Low-Voltage Electron-Probe Microanalysis of Fe-Si Compounds Using Soft X-Rays

Conventional electron-probe microanalysis has an X-ray analytical spatial resolution on the order of 1-4 mu m width/depth. Many of the naturally occurring Fe-Si compounds analyzed in this study are smaller than 1 mu m in size, requiring the use of lower accelerating potentials and nonstandard X-ray lines for analysis. Problems with the use of low-energy X-ray lines (soft X-rays) of iron for quantitative analyses are discussed and a review is given of the alternative X-ray lines that may be used for iron at or below 5 keV (i.e., accelerating voltage that allows analysis of areas of interest <1 mu m). Problems include increased sensitivity to surface effects for soft X-rays, peak shifts (induced by chemical bonding, differential self-absorption, and/or buildup of carbon contamination), uncertainties in the mass attenuation coefficient for X-ray lines near absorption edges, and issues with spectral resolution and count rates from the available Bragg diffractors. In addition to the results from the traditionally used Fe L alpha line, alternative approaches, utilizing Fe L beta, and Fe Ll-eta lines, are discussed.