Effects Of Light And Electric Field On The Eectrical Properties Of MoS₂ Nanometer Sheet

Two-dimensional layered transition metal sulfides?TMDs?,such as WSe₂,WS₂and Mo S₂,have excellent electrical and photoelectric properties,so they are widely used in electron and optoelectronics,and have attracted more and more researchers'interest.Among these layered semiconductors,Mo S₂has attracted much attention due to its direct bandgap of?1.9 e V,high electron mobility and current switch ratio.In this paper,the contact potential difference?CPD?of 1-6 layer Mo S₂nanometer sheets in an environment independent of light is characterized based on kelvin probe force microscope?KPFM?,and the physical mechanism of CPD change is discussed in detail.Finally,based on the conductive atomic force microscope?C-AFM?,the morphology,electrical and photoelectric properties of Mo S₂nanometer sheets were characterized under different loading voltages and different time intervals,and the changes of the morphology and electrical properties under the electric field were explained in detail.This paper mainly includes the following aspects of research:1. The development of 2D layered transition metal chalcogenides is described,especially the basic characteristics of Mo S₂nanosheets;afterwards,the current status of electrical research and applying on two-dimensional materials under light and electric fields.2. The sample preparation method of the Mo S₂nanometer sheet used in this experiment is introduced in detail,and then the instrument used to characterize the structure and morphology of the nanosheet were described.Then the surface potential and electrical signal of the nanometer sheet were tested by using KPFM and C-AFM technology.Finally,the morphologies of Mo S₂nanometer sheets under different loading voltages and action times are loaded.FEM simulation and modified thermal oxidation models are used to explain the mechanism of morphology changes of oxidation induced by electric field.3. The Mo S₂principle device of atomic channel length was constructed by C-AFM technique.The current dramatically drops with the thickness increase of Mo S₂-Mo O₃heterostructure at the voltage of 0.5 V for the loading time intervals,and the decline of barrier height 0.39 e V is verified by combining with Fowler-Nordheim Tunneling model and density functional theory.On the other hand,the difference of barrier height is 0.3 e V for density functional theory simulation,and it approaches the experimental result.4. The CVD method was used to prepare Mo S₂nanosheets with different layers,and the morphology was characterized by AFM to determine the number of layers,and then confirmed according to the peak distance of the Raman main peak.The KPFM was used to test the CPD of the Mo S₂nanosheets with 1-6 layers in the absence of light,and it was found that when the number of layers of the Mo S₂nanosheets increased,the shielding effect became larger and the gradual decrease.In the presence of light,the CPD increases in odd layers and decreases in even layers.The mechanism is explained by combining piezoelectric and photovoltaic theory.