By permanently stressing graphene with a novel laser technique, researchers have been able to provide it with the largest ever band gap. Image: Purdue University image/Gary Cheng.
By permanently stressing graphene with a novel laser technique, researchers have been able to provide it with the largest ever band gap. Image: Purdue University image/Gary Cheng.

Graphene is a super thin material that is at least 100 times stronger than steel, and the best-known conductor of heat and electricity. This means that graphene could help bring about faster electronics than are possible today with silicon.

But to be truly be useful, graphene would need to carry an electric current that switches on and off, like silicon does in the billions of transistors on a computer chip. This switching creates strings of 0s and 1s that a computer uses to process information.

Now, researchers at Purdue University, in collaboration with colleagues at the University of Michigan and the Huazhong University of Science and Technology in China, have shown how a laser technique can permanently stress graphene into having a structure that controls the flow of electric current.

This structure is a so-called ‘band gap’. Electrons need to jump across this gap in order to become conduction electrons, which are capable of carrying an electric current. But graphene doesn't naturally have a band gap; it is a switch that is always on.

Using their novel laser technique, however, the Purdue researchers have been able to create a band gap in graphene and widen it to a record 2.1 electronvolts. To function as a semiconductor such as silicon, the band gap would just need to beat the previous record of 0.5 electronvolts.

"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.

The presence of a band gap allows semiconductor materials to switch between insulating and conducting, depending on whether or not their electrons can be pushed across the band gap.

Surpassing 0.5 electronvolts unlocks even more potential for graphene in next-generation electronic devices, the researchers say. They report their results in a paper in Advanced Materials.

"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 explained.

Cheng and his collaborators not only kept the band gap open in graphene, but were also able to tune the gap width from zero to 2.1 electronvolts. This gives scientists and manufacturers the option to just use certain properties of graphene depending on what they want the material to do.

The researchers made the band gap structure permanent in graphene using a technique called laser shock imprinting, which Cheng developed in 2014 along with scientists at Harvard University, the University of California, San Diego, and the Madrid Institute for Advanced Studies in Spain.

For this study, the researchers used a laser to create shockwave impulses that penetrated an underlying sheet of graphene. The laser shock strains graphene into a trench-like configuration – permanently shaping it. Adjusting the laser power allows the size of the band gap to be finely tuned.

While still far from putting graphene into semiconducting devices, this technique grants more flexibility in taking advantage of the material's optical, magnetic and thermal properties, Cheng said.

This story is adapted from material from Purdue University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.