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X-ray Spectrum Imaging at High Resolution in the STEM and STEM/SEM and SEM

With the advent of large area silicon drift detectors X-ray microanalysis has moved from a technique based on point spectra to one focused more on mapping element distributions. With this change in focus comes a new drive to image using energy dispersive x-ray spectrometry (EDS) at increasing spatial resolution. The standard technique for high resolution EDS, e.g. for features of less than 20 nm, is STEM at high voltage, typically 200 kV or greater. Using aberration corrected STEM at high kV, it has been demonstrated that atomic resolution EDS is achievable in a wide range of specimens [1,2]. It is also understood that at this resolution EDS is no longer a quantitative technique with the effects of electron channelling dominating the relative X-ray intensity between atoms [3]. The achieved spectrum images do however give excellent information on the spatial distribution of elements. If absolute quantitative understanding of elemental distribution is not required then developments in lower kV electron microscopy technology may provide a real alternative to high voltage, to achieve nanometre resolution EDS mapping.