‘Optical forging’ hammers graphene into three-dimensional shapes
Image credit: The University of Jyväskylä
An international team of researchers has developed a technique which allows them to use laser light to form the two-dimensional ‘wonder material’ graphene into three-dimensional shapes.
Graphene is a single atom-thick sheet of carbon atoms in a hexagonal lattice. Although it was only isolated for the first time in Nobel-prize winning work by Manchester physicists Andre Geim and Konstantin Novoselov in 2004, researchers all over the world are now working on countless applications for the material, which is an effective conductor of heat and electricity, and 200 times stronger than the strongest steel.
Atomically thin materials are the “ultimate building blocks” for nanoscale devices, although at present their applications are limited by their flatness: graphene can be "crumpled" or formed into nanotubes, but had not been formed into complex three-dimensional shapes.
However, the Finnish-based team of researchers now offer the potential for a new generation of nanoscale devices and other applications, by creating three-dimensional shapes from graphene for the first time.
They describe their technique as being akin to how a blacksmith hammers a metal sheet into new shapes.
“We call this technique optical forging, since the process resembles forging metals into three-dimensional shapes with a hammer,” said Professor Mika Pettersson, who led the project at the University of Jyväskylä’s Nanoscience Centre. “In our case, a laser beam is the hammer that forges graphene into three-dimensional shapes.”
The researchers employed a very fine laser to shape the graphene. This technique is based on the laser-induced local expansion of graphene, as confirmed with computer simulations.
“At first, we were flabbergasted: the experimental data simply made no sense,” said Dr Pekka Koskinen, who developed the theory. “But gradually, by close interplay between experiments and computer simulations, the actuality of 3D shapes and their formation mechanism started to become clear.”
“The beauty of the technique is that it’s fast and easy to use; it doesn’t require any additional chemicals or processing,” Professor Pettersson continued. “Despite the simplicity of the technique, we were very surprised initially when we observed that the laser beam induced such substantial changes on graphene. It took a while to understand what was happening.”
In addition to some simpler shapes, the researchers were able to create a complex pyramid shape with a height of 60nm (200 times higher than the thickness of a graphene sheet).
Contrary to their expectations, they did not find any traces of chemical species contaminating the graphene when they investigated the final product, and they concluded that the huge laser-induced changes were purely structural defects (rather than chemical doping).
The three-dimensional graphene, they report, is stable and its electronic and optical properties are slightly different from regular sheet graphene. The researchers hope that this graphene could be useful in creating three-dimensional architectures for electronic graphene-based devices.