Depth dependent charge state distributions of heavy MeV ions in RBS and ERD experiments

At the Max-Planck-Institut für Metallforschung in Stuttgart, Germany, a 6 MV Pelletron accelerator is being used for surface analysis by means of high resolution RBS and ERD using an electrostatic spectrometer. For the ERD analysis of ions heavier than hydrogen the recording of a second parameter is necessary to identify the particle species and its charge state. For this purpose a set-up was installed that combines the high energy resolution of the spectrometer with a measurement of the time of flight of the ions through the spectrometer using a chopped ion beam. The technique also allows to measure charge state dependent depth profiles. Energy spectra of all observable charge states were recorded for backscattered Ne and Ar ions from Au and of recoil O ions from Ta ₂O ₅ and Al ₂O ₃. The comparison of a computer simulation of the charge exchange processes with the measurements of Ar scattering on Au yields mean free path lengths for electron capture and loss.