Limitations to depth resolution in ion scattering experiments

The energy spectra of scattered ions in Rutherford backscattering and elast ic recoil scattering experiments are commonly described using stopping powe r and straggling data. These, in turn, are based on statistical approximati ons and thus neglect the characteristics of individual ion-atom collisions. This simplified analysis is not justified when considering experiments wit h high-energy resolution. We have performed theoretical and experimental st udies to understand the shape of high-energy resolution ion scattering spec tra. The impact parameter dependent energy loss in single ion-atom collisio ns has been calculated using the semi-classical approximation (SCA). We sho w that limitations for extracting monolayer depth resolution become obvious from this non-statistical approach. Experiments were performed using a med ium energy ion scattering (MEIS) system. For the case of 100 keV protons sc attered on sulfur atoms, good agreement between the theoretical description and experimental data was found. The influence of thermal vibrations of th e sample atoms on the backscattering spectra is discussed. (C) 2001 Elsevie r Science B.V. All rights reserved.