Study On Growth And Regulation Of Centimeter-Scale Single-Crystal Graphene

Due to its unique structure and properties,two-dimensional（2D）materials have shown enormous application potential in these fields such as energy,medicine,and optoelectronic devices,and have significant economic and social values.Among them,graphene,as one of the most concerned 2D materials,is a gapless semiconductor material with extremely excellent conductivity,thermal conductivity,optical properties,and mechanical properties.At present,chemical vapor deposition（CVD）is one of the mainstream methods for preparing high-quality and large-area graphene films.However,there are still problems with the growth of graphene using CVD method,such as the small size of graphene domains,the formation of graphene films being polycrystalline,and the presence of numerous grain boundaries.Therefore,this article aims to optimize and improve the quality of catalytic metal Cu substrates and regulate the growth parameters of graphene films.Large-area single-crystal Cu（111）and centimeter high-quality single-crystal graphene films were prepared,and field-effect transistors（FETs）using single-crystal graphene as the channel material were prepared to study their electrical properties.The main research content of this paper is as follows:1.By adopting a high-temperature annealing process,adjusting the annealing temperature,annealing pressure and carrier gas flux,the goal of rapidly preparing large-area single-crystal Cu（111）is achieved.Research has found that using Cu foil with a thickness of 25μm can anneal larger Cu single-crystal domains at lower temperatures and in a shorter period of time.On this basis,high-quality single-crystal Cu（111）with an area of 8 cm² were prepared by appropriately increasing annealing temperature and time.In addition,we also found that with the increase of annealing temperature,the one-dimensional（1D）ridge like structure on the surface of Cu foil gradually disappears,and the surface of Cu foil tends to be flat and smooth.As the annealing time increases,the undulating morphology on the surface of Cu foil becomes smoother,enabling the production of large-area single-crystal Cu（111）.At the same time,during the annealing process of Cu foil,some surface needle like structures and step-edge structures will be generated.Among them,step-edges with a width of several hundred nanometers are generated by the aggregation of multiple atomic steps and the reconstruction of the Cu foil surface during the cooling process.These structures serve as internal energy release channels for high-temperature annealing of Cu foil and have a certain promoting effect on Cu foil annealing.2.We conducted a study on the growth regulation of large-area single-crystal graphene on a single-crystal Cu（111）substrate using a CVD dual temperature zone tube furnace with a growth chamber diameter of 4 inches.Research has found that graphene can grow domains with consistent orientation on single-crystal Cu（111）substrates.Therefore,single-crystal Cu（111）substrates have great potential in preparing large-area single-crystal graphene films.A comparative study of large-area single-crystal graphene grown on single-crystal Cu（111）and graphene grown on polycrystalline Cu substrate shows that graphene grown on Cu（111）substrate has larger domain size,lower nucleation density,better domain direction consistency,and fewer defects and grain boundaries.On this basis,centimeter-scale single-crystal graphene thin films were successfully prepared.Single-crystal graphene has better conductivity,with an average sheet resistance decreasing from～1415.7Ωsq^-1 to～607.5Ωsq^-1.A full back grid graphene field-effect transistor（GFET）was prepared using single-crystal graphene as the channel material,and the electrical performance of the GFET device was tested.The results show that the switching ratio(I_on/I_off)and carrier mobility(μ_FET)of GFET devices reach～145.5 and 2.3×10³ cm²·V^-1s^-1,respectively.