A method for the correction of size effects in microparticles using a peak-to-background approach in electron-probe microanalysis

Abstract

We describe a correction method in electron probe microanalysis (EPMA) for size effects in microparticles. Accounting for size effects is important in quantitative EPMA of microparticles, where bulk standards are usually used for quantification. In this work, the correction was applied using peak-to-background ratios PB that are quasi-independent of absorption path lengths, which enables the difference in absorption between a microparticle and a bulk sample to be taken into account. For microparticles smaller than the X-ray generation volume, the X-ray emission inside the particle can be significantly affected by the transmission of electrons through the particle, thus requiring a correction in the measured PB ratios. Moreover, transmitted electrons induce Bremsstrahlung from the substrate that can also affect the PB ratios. This raises the necessity to include a correction of the substrate emission in the PB methods applied for microparticles. The present method enables to correct for the effects due to electron transmission as well as the parasitic emission of the substrate. In order to assess the validity of our method, the corrected PB of small particles were compared with those obtained for a bulk sample or a pseudo-bulk particle where size effects are negligible. Corrected PB were further used in a ZAF PB method [J. Lábár, S. Török, X-Ray Spectrom. 21 (1992) 183–190] to evaluate the correction model in terms of quantitative analysis. The study was performed on homogeneous spherical microparticles of K411 glass and microparticles of UO2. Both substrate and transmission effects were taken into account in the K411 glass particles, which led to significant improvements in terms of quantitative results. For UO2 particles, size effects did not have much impact on the PB ratios and accurate quantification was obtained from both uncorrected and corrected ratios.