Optical Properties of Surfaces and Interfaces

Abstract

Light reflected from a crystal surface carries information both on bulk and surface optical properties. In this context the surface is defined as the transition region where the value of the dielectric function is different from both the ambient and the bulk values. The width of this region is tipically of the order of 5–10 Å. The main problem encountered in surface optical spectroscopies is to separate the surface term from the bulk term, which is usually much larger. There are two reasons why the surface dielectric function (DF) is distinct from the usual bulk-like DF, namely the peculiar electronic structure characteristic of the surface (surface states) and the fact that bulk-like optical transitions are modified by the surface, for example because of the loss of translational symmetry in the direction perpendicular to the surface. In principle, both the abovementioned aspects contribute to the surface optical properties. Consequently great care must be taken in order to disentangle them and-for instance-extract the information regarding surface states alone from the experimental data.