Topography and angular distribution of sputtered atoms of silver target bombarded by Si_n~- (n = 1,2) ions

摘要

The experimental evidence for molecular effects in sputtering from a metallic target is convincing. Deviations from linearity in the collision cascade have been determined directly by comparing yields for molecular-ion bombardment to these observed in atomic-ion bombardment [1-4], in which the atomic doses and energy are kept the same. A given system exhibits a molecular effect when the so-called molecular yield enhancement factor Y(n)Y(l) is larger than unity (Y(n) is the sputtering yield of an n-atomic molecular ion), while, in the case of linear collision cascade, no molecular enhancement is expected upon bombardment with molecular ions. Up to now several workers have investigated the problem of deviations from linear cascade theory, but there is less agreement concerning the mechan-isms responsible for the excess yields. Some authors have argued that the non-linear components arise from thermal spike [2,4,5], while others have suggested that the non-linear yield, in particular, is caused by major disruptions of the target surface, which lower the effective surface binding energy [3, 6-9]. In the present work we have measured the angular distributions of atoms sputtered from a heavier target (Ag) by dimer and monomer ion projectiles (28SiJ and 28SiJ~), in order to investigate the non-linear effects at these bombarding energies and the influence of the surface topographic features on the differential sputtering yield.