Research On In-Situ Mechanical Testing Method Of MoS₂ Two-Dimensional Material Mechanical Performance

With the development of science and technology,the size of structures and components are constantly developing in the direction of precision and miniaturization,so a new discipline-nano discipline has been developed.When the size of a material is reduced to nanometer,its strength,density,and physical and chemical properties are far cry from traditional materials.Two-Dimensional materials have good application prospects in the fields of flexible electronic devices,micro-electro mechanical systems,etc.due to their large specific surface area,atomic-level planar structure,extreme out-of-plane strain,and the excellent physical and chemical properties,have always attracted the attention of researchers.As a typical two-dimensional semiconductor material,MoS₂nanosheets are expected to complement graphene in the application of electronic devices,therefore they are selected as the research object.In terms of materials and devices,the structural stability and mechanical properties of two-dimensional materials under external loads and environments are very important for their service life and stability.However,traditional mechanical measurement methods cannot effectively measure two-dimensional materials with a thickness at the range of a few nanometer.Therefore,it is very important to develop accurate measurement and characterization methods with simple operation.Young’s modulus and fracture strength are the typical mechanical performance indicators,which have important research significance for the experimental measurement of them.In this paper,the Young’s modulus and fracture strength of MoS₂ are studied by using nanoindentation technology and designed in-situ adhesion fracture experiments.The main research contents and conclusions are as follows:1、MoS₂nanosheets with large size,uniform thickness,adjustable number of layers and good crystallinity were prepared by adjusting the experimental parameters of the chemical vapor deposition（CVD）method for the self-built CVD system,and they provide experimental samples to measure their Young’s modulus and breaking strength.2、Using the nanoindentation method,nanoindentation experiments were carried out on MoS₂ nanosheets grown on a single crystal silicon oxide substrate.The Oliver&Pharr model is used to calculate the hardness and Young’s modulus of MoS₂nanosheet,and they are 7.3 MPa and 110 GPa.3、The adhesion fracture experiment was designed according to the adhesion force between the probe tip and MoS₂ nanosheet was found in the indentation experiment.The charging effect often affects SEM’s imaging quality.By transferring MoS₂nanosheet to the interdigital electrode,the conductivity of the nanosheetis enhanced,and the van der Waals force between the nanosheet and substrate is reduced,making it easier to be pulled up by the probe.4、According to the deformation process recorded by SEM,the fracture of MoS₂nanosheet can be divided into adhesion deformation and tear.Through the analysis of the adhesion deformation and fracture,the Young’s modulus of MoS₂ nanosheet with the double-layer is calculated 206.37±10.8 GPa,and the fracture strength is 32.49±1.29GPa.Based on density functional theory,the Young’s modulus and breaking strength calculated as 225 GPa and 34 GPa for the MoS₂ nanosheet,,therefore the accuracy of the experimental measurement could be verified.