FORMATION AND STRUCTURE OF TIN-IRON OXIDE THIN-FILM CO SENSORS

Rheotaxial growth and thermal oxidation (RGTO) for depositing thin fil ms is a recognized technique in preparing gas sensitive semiconducting oxides. This paper presents a study performed by x-ray diffraction an d scanning Auger microscopy of the mechanisms of growth and formation of the thin films of the new ternary compound Sn1-xFexOy with an iron content in the range 0 < x < 25 at. %. A structural model of this comp ound, which is found to be stable over a very large range of Sn/Fe rat ios, can be derived by partially substituting Fe3+ ions in Sn4+ sites. This is an easy substitution in view of the similar values shown by t he ionic radii (Fe3+ = 0.64 angstrom, Sn4+ = 0.71 angstrom) and the Pa uling electronegativity (Fe3+ = 1.8, Sn4+ = 1.8) of these two ions. Ex perimental data, showing that this material is an excellent CO sensor, are reported.