Thickness-dependent bending modulus of hexagonal boron nitride nanosheets

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Physics

Background:

• Hexagonal boron nitride nanosheets (BNNSs) are advanced 2D materials with unique properties.
• Understanding the mechanical properties of BNNSs is crucial for their application in nanoelectronics and composites.
• Exfoliation is a common method for producing single-crystalline BNNSs.

Purpose of the Study:

• To measure the bending modulus of single-crystalline hexagonal boron nitride nanosheets (BNNSs).
• To investigate the relationship between BNNS thickness and their bending modulus.
• To explore the underlying reasons for the observed thickness-dependent mechanical behavior.

Main Methods:

• Utilized atomic force microscopy (AFM) to perform three-point bending tests on BNNSs.
• Fabricated microstructures by clamping BNNSs on SiO(2) trenches using metal films via electron beam lithography.
• Applied plate theory for doubly clamped plates under concentrated load to calculate the bending modulus.

Main Results:

• Measured the bending modulus of BNNSs with thicknesses ranging from 25 to 300 nm and sizes of 1.2-3.0 microm.
• Observed that the bending modulus increases as the thickness of BNNSs decreases.
• Found that thinner BNNSs (thickness < 50 nm) approach the theoretical C(33) value of hexagonal boron nitride single crystals.

Conclusions:

• The bending modulus of BNNSs is dependent on their thickness.
• Layer distribution of stacking faults is proposed as the cause for the thickness-dependent bending modulus.
• Stacking faults are also suggested to play a role in the layer-by-layer exfoliation process of BNNSs.