Synthesis And Charaterization Of Two-Dimensional ZnO And MoS₂

Two-dimensional（2D）materials have excellent mechanical flexibility,high optical transparency,large transverse dimensions,large specific surface area,high electron mobility and unique surface structure,which have potential applications in flexible,piezoelectric,catalytic,sensing and energy storage,etc.The optical and electrical properties of 2D materials are sensitive to the structure of size,number of layers,morphology,grain boundaries,defects and doping,and further determine the performance of optoelectronic devices fields.Therefore,the practical application of 2D materials in optoelectronics is inextricably connected with controlled synthesis,which requires an in-depth study of the growth mechanism of synthesized 2D materials.We have systematically carried out research on the controllable preparation methods and intrinsic growth mechanisms of 2D materials containing layers and non-layers,such as Zn O and Mo S₂.The findings of this paper are as follows:（1）By using surfactant-assisted ionic layer epitaxy to synthesize 2D Zn O,the controlled growth of 2D Zn O was achieved by regulating the surfactant,temperature,precursor concentration,and growth time.And the growth mechanism was further explored.We find that the surfactant determines the location of nucleation and the number of nucleation;temperature controls the diffusive transfer of Zn²⁺/OH^-and the growth of 2D Zn O;the concentration of precursors mainly affects the Zn²⁺/OH^-number at the water-air interface,which in turn affects the size and thickness of 2D Zn O;suitable growth time promotes the growth of 2D Zn O,but too long growth time leads to the dissolution of 2D Zn O.The excellent growth parameters for 2D Zn O are following:the ratio of sodium oleyl sulfate to zinc ions was 10×10^-5,the temperature was 70℃,the precursor concentration was 50 m M,and the growth time was 50 min.Finnally,the 2D Zn O has a regular triangular shape,size up to 20μm and thickness down to 2.02 nm.（2）2D MoS₂ was synthesized by substrate trapping effect-assisted chemical vapor deposition method.The controlled growth of 2D Mo S₂ was achieved by the molybdenum source temperature,growth time,distance between the evaporation source and the substrate,and hydrogen flow rate.And the growth mechanism was further analyzed.The temperature in the material area determines the amount of highly active material Mo O_3-x;the increasing growth time promotes the growth of Mo S₂,but once exceeding the limit of the substrate trapping effect,an increased thickness is presented;the distance from the evaporation source to the substrate affects the amount of highly active material Mo O_3-x,which further influences the morphology,size and thickness of Mo S₂.Hydrogen as a reducing agent and catalyst can accelerate the generation of Mo O_3-x and provide sufficient active material Mo O_3-x for the growth of Mo S₂.However,the etching effect will be appeared accompanied with a small size and thick Mo S₂ when a high concentration of H₂ is performed.The optimized growth parameters are as follows:745°C in the molybdenum source,5 min of the growth time,16 cm between the evaporation source and the substrate,and 10sccm of the hydrogen flow rate.Soda lime glass enables the synthesis of uniform monolayers of Mo S₂ with the assistance of the substrate trapping effect.The size of the synthesized single-layer Mo S₂ is as large as 80μm.（3）Field effect transistors（FET）of MoS₂ were prepared and the optoelectronic properties of Mo S₂ were analyzed.The synthesized Mo S₂presents a favorable uniformity and excellent back-gate tunability.The migration of defects such as sulfur vacancies causes dynamic Schottky barrier modulation leads to hysteresis of output curves and transfer curves,which is originated from the carrier capture and release.The optoelectronic of Mo S₂ FET suggests the potential applications in artificial synaptic devices and neural networks.In this paper,the synthesis of non-layered 2D ZnO and layered 2D Mo S₂was studied to explore the effect of growth parameters and growth mechanism.Our results might promote the synthesis and development of ultrathin,large-size and regular-shaped 2D materials,and provide high-quality materials of ZnO and MoS₂ in artificial synapses and other optoelectronic fields.