Invited Lecture
3D imaging of dislocations with x-rays: recent trends and future prospects

Dislocations in crystals produce long range rotation and strain fields that allow them to be detected by diffraction. A full quantification of the displacement field is, however, often challenging. The first visualization of dislocations was performed by Hirsch et al. [1] in 1956 by transmission electron microscopy (TEM) and TEM has remained since then the tool of choice for imaging dislocations and investigating their dynamics. The very high sensitivity of x-ray diffraction to lattice distortions was early recognized as a strong asset for detecting dislocations in crystals [2]. But, for a long time, the low spatial resolution of x-ray diffraction imaging has limited its large spread use. Strain and defect imaging with x-rays have, however, made very impressive progress lately. On one hand progress in x-ray focusing optics allows nowadays scanning x-ray diffraction mapping to be performed with a resolution in the 50-100 nm range. Full field x-ray microscopy is improving a lot too with resolutions in the 100 nm range [3]. By far the best spatial resolution is obtained with Bragg coherent diffraction imaging (BCDI), which is a lensless imaging technique, with a typical resolution of 6-10 nm [4-6]. BCDI has made impressive progress in the last decade and allows non-destructive 3D imaging of dislocations in various environments (mechanical testing, catalysis, annealing …). I will present and discuss some of these latest results and discuss future prospects opened by new synchrotron sources that are being developed worldwide.

1. P. Hirsch, R. Horne, M. Whelan, Phil. Mag. 1, 677 (1956).
2. B. Newkirk, Phys. Rev. 110, 1465 (1958).
3. H. Simons et al., Nature Comm. 6, 6098 (2015).
4. M. Pfeifer et al., Nature 442, 63 (2006).
5. S. Labat et al., ACS Nano 9, 9210 (2015).
6. M. Dupraz et al., Nano Letters 17, 6696 (2017).