Shadowing effects in ion scattering spectrometry

In backscattering experiments performed on a (100)Cu crystal with a 450 oblique incidence, the crystal rotation induces variations of the scattered intensity. When the collection is done along the normal direction, these variations are only due to shadowing effects, independent of any blocking influence. The experimental results obtained with 3 to 10 keV 20Ne+ ions are compared to numerical simulations using the MARLOWE computational code. Since only narrow zones of the crystal surface can give rise to the events of interest, the calculation has been restricted to an automatic determination of these 'useful impact zones'. Although a good agreement at high energies, important discrepancies between experiment and computation are observed. The effects of several factors which may give rise to these discrepancies are discussed. (orig.)