Composition and structure of tin/vanadium oxide surfaces for chemical sensing applications

The aim of this study is to obtain data useful to elucidate the sensing mec hanism of solid state microsensors for hydrocarbon detection based on mixed vanadium/tin oxides. The sensors studied here were prepared by deposition of an active layer of Sn and V oxides on pre oxidized porous silicon. The s urface composition of those sensors was studied by a combination of low ene rgy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS). Paral lel studies were performed on a 'model' system prepared by depositing a thi n film of vanadium on a single crystal SnO2(1 1 0) surface and by successiv e thermal treatment. The results obtained show that vanadium is detectable by LEIS in the topmost atomic layer of both the polycrystalline and the s.c . sample in similar amounts. On the model system, the results of X-ray phot oelectron diffraction (XPD) measurements show the formation of epitaxial VO 2. The main conclusions of the present study are that in these sensors vana dium and tin oxide form separate phases and that vanadium species are prese nt in the outermost surface. Both phases may take an active part in the mec hanism of hydrocarbon detection in these sensors. (C) 2000 Elsevier Science B.V. All rights reserved.