SPUTTERING OF TANTALUM BY ATOMIC AND MOLECULAR GOLD IONS - COMPARATIVE-STUDY OF YIELDS AND KINETIC-ENERGY DISTRIBUTIONS OF ATOMIC AND CLUSTER IONS

Relative secondary ion yields and kinetic energy spectra of Ta-n(+) io ns (n less than or equal to 12) sputtered from a tantalum target by Au - atomic ions with energies of 6 keV and 12 keV as well as by 12 keV A u-2(-) molecular ions have been measured under identical experimental conditions. Under molecular ion bombardment, an anomalous high non-add itive sputtering yield was observed for large metal clusters. In this case, for instance, the yield of Ta-10(+) clusters was determined to b e approximately 320 times higher than that under corresponding atomic ion bombardment (6 keV per constituent atom of the projectile). Compar ison between mass spectra and kinetic energy spectra determined under molecular ion bombardment with those for atomic ion bombardment showed both qualitative and quantitative differences. Taking into account th e experimentally observed regularities, a hypothesis regarding the exi stence of two different cluster ion emission mechanisms for small clus ters (n < 5) and for larger ones (n > 5) has been proposed.