A team of engineers have developed an incredibly thin electric generator, only one atom thick. This study also provided the first experimental evidence that the material is piezoelectric, or capable of producing electricity through pressure. The paper was published in Nature, and the lead author is Wenzhuo Wu of the Georgia Institute of Technology.
Two-dimensional molybdenum disulfide (MoS2) is light, flexible, and transparent, making it highly desirable for use in nanoelectrics. Though researchers have theorized that MoS2 would be piezoelectric, it had never been demonstrated before. Piezoelectricity comes from generating electricity through pressure or movement of certain solid materials. When flakes of the material between 1 and 8 atoms thick were placed on a flexible base, MoS2 was able to generate electricity as it was stretched and pressed.
“Proof of the piezoelectric effect and piezotronic effect adds new functionalities to these two-dimensional materials,” Zhong Lin Wang, co-senior author of the paper, said in a press release. “The materials community is excited about molybdenum disulfide, and demonstrating the piezoelectric effect in it adds a new facet to the material.”
However, the piezoelectric effect could only be achieved under certain conditions. First, the researchers noted that an even number layers of the MoS2 did not generate electricity, only an odd number of layers did. Additionally, less was more. A single atomic thickness of MoS2 was bent and stretched into generating 15 millivolts. The thicker the layers got, the less electricity they were able to generate. According to the researchers, 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.
“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,” co-senior author James Hone added. “With what we’re learning, we’re eager to build useful devices for all kinds of applications.”
Earlier this year, a team from the Vienna University of Technology speculated that it could be possible to make solar cells just a few atoms thick using molybdenum disulfide. Because it is transparent, the material could cover existing windows in buildings, providing energy without sacrificing aesthetics. Additionally, since the material is flexible, the possible applications are endless
“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,” Hone said.
If the movement from clothing isn’t enough to meet one’s electricity desires, imagine if the material was integrated into the fabric of a flag, which are nearly constantly in motion. Additionally, it could allow medical implants to be smaller and less intrusive. Now that MoS2 has been shown to be piezoelectric, a host of innovative applications could be possible in the future.