The Investigation On The Photoelectric Properties And Failure Behavior Of MoS₂ Nanosheets Under External Fields

Recently,two-dimensional nanomaterials have attracted more and more researchers'attention because of their potential applications in electronic/optoelectronic devices.Among them,molybdenum disulfide?MoS₂?consists of layered S-Mo-S structure which depends on van der waals force.The band gap ranges from 1.2 to 1.8 eV when the thickness is reduced from the bulk material to the single layer.The single-layer or multi-layer MoS₂ field effect transistor has a current on/off ratio of up to 10⁸.Therefore,layered MoS₂ is one of the most promising materials in the future of electronic applications.As devices such as electronic devices,sensors,and field effect transistors tend to be miniaturized,the channel length between source and drain is also shrinking.However,reducing the channel length to the nanometer size may result in properties that are different from macroscopic counterparts.At the same time,the research on the failure behavior of low-dimensional nanomaterials such as nanowires,nanobelts and nanosheets is still in the initial stage.Therefore,in-depth study of the optoelectronic properties and failure behavior of MoS₂ nanosheets under external field is essential for controlling and adjusting device performance.The main content of this paper include the following aspects.?1?Platinum?Pt?conductive substrates were prepared on single crystal silicon wafers by electron beam evaporation,and then layered MoS₂ nanosheets were prepared on the conductive substrates by the mechanical exfoliation method.The samples were annealed at250?for 1 hour in argon to remove tape residue and improve the quality of contact between the sample and the substrate surface.Finally,the microstructure of MoS₂ were characterized by optical microscopy,XRD,Raman and TEM.?2?In order to investigate the effect of loading force on the tunneling current of MoS₂nanosheets,we used a built-in photoelectric performance test system to apply a certain loading force on the surface of MoS₂ nanosheets and measure its I-V characteristic curve in situ.At the same time,the effects of voltage and sample thickness on photoelectric performance were investigated.A the oretical model of photo-electric coupling response is established to illustrate the coupling relationship between strain,light intensity and current density.The in-situ test scheme for the photoelectric properties of MoS₂ nanosheets under the light field was designed to realize the in-situ test of the force photon and electric coupling properties of semiconductor nanomaterials.?3?In order to establish the relationship between the morphology and the time and voltage,the morphology changes of MoS₂ nanosheets were recorded by adjusting the magnitude and time of applied voltage by C-AFM.The results show that the area and height of morphology change of MoS₂ nanosheets gradually increase with the increase of voltage and time.Then,the two-dimensional current distribution of MoS₂ nanosheets was measured by scanning the samples with C-AFM under different voltage conditions.We found that the darker areas of the current distribution of MoS₂ nanosheets are almost identical to the parts of its morphological changes.?4?The I-V and I-T characteristic curves of MoS₂ nanosheets were tested by increasing the time of the electric field to obtain the evolution of the photoelectric properties of MoS₂nanosheets.The I-V curve was fitted according to the formula,which is consistent with the experimentally measured I-V characteristic curve.The conductivity and current on/off ratio were calculated,and the results show that the electrical properties gradually deteriorate with the increase of morphology height.The current on/off ratio is gradually reduced to nearly 1,indicating that the change in the morphology of the MoS₂ nanosheet results in failure of the photoelectric properties.Finally,the failure mechanism of the photoelectric properties of MoS₂ nanosheets was investigated based on the thermal oxidation model.