Forbidden reflections Si (200) and (600) in CBED and their computer simulation

Abstract

The forbidden reflections Si (200) and (600) are observed with high intensity with a [001]-oriented Si perfect crystal along the (400) Kikuchi line in convergent beam electron diffraction (CBED) patterns with 100–600 keV high-energy electrons. A condition for the occurence of such forbidden reflections is found. The incident angle of electrons satisfies the Bragg conditions for the forbidden reflection and for at least one high-order reflection simultaneously. Two-dimensional computer simulations based on the many-beam Bloch wave method show very good agreement with the experimental results. It is concluded that the forbidden reflections are caused by dynamic scattering effects rather than by a defect structure of the specimen and surface scattering effects. Associated Bloch waves ψ 200 and ψ 600 are confirmed to be excited.