Researchers using SALVE transmission electron microscopy observed that a small number of atoms in molten metal nano-droplets can remain fixed to a graphene support, forming an "atomic corral." When enough atoms are immobilised around the melt, the droplet can remain liquid at temperatures far below its normal freezing point — for platinum, experiments showed stability down to about 350°C. The confined melt later forms an unstable amorphous solid that recrystallises if the corral is disrupted. The discovery suggests new ways to control metal solidification and improve catalysts and energy materials.
Researchers Create an "Atomic Corral" That Holds Molten Metal Between Liquid and Solid
There’s a Form of Matter Between Liquid and SolidFlavio Coelho - Getty Images
Scientists have observed a hybrid state of matter in metals where a molten droplet behaves like both a liquid and a solid. By immobilising a small number of atoms on an atomically thin support, researchers can alter how a metal solidifies — and in some cases keep it liquid at temperatures far below its normal freezing point.
In a paper published this week in ACS Nano, teams from the University of Nottingham (U.K.) and the University of Ulm (Germany) used the Sub-Angstrom Low-Voltage Electron (SALVE) microscope to watch metal nano-droplets solidify in real time. The SALVE microscope enabled high-resolution transmission electron microscopy of radiation-sensitive materials, letting the researchers track individual atomic movements during melting and cooling.
Stationary Atoms and the Atomic Corral
Metals studied included platinum, gold, and palladium deposited on an atomically thin graphene support. As the researchers heated the nanoparticles to melt them, most atoms moved as expected for a liquid. Unexpectedly, however, a small fraction of atoms stayed fixed — anchored to the graphene at or near point defects.
“We began by melting metal nanoparticles, such as platinum, gold, and palladium, deposited on an atomically thin support — graphene,” said Christopher Leist, a co-author from the University of Ulm. “We used graphene as a sort of hob for this process… To our surprise, we found that some atoms remained stationary.”
The team found they could increase the number of these fixed atoms by creating additional defects with an electron beam. When enough immobilised atoms surround a molten region — effectively forming an "atomic corral" or ring — the trapped melt resists normal crystallisation and remains liquid-like even as the temperature is dropped well below the metal's usual freezing point.
What Happens Next: Amorphous Solids and Recrystallisation
In these experiments the confined liquid eventually solidified, but not into a conventional crystalline lattice. Instead it formed an amorphous solid that the authors describe as thermodynamically unstable. If the ring of pinned atoms is disturbed, the unstable material rapidly reorganises into a normal crystal.
“Once the liquid is trapped in this atomic corral, it can remain in a liquid state even at temperatures significantly below its freezing point, which for platinum can be as low as 350°C — that is more than 1,000°C below what is typically expected,” said Andrei Khlobystov, a co-author from the University of Nottingham.
Implications and Applications
While the experiments were performed on noble metals rather than true rare-earth elements, the ability to control atomic mobility at the melt–solid boundary could have broad implications. Potential applications include improved design and stability of platinum-on-carbon catalysts used in fuel cells, and new strategies to control microstructure in metals for energy conversion and storage technologies. More generally, the findings highlight how nanoscale defects and supports can be used to tune phase transitions at the atomic scale.
The study deepens our understanding of liquids at the atomic scale and opens new directions for controlling material properties by engineering support defects and atomic pinning during solidification.
