Imaging point defects using a transmission electron microscope with controllable spherical aberration

Abstract

Computer simulations are utilized to show how to use a transmission electron microscope which has an objective lens with an adjustable coe cient of spherical aberration to determine the three spatial coordinates of a single heavy atom embedded in a crystal. This information can be obtained by forming an image with only those electrons that have been scattered through a large angle by the crystal. By using a high-angle annular dark-®eld aperture the atoms can be considered as independent scatterers, in contrast with imaging with low-angle coherent scattering. In addition, by reducing the aberration coe cients of the lens, the e ective outer radius of the aperture can be made large, thereby leading to a small depth of focus. Calculations show that this form of imaging produces detectable contrast with currently available aberration correctors, sources and detectors.