In two-beam conditions in TEM, low index reflections are normally excited instead of high index reflections. In the two-beam condition, the two beams have the same intensity in the form of Bloch waves:
i) one is peaked at the specimen atoms,
the other one is peaked at half way between the atoms.
It is difficult to obtain diffraction disks in CBED and true 'two-beam' kinematic conditions from the small reciprocal lattice dimensions in some materials with the large lattice parameters.
Defocus CBED using high-index reflections provides a more accurate determination method of displacement vectors (R) of stacking faults than two-beam method with exciting low-index reflections, selected area electron diffraction method with low index reflections, and HRTEM technique.
Table 3769. Applications of two-beam diffraction conditions.
|Sample thickness determination using CBED
|Determination of Burgers vectors of dislocations