DTSA-II – Pushing the limits of energy dispersive X-ray spectrometry

X-ray microanalysis is a technique that dates back to the early 1950's. After almost sixty years, much is known about the fundamental physics behind the technique but a surprising amount remains unresolved. Using state of the art algorithms it is possible to simulate x-ray spectra, using first principle expressions, to within about 10% accuracy when one line family of one element is used to normalize the scale. Some of this difficulty comes from poor knowledge of the efficiency of the detectors but more critically some comes from poor understanding of the ionization cross section, decay rates, mass absorption coefficients and other basic parameters required to model the spectra. Some improvements have been made in recent years in particular to the ionization cross section. However, the absolute intensity is so dependent upon the ratio of auger to x-ray emission, called the fluorescence yield, which is particularly poorly characterized for the L and M families of shells.

DTSA-II pulls together most of the state-of-the-art algorithms, cross-sections and parameters required for modeling x-ray spectra into a single toolkit. In addition, DTSA-II adds tools for visualizing, comparing and analyzing measured x-ray spectra. The combination of simulation and analysis tools is very powerful for practical day-to-day modeling and for evaluating and comparing simulation algorithms. DTSA-II provides tools for simulating many challenging sample geometries including particles and films which are typically poorly handled by commercial tools. The visualization tools provided by DTSA-II provide novel capabilities to understand the electron interaction and x-ray generation volumes (see Figure 1). This understanding in the hands of industrial and commercial laboratory microanalysts will help them to make better, more accurate measurements for material science, quality control, forensic and other applications. For those interested in improving the fundamental physics, DTSA-II is a toolkit. The source code for DTSA-II is freely available. As a government product, the microanalysis community is able to extend and modify the product as they see fit to further their research goals. Those who are interested may contribute their improvements back to the project.

DTSA-II also provides simple tools that lead analysts through the process of making standards-based measurements. Standards-based measurements remain the most accurate, most well characterized and most reliable measurements. However commercial tools are drifting away from providing standards based tools because they are typically considered too complex and time consuming. DTSA-II attempts to lead analysts through the process of making a standards-based analysis.

Since its introduction in 2008, DTSA-II combined with high count spectra from energy dispersive silicon drift detectors (SDD) have become the foundation on which around which a revolution has occurred in X-ray microanalysis.  The best-available quantification routines in DTSA-II fit measured spectra to measured spectra to produce k-ratios that rival and often exceed the accuracy of k-ratios measured with wavelength dispersive spectrometers (WDS).  The k-ratios have served as the basis for a series of articles which have pushed the bounds of x-ray microanalysis to quantify soft X-rays, interferences, complex spectra and other challenging problems.  Starting with “EDS measurements of X-ray intensity at WDS precision and accuracy using a silicon drift detector” (Ritchie et al, 2012), DTSA-II has been used to systematically address each of the challenging sample types for which the “SDD would never be able to match WDS.”  With the exception of the measurement of extreme trace elements (Newbury & Ritchie, 2016), we have demonstrated that the SDD can meet or exceed the performance of WDS for interferences (Newbury & Ritchie, 2015), borides, carbides, oxides and fluorides  (Newbury & Ritchie, 2015) and low beam energy (Newbury & Ritchie, 2016).

MAJOR ACCOMPLISHMENTS

The first official release of the software was made available to the community to coincide with the 2008 Microscopy and Microanalysis meeting.

The author was invited to give the Microbeam Analysis Society's presidential keynote lecture at this meeting to introduce the product.

A website provides access to the tool and an overview of the functionality and basic usage.

DTSA-II is an integral part of the forthcoming new edition to the classic electron microscopy text – Scanning Electron Microscopy and X-ray Microanalysis (known to the community as simply “Goldstein”)

RELATED PUBLICATIONS

Newbury, D. E. and Ritchie, N. W. M. (2013), 'Is Scanning Electron Microscopy/Energy Dispersive X-ray Spectrometry (SEM/EDS) Quantitative?', Scanning  35(3), 141-168.

Newbury, D. E. and Ritchie, N. W. M. (2015), 'Performing elemental microanalysis with high accuracy and high precision by scanning electron microscopy/silicon drift detector energy-dispersive X-ray spectrometry (SEM/SDD-EDS)', Journal of Materials Science 50(2), 493-518.

Ritchie, N. W. M. (2009), 'Spectrum Simulation in DTSA-II', Microscopy and Microanalysis 15(5), 454-468.

Ritchie, N. (2005), 'A new Monte Carlo application for complex sample geometries', Surface and Interface Analysis 37(11), 1006-1011.

Ritchie, N. W. M., Newbury, D. E. and Davis, J. M. (2012), 'EDS Measurements of X-Ray Intensity at WDS Precision and Accuracy Using a Silicon Drift Detector', Microscopy and Microanalysis 18(4), 892-904.

Newbury, D. E. and Ritchie, N. W. M. (2013), 'Elemental mapping of microstructures by scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS): extraordinary advances with the silicon drift detector (SDD)', Journal of Analytical Atomic Spectrometry 28(7), 973-988.

Ritchie, N. W. M. (2010), 'Using DTSA-II to Simulate and Interpret Energy Dispersive Spectra from Particles', Microscopy and Microanalysis 16(3), 248-258.

Newbury, D. E. and Ritchie, N. W. M. (2018), 'An Iterative Qualitative-Quantitative Sequential Analysis Strategy for Electron-Excited X-ray Microanalysis with Energy Dispersive Spectrometry: Finding the Unexpected Needles in the Peak Overlap Haystack', Microscopy and Microanalysis 24(4), 350-373.

Ritchie, N. W. M. (2020), 'Embracing Uncertainty: Modeling the Standard Uncertainty in Electron Probe Microanalysis-Part I', Microscopy and Microanalysis 26(3), 469-483.

Boettinger, W. J., Newbury, D. E., Ritchie, N. W. M., Williams, M. E., Kattner, U. R., Lass, E. A., Moon, K. W., Katz, M. B. and Perepezko, J. H. (2019), 'Solidification of Ni-Re Peritectic Alloys', Metallurgical and Materials Transactions A – Physical Metallurgy and Materials Science  50A(2), 772-788.

Newbury, D. E. and Ritchie, N. W. M. (2022), 'Energy-Dispersive X-Ray Spectrum Simulation with NIST DTSA-II: Comparing Simulated and Measured Electron-Excited Spectra', Microscopy and Microanalysis 28(6), 1905-1916.

Newbury, D. E. and Ritchie, N. W. M. (2021), 'Quantitative Electron-Excited X-ray Microanalysis With Low-Energy L-shell X-ray Peaks Measured With Energy-Dispersive Spectrometry', Microscopy and Microanalysis 27(6), 1375-1408.