ABSTRACT
This chapter examines the prospects for the location and identification of single atoms. It shows how aberration correction is becoming an established and essential tool for increasing the sensitivity in electron microscopy. The scanning transmission electron microscope (STEM) configuration offers both considerable advantages and some additional challenges relative to the conventional TEM configuration. This was highlighted by A. V. Crewe in 1970, when a STEM was the first form of electron microscope to directly visualize single uranium atoms. Aberration correction increases the resolution, sensitivity and signal to noise ratio available in STEM. The STEM is often introduced by comparison to the more familiar conventional TEM, because there are some important similarities. The chapter demonstrates that the STEM provides some unique advantages for the detection and electronic analysis of very small quantities of dopant atoms in the bulk of a sample. By the principle of reciprocity, the bright field STEM image is equivalent to the conventional TEM image for elastic scattering.
