PERIODIC CHARGE-DENSITY MODULATIONS ON GRAPHITE NEAR PLATINUM PARTICLES

We have imaged ten different superstructures on highly oriented pyrolytic graphite near adsorbed platinum particles using a scanning tunneling microscope. These superstructures are localized in small areas near the platinum particles and decay within a distance of 2-5 nm into the graphite lattice. When Fourier transformed, the observed structures contain up to three pairs of first-order Fourier components in addition to those of graphite. These Fourier components have different intensities and phases in different directions, but they have the same period of 1.5a (a is the lattice constant of graphite) and are rotated 30-degrees relative to the graphite lattice. We show that the observed features are mainly due to a periodic charge-density modulation superimposed onto the graphite lattice, i.e., the platinum particles perturb the surface charge density of graphite giving rise to the superstructures in the nearby regions.