SIMS yields from glasses; secondary ion energy dependence and mass fractionation

Abstract

SIMS studies of glasses indicate that calibration of positive monatomic ion yields via relative sensitivity factors (RSF) is significantly dependent both on the kinetic energyE _k and on the massM _t of the analyzed ions. Due to elemental differences in the energy distributions of the sputtered ions, relative emissivities at highE _k are radically different from those at the tops of the distributions. While the RSF values of cations from glasses range within ca. 3 powers of ten, atE _k above ca. 40 eV the range remains within a factor of ten or less, and further change of relative elemental sensitivities withE _k is slow. At low exit energy the LTE formalism is reasonably well obeyed. At highE _k , a trend is noted towards a relative suppression of the ion yields of lowvalent elements.

Measurements of isotope fractionation in secondary ion yield were performed on 17 elements sputtered from glasses. The mass factorα (defined by the proportionality of the yield toM ^−α _i ) is found to range from near-zero toα≅2.5, dependent on the element and onE _k . For most elements a drops steeply at lowE _k , but generally a slow rise is noted at higher energies. The behaviour ofα appears to be to some extent connected with the shape of the energy distribution curve. The dependence ofα onE _k and on elemental parameters can qualitatively be described in terms of a simple phenomenological model.