Analysis and detection of low-energy electrons in scanning electron microscopes using a Bessel box electron energy analyser

The interpretation of images generated by scanning electron microscopes (SEMs) requires quantifiable and well-understood contrast. Furthermore, recent interest in probing samples using low-energy electrons to extract surface information is pushing towards the quantification of relative contrast in secondary-electron (SE) images. The detection and analysis of low-energy SEs remains at the heart of the development of such instruments and techniques. However, state-of-the-art SE detectors in most SEMs, which are largely using in-lens configurations, are mainly designed to favour the collection of primary-induced SEs, and hence fail to provide electron energy information that could be related to the sample composition. Here, we report on the development of a novel SE detector which makes use of the Bessel box (BB) electron energy analyser. We demonstrate a very compact analyser design (˜a volume of 12 mm³) through simulations and by acquiring an electron spectrum from a sample of graphene on copper. A resolution of 0.3% has been numerically computed and experimentally verified for the BB analyser.