Piezoelectricity in monolayer hexagonal boron nitride

TL;DR

This study provides experimental evidence of piezoelectricity in monolayer hexagonal boron nitride using electrostatic force microscopy, highlighting its potential for novel electromechanical applications and strain-controlled electronic properties.

Contribution

First experimental confirmation of piezoelectricity in monolayer hBN, demonstrating strain-induced electric field changes and expanding its application potential.

Findings

Piezoelectricity observed in monolayer hBN

No piezoelectricity in bilayer and bulk hBN

Method enables nanoscale piezoelectric property investigation

Abstract

Two-dimensional (2D) hexagonal boron nitride (hBN) is a wide-bandgap van der Waals crystal with a unique combination of properties, including exceptional strength, large oxidation resistance at high temperatures and optical functionalities. Furthermore, in recent years hBN crystals have become the material of choice for encapsulating other 2D crystals in a variety of technological applications, from optoelectronic and tunnelling devices to composites. Monolayer hBN, which has no center of symmetry, has been predicted to exhibit piezoelectric properties, yet experimental evidence is lacking. Here, by using electrostatic force microscopy, we observed this effect as a strain-induced change in the local electric field around bubbles and creases, in agreement with theoretical calculations. No piezoelectricity was found in bilayer and bulk hBN, where the centre of symmetry is restored. These results add piezoelectricity to the known properties of monolayer hBN, which makes it a desirable candidate for novel electromechanical and stretchable optoelectronic devices, and pave a way to control the local electric field and carrier concentration in van der Waals heterostructures via strain. The experimental approach used here also shows a way to investigate the piezoelectric properties of other materials on the nanoscale by using electrostatic scanning probe techniques.