EFFECT OF VISCOUS LIQUID FILM ON DYNAMIC CONTACT IN ATOMIC FORCE MICROSCOPY

Abstract

This letter incorporates squeezing flow with the Hertz contact theory in analyzing the dynamic behavior of an AFM tip in contact with an elastic substrate and a liquid film. To the first order of approximation, a new dynamic equation describing the motion of the AFM tip is presented, from which closed-form solutions of the stored contact modulus and loss contact modulus are obtained. The results show that the stored contact modulus depends on the frequency of the oscillation, the elastic properties of the elastic material and the mass of the tip, while it is independent of the viscosity of the liquid film. These provide a theoretical basis for the characterization of the elastic properties of biological materials and nanostructures by using the technique of continuous stiffness measurement.