Optical second harmonic generation spectra obtained from the clean 7 x 7 surface were compared to those of surfaces with Au and Ag induced (√3 x √3)-reconstructions. All three reconstructions lead to broad spectra in the region below the bulk direct interband transition energy due to excitation of surface states. Variations in the spectra with sample temperature and oxygen exposure were used to identify resonances in the spectra. In this way several transitions consistent with energy separations between surface states known from photoemission were identified.

Second-Harmonic Generation Spectroscopy on Reconstructed Si(111) Surfaces. K.Pedersen, P.Morgen: Physica Status Solidi C, 2003, 0[8], 3065-9