Because graphene lacks an inherent band gap, some critics have claimed that it is a dead-end line of research for electronics. But it's important to note that graphene comes in several varieties.
At the University of Wisconsin-Milwaukee (UWM) researchers have developed a new form of graphene they have dubbed “graphene monoxide (GMO).” With GMO, the UWM researchers believe they have brought graphene electronics applications one-step closer to reality. Instead of merely behaving as a conductor or insulator, the new material is capable of acting like a semiconductor. As a bonus, it also can be mass produced inexpensively.
“A major drive in the graphene research community is to make the material semiconducting so it can be used in electronic applications,” says Junhong Chen, professor of mechanical engineering and a member of the research team. “Our major contribution in this study was achieved through a chemical modification of graphene.”
The research, which was initially published in the journal ACS Nano in November of last year, didn’t really start off as graphene research at all. Instead it was based around graphene’s forgotten cousin, carbon nanotubes (CNTs). Chen and his UWM colleagues had developed a hybrid material based around CNTs that they mixed with tin oxide nanoparticles to create sensors.
The researchers wanted to be able to image this hybrid material as it was in the process of sensing. In order to do this they approached Carol Hirschmugl, who had developed an infrared imaging technique. But in order to see more molecules attaching themselves to the CNT, Chen and his colleague Marija Gajdardziska realized that they needed to unroll the CNT, thereby making it graphene.
Once the researchers had made the hybrid material into graphene, they decided to experiment with another cousin of graphene—graphene oxide (GO). GO is essentially layers of graphene that have been stacked on top of one another in an unaligned orientation. One of the experiments they undertook with GO was to put it in a vacuum to reduce the oxygen and heat it. Quite unexpectedly, instead of the material being damaged or even destroyed the unaligned orientation suddenly became aligned. With the addition of heat and a vacuum, GO had become the semiconducting GMO.
“We thought the oxygen would go away and leave multilayered graphene, so the observation of something other than that was a surprise,” says Eric Mattson, a doctoral student of Hirschmugl’s.
While this material they stumbled upon sounds quite promising for further development, it should be noted that the researchers plan to be focusing their attention on determining what the actual trigger mechanism was for the self-ordering of the GMO. In other words, there seems to be a good deal more science to be done before the engineering can begin.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.