Enhanced surface second-harmonic sensitivity to electronic states: Study of O(2)/Si(111)-7x7.

More sensitivity to specific electronic states may be obtained than previously thought possible with surface second-harmonic generation by exploiting the symmetry and resonant-enhancement properties of the nonlinear susceptibility tensor. We have identified 3 tensor elements of the Si(111) -7X7 surface with either the surface free electron response (associated with dangling bonds) or a particular interband transition (associated with Si backbonds) and used this identification to study the room temperature oxidation of the surface.