Graphene can tear itself into ribbons from larger sheets, a pair of materials scientists at Trinity College, Dublin in Ireland have found.
And while the ribbons tend to “grow” faster when heated, the technique – published in Nature – also works at room temperature.
Making 3-D structures out of an atom-thick layer of carbon isn’t new. Last year, Chinese researchers showed graphene could fold itself, and even “walk”, when controlled by light and heat. But was there a way for it to slice itself?
James Annett and Graham Cross have found a way. They found when a single-layer sheet of graphene was heated on a hot plate at 150 ºC for the best part of two weeks, it spontaneously tore – triggered, they think, by a defect in the sheet too small to see with their powerful microscopes.
Next, they punched a triangular hole into a sheet, around a micron wide (about the size of a small bacterium), and let it sit at room temperature. They saw the edges of the triangle lift and peel back – a technique they repeated with sheet two, three and even four layers thick.
In the video at the top, each ribbon started around 0.6 microns wide and tapered inwards at a 15 º angle. The upper and lower left ribbons grew to around 1.5 microns, while the lower right ribbon stopped when it hit the edge of the graphene flake.
All in all, the made hundreds of ribbons, with widths from 300 nanometres to more than 2,000 nanometres and some reaching more than five microns long.
So what’s causing this spontaneous tearing?
The pair thinks stored energy is converted to motion as the graphene peels from the underlying substrate – in this case, an oxide layer on a silica wafer.
This interfacial force, as they called it, drives the 2-D graphene to tear and coalesce to a lower-energy, 3-D form.