Towards 1·0 Å resolution: taking advantage of dynamical scattering, and the benefits for structure retrieval

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This paper is an exploration of the behaviour of high-resolution transmission electron microscope (HRTEM) images at up to 1 Å resolution. The ultimate limits to HRTEM (structure) resolution and the manner in which strong scattering may lead to weak diffraction in heavy fcc metals are discussed. A resolution of 1·0 Å is somewhat better than the ultimate resolution presently achievable in a 400-kV electron microscope. In heavy metals, such as platinum, it is found that the lattice fringe contrast is very low in the [011] projection, but that fringe contrast may be improved by imaging in the [111] projection. For atomic resolution imaging of the heavy metals in the [111] projection a resolution of 1·2 Å is required. For the study of oxygen position in high-temperature superconducting (HTS) oxides a resolution of between 1·2 and 1·4 Å is required. At better than 1·2 Å resolution the thick crystal images in HTS oxides remain simple and are easily interpreted. At such resolution all atomic columns are separated for the HTS [010] projection and the dynamical diffraction effects improve the contrast of oxygen atoms relative to the metal atoms.

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