Convergent beam electron diffraction

[1] The development of the Field Emission Gun (FEG) in the 1970s,[2] the Scanning Transmission Electron Microscopy (STEM), energy filtering devices and so on, made possible smaller probe diameters and larger convergence angles, and all this made CBED more popular.

In the seventies, CBED was being used for the determination of the point group and space group symmetries by Goodman and Lehmpfuh,[3] and Buxton,[4] and starting in 1985, CBED was used by Tanaka et al. for studying crystals structure.

Since the diameter of the probing convergent beam is smaller than in the case of a parallel beam, most of the information in the CBED pattern is obtained from very small regions, which other methods cannot reach.

The focused probe may generate contamination, which can cause localized stresses.

But this was more of a problem in the past, and now, with the high vacuum conditions, one should be able to probe a clean region of the specimen in minutes to hours.

Another disadvantage is that the convergent beam may heat or damage the chosen region of the specimen.

Recently, CBED was applied to study graphene[43] and other 2D monolayer crystals and van der Waals structures.

For 2D crystals, the analysis of CBED patterns is simplified, because the intensity distribution in a CBED disk is directly related to the atomic arrangement in the crystal.

The deformations at a nanometer resolution have been retrieved, the interlayer distance of a bilayer crystal has been reconstructed, and so on, by using CBED.