In 2004, a team of researchers discovered a thin material that is at least 100 times stronger than steel and it is best known as a conductor of electricity and heat. This means that graphene could bring faster electronics than is possible today with silicon.
But for graphene to be truly useful, it would need to carry an electric current that switches on and off, like what silicon does in the form of billions of transistors on a computer chip. The switching creates strings of 0s and 1s that a computer uses as a code for processing information.
The researchers in Purdue University collaborated with the University of Michigan and the Huazhong University of Science and Technology, to show how a laser technique could permanently stress graphene into having a structure that allows the flow of current.
The structure is also called the "band gap." The Electrons need to jump across a gap in order to become conduction electrons, that enables them to carry electric current. But graphene does not naturally have a band gap.
The researchers from Purdue University created and widened the band gap in graphene to a record 2.1 electron volts. They did this so that it could function as a semiconductor such as silicon. The band gap would need to be at least the previous record of 0.5 electron volts.
"This is the first time that an effort has achieved such high band gaps without affecting graphene itself, such as through chemical doping. We have purely strained the material," said Gary Cheng, professor of industrial engineering at Purdue, whose lab has investigated various ways to make graphene more useful for commercial applications.
Band gap allows semiconductor materials to switch between conducting or insulating an electric current, depending on whether their electrons are pushed across the gap or not. Surpassing the 0.5 electron volts unlocks more potential for graphene in next-generation electronic devices.
"Researchers in the past opened the band gap by simply stretching graphene, but stretching alone doesn't widen the band gap very much. You need to permanently change the shape of graphene to keep the band gap open," Cheng said.
Cheng and his colleagues not only kept the band gap open in graphene, they also made it to where the band gap width could be tuned from zero to 2.1 electron volts, giving manufacturers and scientists the option to just use certain properties of graphene depending on what they want it to do.
They also made the band gap structure permanent in graphene by using a technique called laser shock imprinting, which Cheng made in 2014 along with other scientists at Harvard University, the University of California, San Diego and Madrid Institute for Advanced Studies.
