Simple approximation to thermal attenuation in low energy atom-surface scattering: Multiple phonon processes

Abstract

Within the context of a recently developed simple approximation model, we consider miltiple phonon processes in the thermal attenuation of elastic peaks in atom-surface diffraction. A discussion of two phonon processes results in a set of parameters which indicate the relative importance of the three distinct types of multiphonon processes. We discuss multiple virtual phonon exchange, and the summation of certain classes of multiphonon transfers is carried out to all orders. This model illustrates clearly the distinction between thermal attenuation in atom-surface scattering and the more familiar Debye-Waller analysis valid for neutron or X-ray scattering. We obtain closed form expressions which are just as easy to apply as a Debye-Waller factor.