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+-irr adiated graphite surfaces at ion energies between 2 and 50 keV, the relatio ns between mean depth, longitudinal and lateral straggling of the damage ca scade were obtained. Their evolution with the ion energy was found to follo w power laws for both ion masses and implies an energy-independent lateral spread of the damage cascade, while depth and longitudinal spread scale wit h the ion energy. This can be explained by the nuclear stopping power being nearly independent of energy in the observed region. High-resolution micro graphs of single-ion impacts support this interpretation, as the hillock-sh aped surface defects found in the experiments show a lateral extension bein g independent of the ion energy.