Anomalous versus Normal Room-Temperature Diffusion of Metal Adatoms on Graphene

Abstract

Fabrication of high-performance heterostructure devices requires fundamental understanding of the diffusion dynamics of metal species on 2D materials. Here, we investigate the room-temperature diffusion of Ag, Au, Cu, Pd, Pt, and Ru adatoms on graphene using <i>ab initio</i> and classical molecular dynamics simulations. We find that Ag, Au, Cu, and Pd follow Lévy walks, in which adatoms move continuously within ∼1-4 nm² domains during ∼0.04 ns timeframes, and they occasionally perform ∼2-4 nm flights across multiple surface adsorption sites. This anomalous diffusion pattern is associated with a flat (<50 meV) potential energy landscape (PEL), which renders surface vibrations important for adatom migration. The latter is not the case for Pt and Ru, which encounter a significantly rougher PEL (>100 meV) and, hence, migrate via conventional random walks. Thus, adatom anomalous diffusion is a potentially important aspect for modeling growth of metal films and nanostructures on 2D materials.