Abstract
The intensity of optical second-harmonic generation from Si(111) 7×7 has been followed during oxygen adsorption using photon energies between 1.17 and 2.34 eV. Previously, dangling-bond surface state resonances and a so-called strain resonance have been found in this range. The influence of oxygen adsorption on these resonances has been investigated. It is found that the surface-state resonances decay with oxygen exposure while the main effect on the strain resonance is a broadening of the spectral peak. The combination of these effects leads to a minimum in the signal versus exposure which is displaced with photon energy. © 1996 The American Physical Society.