Molecular Dynamics Simulation And Experiment Study On Wear Mechanisms Of Single Crystal Silicon Tip With AFM Tapping Mode

The tapping mode of the atomic force microscope is an important tool for nanometer measurement,and it is widely used because it can eliminate lateral forces and reduce damage to samples.However,the tip will wear when striking the sample,which will reduce the lateral resolution of the instrument.It has been shown that the scanning parameters such as amplitude setpoint and free amplitude and the impact in the tapping mode measurement will affect the wear of the single crystal silicon tip by changing the kinetic energy at the tapping,but the wear mechanism in the tapping mode is not clear.Therefore,in this paper,a combination of molecular dynamics simulation and experimentation methods was used to study the wear mechanisms of the single crystal silicon probe in the tapping mode from the characteristic of tapping kinetic energy.The main contents are as follows:(1)Based on the simulation scale and the working characteristics of the probe,a three-dimensional molecular dynamics simulation model was established,which is suitable for tapping mode.And it was found that the deformation of the tip and the loss of kinetic energy was the same when the tips with the different mass and the same kinetic energy were tapping with the sample,which proves that the molecular dynamics simulation model is correct and reliable.(2)The effects of kinetic energy on the wear of single crystal silicon tip were studied by simulation.The wear mechanisms of the single crystal silicon tip base on the kinetic energy under the tapping mode was proposed by combining with the change of the overall deformation and microstructure of the tip during the single tapping.The wear mechanisms can be expressed as an Atom-by-atom wear mechanisms in contact surface when the tapping kinetic energy is low,and a plastic deformation and edge fracture wear mechanisms caused by phase transition and dislocation when the tapping kinetic energy is high.(3)Based on the characteristics of practical measurement,the effect of multiple tapping on the tip wear was investigated by simulation.The distribution and variation of microstructure in two tapping were compared and it is can be pointed out that the phase transformation in continuous tapping will be suppressed to a certain extent.The dislocation will be further expanded,which will lead to brittle fracture caused by cracks.(4)The relationship between the tapping kinetic energy and the blunt radius and the wear characteristics of the single crystal silicon probe in the tapping mode was studied experimentally.The wear mechanisms of the tip was found to be the Atom-by-atom wear,which wear rate starts very fast,then the speed becomes slower,and after a while,the wear speed increases,and finally the smooth change.It is also found that under high kinetic energy percussion,the fracture wear of the needle tip is different in the early and late stages.The fracture in the early stage is transverse,which caused by the contact state and the stress,and the later fracture wear is longitudinal spalling,distributed at the edge of the tip,which is caused by dislocation.The later longitudinal spalling fracture can greatly increase the wear speed of the tip.