Simulating Electron-Excited Energy Dispersive X-Ray Spectra with the NIST DTSA-II Open-Source Software Platform

Spatially-resolved elemental analysis by electron-excited X-ray excitation is a critical measurement capability for materials science applications¹. “NIST DTSA-II” is an open-source comprehensive software platform that supports many aspects of electron-excited X-ray microanalysis with energy dispersive X-ray spectrometry (EDS), including performing accurate standards-based quantitative analysis with matrix corrections^2-4. NIST DTSA-II includes a Monte Carlo electron trajectory simulation tool that enables “first principles” calculation of EDS spectra with user-specified composition and measurement conditions for a variety of target geometries (flat bulk material; vertical interface between two bulk materials; thin film on bulk; free-standing particles of various shapes (e.g., sphere, cube, cylinder; pyramid); inclusion embedded in a bulk matrix). The Monte Carlo simulation provides an absolute estimate of the characteristic and continuum (bremsstrahlung) X-ray intensity received by the detector based on the user-specified electron dose (beam current and detector acquisition time) and the EDS detector parameters (solid angle of acceptance; window transmission as a function of photon energy as calculated from the specified detector and window materials). Comparisons of intensities of measured and simulated EDS spectra for pure elements and multi-element standards (e.g., NIST Standard Reference Materials) show general agreement within ±25% for characteristic and continuum photon energies &gt; 1 keV. The simulated EDS spectra are useful for developing and optimizing analytical strategy, including estimating limits of detection for a specified electron dose and detector, lateral and depth spatial resolution as a function of beam energy, and the effects of particle geometry on the accuracy of analysis.<br/><br/>References<br/>Goldstein, J.I., Newbury, D.E., Michael, J.R., Ritchie, N.W., Scott, J.H., and Joy, D.C., Scanning Electron Microscopy and X-ray Microanalysis, 4^th ed., Springer, New York (2018).<br/>Ritchie, N.W., NIST DTSA-II software for quantitative electron excited X-ray microanalysis with energy dispersive spectrometry; available for free, including tutorials, at the NIST website: https://www.nist.gov/services-resources/software/nist-dtsa-ii (2021).<br/>Newbury, D. and Ritchie, N. “Review: Performing Elemental Microanalysis with High Accuracy and High Precision by Scanning Electron Microscopy/Silicon Drift Detector Energy Dispersive X-ray Spectrometry (SEM/SDD-EDS)”, J. Mats. Sci., 50, 493-518 (2015).<br/>Newbury, D. and Ritchie, N. “Electron-Excited X-ray Microanalysis by Energy Dispersive Spectrometry at 50: Analytical Accuracy, Precision, Trace Sensitivity, and Quantitative Compositional Mapping”, Micros. Microanal., 25, 1075-1105 (2019).