YIELDS AND ENERGY-DISTRIBUTIONS OF SPUTTERED SEMICONDUCTOR CLUSTERS

We have investigated the formation of clusters during sputtering of a germanium surface by 5-keV Ar+ ions impinging under 45 degrees with re spect to the surface normal. Charged clusters were detected directly b y time-of-flight mass spectrometry (TOF-MS), the corresponding neutral species were post-ionized prior to mass and energy analysis by means of single photon ionization from an intense VUV laser beam. It is show n that the photoionization process can be saturated without indication of significant photofragmentation of the clusters. The relative yield s of sputtered Ge-n clusters are found to obey a power law dependence on the cluster size n with an exponent around -6.5. The kinetic energy distributions exhibit a shift of the maximum towards lower energies w ith increasing cluster size, the asymptotic decay towards high energie s is found to be virtually identical for all measured atoms and cluste rs. The experiments were repeated on two different single crystalline Ge surfaces ([100]and[111]) which could be reproducibly amorphized by ion bombardment and re-annealed. As a result, it is found that the cry stalline structure of the ion bombarded surface does not play a signif icant role in the formation of sputtered clusters. (C) 1998 Elsevier S cience B.V.