Two-beam features in electron diffraction patterns – application to refinement of low-order structure factors in GaAs

Abstract

Progress in theoretical approaches to the refinement of structure factors and structure determination by electron diffraction is briefly reviewed. A strategy based on the use of two-beam-like features in convergent-beam electron diffraction (CBED) patterns is advocated, based on an effective potential and a reduced excitation error. Model calculations suggest inversion of the Bethe potentials to be useful. New experimental measurements for CBED rocking curves in GaAs are reported and these give the refined values V(200) = 0.432 (9), V(400) = 4.53 (4) V at 90 K, including Debye-Waller factor. The results from the inverse Bethe potential method are in excellent agreement with full many-beam calculations. These experimental values are compared with the results of recent pseudopotential total-energy calculations.