Molecular Dynamics Simulation Of Molybdenum Disulfide Surface SPM Imaging

Sandwich atomic layer monolayer molybdenum disulfide has excellent physical and chemical properties and has great potential application in the field of micro-nano photoelectric components.Scanning probe microscope(SPM),which includes atomic force microscope(AFM)and lateral force microscope(LFM),is one of the main nano-characterization techniques used to characterize the surface properties of monolayer molybdenum disulfide.However,the experimental study of the surface characteristics of monolayer molybdenum disulfide by SPM has failed to directly observe and reveal the atomic scale information and dynamic evolution process of the lattice structure of the monolayer molybdenum disulfide.In this paper,the elastic hysteresis phenomenon and the high-resolution atomic imaging problem in AFM indentation characterization technique of monolayer molybdenum disulfide,and the high-resolution atomic imaging of friction force based on LFM are discussed.The surface/ interface mechanical properties of the monolayer molybdenum disulfide were studied by molecular dynamics simulation(MDs)method,and the nano-mechanism of SPM characterization of the surface characteristics of the monolayer molybdenum disulfide was revealed.The main research work is as follows:Firstly,the AFM indentation experiment of a circular monolayer molybdenum disulfide film was simulated by MDs method.The load-deflection displacement curve was recorded and the mechanical properties such as Young’s modulus and ultimate stress of the monolayer molybdenum disulfide were obtained by the data fitting method.The results show that the AFM indentation experiment of the monolaye molybdenum disulfide is difficult to directly observe and identify the local lattice structure phase transition,and the cyclic ballast-unloading process further reveals the plastic transformation mechanism.In addition,it is found that the effect of the shape and size of the monolayer molybdenum disulfide on the ultimate stress is almost negligible.Then,the AFM scanning imaging of monolayer molybdenum disulfide film and the influence of tip size and tip-sample spacing on AFM scanning imaging are simulated by MDs method.The normal force and scanning displacement curve of AFM probe during the moving process are recorded.The results show that under the same tip-sample spacing condition,the smaller the tip radius is,the higher the resolution of AFM scanning imaging is,and the clearer the details are.However,for the tip with larger radius,such as the worn probe,increasing the tip-sample spacing properly can also obtain the same imaging quality as the tip with small radius.The research results are of great theoretical significance to improve the resolution of AFM scanning imaging of monolayer two-dimensional nanomaterials and reduce the cost of probe in scanning experiments.Finally,the LFM scanning imaging of monolayer molybdenum disulfide film and the influence of tip size and tip-sample spacing are simulated by MDs method,and the lateral friction force-scanning displacement curve is recorded.The surface morphology of monolayer molybdenum disulfide was obtained.The results show that the periodic characteristics of friction force-scanning displacement curves can represent the lattice constants of monolayer molybdenum disulfide.When the probes with different tip radius scan along the armchair direction on the surface of monolayer molybdenum disulfide,there is a typical atomic-scale stick-slip phenomenon,and the small radius tip even appears a sub-nano scale stick-slip phenomenon.If the tip-sample distance is adjusted reasonably,the surface topography imaging resolution of the small radius tip can also be achieved by the tip with larger radius.The results provide new insights into the atomic-scale friction behavior and mechanism of two-dimensional nanomaterials.