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The quantification of SIMS depth profiles by Maximum Entropy\ud reconstruction

By Paul Nicholas Allen


The quantification procedures applied to raw SIMS data were devised\ud on the basis of a simple model for the sputtering and ionisation that occur\ud during measurement. The model and the associated quantification\ud procedures have long been known to be inaccurate. If SIMS is to remain a\ud useful analysis tool in the future, the quantification procedures must be\ud adjusted such that current features of interest are accurately measured.\ud This thesis describes the development of a more accurate (though\ud empirical) model for the effects of the analysis, using the convolution integral.\ud We propose a method for the quantification of SIMS depth profiles\ud appropriate to this model, using Maximum Entropy (MaxEnt) reconstruction.\ud SIMS depth profile data differ significantly from previous applications of the\ud MaxEnt method: the very high signal to background ratio of the technique has\ud lead users to plot the results on a logarithmic axis, giving much importance to\ud extremely small signals.\ud The noise on SIMS depth profiles has been characterised. A number\ud of optimisation algorithms have been developed and tested, and the\ud performance of the MaxEnt method on SIMS data has been assessed. A\ud novel form of the entropy, particularly suited to SIMS depth profiles, has been\ud suggested. This form has given excellent results

Topics: QC, QD
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