Preparation And Electrical Properties Of Monolayer Molybdenum Disulfide By Chemical Vapor Deposition

Two-dimensional transition metal chalcogenides have a different tunable band gap from the graphene with zero band gap,and exhibit excellent optical and electrical properties,which have aroused research interest in a wide range of interdisciplinary fields.Due to its robustness,molybdenum disulfide has become the main research object in the two-dimensional transition metal chalcogenide family.However,mass production of wafer-size continuous and uniform monolayer molybdenum disulfide films is still a challenge that hinders its industrial application.At present,chemical vapor deposition is considered to be an effective and simple technique for large-scale synthesis of large-area monolayer molybdenum disulfide thin films.However,the disadvantages of the traditional chemical vapor deposition method are that the metal precursors have low pressure and high melting point,so it is difficult to obtain the large size monolayer single-crystal film,and most of the grown polycrystalline molybdenum disulfide has more grain boundaries,which makes the device performance decline sharply.In this paper,a simple and low-cost chemical vapor deposition method is proposed.By precisely controlling the mass percent concentration of sodium chloride solution and the thickness of molybdenum film deposited by electron beam evaporation,and cooperating with the modification effect of oxygen plasma on the substrate,large area single-crystal molybdenum disulfide can be synthesized in a controllable manner,the maximum size can reach 300?m,and the optimal growth value of the mass percentage concentration of sodium chloride solution is between 1%and 3%.In addition,the research also found that an appropriate increase in sodium chloride could affect the edge growth rate of sulfur and molybdenum,thereby affecting the relative stability of the growth mode of the crystal.This provides a new insight and research direction for the specific mechanism of fractal growth,which can also be used for the controllable growth of molybdenum disulfides with high-density molybdenum-terminated edges for catalytic applications.Raman spectroscopy and photoluminescence spectroscopy showed that the growth single-layer molybdenum disulfide showed excellent optical properties,and then the PVA-assisted transfer method was used to transfer the monolayer molybdenum disulfide to a clean Si/Si O₂substrate.The electron mobility of the fabricated field-effect transistor is 0.868 cm² V^-1S^-1,the switching current ratio is 10⁴,the subthreshold swing is 2.66V/dec,and it shows n type characteristics.This work is compatible with silicon-based device manufacturing processes,and provides some insights in the industrial mass production of wafer-size monolayer two-dimensional transition metal chalcogenides,and promotes the wide application of two-dimensional transition metal chalcogenides and other two-dimensional nanomaterials in practical fields such as electronics and optoelectronics.