Interaction of Ti with the (0001) surface of highly oriented pyrolitic graphite

The nature of the interaction between highly oriented pyrolitic graphite (H OPG) and adsorbed Ti is examined by soft x-ray photoelectron spectroscopy. By monitoring the C 1s signal, it is found that Ti does not chemically bond to, but only interacts through the Van der Waals force with, a pristine HO PG surface. Time-dependent variations in the C 1s peak intensity are interp reted in terms of diffusion of adsorbed Ti atoms, which results in the form ation of clusters. This behavior is further evidence for a weakly adsorbed overlayer and implies that this surface is a priori unable to support a lay er-by-layer growth. A chemical reaction occurs only when oxygen is incorpor ated or defects are present. The presence of adatoms on HOPG has an effect on the screening process of the HOPG C 1s core hole, which can be detected even at the Van der Waals interaction level. This may be used as a measure of the strength of interfacial interactions, especially for cases of weak o r small-scale interactions. [S0163-1829(99)03728-5].