8/15/2023 0 Comments Bragg diffraction![]() strains) they cause in the crystal lattice. As such there is an urgent need for techniques able to determine the “invisible” defect number density and spatial distribution.Ī promising alternative is to infer the concentration of these small defects by measuring the distortions (i.e. However, these predictions cannot be verified by existing experiments. ![]() Recent simulations have successfully predicted the presence and evolution of large populations of “invisible” defects during irradiation 22. Although small, these “invisible” defects can dramatically change the mechanical properties 18 or thermal transport behaviour 19, and may lead to irradiation-induced dimensional change 20, 21. the vast majority of defects are below the visibility limit 17. Defects produced by irradiation range from single atom defects to clusters tens of nanometres in size, where the number density of defects is typically linked to the defect size by a power law with a negative exponent, i.e. ![]() However crystals that contain a population of small defects with a broad size distribution constitute a large class of materials, such as those resulting from intense irradiation exposure (materials for future fusion and fission technologies 1, accelerator targets 15 or modified surfaces for biocompatibility 16). In inherently thin TEM samples, defects may also be lost to nearby surfaces that act as strong defect sinks, thus reducing the apparent defect density 13.Ī further challenge concerns the visibility of small defects: In structures containing more than a few thousand atoms, TEM is insensitive to defects smaller than ~1.5 nm 14. This is insufficient for understanding complex defect-defect interplays, since defects interact via their 3D strain fields and resulting stresses 12. straight dislocations of edge character 11). While TEM is also sensitive to the associated lattice strains, their investigation is restricted to 2D and only possible for a small subset of samples (e.g. At near atomic resolution, transmission electron microscopy (TEM) is an essential method, which allows the direct visualisation of lattice defects in two (2D) and even three dimensions (3D) 9, 10. Understanding and exploiting defects in crystalline materials requires probing the material structure from atomic- to macro-scale. Conversely, the behaviour of defects is strongly dependent on the microstructural environment, which provides fantastic potential for tuning material properties 8. Native or induced defects localise distortion of the crystal lattice and thereby reduce the overall strain energy 7. energy generation (nuclear 1 or photo-voltaic 2), energy storage 3, aerospace 4, micromechanics 5 and semiconductor miniaturisation 6. These findings open up exciting perspectives for the modelling of irradiation damage and the detailed analysis of crystalline properties in complex materials.Ītomic defects play a fundamental role in controlling the mechanical and physical properties of crystalline materials, resulting in critical hurdles for advanced applications, as epitomised in e.g. A partially defect-denuded region is observed close to a grain boundary. ![]() Our results lead to the conclusions that few-atom-large ‘invisible’ defects are likely isotropic in orientation and homogeneously distributed. Using this enhanced Bragg ptychography tool, we study the damage helium-ion-irradiation produces in tungsten, revealing a series of crystalline details in the 3D sample. Here we present an x-ray crystalline microscopy approach, able to image with high sensitivity, nano-scale 3D resolution and extended field of view, the lattice strains and tilts in crystalline materials. As such, our understanding of their impact is largely based on simulations with major unknowns. ![]() Unfortunately, most of the defects irradiation creates are below the visibility limit of state-of-the-art microscopy. Small ion-irradiation-induced defects can dramatically alter material properties and speed up degradation. ![]()
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