nano-beam diffraction, NBD

A method for qualitative analysis of crystal structures from a diffraction pattern, acquired from a nanometer specimen area. An electron diffraction pattern is first obtained by illuminating the specimen with a parallel electron beam. Then, the electron beam is converged onto a nanometer specimen area using a small condenser aperture, diffraction spots being transformed to disk-like corresponding to the convergence angle of the electron beam. The method enables us to determine the lattice parameter, lattice type and crystal orientation of a specific nano-area. It is useful for crystallographic analysis of fine precipitates and interfaces. It is noted that the selection of a specimen area is made with a selector aperture in the case of SAD, but made with a condenser aperture and the convergence angle of the incident beam in NBD.

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