Theory of zone axis electron diffraction

The theory of high-energy electron diffraction is reviewed, with an emphasis on methods that help most in understanding the form of zone axis convergent-beam patterns. A Bloch wave description is used throughout the paper, and the theory is formulated in real space, leading to general expressions for both zero-layer and higher-order Laue zone (HOLZ) diffraction amplitudes. HOLZ diffraction is discussed in detail, and it is shown that first-order perturbation theory is usually applicable and provides a clear picture of the diffraction. The computation of diffracted intensities is discussed with reference to the many-beam equations. Diffraction at the [0001] axis in 1T-VSe2 is analysed both to illustrate the theory and to provide an example of the special effects that occur at well defined string zone axes.