Metallic snowflakes test new nanoscale engineering

New Zealand and Australian scientists working at the atomic level have created something as unexpected as tiny metallic snowflakes.

An experiment that ‘persuades’ individual atoms to cooperate is leading to a revolution in engineering and technology through nanomaterials.

Nanoscale structures can aid electronic manufacturing, make materials stronger but lighter, or aid environmental cleanup by binding to toxins.

To create metallic nanocrystals, the research team has been experimenting with gallium, a soft, silvery metal that is used in semiconductors and unusually liquefies just above room temperature.

Their results have just been published in the journal Science.

The Australian team, from the University of New South Wales, worked in the laboratory with nickel, copper, zinc, tin, platinum, bismuth, silver and aluminium. The metals were dissolved in gallium at high temperatures. Once cooled, the metallic crystals emerged while the gallium remained liquid.

The New Zealand team, part of the MacDiarmid Institute for Advanced Materials and Nanotechnology, a National Center of Research Excellence, carried out molecular dynamics simulations to explain why crystals of different shapes arise from different metals.

“What we are learning is that the structure of liquid gallium is very important,” says Professor Nicola Gaston, from the University of Auckland. “That’s novel because we generally think of liquids as having no structure or just random structure.”

The interactions between the atomic structures of the different metals and the liquid gallium give rise to crystals of different shapes, the scientists have shown.

The crystals included zinc cubes, rods, hexagonal plates, and snowflake shapes. The six-branch symmetry of zinc, with each atom surrounded by six neighbors at equal distances, explains the snowflake’s design.

“In contrast to top-down approaches to forming nanostructures, by cutting material, this bottom-up approach relies on the self-assembly of atoms,” says Gaston. “This is how nature produces nanoparticles, and it’s less wasteful and much more precise than top-down methods.”

In his view, the research has opened a new and unexplored path for metal nanostructures. “There’s also something cool about creating a metallic snowflake.” (Europe Press)