Research On Preparation Of Graphene Terahertz Devices And Graphene Terahertz Devices Based On PVD/CVD Method

Metamaterials are often used in the research of terahertz devices because of their extraordinary physical properties that natural materials do not have.In recent years,the research of terahertz metamaterial has developed rapidly,and new functions and operating frequency range have been greatly developed.Among them,the combination of metamaterial and graphene provides a new idea for the development of dynamically tuned terahertz functional devices,and it is found that graphene terahertz metamaterial has broadband optical response,ultrafast relaxation time,high nonlinear coefficient,and flexible and controllable physical properties of its element structure,thus realizing ultrafast and broadband absorption of terahertz waves.Therefore,the quality of graphene growth will directly affect its application in the terahertz field.At present,in the preparation methods of graphene,the graphene obtained by chemical vapor deposition technology has good controllability and uniformity.Under the atmosphere of H₂ gas,CH₄ is pyrolysed on the surface of Cu foil at high temperatures,and graphene is epitaxially grown on the surface of copper foil.This thesis uses the PVD method to prepare Cu thin films to replace copper foil（25μm）.The crystallization behavior of Cu thin films prepared by the PVD method was studied using annealing technology,and the effects of annealing temperature and time on the grain size and surface roughness of copper thin films were explored.Meanwhile,the CVD method was used to prepare graphene using annealed Cu thin films,and the effects of growth temperature,growth time,and CH₄ content on the quality of graphene were analyzed.Finally,the electromagnetic regulation ability of graphene terahertz wave absorbers was analyzed and discussed using CST simulation software.These works have provided strong support for the development of terahertz modulators.The main research content of this paper is as follows:1.Research on Hot Steam Plating of Copper Film:A copper film was prepared using hot steam plating,and the influence of different hot steam plating currents on the surface properties of the copper film was analyzed.It was found that when the current of hot evaporation plating is high,the resulting copper film surface is smoother and has higher flatness.Explore the surface morphology and crystallization of annealed copper films at different temperatures,times,and thicknesses using a high-temperature tube furnace.Comparing different annealing parameters,it was found that the annealing temperature was 1050℃,the annealing time was 60 minutes,and the copper film thickness was 1020 nm.A copper film with a flat surface and larger grain size could be obtained.2.Research on the Preparation of Graphene by Chemical Vapor Deposition:Exploring the Effect of Annealing Temperature on the Nucleation Density,Defect Formation,and Layer Number of Graphene during the CVD Process.It was found that graphene with larger size,fewer defects,and a single layer can be obtained at an annealing temperature of 1050℃.Explore the effects of different CVD experimental parameters such as methane flow rate,growth time,and growth temperature on graphene.By comparing microscope images and Raman spectra under different parameters,it was concluded that when the methane flow rate is 5 sccm,the growth time is 15 minutes,and the growth temperature is 1050℃,high-quality graphene with large single crystal monolayer and flat surface can be obtained.3.Simulation of graphene terahertz device:A three-dimensional tunable terahertz wave absorber is designed and discussed.The metamaterial consists of metal plate,dielectric layer,graphene ring,and shape memory alloy cross.Metamaterial can achieve three perfect absorption peaks at 0.708 THz,1.929 THz,and 2.334 THz,and the absorption peak intensities are 99.99%,99.57%,and 94.13%respectively.By bending shape memory alloys,dual tuning of terahertz wave frequency and intensity can be achieved.When the bending angle of the shape memory alloy increases from0°to 5°,the absorption peak of 0.708 THz undergoes a blue shift and the center frequency shifts by 0.147 THz.The intensity of the absorption peak decreased from99.99%to 95.17%.However,the absorption peaks of 1.929 THz and 2.334 THz both showed a red shift,with the center frequencies shifted by 0.034 THz and 0.027 THz,respectively.The intensity of the absorption peaks increased to 99.65%and 97.3%,respectively.4.The influence of graphene layers on the absorption spectrum of metamaterial:By changing the bias voltage to adjust the Fermi level of graphene,the dual tuning of THz wave frequency and intensity can be achieved.When the Fermi level of graphene increases from 0 to 3 e V,the absorption peak intensity of 0.44 THz increases to 87.77%,but the absorption peak intensity of 0.708 THz decreases to 85.55%.The research results provide new ideas for the future research of actively tuned terahertz devices and intelligent terahertz devices.