Fourier transform plays an important role in HRTEM imaging and analysis.
The phases of the Fourier components of the HRTEM (high-resolution TEM) images are determined by two ways:
i) The Fourier components at sinχ(u) > 0 have the same phases as the phases of structure factors. This raises the same contrast in the image as the projected potential.
ii) The Fourier components at sinχ(u) < 0 have a phase change of 180°. This raises a reversed contrast in the image.
In general, the HRTEM images are usually formed by the combination of those two Fourier components above.