stock solution was converted into fine mist droplets using ultrasonic nebulizer (Gapusol 9001 RBI Meylan, France with frequency of operation 2.1-2.3MHz). The fine mist generated by nebulizer was allowed to pass and pyrolyzed onto previously kept inline glass substrates in horizontal quartz reactor heated using double zone furnace with first zone at room temperature (25 o C) while second zone at 500 o C. The thin film so prepared was termed as S1. Repeating above procedure and changing first zone temperature to 200 o C, 300 o C and 400 o C respectively the films are called as S2, S3 and S4. The structural properties were analyzed by XRD patterns of the thin films. Microstructural properties of the films were studied using FESEM micrographs. The optical properties of the films were characterized using UV-Visible and Photoluminescence (PL) spectroscopy. The results are discussed and interpreted.