Two Beam Kinematical Theory for the Diffraction of Electrons by Crystals with Stacking Faults

The intensity of weak diffraction spots is calculated on the basis of “a two‐beam kinematic” theory. The assumption is made that apart from the incident beam there is one strongly scattered beam. The incident and the strongly scattered beams are considered to interact according to the dynamic theory, but the dynamic interaction between the strongly and weakly scattered beams is neglected. Expressions are developed for the amplitudes and intensities of the weakly scattered beams both for perfect crystals and for crystal slabs containing stacking faults. The theory leads to the prediction that the dark field image of stacking faults taken in a weak diffraction spot should represent the fringe periodicy characteristic of the strongly diffracted beam. This is confirmed by observations. It is suggested that much weaker fringes with spacing characteristic of the s‐value of the weak spots may be superposed on the strong fringes. These fringes have not been observed.