Scientists and engineers at the University of Wisconsin-Milwaukee (UWM) have discovered an entirely new carbon-based material that is synthesized from the “wonder kid” of the carbon family, graphene. The discovery, which the researchers are calling “graphene monoxide (GMO),” pushes carbon materials closer to ushering in next-generation electronics.
Graphene, a one-atom-thick layer of carbon that resembles a flat sheet of chicken wire at nanoscale, has the potential to revolutionize electronics because it conducts electricity much better than the gold and copper wires used in current devices. Transistors made of silicon are approaching the minimum size at which they can be effective, meaning the speed of devices will soon bottom out.
Graphene could also enable terahertz processor speed, so even if the size is larger graphene electronics should still be faster than silicon electronics.
Graphene monoxide exhibits characteristics that will make it easier to scale up than graphene. And, like silicon in the current generation of electronics, GMO is semiconducting, necessary for controlling the electrical current in such a strong conductor as graphene. Now all three characteristics of electrical conductivity – conducting, insulating and semiconducting – are found in the carbon family, offering needed compatibility for use in future electronics.
Physics Professor Michael Weinert and engineering graduate student Haihui Pu display the atomic structure on GMO. (Photos by Alan Magayne-Roshak)
As silicon-based electronics are reaching the nanosize limits of the semiconductor roadmap, carbon-based nanoelectronics has become a rapidly growing field, with great interest in tuning the properties of carbon-based materials. Chemical functionalization is a proposed route, but syntheses of graphene oxide (G-O) produce disordered, nonstoichiometric materials with poor electronic properties. We report synthesis of an ordered, stoichiometric, solid-state carbon oxide that has never been observed in nature and coexists with graphene. Formation of this material, graphene monoxide (GMO), is achieved by annealing multilayered G-O. Our results indicate that the resulting thermally reduced G-O (TRG-O) consists of a two-dimensional nanocrystalline phase segregation: unoxidized graphitic regions are separated from highly oxidized regions of GMO. GMO has a quasi-hexagonal unit cell, an unusually high 1:1 O:C ratio, and a calculated direct band gap of 0.9 eV.
The team created GMO while conducting research into the behavior of a hybrid nanomaterial engineered by Chen that consists of carbon nanotubes (essentially, graphene rolled into a cylinder) decorated with tin oxide nanoparticles. Chen uses his hybrid material to make high-performance, energy-efficient and inexpensive sensors.
At different high temperatures, the team actually produced four new materials that they collectively refer to as GMO. They captured video of the process using Selected Area Electron Diffraction (SAED) in a transmission electron microscope.
Because GMO is formed in single sheets, Gajdardziska says the material could have applications in products that involve surface catalysis. She, Hirschmugl and Chen also are exploring its use in the anode parts of lithium-ion batteries, which could make them more efficient.
The next step is more science. The team will need to find out what triggered the reorganization of the material, and also what conditions would ruin the GMO’s formation.
“In the reduction process, you expect to lose oxygen,” says Michael Weinert, professor of physics and director of UWM’s Laboratory for Surface Studies. “But we actually gained more oxygen content. So we’re at a point where we’re still learning more about it.”
Weinert points out that they have only made GMO at a small scale in a lab and are not certain what they will encounter in scaling it up.
The team had to be careful in calculating how electrons flowed across GMO, he adds. Interactions that occur had to be interpreted through a painstaking process of tracking indicators of structure and then eliminating those that didn’t fit.