ESRF News December 2023

December 2023 ESRFnews

DARK-FIELD X-RAY MICROSCOPY

for mapping grains at a coarser scale. Poulsen saw the

potential for multiscale studies within materials science

and obtained an ERC advanced grant to develop DFXM

at the ESRF, hiring Hugh Simons as a postdoc.

Simons recalls how during every beamtime, he,

Poulsen and Detlefs would be rebuilding the experiment

from scratch, surrounded by lenses, mirrors, lasers, and

X-ray sensitive sticky tape, in an effort to obtain the beam

alignment they needed. “The alignment was like trying

to get a hole in one from eight kilometres away,” he says.

“I’ve never turned a five millimetre allen key so often.”

But it worked. By 2016, they found that they could

generate a magnified, full-field image of the individual

dislocations in a diamond sample. With coordinated

movement of the sample and optics, they could

PROVEN APPLICATIONS OF DFXM AT THE ESRF

• Scientists at the Technical University of Darmstadt in Germany and elsewhere

have used it to reveal how introducing dislocations into ceramics can make

them much tougher (Mater. Horiz. 8 1528).

• Scientists at the University of Leoben in Austria and elsewhere have used it

to understand why the copper used in microelectronics for charge transfer and

heat sinks undergoes fatigue in thermal cycling Acta Mater 253 118961

Scientists at Lawrence Livermore National Laboratory in California US and

elsewhere have used it to create realtime movies of how dislocations move and

interact at depths over hundreds of micrometres inside bulk aluminium Sci

Adv DOI 101126sciadvabe831

Scientists at the Chalmers University in Sweden and elsewhere have used

it to map with nanometre resolution the local residual stress and orientation

within embedded steel grains Scr Mater 197 113783

Scientists at OCAS part of the multinational steel manufacturing corporation

ArcelorMittal in Belgium have used it to track a single grain within a heavily

deformed ferritic alloy as the material undergoes several steps of annealing

Scr Mater 214 114689

objective

sample

incident

beam

axis of rotation (ω)

2θ

qʹ

pʹ

detector

quantitatively map local crystal strain and symmetry

with a resolution of 100 nm, showing how dislocations

and stacking faults self-organise into networks with

long-range strain fields and lattice distortions.

The results were enticing, and not just for the users.

The ERC could see the potential, and in 2018 awarded

Simons a starting grant to develop a particular in situ

methodology of DFXM for piezoelectrics, ferroelectrics

and other polar materials whose structural dynamics

can be thermally and electrically induced (see fig. 2,

opposite). Two years later, the funding body awarded

Poulsen another advanced grant, this time to use

DFXM to build a multi-scale model that can predict

how the internal structure of a metal changes during

plastic deformation – a long-standing conundrum in

materials science.

Meanwhile, the ESRF Science Advisory Committee

selected the ID06 prototype as the basis of one of four

“flagship” beamlines to be built in parallel with the

ESRF’s EBS upgrade. Currently under commissioning

at the ID03 port, the new beamline will deliver a spatial

resolution of about 100 nm, while making experiments

hundreds of times faster, opening up the possibility

of capturing realtime movies of structural dynamics

across multiple length scales Its true that its been a bit

of a gamble as there is no existing user community says

Detlefs But the prototype was given over to half of the

beamtime at ID06 and that was already oversubscribed

by factor of two or so It gave us confidence that there

was interest Indeed the interest is visible from a stack

of DFXM publications from ID06 by different user

groups on systems ranging from ceramics to additively

manufactured alloys to ferrous materials see Proven

applications of DFXM at the ESRF left

One of the potential disadvantages of DFXM is

that because of the large magnification of a very small

Figure 1 The novelty of DFXM is that an objective lens is placed

after the sample, not before as it would be in usual X-ray

microscopy. Here, the lens isolates the diffraction signal from a

particular crystallographic grain, free from the confusing

diffraction signals coming from elsewhere in the sample. The

number of lenses in the objective, and the ratio of p’ and q’, sets

the zoom factor. Using reconstruction algorithms to combine

repeated exposures during a 360° rotation of the sample about

the diffraction axis, G, a 3D map of a grain’s structure can be

obtained. Tilting the axis by α or β accommodates a grain’s

internal spreads of crystalline orientations.