Temporal and spatial resolution of scattered and recoiled atoms for surface elemental and structural analysis

Abstract

Developments in low-energy ion scattering over the past 10 years have led to new techniques for surface elemental and structural analyses. The fundamental physics involved in these new methods is summarized herein and some examples of the applications of the techniques are presented. Three major new developments are considered. First, time-of-flight scattering and recoiling spectrometry (ToF-SARS) takes advantage of ToF techniques to detect simultaneously both ions and fast neutrals that are scattered and recoiled from surfaces. Elemental analyses are obtained by application of binary collision theory, and structural analyses are performed by rotation of the sample in order to measure intensity changes as a function of incident and azimuthal angles. Second, scattering and recoiling imaging spectrometry (SARIS) takes advantage of a large position-sensitive microchannel plate detector, coupled with ToF techniques, to capture element-specific, time-resolved, spatial and intensity distributions of scattered and recoiled atoms from surfaces. These images combine atomic scale microscopy and spatial averaging because they are created from a macroscopic surface area but they are directly related to the atomic arrangement of the surface at the subnanoscale level; the features of the images are sensitive to changes in interatomic spacings at a level of <0.1 A. Third, a classical ion trajectory simulation program, called scattering and recoiling imaging code (SARIC), which is designed specifically for structural interpretation of ToF-SARS and SARIS data, has been developed. This program allows quantitative comparison of experimental and simulated data for surface structure determinations.