Interpretation of static secondary ion spectra

A model is presented in which electron impact (EI)/electronic excitation plays a pivotal role in the formation of secondary ions in the SIMS experiment, especially those originating from discrete molecular species. Positive ions are formed by electron loss whereas negative ions are formed by electron capture. Collisions of the new ions with the surface and with other species directly above the sample, along with metastable decay events, reduce the number of odd electron ions detected and produce the changes that make SIMS spectra so different from EI mass spectra. Primary support for this model is gathered from static SIMS spectra themselves, which can be rationalized to a large degree by assuming that the same rearrangement and fragmentation mechanisms that are invoked to explain Ell mass spectra take place at the surface after kiloelectron-volt ion impacts. The static secondary ion spectra of a variety of simple discrete molecular species, of simple hydrocarbons, of monofunctional organic species and of more complicated multifunctional organic species are analyzed in this way and the utility of this model is demonstrated. Copyright (C) 2004 John Wiley Sons, Ltd.