THE GROWTH OF THIN, EPITAXIAL SNO2 FILMS FOR GAS SENSING APPLICATIONS

Reactive r.f. sputter deposition was used to grow epitaxial tin oxide (SnO2) films on TiO2 and sapphire substrates. Films were fabricated in an ultrahigh vacuum based system using high purity 02 and argon gases. Epitaxial films were obtained at deposition temperatures of 500-degrees-C and growth rates of 4-10 amgstrom min-1. The SnO2 films were pure and appeared to be stoichiometric. X-ray and low energy electron diffraction indicated that most of the films were crystalline and in registry with the substrates Primary orientations observed on the various substrates included: (110) on TiO2(110), (100) on sapphire(0001), and (101) on sapphire(11BAR02). Films grown at 30-degrees-C were not epitaxial. In situ conductance measurements were used to investigate the electrical behavior of the various films. As a demonstration of one potential application of epitaxial SnO2, we measured the response characteristics of a palladium-modified film grown on sapphire under a model sensing cycle of gas treatments. The gas-induced conductance changes were comparable with those observed for a similarly modified SnO2(110) single crystal.