Surface Elementary Excitations

Abstract

The presence of the surface (or interface) in a crystal modifies the elementary excitations of the infinite crystal, but it also leads to the creation of the new elementary excitations characteristic for the particular surface or interface, and to the onset of the single-particle or collective excitations of the species (atoms, molecules) adsorbed on the surface. In particular, some of the bulk modes are suppressed and replaced by the surface modes, the continuum of the bulk modes can become a discrete band of excitations in finite crystals, and these excitations may acquire a finite lifetime. The modification of the bulk modes and the onset of the new, surface elementary excitations have consequences for some microscopic and also macroscopic properties of the solid surfaces. For example, the electrostatic potentials — classical image potential and van der waals potential in the physisorption — have their quantum-mechanical origin in the interaction of external charges with the long-wavelength surface modes, as will be discussed later.