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![[Figure 1]](ui5006fig1mag.jpg)
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Figure 1
The effects of specimen morphology on diffracted intensities in CBED patterns from on-zone and tilted near-zone orientations. The present examples show multislice-simulated CBED patterns at or near the [001] zone axis in pure aluminium (Fm3m – a centrosymmetric space group) with 200 keV electrons. The total matrix–void–matrix thickness in all simulations shown here is 1200 Å, with individual segment thicknesses applied in the calculations of the patterns labelled in the accompanying schematic models. In cases (a) and (c) the cube root of the intensities and in cases (b) and (d)–(f) the square root of the intensities were taken to flatten the dynamic range and make the intensity distributions visible in all reflections. In all cases, the location of the zone-axis orientation is marked by a cross in the centre of the pattern. The schematic slicing models give the multislice representation of each situation, but with angles and slice dimensions exaggerated for illustrative purposes. The slice thicknesses shown in these diagrams correspond to 60 Å, while the slice thickness used in all multislice simulations was 2.0245 Å (d002 in aluminium). In all cases, the incident wavevector K is used schematically to indicate the centre of what in CBED would be a cone of incident wavevectors. (a) Zone-axis orientation where the incident wavevector K is perpendicular to the slices. (b) Tilting so that the incident beam is not parallel to the zone axis is equivalent to shearing the sequence of slices. (c)–(f) Removal of slices containing atomic structure allows voids to be simulated. (c) On-zone incident beam with a void closer to the entrance face of the specimen. (d) Tilted near-zone orientation in which the zone axis bisects the primary scattering vector (white) to the Bragg condition in the 220 reflection, where the void is closer to the entrance face of the specimen. (e) The same orientation as in (d) but with the void centred between the entrance and exit faces of the specimen. (f) The same orientation as in (b), (d) and (e) but with the void closer to the exit face of the specimen. The structural tilt projection given for every case shows the projection of periodically conjugate points in each slice in the incident beam direction. If the structural tilt projection is centrosymmetric, then the Bragg-satisfied reflection whose primary scattering vector is bisected by the zone axis will contain a centre of symmetry. This is not the case for (d) and (f). |
![[Figure 1]](ui5006fig1.jpg)
 | JOURNAL OF APPLIED CRYSTALLOGRAPHY |
ISSN: 1600-5767
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