ROLE OF INITIAL CONDUCTANCE AND GAS-PRESSURE ON THE CONDUCTANCE RESPONSE OF SINGLE-CRYSTAL SNO2 THIN-FILMS TO H-2, O2, AND CO

Gas-induced conductance changes were measured on palladium-dosed singl e-crystal tin oxide (SnO2) thin films having well-characterized surfac e properties. Films were fabricated using two methods: reactive sputte ring and chemical vapor deposition. Film orientation and crystal struc ture were determined by x-ray diffraction, while surface morphology wa s characterized using atomic force microscopy. Conductance changes wer e measured continuously on film surfaces during alternating exposure a nd evacuation cycles to partial pressures of H-2, O2, and CO in a vacu um chamber. The conductance change was found to be proportional to the square root of the initial film conductance and was interpreted in te rms of gas-induced changes in the width of a near-surface space-charge layer. The variation of conductance as a function of gas pressure dur ing alternating exposure and evacuation cycles of H-2 and O2 is consis tent with a model that involves surface reactions between coadsorbates .