How a pink beam can take scientists to heart of complex materials

Traditional Dark Field X-ray Microscopy (DFXM) has been an invaluable tool for visualising three-dimensional strain and orientation fields inside bulk crystalline materials. However, its monochromatic beam configuration has always imposed some limitations. Because DFXM is “photon-hungry,” it struggles with highly deformed or weakly crystalline materials. This has hindered time-resolved studies and made certain technologically important systems inaccessible.

Now, scientists led by Can Yildirim, scientist at beamline ID03 and recipient of an ERC Starting Grant, have used pink beam rather than a narrow monochromatic beam to overcome the limitations of DFXM. They tested the new technique on various materials, including aluminium and iron alloys.

“Pink beam brings a huge leap in intensity, which makes it possible to look at crystals that were previously impossible to study and to follow real-time events, such as grain growth, with around 100-150 nanometre resolution in the millisecond regime”, explains Yildirim. 

Specifically, the new technique provides a 27-fold increase in diffracted intensity while maintaining 100-150 nanometre spatial resolution. 

The team imaged a partially recrystallised aluminum grain in real time. Movies of its evolution during high-temperature annealing were recorded with millisecond time resolution, providing key parameters of grain growth dynamics (see Movie 1). The experiment demonstrated that the technique offers sufficient angular resolution to map evolving microstructures and resolve subgrain structures.
 

Movie 1: Pink-beam DXFM video showing full aluminium grain boundary evolution during high-temperature annealing.

The team also used pDFXM on highly deformed ferritic iron grain. Under conventional monochromatic DFXM, such imaging would not be possible without focusing optics. With pDFXM, however, the strong diffracted signal allowed clear visualisation, marking an important milestone for studying real-world engineering materials that often undergo significant deformation in service. 

Energy materials and alloys

The applications that can benefit from this new technique range from catalytic reactions to battery degradation, phase transformations, fatigue, and hydrogen charging. With 100-nanometre resolution over large fields of view, researchers can now image challenging systems such as highly textured crystals, semi-crystalline polymers, biominerals, and heavily deformed metals that were previously inaccessible.

“It is perfectly suited to study dynamic changes in energy materials and structural alloys under real-world conditions”, says Yildirim.

The technique also integrates with complementary imaging methods to provide multi-scale insights, while advances in X-ray optics and computational tools will further improve resolution, reduce beam damage, and expand its use across energy, structural, and biomaterials research.

The findings are part of the goals of Yildirim’s ERC project 'Deformation and Recrystallization Mechanisms in Metals (D-REX)', which started last year.

“It feels like a dream to be able to have achieved this milestone at this early stage in my project”, he says. 

Reference:

Yildirim, C. et al., 3D/4D imaging of complex and deformed microstructures with pink-beam dark field X-ray microscopy. Communications Materials 6, 198 (2025); https://doi.org/10.1038/s43246-025-00926-9

Text by Montserrat Capellas Espuny

Top image: Top image: In-situ observation of aluminum grain growth during isothermal annealing using pDXFM single-frame projection imaging