Research On Mechanical Properties Of 2D MoS₂ Assembled In Van Der Waals Heterostructures

Two-dimensional（2D）materials,for instance,molybdenum disulfide（MoS₂）of transition metal chalcogenides（TMDs）,have received people’s high attention for their remarkable electrical,chemical,optical,thermal,and mechanical properties.Especially,van der Waals（vdW）interlayer interactions between 2D materials provide considerable flexibility for integrating materials of different heights without the limitations of traditional lattice mismatch and other material incompatibilities.Therefore,the new generation of optoelectronic devices based on 2D materials has received high attention.Further,the assembled van der Waals heterostructures（vdWHs）could be disassembled into individual 2D materials and reassembled with different combinations,sequences,angles and hence different device functions.Once vdWHs disassembled,2D mechanical properties,for instance Young’s modulus of 2D materials assembled and vdW interlayer binding energy density,become the most critical properties for the application of diverse vdWHs devices.However,Young’s modulus of 2D materials assembled and disassembled in vdWHs can hardly be probed mainly due to the lack of technology for detecting the mechanical properties of vdWHs assembled for the present methods.Therefore,understanding mechanical behaviors,such as Young’s modulus and interface adhesion force of 2D building blocks at vdW heterointerfaces is the key to the sophisticated construction of assembled vdWHs and manipulation of 2D vdWHs devices.Combining in situ nanomechanical testing system and scanning electron microscope（SEM）technologies,we report a novel in situ indentation adhesion peeling method to precisely measure Young’s modulus of 2D MoS₂ assembled in vdWHs.The concrete research contents and results are as follows:1.Different layers of 2D MoS₂ nanosheets were grew by chemical vapor deposition（CVD）method under adjusting different parameters,and transferred to the interdigital electrodes by wet method to form MoS₂/SiO₂ vdWHs.MoS₂/SiO₂ vdWHs were prepared by in situ indentation adhesion-scrape to fracture method,then characterized by different micro-nano test methods.2.The bulges formed by the vdW interaction between the vdW interface of W/MoS₂ and MoS₂/SiO₂ vdWHs were observed by the in situ indentation adhesion peeling method.The adhesion force and bulge size of the interface which was measured by the nanomechanical testing system and SEM were analyzed based on theory of plates and shells.The Young’s modulus of the individual 2D materials disassembled from vdWHs was calculated that Young’s modulus of bilayer and 8 layers MoS₂ is 238.64±19 GPa and 191.60±23 GPa.3.The Young’s modulus and interface binding energy density of bilayer and 8 layers MoS₂were calculated by density functional theory,which verified the accuracy of the test method of Young’s modulus by in situ indentation adhesion peel method.And The competition mechanism of vdW interfacial separation is explored by DFT.4.The electromechanical control performance of MoS₂ vertical electronic devices was explored in C-AFM.By analyzing I-V curves,it was indicated that with the increase of loading force,the resistance on MoS₂ decreased,the current output value increased,and the conductivity increased.Then the corresponding mechanism was explained based on experimental results.Meanwhile,based on the electrochemical workstation and semiconductor analyzer,the photoelectric performance of MoS₂ in-plane electronic devices was explored.With the increase of laser intensity,photogenerated electrons promote the transport current of MoS₂ in-plane electronic devices also increased.