COMPARATIVE-STUDY OF KINETIC-ENERGY SPECTRA AND MASS DISTRIBUTIONS OFTA-N(-BOMBARDMENT() IONS SPUTTERED FROM TANTALUM BY ATOMIC AND MOLECULAR ION)

Mass distributions and kinetic energy spectra of Ta-11(+) ions (n less than or equal to 12) sputtered from a tantalum target by Au-m(-) prim ary ions (m = 1,2,3), with energies of 6 keV per constituent atom, hav e been determined under identical experimental conditions, Under the m olecular ion bombardment, anomalous high non-additive sputtering yield s were observed for large metal clusters. For instance, a relative yie ld of Ta-10(+) clusters under Au-3(-) molecular ion bombardment was ob served approximately 2000 times higher than that under Au- atomic ion bombardment, The comparison between mass distributions and kinetic ene rgy spectra determined under the molecular ion bombardment and those f or the atomic ion bombardment showed both qualitative and quantitative differences. A hypothesis about the existence of different cluster io n emission mechanisms for small clusters of several atoms and for larg er ones is proposed. (C) 1998 Elsevier Science B.V.