A NEW TECHNIQUE FOR GROWING LARGE SURFACE-AREA SNO2 THIN-FILM (RGTO TECHNIQUE)

A new technique for growing SnO2 thin films with high surface area is described, based on tin rheotaxial growth and its thermal oxidation (RGTO). Tin thin films, when grown, present a surface characterized by spheroidal agglomerates due essentially to the surface tension of the liquid metal; these agglomerates do not seem to have any electrical continuity. By means of a thermal oxidation, both the transformation of the metal into a semiconductor and the thin film continuity are obtained, owing to the volume increase during the above-mentioned phase transformation. After this annealing cycle, SnO2 thin films are slightly oriented in the (101) direction and present an electrical resistivity equal to about 10(2)-OMEGA-cm. So, the surfaces of SnO2 films appear to be formed by spongeous agglomerates, which are in electrical contact with the nearest agglomerates. SnO2 thin films grown by this method show a high sensitivity (defined as the relative percent conductance variation) to H-2; in fact, sensitivity to 200 PPM H-2 in synthetic air at ambient pressure is equal to 400%. It seems to be possible to prepare other metal oxide semiconducting thin films with a high surface area using this technique.