Optimum correction conditions for aberration-corrected HRTEM SiC dumbbells chemical imaging

Over the last decade, the spatial resolution of transmission electron microscopes has been considerably improved thanks to the development of aberration correctors. At the same time, image interpretation has become easier as the influence of instrument aberrations on image intensity has been reduced for phase contrast imaging. New aberration-corrected microscopes now offer the possibility to extract both the structural and the chemical information from a quantitative analysis of the image's contrast, which is promising in many fields of materials science where knowledge of the chemical content at the atomic scale is crucial. However, appropriate imaging conditions must be used for a quantitative analysis of the image at the sub-angström scale. In this paper, we focus on the impact of chromatic and geometric aberrations on phase contrast and we compare the advantages offered by the few optimum imaging conditions proposed in the literature. Effects of residual aberrations are also considered while the influence of chromatic aberration correction in future Cs/Cc-corrected instruments is emphasized. A critical value of Cc is given depending on the instrumental parameters. Silicon carbide imaging using a Cs-corrected microscope is presented and illustrates the assessments derived from the theoretical study of residual aberration influence on phase contrast imaging.

► In this paper, we focus on the impact of chromatic and geometric aberrations on phase contrast.
► Advantages offered by a few optimum aberration correction conditions are compared.
► Effect of residual aberrations on phase contrast is examined for Cs and Cs/Cc-corrected microscopes.
► The need of an appropriate tuning of Cc in future Cs/Cc-corrected instruments is emphasized.
► Example of SiC imaging using a Cc-corrected microscope illustrates the theoretical assessments.