Segregation of H as a surfactant during the formation of an Ag cluster on H-terminated Si(111): First-principles total-energy calculations

The initial stages of Ag nanocluster formation on the H-terminated Si(111) surface are investigated using first-principles total-energy calculations. The surface remains structurally unchanged by the adsorption of a single Ag adatom that slides nearly freely with a diffusion barrier of 0.14 eV on the H/Si (111) surface [Phys. Rev. B 71, 035310 (2005)]. When the Ag adatoms aggregate on this surface, however, the H atoms segregate from the substrate with extremely small energy barriers of ∼0.2 eV. The Agn clusters (n≥2) with H segregation, where n is a number of Ag atoms in a cluster, are more tightly bound to the Si substrate than the clusters without H segregation since they make strong Ag-Si bonds, suggesting that such clusters can serve as seeds for island growth. The present findings are consistent with the depth-resolved measurement of H and real-space observations of the Ag islands on the H/Si (111) surface.