COHERENT OVERLAPPING LACBED PATTERNS IN 6H SIC

In a previous publication, it was shown that interference fringes due to the coherent addition of amplitudes were observed in the overlap re gions of adjacent discs in convergent beam electron diffraction (CBED) patterns recorded with a defocused probe in a conventional transmissi on electron microscope equipped with a cold field-emission source (Hit achi HF-2000). This research has been extended to describe coherent la rge-angle CBED (LACBED) patterns from 6H SiC, where the angular field of an overlap region is expanded by use of a small (1 mum) selected-ar ea aperture that transmits only a restricted set of beams. The number of fringes visible within an overlap is increased to over 100, where t he fringe shifts and rotations are directly related to angular variati ons in the relative phase of the two beams. In a direct analogy with p rocessing of images produced by electron holography, it is shown that coherent LACBED patterns encode the amplitude product and the phase di fference of the overlapped beams. Examples are discussed where the gli de plane in 6H SiC produces a pi phase shift of fringes across the Gjo nnes-Moodie dark bar, equivalent to a direct representation of the gli de operator. The minimum demagnified source size in the object plane i s 3.5 angstrom, suggesting that fringes with 5 angstrom period should be visible in the diffraction plane.