The Action of a Crystal as a Two-Dimensional Lattice in Diffracting Electrons

Abstract

KIKUCHI^l first described examples of electron diffraction in which a crystal appeared to behave as a two-dimensional or cross-grating. Very thin sheets of mica give an equilateral net-like pattern of diffracted beams on the photographic plate (the N pattern), as if the only conditions for interference were those required by the lattice-net of the mica cleavage plane. Kikuchi further showed that, with increasing thickness of the mica, some spots are enhanced and others weakened until what he termed the L pattern is obtained. The selection of the enhanced spots was accounted for satisfactorily by the operation of the third condition for interference, which depends on the regular repetition of the crystal structure in successive planes. The L pattern, in other words, is explained by diffraction at a three-dimensional lattice, in the manner familiar in the case of X-rays. FIG. 1.