FORBIDDEN REFLECTIONS SI (200) AND (600) IN CBED AND THEIR COMPUTER-SIMULATION

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 occurrence 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 psi(200) and psi(600) are confirmed to be excited.