Ripple topography of ion-beam-eroded graphite:: A key to ion-beam-induced damage tracks

The ripple topography of ion-beam-eroded surfaces offers a novel method to determine the shape of collision cascades and the distribution of deposited energy From the energy dependence of the ripple spacing of Ar+ and Xe+-irradiated graphite surfaces at ion energies between 2 and 50 keV, the relations between mean depth, longitudinal and lateral straggling of the damage cascade were obtained. Their evolution with the ion energy was found to follow power laws for both ion masses and implies an energy-independent lateral spread of the damage cascade, while depth and longitudinal spread scale with the ion energy. This can be explained by the nuclear stopping power being nearly independent of energy in the observed region. High-resolution micrographs of single-ion impacts support this interpretation, as the hillock-shaped surface defects found in the experiments show a lateral extension being independent of the ion energy.