Physical Vapor Deposition of Metal Nanoparticles on Chemically Modified Graphene: Observations on Metal-Graphene Interactions

The growth of metallic nanoparticles formed on chemically modified graphene (CMG) by physical vapor deposition is investigated. Fine control over the size (down to similar to 1.5 nm for Au) and coverage (up to 5 x 104 mu m-2 for Au) of nanoparticles can be achieved. Analysis of the particle size distributions gives evidence for Au nanocluster diffusion at room temperature, while particle size statistics differ clearly between metal deposited on single- and multilayer regions. The morphology of the nanoparticles varies markedly for different metals (Ag, Au, Fe, Pd, Pt, Ti), from a uniform thin film for Ti to a droplet-like growth for Ag. A simple model explains these morphologies, based only on consideration of 1) the different energy barriers to surface diffusion of metal adatoms on graphene, and 2) the ratio of the bulk cohesive energy of the metal to the metalgraphene binding energy. Understanding these interactions is important for controlling nanoparticle and thin-film growth on graphene, and for understanding the resultant charge transfer between metal and graphene.