Thinnest generator of electricity
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Thinnest generator of electricity
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single layer of molybdenum disulfide (MoS2), 0.6 nm thick, generates a peak electrical output of 15 mV and 20 pA when strained by 0.53%, which corresponds to a mechanical-to-electrical energy conversion of 5.8%. These observations were made by a research team from Georgia Institute of Technology (Georgia Tech) and Columbia University, who published their results in the October 15 online edition of Nature (DOI:10.1038/ nature13792). The accumulation of electric charge in a material when it is stressed is known as piezoelectricity, a phenomenon discovered in 1880 by the brothers Pierre and Jacque Curie. MoS2 (molybdenite in its mineral form) was studied as a source of molybdenum by Scheele in 1778. However, this material in bulk form cannot be piezoelectric because it has a center of symmetry, and charges from the layers cancel each other out. But in the form of a monolayer—that is a single atomic layer of Mo sandwiched between two adjacent atomic layers of S packed in a hexagonal lattice—it is no longer centrosymmetric and hence becomes piezoelectric. Theoretical work has suggested this possibility for many transition-metal dichalcogenides. Karel-Alexander Duerloo, Mitchell Ong, and Evan Reed at Stanford University calculated the piezoelectric coefficient of the MoS2 monolayer to be 364 pC/m, using density functional theory. A research team from
Digital metamaterial bits for simpler optical elements
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n this Information Age, digital electronics have become a crucial part of our everyday lives. Binary, or Boolean, logic has become ubiquitous in a society so closely affiliated with personal electronics. The deceptively simple nature of the mathematical structure that uses 1s and 0s has enabled
the University of California–Berkeley and Lawrence Berkeley National Laboratory posted a value of 290 pC/m on the arxiv. org website on August 29, 2014, from inverse piezoelectric measurements (i.e. apply voltage and measure change in force). Electronics fabricated using piezopotential as a gate voltage to tune or control the charge-transport behavior across a metal/semiconductor interface or a p–n junction are called piezotronics. Transport measurements show for the first time a strong piezotronic effect in single-layer MoS2, but not in bilayer and bulk MoS2. According to Zhong Lin Wang of Georgia Tech, a corresponding author of the article in Nature, “Proof of the piezoelectric effect and piezotronic effect adds new functionalities to these two-dimensional materials.” These properties greatly expand the application of layered materials for human-machine interfacing, robotics, microelectromechanical systems, and active flexible electronics. James Hone, whose team at Columbia prepared the MoS2 flakes and determined their crystal orientations, says, “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 to supply enou
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