Simulating high-angle annular dark-field stem images including inelastic thermal diffuse scattering

Abstract

A generalized multislice theory is employed to simulate the annular dark-field (ADF) images, in scanning transmission electron microscopy (STEM), taking into account the inelastic thermal diffuse scattering (TDS). It is shown that the ADF image has the following characteristics if the first-order Laue zone (FOLZ) (or high-order Laue zones (HOLZ)) is excluded: (1) there is no contrast reversal with change of focus; (2) there is no contrast reversal with change of specimen thickness and (3) the ADF image shows highly localized scattering from each atomic column and can provide some chemical information for a specimen having two or more atoms with very different atomic numbers. It is shown that the TDS may take a dominant role in determining the ADF imaging contrast, depending strongly on the atomic number, the sizes (or shapes) of the atoms and their relative vibration amplitudes. TDS may increase the visibility of light elements. A full dynamical calculation including TDS is required to interpret the ADF imaging contrast. It is therefore not proper to consider the ADF imaging contrast as purely Z dependent. The HOLZ can introduce strong diffraction contrast in the ADF image.