Intrinsic Wrinkling of Free-Standing Polycrystalline Atomically Thin Films

Area of Science:

• Materials Science
• Nanotechnology
• Mechanical Engineering

Background:

• Atomically thin films, such as transition metal dichalcogenides, are synthesized at wafer scale with monolayer thickness.
• Extreme aspect ratios challenge existing methods for measuring mechanical effects of intrinsic features like polycrystallinity.
• Pinned boundaries and solid substrates interfere with direct measurement of mechanical properties in 2D materials.

Purpose of the Study:

• To develop a versatile approach for measuring mechanical properties of large-scale free-floating 2D membranes.
• To investigate the influence of intrinsic features, specifically polycrystalline grain size, on wrinkle formation and mechanical behavior.
• To understand and engineer strain-controlled nanomechanical responses in 2D materials.

Main Methods:

• Realization of large-scale free-floating membranes on water.
• Measurement of mechanical properties using atomic force microscopy (AFM) adapted to water's surface.
• Characterization using Raman spectroscopy adapted to water's surface.
• Application of continuum theory and minimal mathematical models.

Main Results:

• Free-standing polycrystalline membranes spontaneously form large athermal wrinkles.
• Wrinkle size and shape are dependent on the polycrystalline grain size of the 2D material.
• Wrinkles introduce dramatic softening and spatial heterogeneity in mechanical response.
• Experimental demonstration of altered mechanical properties due to intrinsic wrinkles.

Conclusions:

• The study illuminates the mechanics of polycrystalline nanomaterials at extreme aspect ratios.
• Polycrystalline grain size is a key factor in intrinsic wrinkle formation in 2D materials.
• Principles for engineering strain-controlled nanomechanical responses are suggested.