Analysis of cluster ion sputtering yields: correlation with the thermal spike model and implications for static secondary ion mass spectrometry

Abstract

AbstractAn assessment is made of the behaviours in ion sputtering and static secondary ion mass spectrometry to provide a framework to understand the enhanced secondary ion yield of molecular fragments, from molecules on defined substrates, achieved by using primary ion clusters. First, an analysis is made of the published ion sputtering yield data for mono‐elemental solids sputtered by mono‐elemental primary ion clusters, mainly of the type Aun+. These are evaluated using Sigmund and Claussen's thermal spike model. That theory is shown to be consistent with, and an excellent description of, the published ion sputtering yields for elemental targets over a wide energy range for primary ion cluster sizes from 1 to 13 for gold primary ion clusters and for a number of different primary ion species. This theory is then used to evaluate the molecular ion yield behaviour of interest in static secondary ion mass spectrometry (SIMS). This is done for measurements on Irganox 1010. The thermal spike sputtering yield is first related to the total secondary ion yield. The secondary ion yield of the molecular ion, whether protonated or de‐protonated, is then shown to be proportional to the square of the total secondary ion yield and hence to the square of the sputtering yield. This rule is valid for all primary ions, both single atom and cluster, over 5 decades of emission intensity, largely independent of the chemical identity of the primary ions for those data. This enables recommendations for future sources of higher efficiency for the analysis of organic materials. © Crown copyright 2007. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.