MoO3-WO3 mixed oxide powder and thin films for gas sensing devices: A spectroscopic characterisation

This work gives results about the characterisation of MoO3-WO3 binary systems in powder or deposited in thin films on alumina and silicon substrates. Morphological and structural characterisation was carried out by XRD and SEM techniques, the powder texture by volumetric measurements. Absorbance FT-IR and diffuse reflectance UV-vis-NIR spectroscopies were employed to study the influence of different atmospheres on the electronic properties of the materials. Spectra were recorded after treatments in O2, in vacuum, in NO2/O2 and in CO/O2 at increasing temperature. The spectra of all the samples show, both in the vis-NIR and medium IR regions, the increase of a variety of broad absorptions after reducing atmospheres and the decrease of these absorptions after oxidising ones, so that they are all assignable to electronic transitions related to oxygen defects. Some electrical measurements on thin film supported on alumina are also presented. The electrical response toward CO at increasing temperature can be correlated with the intensity changes in the vis-NIR absorptions observed after interaction with CO/O2 at increasing temperature.