Multi-beam lattice images from germanium oriented in (011)

Abstract
Lattice images from germanium oriented in (011) are studied both experimentally and theoretically. Two dimensional lattice images are produced by five-beam interference (000 and Ill-type beams) using axial illumination. Conditions for the best observation of this type of image are presented with regard to specimen thickness, defocusing distance and illumination aperture. The different patterns obtained in the image (hexagonal or rectangular) are correlated with the projection of columns of atoms. In the hexagonal pattern each bright spot represents the projection of two columns of atoms whose images overlap. The Fourier analysis of the image, containing high frequency terms such as 200, 222 and 022, is interpreted as arising from interference between diffracted beams (a strong phase object).