Effects of oxygen partial pressure and annealing temperature on the formation of sputtered tungsten oxide films

Thin films of tungsten oxide were deposited on silicon substrates using reactive radio frequency sputtering. The structure of the films strongly depends on the conditions of deposition and post-treatment. Important issues are the influences of oxygen pressure during deposition and annealing temperature on the morphology. Atomic force microscopy and scanning electron microscopy revealed that films were formed by grains. The sample deposited with an Ar:O(2) partial pressure ratio of 1: 1 showed the highest roughness and the smallest grains when annealed at 350degrees C. X-ray photoelectron spectroscopy analysis revealed that the films were close to their stoichiometric formulation irrespective of the oxygen partial pressure used during film deposition. The number of W=O bonds at the grain boundaries was found to be dependent on the oxygen partial pressure. Analysis by Raman spectroscopy suggested that the structure of the films was monoclinic. On the basis of these results, an annealing temperature of 350degrees C was selected as post-treatment for the fabrication of WO(3) gas sensors. These sensors were highly sensitive, highly selective to ammonia vapors, and moderately responsive to humidity. (C) 2002 The Electrochemical Society.1493H81H8

Influence of the deposition method on the morphology and elemental composition of SnO2 films for gas sensing: atomic force and X-ray photoemission spectroscopy analysis

The performance of metal oxide gas sensors is affected by their surface states, elemental composition, electronic and morphologic structures. Films of tin oxide were deposited onto silicon substrates using reactive radio frequency sputtering and drop-coating. In order to understand how the deposition procedure affects the morphology of the films, a structural characterisation based on atomic force microscopy was performed. The differences in elemental composition were analysed by X-ray photoemission spectroscopy. For sensors deposited by sputtering, a granular morphology and the presence of stannic sub-oxide (SnO) was observed. Sensors deposited by drop coating had a granular morphology but no stannic sub-oxide was present. The sensitivity of the drop-coated sensors to ethanol was found to be up to five times higher than the one of sputtered sensors. This difference can be associated to the presence of the stannic sub-oxide, grain size and intergranular coupling. (C) 2003 Elsevier Science B.V. All rights reserved.9241671677