Optical second-harmonic generation studies of Si(111)- √3×√3-Ag and Si(111)-3x1-Ag grown on vicinal Si(111)

Optical second-harmonic generation (SHG) studies, at room temperature, of Si(111)-√3×√3 -Ag and Si(111)-3x1 -Ag structures grown on vicinal Si(111) are reported. The vicinal substrate produces a predominant domain on the (111) terrace that reveals the full surface symmetry. The ratio of p- to s-output polarization intensity of these Ag structures was found to be very large, requiring precise alignment procedures. For the Si(111)-3x1 -Ag structure it is shown, using s-output measurements, that there are tensor components making significant contributions to the SH intensity that are identically zero in the presence of a mirror plane. This proves that the 3x1 -Ag structure does not possess such a mirror plane, in agreement with a previous SHG study of this structure grown on a singular surface. These results are contrasted with those from Si(111)-√3×√3 -Ag, where the response is consistent with the presence of a mirror plane.