Particle growth of palladium on epitaxial tin oxide thin films

Thin films of SnO2 were deposited on r-axis Al2O3 and characterized using scanning tunneling microscopy (STM), low energy electron diffraction, and x-ray photoelectron spectroscopy (XPS). The films grew in an epitaxial, layer-by-layer mode. A small miscut of the Al2O3 substrate (0.2°) resulted in parallel, uniformly-spaced, monatomic steps on the SnO2 film surface. Pd was deposited on the SnO2 films and characterized by STM and XPS. Below 2 monolayers, the Pd formed 10–20 nm islands with an apparent height of 0.5 nm. Increasing the Pd coverage eventually results in a continuous metal film that retains the granular surface topography of the isolated particle film. Annealing the films created a population of reduced metallic Sn that we attribute to Sn–Pd alloying but no significant change in the palladium particle morphology was observed.