Quantitative strain and structure factor phase measurement by cbed.

Abstract

CBED is highly efficient - a large amount of quantitative information is obtained from an extremely small volume. Different regions of the pattern contribute different kinds of information. Outer reflections and HOLZ line intensities may be refined for atomic positions and temperature factors, inner reflections for bonding effects, and HOLZ line positions for lattice parameters and strain. Recently we have automated the process of comparing elastically filtered intensities with Bloch-wave and dynamically corrected kinematic computations by combining them with the “Simplex” leastsquares refinement algorithm, as used in the Reitvelt method. Adjustable parameters may be structure factors, cell constants, atomic position parameters etc. Perturbation methods are used for weak beams and error matrix elements.Strains due to oxygen disorder near a grain boundary in YB2Cu3O7-x have been measured on a 2 nm scale with an accuracy of 0.015% using HOLZ line intersection measurements. From these, the oxygen deficit x may be mapped out. A CBED pattern near [0-12] was recorded using an EM400ST FEG microscope and digitized into SEMPER.