When you think of electrical generators you would normally imagine loud cumbersome devices that chug on fuel to produce electricity. But how small and quiet could an electrical generator be? According to researchers at the Georgia Institute of Technology and Columbia Engineering, it could be just one atom thin.
A sample of molybdenum disulfide (MoS2) used in the experiment [Rob Felt/Georgia Tech]
Their research was published online October 15, 2014, in Nature and as you can imagine, there is always excitement over one-atom-thin materials as they open up new possibilities in a world where devices and electronics are continually decreasing in size. The one-atom-thin carbon material, Graphene, won the Nobel Prize in Physics back in 2010.
In the publication, the team made the ‘first experimental observation of piezoelectricity and the piezotronic effect in an atomically thin material, molybdenum disulfide (MoS2)’, resulting in a ‘unique electric generator and mechanosensation devices that are optically transparent, extremely light, and very bendable and stretchable’.
“This material — just a single layer of atoms — could be made as a wearable device, perhaps integrated into clothing, to convert energy from your body movement to electricity and power wearable sensors or medical devices, or perhaps supply enough energy to charge your cell phone in your pocket,” says James Hone, professor of mechanical engineering at Columbia and co-leader of the research.
Piezoelectricity is a well known process in which the stretching or compression of a material causes it to generate electric voltage (or vice versa where an applied voltage causes the material to expand or contract). Until now the effect had not been observed in thin materials, but the team of researchers discovered that if you have an odd number of atom layers (even one atom thin) and bend it in the right way, molybdenum disulfide (MoS2) generates electricty via the piezoelectric effect.
From the abstract of the paper: “A single monolayer flake strained by 0.53% generates a peak output of 15 mV and 20 pA, corresponding to a power density of 2 mW m−2 and a 5.08% mechanical-to-electrical energy conversion efficiency. In agreement with theoretical predictions, the output increases with decreasing thickness and reverses sign when the strain direction is rotated by 90°.”
“Proof of the piezoelectric effect and piezotronic effect adds new functionalities to these two-dimensional materials,” says Zhong Lin Wang, Regents’ Professor in Georgia Tech’s School of Materials Science and Engineering and a co-leader of the research. “The materials community is excited about molybdenum disulfide, and demonstrating the piezoelectric effect in it adds a new facet to the material.”
In the future, designers and engineers may be looking into incorporating the tech into small and self powered devices that harvest mechanical energy from the environment. As it needs to be stretched, it probably wouldn’t be of much use in tablets and smartphones, however, imagine wearing clothes where your body movement produces electricity that can be stored in a battery, later used to power wearable devices.
“This is the first experimental work in this area and is an elegant example of how the world becomes different when the size of material shrinks to the scale of a single atom,” Hone adds. “With what we’re learning, we’re eager to build useful devices for all kinds of applications.”
The study was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences (BES) (No. DE-FG02-07ER46394) and U.S. National Science Foundation (DMR-1122594)
