Study On The Dynamic Behavior Of Atomic Force Microscopy In Tapping Mode

The core components of Micro/Nano-electromechanical systems(MEMS/NEMS)——Micro-nano resonator has many superior performances such as high sensitivity,high quality factor,high resonance frequency,etc.The core component probe of the Atomic Force Microscopy(AFM)is a Micro-nano resonator.In the course of work,as the probe moves away from the sample surface to gradually approach the sample,and finally contacts the sample surface,the dynamic characteristics of the probe system has been changing.In this paper,by establishing the AFM dynamic model in tapping mode,the dynamic behaviors of the probe during the working process are analyzed and verified,and on this basis,a method to improve the imaging quality of the phase diagram is proposed and experimentally verified.The details are as follows:First,establish the dynamic model of the AFM system in tapping mode.The force analysis of the unit microelement on the micro-cantilever beam is carried out and the vibration differential equation of the Euler-Bernoulli beam model is solved.These continuum models are further simplified into single-degree-of-freedom mass-spring-damping systems,then the equivalent principles of the two models are derived and the concepts of equivalent damping and equivalent displacement excitation are proposed.Secondly,the energy dissipation mechanisms of the AFM system during operation are analyzed and verified.The model of air viscous damping dissipation when the probe is far away from the sample,the model of the air pressure film damping change when the probe is close to the sample and the broken model of the liquid bridge generation when the probe contacts the sample are established respectively.The sweep frequency experimental curves when probe away from the sample,close to the sample,or touching the sample verify the accuracy of the theoretical model.Finally,by analyzing the influencing factors of the phase shift of the AFM system,a method to improve the imaging quality of the phase map is proposed.When the probe is close to the sample surface,different probe-sample interaction mechanisms will cause the system’s damping characteristics and system stiffness to change;selecting different excitation frequencies according to the physical properties of the sample surface can increase the phase of the phase diagram.The amount of phase shift improves the imaging quality of the phase image;the relationship between the phase offset of different samples and the excitation frequency is analyzed through experiments to verify the accuracy of the theory.