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Nanocrystalline ZrO2 (Zirconia) has been synthesized by a conventional precipitation method. The structural, morphological, microstructural, optical and gas-sensing properties of ZrO2 were investigated by using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis spectroscopy and static gas sensing unit, respectively. X-ray diffraction pattern and TEM of the synthesized product reveal their nano-crystalline nature with grain size 18 nm and 20 nm, respectively. Gas sensing properties of their thick films, which were fabricated by screen-printing to various gases (O2, NO2, C2H5OH, CO, CO2, NH3, LPG, H2S and H2) were tested in ambient air. The ZrO2 thick films showed a high response and selectivity to H2S gas. The effect of operating temperature, gas concentration on the sensing characteristics of these films towards H2S was discussed. [ABSTRACT FROM AUTHOR]

Thick films of AR Grade nano Fe2O3 material with n-type semiconducting properties were prepared and tested for their gas sensing performances. Thick films of the materials were prepared by screen printing technique. The gas sensing performance was studied using static gas sensing system. The material was tested for various gases such as CO, CO2, NH3, Cl2, H2, LPG, ethanol and H2S. The nano Fe2O3 film showed maximum sensitivity to ethanol gas at 350 °C temperature at 250 ppm concentration with short response time and large recovery time. Physical and structural properties of the film material were studied by SEM, TEM, XRD and UV spectroscopy. [ABSTRACT FROM AUTHOR]

Strontium titanate (SrTiO3) nanopowder has been synthesized through a sol-gel-hydrothermal method. The X-ray diffraction studies of SrTiO3 nanopowder have shown that the as-prepared powder was single phase, crystalline, and has a cubic perovskite structure (ABO3) with a lattice constant a = 3.903 Å. The particle size calculated from FWHM was ∼22 nm. SrTiO3 nanopowder was examined using thermo gravimetric analysis; differential thermal analysis and UV-visible 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 H2S based on glass substrate were fabricated successfully by screen-printing technique. Sensitivity, selectivity, response time, and recovery time of the sensors were systematically investigated as a function of operating temperature, using H2S, CO, CO2, H2, Cl2, LPG, C2H2OH, O2, NH3 and NO2 as test gases. The sensitivity was found to lie below and around the ppm level for H2S gas at 150 °C. [ABSTRACT FROM AUTHOR]

Tin oxide thin films were deposited on alumina substrates at 350°C by spray pyrolysis technique. The films were studied after annealing them in air at different temperatures 550°C, 750°C and 950°C for 30 min. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical absorption spectroscopy technique. The grain size was observed to be increased, ranging from 40 to 56.1 nm, with the increase in annealing temperature. Absorbance spectra were taken to examine the optical properties. The band gap energy was observed to be decreased with the increase in annealing temperature. These films were tested to various gases at different operating temperature ranging from 50°C to 450°C. The Tin Oxide film showed maximum sensitivity to H2S gas. The H2S sensing property of the SnO2 films was investigated with different annealing temperatures of the films and at different concentrations of H2S gas. It was found that the annealing temperature of the film significantly affects the sensitivity of the SnO2 to the H2S gas. The maximum sensitivity was found in case of the film annealed at temperature 950°C at the operating temperature 100°C. The sensitivity was found to be increased by 24% in case of the film annealed at 950°C as compared to the sensitivity of the film annealed at 550°C. The observed response of the film was for gas concentration of 10 ppm for H2S with reasonable sensitivity. The quick response and fast recovery are the main features of this film. The effect of annealing temperature on the structural, microstructural, optical and gas sensing properties of the nanocrystalline tin oxide thin films were studied and discussed. [ABSTRACT FROM AUTHOR]

Thick films of AR grade In2O3 were 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, In2O3 sensors 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/ In2O3 sensor is several times larger than that of pure In2O3 sensor. In comparison with pure In2O3 sensor, 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) In2O3 sensor 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. [ABSTRACT FROM AUTHOR]

Nanostructured SnO2 thin films were prepared by spray pyrolysis technique onto glass substrates with different thickness by varying quantity of precursor solution. The structural, optical and electrical properties of these films have been studied. The crystallographic structure of the films was studied by X-ray diffraction (XRD). It is found that the films are tetragonal with (110) orientation. The grain size increases with thickness. Atomic Force Microscopy (AFM) showed that the nanocrystalline nature of the films with porous nature. The grain size increased 14 to 29 nm with increase in film thickness. The studies on the optical properties show that the direct band gap value decreases from 3.75 to 3.50 eV. The temperature dependence of the electrical conductivity was studied. The activation energies of the films are calculated from the conductance temperature characteristics. The nanostructured SnO2 thin films were used as sensing layers for resistive gas sensors. The dependence of gas sensing properties on the thickness of SnO2 thin films was investigated. The gas response of the SnO2 thin films towards the H2S gas was determined at an operating temperature of 150 degrees C. The sensitivity towards H2S gas is strongly depending on surface morphology of the SnO2 thin films.