Improvement of gas-sensing properties of SnO2 by surface chemical modification with diethoxydimethylsilane

SnO2 powder was subjected to repeated surface chemical modification with diethoxydimethylsilane (DMES) through condensation reaction with hydroxyl groups on the surface Sn4+ sites, followed by calcination at 600 degrees C, in order to investigate the effects of the incorporation of the SiO2 component on the gas-sensing properties of a partially sintered SnO2 sensor. Secondary ion mass spectroscopy and elemental analysis confirmed the incorporation of the SiO2 component on the SnO2 surface. The amount of the Si atoms introduced with a single time modification was about 25% of the surface Sn4+ sites. Temperature programmed desorption peaks of oxygen adsorbates and surface hydroxyl groups on the SnO2 surface apparently disappeared with the repeated modification, but it was suggested that the surface was not completely covered with a monolayer of SiO2 suggesting that the SiO2 component aggregated to some extent into fine particles. Gas sensitivity to H-2 was found to be markedly enhanced by the surface chemical modification, though the recovery rate became very slow. In contrast, sensitivity to CH4 and C3H8 increased up to two cycles of modification. The variations in the gas-sensing properties are discussed in terms of the variations in the potential barrier height at the grain boundaries or necks. (C) 1998 Elsevier Science S.A. All rights reserved.