Damage production yield by electron excitation in mica for ion and clusterirradiations

The production of extended defects by a high density of electron excitation has been described in many materials for ion irradiation and high-energy c luster irradiation. The parameter used to characterize these irradiations i s generally the electronic stopping power or linear energy transfer (LET). We have studied the damage production at the surface of mica by near-field microscopy for irradiations by ions at different velocities and by high-ene rgy clusters. At a given LET, the damage yield depends on the velocity of t he ions. To describe this velocity effect, we der ne a reduced LET in which only the ionizations close to the ion path are taken into account. With th is reduced LET, there is no difference between high- and low-velocity ion i rradiations. However, in this description, we observe a deviation for the c luster irradiation which comes from the lower charge of the clusters. The m ean charge of the clusters below the surface can be extracted from this dev iation.