Recently a team of researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have, for the first time, observed piezoelectricity in a free standing two-dimensional semiconductor. This could lead to even lower power on/off switches in MEMS and nanoelectronic devices, as well as ultrasensitive bio-sensors.
Xiang Zhang, director of Berkeley Lab's Materials Sciences Division and an international authority on nanoscale engineering, led a study in which piezoelectricity — the conversion of mechanical energy into electricity or vice versa — was demonstrated in a free standing single layer of molybdenum disulfide, a 2D semiconductor that is a potential successor to silicon for faster electronic devices in the future.
"Piezoelectricity is a well-known effect in bulk crystals, but this is the first quantitative measurement of the piezoelectric effect in a single layer of molecules that has intrinsic in-plane dipoles," Zhang says. "The discovery of piezoelectricity at the molecular level not only is fundamentally interesting, but also could lead to tunable piezo-materials and devices for extremely small force generation and sensing."
Zhang, who holds the Ernest S. Kuh Endowed Chair at the University of California (UC) Berkeley and is a member of the Kavli Energy NanoSciences Institute at Berkeley, is the corresponding author of a paper in Nature Nanotechnology describing this research. The paper is titled "Observation of Piezoelectricity in Free-standing Monolayer MoS2." The co-lead authors are Hanyu Zhu and Yuan Wang, both members of Zhang's UC Berkeley research group.
To maximize piezoelectric coupling, electrodes (yellow dashed lines) were defined parallel to the zigzag edges (white dashed lines) of the MoS2 monolayer. Green and red colors denote the intensity of reflection and photoluminescence respectively. Image courtesy of Xiang Zhang, Berkeley Lab.