Center for Functional Nanomaterials Seminar

Scanning electron microscopes (SEM) are poorly characterized imaging instruments. The SEM optics (lens and aperture assembly) is designed to form a focused electron probe that scans the specimen to produce images. Therefore, the imaging efficacy in SEM strongly depends on the quality of the optics. However, there is no way to accurately characterize the optics in an uncorrected SEM (without multipole correctors) due to the lack of an exit wave. This talk will focus on improving the imaging capabilities of an uncorrected SEM by understanding its optical performance using wave optical theory, simulation, and experiment. We have developed two different simulations based on wave optical treatment of the electron beam to model the optical column and probe formation. Using one of the simulations for data generation, we have developed an aberration diagnostic method for the uncorrected SEM based on deep learning. Further, we have developed an experimental technique to perform non-interferometric phase retrieval of the electron probe. We have used the recovered phase information to visualize the point-spread function of the SEM optics (PSFoptics) for the first time. Finally, we have proposed an experiment based on electron vortex beams to improve phase retrieval. This work lays out the initial steps required to move towards "aberration-corrected" imaging in SEM without the use of multipole correctors.