Material-Dependent Evolution of Mechanical Folding Instabilities in Two-Dimensional Atomic Membranes

Area of Science:

• Materials Science
• Nanotechnology
• Mechanical Engineering

Background:

• Controlling 3D deformations in 2D materials is crucial for advanced applications like stretchable electronics and nanoelectromechanical systems.
• Understanding material properties' influence on 2D membrane morphology under mechanical stress is essential.

Purpose of the Study:

• To systematically investigate mechanical folding instabilities in uniaxially compressed monolayer graphene and MoS2 on a polydimethylsiloxane substrate.
• To analyze the material-dependent transition between different stress release mechanisms.

Main Methods:

• Atomic force microscopy (AFM) was used to examine membrane morphology under 0-33% compression.
• A simple shear-lag model was developed to analyze interfacial friction and adhesion.

Main Results:

• Observed evenly spaced folds with two distinct stress release mechanisms: delamination (low compression) and slipping (high compression).
• Identified material-dependent critical fold spacing for the transition: ~1000 nm for graphene and ~550 nm for MoS2.
• Quantified maximum interfacial static friction: 3.8 MPa for graphene and 7.7 MPa for MoS2 on polydimethylsiloxane.
• Observed a transition from standing to fallen folds in graphene at 8.5 nm fold height.

Conclusions:

• The study provides a framework for controlling nanoscale fold structures in 2D materials.
• Results are critical for designing stretchable or foldable nanosystems based on 2D materials.
• The findings highlight the interplay between material properties, substrate interactions, and mechanical deformation.