SCANNING TUNNELING MICROSCOPIC AND AUGER-ELECTRON SPECTROSCOPIC CHARACTERIZATION OF A MODEL CATALYST - RHODIUM ON TIO2(001)

Rhodium films were vapor deposited on TiO2(001) rutile and examined in situ at various coverages and following various annealing procedures by using scanning tunneling microscopy (STM) and Auger electron spectr oscopy (AES). Rh deposition at ambient temperature leads to STM images that indicate nucleation and growth of three-dimensional particles. T he particles have a narrow size distribution centered around 30 angstr om with an aspect ratio of 0.3 and are not arranged with long-range or der. AES results corroborate the film thickness measured by STM. Annea ling in vacuum decreases both the Rh/Ti Auger intensity ratio and the number density of particles, indicating particle coalescence at the on set of surface diffusion. Simultaneously, the apparent included volume of the particle film increases, an effect that is consistent with Rh particle encapsulation but may also be due to tip convolution. The uti lity of STM in morphologic characterization of oxide-supported metal p articles, such as those found in catalysts and gas sensors, is demonst rated.