Experimental Study On Mechanical Properties Of Multilayer Two-dimensional Materials

Owing to the unique two-dimensional crystal structure and novel physical properties,the well-known two-dimensional materials such as graphene,transition metal chalcogenide and hexagonal boron nitride gradually become the new darlings in many application fields.Their excellent optical,thermal,electromagnetic properties and good flexibility,light transmission and other functional properties have received widespread attention,while their mechanical properties determine the overall performance and lifetime of devices and composite materials.However,in previous works upon the mechanical characterization on 2D materials,the multilayer system is typically treated as a single sheet where the influence of interlayer interaction on the deformation is often overlooked.Additionally,the increasingly dominant role of bending stiffness in the deformation with growing thickness also lacks enough attention in the mechanical analysis.In this paper,the bending stiffness effect of two-dimensional materials in the deformation process and the effect of coupling between different layers in the multilayer system on the measurement of mechanical properties were studied.Our results are summarized as following:1.Based on the AFM nanoindentation tests,the mechanical properties of multi-layered two-dimensional materials were studied.The force-displacement curves of nanoindentation were analyzed from the behavior of the membrane to the behavior of the plate.The "flexibility method" was used to calculate the thickness of the two-dimensional material.Young's modulus,by comparing the layer correlations of the mechanical properties of different two-dimensional materials,then it revealed the influence of the different interlayer coupling on the measurement of Young's modulus.2.Based on bubbling tests combined with atomic force microscopy(AFM)technology,the mechanical properties of multi-layered two-dimensional materials were studied.By controlling the initial loading pressure to achieve the bulging of different shapes,such as spherical cap shapes and bulge-shaped blisters.The membrane theory and nonlinear plate theory were used to describe their micromechanical behaviors,and then the mechanical parameters such as bending stiffness were extracted.The relationship between the mechanical properties of different two-dimensional materials and the number of layers is obtained,and it revealed the influence of the different interlayer coupling on the measurement of mechanical properties.