Bending of Multilayer van der Waals Materials

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Multilayer van der Waals materials exhibit complex out-of-plane deformations (buckling, wrinkling, folding).
• Bending rigidity is a critical but controversial parameter influencing these deformations.
• Existing research has not resolved discrepancies in bending rigidity measurements for over a decade.

Purpose of the Study:

• To directly measure the bending rigidity of multilayer graphene, molybdenum disulfide (MoS2), and hexagonal boron nitride (hBN).
• To investigate the relationship between material properties and out-of-plane deformation in van der Waals multilayers.
• To resolve controversies surrounding the bending rigidity of these materials.

Main Methods:

• Utilized pressurized bubbles to induce controlled out-of-plane deformations.
• Varied sample thickness and bubble deflection to observe platelike responses.
• Applied nonlinear plate theory to extract Young's modulus and bending rigidity.

Main Results:

• Measured Young's moduli align with literature values (E_graphene > E_hBN > E_MoS2).
• Observed bending rigidity trends (D_graphene < D_hBN < D_MoS2) contradict classical plate theory for comparable thicknesses.
• Discrepancies are attributed to significant interlayer shear effects in van der Waals multilayers.

Conclusions:

• Direct measurements provide new insights into the mechanical behavior of multilayer van der Waals materials.
• The interlayer shear effect plays a crucial role in determining the bending rigidity of these systems.
• Findings challenge classical plate theory and offer a more accurate model for multilayer deformation.