Laser cleaned silicon surfaces—electronic structure and surface crystallography

Abstract

Clean (111) silicon surfaces have been generated by irradiation with light from a fast pulsed laser and probed by a range of surface sensitive techniques. Low energy electron diffraction indicates a 1 × 1 structure. We compare the electronic structure established by angle resolved photoemission with (a) 1 × 1 surfaces prepared by thermal cleaning, (b) 7 × 7 and 2 × 1 reconstructed surfaces, and (c) surface state distributions calculated using the semi-empirical pseudopotential approach for a variety of surface structures. We show that recently proposed surface structures involving a simple inward relaxation of the surface atomic layer cannot be correct. The semiconducting nature of the 1 × 1 surface and the periodicity of features in the angle resolved photoemission spectra strongly suggests that its structure is more like the 2 × 1 surface where neighbouring rows of surface atoms are shifted in opposite directions but with a considerable degree of surface disorder.