Irradiation by swift heavy ions: Influence of the non-equilibrium projectile charge state for near surface experiments

When dealing with surface and/or thin film modifications of materials under irradiation by swift heavy ions, special attention should be given to the choice the incident projectile charge state delivered by the accelerator. This charge state should be of the order of the effective charge defined in the electronic energy loss theory. Under some hypothesis, this effective charge is assumed to be equivalent to the mean charge state deduced from measurements of ion charge state distribution. To reach such a charge state, it is necessary to introduce before the irradiated sample a thin stripper foil of carbon, the thickness of which is in between ∼5 and ∼1500 μg/cm2 for beam energies ranging between 1 and 44 MeV/u, respectively.