Binding of Ag adatoms to dangling bond defects on a H-terminated Si(001) surface

Using a first-principles calculation method, we investigate the binding of Ag adatoms with dangling bond (DB) defects on a H-terminated Si(001) surface and the diffusion of a single Ag adatom near the DB defects. We find that the Ag adatoms saturate DBs with binding energies ∼2.0 eV/Ag, much larger that on a perfect H/Si(001) surface. This means that Ag atoms preferentially bind to the DB sites on the surface. The addition energy, which reflects the energy gain when a Ag atom is added from the perfect region (0.35 ∼ 1.72 eV), decreases very much when the number of Ag atoms exceeds the number of DBs. This suggests that the Ag atoms cover the DB areas to form Ag nanostructures. The simulated scanning-tunneling microscopy (STM) images of the Ag/H/Si(001) surfaces with the DB defects reproduce the experimental ones well. It is also found that a Ag adatom diffuses anisotropically (along the dimer rows) and that the Schwoebel barriers are small near the DB defects.