Uncertainty and capability of quantitative EPMA at low voltage – A review

The use of electron probe microanalysis (EPMA) at low voltage allows improvements in the lateral resolution and surface sensitivity of the technique down to the sub-micrometre scale, and it is also useful in minimizing X-ray absorption (for the analysis of ultra-light elements), charging effects and secondary fluorescence. However, EPMA at low voltage is accompanied by a number of problems which may affect the accuracy of quantitative results. A large number of these problems arise from the need of using low-energy X-ray lines such as L- and M-lines, which have low fluorescence yields, large uncertainties in the mass attenuation coefficients, and are affected by several spectroscopic difficulties (e.g., peak shifts and overlaps). Other factors that play an important role at low voltage are carbon contamination, surface oxidation, the quality of sample polishing, the influence of a conductive coating and the limitations of matrix correction procedures. In this paper, we illustrate the capabilities of EPMA at low voltage and we examine in detail the different sources of uncertainty that may affect the accuracy of quantitative results.