High spatial resolution tomographic reconstruction from STEM high angle annular dark field (HAADF) images
The analysis of structure by TEM is limited by the nature of the microscope as a structure projector; a three dimensional (3D) object is reduced to a two dimensional (2D) projection. While a projection often contains sufficient information to make valid materials conclusions there are an increasing number of systems whose structural complexity requires 3D analysis at high spatial resolution. Similar problems are routinely solved in the biosciences by electron tomography (Frank 1992), mathematically reconstructing the object from tilt series of bright field (BF) images. For most materials specimens, however, BF images are unsuitable for reconstruction due to the effects of diffraction contrast. A tomography method is introduced that uses tilt series of scanning transmission electron microscopy (STEM) high angle annular dark field (HAADF) images to achieve high spatial resolution 3D reconstruction. The advantages of HAADF images for tomographic reconstruction will be covered, illustrating them with two different experimental applications and a number of conclusions made as to the limits and power of the technique.