Improvement of precision in refinements of structure factors using convergent-beam electron diffraction patterns taken at Bragg-excited conditions

Abstract

A local structure analysis method based on convergent-beam electron diffraction (CBED) has been used for refining isotropic atomic displacement parameters and five low-order structure factors with sin θ/λ ≤ 0.28 Å−1 of potassium tantalate (KTaO3). Comparison between structure factors determined from CBED patterns taken at the zone-axis (ZA) and Bragg-excited conditions is made in order to discuss their precision and sensitivities. Bragg-excited CBED patterns showed higher precision in the refinement of structure factors than ZA patterns. Consistency between higher precision and sensitivity of the Bragg-excited CBED patterns has been found only for structure factors of the outer zeroth-order Laue-zone reflections with larger reciprocal-lattice vectors. Correlation coefficients among the refined structure factors in the refinement of Bragg-excited patterns are smaller than those of the ZA ones. Such smaller correlation coefficients lead to higher precision in the refinement of structure factors.

Observations of specimen morphology effects on near-zone-axis convergent-beam electron diffraction patterns

“…(1) Tilted near-zone orientations make QCBED more sensitive to the structure factors of reflections at or near Bragg conditions than on-zone orientations (Streltsov et al, 2003;Nakashima, 2017;Aryal et al, 2021).…”

Toward quantitative analysis of 3D nanostructures using convergent-beam electron diffraction

“…By applying an electric field, significant changes in the distributions of the polar nanostructures. 4D-STEM is advantageous for the analysis of such nanoscale local structural variations related to novel physical properties.CBED was also applied to quantitative refinements of local crystal structures and electrostatic potentials fully based on the dynamical diffraction theory [12][13][14][15][16][17][18]. Toward the quantitative analysis of 3D nanostructures using CBED or 4D-STEM, functions to deal with nanostructures in the depth and lateral directions of the electron probe have been implemented into our CBED pattern simulation code MBFIT [12,13], which is based on the Bloch wave formulation.…”