DISPERSION OF OPTICAL 2ND-HARMONIC GENERATION OF SI(111)7X7 DURING OXYGEN-ADSORPTION

The intensity of optical second-harmonic generation from Si(111) 7x7 h as been followed during oxygen adsorption using photon energies betwee n 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 i nfluence of oxygen adsorption on these resonances has been investigate d. It is found that the surface-state resonances decay with oxygen exp osure while the main effect on the strain resonance is a broadening of the spectral peak. The combination of these effects leads to a minimu m in the signal versus exposure which is displaced with photon energy.