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December 2023 ESRFnews

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DARK-FIELD X-RAY MICROSCOPY

J E F F W A D E

I

TS HARD to build a career out of instrumentation

Those who try says Hugh Simons at the Technical

University of Denmark DTU near Copenhagen

usually share the same fate as football midfielders for

ever passing the ball to the strikers but never getting

any credit for goals scored But for Simons and his col

leagues this has not been the case Known as darkfield

Xray microscopy DFXM their pioneering technique

has already been recognised by three prestigious grants

from the European Research Council ERC and is

now remarkably the subject of a fourth It has also been

supported for well over a decade by the ESRF, both with

long-term access and the investment in a flagship EBS

beamline at the ID03 port. “Only now is the technique

taking flight,” says Simons. “But for all that time, more

than 10 years, we’ve had the trust of the ESRF manage-

ment. They’ve really believed in the project.”

DFXM piques everyone’s interest because it can

shed light on materials that are common and yet very

difficult to study: those with crystalline structures that

are hierarchically organised over several length scales.

Biominerals, ice, sand and most geological materials fit

into this category, not to mention most technological

materials, such as metals, ceramics and semiconductors.

Scientists are very keen to understand how structural

changes that occur on nanometre scales in these

materials can ripple out into greater structures at the

millimetre scale and beyond – but in one way or another,

existing instrumentation has fallen short. Electron

techniques are limited to thin foils or involve serial,

destructive sectioning, while classical non-destructive

X-ray diffraction techniques are usually limited to small

sample volumes. Worse, all methods struggle with the

cacophony of overlapping signals coming from millions

of individual structural elements at once.

DFXM does not. In essence, it is a mix of two long-

existing techniques: X-ray microscopy and X-ray

diffraction. In DFXM , specialised X-ray lenses for high-

energy X-rays are placed both before and after a sample.

The lens placed after collects a beam of Braggdiffracted

Xrays from a crystalline grain deeply inside the sample

and generates a magnified 2D image of it Afterwards

3D images can be generated by tomographic methods

or by illuminating one layer in the sample at a time and

stacking the resulting 2D maps By varying goniometer

tilts DFXM can generate highresolution 3D maps of

the structure within bulk samples see fig 1 overleaf

The ESRFs Carsten Detlefs then beamline scientist

at ID06 was the first to try the idea back in 2010

His results caught the eye of Henning Friis Poulsen a

physicist at the DTU who had previously pioneered

another technique 3D Xray diffraction 3DXRD

Far left: In the early 2010s, Simons was one of several who worked

hard to establish DFXM at the ID06 beamline, with painstaking

beam alignment. Left: Today, with benefit of an ERC grant, Yıldırım

continues their pioneering work in the development of “pink

beam” DFXM, for much faster data collection.

“DFXM can generate a high-resolution

3D map of all a sample’s grains”