ULTRAHIGH-VACUUM SCANNING TUNNELING MICROSCOPY STUDIES OF PLATINUM ON GRAPHITE

The surface morphology of submonolayer coverages of platinum vapor deposited onto highly oriented pyrolytic graphite (HOPG) has been studied. With coverages of 5%-30% of a monolayer, we have observed both three-dimensional clusters and two-dimensional (2D) islands of Pt on the substrate. Our studies concentrated on the 2D islands of Pt, which exhibited several interesting features. Small islands exhibited epitaxial growth on the HOPG with markedly small Pt-Pt bond lengths, as well as occasional features of larger spacings. Similar larger structures on graphite islands and near graphite steps on the clean HOPG surface were observed. Results of scanning tunneling spectroscopy show that spectra on platinum deposits exhibit a broader character than those on clean graphite and show some structure consistent with bulk Pt.