A new approach for electron tomography: Annular dark-field transmission electron microscopy

Transmission electron microscopy (TEM) images yield valuable information about the structure and chemistry of (in)organic materials. However, they “only” provide a 2D projection of a 3D object. Therefore, electron tomography was developed to reconstruct objects in three dimensions from a tilt series of TEM images. This technique is well accepted in the life sciences as a method used to study viruses or cells. The resolution in the reconstructions, however, is limited to a few nanometers, mainly because of the low resistance of biological materials to electron-beam damage. Electrontomography techniques have recently been adopted by researchers in materials science. [1–5] Here, atomic resolution could be achieved in principle. In practice, however, the resolution is still of the order of one to two nanometers because of the limited stability of the sample holders and the presence of dynamic diffraction in crystalline solids, to name but two reasons. In particular, dynamic diffraction in strongly diffracting materials violates the projection requirement in bright-field (BF) TEM images, since image intensities no longer increase monotonically with sample thickness. In these cases, BF-TEM tomography has been avoided and other techniques such as high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) tomography and energy-filtered transmission electron microscopy (EFTEM) tomography have been successfully applied. [2] Although these