Piezoelectricity in Monolayer Hexagonal Boron Nitride.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional (2D) hexagonal boron nitride (hBN) is a wide-bandgap van der Waals crystal known for its strength, oxidation resistance, and optical properties.
• hBN is widely used for encapsulating other 2D materials in optoelectronics and composites.
• Monolayer hBN lacks a center of symmetry, theoretically predicting piezoelectric properties, but lacking experimental validation.

Purpose of the Study:

• To experimentally investigate and confirm the predicted piezoelectric properties of monolayer hexagonal boron nitride (hBN).
• To explore the strain-induced piezoelectric effect in 2D hBN materials.
• To assess the piezoelectric behavior in different hBN layer configurations (monolayer, bilayer, bulk).

Main Methods:

• Utilizing electrostatic force microscopy (EFM) to probe local electric field changes.
• Inducing strain in hBN samples to observe piezoelectric responses.
• Comparing experimental observations with theoretical calculations.

Main Results:

• Experimental observation of strain-induced piezoelectricity in monolayer hBN via changes in the local electric field.
• The observed effect aligns with theoretical predictions.
• No piezoelectricity was detected in bilayer or bulk hBN, consistent with their restored center of symmetry.

Conclusions:

• Monolayer hBN exhibits piezoelectric properties, adding to its known characteristics.
• This discovery positions monolayer hBN as a promising material for electromechanical and stretchable optoelectronic devices.
• The study demonstrates a nanoscale method for investigating piezoelectricity in 2D materials and controlling electric fields in van der Waals heterostructures through strain.