Investigation of the formation of M-2(+)-molecular ions in sputtering processes

The formation process of M-2(+) molecular ions sputtered from elementary ta rget materials is investigated. in a previous article it was shown that the se molecules can be used to quantitate major elements [1]. The quantitation method was based on the assumption that the M-2(+) molecular ions are form ed by the atomic combination of independently sputtered M and M+ particles above the surface. In this paper this assumption will be investigated using a Monte Carlo model to simulate the formation mechanism. The model is used to calculate the velocity distribution of the M: dimers sputtered from thr ee different elementary target materials (Fe, Ge, and Ni). The results are compared with experimental data. Good agreement exists between theory and e xperiment that supports the Monte Carlo model and hence also the assumed fo rmation mechanism. (C) 1999 American Society for Mass Spectrometry.