Scientists have succeeded in endowing graphene with yet another useful property. Already, it is the thinnest, strongest and stiffest material ever measured, while also proving to be an excellent conductor of heat and electricity. These qualities have allowed it to find use in everything from transistors to supercapacitors to anti-corrosion coatings. Now, two materials engineers from Stanford University have used computer models to show how it could also be turned into a piezoelectric material – this means that it could generate electricity when mechanically stressed, or change shape when subjected to an electric current.
Graphene, for the uninitiated, consists of a flat sheet of carbon atoms, arranged in a hexagonal pattern. Each sheet is just one atom thick.
Utilizing high-performance supercomputers running a modeling application, the Stanford researchers experimented with depositing lithium, hydrogen, potassium and fluorine atoms on one side of a graphene sheet. They also tried out combinations of hydrogen and fluorine, and lithium and fluorine, where the two types of atoms were deposited on opposite sides of the same sheet.
In all cases, adding the atoms broke the graphene's perfect physical symmetry – this symmetry is what ordinarily keeps it from displaying piezoelectric properties. "We thought the piezoelectric effect would be present, but relatively small," said study leader Evan Reed. "Yet, we were able to achieve piezoelectric levels comparable to traditional three-dimensional materials. It was pretty significant."
It was even possible to fine-tune where, when and how much the graphene would deform in response to an electric current, by only placing atoms on select areas of its surface.
Reed and his colleague, Mitchell Ong, hope that piezoelectric graphene could find use in applications such as energy harvesting, high-frequency acoustics, chemical sensing, photonics, and electronic devices.
A paper on the research was recently published in the journal ACS Nano.
Source: Stanford University