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 single-crystal tin oxide (SnO2) thin films having well-characterized surface properties. Films were fabricated using two methods: reactive sputtering and chemical vapor deposition. Film orientation and crystal structure were determined by x-ray diffraction, while surface morphology was characterized using atomic force microscopy. Conductance changes were measured continuously on film surfaces during alternating exposure and evacuation cycles to partial pressures of H-2, O2, and CO in a vacuum chamber. The conductance change was found to be proportional to the square root of the initial film conductance and was interpreted in terms of gas-induced changes in the width of a near-surface space-charge layer. The variation of conductance as a function of gas pressure during alternating exposure and evacuation cycles of H-2 and O2 is consistent with a model that involves surface reactions between coadsorbates.