Comprehensive approach enables 3D view of crystal dislocations
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Comprehensive approach enables 3D view of crystal dislocations
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etworks of dislocations can now be three-dimensionally characterized on a new scale, according to research recently published in Physical Review Letters (doi:10.1103/PhysRevLett.119.215504) by a team of German researchers. This unprecedented view of these crystalline defects can provide insights into the behavior of individual dislocations even inside complex arrangements of dislocations and their relationship to the surface features of a crystal. The method is widely applicable, nondestructive, and compatible with industrial elements such as wafers. The presence of dislocations can significantly impact the properties of a material and lead to structural compromises. However, dislocations are difficult to study because their activity occurs over several length scales, from angstroms to millimeters. Transmission electron microscopy has been a very successful tool to date for the small scale from angstroms to micrometers, but requires a small sample size and is highly destructive. Motivated by the need for complementary tools that work over larger scales, which are particularly crucial for many industrial applications, a team led by Daniel Hänschke from the Karlsruhe Institute of Technology (KIT) developed and tested a new approach. The team used numerical simulations in conjunction with and to correlate x-ray diffraction techniques and visible light microscopy. First, defects in the crystal are imaged with x-ray diffraction laminography (XDL). This technique uses x-ray diffraction to create two-dimensional (2D) projections of the defects at different viewing angles, which are then reconstructed into a three-dimensional (3D) image highlighting the spatial arrangements of the defects. The defects are subsequently imaged with conventional x-ray white beam topography (XWBT). This technique produces 2D images that contain information on the Burgers vector associated with a dislocation, the vector describing the magnitude and direction of the resulting lattice distortion. In order to reliably
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(a) Conventional 2D x-ray white beam topography (XWBT) image of a dislocation arrangement; (b) top view of the 3D picture obtained using the novel correlative approach, with the Burgers vectors color-coded; and (c) isolated view of a slip-band that enabled the researchers to identify the activity of a regenerative source of dislocations, noted in blue. XDL is x-ray diffraction laminography and CDIC is (circularly polarized) visible light differential interference contrast (CDIC) microscopy. Credit: D. Hänschke, KIT.
identify individual dislocations in these images, the team used a simulation based on the XDL data to predict the location and appearance of defects in the XWBT images. By overlaying the simulated data on the XWBT images, the Burgers vector could be determined for individual dislocations. The final imaging technique, visible light differential interference contrast (DIC) microscopy, is useful for visualizing height differe
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