Kikuchi-band formation in medium-energy electron-diffraction patterns

To reveal the mechanism of Kikuchi-band formation, the total Si(100) diffraction pattern produced by 2-keV quasi-elastically backscattered electrons is compared to model calculations made in the single-scattering approximation for clusters constructed with different numbers of close-packed (110) planes. The formation of the Kikuchi bands is shown to be governed by two types of electron scattering in a crystal. The dominant contribution to enhanced electron-scattering intensity within a band comes from the forward-focusing effect as the electrons move along the numerous interatomic directions in the (110) planes. The other mechanism responsible for the sharp edge regions in the Kikuchi bands involves electron scattering from the nearest planes. It is proposed to use the specific profile of the Kikuchi bands in estimating the shape and size of light-element crystallites forming during initial stages of island-film growth.