The growth of thin, epitaxial SnO 2 films for gas sensing applications

Abstract

Reactive r.f. sputter deposition was used to grow epitaxial tin oxide (SnO 2) films on TiO 2 and sapphire substrates. Films were fabricated in an ultrahigh vacuum based system using high purity O 2 and argon gases. Epitaxial films were obtained at deposition temperatures of 500 °C and growth rates of 4–10 Å min −1. The SnO 2 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 TiO 2(110), (100) on sapphire(0001), and (101) on sapphire(1 1 02). Films grown at 30 °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 SnO 2, 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 SnO 2(110) single crystal.