Scanning Tunneling Microscopy of Platinum Deposits on the Basal Plane of Highly Oriented Pyrolytic Graphite

Scanning tunneling microscopy images of Pt vapor deposited on the basal plane of highly oriented pyrolytic graphite, HOPG(bp), under ultrahigh vacuum have been recorded in air at room temperature. Areas of specimens masked during Pt deposition displayed characteristic corrugations associated with bare graphite over 20˟ 20 nm2 areas, with no indication of surface damage or contamination over much larger sections, 400 ˟ 400 nm2. Unmasked areas of samples with coverages in the range between ca. 10‥ and 40‥, as estimated from X-ray photoelectron spectroscopy, contained small features (5-nm average lateral dimension) with internal structures of atomic dimensions. An analysis of variance of the maximum heights for clusters observed on representative areas of 10 ‥, 28 ‥, and 40 ‥ Pt/ HOPG(bp) specimens provided evidence that the means (ca. 0.38 nm) are not significantly different (P = 0.80). Hence, the three distributions appear to have been drawn from the same parent distribution. This strongly suggests that deposition of Pt on HOPG(bp) under the experimental conditions employed in this work gives rise to the preferential formation of essentially two-dimensional Pt structures on the surface.