Size-dependent mobility of platinum cluster on a graphite surface

Abstract

Molecular dynamics simulations of platinum (Pt) clusters on a graphite surface were performed to study their diffusion and aggregation. The Sutton-Chen many-body potential was used for the Pt–Pt interaction, whereas, a Steele potential was used to calculate the interaction between Pt atoms and carbon (C) atoms of graphite. The results show that at room temperature, the Pt clusters with less than 40 atoms are very mobile with a two-dimensional diffusion coefficient higher than 10−11m2 s−1, but decreasing rapidly with size. The diffusion coefficient of larger cluster has variable size-dependence with local minima at cluster sizes of 50 and 300 Pt atoms and a local maximum at cluster size of 100 atoms. In additional to the overall size of the Pt cluster or nanoparticle, the mismatch between the bottom layer of Pt and graphite also affected the overall Pt–graphite affinity and hence the Pt cluster mobility. The presence of a neighboring Pt cluster can greatly affect mobility. The aggregation of two 50-atom clusters to form a single cluster was observed with the simulation. The relatively stable short dumbbell-like structure of the new cluster resembles previous experimentally observed network of connected Pt nanoparticles on graphite.