Resonant Optical Second Harmonic Generation at the Steps of Vicinal Si(001)

Resonant optical second harmonic generation from vicinal Si(001) and Si(001)-Sb around 3.3 eV is shown to be dominated by electronic states associated with reconstruction of the surface step. The mirror plane perpendicular to the step edge, which is present in the macroscopic surface and in the bulk and terrace crystallographic structures, is absent in the resonant second harmonic response from vicinal Si(001)-( $1\times 1$)-Sb.