Scientists image highly strained nanocrystals using a new methodology

The Bragg coherent diffraction imaging (BCDI) technique is a tool used by scientists to study crystalline materials with the aim of getting non-destructive 3D imaging of internal strain, defects, and domain evolution, linking nanoscale structure to material performance. Materials that can be studied using this technique are crystalline and less than one cubic micron in size and include metals and alloys for catalysis, semiconductors for optoelectronic devices, ferroelectric materials.

BCDI relies on a highly coherent and intense X-ray beam to image nanoscale strain and morphology.

In BCDI, scientists measure the 3D volume around a Bragg peak in reciprocal space. Since only the intensity of the scattered X-rays is recorded, the phase information is lost and must be recovered using computational algorithms. The reconstructed 3D image shows both the crystal’s internal structure (from the amplitude) and how its atomic planes are slightly displaced or strained (from the phase).

Highly strained crystals

So far, most BCDI studies have focused on tiny crystals with only small amounts of strain, where the atomic distortions are easy to interpret. When the strain becomes larger and more complex, the algorithms struggle to produce accurate 3D images. This can lead to artefacts and  misinterpretation of the results.

Now a team led by the ESRF has demonstrated experimentally a new approach, called Bragg coherent modulation imaging (BCMI), which incorporates wavefront modulation into the diffracted beam andenables the successful imaging of highly strained crystals.

The only limitation of the new technique is that the sample environment should not take too much space, as the modulator and the sample need to be in close proximity.

 “Implementing this concept at the beamline posed several technical challenges, including a precise positioning of the modulator within a few millimeters of the sample, accurate calibration of its structure, and strong sensitivity to sample drift during data acquisition" explains Jiangtao Zhao, first and corresponding author of the publication.

"These challenges were overcome by developing a dedicated nano-goniometer for stable modulator control, using ptychographic measurements to calibrate the modulator function, and incorporating position-correction algorithms into the BCMI phase-retrieval framework, respectively. Together, these developments allowed us to address the major experimental and computational challenges associated with this new technique”, he adds Zhao.

The new technique will benefit academics and industries studying nanoscale strain and defect evolution in functional materials. It is primarily fundamental research, but it lays the groundwork for future applied studies and technology development as it extends the application of the method to more prevalent and applied materials.

The team will now focus on making this new technique more user-friendly by refining the methodology and further exploring the advantages introduced by wavefront modulation. In parallel, they plan to apply BCMI to sample systems that are difficult or inaccessible for conventional BCDI, thereby demonstrating its broader applicability and unique capabilities.

Reference:

Jiangtao Zhao et al., Phys. Rev. Lett. 135, 256101 (2025).

Text by Montserrat Capellas Espuny

Top image: Wavefront-modulated (left) and conventional (right) Bragg coherent diffraction patterns from a highly strained Pt nanocrystal. The new technique enables unambiguous 3D structure and strain imaging. Selected for a Synopsis in Physics Magazine and for an Editors' Suggestion. [Jiangtao Zhao et al., Phys. Rev. Lett. 135, 256101 (2025)]