Number density distribution of solvent molecules on a substrate: a transform theory for atomic force microscopy

Area of Science:

• Surface science
• Physical chemistry
• Nanotechnology

Background:

• Atomic force microscopy (AFM) in liquids measures forces between a probe and substrate.
• Force curve shape relates to substrate hydration structure.
• A practical theory to link force curves to hydration structure was lacking due to challenges in modeling confined liquids.

Purpose of the Study:

• To develop a robust and practical theory for transforming AFM force curves into hydration structure.
• To demonstrate the theory's application in analyzing solvent molecule distribution.
• To determine the effective diameter of AFM probe apexes.

Main Methods:

• Proposed a novel transform theory to analyze force curves from liquid-based AFM.
• Utilized a high-resolution AFM with an ultrashort cantilever for measurements.
• Applied the theory to reproduce hydration structure from experimental force curves.

Main Results:

• Successfully generated the number density distribution of solvent molecules on a substrate from AFM force curves.
• Reproduced the hydration structure of a muscovite mica (001) surface.
• Obtained the effective diameter of the AFM probe apex.

Conclusions:

• The developed transform theory enables the conversion of force curves into detailed hydration structures.
• This significantly enhances AFM capabilities for solid/liquid interface analysis.
• The method provides crucial data for molecular-scale simulations and probe design.