Adventures In Nanotechnology… The Case Of The Metallic Snowflake
Scientists in New Zealand and Australia working
at the level of atoms created something unexpected: tiny
metallic snowflakes.
Why’s that
significant? Because coaxing individual atoms to cooperate
in desired ways is leading to a revolution in engineering
and technology via nanomaterials. (And creating snowflakes
is cool.)
Nanoscale
structures (a nanometre is one billionth of a metre) can aid
electronic manufacturing, make materials stronger yet
lighter, or aid environmental clean-ups by binding to
toxins.
To create metallic nanocrystals, New Zealand
and Australian scientists have been experimenting with
gallium, a soft, silvery metal which is used in
semiconductors and, unusually, liquifies at just above room
temperature.
Their results were just reported in the
journal Science.
Professor Nicola Gaston and
research fellow Dr Steph Lambie, both of Waipapa Taumata
Rau, University of Auckland, and Dr Krista Steenbergen of Te
Herenga Waka, Victoria University of Wellington,
collaborated with colleagues in Australia led by Professor
Kourosh Kalantar-Zadeh at the University of New South
Wales.
The Australian team worked in the lab with
nickel, copper, zinc, tin, platinum, bismuth, silver
and
aluminium, growing metal crystals in a liquid solvent
of gallium.
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 Centre of Research
Excellence, carried out simulations of molecular dynamics to
explain why differently shaped crystals emerge from
different metals. (The government’s Marsden Fund supported
the research.)
“What we are learning is that the
structure of the liquid gallium is very important,” says
Gaston. “That’s novel because we usually think of
liquids as lacking structure or being only randomly
structured.”
Interactions between the atomistic
structures of the different metals and the liquid gallium
cause differently shaped crystals to emerge, the scientists
showed.
The crystals included cubes, rods, hexagonal
plates and the zinc snowflake shapes. The six-branched
symmetry of zinc, with each atom surrounded by six
neighbours at equivalent distances, accounts for the
snowflake design.
“In contrast to top-down
approaches to forming nanostructure – by cutting away
material – this bottom-up approaches relies on atoms
self-assembling,” says Gaston. “This is how nature makes
nanoparticles, and is both less wasteful and much more
precise than top-down methods.”
She says the
research has opened up a new, unexplored pathway for
metallic nanostructures. “There’s also something very
cool in creating a metallic
snowflake!”
