| Graphene/MoS2van der Waal heterostructure can effectively combine high conductivity of graphene and wide band-gap of Mo S2,which has broad application prospects in flexible optoelectronics,semiconductors,photochemical sensors and other fields.Because the size of two-dimensional heterostructure is generally in micro/nano scale,the heterostructure needs to be assembled onto a macroscopic substrate,forming a composite structure for a better development and application in the devices.The key factors affecting the performance and life of the device mainly include the stability of this composite structure,the interfacial mechanical problems between the substrate and two-dimension materials,as well as those between the layers of heterogeneous materials respectively.Thus,to promote the development of its engineering application,a stable interface for two-dimension heterostructure should be provided and the interfacial mechanical behavior under large substrate deformation should also be studied.In this work,the graphene/MoS2van der Waals heterostructures were studied.Based on the existing wet-transfer methods,a new assemble method of van der Waals heterostructure was proposed for soft substrate with high toughness interface between substrate and two-dimension materials.The van der Waals heterostructure was established by transferring mono-layer graphene and then mono-layer Mo S2to the surface of PDMS/formvar composite substrate.In order to investigate the interfacical mechanical behavior of the heterostructure under different deformation conditions,a cross specimen was designed for bi-direction loading.The full-field distribution and value of the specimen strain were demonstrated under three loading states of equal biaxial,non-equal biaxial and uniaxial,by the method of finite element simulation（FEM）and digital image correlation（DIC）experiment.In view of the interfacical mechanical behavior of heterostructure under large substrate deformation,mechanical loading experiments of heterostructure were carried out.In the experiments,the spectral mechanical behavior of graphene and Mo S2were characterized by micro-Raman spectroscopy and fluorescence spectroscopy respectively.Firstly,the strain-frequency/wavenumber shift coefficients of graphene and Mo S2on PDMS/formvar composite substrate were calibrated,and the strain transfer capacity of PDMS/formvar composite substrate to the two-dimension materials was quantified.Then,equal biaxial,non-equal biaxial and uniaxial loading experiments were conducted,respectively.The transfer effects of the normal strain and normal stress to graphene and Mo S2layers were analyzed under different loading states.According to the experimental results,the competition phenomenon was found between the two interfaces during deformation transferring and consequently a phenomenological model was proposed to analysis the mechanism of stress and strain transfer at the interfaces of heterostructure. |
