Desorption/ionization of molecular nanoclusters: SIMS versus MALDI

Molecular nanoclusters, consisting of a core with a few metal atoms surrounded by a protective layer of organic ligands and potentially useful for heterogeneous catalysis applications, have been analyzed using energetic beam (particle/laser)-induced mass spectrometry. The results are mainly illustrated by the study of the molecular precursor [Ru5C(CO)(14)Pt(C8H12)] cast on a silicon substrate from dilute acetone or acetonitrile solutions. In both ToF-SIMS and MALDI-ToF, the molecular ion does not dominate the high-mass range of the mass spectrum. Instead, the dominant peak series correspond to the molecular cluster having lost its hydrocarbon residue and/or a number of CO ligands, with some specifics for each desorption/ionization method. The processes leading to the constitution of the mass spectrum for such compounds (surface fragmentation, unimolecular dissociation) are investigated through the comparison of the SIMS and MALDI data. Perspectives concerning the usefulness of these two techniques for the analysis of supported nanoclusters (real catalysts) are provided in the conclusion. (C) 2004 Elsevier B.V. All rights reserved.