Quantiative x-ray microanalysis at higher voltages

Abstract

The advantages of analytical electron microscopy (AEM) at accelerating voltages of 200 kV and above have been discussed for years. However, the practical realization of significant improvements in spatial resolution, elemental detectability, and quantitative elemental measurements have awaited the combination of higher kV with field emission sources, more efficient EDS x-ray detector systems, and system stabilities that allow longer counting times. Improved spatial resolution of analysis is the reason quantitative x-ray microanalysis is sought from thin specimens rather than bulk specimens. With a 100kV field emission source, producing a 2nm probe of 0.3 nA, spatial resolution across a chemically distinct phase boundary can be on the order of 2-3 run in a foil 20nm thick. Michael et al. have predicted that such a thin specimen would not show an improvement in spatial resolution at 300 kV versus 100 kV because beam spreading is small compared to the beam diameter; whereas, specimens 100 times thicker would exhibit the expected 3-fold improvement in spatial resolution at 300 kV.