Accurate structure determination from image reconstruction in ADF STEM

Abstract

Annular dark‐field (ADF) imaging in a scanning transmission electron microscope results in direct structure images of the atomic configuration of the specimen. Since such images are almost perfectly incoherent they can be treated as a convolution between a point‐spread function, which is simply the intensity of the illuminating electron probe, and a sharply peaked object function that represents the projected structure of the specimen. Knowledge of the object function for an image region of perfect crystal allows the point‐spread function to be directly determined for that image. We examine how the object function for an image can then be reconstructed using a Wiener filter, the CLEAN algorithm and a maximum entropy reconstruction. Prior information is required to perform a reconstruction, and we discuss what nature of prior information is suitable for ADF imaging.