Resolution enhancement in transmission electron microscopy with 60-kV monochromated electron source

Abstract

Transmission electron microscopy (TEM) at low accelerating voltages is useful to obtain images with low irradiation damage. For a low accelerating voltage, linear information transfer, which determines the resolution for observation of single-layered materials, is largely limited by defocus spread, which improves when a narrow energy spread is used in the electron source. In this study, we have evaluated the resolution of images obtained at 60 kV by TEM performed with a monochromated electron source. The defocus spread has been evaluated by comparing diffractogram tableaux from TEM images obtained under nonmonochromated and monochromated illumination. The information limits for different energy spreads were precisely measured by using diffractograms with a large beam tilt. The result shows that the information limit reaches 0.1 nm with an energy width of 0.10 eV. With this monochromated source and a higher-order aberration corrector, we have obtained images of single carbon atoms in a graphene sheet by TEM at 60 kV.