Small angle multiple reflection of low energy (6keV) noble gas ions from single crystal surfaces as a means to study surface texture and contamination

Abstract

The elemental composition of a surface can be derived from the energy spectrum of singly reflected noble gas ions. It is shown that it is also possible to obtain information about certain structural features on the surface from the energy spectra of multiply reflected ions. By carefully studying the multiple reflection energy spectra when the angle of incidence ψ is varied at a given scattering angle θ, many different multiple reflection peaks can be resolved and identified. The ideal conditions for measurements on atomically clean and undisturbed surfaces have been closely approached by working with a low residual gas pressure (10 −10 torr) in the collision chamber and small primary ion current densities ( < 10 −8 A cm 2 ). For Ar + and Kr + on (100)-Cu, peaks have been found resulting from an ideal, flat surface and peaks resulting from surface ridges (steps) and surface vacancies. This technique opens possibilities to study nucleation and early stages of growth of thin films, surface defect formation as a result of ion bombardment, the annealing behaviour of surface defects, thermal vibrations of surface atoms and neutralization processes in multiple collision sequences.