Abstract:
Computer simulations are utilized to show how to use a transmission electron
microscope which has an objective lens with an adjustable coefficient 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-field aperture the atoms can be
considered as independent scatterers, in contrast with imaging with low-angle
coherent scattering. In addition. by reducing the aberration coefficients of the
lens, the effective 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.
