Shear Failure in Supported Two-Dimensional Nanosheet Van der Waals Thin Films

Area of Science:

• Materials Science
• Nanotechnology
• Mechanical Engineering

Background:

• Liquid-phase deposition of 2D nanosheets enables technologies like electronic inks and protective coatings.
• Nanosheet films, held by van der Waals forces, can delaminate under shear stress, limiting applications.
• Understanding shear stability is vital for the reliability of nanosheet-based devices.

Purpose of the Study:

• To investigate the shear stability of graphene oxide and MoSe2 nanosheet films.
• To explore the influence of film thickness and cross-linking on shear strength.
• To develop a mechanical model explaining failure mechanisms in nanosheet films.

Main Methods:

• Fabrication of polymer-nanosheet-polymer laminates for lap shear experiments.
• Measurement of critical shear forces and fracture energies.
• Development and application of a mechanical model for failure analysis.

Main Results:

• Nanosheet films exhibited mixed cohesive and interfacial failure modes with critical shear forces of 40-140 kPa.
• Fracture energies (0.2-6 J/m²) were higher than expected, attributed to energy dissipation during crack propagation.
• Film thickness significantly impacted critical shear force and dissipated energy.
• A shear-to-tensile failure mode transition was observed in graphene oxide films with increasing thickness.
• Electrostatic cross-linking with metal cations enhanced the critical shear force of graphene oxide films.

Conclusions:

• The shear stability of 2D nanosheet films is influenced by film thickness and failure mechanisms.
• Higher fracture energies suggest robust energy dissipation in these discontinuous films.
• Graphene oxide films can be strengthened via electrostatic cross-linking, improving device stability.
• These findings are crucial for designing durable and reliable 2D nanosheet-based technologies.