Effect of substrate surface reconstruction on interaction with adsorbates: Pt on 6H-SiC(0001)

Three reconstructed 6H-SiC(0001) surfaces, including a Si-rich 3 x 3 surface, a C-rich 6 square root(3) x 6 square root(3) surface, and a graphitized SiC surface, were used as substrates for the deposition of Pt overlayers. The interaction between Pt and the SiC(0001) surfaces was studied by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Pt reacts readily with the 3 x 3 surface to form platinum silicide even at room temperature. On the graphitized SiC surface, metal particles with low lateral dispersion form and keep on aggregating upon annealing. In contrast, homogeneously distributed small Pt nanoclusters were grown on the C-rich 6 square root(3) x 6 square root(3) surface. The unique nanomesh surface structure helps to stabilize the Pt nanoclusters until 800 degrees C. Above 1000 degrees C, Pt tends to diffuse into the subsurface region, forming the C/Pt silicide/SiC(0001) interface structure. The different surface electronic structures of the three Pt/SiC(0001) systems were discussed as well. The present data show that surface reconstruction provides an effective route to control the growth of metal overlayers and the formation of metal/substrate interfaces.