Unveiling the Secrets of Motionless Atoms in Molten Metal
Imagine a world where not all atoms are in constant motion, even in the hottest of liquids. This intriguing phenomenon has been uncovered by researchers, revealing a hidden key to understanding how liquids solidify and transform into solids.
The Mystery of Solidification
Solidification, a process central to nature and technology, is often taken for granted. From the formation of ice to the creation of minerals and the folding of protein fibrils, it's a process that shapes our world. Yet, the moment when a liquid becomes a solid remains shrouded in complexity.
Unveiling the Atomic Secrets with Microscopy
Scientists from the University of Nottingham and the University of Ulm in Germany embarked on a mission to observe this mysterious moment. Using transmission electron microscopy, they watched molten metal nano-droplets solidify, publishing their findings in ACS Nano on December 9.
The Complexity of Liquids
Liquids are a bustling crowd of atoms, zipping past each other at high speeds while interacting. This chaotic dance is especially challenging to study during solidification, a critical stage that determines a material's structure and properties.
The 'Hob' Experiment and the SALVE Instrument
Dr. Christopher Leist, who conducted the microscopy experiments, explained their unique approach. They melted metal nanoparticles on an atomically thin support, graphene, using it as a 'hob' to heat the particles. Surprisingly, some atoms remained stationary, defying expectations.
Further analysis revealed these atoms were strongly bonded to the graphene at specific point defects, even at high temperatures. By manipulating the electron beam, the team could create more defects, controlling the number of pinned atoms.
Wave-Particle Duality and a New Phase
Professor Ute Kaiser, founder of the SALVE center, was surprised by the wave-particle duality of electrons observed. The team visualized the material using electron waves, but electrons also behaved as particles, moving or fixing atoms at the liquid's edge. This led to the discovery of a new phase of matter.
Directly Recording Chemical Reactions
The same team has previously recorded chemical reactions at the molecular level, including the breaking and reforming of chemical bonds. Their technique allows them to observe chemistry at the atomic scale, providing a unique perspective.
Atomic Corrals and the Power of Stationary Atoms
In their new study, the scientists found that stationary atoms guide the solidification process. When a few atoms are pinned, a crystal can grow and expand, solidifying the entire nanoparticle. However, when many atoms are held in place, they disrupt this process, preventing crystal formation altogether.
The Striking Effect of Atomic Corrals
Professor Andrei Khlobystov described the impact of stationary atoms creating a ring around the liquid. This 'atomic corral' traps the liquid, preventing it from solidifying, even at temperatures far below its freezing point. For platinum, this could be as low as 350 degrees Celsius, a remarkable deviation from typical expectations.
Corralled Supercooled Liquid and Amorphous Metal
Lowering the temperature further solidifies the corralled liquid, but not into a regular crystal. Instead, it forms an amorphous solid, a metal without the crystal's ordered structure. This unstable amorphous metal exists only as long as the stationary atoms confine it, rearranging into a crystal when that confinement ends.
Hybrid Metal State and Catalysis
Dr. Jesum Alves Fernandes, an expert in catalysis, highlighted the significance of this new hybrid metal state. With platinum on carbon being a widely used catalyst, understanding this confined liquid state could revolutionize our knowledge of catalysis, potentially leading to self-cleaning catalysts with enhanced performance.
Towards a New Form of Matter and Cleaner Technologies
This study is the first to demonstrate atomic corralling, previously achieved only for photons and electrons. Professor Khlobystov suggests this achievement may lead to a new form of matter, combining solid and liquid characteristics. By carefully arranging pinned atoms, larger and more complex atomic corrals could be built, potentially improving the efficiency of rare metals in clean technologies.
This research, funded by the EPSRC Program Grant 'Metal atoms on surfaces and interfaces (MASI) for sustainable future,' opens up exciting possibilities for the future of materials science and technology.
