Improved X-ray Spectrum Simulation for Electron Microprobe Analysis

Abstract

The accurate calculation of characteristic peak intensity is essential for interpreting X-ray spectra in electron microprobe analysis. Conventionally, the measured intensity from a standard of known composition is used as a reference to simplify the calculation. However, if no such standard is available, then all factors influencing X-ray generation and X-ray detection efficiency must be included. If the intensity and energy distribution of the background radiation can also be calculated, the investigator can simulate an entire spectrum from an assumed composition, gaining powerful benefits in setting up an experiment and in confirming the results. The study presented here demonstrates a fast method of spectrum simulation, suitable for energydispersive spectroscopy (EDS), and assesses the accuracy using 309 spectra from samples of known composition. These include K, L, and M lines from elements of atomic number 6–92, excited by beam energies in the range of 5–30 keV. The RMS error between 360 measured and calculated peak intensities was found to be 7.1%. Central to the method is the use of the ratio of peak intensity/total background intensity, which allows spectra to be compared from instruments of differing collection efficiency, thereby easing the collection of data over a wide range of conditions.

Uncertainty Is Our Friend-Rethinking Microanalysis Around Uncertainty Metrics

“…If the results for the K and L lines don't agree to within the uncertainties, we need to know why. The software needs to simulate the resulting composition and compare the simulated spectra to the measured spectra [1]. It needs to verify every piece of information entered by the analyst.…”

Enhanced Theoretical Model for Avoiding Mistakes in SEM-EDS Analysis

“…Many years ago, Duncumb suggested display of a synthesised spectrum might be helpful [2]. The potential to realise this principle came with subsequent development of a theoretical model optimised to match measured ratios of peak intensity to total background (P/Btot) [3]. In any attempt to develop parameterised expressions, a critical factor is the calculation of detector efficiency as a function of energy.…”

“…Instead of a calculation, an efficiency characteristic has now been measured for a large solid angle SDD detector [4] and data acquired from an extensive set of standard materials at both 5kV and 20kV. The original theoretical model [3] has been enhanced to incorporate differential absorption and excitation of emission lines, including the effect of Coster-Kronig transitions. The parameterisation has been adjusted to fit measured characteristic intensities and both background shape and intensity at the same beam current.…”

Prospects for Single Standard Quantitative Analysis with SDD

“…6400GS was mounted on an SEM with a special tilt stage and take-off-angle was determined to within 0.5 degrees. A large series of measurements on reference standards were taken under conditions of stable beam current and spectrum synthesis [4] was used to expose potential outliers. This provided a new analysis calibration consistent with the measured 6400GS efficiency curve.…”