Mixed metal–silicon clusters formed by chemical reaction in a supersonic molecular beam: Implications for reactions at the metal/silicon interface

Abstract

We report observation of a reaction between a metal atom and silicon in a supersonic jet to form metal atom–silicon clusters. Using the technique of laser vaporization supersonic expansion with metal carbonyl seeded carrier gas, clusters of the form MSin have been detected by ArF and F2 laser photoionization time-of-flight mass spectrometry. Three group-VIB transition metals and copper have been investigated. The dominant product cluster peaks observed in the mass spectra obtained for all three group VIB metals corresponds to identical but remarkable cluster stoichiometries. The dominant product peaks have formulas given by MSin where n=16. Copper results are different than the other three metals, indicating the importance of the metal valence electronic structure to the chemistry. The metal–semiconductor clusters are relatively more stable towards photofragmentation than the bare silicon cluster of the same size. The observation of these new species may be relevant to reactions which occur at the interface between a silicon wafer and deposited metals.