Anisotropic Behavior Of Friction Properties Of MoS₂ Nanosheets Based On Atomic Force Microscopy

As the most popular two-dimensional material in nano-friction,MoS₂ has many properties such as lubrication,catalytic hydrogen evolution,energy storage and corrosion resistance,and it is also used in lubricants,hydrogen evolution catalysts,batteries and anti-wear coatings.Compared with other properties,MoS₂ has been the research focus of nanotribology for its important applications in solid lubricants,metal protective coatings and additives for micro-electromechanical systems.In the friction experiment of MoS₂,the friction performance of nano-materials is characterized as the friction,adhesion and ultimate shear stress.We further studied the friction of MoS₂ with the different layers based on atomic force microscopy?AFM?module technology.The friction properties of MoS₂ are varied under the different loads,adhesions and relative angles in order to quantitatively control the friction between MoS2 atomic layers.This paper is divided into three parts.1.Using the advanced modular technology of AFM,the changes of adhesion and friction of MoS₂ samples with the different thicknesses were measured under the different loads,and the software was developed to process multi-group friction data.The experimental results show that the greater the load,the greater the adhesion and friction forces of MoS2.The variations of adhesion and friction forces of MoS2samples with thick layers are bigger than those of thin layers.The software is developed to process multi group complex experimental data,and they can be efficiently fitted for the different periods at the same time in friction experiment.2.The friction coefficients of MoS₂ with different layers were measured at the different relative angles.The results show that the variation range of MoS₂ friction coefficient decreases with the increase of layers.In addition,the relationship between MoS₂ friction coefficients of different layers and relative angle is 180 degree anisotropy,and the friction coefficient reaches the maximum at 90 degree of relativity,and the minimum at 180 degree of relativity.The remarkable differences in friction properties provide theoretical basis for the study of atomic phase and"zero"friction,which guide the application of MoS2 lubrication performance.3.Based on B-JKR interface friction theory,we propose the model to characterize the ultimate shear stress of two-dimensional materials,before anisotropy of ultimate shear stress is measured at the different relative angles.The results show that the relationship between the ultimate shear stress of MoS₂ with different layers and the relative angle is 180 degree periodic,and the ultimate shear stress reaches the maximum at 90 degree of relativity,and the minimum at 180 degree of relativity.The larger the layers of MoS₂,the smaller the change range of the ultimate shear stress.They provides an important experimental support for quantitative selection of two-dimensional material properties,prediction and control of shear strength.