Self organisation of Pt and Au clusters deposited on graphite: the role of reactivity

Spontaneous organisation of preformed size selected platinum and gold clusters on graphite is discussed in terms of reactivity with residual gases. The difference in reactivity between gold and platinum can explain the spontaneous organisation in an high vacuum for platinum and poor vacuum for gold. Contrary to earlier assumptions (Friedel oscillations, moirés and graphite stiffness), the hypothesis of a chemical surface modification agrees with the evolution of thin film morphologies with the deposition pressure as well as with the constant edge-edge distance between two neighbouring clusters (1.2 nm). The possibility of cluster decoration by CO is discussed