Gold-thiolate cluster emission from SAMs under keV ion bombardment: Experiments and molecular dynamics simulations

In this contribution the emission of gold-molecule cluster ions from self-assembled monolayers (SAMs) of alkanethiols on gold is investigated using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Layers of alkanethiols [CH3(CH2)nSH] with various chain lengths (n 1⁄4 8, 12, 16) have been chosen because they form well-ordered molecular monolayers on gold. First, we compare and interpret the yields and energy spectra of gold-thiolate cluster ions, obtained for different thiol sizes. Our results show that the unimolecular dissociation of larger aggregates in the acceleration section of the spectrometer constitutes a significant formation channel for gold-molecule clusters. Second, we present preliminary results of molecular dynamics simulations performed in order to improve our understanding of the cluster emission processes. These calculations have been conducted using 8 keV projectiles and a long-range term in the hydrocarbon potential in order to account for the van der Waals forces between the thiol chains. 2003 Elsevier B.V. All rights reserved.