As part of an international research team, researchers from the University of Arkansas have discovered a two-dimensional (2D) ferroelectric material with a thickness of just two atoms.
2D materials are ultrathin membranes that exhibit the potential for novel mechanical, thermal, and optoelectronic applications, such as ultra-thin data-storage devices that would be both information-dense and foldable.
Ferroelectric materials exhibit an intrinsic dipole moment, which is a measure of the separation between positive and negative charges. An electric field can be applied to switch this dipole moment, stated Salvador Barraza-Lopez, associate professor of physics at the University of Arkansas.
For example, a single water molecule has an intrinsic electron dipole moment as well, but the thermal motion of individual water molecules under ordinary conditions (for instance, in a water bottle) prevents the creation of an intrinsic dipole moment over macroscopic distances.
Salvador Barraza-Lopez, Associate Professor of Physics, University of Arkansas
In the last five years, researchers have been making rigorous efforts to deploy atomically thin, 2D ferroelectrics, he added. The new material unraveled by the researchers is a tin selenide monolayer, which is only the third 2D ferroelectric that belongs to the chemical family of group-IV monochalcogenides experimentally developed to date.
Apart from researchers from the University of Arkansas, scientists from the Max Planck Institute for Microstucture Physics in Germany and the Beijing Academy of Quantum Information Sciences in China were also part of the team. The discovery has been reported in a paper published in the Nano Letters journal.
The researchers used a scanning tunneling microscope to switch the electron dipole moment of tin selenide monolayers formed on a graphitic substrate. Brandon Miller, a graduate student at the University of Arkansas performed calculations, which confirmed a highly oriented growth of this material on such a substrate.
The experimental implementation of such materials facilitates the validation of theoretical predictions behind truly unique physical behavior.
For instance, such semiconducting ferroelectric materials experience phase transitions caused by temperature, which lead to quenching of their intrinsic electric dipole (individual intrinsic electric dipoles fluctuate similar to what they do in water). In addition, they exhibit non-linear optical effects that could be helpful for ultra-compact optoelectronics applications.
Research at Arkansas was financially supported by an Early Career Grant to Barraza-Lopez from the U.S. Department of Energy, Office of Basic Energy Sciences.
Researchers performed calculations on the Trestles system at the Arkansas High Performance Computing Center, financially supported by grants from the National Science Foundation, the Arkansas Economic Development Commission, and the Office of the Vice Provost for Research and Innovation.
Further calculations were performed on the Cori system at the National Energy Research Scientific Computer Center. Experimental collaborators of the study are Kai Chang, Felix Küster, Jing-Rong Ji, Jia-Lu Zhang, Paolo Sessi, and Stuart S. P. Parkin.
Barraza-Lopez, S & Kaloni, T P (2020) Water Splits To Degrade Two-Dimensional Group-IV Monochalcogenides in Nanoseconds. ACS Central Science. doi.org/10.1021/acscentsci.8b00589.