Cratering by MeV-GeV ions as a function of angle of incidence

We report on a systematic scanning force microscope study of crater formation induced by swift heavy ions as a function of angle of incidence. PMMA films were bombarded with Au-197 (20 MeV), Bi-209 (2320 MeV) and U-238 (2640 MeV) ions at angles 0 varying from 0degrees to 84degrees to the surface normal. In all cases, the length of the craters as well as rim height and length scale with (cos 0)(-1). Crater width showed a much weaker (cos 0)(-0.3) dependence. Similar angular dependences were observed for the different ion species and energies used. The experimental data is compared to molecular dynamics simulations of crater formation in a model solid. The simulations show a (cos 0)(-1) dependence for the crater length, but no dependence for the crater width, unless a wide initial track of excitation is used. (C) 2003 Elsevier Science B.V. All rights reserved.