Journal Highlights
Techniques and Instrumentation Development
Electron-Excited X-ray Microanalysis at Low Beam Energy: Almost Always an Adventure! by DE Newbury and NWM Ritchie, Micros Microanal 22 (2016) 735–53
“Low beam energy” x-ray microanalysis performed in the scanning electron microscope at landing energies E 0 ≤5 keV off ers improved lateral and depth resolution, typically sampling volumes with linear dimensions of a few hundred nanometers or less. Special analytical challenges arise because the reduced beam energy can only stimulate x rays from low-ionization-energy atomic shells. T us, transition metals usually analyzed with K-shell x rays must instead be analyzed with L-shell x rays, while for intermediate and high atomic number elements the M-shell must be used. Low photon energy x-ray families have low yield and complex, variable shapes from multiple, closely spaced peaks. Nevertheless, accurate quantitative analysis (relative to elemental and simple compound standards) can oſt en be achieved by employing the peak fi tting and matrix correction procedures embedded in the NIST DTSA-II EDS analysis and modeling soſt ware engine. Other challenges to analytical interpre- tation arise because surface layers such as natural oxides, which are so thin as to be insignifi cant at high beam energy (E 0 ≥10 keV), account for a much larger fraction of the material sampled at low beam energy. Iterative DTSA-II analysis must be performed wherein the residual spectrum aſt er peak fi tting is inspected for peaks of unanticipated constituents.
Monte Carlo simulation (NIST DTSA-II) of electrons bombarding a 100 nm cube of SiO 2 in a Cu matrix. At 5 keV, electrons penetrate the SiO 2 cube and excite Cu x rays, but at 2.5 keV few electrons reach the Cu, so the Cu peak is barely detectable above background.
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