Study On Energy Dissipation In Tapping Mode Atomic Force Microscopy

Since its invention in 1986,the Atomic Force Microscope(AFM)has become the primary tool for surface topography imaging and quantitative measurement/draw physicochemical properties of various materials.Unlike most imaging techniques that rely on photon interaction,the AFM core component is a micro-cantilever that is extremely sensitive to weak forces,with one end fixed and the other end close to the surface of the sample,vibrating at the free end under excitation.The information to be scanned is obtained by the change in the intermolecular force.In the process of the free end of the micro-cantilever from the far and near approach to the surface of the sample,there are various effects such as squeeze film air damping effect,van der Waals force,electrostatic force,and liquid bridge.When the tip of the probe has not reached the surface of the sample and is in contact with it,the main effect is squeeze film air damping.Which is closely related to the distance between the tip and the sample.The squeeze film air damping has an important influence on the AFM scanning effect.The effect of different types of probes and samples on the vibration characteristics of the tapping mode AFM was investigatedFirstly,the frequency scanning experiment is carried out using the probe with the microsphere tip.The experimental results are verified by simplifying the action model of the micro-cantilever-probe-sample.The obtained one-dimensional oscillator model can accurately describe the squeeze film damping between the microsphere tip and samples including the effect of this effect on the vibration characteristics of micro-cantileverSecondly,the frequency scanning experiment of the same sample was carried out using a pyramid-shaped AFM probe with a tip shape,and the amplitude of the vibration in the amplitude-frequency curve was "truncated".Through qualitative comparison of van der Waals force and squeeze film damping force and the characteristics of "fine" and "long of such probe tip,it is considered that the film is mainly subjected to the squeeze film damping effect and the tip-sample when the tip-sample distance is far away.The closer to the van der Waals force role.The concept of "forbidden zone" when the needle tip and the sample are applied is proposed.Finally,the same frequency scanning experiment was performed using a tipless AFM probe,in which the probe was viewed as a micro-cantilever that vibrates under excitation.Then,the damping coefficient of the squeeze film is added to the vibration equation of the micro-cantilever.The numerical solution is obtained by using MATLAB to obtain the relationship between the quality factor and the tip-sample distance.The experimental results are compared to verify the accuracy of the model.