Graphene is a very special material, only one atom thick. It has a rare combination of properties, including quantum and magnetic characteristics, that make it unique in many respects.
Now, researchers in the US and UK have discovered something peculiar about graphene’s electrical behavior.
Microscopic wrinkles in the super-thin, super-strong material are enough to significantly change its electrical properties.
It’s a phenomenon known as flexoelectricity, where electrical charge is created through the bending or deforming of a material. This is the quantum version of it in action, previously theorized in graphene but without much direct evidence.
As the study team explains in Advanced Materials, flexoelectricity promises a fundamentally different way of connecting physical and electrical properties – potentially controlling electricity in atomically thin materials like graphene, without the need for extra chemicals or materials.
“Our work shows that even an ordinary wrinkle can become an extraordinary electronic feature when viewed at the atomic scale,” says materials scientist Pulickel Ajayan, from Rice University in the US.
“By demonstrating that geometry alone can reshape electrical behavior in graphene, we open a new pathway for designing materials whose properties can be controlled through structure rather than chemistry.”
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>The researchers created natural nanowrinkles in the graphene that measured less than a billionth of a meter. These were then carefully probed to check up on their shape, local electrical energy, and electrical current.
Together with computer simulations of the physical changes and their effect on electrons, and comparisons to flat graphene, the researchers discovered the rather remarkable difference that these wrinkles made.
“Imagine bending a flexible ruler, except the bend is squeezed into a space smaller than a billionth of a meter,” says materials scientist Sathvik Ajay Iyengar, who led the study while at Rice University.
“At that scale, the electrons in graphene shift slightly toward one side, creating two opposite electrical sides like the ends of a tiny battery.”
The nanowrinkles transformed the way graphene handled electricity. Its electric polarization, essentially how strongly opposite the two ends of the ‘tiny batteries’ are, was up to 10 million times greater than in much larger flexoelectric systems.
Another way to think about it is to see the wrinkles as tiny speed bumps for electricity, changing the way graphene acts as a conductor.
This kind of material manipulation has a lot of potential uses, provided it can be further refined and scaled up.
“The sharpness of the wrinkle turned out to be much more important than its overall size,” says Iyengar.
“That tells us we can potentially tune electrical behavior by carefully controlling curvature at the nanoscale.”
Further down the line, we could be looking at upgrades for sensors and other electronic devices built in ultra-small, ultra-thin designs – essentially using the physical shape of these designs to control how the devices handle electricity.
However, it’s worth bearing in mind that the researchers relied on some model estimates as well as direct observations for their study, simply because the nanowrinkles were so tiny (and pushing the limits of microscopic analysis).
Additional confirmation of the results should come with future studies.
Meanwhile, graphene continues to amaze, whether it’s working on its own, in combination with other materials and chemicals, or in a changed state. Scientists have previously used wrinkled graphene to act as an effective water filter, for example.
Thanks to these findings, researchers now have a platform for studying flexoelectricity at the quantum level, some 20 years after they predicted the phenomenon could be produced by bending graphene.
Related: Two Studies Just Revealed How Twisted Graphene Gets Even Weirder at a ‘Magic Angle’
“Nature already creates these tiny wrinkles for us,” says Iyengar.
“Understanding how they influence electrical behavior gives scientists another tool for designing future technologies using the structure of a material itself.”
The research has been published in Advanced Materials.
This article was fact-checked by Clare Watson and edited by Clare Watson. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
