The original NBS/NIH DTSA (Desktop Spectrum Analyzer) software was widely used in the x-ray microanalysis research community. The combination of analytical and simulation tools was unavailable elsewhere. However DTSA was locked to an archaic Apple operating system and though many retain an old Mac to run it, many were asking for a replacement. DTSA-II takes much of the philosophy that made DTSA popular and has built a new platform independent replacement. DTSA-II provides similar analytical and simulation tools as the original but adds the ability to model more complex geometries with more sophisticated physical models.
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.
DTSA-II while highly functional today remains a work-in-progress. As we continue to develop the product we will place our focus in two directions. We will focus on fundamental physics and improving our ability to simulate spectra from simple and complex sample geometries. Second, we will focus on providing tools for challenging experiment types that are poorly addressed by the commercial products. In this way, we hope to develop the same kind of community following as the original DTSA.
A 25 keV beam incident on a 1.5 µm sphere of SRM-2066 glass, top O x-rays, center Ca x-rays and bottom substrate x-rays.
Start Date:April 1, 2004
Lead Organizational Unit:mml
Customer: Microanalysis Community
Collaborators: John Villarubia, Nanometrology Group – He is developing the Monsel-3D tool for simulating secondary electron images using the electron transport algorithms from DTSA-II
JEOL JXA-8500F, FEI Quanta-200F, Bruker 4040 detector, ASPEX Personal SEM