Methods for quantitative analysis in secondary ion mass spectrometry

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Abstract
Methods for quantitative analysis in secondary ion mass spectrometry must be capable of correcting for strong matrix effects on emitted secondary ion intensities as well as strong instrumental effects on measured secondary ion intensities. Both empirical methods, based on sensitivity factors and working curves, and theoretical models for secondary ion emission, are available. Absolute sensitivity factors are not satisfactory because of the lack of compensation for matrix effects. Working curves are capable of yielding analysis with 5% relative accuracy but offer poor flexibility in dealing with unknowns which differ strongly from the standards. Relative sensitivity factors offer both flexibility in the analysis of unknowns and an error distribution in which 80% of the analyses fall within a factor of 2 of the unknown and 99% within a factor of 5. Numerous physical models for secondary ion emission are available but are generally limited in application due to uncertainties in the required physical data. The local thermal equilibrium (LTE) model is broadly applicable with partial constraint on the composition of the unknown. The LTE error distribution places about 50% of the analyses within a factor of 2 and 80% within a factor of 5. Large errors, exceeding a factor of 10, are observed for heavy elements, possibly due to uncorrected instrument effects.Future development of analytical methods may combine the relative sensitivity factor method (which minimizes the influence of instrument artifacts) with the theoretical description of secondary ion emission (to calculate matrix effects).