The Anisotropy Of Two Dimensional Transition Metal Sulfide Friction And Critical Shear Stress

There is the weak van der Waals force between the transition metal sulfide?TDMs?layered structures,so that it has the weak shear strength between the layers.Since TDMs is of excellent friction characteristics and mechanical properties,it has been widely used in surface lubrication,sensor parts and energy devices of mems.The frictional anisotropy has an important effect on the frictional performance of mems regulated by two-dimensional materials as solid lubricants.There are many studies on the friction anisotropy of two-dimensional materials,but the mechanism of periodic anisotropy of friction is controversial.In this paper,the anisotropy of friction and critical shear stress of TDMs are investigated by the advanced atomic force microscope technique.1. MoSe₂nanometer sheets were prepared by CVD method and characterized by AFM and Raman.The friction and critical shear stress of MoSe₂nanometer sheets were measured under different normal forces with rotation angle.The periodicities of the nano-friction and critical shear stress are analyzed by the two-dimensional material honeycomb lattice,and the anisotropy of the critical shear stress is consistent with that of the friction.2. By rotating the sample,the atomic image and friction contour curves of the MoSe₂ nanometer sheet were obtained at rotation angles of 0,15 and 30 by using the atomic image module of AFM.The stick-slip behavior of the tip along the lattice orientation of MoSe₂ surface and the friction contour force curve of atomic scale image were simulated based on the two-dimensional PT model.3. MoS₂nanometer sheet was prepared by mechanical stripping method,and the morphology and composition of MoS₂nanometer sheet were characterized by AFM,XRD and Raman.The friction and critical shear stress of MoS₂nanometer sheets were measured under different normal forces with rotation angle.The anisotropies of the friction force and critical shear stress of the MoS₂nanometer sheet show the periodicity of 180°,and the periodicity of the nano-friction is the same as that of the graphene frictional anisotropy caused by the folding effect.Friction anisotropy is caused by the formation of ripples on the surface of MoS₂nanosheets.The wrinkle effect can be used to explain the 180°periodicity of the anisotropy of friction and critical shear stress of MoS₂ nanosheets.