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Most Flexible 2D Material Discovered at UT Austin

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This figure shows the crystal structure of a monolayer of arsenic sulfide, which has special properties for making non-volatile memory devices and piezoelectric sensors. Credit: Center for Computational Materials

AUSTIN, Texas — A new kind of two-dimensional (2D) material with unique properties has been discovered by researchers with The University of Texas at Austin, bringing next-generation flexible electronic devices one step closer.

In materials science, size matters. And currently 2D materials are the hottest ticket. Thanks to their atomically-thin size, light weight, high stretchability, impressive biocompatibility, and the high performance rate of those with unique properties, 2D materials such as graphene have proved useful in a variety of ways including for technologies such as wearable human health care monitoring systems.

Researchers at UT Austin’s Center for Computational Materials and the Oden Institute for Computational Science and Engineering used supercomputers to discover the 2D materials that show ferroelectric, piezoelectric properties. These atomically-thin materials are ferroelectric on account of their capacity for switchable, spontaneous electric polarization, and piezoelectric because that electric current is the result of applying pressure and heat.

The group of crystal structures, known as arsenic chalcogenides, are two dimensional. The super-thin structure makes them ideal for use in the miniaturization of next-generation flexible electronic devices.

“The advantage of 2D ferroelectric materials is that they can be made atomically thin, meaning they are measured at the sub-nanometer scale,” said Weiwei Gao, a postdoctoral fellow in the Center for Computational Materials and co-author of the study. Working alongside Center Director and UT Physics Professor James R. Chelikowsky, the Oden Institute researchers revealed their findings in a paper published in a recent edition of the journal Nano Letters.

Materials scientists are aware of several ferroelectric materials in the three-dimensional (3D) world. Less is known about atomically-thin two-dimensional materials with similar properties. These super-thin materials are all around us but were only discovered in recent years.

Graphene is considered the world’s first known two-dimensional material. In 2004, scientists peeled flakes of the material from 3D bulk graphite — found in pencil leads, lubricants and tennis rackets — using sticky tape. This material has the highest known thermal and electrical conductivity. It is also stronger than steel but is light, flexible and transparent.

Although most people would imagine the lab setting of a materials scientist as being filled with test tubes and petri dishes, computational scientists bypass the physical experimentation part of their role. Instead, they rely upon complex mathematical tools powered by supercomputers to simulate experiments with different compounds. They can accurately identify and record the properties of new materials using the computational model alone.

This is how Gao and Chelikowsky conducted their research on arsenic chalcogenides. And, the ferroelectric and piezoelectric properties they found make this discovery potentially very significant.

Two-dimensional materials with ferroelectricity have potential applications in state-of-the-art memory devices, piezoelectric sensors, and nonlinear optical devices, the researchers said. In addition, their unmatched flexibility means they could be used in soft polymers or plastics, opening up more economically viable options for wearable devices and other flexible electronics.  

There are a lot of examples of non-centrosymmetric 2D materials showing spontaneous electric polarization” Gao said. “But not all of them are switchable. In fact, only a few two-dimensional ferroelectric materials have ever been confirmed in experiments.”

The research was conducted using the high-performance computing capabilities at the Texas Advanced Computing Center.