Hamaker Constants of van der Waals Materials under Clean-Interface Conditions

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Adhesion is vital for van der Waals (vdW) materials and heterostructures.
• Reported adhesion strengths vary widely, complicating links between microscopic forces and macroscopic properties.

Purpose of the Study:

• To experimentally determine clean-interface adhesion strengths for vdW materials.
• To establish benchmark values for dispersive interactions.
• To investigate the influence of humidity on adhesion.

Main Methods:

• Utilized ultrahigh vacuum atomic force microscopy (AFM) with calibrated probes.
• Employed in situ thermal cleaning and realistic contact distances.
• Performed static adhesion spectroscopy and noncontact frequency-modulation AFM (FM-AFM).
• Investigated adhesion under controlled humidity cycles.

Main Results:

• Extracted mixed Hamaker constants for SiO2 with few-layer graphene (12 × 10⁻²⁰ J), MoS2 (13 × 10⁻²⁰ J), and SiO2 (6.1 × 10⁻²⁰ J).
• Static adhesion and FM-AFM measurements showed consistent interaction scales.
• Humidity significantly enhances adhesion, with capillary forces causing reversible increases.

Conclusions:

• Established benchmark values for clean-interface dispersive interactions in layered materials.
• Humidity is a major factor contributing to the variability in reported adhesion values.
• Results enable quantitative comparisons with theoretical models like Lifshitz theory.