The phase and intensity of optical second harmonic generation (SHG) were studied in Ag deposition on the Si(I 1 1) surfaces. The 7 x 7 reconstruction of the surface changed to the 1 x 1 structure in room temperature deposition. The SHG intensity reduced and the phase shifted to +180degrees with this structural change. Meanwhile, the 7 x 7 reconstruction changed to the root3 x root3 reconstruction in 400 degreesC deposition. With this structural change, the SHG intensity increased and the phase shifted to -250degrees. An analysis with anharmonic oscillator model showed that the changes in room temperature deposition were due to the quenching of the surface dangling bond states of the 7 x 7 reconstruction by the Ag deposition, whereas those in 400 degreesC deposition were due to the appearance of new surface states of the root3 x root3 reconstruction. (C) 2002 Elsevier Science B.V. All rights reserved.