A ‘Super’ Material Substitute
This year UWM became a front-runner in a worldwide race to find less expensive ways to replicate a revolutionary “super” material called graphene. UWM scientists and graduate students have chemically changed a close cousin of the highly touted material into an easy-to-make and cost-effective form.
Graphene is a one-atom-thick layer of carbon that resembles a flat sheet of chicken wire at nanoscale. Since it conducts electricity better than any metal, it has the best potential to replace today’s silicon transistors and usher in the next generation of lightning-speed computing and tinier electronics.
But currently graphene is too expensive to mass-produce and it exists only as a conductor or an insulator, not in the valuable semiconductor state essential for electronic devices.
UWM physicists are calling the new form “graphene monoxide” (GMO), and say it exhibits characteristics that could make it a viable substitute. Like silicon in the current generation of electronics, for example, GMO is a semiconductor.
The discovery began as an ordinary imaging task: Engineering Professor Junhong Chen developed a hybrid material for use in high-performance, energy-efficient and inexpensive sensors. His material consists of carbon nanotubes decorated with nanoparticles of tin oxide.
Using a high-resolution transmission electron microscope, Chen and Physics Professor Marija Gajdardziska hoped to observe the hybrid material as it was sensing. The pair soon found they needed to know which molecules were attaching to the nanotube surface, which were attaching to the tin oxide surface, and how they changed upon attachment.
So they turned to Physics Professor Carol Hirschmugl (pictured with Gajdardziska below), who recently pioneered a method of infrared imaging that not only offers high-definition images of samples, but also renders a chemical “signature” that identifies which atoms are interacting in a sample.
To give them more points of attachment to examine, the scientists unrolled the carbon nanotubes into single sheets. With these single layers of carbon and two forms of precision imaging equipment at their disposal, the researchers and their students looked for a way to make graphene from its cousin, graphene oxide (GO).
GO consists of layers of graphene stacked on top of one another in an unaligned orientation, and it is the focus of much current graphene research.
In one experiment, students and faculty heated the GO in a vacuum to reduce oxygen. Instead of being destroyed, however, the carbon and oxygen atoms in the layers of GO became aligned, transforming themselves into an “ordered,” semiconducting carbon oxide – GMO.
It was not the result they expected.
“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, who is the first author on the research paper published in the journal ACS Nano.
Because GMO is formed in single sheets, Gajdardziska says the material could have applications in products such as fuel cells or industrial processes that involve surface catalysis, an accelerated chemical reaction occurring at the surface of materials. She, Hirschmugl and Chen also are exploring its use in making lithium-ion batteries more efficient.
Working through UWM’s Center for Surface Studies, the research team also included UWM Distinguished Professor of Physics Michael Weinert, physics research associate Marvin Schofield, postdoctoral associate Michael Nasse, engineering graduate students Haihui Pu and Shumao Cui, engineering research associate Ganhua Lu, and Rodney Ruoff of the University of Texas. Pictured here are physics professors Carol Hirschmugl (left) and Marija Gajdardziska.