Structural characterization of Pt nanoclusters deposited on graphite: Effects of substrate and surrounding medium

The structure of Pt-6, Pt-13, Pt-20, Pt-40, Pt-60, Pt-100, and Pt-150 nanoparticles deposited on graphite surfaces, and the changes on such structures induced by the interactions with OH-terminated polyamidoamine dendrimers of the lowest generations G0OH and G1OH are examined using classical molecular dynamics simulations. It is shown that the particle/substrate interaction depends strongly on the particle size, with variations following an oscillatory pattern according to the degree of completeness of the particle's outer atomic shell. The results for the bare clusters suggest the existence of ordered structures with mixed fcc and help structures. Less ordered structures show a tendency of the nanoparticle to adopt a spherical shell. Details of the morphology and interactions of Pt-6, Pt-13, and Pt-20 with the substrate in the presence of the dendrimers are compared with those for the bare nanoparticles deposited on graphite. Simulation results reveal a strong attachment of the dendrimer branches to the metal particle. The binding, which is driven by the oxygen and nitrogen amide atoms, the tertiary amines, and the dendrimer terminal groups, has significant effects on the structure of Pt nanoparticles on graphite surfaces, manifested by atomic rearrangements in the metal clusters causing modifications to their initial structure and the appearance of new layers. (c) 2005 Elsevier B.V. All rights reserved.