Adsorption of Cu, Pd, and Cs atoms on regular and defect sites of the SiO2surface

The interaction of isolated Cu, Pd, and Cs atoms on regular and defect site s of the SiO2 surface has been studied with cluster models. Hartree-Fock, d ensity functional theory, and multireference configuration interaction meth ods have been used to characterize the bonding of the metal atoms at the fo llowing sites: bridging oxygens at the regular surface, =Si-O-Si=, Si singl y occupied sp(3) dangling bonds (E' centers), =Si-., nonbridging oxygen cen ters, =Si-O-., and neutral oxygen vacancies, =Si-Si=. The bonding with the nondefective sites of the surface is very weak, <0.2 eV. Sticking of the at oms occurs only at the defect sites with adsorption energies ranging from 1 to 3 eV. Several spectral signatures of the bond at the silica defects hav e been considered: core level shifts, impurity levels in the band gap, and optical transitions.