Scattering from Surfaces and Thin Films

Abstract

As in many branches of modern physics, scattering experiments are an important source of information in surface and thin film research. The scattering process on a surface is therefore a central topic among the various interactions of a solid. Like in bulk solid-state physics, elastic scattering can tell us something about the symmetry and the geometric arrangement of atoms near the surface, whereas inelastic scattering processes, where energy quanta are transferred to or from the topmost atomic layers of a solid, yield information about possible excitations of a surface or interface, both electronic and vibronic ones. In principle, all kinds of particles, X-rays, electrons, atoms, molecules, ions, neutrons, etc. can be used as probes. The only prerequisite in surface and interface physics is the required surface sensitivity. The geometry and possible excitations of about 10¹⁵ surface atoms per cm² must be studied against the background of about 10²³ atoms present in a bulk volume of one cm³. In surface and interface physics the appropriate geometry for a scattering experiment is thus the reflection geometry. Furthermore, only particles that do not penetrate too deeply into the solid can be used. Neutron scattering, although it is applied in some studies, is not a very convenient technique because of the “weak” interaction with solid material. The same is true to some extent for X-ray scattering. X-rays generally penetrate the whole crystal and the information carried by them about surface atoms is negligible.