Posted in | 2D Materials

New Study Reveals Piezotronic Effect in Atomically Thin 2D Materials

Columbia Engineering and the Georgia Institute of Technology researchers have developed an optically transparent, light-weight, flexible electric generator made of an atomically thin material, molybdenum disulfide (MoS2). In a paper published in the Nature journal, the researchers reported the observation of piezotronic and piezoelectric effects in the two-dimensional (2D) MoS2 material.

Positive and negative polarized charges are squeezed from a single layer of atoms, as it is being stretched. —Image courtesy of Lei Wang/Columbia Engineering

Piezoelectricity is a common effect wherein electricity is generated when a material is stretched or compressed. However, until now, this effect has not been studied in materials with less thickness. This research demonstrates a new facet of 2D materials such as MoS2 and its application in developing new forms of mechanically controlled electronic devices.

The research team members are the pioneers in the field of piezoelectric nanogenerators that convert mechanical energy into electric energy. The team is involved in developing piezotronic devices that control the electric flow via material using piezoelectric charges.

MoS2 can be triggered in two ways to produce electricity – one is by flexing it in appropriate direction and other is forming an odd number of layers. As the material is polar in nature, developing an even number of layer cancels the generation of piezoelectric effect. The crystalline nature of the material is piezoelectric only in certain orientations.

The researchers used thin flakes of MoS2 laid on flexible plastic substrates to determine the orientations of crystal lattice through optical techniques. Following this, metal electrodes were patterned on the flakes. Using the measurement electrodes, they measured the current flow in mechanically deformed samples in order to monitor the conversion of mechanical energy into electrical energy, and determine current and voltage outputs. Reversal of output voltage was observed upon changing the direction of strain applied, confirming the presence of piezoelectric effect in odd layer MoS2.

Therefore, it is evident from the research findings that piezoelectricity can be generated in MoS2 material that is thinned down to a single atomic layer. The research could be applied in the development of self-powered atomic-thick nanosystems and the layered materials for active flexible electronics, MEMS, robotics, and human-machine interfacing.

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