Diffraction contrast between inversion domains and at inversion domain boundaries

Inversion domains are revealed in dark field images by a difference in background intensity. The inversion boundaries show an α‐like fringe contrast i.e. a symmetrical fringe pattern in bright field and an asymmetrical pattern in the dark field image. Experimental evidence for these contrast features are obtained from the non‐centrosymmetrical α‐GeTe. A theoretical analysis of the contrast characteristics is presented which is based on the logical assumption that for a non‐centro‐symmetrical crystal, the phases of extinction distance and of the absorption length are different. A very good agreement is found between theory and experiment for the contrast between the domains as well as for the fringe patterns at the boundaries. Also a particular multiple beam situation is treated.