Fracture Behavior And Mechanism Of 2D MoS₂ Van Der Waals Heterostructure

Two-dimensional（2D）nanomaterials have revived the research interest of researchers,and have gradually become a research hotspot in various disciplines.2D heterostructures assembled via van der Waals（vd W）interactions have attracted great interests due to their remarkable mechanical and electrical properties that can significantly influence vd W heterostructures（vd WHs）device.Understanding failure behavior of 2D vd WHs assembled is essential for disassembling the assembled vd WHs into individual building blocks.The previous experimental studies mainly focused on adhesion and friction of 2D heterointerface by vd W interaction and the 2D building blocks peeled by the mechanical exfoliation,however the failure phenomenon caused by vd W interaction has never been reported for 2D vd WHs.Molybdenum disulfide（Mo S₂）is one of the most frequently studied members of transition metal dichalcogenides（TMDs）,which has very attractive optical,electrical and mechanical properties.In this paper,the in-situ nanomechanical testing system was assembled in combination with the nanomechanical testing system in scanning electron microscope（SEM）,and the in-situ indentation adhesion stripping fracture method was proposed to study the Mo S₂failure behavior during vd WHs junction and assembly.The fracture strength of Mo S₂and the energy density at the interface between Mo S₂and Si O₂were measured theoretically.The main research contents and conclusions are as follows:1,MoS₂nanosheets with micron size and area were produced by chemical vapor deposition（CVD）method under the condition of modulation of the best parameters,and transferred to the interfingered electrode to provide experimental samples for in-situ indentation adhesion peel fracture experiment.2,The in situ mechanical test system was established,and the in situ indentation adhesion stripping fracture experiment was carried out for Mo S₂transferred to the interfingered electrode.SEM was used to record the experimental process in real time,and it was observed that Mo S₂was stripped from the substrate and formed bulges,and there were two destructive behaviors of penetration fracture and cleavage tear.3.The penetration fracture process of MoS₂was analyzed by plate and shell theory,and the fracture strength was 35.085 GPa.The cleavage tearing process of Mo S₂was analyzed by thin film tearing theory,and the energy density at the interface between Mo S₂and Si O₂was 0.4215 N/m.4.Density Functional Theory（DFT）was used to simulate the change of interface binding energy caused by interface separation with interlayer displacement during vd WHs peeling.The energy density of the interface between bilayer Mo S₂and Si O₂was 0.366 N/m.The tensile stress-strain curve of bilayer Mo S₂is calculated,and the ideal fracture strength of Mo S₂is 21-32 GPa.Molecular dynamics（MD）was used to simulate the experimental process of indentation adhesion peel fracture,and two kinds of failure behaviors were obtained,and the fracture mechanism of the two kinds of failure behaviors was explained qualitatively.