Charge state-dependent effects in electronic sputtering by fast ions

Reported yields of ejecta sputtered from dielectric and organic materials by MeV/amu O and F ions show a strong dependence on the incident ion charge state. These observations are consistent with a (dE/dx)2-dependence of sputtering yield, provided that proper account is taken of the charge-state equilibration process as the ion beam enters the solid. From a knowledge of this process, an effective interaction depth for the coupling of electronic excitation to prompt sputtering is inferred to be ≲ 6 nm for the case of 1.24 MeV/amu O incident on glycylclycine. A somewhat smaller depth is inferred for uranium sputtered by 1 MeV/amu F incident on UF4.