  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.
