Electronic properties of solid surfaces - Electronic surface state of metals and semi-conductors

Most of the physico-chemical properties of solid materials - electrical, magnetic, optical, thermal - as well as their equilibrium crystal structure, derive from their electronic structure, which describes the distribution of electron energy levels within the solid. Modern techniques for calculating electronic structures are generally based on single-crystal solids that are infinite in three dimensions, whereas any real solid is necessarily bounded by a surface. However, at the surface of a solid, the environment of an atom is not the same as in the volume, if only because the atoms at the edge of the solid (i.e. the atoms in the first atomic layer, at the solid-vacuum or solid-atmosphere interface) do not have the same number of first neighbors as in the volume. When the surface is created, some of the chemical bonds of the surface atoms have to be broken, which costs a certain amount of energy (surface tension). The electronic structure in the vicinity of the surface therefore differs more or less markedly from the properties of the volume. Even an ideal surface terminating a truncated volume (surface atoms remaining in the same positions whether or not they are at the edge) can possess specific electronic states (surface states) and manifest multi-electronic effects that differ from the volume. This change in local electronic structure is at the origin of macroscopic phenomena and surface-specific properties, such as surface energy, adhesion forces, chemical reactivity...

In the first instalment of this triple dossier dedicated to the electronic properties of solid surfaces [AF 3 716] , we introduced the general concepts that enable us to describe the electronic structure of solids and their surfaces, gave some elements of the crystallographic structure of surfaces, and described the macroscopic charge distribution in the peri-surface region of metals and semiconductors. We then describe experimental methods for probing the electronic properties of surfaces [AF 3 717] . Here, we discuss the nature of the electronic states of ordered and periodic two-dimensional surfaces, giving some concrete examples of typical surfaces for metals and semiconductors. The last two sections 2 and...