Analysis of AFM cantilever dynamics close to sample surface

Robotic Research Laboratory, School of Mechanical Engineering, Iran University of Science and Technology, Tehran 18846, Iran

^a e-mail: hkorayem@iust.ac.ir

Received: 14 August 2012
Revised: 19 March 2013
Accepted: 31 May 2013
Published online: 26 July 2013

Abstract

For imaging and manipulation of biological specimens application of atomic force microscopy (AFM) in liquid is necessary. In this paper, tapping-mode AFM cantilever dynamics in liquid close to sample surface is modeled and simulated by well defining the contact forces. The effect of cantilever tilting angle has been accounted carefully. Contact forces have some differences in liquid in comparison to air or vacuum in magnitude or formulation. Hydrodynamic forces are also applied on the cantilever due to the motion in liquid. A continuous beam model is used with its first mode and forward-time simulation method for simulation of its hybrid dynamics and the frequency response and amplitude versus separation diagrams are extracted. The simulation results show a good agreement with experimental results. The resonance frequency in liquid is so small in comparison to air due to additional mass and also additional damping due to the viscosity of the liquid around. The results show that the effect of separation on free vibration amplitude is great. Its effect on resonance frequency is considerable too.