To study the CBED symmetry and extinction, the multiple scattering formula was generalized with the reciprocity theorem. Using this formula, the dynamical extinction resulting from the horizontal diamond glide plane of the space group Fd3m was studied. It was demonstrated that the relationship between structure factor products is the same as that between kinematical structure factors. This denies the contention by Liu [Ultramicroscopy 25 (1988) 35] that the observed extinction for the glide plane is only approximate. Using the single-layer approximation, it was shown that even for the horizontal glide plane at an arbitrary position, the same CBED symmetry and extinction as those derived for the glide plane located at the specimen mid-plane is obtained. It was further shown that when kinematically forbidden ZOLZ reflections are composed of only the HOLZ lines which show a twofold rotation symmetry, we can reliably conclude the presence of the horizontal glide plane without observing the spot-shaped extinction at the exact Bragg position.
ASJC Scopus subject areas