Exploring The Plasticity Effect Of Afm Probe Tips On Samples

During the operation of an atomic force microscope(AFM),recording the phase shift of the tip can generate phase image information of the sample,which has an irreplaceable advantage over the topography image in reflecting the different characteristics of multi-component samples.The phase shift of the tip is related to the energy dissipation of the tip.During vibration,the tip is affected by various energy dissipations,such as air adhesion,squeeze film,liquid bridge,and contact adhesion,plastic deformation,among which the most important sample characteristic information is only related to the adhesion dissipation of the tip after contacting the sample,while other energy dissipations will interfere with the phase information of the sample.Plastic deformation caused by tip contact with the sample is an important energy dissipation process where atoms in the sample create dislocations,frictional resistance occurs and tip energy is lost in the form of heat,changing the phase of the tip.To investigate whether plastic deformation occurs and the magnitude of the energy dissipation during tip tapping of the sample,this paper uses a combination of molecular dynamics simulation and experiment to perform repeated nanoindentation tests.First,a molecular dynamics simulation model is established and single crystal copper is selected as the simulation sample in the experiment.The simulation algorithm and boundary conditions are set accordingly.A single crystal silicon spherical indenter is selected,and the potential functions between Cu-Cu atoms and Cu-Si atoms are determined,and relaxation is performed in the microcanonical ensemble.To ensure that the model structure is not destroyed,a three-layer structure including a fixed layer,a constant temperature layer and a Newton layer is established for nanoindentation simulation.To eliminate the effect of indentation speed,different indenter loading cycles are selected for preliminary experimental analysis,and finally the loading cycle that can eliminate the speed effect is determined.After ten repeated nanoindentations,the relationship between indentation force and indentation depth is obtained and its energy dissipation is calculated.At the same time,based on the dislocation extraction algorithm and the common neighbor analysis method,the interaction relationship between the tip and the copper atoms during the indentation process is analyzed.Secondly,nanoindentation tests are performed in AFM Ramp mode to obtain the original force-displacement curve data.The original piezoelectric displacement data is converted into tip-sample distance to obtain the forcedistance curve,and its energy dissipation value during indentation is calculated.Through simulation and experimental verification,it is found that the tip tapping causes plastic deformation of the sample and generates dislocation rings,but its energy dissipation decreases sharply with increasing indentation times and remains stable,so the energy dissipation value can be ignored in the actual AFM detection process.