Published on May 9th, 2012 | by Tina Casey1
Graphene Might Have a Plastic Cousin
Shake the family tree of a decidedly weird material like graphene and you never know what might fall out. In the most recent development, researchers in Spain have found that they can replicate a distinctive feature of graphene simply by drilling a pattern of holes in a sheet of plastic.
The discovery of a plastic “cousin” is significant because graphene has tantalizingly unique properties that could spark a new generation of smaller, lighter, more powerful and less energy-sucking electronic devices, but it is a notoriously finicky material.
Plastic, on the other hand, is – well, plastic.
Dirac cones and graphene
The key to the outstanding electronic properties of graphene is the “unusual relationship” between the two points of a double-cone feature called Dirac cones. Electrons accelerate to high speeds as they move up the cone, and that accounts for the incredibly fast movement of electrons through graphene.
Loosely speaking, the Dirac phenomenon is similar to those change-donation stations at museums, where a penny dropped into the wide end of an inverted cone gathers speed as it whirls toward a small hole at the bottom.
If Dirac cones can be identified in other, more stable materials, that could lead to more cost-effective ways of mass producing foundational materials for next-generation electronics.
A plastic version of graphene
As a stand-in for graphene, they used a compound called methyl methacrylate, which in the form of poly methyl methacrylate is more commonly known as Plexiglass.
They drilled a pattern of cylindrical holes in the plastic sheet to mimic the lattice structure of carbon atoms in graphene, which resembles honeycomb or chickenwire. Each hole represented a carbon atom.
When exposed to carefully calibrated sounds from a loudspeaker, the surface of the plate produced acoustic waves that varied in relation to the depth and radius of the cylindrical holes.
According to the researchers, this phenomenon is analogous to the way that the lattice structure of graphene produces electronic waves.
As described in a recent article at physicsworld.com by editor Hamish Johnston, the researchers identified analogs to Dirac cones at about 22kHz, confirming their theoretical modeling.
The next step, according to Johnston, is to confirm that the acoustic waves also travel unimpeded across the sheet.
Applications for plastic “graphene”
Though practical applications for an acoustic Plexiglass version of graphene appear somewhat limited, the finding could be significant at the research end.
In its natural state, graphene comes in sheets of carbon only one atom thick. The researchers who discovered graphene in 2004 fabricated it by literally lifting a layer of carbon atoms from a chunk of graphite, a technique that is obviously lacking in quality control. Fabricating quantities of graphene with a consistent quality has bedeviled the field ever since.
With a cheap, easily manipulated material like Plexiglass at hand, researchers could use the acoustic analog as an initial step in graphene research, to predict the behavior of electrons under varying conditions.
Scientists at Columbia University have been working along these lines to create a simplified form of “artificial graphene” that could be used as a research tool in lieu of natural graphene.
Other graphene variants are under investigation at the University of Erlangen-Nürnberg in Germany, where researchers are using computer models to detect Dirac cones in graphynes, which are atom-thick carbon sheets that depart from the honeycomb structure of graphene.
At Manchester University, researchers are also tweaking graphene with hydrogen atoms to develop a sort of nano-sandwich called graphane, which could be cut into strips or ribbons for commercial use.