IR Technique Sees Through Graphene Stacks

An IR technique identifies and characterizes individual graphene layers in a large stack, providing information on the electronic properties of each layer. Such information opens the possibility of graphene-based optical devices for communications, imaging and signal processing.

A University at Buffalo-led team developed the technique, which involves shooting a beam of IR light at a stack of graphene sheets and measuring how the light wave’s polarization changes as it bounces off the layers within.

The direction that a light wave is oscillating changes as the wave is reflected by a sheet of graphene. This changing direction of oscillation — also known as polarization — enabled researchers to identify the electronic properties of multiple sheets of graphene stacked atop one another, even when they were covering each other up. Courtesy of Chul Soo Kim, US Naval Research Laboratory.

Graphene, a nanomaterial that consists of a single layer of carbon atoms, has generated huge interest due to its remarkable fundamental properties and technological applications. It is lightweight but also one of the world’s strongest materials.

When a magnetic field is applied and increased, different types of graphene alter polarization in different ways. A graphene layer stacked neatly on top of another will have a different effect on polarization than one that is messily stacked.

“By measuring the polarization of reflected light from graphene in a magnetic field and using new analysis techniques, we have developed an ultrasensitive fingerprinting tool that is capable of identifying and characterizing different graphene multilayers,” said John Cerne, Ph.D., a UB associate professor of physics who led the project.

Cerne’s new research looks at graphene’s electronic properties, which change as sheets of the material are stacked on top of one another, and seeks to answer the question of why all graphene layers don’t affect polarization the same way.

The answer, he said, lies in the fact that different layers absorb and emit light in different ways.

His study showed that absorption and emission patterns change when a magnetic field is applied, so the polarization can be turned on and off either by applying a magnetic field to graphene layers or, more quickly, by applying a voltage that sends electrons flowing through the graphene.

“Applying a voltage would allow for fast modulation, which opens up the possibility for new optical devices using graphene for communications, imaging and signal processing,” said Chase T. Ellis, a former graduate research assistant at UB and current postdoctoral fellow at the Naval Research Laboratory.

Cerne’s collaborators included colleagues from UB and the US Naval Research Laboratory. The findings appeared Nov. 5 in Scientific Reports, (doi: 10.1038/srep03143). Ellis was first author on the paper.

For more information, visit: www.buffalo.edu