World's thinnest electric generator developed

Researchers claim to have developed the world's thinnest electric generator that is optically transparent, extremely light, very bendable and stretchable.
Investigators from Columbia Engineering and the Georgia Institute of Technology made the first experimental observation of piezoelectricity and the piezotronic effect in an atomically thin material, molybdenum disulfide (MoS2).
The finding resulted in a unique electric generator and mechanosensation devices that are optically transparent, extremely light, and very bendable and stretchable.
Researchers demonstrated the mechanical generation of electricity from the two-dimensional (2D) MoS2 material.
The piezoelectric effect in this material had previously been predicted theoretically.
Piezoelectricity is a well-known effect in which stretching or compressing a material causes it to generate an electrical voltage (or the reverse, in which an applied voltage causes it to expand or contract).

But for materials of only a few atomic thicknesses, no experimental observation of piezoelectricity has been made, until now.

The observation provides a new property for two-dimensional materials such as molybdenum disulfide, opening the potential for new types of mechanically controlled electronic devices.
"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," said James Hone, professor of mechanical engineering at Columbia and co-leader of the research.

"Proof of the piezoelectric effect and piezotronic effect adds new functionalities to these two-dimensional materials," said Zhong Lin Wang, Professor in Georgia Tech's School of Materials Science and Engineering and a co-leader of the study.
For the study, Hone's team placed thin flakes of MoS2 on flexible plastic substrates and determined how their crystal lattices were oriented using optical techniques. They then patterned metal electrodes onto the flakes.
Researchers installed measurement electrodes on samples, then measured current flows as the samples were mechanically deformed. They monitored the conversion of mechanical to electrical energy, and observed voltage and current outputs.
The researchers also noted that the output voltage reversed sign when they changed the direction of applied strain, and that it disappeared in samples with an even number of atomic layers, confirming theoretical predictions published last year.

The research was published in the journal Nature.