Figure 4: (a) Schematic representation of a diffusion event. The adatom of interest (blue) diffuses from position 1 to 2, while the next-nearest neighbor positions 3–12 can be either occupied (yellow) or empty. (b) Hard-sphere model of a possible diffusion process. The red atom would correspond to position 1, while the blue atoms are occupied adsorption sites (yellow spheres in (a)) and yellow atoms are the underlying Au(100) surface.