Journal of Applied Crystallography最新文献

Wombat is the high-intensity neutron diffractometer in operation at the Australian Centre for Neutron Scattering. While Wombat is primarily used as a high-speed powder diffractometer, the high-performance area detector allows both texture characterization and single-crystal measurements. The instrument can be configured over a large range of operational parameters, which are characterized in this contribution to aid experimental planning. Wombat is particularly optimized for the study of materials in situ and in operando using the wide range of sample environments available at the centre. Over 17 years of operation, Wombat has been used to explore a broad range of materials, including novel hydrogen-storage materials, negative-thermal-expansion materials, cryogenic minerals, piezoelectrics, high-performance battery anodes and cathodes, high-strength alloys, multiferroics, superconductors, and novel magnetic materials. This paper will highlight the capacity of the instrument, recent comprehensive characterization measurements and how the instrument has been utilized by our user community to date.

The rapid evolution of X-ray critical dimension (XCD) metrology demands an accurate and efficient forward model that describes the interaction between incident X-rays and nanostructures under test to support high-throughput experimental data analysis. However, the intricate design of high-aspect-ratio (HAR) nanostructures poses significant computational challenges to the forward model. In this work, we propose a semi-analytical method based on Green's theorem for fast and accurate calculation of small-angle X-ray scattering spectra from HAR nanostructures. Compared with conventional numerical approaches such as the non-uniform fast Fourier transform, the proposed method significantly reduces the number of required sampling points while maintaining high numerical accuracy and stability. Benchmark simulations demonstrate that the method yields a baseline speedup of one to three orders of magnitude over existing techniques, while consistently achieving relative errors below 1%, even for geometrically complex structures. Further acceleration and optimization strategies are also discussed, through which the overall speedup can be extended to two to four orders of magnitude on the current platform. These results highlight the potential of the proposed method as a powerful tool for rapid modeling and large-scale synthetic dataset generation for advanced XCD applications.

Transmission electron microscopy (TEM) imaging relies on specific orientations of the incident electron beam relative to the sample in both conventional TEM and high-resolution TEM/scanning transmission electron microscopy (STEM). In conventional TEM, contrast arises from diffraction, where elastically scattered electrons form diffracted beams at angles defined by the Bragg law. In high-resolution TEM/STEM, contrast results from phase interference between the transmitted and diffracted waves, each acquiring a distinct phase at the exit surface due to their different path lengths. This interference can be constructive, destructive or intermediate between the two. The visibility of these contrasts depends critically on sample orientation. Traditionally, achieving optimal alignment has relied on empirical trial and error, requiring user expertise and considerable time. To overcome this limitation, we developed a new method supported by a specially written module in the ATEX software. This method leverages the determined crystal orientation, expressed by Euler angles with respect to the sample holder. It establishes the geometric relations between the incident beam, the desired diffraction vector g (for the two-beam condition) or a zone axis (for on-axis imaging), and the tilt/rotation axes of the holder. Using this information, the software provides precise tilt and rotation instructions to reach the desired beam condition efficiently. Unlike conventional methods, this approach significantly reduces the alignment effort, typically requiring no more than two tilts of the sample holder.

While the dimensional constraints of crystal systems are well documented in crystallography, chemistry and materials science textbooks, their pedagogical presentation predominantly relies on descriptive narratives lacking rigorous mathematical derivation, resulting in incomplete comprehension and persistent misconceptions among both instructors and learners. This study establishes a mathematical framework connecting symmetry operations with metrical restrictions through a systematic analysis of symmetry operation representation matrices. By developing transformation matrix derivations for the basis vectors, a, b and c, we demonstrate how dimensional constraints emerge inherently from rotational symmetry requirements. Our derivations rigorously confirm the conventional unit-cell dimensional constraints while providing critical arguments against the use of inequality constraints in non-cubic systems. Examples across representative non-cubic crystals with cubic metric specializations are provided to fulfill the conventional teaching paradigms. The formalization process offers a pedagogically understandable and accessible methodology to replace current approaches.