The Analysis of Particles at Low Accelerating Voltages (≤ 10 kV) With Energy Dispersive X-Ray Spectroscopy (EDS)

Abstract

In recent years, there have been a series of advancements in electron beam instruments and x-ray detectors which may make it possible to improve significantly the quality of results from the quantitative electron-probe analysis of individual particles. These advances include: (1) field-emission gun electron beam instruments such as scanning electron microscopes (FEG-SEMs) that have high brightness electron guns with excellent performance at low beam energies, E 0 ≤ 10 keV and (2) high-resolution energy-dispersive x-ray spectrometers, like the microcalorimeter detector, that provide high-resolution (< 10 eV) parallel x-ray collection. These devices make it possible to separate low energy (< 4 keV) x-ray lines including the K lines of carbon, nitrogen and oxygen and the L and M lines for elements with atomic numbers in the range of 25 to 83. In light of these advances, this paper investigates the possibility of using accelerating voltages ≤ 10 kV, as a method to improve the accuracy of elemental analysis for micrometer-sized particles.

Keywords: electron probe analysis; low voltage analysis; particle analysis; scanning electron microscopy; x-ray microanalysis.

Fig. 1

Relative error distributions for the analysis of glass particles and bulk glass samples.

Fig. 2

Monte Carlo plots for the interaction of a 20 kV electron beam with a 2 μm K-411 particle. a) Electrons trajectories. b) Mg Kα x-ray generation.

Fig. 3

Monte Carlo plots for the interaction of a 5 kV electron beam with a 2 μm K-411 particle. a) Electrons trajectories. b) Mg Kα x-ray generation.

Fig. 4

Secondary electron image of K-411 microspheres.

Fig. 5

Plots of Fe and Ca Particle/Bulk values vs particle diameter for K-411 microspheres at different kV. (a) 25 kV, (b) 15 kV, (c) 10 kV.

Fig. 6

Plots of Mg and Si Particle/Bulk values vs particle diameter for K-411 microspheres at different kV. (a) 25 kV, (b) 15 kV, (c) 10 kV, (d) 5 kV.

Fig. 7

Ca Particle/Bulk ratios at 5 kV.

Fig. 8

RD values for glass shards vs electron beam accelerating voltage.

Fig. 9

RD values for (a) unnormalized and (b) normalized Mg analyses vs accelerating voltage.

Fig. 10

RD values for (a) unnormalized and (b) normalized Fe analyses vs accelerating voltage.

Fig. 11

Monte Carlo calculations of the percent change in k-ratios for elements in K-411 glass as a function of carbon thickness.

Fig. 12

Plot of Fe/Ca and Fe/Si intensity ratios for the area and spot analyses of glass K-3189 at 20 kV.

Fig. 13

Plot of Fe/Ca and Fe/Si intensity ratios for the area and spot analyses of glass K-3189 at 10 kV.

Fig. 14

Monte Carlo calculations of the percent change in k-ratios for elements in K-411 glass as a function of carbon thickness.