Metallic cluster beams from a 2.5 MV Van de Graaff accelerator for cluster-solid interaction studies: preliminary results with Au-n(+) clusters

A liquid metal ion source (LMIS) was installed on the high-voltage terminal of the 2.5 MV single-stage Van de Graaff accelerator of the Institut de Ph ysique Nucleaire de Lyon and mas used to deliver intense MeV energy beams o f cluster ions. After acceleration, the ions produced from an eutectic Au-S i alloy were mass-selected by means of a magnetic analysis. The beam was ma inly composed of the monoatomic ions Au+ and Si+ and of the clusters Au-n(), AunSi+, and AunSi2+ (n = 2 - 13). The intensities decreased for increasi ng n values, but remained remarkably high. For pure gold ions, the maximum intensity measured at the target site varied from 250 nA, for Au+, down to 20 pA, for Au-9(+). The research program on the study of the specific effec ts of the impact of energetic dusters on solid surfaces concerns the fundam ental interaction processes and the solid modifications induced by high-den sity energy deposits. Our first experiments with Au-n(+) clusters led to th e following results: Nonlinear dependence on the cluster size of kinetic se condary electron emission from thin carbon foil enhances the damage rate of irradiated silicon crystals as compared to monoatomic Au+ ion effects.