Formation and Diffusion of S-Decorated Cu Clusters on Cu(111)

S-decorated Cu trimers are a likely agent of S-enhanced Cu transport between islands on Cu(111). According to ab initio calculations, excellent S bonding to trimer-Cu dangling valence results in an ad- $\mathrm{Cu}{}_3\mathrm{S}{}_3$ formation energy of only $\sim 0.28\mathrm{eV}$, compared to 0.79 eV for a self-adsorbed Cu atom, and a diffusion barrier $\le 0.35\mathrm{eV}$.