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A group of engineers and researchers from both Columbia Engineering and the Georgia Institute of Technology revealed that they have made the first thin electric generator, that is remarkably only one atom thick. The results were uncovered in an article published online on October 15, 2014 in Nature by lead author Wenzhuo Wu of the Georgia Institute of Technology.

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According to Science Alert, the engineers revealed that they can generate electricity from a layer of material made from molybdenum disulphide (MoS2), providing the first experimental evidence that the material is piezoelectric, or capable of producing electricity through pressure.

Exploring Piezoelectricity

Piezoelectricity is a well-known effect in which stretching or compressing a material causes it to generate an electrical voltage. The material MoS2 is also known for its flexibility and lightness, making this just the starting point of an endless number of opportunities involving it to be explored within the realm of electricity generation.

Professor of mechanical engineering at Columbia and co-leader of the research, James Hone said:

“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.”

Zhong Lin Wang was another co-leader of the project; a partner in creating the world’s first practical piezoelectric nanogenerator and a professor in Georgia Tech’s School of Material Science and Engineering. He worked with fellow professor James Hone to achieve the world’s thinnest electric generator. Professor Lin Wang commented:

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“Proof of the piezoelectric effect and piezotronic effect adds new functionalities to these two-dimensional materials … the materials community is excited about molybdenum disulfide, and demonstrating the piezoelectric effect in it adds a new facet to the material.”

But according to researchers, the piezoelectric effect could only be achieved under certain conditions. The conditions include the need for an odd number of layers of the MoS2 in order to generate electricity – as an even number of layers won’t generate it.

Postdoctoral fellow Wenzhuo Wu and Professor Zhong Lin Wang. Photo Credit: Rob Felt.

Postdoctoral fellow Wenzhuo Wu and Professor Zhong Lin Wang. Photo Credit: Rob Felt.

The Devices Creation

The device was produced by placing thin layers of MoS2 on easily-bent plastic substrates and using optical techniques to define how the material’s crystal lattices were directed. In fact, the scientists defined MoS2 as one of a group of 2D semiconducting materials known as transition metal dichalcogenides, all of which are predicted to have comparable piezoelectric properties.

Experiments also proved that as the number of layers increased, the amount of current generated decreased; finally the material got too thick and stopped producing any electricity at all. But when the one-atom-thick layers of MoS2 were arranged into arrays, they were capable of generating a large amount of electricity.

Positive and negative polarized charges are squeezed from a single layer of atoms, as it is being stretched (Photo: Lei Wang/Columbia Engineering)

Positive and negative polarized charges are squeezed from a single layer of atoms, as it is being stretched (Photo: Lei Wang/Columbia Engineering)

The Nature study reported that a single monolayer flake of MoS2 strained by 0.53 percent generates a peak output of 15 mV and 20 pA, corresponding to a power density of 2 mW m-2 and a mechanical-to-electrical energy conversion efficiency of 5.08 percent.

Furthermore, IFL Science reported:

“A single atomic thickness of MoS2 was bent and stretched into generating 15 megavolts. The thicker the layers got, the less electricity they were able to generate. The random organization of the MoS2 led to electric charges getting canceled out as additional layers were added. This also explains why even layers didn’t work.”

Professor James Hone said:

“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, with what we’re learning, we’re eager to build useful devices for all kinds of applications.”

This study wasn’t the first one in this field, as a team from the Vienna University of Technology previously explored whether or not this was possible. They research focused on the possibility of using solar cells just a few atoms thick using molybdenum disulfide.

But now, with MoS2 having been proven the possible applications involving it are endless.

Sources:

(1) The Main Study

(2) Engineering

(3) Gizmag

(4) Nature


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