Mechanical Properties Of Two-Dimensional Materials Based On Blister And Nanoindentation Tests

Two-dimensional(2D)materials such as graphene,hexagonal boron nitride,silicene,black phosphorus and 2D transition metal dichalcogenides(TDMs)have attracted wide attention in recent years due to their atomic thickness crystal structures and novel physical properties.It is expected that they will have great application prospects in optoelectronic devices and structures,flexible devices,energy materials and other fields.In terms of materials and devices,the structural stability of 2D materials and the mechanical response under external field such as load and environment are particularly important for device fabrication,functionality,stability and lifetime of nanodevices.Owing to its atomic thickness,micro-nano manipulation and experimental mechanical measurement of 2D materials have been facing technical challenges.At present,the test methods for mechanical properties of 2D materials mainly include in situ mechanical measurement under scanning electron microscopy,nanoindentation test and blister test.For the continuous 2D material thin films prepared by chemical vapor deposition(CVD),the above technology is difficult to achieve high-throughput measurement of mechanical parameters.Therefore,it is urgent to develop high-throughput,fast,universal and in situ experimental testing technique for 2D materials.On the basis of obtaining the intrinsic mechanical parameters of 2D materials,it lays a foundation for regulating the optical and electrical properties of 2D materials by strain engineering.Recent theoretical predictions show that,compared with other TDMs materials,the strain-induced phase transition of molybdenum ditellurid(MoTe2)occurs more easily due to the smaller energy difference between the two phases.Previous studies have focused on the induction method of MoTe2 phase transition such as temperature field,laser irradiation and electrostatic doping,but few experimental studies have been reported on the mechanical response of MoTe2 under strain by experimental methods.In this paper,on the basis of the development of testing technique to obtain mechanical parameters of 2D materials,the mechanical properties of graphene and MoTe2 were systematically measured,and the strain engineering of MoTe2 tuning optical properties were explored.Our results are summarized as following:1.A universal through-hole bubble test for measuring Young's modulus of 2D materials was proposed,which can simutaneously realize continuous loading and in situ AFM characterization of mechanical response under controllable pressures.Taking monolayer and bilayer graphene as examples,the height and diameter of bubbles can be measured in situ by the through-hole bubble test combined with AFM.On the basis of Hencky solution,Young's moduli are obtained which are consistent with those reported in literature.Moreover,the stability of this method under triangular wave and sinusoidal wave cyclic loading was studied.It provides necessary technical support for the further study of mechanical properties of 2D continuous thin films prepared by CVD.2.Based on atomic force microscopy,the mechanical properties of 2H-and 1T'-MoTe2 were systematically studied by nanoindentation experiment.The dependence of intrinsic mechanical properties of MoTe2 nanosheets on the number of layers was discussed.Besides,the fracture mechanics behavior of 2H-MoTe2 film was studied.The effect of interlayer coupling on the mechanical properties of multilayer MoTe2 was revealed.In addition,the mechanical properties of 2H-MoTe2 and the relationship between strain and Raman characteristic peak position were studied by blister test.