Three-phase structure invariants and structure factors determined with thequantitative convergent-beam electron diffraction method

Quantitative convergent-beam electron diffraction is used to determine stru cture factors and three-phase structure invariants. The refinements are bas ed on centre-disc intensities only. An algorithm for parameter-sensitive pi xel sampling of experimental intensities is implemented in the refinement p rocedure to increase sensitivity and computer speed. Typical three-beam eff ects are illustrated for the centrosymmetric case. The modified refinement method is applied to determine amplitudes and three-phase structure invaria nts in noncentrosymmetric InP. The accuracy of the results is shown to depe nd on the choice of the initial parameters in the refinement. Even unrealis tic starting assumptions and incorrect temperature factor lead to stable re sults for the structure invariant. The examples show that the accuracy vari es from 1 to 10 degrees in the electron three-phase invariants determined a nd from 0.5 to 5% for the amplitudes. Individual phases could not be determ ined in the present case owing to spatial intensity correlations between ph ase-sensitive pixels. However, for the three-phase structure invariant, sta ble solutions were found.