We have developed an efficient detector of secondary electrons (SEs) for a high-performance scanning transmission electron microscope (STEM) and tested it on several materials. Using the detector at 60 keV, we resolved the nearest neighbor atoms separated by 0.142 nm in SE images of graphene, and detected single-atom substitutions in graphene and monolayer MoS2. We imaged single heavy atoms on an amorphous carbon thin film, and the surface structure of gold nanoparticles supported on a thin film as well as on a bulk substrate. Other application examples shown in this paper include SE imaging combined with 4D STEM, simultaneous SE and electron energy loss spectroscopy (EELS) imaging, and simultaneous imaging of entrance and exit sides of a sample using two separate SE detectors. The results point to an exciting future for atomic-resolution SE imaging.
Martis et al. (Thu,) studied this question.