Measurement of kinematic intensities from large-angle electron diffraction patterns

Abstract

A new method for measuring a two-dimensional set of kinematic intensities from electron diffraction patterns is described, where a beam with a large convergence angle is focused parallel to a zone axis on to the crystal. If the convergence semi-angle is adjusted to match the angular radius, α₁ of the first-order Laue zone, then all electrons diffracted by planes in layer n of the reciprocal lattice are confined to an annulus around the zone-axis direction with inner and outer radii equal to α_n and an α_n+1, respectively. As the convergence semi-angle of the incident beam is increased from zero to α₁, the set of g vectors in layer n which satisfy the Brag condition expands from a circle with radius R _n(≈ n ^1/2 R ₁) to an annulus with radii equal to R _n+1±R ₁. The measured intensities for electrons diffracted around a Si〈114〉 axis are shown to fit kinematic calculations, where reflections with either odd or even indices are separated into two distinct sets.