Single and double cationization of organic molecules in SIMS

The cationization of sputtered organic species via metal particle adduction is investigated using a series of molecules and metallic substrates. Analyte molecules include styrene-based oligomers with various molecular weights, poly(methyl methacrylate) and a polymer additive. The chosen substrates are Al, Cr, Cu, Pd, Ag, In, An and Pb. Metal-cationization occurs for all the substrates except Al. The cationized molecule yields vary strongly with the considered molecule and substrate and they are not correlated with the metal ion yields. In addition, double cationization with two metal particles is observed in specific cases (Cu, Pd, Ag, and Au supports, styrene-based polymers with similar to13 repeat units or more). The combination of electronic structure calculations, molecular dynamics and Monte-Carlo simulations supports an emission scheme in which excited molecules and metal atoms recombine above the surface and decay via electron emission, thereby locking the complex in the ionic state. (C) 2002 Elsevier Science B.V. All rights reserved.