Preparation Of Graphene,Boron Nitride And Heterojunction By Chemical Vapor Deposition

In recent years,two-dimensional materials have set off a research boom in the scientific research community.Graphene is favored by most researchers because of its excellent properties-high electron mobility,large specific surface area,excellent light transmittance,high thermal conductivity,high Young's modulus and hardness.However graphene is a semi-metal with zero band gap.The two-dimensional hexagonal boron nitride?h-BN?has a similar structure to graphene,due to its excellent thermal stability,good thermal conductivity and electrical insulation,unique ultraviolet luminescence properties,high mechanical strength and dielectric properties,h-BN have very broad application prospects in optoelectronic devices,multi-functional coating materials and dielectric materials.The quantum Hall effect fractal energy spectrum was found in the graphene/h-BN heterojunction and the carrier mobility of graphene-based device based on h-BN film have been greatly improved.The appearance of graphene/h-BN heterojunctions has brought a new direction for the study of graphene and h-BN.How to prepare high-quality,large-sized two-dimensional materials has become a research hotspot.Chemical vapor deposition?CVD?is the most promising method for preparing large-size,high-quality two-dimensional materials.This paper studied the preparation of two-dimensional materials by CVD method,which mainly has the following contents:?1?Large-area,high-quality,layer-controllable graphene was prepared rapidly on polycrystalline nickel foil by laser chemical vapor deposition,which use a continuous laser with low power density and super Gaussian distribution as a heating source.We modified the growth time,laser power density,cooling rate and methane concentration to control the quality and layer number of graphene,3-29 layers of graphene were obtained;the prepared samples were characterized by optical microscopy,scanning electron microscopy,transmission electron microscopy and Raman.The sample identified as graphene by Raman spectroscopy.In the Raman spectrum,the defect peak?D peak?of graphene is low or even absent,indicating that graphene is of high quality.?2?Large single crystal h-BN was synthesized by low pressure chemical vapor deposition?LPCVD?,using ammonia borane as the precursor and argon?Ar?and hydrogen?H₂?as the carrier gases.Besides,high-throughput preparation of h-BN was realized through using a gradient concentration of copper-nickel alloy envelope as the substrate.The influence of nickel content,deposition temperature,deposition pressure,precursor quality,heating temperature of precursor,hydrogen flow rate,carrier gas flow on the nucleation density,single crystal size and morphology of h-BN were systematic studied.The single crystal h-BN film with 60?m and 1 layer was prepared,wherein the lateral growth rate of h-BN was¹?m/min.The growth mechanism of the copper-nickel alloy and copper-nickel alloy envelope were discussed.?3?Using a copper-nickel alloy envelope as the substrate and ammonia borane,methane as a raw material,the in-plane graphene/h-BN heterojunction was synthesized by a two-step chemical vapor deposition.and the in-plane graphene/h-BN heterostructures with different morphology and size were obtained by controlling the methane flow rate,the growth time of h-BN and hydrogen flow rate.