Nonadditive sputtering of silicon by keV energy molecular projectiles of heavy and light elements

In the present work a positive secondary ion emission from a silicon produc ed by Au-m(-) projectiles (m = 1-3) with energies of E-o = 9 and 18 keV and by Al-m(-) projectiles (m = 1,2) with energies of E-o = 6, 9, 12, and 18 k eV have been studied. Anomalous high nonadditivity of sputtering as large c luster Si-n(+) ions (n > 4) under molecular Au-m(-) ion bombardment has bee n found. As compared with heavy (Au-m(-)) projectiles, the light (Al-m(-)) projectiles are not effective for sputtering of large cluster ions. For mol ecular Al-m(-) ion bombardment nonadditivity of sputtering of small cluster Si-n(+) ions (n less than or equal to 4) increases with decreasing of the energy E-o from 9 to 6 keV/atom. This effect shows that the efficiency of n onadditive sputtering strongly depends on the penetration depth of molecula r projectile and, hence, on the energy density deposited by molecular proje ctile into subsurface layers of the target from which the cluster ion emiss ion occurs. (C) 2001 Elsevier Science B.V.