By modifying a Si(111) surface through the introduction of a variable number of steps, the anisotropic surface and bulk contributions to the optical second-harmonic generation could be determined separately and were found to be of the same order of magnitude for a Si-${\mathrm{SiO}}_2$ interface. This approach is based on the lowering of the surface symmetry by the steps and by the apparent enhancement of the nonlinear susceptibility at the step edges.

• Received 29 May 1990

DOI:https://doi.org/10.1103/PhysRevB.42.9263