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NEWS

December 2024 ESRFnews

C O M M U N. P H Y S. 7 3 0 5 A C S N A N O 1 8 1 9 6 0 8

Ultrafast switch observed

An international team has used the

ESRF’s ID09 beamline to observe

how light can turn an insulator into

a metal in just trillionths of a second.

The understanding could help in

the development of ultrafast state

manipulations in new quantum

technologies.

Switching lies at the heart of all

modern computing. In principle, light

can be used to switch materials from

one state to another, faster than electric

currents, but the mechanisms at play

are not all well understood.

Now, scientists at the France-Japan

International Research Laboratory

DYNACOM in Japan, and the CNRS

and the ESRF in France, have found

that time-resolved analysis of X-ray

diffraction data at ID09 – combined

with results from an ultrafast laser

pump at Tohoku University in Japan,

and the MAX IV synchrotron in

Sweden – can help to expose the

switching in vanadium oxide (V

2

O

3

).

They found that laser light generates

internal stresses in the material, which

subsequently relaxes by generating

strain waves. In the wake of these

waves, the electron ordering changes

to make the vanadium oxide a

conductor (Nat. Phys. DOI: 10.1038/

s41567-024-02628-4).

“Our breakthrough experiment was

performed with the polychromatic

pink beam at ID09 before the launch

of the EBS,” says the ESRF scientist

and study co-author Céline Mariette.

“With the gain in beam intensity

from the EBS, however, we could

use a monochromatic beam instead.

This was a real game changer, since

we were then able to unambiguously

characterise the photo-induced

metallic phase.”

ID01 captures nanoparticle

strain dynamics

A team led by CEA-Irig working with

the ESRF has observed the evolution

of strain in platinum nanoparticles

during the oxidation of carbon

monoxide, at nanometre spatial and

sub-second temporal resolutions. The

feat is the result of new developments

in instrumentation for Bragg coherent

diffraction imaging (BCDI) at the ID01

beamline, and will help in the tuning

of catalytic reactions in operational

conditions.

The oxidisation of carbon monoxide

by catalysis is an important reaction,

as it helps protect the environment

from exhaust fumes. The structural

evolution of the catalysts has been

studied previously and in depth by

X-ray diffraction and photoemission

spectroscopy, but the finer dynamics

have remained poorly understood.

Michael Grimes, Marie-Ingrid

Richard and colleagues focused

their study on a particular facet of

platinum nanoparticles, known for

facilitating carbon monoxide and

oxygen adsorption. The researchers

exposed the nanoparticles to pulses

of the reactant gases, recording

diffraction data of strain in steps.

This “stroboscopic” BCDI approach

delivered a time resolution of

0.25 seconds and a spatial resolution of

20 nm; for the first time, the researchers

could also correlate the strain dynamics

with exhaust gas flux conditions, as

recorded by a mass spectrometer.

The data showed that the strain

evolved according to the initial gas

environment, with the nanoparticle’s

crystal lattice compressing at the key

facet under oxygen but expanding

upon arrival of carbon monoxide The

strain change rate and oscillation

time correlated with carbon dioxide

production and carbon monoxide

adsorption rate ACS Nano 18 19608

The technique offers the potential to

study a wide range of catalystassisted

in situ and operando reactions

providing new insights into catalyst

particle strain evolution during these

processes the researchers write

Céline Mariette,

scientist at ID09,

with Aleksandra

Chumakova on the

beamline.

New iron oxides found

High-pressure studies at the ESRF

have revealed new phases of iron

oxide. Focusing on single crystals, and

relying on very small X-ray beams, the

results contradict conclusions from

those of previous studies, which have

relied on powder samples.

Iron oxides might seem like simple

compounds chemically, but they can

be complicated and difficult to study,

especially under high pressure. In

particular, wüstite (Fe

1–x

O), one of

the main iron-bearing materials in

the lower mantle, is hard to synthesise

as a pure phase, without impurities

leaking in.

Now, a team of scientists from the

University of Bayreuth in Germany

the ESRF and elsewhere have used

Mössbauer spectroscopy at the ESRFs

ID18 beamline and Xray diffraction

at the ESRFs ID15B beamline and the

PETRA III synchrotron in Germany

to chart the transitions of wüstite as the

applied pressure increases Previously

based on powder diffraction data

researchers believed the materials

atoms began in a cubic arrangement

before becoming rhombohedral and

finally cubic again However the new

results show that wüstite actually

turns from rhombohedral to

monoclinic (a structure made of

a prism of parallelograms), and

finds another monoclinic phase

under additional high temperature

Commun Phys 7 305

According to Xiang Li a visiting

student at the ESRF and the first

author of the study the next step is

to study the materials at yet higher

pressures and temperatures In

highpressure studies we need a

very small beam he says We can

now take this project a step further

reaching pressures of 200 gigapascals

This wouldnt have been possible

before the EBS

E S R F/ S T E F C A N D É

One of the new

phases of wüstite

is a monoclinic

structure Blue

and red spheres

represent iron

and oxygen atoms

respectively

dashed lines

outline the unit cell

BCDI snapshot of strain changes in a single

nanoparticle.