Scientists at the US Department of Energy’s Lawrence Berkeley National Lab have discovered what they describe as “an unexpected gap-like feature in the energy spectrum of electrons tunneling into graphene’s single layer of atoms.”
The full press release is here.
Call me “one atom thick,” but that sounds like quite a mouthful.
So, a brief backgrounder: Graphene is a two-dimensional crystal form of carbon carbon. The one atom thick substance is the basic building block of carbon nanotubes and fullerenes.
Carbon nanotubes are already being used in computer displays and other consumer products, but over recent years, researchers have claimed that carbon nantoubes could be used for a variety of purposes from mending broken bones to creating supercapacitors.
As I reported for Wired News in November 2007, a single carbon nanotube molecule was even used by Berkeley scientists to build the world’s smallest functioning radio. Wired News story here. It turns out that Alex Zettl –one of the brains behind the world’s smallest radio– is also involved in the new Berkeley research.
[Less widely known is the research published in May which found that inhaling carbon nanotubes had a carcinogenic effect on mice similar to that caused by asbestos. But let's keep this positive.... and graphene-focused.]
The Berkeley team were particularly interested in graphene’s electronic properties, so they performed the first analysis of graphene using a scanning tunneling microscope (STM).
STMs are nanoscopes (microscopes that operate on the nano-scale) that can be used to create images of single atoms –enabling scientists to study the behaviour of various substances at the atomic level. STMs use a stream of electrons from a tiny metallic tip (see diagram above) to capture an image of any surface –and study its electrical properties.
So what did the Berkeley team find? A veritable floodgate of phonon activity.
As one of the researchers put it:
“We started this research by simply asking, what do you see when you measure a graphene device with STM?” Crommie says. “In the process, we discovered a completely unexpected phonon floodgate. This gives us new insight into how electrons and phonons behave in graphene and creates new opportunities for future graphene-based nanodevice applications.”
“Almost no electrons tunneling from the STM tip could enter the graphene at low energies [...] but at slightly higher energies there was an abrupt, giant enhancement in tunneling, like a floodgate opening up for electrons.”
The paper “Giant phonon-induced conductance in scanning tunneling spectroscopy of gate-tunable graphene” by Michael F. Crommie, Alex Zettl, and others appears in the advance online publication of Nature Physics at http://dx.doi.org/10.1038/nphys1022.
