PARTICLE GROWTH OF PALLADIUM ON EPITAXIAL TIN OXIDE THIN-FILMS

Thin films of SnO2 were deposited on r-axis Al2O3 and characterized us ing scanning tunneling microscopy (STM), low energy electron diffracti on, and x-ray photoelectron spectroscopy (XPS). The films grew in an e pitaxial, layer-by-layer mode. A small miscut of the Al2O3 substrate ( 0.2-degrees) resulted in parallel, uniformly-spaced, monatomic steps o n the SnO2 film surface. Pd was deposited on the SnO2 films and charac terized by STM and XPS. Below 2 monolayers, the Pd formed 10-20 nm isl ands with an apparent height of 0.5 nm. Increasing the Pd coverage eve ntually results in a continuous metal film that retains the granular s urface topography of the isolated particle film. Annealing the films c reated a population of reduced metallic Sn that we attribute to Sn-Pd alloying but no significant change in the palladium particle morpholog y was observed.