Cluster primary ions: Spikes, sputtering yields, secondary ion yields, and interrelationships for secondary molecular ions for static secondary ion mass spectrometry

Abstract

A framework is provided to describe the enhanced sputtering yields and secondary ion yields of molecular fragments, from molecules on substrates, achieved when using cluster primary ions. Analysis of published sputtering yield measurements shows that one particular model of sputtering, which includes the thermal spike, is an excellent quantitative description of the yields for a wide range of monatomic and polyatomic primary ions. The model is valid for describing clusters of up to more than ten atoms over three orders of magnitude in sputtering yield. Using data from one primary ion, extremely good descriptions of measurements reported with other primary ions are achieved. This is then used to evaluate the important molecular ion yield behavior for static secondary ion mass spectrometry based on data for Irganox 1010. Universal dependences for the deprotonated molecular ion yields, valid for all the primary ions studied, both single atom and cluster, over five decades of emission intensity are obtained. This permits the prediction of the (M−H)− secondary ion yield for different, or new, cluster primary ions, e.g., Bin+ and C70+, for the analysis of organic materials. Optimal primary ion sources are predicted and discussed. For analyzing materials, raising the molecular secondary ion yield is extremely helpful but it is the ratio of this yield to the disappearance cross section that is critical for obtaining the maximum useful molecular yield and/or the best spatial resolution for molecular signals from molecular monolayers. Data are evaluated and a description is given to show how this ratio varies with the cluster to provide further universal dependences.