Metal snowflakes the thickness of a human hair could lead to new tech | Science | News

Metal snowflakes the thickness of a human hair could lead to new tech | Science | News

The creation of beautiful, tiny metallic snowflakes – each as wide as a human hair – could pave the way to new sensors, better industrial processes and even advanced and smaller electronic components for the computers of the future. This is the conclusion of a new study by researchers from Australia and New Zealand who grew the expanded metal crystals atom by atom inside a liquid gallium solvent. Gallium is a soft, silvery metal commonly used to make semiconductors that has the unusual property of melting at 85.6F – just above room temperature.

In the new study, the Australia-based members of the team worked with various metals – aluminium, bismuth, copper, nickel, tin, platinum, silver and zinc – to dissolve them in liquid gallium at high temperatures.

When the solutions were allowed to cool, metal crystals precipitated while the gallium remained liquid. Because liquid gallium has a high surface tension, it was a considerable challenge to extract the crystals without damaging their fine microscopic features.

However, the team was able to develop a method to do this by first using an electric field to lower the liquid metal’s surface tension, and then vacuum filtration to isolate the metal crystals from the solvent.

The crystals were found to come in various shapes – from cubes and rods to hexagonal plates and, in the case of zinc, snowflakes.

Across the Tasman Sea, materials science professor Nicola Gaston from the University of Auckland and the rest of the New Zealand members of the team carried out molecular dynamics simulations to help explain why different shapes of crystals formed from different metals.

Prof. Gaston said: “What we are learning is that the structure of the liquid gallium is very important. This is new because we usually think of liquids as lacking structure or being just randomly structured.”

The work, the scientist explains, builds on a previous study investigating potential catalysts which found that when precious metals such as gold or platinum are dissolved in liquid gallium and then allowed to crystallize out, they form different surface patterns. The new study shows that these patterns continued below the surface as well.

From their simulations, the researchers determined that it is the results of interactions between the atomistic structures of the liquid gallium solvent and the dissolved metals that cause crystals with different shapes to emerge.

In the case of zinc, the team explained, it is the metal’s sixfold symmetry — with each atom surrounded by six equidistant neighbors — that led to the snowflake design.

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Prof. Gaston told that with zinc, for example, “the liquid metal stabilizes the hexagonal face of the crystal and destabilizes the other faces – and we get these snowflakes.”

She continued, “What’s actually quite cool is that we will be able to design nanostructures using this principle.” Nanostructures can be used for various applications – from the catalysis of industrial reactions to the observation of molecules in the air.

Furthermore, she explained, because gallium is a liquid at about room temperature, the nanostructure design process will be fairly low energy — and produce no waste.

Prof. Gaston added: “You’re not using complicated solvents or molecules that you then have to throw away at the end after you’ve made the nanocrystals.

“Everything is in a fairly low temperature environment, and the gallium you use to form the structures is completely recoverable and reusable afterwards.”

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Prof. Gaston continued: “In contrast to top-down approaches to forming nanostructure – by cutting away material – this bottom-up approach relies on self-assembling atoms.

“This is how nature makes nanoparticles, and is both less wasteful and much more precise than top-down methods.”

“If we can do this in situ, we can also think about creating electronic devices for computers using these kinds of techniques in the future.”

And, she said, “There’s also something really cool about creating a metallic snowflake.”

The full findings of the study were published in the journal Science.

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