Resonant effects in optical second-harmonic generation from alkali covered Si(111)7 x 7

Abstract

Polarized second-harmonic generation (SHG) coverage dependencies for alkali (Na, Li) adsorption on Si(111) 7 x 7 both at room and at low temperatures are obtained for fundamental wavelengths of 497 nm, 570 nm and 1067 nm, showing characteristic and reproducible non-monotonic changes of SHG efficiency. At submonolayer coverage the SHG intensities are qualitatively different for visible vs. near-resonant IR radiation. In the coverage regime theta< 1/3, low-symmetry Na-Si bonds, resulting from a Na-induced surface reconstruction, are formed, which are resonant with 1067 nm radiation. By comparing parallelly and perpendicularly polarized coverage dependencies, we deduce that the resonant contribution in the parallel configuration is due to the χ((2))(zzz)-component.