Atoms Standing Still in Molten Metal: New Research Reveals
“`html
Stationary Atoms in Liquids Challenge Understanding of Solidification
Table of Contents
The Unexpected Stillness Within
Researchers have found that,inside a liquid,not every atom is moving. Some atoms stay fixed in place even when the temperature is very high.These motionless atoms have a major effect on how a liquid turns into a solid, including the creation of an unusual state of matter known as a corralled supercooled liquid.
The way materials solidify is crucial in many natural processes,such as mineralization,the formation of ice,and the folding of protein fibrils. Solidification is also central to many technologies, from pharmaceuticals to metal-based industries, including aviation, construction, and electronics.
Imaging Molten Metal at the Atomic Scale
To explore how solids form, scientists from the University of Nottingham and the University of Ulm in Germany used transmission electron microscopy to watch molten metal nano-droplets as they solidified.Their findings were published on December 9 in the journal ACS Nano.
Professor andrei Khlobystov, who led the team, said, “When we consider matter, we typically think of three states: gas, liquid, and solid. While the behavior of atoms in gases and solids is easier to understand and describe, liquids remain more mysterious.”
Complex Motion and the Surprise of Stationary Atoms
In liquids, atoms move in a elaborate, crowded way, similar to people jostling through a busy street. They zip past one another at high speed while still interacting. This motion is especially tough to study during the key moment when a liquid begins to solidify, a stage that sets the material’s structure and many of its functional properties.
Graphene “Hob” Experiments and the SALVE Instrument
Dr. Christopher Leist, who performed transmission electron microscopy experiments at Ulm using the unique low-voltage SALVE instrument, said, “We began by melting metal nanoparticles, such as platinum, gold, and palladium, deposited on an atomically thin support — graphene. We used graphene as a sort of hob for this process to heat the particles,and as they melted,their atoms began to move rapidly,as expected. However, to our surprise, we found that some atoms remained stationary.”
Further analysis showed that these stationary atoms are strongly attached to the supporting material at specific locations called point defects, and this strong bonding persists even at very high temperatures. By concentrating the electron beam on selected areas,the team could create more defects and therefore adjust how many atoms stayed pinned in place within the liquid.
Wave-Particle Duality and a New Phase of Matter
Professor Ute Kaiser, who established the SALVE center at Ulm University, said, “Our experiments have surprised us as we directly observe the wave-particle duality of electrons in the electron beam. We visualize the material using electrons as waves. At the same time, electrons behave like particles, delivering discrete bursts of momentum that can either move or, surprisingly, even fix atoms at