Cluster primary ion sputtering: correlations in secondary ion intensities in TOF SIMS

A brief review is given of some of the behaviors of cluster primary ions in secondary ion mass spectrometry (SIMS). The increased secondary ion yields for cluster primary ions are covered as well as the raised sputtering threshold energies. For organic materials, the increase in intensity as the sputtering yield rises varies with the fragment mass through the spectrum. For Irganox 1010, the intensity of the deprotonated negative and the positive molecular ions increase as the square of the total ion yield. However, the intensity of intermediate fragments increase with a lower power, rising monotonically from unity at m/z similar to 400 to 2 at the molecular ion. The constitution of the Irganox 1010 spectra for Ar+, Bi+, Bi-3(+) and Bi-5(+) may be described by a basic spectrum such as that for Ar+ and two further 'spectra' which are product terms that multiply the intensity to a power defined by the cluster primary ion species, cluster number and energy. This resolution of the spectra into three components may be translated, for example, to the published data for Si where, for Si-t(+) secondary ion clusters, the terms are very much simpler: one is a constant, the second is a single exponential term dependent of the energy-deposition density, and the third is related to the cluster-binding energy. Finally, for studying molecular structure, the use of cluster primary ions in G-SIMS is outlined. Here, the cluster primary ions are critical for analyzing the weaker, high-mass peaks. (C) Crown copyright 2010. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.