Sputtering of Tantalum by Atomic and Molecular Gold Ions: Comparative Study of Yields and Kinetic Energy Distributions of Atomic and Cluster Ions

Abstract

Relative secondary ion yields and kinetic energy spectra of Ta_n ⁺ ions (n ≤12) sputtered from a tantalum target by Au^- atomic ions with energies of 6keVand 12keVas well as by 12keVAu₂ ^- molecular ions have been measured under identical experimental conditions. Under molecular ion bombardment, an anomalous high non-additive sputtering yield was observed for large metal clusters. In this case, for instance, the yield of Ta₁₀ ⁺ clusters was determined to be approximately 320 times higher than that under corresponding atomic ion bombardment (6keV per constituent atom of the projectile). Comparison 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 the experimentally observed regularities, a hypothesis regarding the existence of two different cluster ion emission mechanisms for small clusters (n<5) and for larger ones (n>5) has been proposed.