By firing a beam of infrared light at a stack of graphene sheets, scientists can identify and describe the electronic properties of each individual sheet—even when the sheets are covering each other up.
After shooting the beam, they measure how the direction the light wave is oscillating changes as it bounces off the layers within.
To explain further: When a magnetic field is applied and increased, different types of graphene alter the light wave’s direction of oscillation, or polarization, in different ways. A graphene layer stacked neatly on top of another will have a different effect on polarization than a graphene layer 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,” says John Cerne, a University at Buffalo associate professor of physics, who led the project.
Each layer is different
Cerne’s new research looks at graphene’s electronic properties, which change as sheets of the material are stacked on top of one another. The findings appeared in Scientific Reports.
So, why don’t all graphene layers affect the polarization of light the same way?
Cerne says the answer lies in the fact that different layers absorb and emit light in different ways.
The study shows that absorption and emission patterns change when a magnetic field is applied, which means that scientists can turn the polarization of light 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,” says the study’s first author, Chase T. Ellis, a former graduate research assistant at Buffalo and current post-doctoral fellow at the US Naval Research Laboratory.
Source: University at Buffalo