Controlling adsorbate diffusion on a high-symmetry surface through molecular shape selection

Using a simple rigid model of a chemisorbed molecule, we explore the relationship between a molecule's shape and its diffusion on a (111) surface of a face-centered-cubic crystal. Anisotropies in the diffusion constant of up to a factor of 15 are found, along with the enhancement of diffusion perpendicular to an applied field and an approximate decoupling of the size of the diffusion barrier from the surface binding energy. The model reproduces experimental measurements of adsorbate diffusion both qualitatively and with reasonable quantitative accuracy yet is simple enough that all possible diffusion pathways can be enumerated with little computational expense. © 2011 American Chemical Society.David M. Huang and Peter Harrowel