Property Modulation Of 2D MoS₂ By Force,Photon And Electric Coupling Effect And Its Potential Device Application

The miniaturization of electronic components has promoted the rapid development of low-dimensional nanomaterials,and two-dimensional(2D)materials has attracted much attention owning to their small size.2D MoS2 semiconductor has great promise for new-generation photoelectric information technology due to their outstanding electronics and optoelectronics properties,good thermal stability,diverse preparation methods and flexible and transparency character.However,the performance and preparative technique of 2D MoS2 still face many problems and challenges.In this work,the effect of force,photon and electric coupling on the Raman scattering,band structure,surface potential,transport properties of CVD growth 2D MoS2 were systematically studied.And the influence rules and mechanisms of force photon and electric coupling effect on transport performance were discussed.The details are summatized as follows:Few layers continuous polycrystalline,monolayer and bilayer single crystal MoS2 were synthesized by CVD method under optimized preparation process parameters,the morphology and crystal structure of grown MoS2 were characterized by Raman spectroscopy,AFM,SEM,XRD and XPS,and the growth mechanism was discussed.The effect of polarized and orbital angular momentum(OAM)light on Raman scattering and band structure of 2D MoS2 were investigated.We found that the frequency and intensitiy difference of E2g1 and A1g Raman peaks of MoS2 is associated with the crystal orientations of monolayr MoS2 and stacking modes of bilayer MoS2.With the increase of linear polarization angle of the excitation light,the frequency difference of the Raman characteristic peaks of the monolayer MoS2 decreases from 19.5 cm-1 to 16.3 cm-1 monotonously,while the intensity difference increases to a max value at 90° and then decreases.Under the coupling effect of circular polarized and OAM light,with increasing of OAM,the alternate changed intensity of E2g1 and A1g peaks was probed by the circularly polarized light.The band gap of the monolayer MoS2 gradually increases to a certain value with the increase of OAM,while the bilayer MoS2 increases monotonously and can be tunned in a large range.The effect of thickness,morphology,substrate and light intensity on the surface potential of 2D MoS2 were systematically studied by using a KPFM apparatus.The surface potential of MoS2 gradually decreases with increasing thickness of it due to the enhancement of screening effect.The morphology of the sample can also affect the surface potential.The surface potential of MoS2 can be tunned by different substrates through forming different interface.With the increase of light intensity,the surface potential of monolayer MoS2 on Si/SiO2 substrate decreases while increases on Pt substrate.The variation of surface potential can be explained by the change of surface adsorption,charge transfer,photovoltaic effect and local electric field.The vertical transport behavior of bilayer MoS2 was studied in situ on a C-AFM apparatus and was also explored the force,photon and electric coupling effect.The tunneling current across vertical of bilayer MoS2 is confirmed by a Simmons approximation,which is direct tunneling at low bias and Fowler-Nordheim tunneling at high bias.The tunneling current drops surprisingly when we continually increase the force,and the dropping point is altered by the provided light,decrease from 500 nN to 350 nN.The potential mechanism is attributed to the changed of tunneling barrier height and width.The force photon and electric coupling effect of in plane monolayr MoS2 was studied on a flexible device.The strain was applied by three-point bending method and the effect of strain on the current cross different orientations of monolayer MoS2 was investigated.The piezoelectric effect was observed in the"armchair" direction when applied 1%strain,the Schottky barrier height of two terminals asymmetric changed by piezoelectric effect.The photoelectric performance of the device was significantly improved.When the strain reaches to 2.2%,the current increases markedly due to the piezoresistive effect,while the photoresponsive performance is deteriorated.The current in the "Zigzag" direction increases on both side under 1%strain due to the piezoresistive effect,but the photoresponsive performance is almost unchanged.This work provides a new way to explore the interaction between light and matter,design ultra-short channel electronic devices and force sensors,and has significance for improving the photoelectric performance and developing photon and electric coupling devices of 2D materials for photoelectric information technology.