Internal energy of sputtered clusters: The influence of bombarding conditions

We have investigated the internal (vibrational) excitation of nascent clusters formed during sputtering of metal surfaces. On one hand, theoretical model calculations were performed by Molecular Dynamics computer simulation using the MD/MC-CEM many body interaction potential. On the other hand, experimental data were collected by studying the fragmentation lifetimes of sputtered cluster ions on time scales of 10(-9)-10(-6) s after their ejection and conversion of the resulting lifetime distributions into the distributions of internal energies. It is found that sputtered clusters possess average internal energies of about 1 eV per constituent atom, corresponding to vibrational temperatures of several thousand K. Special emphasis was put on the influence of the bombarding conditions on these results. Surprisingly, neither the nature or kinetic energy of the primary ions nor the bond strength of the ejected clusters seem to significantly influence the average internal energy. (C) 1998 Published by Elsevier Science B.V.