Free energy analysis of system comprising biased atomic force microscope tip, water meniscus and dielectric surface

TL;DR

This paper analyzes the free energy of an AFM system with a water meniscus and dielectric surface, revealing how electrostatic potential influences equilibrium distance and highlighting water polarization as key for mechanical work.

Contribution

It provides a detailed free energy analysis of the AFM system, emphasizing the roles of tip bias, cantilever stiffness, and water polarization in system behavior.

Findings

Equilibrium distance increases with applied electrostatic potential.

Water polarization enables mechanical work during tip retraction.

Variations in dielectric constants and film thickness have lesser effects.

Abstract

We are concerned with free energy analysis of the system comprising an AFM tip, water meniscus, and polymer film. Under applied electrostatic potential, the minimum in free energy is at a distance greater than the initial tip--substrate separation in the absence of potential. This equilibrium distance, t_0, mostly depends on the tip bias V and cantilever spring constant k_s, where as variations of t_0 is less pronounced with respect to the dielectric constants, and polymer film thickness. Polarization of water meniscus under the AFM tip appears to be the dominant factor enabling the creation of mechanical work for tip retraction.