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Abstract-MoO 3 thin films have been prepared by a simple spray pyrolysis technique at substrate temperature 250 o C. The structure and morphology of thin films are characterized by X-ray powder diffraction (XRD), scanning electron microscopy and UV-vis spectroscopy. The gas sensing properties of MoO 3 thin film is studied at gas concentration 400 ppm and working temperature of 100-400 o C. It was found that the sensitivity depended on the working temperatures and also H 2 S gas concentration.The results show that the MoO 3 thin film can be used to fabricate high performance H 2 S gas sensors.Index terms: MoO 3 thin film, spray pyrolysis, sensor.

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A hydrothermal process was used for the synthesis of nanostructured Nickel Oxide (NiO) with and without capping reagent (surfactant). Nickel Chloride (NiCl 2 ) a precursor of Nickel and Thioglycerol, a capping reagent, was used for this preparation. The structure, morphology and crystalline phase of the nickel oxide nanocrystal have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). TEM images showed that the nickel oxide nanoparticles have hexagonal structure with uniform size distribution around 20-38 nm for NiO with capping agent and 23-100 nm for NiO without capping agent. Phase pure, cubic nickel oxide formation was identified from the XRD data. The thick films of NiO were prepared by screen-printing technique to study their gas sensing properties. The gas sensing performance of NiO thick films (with and without surfactant) were tested to H 2 S, LPG, H 2 , NH 3 , Ethanol, CO, CO 2 , and O 2 , to operating temperature ranging from 100 to 450°C, they showed maximum response to H 2 S for 10 ppm gas concentration at 150°C. The response and recovery values upon the exposures to 10 ppm H 2 S gas and air were 4 and 58 s for NiO (with surfactant) thick film sensor, while those were 10 and 64 s for NiO (without surfactant) thick film sensor respectively. The NiO thick films have potential applications in H 2 S gas sensor applications. The results are discussed and presented in this paper.