Preparation And Electrical Properties Of CVD-Grown Graphene With Controllable Domain Size

Graphene has attracted a great deal of attention due to its unique structure,excellent properties and broad application prospects.In particular,graphene’s ultra-high carrier mobility makes it very suitable for high-performance electronic devices.Chemical vapor deposition（CVD）method based on copper substrate for graphene preparation is considered to be an effective method to prepare large-area and high-quality graphene films because of its good controllability and scalability.Generally,graphene prepared by CVD method is polycrystalline graphene film with grain boundary defects,and the scattering of carriers by grain boundary will lead to the reduction of graphene’s electrical transport properties;reducing the formation of graphene grain boundary is mainly achieved by inhibiting the nucleation process of graphene and the orientational growth of graphene domains,but this often makes the preparation conditions harsh and increases the preparation cost;at the same time,the effect of grain boundary on the electrical transport properties of graphene shows sensitivity to growth conditions.It is of fundamental scientific significance and engineering application value to understand the key factors affecting the growth process of graphene and the effect of domain size on the macroscopic electrical transport properties of graphene.Therefore,comprehensively considering the cost of preparing large domain size graphene and the low tolerance for performance difference in electronic device application,the regulation of domain size of continuous graphene film and the influence of domain size on the overall electrical transport performance of graphene film were studied from the macroscopic level,and the influence of copper substrate pretreatment conditions on the growth process of graphene was further studied.The main research contents and results of this thesis are as follows.（1）The regulation of domain size in the CVD growth of continuous graphene films was studied.The results have shown that heating up in argon and introducing hydrogen during annealing of copper substrate could help to improve the controllability of graphene domain size.The preparation of monolayer continuous graphene films with sub millimeter different domain sizes was achieved by atmospheric pressure CVD.The prepared graphene has good uniformity in both the distribution of domain size and the integrity of growth.（2）The electrical transport properties of continuous graphene films with different domain sizes on Si O₂/Si substrate was investigated.The study have shown that the key electrical parameters such as carrier mobility,carrier density and surface resistivity could be extracted by van der Pauw-Hall measurement,and the normalized carrier mobility could be used as the standard to evaluate the electrical transport performance of graphene;on the micron and submillimeter scales,the domain size has no significant effect on the overall electrical transport properties of continuous graphene films;a simplified model based on Ohm’s law was proposed,which could well explain the experimental results of electrical transport test.（3）The effects of copper substrate annealing and electropolishing pretreatment on the growth of graphene were studied.Studies have shown that the cooling process after annealing pretreatment would cause impurities inside the copper substrate to diffuse and precipitate to the surface,resulting in an increase in the nucleation density of graphene,while oxygen treatment of the copper substrate at high temperature could remove the impurities on the surface and reduce the nucleation density of graphene;electropolishing pretreatment of copper substrate could reduce its surface roughness,reduce the nucleation density of graphene while accelerating its growth rate,and make the grown graphene film have better electrical transport properties.