Optical second harmonic generation spectrum of Ag/Si(111) reconstructed surfaces - art. no. 155413

Optical second harmonic generation (SHG) spectra were measured at Ag/Si(111 ) reconstructed surfaces; the excitation photon energy ranged from 1.0 to 1 .7 eV. The Si(111) surface exhibited two peaks resonant to the transition b etween the surface states of the 7 x 7 reconstruction at 1.15 and 1.35 eV. These peaks disappeared in the Ag deposition at room temperature with the c ompletion of the Ag-induced 1 X 1 surface structure. Instead, the E-0' tran sition peak red-shifted to appear at 1.6 eV. The peaks of the 7 x 7 reconst ruction disappeared at 0.5 monolayers in the deposition at 400 degreesC, an d two new peaks then grew at 1.15 and 1.45 eV with the appearance of the Ag -induced root3 X root3 reconstruction. The peak at 1.15 eV was reasonably a ssumed to be the transition from the free-electron-like surface state to th e surface Umklapp empty state of the root3 X root3-Ag reconstruction. The i ntense peak at 1.45 eV was tentatively assigned to the multipole plasmon ex citation at the Si(111) root3 X root3-Ag reconstructed surface with a metal lic nature.