Research On Controllable Synthesis Of Monolayer MoS₂ And Its Electronic Properties

Recently,with the rapid development of the chips industry,chips have trouble in shrinking the size,and demand for advanced chips has continued to grow.Two-dimensional ultra-thin nanomaterials have been widely studied as candidates that are expected to replace traditional silicon-based materials.Among them,single-layer molybdenum disulfide(MoS₂)has shown great application prospects due to its unique electrical,mechanical and optoelectronic properties.However,in order to realize the industrial application of monolayer MoS₂ ,it is necessary to solve the problem of uniform,high-quality monolayer monocrystalline MoS₂ and the unclear growth mechanism of MoS₂ .The quality of film crystals is difficult to achieve in the existing film preparation methods.It is guaranteed that the generated vacancy defects will also affect its mechanical and electrical properties.At the same time,insufficient research on the performance of MoS₂ largely limits the wide application of MoS₂ in electronic devices.This work mainly studies and explores the following aspects:1.Study on the controllable synthesis of uniform,single-layer and single crystal MoS₂ based on the chemical vapor deposition method.1)The growth conditions were optimized,especially the influence of the relative position of molybdenum source and substrate on the growth of MoS₂ thin films was discussed and analyzed.The film surface morphology and thickness,molecular structure,element composition and bonding,crystal structure,etc.were characterized and analyzed based on AFM,XPS,Raman,TEM advanced methods.Comparing the test results of different placement positions,it is concluded that the vertical placement of the substrate can reduce the nucleation density and secondary nucleation points,and achieve the uniformity of the spatial distribution of the growth of the monolayer molybdenum sulfide.At the same time,the gas flow rate and the distance between the molybdenum source and the substrate were optimized.The process parameters such as gas flow rate and the distance between molybdenum source and substrate are optimized to realize the controllable growth of monolayer two-dimensional MoS₂ with 80 micron and uniform distribution.2)Research on the growth mechanism of monolayer MoS₂.Based on the principle of boundary layer,hydrodynamics and the analysis of the growth results of different substrate positions,the mechanism of controlling the nucleation of two-dimensional MoS₂ and the uniform growth of monolayer were proposed by adjusting the relative position of molybdenum source and substrate to control the concentration of molybdenum oxide on the substrate surface.2.Study on the electrical properties of single-layer MoS₂ .1)Based on the piezoelectric force microscope(PFM),the out-of-plane piezoelectric properties of the single-layer MoS₂ were studied.The electrode was patterned through an etching process,and the films were transferred to the hollow substrate to bend naturally.Compared the piezoelectric amplitude of the film under different bending degrees.It is found that the bending of the film can improve its piezoelectric performance.2)Exploration of the strain-tuning photoelectric performance of the single-layer MoS₂ flexible devices.A single layer of MoS₂ was used as the channel material to prepare a flexible two-end device on a PI substrate,and mechanical tensile strain was applied to the device(strain parameters were 0%,0.2%,0.4%,0.5%),and the strain effect was studied through electrical testing.The electrical and optoelectronic properties of flexible devices are affected.It is found that as the tensile strain increases,the current and photocurrent also increase;3)The back-gate transistors based on single-layer MoS₂ were prepared,and the electron mobility(average value:1.9 cm²/Vs)and current switching ratio(?10⁷)of multiple devices were counted,indicating that the prepared monolayer MoS₂ has good uniformity.