SIMS molecular cluster intensities of inorganic salts containing sulfur and nitrogen oxyanions

Abstract

Secondary ion mass spectrometry (SIMS) is used to examine alkali sulfur oxyanion and nitrogen oxyanion salts. The secondary ion spectra, filtered about a nominal 1-eV kinetic energy, are measured in the dynamic SIMS mode using a 1—5 μA/cm 2 beam intensity of 1-keV Ar + primary ions. Charge build-up on the sample surface is neutralized by thermal electrons. The positive (+) secondary ion spectra are dominated by cation species (M +, MO +, M 2 +, M 2O +). The negative (−) secondary ion spectra include the anion central atom (A)—oxygen series (O −, A −, AO −, AO 2 −, AO 3 −, AO 4 −). The relative ion intensity pattern of the (−) series shows a clear dependence on anion stoichiometry. For sulfur oxyanions and a 1-keV Ar + ion beam, the pattern can be represented by a modified Poisson distribution if dissociation of AO 4 t- and AO 3 − is assumed for sulfate and sulfite, respectively. The Poisson distribution mean values for oxygen loss are found to be 4̃.5 for sulfate and sulfite and 3̃ for thiosulfate. The mean value for loss increases with increasing Ar + ion energy in the range 0.5–2.0 keV. The nitrogen oxyanion intensifies are complicated by ion beam damage and by neutralization effects. Primary ion beam damage of the substrate is monitored by X-ray photoelectron spectroscopy (XPS).