STRUCTURE FACTOR DETERMINATION IN NONCENTROSYMMETRIC CRYSTALS BY A 2-DIMENSIONAL CBED-BASED MULTIPARAMETER REFINEMENT METHOD

Convergent-beam electron diffraction patterns from non-centrosymmetric crystals have been analyzed for the purpose of determining large numbers of structure factor amplitudes and phases from two-dimensional experimental data. The theoretical intensity analysis of the sensitivity to changes in the parameters is focused on areas in the disks where few-beam effects dominate. Examples of which parts of the disks are sensitive to which parameters are given. The determination of structure factors is an inverse problem which is solved by iterative calculations to fit theory to experiment. The fit index is minimized to a global minimum in the multi-parameter space, and the sensitivity of the index to individual parameters is discussed. The first example of structure factor determination based on a two-dimensional fit index minimalization is given for U002 and U002' in InP. The total number of parameters minimized is 7.