UnitCell Tools, a package to determine unit-cell parameters from a single electron diffraction pattern

Electron diffraction techniques in transmission electron microscopy (TEM) have been successfully employed for determining the unit-cell parameters of crystal phases, albeit they exhibit a limited accuracy compared with X-ray or neutron diffraction, and they often involve a tedious measurement procedure. Here, a new package for determining unit-cell parameters from a single electron diffraction pattern has been developed. The essence of the package is to reconstruct a 3D reciprocal primitive cell from a single electron diffraction pattern containing both zero-order Laue zone and high-order Laue zone reflections. Subsequently, the primitive cell can be reduced to the Niggli cell which, in turn, can be converted into the unit cell. Using both simulated and experimental patterns, we detail the working procedure and address some effects of experimental conditions (diffraction distortions, misorientation of the zone axis and the use of high-index zone axis) on the robustness and accuracy of the software developed. The feasibility of unit-cell determination of the TiO2 nanorod using this package is also demonstrated. Should the parallel-beam, nano-beam and convergent-beam modes of the TEM be used flexibly, the software can determine unit-cell parameters of unknown-structure crystallites (typically >50 nm).

Topochemical conversion of the discontinuous-zone-axis to form bismuth titanate oriented polycrystal nanocomposites

A topochemical transformation of discontinuous band axis has been found in the preparation of bismuth titanate.

Twin relationship in between the variant-pair of η precipitates in the Al-Zn-Mg-Cu aluminium alloy

For Al-Zn-Mg-Cu aluminium alloys, 15 types of η precipitates would possess the symmetrically variants distributed on the closed planes of the Al matrix, parallel to the (0001)η, (21̅1̅0)η, or (101̅0)η interfaces of precipitates. The η2 precipitates, possessing the crystallographic orientation of (111̅1̅)al // (0001)η2 and [110]al // [101̅0]η2, would exhibit four equivalent variants, i.e., η2(1) to η2(4), on the (11̅1̅)al habit planes. In the present work, along the zone axis of [110]al // [101̅0]η, the edge-on configurations showing the twin-like atomic arrays would occur as the growth/coalescence of two η2 variants grown on (111̅1̅)al and (11̅1)al planes, respectively. The twin relationship can be revealed in term of the crystallographic relationship at 70.5° with respect to their habit planes. Alternatively, on the (11̅1̅0)al image, it also indicates the nearly-twinning configuration in between the variant-pair of η2.

Single-pass STEM-EMCD on a zone axis using a patterned aperture: progress in experimental and data treatment methods

Measuring magnetic moments in ferromagnetic materials at atomic resolution is theoretically possible using the electron magnetic circular dichroism (EMCD) technique in a (scanning) transmission electron microscope ((S)TEM). However, experimental and data processing hurdles currently hamper the realization of this goal. Experimentally, the sample must be tilted to a zone-axis orientation, yielding a complex distribution of magnetic scattering intensity, and the same sample region must be scanned multiple times with sub-atomic spatial registration necessary at each pass. Furthermore, the weak nature of the EMCD signal requires advanced data processing techniques to reliably detect and quantify the result. In this manuscript, we detail our experimental and data processing progress towards achieving single-pass zone-axis EMCD using a patterned aperture. First, we provide a comprehensive data acquisition and analysis strategy for this and other EMCD experiments that should scale down to atomic resolution experiments. Second, we demonstrate that, at low spatial resolution, promising EMCD candidate signals can be extracted, and that these are sensitive to both crystallographic orientation and momentum transfer.

3D electron diffraction techniques

3D electron diffraction is an emerging technique for the structural analysis of nanocrystals. The challenges that 3D electron diffraction has to face for providing reliable data for structure solution and the different ways of overcoming these challenges are described. The route from zone axis patterns towards 3D electron diffraction techniques such as precession-assisted electron diffraction tomography, rotation electron diffraction and continuous rotation is also discussed. Finally, the advantages of the new hybrid detectors with high sensitivity and fast readout are demonstrated with a proof of concept experiment of continuous rotation electron diffraction on a natrolite nanocrystal.