Dual Au-Si bonding character and Au surfactant effect on Au/Si(111) surfaces

dElectronic structures of Au/Si(111) surfaces have been calculated by the ab initio pseudopotential method in a local density approximation. We found that there are strong electronic-state couplings between Au trimers and surface Si, which induce the charge transfer from Si to Au-Si covalent bonds and the charge redistribution from d to s orbitals around Au. It is shown that Au overlayer acts as a surfactant through Au-Si rebonding during Si growth.