| Abstract: | Alkanethiol self‐assembled monolayers/multilayers (SAMs) have been applied as model organic systems with which to investigate secondary ion formation and emission processes during kiloelectronvolt ion bombardment. Self‐assembled monolayer and multilayer films of 11‐mercaptoundecanoic acid capped with 1‐dodecanethiol were prepared on gold‐coated substrates. Samples with varying number of thiolate layers were studied using static secondary ion mass spectrometry to investigate the origin of molecular secondary ions and the influence of surface chemistry and structure. The nature of the thiolate bonding affects the type and abundance of the observed ions. The intensity of atomic and cluster ions derived from the substrate decreases exponentially with increasing number of thiolate overlayers because of losses in transmission through the organic overlayers. Intact molecular and cluster ions can escape from >100 Å below the surface of these structures. The variation of molecular‐ion yields with multilayer thickness suggests that a significant proportion of molecular ions originate from subsurface thiolate layers. The detection of ions comprised species from the substrate or bottom of the multilayer associated with species from the top layer supports the view that chemical association at or near the surface is a viable mechanism of formation for molecular secondary ions. Copyright © 2005 John Wiley & Sons, Ltd. |
