Low-energy Ion Scattering (LEIS) probes composition and/or surface structure by measuring the signal of keV range ions backscattered by a sample. Since the scattering by target atoms can be described as binary collision, the backscattering energy is a measure for the target atom mass and hence reflects target composition.
Surface sensitive analysis
For surface sensitive analysis, noble gas ions are used. These ions efficiently neutralise when they penetrate the target, such that only ions that scatter on the outermost surface yield a so-called surface peak (when using an electrostatic detector as analyser). This superior surface sensitivity is one of the key features of the LEIS technique.